Gastroenterology
Abstract
Fatty liver is commonly associated with alcohol ingestion and abuse. While the molecular pathogenesis of these fatty changes is well understood, the biochemical and pharmacological mechanisms by which ethanol stimulates these molecular changes remain unknown. During ethanol metabolism, adenosine is generated by the enzyme ecto-5′-nucleotidase, and adenosine production and adenosine receptor activation are known to play critical roles in the development of hepatic fibrosis. We therefore investigated whether adenosine and its receptors play a role in the development of alcohol-induced fatty liver. WT mice fed ethanol on the Lieber-DeCarli diet developed hepatic steatosis, including increased hepatic triglyceride content, while mice lacking ecto-5′-nucleotidase or adenosine A1 or A2B receptors were protected from developing fatty liver. Similar protection was also seen in WT mice treated with either an adenosine A1 or A2B receptor antagonist. Steatotic livers demonstrated increased expression of genes involved in fatty acid synthesis, which was prevented by blockade of adenosine A1 receptors, and decreased expression of genes involved in fatty acid metabolism, which was prevented by blockade of adenosine A2B receptors. In vitro studies supported roles for adenosine A1 receptors in promoting fatty acid synthesis and for A2B receptors in decreasing fatty acid metabolism. These results indicate that adenosine generated by ethanol metabolism plays an important role in ethanol-induced hepatic steatosis via both A1 and A2B receptors and suggest that targeting adenosine receptors may be effective in the prevention of alcohol-induced fatty liver.
Authors
Zhongsheng Peng, Pier Andrea Borea, Tuere Wilder, Herman Yee, Luis Chiriboga, Michael R. Blackburn, Gianfranco Azzena, Giuseppe Resta, Bruce N. Cronstein
Abstract
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.
Authors
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
Abstract
The proinflammatory cytokine IL-6 seems to have an important role in the intestinal inflammation that characterizes inflammatory bowel diseases (IBDs) such as Crohn disease and ulcerative colitis. However, little is known about the molecular mechanisms regulating IL-6 production in IBD. Here, we assessed the role of the transcriptional regulator IFN regulatory factor–4 (IRF4) in this process. Patients with either Crohn disease or ulcerative colitis exhibited increased IRF4 expression in lamina propria CD3+ T cells as compared with control patients. Consistent with IRF4 having a regulatory function in T cells, in a mouse model of IBD whereby colitis is induced in RAG-deficient mice by transplantation with CD4+CD45RBhi T cells, adoptive transfer of wild-type but not IRF4-deficient T cells resulted in severe colitis. Furthermore, IRF4-deficient mice were protected from T cell–dependent chronic intestinal inflammation in trinitrobenzene sulfonic acid– and oxazolone-induced colitis. In addition, IRF4-deficient mice with induced colitis had reduced mucosal IL-6 production, and IRF4 was required for IL-6 production by mucosal CD90+ T cells, which it protected from apoptosis. Finally, the protective effect of IRF4 deficiency could be abrogated by systemic administration of either recombinant IL-6 or a combination of soluble IL-6 receptor (sIL-6R) plus IL-6 (hyper–IL-6). Taken together, our data identify IRF4 as a key regulator of mucosal IL-6 production in T cell–dependent experimental colitis and suggest that IRF4 might provide a therapeutic target for IBDs.
Authors
Jonas Mudter, Lioubov Amoussina, Mirjam Schenk, Jingling Yu, Anne Brüstle, Benno Weigmann, Raja Atreya, Stefan Wirtz, Christoph Becker, Arthur Hoffman, Imke Atreya, Stefan Biesterfeld, Peter R. Galle, Hans A. Lehr, Stefan Rose-John, Christoph Mueller, Michael Lohoff, Markus F. Neurath
Abstract
Chronic Helicobacter pylori infection is recognized as a cause of gastric cancer. H. pylori adhesion to gastric cells is mediated by bacterial adhesins such as sialic acid–binding adhesin (SabA), which binds the carbohydrate structure sialyl–Lewis x. Sialyl–Lewis x expression in the gastric epithelium is induced during persistent H. pylori infection, suggesting that H. pylori modulates host cell glycosylation patterns for enhanced adhesion. Here, we evaluate changes in the glycosylation-related gene expression profile of a human gastric carcinoma cell line following H. pylori infection. We observed that H. pylori significantly altered expression of 168 of the 1,031 human genes tested by microarray, and the extent of these alterations was associated with the pathogenicity of the H. pylori strain. A highly pathogenic strain altered expression of several genes involved in glycan biosynthesis, in particular that encoding β3 GlcNAc T5 (β3GnT5), a GlcNAc transferase essential for the biosynthesis of Lewis antigens. β3GnT5 induction was specific to infection with highly pathogenic strains of H. pylori carrying a cluster of genes known as the cag pathogenicity island, and was dependent on CagA and CagE. Further, β3GnT5 overexpression in human gastric carcinoma cell lines led to increased sialyl–Lewis x expression and H. pylori adhesion. This study identifies what we believe to be a novel mechanism by which H. pylori modulates the biosynthesis of the SabA ligand in gastric cells, thereby strengthening the epithelial attachment necessary to achieve successful colonization.
Authors
Nuno T. Marcos, Ana Magalhães, Bibiana Ferreira, Maria J. Oliveira, Ana S. Carvalho, Nuno Mendes, Tim Gilmartin, Steven R. Head, Céu Figueiredo, Leonor David, Filipe Santos-Silva, Celso A. Reis
Abstract
Mutations in the RET gene are the primary cause of Hirschsprung disease (HSCR), or congenital intestinal aganglionosis. However, how RET malfunction leads to HSCR is not known. It has recently been shown that the binding of glial cell line–derived neurotrophic factor (GDNF) to GDNF family receptor α1 (GFRα1) activates RET and is essential for the survival of enteric neurons. In this study, we investigated Ret regulation of enteric neuron survival and its potential involvement in HSCR. Conditional ablation of Ret in postmigratory enteric neurons caused widespread neuronal death in the colon, which led to colonic aganglionosis. To further examine this finding, we generated a mouse model for HSCR by reducing Ret expression levels. These mice recapitulated the genetic and phenotypic features of HSCR and developed colonic aganglionosis due to impaired migration and successive death of enteric neural crest–derived cells. Death of enteric neurons was also induced in the colon, where reduction of Ret expression was induced after the period of enteric neural crest cell migration, indicating that diminished Ret expression directly affected the survival of colonic neurons. Thus, enteric neuron survival is sensitive to RET dosage, and cell death is potentially involved in the etiology of HSCR.
Authors
Toshihiro Uesaka, Mayumi Nagashimada, Shigenobu Yonemura, Hideki Enomoto
Abstract
IL-10 is an immunomodulatory cytokine that plays an obligate role in preventing spontaneous enterocolitis in mice. However, little is known about IL-10 function in the human intestinal mucosa. We showed here that IL-10 was constitutively expressed and secreted by the human normal colonic mucosa, including epithelial cells. Depletion of IL-10 in mucosal explants induced both downregulation of the IL-10–inducible, immunosuppressive gene BCL3 and upregulation of IFN-γ, TNF-α, and IL-17. Interestingly, TGF-β blockade also strongly induced IFN-γ production. In addition, the high levels of IFN-γ produced upon IL-10 depletion were responsible for surface epithelium damage and crypt loss, mainly by apoptosis. Polymyxin B, used as a scavenger of endogenous LPS, abolished both IFN-γ production and epithelial barrier disruption. Finally, adding a commensal bacteria strain to mucosa explant cultures depleted of both IL-10 and LPS reproduced the ability of endogenous LPS to induce IFN-γ secretion. These findings demonstrate that IL-10 ablation leads to an endogenous IFN-γ–mediated inflammatory response via LPS from commensal bacteria in the human colonic mucosa. We also found that both IL-10 and TGF-β play crucial roles in maintaining human colonic mucosa homeostasis.
Authors
Anne Jarry, Céline Bossard, Chantal Bou-Hanna, Damien Masson, Eric Espaze, Marc G. Denis, Christian L. Laboisse
Abstract
The mechanisms underlying the susceptibility of individuals with caspase recruitment domain 15 (CARD15) mutations and corresponding abnormalities of nucleotide-binding oligomerization domain 2 (NOD2) protein to Crohn disease are still poorly understood. One possibility is based on previous studies showing that muramyl dipeptide (MDP) activation of NOD2 negatively regulates TLR2 responses and that absence of such regulation leads to heightened Th1 responses. We now report that administration of MDP protects mice from the development of experimental colitis by downregulating multiple TLR responses, not just TLR2. The basis of these in vivo findings was suggested by in vitro studies of DCs, in which we showed that prestimulation of cells with MDP reduces cytokine responses to multiple TLR ligands and this reduction is dependent on enhanced IFN regulatory factor 4 (IRF4) activity. Further studies of mouse models of colitis showed that this inhibitory role of IRF4 does in fact apply to MDP-mediated protection from colitis, since neither IRF4-deficient mice nor mice treated with siRNA specific for IRF4 were protected. These findings indicate that MDP activation of NOD2 regulates innate responses to intestinal microflora by downregulating multiple TLR responses and suggest that the absence of such regulation leads to increased susceptibility to Crohn disease.
Authors
Tomohiro Watanabe, Naoki Asano, Peter J. Murray, Keiko Ozato, Prafullakumar Tailor, Ivan J. Fuss, Atsushi Kitani, Warren Strober
Abstract
Patients with protein-losing enteropathy (PLE) fail to maintain intestinal epithelial barrier function and develop an excessive and potentially fatal efflux of plasma proteins. PLE occurs in ostensibly unrelated diseases, but emerging commonalities in clinical observations recently led us to identify key players in PLE pathogenesis. These include elevated IFN-γ, TNF-α, venous hypertension, and the specific loss of heparan sulfate proteoglycans from the basolateral surface of intestinal epithelial cells during PLE episodes. Here we show that heparan sulfate and syndecan-1, the predominant intestinal epithelial heparan sulfate proteoglycan, are essential in maintaining intestinal epithelial barrier function. Heparan sulfate– or syndecan-1–deficient mice and mice with intestinal-specific loss of heparan sulfate had increased basal protein leakage and were far more susceptible to protein loss induced by combinations of IFN-γ, TNF-α, and increased venous pressure. Similarly, knockdown of syndecan-1 in human epithelial cells resulted in increased basal and cytokine-induced protein leakage. Clinical application of heparin has been known to alleviate PLE in some patients but its unknown mechanism and severe side effects due to its anticoagulant activity limit its usefulness. We demonstrate here that non-anticoagulant 2,3-de-O-sulfated heparin could prevent intestinal protein leakage in syndecan-deficient mice, suggesting that this may be a safe and effective therapy for PLE patients.
Authors
Lars Bode, Camilla Salvestrini, Pyong Woo Park, Jin-Ping Li, Jeffrey D. Esko, Simon Murch, Hudson H. Freeze
Abstract
Milk fat globule–EGF factor 8 (MFG-E8)/lactadherin participates in several cell surface–mediated regulatory events. Although its mRNA is present in the gut, the physiological roles of MFG-E8 in the intestinal mucosa have not been explored. Here we show that MFG-E8 was expressed in intestinal lamina propria macrophages from mice. Using a wound-healing assay, MFG-E8 was shown to promote the migration of intestinal epithelial cells through a PKCε-dependent mechanism. MFG-E8 bound to phosphatidylserine and triggered reorientation of the actin cytoskeleton in intestinal epithelial cells at the wound edge. Depleting MFG-E8 in mice by administration of anti–MFG-E8 antibody or targeted deletion of the MFG-E8 gene resulted in a slowing of enterocyte migration along the crypt-villus axis and focal mucosal injury. Moreover, in septic mice, intestinal MFG-E8 expression was downregulated, which correlated with intestinal injury, interrupted enterocyte migration, and impaired restitution. Treatment with recombinant MFG-E8 restored enterocyte migration, whereas deletion of MFG-E8 impeded mucosal healing in mice with sepsis. These results suggest that a decrease in intestinal MFG-E8 impairs intestinal mucosal repair in sepsis. Together, our data indicate that MFG-E8 plays an important role in the maintenance of intestinal epithelial homeostasis and the promotion of mucosal healing and suggest that recombinant MFG-E8 may be beneficial for the treatment of bowel injuries.
Authors
Heng-Fu Bu, Xiu-Li Zuo, Xiao Wang, Michael A. Ensslin, Vjola Koti, Wei Hsueh, Adam S. Raymond, Barry D. Shur, Xiao-Di Tan
Abstract
Endothelial protein C receptor (EPCR) and thrombomodulin (TM) are expressed at high levels in the resting microvasculature and convert protein C (PC) into its activated form, which is a potent anticoagulant and antiinflammatory molecule. Here we provide evidence that in Crohn disease (CD) and ulcerative colitis (UC), the 2 major forms of inflammatory bowel disease (IBD), there was loss of expression of endothelial EPCR and TM, which in turns caused impairment of PC activation by the inflamed mucosal microvasculature. In isolated human intestinal endothelial cells, administration of recombinant activated PC had a potent antiinflammatory effect, as demonstrated by downregulated cytokine-dependent cell adhesion molecule expression and chemokine production as well as inhibited leukocyte adhesion. In vivo, administration of activated PC was therapeutically effective in ameliorating experimental colitis as evidenced by reduced weight loss, disease activity index, and histological colitis scores as well as inhibited leukocyte adhesion to the inflamed intestinal vessels. The results suggest that the PC pathway represents a new system crucially involved in governing intestinal homeostasis mediated by the mucosal microvasculature. Restoring the PC pathway may represent a new therapeutic approach to suppress intestinal inflammation in IBD.
Authors
Franco Scaldaferri, Miquel Sans, Stefania Vetrano, Cristina Graziani, Raimondo De Cristofaro, Bruce Gerlitz, Alessandro Repici, Vincenzo Arena, Alberto Malesci, Julian Panes, Brian W. Grinnell, Silvio Danese
Copyright © 2020 American Society for Clinical Investigation
ISSN: 0021-9738 (print), 1558-8238 (online)