Transcript Molecular Biology of Amyotrophic Lateral Sclerosis

Molecular Biology and
Genetics of Amyotrophic
Lateral Sclerosis
Michael Sidel
February 13, 2008
Goals
• To have a basis for the understanding of
the genetics involved in ALS
• To understand the current theories and
concepts that underlie the pathogenesis of
ALS
Outline
• Brief clinical overview of the disease
– 1 slide
• The genetics of ALS
– 6 Slides
• The pathology of ALS
– 5 Slides
• An understanding of the disease
pathogenesis
– Priceless (or 8 slides)
Some Clinical Factoids about ALS
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A progressive neurodegenerative disease
Involvement of motor neurons at all levels
50% mortality at 3 years
Several clinically related variants:
– Primary lateral sclerosis
– Primary muscular atrophy
– Progressive bulbar palsy
• 90% of the cases are considered “sporadic”
• 10% of cases are considered familial
Some of the Genetics of ALS
Genetics of ALS
• 10% of cases of ALS have history of firstdegree relative with the disease
– Suggests Autosomal Dominant inheritance
• Research direction:
– Isolating genes involved in clear familial
disease
– Isolating polymorphisms that are potentially
risk factors in sporadic disease
Genetics of Familial ALS
Mitchell and Borasio, Lancet2007; 369: 2031–41
Genetics of Familial ALS
Mitchell and Borasio, Lancet2007; 369: 2031–41
Genetics of Familial ALS
Mitchell and Borasio, Lancet2007; 369: 2031–41
Genetics of Familial ALS
Mitchell and Borasio, Lancet2007; 369: 2031–41
Genetics of Familial ALS
• Represents 10-20% of cases of familial
ALS
• Over 100 mutations to the gene are
related to pathology
• Gain of function mutation causes the
disease pathology
– From mouse model data
Genetics of Familial ALS
Mitchell and Borasio, Lancet2007; 369: 2031–41
Genetics of Familial ALS
Mitchell and Borasio, Lancet2007; 369: 2031–41
Genetics Associations in ALS
• There are other genetic mutations that
may alter the risk of developing ALS:
• Examples:
– Angiogenin (14q11.2)
– Vascular endothelial growth factor (6p12)
– Survival motor neuron (5q12.2-q13.3)
– Neurofilament protein (22q12.2)
– Multivesicular body protein 2B (2p11.2)
PATHOLOGY OF ALS
Gross Pathology
• Motor neuron
degeneration and
death with gliosis
• Gliosis of the CST
• Atrophy of ventral
nerve roots
Microscopic Pathology
• Intracellular inclusions
- Bunina bodies
- Ubiquinated inclusions (not tau)
PATHOGENIC MECHANISMS
OF ALS
Proposed Pathogenic
Mechanisms in ALS
• Oxidative Stress
• Excitotoxicity
• Abnormal Protein Precipitation and/or
Aggregation
• Cytoskeletal defects
• Axonal transport
• Neuroinflammation
• Abnormalities in hypoxia-regulated genes
• Apoptosis
Oxidative Stress
• Motor neuron damage as a result of
oxidative stress
• Not necessarily linked to gene mutation
– i.e. SOD1
• Post-mortem studies have shown
evidence of increased oxidative byproducts
• Linked to other mechanisms
Excitotoxicity
• Glutamate mediated
• Possible mechanisms of disease include:
– Production of free radicals
– Increased intracellular calcium
• Decreased EAAT2 functions has been
described in some ALS post-mortem
studies
More on Excitoxocity
Goodall and Morrison Expert Reviews in Molecular Medicine. Vol. 8(11) 24 May 2006.
Abnormal Protein Precipitation
and/or Aggregation
• Abnormal protein aggregates, including
Bunina bodies, ubiquitinated inclusions
and neurofilament rich hyaline inclusions
are pathological hallmarks of ALS
• Unknown cause and effect relationship
• SOD1 mutants can misfold and
coprecipitate with other molecules as well
Cytoskeletal Defects
• Neurofilament proteins
are the most abundant
structural protein in motor
neurons, and aggregates
of neurofilament proteins
motor neurons are
commonly seen in ALS
• Can be found as part of
inclusions
• Overexpression of
peripherin or alphainternexin in mice can
cause motor neuron
disease
Axonal Transport
• Axonal transport of materials is essential
for neuronal function and survival
• Dynactin is a protein involved in fast
retrograde transport in the axon
• Mutations in this gene have been
associated with motor neuron disease
Neuroinflammation
• Microglia have been
found to be
activated in parts of
CNS affected by
ALS
• COX-2 Receptors
and downstream
prostaglandins are
elevated in ALS
brains
Apoptosis
• Represents eneergy-dependent
programmed cell death
• In human ALS spinal cord tissue,
increases in caspase-1 and -9 activation
have been detected
• Very unclear how much this plays a role in
the pathogenesis of the disease
Goodall and Morrison. Expert Reviews in Molecular
Medicine. Vol. 8(11) 24 May 2006.
Why Motor Neurons?
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Extreme size of cells
High metabolic activity
Sensitivity to mitochondrial dysfunction
Elevated neurofilament content
Reduced capacity to buffer calcium
Conclusions
• We do not understand ALS
• Familial ALS is caused by genetic
mutations and is rare
• Sporadic ALS is caused by a combination
of:
– Genetic susceptibility
– Environmental triggers
– Motor neuron specific cellular damage
Key Points to Remember
1. Main cause of familial ALS is SOD1
mutations with are gain of function
2. Bunina bodies are inclusions found in
ALS motor neurons
3. Excitoxicity and oxidative damage are
likely major contributors to motor neuron
death in ALS
References
• Valdmanis, P.N. and Rouleau, G.A. Genetics of
familial amyotrophic lateral sclerosis. Neurology.
2008;70:144-152.
• Goodall, E.F. and Morrison, K.E. Amyotrophic
lateral sclerosis: proposed mechanisms and
pathways to treatment. Expert Reviews in
Molecular Medicine. Vol. 8; Issue 11; 24 May
2006.
• Mitchell, J.D. and Barasio, G.D. Amyoptrophic
Lateral Sclerosis. Lancet 2007; 369: 2031-41.