Interferon Regulatory Factor 4 (IRF4) Promotes Lipopolysaccharide-Induced Colonic Mucosal Epithelial Cell Proliferation by Regulating Macrophage Polarization

Abstract

Introduction: Ulcerative colitis (UC) is a chronic disease characterized by diffuse inflammation of the mucosa of colon and rectum. Interferon regulatory factor 4 (IRF4) mediates macrophage anti-inflammatory phenotype (alternatively activated macrophages [M2]). This study aimed to investigate the mechanism of IRF4 in lipopolysaccharide (LPS)-induced colonic mucosal epithelial cell proliferation via the regulation of macrophage polarization. Methods: Human bone marrow-derived macrophages were subjected to interleukin 4 (IL-4) induction. M2 macrophages were identified using flow cytometry and quantitative real-time polymerase chain reaction (qRT-PCR). IRF4 expression in M2 macrophages was detected using Western blot and qRT-PCR. IRF4 expression was silenced in M2 macrophages. IL-10 mRNA expression and protein level were detected using qRT-PCR and Western blot. The binding relation between IRF4 and IL-10 was verified using dual-luciferase and chromatin immunoprecipitation assays. Macrophages under different treatments were cocultured with LPS-induced human colonic mucosal epithelial cells. The levels of inflammatory factors (TNF-α, IL-6, and IL-1β) were detected using enzyme-linked immunosorbent assay. The proliferation of inflammatory cells was measured using Cell Counting Kit-8 assay, and the healing of inflammatory cells was detected using wound healing assay. Results: M2 macrophages alleviated LPS-induced inflammatory responses. IRF4 bound to IL-10 and promoted IL-10 expression. Inhibition of IRF4 reduced IL-10 expression and attenuated the alleviating effect of M2 macrophages on inflammatory responses. Inhibition of IRF4 combined with IL-10 overexpression enhanced the promoting effect of M2 macrophages on inflammatory healing. Conclusion: IRF4 promoted colonic mucosal epithelial cell proliferation by increasing IL-10 expression and regulating macrophage polarization to M2 phenotype, which might be related to UC mucosal healing.