Role Of Mitochondrial Calcium Uniporter/Calpain In Myocardial Ischemia-reperfusion Injury

The occurrence and development of myocardial ischemia-reperfusion(I/R)injury has been an important factor threatening the survival rate of patients in cardiac surgery.The molecular mechanisms and therapeutic targets have also been studied.In recent years,more and more studies have shown that I/R injury is closely related to the structure and function of mitochondria.Mitochondria are the unit of energy output of cells,and the heart is one of the organs that consumes a lot of oxygen in the body,and it is very sensitive to damage to mitochondria.Ca2+ play an important role in this process.Under physiological conditions,Ca2+ are the most important ions in muscle cells that maintain expansion and relaxation and neuromuscular conduction.In addition,as a second messenger,it activates intracellular important calcium-dependent proteases.However,Ca2+ overload caused by I/R injury is one of the main mechanisms for its development.The mitochondrial calcium uniporter(MCU)is a calcium-dependent protein localized in the mitochondrial inner membrane.Its expression and functional status not only affect the uptake of Ca2+ by mitochondria,but also cause the redistribution of intracellular Ca2+.In turn,intracellular calcium-dependent proteases such as calpain are activated.Calpain belongs to the family of calcium-dependent cysteine proteases.However,the role of MCU/calpain in acute I/R injury remains unclear.In cultured Neonatal rat ventricular cardiomyocytes,hypoxia/reoxygenation(H/R,12/3h)increased MCU expression and induced mitochondrial fission and cardiomyocyte apoptosis,concomitant with the activation of calpain.These effects of H/R on cardiomyocytes were abolished by pharmacological MCU inhibitors(Ru360,a specific inhibitor of MCU),knockdown of MCU using si RNA.The effect of MCU on mitochondrial fission and cardiomyocyte apoptosis was abrogated by PD150606(a selective inhibitor of calpain)or overexpression calpastatin(a calpain endogenous inhibitor),which suggested that calpain was involved in myocardial injury.Furthermore,blocking mitochondrial fission prevented cardiomyocyte apoptosis partly in H/R-stimulated cardiomyocytes.The results from in vitro experiments were consistent with those from Ru360 treated wild-type mice and transgenic calpastatin(Tg-CAST)mice.The present investigation was the first to highlight the key role of MCU/calpains in acute I/R injury,and our results indicated that MCU/calpains might be a potential therapeutic target for the treatment of I/R injury.Calpain has been playing an important physiological and pathological role with its unique cleavage function.OPA1 is well known as a mitochondrial fusion protein,and OPA1 is involved in mitochondrial inner membrane fusion.Drp1 is a mitochondrial fission protein that is phosphorylated and then transferred to mitochondria,which acts on mitochondrial mitochondria in vitro.After mitochondrial fission,a large number of pro-apoptotic substances,such as cytochrome c,are released,and this dynamic imbalance of mitochondria can aggravate apoptosis.