mTORC1 hyperactivation and resultant suppression of macroautophagy contribute to the induction of cardiomyocyte necroptosis by catecholamine surges

Abstract

Previous studies revealed a controversial role of mechanistic target of rapamycin complex 1 (mTORC1) and mTORC1‐regulated macroautophagy in isoproterenol (ISO)‐induced cardiac injury. Here we investigated the role of mTORC1 and potential underlying mechanisms in ISO‐induced cardiomyocyte necrosis. Two consecutive daily injections of ISO (85 mg/kg, s.c.) or vehicle control (CTL) were administered to C57BL/6J mice with or without rapamycin (RAP, 5 mg/kg, i.p.) pretreatment. Western blot analyses showed that myocardial mTORC1 signaling and the RIPK1–RIPK3–MLKL necroptotic pathway were activated, mRNA expression analyses revealed downregulation of representative TFEB target genes, and Evan's blue dye uptake assays detected increased cardiomyocyte necrosis in ISO‐treated mice. However, RAP pretreatment prevented or significantly attenuated the ISO‐induced cardiomyocyte necrosis, myocardial inflammation, downregulation of TFEB target genes, and activation of the RIPK1–RIPK3–MLKL pathway. LC3‐II flux assays confirmed the impairment of myocardial autophagic flux in the ISO‐treated mice. In cultured neonatal rat cardiomyocytes, mTORC1 signaling was also activated by ISO, and inhibition of mTORC1 by RAP attenuated ISO‐induced cytotoxicity. These findings suggest that mTORC1 hyperactivation and resultant suppression of macroautophagy play a major role in the induction of cardiomyocyte necroptosis by catecholamine surges, identifying mTORC1 inhibition as a potential strategy to treat heart diseases with catecholamine surges.