Quantification of SARM1 NADase Activity in Human Peripheral Blood Mononuclear Cells

SARM1 (sterile α and TIR motif-containing protein-1) is an NADase enzyme that serves 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 treatment of neurodegeneration. Beyond neuroscience, emerging studies reveal that SARM1 may also drive aspects of bone fragility, liver pathology, adipose expansion, and insulin resistance in metabolic disease. However, we lack methods to quantify SARM1 activation in humans to better define patients at high risk of SARM1-mediated tissue damage. Unlike neurons, peripheral blood mononuclear cells (PBMCs) represent an easily accessible population for clinical screening. While SARM1 gene expression has been identified in PBMCs, it is less known whether functional SARM1 NADase is present. We hypothesized that by pairing activators and inhibitors of SARM1 with analysis of downstream changes in cellular metabolites, we could identify and quantify both 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. Changes in secondary metabolites including NAD+, NMN, NaMN, ATP, AMP, IMP, inosine, and succinyl adenosine were also characterized and used to generate a working model of PBMC SARM1 activation. 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.