Exam 1: ALS Flashcards by jnauman@tulane.edu Nauman

Lateral corticospinal tract

3/4

cross MEDULLA

LIMBS

LATERAL alpha-MN

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Ventral corticospinal tract

1/4 axons

axons don’t cross

Neck, should, trunk

MEDIAL alpha-MN

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Upper motor neuron disturbances

spasticity, weakness, enhanced deep tendon reflexes

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Lower motor neuron disturbances

fasciculations, wasting, weakness

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Who? Inheritance?

mostly Caucasian men

90% sporadic
10% familial dominance pattern

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ALS symptoms

Clumsy hand 
hoarse voice (dysarthria)
shoulder dysfunction
weak foot (drop foot)
difficulty walking (spastic gait)
exercise intolerance
fasciculation
respiratory insufficiency 
cognitive impairment

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As ALS symptoms spread throughout the body

weigth loss, fatigue, exaggerated reflexes, decreased coordination

Bizarre affect, uncontrolled inappropriate crying and laughing, inappropriate responses

overlap with frontotemporal dementia

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With progression

can’t walk, stand, eat, or breathe

relentless progression
50% die in 30 months symptom onset
20% survive 5-10 years

lack of sensory involvement

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3 presentations of ALS

1) 70% limb onset
2) 25% bulbar onset- speech/swallowing, respiration, dysapnea
3) 5% trunk and/or respiratory onset

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Typical pathological features: SOD1

SOD1 aggregates in spinal motor neurons (Familial)

TDP-43 redistribution to cytoplasmic inclusions in spinal motor neurons in sporadic ALS

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3 types of ALS genes

1) alter proteostasis and protein quality control
2) disrupt RNA stability and function
3) disrupt cytoskeleton dynamics of MN

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Theories and predictive factors of ALS

unknown

bets predictive factors: age and family hisotyr

unsubstantiated: viral infection and lyme disease

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Inherited ALS: SOD1 mutation

autosomal dominant
free radical scavenging enzyme

mouse = hind limb weakness.

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Inherited ALS: TAR DMP (TDP-43) and FUS

multifunctional proteins involved in gene expression transcription/translation/transport

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Inherited ALS: OPTN

encodes optineurin

involved in regulation of NFkB

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Inherited ALS: ALS2: Alisin mutation

rare, recessive

encodes alsin protein, involved in cycling G protein between GDP-GTP state. pathology not understood

Chromosome 9p21 locus

GGGCC repeats on C9ORF72.
normal <16 while ALS patients have up to 1600. Patients present with aggressive disease, cognitive impairments toxicity not understood

Mechanisms of Motor Neuron Death: Cu/Zn SOD1

mutations in SOD1 identified, loss of antioxidant thought to cuase injury by superoxide. SOD1 catalyzes conversion of superoxide to hydrogen peroxide and oxygen

SOD1 mice not rescued by wildtype SOD
SOD1 KO don’t have issue

Animal model DOES NOT support SOD1/free radical theory

mutant = toxic gain of function

Mechanisms of Motor Neuron Death: Glia Cells

inflammation from microglial in response to SOD1 mutations

C9orf72 mutations associate with microglia activation

SOD1 mutations in oligodendrites induces demyelination

mutations impair astrocytes in buffering glutamate, promote excitotoxicity

mutant SOD1 slows antero/retrograde transport, no transport of RNA model

PROINFLAMMATORY CYTOKINES IN MICROGLIA

Mechanisms of Motor Neuron Death: ER stress

ER stress from misfolded proteins inpeeds degrading and removing non functional proteins

disrupted ubiquitin-proteasome system and autophagy

Mechanisms of Motor Neuron Death: Apoptotic factors

DNA fragmentation and elevated Bax

strengthened by data showing SOD1 mutants induce apoptosis

SOD1 mice have elevated Bad and Bax and decreased bcl-2/Bcl-xL

If you overexpress BCL2, delay onset

SOD1 mice show caspase activation (proteases), inhibition prolongs SOD1 life span

Mechanisms of Motor Neuron Death: Intermediate filaments

neurofilament proteins form cytoskeleton, abnormal synthesis/accumulation

abnormal transport. Unclear if accumulation of NFs causes or is caused by blockage.

mRNA analysis shown reduced NF light mRNA

Mechanisms of Motor Neuron Death: Defects in axonal transport

SOD1 mice = slow axon transport

mutations in dynactin (need for retrograde transport)

Mechanisms of Motor Neuron Death: Excitotoxicity

40% sporadic ALS patients elevated CSF.

EAAT2 is reduced in 95% biopsies from ALS patients

Theory is aberrant splicing of EAAT2 in mRNA, making truncated proteins. Unclear since splices also found in normal tissue.

Mechanisms of Motor Neuron Death: Growth Factors

vascular endothelial cell growth factor (VEGF) controls growth of blood vessels KO mice for VEGF = motor neuron disease. Intracerebroventricular injection of VEGF slows disease clinical trials anticipated

Mechanisms of Motor Neuron Death: Mitochondrial dysfunction

some version of SOD1 show vacuoles with damaged mitochondria. not in all SOD1 versions Creatine- enhances energy storage and slows progression in SOD1 mice. Failed in human clinical trials

Main point: LOTS wrong in ALS. List all you can

``` over excited aberrant RNA metabolism dysregulated vesicle transport mitochondrial dysfunction impaired DNA repair failure to clear glutamate (hyperexcited) axonopathy disrupted cytoskeleton bad quality control system NF accumulation ```

Treatment: Glutamate modulators

Riluzole: blocks voltage dependent Na+ channels, inhibits glutamate release, blocks amino acid receptors. increase in survival, but no difference in end morality Also no benefit in strength and neurological function

Treatment: Antioxidants

Edaravone: free radical scavenger slowed symptom progression, no cure Vitamin E also slow progression.

Treatment: Energy Metabolism

Creatine/phospjocreatine- intracellular transporter of ATP from site of synthesis to location of use, helps energy production in mitochondria, maintains ATP levels. Survival improved in SOD1 mice, ineffective in human clinical trials.

Treatment: Antinflammatory Agents

Prostaglandins synthesized from arachidonic acid by COX2 induce release of glutamate from astrocytes- role in excitotoxicity COX2 inhibitors helped neuronal survival in in vitro studies and SOD1 mice, failed human clinical trials

Treatment: Neurotrophins

BDNF/GDNF/CNTF tested in multiple clinical trials. Failed to show response, produced adverse side effects (anorexia, nausea) IGF-1 produced mixed results more trials underway with stem cells, viral vectors, siRNA techniques

Paper: Retrograde viral delivery of IGF-1 prolongs survival in mouse

GFP expression in lumber motor neurons Disease onset/mortality delayed by delivery of trophic factors AAV retrogradely transported from presynaptic to cell body/nuc Results: IGF-1 treatment prolonged life of SOD1 mice, improved muscle performance, even when delivered after symptom onset. IGF-1 animals also maintained body weight and muscle mass longer

Paper: VEGF delivery with retrogradely transported lentivector prolongs survival in a mouse ALS model

pseduotyping-engineering alternative viral envelopes to maintain tropism. Plasmids with envelope, packaging, and transfer gene (viral genome) are used to make non-replication competent virus. This paper used EIAV with Rabies envelope to produce integrating virus with retrograde transport capabilities. EIAV-VEGF INJECTed into hindlimb results in elevated VEGF expression in spinal tissue- virus can induce VEGF in target tissue point: RETROGRADE WORKS delayed decrease in rotarod task in SOD1 mice delayed disease onset increased lifespan

Paper: Lentiviral silencing of SOD1 by RNA

siRNA construct for SOD1 delays onset of disease in SOD1 mice

Paper: AAV4-mediated expression IFG-1 and VEGF

AAV deliver IGF-1 or VEGF ALS survive better when added. prolonged survival/motor function in animals