Objective MicroRNA (miR)-301a is known to be involved in the tumourigenesis and pathogenesis of several autoimmune diseases, but it remains unclear whether miR-301a is associated with the pathogenesis of IBD. Methods miR-301a expression was assessed in peripheral blood mononuclear cells (PBMC) and inflamed mucosa of patients with IBD by quantitative real-time-PCR. Peripheral blood CD4+ T cells were transduced with lentivirus-encoding pre-miR-301a (LV-miR-301a) or a reverse complementary sequence of miR-301a (LV-anti-miR-301a), and their differentiation and activation were investigated in vitro. Antisense miR-301a was administered into mice during trinitrobenzene sulphonic acid (TNBS)-induced colitis to determine its role in colitis. Results miR-301a expression was significantly upregulated in PBMC and inflamed mucosa of patients with IBD compared with healthy controls. Stimulation with tumour necrosis factor-α (TNF-α) significantly enhanced miR-301a expression in IBD CD4+ T cells, which was markedly reversed by anti-TNF-α mAb (Infliximab) treatment. Transduction of LV-miR-301a into CD4+ T cells from patients with IBD promoted the Th17 cell differentiation and TNF-α production compared with the cells with expression of LV-anti-miR-301a. SNIP1 as a functional target of miR-301a was reduced in miR-301a expression but increased in LV-anti-miR-301a expression. Knockdown of SNIP1 could enhance Th17 cell differentiation. Furthermore, intracolonical administration of antisense miR-301a in TNBS-induced mouse colitis model significantly decreased numbers of interleukin (IL)-17A<sup>+</sup> cells and amounts of pro-inflammatory cytokines (eg, IL-17A, TNF-α) in inflamed colon. Conclusions Our data reveal a novel mechanism in which the elevated miR-301a in PBMC and inflamed mucosa of IBD promotes Th17 cell differentiation through downregulation of SNIP1. Blockade of miR-301a in vivo may serve as a novel therapeutic approach in the treatment of IBD.
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