Week 8 part 2 Flashcards
What are major neurodegenerative disease?
- Alzheimers
- Parkinson
- Triplet repeat disease (Huntington and spino-cerebellar ataxias)
- Spinal muscular atrophy
- ALS/FTD (frontotemporal dementia)
What does major neurodegenerative disorders affect?
More than 25 million people worldwide
What does major neurodegenerative disorders bring?
Disproprionate amount of suffering and economic loss
Prion disease
Location: diffuse cortical
Macro: cerebral atrophy
Micro: Spongiosis, PrP deposits
AD
Location: temporoparietal
Macro: cerebral atrophy
Micro: AB plaques, tangles
PD
Location: midbrain
Macro: pallor of substantia nigra
Micro: Lewy bodies
ALS
Location: motor cortex, brain stem and spinal cord
Macro: atrophy of motor neurons and muscles
Micro: Inclusions (Bunina bodies, Lewy body-like)
HD
Location: Basal Ganglia
Macro: Neostratial atrophy
Micro: neuronal loss and astrocytosis
LBD
Location: frontrotemporal
Macro: cerebral atrophy
Micro: Lewy bodies
FTD
Location: Frontotemporal
Macro: cerebral atrophy
Micro: tau deposits, Pick bodies
What are some features of Neurodegenerative diseases?
- Most strike at mid-life or later
- Aging may contribute to susceptibility
- The first symptoms usually involve loss of fine motor movement control
- Duration can be 10-20 years with progressive deterioration and quite a helpless, terrible death
What are the two caterogies of Neurodegenerative diseases?
- Sporadic (unknown ateiology, most of Alzheimers and Parkinson)
- Inherited (Huntington
What are most neurodegenerative disorders characterised by?
Presence of insoluble protein aggregates
What is one of the causes of neurodegenerative disease?
- protein misfolding
2. The inability of the body/cells to properly fold and/or dispose of misfolded protein accumulations
What happens in Parkinson’s patients?
Alpha-synuclein form clumps known as Lewy bodies
What happens in Alzheimer’s disease
sees tau tangles form inside brain cells and amyloid plaques accumulate near them
What happens in Huntington’s?
the nucleus becomes gummed up with clusters formed by an abnormal version of the huntingtin protein
What happens in ALS?
The proteins superoxide dismutase (SOD) and TDP43 or FUS accumulate in the body and projections of nerve cells
What are animal models to study neurodegenerative diseases?
- Transgenic mouse models
- Drosophila
- C. Elegans
What do lots of transgenic animals mimick?
A lot of human mutations
study some mechanisms
C. Elegan worm
- Short half life span
- Quick generation time
- Study the effects quicker
- Ask questions about aging better than mouse
What are the most common pathologies in the family of MND (motor neuron diseases)?
- SMA (spinal muscle atrophy)
2. ALS
What are SMA and ALS characterised by?
Progressive degeneration of motor neurons in the anterior horns of the spinal cord
What are the incidence of SMA and ALS?
- SMA - 1/6000-10000 newborns
2. ALS - 1-2 people/10,000 (Age of onset ca 50 years)
What varies between SMA and ALS?
- Disease onset
- Genetic causes
- Affected neurons
What is the most common genetic cause of infant mortality?
Proximal SMA
What is SMA caused by?
95% of the patients
deletions of SMN1 gene
the remaining 5% carry small mutation in this gene
What are the differences between SMN1 and SMN2?
When SMN1 is made it encodes a functional SMN and degrades very quickly
The way the genes are spliced
what they encode as a result of this alternative splicing
What happens if SMN1 is mutated or lost?
SMN2 cannot compensate for it because its not functional/processed in the right way
What does functional SMN1 when it is spliced together incorporate?
Exon 7 that gives the function of the protein
SMN2
It is spliced out generating a fusion between exon 6 + 8
This gene is non-functional
Why doesnt SMN1 never sit independently?
The muscle tone never develops
What does SMN1 die from?
Respiratory defect
The motor innervation doesn work so they cant breathe
SMA1 Werdnig-Hoffman disease
Age of onset: Antenatal-before 6 months
Maximum motor milestones: Never sits independently
Other features: Flkoppy child, no control of head movements, normal facial expression, swallowing difficulty, paradoxal breathing, Fasciculation of tongue
Life expectancy: median survival of < 6 months
Death from respiratory insufficiency
SMA2 intermediate type
Age of onset: 7-18 minths
Maximum motor milestones: sits independently, never walks independently
Other featurs: Scoliosis, joint contractutes, Postural tremors of hands, Fasciculation of tongue and/or limb muscles
Life expectancy: most patients die < age 30-40 from respiraotry insufficiency, some survive longer
SMA3 Kugelberg Welander disease
Age of onset: 18 month- 30 year
Maximum motor milestones: Walks independently , some patients become wheelchair dependent in childhood
Other featureS: Joint contractures, postural tremors of the hands
Fasciculation of limb muscles
some patients require NIV
Life expectancy: normal
SMA4 Adult-onsent (very rare)
Age of onset: 30 year
Maximum motor milestones: Normal
Other features: patient can become wheelchair dependent
some patients require NIV
Life expectancy: normal
What does SMN protein do?
- Has a crucial role in regulating pre-MRNA splicing
2.Catalyses the assembly of Sm proteins on to the snRNPs
(small nuclear ribonuclearproteins) which form the functional
core of the splicing machinery.
What is SMN required for?
Cell survival
How is complex of SMN assembled?
arginine methylation dependent manner
JBP1
Arginine methylase
methylates 3 of these proteins
What does SMN complex help assemble
the cellular machinery needed to process pre-mRNA
What is SMN complex important for?
development of specialized outgrowths from nerve cells called dendrites and axons
What are dendrities and axons required for?
the transmission of impulses between neurons and from neurons to muscles.
What has damaging effects on motor neuron development and survival
A lack of mature mRNA, and subsequently the proteins needed for normal cell functioning
Spinal muscular atrophy type III (also called Kugelberg-Welander disease)
causes muscle weakness after early childhood. Individuals with this condition can stand and walk unaided, but over time, walking and climbing stairs may become increasingly difficult. Many affected individuals require wheelchair assistance later in life. People with spinal muscular atrophy type III typically have a normal life expectancy.
Why is alternative splicing affected?S
So many RNA binding proteins are affected
What happens in mammals?
95% of genes are spliced increasing the proteome
What is alternative splicing mediated by?
interaction of basal splicing machinery with proteins that either stimulate or inhibit the assembly of the processing complex on alternative exons
What are the 3 classes of factors that plays a major role in splice-site selection?
1.SR proteins normally activate nearby splice sites, the bound
region is included as an exon during splicing
2.hnRNPs – usually silence nearby splice sites – the bound region becomes an intron
3.U1 and U2 snRNPs recognise potential splice donors and
interact with possible splice acceptors
What determines the choice of splice site?
• Competition between positive (SR and U1/U2snRNPs) and negative
(hnRNPs) regulators of splicing
What does SMN protein do?
Involved in the assembly and/or function of additional
RNPs
Transport of mRNA in neurites – especially long ones
Proteins other than Sm ones interact with SMN in mRNPs
which are transported to distant location of neurons for
local protein translation of bound mRNA
What does SMN1 produce?
full-length functional SMN protein
What does SMN2 produce?
shorter non-functional form of SMN protein
What happens in SMA patients?
SMN1 is either missing or mutated, leading to a large decrease in the available SMN protein
What binds to SMN2 mRNA and encourages the inclusion of important regions needed to make SMN protein?
Anti-sense oligonucleotide ASO-10-27
hat is the function of anti-sense oligonucleotides?
Prevents the exons from being spliced in
Injected in patients at high doses
What is ALS?
- kills more than a 100000 people annually
- Characterised by degeneration of upper and lower motor neurons in the brain and spinal cord
- Rapidly progressing
- Patients lose ability to speak, swallow, move breath
- ca 10% of ALS cases have genetic origin
What is the hallmarks of ALS?
In most cases of ALS there is nuclear depletion of
the RNA-binding protein TDP-43 and its cytoplasmic
accumulation in degenerating neurons.
Nucleocytoplasmic trafficking has emerged as an
important mechanism contributing to ALS pathology.
Nucleocytoplasmic trafficking defects are found in
other neurodegenerative disease and in normal
physiological ageing.
What are the molecular causes of ALS?
Factors identified in ALS which are linked to mRNA metabolism
Examples are FUS and TDP-43 (RBPs)
C90rf72 hexanucleotide repeat expansion
What is Neuropathology of ALS?
the abnormal accumulation of insoluble proteins in the cytoplasm of degenerating motor neurons
What is the pathological condition of TDP-42?
Abnormally accumulated from the nucleus of neurons and glia cells, to the neuronal cytoplasmic inclusions (NCI)
What is FUS?
1.similar to hnRNP, binds to mRNAs and to SR proteins and influences splice site selections
Where is most mutations of FUS clustered?
Nuclear localisation signal leading to its accumulation in the cytoplasm and inclusion formation
What does FUS interact with?
SMN
What does mutant form of FUS change?
Sub-cellular localisation of SMN
What does wild type and mutant FUS interact with?
U1 and U2 snRNAs leading to their mislocalisation to the cytoplasm and reducing their availability for splicing in the nucleus.
TDP-43
has a domain structure similar to hnRNP, binds to RNA and other hnRNPs as well as SR proteins
What is TDP-43 linked to?
SMN and U snRNPs biogenesis
What does mutant TPD-43 have an effect on?
SMN levels
changes its subcellular distribution
What do FUS and TDP-43 do?
interact
What is hnRNP?
are complexes of RNA and protein present in the cell nucleus during gene transcription and subsequent post-transcriptional modification of the newly synthesized RNA (pre-mRNA)
What became a prominent feature of the aggregate formation?
Biophysical properties of the proteins
What tends to aggregate?
proteins containing prion like domains
What is complexity domain?
They don’t have alpha helices or beta sheets like you would in structure proteins
What is the first intron of C9orf72?
C9orf72 non-coding GGGGCC repeat expansion
What do the repeats have propensity to form?
Stable quadruplex structure in RNA
What can the expanded RNA repeats be?
the toxic species which compromises
the function of affected neurons
What does expanded repeats sequester away?
RNA binding proteins causing splicing deficit
Where is C9orf72 detected in?
RNA foci of patients
Where does C9orf72 repeats bind?
proteins of hnRNP A family
What is a common histopatholgoical hallmark of ALS and TFD?
The cytoplasmic mislocalization and aggregation of TAR DNA-binding protein-43 (TDP-43)
what is proximity-dependent biotin identification (BioID ) used for?
to interrogate the interactome of detergent-insoluble TDP-43 aggregates and found them enriched for components of the nuclear pore complex and nucleocytoplasmic transport machinery
What did aggregated and disease-linked mutant TDP-43 trigger ?
sequestration and/or mislocalization of nucleoporins and transport factors, and interfered with nuclear protein import and RNA export in mouse primary cortical neurons, human fibroblasts and induced pluripotent stem cell–derived neurons
Where is nuclear pore pathology present?
brain tissue in cases of sporadic ALS and those involving genetic mutations in TARDBP and C9orf72.
What did data strongly implicate?
TDP-43-mediated nucleocytoplasmic transport defects as a common disease mechanism in ALS/FTD.
What is a staining for nuclear lamina?
lamina b
What does oligo-dt recognise?
Oligo tails of RNA
you can detect localization within the cell
What happens in healthy neurons?
nucleocytoplasmic trafficking of RNAs and proteins through nuclear pores is tightly regulated
TDP-43 normally shuttles between the nucleus and cytoplasm, but is predominantly nuclear
In neurodegenerative diseases with TDP-43 proteinopathy, including sporadic ALS and familial ALS
TDP-43 mutation, cytoplasmic aggregates of pathological TDP-43 co-localize with several nucleoporins (including FG-Nups, scaffold Nups and cytoplasmic Nups) and export factors (including Gle1)
Several transmembrane Nups and proteins of the nuclear lamina are mislocalized, and nuclear accumulation of DNA damage and poly(A) RNAs are observed
C9ORF72 ALS/FTD
transcripts containing expanded G4C2 repeats interact with the import factor RanGAP1 and are translated into dipeptide repeat (DPR) proteins through repeat-associated non-ATG (RAN) translati on
Arginine-containing DPRs associate with nuclear pore proteins, leading to abnormal nucleocytoplasmic transport, nuclear accumulation of poly(A) RNA and DNA damage. Deficit in protein nuclear import may participate in a feedforward mechanism, with subsequent cytoplasmic accumulation of TDP-43 enhancing the disruption of nuclear pores
In Huntington’s disease
expanded polyglutamine (poly(Q))-containing huntingtin coaggregates with Nups (including Nup62 and Nup88) and the transport factors Gle1 and RanGAP1. Abnormal nuclear architecture, accumulation of DNA damage and nuclear retention of poly(A) RNAs, as well as cytoplasmic accumulation of TDP-43, are observed
What are the key challenges and perspectives?
Some mechanistic insight into the pathology mechanisms in various neurodegenerative disorders allows to begin rational design of medications
Targets include – dopamine replacement therapy for Parkinson, targeting machinery which controls protein folding, e.g., heat-shock proteins; inhibitors of histone deacetylases (HDACs), e.g., sodium butyrate all improve viability and suppress cell death in a variety of model systems.
Ideally, therapies should be targeted at some early stages of disease development as these may allow recovery of function
