Mitochondrial dynamic disorder is involved in myocardial ischemia/reperfusion (I/R) injury. To explore the effect of mitochondrial calcium uniporter (MCU) on mitochondrial dynamic imbalance under I/R and its related signal pathways, a mouse myocardial I/R model and hypoxia/reoxygenation model of mouse cardiomyocytes were established. The expression of MCU during I/R increased and related to myocardial injury, enhancement of mitochondrial fission, inhibition of mitochondrial fusion and mitophagy. Suppressing MCU functions by Ru360 during I/R could reduce myocardial infarction area and cardiomyocyte apoptosis, alleviate mitochondrial fission and restore mitochondrial fusion and mitophagy. However, spermine administration, which could enhance MCU function, deteriorated the above‐mentioned myocardial cell injury and mitochondrial dynamic imbalanced. In addition, up‐regulation of MCU promoted the expression and activation of calpain‐1/2 and down‐regulated the expression of Optic atrophy type 1 (OPA1). Meantime, in transgenic mice (overexpression calpastatin, the endogenous inhibitor of calpain) I/R model and OPA1 knock‐down cultured cell. In I/R models of transgenic mice over‐expressing calpastatin, which is the endogenous inhibitor of calpain, and in H/R models with siOPA1 transfection, inhibition of calpains could enhance mitochondrial fusion and mitophagy, and inhibit excessive mitochondrion fission and apoptosis through OPA1. Therefore, we conclude that during I/R, MCU up‐regulation induces calpain activation, which down‐regulates OPA1, consequently leading to mitochondrial dynamic imbalance.

To explore the role of autophagic flux in the increased susceptibility of the experimental diabetic heart to ischaemia‐reperfusion (I/R) injury, we established STZ‐induced diabetic mice and performed I/R. In vitro, neonatal mouse cardiomyocytes were subjected to high glucose and hypoxia/reoxygenation challenge to mimic diabetic I/R injury. We found that experimental diabetes aggravated I/R‐induced injury than compared with nondiabetic mice. Autophagic flux was impaired in I/R hearts, and the impairment was exacerbated in diabetic mice subjected to I/R with defective autophagosome formation and clearance. Calpains, calcium‐dependent thiol proteases, were upregulated and highly activated after I/R of diabetes, while calpain inhibition attenuated cardiac function and cell death and partially restored autophagic flux. The expression levels of Atg5 and LAMP2, two crucial autophagy‐related proteins, were significantly degraded in diabetic I/R hearts, alterations that were associated with calpain activation and could be reversed by calpain inhibition. Co‐overexpression of Atg5 and LAMP2 reduced myocardial injury and normalized autophagic flux. In conclusion, experimental diabetes exacerbates autophagic flux impairment of cardiomyocytes under I/R stress, resulting in worse I/R‐induced injury. Calpain activation and cleavage of Atg5 and LAMP2 at least partially account for the deterioration of autophagic flux impairment.

Background: is a chronic metabolic disease characterized by hyperglycemia, which has negative effects on cardiac revascularization in patients with coronary artery disease (CAD). Methods: This study focused on the role of autophagic flux in regulating susceptibility of STZ-induced diabetic heart to ischemia-reperfusion (I/R) injury. We established STZ-induced diabetes mice and perform I/R process by coronary artery ligation, and neonatal mice cardiomyocytes culture subjected to high glucose and hypoxia/reoxygenation(H/R). Results: Diabetic heart was more sensitive to I/R injury. Autophagic flux, represented by TEM, relative LC3Ⅱ changes under CQ intervention and P62 expression, was impaired in diabetic hearts and deteriorated during subsequent I/R. Calpains were activated in diabetic I/R heart, and the inhibition of calpains partially rescued autophagic flux, cardiac function, and cell death. The expression of autophagic flux related proteins Atg5 and LAMP2 decreased significantly in diabetic I/R heart. Further studies suggested that calpain could cleave Atg5 and LAMP2, and generate cleaved fragments, which might be reversed by calpain inhibition. Inhibition of calpain，or in company with overexpression of Atg5 and LAMP2 , could reduce myocardial injury in diabetic heart subject to I/R. But overexpression of Atg5 alone could worsen the I/R injury. Conclusion: In conclusion, calpain-mediated cleavage of Atg5 and LAMP2 accounts for the impaired autophagic flux which increases the susceptibility to myocardial I/R injury in experimental diabetic mice.