摘要Calpains have been implicated in heart diseases.While calpain-1 has been detrimental to the heart,the role of calpain-2 in cardiac pathology remains controversial.In this study we investigated whether sustained over-expression of calpain-2 had any adverse effects on the heart and the underlying mechanisms.Double transgenic mice(Tg-Capn2/tTA)were generated,which express human CAPN2 restricted to cardiomyocytes.The mice were subjected to echocardiography at age 3,6,8 and 12 months,and their heart tissues and sera were collected for analyses.We showed that transgenic mice over-expressing calpain-2 restricted to cardiomyocytes had normal heart function with no evidence of cardiac pathological remodeling at age 3 months.However,they exhibited features of dilated cardiomyopathy including increased heart size,enlarged heart chambers and heart dysfunction from age 8 months;histological analysis revealed loss of cardiomyocytes replaced by myocardial fibrosis and cardiomyocyte hypertrophy in transgenic mice from age 8 months.These cardiac alterations closely correlated with aberrant autophagy evidenced by significantly increased LC3BII and p62 protein levels and accumulation of autophagosomes in the hearts of transgenic mice.Notably,injection of 3-methyladenine,a well-established inhibitor of autophagy(30 mg/kg,i.p.once every 3 days starting from age 6 months for 2 months)prevented aberrant autophagy,attenuated myocardial injury and improved heart function in the transgenic mice.In cultured cardiomyocytes,over-expression of calpain-2 blocked autophagic flux by impairing lysosomal function.Furthermore,over-expression of calpain-2 resulted in lower levels of junctophilin-2 protein in the heart of transgenic mice and in cultured cardiomyocytes,which was attenuated by 3-methyladenine.In addition,blockade of autophagic flux by bafilomycin A(100 nM)induced a reduction of junctophilin-2 protein in cardiomyocytes.In summary,transgenic over-expression of calpain-2 induces age-dependent dilated cardiomyopathy in mice,which may be mediated through aberrant autophagy and a reduction of junctophilin-2.Thus,a sustained increase in calpain-2 may be detrimental to the heart.