MicroRNA‐9a‐5p inhibits mucosal barrier injury in inflammatory bowel disease

Abstract Our previous research found that FOXO1 aggravates the mucosal barrier injury in inflammatory bowel disease (IBD) by regulating TLR4/MD2 signaling. In this study, we further reveal the mechanism of action whereby miRNA‐9a‐5p inhibits the mucosal barrier injury after regulating FOXO1. An IBD model was established in C57BL/6N mice using dextran sulfate sodium (DSS). The effects of endogenous miRNA‐9a‐5p were mimicked/antagonized by intraperitoneally injecting miRNA‐9a‐5p agomir and antagomir. Body weights of mice were monitored and the disease activity index scores were assessed. H&E staining was performed to examine pathological changes, while immunohistochemical (IHC) staining was conducted to measure the expressions of TJ proteins (ZO‐1, Occludin), as well as FOXO1 and TLR4. The mucosal permeability was assessed by FITC‐D, the tissue inflammatory cytokines were detected by enzyme linked immunosorbent assay, and the expressions of ZO‐1 and Occludin were measured through Western blot analysis. Caco‐2 cells were cultured in vitro to establish a monolayer model of the mucosal barrier. TNF‐α was used to induce the cell damage, while agomir and antagomir were transfected to mimic/antagonize the miRNA‐9a‐5p action, followed by determination of barrier permeability. There was a targeted regulatory relationship between MiRNA‐9a‐5p and FOXO1. MiRNA‐9a‐5p could suppress the FOXO1 expression, thereby downregulating the TLR4 signaling activation, inhibiting the mucosal barrier injury, and elevating the expressions of TJ proteins. We also found in Caco‐2 cells that miRNA‐9a‐5p could protect cells from inflammatory injury and reduce permeability. In rescue experiments, the effect of agomir was found inhibited by the overexpression of FOXO1 in agomir‐treated cells. This study found that miRNA‐9a‐5p could inhibit the TLR4 signaling activation by targeting FOXO1, thereby exerting a protective effect on the mucosal barrier injury in IBD.