ETS translocation variant 5 (ETV5) promotes CD4+ T cell–mediated intestinal inflammation and fibrosis in inflammatory bowel diseases

E26 transformation-specific translocation variant 5 (ETV5) has been implicated in the pathogenesis of inflammatory bowel diseases (IBD). However, the exact roles of ETV5 in regulating CD4⁺ T cell–mediated intestinal inflammation and fibrosis formation remain unclear. Here, we reveal that ETV5 overexpression induced interleukin (IL)-9 and its transcription factor IRF4 expression in IBD CD4⁺ T cells under T helper type 9 (Th9) cells–polarizing conditions. The silencing of IRF4 inhibited ETV5-induced IL-9 expression. CD4⁺ T cell–specific ETV5 deletion ameliorated intestinal inflammation and fibrosis in trinitrobenzene sulfonic acid (TNBS)–induced experimental colitis and CD4⁺ T cell–transferred recombination-activating gene-1 knockout (Rag1^−/−) colitis mice, characterized by less CD4⁺ T cell infiltration and lower fibroblast activation and collagen deposition in the colonic tissues. Furthermore, IL-9 treatment aggressive TNBS–induced intestinal fibrosis in CD4⁺ T cell–specific ETV5 deletion and wild-type control mice. In vitro, human intestinal fibroblasts cocultured with ETV5 overexpressed-Th9 cells expressed higher levels of collagen I and III, whereas an inclusion of anti-IL-9 antibody could reverse this effect. Ribonucleic acid sequencing analysis demonstrated that IL-9 upregulated TAF1 expression in human intestinal fibroblasts. Clinical data showed that number of α-smooth muscle actin⁺TAF1⁺ fibroblasts are higher in inflamed mucosa of patients with IBD. Importantly, TAF1 small interfering ribonucleic acid treatment suppressed IL-9–mediated profibrotic effect in vitro. These findings reveal that CD4⁺ T cell–derived ETV5 promotes intestinal inflammation and fibrosis through upregulating IL-9–mediated intestinal inflammatory and fibrotic response in IBD. Thus, the ETV5/IL-9 signal pathway in T cells might represent a novel therapeutic target for intestinal inflammation and fibrosis in IBD.