Human buccal epithelium acquires microbial hyporesponsiveness at birth, a role for secretory leukocyte protease inhibitor.

OBJECTIVE: Repetitive interaction with microbial stimuli renders epithelial cells (ECs) hyporesponsive to microbial stimulation. Previously, we have reported that buccal ECs from a subset of paediatric patients with Crohn's disease are not hyporesponsive and spontaneously released chemokines. We now aimed to identify kinetics and mechanisms of acquisition of hyporesponsiveness to microbial stimulation using primary human buccal epithelium. DESIGN: Buccal ECs collected directly after birth and in later stages of life were investigated. Chemokine release and regulatory signalling pathways were studied using primary buccal ECs and the buccal EC line TR146. Findings were extended to the intestinal mucosa using murine model systems. RESULTS: Directly after birth, primary human buccal ECs spontaneously produced the chemokine CXCL-8 and were responsive to microbial stimuli. Within the first weeks of life, these ECs attained hyporesponsiveness, associated with inactivation of the NF-κB pathway and upregulation of the novel NF-κB inhibitor SLPI but no other known NF-κB inhibitors. SLPI protein was abundant in the cytoplasm and the nucleus of hyporesponsive buccal ECs. Knock-down of SLPI in TR146-buccal ECs induced loss of hyporesponsiveness with increased NF-κB activation and subsequent chemokine release. This regulatory mechanism extended to the intestine, as colonisation of germfree mice elicited SLPI expression in small intestine and colon. Moreover, SLPI-deficient mice had increased chemokine expression in small intestinal and colonic ECs. CONCLUSIONS: We identify SLPI as a new player in acquisition of microbial hyporesponsiveness by buccal and intestinal epithelium in the first weeks after microbial colonisation.

Endoplasmic reticulum stress, unfolded protein response and altered T cell differentiation in necrotizing enterocolitis.

BACKGROUND: Endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) play important roles in chronic intestinal inflammation. Necrotizing enterocolitis (NEC) is the most common gastrointestinal emergency in preterm infants and is characterized by acute intestinal inflammation and necrosis. The objective of the study is to investigate the role of ER stress and the UPR in NEC patients. METHODS: Ileal tissues from NEC and control patients were obtained during surgical resection and/or at stoma closure. Splicing of XBP1 was detected using PCR, and gene expression was quantified using qPCR and Western blot. RESULTS: Splicing of XBP1 was only detected in a subset of acute NEC (A-NEC) patients, and not in NEC patients who had undergone reanastomosis (R-NEC). The other ER stress and the UPR pathways, PERK and ATF6, were not activated in NEC patients. A-NEC patients showing XBP1 splicing (A-NEC-XBP1s) had increased mucosal expression of GRP78, CHOP, IL6 and IL8. Similar results were obtained by inducing ER stress and the UPR in vitro. A-NEC-XBP1s patients showed altered T cell differentiation indicated by decreased mucosal expression of RORC, IL17A and FOXP3. A-NEC-XBP1s patients additionally showed more severe morphological damage and a worse surgical outcome. Compared with A-NEC patients, R-NEC patients showed lower mucosal IL6 and IL8 expression and higher mucosal FOXP3 expression. CONCLUSIONS: XBP1 splicing, ER stress and the UPR in NEC are associated with increased IL6 and IL8 expression levels, altered T cell differentiation and severe epithelial injury.

High beta-palmitate fat controls the intestinal inflammatory response and limits intestinal damage in mucin Muc2 deficient mice.

BACKGROUND: Palmitic-acid esterified to the sn-1,3 positions of the glycerol backbone (alpha, alpha'-palmitate), the predominant palmitate conformation in regular infant formula fat, is poorly absorbed and might cause abdominal discomfort. In contrast, palmitic-acid esterified to the sn-2 position (beta-palmitate), the main palmitate conformation in human milk fat, is well absorbed. The aim of the present study was to examine the influence of high alpha, alpha'-palmitate fat (HAPF) diet and high beta-palmitate fat (HBPF) diet on colitis development in Muc2 deficient (Muc2(-/-)) mice, a well-described animal model for spontaneous enterocolitis due to the lack of a protective mucus layer. METHODS: Muc2(-/-) mice received AIN-93G reference diet, HAPF diet or HBPF diet for 5 weeks after weaning. Clinical symptoms, intestinal morphology and inflammation in the distal colon were analyzed. RESULTS: Both HBPF diet and AIN-93G diet limited the extent of intestinal erosions and morphological damage in Muc2(-/-) mice compared with HAPF diet. In addition, the immunosuppressive regulatory T (Treg) cell response as demonstrated by the up-regulation of Foxp3, Tgfb1 and Ebi3 gene expression levels was enhanced by HBPF diet compared with AIN-93G and HAPF diets. HBPF diet also increased the gene expression of Pparg and enzymatic antioxidants (Sod1, Sod3 and Gpx1), genes all reported to be involved in promoting an immunosuppressive Treg cell response and to protect against colitis. CONCLUSIONS: This study shows for the first time that HBPF diet limits the intestinal mucosal damage and controls the inflammatory response in Muc2(-/-) mice by inducing an immunosuppressive Treg cell response.

Mucin Muc2 deficiency and weaning influences the expression of the innate defense genes Reg3ß, Reg3γ and angiogenin-4.

BACKGROUND: Mucin Muc2 is the structural component of the intestinal mucus layer. Absence of Muc2 leads to loss of this layer allowing direct bacterial-epithelial interactions. We hypothesized that absence of the mucus layer leads to increased expression of innate defense peptides. Specifically, we aimed to study the consequence of Muc2 deficiency (Muc2(-/-)) on the expression of regenerating islet-derived protein 3 beta (Reg3ß), regenerating islet-derived protein 3 gamma (Reg3γ), and angiogenin-4 (Ang4) in the intestine shortly before and after weaning. METHODS: Intestinal tissues of Muc2(-/-) and wild-type (WT) mice were collected at postnatal day 14 (P14, i.e. pre-weaning) and P28 (i.e. post-weaning). Reg3ß, Reg3γ, and Ang4 expression was studied by quantitative real-time PCR, Western-blot, in situ hybridization, and immunohistochemistry. RESULTS: Reg3ß and Reg3γ were expressed by diverging epithelial cell types; namely enterocytes, Paneth cells, and goblet cells. Additionally, Ang4 expression was confined to Paneth cells and goblet cells. Expression of Reg3ß, Reg3γ, and Ang4 differed between WT and Muc2(-/-) mice before and after weaning. Interestingly, absence of Muc2 strongly increased Reg3ß and Reg3γ expression in the small intestine and colon. Finally, morphological signs of colitis were only observed in the distal colon of Muc2(-/-) mice at P28, where and when expression levels of Reg3ß, Reg3γ, and Ang4 were the lowest. CONCLUSIONS: Expression of Reg3 proteins and Ang4 by goblet cells point to an important role for goblet cells in innate defense. Absence of Muc2 results in up-regulation of Reg3ß and Reg3γ expression, suggesting altered bacterial-epithelial signaling and an innate defense response in Muc2(-/-) mice. The inverse correlation between colitis development and Reg3ß, Reg3γ, and Ang4 expression levels might point toward a role for these innate defense peptides in regulating intestinal inflammation.

GATA-4/-6 and HNF-1/-4 families of transcription factors control the transcriptional regulation of the murine Muc5ac mucin during stomach development and in epithelial cancer cells.

During human embryonic and fetal development of the gastrointestinal tract, the gene encoding the MUC5AC mucin has a spatio-temporal pattern of expression restricted to the stomach. In order to better understand the molecular mechanisms responsible for this restricted pattern of expression, we have studied Muc5ac expression in the developing stomach of the mouse and correlated it to that of transcription factors known to be involved in cell differentiation programs during development. Our results indicate that GATA-6 and HNF-4α expression increased concomitantly with the induction of Muc5ac expression in embryonic stomach. We then studied Muc5ac transcriptional regulation by these transcription factors and showed that they all transactivate Muc5ac promoter. We also identified several active GATA-4/-5/-6 and HNF-1/-4 cis-elements using gel shift assays, chromatin immunoprecipitation and site-directed mutagenesis. Among all Muc5ac regulators, only GATA-6 and HNF-4a expression was concomitant to that of Muc5ac in the developing stomach. This is thus in favor of an important role for these two transcription factors as regulators of expression of the Muc5ac mucin during stomach development and in epithelial cancer cells.

Colitis development during the suckling-weaning transition in mucin Muc2-deficient mice.

The mucin Muc2 is the structural component of the colonic mucus layer. Adult Muc2 knockout (Muc2(-/-)) mice suffer from severe colitis. We hypothesized that Muc2 deficiency induces inflammation before weaning of mother's milk [postnatal day (P) 14] with aggravation of colitis after weaning (P28). Muc2(-/-) and wild-type mice were killed at embryonic day 18.5 and P1.5, P7.5, P14, P21, and P28. Colonic morphology, influx of T cells, and goblet cell-specific protein expression was investigated by (immuno)histochemistry. Cytokine and Toll-like receptor (TLR) profiles in the colon were analyzed by quantitative RT-PCR. Muc2(-/-) mice showed an increased and persistent influx of Cd3ε-positive T cells in the colonic mucosa as of P1.5. This was accompanied by mucosal damage at P28 in the distal colon but not in the proximal colon. At P14, the proinflammatory immune response [i.e., increased interleukin (IL)-12 p35, IL-12 p40, and tumor necrosis factor-α, expression] in the distal colon of Muc2(-/-) mice presented with an immune suppressive response [i.e., increased Foxp3, transforming growth factor (TGF)-ß1, IL-10, and Ebi3 expression]. In contrast, at P28, a proinflammatory response remained in the distal colon, whereas the immune suppressive response (i.e., Foxp3 and TGF-ß1 expression) declined. The proximal colon of Muc2(-/-) mice did not show morphological damage and was dominated by an immune suppressive response at P14 and P28. Interestingly, changes in expression of TLRs and TLR-related molecules were observed in the distal colon at P14 and P28 and in the proximal colon only at P28. Colitis in Muc2(-/-) mice is limited before weaning by immune suppressive responses and exacerbates in the distal colon after weaning because of the decline in the immune suppressive response.

Forkhead box transcription factors Foxa1 and Foxa2 are important regulators of Muc2 mucin expression in intestinal epithelial cells.

The mucin Muc2 is the main component of the intestinal mucus layer and thus plays important roles in intestinal protection. Therefore, it is important to understand its regulation during goblet cell differentiation. Foxa1 and Foxa2 forkhead box transcription factors (TFs) participate in transcriptional programs governing intestinal cell differentiation. Using immunohistochemistry, we showed a spatio-temporal pattern of expression of both TFs in developing and adult mouse intestine and their expression in Muc2-expressing intestinal cells. Down-regulation of Foxa1 and Foxa2 by RNA interference in cultured intestinal cells decreased Muc2 mRNA level by half, and abolished Muc2 protein expression. Chromatin immunoprecipitation and gel shift assays showed that these two TFs directly bind to the Muc2 promoter. Co-transfection experiments indicated that both TFs activate the Muc2 promoter and that mutations of three Foxa cis-elements inhibit Muc2 transactivation. In conclusion, this work identifies Foxa1 and Foxa2 as important regulators of Muc2 expression in the intestine.

Infection with Helicobacter pylori affects all major secretory cell populations in the human antrum.

We have investigated how gastric H. pylori infection affects antrum secretory cell types by studying the expression of secretory proteins in antrum epithelium. Antrum biopsy specimens were prospectively collected from 102 individuals (49 H. pylori-infected). Immunohistochemistry was performed for secretory mucins (MUC5AC, MUC5B, MUC6), Trefoil factor family (TFF)-peptides (TFF1, TFF2), endocrine peptides (gastrin, chromogranin A), and proliferating cells (Ki-67). Protein expression was quantified morphometrically. H. pylori infection was significantly correlated to mucosal inflammation and to epithelial atrophy and proliferation. In H. pylori-infected patients the number of proliferating cells increased significantly, and the zone of proliferating cells shifted toward the surface epithelium of the antral glands. Infection was correlated with decreased MUC5AC, TFF1, and TFF2 expression and increased MUC6 and MUC5B expression. Endocrine cells expressing chromagranin A and gastrin shifted toward the surface epithelium of the antral glands in H. pylori-infected patients. H. pylori infection and concomitant inflammation induced increased epithelial proliferation and triggered coordinate deregulation of secretory cell populations in the antrum. In particular, infection led to a coordinated increase in cells expressing MUC6 and MUC5B at the expense of MUC5AC-producing cells.

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.

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.

The MUC5AC glycoprotein is the primary receptor for Helicobacter pylori in the human stomach.

BACKGROUND AND OBJECTIVES: Helicobacter pylori shows a characteristic tropism for the mucus-producing gastric epithelium. In infected patients, H. pylori colocalizes in situ with the gastric secretory mucin MUC5AC. The carbohydrate blood-group antigen Lewis B (LeB) was deemed responsible for the adherence of H. pylori to the gastric surface epithelium. We sought to determine if MUC5AC is the carrier of LeB, and thus if MUC5AC is the underlying gene product functioning as the main receptor for H. pylori in the stomach. METHODS: We studied three types of human tissue producing MUC5AC: Barrett's esophagus (BE), normal gastric tissue, and gastric metaplasia of the duodenum (GMD). Tissue sections were immuno-fluorescently stained for MUC5AC or LeB, and subsequently incubated with one of three strains of Texas red-labeled H. pylori, one of which was unable to bind to LeB. We determined the colocalization of MUC5AC or LeB with adherent H. pylori. RESULTS: The binding patterns for the two LeB-binding strains to all tissues were similar, whereas the strain unable to bind to LeB did not bind to any of the tissues. In normal gastric tissue, the LeB-binding strains always bound to MUC5AC- and LeB-positive epithelial cells. In four nonsecretor patients, colocalization of the LeB-binding strains was found to MUC5AC-positive gastric epithelial cells. In BE, the LeB-binding H. pylori strains colocalized very specifically to MUC5AC-positive cells. MUC5AC-producing cells in GMD contained LeB. Yet, LeB-binding H. pylori not only colocalized to MUC5AC or LeB present in GMD, but also bound to the LeB-positive brush border of normal duodenal epithelium. CONCLUSIONS: Mucin MUC5AC is the most important carrier of the LeB carbohydrate structure in normal gastric tissue and forms the major receptor for H. pylori.

Metaplasia of the duodenum shows a Helicobacter pylori-correlated differentiation into gastric-type protein expression.

The origin of gastric metaplasia of the duodenum (GMD) remains enigmatic. We studied expression of mucins and trefoil peptides in GMD to gain insight into its phenotype and origin. We examined duodenal tissue of 95 patients (0 to 83 years old, 26 with gastric Helicobacter pylori infection) for the presence of GMD. Expression was examined immunohistochemically of secretory mucins (MUC2, MUC5AC, MUC5B, and MUC6), trefoil peptides (TFF1, TFF2, and TFF3), and sucrase-isomaltase (SI). GMD, found in 37 patients, correlated positively to gastric H. pylori infection, age, and villus atrophy. MUC2 and TFF3, expressed in normal goblet cells, were absent from 100% and 87% of GMD, respectively. GMD ubiquitously expressed MUC5AC, whereas MUC5AC expression in adjacent goblet cells was closely correlated with the extent of GMD. TFF1, TFF2, and MUC6 were found in 84%, 92%, and 65% of GMD, respectively. MUC5B was absent from epithelium and GMD. SI, expressed by villus enterocytes, was absent from GMD. Brunner's glands ubiquitously expressed MUC5B, MUC6, and TFF2. GMD was characterized by the expression of gastric-type proteins MUC5AC, MUC6, TFF1, and TFF2 and the absence of intestinal markers MUC2, TFF3, and SI. In terms of the location of metaplastic cells, our results suggest that epithelial cells migrating toward villus tips switch to gastric-type secretory cells. Positive correlation with infection suggests an inductive role H. pylori in the development of GMD.

Barrett's esophagus is characterized by expression of gastric-type mucins (MUC5AC, MUC6) and TFF peptides (TFF1 and TFF2), but the risk of carcinoma development may be indicated by the intestinal-type mucin, MUC2.

Barrett's esophagus (BE) consists of metaplastic epithelium of the esophagus, generally diagnosed by mucin histochemistry. We aimed to determine which mucins were expressed in BE, and to relate their expression to BE pathology. Archival biopsies of 4 patient groups were selected, based on standard histochemistry: BE without inflammation, BE with inflammation, ulcerating BE, and BE with dysplasia. Sections were stained by immunohistochemistry for secretory mucins (MUC2, MUC5AC, MUC5B, and MUC6), the proliferation marker Ki-67, and mucin-associated trefoil factor family (TFF) peptides (TFF1, TFF2, and TFF3). MUC5AC and TFF2 were expressed at similar high levels in each clinical group. Intestinal metaplasia (IM), detected both histochemically and by the intestinal mucin MUC2, was lowest in inflamed BE. The expression of the intestinal-type TFF3 did not differ among the groups. Ulcerating BE was distinguished by very low expression of MUC6 and MUC5B, but very high expression of TFF1. Proliferation was not different among the groups. In the total group of BE patients, H. pylori infection of the stomach correlated with decreased TFF2 expression in the BE epithelium. We conclude that BE is best characterized by the specific expression of the gastric-type markers, MUC5AC, MUC6, TFF1, and TFF2. Ulcerating BE constitutes the most distinguished group with respect to mucin and TFF expression. Of the intestinal markers, MUC2 is very specific for IM in BE, whereas TFF3 is not a marker for IM. The low occurrence of IM in inflamed BE suggests that these patients may have the lowest risk of developing carcinoma.