SHARPIN, a novel regulator of the NLRP3 inflammasome (INM6P.334)

Abstract

Abstract NLRP3 recruits adaptor ASC and protease caspase-1 to assemble the inflammasome, which is critical for maturation of IL-1β and IL-18. Although, NLRP3 is one of the most-studied inflammasome, the direct ligand or the mechanisms that govern activation of NLRP3 inflammasome remains obscure. Recent study with Hoil1-/- mice demonstrated that HOIL1 is required for NLRP3 inflammasome activation. It was further proposed that HOIL1 was required for linear ubiquitination of ASC to regulate NLRP3 inflammasome assembly. HOIL1 along with HOIP and SHARPIN form linear ubiquitin assembly complex (LUBAC) that is essential for linear ubiquitination of target proteins. Herein, we wanted to determine whether SHARPIN is also involved in the activation of NLRP3 inflammasome. Using Sharpincpdm mice (spontaneous mutation that results in SHARPIN deficiency), we demonstrated that SHARPIN is critically required for activation of both canonical and non-canonical NLRP3 inflammasome, but dispensable for activation of NLRC4 and AIM2 inflammasome. Interestingly, our studies further show that unlike HOIL1, SHARPIN regulates NLRP3 inflammasome by controlling priming events. To this end, we demonstrated that Sharpincpdm BMDMs have dramatically reduced NFkB, ERK, p38 MAP kinase activation and pro-Il1b expression. Thus, our study for the first time demonstrates SHARPIN as a novel regulator of NLRP3 inflammasome adding to the complexity of our understanding of NLRP3 inflammasome.