4E-BP3 deficiency impairs dendritic cell activation and CD4+ T cell differentiation and attenuates α-myosin-specific T cell-mediated myocarditis in mice

Immune checkpoint inhibitor (ICI)-associated myocarditis is a rare but potentially fatal immune-related adverse event. Previously, we reported a case of ICI-associated myocarditis with elevated autoantibodies to 4E-binding protein 3 (4E-BP3). Recent studies have suggested that 4E-BP3 may play an important role in tumor development. However, its role in cardiac diseases including myocarditis is unknown. We investigated the role of 4E-BP3 in an autoimmune myocarditis mouse model. Myocarditis was induced in wild-type and 4E-BP3 knockout mice by immunization with murine α-myosin peptide. 4E-BP3 gene expression was upregulated in the heart of myocarditis mouse. We found that genetic deletion of 4E-BP3 attenuated myocardial inflammation, reduced fibrosis area, and improved cardiac function in myocarditis mice. Studies in bone marrow-chimeric mice demonstrated that immune cell-derived 4E-BP3 plays a pivotal role in the pathogenesis of myocarditis. Immune cell transfer experiments revealed that 4E-BP3 deficiency in dendritic cells and CD4⁺ T cells decreased disease severity in recipient mice. Furthermore, dendritic cells that were deficient in 4E-BP3 exhibited a diminished capacity to produce IL-6 and IL-1β. Naive CD4⁺ T cells lacking 4E-BP3 had a reduced ability to differentiate into T-helper (Th)1 and Th17 cells. These findings suggest that 4E-BP3 in dendritic cells and CD4⁺ T cells may be critically involved in the pathogenesis of α-myosin-specific T cell-mediated myocarditis. Thus, 4E-BP3 could be a possible therapeutic target for myocarditis.