Inactivation of TOPK Caused by Hyperglycemia Blocks Diabetic Heart Sensitivity to Sevoflurane Postconditioning by Impairing the PTEN/PI3K/Akt Signaling

The cardioprotective effect of sevoflurane postconditioning (SPostC) is lost in diabetes that is associated with cardiac phosphatase and tensin homologue on chromosome 10 (PTEN) activation and phosphoinositide 3-kinase (PI3K)/Akt inactivation. T-LAK cell-originated protein kinase (TOPK), a mitogen-activated protein kinase- (MAPKK-) like serine/threonine kinase, has been shown to inactivate PTEN (phosphorylated status), which in turn activates the PI3K/Akt signaling (phosphorylated status). However, the functions of TOPK and molecular mechanism underlying SPostC cardioprotection in nondiabetes but not in diabetes remain unknown. We presumed that SPostC exerts cardioprotective effects by activating PTEN/PI3K/Akt through TOPK in nondiabetes and that impairment of TOPK/PTEN/Akt blocks diabetic heart sensitivity to SPostC. We found that in the nondiabetic C57BL/6 mice, SPostC significantly attenuated postischemic infarct size, oxidative stress, and myocardial apoptosis that was accompanied with enhanced p-TOPK, p-PTEN, and p-Akt. These beneficial effects of SPostC were abolished by either TOPK kinase inhibitor HI-TOPK-032 or PI3K/Akt inhibitor LY294002. Similarly, SPostC remarkably attenuated hypoxia/reoxygenation-induced cardiomyocyte damage and oxidative stress accompanied with increased p-TOPK, p-PTEN, and p-Akt in H9c2 cells exposed to normal glucose, which were canceled by either TOPK inhibition or Akt inhibition. However, either in streptozotocin-induced diabetic mice or in H9c2 cells exposed to high glucose, the cardioprotective effect of SPostC was canceled, accompanied by increased oxidative stress, decreased TOPK phosphorylation, and impaired PTEN/PI3K/Akt signaling. In addition, TOPK overexpression restored posthypoxic p-PTEN and p-Akt and decreased cell death and oxidative stress in H9c2 cells exposed to high glucose, which was blocked by PI3K/Akt inhibition. In summary, SPostC prevented myocardial ischemia/reperfusion injury possibly through TOPK-mediated PTEN/PI3K/Akt activation and impaired activation of this signaling pathway may be responsible for the loss of SPostC cardioprotection by SPostC in diabetes.

Diabetes impairs the protective effects of sevoflurane postconditioning in the myocardium subjected to ischemia/ reperfusion injury in rats: important role of Drp1

Background Sevoflurane postconditioning (SevP) effectively relieves myocardial ischemia/reperfusion (I/R) injury but performs poorly in the diabetic myocardium. Previous studies have revealed the important role of increased oxidative stress in diabetic tissues. Notably, mitochondrial fission mediated by dynamin-related protein 1 (Drp1) is an upstream pathway of reactive oxygen production. Whether the ineffectiveness of SevP in the diabetic myocardium is related to Drp1-dependent mitochondrial fission remains unknown. This study aimed to explore the important role of Drp1 in the diabetic myocardium and investigate whether Drp1 inhibition could restore the cardioprotective effect of SevP. Methods In the first part of the study, adult male Sprague-Dawley rats were divided into 6 groups. Rats in the diabetic groups were fed with high-fat and high-sugar diets for 8 weeks and injected intraperitoneally with streptozotocin (35 mg/kg). Myocardial I/R was induced by 30 min of occlusion of the left anterior descending branch of the coronary artery followed by 120 min of reperfusion. SevP was applied by continuous inhalation of 2.5 % sevoflurane 1 min before reperfusion, which lasted for 10 min. In the second part of the study, we applied mdivi-1 to investigate whether Drp1 inhibition could restore the cardioprotective effect of SevP in the diabetic myocardium. The myocardial infarct size, mitochondrial ultrastructure, apoptosis index, SOD activity, MDA content, and Drp1 expression were detected. Results TTC staining and TUNEL results showed that the myocardial infarct size and apoptosis index were increased in the diabetic myocardium. However, SevP significantly alleviated myocardial I/R injury in the normal myocardium but not in the diabetic myocardium. Additionally, we found an elevation in Drp1 expression, accompanied by more severe fission-induced structural damage and oxidative stress in the diabetic myocardium. Interestingly, we discovered that the beneficial effect of SevP was restored by mdivi-1, which significantly suppressed mitochondrial fission and oxidative stress. Conclusions Our study demonstrates the crucial role of mitochondrial fission dependent on Drp1 in the diabetic myocardium subjected to I/R, and strongly indicates that Drp1 inhibition may restore the cardioprotective effect of SevP in diabetic rats.

Diabetes impairs the protective effects of sevoflurane postconditioning in myocardium subjected to ischemia/reperfusion injury in rats: important role of Drp1

Background Sevoflurane postconditioning (SevP) is an effective way in relieving myocardial ischemia/reperfusion (IR) injury, which doesn’t work well in diabetic myocardium unfortunately. Prior studies have noted the importance of increasing oxidative stress in diabetic tissues. Noteworthily, mitochondrial fission mediated by dynamin-related protein 1 (Drp1) is an upstream pathway of reactive oxygen production. Whether Drp1 dependent mitochondrial fission is associated with the ineffectiveness of SevP in diabetic myocardium remains unknown. The aim of this study was to explore the important role of Drp1 in diabetic myocardium and investigate whether Drp1 inhibition could restore the cardioprotective effect of SevP. Methods In the first part, adult male Sprague-Dawley(SD) rats were divided into 6 groups. Rats in diabetic groups were fed with high-fat and high-sugar for 8 weeks, and then received a injection of streptozotocin (35 mg/kg) intraperitoneally. Myocardial IR was induced by 30 min occlusion of left anterior descending branch of coronary artery followed by 120 min reperfusion༎SevP was applied by continuous inhalation of 2.5% sevoflurane 1 min before reperfusion, which lasted for 10 min. In the second part, mdivi-1 was used to investigate whether Drp1 inhibition could restore the cardioprotective effects of SevP in diabetic myocardium against I/R injury. The myocardial infarct size, pathology, mitochondrial ultrastructure, cardiomyocyte apoptosis, total SOD activity, MDA content, and Drp1 expression were detected. Results The diabetic myocardium displayed severer injury with greater infarct size and apoptosis. Up-regulated Drp1 expression concomitant with increased mitochondrial fission and oxidative stress were observed in diabetic myocardium subjected to I/R. The deteriorated changes were alleviated in normal but not in diabetic rats. Importantly, mdivi-1 administration significantly suppressed mitochondrial fission and oxidative stress, and the beneficial effects of SevP were restored by mdivi-1. Conclusions The present study indicates a crucial role of Drp1 dependent mitochondrial fission in diabetic myocardium subjected to IR. Drp1 inhibition may be effective in restoring the effect of SevP in reducing diabetic myocardial IR injury.