Quantification of SARM1 activity in human peripheral blood mononuclear cells

Abstract

SARM1 (sterile and TIR motif-containing protein-1) is an NADase enzyme that has been identified as the central executioner of Wallerian axon degeneration. Given this, SARM1 is of high interest as a candidate therapeutic target and SARM1 inhibitors are currently in clinical trials for prevention and treatment of neurodegeneration. Beyond neuroscience, emerging studies reveal that SARM1 activation may also drive aspects of bone fragility, liver pathology, adipose tissue expansion, and insulin resistance in settings of metabolic disease. However, we lack methods to quantify SARM1 activation in humans using clinical isolates to better define patients at high risk of SARM1-mediated tissue damage, informing the future clinical application of SARM1 inhibitors. Unlike neurons, peripheral blood mononuclear cells (PBMCs) represent an easily accessible population of cells for clinical screening. We hypothesized that by pairing activators and inhibitors of SARM1 with analysis of downstream changes in cellular metabolites, we could quantify both the basal SARM1 activity and the SARM1 activation potential of human PBMCs. Our results reveal that SARM1 agonist pyrinuron, also known as Vacor, activates a dose-dependent increase in cAPDR and the cADPR:ADPR ratio that is arrested when paired with SARM1 inhibitor DSRM-3716. Various changes in secondary metabolites were also characterized and reported herein. Overall, these findings demonstrate that human PBMCs have detectable SARM1 activation potential and could be leveraged as a clinical readout of SARM1 expression and activity across diverse disease contexts.