BackgroundMUC2 mucin produced by intestinal goblet cells is the major component of the intestinal mucus barrier. The inflammatory bowel disease ulcerative colitis is characterized by depleted goblet cells and a reduced mucus layer, but the aetiology remains obscure. In this study we used random mutagenesis to produce two murine models of inflammatory bowel disease, characterised the basis and nature of the inflammation in these mice, and compared the pathology with human ulcerative colitis.Methods and FindingsBy murine N-ethyl-N-nitrosourea mutagenesis we identified two distinct noncomplementing missense mutations in Muc2 causing an ulcerative colitis-like phenotype. 100% of mice of both strains developed mild spontaneous distal intestinal inflammation by 6 wk (histological colitis scores versus wild-type mice, p < 0.01) and chronic diarrhoea. Monitoring over 300 mice of each strain demonstrated that 25% and 40% of each strain, respectively, developed severe clinical signs of colitis by age 1 y. Mutant mice showed aberrant Muc2 biosynthesis, less stored mucin in goblet cells, a diminished mucus barrier, and increased susceptibility to colitis induced by a luminal toxin. Enhanced local production of IL-1β, TNF-α, and IFN-γ was seen in the distal colon, and intestinal permeability increased 2-fold. The number of leukocytes within mesenteric lymph nodes increased 5-fold and leukocytes cultured in vitro produced more Th1 and Th2 cytokines (IFN-γ, TNF-α, and IL-13). This pathology was accompanied by accumulation of the Muc2 precursor and ultrastructural and biochemical evidence of endoplasmic reticulum (ER) stress in goblet cells, activation of the unfolded protein response, and altered intestinal expression of genes involved in ER stress, inflammation, apoptosis, and wound repair. Expression of mutated Muc2 oligomerisation domains in vitro demonstrated that aberrant Muc2 oligomerisation underlies the ER stress. In human ulcerative colitis we demonstrate similar accumulation of nonglycosylated MUC2 precursor in goblet cells together with ultrastructural and biochemical evidence of ER stress even in noninflamed intestinal tissue. Although our study demonstrates that mucin misfolding and ER stress initiate colitis in mice, it does not ascertain the genetic or environmental drivers of ER stress in human colitis.ConclusionsCharacterisation of the mouse models we created and comparison with human disease suggest that ER stress-related mucin depletion could be a fundamental component of the pathogenesis of human colitis and that clinical studies combining genetics, ER stress-related pathology and relevant environmental epidemiology are warranted.

Maintaining the integrity of the gastrointestinal tract, despite the continual presence of microbial flora and injurious agents, is essential. Epithelial continuity depends on a family of small, yet abundant, secreted proteins--the trefoil factors (TFFs). TFFs protect mucous epithelia from a range of insults and contribute to mucosal repair, although the signalling events that mediate these responses are only partially understood.

Intestinal trefoil factor (ITF) is an essential regulator of colonic epithelial restitution, the rapid migration of colonocytes over mucosal wounds. High levels of ITF are frequently present in colorectal cancers and derived cell lines. Mucosal restitution requires the detachment of epithelium from substrate, which would be expected to induce apoptosis. However, mice deficient in ITF showed an increase in colonocyte apoptosis unaccompanied by changes in expression of receptor-related (TNFR͞Fas) or stressrelated (Bcl-family) cell death regulators. An ITF-expressing colonic (HT-ITF1) cell line was resistant to apoptosis induced by serum starvation and ceramide. Exogenous ITF also protected another human colonic carcinoma-derived cell line (HCT116) and a nontransformed rat intestinal epithelial cell line (IEC-6) from apoptosis. This effect was abrogated by wortmannin and tyrphostin A25, indicating the potential involvement of phosphatidylinositol 3-kinase and epidermal growth factor (EGF) receptor activation. Expression of phosphorylated Akt, which lies downstream of phosphatidylinositol 3-kinase activation, was elevated in this HT-29-ITF line. p53-dependent cell death in the AGS human gastric cancer cell line after etoposide was similarly inhibited by transient expression of ITF but not a C-terminal truncation mutant of ITF, and it required functional phosphatidylinositol 3-kinase and EGF receptor. These findings support a central role for ITF in the maintenance of intestinal mucosal continuity, and conversely demonstrate the potential for ITF expression to confer resistance of colorectal tumors to therapy.cell survival ͉ signal transduction ͉ cell adhesion ͉ colonic neoplasm ͉ cultured tumor cells R estitution, the ability of epithelial cells to spread and migrate across the basement membrane to cover shallow defects, is the key initial step in repair of mucosal injury and can achieve restoration of mucosal continuity over broad areas of damage within hours (1-3). This resurfacing, which is independent of proliferation, is followed over a period of days by a remodeling phase of epithelial proliferation and differentiation. Brisk restitution after injury is desirable both to limit fluid and electrolyte losses and to prevent diffusion of foreign antigens from the gastrointestinal lumen into local and systemic immune compartments. Both these aspects underlie the morbidity after therapeutic abdominal irradiation, and they limit dose and dose intervals (4).The trefoil peptide family, comprising the intestinal peptide ITF and the gastric peptides SP and pS2, play a critical role in epithelial restitution within the mammalian gastrointestinal tract. These small (7-12-kDa) protease-resistant proteins are abundantly secreted onto the mucosal surface by specialized mucus-secreting cells of the gut. They are rapidly up-regulated at the margins of mucosal injury, and they are believed to promote epithelial cell migration (5, 6). Colonic restitution is absent in mice made ITF deficient by homologous recombination (7), renderi...

The trefoil peptide intestinal trefoil factor (ITF) plays a critical role in the protection of colonic mucosa and is essential to restitution after epithelial damage. These functional properties are accomplished through coordinated promotion of cell migration and inhibition of apoptosis. ITF contains a unique three-looped trefoil motif formed by intrachain disulfide bonds among six conserved cysteine residues, which is thought to contribute to its marked protease resistance. ITF also has a seventh cysteine residue, which permits homodimer formation. A series of cysteine-to-serine substitutions and a C-terminally truncated ITF were made by PCR site-directed mutagenesis. Any alteration of the trefoil motif or truncation resulted in loss of protease resistance. However, neither an intact trefoil domain nor dimerization was required to promote cell migration. This pro-restitution activity correlated with the ability of the ITF mutants to activate mitogen-activated protein (MAP) kinase independent of phosphorylation of the epidermal growth factor (EGF) receptor. In contrast, only intact ITF retained both phosphatidylinositol 3-kinase and the EGF receptor-dependent antiapoptotic effect in HCT116 and IEC-6 cells. The inability to block apoptosis correlated with a loss of trefoil peptide-induced transactivation of the EGF receptor or Akt kinase in HT-29 cells. In addition to defining structural requirements for the functional properties of ITF, these findings demonstrate that distinct intracellular signaling pathways mediate the effects of ITF on cell migration and apoptosis.

Trefoil factor family 2 (TFF2), also known as spasmolytic polypeptide, is a member of the trefoil family of peptides and is expressed primarily in the mucous neck cells of the gastric mucosa. To study the physiologic role of TFF2, we have generated TFF2-deficient mice through targeted gene disruption. Homozygous mutant mice were viable and fertile without obvious gastrointestinal abnormalities. However, quantitative measurements revealed a significant decrease in gastric mucosal thickness and in gastric mucosal proliferation rates. In addition, there was a twofold increase in activated parietal cells resulting in a twofold increase in basal and stimulated gastric acid output and an undetectable serum gastrin level. The TFF2-deficient mice also showed a significant increase in the degree of gastric ulceration after administration of indomethacin. Taken together, these results suggest a physiologic role for TFF2 to promote mucosal healing through the stimulation of proliferation and downregulation of gastric acid secretion.