Neur0010 general knowledge Flashcards
protocols of whole brain examinations (common investigations)
Whole brain is fixed in formalin 2-3 weeks before examination.
The hindbrain is often seperated with the cerrbellum being removed.
The top of the brain is commonly investigated to look for signs of atrophy indicated by wider sulci.
The bottom of the brain is often investigated to looked for inflamation and squashing of the brain.
Saggital sectons are used to investigate te ventircualr system.
Thin progressive cuts are used for indepth analysis using staining procedures such as immunohichemistry (anitbodies) and staining to assess cellualr pathology.
Staining examples are the H+E stain, Nissl stain
What is the H+E stain?
This is the Haemotoxylin and Eosin stain
what can we look for using immunohistochemistry or other staining procedures?
Immunohistochemistry allows the digitaton of findings and the assessment of cell density of stained cells.
imunohistochemistry specificity can allow for multiple staining of specific cells and leayers of the cortex.
Immunohitsochemtisry can be used to ientify swollen of achromatic neurons, signs of inlfamation and other neurodgeenrative conditions.
Can be used to identify sepecific cells and thus abnormal cells that act as biomarkers of disease for exampe HIRONO cells in AD.
Other stains can be used to look at the anatomy of cells. For example identifiying Eosinophillic neurons (lacking neuronal detail).
what can we look for using immunohistochemistry or other staining procedures?
Immunohistochemistry allows the digitaton of findings and the assessment of cell density of stained cells.
imunohistochemistry specificity can allow for multiple staining of specific cells and leayers of the cortex.
Immunohitsochemtisry can be used to ientify swollen of achromatic neurons, signs of inlfamation and otherneurodgeenrative conditions.
Can be used to identify sepecific cells and thus abnormal cells that act as biomarkers of disease for exampe HIRONO cells in AD.
Other stains can be used to look at the anatomy of cells. For example identifiying Eosinophillic neurons (lacking neuronal detail).
describe a method of identifying amyloid protein
Amyloid protein form a beta sheet confrirmation. this structure alters its optical propeties in reponse to polarised light (BIREFRINGENCE).
staining with Congo red and exposing smaples to polarised loght shows a APPLE-GREEN BIREFRINGENCE.
important neurological landmarks in the investigation of astrocytes in disease?
Immunohostochemistry can be used to identify them by trageting GLIAL FIBRILLIARY ACID PROTEIN (GFAP).
in Injury astrocytes become larger as a result of hypertrophy, hence this can be used as a biomarker of disease.
astrocytes can be found in Glial scars following CNS lesions.
Alot of tumours ae gliomas these stem from dividing astrocytes. GFAP cytology can be used to assess the extent of Gliosis.
How can we apply immunohistochemisry to the assessment of oligodendrocytes?
Oligodendrocyte are produced from rogenetior and immunohistochemistry can be used to assess the maturity of glia.
Given their importance to CNS myelination and a detecton of less glia or less mature glia could be a sign of demyelination which is seen in codton such as mutliple sclerosis.
possible insights from marking for microglia and macrophages?
Microglia are important in the inflamatory resposne, responding to damge or infection through enetering a ramfied state.
for example. in inflamtory disease such as encephalitis the microglia will surround neurons.
Macrophges surrounding blood vessels, froming perivascular plaques.
what is subcortical laminar heteropia and what is the normal Doublecortin (DCX) function?
This is the formation of a second band of neurons under the cortical plate.
This stems from defficient neuronal mriration during developemnt and a cause of leanring dissabilties in later life.
This can be attributed to mutations on the X-chromosome in a gene called DCX, a microtuble associated protein (MAP) that palys a key role in neuronal migration.
briefly outline the physiological role of Pink1 and Parkin and explain how their mutations contribute to the pathology of Parkinsons disease?
Pink1 and Parkin are part of the primary mitophagy pathway.
In this mechanism Pink1 acts as an ignition key and damge detector, under basal conidtion it is taken up by the TOM complex and degraded through a sequence of clevages. However, following mitochondrial damage the mitochondria becomes depolarised and thus cannot take up PINK1 and it begins to accumulate on the OMM due to anchoring by TOM complex subunit Tomm7.
PINK1 fascilitates the colocalisation of Parkin (as shown studies showing ectopic expression of PINK1 on the OMM triggered Parkin recruitment and KO studies showing the loss of Parkin recruitment.)
PINK1 then phophorylates two targets at their serine 65 residues. Ubiquitin and Parkin. This fasciliates the intercation of the 2 proteins. (Parkin is phosphorylated at ubiquitin like site to stabilise its confirmation following ubiquitin binding)
the binding of now pUB to Parkin drives a conformatonal change in which the UBL is released from the parkin core and thus removing the autoinhibition of parkin.
ubiquitinated and activated parkin will now go on to ubiquitinate several down stream targets to aid the seperation of damaged mitochondria from the mitochondria network.. It will also go on to ubiquitinate OMM proteins to build and extend denovo and exisiting phospho-ubiquitin chains. These are recognised by autophagic adaptor proteins to drive the recruitment of the autophagesome machinery.
The autophagesome will then engulf the damaged mitochondria and transport it to lysosomes for degredation.
Hence, mutations in Parkin and PINK1 found in monogenic forms of PD found in a japanese (matsumine) and itallian (valente) respectively cause disrupted mitophagy. This leaves neurons without the appropriate machinery to regulate the quality of their mitochondria resulting in the accumualtion of damage and dysfunction evventually resulting in neuronal death.
Describe the main evidence for and against alpha-synucelins toxicity (differentiate between photofibrills in aggregtaes vs in soluble oligomers
alpha synuclein forms oligomers called photofibrils through fibrillation. The can go on to form large insolu ble aggregate termed lewy bodies.
+ve lewy bodies are a primary clinical charcteristic of PD and their spread reliably tracks disease progression in Braak staging, suggestion they cause neuronal death. there, is very little better explantion of spread of disease.
- ve However, Often neurons with lewy body inclusions survive and studies have shown co-expressing with synphillin which prevents their breakdwon increased survival.- shown by a study using synphillin to prevent the targetting of alpha syn for breakdwon by Blocking STAHI. This increased aggeragtes and increased survival.
- ve expression of mutants in transgenic mice has not been able to induce dopaminergic neuronal death alone despite increasing their suceptibility to oxidative stress.
+ve however, direct injections of photofibrils was able to induce dopmainergic neurodegeneration. This occured with one innoculation in wild type non-trangenic mice and corrlated with the spread and accumualtion of lewy bodies.
there is large debate over why wee see this discrepancy many now argue to insoluble aggergates, lewy bodies, are not the primary toxic species. in fact it is the soluble portion that are exttrenmely toxic, hence why we struggle to directly relate alpha synulcein to toxicity. studies expressing E35K and E57K mutations that promote soluble oligomers (Winner et al 2013) found they were more toxic.
How does MPTP selectively Kill dopaminergic neurons?
MPTP is a contaminant stemming from the incorrect production of the recreational drug MPPP. this drug when used is taken up and metabolised by mono amine oxidase B forming the toxic protein MPP+. This has an very high affinity for the dopamine uptake transporter and thus selectively accumulates in dpaminergic neurons. it then will translocate to the mitochindira where it will inhibit complex-1 of the MRC halting ATP production and resulting in neuronal dysfunction and death specifically in dopaminergic neurons.
Describe the pros and cons of IPSCs and mouse models in the study of neurodegenerative diseases?
MOUSE MODELs
+ve / they are extremely genetically felexible allowing for indepth investigation of the imoacts of genetics discovered in humans.
+ve They are extremely easy to analyse behaviourally with several established trials to test apects f memory, motor incoordination e.t.c.
+ve they have relatively high breeding rates and short life spans and so there is a ready supply and you can investigate them postmortem at several different stages of lif, cannot do this with a human brain. (INVIVO)
-VE Although their life spans are accelerated relative to ourthis is not so on a linear time scale. this means that in the case of neurodegenrative diseases that progress over life and with age being the biggest risk factor for many they present very late in life these trodents simply may not live long enough to accumulate a toxic threshold of dysfuncton. possil leading to false negatives (this appears to hav been the case in many mice studies of disrupted mtiophagy.)
INDUCED PLEURIPOTENT STEM CELLS (IPSCs)
+ve these can be produced directly from the fibroblasts of patients and thus allowing for the investigation of a mutation in the context of its genetic environment.
+ve can be used to induce a wide range of different neurons. excellent fo cases like PD when a specific SUBSET is degenrated. (Chung et al 2016 used methods to produce midbrain DA neurons that expressed comparale levels of DA neurons markers and had the same calcium meadited tonic pacekeeping aactivity of SNpc neurons.
- ve cannot produce all forms of neurons
- ve takes a long time for neurons to mature, its is difficult to investigate late onset diseases as we currently cannot aritifcially age neurons.
- ve only can be studies invitro
- ve difficult to investigate function within the context of a neural circuit. although organoids can be produced they are not perfect replicas of the real thing. Hence the neural architecture of neruons is often not maintained.
Describe the primary findings and aplications from Mazzuli et al 2011
Mazzuli et al 2011-
This stduy investigated Gauchers disease a lysosomal disroder in which 20% of pateints can display parkinsonism. This is in cases type 2 and 3 where there in nerualdegeration. they wanted to investigate whether neuronal death could be atribbuted to alpha synuclein.
Firstly they use short hairpin RNA to knock down glucocerebrocidase (Gcase) the protein that is KO in GD. they found this caused a increased neurotoxicity and concomitant increase in alpah synuclein ecpression in cell cultures.
secondly they investigated how it increased alpha syn toxicity. They carried out Gcase KD in cells expressing the A53T mutant (increased fibrilliation) or artificially fibrilation inept delta (triangle) 71-82 alpha syn. They found that Gcase KD only increased toxicitywith A53T showing that fibrillation was neccessary.
Further investigation showed Gcase KD lead to the a particular increase in insoluble and soluble oligomers. Significally toxicity was associated with a soluble high weight molecular form. Ti show this wad the result of LOF of Gcase and no just lysosomal dysfcuntion they using leupeptidin to cause lysosomal dysfuntion and reported neither increased toxicity of a HMW alpha syn.
following from this they tried to explain it from the ffects of LOF of Gcase this being the accumualtion of its substrate Glucosylceramide (CLcer). They found Glcer accumulation stbailised the soluble oligomeric forms of alpha syn. showing that purified solutions with higher proportions of Glcer would increase alpha syn accumulation.
To assess this invivo they investigated the effects in GD mouse models with Gcase defficiency. They reported accumualtion of alpha syn species and neurodgeen suggested from eosinopillic cells found in areas like the SNpc.
To investigate the impact of alpha syn accumualtion of Gcase function they again expressed A53T or defficient 71-82 alpha syn in inducible H4 cells. they then assessed for the abundance of pre and post-ER Gcase (immature and mature) (assessed using endo-H analysis). They found a inhbition of Gcase maturation which was fibrillation dependant.
Thus they believe to have idnetified a toxic pathogenic lop in which Gcase defficieincy or the accumualtion o toxic soluble alpha synuclein oligomers can trigger the other contributing to neurodegen and pottentially explain the comorbidity of enruooxic forms of GD and PD.
Describe and assess at least 4 pieces of evidence for and against the role of disrupted mitophagy in PD pathology.
Monogenic PD- a mutation in japanese, matsumine et al, and a itallian fammily, valente et al. were discovered causing monogenic EOPD. this truned out to be muations in Parkin, an E3-ubiquitin ligase. and PTEN induced putative kinase 1 (PINK1). these are now recognised as core parts of the prinmary mitophagy pathway.
Vincow et al 2013- they investigated the impacts of Parkin KO and general autphagy KO through ATG7 in the runover of mitchondrial proteins. expectedly ATG7 having both general and effects downstream of Parkin had a larger overall effect. However, in 53% of all MRC proteins inlcuding all 5 complexes the trunover was more dependant on Parkin (KO led to longer turnover). simmilar but less significant findings were found for Pink1. this isndicates the the parkin-pink1 mitophagy pathway has a speccific role in regulating MRC function. Given the link of mitochondrial dysfinction to PD, particualrlly complex 1 efficieny indicated by scahpira et al this again gives an intircate link between mitophagy and dysfunction seen in PD.
PINK1 and complex 1 efficacy. KO of PINK1 in drosophilla has been shown to decrease the functionality of complex 1 and decrease the repiratory capacity of the the MRC. Villain et al 2012 also used the expression of yeast complex 1 to reverse the effects o PINK1 KO again making this link.
Pickrell 2015- invented the most conivincing invivo recapitualtion of PD. he crossed a Parkin-ko AND the mutator-mouse (polg mutation) to produce te Parkin-KO mutator. Both phenotypes were shown to be essential to the phenotype. Motor defficiency shown on pole tests, the first model to show dopaminergic neurodegen shown by TH staining and nissle stain counts, slectiv degen as shown by normal number in Neun marking in other cortical areas. Meets PD criteria as after 4 weeks of L-dopa reatments the motordeficits were much improved. Hence, this showed bpoth mitochondrial damage and deffiecient mitophagy were needed for neurodegen. As the myuatotor pheotype confers an accumualton of mtDNA mutations and thus mitpohcnodrial dysfunction something that been shown to occur over normal life with againg this can be seen as acclerating te nrmla animals aging process and thus suggesting the loss of mtiophjagy is the key factorin inducing neuronal detah throigh the risk of age in PD.
Sun et al 2015- used the mt-keima mouse model to track basal levels of mitophagy/.
showed that it was heterogeneous acorss the brain with ares liek the DG having high levels and areas like the the SNpc having intermediate levels. Interestingly KO of autophagy via ATG5/7 KO led to almost complete KO in the intermediate areas but some remained in others. hence, this implies a varienace in redundnacy which may explain slective degen in diurupted mitopahgy.
showed that mitophagy declined with life between a 3month and 21 month old neuron. again supporting this idea that a loss of mtiophagy function was key to the risk of age in PD. this is furter supported by the expression of the mutator phenotype increasing mitophagy rate showing that our cells usually deal with increased stress and thus the loss of mtiophagy is more significant in terms of toxicity
is there any indication of an overlap between alpha-synuclein pathology and disrupted mitophagy in PD,
it is possible that alpha syn mediates its toxicity through disrupting mitophagy.
LI etal 2019 recently showed that the toxicity of defficent Gcase function i partly mediated through a loss of mitophagy function shown using mt-keima trangenic mice expressing a common Gcase mutation (L444P) homozygously. they were able to attribute this to reduced expression of proteins involved in mitochondrial priming, showed by wetstern blot, and deffiecieny in the induction of autophagy, shown using rapamycin to induce autophagy through te inhibition of MTOR and showing a reduced increase in the formation of autophagic vacuoles in GD modles than controls. (60 vs 25%)
Given the existence of a Gcase alpah syn pathogenic loop, identified by mazzuli et al 2011 this could present a pathogenic mechanism for this.
Disrupted mitophagy may fascilitate alpha syn acucmualtion.
Chung et al 2016 showed that in IPSCS PINK1 over expression led to a reduction in alpha syn accumualtion.
Schlossmacher et al reported that Parkin colocalised with Alpha syn in lewy bodies.
Hence it is possible mitophagy mechanisms play a defensive role against the toxic species of alpha syn, this would explain why Farrer et al reportred in some Parkin lof exmaples no lewy bodies are seen. this being because the parkin sequestering role is lossed.
oultine the primary pathology and symptoms of parkinsons disease.
Parkinsons stems There is progressive degeneration of dopaminergic neurons (DAs) in the Substantia nigra pars compacta (SNpc) (Gröger et al,.2014), this results in the loss of dopaminergic activity in the Nigrostriatal pathway projecting to the striatum ; Existing as both the posterior head of the caudate and the putamen, the striatum is the hub that drives wanted movement and prevents those unwanted. Nigrostriatal activity at D2 dopamine receptors usually excites the direct pathway to disinhibit the motor relay in the thalamus. Activity at D1 receptors, inhibits the obstruction of motor drive through the indirect pathway. Therefore, motor drive is obstructed in PD (Hisahara and Shimohama, 2011).
This results in a deffiency in voluntary movements. Patients often show slow distorted movement bradykinesia, cog like rigid joints, classic resting tremor starting unilateal and progressive to a bilateral experience.
there are also pre and post-motor symtpoms
pre- prior to motor symptoms 90% will experince olfactory deficits and 50% can be depressed.
Post- after onset of motor sympotms patients can develop dementia further down the line and many develop a bent over posture.
what form of neurodegenrative disease does PD fall under?
PD is a sycleineophathy
what ar lewy bodies? state the two disease they are best associted with.
Lewy bodies are alrge insoluble aggregates of alpha synuclein primarily and many othe proteins such as Parkin and ubiquitin. they are primarily asociated with the sequestering of toxic alpha syn species.
They are associated with PD and dementia with lewy bodies.
outline the 3 pathways modulating motor activity through the striatum?
Direct- This promotes movement. receieving excitatory input from the cortex the GABAergic neurons in the striatum prpject to and inhibit the internal segemtnof the globus plaidus. this usually prjects to an inhibits the thalamus and thus thispathwa dishinibits the thalamus fascilitatijng the relay of motor comands and drive to the motor cortex. this is modulated by the SNpc through the nigrostriatla pathway. dopamiergic neurons acts of D1 receptors to excite the drive of movement.
Indirect- This inhibits movement, This time the striatum projects to the external segemnt of the globus pallidus this time disinihibiting the subthalamic nuclei. The subthalmaic neucleis excitatory projects can then excite the internal segemnt of the globuc pallidus to inhibit the thalamus and stop movement. This is also modulated by the SNpc, this time dopaminergic neurons acts on inhIBITORY D2 receptors to turn off this pathway.
Hyper direct- inhibits movement through direct projections form the coretx to the subtlamic nuclei.
Given an example of how the reduced dopamine population of the SNpc is demonstrated through imaging
Brook et al using single positron emission computed tomography (SPECT) to mark for the dopamine uptaker showing a much small level in the SNpc of PD patients. other studies have used a the sma method to demonstarated the progressive decline.
provide support for mitochondrial dyfunction in PD (in particular mitochondrial resppiratory chain (MRC)
Schapira et al reported reduced Complex 1 activity in the PD brain.
MtDNA muations- studies investigating the brain in postmortem samples have reported a life long accumualtion fo mtDNA mutations demonstarted by increased levels of fractionated MtDNA. These muattions were correlated with a defficieny in the function of cyclooxidase (COX) a key MRC mediator.
Bender et al have shown that the SNpc of PD patients has significantly higher mtDNA muations. hence this correlates with disease and MRC dyfunction.
MPTP example- MPTP is a contaminant stemming from the incorrect production of the recreational drug MPPP. this drug when used is taken up and metabolised by mono amine oxidase B forming the toxic protein MPP+. This has an very high affinity for the dopamine uptake transporter and thus selectively accumulates in dpaminergic neurons. it then will translocate to the mitochindira where it will inhibit complex-1 of the MRC halting ATP production and resulting in neuronal dysfunction and death specifically in dopaminergic neurons.
What features of SNpc DA neurons might make them particuarly sucetpible to mitochondrial dysfunction?
Like all neurons that produnction of APS and maintencae of the membrane pottential is an energ demnading process requring ATP. the same can be said for axonal transport.
Dopamine neruons in particular have a autonomous activation know as pace maker activity. this produces slow wave APs uniquely reliant on calcium influc. calcum in toxic if not remove dand thus is through active mechnaims making the nergy demnd even high..
when the MRC produced ATP it also [produced dmaging reactive oxygen species like superoxides which can damge the mitchondira and mtDNA. this increases oxidative stress and reduces the efficacy of the MRC. hence dopaminergic neruons are more succeptibel to this.
outline the role of oxidative stress and ROS release may cause in disease? how can this be dealt with?
ROS release can damge cell proteins, mitochondrial walls and mtDNA. this causes oxidative stress which fascilktates more dmage, more ROS production and more dysfunction. ROS molecules can also act as signalling molecules between mitochnidra inducing a wave of mitochondria release troughout the mitochjndrial network, this is ROS induced ROS rlease.
to stop this and maintain neruonal health dmaged mitochindria must be seperated from the mitochindrial network and destroyed via mitophagy.
ANTIOXIDANTS like superoxide dismutase 1 (SOD1) are vital here. SOD1 converts superoxide to hydrogen peroxide.
What is PARK2 and what is PARK6
Park2 is the loci of Parkin and Park6 is the loci of Pink11 (PTEN induced putative kinase)
Outline the primary findings from FIESEL 2015. how does this support disrupte mitophagy in PD?
fiesel used Pub as a marker of the parkin-pink1 pathwy. he used the mitochondrial uncupler CCCP to depolarise mitochnodria and mimic damage .he showed that pink1 was neccesary for accumuatlion of Pub, this makes sense with the pathway as UB is a PINK1 substrate. Parkin was not neccesary but boosted accumualtion which is intouch with parkin parimily being a Pub substrate and the feedforward pottentiation.He also showed the stress induced accumualtion of Pub co localised with stains of Parkin and of TOM complex markers for mitochindria, so the pathway is functional in humans
invetsigating PUB ACCUMUALTION SIN diseaseowed accumualtion in normal PD patients and controls but in PINK1 KO mutants there were no snPC accumualtions. ence this is is evidence that this pathwa is infact deffiencient in at least monogenic PD.
Oultine genetic support for disrupted mitophagy in PD (min4) (incude detail on studies shwoing the significance of genetic links)
Parkin and PINK1 monogenic PD.
Fbx07- they discovered unique mutations in the taiwanese EOPD popualtion and in some other parkinsonian populations. Fbx07 has now been shown to interact with both PINK1 and PARKIN and to play a vital role in the degredatiuon of MNFs. It also was shown to partially rescue Parki-KO phenotype. thus is appears its fucntion is linked to mitophagy.
GBA1 mutations- Recently Li et al 2019 showed that the neurotoxicity seen in GD through th dysfunction of Gcase can be partially attirbuted to defficiency in mitophagy shown using mt-keima trangenic mice expressing a common Gcase mutation (L444P) homozygously. they were able to attribute this to reduced expression of proteins involved in mitochondrial priming, showed by wetstern blot, and deffiecieny in the induction of autophagy, shown using rapamycin to induce autophagy through te inhibition of MTOR and showing a reduced increase in the formation of autophagic vacuoles in GD modles than controls. (60 vs 25%).
DJ1- muations in this protein have been shown to cause monogenic PD. despite a lack of knowledge on its direct function it can be seen to selctively locsalise to damage mitochondria a charcaterisic that is lossed in mutants, this suggests that its finction is associated with mitophagy.
outline the significance of the Mitochondrial targetted Keima method and the mutator-Parkin KO mouse?
Mt-keima is decribed by katayama et al. Using a COX VIII targetting seuqence it is tragetted to mitochondria.
taken from coralls this proetin is fluroescent with unique charcteristics.
lysosomal resistance- thus we can vouslaise the gradual accumualtion in lysosomes during mitophagy.
PH dependant flurescence- it has a dominant green fluroecsnce in mor enutral conition like that of the mtichonchondira. Hoever, at more acidic PHs like that in the lysosome it has a dminat red fluorescence and thus we can distinguosh betwen the 2. this allows us to quantify mitophagic flux measuring the level of mtiopahgy through the number of red pixels over the toal number of pixel.s
this has now been succesfully expressed in transgenic mice and facilitates the measure of mitophagy invivo.
outline and explain the comorbidity of Gauchers disease and Pakinsonism
Gauchers diseas, GD, is a lysosomal storage disorder stemming from muations in the Glycocerbrocidase, GCase enzyme, and thus a loss of its function degrdaing Glycosylceramide, GLcer, to clucose and ceramide.
There are 3 types. 1 in less severes and hassolely liver and spleen effects.
Type 2 is the worst and type 3 is also sever both effecting the slpeen lver and cause neurological issue through degenration.
in some of these infividuals neurodegenration causes parkinsonisms.
equally GBA1 muations are the most common in th PD population.
what are the 4 basic treatments for PD?
L-dopa treament, this boosts dopamine producntion howveer as neurons die this has dimisnishing returns.
dopamine agonists- dopmaine agonists like bromocriptone are used to directly stimualte neurons this time no having dimishing returns as dopoaminergic neurons ae not required.
DBS- here this tragtes the STN and has been shwon to be particuarly useful for treating the resting tremor.
monoamine oxidase inhibitors- the like of Rsagline will prevent the breakown of dopamine working to a simmilar effect of L-dopa.
Oultine BRAAK staging
BRAAK staging was introduced in 2003 it tracks the spread of LB pathology as a measure of the progression of PD. we can see that it often strats in the brain stem working through to the locus coerulus and then the SNpc. by the time motor symptoms are seen degenration in the SNpcis significant.
What are the 3 primary risk factors of PD?
Age
environment- some old farm treatment were MRC blockers like Rotenone (herbicide). MPTP through drg se can also cause PD.
-smoking (tobacco) and caffeine has also been associated as neuroprotectants factors.
Genetics- their are extremely rare genetic inheritable forms fo the disease but there are also many risk factors pedisposing individuals to PD.
Outline in detail the 7 main mutations in PD (treating PINK2/6 as 1)
Parkin and PINK1- mongenic forms of the disease discovered by matsumine and Valente. These rare now know as the 2 core proteins in the primary mitophagy response. linking disrupted mtiophagy to PD pathology
SNCA- the gene encoding alpha synuclein this has several mutations in monogenic LOPD and EOPD. examples like A53T and A30P confer alpha syn which inensified aggregation. E57K and E35K promote soluble oligomer formation and are highly toxic. there are also rare pedigrees of duplications and triplications in which the diseas eis highly agressive with Early onset and rapid progression.
LRRK2- leucine rich repeat kinase 2. another proetin with an unclear fucntion but very common in the PD [population at 2% and in some rare population up top 40%. most mutations occur in th kinase domain and the is though to influence the fucntion of the protein in the cytosol where it is though to intercat with mitochindria and lysosmes.
GBA1- the most common genetic risk factor of PD. this muation is the source of a commoridity with lysosomal storgae disroder GD.
DJ1- this is another monogenic source of PD. its function is unknown but it is though to be linked to mitophagy as it has been shown to selectively localise to damge mitochondria and in mutants this behvaiour is lossed.
ATP13A2- this cause EOPD. it is involved with the entry of zinc 2+ ions into the lysosomes. it sis though its dysfunction may drive zinc dysregulation to reduce th repiratory capacity of the MRC and disrupt lysosomal fucntion and prietien degredation.
VPS35- effects lysosomal function. thi sis part of a retromer complex playing a key role in the traffciking of Manose 6 phosphate back to the goli, hence it mutation disrupts trafficking and developemnt of protein consequenting in lysosomal dysfunction.
How do Mutant alpha synuclein species promote their own accumualtion through the Chaperone mediated autophagy (CMA) pathway, what PD linked changes may also contribute here.
In the CMA cha[perones bind and traget alpha synuclein to the lysosomal receptors to dirve their degredation
the highly aggeragting species with bind particualry strongly to the Lamp2A RECEPTOR of the CMA pathway acting as inhibitors of their own degredation pathway. Cuervo et al., 2004
equally, they avoid binding to Lamp1 receptor.
During PD a decrease in the expression of Lamp2a and Hsc70 is seen also.-
Injecting inhibitors of the ubiquitin proteasome system also pottentiates SN degen in rats. This involves the ubiquitination of proteins in Lewy bodies
How might alpha synuclein toxicity explain selective degeneration of dopaminergic neurons?
dopamine was shown to stabilise alpha syn. more interestingly a stduy showed the effect on the dopamine metabolite oxidised dopamine , dopaminochrome, on alpha syn. they showed modification of wild type alpha vis dpminochrome or usual dopmaine allowed the WT alpha to inhibit the CMA to a simmilar extent as the mutant forms. this is oemthing wt alpha syn cannot do alone (Martinez-Vincente et al., 2008). interestingly the 2 areas primarily dissociated in PD the locus coerulus and the SNpc both have melatonin of which dopaminochrome is a subunit.
alpha syn shows alot of connections to dopamine metabolism. it has been shown to inhibit the core dopamine producing enyzme TH. and the dopamine metabolite 3,4-dihydroxy phenylacetaldehyde, was shown to induce α-syn accumulation (Burke et al., 2007)
How might alpha synuclein toxicity explain selective degeneration of dopaminergic neurons?
dopamine was shown to stabilise alpha syn. more interestingly a stduy showed the effect on the dopamine metabolite oxidised dopamine , dopaminochrome, on alpha syn. they showed modification of wild type alpha vis dpminochrome or usual dopmaine allowed the WT alpha to inhibit the CMA to a simmilar extent as the mutant forms. this is oemthing wt alpha syn cannot do alone. interestingly the 2 areas primarily dissociated in PD the locus coerulus and the SN pc both have melatoning of which dopaminochrome is a subunit.
alpha syn shows alot of connections to dopamine metabolism. it has been shown to inhibit the core dopamine producing enyzme TH (Peng et al., 2005).. and the dopamine metabolite 3,4-dihydroxy phenylacetaldehyde, was shown to induce α-syn accumulation (Burke et al., 2007)
What are the current theories surrounding the spread of lewy body pathology.
many believe given the visible spread is of lewy bodies then this underpins it.
foetal grafts was shown to develope LBs within 15 years of implant. this means that either alpha synuclein can traverse through connections between cells. or the PD environement can induce dysfunction.
Many believe prion like mechanisms now modulate this. alpha syn can be excreted in exosomes, or tunnelling nano tubes. it can then induce wt alpha syn to tak on the pathogenic conformation through permissive templating. To fascilliatate this it is believed that the beta-sheet structure of ologomers allows foor promiscuous binding.
what are the heterogeneous pre-motor and post-motor symtoms of PD?
pre - olfactory impairment 90%, depression 50%, erectile dysfucntion.
post- dementia, visual hallucination, dysathria (issues with speech)
result of Permeabiltiy transition pore opening on mitochondria and result of pathogenic state?
the opening of the PTP can cause a loss of the H+ gradient and thus depolarisation of the Mitochindrion and a loss of function in the MRC. this can be a consequence of oxidative stress.
PTP pore opening can also enter a pathogenic state, a high cnducting state whichtriggers a calcium ion flood and triggers apotosis signalling. resulting i cell death.
in what disease is SOD1 mutated? What is the role of SOD1?
superoxide dismutase 1 converts superoxide to hydrogen peroxide. it is an antixodiant. mutations in this can be found in friedreichs ataxia. mutations allow for ferrous activity to drive hydrogen peroxide to from OH=
Which primary proteins mediate mitchondrial fission and fusion?
MFNs drive fusion.
DRP1 and FIS1 drive fission
outline the possible role of Parkin in Biogeneisis
Parkin may also play a role in biogeneisis of Mitcondrion.
this is associated with the Ring domain and the ring-finger motif
the application of anti-proliferative drugs triggers the release of parkin from the mitochondria into the cytosol.
parkin overexpression was shown to increase mtDNA replication.
Parkin has been shwon to interact with mitochindrial transcription factor to drive the expression of proteins related to mitochondrial biogenesis.
what is friedreichs ataxia
This is a reccessive form of ataxia stemming from the accumualtion of GAA repeats in the FRATAXIN gene.
this results in increased oxidative stress as a consequence of increased ROS production and mtDNA, Lipid and protein damage,
it has also been linked to mutations in SOD1.
Usually number of GAA repeats in the frataxin gene, how does this change?
usually only repeats 7-22 times and this 100 or even 1000 times.
The number has been related to the severity and rate of disease progression.
what is the effect of frataxin defficiency
the triplet repeat expansion greatly disrupts the normal production of frataxin. Frataxin is found in the energy-producing parts of the cell called mitochondria. Research suggests that without a normal level of frataxin, certain cells in the body (especially peripheral nerve, spinal cord, brain and heart muscle cells) produce energy less effectively and have been hypothesized to have a buildup of toxic by products leading to what is called “oxidative stress.” Lack of normal levels of frataxin also may lead to increased levels of iron in the mitochondria. When the excess iron reacts with oxygen, free radicals can be produced. Although free radicals are essential molecules in the body metabolism, they can also destroy cells and harm the body.
outline a epigenetic role in fiedreich and possible therapeuticondrial dysfunctions s
HDAC inbitors increased frataxin
PimelicdiphenylamideHDACi109 (RG2833)– Increased frataxin in cell models– but has Potentially toxic metabolic by-products
• Nicotinamide (vitamin B3)– Improved frataxin levels in Phase IIb clinical trial (promising showed sustained improvement and plays role in switching back on gene)
list two different mitochondrial dysfunctions and briefly explain how they contribute to neurodgenerative disease?
.MRC dysfunction. This results from oxidative stress and ROS production and mtDNA mutations. this are seen in PD and HD
PTP- activation can drive calcium flooding and activation of the apoptosis pathway. resulting in cell death.
mtDNA damage
explain the mechanism of ASO therapeutics and give one example of its use in disease.
Antisense oligomers are small stretchers of RNA that bind RNA to prevent splicing.
This method has been applied in spinal muscular atrophy. An ASO now trialed in humans developed by Biogen and Ionis workds by binding to the intronic element ISN-1 on the SMN2 RNA preventing the splicing out of exon 7 allowing it to form a complete SMN protein.
.outline the main pathology of SMA, include findings from mouse studies.
SMA involves the selective loss of secondary motor neurons in the anterior horn of the spine. (ventral horn in mice). The central primary neurons are sparred (unlike in ALS). This reslts in symmertrical muscle weakness.
Mouse models have provided other insight. they showed that there was significant loss in the ventral horn. surviving motor neurons are swollen and chromatolytic, this often occurs along sided increased phosphorylated neurofilaments and autophagic vesicles.
these models have also shown wallerrian degeneration of intramuscular nerves.
muscle fibre is denervated and in severe cases cannot be reinervated and adapt an immature structure like myotubes, in less severe cases the fibres show grouping of fibres types and undergo cycles of innervation and dennervation.
They have very low SMN levels.
.What are the underlying genetics of SMA?
SMA is caused by mutations in the SURVIVAL MUSCULAR NEURON 1 (SMN1) gene. This is a RECESSIVE condition.
the gene is found at 5q and a inverted replication has been identified (5q11.2-5q13.2)
in 95% of cases then mutation drives a loss of function due to a mutation of 5q. in other cases mutations alter the reading frame.
on the same arm there is the SMN2 gene, this has a 1 nucleotide difference which drives the alteration the splicing modulator and the splicing out off exon 7 froming an incomplete protein (this occurs MOST of the time). All patients have atleast 1 copy of the SMN2 gene, variations in its copy number can alter the risk of disease.
what are the main diferences between the different types of SMA?
Type 1: This is the most severe form seen in 50% of cases.
This has a onset before 6 months usually at birth. The children will never walk and will die before 2.
They require both respiratory help and nutritional support (gastrotomy tube)
They have symmertical muscle weakness. this can be seen in the respiratory muscles in partuclular with a relative sparring of the diphram. This results in a bulb shaped stomack as they breath solely with the diaphram. also causes : WEAK CRY/COUGH, DIFFICULTY CLEARING SECRETIONS,
bulbar dennervation which can be visualised by visble fasciculation in the tongue and swallowing issues.
There are 3 subtypes- A presents at birth with joint contracture and repiratory compromise, B- has an onset before 3 months and C- has a onset after 3 months.
TYPE 2: this is the intermediate form. onset is seen after six months with patients often dying after 2 (Now with impoved awareness and care care survive till adulthood.). often DO NOT require ventilation support also respiratory weakness is still present.
These are able to sit but will never stand. This means that they develop bad scoliosis requring surgery and have frequent hip disclocations.
They also have Oro-bulbar dysfunction and malanutrition.
Type 3: this is the least sevevere from with an onset after 18 months and often after they have developed walking and so can stand.
they oten shown issues getting up from the sitting position called the GOWERS SIGN.
Best signs are a wobbling gate walk and msucular fasciculations.
Note: there is a very rare type 4 whcih can have adult onset.
How can varying SMN2 copy numbers alter the risk of SMA?
The SMN2 gene doesnt profuce a functional protein most of the time but it does sometimes.
It is a POLYMOROPHIC gene in the population with varied copy number.
Assesments of the risk of type 1 SMA shows are large shift from 97% at 1 copy to only 8% with 3 copies. by 5 copies the risk is 0%.
What is the main fucntional domain of SMN, what is SMNs main functional role? provide eveidence where possible
SMN has a Gems domain- This is a nuclear domain implicatesd in the modification of snRNPs (Small nuclear ribo-nuclear proteins). through this it is involved in RNA regulation.
SMN forms the complex with other Gemins and mediated the biogenesis of snRNP. it does this though loading the heptameric ring f splicesome fibres onto the snRNPs and this aids the formation of splicesomes for pre-mRNA intronic splicing splicing.
The SMN also has fucntions in altering the cytoskeletal elements of dendrites and axons. this is clear in axons where it is key to axonal transport and growth.
KO study showed reduced mature mRNA levels in the distal end of the axon, this was seen with reduced axonal growth and reduced levels of beta actin.
What is thought to underly the selectively neuronal death in SMA , provide evidence for a motor circuit specific SMN function.
One factor is the selctive role of SMN in the function of the U12 splicesome which meadites a minority of splicing.
Lottie et al- Studdies in mammalian (mouse) cell cultures and drosophilla with KD of SMN1 showed that SMN defficiency effected the u12-splicing and mRNA expression of a novel portein linked to the motor circuit Stansimon. they also showed that Stansimmon KO mimicked SMN KO phenotype.
Zhang et al- showed genes a;ltered in SMN KO involved many related to the NMJ maintencae like Agrins exon skipping (kEY TO ACHr cumulation in NMJ due to interaction with a synaptic complex of proteins consisting of LRP4 and MuSK which act to autophosphorylate themselves and down stream targts, DOK7, rapsyn and the delta subunit of AChrs to drive clustering at NMJ). Also upregulated the expression of synaptic pruning promoter compelment factor C1q.
effect on afferents- Mantis et al reported reduction in primary afferent inputs and porpprioceptive inputs into the Ventral horn prior to MN deficits. This is aslo shown in prior reductions in the Afferent provoked responses seen in the first 2 post natal weeks.
Fletcher et al 2017- The reduced MN firing has been related to a reduction in Kv2.1 on MNs. Pharmoclogical upregualtion of central activity resulted in an increase in the expression of Kv1.2 and relief of the phenotype.
(smae study to show evidence of entral activity in the correct wiring of sensory-motor connectivity)
what is the issue with drosophilla and zebra fish models of SMN KO.
Zebra fish and drosophilla only have the 1 SMN copy and thus KO of SMN1 has not SMN2 for partial recovery and this leads to embryonic death.
are there lifelong changes in SMN importance, what can evidence around this tell us about theapeutics.
Kariya et al 2014- They did age progressive KD in mouse models and identified a point at which KD did not reuslt in the prgressive developement of SMA, this COINCIDED WITH NMJ MATURATION.
This suggests that its significance is seen in adulthodd. this means that treatment maybe not needed thoughout life. and more acute action early on is most important.
does SMN dysfucntion soleley effect the spinal motor neurons? provide evidence
Hunter et al- they showed the impact of SMN LOF on schwann cell function. showing over expfression of SMN in schwann cells reduced the volume of demyelinated muscular neurons. hence, LOF is also linked to wallerian degeneration.
role and support for central motor drive in regulating the correct wiring an connectivity of the Motor neuron systems and its disruption in SMA (SMA)
Fletcher et al 2017- The reduced MN firing has been related to a reduction in Kv2.1 on MNs. Pharmoclogical upregualtion of central activity resulted in an increase in the expression of Kv1.2 and relief of the phenotype.
(smae study to show evidence of entral activity in the correct wiring of sensory-motor connectivity)
what underpins SMA Motor neruon death?
This is though to be a Cell automnomous event.
SMN loss of function results in the increased expression of P53 which shows selective accumulation in vulnerbale vs resistant MNs.
Phosphorylation of P53 on serine residues marks vulnerable MNS for cell death.
Later on this is ransferred to resistant MNs causing there death.
shRNA KD of p53 in models by Simoni et al 2017- this was able to rescue motor neurons and increase MN survival.
What are the main therapeutic methods in SMA.
there are both those effecting expresion of SMN (expression) and those effecting the symptoms without effect SMN (agnostic)
Agnostic- FDA have approved the use of FASUDIL. this acts as a ROCK/RHOA kinase inhibitor. this was reported to mitigate the SMA phenotype and greatly improve motor function. would be a good option alongside ASOs.
(Neuroprotective driugs like Gabapentin hav been traialed to limitted application.)
Expression
ASOs-antisense oligomers have been sed to prevent the splicing of SMN2 thus allowing it to form a full SMN1 protein and replace the lossed SMN1.
One developed by Ionis and biogen was traille din humans called NUSINERSEN. This targets the intonic element ISN-1 to prevent the splicing out of exon 7 to allow for a full protein.
-ve These cannot cross the BBB and so hav to be introduced intrathecally. +ve this means they have a long life span. after a LOADING set of 6 injections only 3 are required a year.
Early studies in mice in whic the SMA mice were alot smaller and has shrotened life spans. ASO injections into liver was able to reverse issues with size and significntly prolong life. Through this they identified a THERAPEUTIC WINDOW OF ACTION.
ENDEAR trial 0They trialled this type 1 SMA patients in comparision ot a vehicle. and found that it extremely effective. it improved mortality by 63% and reduced the likely hood of needing repiratiry intervention by 47%. long term trials recently eneded in may 2018.
small molecules- The main benefit f these is they can cross the blood brain barrier.
1 produced by Roche and PTC was shown to be extremely selctive affecting SMN2 and a few others showing very little side affects in mice.
small doses were able o induces A LIFE SPAN SHIFT FROM 20D TO 60D. in large doses this was shown to almost increase life span to normal lab life spans (1 year)
Pharmacological- The work by infleuncing th prevention of alternative splicing or by transcriptional activation.
a drug developed by PTC RG3039 targets the DcpS enezymes and ha d dramtic effect on mouse life span. 14 days going to 6 months.
This is now being optimised fro humans.
Gene replacement therapy> the best example is being worked on by avexis. this uses a novel ADENO-ASSOCIATED VIRUS that can cross the BBB and infect many cell types. AAV9-SMN greatly increased the expression of SMN and counterers disease poehenotype.
outline in detail the efficacy of ASOs in SMA.
antisense oligomers have been sed to prevent the splicing of SMN2 thus allowing it to form a full SMN1 protein and replace the lossed SMN1.
One developed by Ionis and biogen was traille din humans called NUSINERSEN. This targets the intonic element ISN-1 to prevent the splicing out of exon 7 to allow for a full protein.
-ve These cannot cross the BBB and so hav to be introduced intrathecally. +ve this means they have a long life span. after a LOADING set of 6 injections only 3 are required a year.
Early studies in mice in whic the SMA mice were alot smaller and has shrotened life spans. ASO injections into liver was able to reverse issues with size and significntly prolong life. Through this they identified a THERAPEUTIC WINDOW OF ACTION.
ENDEAR trial 0They trialled this type 1 SMA patients in comparision ot a vehicle. and found that it extremely effective. it improved mortality by 63% and reduced the likely hood of needing repiratiry intervention by 47%. long term trials recently eneded in may 2018.
Outline the findings of DUQUE ET AL 2015, how does this support the role of SMN in SMA?
Duque et al 2015 used intrathecal injections to introduce scAAV9 linked SMN1 shRNA (short hair pin RNA) this KD of SMN1 caused proximal muscle weAkness, fibrillations and reduced expression of CMAP and MUNE in pigs.
shows that SMN1 loss causes the condition.
What is the cause of anticipation and in what neurodegenerative diseases is this observed?
Anticipation is a process by which the Polyglutamine repeats (polyq/CAG) expand between generations.
This is observed in both HD and SCAs.
In HD this correlates and explains why between generations the age of onset of sufferers gets progressively earlier.
expansions in though to occur by toxic cycles of DNA damage and repair. Hence, why several risk factors for HD are associated to DNA repair Chr3-MLH1 Mismatch repair Chr5-MSH3-Mismatch repair (Massey disease model)
expansion is enhanced when inherited from males. something that has been associated to the germ line instability of male sperm.
briefly discuss the involvement of medium spiny neurons in the pathology of huntingdons
medium spiny neurons make up 95% of the striatum, these neruons are selectively damged in HD.
In HD pothology the degeneration of the MSNs underpin the motor symptoms of HD, with those associated with the ndirect pathway being degenrated early on causes the loss of silencing in involuntary unwated movement (chorea), and then this spreads to other MSNs later on reslting in the mpore parkinsonian like rigidity.
how was the Huntigitin protein structure visualised?
the Huntigtin protein was fixed to a HTT protein associated protein and the frozen to nearl absolute 0. This allowed for the visualisation of the crystal struture.
The N-terminal which is associated with the toxic exon 1 fraction and the CAG repeas is not able to be visualised so little is known how the polyq effects the structure.
Outline the background of Huntington’s disease: Genetics (protein effected), inheritance pattern, clinical symptoms and pathophysiology
Huntingtons stems from a mutation in the huntingtin protein. this stems from the expansion of CAG repeats in the gene with 40+ causing 100% chance of disease.
this has an autosomal dominat inheritance pattern so only 1 mutant allele is required.
symptoms=
There are motor, cognitive and psychiatric symptoms, as well as pathophysiological clinical features not decribed here.
Motor- CHOREA- this is semi-directed involuntary movements.
RIGIDITY- this occurs when the MSN degenration spreads to those associated woth the direct pathway later in progression.
Pschiatric- AFFECTIVE DISORDERS- patients often show depression and high suicide risk (pottentially linked to reducion in BDNF xpression)
ANXIETY/PANIC DISORDERS.
PSYCHOSIS simmilar to SCZ
Complsuions and obsessions
Cognitive- DEMENTIA= OCCURS IN 100% OF PATEINTS. FRONTAL DEFFICIENCIES- issues with planninng, multi tasking and increased complusivity and irritatability.
issues with psychomotor drive and meotional recognition
memory and speaking is sparred.
These symptoms often PRE-DATE motor smtoms b p to 10 years
A physiological symptom is weightloss which as been asspociated to mitochondrial dysfucntion stemming forom the transcriptional dysregulation of PGC-1 alpha function.
pathophysiology-
HD patients suffer from the degenrations of striatal MSNs. this is at first slectively associated with thos emediating the indirect striatal pathway and then this spreads to other in later stages.
The existence of intranuclear inclusions of mHTT is hall mark of the disease.
we can also observe mitochndrial dysfucntion, reduced BDNF expression and impared proteolysis due to mHTT action.
over representation of NMDA in striatal regiona n reduced glutamate uptake also observed.
what is a polyq expansion, how are they passed on and what diseases is this associated to.
The polyq expansiuon is a polyglutamine expansion due to the expansion of the triplet CAG repeat.
This is what is associated with the disruption of HTT functions in HD and the disruption of ataxin in SCAs.
Ths is inherited much like normal genes but the repeat number within the gene can exapnd between generations, in anticipation.
In HTT there are several variations in th number of CAG repeats, describe them and what the impact of these ranges?
in HD there is 4 main variations of the number of CAG repeats in the HTT gene.
- in normal individuals this is between 1 and 26
- 27-35 These individuals will never develop HD, However this is still suceptible to anticipation and so their children are at risk of carrying a HD inducing mutant form of HTT
- 36-39 this section has the biggest split in penotype. 36 is related to a 50% risk of HD before death and 39 is 80% risk
4- 40+ 100% risk of HD , expansion on top of this will result in an earler age of onset.
what are the 3 ways of reffering to the Huntington gene?
HD protein, HTT, IT-15
which age of onset to referred to as early onset HD, is this associated with more or less CAG repeats.
onset at the age of 20 and below is reffered to as ealy onset HD. This is associated with more CAG repeats.
What is the parent influence of the extent of anticipation in HD?
Whether the mutant HTT gene is inherited from the mum or the father has a large impact on the extent of anticipation.
The GERM LINE INSTABILITY of the male sperm results in a much larger expansion of the CAG repeat number.
What is the toxic part of the HTT protein? Is this seen in post-mortem study?is it soleley this gain of function associated to disease?
There is a rowing suggestion the toxic gain of function stems from the n-terminal exon 1 region of the mutant HTT protein. (MANGIARNI et al showed this expression in R/6 HD model alone could caus symptoms.)
The Exon 1 mRNA is not seen in post-mportem studies of adult HD patients this is an argument agaisnt the abberant splicing theory. HOWEVER, it can be seen in Juvenile cases of HD. one argument in that mRNA is incredibly suceptible to degredation thus expalining absence post-mortem.
HD is not solely a gain of toxic function.
performed KO studies in mice showing that this was lethal. This suggests that a LOSS OF FUnction is also involved in pathology.
(normal function has been related to endocytosis, vesicular transport, autophagy, cell division and transcriptional regulation)
outline to the 2 main HD mouse models and there differences
There are 2 mouse models>
One focusses on the Exon1. this was created in a study by MANGIARNI ET AL. the specificall express the toxic exon 1 shwoing that tis was suffieicent to induce a HT like phenotype. this is how the theory that this was essential t the toxic function came from (THIS IS THE R/6 HD model.
other models Knock in CAG expandsed repeats t normal HTT gene. this created a more subtle slowly prgressing HD phenotype.
the R6 HD and q150 knockin mice both shows similar end stage phenotypes. they only differ on age of onset and progression. This may suggest that the toxicity of the q150 knockin stems from this same abberant splicing but only differes by abundance and rate of accumulation of exon1 fragments. suggesting this is the primary toxic HTT species.
Outline the two theories by which the toxic HTT (Huntigtin) fragment forms? include questions raised from post-mortem study?
1- This suggests that the HD gene is transcribed and translated normally producing a full Htt PROTEIN. The polyq expansions on mutant Htt then causes the porteoloysis of the protein froming an EXON1 sepcific fragment.
studies have identified some proteases that may fascilitate this (caspase-3 and caspase-6)
2- This is related to abberant splicing of the mutant HTT pre-mRNA as a result of polyq expansions in the N-terminal domain. This causes the premature termination of transcription and slective snipping of exon 1 which is released and individually transcribed resulting in the formation of a toxic exon1 specifc HTT protein fragment downstream.
SATHASIVAM et al- they showed this was caused by abberat splicing. investigations in mouse models sowed the existene of unspliced exon1-intron polyadenylated mRNA solely in mutant models indicator of abberant splcing between exon 1 and 2. using transgenic mouse lines expressing the human equivalent of the gene has simmilar findings. IMMUNOPRECIPITATION and westernblot was used to show that this RNA was indeed translated to form an exon1 specific protein fragement in HD models.
They showed this was CAG dependant by showing abberantly spliced RNA in several mouse models with varying repeat lengths abover 40. was seen in all but 20 repeat model.
They investigated post mortem samples of juvenile HD paitients using RNA sequencing identifying signals that correlated with the exon1-intro1 mRNA. so it is present i human HD patients.
The exon 1 mrna is not seen in adult post-mortem brains. this sugests that the abberant splicing mech is not sginificant. however rna is inredibly suceptible to degredation possibly explaining the absence.
It is seen juvenile forms of HD.
What is the issue of genotyping the extent of CAG repeats using blood tests or sperm smaples e.t.c in HD?
SOMATIC INSTABILITY- there is variation in the stability of CAG expansions between cell types.
a blood test yielding DNA with 40 repeats might actually be found in a individual in which the exten in the neuronal population is much worse.
Moreover, sperm have a much higher instability so an individual with safe blood levels may pass on much more sevre enes to the next generation. westernblotting in sperm often produces smear of band indicatiing large variations in the extent of expansion even in thhis 1 cell type.
what is the core pathology of HD?
HD patients suffer from the degenrations of striatal MSNs. this is at first slectively associated with thos emediating the indirect striatal pathway and then this spreads to other in later stages.
The existence of intranuclear inclusions of mHTT is hall mark of the disease.
we can also observe mitochndrial dysfucntion, reduced BDNF expression and impared proteolysis due to mHTT action.
over representation of NMDA in striatal regiona n reduced glutamate uptake also observed.
what are the symptoms of HD?
There are motor, cognitive and psychiatric symptoms, as well as pathophysiological clinical features not decribed here.
Motor- CHOREA- this is semi-directed involuntary movements.
RIGIDITY- this occurs when the MSN degenration spreads to those associated woth the direct pathway later in progression.
Pschiatric- AFFECTIVE DISORDERS- patients often show depression and high suicide risk (pottentially linked to reducion in BDNF xpression)
ANXIETY/PANIC DISORDERS.
PSYCHOSIS simmilar to SCZ
Complsuions and obsessions
Cognitive-DEMENTIA= OCCURS IN 100% OF PATEINTS. FRONTAL DEFFICIENCIES- issues with planninng, multi tasking and increased complusivity and irritatability.
issues with psychomotor drive and meotional recognition
memory and speaking is sparred.
These symptoms often PRE-DATE motor smtoms b p to 10 years
A physiological symptom is weightloss which as been asspociated to mitochondrial dysfucntion stemming forom the transcriptional dysregulation of PGC-1 alpha function.
what is thought to be the role of Endogenous HTT? 5
vesicular transport, endocytosis, cell division, transcriptional regulation, autophagy
what insights can MRI studies of the prodromal phase of HD provide?
Magnetic resonance imaging done in prodromal phase of HD offer alot of insights.]
Degeneration of the Cingulate cortex (layers III, V, VI pyramidal neurons) and white matter in the thalamus and hippocamps can be obsered. This may expalin the earlier expereince of Cognitive defects.
Ths ould be used as a pottential biomarker.
What makes up MSNs in the striatum? What might underpin their vulnerability?
MSNs are 95% of the neruons in the striatum.
They are mostly GABAergic spiny neurons, but there are aslo GABAergic and cholinergic interneuorns.
The vulnerability of these neurons likely stems from their inherent vulnerability to excitiotoxicity, transcription dysregulation, mitochondrial dysfnction and BDNF defficienncies.
A clinical feature of HD is increased extra synaptic expression of the calcium permeable NMDA receptor and decreased glutamate uptake. Striatal neurons are heavily innervated by gabaergic neruons from the thalamus and cortex, hence this upregulation could lead to large increase in calcium entry and hus excitotxicity and MSN death.
The slectively targetting of mHTT dysfunction to striatal MSNs has een associted to a process known as SUMOyaltion. this involves the addition of a small ubiqutin like modifier (SUMO) to lysine residues on HTT.
This process compete with usuall ubiquinoyaltion for the same targets. ubiqutinoyaltion has been asspociated with the marking of HTT for degredation whilst SUMOyaltion has been shown to stabilise toxic HTT
further study has now identified the protein RHES, a small guanine nucleotide binding protein that has a greater affinciy for mHTT than wild type. This pottentiated binding of SUMO to HTT. RHES has a much reater expression in striatal region than extrastriatal regions explining the pottentiation of mHTT driven dysfucntion and neuronal death in the striatal MSNs
How is mutant HTT thought to instigate disease? in what form is it found in cells? (include interaction examples, relate to alterations seen in HD pateints and evidence)
mutant HTT has been associated with specific alterations reslting in transcriptional dyregualtion.
mHTT forms globlar aggregates. these impare proteolysis and lead to the aggregation of other functionla proteins like chaperones causing dysfunction but mHTT also can overide the NUCLEAR EXPORT SIGNAL resutling in re-entry into te nucleus to from INTRANUCLEAR INCLUSIONS (a hallmark HD feature( and this causes transcriptional dyregulation)
the selective patterning of dysregulation can be seen to down regualte genes associated with neuronal sutvival, calcium homesostasis and cell growth and synaptic transmission. upregulation of thos eassociated with apoptosis and Cell stress.
specific examples linked to MSNs.
REST(repressor element 1 silencing transcription factor) This is a well established silencer and modulator of neuronal gene expression, 1 example is BDNF. REST has been shwon to translocate in and out of the nucleus in the absence of HTT, Normal HTT has been shown to indirectly-bind and sequester REST in the cytoplasm preventing impact on DNA hence it would appear HTT normally regualtes BDNF expression. However, polyq expanded mHTT has been shwon to have a weaker binding allowing for REST translocation into nucleus to inhibti BDNF expression. explaining te defficiency in MSNs.
It is also shown to dysregulate the expression of CREB binding protein CBP
The common feature of weight loss in HD pateints has been associated to mtico=hondrial dysfunction, a featre reported in both HD mouse models and human patiens. (decreased calcium buffering capacity, dysregualted membrane pottential, reduced activity of MRC complexes)
This can be related to mHTT specific intercation with peroxisome proliferator activated actived receptor-y- coactivator 1 alpha (PGC1-alpha). this is a factor related to expression of mitochondrial biogeneisis proteins (link to effects of parkin deffiecieny in PD).
The N-terminal of HTT has been shwn to intercat with mitochondria through this. stduies show that mHT causes a 30% decrease in striatal expression PGC-1 alpha through binding its promoter and reducing transcription.
In addition the over expression of PGC-1 alpha in the toxic R/6 HD mouse mdeol was shwon to revrse and halt striatal neuronal loss suggesting this is key to pathology.
Expalin how the process of SUMOylation maybe involved in the selective toxicity of the mutant HTT protein.
The slectively targetting of mHTT dysfunction to striatal MSNs has een associted to a process known as SUMOyaltion. this involves the addition of a small ubiqutin like modifier (SUMO) to lysine residues on HTT.
This process compete with usuall ubiquinoyaltion for the same targets. ubiqutinoyaltion has been asspociated with the marking of HTT for degredation whilst SUMOyaltion has been shown to stabilise toxic HTT
further study has now identified the protein RHES, a small guanine nucleotide binding protein that has a greater affinciy for mHTT than wild type. This pottentiated binding of SUMO to HTT. RHES has a much reater expression in striatal region than extrastriatal regions explining the pottentiation of mHTT driven dysfucntion and neuronal death in the striatal MSNs
what are the developing methods of treating HD and what areas do they target? what benefits does genetic testing provide (include evidence)
better diagnosis- the use of genetic screening to identify individauls with large polyq expansions is growing.
This has been used to identify a golden window of action which exists when neruons are dysfucntional but not yet destined fro death.
pre-natal screening is also now avalable at specialised HD units.
Neurofilament Light protein in plasma (NFL)- research by BYRNE et al 2017 has suggested that the presence of enhanced levels of Nfl in plasma may be a biomarker of disease. they showed progressive increased in this from controls to premanifest HD to manifest HD to late stage HD. this biomarker is also being investigated for parkinsonian conditions.
Therapeutics look to target both the standard and abberant splcing mechanisms.
RNAi- interfearing RNAs have been investiagted in mouse models by YAMAMOTO et al 2000. these work by binding mature RNA and preventing translation and ften causing their degredaion by association with the RISC COMPLEX. he found that they could be used t turn the gene on and off and drive PARTIAL recovery of the HD phenotype, through improved ROTAROD tests in mice.
These ideas have now been applied in the investigation of ASOs. these bid to pre-Mrna to prevent splicing and fomation of a mature RNA.
this has been investigated in MOUSE MODELS. injection of HuASO caused improved rotarod latency and survival (slightly) compared to inject of saline.
IONIS have now produce IONIS-httrx. this ASO has been trialed in humans. showing a 50% KD of mHTT and HTT in hetrozygous individuals. 46 TESTED It was shown to cause dose dependant reduction in mHTT which corellated with improvement in clinical scores. There were NO adverse effcts and 100% completed the trial with some now on extended trailling.
RNAi could be applied in the abbernat patwhay through exon 1 specific RNAi and this is being worked on. this would offer a more selective treatment without effecting WT HTT whose LOF may contribute to pathology.
why is toxicity pottentially a product of soluble mHTT forms.
researchers have struggled to draw direct relationships between the expression of aggreagtes and toxic changes. suggesting that it is likely soluble forms involved.`
outline and describe the main histopathological features of AD
Severe atrophy of neurons. looking at a brain i postmortem it will ave large sulci and enlarged lateral ventricle.
severe atrophy of the HPC is also a sign.
Extracellular depostions of amyloid beta plaques. Large insoluble aggregates fromed from the abberant proteolysis of precursor APP.
A-beta deposition is also visualised in cerebral amyloid angiopathy (CAA) where plaques from in the walls of blood vessels.
Intracelular inclusions of NeuroFibillary Tangles. These consist of hyper phosphorylated microtuble associated protein Tau. (MAPT). look like Whispy Flames.
Neuroinflamation. This can be seen by the surrounding of plaques by microglia that have undergone hypertrophy to enter a Ramified state.
briefly outline the Thal phases of AD compare this to BRAAK staging of AD.
THAL phases tracks the progression of AD through the depostion of AMYLOID BETA. spread being anterograde transmission to regions innervated by infected regions.
1- neocortical depostion
2- inclusions of allocortical regions
3- involvement of striatum, cholinergic nuclei of basal forebrain, diencephallic nuclei
4- inclusion of several brain stem nuceli
5- the final phase with inclusion of the cerebellum.
Phases 1-3 are associated with the preclinical phases and phase 4+5 with the clinical symptoms.
Braak staging tracks the deposition of tau pathology (neuro fibilliary tangles)
1+2- these involve primarily the entorhinal cortex and hippocampus.
3+4- these involve the inclusion of limbic structures
5+6- nemerous regions of the cortex now included.
1+2 confer a non symptomatic stae with the onset of symptoms in stages 3+4 and 5+6 conferring severe stages of AD.
Tau progression has been shown to correlate with the progression of AD. However, Amyloid beta depostion has not with man dying with abundant amyloid beat deposits and no symptoms. Hence, Braak staging may be more reliable in AD.
provide a breif descripion of the clinical progression of AD and its correlation pathological changes.
The progression of AD follows a predictable pattern of atrophy.
atrophy can be visualised by MRI far before the symptomapric pahse in a preclinical phase. early on here atrophy can be seen in the EC and HPC, are associated with spatial cognition, something that can be seen in ealry phase AD patients.
soon atrophy in limbic and later cortical areas is observed. conferring with the onset of symptoms like memory loss and later confusion, and the detrioation of intelectual capacity associated with dementia.
Although a hall mark of AD histopathology this does not correlate with the spread of AB pathology. However, it does correlate with the predictable spreading pattern of tau pathology described in Braak staging.
1+2- this being the preclinical phase where there is accumualtion in EC and HPC areas, confers with spatial cognition deficits.
3+4- There is inclusion of limbic areas and the onset of symptoms like memory loss confer with this.
5+6 this is where multiple cortical regiosn begin to be involved, this is seen in late stage AD and correlates with the progressive severity of dementia.
what are the main therapeutic targets in AD?
stop amyloid plaque formation
stop the formation of hyperphosphorylated Tau tangles
reduce neuroinflamation (thought to be a cause of issues with synaptic efficacy, a early contributo to neurodegenerative cascades
modulate neurotransmission
use genetics to identify novel targets
what are the early behvaioural warning signs of AD?
memory loss, in particular issues with spatial memory as the hippocampus is degenerated early on, we can assess this through the 3 peaks study which test both spatial memory and perception (perception is normally fine)
changes in personality issues with pallning and decision making. misplacing things, change in mood disorientiation is space an time. difficutly performing familiar tasks.
what is the difference between primary,secondary and tertiary prevention
Primary- this attempts to prevent the onset of disease
Secondary- This attempts to trrea the undelrying pathology and cure disease
Tertiary- This attempts to treat the symptoms of the disease.
what risk of bias can be associated with randomised studies of neruodegenrative disease like AD, what is the issue of the currently known markers?
In neruodegenrative conditions the rate of progression can vary alot.
Randomised smapling runs the risk of having fast progressor and slow porgressors dominantly in placebo vs test trials. this can cause false positive/negative results when analysing the progression od symptoms in tertiary studies or disease markers in secondar trials.
The issue with current biomarkers is there are alot of RETROSPECTIVE markers that provde inof on risk of onset but very few that tell uss how a disease will progress. making it hard to distinguish between fast and slow progressors.
Tertiary efficacy outline a test used to measure the change in AD patient cognition? Give an example of a clinically meaningful exam.
ADAS-COG (Alzheimers disease assessment scale cognitive subscale) this is used to assess the changes in cognitive symptoms. the score ranges between 1-70 with normally elderly individuals scoring 0-1 and AD patients score usually increasing yearly. (score is number of errors
A clinically meaniful exam would be the Clinical interview based impression of change with carer input (CBIC-plus). this is a score of improvement between 1-7
either halting of worsening or improvement is considered successful.
importance of placebo efficacy on AD trials for tertiary cures
Here improvement in test drug and decline in placebo is a sign of efficacy.
However, improvement with drug and no decline in placebo is not strng evidence of efficacy. as this could simply mean that trial drug is beinmg tested on slow progressors.
In secondary studies what is seen as a sign of effectiveness, what do you need to assess this.
Secondary studies a sign of effectiveness in the halting of progression of a dynamic biomarker (cannot uno damage)
In order to assess this you need a dynamic biomarker who changes correlate with the progression of symptoms. in PD this is MRI to investigate atorphy of neural tissue that racks decline in cognition.
Why is amyloid plaque accumualtion not a good biomarker of disease progression, How can we visualise it and what is it used for?
amyloid plaques do accumualte throughout the disease and indeed accumualtion can be seen even 15 years before onset as a toxic threshold is need for disease.
This can be visusalised using postiron emisiion tomography using a Amyloid specific radioactive marker.
Issue is this does not correlate with disease progression.
Give the best cuurent exmaple of a dynamic marker that can be used to track changes in disease pogression for secondary trials of AD?
currently the best marker is magnetic resonance imaging of the brain.
There used to be some issues as movement of the head could make images appear to be shifted and the images never where done with the exact same point of reference.
Now days a computer program can precisely sperimpose several images alllwoing the visualisation and calculation of the prgressive atrophy. we now Know in a healthy 40 year old this is 0.2% a yar and rises to 2.8% a year in AD hence this is a rnage of reference for reductions in progression.
severe atrophy is is seen far before the onset of symptoms and Atrophy does correlate with the progression of cognitve deffiencies.
How do you overcome issues of bias in secondary efficacy trials?
In secondary trial the risk of fast and slow progressos still exists so instead STRATIFIED SAMPLES are used.
The take individuals once they have been analysed and are confirmed fast or slow progressors.
Although logic suggest using fast progressors as the change in disease progression will be most visible.
It is also importnat to test in slow progressors as fats progressors once identified may have already passed a irreversible threshold and thus may produce false negatives.
issues with using Event related pottentials (ERP) as a marker of impairment and progression in AD, equally wat are the weakness of EGG.
ERP work as declines have been both correlated with cognitve deffiencies and disease progression in AD. usually tested using a constat repeated tone with infrequent changes to investigate the neuronal reponse. this is reduced in amplitude and latency
Issue is this is aslo observed in PD, schizophrenia and dyslexia and so is not a specific AD test.
simmilarly testing for EEG in which in AD patients we observe a progressive INCREASE in slow wAVE THETA AND DELTA WAVE AND reduction IN FAST BETA AND ALPHA WAVES. this is also observed with normal aging in elederly and several othe rpathological isues.
Benefits of double blind
In these trial neither the patient o experimenter Know who has the placebo and who has the dru. ence, ths can reduce psychological or experimental bias, improving the validity of findings.
Can we diagnose AD in life?
NO given the biomarkers today we can predict the likelihood of AD onset and the probability that somebody has AD but we cannot diagnose it as AD until postmortem studes are done.
outline the process by which Amyloid beta plaques from APP and how Neurofibilliary tangles form from TAU.
Amyloid beta is produced by the from th precursor APP.
APP is usually cleaved by alpha-secretase and then gamma-secretase this produces the normal peptides.
However, it can be alternatively cleaved by Beta-secretase and them gamma secretase froming the toxic amyloid beta peptides. gamma secretase can cleave at multiple points primrily producing amyloid beta 40 or 42. These will then form plaques. 42 has MORE hydrophobic amino acids and further promotes aggregation. (Idea is that then mutations in APP or subunits of gamma-secretase will increase the cleaving to produce amyloid beta)
NFTs- Tau is a microtuble associated proteina dn stabilist microtubules. It binds via c-terminal repeats of which there are 2 (3+4). The Reverisble binding is regulated by phophorylation.However, in pathogenic state there is hyperphosphorylation of MAPT resulting in the formation of Paired helical filaments of MTs and TAU. These are deposited intracelluarly as NFTS.
Note there are normally equall amounts of 3 and 4 but in AD taus express the C-terminal repeat 4 more than 3.
what is the social importance of treating alzheimers?
We have an aging population and the greatest risk f AD is age. hence, the AD population is growing.
forms of dementia like this are evermore prevalent with 1:3 being ascoiated with someone with dementia.
The estimates cost to society is 26billion a year.
Hence is is of great soceital importance to treat this condition.
what are the main risk factors of AD outside of genetics?
Age is the main risk factor of AD.
outline and decribe some of the identified genetic causes and risk factors (not including GWAS) of AD. (3)+(2)
Monogenic EOAD: less tan 5% of cases are fammilial.
APP mutations- this is the precursor of amyloid beta and muations here promote cleavage via the beta-gamma pathway and thus increase the production of AMyloid beta.
Trisonomy 21- this is the cause of down syndrome and chromosome 21 in the location of the APP gene. Hence, this is a dose dependat increase in APP and subsequently in Amyloid beta.
PSEN1+PSEN2- these are subunits of gamma secretase and mutations promote the lesion to produce the aggreagation-enhanced Amyloid beta 42.
Risk factors
APOE4- there are 4 allels of this gene, APOE2 asscoaited with protection against AD, APOE3 which is AD neutral and APOE4 whcih increases the risk of AD. These are involved with the transport of ch=olesterol to neruosn and APOE4 is thought to slow A-BETA removal.
TREM2- triggering receptor on myeloid cells 2. This is associated with the response to amyloid beta by microglia.Thus mutations inhibit the immune removal (phagocytosis) of toxic amyloid beta.
what is dementia
Dementia is caused by several diseases and is defined by the detrioration of intelectual capacity. (Judgement , memory e.t.c)
outline the amyloid beta theory and the brief evidence behind it. include varied roles of tau an amyloid in pathology.
The amyloid beta theory states that abberant proteolysis of APP froms toxic species of amyloid beta. These then act ia 3 mechanisms.
1- they intefear with the kinases asscoiates with MAPT an drive the formations of hyperphosphorylated tau and NFTs, leading to neruonal death.
2- AB plaques form and drive the subsequent dysfunction of neruons and contributes to neuronal death.
3- the fromation of soluble AB oligomer causes synaptic dysfunction (shown in mouse models) and contributes to neuronal death.
hence within this theory AB acts upstream of NFT formation and neuronal death.
evidnece:
Mutations related to the fromation of AB can cause familial AD suggesting it is the driver of the disease.
Crossing APP mutant mice with a tau KO was unable to cause pathology, neuronal death or cognitive deficits. But APP cross with WT did. This suggests Tau pathology is key to the neurotoxic aspects of the disease and AB is key to the onset. (Hence need to target both)
MAPT mutations do not cause AD (although they do cause deeneration asscoiated with FTD shown by P301 mutation mouse models)
Injection of AB into mice was able to induce and pottentiate the spread of tau pathology (note soon tau pathology became self-maintaining)
Do Tau mutations have varied impacts of AD an FTD.
MAPT muations do not cause AD. However, they have identified roles in FTD.
discuss the efficacy and usefullness of early mouse line trials in targetting Tau kinases in therpeutics?
GSK3beta and CDK5 are both kinases that have been associated with the phophoryaltion of tau. trials have been run in mice attemtping to stop this to stop the formation of NFTs.
This was able to reduce progression of cognitive defects.
But these are not clinnically useful because the fucntion of Tau phosphryaltion and the function of these kinases besides tau is important and thus this has severe off target effects.
discuss the importance of critical periods of actions to therapeutics. Imapact of likely hood of certain targets being effective.
amyloid beta accumualtion and atrophy can be seen 15+20 years, respectively before symptoms onset. hence this offers a critical period of action in which we can stop AB action efore it is too late.
Moreover, studies injecting AB into the brain of rats found that it could induce the spread of tau pathology.However, aafter a period tau pathology became self-maintaining. thus there is a periodin which inhibtiing the formation of AB would not stop disease progression and thus stopping the action of tau is also important.
How has GWAS been used in AD and what is the next step?
GWAS has been used to idnetifiy several common variants that contribute to the risk of AD. there are now 20.
However, these all confer relatively small risks.
The next step is to investigate the effcts of cummlative risk. would it increase rsk to have 5 muattions in different aspects of a pathway as compared to 1 muatation.
outline the investigation of mechanism of how tau pathology spreads.
A indepth study has been performed. in neuronal cell cultures pulled from the MAPT mutant P301 mouse line
In Braak saging we see that the pathology spreads from the EC and then to limbic regions and thus it appears to spread between connected regions.
Expressing the MAPT mutant neuron in culture with a WT neuron the MAPT acts as a donor. After 2 WEEKS intracellular Tau inclusions are seen in the wild type neurons.
They investigated whether direct contact was needed:
In IPSC cells they placed mutant tau neurons and tau KO neurons in a medium and then tested the medium for phosphoryalted tau and the tau-KO neurons using tau specific antibodies in an ELISA test. This showed that the TAU-KO neuron took up tau from the medium and thus cell to cell contact is NOT neccesary.
Finally the investigated the role neural activity.
They expressed the optogenetic channel; CHR2 in tau expressing neurons and stimulated them whilst assessing thelevel sof tau in the media. they reported a 250% increase after 30 mins of stimulation.
Hence, it would appear that mutant tau can spread between cells and thus neural regions connected by active synaptic connections.
Many believe that NFTs induce the abberant folding of other tau molecules
What is the theroy on how Tau dysfunction may cause neuronal dysfucntion and death? (evidence)
Some studies have linked this LOF of tau.
Ittner et al, showed that ta has a key role in synaptic targetting highlighting the trageting of Src kinase fin to NMDA as a example.
Hence, disruption of this in AD dirsupts post-synaptic targetting and uncouples NMDAR which could lead to it mediating excitotoxicty through Calcium inlfux.
who are possibly a underused population of patients for AD therapy trialing
Down syndrome patients, due to trisonomy 21 they have an extremely high likelyhood of AD and thus act as a good sample who can be treated in the preclinical phase to investigate the efficacy of stopping AB formation. This is an issue with normal trialling and you dont know if participants have already progressed too far.
what behvaioural deficits are observed in the FTD p3015 mutated MAPT model shown in 2012 MWM study.
This study investigated the impact on MVM training in 2012.
They reported cognitive deficots in spatial learning and memory.
motor abnormalities such as clasping when raised by te tails and limb weakness.
what are the links of amyloid beta oligomers instead of aggreagtaes to neruonal dysfunctions?
studies have indicated that plaques may be an attempt to sequester toxic soluble AB oligomers.
studie have suggested these oligomers disrupt synaptic function in mouse models.]
In human Post-mortem they found a distinguishable difference between mildly and severely demented patients was the level of AB oligomer, identified by ELISA, higher wehn severe.
This suggests in worsens of pottentiates the severity of the pathology and thus may cause toxicity.
Discuss the heterogeneity of Amyloid beta
The heterogenitiy of AB peptides mainly 40 and 42 makes it hard to target them with therpeutics.
There is growing research to devlop specific antibodies fro eaach to better undertsand the contribtion of each to patholgy, these would also be able to drive nearby microglia to clear the AB build up.
what is the prion-like spread theorised in AD
There is an argument over whether the spread of patholpogy is temporally dependant, I.e mre vulnerable neurons go first and more resistant later.
Or is this linked to physiological spreading of pathology. This is what would be suggested by Braak staging and optogenetic study on the spread of tau.
the prion like theory is that misfolded protein act as templates to drive the misfolfing of endogenous proteins through permissive templating thus spreadinmg apthology and dysfucntion.
studies have now shown that the use of surgical tools used in AD can transfer AB pathology to new patients. This Iatrogenic inheritance suggets The may spread in a prion like fashion.
