A phase transition enhances the catalytic activity of SARM1, an NAD+ glycohydrolase involved in neurodegeneration

Abstract

Sterile alpha and toll/interleukin receptor (TIR) motif-containing protein 1 (SARM1) is a neuronally expressed NAD+ glycohydrolase whose activity is increased in response to stress. NAD+ depletion triggers axonal degeneration, which is a characteristic feature of neurological diseases. Notably, loss of SARM1 is protective in murine models of peripheral neuropathy and traumatic brain injury. Herein, we report that citrate induces a phase transition that enhances SARM1 activity by ~2000-fold. This phase transition can be disrupted by mutating a residue involved in multimerization, G601P. This mutation also disrupts puncta formation in cells. We further show that citrate induces axonal degeneration in C. elegans that is dependent on the C. elegans orthologue of SARM1 (TIR-1). Notably, citrate induces the formation of larger puncta indicating that TIR-1/SARM1 multimerization is essential for degeneration in vivo. These findings provide critical insights into SARM1 biology with important implications for the discovery of novel SARM1-targeted therapeutics.

A TIR-1/SARM1 phase transition underlies p38 immune pathway activation in theC. elegansintestine

“…4C). Crowding agents also increase the activity of the TIR domain of human SARM1, as well as plant TIR domains [15,42], suggesting that the mechanism of TIR regulation is strongly conserved.…”

“…C. elegans carrying these same mutations, edited into the genome using CRISPR/Cas9, fail to induce p38 PMK phosphorylation, are unable to upregulate immune effector expression, and have enhanced susceptibility to bacterial infection. Importantly, we labeled the TIR-1/SARM1 protein with a fluorescent tag at its genomic locus and demonstrated for the first time that TIR-1/SARM1 oligomerizes into visible puncta within the intestine in response to physiologic stimuli, including both a pathogen and non-pathogen stress.In a contemporaneous study, Loring et al demonstrated that human SARM1 aggregates and undergoes a phase transition to potentiate its intrinsic NAD + glycohydrolase activity [15]. These authors studied SARM1 in the context of neuronal degeneration as it was previously demonstrated that loss of mammalian SARM1 protects against axonal degeneration following neuronal injury [16][17][18].…”

“…These authors studied SARM1 in the context of neuronal degeneration as it was previously demonstrated that loss of mammalian SARM1 protects against axonal degeneration following neuronal injury [16][17][18]. Treatment with non-physiologic concentrations of citrate, a molecule that induces protein aggregation, led to oligomerization of C. elegans TIR-1 in neurons, which was correlated with enhanced axonal degeneration [15]. We demonstrate here that C. elegans TIR-1/SARM1 oligomerizes to form puncta in response to physiological stresses, providing an important characterization of the mechanism inferred by Loring, et al, and establish that the TIR-1/SARM1 phase transition occurs in non-neuronal tissues in the regulation of intestinal immunity.Thus, a phase transition of TIR-1/SARM1 as a prerequisite for its NAD + glycohydrolase activity is strongly conserved, occurs in multiple cell types, and is essential for diverse physiological processes, including intestinal immune regulation and axonal degeneration.Finally, we report that a non-pathogen stress can induce TIR-1/SARM1 oligomerization and p38 PMK-1 pathway activation as part of a mechanism to preempt pathogen attack during a time of relative vulnerability to infection.…”

“…In a contemporaneous study, Loring et al demonstrated that human SARM1 aggregates and undergoes a phase transition to potentiate its intrinsic NAD + glycohydrolase activity [15]. These authors studied SARM1 in the context of neuronal degeneration as it was previously demonstrated that loss of mammalian SARM1 protects against axonal degeneration following neuronal injury [16][17][18].…”

“…These authors studied SARM1 in the context of neuronal degeneration as it was previously demonstrated that loss of mammalian SARM1 protects against axonal degeneration following neuronal injury [16][17][18]. Treatment with non-physiologic concentrations of citrate, a molecule that induces protein aggregation, led to oligomerization of C. elegans TIR-1 in neurons, which was correlated with enhanced axonal degeneration [15]. We demonstrate here that C. elegans TIR-1/SARM1 oligomerizes to form puncta in response to physiological stresses, providing an important characterization of the mechanism inferred by Loring, et al, and establish that the TIR-1/SARM1 phase transition occurs in non-neuronal tissues in the regulation of intestinal immunity.…”