Connexin43 Overexpression Exacerbates Myocardial Ischemic Reperfusion Injury in Diabetes via Modulating Cardiac Autophagy

Abstract

Background Patients with diabetes are more vulnerable to myocardial ischemia/reperfusion injury (MIRI). Abnormal increases of cardiac Connexin43 (Cx43) were shown to be associated with a variety of pathological conditions including myocardial ischemia and diabetic cardiomyopathy, concomitant with various degrees of changes in autophagy. However, the role of Cx43 in MIRI in diabetic conditions and in particular its potential interplay with cardiac autophagy in this pathology is unknown. Thus, the present study was aimed to explore the role and mechanism of Cx43 in diabetic MIRI. Methods and Results Streptozotocin (STZ)‐induced diabetic and age‐matched control rats were subjected to MIRI by occluding the left coronary artery for 30 minutes followed by 2 hours of reperfusion at 5 weeks of diabetes induction. In vitro, rat origin H9C2 cardiomyocytes (H9C2) were exposed to 35mmol/L high glucose(HG)for 48 hours(h) in the absence or presence of Cx43 gene knockdown with siRNA, followed by hypoxia for 6h and reoxygenation for 12h. Myocardial infarct size was assessed by TTC staining. Cell viability was detected by the CCK‐8 assay, apoptosis by TUNEL assay. Cardiac Cx43 protein, apoptosis‐related proteins and autophagy‐related LC3, p62 and mTOR proteins were assessed by Western blotting. Post‐ischemic myocardial infarct size and cardiac CX43 protein expression were significantly increased in diabetic rats as compared with that in the control (p<0.05), concomitant with increases in the ratio of LC3 II/I and in the protein expression of P62 and mTOR (all p<0.05). In vitro, exposure of H9C2 cells to HG significantly increased cell injury evidenced by increased LDH release and reduced cell viability, and significantly enhanced cell apoptosis and reactive oxygen species(ROS) production that was accompanied by increased cardiomyocyte CX43 overexpression and enhanced autophagy but paradoxically also enhanced mTOR activation, similar to that seen in vivo. All these changes were further exacerbated following H/R under HG. Cx43 Knockdown in H9C2 results in decreased ROS production and decreased apoptosis after H/R under HG leading to increased cell viability (all p<0.05), while Cx43 knockdown attenuated autophagy. Application of the selective mTOR inhibitor rapamycin abolished the abovementioned beneficial effects of Cx43 Knockdown. Conclusion Overexpressed CX43 in the diabetic heart exacerbates MIRI in diabetes through enhanced cardiac autophagy under hyperglycemic condition.

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“… 172 , 230 Similarly, patients with diabetes are vulnerable to myocardial ischemia and diabetic cardiomyopathy and the expression of Cx43 is abnormally increased. 231 …”

“…172,230 Similarly, patients with diabetes are vulnerable to myocardial ischemia and diabetic cardiomyopathy and the expression of Cx43 is abnormally increased. 231 Based on studies in transgenic mice, it has been found that the differential phosphorylation of Cx43 is important for the modulation of gap junction function at the intercalated disks and that remodelling of gap junctions contributes to arrhythmias by slowing the propagation of impulses. This remodelling may provide the basis for arrhythmogenesis.…”