Probiotic bacteria can potentially have beneficial effects on the clinical course of several intestinal disorders, but our understanding of probiotic action is limited. We have identified a probiotic bacteria–derived soluble protein, p40, from Lactobacillus rhamnosus GG (LGG), which prevents cytokine-induced apoptosis in intestinal epithelial cells. In the current study, we analyzed the mechanisms by which p40 regulates cellular responses in intestinal epithelial cells and p40’s effects on experimental colitis using mouse models. We show that the recombinant p40 protein activated EGFR, leading to Akt activation. Activation of EGFR by p40 was required for inhibition of cytokine-induced apoptosis in intestinal epithelial cells in vitro and ex vivo. Furthermore, we developed a pectin/zein hydrogel bead system to specifically deliver p40 to the mouse colon, which activated EGFR in colon epithelial cells. Administration of p40-containing beads reduced intestinal epithelial apoptosis and disruption of barrier function in the colon epithelium in an EGFR-dependent manner, thereby preventing and treating DSS-induced intestinal injury and acute colitis. Furthermore, p40 activation of EGFR was required for ameliorating colon epithelial cell apoptosis and chronic inflammation in oxazolone-induced colitis. These data define what we believe to be a previously unrecognized mechanism of probiotic-derived soluble proteins in protecting the intestine from injury and inflammation.
Fang Yan, Hanwei Cao, Timothy L. Cover, M. Kay Washington, Yan Shi, LinShu Liu, Rupesh Chaturvedi, Richard M. Peek Jr., Keith T. Wilson, D. Brent Polk
Patients with prolonged ulcerative colitis (UC) frequently develop colorectal adenocarcinoma for reasons that are not fully clear. To analyze inflammation-associated colonic tumorigenesis, we developed a chronic form of oxazolone-induced colitis in mice that, similar to UC, was distinguished by the presence of IL-13–producing NKT cells. In this model, the induction of tumors using azoxymethane was accompanied by the coappearance of F4/80+CD11bhighGr1low M2 macrophages, cells that undergo polarization by IL-13 and are absent in tumors that lack high level IL-13 production. Importantly, this subset of macrophages was a source of tumor-promoting factors, including IL-6. Similar to dextran sodium sulfate–induced colitis, F4/80+CD11bhighGr1intermediate macrophages were present in the mouse model of chronic oxazolone-induced colitis and may influence tumor development through production of TGF-β1, a cytokine that inhibits tumor immunosurveillance. Finally, while robust chronic oxazolone-induced colitis developed in myeloid differentiation primary response gene 88–deficient (Myd88–/–) mice, these mice did not support tumor development. The inhibition of tumor development in Myd88–/– mice correlated with cessation of IL-6 and TGF-β1 production by M2 and F4/80+CD11bhighGr1intermediate macrophages, respectively, and was reversed by exogenous IL-6. These data show that an UC-like inflammation may facilitate tumor development by providing a milieu favoring development of MyD88-dependent tumor-supporting macrophages.
Gabriela Schiechl, Bernhard Bauer, Ivan Fuss, Sven A. Lang, Christian Moser, Petra Ruemmele, Stefan Rose-John, Markus F. Neurath, Edward K. Geissler, Hans-Jürgen Schlitt, Warren Strober, Stefan Fichtner-Feigl
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
Ulcerative colitis (UC) is a chronic inflammatory bowel disease that is closely associated with colon cancer. Expression of the enzyme heparanase is clearly linked to colon carcinoma progression, but its role in UC is unknown. Here we demonstrate for what we believe to be the first time the importance of heparanase in sustaining the immune-epithelial crosstalk underlying colitis-associated tumorigenesis. Using histological specimens from UC patients and a mouse model of dextran sodium sulfate–induced colitis, we found that heparanase was constantly overexpressed and activated throughout the disease. We demonstrate, using heparanase-overexpressing transgenic mice, that heparanase overexpression markedly increased the incidence and severity of colitis-associated colonic tumors. We found that highly coordinated interactions between the epithelial compartment (contributing heparanase) and mucosal macrophages preserved chronic inflammatory conditions and created a tumor-promoting microenvironment characterized by enhanced NF-κB signaling and induction of STAT3. Our results indicate that heparanase generates a vicious cycle that powers colitis and the associated tumorigenesis: heparanase, acting synergistically with the intestinal flora, stimulates macrophage activation, while macrophages induce production (via TNF-α–dependent mechanisms) and activation (via secretion of cathepsin L) of heparanase contributed by the colon epithelium. Thus, disruption of the heparanase-driven chronic inflammatory circuit is highly relevant to the design of therapeutic interventions in colitis and the associated cancer.
Immanuel Lerner, Esther Hermano, Eyal Zcharia, Dina Rodkin, Raanan Bulvik, Victoria Doviner, Ariel M. Rubinstein, Rivka Ishai-Michaeli, Ruth Atzmon, Yoav Sherman, Amichay Meirovitz, Tamar Peretz, Israel Vlodavsky, Michael Elkin
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
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
The pathogenic mechanisms underlying acute pancreatitis are not clear. Two key pathologic acinar cell responses of this disease are vacuole accumulation and trypsinogen activation. We show here that both result from defective autophagy, by comparing the autophagic responses in rodent models of acute pancreatitis to physiologic autophagy triggered by fasting. Pancreatitis-induced vacuoles in acinar cells were greater in number and much larger than those induced with fasting. Degradation of long-lived proteins, a measure of autophagic efficiency, was markedly inhibited in in vitro pancreatitis, while it was stimulated by acinar cell starvation. Further, processing of the lysosomal proteases cathepsin L (CatL) and CatB into their fully active, mature forms was reduced in pancreatitis, as were their activities in the lysosome-enriched subcellular fraction. These findings indicate that autophagy is retarded in pancreatitis due to deficient lysosomal degradation caused by impaired cathepsin processing. Trypsinogen activation occurred in pancreatitis but not with fasting and was prevented by inhibiting autophagy. A marker of trypsinogen activation partially localized to autophagic vacuoles, and pharmacologic inhibition of CatL increased the amount of active trypsin in acinar cells. The results suggest that retarded autophagy is associated with an imbalance between CatL, which degrades trypsinogen and trypsin, and CatB, which converts trypsinogen into trypsin, resulting in intra-acinar accumulation of active trypsin in pancreatitis. Thus, deficient lysosomal degradation may be a dominant mechanism for increased intra-acinar trypsin in pancreatitis.
Olga A. Mareninova, Kip Hermann, Samuel W. French, Mark S. O’Konski, Stephen J. Pandol, Paul Webster, Ann H. Erickson, Nobuhiko Katunuma, Fred S. Gorelick, Ilya Gukovsky, Anna S. Gukovskaya
The mechanisms underlying mucus-associated pathologies in cystic fibrosis (CF) remain obscure. However, recent studies indicate that CF transmembrane conductance regulator (CFTR) is required for bicarbonate (HCO3–) transport and that HCO3– is critical for normal mucus formation. We therefore investigated the role of HCO3– in mucus secretion using mouse small intestine segments ex vivo. Basal rates of mucus release in the presence or absence of HCO3– were similar. However, in the absence of HCO3–, mucus release stimulated by either PGE2 or 5-hydroxytryptamine (5-HT) was approximately half that stimulated by these molecules in the presence of HCO3–. Inhibition of HCO3– and fluid transport markedly reduced stimulated mucus release. However, neither absence of HCO3– nor inhibition of HCO3– transport affected fluid secretion rates, indicating that the effect of HCO3– removal on mucus release was not due to decreased fluid secretion. In a mouse model of CF (mice homozygous for the most common human CFTR mutation), intestinal mucus release was minimal when stimulated with either PGE2 or 5-HT in the presence or absence of HCO3–. These data suggest that normal mucus release requires concurrent HCO3– secretion and that the characteristically aggregated mucus observed in mucin-secreting organs in individuals with CF may be a consequence of defective HCO3– transport.
Mary Abigail S. Garcia, Ning Yang, Paul M. Quinton
Although oxidative stress has been implicated in acute acetaminophen-induced liver failure and in chronic liver cirrhosis and hepatocellular carcinoma (HCC), no common underlying metabolic pathway has been identified. Recent case reports suggest a link between the pentose phosphate pathway (PPP) enzyme transaldolase (TAL; encoded by TALDO1) and liver failure in children. Here, we show that Taldo1–/– and Taldo1+/– mice spontaneously developed HCC, and Taldo1–/– mice had increased susceptibility to acetaminophen-induced liver failure. Oxidative stress in Taldo1–/– livers was characterized by the accumulation of sedoheptulose 7-phosphate, failure to recycle ribose 5-phosphate for the oxidative PPP, depleted NADPH and glutathione levels, and increased production of lipid hydroperoxides. Furthermore, we found evidence of hepatic mitochondrial dysfunction, as indicated by loss of transmembrane potential, diminished mitochondrial mass, and reduced ATP/ADP ratio. Reduced β-catenin phosphorylation and enhanced c-Jun expression in Taldo1–/– livers reflected adaptation to oxidative stress. Taldo1–/– hepatocytes were resistant to CD95/Fas-mediated apoptosis in vitro and in vivo. Remarkably, lifelong administration of the potent antioxidant N-acetylcysteine (NAC) prevented acetaminophen-induced liver failure, restored Fas-dependent hepatocyte apoptosis, and blocked hepatocarcinogenesis in Taldo1–/– mice. These data reveal a protective role for the TAL-mediated branch of the PPP against hepatocarcinogenesis and identify NAC as a promising treatment for liver disease in TAL deficiency.
Robert Hanczko, David R. Fernandez, Edward Doherty, Yueming Qian, Gyorgy Vas, Brian Niland, Tiffany Telarico, Adinoyi Garba, Sanjay Banerjee, Frank A. Middleton, Donna Barrett, Maureen Barcza, Katalin Banki, Steve K. Landas, Andras Perl
The accumulation of certain species of bacteria in the intestine is involved in both tissue homeostasis and immune-mediated pathologies. The host mechanisms involved in controlling intestinal colonization with commensal bacteria are poorly understood. We observed that under specific pathogen–free or germ-free conditions, intragastric administration of Pseudomonas aeruginosa, E. coli, Staphylococcus aureus, or Lactobacillus gasseri resulted in increased colonization of the small intestine and bacterial translocation in mice lacking Cd1d, an MHC class I–like molecule, compared with WT mice. In contrast, activation of Cd1d-restricted T cells (NKT cells) with α-galactosylceramide caused diminished intestinal colonization with the same bacterial strains. We also found prominent differences in the composition of intestinal microbiota, including increased adherent bacteria, in Cd1d–/– mice in comparison to WT mice under specific pathogen–free conditions. Germ-free Cd1d–/– mice exhibited a defect in Paneth cell granule ultrastructure and ability to degranulate after bacterial colonization. In vitro, NKT cells were shown to induce the release of lysozyme from intestinal crypts. Together, these data support a role for Cd1d in regulating intestinal colonization through mechanisms that include the control of Paneth cell function.
Edward E.S. Nieuwenhuis, Tetsuya Matsumoto, Dicky Lindenbergh, Rob Willemsen, Arthur Kaser, Ytje Simons-Oosterhuis, Sylvia Brugman, Keizo Yamaguchi, Hiroki Ishikawa, Yuji Aiba, Yasuhiro Koga, Janneke N. Samsom, Kenshiro Oshima, Mami Kikuchi, Johanna C. Escher, Masahira Hattori, Andrew B. Onderdonk, Richard S. Blumberg
HIF transcription factors (HIF-1 and HIF-2) are central mediators of cellular adaptation to hypoxia. Because the resting partial pressure of oxygen is low in the intestinal lumen, epithelial cells are believed to be mildly hypoxic. Having recently established a link between HIF and the iron-regulatory hormone hepcidin, we hypothesized that HIFs, stabilized in the hypoxic intestinal epithelium, may also play critical roles in regulating intestinal iron absorption. To explore this idea, we first established that the mouse duodenum, the site of iron absorption in the intestine, is hypoxic and generated conditional knockout mice that lacked either Hif1a or Hif2a specifically in the intestinal epithelium. Using these mice, we found that HIF-1α was not necessary for iron absorption, whereas HIF-2α played a crucial role in maintaining iron balance in the organism by directly regulating the transcription of the gene encoding divalent metal transporter 1 (DMT1), the principal intestinal iron transporter. Specific deletion of Hif2a led to a decrease in serum and liver iron levels and a marked decrease in liver hepcidin expression, indicating the involvement of an induced systemic response to counteract the iron deficiency. This finding may provide a basis for the development of new strategies, specifically in targeting HIF-2α, to improve iron homeostasis in patients with iron disorders.
Maria Mastrogiannaki, Pavle Matak, Brian Keith, M. Celeste Simon, Sophie Vaulont, Carole Peyssonnaux
Zhongsheng Peng, Pier Andrea Borea, Katia Varani, Tuere Wilder, Herman Yee, Luis Chiriboga, Michael R. Blackburn, Gianfranco Azzena, Giuseppe Resta, Bruce N. Cronstein
The epithelial anion channel CFTR interacts with multiple PDZ domain–containing proteins. Heterologous expression studies have demonstrated that the Na+/H+ exchanger regulatory factors, NHERF1, NHERF2, and PDZK1 (NHERF3), modulate CFTR membrane retention, conductivity, and interactions with other transporters. To study their biological roles in vivo, we investigated CFTR-dependent duodenal HCO3– secretion in mouse models of Nherf1, Nherf2, and Pdzk1 loss of function. We found that Nherf1 ablation strongly reduced basal as well as forskolin-stimulated (FSK-stimulated) HCO3– secretory rates and blocked β2-adrenergic receptor (β2-AR) stimulation. Conversely, Nherf2–/– mice displayed augmented FSK-stimulated HCO3– secretion. Furthermore, although lysophosphatidic acid (LPA) inhibited FSK-stimulated HCO3– secretion in WT mice, this effect was lost in Nherf2–/– mice. Pdzk1 ablation reduced basal, but not FSK-stimulated, HCO3– secretion. In addition, laser microdissection and quantitative PCR revealed that the β2-AR and the type 2 LPA receptor were expressed together with CFTR in duodenal crypts and that colocalization of the β2-AR and CFTR was reduced in the Nherf1–/– mice. These data suggest that the NHERF proteins differentially modulate duodenal HCO3– secretion: while NHERF1 is an obligatory linker for β2-AR stimulation of CFTR, NHERF2 confers inhibitory signals by coupling the LPA receptor to CFTR.
Anurag Kumar Singh, Brigitte Riederer, Anja Krabbenhöft, Brigitte Rausch, Janina Bonhagen, Ulrich Lehmann, Hugo R. de Jonge, Mark Donowitz, Chris Yun, Edward J. Weinman, Olivier Kocher, Boris M. Hogema, Ursula Seidler