Therapeutically Targetable Th17-Derived miR-721 Drives Autoimmune Myocarditis

BACKGROUND: Myocarditis is an inflammatory cardiac disease in which T helper 17 (Th17) cell–driven immune responses contribute to progression toward dilated cardiomyopathy and heart failure. Current therapies mainly rely on corticosteroids but lack specificity, while the role of miR-721, synthesized by Th17 cells, remains largely unexplored in disease pathogenesis. METHODS: We characterized the presence of mmu-miR-721 and its human homolog hsa-RNA-Chr8:96 in extracellular vesicles secreted by Th17 cells from IL-17 (interleukin-17) eGFP mice with experimental autoimmune myocarditis and from patients with myocarditis. MxCre ± Pparg fl/fl mice and luciferase reporter assays were used to validate the target genes of miR-721 and hsa-RNA-Chr8:96, respectively. The functional role of miR-721 in experimental autoimmune myocarditis was investigated using lentiviral vectors overexpression and miRNA sponge molecules for inhibition. Th17 responses and heart inflammation were assessed, and echocardiography was performed after in vivo blockade of mmu-miR-721 in experimental autoimmune myocarditis mice. RESULTS: Both mmu-miR-721 and hsa-RNA-Chr8:96 were encapsulated in extracellular vesicles and secreted by Th17 cells of mice and patients with myocarditis. Overexpression of mmu-miR-721 in draining lymph node cells from experimental autoimmune myocarditis mice promoted Th17 differentiation via Pparg inhibition and increased RORγt and IL-17 expression. In contrast, no differences in RORγt expression were observed in the absence of Pparg , a target of miR-721, indicating that miR-721 promotes Th17 responses through Pparg repression. In addition, human PPARG was validated as a target gene of hsa-RNA-Chr8:96, as its overexpression in peripheral blood leukocytes downregulated PPARG mRNA levels, suggesting that similar pathways are involved in human pathology. Finally, in vivo blockade of mmu-miR-721 increased Pparg expression, reducing RORγt and IL-17 activation in T cells, leading to decreased leukocyte infiltration in the heart and improved cardiac function thereby ameliorating disease progression. CONCLUSIONS: miR-721 is released by Th17 cells in extracellular vesicles and promotes Th17 responses during myocarditis through repression of PPARγ, identifying this miRNA as both a mechanistic driver of disease and a potential therapeutic target.