Implication of microRNA as a potential biomarker of myocarditis.

Myocarditis was previously attributed to an epidemic viral infection. Additional harmful reagents, in addition to viruses, play a role in its etiology. Coronavirus disease 2019 (COVID-19) vaccine-induced myocarditis has recently been described, drawing attention to vaccine-induced myocarditis in children and adolescents. Its pathology is based on a series of complex immune responses, including initial innate immune responses in response to viral entry, adaptive immune responses leading to the development of antigen-specific antibodies, and autoimmune responses to cellular injury caused by cardiomyocyte rupture that releases antigens. Chronic inflammation and fibrosis in the myocardium eventually result in cardiac failure. Recent advancements in molecular biology have remarkably increased our understanding of myocarditis. In particular, microRNAs (miRNAs) are a hot topic in terms of the role of new biomarkers and the pathophysiology of myocarditis. Myocarditis has been linked with microRNA-221/222 (miR-221/222), miR-155, miR-10a*, and miR-590. Despite the lack of clinical trials of miRNA intervention in myocarditis yet, multiple clinical trials of miRNAs in other cardiac diseases have been aggressively conducted to help pave the way for future research, which is bolstered by the success of recently U.S. Food and Drug Administration-approved small-RNA medications. This review presents basic information and recent research that focuses on myocarditis and related miRNAs as a potential novel biomarker and the therapeutics.