lecture 3 Flashcards
(15 cards)
What is a degenerative disease?
“A disease in which the function or structure of the affected tissues or organs changes for the worse over time.”
- NIH
What is neurodegeneration?
As brains age, more inclusion bodies & abnormal lysosomes seen
Risk of dementia / neurodegenerative disease increase precipitously with age (main risk factor)
Unclear whether cellular changes cause neurodegeneration or if they’re benign
Cellular changes occur
Most of brain post-mitotic, has differentiated
When process becomes rapid and irreversible this is neurodegeneration
Give examples of age-related changes seen in neurodegenerative disease
Ageing related changes seen in neurodegenerative disease: Autophagy defects Mitochondrial dysfunction Accumulation of DNA damage Telomere shortening
Describe Alzheimer’s disease
Accounts for 60-70% of dementia cases Age of onset usually over 65 Life expectancy ~8-10 years Heritability between 50-80% Progressive memory loss Often also with vascular changes
Describe motor neurone disease (ALS)
Most common neurologic cause of death in adults
Peak age of onset is 58-63 in adults, but juvenile forms (10% <45, 1% <25) exist
Average life expectancy ~3 years post diagnosis
Mostly sporadic (90-95%) but c9orf72 mutation a common genetic cause
Causes muscle weakness, atrophy and spasms. eventually paralysis
~30% of cases can also have behavioural dysfunction (dementia, loss of inhibition)
Atrophy of vental root, loss of myelinated neurons
Describe Parkinson’s disease
second most common neurological disorder after Alzheimer’s (accounts for ~15% of cases)
Age of onset ~60 (but juvenile forms exist)
Life expectancy 7-15 years post diagnosis
Most cases sporadic. Familial component to ~10% of cases
Distinct tremor, movement rigidity, eventual dementia and death
Substantial loss of dopaminergic neurons
Inhibits fine motor movement
Distinct tremor and slow movement
Describe Huntington’s disease
Prevalence ~5-10 per 100,000 worldwide
Age of onset depends on number of repeats (36-39 repeats ~60yo, 40+ ~30-50yo)
Life expectancy ~20 years after onset of symptoms
Genetic cause: tripeptide repeat expansions in Huntintin gene (autosomal dominant)
Initial symptoms are corea (uncoordinated movements)
Later symptoms - rigidity, behavioural disorders, dementia
Less common dementia
Very strongly genetic
Huntington’s gene – stretch of tripeptide repeats – code for glutamine tracks within Huntintin protein
Repeats very prone to replication slippage
Reach 36-39 repeats and you start to see protein aggregation
Characteristic sign is ventricle enlargement
What are stem cell treatments?
Idea is isolate mesenchymal stem cells from adipose tissue, blood
Expand stem cells – try to differentiate them down particular pathway
Dependent on transcription factor
Inject into nervous system – spinal canal
Replacing neurons very difficult
Neurogenesis from stem cells rare, modest benefits
Immunomodulation: MSCs inhibit inflammatory microglia – the immune cells of the brain, overactive in some of these disorders and clearing healthy neurons too frequently.
MSCs are either secreting factors that inhibit inflammatory microglia and activate anti-inflammatory microglia or differentiating into healthy microglia
Aggregate clearance: MSCs activate endogenous microglia in order to clear some of these proteins
Neuroprotection: MSCs excrete growth factors which kick off proliferation of neurons already resident in the brain
Aggregate clearance
Describe multiple sclerosis
Demyelinating disease
Predominantly T & B lymphocyte attack of oligodendrocytes (OLs) - myelinating cells
Some involvement of reprogrammed oligodendrocytes
Oligodendrocytes – supporting cells in brain
Role is to produce myelin sheath around cells – improves conductivity
Attacked in MS
Oligodendrocytes die, myelin sheath gets removed and then the neurons start selectively dying
Predominantly an inflammatory condition
Turns into neurodegeneration in later stages
Broadly relapsing remitting and primary progressive forms
RR form – bouts of inflammation
Describe regenerative therapies in MS
Current and potential therapies focus on:
Remyelination via:
Reprogramming cells into OL
Reactivation of endogenous cells
Autologous haematopoetic stem cell transplant
Ablative conditioning removes problematic cell populations
Leads to loss of host immune response
Reprogamming oligodendrocyte precursors
Involves sequential exposure of precursors to various different tissue culture conditions and growth factors
Take HSCs from patient – ablative conditioning destroys endogenous immune cells which damage oligodendrocytes
Transplant back in – get repopulation and new immune repertoire
What are muscular dystrophies?
Many different types
Most common: Duchenne muscular dystrophy (DMD)
Single gene involved: Dystrophin
X linked disorder
Wheelchair dependency by age 12
Ventilation dependency by age 20
Premature death 20s-30s
Many dystrophies linked to defects in members of the dystrophin associated protein complex (DAPC)
DAPC very important in force sensing / transduction
Also important in some signalling events (e.g NO signalling)
Transmembrane complex linked to extracellular matrix
On intracellular side you have dystrophin bound to dystroglycan complex bound to active microfilaments in cells
Complex senses force and transduces information from inside to outside of the cell
Describe Duchenne muscular dystrophy
Largest gene in human genome
2.5Mb (~0.1% of genome, 1.5% of X chromosome!)
7 different promoters
Many different isoforms
Lots of mutations tolerated to varying degrees (Becker MD)
Mutations causing NMD most pathogenic
Huge gene
Different promoters lead to different tissue specific isoforms
Many mutations tolerated
NMD – nonsense mediated decay
Nonsense mutation can cause complete decay of RNA – no dystrophin expression
So many exons and domains – amenable to exon skipping strategies
If you skip exon with nonsense mutation you can reconstitute some function
Main DAPC role seems to be protection of muscle fibres from long term contraction induces damage
Utrophin is upregulated in absence of dystrophin and can partially compensate, but it is less effective than dystrophin
Constant turnover of muscle stem cell reserve leads to eventual depletion
Disease associated changes (calcification, inflammation, DNA damage) accumulate and pathology worsens
Leads to rupture of sarcolemma and rearrangement of cytoskeleton – this can lead to mitochondrial dysfunction
Increase in production of reactive oxygen species
Because of constant turnover of muscle because of deficiency of dystrophin leads to upregulation of muscle stem cell turnover
Self renew into muscle stem cells and myoblasts
Myoblasts fuse to form myofiber
Problem with this is there is constant turnover of muscle stem cell reserve which eventually leads to depletion and inflammation
Describe DMD treatment strategies
Pharmacological
Growth factor supplementation
Steroids
Gene based
Exon skipping
Cell based
Stem cell transplant
Requires production of antisense morpholino oligonucleotide
Antisense – complementary to sequence in patient’s RNA
Morpholino backbone rather than sugar-phosphate backbone, not available for digestion by RNAse
Have to be conjugated to peptide that targets them to the muscle
Injected into blood stream, clathrin mediated endocytosis
Ends up in muscle cells
Morpholino binds to mutant dystrophin mRNA – leads to exon skipping, restores normal dystrophin
Problems with genetic method:
Getting the genetic agent into cells
Naked nucleotide won’t cross membrane by itself like a drug. Need to make some form of conjugate
Viruses – risk of immune response, low efficiency
Making it permanent
Viral – If gene editing could be one shot
Otherwise – repeated infusions required
CRISPR/Cas9 systemic delivery?
Stem cell treatments so far:
Very low engraftment rate
Heterogeneous tissue with difficult access
What is sarcopenia?
Sarocpenia = degenerative loss of skeletal muscle mass associated with ageing
Exacerbated significantly by lack of exercise
Evidence that progressive loss of muscle stem cell potential an important factor
What is Coronary Artery Disease?
Driven by atherosclerosis
Focal disease
Occurs preferentially at branch points of arteries & inside of Aorta
Whilst major risk factors are controllable (diet, diabetes status, smoking status) age is also a major risk factor
Capacity of endothelial cells to repair damaged luminal surface declines with age
ROS damage accumulation
DNA damage accumulation
Telomere shortening
Leads to increase in senescent cells
SASP – increases inflammation further & drives plaque progression
