Abstract
Previous studies suggest that the renin-angiotensin system (RAS) is a pathogenic factor for colitis. The goal of this study was to elucidate the molecular mechanism whereby angiotensin II (ANG II) promotes colonic inflammation. We found that renin was highly induced in colonic biopsies from patients with ulcerative colitis or Crohn's disease, and colonic renin and ANG II levels were markedly increased in a 2,4,6-trinitrobenzene sulfonic acid (TNBS)-induced colitis model, indicating that the colonic RAS is activated in colitis. Renin transgenic (RenTg) mice exhibited increased phosphorylation in Janus kinase-2 (JAK2) and signal transducer and activator of transcription1/3 (STAT1/3) within colonic mucosa at baseline and following TNBS induction, suggesting that ANG II promotes colonic inflammation via the JAK2/STAT1/3 pathway. Treatment with pan-JAK inhibitor tofacitinib blocked JAK2 and STAT1/3 phosphorylation, attenuated T helper (TH)1 and TH17 responses, alleviated colitis, and prevented death of RenTg mice in TNBS model. ANG II stimulated JAK2/STAT1/3 phosphorylation in both Jurkat T lymphocytes and HCT116 epithelial cells. In vitro polarization assays demonstrated that ANG II directly promoted TH17 polarization, but not TH1 polarization, via JAK2/STAT1/3. ANG II stimulation of transforming growth factor-β1 (TGFβ1), IL-6, myosin light chain kinase, and p53 upregulated modulator of apoptosis in HCT116 cells was also mediated by JAK2/STAT1/3. These observations suggest that ANG II promotes TH17 polarization directly as well as indirectly by inducing production of TH17-polarizing cytokines (e.g., TGFβ1 and IL-6) from colonic epithelial cells, both via the JAK2/STAT pathway. Therefore, colonic RAS promotes colonic inflammation, at least in part, by stimulating TH17 activation. NEW & NOTEWORTHY This study demonstrates that the local renin-angiotensin system in the colon is activated in colitis development, which promotes mucosal T helper cell activation through the JAK2/STAT pathway. These observations provide molecular evidence that the renin-angiotensin system is a pathogenic factor for the development of inflammatory bowel diseases.