Abstract 9345: Midline1 is a Critical Regulator of Viral Myocarditis

Abstract

Introduction: Infections by viruses including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) could cause viral myocarditis. Innate immunity to viral nucleic acids mediates antiviral immunity as well as inflammatory organ injury. However, the innate immune mechanisms that control the pathogenesis of viral myocarditis are unclear. Methods: To understand the role of the E3 ligase Midline1 in controlling viral myocarditis, wild-type and Midline1 knockout mice were infected with coxsackievirus B3 (CVB3) or encephalomyocarditis (EMCV) for inducing viral myocarditis. Mice survivals and heart functions were monitored by transthoracic echocardiography, and hearts were harvested for histology analysis. Real-time PCR, western blotting, co-immunoprecipitation, enzyme-linked immunoassay, luciferase assay, flow cytometry, over-expression and knockdown techniques were used to understand the molecular mechanisms of Midline1 in regulating type I interferon production after virus infection in this study. Results: We find that Midline1 is induced by RNA viruses with heart tropisms CVB3 and EMCV. Knockdown or deletion of Midline1 in human or mouse macrophages enhances production of type I interferon (IFN) in response to double strand (ds) RNA, RNA viruses CVB3 or EMCV. Importantly, deletion of Midline1 protects mice from viral myocarditis induced by CVB3 or EMCV due to enhanced type I IFN production in vivo. Mechanistically, we show that Midline1 recruits protein phosphatase 1A (PPM1A) to dephosphorylate TANK binding kinase 1 (TBK1), which inactivates TBK1 to block TBK1 from interacting with its upstream adaptor mitochondrial antiviral signaling (MAVS), thereby dampening antiviral signaling during viral infections. Moreover, Midline1 stabilizes PPM1A by inducing K63-linked ubiquitination of PPM1A. Conclusions: Our results indicate that Midline1 serves as a negative regulator of viral myocarditis by downregulating innate immune activation induced by RNA viruses CVB3 and EMCV. Our data reveal that Midline1 is a critical regulator of innate immunity in viral myocarditis, thereby identifying a potential therapeutic target for treating viral induced cardiovascular diseases.