BS42023 L5

Question 1

what are newer diagnostic techniques for AD?

Answer 1

PET and functional neuroimaging (FTD)

Question 2

describe the levels of CSF biomarkers in AD

Answer 2

tau increases by 300%

Ab decreases to about 50% (as there is increased deposition in plaques)

Question 3

AD is pathologically defined by what?

Answer 3

presence of plaques and tangles

Question 4

what are beta-amyloid plaques and neurofibrillary tangles?

Answer 4

plaques- insoluble aggregates of b-amyloid proteins that form outside of neurons
tangles- insoluble aggregates of hyperphosphorylated tau proteins that form inside neurons

Question 5

how do Ab1-42 peptides come about?

Answer 5

b-secretase and y-secretase cleave at their sites on APP leaving a harmful AB1-42 peptide.

Question 6

what happens to;
APP-null mice
APLP2-null mice
APP/APLP2-null mice

Answer 6

• relatively normal
• relatively normal
• 80% die after 1 week

Question 7

aggregation of b-amyloid peptide is facilitated by which metals?

Answer 7

zinc and copper

Question 8

what properties does the Ab1-42 variant have?

Answer 8

• more hydrophobic than Ab1-40
• more prone to fibril formation
• is the predominant isoform found in cerebral plaques

Question 9

What is the toxic form of Ab-peptide: soluble or insoluble aggregates?

Answer 9

soluble monomeric Ab peptides are toxic to cells in culture and in brains of rhesus monkeys

Question 10

The evidence for Ab as a cause of AD is (6)

Answer 10

• There is an increased number of plaques in brains of patients with AD
• Genetic mutations in familial (early-onset) AD cause increased production/deposition of Ab peptides (e.g. APP, PS1, PS2).
• Ab plaques appear in Down Syndrome patients (trisomy 21) that carry an extra copy of the APP gene
• APOE4 allele increases the risk of sporadic (late-onset) AD
• Transgenic mice expressing mutant human APP genes develop plaques and neurodegeneration (but not extensive and no tangles)
• Aggregated or fibrillar (but not soluble/monomeric) Ab peptide is toxic to cells in culture and the brains of aged rhesus monkeys.

Question 11

what do Ab peptides induce?

Answer 11

production of reactive oxygen species, leading to cell damage and apoptosis

Question 12

Cell culture, clinical and epidemiological studies suggest that what is protective of effects of Ab?

Answer 12

anti-oxidants, Vitamin E and oestrogen

Question 13

how might Ab peptides act?

Answer 13

as non-selective ion channel or allow release of ROS. Ab may promote the aggregation of tau to form neurofibrillary tangles.

Question 14

what are the two major hypotheses for AD?

Answer 14

1. BAPtists- the accumulation of a fragment of the amyloid precursor protein or APP (the amyloid beta 42 residue fragment or Ab-42) leads to the formation of plaques that some kill neurons.
2. TAUists- abnormal phosphorylation of tau proteins makes them “sticky” leading to the break up of microtubules. The resulting loss of axonal transport causes cell death.

Question 15

where are neurofibrillary tangles expressed and found?

Answer 15

predominantly expressed by neurons in the CNS and predominantly found in axons.

Question 16

why do NTs interact with tubulin/MTs?

Answer 16

They co-purify with tubulin/MTs, stabilise MTs integrity and promote MT assembly.

Question 17

where is tau normally/in AD found?

Answer 17

in axons but in AD aggregates and is redistributed to cell bodies and dendrites.

Question 18

transgenic mice expressing FTDP-17 (disease caused by tau mutations) exhibit what?

Answer 18

Neurofibrillary tangles and neurodegeneration

Question 19

tau knockout mice exhibit what?

Answer 19

they are normal and show no obvious developmental, cognitive or neuronal polarity defects

Question 20

together, what do transgenic mice expressing FTDP-17 and tau knockout mice demonstrate?

Answer 20

the presence of abnormal tau/NFTs rather than the loss-of-function contributes to development of AD.

Question 21

when is tau hyperphosphorylated and by which enzymes?

Answer 21

early in AD- by kinases including GSK3, Cdk5, MAPK, DYRK

Question 22

what might hyperphosphorylated tau result in?

Answer 22

impair its ability to bind MTs and promotes its aggregation, forming NFTs creating imbalance between kinases and phosphatases and generate excessive NFTs

Question 23

how might imbalance of kinases/phosphatase activity result in tau hyperphosphorylation and NFTs? (5)

Answer 23

• Association of p25 with Cdk5 leads to activation of Cdk5.
• Activated Cdk5 can inhibit GSK3 by indirect regulation of the inhibitory serine phosphorylation of GSK3.
• Consistently, results and data from studies indicate that Cdk5 acts via protein phosphatases such as PP1 and PP2A, possibly by affecting regulatory subunits.
• GSK3 phosphorylates tau.
• Thus, disruption of inhibitory GSK3 regulation, for example, by altered Cdk5 function, or pharmacological GSK3 inhibitor, like lithium may lead to tau hyperphosphorylation.

Question 24

what is the importance of tau pathology in AD?

Answer 24

NFTs are common to many forms of dementia and are often the only pathological lesion in these diseases- no conditions where there are plaques only.

NFTs show higher correlation with AD progression than plaques

Question 25

describe the tau hypothesis (5)

Answer 25

• Ordinarily, the tau protein is a microtubule-associated protein that acts as a three-dimensional “railroad tie” for the microtubule.
• The microtubule is responsible for axonal transport.
• Accumulation of phosphate on the tau proteins cause “paired helical filaments” or PHFs (like two ropes twisted around each other) that accumulate and lead to the neurofibrillary tangles (NFT).
• PHFs are the main component in NFTs.
• Impaired axonal transport is the probable cause of cell death but the focus is on MAPT genes (microtubule-associated protein tau).

Question 26

describe the amyloid hypothesis (4)

Answer 26

• The amyloid precursor protein (APP) is broken down by a series of secretases.
• During this process, a non-soluble fragment of the APP protein (called Ab-42) accumulates and is deposited outside of the cell.
• The non-soluble or “sticky” nature of Ab-42 helps other protein fragments (including apoE) to gather into plaques.
• Somehow the plaques (or possibly the migration of Ab-42 outside the cell) cause neuronal death.

Question 27

what is apolipoprotein E? (ApoE)

Answer 27

• a glycoprotein produced in high levels in the liver and brain.
• synthesised by glia in the brain (predominantly astrocytes)
• binds to soluble and aggregated amyloid-B

Question 28

what role does ApoE have?

Answer 28

ApoE is the body’s primary cholesterol transport protein. It is secreted mainly from astrocytes and microglia.

Question 29

what mediates influx of Ab peptide across the BBB?

Answer 29

RAGE

Question 30

what mediates influx of Ab peptide across the BBB?

Answer 30

RAGE

Question 31

what are two major proteases involved in Ab (monomer) degradation?

Answer 31

IDE and NEP

Question 32

where are IDE and NEP located?

Answer 32

IDE is mostly cytoplasmic, NEP is a transmembrane protein whose catalytic site is located in its extracellular domain.

Question 33

One of the earliest changes in AD progression is loss of what?

Answer 33

acetylcholine transferase activity in the cortex and hippocampus (catalyses choline + Acetyl-CoA –> ACh).

Question 34

Cholinesterase inhibitors are designed to combat impairment of cholinergic neurons by slowing degradation of acetylcholine after its release at synapses. Three major AChE inhibitors currently in clinical use are…

Answer 34

donepezil, rivastigmine, and galantamine

Question 35

what effects do AchE inhibitors have?

Answer 35

delay neurodegeneration by 6 months, this is most effective early on.

Question 36

what is memantine?

Answer 36

an NMDA receptor antagonist which has similar effects as AChE inhibitors

Question 37

What does a good model of AD need to show? (4)

Answer 37

• Face validity; have plaques and tangles, cognitive deficits and neurodegeneration
• Reliability/reproducibility; needs to be able to be observed consistently in the same animals
• Construct validity; observed in different environments, in different tests measuring the same thing AND across species.
• Predictive validity; it needs to show temporal relevance to the disease and it needs to show that treatment aimed at the insult will make it better.

Question 38

what are the three main therapeutic opportunities for treatment of AD?

Answer 38

1. Reducing Ab production
2. Prevention of Ab aggregation
3. Influencing Ab clearance/degradation

Question 39

how would you reduce Ab production therapeutically?

Answer 39

y-secretase- cleaves other important substrates (e.g. notch) hence specificity is important. E.g. substrate docking sites are different so target APP binding site. E.g. likewise, ATP-binding site modulates APP processing specifically.
Certain nonsteroidal anti-inflammatory drugs (NSAIDs) allosterically modulate y-secretase to favour production of Ab40 over Ab42.
Inhibitor LY450139 lowered Ab in plasma but not CSF.

b-secretase- lacks other substrates (KO is viable with very minor anomalies) and therefore is a safer target.

a-secretase- stimulating its activity could decrease Ab since it cleaves within the peptide e.g. bryostatin, a protein kinase C inhibitor enhances activity.

Question 40

how would you prevent aggregation of Ab therapeutically?

Answer 40

using alzhemed or clioquinol (although these treatments have been tried and failed)

Question 41

how would you influence the clearance/degradation of Ab?

Answer 41

• by enhancing molecules that help transport Ab out of the brain and inhibit those that help transport Ab into the brain.
• immunotherapy
• antibody aducanumab
• use ultrasound to break up the plaques (doesn’t work)