Background & Aims Mechanisms responsible for crypt architectural distortion in chronic ulcerative colitis (CUC) are not well understood. Data indicate that Akt signaling cooperates with Wnt to activate β-catenin in intestinal stem and progenitor cells through phosphorylation at Ser552 (P-β-catenin552). We investigated whether phosphoinositide 3- kinase (PI3K) is required for Akt-mediated activation of β-catenin during intestinal inflammation. Methods The class IA subunit of PI3K was conditionally deleted from intestinal epithelial cells in mice. Acute inflammation was induced in these mice (I-pik3r1KO) and their intestines were analyzed by biochemical and histological methods. The effects of chemically blocking PI3K in colitic IL-10−/− mice were examined. Biopsy samples from patients were examined. Results Compared to wild type mice, I-pik3r1KO mice had reduced T-cell–mediated Akt and β-catenin signaling in intestinal stem and progenitor cells and limited crypt epithelial proliferation. Biochemical analyses indicated that PI3K–Akt signaling increased nuclear total β-catenin and P-β-catenin552 levels and reduced phosphorylation of N-terminal β-catenin, which is associated with degradation. PI3K inhibition in IL-10−/− mice impaired colitis-induced epithelial Akt and β-catenin activation, reduced progenitor cell expansion, and prevented dysplasia. Human samples had increased numbers of progenitor cells with P-β-catenin552 throughout expanded crypts and increased mRNA expression of β-catenin target genes in CUC, colitis-associated cancer, tubular adenomas, and sporadic colorectal cancer, compared with control samples. Conclusions PI3K–Akt signaling cooperates with Wnt to increase β-catenin signaling during inflammation. PI3K-induced and Akt-mediated β-catenin signaling are required for progenitor cell activation during the progression from CUC to CAC; these factors might be used as biomarkers of dysplastic transformation in the colon.

TNF plays an integral role in inflammatory bowel disease (IBD) as evidenced by the dramatic therapeutic responses in Crohn’s disease (CD) patients induced by chimeric anti-TNF mAbs. However, treatment of CD patients with etanercept, a decoy receptor that binds soluble TNF, fails to improve disease. To explore this discrepancy, we interrogated the role of TNF signaling on Wnt/β-catenin-mediated intestinal stem and progenitor cell (ISC/PC) expansion in CD patients, human cells, and preclinical mouse models. We hypothesized that TNF exerts beneficial effects on intestinal epithelial cell (IEC) responses to injury. In CD patients, ISC/PC Wnt/β-catenin signaling correlates with inflammation status. TNF-deficient (Tnf−/−) mice exhibited increased apoptosis, less IEC proliferation, and less Wnt signaling when stimulated with anti-CD3 mAb. Bone marrow chimera (BMC) mice revealed that mucosal repair depended on TNF production by BM-derived cells and TNFR expression by radioresistant IEC. WT-> Tnfr1/2−/− BMC mice given chronic DSS colitis exhibited delayed ulcer healing, more mucosal inflammation, and impaired Wnt/β-catenin signaling, consistent with the hypothesis that epithelial TNFR signaling participates in mucosal healing. The direct effect of TNF on stem cells was demonstrated by studies of TNF-induced Wnt/β-catenin target gene expression in murine enteroids and colonoid cultures and TNF-induced β-catenin activation in non-transformed human NCM460 cells (TOPFlash) and mice (TOP-GAL). Together these data support the hypothesis that TNF plays a beneficial role in enhancing Wnt/β-catenin signaling during ulcer healing in IBD. These novel findings will inform clinicians and therapeutic chemists alike as they strive to develop novel therapies for IBD patients.

BACKGROUND & AIMS Inflammatory bowel disease (IBD) is associated with increased apoptosis of intestinal epithelial cells (IECs). Mutations in the tumor suppressor p53 appear during early stages of progression from colitis to cancer. We investigated the role of p53 and its target, p53-upregulated modulator of apoptosis (PUMA), in inflammation-induced apoptosis of IECs. METHODS Apoptosis was induced in mouse models of mucosal inflammation. Responses of IECs to acute, T-cell activation were assessed in wild-type, p53−/−, Bid−/−, Bim−/−, Bax3−/−, Bak−/−, PUMA−/−, and Noxa−/− mice. Responses of IECs to acute and chronic colitis were measured in mice following 1 or 3 cycles of dextran sulfate sodium (DSS), respectively. Apoptosis was assessed by TUNEL staining and measuring activity of caspases 3 and 9; levels of p53 and PUMA were assessed in colon tissue from patients with and without ulcerative colitis. RESULTS Apoptosis of IECs occurred in the lower crypts of colitic tissue from humans and mice. Colitis induction with anti-CD3 or 3 cycles of DSS increased apoptosis and protein levels of p53 and PUMA in colonic crypt IECs. In p53−/− and PUMA−/− mice, apoptosis of IECs was significantly reduced but inflammation was not. Levels of p53 and PUMA were increased in inflamed mucosal tissues of mice with colitis and in patients with UC, compared with controls. Induction of PUMA in IECs of p53−/− mice indicated that PUMA-mediated apoptosis was independent of p53. CONCLUSIONS In mice and humans, colon inflammation induces apoptosis of IECs via p53-dependent and -independent mechanisms; PUMA also activates an intrinsic apoptosis pathway associated with colitis.