MG53 Negatively Regulates NLRP3 to Inhibit Inflammation Associated with Tissue Injury

MG53 is a member of the tripartite motif family with E3 ubiquitin ligase activity, and plays important roles in cell membrane repair, tissue regeneration and wound healing. We previously showed that topical or systemic administration of recombinant human MG53 (rhMG53) protein protected against tissue injury and reduced the level of inflammatory cytokines (e.g. IL-1β) in circulation. NLRP3 is a key member of the inflammasome complex that mediates the cleavage and activation of caspase-1 for control of IL-1β release into circulation. As tissue injury is often associated with inflammation, we hypothesize that MG53 interacts with NLRP3 to control inflammasome signaling associated with tissue injury. With the mg53-/- mice, we found the spleen organ was significantly enlarged compared with the wild type littermates. The protein level of NLRP3 in the spleen was up-regulated in the mg53-/- mice. In cultured HEK293 cells, co-expression of MG53 with NLRP3 led to down-regulation of NLRP3 in a proteasome-dependent manner. Down-regulation of NLRP3 was not observed in cells co-transfected with a mutant MG53 lacking E3-ligase activity. Co-immunpprecipitation studies revealed a physical interaction between MG53 and NLRP3. With human monocytes (THP-1 cells) transfected with RFP-MG53 and GFP-NLRP3, we observed the trafficking of MG53 and NLRP3 associated with inflammasome formation. Upon treatment with LPS and ATP, THP-1 cells responded with formation of inflammasomes and co-segregation of NLRP3 and MG53. The level of NLRP3 in THP-1 cells co-expressing MG53 was significantly lower compared with cells do not express MG53. Together, these findings suggest that MG53 act as a negative regulator of NLRP3 to control inflammasome signaling. More in vivo studies are required to dissect the physiological role of MG53 in modulating the immune response associated with tissue injury.