SARM1 is a multi-functional NAD(P)ase with prominent base exchange activity, all regulated bymultiple physiologically relevant NAD metabolites

Carlo Angeletti,Adolfo Amici,Jonathan Gilley,Andrea Loreto,Antonio G Trapanotto,Christina Antoniou,Elisa Merlini,Michael P Coleman,Giuseppe Orsomando

doi:10.1016/j.isci.2022.103812

Carlo Angeletti, Adolfo Amici + Show 7 more

Open Access

https://doi.org/10.1016/j.isci.2022.103812

Copy DOI

Abstract

SummarySARM1 is an NAD(P) glycohydrolase and TLR adapter with an essential, prodegenerative role in programmed axon death (Wallerian degeneration). Like other NAD(P)ases, it catalyzes multiple reactions that need to be fully investigated. Here, we compare these multiple activities for recombinant human SARM1, human CD38, and Aplysia californica ADP ribosyl cyclase. SARM1 has the highest transglycosidation (base exchange) activity at neutral pH and with some bases this dominates NAD(P) hydrolysis and cyclization. All SARM1 activities, including base exchange at neutral pH, are activated by an increased NMN:NAD ratio, at physiological levels of both metabolites. SARM1 base exchange occurs also in DRG neurons and is thus a very likely physiological source of calcium-mobilizing agent NaADP. Finally, we identify regulation by free pyridines, NADP, and nicotinic acid riboside (NaR) on SARM1, all of therapeutic interest. Understanding which specific SARM1 function(s) is responsible for axon degeneration is essential for its targeting in disease.

Highlights

SARM1 is an intracellular adaptor of Toll-like receptor (TLR) signaling and a prodegenerative enzyme with a central role in programmed axon death, or Wallerian degeneration (Coleman and Hoke, 2020; Osterloh et al, 2012)
We characterised SARM1 base exchange activity for NAD or NADP paired with three different pyridine bases: 3-acetylpyridine (AcPyr), vacor (1-(4-nitrophenyl)-3-(pyridin-3-ylmethyl)urea), and nicotinic acid (Na) at pH 7.5 (Figure 4, Table S1). Both human CD38 (hCD38) and Aplysia cyclase showed much lower base exchange reactions than human SARM1 full length (hSARM1) under these conditions, and we confirmed previous reports about their undetectable activity at this pH with Na in particular (Figure 4A left, middle panels). For both full-length SARM1 and its ARM-lacking fragment, base exchange was detectable for all three bases, including Na (Figures 4A right and 4B left), and we found that the base exchange activity can displace hydrolysis and cyclization for both NAD and NADP to a degree dependent on the base used
We found that the two vitamin B3 precursors nicotinic acid riboside (NaR) and NR (Belenky et al, 2009; Bogan and Brenner, 2008; Bogan et al, 2009), exerted inhibitory effects but with opposing selectivity for hSARM1 vs both hCD38 and Aplysia cyclase (Figure 6A)

Summary

Introduction

SARM1 is an intracellular adaptor of Toll-like receptor (TLR) signaling and a prodegenerative enzyme with a central role in programmed axon death, or Wallerian degeneration (Coleman and Hoke, 2020; Osterloh et al, 2012). Wallerian degeneration occurs when axons are physically transected but it is clear that the underlying programmed axon death mechanism is activated by many toxins, gene mutations, or metabolic disruption (Conforti et al, 2014; Loring and Thompson, 2020). The rise in NMNAT2 substrate, NMN, when this enzyme is depleted, plays a important role in activating the pathway (Di Stefano et al, 2015, 2017; Loreto et al, 2015, 2020).

Results

Discussion

Conclusion