Virus myocarditis (VMC) is a common cardiovascular disease and a major cause of sudden death in young adults. However, there is still a lack of effective treatments. Our previous studies found that calpain activation was involved in VMC pathogenesis. This study aims to explore the underlying mechanisms further. Neonatal rat cardiomyocytes (NRCMs) and transgenic mice overexpressing calpastatin (Tg-CAST), the endogenous calpain inhibitor, were used to establish VMC model. Hematoxylin and eosin and Masson staining revealed inflammatory cell infiltration and fibrosis. An ELISA array detected myocardial injury. Cardiac function was measured using echocardiography. CVB3 replication was assessed by capsid protein VP1. Apoptosis was measured by TUNEL staining, flow cytometry, and western blot. The endoplasmic reticulum (ER) stress-related proteins were detected by western blot. Our data showed that CVB3 infection resulted in cardiac injury, as evidenced by increased inflammatory responses and fibrosis, which induced myocardial apoptosis. Inhibiting calpain, both by PD150606 and calpastatin overexpression, could attenuate these effects. Furthermore, ER stress was activated during CVB3 infection. However, calpain inhibition could downregulate some ER stress-associated protein levels such as GRP78, pancreatic ER kinase-like ER kinase (PERK), and inositol-requiring enzyme-1α (IRE-1α), and ER stress-related apoptotic factors, during CVB3 infection. In conclusion, calpain inhibition attenuated CVB3-induced myocarditis by suppressing ER stress, thereby inhibiting cardiomyocyte apoptosis.

病毒性心肌炎（VMC）是一种常见的心血管疾病，也是青壮年猝死的主要原因。然而，目前仍缺乏有效的治疗方法。我们之前的研究发现钙蛋白酶激活参与了VMC的发病机制。本研究旨在进一步探讨其潜在机制。使用新生大鼠心肌细胞（NRCM）和过表达钙蛋白酶抑制素（Tg-CAST）（内源性钙蛋白酶抑制剂）的转基因小鼠建立VMC模型。苏木精和伊红以及马森染色显示炎症细胞浸润和纤维化。 ELISA 阵列检测到心肌损伤。使用超声心动图测量心脏功能。通过衣壳蛋白 VP1 评估 CVB3 复制。通过TUNEL染色、流式细胞术和蛋白质印迹来测量细胞凋亡。通过蛋白质印迹法检测内质网（ER）应激相关蛋白。我们的数据表明，CVB3 感染会导致心脏损伤，炎症反应和纤维化增加，从而诱导心肌细胞凋亡。通过 PD150606 和钙蛋白酶抑制素过度表达抑制钙蛋白酶，可以减弱这些作用。此外，CVB3 感染期间内质网应激被激活。然而，钙蛋白酶抑制可下调一些与 ER 应激相关的蛋白水平，例如 GRP78、胰腺 ER 激酶样 ER 激酶 (PERK) 和肌醇需求酶 1α (IRE-1α)，以及 ER 应激相关的凋亡因子。 CVB3 感染。总之，钙蛋白酶抑制通过抑制 ER 应激来减轻 CVB3 诱导的心肌炎，从而抑制心肌细胞凋亡。