Abstract 18247: Inhibition of PKCβ2 Attenuates Myocardial Ischemia Reperfusion Injury in Diabetic Rat Through Cavolin-3-dependant Akt Activation

Abstract

Background: Activation of PKCβ has been shown to play a critical role in myocardial ischemia/reperfusion (MI/R) injury in hearts from non-diabetic rodents. Our recent studies showed that PKCβ2 is overexpressed in the myocardium of diabetic rats that were associated with more severe post-ischemic MI/R injury relative to non-diabetic rats. We hypothesized that myocardial PKCβ overexpression is a major contributor responsible for the exacerbation of MI/R injury in diabetes and that PKCβ inhibition can attenuate MI/R injury in diabetes. Methods and results: Five-week streptozotocin-induced diabetic rats were treated with the selective PKCβ inhibitor ruboxistaurin (RBX, 1 mg/kg/day delivered via oral gavage) for 4 weeks, starting from 1 week after diabetes induction, before inducing MI/R achieved by 30 min of left descending coronary artery ligation followed by 2 hours of reperfusion. Cardiac function was measured using pressure-volume conductance system. In in vitro study, cardiac H9C2 cells were exposed to high glucose (30 mM/L) and subjected to 4 hours hypoxia followed by 4 hours reoxygenation (H/R) in the with or without selective PKCβ2 inhibitor CGP53353 (1 mol/L), siRNAs of PKCβ2 or Caveolin (Cav)-3. Cell apoptosis and mitochondrial transmembrane potential were respectively assessed by TUNEL and JC-1 staining. At the end of reperfusion, RBX significantly decreased myocardial infarct size (% of area at risk, 35±5% vs. 49±3% in control, P <0.05) and attenuated cardiac dysfunction, and increased cardiac protein expression of Cav-3 and phosphorylated/activated Akt (p-Akt) in diabetic rats (All P <0.05 vs. control). H/R significantly increased H9C2 cell injury under high glucose condition evidenced as increased TUNEL-positive and JC-1 monomeric cells (All P <0.05 vs. control), which was associated with increased PKCβ2 phosphorylation and decreased Cav-3 protein expression. Either CGP53353 or PKCβ2 siRNA significantly attenuated all these changes and enhanced p-Akt. Cav-3 gene knockdown significantly reduced p-Akt and increased post-hypoxic cell injury despite of concomitant reduction in PKCβ2 phosphorylation. Conclusions: PKCβ2 inhibition with RBX protects diabetic hearts from MI/R injury through Cav-3-dependent activation of Akt.