Expression of the transmembrane glycoprotein CD98 (encoded by SLC3A2) is increased in intestinal inflammatory conditions, such as inflammatory bowel disease (IBD), and in various carcinomas, yet its pathogenetic role remains unknown. By generating gain- and loss-of-function mouse models with genetically manipulated CD98 expression specifically in intestinal epithelial cells (IECs), we explored the role of CD98 in intestinal homeostasis, inflammation, and colitis-associated tumorigenesis. IEC-specific CD98 overexpression induced gut homeostatic defects and increased inflammatory responses to DSS-induced colitis, promoting colitis-associated tumorigenesis in mice. Further analysis indicated that the ability of IEC-specific CD98 overexpression to induce tumorigenesis was linked to its capacity to induce barrier dysfunction and to stimulate cell proliferation and production of proinflammatory mediators. To validate these results, we constructed mice carrying conditional floxed Slc3a2 alleles and crossed them with Villin-Cre mice such that CD98 was downregulated only in IECs. These mice exhibited attenuated inflammatory responses and resistance to both DSS-induced colitis and colitis-associated tumorigenesis. Together, our data show that intestinal CD98 expression has a crucial role in controlling homeostatic and innate immune responses in the gut. Modulation of CD98 expression in IECs therefore represents a promising therapeutic strategy for the treatment and prevention of inflammatory intestinal diseases, such as IBD and colitis-associated cancer.
Hang Thi Thu Nguyen, Guillaume Dalmasso, Leif Torkvist, Jonas Halfvarson, Yutao Yan, Hamed Laroui, Doron Shmerling, Tiziano Tallone, Mauro D’Amato, Shanthi V. Sitaraman, Didier Merlin
Intestinal epithelial cell (IEC) apoptosis contributes to the development of ulcerative colitis (UC), an inflammatory bowel disease (IBD) that affects the colon and rectum. Therapies that target the inflammatory cytokine TNF have been found to inhibit IEC apoptosis in patients with IBD, although the mechanism of IEC apoptosis remains unclear. We therefore investigated the role of p53-upregulated modulator of apoptosis (PUMA), a p53 target and proapoptotic BH3-only protein, in colitis and IEC apoptosis, using patient samples and mouse models of UC. In UC patient samples, PUMA expression was elevated in colitis tissues relative to that in uninvolved tissues, and the degree of elevation of PUMA expression correlated with the severity of colitis and the degree of apoptosis induction. In mice, PUMA was markedly induced in colonic epithelial cells following induction of colitis by either dextran sulfate sodium salt (DSS) or 2,4,6-trinitrobenzene sulfonic acid (TNBS). The induction of PUMA was p53-independent but required NF-κB. Absence of PUMA, but neither absence of p53 nor that of another BH3-only protein (Bid), relieved DSS- and TNBS-induced colitis and inhibited IEC apoptosis. Furthermore, treating mice with infliximab (Remicade), a clinically used TNF-specific antibody, suppressed DSS- and TNBS-induced PUMA expression and colitis. These results indicate that PUMA induction contributes to the pathogenesis of colitis by promoting IEC apoptosis and suggest that PUMA inhibition may be an effective strategy to promote mucosal healing in patients with UC.
Wei Qiu, Bin Wu, Xinwei Wang, Monica E. Buchanan, Miguel D. Regueiro, Douglas J. Hartman, Robert E. Schoen, Jian Yu, Lin Zhang
Mucin-type O-linked oligosaccharides (O-glycans) are primary components of the intestinal mucins that form the mucus gel layer overlying the gut epithelium. Impaired expression of intestinal O-glycans has been observed in patients with ulcerative colitis (UC), but its role in the etiology of this disease is unknown. Here, we report that mice with intestinal epithelial cell–specific deficiency of core 1–derived O-glycans, the predominant form of O-glycans, developed spontaneous colitis that resembled human UC, including massive myeloid infiltrates and crypt abscesses. The colitis manifested in these mice was also characterized by TNF-producing myeloid infiltrates in colon mucosa in the absence of lymphocytes, supporting an essential role for myeloid cells in colitis initiation. Furthermore, induced deletion of intestinal core 1–derived O-glycans caused spontaneous colitis in adult mice. These data indicate a causal role for the loss of core 1–derived O-glycans in colitis. Finally, we detected a biosynthetic intermediate typically exposed in the absence of core 1 O-glycan, Tn antigen, in the colon epithelium of a subset of UC patients. Somatic mutations in the X-linked gene that encodes core 1 β1,3-galactosyltransferase–specific chaperone 1 (C1GALT1C1, also known as Cosmc), which is essential for core 1 O-glycosylation, were found in Tn-positive epithelia. These data suggest what we believe to be a new molecular mechanism for the pathogenesis of UC.
Jianxin Fu, Bo Wei, Tao Wen, Malin E.V. Johansson, Xiaowei Liu, Emily Bradford, Kristina A. Thomsson, Samuel McGee, Lilah Mansour, Maomeng Tong, J. Michael McDaniel, Thomas J. Sferra, Jerrold Turner, Hong Chen, Gunnar C. Hansson, Jonathan Braun, Lijun Xia
Epithelial-cadherin (E-cadherin) is a master organizer of the epithelial phenotype. Its function is regulated in part by p120-catenin (referred to herein as p120), a cytoplasmic binding partner that directly regulates cadherin stability. As it has been suggested that cadherins have a role in inflammatory bowel disease (IBD), we sought to investigate this further by assessing the effect of p120 deficiency in mouse small intestine and colon. p120 conditional KO mice were superficially normal at birth but declined rapidly and died within 21 days. Cell-cell adhesion defects and inflammation led to progressive mucosal erosion and terminal bleeding, similar to what is observed in a dominant-negative cadherin mouse model of IBD. Additionally, selective loss of adherens junctions and accumulation of atypical COX-2–expressing neutrophils in p120-null areas of the colon were observed. To elucidate the mechanism, direct effects of p120 deficiency were assessed in vitro in a polarizing colon cancer cell line. Notably, transepithelial electrical resistance was dramatically reduced, neutrophil binding was increased 30 fold, and levels of COX-2, an enzyme associated with IBD, were markedly increased in neutrophils. Our data suggest that p120 loss disrupts the neonatal intestinal barrier and amplifies neutrophil engagement and that these changes lead to catastrophic inflammation during colonization of the neonatal gut with bacteria and other luminal antigens. Thus, we conclude that p120 has an essential role in barrier function and epithelial homeostasis and survival in the intestine.
Whitney G. Smalley-Freed, Andrey Efimov, Patrick E. Burnett, Sarah P. Short, Michael A. Davis, Deborah L. Gumucio, M. Kay Washington, Robert J. Coffey, Albert B. Reynolds
Epithelial-mesenchymal interactions regulate normal gut epithelial homeostasis and have a putative role in inflammatory bowel disease and colon cancer pathogenesis. Epimorphin is a mesenchymal and myofibroblast protein with antiproliferative, promorphogenic effects in intestinal epithelium. We previously showed that deletion of epimorphin partially protects mice from acute colitis, associated with an increase in crypt cell proliferation. Here we explored the potential therapeutic utility of modulating epimorphin expression by examining the effects of epimorphin deletion on chronic inflammation–associated colon carcinogenesis using the azoxymethane/dextran sodium sulfate (AOM/DSS) model. We found that mice in which epimorphin expression was absent had a marked reduction in incidence and extent of colonic dysplasia. Furthermore, epimorphin deletion in myofibroblasts altered the morphology and growth of cocultured epithelial cells. Loss of epimorphin affected secretion of soluble mesenchymal regulators of the stem cell niche such as Chordin. Importantly, IL-6 secretion from LPS-treated epimorphin-deficient myofibroblasts was completely inhibited, and stromal IL-6 expression was reduced in vivo. Taken together, these data show that epimorphin deletion inhibits chronic inflammation–associated colon carcinogenesis in mice, likely as a result of increased epithelial repair, decreased myofibroblast IL-6 secretion, and diminished IL-6–induced inflammation. Furthermore, we believe that modulation of epimorphin expression may have therapeutic benefits in appropriate clinical settings.
Anisa Shaker, Elzbieta A. Swietlicki, Lihua Wang, Shujun Jiang, Birce Onal, Shashi Bala, Katherine DeSchryver, Rodney Newberry, Marc S. Levin, Deborah C. Rubin
Enteropathy-associated T cell lymphoma is a severe complication of celiac disease (CD). One mechanism suggested to underlie its development is chronic exposure of intraepithelial lymphocytes (IELs) to potent antiapoptotic signals initiated by IL-15, a cytokine overexpressed in the enterocytes of individuals with CD. However, the signaling pathway by which IL-15 transmits these antiapoptotic signals has not been firmly established. Here we show that the survival signals delivered by IL-15 to freshly isolated human IELs and to human IEL cell lines derived from CD patients with type II refractory CD (RCDII) — a clinicopathological entity considered an intermediary step between CD and enteropathy-associated T cell lymphoma — depend on the antiapoptotic factors Bcl-2 and/or Bcl-xL. The signals also required IL-15Rβ, Jak3, and STAT5, but were independent of PI3K, ERK, and STAT3. Consistent with these data, IELs from patients with active CD and RCDII contained increased amounts of Bcl-xL, phospho-Jak3, and phospho-STAT5. Furthermore, incubation of patient duodenal biopsies with a fully humanized human IL-15–specific Ab effectively blocked Jak3 and STAT5 phosphorylation. In addition, treatment with this Ab induced IEL apoptosis and wiped out the massive IEL accumulation in mice overexpressing human IL-15 in their gut epithelium. Together, our results delineate the IL-15–driven survival pathway in human IELs and demonstrate that IL-15 and its downstream effectors are meaningful therapeutic targets in RCDII.
Georgia Malamut, Raja El Machhour, Nicolas Montcuquet, Séverine Martin-Lannerée, Isabelle Dusanter-Fourt, Virginie Verkarre, Jean-Jacques Mention, Gabriel Rahmi, Hiroshi Kiyono, Eric A. Butz, Nicole Brousse, Christophe Cellier, Nadine Cerf-Bensussan, Bertrand Meresse
Anion transport by the colonic mucosa maintains the hydration and pH of the colonic lumen, and its disruption causes a variety of diarrheal diseases. Cholinergic agonists raise cytosolic Ca2+ levels and stimulate anion secretion, but the mechanisms underlying this effect remain unclear. Cholinergic stimulation of anion secretion may occur via activation of Ca2+-activated Cl– channels (CaCCs) or an increase in the Cl– driving force through CFTR after activation of Ca2+-dependent K+ channels. Here we investigated the role of a candidate CaCC protein, bestrophin-2 (Best2), using Best2–/– mice. Cholinergic stimulation of anion current was greatly reduced in Best2–/– mice, consistent with our proposed role for Best2 as a CaCC. However, immunostaining revealed Best2 localized to the basolateral membrane of mucin-secreting colonic goblet cells, not the apical membrane of Cl–-secreting enterocytes. In addition, in the absence of HCO3–, cholinergic-activated current was identical in control and Best2–/– tissue preparations, which suggests that most of the Best2 current was carried by HCO3–. These data delineate an alternative model of cholinergic regulation of colonic anion secretion in which goblet cells play a critical role in HCO3– homeostasis. We therefore propose that Best2 is a HCO3– channel that works in concert with a Cl:HCO3– exchanger in the apical membrane to affect transcellular HCO3– transport. Furthermore, previous models implicating CFTR in cholinergic Cl– secretion may be explained by substantial downregulation of Best2 in Cftr–/– mice.
Kuai Yu, Rafael Lujan, Alan Marmorstein, Sherif Gabriel, H. Criss Hartzell
At least 10 enteroendocrine cell types have been identified, and the peptide hormones they secrete have diverse functions that include regulation of glucose homeostasis, food intake, and gastric emptying. Mice lacking individual enteroendocrine hormones, their receptors, or combinations of these have shed light on the role of these hormones in the regulation of energy homeostasis. However, because enteroendocrine hormones have partially overlapping functions, these loss-of-function studies produced only minor phenotypes, and none of the enteroendocrine hormones was shown to be essential for life. To examine the effect of loss of all enteroendocrine cells and hormones on energy homeostasis, we generated mice with intestinal-specific ablation of the proendocrine transcription factor neurogenin 3 (referred to herein as Ngn3Δint mice). Ngn3Δint mice were deficient for all enteroendocrine cells and hormones, and died with a high frequency during the first week of life. Mutant mice were growth retarded and had yellowish stool suggestive of steatorrhea. Subsequent analyses revealed that Ngn3Δint mice had impaired lipid absorption, reduced weight gain, and improved glucose homeostasis. Furthermore, intestinal epithelium of the mutant mice showed an enlarged proliferative crypt compartment and accelerated cell turnover but no changes to goblet and Paneth cell numbers. Enterocytes had shorter microvilli, but the expression of the main brush border enzymes was unaffected. Our data help unravel the role of enteroendocrine cells and hormones in lipid absorption and maintenance of the intestinal epithelium.
Georg Mellitzer, Anthony Beucher, Viviane Lobstein, Pascal Michel, Sylvie Robine, Michèle Kedinger, Gérard Gradwohl
Mary Abigail S. Garcia, Ning Yang, Paul M. Quinton
Intestinal ganglioneuromatosis is a benign proliferation of nerve ganglion cells, nerve fibers, and supporting cells of the enteric nervous system (ENS) that can result in abnormally large enteric neuronal cells (ENCs) in the myenteric plexus and chronic intestinal pseudoobstruction (CIPO). As phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a phosphatase that is critical for controlling cell growth, proliferation, and death, we investigated the role of PTEN in the ENS by generating mice with an embryonic, ENC-selective deletion within the Pten locus. Mutant mice died 2 to 3 weeks after birth, with clinical signs of CIPO and hyperplasia and hypertrophy of ENCs resulting from increased activity of the PI3K/PTEN-AKT-S6K signaling pathway. Further analysis revealed that PTEN was only expressed in developing mouse embryonic ENCs from E15.5 and that the rate of ENC proliferation decreased once PTEN was expressed. Specific deletion of the Pten gene in ENCs therefore induced hyperplasia and hypertrophy in the later stages of embryogenesis. This phenotype was reversed by administration of a pharmacological inhibitor of AKT. In some human ganglioneuromatosis forms of CIPO, PTEN expression was found to be abnormally low and S6 phosphorylation increased. Our study thus reveals that loss of PTEN disrupts development of the ENS and identifies the PI3K/PTEN-AKT-S6K signaling pathway as a potential therapeutic target for ganglioneuromatosis forms of CIPO.
Isabel Puig, Delphine Champeval, Pascal De Santa Barbara, Francis Jaubert, Stanislas Lyonnet, Lionel Larue