Novel Translational Animal Model Of Pediatric Viral Myocarditis

Myocarditis is a heart condition characterized by inflammation of cardiac myocytes. This inflammation is instigated by the activation of both the innate and acquired immune responses and is most often caused by viruses (flu, hand foot and mouth and COVID-19). Myocarditis may progress to dilated cardiomyopathy (DCM), a chronic heart condition in which fibrosis and remodeling weakens the ability of the heart to effectively pump. Myocarditis is a leading cause of sudden death in children and young adults. In this study, we investigated the progression and severity of myocarditis within the pediatric population as compared to an adult population. Prior to this study there were no mouse models for pediatric myocarditis but a large percent of patients with myocarditis are children. We utilized our knowledge from our adult mouse model of coxsackievirus B3 (CVB3) myocarditis to create a pediatric CVB3 myocarditis model in order to better understand the development of myocarditis in children. We hypothesized that myocarditis would have sex-specific differences in the manifestation and severity similar to the adult model but the mechanisms of disease would very between ages. We utilized 4-week-old male and female BALB/c mice to model pediatric myocarditis as compared to 8-week-old mice. Mice were be infected with heart-passaged CVB3 intraperitoneally (ip) on day (d) 0. Disease severity and progression was evaluated during acute myocarditis (d8-12 pi) and during DCM (d35pi). After anesthesia, body weight, heart weight and tibia length, blood, hearts, pancreas and spleens were harvested. Echocardiography was conducted on mice at the chronic DCM timepoint. We found that adult male and female mice develop myocarditis with male mice have more severe disease and progress to DCM as compared to female mice. The main immune cells and pathways involved in myocarditis severity were macrophages, complement and the inflammasome in male adult mice. This increase in disease was driven by testosterone and reduced by estrogen as seen utilizing gonadectomies. In the pediatric population we did not see as drastic of differences in sex hormone levels as the mice are pre-pubescent, this led to less dramatic sex differences in disease and altered immune mechanisms leading to disease in the pediatric population compared to the adults. We do see induction of myocarditis in both male and female pediatric mice compared to uninfected controls but severity in the pediatric population is less than adult population. Successful development of a pediatric translational mouse model of viral myocarditis will significantly impact the myocarditis field by allowing the ability to assess differences between pediatric and adult populations and develop targeted diagnostics and treatments. Myocarditis is a heart condition characterized by inflammation of cardiac myocytes. This inflammation is instigated by the activation of both the innate and acquired immune responses and is most often caused by viruses (flu, hand foot and mouth and COVID-19). Myocarditis may progress to dilated cardiomyopathy (DCM), a chronic heart condition in which fibrosis and remodeling weakens the ability of the heart to effectively pump. Myocarditis is a leading cause of sudden death in children and young adults. In this study, we investigated the progression and severity of myocarditis within the pediatric population as compared to an adult population. Prior to this study there were no mouse models for pediatric myocarditis but a large percent of patients with myocarditis are children. We utilized our knowledge from our adult mouse model of coxsackievirus B3 (CVB3) myocarditis to create a pediatric CVB3 myocarditis model in order to better understand the development of myocarditis in children. We hypothesized that myocarditis would have sex-specific differences in the manifestation and severity similar to the adult model but the mechanisms of disease would very between ages. We utilized 4-week-old male and female BALB/c mice to model pediatric myocarditis as compared to 8-week-old mice. Mice were be infected with heart-passaged CVB3 intraperitoneally (ip) on day (d) 0. Disease severity and progression was evaluated during acute myocarditis (d8-12 pi) and during DCM (d35pi). After anesthesia, body weight, heart weight and tibia length, blood, hearts, pancreas and spleens were harvested. Echocardiography was conducted on mice at the chronic DCM timepoint. We found that adult male and female mice develop myocarditis with male mice have more severe disease and progress to DCM as compared to female mice. The main immune cells and pathways involved in myocarditis severity were macrophages, complement and the inflammasome in male adult mice. This increase in disease was driven by testosterone and reduced by estrogen as seen utilizing gonadectomies. In the pediatric population we did not see as drastic of differences in sex hormone levels as the mice are pre-pubescent, this led to less dramatic sex differences in disease and altered immune mechanisms leading to disease in the pediatric population compared to the adults. We do see induction of myocarditis in both male and female pediatric mice compared to uninfected controls but severity in the pediatric population is less than adult population. Successful development of a pediatric translational mouse model of viral myocarditis will significantly impact the myocarditis field by allowing the ability to assess differences between pediatric and adult populations and develop targeted diagnostics and treatments.