Hsa-miR-375 promotes the progression of inflammatory bowel disease by upregulating TLR4

To elucidate the biological function of hsa-miR-375 in the progression of inflammatory bowel disease (IBD) and the potential mechanism.

Intestinal mucosa tissues of 26 IBD patients and 30 healthy volunteers who underwent colonoscopy were harvested for determining hsa-miR-375 level by quantitative Real-time polymerase chain reaction (qRT-PCR). Binding of hsa-miR-375 to toll-like receptor 4 (TLR4) was verified by the dual-luciferase reporter gene assay. Changes in the viability and apoptosis in Caco-2 cells influenced by hsa-miR-375 were examined by cell counting kit-8 (CCK-8) assay and flow cytometry, respectively. The regulatory effect of hsa-miR-375 on the intestinal epithelial barrier was examined by detecting transepithelial electrical resistance (TEER) and lucifer yellow flux. Relative levels of TLR4, nuclear factor-kappa B (NF-κB), zonula occludens-1 (ZO-1), occludin and inflammatory factors in Caco-2 cells were detected by qRT-PCR, Western blot and enzyme-linked immunosorbent assay (ELISA).

Hsa-miR-375 was downregulated in intestinal mucosa tissues of patients with Crohn's disease (CD) and ulcerative colitis (UC). Knockdown of hsa-miR-375 decreased viability and TEER, but elevated apoptotic rate and lucifer yellow flux. Overexpression of hsa-miR-375 achieved the opposite trends. TLR4 was the direct downstream of hsa-miR-375, and its level was negatively mediated by hsa-miR-375. In addition, TLR4 level in Caco-2 cells was upregulated after LPS induction, while hsa-miR-375 level was unchangeable. Knockdown of hsa-miR-375 upregulated NF-κB and pro-inflammatory factors TNF-α, IL-1β, IL-6 and IL-8, and downregulated ZO-1, occludin and anti-inflammatory factor IL-10.

Hsa-miR-375 is involved in the pathogenesis of IBD by upregulating TLR4 and inducing NF-κB activation.