COP9 Signalosome Suppresses RIPK1-RIPK3 mediated Cardiomyocyte Necroptosis in Mice.

Background: Mechanisms governing the induction of heart failure by the impairment of autophagy and the ubiquitin-proteasome system (UPS) and the molecular pathways to cardiomyocyte (CM) necrosis remain incompletely understood. COPS8 is an essential subunit of the COP9 signalosome (CSN), a key regulator of ubiquitination. Mice with CM-restricted knockout of Cops8 (Cops8-cko) show autophagic and UPS malfunction and massive CM necrosis followed by acute heart failure and premature death, providing an excellent animal model to address the mechanistic gaps specified above. This study was conducted to determine the nature and underlying mechanisms of the CM necrosis in Cops8-cko mice. Methods and Results: Compared with littermate control mice, myocardial protein levels of key factors in the necroptotic pathway (RIPK1, RIPK3, MLKL, the RIPK1-bound RIPK3), protein carbonyls, full-length caspase 8, and BCL2, as well as histochemical staining of superoxide anions were significantly higher but the cleaved caspase 8 and the caspase 8 activity were significantly lower in Cops8-cko mice. In vivo CM uptake of Evans blue dye (EBD) was used as an indicator of necrosis. Cops8-cko mice treated with a RIPK1 kinase inhibitor (necrotstatin-1) showed less EBD uptake (0.005% vs. 0.20%; p<0.0001) and longer median lifespan (32.5 vs. 27 days; p<0.01) than those treated with vehicle control. RIPK3 haploinsufficiency showed similar recuing effects on Cops8-cko but Cyclophilin D deficiency did the opposite. Conclusions: Cardiac Cops8/CSN malfunction causes RIPK1-RIPK3 dependent, but mitochondrial permeability transition pore independent, CM necroptosis in mice and the CSN plays an indispensable role in suppressing CM necroptosis.