A Membrane Potential- and Calpain-Dependent Reversal of Caspase-1 Inhibition Regulates Canonical NLRP3 Inflammasome

The NLRP3 inflammasome senses a range of cellular disturbances, although no consensus exists regarding a common mechanism. Canonical NLRP3 activation is blocked by high extracellular K(+), regardless of the activating signal. We report here that canonical NLRP3 activation leads to Ca(2+) flux and increased calpain activity. Activated calpain releases a pool of Caspase-1 sequestered by the cytoskeleton to regulate NLRP3 activation. Using electrophysiological recording, we found that resting-state eukaryotic membrane potential (MP) is required for this calpain activity, and depolarization by high extracellular K(+) or artificial hyperpolarization results in the inhibition of calpain. Therefore, the MP/Ca(2+)/calpain/ Caspase-1 axis acts as an independent regulatory mechanism for NLRP3 activity. This finding provides mechanistic insight into high K(+)-mediated inhibition of NLRP3 activation, and it offers an alternative model of NLRP3 inflammasome activation that does not involve K(+) efflux.