Phillygenin ameliorates tight junction proteins reduction, fibrosis, and apoptosis in mice with chronic colitis via TGR5-mediated PERK-eIF2α-Ca²⁺ pathway

Ulcerative colitis (UC) is an idiopathic, relapsing, and etiologically complicated chronic inflammatory bowel disease. Despite substantial progress in the management of UC, the outcomes of mucosal barrier repair are unsatisfactory. In this study, phillygenin (PHI) treatment alleviated the symptoms of chronic colitis in mice, including body weight loss, severe disease activity index scores, colon shortening, splenomegaly, oxidative stress, and inflammatory response. In particular, PHI treatment ameliorated the tight junction proteins (TJs) reduction, fibrosis, apoptosis, and intestinal stem cell activity, indicating that PHI exerted beneficial effects on the intestinal mucosal barrier in mice with chronic colitis. In the NCM460 cells damage model, dextran sulfate sodium triggered the sequential induction of TJs reduction, fibrosis, and apoptosis. Takeda G protein-coupled receptor-5 (TGR5) dysfunction mediated NCM460 cell injury. Moreover, PHI treatment enhanced TJs and suppressed fibrosis and apoptosis to maintain NCM460 cell function, depending on TGR5 activation. PHI promoted TGR5 activation and elevated intracellular cyclic adenosine monophosphate levels in HEK 293T cells transfected with TGR5 expression plasmids. Cellular thermal shift assay and molecular docking studies confirmed that PHI directly binds to TGR5, indicating that PHI is an agonist of TGR5. The process of PERK-eIF2α pathway-mediated endoplasmic reticulum Ca²⁺ release was involved in NCM460 cell injury as well, which was associated with TGR5 dysfunction. When NCM460 cells were pretreated with PHI, the PERK-eIF2α pathway and elevated Ca²⁺ levels were blocked. In conclusion, our study demonstrated a novel mechanism that PHI inhibited the PERK-eIF2α-Ca²⁺ pathway through TGR5 activation to against DSS-induced TJs reduction, fibrosis, and apoptosis.