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Principal Investigator: ADAM JOSEPH BLOOM
Organization: WASHINGTON UNIVERSITY
Fiscal Year: 2024
Award: $578,847
Funding agency: National Institute of Neurological Disorders and Stroke
Motor axon loss is a cardinal symptom of amyotrophic lateral sclerosis (ALS). Axon loss can be driven
by a genetically encoded program in which the axon survival factors NMNAT2 and STMN2 inhibit the activity of
the axon destruction factor SARM1. Recent data suggest that this program of axon self-destruction may
contribute to pathology in ALS. First, aggregation of TDP-43, a hallmark of most ALS cases, results in the
selective loss of mRNA encoding functional STMN2, a key axon survival factor. Second, loss of SARM1
suppresses some neurodegenerative phenotypes in a mouse ALS model that expresses pathogenic human
TDP-43. Here we investigate the contribution of this axon degeneration pathway to ALS. We have defined the
mechanism of action of SARM1, demonstrating that it is the founding member of a new class of NAD-cleaving
enzymes. SARM1 enzyme activity is normally held in check via an autoinhibitory domain. Injury- or disease-
induced loss of NMNAT2 and STMN2 disinhibits SARM1, leading to rapid NAD+ depletion, metabolic
catastrophe, and axon fragmentation. Our structure-function studies of the SARM1 protein have identified
mutations with a range of consequences, from constitutively active variants that promote cell death and axon
loss, to dominant negative variants that are neuroprotective. These findings imply that human variants may exist
that either promote or protect against neurodegeneration, and that understanding the phenotypic consequences
of genetic variation requires functional studies of enzyme activity. In support of this hypothesis, we have identified
several rare SARM1 variants in ALS patients, but not in controls, that have constitutive NADase activity and
promote neuron death and axon loss. These variants also cause motor dysfunction and paralysis when
expressed in the mouse CNS, suggesting that activating SARM1 mutations may contribute to ALS pathogenesis.
Here we propose to define the function of SARM1 variants from ALS patients, controls, and the general
population. These studies will allow us to categorize SARM1 variants as putatively pro-degenerative,
neuroprotective, or neutral. In parallel, we will dissect the contribution of variation in components of the
programmed axon destruction pathway to ALS phenotypes, alone and in combination with known ALS genetic
risk-factors, in motor neurons differentiated from human induced pluripotent stem cells (iPSCs). Finally, we will
investigate neurodegeneration in a mouse knock-in model carrying a Sarm1 allele equivalent to a pro-
degenerative allele found in ALS patients, alone and in combination with a SOD1 model, based on a specific
patient genotype that we identified. We will attempt to suppress ALS phenotypes with SARM1 inhibition via a
proven gene therapy approach and with experimental small molecule inhibitors. Results of these studies will
establish the relationship between the SARM1-mediated axon destruction program and ALS, and build the
foundation to develop axoprotective therapeutics to treat this devastating disease.
Terms: <ALS pathology><ALS patients><Affect><Alleles><Allelomorphs><Amino Acids><Amyotrophic Lateral Sclerosis><Amyotrophic Lateral Sclerosis Motor Neuron Disease><Amyotrophic Lateral Sclerosis patients><Antimorphic mutation><Assay><Attenuated><Axon><Bioassay><Biological Assay><CRISPR><CRISPR/Cas system><Categories><Causality><Cell Death><Cessation of life><Chemicals><Clustered Regularly Interspaced Short Palindromic Repeats><Complex><DNA Therapy><DPN hydrolase><DPNase><Data><Death><Development><Diphosphopyridine Nucleotidase><Disease><Disinhibition><Disorder><Dominant Negative><Dominant-Negative Mutant><Dominant-Negative Mutation><Dysfunction><Enzyme Gene><Enzymes><Etiology><Face><Foundations><Functional disorder><GWA study><GWAS><Gehrig's Disease><Gene Transfer Clinical><Gene variant><General Population><General Public><Genes><Genetic Alteration><Genetic Change><Genetic Diversity><Genetic Intervention><Genetic Polymorphism><Genetic Variation><Genetic defect><Genetic predisposing factor><Genetic study><Human><Human Genetics><Injury><Investigation><KI mice><KO mice><Knock-in><Knock-in Mouse><Knock-out Mice><Knockout Mice><Link><Lou Gehrig Disease><Maintenance><Mediating><Medulla Spinalis><Messenger RNA><Metabolic><Methods><Mice><Mice Mammals><Modeling><Modern Man><Molecular><Motor><Motor Cell><Motor Neurons><Murine><Mus><Muscle><Muscle Tissue><Mutate><Mutation><NAD+ Glycohydrolase><NAD+ Nucleosidase><NADase><Nerve Cells><Nerve Degeneration><Nerve Unit><Nervous System><Neural Cell><Neurocyte><Neurologic Body System><Neurologic Organ System><Neuron Degeneration><Neuronal Differentiation><Neurons><Neuropathy><Null Mouse><Palsy><Paralysed><Pathogenesis><Pathogenicity><Pathology><Pathway interactions><Phenotype><Physiopathology><Plegia><Process><Protein Truncation><Proteins><Risk><Role><Route><SOD-1><SOD-1 protein><SOD1><SOD1 gene><SOD1 gene product><Spinal Cord><Structure><Symptoms><TAR DNA-binding protein 43><TDP-43><TDP-43 aggregate><TDP-43 aggregation><TDP43><TDP43 aggregate><TDP43 aggregation><Testing><Therapeutic><Trauma><Variant><Variation><Viral><allele variant><allelic variant><aminoacid><amyotrophic lateral sclerosis pathology><attenuate><attenuates><axon damage><axon injury><axonal damage><axonal degeneration><axonal injury><causation><cohort><degenerative axon><developmental><disease causation><disease model><disease risk><disorder model><disorder risk><druggable target><enzyme activity><experiment><experimental research><experimental study><experiments><faces><facial><falls><gain of function><gain of function mutation><gene repair therapy><gene therapy><gene-based therapy><genetic risk factor><genetic therapy><genetic variant><genome mutation><genome wide association><genome wide association scan><genome wide association studies><genome wide association study><genomewide association scan><genomewide association studies><genomewide association study><genomic therapy><genomic variant><genotyped patients><hiPSC><human iPS><human iPSC><human induced pluripotent cell><human induced pluripotent stem cells><human inducible stem cells><induced human pluripotent stem cells><inherited factor><inhibitor drug><inhibitor therapeutic><inhibitor therapy><injuries><innovate><innovation><innovative><knockin><knockin mice><life span><lifespan><loss of function><mRNA><member><motoneuron><motor disease><motor disorder><motor dysfunction><mouse model><murine model><muscular><necrocytosis><nerve cell death><nerve cell loss><neural degeneration><neurodegeneration><neurodegenerative><neurodegenerative phenotype><neurological degeneration><neuron cell death><neuron cell loss><neuron death><neuron loss><neuronal><neuronal cell death><neuronal cell loss><neuronal death><neuronal degeneration><neuronal loss><neuropathic><neuroprotection><neuroprotective><novel><overexpress><overexpression><paralysis><paralytic><pathology in ALS><pathophysiology><pathway><polymorphism><programs><protein TDP-43><protein TDP43><small molecular inhibitor><small molecule inhibitor><social role><superoxide dismutase 1><whole genome association analysis><whole genome association studies><whole genome association study>