Alzheimer’s

Question 1

Symptoms of Alzheimer’s

Answer 1

Confusion
Forgetfulness
Mood swings
Depression and anxiety
Become withdrawn
Difficulty in everyday tasks

Question 2

Microscopic disease features of Alzheimer’s

Answer 2

Senile plaques. Extracellular fibrillation protein aggregates of beta-amyloid
Neurofibrillary tangles. Intracellular protein aggregates of hyperphosphorylated Tau protein

Question 3

Increased risks of Alzheimer’s

Answer 3

Depression
Traumatic head injury
Cardiovascular factors
Cerebrovascular factors
Aging

Question 4

What decreases risk of Alzheimer’s

Answer 4

Anti-inflammatory treatments

Question 5

Associated genes and proteins in Alzheimer’s pathology

Answer 5

Amyloid precursor protein (APP) is a transmembrane protein with normal functions in neurons but can be cleaved by BACE-1 to yield pathological Aβ42 .
BACE-1 is the beta-site APP cleaving/converting enzyme -1 (or β-Secretase) that produces the aggregation prone Aβ42 .
Amyloid beta (Aβ42) a 42aa peptide derived from the APP that forms insoluble amyloid fibrils when released from the surface of neurons via intra-membrane cleavage by BACE-1.
Presenilin-1 & -2 (PS1/2 or PSEN1/2) are homologous membrane proteins with functions in the regulation of intra-membrane proteases (γ-Secretase) and calcium-mediated neurotransmitter release at synapses.
Tau is a microtubule-associated protein involved in microtubule stabilization.

Question 6

Describe the amyloid cascade hypothesis

Answer 6

Amyloid plaques are pathognomonic of AD
In amyloidases in other organs amyloid accumulation is associated with cellular dysfunction
Amyloid beta is a neurotoxin and pro-inflammatory and in AD there appears to be a shift towards Abeta42
The most important genetic risk factor ApoE4 is associated with an increased amyloid burden
All gene mutations that cause familial onset AD (FAD) increase AB42 (or increase its ratio to the less aggregation-prone AB40)
A mutant form of APP is protective against AD

Question 7

In Alzheimer’s disease there is a fall in ….. and increase in….

Answer 7

Measurable fall in alpha-secretes (ADAM family) activity and a significant increase in the activity of beta-Secretase, originally called the beta-site amyloid precursor protein cleaving enzyme 1 (BACE1)

Question 8

protein structure

Answer 8

Alpha helices and beta sheets within immature PDGF-A

Question 9

Mature amyloid fibrils have what conformation

Answer 9

Highly stable cross-beta sheet formation
Very stable and insoluble
Obtaining amyloid structure is very difficult

Question 10

What is the amyloid precursor protein

Answer 10

Transmembrane protein first associated with iron extrusion from neurons
The secreted extracellular Proteolytic product of APP, soluble APP-alpha sAPPa has several important physiological roles
SAPPa as a GABAbR1a receptor ligand with important roles in synaptic transmission in the hippocampus, a target region in AD

Question 11

Describe APP intracellular domain AICD

Answer 11

APP intracellular domain (AICD) can interact with the Gαs subunit of the G-protein that drives cAMP-pCREB signalling, maintaining spatial memory and inhibiting the amyloidogenic processing of APP. This is significant as pCREB is reduced in the prefrontal cortex in AD (Bartolotti et al 2016) and in the rat hippocampus exposed to amyloid-beta.

Question 12

What is pCREB

Answer 12

pCREB is the active phosphorylated form of the Cyclic-AMP dependent Response Element binding protein, a transcription factor that regulates up to 4000 genes, but in the brain has crucial roles in learning and memory.
Interestingly, when released from the membrane AICD translocates to the cell nucleus where it acts directly as a transcriptional regulator of the regulatory microRNA miR-663, that has multiple roles in preservation of the stem cell state in neural stem cells.

Question 13

Therapeutic implications of soluble APP-alpha

Answer 13

Neuroprotective
Neurotrophic
Synaptogenic
LTP enhancing
Memory enhancing
Stimulates adult neurogenesis

Question 14

Increased sAPPa means

Answer 14

Upregulation of alpha-secretary expression or activity
Direct expression and/or delivery of sAPPa or biologically sAPPa sub fragments

Question 15

Decreased A beta leads to

Answer 15

Beta y secretes inhibitors
Enhanced beta degradation or clearance
A beta directed immunotherapy

Question 16

Increased Abeta

Answer 16

Synaptic dysfunction and neuronal loss

Question 17

Tau normal function

Answer 17

Binds and stabilises microtubules

Question 18

Tau function in disease

Answer 18

Loss of tau binding with microtubule dissociation
Tau sequestered in NFTs
Defective microtubules

Question 19

Describe the negative synergism of mitochondria, Tau and amyloid-Beta

Answer 19

1) Amyloid-β and Tau-mediated pathologies are strongly linked.
2) Recent evidence suggests that Amyloid-β may interact with hyperphosphorylated Tau to induce aggregation into NF-Tangles
3) Fragments of both beta-Amyloid and Tau are involved in primary mitochondrial dysfunction with generation of Reactive Oxygen Species (ROS).
4) Tau-mediated impairment of mitochondrial transport exacerbates energy/nutrient depletion at synapses.

Question 20

Genetic associations of Apo-E4

Answer 20

Humans possess three common APOE alleles: APO-E2, APO-E3 and APO-E4.
Apo-E4 (ε4 allele of Apoliporotein-E) is a major genetic risk factor that functionally impairs the normal function of APOE in the clearance of extracellular β-Amyloid from the brain.
The occurance of APO-E4 has been estimated at 15% in the general population and 40% in Alzheimer’s patients.
One APO-E4 allele lowers age of onset with a 4-fold increase in risk of AD, relative to APO-E3.
Two APO-E4 alleles increase risk of AD to 12-fold.
APO-E3 is neutral and regarded as the reference allele
APO-E2 is protective with a 40% reduced risk of AD

Question 21

ApoE background

Answer 21

APoE is a 299 amino acid glycoprotein with a molecular mass of 34 kDa .
APOE transports cholesterol and other lipids with delivery via cell surface apoE receptors and is a principal ligand for the LDL receptor.
Bulk of APoE produced by the liver with plasma and CSF concs of 40–70 mg/ml and 3–5 mg/ml respectively.
Corresponding to the three common APOE alleles, humans express 3 isoforms of the protein: APO-E2, APO-E3 and APO-E4.
The amino acid (AA) residues that distinguish the APOE isoforms are located at AA positions 112 and 158, where APO-E2 has Cys residues at both positions, APO-E3 has Cys at 112 and Arg at 158, and APO-E4 has Arg in both locations.
ApoE is the primary apolipoprotein lipid and cholesterol transporter in the CNS.
 ApoE is normally produced by the astrocytes but can also be expressed by
microglia and neurons under pathological conditions.

Question 22

Mechanisms of Apo-E4 related pathology in AD

Answer 22

APoE is co-deposited with beta-amyloid (Abeta) in senile plaques and promotes the formation and deposition of extracellular amyloid.
APoE has binding sites both for its cell surface receptor, its cargo lipid and heparin residues in the extracellular matrix and at the cell surface.
Importantly, Abeta shows binding to each of these sites and therefore may compete with their physiological substrates and impair normal lipid delivery to the neurons.
APOE promotes the production of highly toxic Abeta oligomers with a potency order of APO-E4 > APO-E3 > APO-E2.
APO-E4 carriers and AD patients show lower levels of Apo-E/Abeta in their CSF than people with the other isoforms of ApoE, suggesting that APoE is less efficient in removing Abeta from the brain.
APO-E4 has been shown to exacerbate Tau and alpha-synuclein protein toxicity in transgenic mice expressing the human target proteins and the different APOE genotypes.
This is an important finding as both Tau and alpha-synuclein contribute to Alzheimer’s pathology.

Question 23

Apo-E4 and blood brain barrier changes

Answer 23

Recently several studies (see notes) have identified blood-brain barrier breakdown in AD attributed this pathology to pericyte loss.
Now it appears that individuals carrying even one APO-E4 allele show increased levels of the soluble form of the pericyte marker PDGFRβ in their CSF (Montagne et al 2020).
Montagne et al suggest that pericyte loss in APO-E4 carriers is independent of Abeta or Tau pathology.
Although this conclusion is supported by a 2012 study by Bell et al, there remains difficulty in reconciling it with the descriptions of Cerebral Amyloid Angiopathy (CAA), a condition characterized by vascular deposition of amyloid and degenerative changes.
Although estimates vary widely, CAA may be a disease component in up to 85% of AD patients.
A recent study (Shi et al 2020) has demonstrated early pericyte loss and vascular amyloid deposition in the retina of AD patients.

Question 24

What are the current treatments of Alzheimer’s treatments

Answer 24

Acetyl cholinesterase Inhibitors: Potentiate acetylcholine synaptic transmission. These enhance neuronal function but do nothing to delay the underlying pathology.
Fortuitously, the approved AChE inhibitor Rivastigmine has recently been shown to promote alpha-secretase activity, increasing levels of sAPPα
The low-affinity NMDA Receptor Antagonist Memantine: Normalises glutamate activity and reduces glutamate-NMDA excitotoxic cell death in Alzheimer’s and other NDDs.

Question 25

Describe ultrasound treatment for AD

Answer 25

Treatment of AD mice with scanning ultrasound:
-Increased Amyloid-β uptake by microglia
-Reduced incidence of amyloid plaques e
-Improved performance in 3 different memory tasks
Proposed Mechanism:
-BBB disruption admits serum albumin to the extracellular space of the brain
-Albumin binds Amyloid-β and increases it’s clearance by microglia