What is the prevalence of Huntington's disease?
- 5 per 100,000
What is the pattern of inheritance for Huntington's disease?
- Autosomal dominant
What is the genetic defect and underlying mutation responsible for Huntington's disease?
- Mutation in Huntingtin gene (HTT) on Chromosome 4 (4p16.3) which codes for Huntingtin protein (function unknown) - Causes expansion of CAG trinucleotide repeat
How is Huntington's disease diagnosed?
- Genetic test to count CAG repeats within Huntingtin gene - <28: normal - 29-34: normal, next generation at risk - 35-39: some develop HD, next generation at risk - >=40: will develop HD - Increase in CAG repeats associated with younger onset of symptoms and increased in severe disease
How does abnormal Huntingtin protein lead to gradual damage of neurons?
- ? induce apoptosis - Degeneration of Medium Spiny GABAergic neurons in Caudate and Putamen (Caudate > Putamen) - Decreased GABAergic inhibition of Dopaminergic neurons ---> Increased DA release ---> Movements
What are the neuropathological changes that occur in the brains of Huntington's disease carriers?
- General atrophy (widening sulci, narrowing gyri, enlarged ventricles) - Basal ganglia atrophy
What is the prognosis of Huntington's disease?
- Progressive disorder - Death within 10-15 years from symptom onset
What are early symptoms of Huntington's disease?
- MILD SYMPTOMS - Choreic movement (rapid jerky movements of trunk, arms and face) - mask as socially acceptable movements - Depression | Clumsiness | Lack of concentration | Short-term memory lapses
What are late symptoms of Huntington's disease?
- PROGRESSIVE DECLINE - Choreic movements - worsen until patient is fully incapacitated - Loss of coordination and balance - Difficulty swallowing - Cognitive decline/dementia
How are HD symptoms measured?
- Unified Huntington Disease Rating Scale (UHDRS) - Tongue protrusion (cannot) | Maximal chorea | Gait (Decreased mobility) | Dysarthria (mute) | Retropulsion pull test (falls) | Cognitive assessment (dementia) | Behavioural assessment (depression) | Function capacity (full-time nursing care) - (Brackets indicate parameters for maximal score)
What brain imaging can be used to assess HD pathology?
- MRI: Atrophy in Caudate and Putamen - 11C-Raclopride PET
How does 11C-Raclopride PET assess HD pathology?
- Medium Spiny GABAergic neurons express D2 receptors (these are lost in the Caudate and Putamen in HD) - 11C-Raclopride is a ligand for D2 receptor (reversible binding) = indirect marker of neuronal loss in HD (can cross BBB) - 11C attachs to Raclopride which binds to D2 receptor therefore 11C radiation only detected where there are D2 receptors - Need to account for background counts due to remaining tracer in blood - HD: decreased PET signal in Caudate and Putamen due to loss of D2 receptors/neuronal loss
Describe the management of HD
- Pharmacological: Tetrabenazine (only drug for HD) - Psychotherapy - Speech therapy - Physical therapy - Occupational therapy - Experimental treatments
How does tetrabenazine work?
- Tetrabenazine inhibits VMAT ---> Decreased DA packaged in vesicles ---> Decreased synaptic release of dopamine ---> Decreased movements
What is an example of HD experimental treatment?
- Cell transplantation therapy (allogenic transplant fetal neuronal cells into Caudate/Putamen to replace lost cell) - Variation in success | Proof-of-principle that transplanted DA neurons can successful integrate (Increased 11C-Raclopride PET signal)
What is the amyloid cascade and its role in neuroinflammation?
- Unknown trigger ---> Increased amyloid production ---> oligomers ---> activate Microglia ---> neurotoxicity ---> neuronal damage ---> NFT - Neuroinflammation ---> Microglial activation ---> Neuronal death as a catalyst for microglial activation ---> vicious cycle
How does PET imaging work?
- PET ligand with radioisotope binds to target | Radiation (positrons) detected by scanner - Radiation detected from tissue and tracer in blood | Arterial line to take blood sample to subtract radioactivity in blood
Describe 11C-PIB PET
- Measures amyloid - Cerebellum is devoid of amyloid in AD and control (Can use Cerebellum as a reference instead of Art. line) - By 75 years, 20% of cognitively normal people will have Amyloid deposition
How does AD present in 11C-PIB PET?
- Significant amyloid throughout the cortex (+ve in 90% of AD) - Initially starts in the basal forebrain and then spreads | 1st deposition 10-15 years before symptom onset - Longitudinal study over 20 months: AD has no change in Amyloid over time BUT decreased glucose metabolism
How does MCI present in 11C-PIB PET?
- 60% MCI have high amyloid (50% of Amyloid +ve MCI will develop into AD within 2 years - However, even when Amyloid +ve MCI converts into AD after 2 years, there is no change in Amyloid
How does DLB present in 11C-PIB PET?
- Amyloid throughout - 80% DLB have high amyloid (Amyloid is not specific to diagnosing AD)
How does PDD present in 11C-PIB PET?
- Amyloid throughout - 20% PDD have high amyloid
- Measures activated Microglia (binds to TSPO) | Increased microglial activation is associated with decreased MMSE - AD: significant Microglial activation throughout cortex - Some areas overlap with amyloid deposition, some do not - MCI: 60% of Amyloid +ve MCI has increased microglial activation | 30% Amyloid -ve MCI has increased microglial activation (can occur w/o amyloid) - AD: Bimodal peak in microglial activation (1st peak: M2 protective | 2nd peak: M1 damaging - PDD: significant increase in microglial activation compared to PD - In established disease, Microglial activation is associated with neuronal damage and decrease Glucose metabolism
Describe FGD PET
- Measures Glucose metabolism - AD: hypometabolism in Medial Temporal Lobe and Temporal-Parietal Cortices - With disease progression ---> Decreased glucose metabolism - Glucose metabolism is a surrogate measure of measuring cognitive function (Tau is best correlated but limited Tau PET) - Longitudinal study over 20 months: AD has no change in Amyloid BUT decrease in glucose metabolism - MCI: hypermetabolism (short compensatory phase) precedes hypometabolism - PDD & PD: Decreased glucose metabolism (therefore neuronal damage occurs throughout cortex even before cognitive symptoms)
What are limitations to imaging techniques used to assess PD and AD?
- These imaging techniques are not routinely available as they are expensive and no treatment available (no point in knowing)
Describe the disease progression in AD
- With time: (1) CSF Amyloid-beta, (2) Amyloid PET, (3) CSF Tau, (4) MRI Changes + Glucose PET, (5) Cognitive impairment - All these biochemical changes occur before onset of symptoms - CSF: Increased CSF Tau, Decreased CSF Amyloid (Amyloid sequestration theory: Decreased CSF Amyloid as it becomes deposited as plaques in the brain) - Imaging: Increased Amyloid, Increased Tau (T807 is a Tau PET tracer) - Both Tau (marker of disease) and FDG (marker of neuronal death) changes correlate with cognitive disease
What is the clinical presentation of typical AD?
- Impairment of Episodic Memory (recent memories - dysfunction in medial temporal lobe/hippocampus, spared older memory) - Disease progression: Increased impairment in Executive Function, Attention (frontal/parietal atrophy) | Eventually ---> Apraxia (disability/dependence) - Head-turning sign (look at family for reassurance) | Difficulty following conversation | Word-finding issues
What is the clinical presentation of atypical AD?
- May not have Episodic Memory Impairment as presenting Sx but may happen later in disease course - Younger onset | Posterior Cortical Atrophy (visuospatial issues) | Primary Progressive Aphasia (asymmetric L atrophy)
What is dementia?
- Cognitive issue that impairs function AND affects 2 cognitive domains (1 of which is Memory) - DSM-IV - Syndromic diganosis - no assumption on cause
What are different types of dementia?
- AD: associated with Amyloid + Tau | most common cause of neurodegenerative dementia - Dementia with Lewy Bodies (DLB): cognitive impairment before or within 1 year of PD symptoms | 2nd most common dementia - Vascular dementia: step-wise deterioration due to multiple small infarcts (cerebrovascular disease) - Frontotemporal Lobar Degeneration (FTLD): Types: Behavioural variant, Sementic Dementia, Progressive non-fluent Aphasia
What are different investigations for AD?
- MMSE, MoCA, ACE - Neuropsychological assessment: tests multiple cognitive domains, exclude other DDx (e.g. depression), establish baseline - Structural imaging: MRI: AD: General atrophy + hippocampal atrophy, MRI to exclude DDx | CT | Longitudinal imaging studies - Functional imaging: Amyloid PET | FDG PET | Tau PET (no validated Tau ligand, would be useful since Tau ~ clinical pathology) - CSF analysis: Decreased CSF Aβ | Increased CSF Tau | Definitive diagnosis only in Brain biopsy or Post-mortem
What is the neuropathology of AD?
- Extracellular amyloid-β plaques - Intracellular Neurofibrillary Tangles (Tau) - Neuronal loss
What is the aetiology of AD?
- Inflammation | Oxidative Stress | Mit. dysfunction | Interaction with vascular damage | Amyloid/Tau pathology - Amyloid accumulation ---> Increased Aβ accumulation ---> Tau hyperphosphorylation ---> Neurofibrillary Tangle - Tau pathology correlates well with Cognitive deficits in AD | 1st degree relatives will have 2x increased lifetime risk of AD
What are risk factors of AD?
- Increased age - Vascular risk (DM, HTN) - Female > Male (2:1) - Trauma (TBI ---> Inflammation & Increased amyloid) - Dementia pugilistica - Genetics: Familial AD (APP, Presenilin 1/2) - APOE (E4 - 5x risk homozygote, E2 protective) - Trisomy 21 (100% have AD by age 40)
What are protective risk factors of AD?
- Diet - Education (Cognitive reserve effect, neuropathology occurs but onset of AD takes longer) - Exercise
How long prior to symptoms/diagnosis of AD does AD pathology start?
- 10-20 years- Bateman, 2012 - Decreased CSF Aβ, Increased CSF Tau and Aβ deposition, decreased Hippocampal volume, decreased glucose metabolism - However, data based on Familial PD - not typical case | Typical AD has multiple co-morbidities
How does AD develop?
- Asymptomatic (Increased Aβ) ---> MCI (Higher increase in Aβ, Increase in Tau, Decrease in Memory) ---> Dementia (Even higher increase in Aβ, Higher increase in Tau, higher decrease in Memory) - MCI has memory/cognitive issues BUT no function impairment (not dementia) - Should we target MCI (if this is early AD?) | MCI has many causes: AD, depression, hypothyroidism
What are some new terms in AD?
- Subjective Cognitive Impairment (subjective memory issue, some will develop MCI) - Pre-clinical AD stage (normal cognition, pathogenic biochemical changes - if decreased CSF Aβ or increased PET amyloid ---> fMRI change - Prodromal AD-symptomatic pre-dementia stage (memory loss, +ve AD biomarker)
What treatments are in development for AD?
- Acetylcholinesterase inhibitors (Tacrine) - Memantine - Anti-psychotics - Aducanumab
Describe the use of acetylcholinesterase inhibitors
- Mild-moderate AD | small benefit (avg. increase of 1 point MMSE over 1 year) | No effect on survival - Francis 1999: mAChR leads to tau phosphorylation | nAChR leads to APP ---> Aβ - Cholinergic Hypothesis: AD cholinergic denervation of cerebral cortex, especially in Temporal Lobe - Cholinergic innervation is mainly from Nucleus Basalis of Meynert | AChR antagonists cause memory impairment
How does Memantine work?
- NMDA glutamate receptor antagonist - For severe AD if AChEi is not tolerated - Increase in 1 point in MMSE - Synergistic with AChEi
When would anti-psychotics be given?
- If severely agitated or hallucinations - Avoid if possible (decreases cognition, PD S/E, decreased life expectancy)
What is Aducanumab?
- Monoclonal antibody against Aβ - Dose-dependent response - Amyloid cleared from CNS but no clinical effect - given too late? - May slow cognitive decline (awaiting Phase III results) | S/E: oedema, haemorrhage
What are ideal approaches for AD?
- Preventative Strategies ---> - Aβ- or Tau-modification strategies (immunotherapy, enzyme inhibitors, anti-aggregants, kinase inhibitors) - Symptomatic treatment
What is sudden deterioration of AD patient?
- Likely new condition - atypical symptoms e.g. for UTI - Withdrawing or giving medications
What are key neuropathological features of AD?
- Extracellular plaques: within brain parenchyma, poor correlation with clinical picture | Senile plaques = neuritic plaques - Classical (Neuritic) vs Diffuse - Dustbin hypothesis: cells expel out Abeta and it accumulates in the EC space ---> Glial reaction - Neurofibrillary Tangles - Tau tangles have best correlation to Dementia (used to grade pathology) | contains Paired Helical Elements - Stained using Antibody against hyperphosphorylated Tau or Silver staining | Found as NFT or Neuropil threads (dendrites) - Cerebral amyloid angiopathy: Abeta deposition in the blood vessels - Neuronal loss: cerebral atrophy (esp hippocampus, frontal and temporal atrophy, widening sulci/narrowing gyri, S1/M1/Occipital unaffected
What is the cholinergic hypothesis?
- Increase in age ---> Decreased ACh turnover | AD is characterised by cerebral cholinergic denervation - Cholinergic deficits underlie memory loss and cognitive problems | Decrease in cholinergic markers correlate with dementia severity - Lessathine: ineffective - precursor unable to reach pre-synaptic terminal - Ligand (minimally effective) - AChEi (main treatment)
What treatments are used for AD?
- Anticholinesterases (Tacrine, Donepezil): mild benefits in early AD but do not prevent disease progression - Glutamate antagonist: Memantine: believed neuron loss may be due to excitotoxicity - nAChR: Galantamine: MOA Unknown
What is the amyloid hypothesis?
- Any factor that alters to favour Abeta production could favour Alzheimer's disease - Altered APP metabolism ---> Abeta deposition ---> Neuritic Abeta plaques (---> NFTs) ---> Neuronal damage ---> Dementia
What is Braak Staging of tau in AD?
(1) Medial temporal lobe (2) Posterior hippocampus (3) Adjacent Entorhinal Cortex (4) Rest of Temporal Cortex (5) Occipital cortex (visual association areas) (6) Occipital cortex (primary visual cortex) | Cognitive symptoms between Stage 3/4 - Tangles highlighted using Antibody to hyperphosphorylated Tau | Pathology builds 10-15 years before Sx | >65 years have pathology
What are some features about Abeta and APP?
- Amyloid-beta isolated from CAA (Glenner), from Plaques (Masters), Monoclonal Ab to Abeta (replace silver staining) (Allsop), APP isolated (Kang) - Amyloid precursor protein is a membrane bound glycoprotein (Carboxy intracellular, NH2 Extracellular, Abeta in membrane regions - APP is found in all cells (function Unknown) - Non-amyloidogenic cleavage (alpha-secretase cuts within Abeta sequence, non-pathological, main physiological pathway) - Amyloidogenic cleavage (beta-secretase and γ-secretase to release intact Abeta, pathological proteins, physiological role) - La Ferle, 2007: Intracellular Abeta oligomers link to hyperphosphorylated Tau (converts Tau to Tau-P ---> Tangles) intracellular Aβ ---> Ca2+ dysfunction, inhibit mitochondria (---> ROS) and proteasome | Extracellular plaque is just a dustbin
What are risk factors for AD?
- Age - Family - Down's syndrome - Previous head trauma - PD - Depression
What are features of familial AD?
- APP mutation: Codon 717 (point mutation Val ---> Ile) London mutation (1st genetic cause of AD) - Hardy J 1990 - Presenilin 1/2: accounts for most Familial AD | Presenilin has role in intracellular signalling | Presenilin has γ-secretase - Hardy J
What are the AD risk genes?
- ApoE4: ApoE has role in lipid metabolism | 50% of AD have E4 allele | E4 homozygote ---> 10x increased risk | associated with late-onset AD - TREM2: Heterozygous variant associated with increased risk of AD - GWAS SNPs: modify risk, e.g. APOE4
How is head injury associated with AD?
- Acute head injury associated with AD-like changes "dementia puglistica" ---> If they survived, would they develop AD? - 30% head injury develop Aβ deposits within weeks (these 30% have a high incidence of APoE4 - links environmental and genetic factors) - Cytokine cycle: Microglial activation - normally resolves but +ve feedback ---> neuroinflammation (IL-1, APOE4) ---> neurodegenerative
What are possible therapeutic approaches to AD?
- Stop Aβ aggregation: but if extracellular plaques are a dustbin, this would lead to increased intracellular accumulation (toxic) - Clear Aβ plaques: vaccination - Animal studies showed vaccination ---> antibodies against Aβ ---> clear pathology in Brain - Alzheimer vaccine studies in humans stopped due to Meningoencephalitis - Birmingham 2002 - Case report of autopsy showed Aβ cleared but no change to disease course - do we need to immunise earlier? - But 25% did not actually have AD therefore results hard to interpret - Reduce APP expression: But APP is a normal physiological protein - Alter APP metabolism: enhance alpha-secretase, inhibit beta- and γ-secretase - Anti-inflammatories: epidemiological association between NSAID use (e.g. Osteoarthritis) and low risk of AD - Tissue transplant
How does Tau contribute to AD pathology?
- Tau stabilises microtubules - Hyperphosphorylated tau ---> destabilises microtubules ---> Decreased axonal transport - Aggregates ---> neuronal death
How may memory loss occur in AD?
- Possibly synaptic loss due to Aβ - Synthetic Aβ ---> Decreased LTP (amyloid binds to NMDA? Amyloid activates microglia?
Describe APP processing
- β-secretase releases Aβ peptide - Non-amyloidogenic pathway: α- and γ-secretase | releases APP soluble α fragments, p3 and AICD | more common - Amyloidogenic pathway: β-secretase | release APP soluble α fragments, Aβ peptides and AICD | pathological - APP formed in ER and phosphorylated/glycosolated in Golgi ---> secretory vesicles to membrane ---> re-internalised in endosomes
What does β-secretase do?
- Acts in endosomes - BACE-1 ---> intracellular APP cleavage (---> Increased Aβ), also cleaves Neuroregulin (myelination) - BACE-2 (no amyloid)
What does α-secretase do?
- Acts in vesicles/endosomes - ADAM family | ADAM-10 and ADAM-17 involved in APP cleavage | also cleaves other proteins (e.g. TNF-α)
What does γ-secretase do?
- Contains Presenilin-1 which cleaves at cell surface ---> extracellular Aβ | Presenilin-2 acts at lysosomes ---> intracellular Aβ - γ-secretase is a protein complex (Presenilin domain has cleavage enzymatic activity) | also cleaves other proteins
How does clearance of Aβ occur? - Tanzi, 2004
- Phagocytosis (by Microglia and Astrocytes) - Enzymes degrade Aβ: Insulin Degrading Enzyme (IDE) and Neprilysin (NEP) - ApoE removes Aβ (ApoE4 is ineffective at clearing amyloid, ApoE4 carriers have an increased risk of AD - α2 macroglobulin binds to amyloid and directly removes it or indirectly via LRP receptor - Aβ can re-enter the Brain via RAGE - could extra CNS Aβ contribute to AD? Unlikely as BACE-1 and APP expression in CNS
What are genetic risk factors for AD development?
- Early onset ---> Familial AD (mutations in APP, PS1, PS2) - Late onset ---> ApoE4, GWAS (e.g. CR1 SNP), Epigenetic modifications - SNPs confer risk of developing AD but may not necessarily develop AD - APP mutations: London mutation near γ-secretase cleavage site | Icelandic mutation protective against AD (Decreased Aβ) - Presenilin-1 mutations: >150 mutations, tend to have more Aβ-42 and more intracellular Aβ (more endosome cleavage)
What are environmental risk factors for AD development?
- Ageing - Vascular risk factors (T2DM, HTN) - Head injury - F > M - Prions
What is the relationship between Aβ and prions?
- Iatrogenic prion cases due to human GF ---> CJD also had increased Aβ pathology (prion-like spread or auto-catalytic change) - Aβ and Tau spread in a prion-like fashion | Was amyloid already present (>65 likely to have Aβ changes) | Presence of Aβ may not necessarily cause AD | This population required GH - not representative of general population
What is the Amyloid Seeding Hypothesis?
- Amyloid behaves like a prion - Inject AD amyloid into young WT transgenic mice - Results: WT mouse with AD Amyloid develop plaques BUT not in transgenic mice without APP or if synthetic amyloid is used
Describe the Parabiosis experiment
- Transgenic animal with APP linked to WT animal ---> WT had increased amyloid plasma and CNS amyloid deposition - Can you get AD from blood transfusions? Unlikely as Amyloid likely to stick to blood vessels rather than enter Brain
What are the current Aβ-based therapeutic approaches being researched to treat AD?
- Albright, 2008 - BACE inhibitors and γ-secretase inhibitors - Aβ modulators (affect length of Aβ, make more Aβ-37 than Aβ-42) - Catabolism inducer (Increases Aβ metabolism) - Immunotherapy
How does immunotherapy work in AD treatment?
- Inject Aβ ---> Good evidence base in Animals (Decreased Aβ in Brain, Increased memory) | Clinical trials have an increased risk of sepsis - Inject antibodies to Aβ (passive immunisation) ---> Many clinical trials prove unsuccessful
What Tau-based therapeutics are used to treat AD?
- Tau aggregation inhibitors: Autophagy enhancers, Tau assembly inhibitors, Methylene blue - Tau kinase inhibitors (GSK3, CDK5): e.g. Lithium (psychiatric S/E effects) - Microtubule stabilisers - Hsp90 inhibitors (affect proteasome degradation of Tau)
What neuronal-based therapeutics are used to treat AD?
- Growth factors: BDNF, NGF (but does not cross BBB, gene therapy to introduce NGF - limited benefit) - NMDA antagonists: Decreased glutamate excitotoxicity - Anti-oxidants: Decreased oxidative stress - Anti-inflammatories - Anti-diabetic drugs: Decreased risk of AD (e.g. Pioglitazone)
How do anti-inflammatories work to treat AD?
- Regular taking of NSAIDs have lower incidence of AD - NSAIDs reduce Aβ formation and Tau hyperphosphorylation - NSAIDs target COX-1, COX-2, NFkb (Increases TNF-α), PPAR-γ (Increases BACE-1), Presenilin activity (γ-secretase) and Cytoskeleton (Rho, Rock) - Many clinical trials with NSAIDs are unsuccessful - too short? Need long term intake? Need to take earlier on? Use in MCI?
Describe AD progression
- Amyloid plaque (starts in basal forebrain, spreads to rest of cortical areas) | NFT (Tau) start in medial temporal lobe - Pathology starts 5-10 years before onset of symptoms (Aβ plaque and hyperphoshorylated already accumulated by time of Dx) - Therefore clinical trials unlikely to show benefit
How can you identify patients in asymptomatic phase?
- Alzheimer's Prevention Initiative
What are the different stages to those who are at risk of AD?
(1) Increased PET amyloid, decreased CSF amyloid (2) Increased CSF Tau (3) Cognitive changes
What is the order of AD pathology?
(1) Aβ pathology (CSF/PET) (2) Tau pathology (CSF) (3) Brain structural changes (MRI) (4) Cognitive changes
What in vitro models used in Alzheimer's research?
- Transfect cell lines with APP: Neuroblastoma (tumour cell line, as neurons do not replicate) | Measure Aβ level in medium - AD patient-specific iPSCs: same mutations (BUT difficult to find a control, as different people have differences unrelated to AD)
What in vivo models are used in Alzheimer's research?
- Rats/Mice: Similar brain anatomy, behavioural tests, NFT/Plaque staging VS Time-consuming, Expensive, No Aβ plaques - Fish: Giant neurons (microinjections) VS Different brain anatomy, Behaviour/Staging difficult - Worm: Easy + Fast to breed, Cheap, No ethical issues, Powerful genetics VS Different brain anatomy, Behaviour/Staging difficult - Drosophilia: Easy + Fast to breed, Cheap, No ethical issues, Powerful genetics VS Different brain anatomy, Behaviour/Staging difficult
How are rodent models good for AD modelling?
- Behavioural / Cognitive dysfunction - Impaired synaptic plasticity - δ APP processing - Amyloid plaques
What are issues with rodent models for AD?
- Rat and mice do not develop Aβ plaques: amino acid differences ---> Aβ does not aggregate - Therefore transgenic animals express human protein (e.g. APP, Presenilin, Tau) - E.g. APP-23 mice overexpress APP with Swedish mutation | Tau models have mutations similar to FTLD (not true AD) - Double/Triple Transgenic animals may express APP, Presenilin and Tau ---> these will have Aβ plaques & NFTs - However, mice models do not have large neuronal loss / atrophy (seen in human AD)
What is the Cre-LoxP strategy for conditional gene KO?
- Certain gene KO is embryonically lethal (e.g. Presenilin KO) - Conditional KO = gene KO in certain cell type or specific brain area | Method: cross Floxed mouse with Cre mouse - Floxed mouse 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 + gene removed) only in specific cell types - E.g. Conditional KO of Presenilin (---> Decreased γ-secretase) mice crossed with APP transgenic mice do not develop plaques
How are AD rodent models assessed?
- Behavioural tests: assess memory (e.g. Morris water maze, Y maze with Food, Object recognition - only curious of novel objects) - Electrophysiological measures/Long term potentiation: assess strength of synapses - Brain imaging: difficult to distinguish certain brain regions as mouse brain is small, rat models are preferred for imaging
What do intracerebral injections of AAV-vectors into Wild-Type Mice do?
- Adenovirus with Tau ---> neuronal loss in hippocampus (not seen in transgenic Tau, overpression of Tau affects neuronal survival - Adenovirus with APP ---> plaques (some, not all - due to variation in experimental technique)
What are the syndromes of FTDs?
- Syndrome: Semantic dementia | Behavioural variant | Progressive non-fluent aphasia - Pick's disease
What are key neuropathological features of Pick's disease?
- Frontal symptoms - sporadic Tauopathy (no MAPT mutation) - Front-temporal atrophy (knife-edge atrophy) - Neuronal loss (atrophy) - Balloon neurons - Tau +ve Pick bodies (intraneuronal inclusions of hyperphosphorylated Tau)
What are the different types of Tau antibodies?
- PHF1 Tau antibody (general) - 4R-Tau antibody - 3R-Tau antibody (Pick bodies)
What are the different tauopathies?
- 3R/4R tauopathy: AD | FTLD with 3R and 4R Tau (V337M, R406W)
- 4R tauopathy: CBD | PSP | FTLD with 4R Tau (P301L)
- 3R tauopathy: Pick's disease | FTLD with 3R Tau (K257T, G389R)
What are key neuropathological features of Tau FTD pathology?
- PiD (Pick bodies) - CBD (Astrocytic plaques) - PSP (Coiled bodies, tufted astrocytes)
What is the role of progranulin in FTD?
- Some FTD had Tau -ve neuronal inclusions - Function of progranulin is unknown, not know if part of inclusions - Separate gene mutation in Proganulin gene (adjacent to MAPT gene for Tau) | Intracytoplasmic and intranuclear inclusions - MRI imaging changes: Progressive marked asymmetrical atrophy (Laterality) - Fox et al
What is TDP-43?
- Tau subtype based on molecular changes and clinical phenotype: - A (Semantic dementia) - B (C9orf72) - C (Progranulin, FTD) - D
What is FUS?
- Fused in Sarcoma - Characteristic inclusion - Accounts for some atypical FTLD Ubiquitin +ve (aFTLD-U)
What is C9orf72?
- Commonly associated with ALS - Ubiquitin +ve TDP-43 -ve C9orf72 +ve inclusions in Cerebellum (other parts TDP-43 +ve)
What is the current classification of Tau +ve FTLD?
- 4R tauopathy: CBD | PSP | FTLD with 4R Tau - 3R tauopathy: Pick's disease | FTLD with 3R Tau - 3R/4R tauopathy: AD | NFT-dementia | FTLD with 3R and 4R Tau
What is the current classification of Tau -ve FTLD?
- TDP-43 +ve Ubiquitin +ve: FTLD-TDP (subtype A-D) - TDP-43 -ve Ubiquitin +ve: FTLD-FUS | FTLD-UPS - TDP-43 -ve Ubiquitin -ve: DLDH (dementia lacking distinctive histology)
What is the clinicopathological correlations seen in FTDs?
- FTLD-Tau: Pick's disease (3R Tau) | CBD/PSP (4R Tau) | NFT-Dementia - FTLD-TDP: Type A-D (molecular subtypes associated with different clinical phenotypes) - FTLD-FUS: accounts for some aFTLD-U - FTLD-UPS: Mutation in CHMP2B gene
What is Charles Bonnet Syndrome?
- Complex visual hallucinations in individuals with acquired visual loss and insight and no cognitive impairment
What is the DDx of visual hallucinations?
- Neurological: PD, DLB, Epilepsy - Psychiatric: Schizophrenia - Drugs - Sleep deprived
What is dementia?
- Insidious onset of progressive mental decline that interferes with ADLs - Is a syndrome not a disease | Consciousness is clear (no stupor or delirium) - Multiple deficits: Behaviour | Attention | Memory | Language | Visuospatial function - Situation stress may lead to deterioration and bring out dementia - Types: Reversible vs Irreversible | Slow or rapidly progressive | Multiple or isolated deficit
What are different types of neuerodegenerative dementia?
- AD (most common) - Insidious amnesia, language impairment - DLB - Parkinsonism, Fluctuation, Agitation, Hallucinations, Visuospatial function - PDD - PSP, CBD - FTLD - Personality change, poor planning, lack of hygiene - HD - MND - Wilson's disease
What are some investigations for dementia?
- History and Neurological examination ---> Dementia is a clinical diagnosis - Occupational Hx | Education background | Baseline personality | Self Care (ADL) | Memory | Language | Sleep - MMSE | Addenbrooke's Cognitive Examination | MoCA - Biomarkers: CSF Tau, CSF Amyloid - EEG: in dementia ---> slow wave activity (delta waves replace normal organised brain waves) - Imaging: CT | MRI | PET | SPECT - Brain biopsy: (definitive diagnosis)
What can result into traumatic/structural dementia?
- Subdural haematoma - Head injury - Dementia pugilistica - Diffuse Axonal Injury - Cerebral contusions - Normal Pressure Hydrocephalus - Neoplasm
What can result in vascular dementia?
- Multi-infarct dementia - Cerebral Amyloid Angiopathy - Vasculitis (Wegener's)
What are metabolic causes of dementia?
- Hypoxia/Hypercapnia - Uraemia - Hepatic encephalopathy - Thiamine/B12 - Hypoglycaemia
What are toxic causes of dementia?
- Medication (Anticholinergic, Valproate) - Alcohol - CO
What are psychiatric causes of dementia?
- Schizophrenia - Depression (pseudodementia) - Bipolar disorder
What are DDx of Dementia?
- Normal aging - Psychiatric Disease - Drugs e.g. Alcohol, Wernicke-Korsakoff's - Focal neurological syndromes - MCI - MS
How does psychiatric disease cause dementia?
- Depressive pseudo-dementia - prevalent in those who have multiple losses, refuses to engage, give up - Depression: often misdiagnosed as dementia in 8-15% of patients | Only 20% of demented patients have depression
What are examples of focal deficits in dementia?
- Aphasia - Anomia - Amnesia - Inattention - Hemi-neglect - Apraxia - Alien limb - Prosopagnosia
What is delirium?
- Impaired stream of thought and cognitive deficit
What are symptoms of delirium?
- Impaired attention - Hallucinations - Fluctuating course - Apathy - Agitated - Tremor - Asterixis
What is MCI?
- Cognitive impairment insufficient to reach criteria for dementia - Types: Amnestic vs non-amnestic | 10% convert to Dementia every year - Ix: Serial scanning to examine those at risk
How is MS involved in dementia?
- Extensive MS lesions throughout hemisphere may present with dementia or cognitive impairments - Symptoms: Optic neuritis, sensory, motor, gait, autonomic, fatigue
What are some features of TBI
- Disease process - Difficult to research due to heterogeneity - Increased 2x long-term mortality (Glasgow cohort) | Repeated TBI ---> Increased risk of Alzheimer's disease and dementia
What are features of primary injury?
- Mechanical input ---> Primary injury ---> Secondary injuries | These + Restorative processes influence long-term outcome - Force ---> Stress/deformation/strain | If energy applied > threshold ---> Primary injury - Primary injury - impacts effects: Tissue deformation | Contusions | :Lacerations | Haemorrhages - Primary injury - non-impact effects: Diffuse axonal injury | Swelling - Primary injury occurs immediately therefore primary injury is sensitive to preventative measures BUT not therapeutic measures
What is focal injury?
- Contusions | Haemorrhages | Laceration
What is diffuse injury?
DAI | Swelling/Herniation | Ischaemia | Vascular injury
What is the pathophysiology of Secondary injury?
- Primary injury - Ca2+ influx - Release of NT ---> Excitotoxicity - Mitochondria damage ---> ROS - Trigger gene expression - BBB opening ---> inflammation - Oedema ---> Increased ICP ---> Herniation
Describe inflammation of secondary injury
- Inflammation: (DAMPs, Chemokines, Cytokines) released at site of injury ---> Neutrophils, Monocytes ---> Microglia/Astrocytes
Why are in vivo models of TBI necessary?
- Single model cannot truly reproduce complex pathophysiological spectrum of TBI - Catch 22: Balance between reducing complexity to be able to model it VS retain overall validity for translation - BUT animal models are necessary to identify mechanisms and test therapies
How do you assess validity of a model?
- Face validity: same phenomenology - Construct validity: similar underlying mechanisms - Aetiological validity: similar changes in aetiology - Predictive validity: predictive value, accuracy and reliability
What are features of primary mammalian TBI models?
- Gross histopathology: Contusion | BBB disruption | Cell loss | Brain atrophy - Molecular changes: Inflammation | Apoptosis | Oxidative stress | Axonal injury - Functional deficits: Memory and Learning deficits - Long term effects detectable in rodents up to 1 year
How is management for stroke approached?
- Medical history - Vital signs - Neurological exam (NIHSS stroke severity scale) - Imaging (CT)
What does Modified Rankin Scale do?
- Measures level of disability (0-6)
What imaging is used for Stroke?
- MR Angiogram (vascular occlusion) - DWI (infarct core) - Perfusion MRI (hypoperfusion) - MRI Perfusion - DWI ---> core + penumbra
What are the two types of recanalisation therapy?
- IV Thrombolysis (within 4.5 hours symptom onset) - Mechanical Thrombectomy (with 6-24 hours) (If no haemorrhage ---> remove obstruction)
Describe IV thrombolysis
- Thrombolysis increases proportion of patients with good functional outcome (mRS) - For every 100 people, 32 benefit - Early treatment after symptom onset ---> Increased Odds ratio of good outcome (? Ambulance with CT Scanner) - EXTEND Trial: Phase III RCT IV Thrombolysis with rtPA vs Placebo (attempting to increase window 4.5-9hr
Describe mechanical thrombectomy
- Types: Ultrasound | Shock-wave | Laser | Stent retrievers | Aspiration - Recanalisation rates: Mechanical recanalisation (80%) effective vs IV rtPA alone (50%) - Rha, 2007 - 5 RCTs shown higher % good outcomes with Endovascular treatment vs Standard care (number to treat = 5) - Goyal - Benefit has shown 4.5 hours BUT faster is still better - European Stroke Organisation recommendations: Mechanical Thrombectomy (+/- IV tPA) recommended for large artery occlusions in Anterior circulation up to 6hr after symptom onset, should not delay IV thrombolysis, should be done ASAP
What types of neuroprotection is done for stroke?
- Surgery (if severe) - e.g. basilar artery thrombosis | 50-90% mortality | Severe morbidity | Early recanalisation is key - Davis, 2006 - Hemicraniectomy (allow Brain to swell to prevent increased ICP ---> respiratory depression | DESIRE trial ---> major reduction in mortality BUT survivors had long-term disability - Physical (hypothermia) - Pharmacological: Energy failure | Peri-infarct depolarisation | Excitotoxicity | Microglial activation | Inflammatory infiltrate
What is involved in stroke unit care?
- Stroke unit (interdisciplinary team consisting of vascular surgery, neuroradiology/surgery, cardiology, SALT, OT, PT - Monitor acute stroke patient >24 hours (as high risk of 2nd stroke) | Monitor vital signs | Prevent complications - Need to know the cause (affects management - antiplatelets for stroke prophylaxis BUT anticoagulant for AF) - Stroke Units ---> Decreased morbidity, mortality and inpatient treatment - Cochrane Review, 2004
What % of strokes are intracerebral haemorrhages?
- 10-15% - 2x higher mortality than Ischaemic stroke
What are the causes of non-traumatic ICH?
- Hypertensive arteriography (70%) - Cerebral amyloid angiopathy (20%)
What is a haematoma extension?
- Minor symptoms/small bleed ---> few hours later, extensive bleed - Occurs in 1 in 3 cases - "Spot sign" patients more likely to undergo haematoma extension (1st desc Becker) | Recent trial found no difference
What are two types of management of ICH?
- Haemostatic therapy - Minimise risk of ICH in patients taking Oral Anticoagulants - Anti-hypertensive therapy - Surgery
How does haemostatic therapy work?
- Recombinant Factor VIIa: F7 interacts with TF to activate coagulation cascade ---> Decreased risk of haematoma expansion - Phase III trial: r7a reduces risk of haematoma expansion c.w. placebo BUT no difference in outcomes - Mayer et al - Tranexamic acid - TICH-2 trial: Administration of Haemostatic drug not currently recommended for ICH
How do you minimise risks in patients taking Oral Anticoagulants?
- Oral Anticoagulants responsible for 10% of all ICH strokes | Oral anticoagulation ---> Increased risk of haematoma enlargement - RCT: INR reversal comparing Prothrombin concentrate vs Fresh Frozen Plasma - Steiner, 2016 - Prothrombin concentrate more effect at decreased haematoma expansion and decreased mortality - Reverse effects of NOACs - Idarucizamab (human Fab fragment of Antibody) reverses effects of Dabigatran (immediate) - Animal models show Idarucizamab ---> Decreased haematoma expansion, decreased mortality - Na, 2015 - Andexanet-alfa (recombinant modified human factor 10a) to reverse F10a inhibitors - ANNEXA-4 trial: ongoing
Outline anti-hypertensive therapy
- Haemorrhage pressure pushes on torn vessels - should treat HTN? Controversial as area around haematoma already hypoperfused - INTERACT-2 Trial: intensive BP lowering < 140mmHg vs Standard: Decreased mortality, decreased disability - ATACH-2 Trial: Intensive BP lowering to 110 - 140mmHg: no significant difference in intensive lowering - NICE guidelines (2008): Not recommended to lower BP (unless SBP > 200mmHg)
What has the STICH trial (surgery) shown regarding management of ICH?
- No difference in survival
Why are animal models used in stroke?
- Animal models help understanding important aspects of molecular, cellular and systemic process - Pre-clinical models useful to evaluate the effects of drugs and other therapeutic interventions
What percentage of ischaemic stroke models are rodent models?
What are the limitations of rodent models for stroke?
- Humans have a gyren-cephalic brain - Rodents have a Thelissencephalic brain - Compared to humans, rodents have - Increased capillary density - Decreased inter-capillary diffusion distance - Increased CSF turnover - GM/WM ratio
What are translational issues regarding use of rodent models for stroke?
- Statistical issues (randomisation, blinding etc) - Method in lab vs clinical trial - Different time windows
What are examples of models of Haemorrhagic stroke?
- Collagenase-injection model: collagenase dose-dependent of basal lamina of cerebral blood vessels BUT foreign protein - Blood injection model: direct injection of defined amount of blood into Striatum BUT no vessel damage and Trauma
What is stroke-induced immunodeficiency?
- Lymphocytopenia, decreased responsiveness of immune cells to in vitro stimulation - Release of stress hormones bind to receptors on Immune cells ---> Immunosuppression - Biphasic modulation: Day 1 (massive upregulation of immune cells), Day 2 (downregulation, splenic atrophy), why?
How does stroke lead to infections?
- Increased infarct size ---> Immunosuppression ---> Increased infections - 30% stroke patients develop infections - Pneumonia is main cause of death
How does acute ischaemia increase infarct size?
- Acute ischaemia ---> Acute inflammation (harmful) ---> Infarct enlargement - Microglial activation ---> Pro-inflammatory cytokines ---> Increased adhesion molecules/chemokines ---> Increased transmigration
What's the role of T cells in stroke mediated immunodeficiency?
- Rag2 transgenic mice lack lymphoctyes ---> small infarcts - Liesz
How does Natalizumab work?
(Originally treatment for RR MS) - Blocks Integrin-alpha4 on T cells ----> Decreased VCAM-1 and VLA-4 interaction ---> Decreased transmigration - Phase II: Natalizumab administered up to 9h after stroke onset did not reduce infarct growth BUT increased outcomes - Elkin, 2017 - Translation failure