Neurotoxins subvert the allosteric activation mechanism of SARM1 to induce neuronal loss

Abstract

SARM1 is an inducible TIR-domain NAD+ hydrolase that mediates pathological axon degeneration. SARM1 is activated by an increased ratio of NMN to NAD+, which competes for binding to an allosteric activating site. When NMN binds, the TIR domain is released from autoinhibition, activating its NAD+ hydrolase activity. The discovery of this allosteric activating site led us to hypothesize that other NAD+-related metabolites might also activate SARM1. Here we show that the nicotinamide analogue 3-acetylpyridine (3-AP), first identified as a neurotoxin in the 1940s, is converted to 3-APMN which activates SARM1 and induces SARM1-dependent NAD+ depletion, axon degeneration and neuronal death. Systemic treatment with 3-AP causes rapid SARM1-dependent death, while local application to peripheral nerve induces SARM1-dependent axon degeneration. We also identify a related pyridine derivative, 2-aminopyridine, as another SARM1-dependent neurotoxin. These findings identify SARM1 as a candidate mediator of environmental neurotoxicity, and furthermore, suggest that SARM1 agonists could be developed into selective agents for neurolytic therapy.