NF-κB-driven miR-34a impairs Treg/Th17 balance via targeting Foxp3

The subset of regulatory T (Treg) cells, with its specific transcription Foxp3, is a unique cell type for the maintenance of immune homeostasis by controlling effector T (Teff) cell responses. Although it is common that a defect in Treg cells with Treg/Teff disorder causes autoimmune diseases; however, the precise mechanisms are not thoroughly revealed. Here, we report that miR-34a could attenuate human and murine Foxp3 gene expression via targeting their 3' untranslated regions (3' UTR). The human miR-34a, increased in peripheral blood mononuclear cells (PBMCs) and CD4⁺ T cells from rheumatoid arthritis (RA) or systemic lupus erythematosus (SLE) patients, displayed a positive correlation with some serum markers of inflammation including rheumatoid factor (RF), anti-streptolysin antibody (ASO), erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) as well as Th17 signature gene RORγt, but inversely correlated with the mRNA expression levels of FOXP3. In addition, murine miR-34a levels were downregulated in TGF-β-induced Treg cells but upregulated in Th17 cells induced in vitro compared to activated CD4⁺ T cells. It has also been demonstrated that elevated miR-34a disrupting Treg/Th17 balance in vivo contributed to the progress of pathogenesis of collagen induced arthritis (CIA) mice. Furthermore, IL-6 and TNF-α were responsible for the upregulation of miR-34a and downregulation of Foxp3, which was reverted by the addition of NF-κB/p65 inhibitor BAY11-7082, thus indicating that NF-κB/p65 inhibited Foxp3 expression in an miR-34a-dependent manner. Finally, IL-6 or TNF-α-activated p65 could bind to the miR-34a promotor and enhance its activity, resulting in upregulation of its transcription. Taken together, we show that NF-κB activated by inflammatory cytokines, such as IL-6 and TNF-α, ameliorates Foxp3 levels via regulating miR-34a expression, which provides a new mechanistic and therapeutic insight into the ongoing of autoimmune diseases.