Motor Neuron Disease/Amyotrophic Lateral Sclerosis (ALS) PART II Flashcards
Briefly summarise the common molecular pathway hypothesised for ALS
Nuclear proteins (TDP-43 + FUS) that mislocalise to cytolsol -(TARDBP/FUS/ageing)-> TDP-43 (+ve), FUS (+ve), ubiquitinated protein aggregates -> neurodegeneration
Genetic relationship between ALS and fronto-temporal dementia (FTD)?
[mutation]
Expanded repeats in intron 1 of C9ORF72
[chromosome 9 locus]
NB: non-coding repeat expansions are present for myotonic dystropies, Fragile X, spino-cerebellar ataxias
The most prevalent mutation in FALS?
C9ORF72 mutation
Outcomes of C9ORF72 mutation?
[unknown function]- likely member of DENN proteins involved in membrane fusion
- reduced mRNA levels
- RNA foci accumulate in ALS
- RAN peptides: bi-directional transcrip/translat of expanded repeat sequences
C9ORF72-specific pathology?
p62 +ve cytoplasmic and nuclear inclusions in hippocampus and cerebellum that are TDP-43 positive
Putative mechanism of C9ORF72 pathogenesis?
Bi-directional transcription of expanded repeat containing sequences followed by translation of repeat associated non-AUG initiated (RAN) tranlation of aggregate prone dipeptide repeat peptides (DPRs)
NB: Poly GA is the most aggregatable, interfering w/ proteostasis
Relationship between distribution of dipeptide repeat peptides (DPR) and neurodegeneration
Degeneration and loss of anterior horn cells occurs in the absence of DPR
[5 DPR species seen in unaffected regions: granule cells of hippocampus and cerebellum]
Compare clinical characteristics of C9orf72 FALS cases with other FALS cases?
For C9prf72 FALS:
- slightly lower age of onset
- higher co-morbidity w/ FTD
- slightly reduced survival
FALS genes: overall mechanisms?
Protein-quality control (waste disposal)
- Unfolded protein response: increases levels of protein chaperones to facilitate folding
- Protein degradation via the proteasome and autophagy (via lysosome aggrephagy)
Relevance of VAPB and ALS?
VAPB is localised in motor neurons and is decreased in SALS spinal cord
VAPB mutation -> ER fragmentation -> ubiquitinated protein aggregates -> apoptosis
Relevance of P4HB and ALS?
P4HB is an ER foldase, induced in ER stress and SALS]- it is a disease modifier/risk factor
Disease will vary between ppl with same mutation: Modifies disease onset/progression/penetrance
Function of ER-associated protein degradation (ERAD) proteins?
ER protein export to the proteasome
Superoxide dismutase 1 (SOD1): association w/ ALS and mechanism?
Associated with ALS 1
Binds to Derlin 1
VCP association w/ ALS and mechanism?
Associated w/ ALS14 and IBMPFD (inclusion body myopathy, Paget’s disease, FTD)
Involved in ER protein export to proteasome
Ubiquilin 2 association w/ ALS and mechanism?
Associated w X-linked FALS and SALS
Binds to poly-ubi chains and components of proteasome
Define autophagy
Aggrephagy of misfolded or aggregated proteins. It’s activated by the failure of proteasomal degradation and molecular chaperones to resolve aggregate buildup
Role of P62/SQSTM1?
Allelic disorder
is Pagets disease of bone
Role of OPTN
ALS12 slow
progressing AR/AD
Allelic disorder is primary open
angle glaucoma.
What did whole exome sequencing in ALS yield?
ID’d a novel ALS gene: TANK-binding Kinase 1 (TBK1)
Function of TANK-binding kinase 1 (TBK-1)?
Phosphorylates OPTN (optineurin) and P62 and proteins involved in innate immunity
Enhances OPTN binding to autophagosome protein LC3 -> autophagic turnover of infectious bacteria (coated w/ ubiquitylated proteins)
Implications from the discovery of TBK-1?
Strengthens importance of autophagy in ALS pathogenesis
Riluzole MOA?
Anti-epileptic
Targets VDSC’s and reduces glutamate release
What triggers ALS that is specific for motor neurons?
Constant excitatory activity (NMDArs) activated by glutamate and D-serine
D-serine is sig. elevated in SALS
Function of D-amino acid oxidase (DAO)?
High levels of DAO required to metabolise and regulate D-serine levels
What is the pathological DAO mutation and what condition does it confer?
R199W-DAO
Involved in FALS
Effect of R199W-DAO?
- increased ubiquitinated protein aggregates
- autophagy (increased autophagosomes and LC3-II in motor neuron cell line)
- significant loss of spinal cord motor neurons (in trans-mice expressing R199WDAO)
Overview of clinically effective ALS drugs?
- Riluzole
- Edaravone]- free radical scavenger used in stroke
[drugs tested aren’t clinically effective in large trials…except riluzole]
Edaravone: Pros, Cons and its future?
PROS
- initial study-hint of effect
- second smaller study- normal resp function after 2 years from diagnosis
- treated pts declined 5.1 compared to 7.5 control
CONS
- prev studies show normal decline of 5.6. so 5.1 ain’t that great
- no effect on severely affected cases
FUTURE: longer studies (over 2 yrs) and test effect on survival
ALS treatment, when the causal gene is known?
- targeted gene delivery/deletion using direct delivery of antisense oligonucleotides (ASOs) by adeno-associated viral (AAV) vectors to neutralise mutation]- SOD1 mutation had intrathecal injection w/ adenovirus gene delivery
- CRISPR-Cas9 technology to target mutant genes and re-introduce wild-type copies
Potential future treatment targets (where the affected pathways are known)?
•Motor neuron susceptibility and trigger factors?
•Prevention of nuclear RNA foci (C9orf72 specific)?
•Prevention of cytosolic inclusion formation?
•Up-regulate UPR, UPS, autophagy?
•Upregulate molecular chaperones (HSPs)?
•Reduce D-serine levels?
•Designer Drug treatment: 15,000 patients and
7,500 controls Project MinE (US) to develop basis
for treatment from Whole Genome Sequencing,
metabolomics and proteomic analysis.
