Rab11-Fip1 Deficient Mice Develops Spontaneous Inflammation And Show Dss Susceptibility In The Colon

Background and Aims A small GTPase, Rab11a regulates vesicle trafficking and cell polarity in epithelial cells through interacting with Rab11 family-interacting proteins (Rab11-FIPs). Intestine-specific Rab11a knockout mice demonstrate epithelial hyperplasia, dysplasia, and immune cell infiltration, implicating that Rab11a-mediated protein trafficking is important to maintain mucosal homeostasis. Nevertheless, the specific phenotype for loss of Rab11a-binding protein family members, FIPs, had not been fully characterized. We hypothesize that the deficiency of Rab11-FIP1, also known as RCP, affects mucosal integrity in the intestine. Methods Global Rab11-FIP1 knockout (KO) mice were generated by deletion of the exon 2. The immunoreactivity for Rab11-FIP1 antibody in the intestinal epithelial cells was lost in Rab11-FIP1 KO mouse tissues. Pathology of intestinal tissues were analyzed by immunostaining of intestinal sections and RNA-sequencing of isolated colonic epithelial cells. Low concentration of sodium dextran sulfate (DSS, 2%) was added into drinking water for 5 days and colitis score was compared between Rab11-FIP1 KO and heterozygous littermates. Results Birth rate and body weight gain were normal in the Rab11-FIP1 KO mouse line and no gross phenotype was found by the age of 8 weeks. At the age of 8–12 weeks, some Rab11-FIP1 KO mice spontaneously developed rectal prolapse along with chronic inflammation. The morphology and frequency of trefoil factor (TFF)3+ goblet cells in the colon were altered by Rab11-FIP1 loss. The number of lymphoid patches and neutrophil infiltration, which was quantified by Ly6B.2+ cell numbers, in the colon were significantly increased by Rab11-FIP1 loss before the development of rectal prolapse compared to wild type and Rab11-FIP1 heterozygous mice. The frequency of CD3+ intraepithelial lymphocytes and F4/80+ macrophages in colonic lamina propria were also higher in Rab11-FIP1 KO mice. The crypt height and the ratio of Ki67+ proliferating cells were significantly higher in Rab11-FIP1 KO colon. After DSS treatment followed by a 24-hour-recovery period, Rab11-FIP1 KO mice showed greater body weight loss and more severe colonic mucosal damage than in heterozygous littermates. mRNA signatures indicated that Rab11-FIP1 deletion downregulates genes that mediate stress tolerance response, such as Hsp members, Reg4, Nox1, and Ces1g. Genes that mediate the response to infection, including Pla2g2a, Duox2, Abca13, reg3g, Pecam1, and Optn, were significantly upregulated in Rab11-FIP1 KO colon, consistent with spontaneous neutrophil infiltration. Conclusion Loss of Rab11-FIP1 increases spontaneous and DSS-induced inflammatory response, suggesting a decrease in cytoprotection mechanisms in the colon.