Alzheimer's Disease and Stress related Disorders

Question 1

Give some facts and figures of AD (5)

Answer 1

• most common cause of dementia.
• Affects over 50 million people worldwide
• set to rise to 152 million by 2050.
• Over 50% of carers globally say their health has suffered as a result of their caring responsibilities.
• Worldwide cost of dementia: US$818 bn

Question 2

What is the neuropathology of AD? (4)

Answer 2

• Neuronal and synaptic loss and gliosis
• Extracellular accumulation of Aβ peptide
• Intracellular aggregation of hyperphosphorylated tau
• Atrophy - of entorhinal, hippocampus, amygdala +associated areas of neocortex
• Aβ deposits (neocortex ->hippocampus->striatum-> the midbrain->cerebellum)
• Tauopathy - tau pathology better correlated with
  symptoms

Question 3

Describe the time‐course of disease progression (4)

Answer 3

graph

-> -30yrs to onset = AB plaques start + amyloidosis-associated neuroinflammation

-> -15yrs to onset = NFTs (associated w/disease prog)

-> -11yrs avg = Tauopathy-associated neuroinflammation

-> onset of disease
- a lot of a-beta, GFAP+NFT’s

Question 4

What markers can you use to investigate AD progression? (3)

Answer 4

AB/NFTs = blue

iba1 = red (microglia)

GFAP = green (astrocytes)

Question 5

What is the innate immune response of microglia in normal functioning (4)

Answer 5

Physiological role of microglia:
- clearance of: apoptotic cells, AB, debris

-secretion of neurotrophins + cytokines (eg IL-6, TGFB)

• migration: chemotactic response by ATP receptor to damaged tissues
• expression of: IBA1, CD11b, TREM2, P2Y12

Question 6

Explain the pathological changes seen in microglia in AD (3)

Answer 6

Pathological role of microglia:
- impaired clearance: AB

• secretion of neurotoxins + cytokines (IL-1B, TNFA)
• reactivity to NFTs

Question 7

What is the role of the innate response B-Amyloid in AD? (4)

Answer 7

The role of innate immune responses and neuroinflammation in b-amyloid accumulation and progression of Alzheimer’s disease is seen in image

• microglia go from clearing xs a-beta from CNS to xs microglial activation due to DAMP’s

= further neuroinflam = increase a-beta aggregation + sustained low grade inflam seen in AD

main mediators: -L-1 + TGF-alpha

Question 8

Explain how Pathologic Tau induces Glial Activation (4)

Answer 8

hyperphosphorylated pathological tau can be secreted extracellularly -> progressive spread (tauopathy)

= promotes microglial activation, reactive astrocytes = neurotoxic inflam factors (IL-1, TNF-alpha) due to tau kinases

-> glial activation further perpuates pathological tau = vicious cycle

Question 9

What was observed with microglia and phagocytosed tau? (1)

Answer 9

microglia involved in tau propagation by releasing axonal pathological tau that was phagocytosed

Question 10

Describe neuroinflammation at different stages of AD (4)

Answer 10

A: early stage - following the initial plaque depositions -> inflammasome activation by pathological changes in tissue = apoptosis-microglial->promote a-beta seeding (TREM2)

B: middle stage (TREM2 present): microglia cluster plaques around TREM2 + trim edges of plaque to compact = act as a barrier b/w plaque + surrounding tissue

C: late stage: tau pathogenesis- tau path accumulates + microglia spread extracellular tau = speeds up process + signal IL-1R beta = activate neurons + astrocytes to increase neuronal tau phosphorylation

D: late stage: neurodegeneration - DAMP/MGMD microglia secret neurotoxins = kill neurons (ROS = further kills healthy neurons)

Question 11

what happens when there is TREM2 deficiency? (3)

Answer 11

deficiency:
- hinders full activation of disease associated microglia or microglia neurodegenerative MGD phenotype
- significantly reduces the number of plaque associated microglia

= large a-beta plaque w/whimsy fibre like structures projecting from loosely packed cores and greater neurotic dystrophy in close facility

Question 12

Summary 1 (5)

Answer 12

• There is good genetic and biologic evidence that neuroinflammation contributes to the progression of AD
• AD may be considered as a chronic inflammatory disease
• Pathways of Aβ production and tauopathy accumulation and inflammation may converge and synergize the progression of AD
• There remain gaps in our knowledge on the interactions between the different cell types involved in AD and the pathways which link Aβ accumulation and tauopathy and inflammation
• Unravelling the underlying mechanisms of neuroinflammation may help to identify new therapeutic targets and to provide a deeper understanding as to why current therapeutic strategies have not been effective

Question 13

What are some difficulties of modelling dementia? (6)

Answer 13

There are many challenges in modelling
dementia:
- The greatest risk factor for most is age
- We don’t understand what causes most (sporadic) forms of disease
- Environmental (non-inherited) risk is tricky to accurately model
- Species differences
- Brain size (and complexity) differences
- The diversity of human genetic backgrounds etc etc

Question 14

What are most dementia models? And give an eg (2)

Answer 14

Most dementia transgenic models are mice that express mutant human forms of dementia causing genes e.g. APP, tau, aSyn

eg J20 mouse model overexpresses human
amyloid precursor protein (APP) with Swedish and Indiana mutations (which makes them more susceptible to a-beta xx) = more toxic

Question 15

Designing a transgenic mouse model (9)

Answer 15

1) design transgene construct - incudes reg elements (=promote high exp of protein in neurons)

2) use molecular techniques to put transgene into suitable vector (eg plasmid/viral vector)

3) transgene vector injecting into fertilised embryo

4) fertilised embryo transfected into embryonic stem cell in vitro by microinjection- using pro-nuclei xx

5) embryos planted into pseudo-preg female = dev into trimeric mice

6) detect presence of transgene via pcr etc using tail biopsies

7) is successful, these transgene mice bred further w/ WT -> to establish viral germlines for stable transmission of gene to offspring

8) offspring carrying transgene identified by genotyping too

9) lines w/ high transgene exp = selected for further breeding

Question 16

why are the heterozygous mice chosen for readings? (2)

Answer 16

because they display less of a phenotype

= roughly 50% of offspring will have gene of interest

Question 17

what is argued as being a very good AD mouse model? (2)

Answer 17

triple transgenic model:
- APP overexpression
-Tau mutation
- 3rd mutation

= perfect for recapitulation of human disease -> closer than the other models

Question 18

what is the difficulty of the triple transgene mouse model? (2)

Answer 18

• becomes very complex
• difficult to confirm the mutations quickly -> needs a lot of breeding and confirmatory tests

Question 19

what’s another way of expressing AD in mice? (2)

Answer 19

injecting human dementia-linked protein aggregates into WT mice

eg. Injection of human tauopathy brain into transgenic mice expressing wild-type human tau showed that tau conformation is important for pathology dev

Question 20

Modelling environmental effects - sleep (3)

Answer 20

• Sleep deficits are commonly reported in AD, and are found in models of AD that produce A-beta and tau

eg- looked at ipsilateral + contralateral pathways = increased tau exp

• suggest sleep deprivation makes it worse — so does sleep increase AD progression?

Question 21

iPSC’s (3)9

Answer 21

Induced pluripotent stem cell (iPSC)-based models: differentiation into neural cell types models human AD changes = successfully maintain disease state

Large banks of cells from controls, familial and sporadic AD cases

• important not to just stop spread of disease prog but also see if we can reverse -> thus IPSC’s

Question 22

Making iPSCs (6)

Answer 22

1) adult somatic cells isolated via biopsy

2) cultured in appropriate media - GF’s to maintain prolif rate

3) introduce Yamanaka factors (OKSM) -> reprogramming into pluripotent state

4) cells cultured under specific conditions to support transition into pluripotent state

5) selection methods to see what colonies were reprogrammed successfully

6) expanded + cultured to make more colonies

Question 23

what does the source of stem cells depend on? (3)

Answer 23

• site of access
• ease of isolation
• efficacy of reprogramming

Question 24

Name one of the experimental advances allow iPSC to be differentiated into “aged” cells (1)

Answer 24

Expression of progerin, a truncated form of lamin A associated with premature aging, induces multiple aging related markers and phenotypes in vitro

Question 25

chimeric models (4)

Answer 25

• Implantation of pluripotent human stem cells into AD mice
• Allows differentiation of cells into neurons in a brain environment

-The neurons develop features of human AD

Green shows disruption to human but not mouse neurons around plaques in the chimeric model = human cells respond diff to mice cells

Question 26

Animal models of Neuroinflammation in AD (3)

Answer 26

• A useful model should recapitulate causes, symptoms, and lesions in a chronological order similar to the actual disease
• A model of inflammation in late-onset AD should include the following features:
  (i) primary chronic neuroinflammation
  (ii) manifestations of memory and cognitive impairment
  (iii) late development of tau and Aβ pathologies
• The following models fit these criteria for neuroinflammation in LOAD:
• Streptozotocin,
• PolyI:C-induced,
• p25

Question 27

Exercise-induced effects in mouse models of AD (3)

Answer 27

exercise induced effects in Alzheimer’s disease can actually be neuroprotective

• sedentary mice w/ APP = increased plaques, activated microglia + toxic species + DECREASE in neurogenesis
• active mice w/APP = decreased plaques + toxic species + INCREASE in resting microglia

Question 28

Exercise conclusions (2)

Answer 28

• Exercise ameliorates AD pathology, improves cognitive performance, enhances adult hippocampal neurogenesis and reduces neuroinflam in transgenic mouse models of AD
• Key issues: what is optimum time to start exercise and what is the intensity at which such interventions should be undertaken?

Question 29

CD33 – A novel neuroinflammatory target (3)

Answer 29

• CD33 expression levels in the brain correlated with AD status and cognitive decline
• One study showed that increased expression of CD33
  mRNA was associated with increasing AD pathology in
  temporal cortex brain samples
• These findings suggest that CD33 might play a role in the etiology and pathogenesis of AD.

Question 30

Anti-Neuroinflammatory Targets conclusions (4)

Answer 30

• To date, most therapeutic efforts have been directed towards developing purely symptomatic treatments or agents that target Aβ or tau; however, the strategy of reducing inflam in AD has recently attracted more interest
• Based on our current knowledge, innate immune cells such as microglia and macrophages are the prime targets for modulating neuroinflam
• Microglial cells produce many mediators, some of which may be attractive targets for modulating neuroinflam in AD
• The potential for astrocyte manipulation is challenging
• As the phenotypes and functional properties of microglia change during the course of AD, interventional approaches aimed at modulating neuroinflam crucially depend on when and where to interfere