Background: Enterovirus infection is a cause of cardiomyopathy. We previously demonstrated that enteroviral protease 2A directly cleaves the cytoskeletal protein dystrophin. However, the direct effect of protease 2A in enteroviral cardiomyopathy is less clear because other viral proteins are also expressed with viral infection.
Methods and results: A transgenic mouse with inducible cardiac-restricted expression of enteroviral protease 2A was generated. In the transgenic mouse, a tamoxifen-regulated Cre-loxP system, MerCreMer (MCM), was used to induce genetic recombination in cardiac myocytes, which led to protease 2A expression. Protease 2A and MCM double transgenic (2AxMCM) mice were treated with tamoxifen; the controls included 2AxMCM mice treated with diluents for tamoxifen and tamoxifen-treated MCM littermates. Protease 2A activity was significantly induced after tamoxifen in the 2AxMCM mice compared with controls. Echocardiographic analysis demonstrated an increase in left ventricular end-diastolic and end-systolic chamber size, with decreased fractional shortening in tamoxifen-treated 2AxMCM mice. There was an increase in heart weight-to-body weight ratio in 2AxMCM mice treated with tamoxifen. Only a small increase in interstitial fibrosis and inflammation was found in tamoxifen-treated 2AxMCM mice; however, ultrastructural analysis demonstrated myofibrillar collapse with abnormalities of intercalated discs and sarcolemmal membranes. Evans blue dye-positive myocytes with disruption of dystrophin were present in 2AxMCM mice treated with tamoxifen. Disruption of dystrophin was also found in cultured myocytes isolated from 2AxMCM mice with Cre in the nucleus.
Conclusions: Protease 2A has a significant role in enteroviral cardiomyopathy and alone is sufficient to induce dilated cardiomyopathy, which is associated with disruption of the sarcolemmal membrane and cleavage of dystrophin with protease 2A expression.