Down-regulation of microRNA-451a facilitates the activation and proliferation of CD4⁺ T cells by targeting Myc in patients with dilated cardiomyopathy

CD4⁺ T cells are abnormally activated in patients with dilated cardiomyopathy (DCM) and might be associated with the immunopathogenesis of the disease. However, the underlying mechanisms of CD4⁺ T cell activation remain largely undefined. Our aim was to investigate whether the dysregulation of microRNAs (miRNAs) was associated with CD4⁺ T cell activation in DCM. CD4⁺ T cells from DCM patients showed increased expression levels of CD25 and CD69 and enhanced proliferation in response to anti-CD3/28, indicating an activated state. miRNA profiling analysis of magnetically sorted CD4⁺ T cells revealed a distinct pattern of miRNA expression in CD4⁺ T cells from DCM patients compared with controls. The level of miRNA-451a (miR-451a) was significantly decreased in the CD4⁺ T cells of DCM patients compared with that of the controls. The transfection of T cells with an miR-451a mimic inhibited their activation and proliferation, whereas an miR-451a inhibitor produced the opposite effects. Myc was directly inhibited by miR-451a via interaction with its 3'-UTR, thus identifying it as an miR-451a target in T cells. The knockdown of Myc suppressed the activation and proliferation of T cells, and the expression of Myc was significantly up-regulated at the mRNA level in CD4⁺ T cells from patients with DCM. A strong inverse correlation was observed between the Myc mRNA expression and miR-451a transcription level. Our data suggest that the down-regulation of miR-451a contributes to the activation and proliferation of CD4⁺ T cells by targeting the transcription factor Myc in DCM patients and may contribute to the immunopathogenesis of DCM.