Abstract
In response to injury, neurons activate a program of organized axon self-destruction initiated by the NAD+ hydrolase SARM1. In healthy neurons SARM1 is autoinhibited, but single amino acid changes can abolish autoinhibition leading to constitutively-active SARM1 enzymes that promote degeneration when expressed in cultured neurons. To investigate whether naturally-occurring human variants might similarly disrupt SARM1 autoinhibition and potentially contribute to risk for neurodegenerative disease, we assayed the enzymatic activity of 29 rare SARM1 alleles identified among 8,507 amyotrophic lateral sclerosis (ALS) patients. Ten missense variants or small in-frame deletions exhibit constitutive NADase activity, including more than half of those that are unique to the ALS patients or that occur in multiple patients. Expression of these constitutively active ALS-associated SARM1 alleles in cultured dorsal root ganglion (DRG) neurons is pro-degenerative and cytotoxic. Intrathecal injection of an AAV expressing the common SARM1 reference allele is innocuous to mice, but a construct harboring SARM1V184G, the constitutively active variant found most frequently in the ALS patients, causes axon loss, motor dysfunction, and sustained neuroinflammation. These results implicate rare hypermorphic SARM1 alleles as candidate genetic risk factors for ALS and other neurodegenerative conditions.
Competing Interest Statement
A.D. and J.M. are co-founders, scientific advisory board members and shareholders of Disarm Therapeutics, a wholly owned subsidiary of Eli Lilly. A.J.B. and Y.S. are consultants to Disarm Therapeutics. The authors have no other competing conflicts or financial interests.
Footnotes
Author email addresses: Xianrong Mao maox{at}wustl.edu, Amy Strickland amy.strickland{at}wustl.edu, Yo Sasaki sasaki{at}wustl.edu
Abbreviations
- AAV
- Adeno-associated virus
- ALS
- Amyotrophic Lateral Sclerosis
- ARM
- HEAT/Armadillo motif
- cADPR
- Cyclic adenosine diphosphate ribose
- CD68
- Cluster of Differentiation 68
- DRG
- Dorsal root ganglion
- EGFP
- Enhanced green fluorescent protein
- MLS
- Mitochondrial localization signal
- MTT
- 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide
- NAD
- Nicotinamide adenine dinucleotide
- NMNAT2
- Nicotinamide mononucleotide adenylyltransferase 2
- TIR
- Toll/Interleukin receptor
- TUNEL
- Terminal deoxynucleotidyl transferase dUTP nick end labeling
- SAM
- Sterile alpha motif
- SARM1
- Sterile alpha and TIR motif containing 1