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.