AD: Molecular Mechanisms and Animal Models: Part I

Question 1

The role of tau: physiologically and pathophysiologically?

Answer 1

Phys: tau stabilises microtubules

Pathophys: hyperphosphorylated tau -> destab. MTs -> reduced axonal transport -> aggregates -> neuronal death

Question 2

Outcome of administering synthetic Aβ?

Answer 2

Decreased long term potentiation (amyloid binds to NMDA, amyloid activates microglia?)

Question 3

APP synthesis pathway?

Answer 3

APP formed in ER and phosphorylated/glycosylated in Golgi -> secretory vesciles to membrane -> re-internalised in endosomes

Question 4

Location of action of secretases

Answer 4

alpha-secretase in vesicles + cell surface

gamma-secretase in endosomes + cell-surface

beta-secretase in endosomes

Aβ found intracell and extracell

Question 5

Beta-secretase MOA on Aβ?

Answer 5

BACE-1 -> intracellular APP cleavage (->increased Aβ) -> neuroregulin cleavage (myelination)

BACE-2 (no amyloid)

Question 6

Alpha-secretase MOA on Aβ?

Answer 6

ADAM-10 and ADAM-17 involved in APP cleavage (as well as other proteins e.g. TNF-alpha)

[ADAM family]

Question 7

Gamma-secretase MOA on Aβ?

Answer 7

Presenilin-1 cleaves at cell surface -> extracellular Aβ

Presenilin-2 acts at lysosomes -> intracelluar Aβ

[gamma-secretase is a protein complex, presenilin domain has cleavage enzymatic activity]

Question 8

How the body deals with extracellular Aβ?

Answer 8

• phagocytosis (by microglia and astrocytes)
• enzymes degrade Aβ (insulin degrading enzyme-IDE and neprilysin-NEP)
• AporE removes Aβ (ApoE4 is ineffective at clearing Aβ)
• alpha-2 macroglobulin binds to amyloid and directly/indirectly removes it via LRP receptor
• Aβ can re-enter the brain via RAGE]- could extra CNS amyloid contribute to AD…unlikely as BACE-1 and APP expression in CNS

Question 9

Relationship between Presenilin-1 mutations and amyloid

Answer 9

• tend to have more Aβ42

- more intracellular Aβ (more endosome cleavage)

Question 10

Relationship between Aβ and prions-experimental evidence?

Answer 10

Iatrogenic prion cases due to human GF -> CJD also had increased Aβ pathology (prion-like spread or auto-catalytic change)

NB: GH pts aren’t representative of general popltn.

Question 11

Amyloid seeding hypothesis and experimental evidence?

Answer 11

Amyloid behaves like a prion

[inject AD amyloid into young WT transgenic mice]

-> WT mouse w/ AD amyloid develop plaques but not in trans-mouse w/out APP or if synthetic amyloid used

Question 12

Parabiosis experiment outcome?

Answer 12

Trans-animal w/ APP linked to WT animal -> WT had increased amyloid plasma & CNS amyloid deposition

Question 13

AD from blood transfusion?

Answer 13

Unlikely as amyloid likely to stick in blood vessels instead of entering brain

Question 14

Overview of types of AD treatment?

Answer 14

[current therapies are symptomatic, need disease-modfiying strategies]

• Aβ-based therapeutics
• Tau-based therapeutics
• Neuronal-based therapeutics

Question 15

Overview of Aβ-based therapeutics for AD?

Answer 15

• BACE inhibitors and g-secretase inhibitors
• Aβ modulators (affect length of Aβ, makes more Aβ-37 than Aβ-42)
• catabolism induces (increased Aβ metab)
• immunotherapy

Question 16

Describe evidence of immunotherapeutic targeting of Aβ?

Answer 16

Inject Aβ]- good evidence in animals (decreased Aβ in brain, increased memory)

Clinical trials show increased sepsis risk

Inject antibodies into Aβ (passive immunisation) -> clin trials show unsuccessful

Question 17

Overview of Tau-based therapeutics for AD?

Answer 17

• Tau aggregation inhibitors (autophagy enhancers, tau assembly inhib, methylene blue)
• Tau kinase inhibitors (GSK3, CDK5) e.g. lithium
• microtubules stabilisers
• Hsp90 inhibitors (afrects proteasome degradation of tau)

Question 18

Overivew of neuronal-based therapeutics for AD>

Answer 18

• growth factors (BDGF, NGF)
• NDMA antag (decreased glutamate excitotoxicity)
• anti-oxidants (less ox. stress)
• anti-inflammatories (regular NSAID used correlates with lower AD incidence)
• anti-diabetic drugs -> reduced risk e.g. pioglitazone

Question 19

Experimental results of NGF gene therapy?

Answer 19

NGF can’t cross BBB, limited benefit

Question 20

Importance of NSAIDS in AD?

Answer 20

Regular NSAIDs use = lower AD incidence]- reduces Aβ formation and tau phosph.

Question 21

Results of clinical trials for NSAIDs and AD

Answer 21

Unsuccessful- too short? treat pts earlier in disease course

Question 22

Neuropathological progression of AD overivew?

Answer 22

Amyloid plaque starts in basal forebrain, spreads to rest of cortical areas

NFT (Tau) starts in medial temporal lobe

Question 23

Biomarkers w/ AD correlation w/ stages

Answer 23

Stage 1: increased PET amyloid, decreased CSF amyloid

Stage 2: increased CSF tau

[now a change in brain structure in MRI]

Stage 3: cognitive changes