Activation of CaMKII via ER-stress mediates coxsackievirus B3-induced cardiomyocyte apoptosis.

Cardiomyocyte apoptosis contributes to the development of coxsackievirus B3 (CVB3)-induced myocarditis, but the mechanism for the apoptosis by CVB3 infection remains unclear. Here, we showed that CVB3-induced endoplasmic reticulum (ER) stress response and apoptosis in cultured H9c2 cardiomyocytes. We found that Ca2+ -calmodulin-dependent kinase II (CaMKII) was activated by ER stress-dependent intracellular Ca2+ overload in the CVB3-infected H9c2 cardiomyocytes. Treatment with an inhibitor of ER stress, 4-phenylbutyric acid (4-PBA), attenuated intracellular Ca2+ accumulation indirectly and reduced CaMKII activity. Inhibition of CaMKII with pharmacological inhibitor (KN-93) or short hairpin RNA reduced CVB3-induced H9c2 apoptosis and repressed cytochrome c release from mitochondria to cytoplasm; whereas overexpression of the activated mutant of CaMKII (CaMKII-T287D) enhanced CVB3-induced H9c2 apoptosis and mitochondrial cytochrome c release, which could be alleviated by blocking of mitochondrial Ca2+ uniporter or mitochondrial permeability transition pore. Further in vivo investigation revealed that blocking of CaMKII with KN-93 prevented cardiomyocytes apoptosis and improved cardiac contractile function in CVB3-infected mouse heart. Collectively, these findings provide a novel evidence that CaMKII plays a vital role in the promotion of CVB3-induced cardiomyocyte apoptosis, which links ER stress and mitochondrial Ca2+ uptake.