Alzheimer's Disease Flashcards

Question

What are Bielschowsky Stains used for?

Answer 1

1. Beta-Amyloid Plaques Insoluble aggregates of beta-amyloid proteins that form outside neurons 2. Neurofibrillary Tangles Insoluble aggreates of hyper-phosphorylated Tau protein that form inside neurons * Symptoms not sufficient for diagnosis * Require presence and abundance of identifiable morphological substrates * Plaques and Tangles

Answer 2

Predominantly expressed in the CNS In neurons, predominantly found in axons Co-purifies with tubulin/MT’s, stabilizes MT integrity, promotes MT assembly; Microtubules are responsible for transport of molecules (eg neurotransmitter receptors) within neurons

Answer 3

Function: unknown? Maybe cell adhesion, neurite outgrowth, synaptogenesis, cell survival? APP-null mice: are relatively normal (underweight, decreased locomotor activity, reactive gliosis) APLP2-null mice: are relatively normal APP/APLP2-null mice: 80% die 1 week after birth, deficits in balance and strength Check slide 26 for diagram explanation

Answer 4

The Aβ42 variant is more hydrophobic, more prone to fibril formation, and is the predominant isoform found in cerebral plaques. Normally an individual would have Aβ40 at 50-70% and Aβ42 at 5-20%. However in people with Alzheimers, their Aβ42 is higher. When the Aβ42 fragments are released from their secretory vesicles, these fragments fold to toxic form and aggregate.

Answer 5

New criteria required as it doesn't establish diagnostic criteria for preclinical AD. Additional research is required before this stage of AD can be diagnosed. New criteria recommend biomarker testing for MCI (Mild Cognitive Impairment). - Total tau proteins increases to about 300%, probably as a result of neuronal and axonal degeneration - Aβ decreases to about 50%, probably due to increased deposition in plaques - Phosphorylated tau increases, owing to the hyperphosphorylation associated with NFT - Combining the 3 increase sensitivity and specificity of diagnosis to 90%

Answer 6

Cause/ causes of Alzheimers are not known. Probs the result of many factors (rather than a single cause) Factors include number of brain changes that begin as early as 20 years before clinical phenotype is even evident. Brain functions normally (Initial brain changes) -> Subtle decline in congnitive function (Mild cognitive impairment) -> Obvious decline in cognitive function & memory changes (Advanced Alzheimers) ^this is according to the the 1984 criteria

Answer 7

Preclinical -> MCI (Mild cognitive impairment) -> Dementia Cognitive function decreases as the years goes on and the more the patient ages. Check slide 30 for graph.

Answer 8

Order in which biomarkers become abnormal in relation to the stage of disease progression:. First: (preclinical and plateaus) 1. Amyloid-β accumilation (CSF/PET) (increasing towards the end of preclinical, then sharply & progressively increases during MCI until heightening in Dementia) 2. Synaptic dysfunction (FDG-PET/fMRI) 3. Tau-mediated neuronal injury (CSF) 4. Brain structure (volumetric MRI) 5. Cognition (not affected in preclinical, only slightly increases towards the end of MCI but then sharply and steeply heightens and increases during the late stages of dementia)

Answer 9

1. Biggest risk factor is age 2. AD is not a normal part of aging 3. Majority of cases are diagnosed after 65 years old. This is late-onset Alzheimers 4. Minority of cases before 65 (early onset Alzheimers) check slide 32 for details

Answer 10

* 34 kDa, 299 amino acid glycoprotein * Gene found on chromosome 19 * Produced at high levels in liver and brain * Synthesised by glia in brain (predominantly astrocytes) * Present in lipoprotein particles in the CNS which are HDL-like (apoE in the CNS comes from the CNS) * Binds to soluble and aggregated amyloid- * Exists in 3 common isoforms in humans, e2, e3, e4 * We have 2 copies of each gene, one from each parent * Six possible combinations e2/e2, e2/e3, e3/e3, e3/e4, e2/e4 or e4/e4 APOE4 e4 associated with higher risk. ~ ¼ population. Increases lifetime risk by up to 4 ~2 % population gets a ‘double dose’ increases risk by 10 60 % population has a ‘double dose’ of e3. Approx half develop Alzheimer’s by late 80’s APOE e2 is mildly protective. Carriers less likely to get Alzheimer’s. 11 % pop has e2/e3 and 0.5 % has e2/e2 Greatest impact on age of development. Having gene does not guarantee a person will develop Alzheimer’s

Answer 11

1. Family history- (individuals with a parent, brother or sister increased risk) 2. Mild cognitive impairment (MCI)- (mild but measurable changes in thinking abilities) 3. Cardiovascular disease- (physical inactivity, high cholesterol, diabetes, smoking, obesity) 4. Social engagement/ lifestyle- (mentally and socially active, diets low in saturated fats- relatively little known) 5. Head injury & traumatic brain injury- (moderate injury x2 risk, severe injury x4.5 risk) No treatment is available to slow or stop Alzheimer's disease

Answer 12

1. Senile Neuritic plaques 2. Neurofibrillary tangles 3. Neuronal and synaptic loss Senile plaque (amyloid) & Neurofibrillary Tangles (tau)- the 2 markers are an absolute requirement for AD.

Answer 13

Alzheimer's disease is rarely found without other neurodegenerative co-pathologies – less than half! Macroscopic: * Moderate cortical atrophy * Enlarged sulci and atrophy of gyri (frontal and temporal) * Atrophy posterior cortical areas * Enlarged lateral ventricles * Loss of neuromelanin pigmentation, locus coeruleus Microscopic * Amyloid plaques (dense core or diffuse) – up to 8 types * Neuritic plaques * Cerebral amyloid angiopathy (80-95%) * Neurofibrillary tangles (6 isoforms) * Granulovacuuolar degeneration * Hirano bodies (dendrites) * Inflammatory response * Synaptic lossNo single feature or combination of specific to Alzheimer’s disease - can be highly suggestive Definitive diagnosis requires microscopic examination of multiple brain regions.

Answer 14

3 major subtypes of atypical AD classified by relative density of hippocampal NFT's with respect to neocortical NFT's. Hippocampal Sparing AD: * Earlier age of onset * Rapid rate Cog decline 1 in 20 atypical Limbic Predominant AD: * Later onset * APOE4 Posterior Cortical Atrophy: * Also Hip Sparing * Corticobasal degeneration * Prion disease Frontal variant AD: * About 1 in 50 * Affects frontal lobes Comorbidities * Cerebrovascular pathology - 16% AD CASES * Lewy BodY related pathology - Approx. 25% AD develop Parkinsonian features * TDP-43 pathology - found in hippocampal sclerosis and AD -19 -75% AD * Agyrophilic grain pathology - 4R tauopathy * Age related tau pathology - primary age-related tauopathy (PART) - age-related tau astrogliopathy (ARTAG) * Suspected non-Alzheimer’s disease pathophysiology (SNAP)

Answer 15

Cognitive: * Memory loss * Failing intellect (inability to learn new skills) * Poor concentration * Language impairment * Disorientation/confusion Changes in personality and mood: * Apathy * Depression * Delusions * Anxiety – Out of character behaviours * Aggression * Sleep disturbances * Disinhibition Disability: *Difficulties with activities of daily living *Self-neglect *Incontinence and other physical disabilities A. Age-related B. Progressive 1. mild 2. moderate 3. severe C. Incurable

Answer 16

Neurofibrillary Tangles: * Tangles correlate with cognitive decline * Tangles identified in a number of other dementias * Tangles composed of tau protein * Tau protein in tangles is hyperphosphorylated Paired Helical Filaments * Composed of paired filaments * Twisted in a helix * Twisted at ~ 800 Angstrom intervals * Indefinite length * Somatodendritic localisation * PHFs are insoluble Phosphorylation of tau is a key observation in the pathogenesis of Alzheimer’s disease

Answer 17

* Tau gene consists of 16 exons located on Ch 17q21 * Alternative splicing gives rise to six tau isoforms * Adult brain contains all six isoforms * Fetal brain has a single isoform * Relatively little secondary structure Check slide 44 for images

Answer 18

Function: * Axonal transport * Microtubule binding * Stability

Answer 19

85 potential phosphorylation sites identified on tau 45 sites identified on PHFs isolated from AD brains The order an importance of each phosphorylation site is unclear The kinases and phosphatases responsible for each phosphorylation site remain to be determined No function has been assigned to any single site phosphorylation in Alzheimer’s disease AD-related phosphorylation recapitulates normal phosphorylation during development Phosphorylation of tau is a key observation in the pathogenesis of Alzheimer’s disease

Answer 20

Check slide 47 for images Enzymes that modify sites on tau listed above: Glycogen synthase kinase (GSK3) Cyclin-dependent kinase (cdk5) p42/p44 mitogen-activated kinase (ERK1/2) Stress-activated protein kinase (SAPK1,2a,2b,3,4) Brain specific kinase 1/2 (BRSK1/2) Calcium and Calmodulin-dependent kinase II (CamK II) Casein kinase 1/2 (CK1/2) Microtubule affinity-regulating kinase (MARK) Protein kinase N (PKN) Dual-specificity tyrosine phosphorylation regulated kinase 1A (DYRK1A) Mitogen and stress-activated kinase (MSK1) p38 mitogen-activated kinase(p38 MAPK) p70S6 kinase Phosphorylase kinase Protein kinase B (PKB/AKT) Protein kinase C (PKC)Rho kinase 90kDa Ribosomal S6 kinase (RSK1/2) Serum and glucocorticoid-induced protein kinase 1(SGK1) Tau-tubulin kinase 1/2 (TTBK1/2) c-Jun N-terminal kinase (JNK) Enzymes that modify sites on tau listed above AT8 epitope S202 T205 27/10/202048 CLS6004BR1 R2 R3 R4E2 E3 Acidic region Proline-rich region Repeat region C-term Glycogen synthase kinase (GSK3) Cyclin-dependent kinase (cdk5) p42/p44 mitogen-activated kinase (ERK1/2) Stress-activated protein kinase (SAPK1,2a,2b,3,4) Brain specific kinase 1/2 (BRSK1/2) Calcium and Calmodulin-dependent kinase II (CamK II) Casein kinase 1/2 (CK1/2) Microtubule affinity-regulating kinase (MARK) Protein kinase N (PKN) Dual-specificity tyrosine phosphorylation regulated kinase 1A (DYRK1A) Mitogen and stress-activated kinase (MSK1) p38 mitogen-activated kinase(p38 MAPK) p70S6 kinase Phosphorylase kinase Protein kinase B (PKB/AKT) Protein kinase C (PKC)Rho kinase 90kDa Ribosomal S6 kinase (RSK1/2) Serum and glucocorticoid-induced protein kinase 1(SGK1) Tau-tubulin kinase 1/2 (TTBK1/2) c-Jun N-terminal kinase (JNK)

Answer 21

Tau is hyperphosphorylated early in AD (kinases including GSK3, Cdk5, MAPK, DYRK). It impairs its ability to bind MT's and promotes aggregration, forming NFT's. Check slide 49 for diagram.

Answer 22

* Pretangle tau: Soluble hyperphosphorylated tau. Gallayas-negative (Gallayas silver staining only stains highly aggregated fibrillary material) * PHFs: Paired helical filaments, paired twisted filaments of tau * Neuropil Threads: Short thread like structures. Mostly dendrites which contain PHF’s. Fairly common in cases with tangles * Neurofibrillary tangles: Multiple PHFs aggregated

Answer 23

The development of intraneuronal lesions at selectively vulnerable brain sites is central to the pathological process in Alzheimer’s disease. Lesions consist mainly of hyperphosphorylated tau protein and include pretangle material, neurofibrillary tangles, and neuropil threads. AD-related neuropathologocal process spans decades and the distribution pattern of the lesions occur according to a predictable sequence. Accumulation of these lesions does not appear at random.

Answer 24

* transentorhinal – transitional entorhinal region * Limbic system – Collection of brain structures, include hippocampus, entorhinal region. Variety of functions including emotion behavior and long-term memory * Isocortex/neo-cortex – outer layer of cerebral hemispheres. Made up of six layers labeled I – VI

Answer 25

The point at which tau protein begins to clump into tangles Tangles begin to form in the transitional entorhinal cortex Relay station between cortex and hippocampus

Answer 26

Tau tangles accumulate further in the trans entorhinal region (yellow) In the brains hippocampus (pink) and neocortex (blue) tau begins to aggregate but has not formed tangles Neuritic plaques appear in the CA1

Answer 27

Extensive tangles formed in transentorhinal region Tangles begin to form in hippocampus and in neocortex tau is beginning to aggregate A few neuritic plaques begin to form in outer layers II-IV of neocortex

Answer 28

Tangles still occupy relatively small portion of brain Lesion density increases in sites affected in Stage III Pathology extends to mature neocortex Dense neuritic plaques develop Neocortex, largest part of brain and involved in higher functions

Answer 29

Tangles have caused extensive death Moderate to severe dementia Neocortex pathology extends fanlike in frontal, superolateral and occipital directions Lesion begin to appear in previously unaffected areas (Identify the hippocampus, transitional entorhinal region & neo-cortex using the diagram on slide 58)

Answer 30

Most areas of neocortex show severe lesions Underlying white matter contains AT8 in axons Extensive neuronal death Neuritic plaques widespread

Answer 31

1. Prodromal (Transectorhinal I- II) 2. Early-Moderate (Limbic III-IV) 3. Moderate-Late (Isocortical V-VI) Check slide 60 to show the tangles and plaques develop in each stage

Answer 32

677-770 amino acids type I trans-membrane protein signal peptide membrane cellular function: unknown but ubiquitously expressed Check slide 62 for diagram including all labelling of the protein

Answer 33

Alternative splicing neuronal APP: Predominantly lacks exons 7 (protease inhibitor domain) and exon 8, always contains exon 15. Absence of exon 15 (L-APP) activates a Chondroitin sulfate Glycosaminoglycan-attachment site. Check slide 63 for diagram.

Answer 34

2 pathways- Major or Minor Via the Major pathway, alpha cuts the APP and forms normal harmless fragments (APPs-α or C83) Via the Minor pathway, Aβ1-42 cuts the APP and forms 3 fragments: 1. APPs-β 2. p7 3. Aβ peptide. This Aβ peptide is what leads to Alzheimers.

Answer 35

One of the most important aspects of APP are the different steps of its degradation. Commonly these processing steps have been grouped into the amyloidogenic (Aβ producing) and the non-amyloidogenic pathway. Multiple proteases involved and the specifics of how they are used in this process largely defines the cellular and the pathological role of APP. Aβ related region extracellular or cytosolic domains. Most APP molecules are first cleaved by Aβ-secretase ...if not cleaved by α-secretase APP will be cleaved by α-secretase. BACE – β-site APP cleaving enzyme-1 a membrane bound protease. .. the remaining C-terminal fragments are cleaved by γ-secretase (γ= gamma) and AD relevant Aß42 may be generated

Answer 36

Four subunits: * presenilin (PS)1 or PS2 * nicastrin * anterior pharynx defective 1a or 1b (APH)-1a or APH-1b * PS enhancer (PEN)-2 All four components necessary for γ-secretase activity

Answer 37

α secretase pathway (non-amyloidogenic): α-secretase = ADAM 9, 10, 17 (ADAM = a disintegrin- and metalloproteinase) β-secretase = BACE-1 (β-site APP-cleaving enzyme-1) β secretase pathway (amlyoidogenic): γ-secretase = a complex presenilin (1 or 2), nicastrin, presenilin enhancer -2 anterior pharynx defective -1

Answer 38

In patients wit AD, there are increased Aβ42 levels, Aβ42 variant is more hydrophobic, more prone to fibril formation, and is the predominant isoform found in cerebral plaques.

Answer 39

Check slide 76 for diagram. It is facilitated by metals: Zinc and Copper. Aβ monomers, Aβ oligomers, Aβ fibrils, Diffuse plaques, Amyloid plaques

Answer 40

Fibrillar/aggregated forms of Aβ peptide, but not soluble monomeric Aβ peptide, are toxic to cells in culture and brains of rhesus monkey. Neurodegeneration appears prior to the appearance of plaques in mouse models of AD Plaques are found in people without dementia or brain injury.

Answer 41

Majority of AD cases are sporadic, ~200 family lines in the world that carry mutations Hereditary forms of AD generally induce earlier onset of neurodegeneration Most AD-related mutations cause increased formation of amyloid plaques Pure genetic causes of AD account for < 1% of all AD cases

Answer 42

14 families world wide have a genetic fault on chromosome 21 in the APP gene: Swedish, Flemish, Dutch, Italian, Arctic, Iowa, French, Iranian, Austrian, Florida, London, Indiana, Australian, Tottori All appear to share the same characteristic of altering APP processing such that more Aβ is deposited

Answer 43

Large number of families carry a mutation on chromosome 14 PS1 mutations account for the majority of FAD cases > 100 mutations have been described Very rare group of families have mutations on PS2

Answer 44

Mutations accelerate disease progression through diverse cellular mechanisms resulting in an increase in the amyloidogenic processing of APP. Proves amyloid is a key factor in Alzheimer’s disease, not just a bystander Pathology of genetic and non-genetic AD indistinguishable

Answer 45

There a 2 models used to explain this: 1. Serial Model 2. Dual Pathway Model

Answer 46

That increased Aβ leads to increased Tau phosphorylation. This causes synaptic loss which leads to cell loss.

Answer 47

That both Aβ an Tau phosphorylation increase. This causes synaptic and cell loss. This model, unlike the serial model, does not say that the cause of increase tau phosphorylation is increased Aβ.

Answer 48

1) Increased number of plaques in brains of patients with AD 2) Genetic mutations in familial (early-onset) AD cause increased production/deposition of A peptides (e.g. APP, PS1, PS2) 3) A plaques appear in Down Syndrome patients (trisomy 21) that carry an extra copy of the APP gene (situated on chromosome 21) 4) APOE4 allele increases the risk of sporadic (late-onset) AD 5) Transgenic mice expressing mutant human APP genes develop plaques and neurodegeneration (but not extensive and no tangles) 6) Aggregated or fibrillar (but not soluble/monomeric) Aβ peptide is toxic to cells in culture and the brains of aged rhesus monkeys

Answer 49

Toxicity of Aβ peptides/oligomers/fibrils/plaques on cells is not understood (different experimental conditions, model systems and endpoints) Aβ peptides induced apoptosis in cultured cells and post-mortem brain tissue, but not in transgenic mouse models of AD Aβ peptides induce production of reactive oxygen species, leading to cell damage and apoptosis. Cell culture, clinical and epidemiological studies suggest that the anti-oxidants Vitamin E and oestrogen are protective. Aβ peptides may directly insert into cellular membranes and disrupt cellular integrity, act as a non-selective ion channel, or allow release of ROS Aβ may promote the aggregation of tau to form neurofibrillary tangles

Answer 50

* NFT’s are common to many forms of dementia and are often the only * pathological lesion in these diseases – no conditions where there are plaques only * NFT’s show higher correlation with AD progression than plaques * Familial Alzheimer’s disease is due to mutations in APP processing molecules * and result in high levels of plaques and tangles; FTDP-17 has NFT, never plaques * Transgenic mice that express mutant human APP and develop plaques but not tangles exhibit cognitive defects * Ab injection (or crosses with mutant APP mice) into the brains of transgenic mutant-tau mice accelerate tangle formation * But expression of tau in fruit fly causes neurodegeneration without formation of NFT’s * Neuronal loss in AD brain can occur in regions devoid of NFT’s * Some FTDP-17 patients with extensive neurodegeneration have relatively few NFT’s

Answer 51

Leading perception: Alzheimer’s primary amyloidoses and secondary tauopathy but the tauopathy contributes to neurodegeneration ie plaque formation is initiating event of AD progression. Cause (e.g. gene defect) -> Aβ peptide accumulation -> Neuronal injury -> Altered Tau metabolism and/or ultimately Neuronal dysfunction and death which results in Dementia in the End

Answer 52

Two major proteases involved in Aβ (monomer) degradation are IDE and NEP Presence of IDE or NEP decreases Aβ accumulation Inactivating mutations of IDE and NEP have been detected in AD patients Interestingly, while IDE is mostly cytoplasmic, NEP is a transmembrane protein whose catalytic site is located in its extracellular domain

Answer 53

Mutation of APP, PS1, PS2 (early onset) causes increased production of Aβ1-42 peptide Mutation of ApoE (late onset) causes increased accumulation/decreased clearance of Aβ1-42 peptide Mutation of IDE/NEP (late onset) causes decreased clearance of plaques

Answer 54

Check slide 93

Answer 55

Genetic – APP mutations: proteins preferentially processed by amyloidogenic route – Presenilin (γ-secretase) mutations: increased amyloidogenic processing – Down’s syndrome * 3, not 2 copies of APP gene * more amyloidogenic processing Non-genetic – Head injury – Ischaemia – increases amyloidogenic processing – Unknown factors modify neurotransmission * affect balance between α and β/γ-secretase activity NB pure genetic causes of AD (familial) are <1% of all cases, typically early onset.

Answer 56

Check slide 96 for diagram 1. Production: sAPPα binds to C83, attaching its β-secretase end to the α-secretase end of C83. This causes the γ-secretase of the C99 to snap in the middle of the cell membrane allowing the C99 to fragment into AICD and Aβ 2. Plaque Build up: Aβ Aggregation occurs where plaque is built up, which results in Aβ oligomerisation, which then results in either Neuronal Cell Death (which causes cognitive and behavioural abnormalities) or Clearance. 3. Clearance

Answer 57

Therapeutic tactics: Halt Aβ production –γ-secretase inhibitors –β-secretase inhibitors –α-secretase stimulators? Enhance Aβ removal –Vaccination –Non-vaccine plaque busters NB pure genetic causes of AD (familial) are <1% of all cases, typically early onset.

Answer 58

γ-secretase *cleaves other important substrates (eg notch) hence specificity is important Eg substrate docking sites are different so target APP binding site Eg Likewise ATP-binding site modulates APP processing specifically *certain nonsteroidal anti-inflammatory drugs (NSAIDs) allosterically modulate γ-secretase to favor production of Ab40 over Ab42 *Inhibitor LY450139 lowered A in plasma but not CSF β-secretase lacks other substrates ( KO is viable with very minor anomalies) and therefore is a safer target α-secretase stimulating its activity could decrease A since it cleaves within the peptide Eg Bryostatin a protein kinase C inhibitor enhances activity

Answer 59

AN1792 (Elan): A peptide designed to produce an immune response and clear plaques * Phase I clinical trial in 2000 showed variable antibody response * Phase IIa study saw 6% of patients develop meningoencephalitis due to T-cell mediated autoimmune responses. – No cognitive benefits – Trial halted * 2008 publication of follow up study, 5 years after last inoculation (Holmes et. al. Lancet. 2008) – Of 8 treated patients, 6 showed a reduction in plaques (biggest antibody response, greatest plaque removal) – No apparent difference in time to progression of severe dementia – Not well controlled data, but suggest that cognitive benefit is unlikely * 2019 follow up study (Nicoll et. al. Brain. 2019) – Of 14 of 16 treated patients with AD, 6 showed evidence of plaque removal – 2 patients who had died 14 years after immunization had very sparse or no detectable plaques – Plaque free for many years after therapeutic intervention ceased – Tau pathological spread continued despite plaque removal – Despite modification of amyloid pathology, most had progressed to severe dementia (due to tau propagation) 27/10/2020100 CLS6004B Amyloid Removal Alone is Not Sufficient

Answer 60

* Humanised monoclonal antibody: bapineuzumab (Wyeth – now Pfizer & Elan) – passive Aβ immunotherapy with bapineuzumab results in decreases in CSF T-tau and P-tau (Blennow et al., 2012 Arch Neurol 69:1002-10) – Phase III trial with over 1000 patients halted in summer 2012. “Drug engages with target but fails to produce clinical benefit”. Some hope that the outcome better in group with e4 allele. – Is there a problem with trial design, or is it a failure of mechanism? – Solanezumab (Eli-Lilly) – Targets a different part of A compared to bapineuzumab. – Reported as safe, and effective with respect to lowering CNS plaques (Farlow et al. 2012 Alzheimers Dement. 8:261-71) – Entering phase III trials

Answer 61

* Gamma-secretase inhibitor, Semagacestat (Lilly) * Failed phase III trials (worsened outcome) * Off target effects limit this class of drugs, but some prospects for amyloid selectivity. * BACE Inhibitor * Enzyme initially considered to be “undruggable” * Phase II/III Clinical Trial of MK-8931 (Merck Sharpe & Dohme) commenced December 2012 * Several companies have compounds in the pipeline

Alzheimer's Disease Flashcards

(85 cards)