The Role And Mechanism Of Endoplasmic Reticulum Stress In Coxsackievirus B3Induced Acute Viral Myocarditis

Objective:Acute viral myocarditis (AVMC) is defined as focal or disseminated myocardial immune inflammation caused by viral infection. Among the various infectious agents, coxsackievirus B3(CVB3) is clinically considered the dominant cause of acute viral myocarditis in humans. Clinical observation indicated that CVB3viral load, replication and persistence are directly linked with cardiac injury and progression of this disease, but its mechanism remains poorly understood. Studies have showed that endoplasmic reticulum (ER) stress and its downstream activator, C/EBP homologous protein (CHOP), play essential roles in various viral infectious diseases, which have been linked with host cell apoptosis caused by viral infection. But whether and how ER stress/CHOP signaling is linked with CVB3induced AVMC have not been determined.Methods:AVMC mice model was induced by intraperitoneal injection of CVB3virus, and pharmacological ER stress inhibitor tauroursodeoxycholic acid (TUDCA) was administrated by oral gavage to investigate whether and how ER stress contributed to AVMC development. Echocardiography and hemodynamic measurement were used to assess the cardiac function at day7after CVB3inoculation. Mice hearts and serums were harvested at day7after CVB3inoculation for further examination. Immunohistochemistry, western blot, ELISA and TUNEL analysis were used to determine cardiac inflammation, ER stress level, cardiac injury and cardiomyocyte apoptosis.Result:The AVMC group experienced a significantly reduced survival rate. Millar catheter and echocardiography analysis showed that CVB3infection significantly reduced cardiac contractility and impaired diastolic function, indicated by reduced EF, FS, dP/dt max, dP/dt min and LVSP, and increased LVEDP. Western blot analysis further showed an increased expression of the heart failure marker, ANP, in AVMC hearts. Serum cTnI level is a sensitive indicator of myocardial injury, and ELISA analysis indicated that the serum cTnI level in the AVMC group was significantly higher than that in the control group (P<0.01). In mice AVMC hearts, significant cardiomyocyte necrosis and inflammatory cells infiltration were observed, while no abnormal changes were observed in the control group. Histological staining analysis revealed that CVB3infection significantly increased cardiac pathological score and macrophages (surface marker F4/80) infiltration in heart. ER stress was significantly activated in AVMC hearts. KDEL, an ER stress marker, was exclusively overexpressed in AVMC hearts. Western blot analysis further confirmed the induction of ER stress by assessing the activation of three branches of UPR, p-PERK, p-IREla and ATF6. Cardiomyocyte apoptosis in the AVMC group was significantly increased by TUNEL assay. And western blot analysis confirmed markedly elevated CHOP expression in mice AVMC hearts, which was linked to induction of pro-apoptotic signaling including reduction of Bcl-2, activation of Bax and caspase3. However, the administration of ER stress inhibitor tauroursodeoxycholic acid (TUDCA) significantly attenuated cardiac ER stress and inflammation level, alleviated cardiac damage, ameliorated cardiac dysfunction and increased survival rate after CVB3inoculation. Moreover, TUDCA administration significantly reduced cardiac CHOP, caspase3and Bax protein levels, while increased Bcl-2protein level and reduced cardiomyocyte apoptosis. Conclusion:In CVB3virus induced AVMC mice model, ER stress and its downstream CHOP proapoptotic pathways played a role in AVMC progression through promoting cardiomyocyte apoptosis. Our study provides a novel strategy for AVMC treatment.