RIP3 knockdown inhibits necroptosis of human intestinal epithelial cells via TLR4/MyD88/NF-κB signaling and ameliorates murine colitis

Background: Ulcerative colitis (UC) is a common inflammatory bowel disease, during which cell Necroptosis plays key roles in driving inflammation initiation and aggravation. Previous studies reported Receptor Interacting Protein Kinase 3 (RIP3)-mediated Necroptosis in multiple diseases, and RIP3 protein in Paneth cells significantly enriched in the intestines of both humans and mice. Therefore, we hypothesized targeting RIP3 to inhibit Necroptosis may depress UC.

Methods: We classified clinical UC samples according to the modified Truelove & Witts criterion. The expression of RIP3 was measured by western blot and immunohistochemistry. Cell proliferation and Apoptosis were analyzed by MTT assay and flow cytometry. ROS production and the secretion of inflammatory cytokines were measured by DCFH-DA probe and ELISA assay. TLR4/MyD88/NF-κB signaling pathway was analyzed by western blot. We established experimental colitis model in RIP3 knockout and wild-type mice and disease activity index (DAI) score was calculated. The expression and distribution of tight junction protein were analyzed by immunofluorescence. The ratio of CD4⁺Foxp3⁺ T cells in the spleen was detected by flow cytometry. Oxidative damage of mouse colon was assessed by detecting the levels of SOD, MDA and MPO. Data were analyzed by one-way ANOVA or student's t test.

Results: The expression of RIP3 in human colon is positively associated with the severity of UC. RIP3 inhibitor GSK872 or RIP3 knockdown reverses the inhibitory effect of TNF-α on proliferation and the promoting effect of TNF-α on Apoptosis and necrosis in human intestinal epithelial cells. In addition, RIP3 deficiency inhibits the secretion of inflammatory cytokines (IL-16, IL-17 and IFN-γ) and ROS production induced by TNF-α. In vivo, RIP3 inhibitor Nec-1 effectively improves DSS-induced colitis in mice. In mechanism, RIP3 depression could upregulate the proportion of CD4⁺Foxp3⁺ immunosuppressive Treg cells in the spleen while suppressed TLR4/MyD88/NF-κB signaling pathway and ROS generation, and all these anti-inflammation factors together suppress the secretion of inflammatory cytokines and Necroptosis of intestinal epithelial cells.

Conclusions: This study preliminarily explored the regulating mechanism of RIP3 on UC, and Nec-1 may be a promising drug to alleviate the inflammation and Necroptosis of the colon in UC patients.