Type I interferon signaling and direct cardiomyocyte damages in the pathogenesis of enteroviral myocarditis

Viral myocarditis is an inflammatory heart disease caused by viral infection. CVB3 (coxsackievirus B3) is the predominant pathogen for myocarditis. It is generally proposed that both direct cardiac injury and virus-activated immune response contribute to the pathogenesis of viral myocarditis. However, the molecular determinants mediating the underlying mechanisms remain unclear. ICDs (Intercalated Discs) are substantial connections maintaining cardiac structure and mediating signal communication among cardiomyocytes. NFAT5 (Nuclear factor of activated T-cells 5) is an osmosensitive transcription factor that has been studied well in kidney but rarely in the heart, an organ usually not presented to hypertonic condition as the kidney. Previous studies have shown that NFAT5 protein has antiviral activity but is cleaved during CVB3 infection. Thus, the main objective of this dissertation is to delineate the interplay between direct cardiac damage and NFAT5-mediated innate immune response in CVB3 infected conditions. I hypothesize that 1) CVB3 infection induces destruction of ICD structure by decreasing its key proteins and thus damaging cardiomyocytes; 2) CVB3-induced reduction of NFAT5 leads to the perturbation of immune response, which benefits viral replication and enhances viral pathogenesis. In this dissertation, I first performed studies using HL-1 mouse cardiomyocytes and found that desmosomal proteins, γ-catenin, desmocollin-2, and desmoglein-2, were reduced after CVB3 infection. Since γ-catenin shares high sequence homology with β-catenin in binding with the TCF/LEF transcription factor, I further determined that degradation of γ-catenin benefited Wnt/β-catenin signaling and supressed activation of IFNB1 (type I interferon beta). I further generated a cardiac specific NFAT5 knockout (KO) mouse model by using a tamoxifen-inducible Cre-LoxP system. RNA-seq results showed that IFNB1 and many other antiviral cytokines and chemokines were downregulated due to the deficiency of NFAT5. Also, more cardiac damages and inflammatory immune infiltrates were observed in CVB3-infected NFAT5 KO mice heart than in control mice. Finally, I found that NFAT5 deficiency suppressed the formation of antiviral stress granules and benefited viral replication. Taken together, my study shed light on the mechanisms underlying how CVB3 induces viral myocarditis by both direct cardiac injury and perturbation of innate immune response, and thus provided potential therapeutic strategies against CVB3-induced heart diseases.Medicine, Faculty ofPathology and Laboratory Medicine, Department ofGraduat