Abstract 14287: Oxidative Activation of Ca2+/Calmodulin Activated Kinase II Mediates ER Stress Induced Cardiac Dysfunction and Apoptosis
ER stress occurs in a wide array of pathological conditions and can directly lead to cardiac dysfunction although the exact mechanisms are not well known. ER stress causes oxidative stress and release of intracellular calcium into the cytosol, both of which activate Ca2+/calmodulin activated kinase II (CaMKII) which can trigger cardiac dysfunction. We hypothesized that ER stress activates CaMKII by oxidation, leading to cardiac dysfunction and apoptosis which may be reversed by cardiac specific catalase overexpression. The ER stressor tunicamycin was injected (3mg/kg, i.p., 48 hrs) into FVB wild-type and cardiac specific catalase overexpression mice. In vivo heart function was assessed by echocardiography and protein levels were assessed by immunoblotting. Reactive oxygen species (ROS) and TUNEL labeling were performed in tissue sections. Cardiomyocyte contractile and intracellular calcium properties were assessed in cardiomyocytes from FVB and catalase mice treated with tunicamycin (3µg/ml, 3 hrs) in the absence or presence of the CaMKII specific inhibitor KN93. Echocardiographic analysis revealed that tunicamycin depressed fractional shortening (53±2 vs. 41±4) which was alleviated by catalase overexpression (n=5-7, p<0.05). Tunicamycin stimulated ROS production (52.9±4.6 vs. 92.7±4.4) and CaMKII oxidation (1.8±0.1 vs. 2.4±0.2), decreased BCL-2/Bax ratio (1.5±0.2 vs. 0.7±0.1) and increased TUNEL positive nuclei (2.5±0.3 vs. 4.0±0.6) which were obliterated by catalase overexpression (n=3-4, p<0.05). Single myocyte function showed tunicamycin decreased peak shortening, and maximal velocity of shortening/relengthening and prolonged time to relengthening and were mitigated by KN93 or catalase overexpression (n=96-150 cells, p<0.05), however tunicamycin induced increased cytosolic calcium levels and increased calcium transients were unaffected by KN93 or catalase overexpression (n=50-60 cells, p<0.05). In conclusion, overexpression of catalase or CaMKII inhibition was able to prevent ER stress induced cardiac contractile dysfunction, oxidation of CaMKII, and apoptosis but not changes in calcium cycling suggesting that oxidative activation of CaMKII is required for ER stress-induced cardiac contractile dysfunction.
- © 2011 by American Heart Association, Inc.