Alterations in Muc2 biosynthesis and secretion during dextran sulfate sodium-induced colitis

Respiratory exposure to agricultural dust extract promotes increased intestinal Tnfα expression, gut barrier dysfunction, and endotoxemia in mice

Concentrated animal feeding operations (CAFOs) are responsible for the production of global greenhouse gases and harmful environmental pollutants including hydrogen sulfide, ammonia, and particulate matter. Swine farmers are frequently exposed to organic dust that is proinflammatory in the lung and are thus at greater risk of developing pneumonia, asthma, and other respiratory conditions. In addition to respiratory disease, air pollutants are directly associated with altered gastrointestinal (GI) physiology and the development of GI diseases, thereby highlighting the gut-lung axis in disease progression. Instillation of hog dust extract (HDE) for 3 wk has been reported to promote the development of chronic airway inflammation in mice, however, the impact of HDE exposure on intestinal homeostasis is poorly understood. We report that 3-wk intranasal exposure of HDE is associated with increased intestinal macromolecule permeability and elevated serum endotoxin concentrations in C57BL/6J mice. In vivo studies also indicated mislocalization of the epithelial cell adhesion protein, E-cadherin, in the colon as well as an increase in the proinflammatory cytokine, Tnfα, in the proximal colon. Moreover, mRNA expression of the Paneth cell-associated marker, Lyz1, was increased the proximal colon, whereas the expression of the goblet cell marker, Muc2, was unchanged in the epithelial cells of the ileum, cecum, and distal colon. These results demonstrate that airway exposure to CAFOs dusts promote airway inflammation and modify the gastrointestinal tract to increase intestinal permeability, induce systemic endotoxemia, and promote intestinal inflammation. Therefore, this study identifies complex physiological consequences of chronic exposure to organic dusts derived from CAFOs on the gut-lung axis.NEW & NOTEWORTHY Agricultural workers have a higher prevalence of occupational respiratory symptoms and are at greater risk of developing respiratory diseases. However, gastrointestinal complications have also been reported, yet the intestinal pathophysiology is understudied. This work is novel because it emphasizes the role of an inhaled environmental pollutant on the development of intestinal pathophysiological outcomes. This work will provide foundation for other studies evaluating how agricultural dusts disrupts host physiology and promotes debilitating gastrointestinal and systemic disorders.

Ameliorative effect of two structurally divergent hydrazide derivatives against DSS-induced colitis by targeting Nrf2 and NF-κB signaling in mice

The environmental factors and genetic vulnerability trigger the inflammatory bowel diseases (IBDs) such as ulcerative colitis and Crohn's disease. Furthermore, the oxidative stress and inflammatory cytokines have been implicated in the aggravation of the IBDs. The aim of the present study was to investigate the effect of N-(benzylidene)-2-((2-hydroxynaphthalen-1-yl)diazenyl)benzohydrazides (NCHDH and NTHDH) compounds against the DSS-induced colitis in mice. The colitis was induced by 5% dextran sulfate sodium (DSS) dissolved in normal saline for 5 days. The effect of the NCHDH and NTHDH on the behavioral, biochemical, histological, and immunohistological parameters was assessed. The NCHDH and NTHDH treatment improved the behavioral parameters such as food intake, disease activity index, and diarrhea score significantly compared to DSS control. The NCHDH and NTHDH treatments significantly increased the antioxidant enzymes, whereas oxidative stress markers were markedly reduced. Similarly, the NCHDH and NTHDH treatments significantly suppressed the activity of nitric oxide (NO), myeloperoxidase (MPO), and eosinophil peroxidase (EPO). The histological studies showed a significant reduction in inflammation, immune cell infiltration, and fibrosis in the NCHDH- and NTHDH-treated groups. The immunohistochemical results demonstrated that NCHDH and NTHDH treatments markedly increase the expression level of Nrf2, HO-1 (hemeoxygenase-1), TRX (thioredoxin reductase), and IκB compared to the DSS-induced group. In the same way, the NCHDH and NTHDH significantly reduced the NF-κB and COX-2 (cyclooxygenase-2) expression levels. The NCHDH and NTHDH treatment significantly improved the symptoms associated with colitis via inducing antioxidants and attenuating oxidative stress markers.

Differences in MUC2 Gene Expression Based on the Clinical Severity of Colitis and the Degree of Histopathological Damage to the Colonic Mucosa in Colitis-induced Rat

BACKGROUND: Inflammatory bowel disease (IBD), such as Crohn’s disease (CD) and ulcerative colitis (UC), is characterized by intestinal inflammation and epithelial damage. Impaired mucosal cell barrier function mainly associated with thinning of the mucin layer may be the initial events underlying injury and inflammation in UC. Impaired expression of specific mucins is closely associated with IBD. MUC2 is a gene that produces mucin, which is predominant in the colon in humans and rats. METHODS: This study is an experimental study with a posttest-only design. The sample comprised 16 colitis-induced rats. Induction of colitis was done by giving a solution of dextran sodium sulfate (DSS) 2.5% 1 mL/day orally for 7 days. MUC2 gene expression was measured by rtPCR. The clinical severity of colitis was classified based on the disease activity index (DAI) score. The degree of histopathological damage was classified based on the score of colonic histology observations. The statistical analysis was done by the Shapiro–Wilk normality test and continued with an independent samples t-test. RESULTS: There were differences in MUC2 gene expression in mild and moderate colitis (1.81 vs. 2.99) but the difference was not significant (p > 0.05). MUC2 gene expression also differed in mild and severe histopathological damage degrees (2.32 vs. 2.1) but the difference was not significant (p > 0.05). CONCLUSION: It was concluded in this study that MUC2 gene expression did not have significant differences based on the clinical severity of colitis and the degree of histopathological damage to the colonic mucosa in colitis-induced rats.

The spatial transcriptomic landscape of the healing mouse intestine following damage

The intestinal barrier is composed of a complex cell network defining highly compartmentalized and specialized structures. Here, we use spatial transcriptomics to define how the transcriptomic landscape is spatially organized in the steady state and healing murine colon. At steady state conditions, we demonstrate a previously unappreciated molecular regionalization of the colon, which dramatically changes during mucosal healing. Here, we identified spatially-organized transcriptional programs defining compartmentalized mucosal healing, and regions with dominant wired pathways. Furthermore, we showed that decreased p53 activation defined areas with increased presence of proliferating epithelial stem cells. Finally, we mapped transcriptomics modules associated with human diseases demonstrating the translational potential of our dataset. Overall, we provide a publicly available resource defining principles of transcriptomic regionalization of the colon during mucosal healing and a framework to develop and progress further hypotheses.

The role of the mitochondrial protein VDAC1 in inflammatory bowel disease: a potential therapeutic target

Recent studies have implicated mitochondrial dysfunction as a trigger of inflammatory bowel diseases, including Crohn's disease (CD) and ulcerative colitis (UC). We have investigated the role of the mitochondria gate-keeper protein, the voltage-dependent-anion channel 1 (VDAC1), in gastrointestinal inflammation and tested the effects of the newly developed VDAC1-interacting molecules, VBIT-4 and VBIT-12, on UC induced by dextran sulfate sodium (DSS) or trinitrobenzene sulphonic acid (TNBS) in mice. VDAC1, which controls metabolism, lipids transport, apoptosis, and inflammasome activation, is overexpressed in the colon of CD and UC patients and DSS-treated mice. VBIT-12 treatment of cultured colon cells inhibited the DSS-induced VDAC1 overexpression, oligomerization, and apoptosis. In the DSS-treated mice, VBIT-12 suppressed weight loss, diarrhea, rectal bleeding, pro-inflammatory cytokine production, crypt and epithelial cell damage, and focal inflammation. VBIT-12 also inhibited the infiltration of inflammatory cells, apoptosis, mtDNA release, and activation of caspase-1 and NRLP3 inflammasome to reduce the inflammatory response. The levels of the ATP-gated P2X7-Ca2+/K+ channel and ER-IP3R-Ca2+ channel, and of the mitochondrial anti-viral protein (MAVS), mediating NLRP3 inflammasome assembly and activation, were highly increased in DSS-treated mice, but not when VBIT-12 treated. We conclude that UC may be promoted by VDAC1-overexpression and may therefore be amenable to treatment with novel VDAC1-interacting molecules. This VDAC1-based strategy exploits a completely new target for UC treatment and opens a new avenue for treating other inflammatory/autoimmune diseases.

Ingested Engineered Nanomaterials Affect the Expression of Mucin Genes-An In Vitro-In Vivo Comparison

The increasing use of engineered nanomaterials (ENM) in food has fueled the development of intestinal in vitro models for toxicity testing. However, ENM effects on intestinal mucus have barely been addressed, although its crucial role for intestinal health is evident. We investigated the effects of ENM on mucin expression and aimed to evaluate the suitability of four in vitro models of increasing complexity compared to a mouse model exposed through feed pellets. We assessed the gene expression of the mucins MUC1, MUC2, MUC5AC, MUC13 and MUC20 and the chemokine interleukin-8 in pre-confluent and confluent HT29-MTX-E12 cells, in stable and inflamed triple cultures of Caco-2, HT29-MTX-E12 and THP-1 cells, and in the ileum of mice following exposure to TiO₂, Ag, CeO₂ or SiO₂. All ENM had shared and specific effects. CeO₂ downregulated MUC1 in confluent E12 cells and in mice. Ag induced downregulation of Muc2 in mice. Overall, the in vivo data were consistent with the findings in the stable triple cultures and the confluent HT29-MTX-E12 cells but not in pre-confluent cells, indicating the higher relevance of advanced models for hazard assessment. The effects on MUC1 and MUC2 suggest that specific ENM may lead to an elevated susceptibility towards intestinal infections and inflammations.

Sprouty2 limits intestinal tuft and goblet cell numbers through GSK3β-mediated restriction of epithelial IL-33

Dynamic regulation of intestinal cell differentiation is crucial for both homeostasis and the response to injury or inflammation. Sprouty2, an intracellular signaling regulator, controls pathways including PI3K and MAPKs that are implicated in differentiation and are dysregulated in inflammatory bowel disease. Here, we ask whether Sprouty2 controls secretory cell differentiation and the response to colitis. We report that colonic epithelial Sprouty2 deletion leads to expanded tuft and goblet cell populations. Sprouty2 loss induces PI3K/Akt signaling, leading to GSK3β inhibition and epithelial interleukin (IL)-33 expression. In vivo, this results in increased stromal IL-13+ cells. IL-13 in turn induces tuft and goblet cell expansion in vitro and in vivo. Sprouty2 is downregulated by acute inflammation; this appears to be a protective response, as VillinCre;Sprouty2^F/F mice are resistant to DSS colitis. In contrast, Sprouty2 is elevated in chronic colitis and in colons of inflammatory bowel disease patients, suggesting that this protective epithelial-stromal signaling mechanism is lost in disease.

Dynamic regulation of colonic secretory cell numbers is a critical component of the response to intestinal injury and inflammation. Here, the authors show that loss of the intracellular signalling regulator Sprouty2 in the intestinal epithelial cells is a protective response to injury that leads to increased secretory cell numbers, thus limiting colitis severity.

Mucins in Intestinal Mucosal Defense and Inflammation: Learning From Clinical and Experimental Studies

Throughout the gastrointestinal (GI) tract, a distinct mucus layer composed of highly glycosylated proteins called mucins plays an essential role in providing lubrication for the passage of food, participating in cell signaling pathways and protecting the host epithelium from commensal microorganisms and invading pathogens, as well as toxins and other environmental irritants. These mucins can be broadly classified into either secreted gel-forming mucins, those that provide the structural backbone for the mucus barrier, or transmembrane mucins, those that form the glycocalyx layer covering the underlying epithelial cells. Goblet cells dispersed among the intestinal epithelial cells are chiefly responsible for the synthesis and secretion of mucins within the gut and are heavily influenced by interactions with the immune system. Evidence from both clinical and animal studies have indicated that several GI conditions, including inflammatory bowel disease (IBD), colorectal cancer, and numerous enteric infections are accompanied by considerable changes in mucin quality and quantity. These changes include, but are not limited to, impaired goblet cell function, synthesis dysregulation, and altered post-translational modifications. The current review aims to highlight the structural and functional features as well as the production and immunological regulation of mucins and the impact these key elements have within the context of barrier function and host defense in intestinal inflammation.

p-Cymene and Rosmarinic Acid Ameliorate TNBS-Induced Intestinal Inflammation Upkeeping ZO-1 and MUC-2: Role of Antioxidant System and Immunomodulation

p-Cymene (p-C) and rosmarinic acid (RA) are secondary metabolites that are present in medicinal herbs and Mediterranean spices that have promising anti-inflammatory properties. This study aimed to evaluate their intestinal anti-inflammatory activity in the trinitrobenzene sulphonic acid (TNBS)-induced colitis model in rats. p-C and RA (25-200 mg/kg) oral administration reduced the macroscopic lesion score, ulcerative area, intestinal weight/length ratio, and diarrheal index in TNBS-treated animals. Both compounds (200 mg/kg) decreased malondialdehyde (MDA) and myeloperoxidase (MPO), restored glutathione (GSH) levels, and enhanced fluorescence intensity of superoxide dismutase (SOD). They also decreased interleukin (IL)-1β and tumor necrosis factor (TNF)-α, and maintained IL-10 basal levels. Furthermore, they modulated T cell populations (cluster of differentiation (CD)4+, CD8+, or CD3+CD4+CD25+) analyzed from the spleen, mesenteric lymph nodes, and colon samples, and also decreased cyclooxigenase 2 (COX-2), interferon (IFN)-γ, inducible nitric oxide synthase (iNOS), and nuclear transcription factor kappa B subunit p65 (NFκB-p65) mRNA transcription, but only p-C interfered in the suppressor of cytokine signaling 3 (SOCS3) expression in inflamed colons. An increase in gene expression and positive cells immunostained for mucin type 2 (MUC-2) and zonula occludens 1 (ZO-1) was observed. Altogether, these results indicate intestinal anti-inflammatory activity of p-C and RA involving the cytoprotection of the intestinal barrier, maintaining the mucus layer, and preserving communicating junctions, as well as through modulation of the antioxidant and immunomodulatory systems.

Ulcerative colitis: Gut microbiota, immunopathogenesis and application of natural products in animal models

Ulcerative colitis (UC) is an inflammatory bowel disease with increasing incidence in the world, especially in developing countries. Although knowledge of its pathogenesis has progressed over the last years, some details require clarification. Studies have highlighted the role of microbial dysbiosis and immune dysfunction as essential factors that may initiate the typical high-grade inflammatory outcome. In order to better understand the immunopathophysiological aspects of UC, experimental murine models are valuable tools. Some of the most commonly used chemicals to induce colitis are trinitrobenzene sulfonic acid, oxazolone and dextran sodium sulfate. These may also be used to investigate new ways of preventing or treating UC and therefore improving targeting in human studies. The use of functional foods or bioactive compounds from plants may constitute an innovative direction towards the future of alternative medicine. Considering the above, this review focused on updated information regarding the 1. gut microbiota and immunopathogenesis of UC; 2. the most utilized animal models of the disease and their relevance; and 3. experimental application of natural products, not yet tested in clinical trials.

Original low birth weight deteriorates the hindgut epithelial barrier function in pigs at the growing stage

The deteriorative effect of low birth weight (LBW) on the mucosal permeability of the small intestine in piglets has been widely confirmed. However, whether the hindgut epithelial barrier function in LBW pigs is deteriorated during the growing stage is still unclear. Our study investigated differences in the hindgut epithelial barrier function between LBW and normal birth weight pigs during the growing stage (d 90). Our data demonstrated that the hindgut epithelium of LBW pigs has a high histopathological score, accompanied by decreased antioxidant capacity and increased apoptosis rate, as well as elevated expression and activity of caspase-3. In addition, the number of intestinal goblet cells and gene expression of mucin 2 were significantly down-regulated in LBW pigs. The expression of tight junction proteins (ZO-1 and occludin) was markedly inhibited by the LBW. The mRNA abundance of inflammatory cytokines such as TNF-α, IL-1β, and IL-8 was significantly increased in the hindgut mucosa of LBW pigs. Furthermore, our data revealed that LBW altered the intestinal microbial community in the hindgut mucosa of pigs. Collectively, these finding add to our understanding of the mechanisms responsible for hindgut epithelial barrier dysfunction in LBW pigs during the growing stage and facilitate the development of nutritional intervention strategies.-Tao, S., Bai, Y., Li, T., Li, N., Wang, J. Original low birth weight deteriorates the hindgut epithelial barrier function in pigs at the growing stage.

Metal bashing: iron deficiency and manganese overexposure impact on peripheral nerves

Iron (Fe) deficiency (FeD) and manganese (Mn) overexposure (MnOE) may result in several neurological alterations in the nervous system. Iron deficiency produces unique neurological deficits due to its elemental role in central nervous system (CNS) development and myelination, which might persist after normalization of Fe in the diet. Conversely, MnOE is associated with diverse neurocognitive deficits. Despite these well-known neurotoxic effects on the CNS, the influence of FeD and MnOE on the peripheral nervous system (PNS) remains poorly understood. The aim of the present investigation was to examine the effects of developmental FeD and MnOE or their combination on the sciatic nerve of young and adult rats. The parameters measured included divalent metal transporter 1 (DMT1), transferrin receptor (TfR), myelin basic protein (MBP) and peripheral myelin protein 22 (PMP22) expression, as well as Fe levels in the nerve. Our results showed that FeD produced a significant reduction in MBP and PMP22 content at P29, which persisted at P60 after Fe-sufficient diet replenishment regardless of Mn exposure levels. At P60 MnOE significantly increased sciatic nerve Fe content and DMT1 expression. However, the combination of FeD and MnOE produced no marked motor skill impairment. Evidence indicates that FeD appears to hinder developmental peripheral myelination, while MnOE may directly alter Fe homeostasis. Further studies are required to elucidate the interplay between these pathological conditions.

Dietary red raspberries attenuate dextran sulfate sodium-induced acute colitis

Persistent intestinal inflammation severely impairs intestinal integrity resulting in inflammatory bowel disease. Red raspberries (RB) are a rich source of bioactive compounds; their beneficial effect on the colitis protection was evaluated in the current study using a dextran sulfate sodium (DSS)-induced acute colitis mouse model. Six-week-old mice were fed a standard rodent research diet supplemented with RB (0 or 5% w/w, n=20 each group) for 6 weeks. At the 4th week of dietary treatment, approximately half of mice in each dietary group (n=12 each group) were subjected to 2.5% DSS induction for 6 days, followed by 6 days of recovery, to induce colitis. RB supplementation decreased body weight loss (P≤.01), disease activity index (P≤.01), and colon shortening (P≤.05) in DSS-treated mice. In addition, RB supplementation protected the colonic structure (P≤.01), associated with suppressed NF-κB signaling and reduced expression of inflammatory interleukin (IL)-1β, IL-6, IL-17, cyclooxegenase-2, and tumor necrosis factor-α in DSS-treated mice. RB supplementation reduced neutrophil infiltration, monocyte chemoattractant protein-1 mRNA expression, and xanthine oxidase content, but enhanced catalase content in DSS-treated mice. Consistently, RB supplementation reduced pore forming tight junction protein claudin-2, increased barrier strengthening claudin-3, zonula occluden-1 protein content and mucin (MUC)-2 mRNA level, and activated AMP-activated protein kinase (AMPK) in DSS-treated mice. In conclusion, dietary RB protected against inflammation and colitis symptoms induced by DSS, providing a promising dietary approach for the management of colitis.

Photodynamic therapy relieves colitis and prevents colitis-associated carcinogenesis in mice

BACKGROUND

Inflammatory bowel diseases are incurable illnesses of the gastrointestinal tract, which substantially enhance the risk of developing colorectal carcinogenesis. Conventional photodynamic therapy is a clinically approved therapeutic modality used in the treatment of neoplastic diseases. Recent preclinical and clinical studies have shown that photodynamic therapy with low doses of photosensitizer and/or light improves inflammatory conditions, including colitis. This study aims therefore at investigating the therapeutic potential of low-dose photodynamic therapy (LDPDT) with a liposomal formulation of meta-tetra(hydroxyphenyl)chlorin (namely Foslip) in the prevention of colitis-associated cancer in mice.

METHODS

LDPDT efficacy was evaluated by endoscopic, macroscopic, and histological analysis. Myeloperoxidase levels were quantified by enzyme linked immunosorbent assay and cytokines expression by quantitative RT-PCR analysis. The integrity of the intestinal barrier was evaluated by immunostaining, and bacterial composition of the fecal microbiota was determined by 454 pyrosequencing of V3-V4 region of bacterial 16S rRNA genes.

RESULTS

LDPDT reduced intestinal tumor growth by decreasing the expression of a wide range of inflammatory mediators and by lowering neutrophil influx. LDPDT treatment prevents onset of a dysbiotic microbiota in the colitis-associated cancer model.

CONCLUSIONS

LDPDT with Foslip could be considered as a novel treatment modality to prevent colorectal carcinogenesis in patients with inflammatory bowel disease.

Adaptive response activated by dietary cis9, trans11 conjugated linoleic acid prevents distinct signs of gliadin-induced enteropathy in mice

PURPOSE

The beneficial effects of conjugated linoleic acid (CLA) mixture (cis9, trans11, c9; trans10, cis12, t10) against gliadin-induced toxicity in HLA-DQ8-transgenic mice (DQ8) have been associated with improved duodenal cytoprotective mechanisms [nuclear factor-E2-related factor-2, Nrf2; acylpeptide hydrolase (APEH)/proteasome]. The present study was aimed at investigating the ability of individual CLA isomers to improve the efficacy of these defensive mechanisms and to protect against duodenal injury caused by the combined administration of gliadin and indomethacin (GI).

METHODS

Gluten-mediated enteropathy was induced in DQ8 mice by three intra-gastric administration of gliadin (20 mg kg(-1)/bw) and indomethacin (15 mg L(-1)) in drinking water for 10 days (GI). C9 or t10 CLA (520 mg kg(-1)/bw/day) were orally administered for 2 weeks. Pro-oxidant and toxic effects associated with GI treatment, anti-oxidant/detoxifying ability of c9 or t10-CLA and the protective effect induced by c9 pre-treatment (c9 + GI) were evaluated in DQ8 mice duodenum by combining enzymatic, immunoblotting, histological evaluation and quantitative real-time PCR assays.

RESULTS

GI treatment produces the time-dependent decline of the considered detoxifying mechanisms thus leading to pro-apoptotic and pro-oxidant effects. APEH/proteasome pathway was not markedly affected by individual CLA isomers, but duodenal redox status and activity/mRNA levels of Nrf2-activated enzymes were significantly improved by c9 administration. c9 pre-treatment protects against GI-mediated accumulation of oxidative stress markers, and histological examination reveals the increase of goblet cells number in mouse duodenum but induces only a partial recovery of APEH/proteasome activity.

CONCLUSIONS

The activation of and adaptive response by low doses of c9 supplementation prevents distinct signs of gliadin-induced enteropathy in DQ8 mice.

Preventive and therapeutic effects of nitrite supplementation in experimental inflammatory bowel disease

BACKGROUND

Inorganic nitrate and nitrite have emerged as alternative substrates for nitric oxide (NO) generation in the gastrointestinal tract, and have shown to be protective against drug-induced gastric injury. The aim of this study was to investigate the preventive and therapeutic effects of nitrate and nitrite in a model of experimental colitis.

METHODS

Colitis was induced in mice by administrating dextran sulfate sodium (DSS) with concurrent administration of nitrite (1 mM) or nitrate (10 mM) in the drinking water for 7 days. A therapeutic approach was also investigated by initiating nitrite treatment 3 days after DSS-induced colitis. Clinical and inflammatory markers were assessed and the colonic mucus thickness was measured in vivo. The effect of nitrite on wound healing was evaluated using colon epithelial cells.

RESULTS

Concurrent administration of DSS and nitrite (1 mM) alleviated inflammation as determined by reduced disease activity index score (DAI) and increased colon length, while nitrate (10 mM) only reduced the DAI-score. Nitrite also displayed therapeutic effects by ameliorating established colonic inflammation with reduced colonic expression of iNOS and improving histopathology. DSS-induced decrease in colonic mucus thickness was completely prevented by nitrite administration. In addition, goblet cell abundance was lower by DSS treatment, but was increased by addition of nitrite. Further studies using colon epithelial cells revealed an NO-dependent improvement in wound healing with nitrite administration.

CONCLUSION

Nitrite exerts both preventive and therapeutic effects in colonic inflammation. The protective effects involve preservation of an intact adherent mucus layer and regulation of epithelial cell restitution.

iNOS-dependent increase in colonic mucus thickness in DSS-colitic rats

Aim

To investigate colonic mucus thickness in vivo in health and during experimental inflammatory bowel disease.

Methods

Colitis was induced with 5% DSS in drinking water for 8 days prior to experiment, when the descending colonic mucosa of anesthetized rats was studied using intravital microscopy. Mucus thickness was measured with micropipettes attached to a micromanipulator. To assess the contributions of NOS and prostaglandins in the regulation of colonic mucus thickness, the non-selective NOS-inhibitor L-NNA (10 mg/kg bolus followed by 3 mg/kg/h), the selective iNOS-inhibitor L-NIL (10 mg/kg bolus followed by 3 mg/kg/h) and the non-selective COX-inhibitor diclofenac (5 mg/kg) were administered intravenously prior to experiment. To further investigate the role of iNOS in the regulation of colonic mucus thickness, iNOS −/− mice were used.

Results

Colitic rats had a thicker firmly adherent mucus layer following 8 days of DSS treatment than untreated rats (88±2 µm vs 76±1 µm). During induction of colitis, the thickness of the colonic mucus layer initially decreased but was from day 3 significantly thicker than in untreated rats. Diclofenac reduced the mucus thickness similarly in colitic and untreated rats (−16±5 µm vs −14±2 µm). While L-NNA had no effect on colonic mucus thickness in DSS or untreated controls (+3±2 µm vs +3±1 µm), L-NIL reduced the mucus thickness significantly more in colitic rats than in controls (−33±4 µm vs −10±3 µm). The importance of iNOS in regulating the colonic mucus thickness was confirmed in iNOS−/− mice, which had thinner colonic mucus than wild-type mice (35±3 µm vs 50±2 µm, respectively). Furthermore, immunohistochemistry revealed increased levels of iNOS in the colonic surface epithelium following DSS treatment.

Conclusion

Both prostaglandins and nitric oxide regulate basal colonic mucus thickness. During onset of colitis, the thickness of the mucus layer is initially reduced followed by an iNOS mediated increase.

Beneficial role of the probiotic mixture Ultrabiotique on maintaining the integrity of intestinal mucosal barrier in DSS-induced experimental colitis

The etiology of inflammatory bowel diseases which include ulcerative colitis (UC) and Crohn disease has not yet been clarified. Several hypotheses suggest a change in composition of gut microflora along with an impaired mucosal barrier that lead to excessive mucosal immunologic responses. Increased production of nitric oxide (NO) contributes greatly to the tissue injury caused by chronic inflammation. Evidence indicates that the mucus layer covering the epithelium is altered during UC and experimental colitis. Our aim in this study was to investigate the potential therapeutic effect of probiotic during DSS-induced colitis by modulating the immune system and colonic mucus production. For that purpose, the probiotic formulation Ultrabiotique(®) (Lactobacillus acidophilus, Bifidobacterium lactis, Lactobacillus plantarum and Bifidobacterium breve) was administered daily for 7 d to mice with colitis. Probiotic supplementation improved clinical symptoms and histological alterations observed during DSS induced colitis. Ultrabiotique(®) treatment down regulated the NO production by peritoneal macrophages of DSS-treated mice and enhanced mucus production in both DSS-treated and healthy mice. In conclusion, the modification of microflora by the Ultrabiotique(®) played a beneficial role in maintaining the integrity of the intestinal mucosal barrier and promoted tissue repair.

Protective effect of Clostridium tyrobutyricum in acute dextran sodium sulphate-induced colitis: differential regulation of tumour necrosis factor-α and interleukin-18 in BALB/c and severe combined immunodeficiency mice

One of the promising approaches in the therapy of ulcerative colitis is administration of butyrate, an energy source for colonocytes, into the lumen of the colon. This study investigates the effect of butyrate producing bacterium Clostridium tyrobutyricum on dextran sodium sulphate (DSS)-induced colitis in mice. Immunocompetent BALB/c and immunodeficient severe combined immunodeficiency (SCID) mice reared in specific-pathogen-free (SPF) conditions were treated intrarectally with C. tyrobutyricum 1 week prior to the induction of DSS colitis and during oral DSS treatment. Administration of DSS without C. tyrobutyricum treatment led to an appearance of clinical symptoms - bleeding, rectal prolapses and colitis-induced increase in the antigen CD11b, a marker of infiltrating inflammatory cells in the lamina propria. The severity of colitis was similar in BALB/c and SCID mice as judged by the histological damage score and colon shortening after 7 days of DSS treatment. Both strains of mice also showed a similar reduction in tight junction (TJ) protein zonula occludens (ZO)-1 expression and of MUC-2 mucin depression. Highly elevated levels of cytokine tumour necrosis factor (TNF)-α in the colon of SCID mice and of interleukin (IL)-18 in BALB/c mice were observed. Intrarectal administration of C. tyrobutyricum prevented appearance of clinical symptoms of DSS-colitis, restored normal MUC-2 production, unaltered expression of TJ protein ZO-1 and decreased levels of TNF-α and IL-18 in the descending colon of SCID and BALB/c mice, respectively. Some of these features can be ascribed to the increased production of butyrate in the lumen of the colon and its role in protection of barrier functions and regulation of IL-18 expression.

Tumor necrosis factor-α and Muc2 mucin play major roles in disease onset and progression in dextran sodium sulphate-induced colitis

The sequential events and the inflammatory mediators that characterize disease onset and progression of ulcerative colitis (UC) are not well known. In this study, we evaluated the early pathologic events in the pathogenesis of colonic ulcers in rats treated with dextran sodium sulfate (DSS). Following a lag phase, day 5 of DSS treatment was found clinically most critical as disease activity index (DAI) exhibited an exponential rise with severe weight loss and rectal bleeding. Surprisingly, on days 1-2, colonic TNF-α expression (70-80-fold) and tissue protein (50-fold) were increased, whereas IL-1β only increased on days 7-9 (60-90-fold). Days 3-6 of DSS treatment were characterized by a prominent down regulation in the expression of regulatory cytokines (40-fold for IL-10 and TGFβ) and mucin genes (15-18 fold for Muc2 and Muc3) concomitant with depletion of goblet cell and adherent mucin. Remarkably, treatment with TNF-α neutralizing antibody markedly altered DSS injury with reduced DAI, restoration of the adherent and goblet cell mucin and IL-1β and mucin gene expression. We conclude that early onset colitis is dependent on TNF-α that preceded depletion of adherent and goblet cell mucin prior to epithelial cell damage and these biomarkers can be used as therapeutic targets for UC.

Muc-2-deficient mice display a sex-specific, COX-2-related impairment of gastric mucosal repair

Mucus is known to contribute significantly to the prevention and repair of mucosal damage throughout the gastrointestinal tract. Although not normally expressed in the stomach, mucin-2 (MUC-2, encoded by the MUC2 gene) is expressed in certain disease states. The aim of this study was to determine in a mouse model whether the absence of Muc-2 would result in impaired susceptibility to and healing of gastric mucosal injury. Acute gastric damage was induced in mice deficient in Muc-2 and in wild-type controls, through oral administration of indomethacin. Chronic gastric ulcers were induced by serosal application of acetic acid. The extent of injury and the extent of healing of the damage over time were examined in both models. Indomethacin administration caused similar levels of gastric damage in Muc-2-deficient and wild-type mice, but the erosions healed more slowly in the former. Acetic acid-induced gastric ulcers were initially similar in size in Muc-2-deficient and wild-type mice of both sexes, but ulcer healing was significantly impaired in male Muc-2-deficient mice. Induction of cyclooxygenase-2 in the stomach, in response to indomethacin- or acetic acid-induced ulceration, was significantly reduced in male Muc-2-deficient mice. This phenomenon, and the sex specificity, was also apparent in bone marrow-derived macrophages stimulated with endotoxin. These results demonstrate a marked impairment of gastric mucosal repair in male Muc-2-deficient mice that may be related to an insufficient induction of cyclooxygenase-2, an enzyme known to contribute to mucosal repair.

Bacteria penetrate the inner mucus layer before inflammation in the dextran sulfate colitis model

Background

Protection of the large intestine with its enormous amount of commensal bacteria is a challenge that became easier to understand when we recently could describe that colon has an inner attached mucus layer devoid of bacteria (Johansson et al. (2008) Proc. Natl. Acad. Sci. USA 105, 15064–15069). The bacteria are thus kept at a distance from the epithelial cells and lack of this layer, as in Muc2-null mice, allow bacteria to contact the epithelium. This causes colitis and later on colon cancer, similar to the human disease Ulcerative Colitis, a disease that still lacks a pathogenetic explanation. Dextran Sulfate (DSS) in the drinking water is the most widely used animal model for experimental colitis. In this model, the inflammation is observed after 3–5 days, but early events explaining why DSS causes this has not been described.

Principal Findings

When mucus formed on top of colon explant cultures were exposed to 3% DSS, the thickness of the inner mucus layer decreased and became permeable to 2 µm fluorescent beads after 15 min. Both DSS and Dextran readily penetrated the mucus, but Dextran had no effect on thickness or permeability. When DSS was given in the drinking water to mice and the colon was stained for bacteria and the Muc2 mucin, bacteria were shown to penetrate the inner mucus layer and reach the epithelial cells already within 12 hours, long before any infiltration of inflammatory cells.

Conclusion

DSS thus causes quick alterations in the inner colon mucus layer that makes it permeable to bacteria. The bacteria that reach the epithelial cells probably trigger an inflammatory reaction. These observations suggest that altered properties or lack of the inner colon mucus layer may be an initial event in the development of colitis.

Threonine metabolism in the intestine of mice: loss of mucin 2 induces the threonine catabolic pathway

OBJECTIVES

Previous studies have shown that the intestine uses a major part of the dietary threonine intake for the synthesis of the structural component of the protective intestinal mucus layer, the secretory mucin Muc2. In this context, the high intestinal demand for dietary threonine probably results from its incorporation into secretory mucins rich in threonine residues. Therefore, we compared threonine utilization in the colon of Muc2 knockout (Muc2-/-) and wild-type (Muc2+/+) mice to investigate the intestinal dietary threonine metabolism in the absence of Muc2, which results in inflammation of the colon.

MATERIALS AND METHODS

Concentrations and isotopic enrichment of threonine were measured by gas chromatography-isotope ratio mass spectrometry in the serum, colon, and colonic content of mice given a bolus [U-(13)C]threonine enterally.

RESULTS

We retrieved 37.8% and 40.9% of dietary threonine in Muc2 +/+ and Muc2 -/- mice, respectively, either as free or incorporated threonine. There were no major differences in the availability and concentration of free or incorporated threonine recovered in both serum and colon in both types of mice. However, the Muc2 -/- mice did show overall significantly higher threonine oxidation rates compared with Muc2 +/+ mice.

CONCLUSIONS

In the absence of Muc2, dietary threonine is mainly used for constitutive protein synthesis or becomes a substrate for metabolic oxidation. This indicates that inflammation also requires high threonine amounts.

The thickness of the intestinal mucous layer in the colon of rats fed various sources of non-digestible carbohydrates is positively correlated with the pool of SCFA but negatively correlated with the proportion of butyric acid in digesta

The present experiment aimed to study the influence of six sources of non-digestible carbohydrates (NDC) on the mucous layer in the colon of rats. The NDC sources used were as follows: cellulose (C); pectin (P); inulin; resistant starch (RS); barley hulls. The diets contained 108-140 g NDC/kg DM. A fibre-free (FF) diet served as a control. The diets were fed to forty-eight rats for 34-41 d. The thickness of the total mucous layer in the colon was increased (P < 0.05) in rats fed C, P and RS when compared with rats fed a FF diet. In the colon, positive correlations were observed between the total thickness of the mucous layer and the area of neutral mucins, the pool of SCFA and the pool of acetic acid, while it was negatively correlated with the proportion of butyrate. The total thickness of the mucous layer was not correlated with the MUC gene transcription. The transcription of the gene MUC2 was negatively correlated (P = 0.04), whereas the transcription of MUC3 was positively correlated (P = 0.05) with the butyrate pool in the caecum. No correlations between the MUC2 or MUC3 transcription and SCFA were found in the colon. Hence, the regulation of the MUC genes differs between the compartments of the hindgut and, within compartments, the MUC genes may be regulated differently. In conclusion, a diet providing a large pool of SCFA with a low proportion of butyrate in the colon stimulates the formation of a thick mucous layer, which probably benefits intestinal health.

Rodent IRR-219 (IgGFcgammaBP) and rTFF3, expressed mainly in the intestinal mucosa, depleted during dextran sulfate sodium-induced colitis

IgGFcgammaBP and TFF3 are related with adaptation during injury, mucosal defense, and epithelial healing. In this work, we produced the polyclonal antibodies for rat IgGFcgammaBP or TFF3 and assessed their tissue distributions in adult and prenatal rats, rTFF3 molecular patterns under reduced and nonreduced condition, involvement of IgGFcgammaBP, and TFF3 in dextran sulfate sodium (DSS)-induced colitis. Polyclonal antibodies of rat IgGFcgammaBP or TFF3 were produced with their synthetic polypeptide. Rat TFF3 was detected in the scraped intestinal mucosa by SDS/PAGE and Western blotting. Immunohistochemical stainings of rat IgGFcgammaBP or TFF3 were performed in different tissues, mainly in mucin-producing tissues, of adult rat and prenatal rat intestine. Rat IgGFcgammaBP and TFF3 were immunohistochemically detected in the distal colon of rat colitis model induced with 7% DSS. IgGFcgammaBP and TFF3 were mainly expressed in the intestinal mucosa with different distribution patterns. The scattered staining was also found in the epithelium of bile duct. There was strong expression of IgGFcgammaBP and TFF3 in rat embryonic intestine. There were two kinds of rTFF3 complexes existed with different molecular weights, 250 and 55 kDa, under nonreduced conditions, but shifted to 6 kDa under reduced conditions. In the DSS-induced colitis model, IgGFcgammaBP and TFF3 were significantly decreased in the distal colon mucosa at the onset and active phases comparing with the normal control, partially recovered at the regenerative phase. Based on these findings,IgGFcgammaBP and TFF3 were widely expressed in the intestinal mucosa, depleted during DSS-induced colitis. Rat TFF3 existed mainly in two complexes with 250 and 55 kDa molecular weights. The present findings indicate they are two important goblet cell-derived components possibly related to the pathogenesis of DSS-induced colitis, a rat model of ulcerative colitis.

Increased susceptibility to colitis and colorectal tumors in mice lacking core 3-derived O-glycans

Altered intestinal O-glycan expression has been observed in patients with ulcerative colitis and colorectal cancer, but the role of this alteration in the etiology of these diseases is unknown. O-glycans in mucin core proteins are the predominant components of the intestinal mucus, which comprises part of the intestinal mucosal barrier. Core 3–derived O-glycans, which are one of the major types of O-glycans, are primarily expressed in the colon. To investigate the biological function of core 3–derived O-glycans, we engineered mice lacking core 3 β1,3-N-acetylglucosaminyltransferase (C3GnT), an enzyme predicted to be important in the synthesis of core 3–derived O-glycans. Disruption of the C3GnT gene eliminated core 3–derived O-glycans. C3GnT-deficient mice displayed a discrete, colon-specific reduction in Muc2 protein and increased permeability of the intestinal barrier. Moreover, these mice were highly susceptible to experimental triggers of colitis and colorectal adenocarcinoma. These data reveal a requirement for core 3–derived O-glycans in resistance to colonic disease.

Proliferative capacity of enterochromaffin cells in guinea-pigs with experimental ileitis

Enterochromaffin (EC) cells regulate gut motility and secretion in response to luminal stimuli, via the release of serotonin (5-HT). Inflammatory bowel disease and other gastrointestinal disorders are associated with increased numbers of EC cells and 5-HT availability. Our aim was to determine whether proliferation of EC cells contributed to the hyperplasia associated with intestinal inflammation. Ileitis was induced in guinea-pigs by intraluminal injection of 2,4,6-trinitrobenzene sulphonic acid (TNBS). A single pulse of 5-bromo-2'-deoxyuridine (BrdU) was injected 1 or 24 h before the collection of tissue, 6 or 7 days after TNBS treatment. In the controls, the labelling index (percentage of BrdU-labelled EC cells) was less than 1%. Despite a significant increase in EC cells in the inflamed ileum, the labelling index was similar in the TNBS-treated animals to that of controls. An increased occurrence of EC cells in the BrdU-labelled zone accounted for the increase in EC cells in the inflamed ileum. Goblet cell numbers were also significantly increased in the inflamed ileum, indicating that cell hyperplasia was not limited to the enteroendocrine cell lineage. This study demonstrates that a small portion of EC cells retain some proliferative capacity; however, hyperplasia associated with ileitis is not attributable to the increased proliferation of EC cells and is not limited to one cell lineage. Therefore, EC cell hyperplasia most probably occurs at the level of the stem cell or recruitment from the progenitor pool.

Intestinal barrier failure during experimental necrotizing enterocolitis: protective effect of EGF treatment

Necrotizing enterocolitis (NEC) is the most common intestinal disease of premature infants. Although increased mucosal permeability and altered epithelial structure have been associated with many intestinal disorders, the role of intestinal barrier function in NEC pathogenesis is currently unknown. We investigated the structural and functional changes of the intestinal barrier in a rat model of NEC. In addition, the effect of EGF treatment on intestinal barrier function was evaluated. Premature rats were divided into three groups: dam fed (DF), formula fed (NEC), or fed with formula supplemented with 500 ng/ml EGF (NEC + EGF); all groups were exposed to asphyxia/cold stress to develop NEC. Intestinal permeability, goblet cell density, mucin production, and composition of tight junction (TJ) proteins were evaluated in the terminal ileum, the site of NEC injury, and compared with the proximal jejunum, which was unaffected by NEC. Animals with NEC had significantly increased intestinal paracellular permeability compared with DF pups. Ileal goblet cell morphology, mucin production, and TJ composition were altered in animals with NEC. EGF treatment significantly decreased intestinal paracellular permeability, increased goblet cell density and mucin production, and normalized expression of two major TJ proteins, occludin and claudin-3, in the ileum. In conclusion, experimental NEC is associated with disruption of the intestinal barrier. EGF treatment maintains intestinal integrity at the site of injury by accelerating goblet cell maturation and mucin production and normalizing expression of TJ proteins, leading to improved intestinal barrier function.

Goat milk oligosaccharides are anti-inflammatory in rats with hapten-induced colitis

Oligosaccharides are included among the anti-inflammatory components of milk because of their prebiotic properties and their capacity to act as receptors of microorganisms. Here the intestinal anti-inflammatory effect of goat milk oligosaccharides (O) was assessed in trinitrobenzenesulfonic (T) acid-induced colitis in rats. Rats were randomly assigned to three different groups. Two groups (T and OS) of colitic rats and a control group (C) were studied. Group OS received 500 mg/(kg.d) of goat milk oligosaccharides orally, starting 2 d before the colitis induction until d 6, and groups T and C received the vehicle. When compared with the T group, the OS group showed decreased anorexia and body weight loss; reduced bowel wall thickening and longitudinal extension of necrotic lesions; downregulated colonic expression of interleukin 1beta, inducible nitric oxide synthase, cyclooxygenase 2, and mucin 3; and increased trefoil factor 3. Thus, goat milk oligosaccharides have anti-inflammatory effects in rats with experimental colitis and may be useful in the management of inflammatory bowel disease.

Protection against dextran sodium sulfate-induced colitis by dehydroepiandrosterone and 7alpha-hydroxy-dehydroepiandrosterone in the rat

In this study the anti-oxidant effect of DHEA and 7alpha-hydroxy-DHEA against oxidative stress induced by colitis was investigated in vivo in rats. The two steroids were intraperitoneally injected once daily (50 mg/kg body weight) for 7 days before the induction of colitis that was effected by a daily treatment of 5% (w/v) dextran sodium sulfate (DSS) in drinking water for 7 days. This was quantified by the evidence of weight loss, rectal bleeding, increased wall thickness, and colon length. The inflammatory response was assessed by neutrophil infiltration after a histological examination and myeloperoxidase (MPO) activity measurement. Two markers of oxidative damage were measured in colon homogenates after the onset of DSS treatment: protein carbonyls and thiobarbituric acid-reacting substances. The colonic metabolism of corticosterone by 11beta-hydroxysteroid dehydrogenases types 1 and 2 (11beta-HSD) was investigated in control and treated animals. Results indicated that colitis caused a decrease in body weight and colon length. Severe lesions were observed in the colon with a reduced number of goblet cells which contained less mucins. The lesions were associated with increased MPO activity and oxidative damage. Colonic inflammation down and up regulated the 11beta-HSD2 and 11beta-HSD1, respectively. Treatments by DHEA and 7alpha-hydroxy-DHEA attenuated the inflammatory response when MPO activity decreased; but this did not increase the colonic oxidation of corticosterone into 11-dehydrocorticosterone. Both DHEA and 7alpha-hydroxy-DHEA exerted a significant anti-oxidant effect against oxidative stress induced by colitis through reducing the oxidative damage to proteins and lipids. This resulted in a moderate increase in the amount of colonic mucus. Both DHEA and 7alpha-hydroxy-DHEA may prove useful in the prevention or treatment of colitis.

MUC genes are differently expressed during onset and maintenance of inflammation in dextran sodium sulfate-treated mice

Colonic mucosal protection is provided by mucous gel, mainly composed of secreted (Muc2) and membrane-bound (Muc1, Muc3, Muc4) mucins. Our aim was to determine the expression profile of secreted and membrane-bound mucins in experimental dextran sulfate sodium (DSS)-induced colitis. Acute colitis was induced in Balb/C mice by oral administration of 1.0% DSS (5 days) and chronic colitis was maintained by subsequent 0.15% DSS treatment (28 days). Clinical symptoms (mortality, weight gain), stool scores, and MPO activity confirmed the inflammatory state in the two phases of colitis. Muc2 gene expression was not modified by colitis, whereas Muc3 gene expression was increased (x2) only in the cecum and the distal colon of mice after acute colitis. Muc1 and Muc4 mRNA levels were more significantly increased in the cecum (x8-10) than in colonic segments (x4) after acute colitis. TFF3 involved in mucosal repair was up-regulated during colitis induction. These results indicate that Muc and TFF3 genes are regulated early in inflammation and suggest that their mRNA levels could be used as early markers of inflammation.

Oligosaccharides isolated from goat milk reduce intestinal inflammation in a rat model of dextran sodium sulfate-induced colitis

BACKGROUND AND AIMS

There is increased interest in the study of manipulation of the flora with pro- and prebiotics regarding inflammatory bowel disease. The aim of this work was to evaluate the effect of oligosaccharides from goat milk in a rat model of dextran sodium sulfate- (DSS-) induced colitis.

METHODS

Twenty rats were fed the same diet but with different sources of fiber (5% of the diet): cellulose or a mixture of goat's milk oligosaccharides (GMO) and cellulose. DSS treatment was used to induce a colonic inflammation. Several clinical and inflammatory parameters, as well as intestinal micorbiota and gene expression by DNA microarray technology, were evaluated.

RESULTS

DSS induced a decrease in body weight which was not observed in rats fed the GMO (decrease of 21+/-11% in control rats vs increase of 5.2+/-8.6 in GMO rats, P<0.05). DSS also caused an acute colonic inflammatory process which was weaker in rats fed the GMO, as shown by colon myeloperoxidase activity (0.53+/-0.16 vs 0.14+/-0.07U/mg of protein, P<0.05), as well as clinical symptoms measured by a scoring system (1.25+/-1.14 vs 0.4+/-0.07, P<0.05). GMO rats also showed less severe colonic lesions and a more favorable intestinal microbiota. The expression of genes involved in intestinal function, such as mucine-3, was down-regulated in DSS-control rats but returned to normal values in GMO rats.

CONCLUSION

GMO reduce intestinal inflammation and contribute to the recovery of damaged colonic mucosa.

The VSL# 3 probiotic mixture modifies microflora but does not heal chronic dextran-sodium sulfate-induced colitis or reinforce the mucus barrier in mice

The mucus layer covering the epithelium is one of the main lines of defense of the colonic barrier. Both mucus gel and mucin expressions are altered during colonic inflammation and could be involved in epithelial repair. We postulated that modulating colonic mucus and mucins by probiotic supplementation could contribute to healing inflammatory mucosa. Our aim in this study was to determine whether probiotics could repair dextran-sodium sulfate (DSS)-induced chronic colitis in mice, and whether modifications of the colonic mucins could be involved. For that purpose, the VSL#3 probiotic mixture of 8 lactic acid bacteria probiotic strains was administered daily for 2 wk to mice with a mucosa impaired by a mild DSS treatment, and to mice with a normal mucosa. Probiotic strains survived in the gastrointestinal tract, increased the cecal concentrations of bifidobacteria, and modified cecal microflora metabolic activity in both DSS-treated and healthy mice. However, probiotic supplementation did not reverse the inflammation induced by DSS at either the macroscopic or histological level. Concurrently, probiotics did not modify the colonic mucus barrier, in terms of either mucin gene expression or adherent mucus layer thickness. In conclusion, the modification of microflora by supplementation with the VSL#3 probiotic mixture did not help to repair the colonic barrier breakdown caused by DSS treatment. The potential healing roles of mucins were neither confirmed nor invalidated by this study.

Homeostasis and function of goblet cells during rotavirus infection in mice

Rotaviruses are the leading cause of severe viral gastroenteritis in young children. To gain insight in goblet cell homeostasis and intestinal mucin expression during rotavirus infection, 6-day-old mice were inoculated with murine rotavirus. To determine epithelial cell migration, mice were injected with BrdU just before inoculation. Small intestines were isolated at different days postinfection (dpi) and evaluated for rotavirus and goblet cell-specific gene expression. Small intestinal mucins of control and infected animals at 1, 2, and 4 dpi were isolated and tested for their capability to neutralize rotavirus infection in vitro. After inoculation, two peaks of viral replication were observed at 1 and 4 dpi. During infection, the number of goblet cells in infected mice was decreased in duodenum and jejunum, but was unaffected in the ileum. Goblet cells in infected animals accumulated at the tips of the villi. Muc2 mRNA levels were increased during the peak of viral replication at 1 dpi, whereas at other time points Muc2 and Tff3 mRNA levels were maintained at control levels. Muc2 protein levels in the tissue were also maintained, however Tff3 protein levels were strongly decreased. The number of goblet cells containing sulfated mucins was reduced during the two peaks of infection. Mucins isolated at 1 and 2 dpi from control and infected mice efficiently neutralized rotavirus infection in vitro. Moreover, mucins isolated from infected mice at 4 dpi were more potent in inhibiting rotavirus infection than mucins from control mice at 4 dpi. In conclusion, these data show that during rotavirus infection, goblet cells, in contrast to enterocytes, are relatively spared from apoptosis especially in the ileum. Goblet cell-specific Muc2 expression is increased and mucin structure is modified in the course of infection. This suggests that goblet cells and mucins play a role in the active defense against rotavirus infection and that age-dependent differences in mucin quantities, composition, and/or structure alter the anti-viral capabilities of small intestinal mucins.

Mouse model of enteropathogenic Escherichia coli infection

Enteropathogenic Escherichia coli (EPEC) is an important cause of diarrhea in humans. EPEC infection of cultured intestinal epithelial cells induces attaching and effacing (A/E) lesions, alters intestinal ion transport, increases paracellular permeability, and stimulates inflammation. The lack of a small-animal model has restricted in vivo studies examining EPEC-host interactions. The aim of this study was to characterize the C57BL/6J mouse as a model of EPEC infection. We have shown that EPEC can adhere to and colonize the intestinal epithelium of C57BL/6J mice. Animal weight and water intake were not altered during 10 days of EPEC infection. The proximal colon of infected mice contained semisolid stool, with stool pellets forming only in the distal colon. In contrast, the entire colon of control mice contained formed stool. Microvillous effacement and actin rearrangement, characteristic of A/E lesions, were seen in the intestine of infected mice but not control mice. Histological assessment revealed increased numbers of lamina propria neutrophils with occasional crypt abscesses, intraepithelial lymphocytes, and goblet cells in the intestine of EPEC-infected mice. Altogether, these data suggest that the C57BL/6J mouse is susceptible to infection by EPEC and will provide a suitable in vivo model for studying the consequences of EPEC infection.

The DHE cell line as a model for studying rat gastro-intestinal mucin expression: effects of dexamethasone

The expression of mucin genes was evaluated in rat intestinal cell lines in order to establish an in vitro model for investigating the regulation of intestinal mucin expression in this species. Two rat intestinal cancer cell lines (DHE, LGA) and three nontumoral rat intestinal cell lines (IEC6, IEC17, IEC18) were screened. The mRNA expression of rMuc1, rMuc2, rMuc3, rMuc4, and rMuc5AC mucin genes was studied by semiquantitative RT-PCR, real-time RT-PCR and Northern-blot analysis. Results were correlated with immunohistochemical expression of rat gastric and intestinal mucin proteins, and secretion of glycoconjugates was examined by enzyme-linked lectin assay. We showed that mRNA of rMucl and rMuc2 were constitutively expressed in all IEC cell populations but periodic acid Schiff staining of these cells did not reveal the presence of glycoproteins. DHE cells expressed rMuc1-5AC mRNA and LGA expressed the same mucins but the level of rMuc4 was much lower. Mucin mRNA expression also differed in relation with the length of cultivation. Immunocytochemical studies revealed the presence of gastric and intestinal mucins in the two tumoral cell lines. Functional experiments showed that bethanechol, A23187 and PMA stimulated release of glycoconjugates in DHE but not in LGA cells. Treatment of DHE cells with dexamethasone (10(-7) mol/l) enhanced rMuc2 mRNA but decreased rMuc1 and rMuc5AC mRNA. Real-time RT-PCR showed that the expression of rMuc1 and rMuc5AC genes was reduced by more than tenfold after 24 h. The increased expression of rMuc2 gene was confirmed by Northern blot analysis. In conclusion, DHE cells provide a valuable cellular model for research on rat mucin secretion and expression.

The murine Muc2 mucin gene is transcriptionally regulated by the zinc-finger GATA-4 transcription factor in intestinal cells

MUC2, the major mucin in the intestine, is expressed early during development and shows an altered expression pattern in intestinal bowel diseases. However, the mechanisms responsible for MUC2 expression in the intestine during these events are largely unknown. Having found putative GATA binding sites in the murine Muc2 promoter and that GATA-4 is expressed in Muc2-expressing goblet cells of the mouse small intestine, we undertook to study its regulation by this transcription factor. A panel of deletion mutants made in pGL3 vector and covering 2.2kb of the promoter were used to transfect the murine CMT-93 colorectal cancer cell line. The role of GATA-4 on Muc2 gene regulation was investigated by RT-PCR and co-transfections in the presence of expression vectors encoding either wild-type or mutated GATA-4 or by mutating the GATA-4 site identified within Muc2 promoter. Four GATA-4 cis-elements were identified in the promoter by EMSA and Muc2 promoter was efficiently activated when GATA-4 was overexpressed in the cells with a loss of transactivation when those sites were either mutated or a mutated form of GATA-4 was used. Altogether, these results identify Muc2, a goblet cell marker, as a new target gene of GATA-4 and point out an important role for this factor in Muc2 expression in the intestine.

Rotavirus enterotoxin NSP4 binds to the extracellular matrix proteins laminin-beta3 and fibronectin

Rotavirus is the most important cause of viral gastroenteritis and dehydrating diarrhea in young children. Rotavirus nonstructural protein 4 (NSP4) is an enterotoxin that was identified as an important agent in symptomatic rotavirus infection. To identify cellular proteins that interact with NSP4, a two-hybrid technique with Saccharomyces cerevisiae was used. NSP4 cDNA, derived from the human rotavirus strain Wa, was cloned into the yeast shuttle vector pGBKT7. An intestinal cDNA library derived from Caco-2 cells cloned into the yeast shuttle vector pGAD10 was screened for proteins that interact with NSP4. Protein interactions were confirmed in vivo by coimmunoprecipitation and immunohistochemical colocalization. After two-hybrid library screening, we repeatedly isolated cDNAs encoding the extracellular matrix (ECM) protein laminin-beta3 (amino acids [aa] 274 to 878) and a cDNA encoding the ECM protein fibronectin (aa 1755 to 1884). Using deletion mutants of NSP4, we mapped the region of interaction with the ECM proteins between aa 87 and 145. Deletion analysis of laminin-beta3 indicated that the region comprising aa 726 to 875 of laminin-beta3 interacts with NSP4. Interaction of NSP4 with either laminin-beta3 or fibronectin was confirmed by coimmunoprecipitation. NSP4 was present in infected enterocytes and in the basement membrane (BM) of infected neonatal mice and colocalized with laminin-beta3, indicating a physiological interaction. In conclusion, two-hybrid screening with NSP4 yielded two potential target proteins, laminin-beta3 and fibronectin, interacting with the enterotoxin NSP4. The release of NSP4 from the basal side of infected epithelial cells and the subsequent binding to ECM proteins localized at the BM may signify a new mechanism by which rotavirus disease is established.

Transcriptional activation of the murine Muc5ac mucin gene in epithelial cancer cells by TGF-beta/Smad4 signalling pathway is potentiated by Sp1

The nucleotide sequence of the pMS1 clone was submitted to the GenBank Nucleotide Sequence Database under accession number AF288076. Changes in the expression of mucin genes in gastrointestinal cancers is thought to contribute to the development of the disease. In our laboratory we have shown previously that MUC5AC is aberrantly expressed in rectosigmoid villous adenomas. However, the regulatory mechanisms underlying that altered profile of expression is unknown. In order to study its regulation at the transcriptional level, we have isolated and characterized 5.5 kb of the 5'-flanking region of the mouse Muc5ac mucin gene. The promoter is flanked by a TATA box and a transcriptional start site is located 22 bp downstream of the TATA box. Analysis of the sequence showed a high density of binding sites for Smad4, an essential factor in the signalling cascade activated by TGF-beta (transforming growth factor-beta), and Sp1, an important factor in the regulation of MUC5AC. This led us to study Muc5ac regulation by TGF-beta. We show that exogenous addition of TGF-beta to the cells induces Muc5ac endogenous expression, promoter activity and Smad4 binding to the promoter. By co-transfection studies we show that Smad4 is essential for Muc5ac promoter activation and that it does not synergize with Smad2 or Smad3. By gel-retardation and co-transfection assays, we identified Sp1 and Sp3 as important regulators of Muc5ac expression and showed that Smad4 and Sp1 act in a co-operative manner to transactivate Muc5ac promoter activity. Altogether these results bring new insights into the molecular mechanisms of TGF-beta-mediated up-regulation of Muc5ac and enhance our understanding as to how Muc5ac is regulated in certain pathologies of the gastrointestinal tract.

Antioxidant effects of dehydroepiandrosterone and 7alpha-hydroxy-dehydroepiandrosterone in the rat colon, intestine and liver

This study examined in healthy male Wistar rats the in vivo antioxidant effect of dehydroepiandrosterone (DHEA) and 7alpha-hydroxy-DHEA administered by intraperitoneal injections (50 mg/kg body weight) for 2 or 7 days. Markers of oxidative damage to lipids (thiobarbituric acid-reacting substances, TBARS) and to proteins (protein carbonyls) were assessed in colon, small intestine, and liver homogenates. DHEA and 7alpha-hydroxy-DHEA caused a decrease in body weight. DHEA treatment significantly increased liver, colon, and small intestine cell weights. After 7 days, DHEA exerted an antioxidant effect in all organs studied. In the colon, oxidative damage protection was accompanied by a goblet cell proliferation and increase in acidic mucus production. After 2 days, the antioxidant effect of 7alpha-hydroxy-DHEA was mainly observed in the liver. Nonprotein sulfhydryl groups (mostly glutathione levels) were altered by DHEA in the liver whereas they remained unchanged after 7alpha-hydroxy-DHEA treatment. The results indicate that in healthy animals, DHEA exerts a protective effect, particularly in the colon, by reducing the tissue susceptibility to oxidation of both lipids and proteins. This effect was not limited to a specific tissue, whereas the metabolite 7alpha-hydroxy-DHEA exerted its antioxidant effect towards the two markers of oxidative damage earlier than DHEA, and mainly in the liver.

Changes in small intestinal homeostasis, morphology, and gene expression during rotavirus infection of infant mice

Rotavirus is the most important cause of infantile gastroenteritis. Since in vivo mucosal responses to a rotavirus infection thus far have not been extensively studied, we related viral replication in the murine small intestine to alterations in mucosal structure, epithelial cell homeostasis, cellular kinetics, and differentiation. Seven-day-old suckling BALB/c mice were inoculated with 2 x 10(4) focus-forming units of murine rotavirus and were compared to mock-infected controls. Diarrheal illness and viral shedding were recorded, and small intestinal tissue was evaluated for rotavirus (NSP4 and structural proteins)- and enterocyte-specific (lactase, SGLT1, and L-FABP) mRNA and protein expression. Morphology, apoptosis, proliferation, and migration were evaluated (immuno)histochemically. Diarrhea was observed from days 1 to 5 postinfection, and viral shedding was observed from days 1 to 10. Two peaks of rotavirus replication were observed at 1 and 4 days postinfection. Histological changes were characterized by the accumulation of vacuolated enterocytes. Strikingly, the number of vacuolated cells exceeded the number of cells in which viral replication was detectable. Apoptosis and proliferation were increased from days 1 to 7, resulting in villous atrophy. Epithelial cell turnover was significantly higher (<4 days) than that observed in controls (7 days). Since epithelial renewal occurred within 4 days, the second peak of viral replication was most likely caused by infection of newly synthesized cells. Expression of enterocyte-specific genes was downregulated in infected cells at mRNA and protein levels starting as early as 6 h after infection. In conclusion, we show for the first time that rotavirus infection induces apoptosis in vivo, an increase in epithelial cell turnover, and a shutoff of gene expression in enterocytes showing viral replication. The shutoff of enterocyte-specific gene expression, together with the loss of mature enterocytes through apoptosis and the replacement of these cells by less differentiated dividing cells, likely leads to a defective absorptive function of the intestinal epithelium, which contributes to rotavirus pathogenesis.

Distinct epithelial responses in experimental colitis: implications for ion uptake and mucosal protection

In the present study, we aimed to investigate enterocyte- and goblet cell-specific functions during the different phases of acute colitis induced with dextran sulfate sodium (DSS). Rats were treated with DSS for 7 days, followed by a 7-day recovery period. Colonic tissue was excised on days 2 (onset of disease), 7 (active disease), and 14 (regenerative phase). Enterocyte functions were studied by the expression of carbonic anhydrases (CAs), sodium/hydrogen exchangers (NHEs) and intestinal fatty acid-binding protein (iFABP) and by alkaline phosphatase (AP) activity. The expression and secretion of the mucin Muc2 and trefoil factor family peptide-3 (TFF3) were used as parameters for goblet cell function. DSS induced a downregulation of the CAs, NHEs, and iFABP in some normal-appearing surface enterocytes and in most of the flattened-surface enterocytes during disease onset and active disease. During the regenerative phase most enterocytes expressed these genes again. Quantitative analysis revealed a significant decrease in CAs, NHEs, and iFABP expression levels during onset and active disease. During the regenerative phase, the expression levels of the CAs were restored, whereas the expression levels of the NHEs and iFABP remained decreased. In contrast, enterocyte-specific AP activity was maintained in normal and flattened enterocytes during DSS-induced colitis. Goblet cells continued to express MUC2 and TFF3 during and after DSS treatment. Moreover, Muc2 and TFF3 expression and secretion levels were maintained or even increased during each of the DSS-induced disease phases. In conclusion, DSS-induced colitis was associated with decreased expression of CAs, NHEs, and iFABP. The loss of these genes possibly accounts for some of the pathology seen in colitis. The maintenance or upregulation of Muc2 and TFF3 synthesis and secretion levels implies that goblet cells at least maintain their epithelial defense and repair capacity during acute inflammation induced by DSS.