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

ETS translocation variant 5 (ETV5) has been implicated in the pathogenesis of inflammatory bowel disease (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 IL-9 and its transcription factor IRF4 expression in naïve IBD CD4+ T cells under Th9-polarizing conditions. Silencing of IRF4 inhibited ETV5-induced IL-9 expression. CD4+ T cell-specific ETV5 deletion (CKO) ameliorated intestinal inflammation and fibrosis in TNBS-induced experimental colitis and CD4+ T cell-transferred Rag1-/- colitis mice, characterized by less CD4+ T cell infiltration, lower fibroblast activation and collagen deposition in the colonic tissues. Furthermore, IL-9 treatment aggressive TNBS-induced intestinal fibrosis in CKO and wild type (WT) 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. RNA sequencing analysis demonstrated that IL-9 upregulated TAF1 expression in human intestinal fibroblasts. Clinic data showed that number of α-SMA+ TAF1+ fibroblasts are higher in inflamed mucosa of IBD patients. Importantly, TAF1 siRNA 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.