Intro Flashcards
When was dementia clinically recognised and by who and how?
It was recognised as a medical term in 1797 by Philippe Pinel when we realised memory loss and physiological confusion across patients.
How did Alzheimers disease become identified, when and by who?
In 1906 by Alzheimer when he had a women patient that had symptoms of short-term amnesia, memory loss, disorientation and dysphasia (impairment in speech).
After her death, he monitored the brain and found pathological changes in the brain which he termed plaques and tangles, along side an enhanced neuroinflammation.
These were within the cerebral cortex.
However, it only became termed Alzheimers by his collaborateor Kraepelin.
What is the cerebral cortex important for?
memory, language, judegemnt, thinking
What are the prevalence statistics of AD?
~500,000 in UK
60% of cases
reach 1.1 million by 2030
1.6 million by 2050
List the modifiable and non-modifiable risk factors of AD.
Modifiable - diet, educatonal level, social interaction, comorbidities, physical exercise
Non-modifiable - genetics, age, sex
How can diets be a risk factor? How have they shown this?
They have monitored mediterranean diets or groups of poplethat have a high intake of vitamen E and C and monitored their association with developnent of AD.
They found that these diets had a reduced risk of developing AD – perhaps due to antioxidants egffects.
How might education cause a greater cognitive reserve?
It is thought that the higher education will result in a brain that has greater neuronal synaptoc strength with strong connections.
How can type 2 diabetes increase the risk of developing AD?
It can by 50%
insulin and AB compete for use of insulin degrading enzyme - this is an enzyme that can work to degrade AB which therefore will end up in the accumulation in the brain.
Increased formation of advanced glycosylation end products which increase neuronal damage upon action on their receptors.
How can sports cause increases risk of AD?
becuae it causes tramatic brain injury which will cause an increase in pathological functions in the brain.
Havign apoe4 is thought to enhance this risk.
What does dichotomous disease mean?
This means there are two forms of the disease.
What are the two types of AD and how arer they characterised?
Familial - less dominent form, highly genetic background, early onset, mutations in PSEN and APP
Sporadic - more dominent, late onset, combination of genetic and environmental factors
What is mendelian inhertance?
This refers to how the genes have been passed through a damily based on the laws of Mendel.
It means that gene inherited from either parent segregates into gametes at an equal frequency.
What does autosomal dominent mean?
Autosomal dominant traits pass from one parent onto their child. Autosomal recessive traits pass from both parents onto their child.
Hardy and Higgons are big players how and why?
In 1991, Hardy’s team uncovered the first mutation directly implicated in Alzheimer’s disease leading to the formulation of the highly influential ‘amyloid-cascade’ hypothesis.
Higgons also involved in devlopment on this hypotheiss.
What is APP and what mutations were found?
Amyloid precursor prtoesin that is found on chromosome 21
Dutch - Frangionne
London - first link to AD - Goate 1991
and more
This tends to clustres in regions of the gene which cause enhanced cleavage and production of long fibrillogenic forms.
What is PSEN and what mutations were found?
PSEN is the presenelin protein which are subunits of the gamma-secretase enzyme.
Several mutations have been found which tend to involve a loss of function gamma secretase, impairing the cleavage of APP and therefore, promotirng abnormal AB secretion
What are GWAS? What have they found?
This is an approach used to find genetic mutations in diseased patients. THey use the full genome of humans and search for small variations called single nucleotide polymorphims
This SNP is when one nucleotide in the DNA chain is swapped for another, thereby affecting transcription and normal activity of the protein.
For SAD, they have foound APOE. complement receptor 1. clusterin, PICALM.
What is APOE and what are the different alleles?
APOE is a gene which generates apolipoprotein E which is a glycoprtoein that is involved in transport of choleterol trhough the CNS. It is generally produced by immine cells. It has also been found to bind to AB and promote its transport around the brain, while regulating metabolidm and clearance.
It has been found to have 3 major alleles which are basically three different mutated forms of the gene and involve residues 112 ans 158.
e4 is the biggest risk and increases it by 40fold with one copy and 10-fold with two copies.
What is the allelic ratio?
The likelihood that the allele will occur, calculated by creating a ratio of the area under the curve for the allele and the wild-type gene.
What is trem2?
A gene that is a transmembrane lipoptotein sensor that is largely involved in the regulation of microglia. It forms a receptor-signalling complex with TYROBO.
What mutations in trem2 have been found?
missense mutation (where the change un nuelcotide will change the amino acid) which loses regulation of microglia and increases neurodegeneration.
What are the statistics with age risk factor?
Why is it thougt this occurs?
1 in 14 over 65
1 in 6 over 80
Age related changes in the brain –> atrophy, inflammation, vasculat damage, oxidative stress
Why might oestrogen be protective for females? How did they determine this?
strogen affects cholesterol and lipid transport, and in the brain, estrogen regulates the expression of low-density lipoprotein receptor-related protein, which has been implicated in Aβ processin
It also binds to its ERalpha/beta recpetors which can be found on glial cells, specifically microglia and promote their regulation.
In some sutdies its effect have promoted normal regulation of microglia, preventing its effect on oxidative stess and preventing acitvation of receptors by AB.
What do the genetic studies show for sex differences?
They show differences in neuroinflammatory pathways, synaptic function and apoptosis.
How? ,.
If some sutdies show a reduction in risk of developing AD with NSAIDs/HRT why hasnt it been approved?
For HRT, early studies illustrated that there was a protective effect of oestrogen.
However, later studies were conflicting and actually found that there may be differences on the effect depending on how long they have been using it.
For example more recent findings suggest that there actually is an association between prolonged used and increased risk of developing all dementia and AD.
While chronic NSAID use has been reportedly preferred over short-term use for prevention of AD [3], one review of both epidemiological and clinical trial studies hypothesizes that such usage might only be beneficial in the very early stages of AD pathogenesis, coincident with initial A-β deposition, microglial activation, and release of pro-inflammatory cytokines. Once the process of A-β deposition has started, NSAIDs are not useful; instead, a detrimental effect can occur owing to their inhibitory activity on already activated microglial cells.
What is the general progression of AD?
Pathology in the brain can occur 10-20 years before clinical symptoms.
Then patients will begin showing deterioration of cognitive functions and show peronsality changes which is when they tend to get diagnosed.
Then there is mild where everyday activities are interefered, moderate where nab =y activities are interuppted, and severe strages where most everyday activities are disrupted, before vegetation.
Usually ~8.5 yeats but everyone has a different progression.
What neuropsychological tests are commonly used to diagnose AD?
The Mini Mental State Examination (MMSE) (Folstein 1975) is a 30-question assessment of cognitive function
The Addenbrooke’s Cognitive Examination -
The Mini-Cog is a two part screening test that is used to assess cognitive impairment (Borson 2000).
The Montreal Cognitive Assessment (MOCA)
ADAS-Cog
For diagnosis what do PET and MRI and fMRI scans look for?
A brain MRI can help doctors look for:
brain shrinking (atrophy).
damage following a stroke.
problems with blood vessels.
inflammation.
tumours.
damage following an injury.
In Alzheimer’s disease the hippocampi (circled in the image below) are often affected first. A doctor will use an MRI to see if there are visible changes to these structures, which can help to diagnose Alzheimer’s.
PET scans are used to show:
abnormal build-up of proteins that cause diseases like Alzheimer’s.
how much glucose is present in the brain, to look at brain activity.
fMRI not commonly used in humans but can show
- increased functional connectivity in early stages which may be a compensatory mechanism dealing with the presence of AB/tau
- decreased in clinical stages
What is the cholinergic hypothesis?
That because there is widespread neuronal loss ofin brain regions that have alot of cholinergic neurons, this suggests that the loss of cholinergic signalling is responsible for AD.
These brain regions are hippocampus, neocortex and amygdala.
What are the functions of
hippocampus
neocortex
amygdala
Like many parts of the brain’s limbic system, the hippocampus is involved in memory, learning, and emotion. Its largest job is to hold short-term memories and transfer them to long-term storage in our brains
for execution of higher-order brain functions
t’s a major processing center for emotions
What is the amyloid hypothesis?
Who generated this and why?
That the accumulation of amyloid plaques are responsible for the tauopathy and neuroinglammatory state and neuronal loss throughout AD.
This was generated by Hardy and higgins in 1992 because these were the pathology found in the brain several years before diagnosis and the most comoon mutations were surrounging the production of amyloid.
How did Kidd and Terry characterise amyloid and tau? What did they show?
They used electron microsope which uses electrons as illumination source and this allows high resolution images.
They done this on biopsy human AD patients.
They descriped a detailed struture of plaque sand tangles.
NFTs –> many neurons were abnormal containing thick bundles of parallel filaments around the nucleus, some with double helices
plaques –> some plaques have central masses of filaents and several types depending on surroundings –> identified amyloid structure
they identified that many neurons surrounding plaques contained the PHFs –> therefore suggesting a link between the two
identified teh presence of astrocytic processses surrounding plaque.
Glennor and Wong are referenced alot, what did they do?
Major roles in the isolation and identification of the strcture of APP and AB - and some mutations.
G & W 1984 - purisfied amyloid beta using chromatography and found its amino acid structure – suggeted it may be derived from a precursor protein
G&W 1984 - isolated the amyloid protein on chromosome 21 and identified it in downs patients
Glenner 1979 - investigate cages of amyloid microangiopathy and illustrate that this can reach the brain due to breakdowns in the BBB, also suggest microglia are involved in generation of plaques
E&G 1968 - find the structure of amyloid using x-ray diffraction and find the beta pleated sheets formed in an antiparallel nature, transferse to the filament
How was APP discovered?
What is its structure?
glycoprotein
discovered and sequenced by isolating and purifying the protein from menugeal blood vessels of AD and down syndrome patients
It is single membrane spanning domain with large extracellular glycosylated N-terminus and short cytoplasmic C-terminus
ranges from 695-770 residues
Why is down syndrome patients relevant for AD research?
Down’s syndrome is caused by having an extra copy of a particular chromosome, called chromosome 21. One of the known genetic links to younger onset dementia is the amyloid precursor protein (APP) gene, which is found on chromosome 21.
What are the two pathways of APP proteolysis and how do they work?
Non-amyloidogenic - APP cleaved by alpha secreatase at site within the AB fragment, releases sAPPalpha and a membrane bound C83 remains
Amyloidogenic - APP cleaved by beta-secretase at N-terminus of AB domain, leaving C99 bound to membrane and releases APPsB, gamma-secretase cleaves C99 to generate AB
How is the (non)amyloidogenic pathway controlled?
Can be controlled trhough neuronal activity such as acetylcholine causing enhanced activation of alpha-secretease.
Who found the structure of amyloid beta?
What is it like?
Glenner and Wong in 1984
38-43 amino acids in length, ab40 most common, ab42 most pathogenic
What are the structural differences of AB40 and AB42?
AB40 has an alpha helix structure between res 15 and 36 and a kink before this. Alpha helix is senconday protein structure where the single chain of amino acids is arranged in a coil stabilised by hydrogen bonds.
AB42 has a beta hairpin srtucture at residues 31-41. This is two beta strands which is basically a linear chain of the amino acids which have folded over in a pin like structure where hydrogen bonds form between them. This hydrophobic structure promotes the formation of beta-sheets which is the accumulaton of beta-strands in parallel attached by hydrogen bonds. These are hydrophobic structures.
What is primary and secondary nucleation?
nucleation is usually a term used for biophysics but is not being used to refer to protein due to their stages through different structures.
Paimary –> aggregation of two or more AB monomers throug fibril independent pathway
Secondary – aggregation of AB monomers on fibtrils in fibril dependent pathway.
How can plaques undergo cycles of dissociation and reassociation? What causes this?
The kinetics at each stage has not been identified, with dissociation of AB42 less due to its hydrophobic nature.
Changes in ph and lipid content
pH –> low pH decreases dissoation as it promotes stability of N-terminal, high pH thought to promote aggregation
lipids –> higher cholersterol promotes reassocaition, other lipids can solubuse AB for dissoaciation
How are AB monomers protective?
How have they shown this?
- Synaptic function: study has shown it can act as a protective ligand at a GABAb recpetor to promote synaptic transmission, KO studies shown involvement in synaptic functions and impaired learning ability,
- Dissasembly of tau: potential function is disassembling tau dimers by preventing bonds between them
- Protection against infection: ab binds to neurotoxins and pathogens, aggregates to plaques to trap the microbes into phagocytes
- sealing the BBB - regulate angiogenesis promoting healing of blood vessels to prevent leakage of BBB – localises around damage regions as a scab/sealant to maintain the integrity
Define an oligomer.
Formed through combination of monomers.
Various low and high molecular weight forms and therefore, can be various sizes.
It can be soluble or insoluble depending on the secondary prtoein structures. Soluble has no alpha or beta sheet structures. Insoluble has high beta-sheet presence which will be in parallel or anti-parallel structure. This is where the beta strands are atrtached in the same direction or not and tend to be due to stabilitiy and function - antiparalel more stable. Soluble forms can spread throught he brain and insoluble can aggregate further into fibrils.
What toxic effects can soluble oligomers have?
They can spread throughout the brain and act on various receptors e.g. ach, glutamate, beta2-adrenergic, p75 neurotrophin and prion
This can disrupt calcium signalling, mirochondiral function, oxidative dress, tauopathy, synaptic function, neuronal loss, AB aggregation.
Describe protofibrils.
One of the intermediate products formed which are large soluble fragments with varied dize.
Longer than oligomers but thinner and shorter than fibrils.
They also contain beta-sheets.
Also have silular neurotoxicity as olligomers, shown to have effects on neuroinflammation through accumulation in astrocytes and microglia.
What is meant by fibrils forming in a concentration-dependent manner?
Studies have suggested that fibrils will begin to form only after they have reached a certain concentration within the brain.
Describe fibrils.
AB monomers or oligomers that have aformed into beta sheets in a parallel nature, with hydrogen bonds for stabilisation. This means that the monomers have formed a secondary protein structure which is hydrophobic.
Tgis can progress into a fibril itsellf by formation of more beta sheets or this structure will then aggregate onto an already existing fibtril by attaching through te beta strangs
What pathological features has fibrils been shown to have?
Co-localised with disrupted neurites, regionsof decreased spine density, neuronal loss, nueorindlammation and neurodegeneration.
Describe plaques.
Ab fibrils will aggregate together and form insoluble plaques
These can be diffuse or dense core or neuritic.
Diffuse - no accumulation of glial cells around them
Dense/neuritic - compact dense core of AB fibrils surrounded by glial cells, synapse loss and tauopathy
In Fig 1.3, what is ADAM9,10,17, BACE, nicastribn, PEN2, APH-1?
A disintegrin and a metalloprotease 9,10,17 which can all cleave amyloid beta from APP
BACE - beta-secrease
nicrastin is a regulator of gamma secretase cleavease
APH-1 is a component of the gamma srectase complex that regulates its stabilisation
PEN-2 is required for endoproteolytic processing of presenilin and conferring gamma-secretase activity to the complex.
What is the structure shon in Fig 1.3A?
This is the cell membrane of a cell where the inside is the cytoplasmin and the structure shows the phospholipid bilayer which acts as a barrier between the external and internal fluid.
This is shown because APP is a transmemrbane protein which is sitated on the cell membrane and has some internal and external.
What does this chain show in 1.3B?
This shows the primary amino acid structure of amyloid beta 42.
This is made up of 42 amino acids with their name coded, bound together through peptide bonds.
What are alpha helix
beta sheets
Secondary protein structure is the repetitive folding of polypeptide chains by hydrogen bonds between the hydroxyl (OH) group and the hydrogen molecule of the adjacent amino acid, leading to the unique shape of the protein. The most common examples are the alpha-helix and beta-pleated sheets.
Alpha-helix – a coil formed by hydrogen bonds between the carbonyl group and the amino group of different amino acids. The strong bonds and stability of this structure give it a strong tensile strength, which allows it to form the shape seen in DNA.
Beta-pleated sheet – formed by hydrogen bonds between the carboxyl group of one amino acid on one sheet and the hydrogen molecule of an amino acid on another sheet. The sheets can be in parallel or antiparallel.
What is a primary protein sequence?
Primary protein structure is when amino acids bound are together via covalent peptide bonds to form a polypeptide chain. These bonds form between the N terminal and C terminal of amino acids and are highly resistant to heat or chemicals.W
What are amino acids?
Amino acids are the basic building blocks of proteins. Their structure consists of three main groups as seen in figure 1, namely the amino group or N terminus, the carboxyl group or C terminus, and the R group which contains the functional component of the amino acid. The R group gives the amino acid specific features according to its polarity and charge, which then affect the chemical and biological properties of the protein.
There are a total of 21 amino acid types based on their different R groups. 12 of these can be synthesised in the body, while the other 9 must be consumed in the diet and are termed essential amino acids.
How is the primary sequency made?
Proteins are polypeptide structures that contain chains of AA. The primary is linear chain. Secondary has some regions that are stabilised by hydrogen bonds on polypeptide backbone to create alpha helix and betapleated sheets. Tertiary is based on the interactions of side chains from polypeptide backbone.
Primary
- each amino acid linked through peptide bonds
- rund from N to C terminus
- 20 possible amino acids
1) DNA preserves the code to synthesise the proteins - this will be a nucleotide sequence
2) this nucleotide sequence is transcribed into another called an RNA messenger (basically it copies the structrue and allows transfer out of the nuclei). This occurs though help by transcription factors. The intiaition complex recognises the promter region which is usually a concensus sequence. It will then copy from the stard and end codon.
3) after leaving nucleus, a ribosome attaches to begin translation when it reaches the AUG start codon. The ribosome will contain two subunits which doin and bind to tRNA to translate this and identify each amino acid from their codon. Then peptide bonds are formed between each AA. This runs until it reaches the end cogndon UAD.
What is prion like seeding?
used to descrube molecular events that share similarities with infectious cycle of prion proteins.
This is where it self-aggregates and spreads between cells
How is AB transported across the brain?
Prion like seeding - AB spreads throug neuronal transport from axonally connected brain regions. Here, they will be collected into intraluminal vescile, fuse with PM, rekeased into extracellular space as exosomes
Cell-to-cell transport - fiynd in neurons but nothing reported
Vascular system - transported across BBB through RAGE and LRP1 recepetors
APOE - secreted into ISF by glial cells and interacts with AB which can promote spread and clearance through passing BBB
What receptors are involved in passing the BBB and what is the route that they take?
recpeotrs for advanced glycation end-products – blood to brain
low-density lipoprotein recpeotr-related protein 1 – brain to blood
What are:
axons
axon transport
intraluminal vesicles
exosomes
intracellular space
extracellular space
interstitial fluid
extrastitial fluid
axon -> the long projection of a neuron between the cell body and axon terminal that conducts electrical pulses.It is coated in myelin sheath for conduction
axon transport –> vesciles are foremed in the cell body and transported by motor proteins along the axon microtubules to presynaptic cites. (kinesin and stenein motors) along the microtubule network.
exosomes –> extracellular vesciles that are released from cells upon fusion of multisecivular bodies and the plasma membrane
intraluminal vesicles –>
What are methods for ab clearance from the brain?
ISF draiginage -> diffusion of AB from ISF to CSF through bulk flow, where it will drain into the blood trhough perivascular arterial spaces
proteolytic degradation - degradated by amyloid degrading enzymeas such as insulin degrading enzyme and neprulysin, with the end products being removed by bulk flow or theough blood
cell-mediated clrance –> microglia and astrocytes can be involved through phagocytosis and internatlisation for degradation
active transport –> transport across the BBB into blood through LRP receptors
glymphatic transport –> during sleep there was activation f flial cells that work to increase phagocytosis.
What is bulk flow?
bulk flow is a mechanism where proteins and fluid can travel to and from different cellular compartments due to the presence of a pressure gradient.
Therefore, in the brain, ISF can move in a pressure-dependent manner through ISF spaces into ventricular CSF.
How is AB spread throughout the brain according to Thal
Not widely known as ti varied actoss patients and is not as standardised as tau pathology.
One study found A 5-phase spread which spreads outwards to inwards.
Phase 1 - AB in neocortex
phase 2 - spread to allocortical regions
phase 3 - midbrain regions including diencephalic nuclei, striatum and basal forebrain
phase 4 - brain stem
phse 5 - cerebellum
What is the function of
allocortical regions
midbrain regions
diencephalic nuclei
striatum
basal ganglia
basal forebrian
brainstem
cerebellum
allocortex –> a term used to describe several layers of the cerebral cortex, includes the hippocampus, subiculum, olfactory cortex, entorhinal, retrosplenial and cingulate, the cerebral cortex is divided into allocortex and neocortex, and is the outer layer that lies on top of the cerbum, involved in consiousness, messenger between lobes, and sensory and motor areas
midbrain –> connected to brain stem, involved in movement of body
dienchepalon –> collection of nuelci deep in the brain including thalamus, hypothalamus, subthalamus, relays sensory and motor information to cerebrum
striatum –> nuclei forms part of the basal ganglia, split into ventral (nucleus accumbens and olfactory tubercle_ and forsal (caudate nucleus and putamen), involved in motor and reward
basal ganglia –> group of subcortical cuclei including striatum, globus palidus, ventral pallidum, substantia nigra and subthalamic nucleus, involved with morot, cogntion, emotion
basal forebrain –> in forebrain below the striatum - include basal ganglia, etx, involved in production of acetylcholine which is then distributed widely throguhout the brain, considered major cholinergic output of CNA
brainstem –> region of brain that connects the cerebrum to spinal corte xand cerebellum, contains midbrain, pons and medulla oblongata, regulates breathing, heart rate, coordination, role in sleep
cerebellum –> hind brain, motor and balance control
How did the study of Thal 2002 sicover these finfings?
They took brain section from 47 brains from demented and nondemended patients with AD related pathology
Used a staining technique and analused distinct regions of AB
Why is it thought that oligomers are the most neurotoxic forms of amyloid beta?
Becaue they are soluble which allows them to bind to molecules within the extracellular space such as receptors
These receptors include
glial cells, lipids, protein recpetors like p75 neurotrophin, LRP1, cellular prion protein, metabotropic glutamate receptors, alpha subunit containing nicotinic acetylcholine receptor, NMDA receptor, beta2 AR, etx.
What are the functions of protein recpetors like p75 neurotrophin, LRP1, cellular prion protein, metabotropic glutamate receptors, alpha subunit containing nicotinic acetylcholine receptor, NMDA receptor, beta2 AR, etx.?
p75 –> member of TNF family controls survival of neurons as neurotrophin is protective molecule that regulates development and maintenence, but can also contribute to apoptosis programmed cell death
LRP1 –> endocytic recpeotr modulate trafficking across BBB, also present on microglia to regulate inglammation
CPrp –> antiapoptotic, protection against oxidative stress, regulate trnasnmembrane signalling
metabotropic glutamate –> GPCRs that upon binding of ligant can promote signalling pathways, role in synaptic teansmission and LTP
What types of glutamate, GABA and acetylcholine receptors can you have?
glutamate –>
ion channel which allow passing of sodium and calcium
AMPA, kainate, NMDA
metabotrophic - GPCR
GABA –>
GABAa –> ligand gated ion channels, allows cholrine flow
GABAb –> GPCR which can allow calcium and K flow
Ach –>
nicotonic - ligand gated ion channel, flow of potassium and sidum
M1/3/5 - Gq (PKC) activated GPCR
M1 - Gs (cAMP,PKA) activated GPCT
M2,4 - Gi activated GPCR
What is the GluN2B subunit?
type of subunit for NMDA
thought to play a role in synaptic plasticity and cognitive function
What happens at low concentration of AB on NMDA receptors?
Excessive activation of the receptors which prevents synapse generation, promotes neurona death, increased oxidative stress –> damage to lipids, proteins and DNA, promote AB accumulation trhough protelysois of APP
What happens at high concentrations of AB on NMDA receptors?
AB depress synaptic activity by supressing synaptic strength through internalisation of glutamate receptors, downregulation of voltage-gated sodium channels and loss of dendritic spines, loss of snaptic inhibition
How can tauopathy contribute to excitotoxicity?
Tay interacts with Fyn kinase, which forms a complex with PSD95 and the NMDA recpetor which will be activated by AB
What else can contribute to AB-induced excitotocivity?
Ab acting on presynaptic acetylcholine receptors which will increase intracellular calcium levels and promote flutamate release.
Why would there be these differences on NMDA receptors depending on the concentration of AB?
compensatory function followed by termianl detrimental decline
What is the effect of AB on AMPA recpetors?
reduce AMPA recpetor expression through an increase in degradation and ubiquitnation
or by increasing tau hyperphosphorylation which diminises AMPA signalling
Effects of AB on alpha7nAChR?
endocytosis of NMDA recpetors
increased AB-induced tau photphosryltion through extracellular signal related kilase and Jun0Nterminal kinase pathways
Effects of AB on b2AR?
increased calcium signalling and hyperactivity
promotes tauopathy
How does AB increase tauopathy?
Bind to a2-AR activate glycogen synthase kinase1b and cyclin-dependent kinase 5 which promote hyperphosphorylation of tau.
These kinases will also promote aggregation of tau monomers into oligomers.
activates caspase-3 which will produce a cleaved tau protein that is aggregative
act on cellular prion protein receptor to activate Fyn kinase which will increase another kinase
How can AB increase oxidative stress?
AB bind to p75 neurotrophin recpetor which activates its death domain and caspases which generate ROS
Ros damages proteins which will generate toxic products enhancing oxidative stress.
How can AB cause mitochondrial dysfunction?
APP can act on mitochondiral membrane to blockt ranslocation
AB activates cell death pathways through mitochondrial dission proteins
What is the function of mitochondria?
Why is it bad when they are dysfunctional?
is a membrane bround organelle wgicgh is found within cells.
Its termed the power house of the cell as it is repsonsible fot using areobic respiration to generate ATP –> oxidative phosphotylation
What are microtubules?
microtubules are components of cytoskeletin made up of tubulin protein and it continuously undergoes polymerisation and depolymerisation in a hollow tube
important for cell motiblity, stability
in neurons they can provide a structural backbone for axons and dendrites
What is the normal function of tau protein?
It is a microtubule stabilisation protein that lines the microtubules by having double rings around them.
What is the struucture of tau?
N-terminal projection domain that interacts with other cytoskeletal elements or proteins for signal trasnfuction
C-terminal is microtuble binding domain, involved in polymerisation and stabilisation through binding to functional prtoeins like kinases or phosphatases
This phorphorylated state is in equalibrium
What are the phosphorylation sites?
How does this happen?
What are examples?
There is 79 serine or threnonine phosphorlation sites. These are amino acids in the tau primary structure whih most often undergo this post-translational modification.
Suggests the primary source of phosphorylation is proline directed SerThr kinase. This is a subclass of protein serine-threonine kinases that phosphorylate proteins on a SERINE or THREONINE residue that is immediately preceding a PROLINE residue.
This proline directed protein kinases target the xonsneuss sequence -X-SerThr-Pro-X. T
Examples are MAPK and GSK3
What happens when tau is hyperphosphorylated?
Tau loses affinity for the microtubule, the rings begin to disassesmble and it breaks away from the microtuble.
Then once in the intracellular space, it begins to aggregate together forming paried helical filaments which aggregate into tangles
How is tau spread throughout the brain?
transsynaptic spreading –> pathological tau underwent intracellular transmission, involving the secretion and uptake from neighbouring neurons
Commonly ptermed the prion like model due to similarity to prion diseases
How is tau secreted?
packaged into microvesicles, internalised by exosomes before the fusion of the vesicle with the plasma membrane
in its soluble hyperphosphorylated tau will translocate across the plasma membrane –> unclear full mechanism but perhaps trhough pore like channel structures on the plasma membrane
filament actin-containing channels called nanotubes which allow transport without secretion into the extracellular space
How is pathogenic tau internalised?
receptor-mediated endocytosis
bulk endocytosis
fluid phase translocation
fusion of large containinf cescles with plasma membrane
actin-dependent micropinocytosis
clatrhin-mediated endocytosis
involvement of glial cells
How is the spread of tau throughout AD characterised?
This was characterised by Braak and Braak which processed histological human sections and characterised the pathology into six stages over three units.
Stage I-II –> transentorhinal and entorhinal cortex
Stage III-IV –> hippocampus, limbic allocortex, neocortex
Stage V-VI –> secondary and prunmary fields
Therefore, this speads inward to outward.
What are the pathological effects of tauopathy?
microtubules breakdown and disupt axonal transport
tangles physical obstacle within the axons which prevent transport of vesciles and cargo
tangles can sequester remaining functional tau
contribute to mitochondiral dysfunction, advance AB formation and disrupt calcium signalling through phosphoryltion of Fyn kinase which forms a complex with PSD95, NMBDA2B and NMDAR –> synaptic disruption, mitochrondiria dysfunction
neuroinflammation
What are
transentorhinal cortex
entorhinal cortex
limbin alloctotex
trans –> structure in temporal lobe, within entorhinal cortex, involved with episodic memory
entorhinal –> in allocortex in temporal lobe and main interface between hppocampus and neocortex, memory, navigation, perception of time
limbic allocortex –> regions of the deeper older layers of the cerebral cortex
What is the adaptive immune function like in AD?
adaptive - occurs as response to the disease
increase of T cells which interact with microglia and AB
What are microglia?
resident phagocyte in the CNS that shares properties with peripheral macrophages and monocytes
What is reactive gliosis and what does it involve?
This is when microglia change chemical and morphology depending on its response to the surrounding environment.
Resting –> long processes that extend from small cell body that scan envirnment for foreign insults.
Activated –> cell body enlarges and the processes become ramified which are directed towards the foreign body
What happens when microglia are activated?
They migrate to the foeign body through a process dependent on ATP.
They initiate an inflammatory response through increased production and relase of inflammatory mediators like cytokines chemokines proteases and acute phase reactants which recruit neightbouring microglia.
What are
cytokines
chemokines
proteases
acute phase reactants
cytokines - immune chemical messengers which have various different types to refulate inflammation through telling cells how to behave: cell activation, cell differentiation, cell proliferation
chemkines - direct immine cells
interferons - initiate defens
TNA - regulate inflammation
proteases - enzymes which catalyse the cleavage of epeptide bonds, hydrolysis of proteins
acute phase reactants - inflammatory markers that mediate indlammatory states
What are the different types of activated microglia?
There is M1 proinflammatory or m2 antiinflammatoey and disease associated microglia.
Appears like s apectrium rather than being one or the other.
DAM is activated in two step process through a trem dependent and trem independent process which enahnces inflammation.
What is the role of oligodendrocytes in AD?
general function –> glia cells that create myelin sheath around neuron axons
in AD –> they become damaged through AB or NFTs,
What receptors are present on microglia?
Microglia have cell surface recpetors which are pattern recognition recpetors
They include tol like, complement, scavenfer, immunoglobin, major histocompatobilitu class I and class II glycoproteins nad leucocyte common antigens
What are the examples of the mediators released from activated microglia?
CD36, IL1, TNFa, IL6
through activation of signalling cascades which promote NFkB transcription of genes
What is the protective function of microglia?
Uses its phagocytic function to internalise and degrade AB for clearance –> adided by AB degrading enzymes and cleared by phagocytosis, autophagy, pinocytosis
accumulate around plaques forming a protective barrier to prevent growth
What is
phagocytosis
autophagy
pinocysosis
recpeotr-mediate endocytosis
endocytosis is matter that is tkaen into the cells and can be phagocytosis and pinocytosis.
entocytosis takes matter by forming a vescle by cell membrane.
phagocytosis takes in large matter by forming phagosomes. Only takes in solid particles, merge of lysosomes with phagosome, digestion
pino cytosis –> fluids and solules are aken in by a small vescle called a pinosome on the cell membrane,degradation by lysosome
receptor-mediated –< the receptors on plasma membrane recognise macromolecules in ECF, which promotes formation of vescle
autophagy is clearance of wate from inside the cell - phagosome formed around cytoplasm and organneles, fuse with lysoosme, release of enzymes for regradation
What is the bad function of microglia?
respiratory burst –> generation of superoxide anions which will migrate to insule during phagocutosis which can be realeased into healthy tissue
ROS and RNS can activate the inflammasome which can release apoptosis proteins and promote duther AB agrgegation
decreased phagocytosis – down reg of expression of AB receptors and degrating enzymes and upregulation of beta-secretase
promote spread of tauopathy thrigh increased tau kinase activity and promoting spread through phagocytosis and exosome secretion
What are exosomes
extracellular vesicles
How does noradrenaline effect cx3cr1 and amyloid pathology?
gonzalez-prieto –> noradrenaline increases production of chemokine cx3cl which acts on microglial cx receptor and reduces it sactivation –> contribute to neuronal damage.
They analysed microglia in 4xfad mice and found increased cx production and increases action on plaques
Li –> found that noradrenaline inhibits microglia dynamics throught he beta-1 adrenergic recpetor, which is impaired in 5xFAD mice due to loss of LC neurons, decreased NA, and activating b2A attntuated amyloid pathlogy
What are astrocytes?
glial cell that forms a tiled organisation throughout the CNS which have a wide variation of functions including immune functions, synaptic pruning, gliotransmission, vasicular control
What did the work of Cajal show?
He worked on astrocytes and made several hypotheses surrounding their role.
He believed that they were able to interact with neurons, other flial cells and blood vessels.
This was proved by electron microscopy later on.
What are the two different types of astrocytes and what are their characteristics?
Protoplasmic –> prominent in grey matter, star-shaped structures with protruding processes that interact with neurons and bloood vessels via end feet
Fibrous –> prominent in white matter, elongated, sitated along myelinated axons, interact with nodes of ranvier
What is
white
grey matter
both essential parts of brain tissue
grey - forms on surface of the brain and in deep grooves, consistents of neurons and allows information processing
white - found in deeper tssues and contains nerve fibres covered in myelin, provides communication between grey matter areas
What is gliotransmission?
This is a way astrocytes communicate.
They are not electrically excitable but can increase intracellular calcium concentrations when communicating to neurons, blood vessels or other glial cells thhrough potassium and sodium channels on their membrane
This enahcned calcium levels which can promote release of neuromodulators
What are some roles of astrocytes?
Gliotransmission
release of neuromodulators
contribute to synaptic pruning by guiding migrating axons
uptake neurotransmitters through transporters on cell surface
control blood flow thrrough release of mediators
control nutrient-waste exchange
immune function
What happens when astrocytes acquire their activated form?
neurotoxic A1 –> neurodegeneration
neuroprotective A2 –> protect environment by promoting clearance, BBB repair, neuronal growth and synaptic resoration
How do astrocytes become activated?
Through micorglia-asotrcyte connection
Release of tnf-a, il1a and c1q activates astrocytes through nfkb signalling pathway causing upregulation of proinflammatory genes
What happens to astrocytes in AD?
Early = reduced synaptic activity, reduced metabolic support, remain protective with protein degradation and antioxidaent defence, phagocytosis
Late = advanced microgliosis and AB on astrocytic recpetors activates cellular signalling causing increases in calcium, gliosis, oxidative stress and neuronal death, expression of BACE1, increased AB production, promotion of spread of tauupathy
What recpetors can ab act on in astrocytes and what signalling pathways does it activate?
P2Y1, nicotinic, glutamate metabotropic, RAGE
AGE-RAGE, nfkB, P13K-Akt
What is a brain state?
This is popultoon neuronal activity which represents a cognitive of behavioural state
They are dominent at diffferent frequency bands caharacterised on their PSD
Several of these brain states can exist at one time across different temporal and spatial scales.
How were brain states discovered?
Hans berger first discovered brain states when he used scalp EEG on a monkey and found 8-12 Hz waves which he called alpha wves.
What are the main differences between low and high frequency oscillations?
Low = involved across large neuronal space, non-active states, neuronal acitvity suncronised, high ampltidues
High = more liocalised in neuronal space, active states, desynchronised activity, small amplitudes
How are other oscillations involved or affected by AD?
Slow oscillations are slow wave <1Hz and are most commonly found in sleeping states such as NREM.
These are osccilations characterised by Steriade and collesgues which have a combination of cycles of up (synch) and down (silence) states.
Occur in cerebrl cortex, thalamus, brains te, etc.
Involved in sleep dependent memoty consoliaation
Formed through recurrent excitation and slow adaptation (dynap depression), or with contributions with inhibitory neurons to control the up/down regulation.
Cells involved for up geneation are NDMA, pyramidal
for down, GABAa, PV and SST
Sleep disturbance found in AD in umans, and decreased dlow wave power during W and NREM in mice
What are gamma oscillations and when were they identified and how?
In 1938 by Jasper and colleagues
______
They are waves at 30-80 Hz whcih are fast, local and involved in cognitive functions like attention, memory encoding, object and face recognition and owrking memory.
They are present across several brain regions like neocxortex, entorhinal cortex, amygdala, hippocampus, striatum, olfactory bulb, basal forebrain and thalamus.
How did the studies discover what functions gamma oscilaltions are involbved in?
attention - increased gamma power and coherence during tasks with focussed attention, in human studies EEG show stronger gamma bands in attended visual stimuli than unattended
memory encoding - active learning of visual shaped was shown by enhanced gamma power in temporal EEG, increased gamma in MEG in dpatial task, studies where patients memorise sequenceis show increase in gamma
object and face recognition - MED study showing pictures of lanporks show increased gamma
working memory - two epileptic patients performed wotking memory task and show increased gamma with memory load
Where are gamma oscillations most prominent and what did this mean?
The superficial cortical laters and the dendate dyrus
This suggested the requriement of inhibitory interneurons
What are
inhibitory interneurons
pv neurns
chandlier cells
somatostatin-containing OLM interneurons
cholecytokinin basket cells
Martinotti cells
interneurons are neurons found in CNS and act as middle man between efferanad and afferent neurons, allowing communication, these exhibit inhibitory signals for stabulity of the brain
PV neurons –> an interneuron subtype that express parvalbumin (calcium binding protein) which can be found as basket cells in amygdala, striatum, cortex and hippocampus, and chandelier cells in cortex
chandelier cells - type of GABAergic interneuron which are PV-containing and fast-spiking, they have many branching axons.
SST_OLM - OLM neurons are a subset of GABAergic interneurons which will only express SST, will only be found in the hippocampus
cholecytokinin basket cells –> subset of GAABergic internueorns found in the cortex and cerebellum, the processes form a backet around cells somas and dendrites
PV, SST and CCK are all markers that can be expressed by thes inhibitory neurons which wll alter their function and location.
PV –> calcium binding protrein
SST –> peptide hormone
CCK –> peptide hromone
martinotti neurons - dendritic targeting interneurons that project to layer 1 of cerebral cortex, short branching dendrites, can be found in cortex expressing SST
What is perisomatic inhibition?
a type of synaptic inhibition where inhibitory signals target the soma of a neuron.
it will rlease inhibitroy neurrotrasnnitters which hyperpolarises the neuron, and inhibits it drom gernationg AP.
This is done by inhibitoru interneurons such as basket cells and chandelier cells.
How was the function of gamma oscillations discovered?
montiroing LFP in rat hippocampsus
computerational models
brain slice xperiments
optogenetic experiments
What are the suggested mechansisms of gamma oscillations?
interneuron gamma
pyramidal-interneuon gamma
inheriting gamma
What is the ING mechanism?
mutual inhibition between two inhibitory interneurons through GABAarecpetor mediated inhibition which results in strong inhibitory feedback that generates gamma oscillations
high firing, low noise –> inhib neurons dire with sharp synchrony
irregular noisy –>recurrent synaptoc interactions will overcome asynchrnous allowing generation
synchrony occurs when interneuron and partner neuron discharge and have IPSP in synchrnoy
What are inhibitory postsyanptic potentials?
An inhibitory postsynaptic potential (IPSP) is a type of synaptic potential that reduces the action of a postsynaptic neuron.
The influx of negatively charged ions causes a transient hyperpolarization of the postsynaptic membrane, driving the neuron away down from the membrane potential, away from the action potential threshold so that it wont fire, resulting in an inhibitory postsynaptic potential (IPSP).
What findings support the ING mechanism?
optogenetic experiments showing activation of cortical PV+ GABAergic neurons, but not other subtypes, generated gamma oscillations
in vitro show activating metabotropic flutamate receptros result in muttual inhibition between internaurons and generationof gamma oscillation
What is the PING mechanism?
inhibitory neurons and excitatory pyramdal cells
interaction between quick AMPAR excitation and slow GABAaR feedback inhibition through a cyclic behaviour
Axon conductuon and synaptic delays cause 5ms phase shift between the spikes which determine the freqyency
What is feedback inhibition?
Feedback inhibition in neuronal firing by interneurons refers to a regulatory mechanism in which inhibitory interneurons provide inhibitory feedback to modulate the activity of other neurons within a neural circuit. This feedback inhibition plays a crucial role in shaping the dynamics and function of neuronal networks.
The process typically involves the following steps:
Excitatory input: Neurons within a neural circuit receive excitatory inputs from other neurons or sensory stimuli.
Generation of action potentials: Upon receiving excitatory inputs, the postsynaptic neurons may generate action potentials, leading to neuronal activation.
Inhibitory feedback: In response to neuronal activation, inhibitory interneurons within the circuit release inhibitory neurotransmitters, such as gamma-aminobutyric acid (GABA), onto the postsynaptic neurons. This inhibitory feedback inhibits further neuronal activity by hyperpolarizing the postsynaptic membrane or shunting excitatory currents, thereby reducing the likelihood of action potential generation.
Regulation of network activity: The inhibitory feedback from interneurons helps regulate the overall activity level and excitability of the neural circuit. By providing negative feedback, interneurons can prevent excessive neuronal firing, maintain the balance between excitation and inhibition, and shape the temporal and spatial patterns of neuronal activity within the circuit.
What studies support the PING mechanism?
PING c an work withotu ING as removal of II connections in mice did not effect gamma power in ca1
manipulating connection between interneuron and pytamidal cells by knocking down AMPARs reduces the amplotude of gamma
What is the inheritence approach?
inherited from upstream brain regions
occur through phase-phase or phase-amp coupling occurs
phase-phase –> faster oscillation couples the several phases of slower rhythm
phase-amp –> the amp of faster oscillation is modulated by the phase of slow hythm
How do the basal ganglia and ventral tegmental area lack vital connectyions for PING?
Because while they contain populations of excitatory neurons they do not have interaction with inhibitoru interneurons in the ssme manner as PC-PV
What diseases has gamma alterations been found?
sxhizoprenia
autism
elilepsy
AD
PD
How are gamma oscillations affected in humans?
decline in LTP
dysfunction of PC interneurons
EEG or MEG have conflucting - some show reduction in gamma power while others show an increased
Why might the changes in gamma oscillations in humans vary across findings?
Differences in experimental conditions - awake/eyes closed, resting, music etx
stages of AD
varied conrol gtoups - MCI or healthy
EEG recording –> combination with TMS may help
or
compensatory mechanisms
What are the compensetary mechsnisms thought to exist in human gamma oscillations?
> 300 preAD
inverted u shape relatinship between AB depositions and gamma band power –> gamma power depends on extend of AD pathology
at first at low gamma, gamma increases suggesting compensatory mechanism
at high plaques gamma power decreases, suggesting breakdown of neuronal circuits
Thougtht to be because AB interfere with PING mechanism
What is theta-gamma coupling?
this is where gamma oscillations are modulated by theta oscillatiosn through synchronisatioon or phase locking of gamma oscillations to the phse of theta oscillations
This createes a nested organisation,
Can occur through cross-frequency coupling like phase-amp, phase-phase,
Can be found in hippocampus and neocortex. Involved in memory, attention.
What is found for gamma oscillations in mice?
decreased gamma power seen across various animal models in slice experiments and in vivo
alterations in activity of inhibitory neurons such as PV, SST, CCSK across hippocampus and PFC thought to be due to vulnerability to AB and tau
Why do you think you do not see the inverted u-shape in animal model gamma ocilation trends?
Because of difficulties mirroring the disease progression - need for LOAD models.
What examples of modulating gamma oscillatoons show this to be a good target?
restoring PV interneurons in hAPP mice improved gamma ang cognition
optogenetic activation of PC and SST neurons restored gamma functions like thera-nested gamma induced spike timing
optogenetic actvation of PV neuron in 5xfad improved memory retrieval
What are the current drugs available for AD treatment?
acetylcholinesterase inhibitors - donepezil, rivastigmine, galantamine
NMDA antagonists - memantine
In US, china and japan - antibody treatments avaialble which sequester AB
What is the MOA of acetylcholineesterase inhibitors?
Acetylcholinesterasse is an enzyme involved in the chemical breakdown of acetylcholine
These work to prevent this breakdown and promote the extracellular levels of Ach for action on recpetors in order to enhance signalling
What are the common effects of acetylcholinesterase inhibitors?
First gen (tacrine) was liver toxic
Second gen - delayed disease progression by delaying cog decline in ADAS-Cof score by 6-12 months by imrovement of 3-4 oints
Donepezil - increase cerrebral blood flow, reduce cortical thinning, astrophy
What are the downfalls of acetylcholinesterase inhibitors?
Some mild side effects which are dose related
Patients can be treatment resistent
only 60% show a therapeutic response to drugs
Very mild effect
mild-mod
What is memantine?
NMDA receptor anatagonist
This works to non competitebely bind to the receptor and block glutamate binding, to reduce glutamate signalling
This is done to reduce the exotocic stress found throughout AD and hyperphosphorylation of tau
What are the clinical effects of memantine?
Significant improvements in cognition and behaviour in moderate-severe patients only
Very small effects
Commonly prescribed with acetylcholinesterase inhhibtiros
What do the studies show twhere alterting synaptic activtiy modulates AB levels?
There has been evidence that therre is hyperactivity in preclinical AD which has been shown to modulate AB depositon.
Bero 2011 - vibrissal system - show modulation of activity modfulated AB levels
Cirrito 2005 - in vivo microdialysis they show AB levels in IDF increase when synaptic activity increased
Yuan 2016 - investigate if attentuation of neural acitvity using inhibitroy chemogenetic dreads can reduce plaque pathology. It decreased aggregation, and loss of synaptic loss
Yamamoto 2015 - used optogenetic stimulation of ChR2 in APP mice and microdialysis to m onitor change in AB levels. 5 mo chronic opto incrfeased AB burden.
Rodriguez 2020 - chemogenetic attentuation of EV hyperactivity reduced AB accumulation and tau spread
Why do you think targeting neuronal abberations might help?
Because it can have many functions
1) restore normal neuronal balance which will reduce neuronal damane and promote synaptic plasticity and cognition
2) reduce molecular pathologies
3) improve glia activity
What are the new FDA approved therapies and how do they work?
aducanumab - monoclonal antibody that sequesters AB fibrils
iv administration 45-60min every 4 weeks
lecanemab 0 monoclobal clearing AB
iv infusion every 2 weeks
Why was the approval of these drugs contraversial?
Approved on the FDAs accelerated scheme which means they dont need to finish all phases of a trial before the drug is available with the promise of completeing a recovery trial
was because only one subset of patients showed a slight cognitive benefit with many side ffects like oedeme and microheamorrhages in some
Also this was completed in early ad so no efficacy or safety data at other disease stages
What other drug targets are there?
oxidative stress - antioxidants and vitmin suppkementation (vit E)
antispsychotics
antibiotics
What is neuromodulation?
the manipulation of neuronal ativity to promote or reinstate normal neuronal functionality
What is
DBS
VNS
deep brain stimulation is where electrodes are chronically implanted into the human brain for delivery of electronic pulses
vagus nerve stimulation involves implantation of an electrode into the vagus nerve and supplying electrical stimulation. the vagus nerve is the main nerve of the parasympathetic system (when in resting state) and controls function of various organs.
How has DBS been used for AD?
First done in 1984 but no changes were found.
In 2020 stim n hypothalamus reached phase II after reductions in cognitive decline and increased hippocampus volume, but then some pateitns worsened so the trial terminated.
How has VNS been used for AD?
Some improvement in cognitive tests but none approved.
What did merton and morton do?
They developed an approach for non-invasive brain stimulation which means the skull does not need opened and instead the electrical current is supplied over the human scalp to result in activation of cortical regions.
It resulted in the development of several transcranial brain stimulation methods like TMS, tDCS and tACS
What is
TMS
tDCS
tACS
transcranial magnetic stimulation –> delivers rapidly alternating current hrough a coiled wire above human scalp
transcranial direct current stimulation –> delivers current through electrodes placed on scalp surface with electrical current penetrating skull completing through anodal and cathodal electrodes. Anodal shifts resting potential towards diring, cathodal hyperpolarises surrounding neurons.
transcranial alternating current stimulation –> delivers oscillating current at certain frequency
How has TMS been used for AD?
30 sessions of 20 Hz for 6- weeks improved cognitive score
How has tDCS been used for AD?
Improbeent in cognitive tests after treatment for 10 days in AD patients
How has tACS been used for AD?
helathy subjects show improved cognitive funcitons but limited studies in AD patients.
Why might these neuromodulatory approaches have a benefifcial effect on cognition?
prolonged and enhanced neuronal activity promotes synaptic plasticity through LTP and LTD
What is
EF1alpha
DIO
ChETA
Ai32
ef1alpha - protmotoer expressed in most cell types
DIO - double floxed inverted open reading frame – enables conditional and cell-type specific expression using two loxp sites plaqces inberted orientation flanking the transfene. Then in cre-dependent neurons, this cre recombinase will allow cleavage and expression of the trangene
ChETA - modified version of ChR2 have faster knetics and light sensitivity
Ai32 - mouse line that contains cre-dependent ChETA
What were invasice 40-hz studies?
Optogenetic stimulation of PV interneurons in 5xfad mice at 40-Hz using chr2 in ca1
Increased LFP gamma power
Reduced AB by 50%
increased microglia activation
___________
Anothewr actuvatung medial septum show improved spatial memory
_______
Another increase AB pathology –> potentially due to the AB induction mechanism
How was the induction mechanism different for Wilson 2020?
Because they express channelrhodompson in PV neurons but then oprogenetically stimulatie the basal forebrain PV neurons
They do this as these will project to the cortical GABAergic neurons in order to sllow entrainment of upstream regions.
Why might this paper show an increase in plaque pathology compared to others?
Potentially because gamma oscillations being generated in an alterantive way may ave opposing effects.
What is temporal interference and ultrasound stimulation?
TI –> using multiple electrical fields with a frequency in range of neural activity
US –> ultrasound waves from coils on brain suface, will vibrate neuronal circuits
What are some examples of non invasive 40-hz stimulation (not genus)?
transcranial focused ultrasound at 40-Hz targeting hippocampus for 1-h per day for 5-days increased microglia and colocalisation of microglia and AB
tACS modulated gamma activity
What were the first 40Hz sensory experiments, what did they do?
Rager Singer 1998 - visual light flicker of variable frequency and measured signals by LFP recordings, showed increase in gamma range
Herrmann 2001 - clinica trial in humans presented with flickering light and seen increase at 40-Hz
Jones 2019 - monitored EEG in humans by 40-hz light flicker, seen increase 40-Hz with more entrainement with eyes open
Pastor 2003 - 16 humans EEG, 40-Hz activation of cisual cortex
What did Iaccarino show?
Optogenetics –> decreased sol/insol AB, increaded microglia RNA phenotype, microglia
Acute –> reduction in soluble AB40/42 levles, not insoluble by 50% in virusal cortex and hippocampus, enhanced phagocytic microglia phenotype, reduced phosphorylated tau –> effecrts were transient
Chronic –> 1h/7 days –> reduction in plaque load and area in cisual cortex but not somatosensory or hippocampus
What did Adiaikkan show?
They completed genus and showed an improved cognitin
Is the effect of GENUS specific to 40Hz?
The landmark studies also test other frequencies such as 8, 80 and random and they did not see any other effects.
Buszaki paper test 4hz as he sas this is the normla for visual stimulation.
What do tsai and colleagues show (Martorell)?
A –> entrainment of gamma in AC and hippocampus, reduced AB and improved behavipour in NOR/NOL, vascular association with AB, vascular dilation, reduced tau phosphorlation, increased microglia and astrocytic repsonse
AV –> entrainment in CA1 and PFC, activated cluistering phnepotype of microglia across these regions, reduced AB in mPFC
What did Ismail and colleagues do in 2018?
First clinical trial in humans for sensory stimulus
6 patients with either AD or MCI
10 days of 40Hz light for 2h per day
No significant decrease of AB found
promted an increasin duration of treatment.
What did He 2021 do?
AV stimulation 1h per day at 40 Hz for 4-8 weeks
10 patients with MCI
neuronal activity entrained at 40Hz during sessions
improved functional connectivity in default mode network after 8-weeks
no change in AB athology, tauopathy or immune profiles
What did Cimenser 2021 do?
AV stimulation 1-h per day 40Hz for 6-months with eyes closed
patients with mild to moderate AD
improved circadian rhythmicity
cognition stable, while control groups declined in scores
What did Chan 2022, Da 2024 show?
The same trial but at different phases.
AV stim at 40 Hz for 3-months
What patients??
entrained gamma oscilations across multiple regions 0 cortical and hipoicampus
decreased ventricular enlargement
improved circadian rhythmicity
improved functional connectivity of the DMN
reduced hippocampal atrophy
improvements in face-name associated delayed recall tests
no sig changes in cog score tests
What is the DMN?
a large network of brain regions: mPFC, posterior cingulate cortex, RSC, medial temporal lobe, lateral temproal cortex
Supports various brain functions and is active in awake states.
abnormalities found in AD
What do other clinical trials show?
Assessing the safety of the treatment - find good adherance and mild side effects
___
What are some side effects noted in clinical trials of GENUS?
seem to be rare and mild
worsening of hearing loss
mild dizziness
headaches
What is cognito therapeutics?
This is a company made by Tsai and another colleague where they have made a human headset that has headphones and glasses for AV stimulation.
They have started a large clinical trial in several hundred mild to moderate AD patients
1h AV tratment for up to 1 year
What do Garza 2020 and Prichard 2023 show?
increased activation of NF-kb pathway within 5-60 mins, MAPK pathway after 60-mins
increased gene expression of the proteins involved in these pathways
increased expression of NF-kb in neurons, not microglia,
thought neuron activity increase, increase calcium, increase activation of neuron nf-kb pathway, increase transcrption and release of cytokines, cytokines acitvate microglia
How are glial cells involved in the generation of gamma oscillations?
use their ion buffering functions to regulate ionic flow across cortical layers
secodnary-mediated response through action on noradrenaline pathways
However, it is not through actuon on GABAergic neurons as a GABA antagonist attentuated the neuronal and microglial effects.
How does GENUS effect the inflammatory pathway?
increase activation of the NFkB and MAPK siganllign pathways through phosphorylation of cascade proteins
promote transcription of cytokines
recruitment anda ctivation f microglia
promotion of phagocytosis, clearance of plaques, neurtrophic functions
As well as the inflammatory pathway, what other functions can GENUS work?
It promotes vascular dilation and cerebral blood perfusion, promoring AB clearance
Some human studies also show a decreased hyperexctiability which will restore EI abalance to prevent synaptic damage and astrophy
This can all promote reduction of neirnal loss and promote behaviour imprrovements
What are some benefits of GENUS?
low cost
easy to implement
usef fiently
no tissue damage with other neuromodulation approaches
What are some limitations of GENUS?
lack of cell-type specificity
effects across disease stage, sex differences remain unclear
brain wide effects unknown
MOA unknown
conclicting findings not understoof
normal effect on gamma in AD not known
effect of enhanced mciroglia unknown
Wat arethe considerations needed when choosing an animal model?
not a full representative of human disease
each model has different phenotype
powerful for research
choose a model suitable for your experiment
What types of animal have been used for AD rresearch and how?
rodents - genetic manopuation
non human primaes - lemur and various types of monkeys, gorrilas,chimpanzee, show natural generation of AB, some with tau, some with atrophy
dogs - show agre dpenedent rise in AB and tau, decline in cognition, inglammatory markers
dosophilia - expression of human genes, with APP being same basic structure as human APP, contains all secretases, produces AB fragments, also tragegene can be done using CRISPR
zebradish - tau transgenic, show phosphorylation and congormaiton changes of tau, goof for in vivo imaging
c-elgans - it contains human ortholog of APP and tau genes so can make transgene stains to produce AB40/42
What are other types of model that people can use?
live human brain tissue
IPSCs
zebrafish embyros
cell based cultures
Why are mice the most common aniaml model?
short lifespan
rapid reproduction
easily maintained
What late onset models have been developed?
Trem2 KO mice - mutations associated with LOAD
consortium working on development
humanised AB, APOEe4, TRem2 mutation incorporated into C57 –> no behavioural phenptypes increased inglammation, no plaques
hAB Ki –> agre related increases and impairments
What tau models are there and how are they developed?
3xTgAD - Oddo - triple transgenic mouse model expressing APP and tau301P trangenes on PSEN1 KI background –> forms amyloid, tauopathy, gluosis, synaptic damage and memory deficits –> limitation is the mutation of tau is not found in AD
Tau P301S
eTg4510
For animal models, wht are the promoters?
The promoter ensures the transgene is exressed at the appropriat levels in the relevent cell population
What is the general story of the generation of APP mouse models?
firs establused in 1990s through genetical engunerring where they used trangenesis to express FAD mutations in mice
These increased AB and cognitive decline but did not have tauopathy or neurodegeneration
Decelopment of models using mutations in PSEN instead but failed to have AB
Development of double transgenic mice that coexpress muttations in both APP and PSEN1/2
Have addiditve effects causing enhanced AB formation
What is trangenesis?
genetic engineering techniqie used to introduce foriegn DNA from another species into the genome of an organism.
1) isolate gene of interst
2) construct transfene by adding promoters
3) delivery into organism –> common approach is microinjection into fertilised eggs or embyros
4) integrated into genome
5) PCR
6) breeding
What are limitations of APP models?
APP not authentic
off-taget effects of enhanced APP/AB –> neuronal functions, calciumgomeostasis, transcription
specific to FAD
Who developed the PDAPP model and what does it do?
first generation in 1995 by Games
APP with Indiana mutation with PDGF-b promoter
AB from 6-months in cerebral cortex with spreads wirth gliosis and age
synaptic problems at 8-months
no tauopathy or neurodegeneration
memory loss at 3-months
Who developed Tg2576 micer and what they show?
Hsiao 1996
mutations in APP - swedish under hamster prion promoter
plaque and gliosis from 10-months
memory impariements - spatial - at 10-months
no neuronal loss
Who developed J20 mice and what do they show?
Mucke 2000
overexpress APP through swedish and indiania mutation
plaques from 5-6 months
gliosis form 6-9 months
neuronal loss from 30months
cognitive decline from 4-months
Why might you see cognitive decline before plaque pathology?
Because in APP models there is large overexpression of other AB fragments that usually have physiological functions. So overexpression of these could cause impariments.
Who developed APP/PS1 and what do they show?
Radde 2006
APP swedish mutation and PSEN1 without exon 9
plaques from 6-months with gliosis
memory impariemtns - spatial - from 5-6 months
Who developed 5xFAD and what do they show?
Oakley 2006
express 5 FAD mitatuons in APP (swedish, glotida and london) and PSEN1 mutatiosn
site directed mutagenesis
rapid formation of AB depositions from 2-months with fliosis
synaptic degeneration from 4-months
neuronal loss from 6-months
loss of cholinergic neurons at 6-months
30% less PV cells at 12-months
formation of intraneuronal AB
memory impairements from 6-months
hyperactivity
sleep disturbances
no tauopathy
sex differences
What are the sex differences in 5xFAD mice and why?
AB continues in males and plaques around 10-months
females plaquteu around 14-months
oestrogen acting on the oestrogen response element situated on the Thy-1 promoter
What are KI models?
Made to overcome limitations of APP overexpression
Introduction of humanised AB which contained FAD mutations in APP
First was swedish and Beyretuther/iberian mutations generating APPNL-F
Increased AB, limited change in APP from 6-months
change in synaptic health
cognitive decline at 18-months
To make more aggresive other mutations have been inroduced
What is humanised AB?
humanised AB is a modified version of AB that has been genetically motifiedd to minimic the human form
This was done by changing three amino acids
and is now used for animal model generation
What is the APPNL-G-F model?
An animal model generated by Saido and colleagues.
an APP knock in model that contains swedish, iberian and arctic mutations
No overexpression of APP, but increased AB production, AB42/40 ratio and aggregation
Similar to NL-F but the pathology is accelerated.
plaques ~3-months and cognition and spatial deficits ~6-mo
What are the KO/KI models for LOAD?
humanised AB ki
tau ki
APOEe4 Ki
What other KO models were made third gen?
To prevent use of swedish mutation ad it interfers with use fo beta secretase inhibitors
Sato developed APPNL-F/PSENP117L
Why did you choose your mouse model?
needed aggressive AB load to confirmsystem
not investigating pathological contributions so dont need native pattern
dont need presence of taupathy
quick phenotype
What is histological assessment?
What are the pros/cons?
Sectioning of tissue and undergoing iterations of washing and staining with stains or antibodies ebfore mounting sections and imaging with a specific microscope.
Pros - easy, cheap, qwuick, reliable
Cons - labor intensive, time conduiming, damage to sections, no 3D distbition, single read out
What is microdialysis?
What are the pros/cons?
Usually used to samle neurotransmitters etc within the brain ISF. Soluble AB released by neurons into brain ISF - measure of AB metabolism and degradation.
A probe contains tubular dialysis membrane which lacks whatever you are trying to measure. Then perfusion begins and the molecule will pass into the tubular probe.
Then the probe will be removed and the collected solute will be measured through various techniques like spectrometry.
Pros - precice measure, cna be done in vivo, allows repeat measure, long recording times
Cons - depletes surrounding area, tissue injury, loe temporal resoliton
What did the group of Yuede 2016 do?
Developed a mcriumminoelectrode probe that was coated in AB antibodies to try improbe microdialysis approaches to be quciker
This involved amperometry which quantifies the oxidation of tyrosine residue at position 10 on human AB –> level of current reflects AB levels
had a loss of sensitivity after 2-h and only able to detect human AB so limited.
What is multiphoton imaging?
What are the pros and cons?
Where multiple photons are used at the same time at lower energy to cause the same energy transfer as a single photon. Allows longer wavelengths to be used to allow deeper imaging to occur. It uses pulsed laser to prevent excessve energy use.
Pros - high resolution (~1um), longitudinal monitoring of plaques , repeat measures, low bleaching
Cons - low temporal resolutin. head-fixed, anaesthetised, inflammaiton, low depth resolution
What are the differences between single and two photon?
Single photon
single high eneergy, low wavelength for excitation, limited depth, greater photodamage due to higher energy photons
Two photon
use of two lower energy photons by using two photons at double the wavelength –> generates the same energy, better depth resolution, pulsed laser reduces bleaching
What are endoscopes?
Rigid or flexible small diameter light guice that can be inserted into the brain for light delivery and collection
What are CT scans?
What are the pros and cons
takesseries of xray scans around the body
Pros - hgih reoslution (1mm), low cost, available
Cons - low resolution, hard to implement in lab
What are MRI scans?
Whar are pros/cons?
MRIs employ powerful magnets which produce a strong magnetic field that forces protons in the body to align with that field.
Pros - high spatial sres, moderate cost, probes can be stored long termm, repeat measures,
Cons - no freely behaving, low temporal resolution
What are PET scans?
What are pros/cons?
inj of radioactive tracer, pet system monitors the number of photons emitted from the radioactive substance
Pros - markers, 3D analysis
COns - expensive, low abailaniliy, not accessable, short half life, storage issues, varied results across animal
What did the group of Ni 2022 do?
They worked on developing a 3D scanning approach using large field multifocal ulllumination and optoacoustic tomography
Used Ab probe called HS-169 which was injected IV bolus when mice were anaesthetised. Not been shown for use wwith ip inj. LMI allowed measurements of cortical AB deposits but had limited depth,
Developed a vMSOT sytstem (volumetric multispectral optoacoustic tomography) for mapping AB across whole brain. This had massive tranduar above head with mulriple points for ultrasound waves to pass as a variton of wavelenght
What otoher amyloid probs have been ddeveloped?
Chen 2018
Dong 2010
yang 2021
klunk 2002
klunk 2004
skovronsky 2000
sundaram 2014
Chen 2018 - CRANAD-3 - infraref probe but requires specific maging that limits spatial resolutin
Yang 2021 - Akalumine - luciferase which is sequestered byy AB to re;ease akalumine creating bioluminescence
klunk 2002 - m04
klunk 2004 - benzothiazole amyloid binding agesnts - modified thioflavin T by adding benzothiazoles, allow PET imahing
skovronksky 2000 - ratioligand probe called BSB which show affinity to AB after intravascular injections
What do Yang 2021 shiw?
Developed a new way to monitor AB using bioluminsecence imaging
Previosus work done try to insert luciferase into the AB or APP fragement but this alters its functions.
They developed Akalumine which is a substrate for luciferse which binds to AB to which will promote the rlease of Akalumine and cause bioluminescence.
In normal conditions, Akalumin binds to luviferase to generate bioluminescence which declines rapidly. With AB, Akalumine will be sequestered inside the aggregates and will be slowly released. Therefore, if AB is presenent the bioluminescence should last for longer.
They show good binding properties, an enhanced buoluminsecce, and show gewarer intensity in 5xfad mice
What is bioluminescence?
production of light by a living thing through chemical reactions
in the body, luviferase is an enzyme that catalyses oxidation of luciferin causing it to product a glow
What is fibre photometry?
What is its pros/cons?
optical method where implanting an optic fibre into the brain and illuminating and collecting emitted fluorescence
pros - real time, rapid temporal resolution, access to deep brain regions, awake behaving aniamls, cheap set-up
cons - low spatial resolutoon, indflammation
What did Klunk show?
made m04 by removing carboxyl groups.
showed staining in post mortem brain slices
showed competition goof binding affinity.
injected iv and ip and showed comparable staining with topically applied TS
How did congo red bind to AB?
parallel to the AB fibrils but antiparallel to beta sheets
required minimum of 5 AB monomers
hydrogen bonds formed between positibvely charged amino acid residues on beta sheets and negatively charfed sulfonate groups on CR
What are
hydrogen bonds
sulfonate groups
hydrophilic
nitrogen double bonds
suldonic acid groups
hydrophobic
naphthalenesulfonic acid groups
salicylic groups
carbon double bonds
carboxyl groups
H bonds - weak electrostatic attractions between hydrogen atom –> important for stabilisation
sulfonate - chemical groups containing sulfur atom bonded to three oxygen atoms and one carbon. Negatively charged, hydrophilic and promote water solubulity
hydrophilic - addinity for water, polar, charged, dissolve
nitrogen double bone - two paris of electrons shared between two atoms –> stronger and rigid structure
sulphonic acid - sulfor atom bonded to three oxygen and one hydrogen. Strong acidic groups, water soluble
hydrophobic - repel water, insoluble, nonpolar, aggregate
napthales - sulfonic acid groups attached to napthalene ring structure, used in organic synthesis
salicylic - phenolic ring, caboxyl acid froup, common rganic product
carbon d - two pairs of electrons shared between two carbon atoms –> restricted roataion
carboxyl groups - functional groups containing cabonyl (C=O) and hydrocyl group attached to carbon, acific
What are the pros and cons of congo red?
pros - allows more understanding about AB structure and growth, was used as a derivative to make more dyes
cons - low selectivity, had hydrophilic charge which meant it couldnt pass the BBB, large MW
What dyes did congo red make?
chryamine G
Methoxy-x34
Methoxy-x04
How was chryamine G formed?
Characteristics?
Removal of acidic naphtahalensulfonic acid groups
repaced with less acidic and more lipophloc sallicyclic hroups
Less acific
more lipophilic
poor optical properties
How was methoxy-x34 formed?
Characteristics?
removal of acidic napthalasulfonic acid groups
addition of salicyclic groups
replacement of nitrogen double bonds with carbon double bonds
reduced molecular weight
improved fluorescent properties
rediced lupophilic properties
limited entry to brain
How was methoxy-x04 formed?
Characteristics?
removal of acific napthasulfonic acid groups
addition of salicyclic groups
replacement of nitrogen fouble bonds with carbon double bonds
removal of carboxylic group
reduced molecular wight
improved fluorescent properties
imrpoeved lipophility
What have other studies used M04 shown?
Knlunk 2002
Condello 2011
Crowe and EllisDavis 2013
Hefendehl 2016
Hefendehl 2011
Jung 2015
Mayer-Leuhmann 2008
- development, proof of ip and iv administration in vivo
condello - injected M04 in vivo and then several days later harvested brain and applied TR to see difference in growth, did up to 90-days and M04 rermained, quantified speed of plaque gwoth
Crowe - followed plaque growth over 4-weeks in 5xfad mice
hefendehl 2016 - montiroing glutamate dynamics with new sensor around AB in APPPS1 mice using 2PM, show increased glutamate next to plaques , inj 24 before each imaging session
hefendehl 2011 - use multiphoton to show AB formation over time in APPPS1 to determine their growth rate, m04 injected before each imaging session, some with GFP under iba1, show longitudainal monitoring
jung 2015 - inj 24 before each recording with 2PM in APPPS1 mice to see the accumulation of microglia
Mayer - to monitor plaque gworth and the recruitment of microglia, injected with M04 before imaging sessions
liu - study effects on microglia on AB in Cx3cr1 mdeficit mice with time lapse imaging using 2Pm, see stable signal of m04 over 90 days
Pros and cons of M04
Oros - good BBB permeabiity, administered ip and iv, stably bound, only available
COns - overlapping spectra, low wavelength, binding to beta-sheets
What does Adelsberger 2005 show?
first to use fibre photometry for neuroscience
stained the neocortex through multi-cell bolus loading of calcium indicator oregan green 488 BAPTA-1
monitored spontaenous calcium trnsients
What was fibre photometry used for before neuroscience?
chemical densing
optics
Pros/cons of FF?
Pros - low cost, commercially avalable, reliable
COns - difficult implanting, damage to tissue, one depth
What did the studeis do?
Cui 2013
Gonzalez 2016
Kupferschmidt 2017
Natsubori 2017
Pisanello 2019
Tecuapetia 2014
How are TFs developed?
a fibre is placed into two clamps, leaving a centre region free which is the pulling region.
This pulling region is heated using a special laser causing the fibre to melt.
Upon melting, the clamps begin to move at a specific speed to acquire the desiired taper thickness and angle –> parameters corresponding to higher viscosities (higher VELOCITY and negative DELAY values (continued heating)) produced longer and thinner tapers
this creates two TF
Pros/cons of TF?
pros - better implant, not as inavsive, lowwer inflammation, bettter depth reiltuoon
Cons - limited depth resolutiona cross brain, frahile, not much info on analusis
What are GECIs, GEVIs how they work?
GECI
genetically encoded calcium indicators - change fluorescence in response to changes in intracellular calcium
senses the change in calcium by a calcium protein
can be FRET based and single fluorophore based
GEVI
genetically encoded voltage indicators - change fluorescence in response to changes in membrane potential across neuronal membrane
detects these changes by a voltage sensing domain which can be poteassiu channels or rhodosposns, proton channels
FRET or single fluorphore
What are the main considerations when choosing a sensor?
biocompatibility - not toxic to rodent
SNR - detect a strong signal
photostability - deterioration of signal
excitation/emission spectra - no overlap with other controbutors
kinetics - depends on what your sensing
expressed
How can a sensor be expressed in a mouse? and what do they mean?
trangenesis – genetic manipulation by introducing modified gene
viral gene derlivery - delivery of packaged virus which contains the sensor
in utero electroporation - injected into the ventriles of embyronic brain and then electrical pulses are used to transfer the DNA into cells
multicell bolus loading - injectioninto extracellular spcace, diffusion
Pros/cons of trangenesis as sensor delivery?
brain wide expression
remains stable iver severla generations
varied expression throughout the brain - interfere with region/[athway speciifc experiemnts
Pros/cons of viral delivery?
region and cell specific manner
cellular location
synaptic direction
difficulty targeting, invasive
What can contribute to AF for fibre photoemtry and how?
brain tissue –
m04 spectra short which will absorbed greater
brain depositions exist at this wavelength - lipofuscin emmit at 650 with bandwidth of 100 nm
bleaching of tissue
FP system –
optic fibres and patch cable have internal reflection
conflicting reflectiveindexes cause energy to be released into cladding which transfers to fluorescence
recovery over time
Why do TF have more AF?
the material that is used has greater AF
also the melting of the core and cladding may allow molecules in which increases AF
How do movement artifacts occur?
displacement betweern brain tissue and optic fibre
movements of patch cable
corrected using isospectiv channel
How does Pisano 2019 manupulate light along the TF?
The same way we do by measuring the srea od the light collection prfoile and modelling approach to make it all equal to ~1mWmm2
What was the hypothesis and aims of chapter 3?
combination of M04 and FF will allow detection of plaques in vivo
to conform this novel approach is feasible to monitor plaques by identifing a positive correlation with histology
What was the hypothesis and aims of chapter 4?
that TF photometry allows in vivo real time depth resolved plaque detection
to establish a novel protocol for real time in civo plaque accessment across depth by determining optimal light protocols and analytical approaches for using TFs
What was the hypothesis and aims of chapter 5?
this approach will allow monitoring of plaque modifications caused by GENUS
expose mice to genus and monitor changes in AD pathology by determining the effects on neuronal activity and plaque pathology
What is dementia
What are the different types of dementia
dementia is an umbrella term used to describe a set of diseases that have memory loss.
There are various types which include AD, PD, vascular dementia, dementia with lewy bodies and frontotermporal dementia, and mixed.
AD - cahracterised by AB, tau, memory loss, most common
PD - characterised by motor symptoms, loss of dopaminergic neurons in substantia nigra, can occur with dementia
VD - impaired blood flow to the brain
DLB - characterised by alpha-synucleic in lewy bodies
FTD - loss of temporal and frontal lobes, mutations in TDP
mixed - mix of different types, like AD anf VD
What does livingston 2020 show?
to review all recent meta analysis studies to show the risk factors of dmentia.
- 3 new risk factors: alcohol, TBI and pollution
- charactierisated into early, middle and late life risk factors
- education earl life as after late adenlecsnce protection not as evident
- mid can be heating loss and TBI as these are prevantable with hearing aid and reduced risk of head injuty
late can be poluution and smoking - even stopping smoking for 4 years reduced the tisk
What is selective vulnerability in AD?
selective vulnerability refers to subpopulations of neurons in brain systems that may be more probe to abnromal function or death due to disease.
In neurodegenerative diseases it can be complex due to various proteins that can interfere with various types of neurons and brain regions.
Neurons in EC and CA1 are vulnerable to decreased oxygen and glucose dlivery.
However, most studies have failed to gather a deeper knowledge on this.
RNA-seq studies show that in EC excitatory neuron populations were selectively vulnereable, in layer II including pyramidal neurons.
they found no evidence for selective vulnerability inhibitibitory neurons in EC.
What brain regions are affected in AD first and why?
the entorhinal cortex is one of the first cortical brain regions to exhibit neuronal loss in AD. Particualrly in layer II. This includes principal neurons in layer II. important for memory
this will occur with changes in the hippocampus with signs of molecular pathology and selective loss of pyramisal cells in CA1. important for memory
This begins to spread to the neocortex effecting temporal a and prefonal lobes. There is loss pyramidal neurons in neocortical regions. regions involved in langiage, reasoning and social behaviour
Additionally cholinergic neurons in the basasl forebrain.
Primary sensory cortexes are relaitvely resistent to degeneration until late stages.
What cells are effected in AD?
pyramidal exictatory neurons have been shown to be degenerated in hipocampus, entorhinal cortex and neocortex
cholinergic neurons in basal forebrain are early degenerated
loss of GABA/glutamatergic due to AB/tau/inglammatory functions
What are different types of oscillations and their functions ?
slow (<1), delta (1-4), theta (4-10), alpha (10-15), beta (15-30), gamma (30-90)
slow –> involved in sleep and NREM
delta –> sleep
theta –> occur in REM and when mrunning
alpha –> relaxed wakefulness
beta –> active wakefulness
gamma –> cognitive tasks
SWRs –> occur in quiet wake and NREM - memory consol
What are different cell types involved in gamma? How do these vary across circuits?
pyramidal neurons
interneurons (PV and SST)
glial cells
In cortex –> PV basket and chandelier cells, SST martinotti cells
In hippo –> PV basket, SST OLM
What is your opinion on immunotherapy for AD?
I think it is an exciting route and it is good news to have a new therapeutic available.
I do have concerns that the ffect was only in small groups of people and the effect was miniscule. Also the side effects are large.
I think ensuring targeting of AB that doesnt have any beneficial functions is important.
Combinational theapy
What is the time course of DAPT?
seen reductions after several hours that was maintained for 24h
What is the structure of AA?
Contains a carboxyl group, an amino group and a side chain.
They link by joining the amino group with carbocyl group of an adjacent AA.
Side chains have different properties - acididc, basic, polar, non-polar
What are some examples of AA?
glycine
alanine
leucine
tyrosine
serine
threnonine
gluamine
proline
glutamate
Where does RNA transcription and translation occur?
Transcription –> in the nucleus
Translation –> cytoplasm or rough endoplasmic reticulum - in an cell compartment that has ribosomes
How does RNA transcription work from DNA?
RNA polymerase is used to attach to the DNA recognised by the TATA box.
This binds to the comnlementary base pairs and attaches them to the template strand - A-T, G-C, C-G, T-U
Elongation continues until the end sequence.
Then it gors through convertion into mRNA by RNA spicing where introns are removed.
What is mRNA?
it exits the nucleus and enters the cytoplasm
single stranded RNA correlaponding to nucleix acid sequence of gene
after protein synthesis - it degreated
How do cytokines exert their function?
it acts on a specific receptor.
autocrine –> bind to receptors on same cellt hat released it
paracrine –> bind to recpetors on nearby cells
endocrine –> bidn to receptors on cells far away
How have slow waves been modulated for AD?
Kastaneka group have worked bu optogenetically stimulating APP/PS1 mice for 1 month
at 0.6 Hz hey seen decreased AB
at 1.2 they seen increased AB
What is an EPSP?
excitatory post synaptic potential
local depolarisation of the postsynaptic membrane
action of an excittory neuron on a cell will cause influx of sodium and calcium which increases the membrane potential, brings it to the A threshold, and promotes firing
What did freeman and colleagues show?
1) frequency analysis in vat, rabbit and rat and find the 40-Hz activity in all three of these animals
2) writes a book on neural mechanism, EEG and the oscillations found
What is Chen 2017 (fig 1.3)?
review paper that charactierses and describes the amyloidogenic pathway, including formation of AB and aggreagtion.
What is Yoon and Jo, 2012 (fig 1.4)?
a review that secribes potential rputes for clearance of ab from the brain
What is Jie 2021?
A paper where they develop a new tau probe which was approved by FDA for pet scanning
What is Serrano-Pozo 2011 fig 1.6?
review paper that characterised the progression of neuropathological changes in alzheimers disease including tau, plaques and glia§
What was zhang 2021 (1.7)
a reviw that discusses the interaction between AB and tau and how each of them can promote each others pathology
What was Leng and edison, 2021 fig 1.8?
A review on neuroinglammation and its relationship with amyloid and taus, specific focus on microglia
What is Monterey 2021, fig 1.9?
Review on the role of astrocytes in normal healthy brain and in AD
What does Byron 2021 show?
discussion of brain oscilaltion - particularly slow and gamma - including their generation, loss of function in AD and methods used to improve them.
What is jeremic 2021 fid 1.12?
Review of recent studies on anti-amyloid therapies to summarise and analyse their current clinical power
What is Mannippa 2022?
a review which summarises all animal and human studies that have been completed and discusses potential ways this moa
What is yokoyama 2022?
summarises mouse models of AD and what limitations and pros of each generation there are
What does byron and sakata show?
a review on the use of fibre photoemtry for neuronal and non neuronal cells
overview of the general principle of FP
discuss use in multimodal with electrode - show detection of p-waves
discuss use for non neuronal cells by detecting calcium transidents in calcium signals
What are basket cells?
What are chandaleir cells?
Basket - inhibitory neuron with extensive axonal arborisations which form a basket like structure around the soma of target neurons, they release GABA onto the soma and dendrites of pyramidal neurons causing perisomatic inhibition
Chandelier - inhibitroy internueon, a lot of axonal terminals that form cartrides which attach to the axon of pyramidal neurons for perisomatic inihibtion
What are the main areas of the brain?
Cerebrum
- split into two hemisphers
- have four lobes - frontal (executive functins), parietal (sensory), temporal (audotroy processing), occipital (visual processing)
Cerebellum
- back of brain
- recieves input from cerebral cortex and sends to motor areas of brainstemand cerebrum
- motor
brainstem
- base of brain and contains pons, midbrain, medulla oblongatam
- redulation of breathing, sleeping, balance
Diencephalon
- locaded in deep brain
- consiststs of thalamus, hypothealmus
- relay station for sensoryinfo, homeostatic functions
What is the glymphatic system and what is its role in clearing AB? What does Xie show?
The glymphatic system is a waste clearance which involves rasnfer of ISF anf CSF across perivascular spce through aquaporin water channels on glial end feet.
The ISF is the fluid that surrounds and bathes brain cells, while CSF is the fluid that circulates around the brain and spinal cord.
the perivascular space, which is the space surrounding blood vessels in the brain. Aquaporin-4 (AQP4) water channel protein, which is highly expressed on the surface of astrocytic endfeet in the perivascular space.
Robust during sleep, especially during non-rapid eye movement (NREM) sleep. During sleep, the interstitial space in the brain expands, facilitating the flow of CSF and ISF and promoting the clearance of waste products.
Xie shows that this effect has a role of promoting clearance of AB during sleep.
Why is AF such a large contributor in TF but not in FF?
In TF we are attempting ato acquire real-time signals over a duration of time.
The AF can recover and therefore, over the time of recording will increase.
The FF experiments were completed on a short time scale where AF recovery is minimal.
Additoonally, the low AF cable and LED and FF have lower AF thatn the TF system that showed AF recovery only over days rather than hours if bleached properly.
