RCAN1 deficiency aggravates sepsis-induced cardiac remodeling and dysfunction by accelerating mitochondrial pathological fission

Objective: Cardiac dysfunction and remodeling are serious complications of sepsis and are the main causes of death in sepsis. RCAN1 is a feedback regulator of cardiac hypertrophy. Here, we aim to investigate the role of RCAN1 in septic cardiomyopathy.

Methods: Mice were randomly divided into control-WT, control-RCAN1^-/-, LPS-induced WT and LPS-induced RCAN1^-/- groups, some with Midiv-1 or KN93 treatment. The protein levels of RCAN1, p-ERK1/2, NFAT3, Drp1, p-Drp1, p-CaMKII in mouse hearts or cultured cardiomyocytes were determined by Western blotting. Myocardial function was assessed by echocardiography. Cardiac hypertrophy and fibrosis were detected by H&E and Masson's trichrome staining. Mitochondrial morphology was examined by transmission electron microscope. Serum level of LDH was detected by ELISA.

Results: Our data show that RCAN1 was downregulated in septic mouse heart and LPS-induced cardiomyocytes. RCAN1^-/- mice showed a severe impairment of cardiac function, and increased myocardial hypertrophy and fibrosis. The protein levels of NFAT3 and p-ERK1/2 were significantly increased in the heart tissues of RCAN1^-/- mice. Further, RCAN1 deficiency aggravated sepsis-induced cardiac mitochondrial injury as indicated by increased ROS production, pathological fission and the loss of mitochondrial membrane potential. Inhibition of fission with Mdivi-1 reversed LPS-induced cardiac hypertrophy, fibrosis and dysfunction in RCAN1^-/- mice. Moreover, RCAN1 depletion promoted mitochondrial translocation of CaMKII, which enhanced fission and septic hypertrophy, while inhibition of CaMKII with KN93 reduced excessive fission, improved LPS-mediated cardiac remodeling and dysfunction in RCAN1^-/- mice.

Conclusions: Our finding demonstrated that RCAN1 deficiency aggravated mitochondrial injury and septic cardiomyopathy through activating CaMKII. RCAN1 serves as a novel therapeutic target for treatment of sepsis-related cardiac remodeling and dysfunction.