Motor Neuron Disease/Amyotrophic Lateral Sclerosis (ALS) PART I

Question 1

Define Motor Neuron Disease/ Amyotrophic Lateral Sclerosis (ALS)

Answer 1

Chronic neurodegenerative condition causing
muscle wasting, paralysis and death usually
within 3-5 years due to respiratory failure

Question 2

Neuropathological features of ALS?

Answer 2

• Amyotrophy

- scarring of the corticospinal tracts

Question 3

Compare ALS risk in men vs women

Answer 3

Greater in men

Question 4

Specific targets of ALS?

Answer 4

Upper motor neurons and Lower motor neurons

Question 5

What makes UMN and LMN vulnerable to ALS severe symptoms?

Answer 5

- Both have long axons
(length / cell diameter
~10,000)
- Very active
- High energy demands

Question 6

Briefly describe the outcomes of UMN and LMN pathology in ALS

Answer 6

UMN -> spasticity

LMN -> atrophy

Question 7

Describe the features of ALS symptoms

Answer 7

• progressive denervation + secondary muscle weakness of limbs, trunk, tongue, resp (intercostal) muscles
• Impaired speech & swallowing (bulbar signs)
• Spastic weakness + paralysis in almost all skeletal muscle
• NO impairment of bladder/bowel/sexual function
• SPARED occulomotor/sensory/autonomic function

{NB: cognitive function affected in a minority of cases]

Question 8

Describe the onset and progression of ALS

Answer 8

Starts focally and spreads

Usually starts in distal muscles of limb/bulbar and then spreads

Question 9

Specific examples of early ALS symptoms

Answer 9

• Wasting of thenar eminenence

- Wasting of the tongue (bulbar)

Question 10

Early diagnostic tests for ALS (and positive results)?

Answer 10

• Muscle biopsy -(stain for ATPase)-> atrophic fibres

- Electromyogram (nerve conduction test) -> impaired conduction (and compensatory mechanism)

Question 11

How do motor units compensate for the effects of ALS

Answer 11

Sprouting of neighbouring axons from neighbouring motor units (collateral branches)

Question 12

How to distinguish ALS from other motor neurone diseases?

Answer 12

Presence of both upper and lower motor neurone signs

Question 13

Examples of LMN signs?

Answer 13

Muscle weakness, wasting, fasciculations, cramps

Question 14

Examples of UMN signs?

Answer 14

Stiffness, slowness of movement, slow and clumsy speech, Babinski

Question 15

What could bulbar symptoms indicate in the context of ALS?

Answer 15

(i.e. UMN and LMN)

Progressive bulbar palsy

Question 16

Describe Primary Lateral Sclerosis (PLS)

Answer 16

Effects on UMNs predominate:

• spasticity
• hyperreflexia

{20 yr survival)

Question 17

Features of an MRI of pt with ALS (PLS)

Answer 17

• Wide precentral sulcus

- Atrophy of adjacent gyri

Question 18

Give an overview of the treatment of ALS

Answer 18

speech & swallowing- speech therapist

mobility around home- occupational therapist

swallowing & feeding- NG tube or PEG

breathing- oxygen, assisted ventilation

slowing disease progression- Riluzole (extends survival ~3 months_

Question 19

Sites targeted in ALS?

Answer 19

• motor cortex (UMN)
• brainstem (LMN)
• spinal cord (LMN)

Question 20

Histological features of ALS?

Answer 20

Ubiquinated inclusion in neuronal cell bodies and proximal axons

Question 21

What is an ubiquitinated protein?

Answer 21

Post-translational modification by a small 76 amino acid regulatory protein, ubiquitin

Substrate designated for degradation is tagged w/ ubiquitin. This is recognised by proteosome, which carries out this process.

Question 22

Ubiquitinated proteins are characteristic of what conditions?

Answer 22

ALS (sporadic & familial) and a subset of fronto-temporal dementia

Question 23

Two forms of ubiquitinated inclusions?

Answer 23

• filamentous

- compact

Question 24

What protein is a major component of ubiquitinated inclusions (in SALS/FALS/FTLD)?

Answer 24

TDP-43

Question 25

What proportion of ALS cases are familial?

Answer 25

10%

Question 26

What is the molecular mechanisms that have been identified in ALS?

Answer 26

Abnormalities in: - RNA binding proteins - proteostasis (- cytoskeletal proteins)

Question 27

Gene pathways involved in FALS?

Answer 27

- RNA processing]- (TDP-43, FUS) - protein quality control ("waste disposal")]- (VAPB, P4HB, SOD1, VCP, ubiquitin2, P62, OPTN - excitotoxicity]- DAO

Question 28

What gene encodes for TDP-43?

Answer 28

TARDBP (TAR DNA binding protein) NB: TAR = Trans activating response

Question 29

Describe the actions of TARDBP

Answer 29

TARDBP encodes TDP-43 Binds TAR DNA sequences in DNA/RNA, acting as a transcriptional repressor i.e. inhibits splicing and regulates mRNA transport/local translation

Question 30

Sites possibly responsible for TDP-43 and FUS mislocalisation?

Answer 30

- Nuclear localisation signal (enable protein to be taken into nucleus)]- FUS - Nuclear export signal (enable protein to leave nucleus -> cytoplasm)]- (Importin is the nuclear transport protein)

Question 31

Difference in TDP-43 staining in healthy people and ALS patients

Answer 31

TDP-43 appears in cell nuclei in healthy people TDP-43 is located in the cytoplasm in ALS patients

Question 32

Effect of TDP-43 mutation in animal models?

Answer 32

Neurodegeneration (cortical and spinal neurons) but not consistent forming of inclusions (present in both wild-type and mutant rodents)

Question 33

What genetic changes are found in FALS and FTLD?

Answer 33

FUS positive inclusions

Question 34

What is FUS/TLS?

Answer 34

FUS: fused in sarcoma TLS: translocation in liposarcoma

Question 35

What process is TARDBP and FUS both involved in?

Answer 35

Regulation of RNA processing

Question 36

Effects of TDP-43 on transcription and mRNA splicing?

Answer 36

Transcriptional repressor Exon skipping (binds to CFTR pre-mRNA UG intronic tract)

Question 37

Effects of FUS on transcription and mRNA splicing?

Answer 37

Transcriptional activator Part of spliceosome machinery

Question 38

Main target of action for TDP-43 and FUS

Answer 38

Introns

Question 39

Describe the cytoplasmic stress granule response

Answer 39

Aims to conserves mRNAs during cell stress Activity + cell stress stimulate nuclear efflux of TDP-43 and FUS to the cytoplasm, where they are withing RNA transport granules (stress granules and processing bodies)

Question 40

Effects of TDP-43 and FUS knockout on dendrites?

Answer 40

TDP-43 KO: reduced dendritic branching/ synapse formation FUS KO: reduced spine formation NB: TDP-43 regulates local protein synthesis on dendrites

Question 41

What causes TDP-43 mislocalisation?

Answer 41

Inhibition of TDP-43 nuclear transport protein (importin) -> accumulation of soluble TDP-43 in cytoplasm NB: NLS is NOT affected in TDP-43

Question 42

What causes FUS mislocalisation?

Answer 42

mutation of nuclear localisation signal-NLS [Experimental evidence] Inhibition of FUS nuclear transport protein (transportin) -> FUS accumulation in cytoplasm

Question 43

Pathogenesis of SALS?

Answer 43

[nuclear transport proteins decrease w/ age -> increased cytoplasmic TDP-43] - cell stress/oxid. stress/heat shock/ER stress acts as the trigger - > stress granules in cytoplasm that contain housekeeping mRNAs that don't require translation during stress also contain FUS and TDP-43 [NB: these stress granules could act as precursors for large inclusions]

Question 44

Relation of TDP-43 inclusions to ALS cases

Answer 44

Common to 97% of ALS cases (SALS and FALS) Exceptions are FALS cases w/ FUS mutations (0.5% of ALS cases) and SOD1 (2% of ALS cases)

Question 45

Outcome of TDP-43 knock out in embryos?

Answer 45

Lethal

Question 46

Outcome of partial/conditional TDP-43 knockouts?

Answer 46

Motor neuron defects Progressive motor phenotype

Question 47

Outcome of selective knockout of TDP-43 in glia/muscle

Answer 47

ALS-like phenotypes