AD: Molecular Mechanisms and Animal Models: Part II

Question 1

Overview of in vitro AD models?

Answer 1

• transfect cell lines w/ APP: neuroblastoma (as neurons don’t replicate) -> measure Aβ level in medium
• AD pt specific iPSCs: same mutations]- difficult to find control as diff. ppl have differences unrelated to AD

Question 2

Overview of in vivo AD models and advantages?

Answer 2

[useful for target ID & pre-clinical screening]

• rats/mice (similar brain anatomy, behav tests, NFT/plaque staging)
• fish (giant neurons-microinjections)
• worm (easy + fast breeding, cheap, ethical, powerful genetics)
• drosophilia (easy, fast breeding, cheap, ethical, powerful genetics)

Question 3

Disadvantages of in vivo:

• rats/mice
• fish
• worm
• drosophilia

Answer 3

• rats/mice: time-consuming, expensive, no Aβ plaques
• fish: diff. brain anatomy, behav/staging difficult
• worm: diff. brain anatomy, behav/staging difficult
• drosophilia: diff. brain anatomy, behav/staging difficult

Question 4

Features of rodent models that are similar to AD?

Answer 4

• behavioural/cognitive dysfunction
• impaired synaptic plasticity
• delta-APP processing
• amyloid plaques

Question 5

Issues w/ rodent models of AD?

Answer 5

• dont develop Aβ plaques]- amino acid difference, no Aβ aggregates
• transgenetic animals express human protein (APP, presenilin, tau) e.g. APP-23 mice overexpress Swedish mutation; tau models similar to FTLD, not true AD
• double/triple trans-animals may express APP, presenilin and tau -> Aβ plaques and NFTs
  BUT mice don’t have large neuronal loss/atrophy (like human AD)

Question 6

What is conditional KO?

Answer 6

Gene KO for certain cell type/specific brain area

certain gene KO is embryonically lethal e.g. presenilin KO

Question 7

Overview of Cre-LoxP strategy for conditional gene KO?

Answer 7

Floxed ouse has LoxP sites around target gene (removed)

Cre mouse has Cre-Recomb enzyme inserted after specific promote

Cre recombinase only expressed in certain cell type, therefore KO (LoxP site and gene removed) only in specific cell types

Question 8

Outcome of conditional KO of presenilin?

Answer 8

Decreased gamma-secretase

Mice crossed w/ APP trans-mice don’t develop plaques

Question 9

How to assess results in in vivo AD models?

Answer 9

• Behavioural tests (memory e.g. Morris water maze, Y maze w/ food, object recog)
• electrophysiological measures/ LTP]- assess synaptic strength
• brain imaging]- difficult to distinguish certain brain regions as mouse brains are small…rat brains are preferred for imaging

Question 10

Outcome of intracerebral injection o AAV-vectors in WT mice? (into certain brain regions)

Answer 10

AAV w/ Tau -> neuronal loss in hippocampus (not seen in transgenic tau… overexpressed tau affects neuronal survival?)

AAV w/ APP -> plaques (some, not all- due to variation in experimental technique?)