Inhibition of protein kinase C βII isoform rescues glucose toxicity-induced cardiomyocyte contractile dysfunction: role of mitochondria.

Hyperglycemia leads to cytotoxicity in the heart. Although theories were postulated for glucose toxicity-induced cardiomyocyte dysfunction including oxidative stress, the mechanism involved still remains unclear. Recent evidence has depicted a role of protein kinase C (PKC) in diabetic complications while high concentrations of glucose stimulate PKC. This study examined the role of PKCβII in glucose toxicity-induced cardiomyocyte contractile and intracellular Ca(2+) aberrations. Adult rat cardiomyocytes were maintained in normal (NG, 5.5 mM) or high glucose (HG, 25.5 mM) medium for 12 h. Contractile and intracellular Ca(2+) properties were measured using a video edge-detection system including peak shortening (PS), maximal velocity of shortening/relengthening (±dL/dt), time-to-PS (TPS), time-to-90% relengthening (TR90), rise in intracellular Ca(2+) Fura-2 fluorescence intensity and intracellular Ca(2+) decay. Production of ROS/O2(-) and mitochondrial integrity were examined using fluorescence imaging, aconitase activity and Western blotting. High glucose triggered abnormal contractile and intracellular Ca(2+) properties including reduced PS, ±dL/dt, prolonged TR90, decreased electrically-stimulated rise in intracellular Ca(2+) and delayed intracellular Ca(2+) clearance, the effects of which were ablated by the PKCβII inhibitor LY333531. Inhibition of PKCβII rescued glucose toxicity-induced generation of ROS and O2(-), apoptosis, cell death and mitochondrial injury (reduced aconitase activity, UCP-2 and PGC-1α). In vitro studies revealed that PKCβII inhibition-induced beneficial effects were mimicked by the NADPH oxidase inhibitor apocynin and were canceled off by mitochondrial uncoupling using FCCP. These findings suggest the therapeutic potential of specific inhibition of PKCβII isoform in the management of hyperglycemia-induced cardiac complications.