The role of protein kinase C beta 2 (PKC β2) in myocardial ischaemia-reperfusion injury

Background: Myocardial ischaemia and reperfusion (I/R) injury, a major global public health problem, is associated with significant morbidity and mortality. Diabetic hearts are more sensitive to I/R and consequently are associated with greater morbidity and mortality, while a number of cardioprotective interventions such as ischaemia preconditioning and ischaemia post-conditioning are partly lost or are completely abolished in diabetes. Objectives: I investigated the role of protein kinase C beta 2 (PKC β2) in diabetes induced heart sensitization after I/R and explored the underlying mechanism. Also, I investigated whether remifentanil preconditioning (RPC) ameliorates myocardial infarct size in diabetic rats. Materials and methods: Diabetic rats model was established with streptozotocin (STZ) while ruboxistaurin (RBX), CGP-53353 (CGP), and siRNA of PKC β2 were induced in diabetic rats or high glucose-exposed H9C2 cells to investigate the relationship between PKC β2 and myocardial I/R injury with following indexes including cardiac function, myocardial infarct size, cell apoptosis, concentrations of Creatine kinase-MB (CK-MB) and lactate dehydrogenase (LDH), and mitochondrial membrane potential. The siRNA of caveolin (Cav-3) and Akt were used in H9C2 cells to detect the mechanism of PKC β2 induced aggravating myocardial I/R injury. Both in diabetic rats and high glucose-exposed H9C2 cells, cardiac protective ability of RPC were measured. The naloxone and caveolin (Cav-3) siRNA were used in RPC to detect the mechanism of RPC. The proteins expression of PKCβ2, Cav-3, Akt, and cleaved caspase 3 were measured by western blot. Results: The expression of PKC β2 was significantly up regulated in diabetes after acute myocardial I/R. In diabetic rats, RBX markedly reduced myocardial infarct size and apoptotic cells. RBX also restored left ventricular functions and decreased concentrations of CK-MB and LDH after I/R. In high glucose-exposed H9C2 cells, both CGP and PKC β2 siRNA decreased apoptotic cells and impaired mitochondrion after hypoxia and reoxygenation (H/R). Cav-3 siRNA or Akt siRNA aggravated cell apoptosis and mitochondrial injury after H/R. Proteins expression of Cav-3 and Akt were increased after RBX treatment in diabetic I/R model. Furthermore, RPC attenuated myocardial infarct size and restored cardiac systolic ability in non-diabetic rats. RPC decreased apoptotic cardiomyocytes and attenuated mitochondrial injury in cultured cardiomyocytes. Activation of Akt and Bcl-2 were involved in RPC. Naloxone and Cav-3 siRNA blocked the cardioprotection of RPC against myocardial I/R injury. RPC failed to ameliorate myocardial infarct size in diabetic rats and did not decrease high glucose-exposed H9C2 cell apoptosis after H/R. Conclusions: The high expression of PKC β2 contributed to diabetic hearts being more sensitive to I/R. RBX ameliorates myocardial I/R injury by attenuating post-reperfusion myocardial infarct size and cardiac dysfunction. The plausible mechanism underlying the RBX-induced cardioprotection was through the regulation of PKCβ2-mediated signalling pathway in apoptosis under the hyperglycaemic conditions. Cav-3 level was important for PKCβ2-mediated cardioprotection of Akt activation. Low expression of Cav-3 in diabetes might be an essential reason why RPC failed to provide cardiac protection in diabetes.published_or_final_versionAnaesthesiologyDoctoralDoctor of Philosoph