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.