Cytosolic K+ and extracellular ATP as regulators of NLRP3 inflammasome activation and the IL-1β secretion response of macrophages to crystalline stimuli. (114.9)

Abstract

Abstract The crystalline particulate Alum has widely been used as an adjuvant in vaccines. Alum and other crystalline particulates also stimulate NLRP3/caspase-1 inflammasome assembly and secretion of mature IL-1β via poorly understood mechanisms that involve decreases in cytosolic [K+]. This study characterized mechanisms for K+ efflux in LPS-primed murine bone marrow-derived macrophages (BMDM) stimulated with either Imject Alum or the Na+, K+-ATPase inhibitor ouabain. Treatment with Alum for 3 h induced robust secretion of IL-1β that was similar in the absence or presence of antagonists of the P2X7 receptor, an ATP-gated K+ efflux channel known to regulate NLRP3 inflammasome assembly. However, the ATP-scavenging enzyme apyrase markedly reduced this IL-1β secretion, suggesting that NLRP3 activation and IL-1β release induced by Alum crystals is at least partially dependent on a P2X receptor subtype(s) other than P2X7. Current experiments are testing possible involvement of P2X4 receptor channels. Treatment of LPS-primed BMDMs with ouabain for 6 h also induced significant release of IL-1β. We hypothesize that ouabain causes NLRP3 activation and IL-1β secretion by inhibiting the steady-state Na+, K+ATPase activity which counteracts the slow efflux of cytosolic K+ via leak/rectifier-type K+ channels.