Regulation of apoptosis during homeostasis and disease in the intestinal epithelium

Milk fat globule-epidermal growth factor 8 is decreased in intestinal epithelium of ulcerative colitis patients and thereby causes increased apoptosis and impaired wound healing

Milk fat globule-epidermal growth factor 8 (MFG-E8) plays an important role in maintaining intestinal barrier homeostasis and accelerating intestinal restitution. However, studies of MFG-E8 expression in humans with ulcerative colitis are lacking. We examined MFG-E8 expression in colonic mucosal biopsies from ulcerative colitis patients and healthy controls (n = 26 each) by real-time quantitative polymerase chain reaction (PCR), Western blot analysis and immunohistochemistry. MFG-E8 mRNA and protein expression was lower in ulcerative colitis patients than in controls. MFG-E8 expression was inversely correlated with mucosal inflammatory activity and clinical disease activity in patients. MFG-E8 was present in human intestinal epithelial cells both in vivo and in vitro. Apoptosis induction was also detected in the intestinal epithelium of ulcerative colitis patients by terminal-deoxynucleoitidyl transferase mediated nick-end labeling assay. We used lentiviral vectors encoding human MFG-E8 targeting short hairpin RNA to obtain MFG-E8 knockdown intestinal epithelia cell clones. MFG-E8 knockdown could promote apoptosis in intestinal epithelial cell lines, accompanied by a decrease in level of the antiapoptotic protein B-cell lymphoma 2 (BCL-2) and induction of the proapoptotic protein BCL2-associated protein X (BAX). The addition of recombinant human MFG-E8 led to decreased BAX and cleaved caspase-3 levels and induction of BCL-2 level in intestinal epithelia cells. MFG-E8 knockdown also attenuated wound healing on scratch assay of intestinal epithelial cells. The mRNA level of intestinal trefoid factor 3, a pivotal factor in intestinal epithelial cell migration and restitution, was downregulated with MFG-E8 knockdown. In conclusion, we demonstrated that decreased colonic MFG-E8 expression in patients with ulcerative colitis may be associated with mucosal inflammatory activity and clinical disease activity through basal cell apoptosis and preventing tissue healing in the pathogenesis of ulcerative colitis.

Increased crypt apoptosis is a feature of autoimmune-associated chronic antibiotic refractory pouchitis

BACKGROUND

Restorative proctocolectomy with IPAA is the surgical treatment of choice in patients with ulcerative colitis who require colectomy. Pouchitis is the most common long-term complication in patients with IPAA. While immune-mediated disorders frequently coexist with IBD, they appear to be associated with an increased risk for chronic antibiotic-refractory pouchitis.

OBJECTIVE

This study aimed to evaluate histologic features of autoimmune-associated chronic antibiotic-refractory pouchitis in comparison with controls and to assess their possible diagnostic utility.

DESIGN

Clinical definition for autoimmune-associated chronic pouchitis included 1) chronic antibiotic-refractory pouchitis with response only to corticosteroids, immunomodulators, or biologics; 2) positive serum autoantibodies, including antinuclear antibody, rheumatoid factor, and antimicrosomal antibody; and 3) concurrent immune-mediated disorders. Various histologic features of pouch biopsy specimens were evaluated.

SETTING

The investigation was conducted at a tertiary referral center.

PATIENTS

From our Pouchitis Registry, all eligible patients with autoimmune-associated pouchitis (n = 17) were included. The control groups included 16 patients with nonautoimmune-associated chronic antibiotic-refractory pouchitis, 39 with antibiotic-responsive pouchitis, and 19 patients with normal pouches. Various histologic features of pouch biopsy specimens were evaluated.

RESULTS

In comparison with the control groups, the autoimmune-associated pouchitis group showed a significant increase in deep crypt apoptosis (p < 0.001). It also showed more pyloric gland metaplasia in comparison with antibiotic-responsive pouchitis and normal pouches. With the use of apoptosis score which we developed as a diagnostic marker for autoimmune-associated chronic antibiotic-refractory pouchitis, we constructed a receiver operating curve and obtained an area-under-curve value of 0.89 (95% CI: 0.79, 0.99).

CONCLUSION

Increased deep crypt apoptosis is a distinctive histologic feature of autoimmune-associated chronic antibiotic-refractory pouchitis, and this feature may aid in the diagnosis and differential diagnosis in pouchitis.

Glutathione peroxidase-2 and selenium decreased inflammation and tumors in a mouse model of inflammation-associated carcinogenesis whereas sulforaphane effects differed with selenium supply

Chronic inflammation and selenium deficiency are considered as risk factors for colon cancer. The protective effect of selenium might be mediated by specific selenoproteins, such as glutathione peroxidases (GPx). GPx-1 and -2 double knockout, but not single knockout mice, spontaneously develop ileocolitis and intestinal cancer. Since GPx2 is induced by the chemopreventive sulforaphane (SFN) via the nuclear factor E2-related factor 2 (Nrf2)/Keap1 system, the susceptibility of GPx2-KO and wild-type (WT) mice to azoxymethane and dextran sulfate sodium (AOM/DSS)-induced colon carcinogenesis was tested under different selenium states and SFN applications. WT and GPx2-KO mice were grown on a selenium-poor, -adequate or -supranutritional diet. SFN application started either 1 week before (SFN4) or along with (SFN3) a single AOM application followed by DSS treatment for 1 week. Mice were assessed 3 weeks after AOM for colitis and Nrf2 target gene expression and after 12 weeks for tumorigenesis. NAD(P)H:quinone oxidoreductases, thioredoxin reductases and glutathione-S-transferases were upregulated in the ileum and/or colon by SFN, as was GPx2 in WT mice. Inflammation scores were more severe in GPx2-KO mice and highest in selenium-poor groups. Inflammation was enhanced by SFN4 in both genotypes under selenium restriction but decreased in selenium adequacy. Total tumor numbers were higher in GPx2-KO mice but diminished by increasing selenium in both genotypes. SFN3 reduced inflammation and tumor multiplicity in both Se-adequate genotypes. Tumor size was smaller in Se-poor GPx2-KO mice. It is concluded that GPx2, although supporting tumor growth, inhibits inflammation-mediated tumorigenesis, but the protective effect of selenium does not strictly depend on GPx2 expression. Similarly, SFN requires selenium but not GPx2 for being protective.

Suppression of TNBS-induced colitis in rats by 4-methylesculetin, a natural coumarin: comparison with prednisolone and sulphasalazine

The aim of the present study was to compare the effects of the 4-methylesculetin with those produced by prednisolone and sulphasalazine and to elucidate the mechanisms involved in its action. Colitis was induced in rat by instillation of trinitrobenzenesulphonic acid (TNBS). The colon damage was evaluated using macroscopic, microscopic and biochemical analysis. In addition, in vitro studies were performed to evaluate cytokine production in cell cultures using the murine macrophage cell line RAW264.7, mouse splenocytes and the human colonic epithelial cell line Caco-2. 4-Methylesculetin produced a reduction of the macroscopic damage score and the recovery of the intestinal cytoarchitecture. These effects were associated with a prevention of the GSH depletion and an inhibition in AP activity. After colitis relapse, 4-methylesculetin improved the colonic inflammatory status as evidenced by histological findings, with a reduction in apoptosis, as well as biochemically by inhibition of colonic myeloperoxidase, alkaline phosphatase and metalloproteinase 9 activities. Paired with this inhibitive activity, there was a decrease in malondialdehyde content and in IL-1β levels. In vitro assays revealed that 4-methylesculetin promoted an inhibition in IL-1β, IL-8, IL-2 and IFN-γ production in cell cultures. In conclusion, 4-methylesculetin showed similar efficacy to that obtained with either prednisolone or sulphasalazine, both in the acute phase of colitis as well as following a curative protocol. The intestinal anti-inflammatory activity by 4-methylesculetin is likely related to its ability in reduce colonic oxidative stress and inhibit pro-inflammatory cytokine production.

The role of innate immune-stimulated epithelial apoptosis during gastrointestinal inflammatory diseases

The maintenance of mucosal barrier equilibrium in the intestine requires a delicate and dynamic balance between enterocyte loss by apoptosis and the generation of new cells by proliferation from stem cell precursors at the base of the intestinal crypts. When the balance shifts towards either excessive or insufficient apoptosis, a broad range of gastrointestinal diseases can manifest. Recent work from a variety of laboratories has provided evidence in support of a role for receptors of the innate immune system, including Toll-like receptors 2, 4, and 9 as well as the intracellular pathogen recognition receptor NOD2/CARD15, in the initiation of enterocyte apoptosis. The subsequent induction of enterocyte apoptosis in response to the activation of these innate immune receptors plays a key role in the development of various intestinal diseases, including necrotizing enterocolitis, Crohn's disease, ulcerative colitis, and intestinal cancer. This review will detail the regulatory pathways that govern enterocyte apoptosis, and will explore the role of the innate immune system in the induction of enterocyte apoptosis in gastrointestinal disease.

Alanyl-glutamine promotes intestinal epithelial cell homeostasis in vitro and in a murine model of weanling undernutrition

Alanyl-glutamine (Ala-Gln) has recently been shown to enhance catch-up growth and gut integrity in undernourished children from Northeast Brazil. We hypothesized that the intestinal epithelial effects of Ala-Gln in malnourished weanling mice and mouse small intestinal epithelial (MSIE) cells would include modulation of barrier function, proliferation, and apoptosis. Dams of 10-day-old suckling C57BL/6 pups were randomized to a standard diet or an isocaloric Northeast Brazil "regional basic diet," moderately deficient in protein, fat, and minerals. Upon weaning to their dam's diet on day of life 21, pups were randomized to Ala-Gln solution or water. At 6 wk of age, mice were killed, and jejunal tissue was collected for morphology, immunohistochemistry, and Ussing chamber analysis of transmucosal resistance and permeability. Proliferation of MSIE cells in the presence or absence of Ala-Gln was measured by MTS and bromodeoxyuridine assays. MSIE apoptosis was assessed by annexin and 7-amino-actinomycin D staining. Pups of regional basic diet-fed dams exhibited failure to thrive. Jejunal specimens from undernourished weanlings showed decreased villous height and crypt depth, decreased transmucosal resistance, increased permeability to FITC-dextran, increased claudin-3 expression, and decreased epithelial proliferation and increased epithelial apoptosis (as measured by bromodeoxyuridine and cleaved caspase-3 staining, respectively). Undernourished weanlings supplemented with Ala-Gln showed improvements in weight velocity, villous height, crypt depth, transmucosal resistance, and epithelial proliferation/apoptosis compared with unsupplemented controls. Similarly, Ala-Gln increased proliferation and reduced apoptosis in MSIE cells. In summary, Ala-Gln promotes intestinal epithelial homeostasis in a mouse model of malnutrition-associated enteropathy, mimicking key features of the human disease.

The life and death of epithelia during inflammation: lessons learned from the gut

Epithelial cells form protective barriers that physically separate an organism from the outside world. Rather than being merely static, impregnable shields, epithelia are highly dynamic structures that can adjust their proliferation, differentiation, and death in response to intrinsic and extrinsic signals. The advantages as well as pitfalls of this flexibility are highlighted in inflammatory disorders such as inflammatory bowel diseases and psoriasis, which are characterized by a chronically dysregulated homeostasis of the epithelium. In recent years, it has become increasingly apparent that epithelial cells communicate with their surroundings through converging, integrated signaling cascades and that even minor alterations in these pathways can have dramatic pathologic consequences. In this review, we discuss how inflammatory cytokines and other signaling molecules, directly or through cross talk, regulate epithelial homeostasis in the intestine, and we highlight parallels and differences in a few other organs.

TNF-α converting enzyme-mediated ErbB4 transactivation by TNF promotes colonic epithelial cell survival

Disruption of intestinal epithelial homeostasis, including enhanced apoptosis, is a hallmark of inflammatory bowel disease (IBD). We have recently shown that tumor necrosis factor (TNF) increases the kinase activity of ErbB4, a member of the epidermal growth factor receptor family that is elevated in mucosa of IBD patients and that promotes colon epithelial cell survival. In this study, we tested the hypothesis that TNF transactivates ErbB4 through TNF-α converting enzyme (TACE)-mediated ligand release and that this transactivation is necessary to protect colonic epithelial cells from cytokine-induced apoptosis. Using neutralizing antibodies, we show that heparin-binding EGF-like growth factor (HB-EGF) is required for ErbB4 phosphorylation in response to TNF. Pharmacological or genetic inhibition of the metalloprotease TACE, which mediates HB-EGF release from cells, blocked TNF-induced ErbB4 activation. MEK, but not Src or p38, was also required for transactivation. TACE activity and ligand binding were required for ErbB4-mediated antiapoptotic signaling; whereas mouse colon epithelial cells expressing ErbB4 were resistant to TNF-induced apoptosis, TACE inhibition or blockade of ErbB4 ligand binding reversed the survival advantage. We conclude that TNF transactivates ErbB4 through TACE-dependent HB-EGF release, thus protecting colon epithelial cells from cytokine-induced apoptosis. These findings have important implications for understanding how ErbB4 protects the colon from apoptosis-induced tissue injury in inflammatory conditions such as IBD.

TNF transactivation of EGFR stimulates cytoprotective COX-2 expression in gastrointestinal epithelial cells

TNF and epidermal growth factor (EGF) are well-known stimuli of cyclooxygenase (COX)-2 expression, and TNF stimulates transactivation of EGF receptor (EGFR) signaling to promote survival in colon epithelial cells. We hypothesized that COX-2 induction and cell survival signaling downstream of TNF are mediated by EGFR transactivation. TNF treatment was more cytotoxic to COX-2(-/-) mouse colon epithelial (MCE) cells than wild-type (WT) young adult mouse colon (YAMC) epithelial cells or COX-1(-/-) cells. TNF also induced COX-2 protein and mRNA expression in YAMC cells, but blockade of EGFR kinase activity or expression inhibited COX-2 upregulation. TNF-induced COX-2 expression was reduced and absent in EGFR(-/-) and TNF receptor-1 (TNFR1) knockout MCE cells, respectively, but was restored upon expression of the WT receptors. Inhibition of mediators of EGFR transactivation, Src family kinases and p38 MAPK, blocked TNF-induced COX-2 protein and mRNA expression. Finally, TNF injection increased COX-2 expression in colon epithelium of WT, but not kinase-defective EGFR(wa2) and EGFR(wa5), mice. These data indicate that TNFR1-dependent transactivation of EGFR through a p38- and/or an Src-dependent mechanism stimulates COX-2 expression to promote cell survival. This highlights an EGFR-dependent cell signaling pathway and response that may be significant in colitis-associated carcinoma.

Integrin signaling, cell survival, and anoikis: distinctions, differences, and differentiation

Cell survival and apoptosis implicate an increasing complexity of players and signaling pathways which regulate not only the decision-making process of surviving (or dying), but as well the execution of cell death proper. The same complex nature applies to anoikis, a form of caspase-dependent apoptosis that is largely regulated by integrin-mediated, cell-extracellular matrix interactions. Not surprisingly, the regulation of cell survival, apoptosis, and anoikis furthermore implicates additional mechanistic distinctions according to the specific tissue, cell type, and species. Incidentally, studies in recent years have unearthed yet another layer of complexity in the regulation of these cell processes, namely, the implication of cell differentiation state-specific mechanisms. Further analyses of such differentiation state-distinct mechanisms, either under normal or physiopathological contexts, should increase our understanding of diseases which implicate a deregulation of integrin function, cell survival, and anoikis.

NHE3 modulates the severity of colitis in IL-10-deficient mice

NHE3, the major intestinal Na(+)/H(+) exchanger, was shown to be downregulated and/or inhibited in patients with inflammatory bowel disease (IBD), a phenomenon believed to contribute to inflammation-associated diarrhea. NHE3(-/-) mice spontaneously develop colitis and demonstrate high susceptibility to dextran sulfate-induced mucosal injury. We investigated the effects of NHE3 deficiency on the development of chronic colitis in an IL-10 knockout (KO) mouse model of Crohn's disease. NHE3(-/-) mice were first backcrossed to 129/SvEv mice for >10 generations, with no apparent changes in their survival or phenotype. These mice were crossed with IL-10(-/-) mice on the same genetic background, and the phenotypes of 10-wk-old wild-type (WT), IL-10(-/-), NHE3(-/-), and IL-10(-/-)/NHE3(-/-) (double-KO) mice were studied. Histological and immunohistochemical examination of the colon established important architectural alterations, including increased neutrophilic and mononuclear cell infiltration in double- compared with single-KO mice. Double-KO mice demonstrated increased colonic expression of neutrophil collagenase matrix metalloproteinase-8 and the chemokines macrophage inflammatory protein-2, CXCL1, CXCL10, and CXCL11. Colonic IFNγ, IL-17, and IL-12/23 p40 protein secretion was significantly increased in double- compared with single-KO mice. IL-10(-/-)/NHE3(-/-) mouse colonic epithelium exhibited increased hallmarks of apoptosis, including a significantly increased number of cleaved caspase-3-positive surface epithelial cells. These results highlight the importance of NHE3 in the maintenance of intestinal barrier integrity and in modulating the inflammatory process in IL-10-deficient mice. Chronic NHE3 inhibition or underexpression observed in IBD may therefore contribute to the pathogenesis of IBD by influencing the extent of the epithelial barrier defect and affect the ultimate degree of inflammation.

PUMA-mediated intestinal epithelial apoptosis contributes to ulcerative colitis in humans and mice

Intestinal epithelial cell (IEC) apoptosis contributes to the development of ulcerative colitis (UC), an inflammatory bowel disease (IBD) that affects the colon and rectum. Therapies that target the inflammatory cytokine TNF have been found to inhibit IEC apoptosis in patients with IBD, although the mechanism of IEC apoptosis remains unclear. We therefore investigated the role of p53-upregulated modulator of apoptosis (PUMA), a p53 target and proapoptotic BH3-only protein, in colitis and IEC apoptosis, using patient samples and mouse models of UC. In UC patient samples, PUMA expression was elevated in colitis tissues relative to that in uninvolved tissues, and the degree of elevation of PUMA expression correlated with the severity of colitis and the degree of apoptosis induction. In mice, PUMA was markedly induced in colonic epithelial cells following induction of colitis by either dextran sulfate sodium salt (DSS) or 2,4,6-trinitrobenzene sulfonic acid (TNBS). The induction of PUMA was p53-independent but required NF-κB. Absence of PUMA, but neither absence of p53 nor that of another BH3-only protein (Bid), relieved DSS- and TNBS-induced colitis and inhibited IEC apoptosis. Furthermore, treating mice with infliximab (Remicade), a clinically used TNF-specific antibody, suppressed DSS- and TNBS-induced PUMA expression and colitis. These results indicate that PUMA induction contributes to the pathogenesis of colitis by promoting IEC apoptosis and suggest that PUMA inhibition may be an effective strategy to promote mucosal healing in patients with UC.

PUMA-mediated intestinal epithelial apoptosis contributes to ulcerative colitis in humans and mice

Intestinal epithelial cell (IEC) apoptosis contributes to the development of ulcerative colitis (UC), an inflammatory bowel disease (IBD) that affects the colon and rectum. Therapies that target the inflammatory cytokine TNF have been found to inhibit IEC apoptosis in patients with IBD, although the mechanism of IEC apoptosis remains unclear. We therefore investigated the role of p53-upregulated modulator of apoptosis (PUMA), a p53 target and proapoptotic BH3-only protein, in colitis and IEC apoptosis, using patient samples and mouse models of UC. In UC patient samples, PUMA expression was elevated in colitis tissues relative to that in uninvolved tissues, and the degree of elevation of PUMA expression correlated with the severity of colitis and the degree of apoptosis induction. In mice, PUMA was markedly induced in colonic epithelial cells following induction of colitis by either dextran sulfate sodium salt (DSS) or 2,4,6-trinitrobenzene sulfonic acid (TNBS). The induction of PUMA was p53-independent but required NF-κB. Absence of PUMA, but neither absence of p53 nor that of another BH3-only protein (Bid), relieved DSS- and TNBS-induced colitis and inhibited IEC apoptosis. Furthermore, treating mice with infliximab (Remicade), a clinically used TNF-specific antibody, suppressed DSS- and TNBS-induced PUMA expression and colitis. These results indicate that PUMA induction contributes to the pathogenesis of colitis by promoting IEC apoptosis and suggest that PUMA inhibition may be an effective strategy to promote mucosal healing in patients with UC.

Bifidobacterium lactis attenuates onset of inflammation in a murine model of colitis

AIM

To assess the anti-inflammatory effect of the probiotic Bifidobacterium lactis (B. lactis) in an adoptive transfer model of colitis.

METHODS

Donor and recipient mice received either B. lactis or bacterial culture medium as control (deMan Rogosa Sharpe) in drinking water for one week prior to transfer of a mix of naive and regulatory T cells until sacrifice.

RESULTS

All recipient mice developed signs of colonic inflammation, but a significant reduction of weight loss was observed in B. lactis-fed recipient mice compared to control mice. Moreover, a trend toward a diminution of mucosal thickness and attenuated epithelial damage was revealed. Colonic expression of pro-inflammatory and T cell markers was significantly reduced in B. lactis-fed recipient mice compared to controls. Concomitantly, forkhead box protein 3, a marker of regulatory T cells, was significantly up-regulated by B. lactis.

CONCLUSION

Daily oral administration of B. lactis was able to reduce inflammatory and T cells mediators and to promote regulatory T cells specific markers in a mouse model of colitis.

Subsite-specific differences of estrogen receptor beta expression in the normal colonic epithelium: implications for carcinogenesis and colorectal cancer epidemiology

OBJECTIVE

This study aimed at investigating whether a differential estrogen receptor beta (ER-beta) expression between the colonic subsites could correspond to a modification in proliferation, apoptosis, and adhesion of the normal colonocytes.

METHODS

ER-beta, Ki-67, Bcl-2, and E-cadherin expressions were investigated immunohistochemically, in normal epithelium biopsies from the ascending and the descending colon of 53 individuals, who underwent colonoscopy for the investigation of anemia and in whom no local pathology was identified.

RESULTS

ER-beta immunoreactivity has been shown to be stronger at the superficial epithelium than the crypts' base, the difference being important only for the ascending colon. In addition, ER-beta expression was higher in the superficial epithelium of the ascending colon than that of the descending colon. The variations of ER-beta expression did not correspond to the alterations in Ki-67, Bcl-2, and E-cadherin expression.

CONCLUSION

A subsite-specific variation of ER-beta expression has been shown in the normal colonic epithelium. This modulation of ER-beta might account for some well established specificities of colorectal cancer epidemiology like the right-sided predominance of the neoplasm in women and its gradual shift to more proximal sites over time.

Epithelial uptake of [18F]1-(2'-deoxy-2'-arabinofuranosyl) cytosine indicates intestinal inflammation in mice

BACKGROUND & AIMS

Uptake of [18F]1-(2'-deoxy-2'-arabinofuranosyl)cytosine (D-FAC) is a trait of activated lymphocytes; its biodistribution predominates in the spleen, thymus, and bone marrow. In addition, D-FAC is taken up at high levels by the intestine. We analyzed the regional specificity of uptake and cell types that mediate it.

METHODS

In mice, 3-dimensional isocontour regions of interest were drawn based on computed tomographic images to quantify intestinal signals from micro-positron emission tomography scans. To ascertain the cell type responsible, intestinal epithelium and immune cells were isolated and D-FAC uptake was analyzed in vitro. Mice deficient in mucosal homing (beta7 integrin-/-), enteric microbiota (germ-free), or active for immune colitis (G alpha i2-/- CD3+ transferred into Rag-/- recipients) were studied.

RESULTS

Strong uptake of D-FAC was detected throughout the intestine, with greatest signal per region of interest in the duodenum. Fractionation of intestinal cell types after in vivo uptake revealed that the signal was almost entirely from epithelial cells. Among resident immune cell types, CD4+ T cells showed the greatest per-cell and total uptake. D-FAC uptake increased in both intestinal and systemic lymphoid sites during colitis. Compared with fluorodeoxyglucose, increased uptake of D-FAC in the small and large intestine occurred at an earlier stage of disease development.

CONCLUSIONS

Uptake of D-FAC is a prominent trait of normal mouse intestinal epithelial cells, which is useful for their noninvasive visualization by positron emission tomography. Increased uptake of D-FAC reflects the activity of the epithelium and lymphocytes, providing a unique early marker of intestinal inflammation.

Post-transcriptional regulation of MEK-1 by polyamines through the RNA-binding protein HuR modulating intestinal epithelial apoptosis

MEK-1 [MAPK (mitogen-activated protein kinase) kinase-1] is an important signal transducing enzyme that is implicated in many aspects of cellular functions. In the present paper, we report that cellular polyamines regulate MEK-1 expression at the post-transcriptional level through the RNA-binding protein HuR (Hu-antigen R) in IECs (intestinal epithelial cells). Decreasing the levels of cellular polyamines by inhibiting ODC (ornithine decarboxylase) stabilized MEK-1 mRNA and promoted its translation through enhancement of the interaction between HuR and the 3'-untranslated region of MEK-1 mRNA, whereas increasing polyamine levels by ectopic ODC overexpression destabilized the MEK-1 transcript and repressed its translation by reducing the abundance of HuR-MEK-1 mRNA complex; neither intervention changed MEK-1 gene transcription via its promoter. HuR silencing rendered the MEK-1 mRNA unstable and inhibited its translation, thus preventing increases in MEK-1 mRNA and protein in polyamine-deficient cells. Conversely, HuR overexpression increased MEK-1 mRNA stability and promoted its translation. Inhibition of MEK-1 expression by MEK-1 silencing or HuR silencing prevented the increased resistance of polyamine-deficient cells to apoptosis. Moreover, HuR overexpression did not protect against apoptosis if MEK-1 expression was silenced. These results indicate that polyamines destabilize the MEK-1 mRNA and repress its translation by inhibiting the association between HuR and the MEK-1 transcript. Our findings indicate that MEK-1 is a key effector of the HuR-elicited anti-apoptotic programme in IECs.

Hemin exerts multiple protective mechanisms and attenuates dextran sulfate sodium-induced colitis

OBJECTIVE

Inflammatory bowel disease (IBD) is characterized by recurrent and severe gastrointestinal inflammation. Activation of inflammatory cells, such as TH17 lymphocytes, and/or deficiency of regulatory T cells (Treg) are responsible for the pathogenesis of IBD. As an acute phase reactant, heme oxygenase-1 (HO-1) has been shown to play an anti-inflammatory and immunomodulatory role in many disease processes. In this study, we used a dextran sulfate sodium (DSS)-induced murine colitis model to investigate the effect of upregulating HO-1 by hemin on the development of colonic inflammation.

MATERIALS AND METHODS

The mice were enterically challenged with 4% DSS. In addition, some mice were intraperitoneally administered with hemin or Sn-protoporphyrin (SnPP) on days 0, 1, and 6 after DSS treatment. The severity of colitis was evaluated by daily monitoring of weight change and diarrhea. At the end of the experiment, the colon, spleen, and mesenteric lymph nodes were harvested for histology and various immunological assays.

RESULTS

Compared to control groups, DSS challenge markedly induced HO-1 expression in the colon epithelium. Upregulation of HO-1 by hemin was further correlated with attenuation of DSS-induced colitis. In contrast, inhibition of endogenous HO-1 by SnPP aggravated the colitis. To further assess the anti-inflammatory mechanisms, we examined whether hemin enhanced the proliferation of Treg cells and suppressed the production of interleukin (IL)-17. Flow cytometry analysis revealed that hemin markedly expanded the CD4 + CD25 + Foxp3+ Treg population. Moreover, hemin attenuated IL-17 and TH17-related cytokines. This inhibition coincided with the attenuation of DSS-induced colitis. Finally, terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick end-labeling assay showed that hemin treatment markedly reduced programmed cell death of colonic epithelium, indicating that hemin exerts a modulatory effect on the induction of Treg, IL-17, and apoptosis.

CONCLUSIONS

These results demonstrate that upregulation of HO-1 by hemin ameliorated experimental colitis. Moreover, our study suggests a broader protective mechanism of hemin.

NleH effectors interact with Bax inhibitor-1 to block apoptosis during enteropathogenic Escherichia coli infection

The human pathogens enteropathogenic (EPEC) and enterohemorrhagic Escherichia coli and the related mouse pathogen Citrobacter rodentium subvert a variety of host cell signaling pathways via their plethora of type III secreted effectors, including triggering of an early apoptotic response. EPEC-infected cells do not develop late apoptotic symptoms, however. In this study we demonstrate that the NleH family effectors, homologs of the Shigella effector kinase OspG, blocks apoptosis. During EPEC infection, NleH effectors inhibit elevation of cytosolic Ca(2+) concentrations, nuclear condensation, caspase-3 activation, and membrane blebbing and promote cell survival. NleH1 alone is sufficient to prevent procaspase-3 cleavage induced by the proapoptotic compounds staurosporine, brefeldin A, and tunicamycin. Using C. rodentium, we found that NleH inhibits procaspase-3 cleavage at the bacterial attachment sites in vivo. A yeast two-hybrid screen identified the endoplasmic reticulum six-transmembrane protein Bax inhibitor-1 (BI-1) as an NleH-interacting partner. We mapped the NleH-binding site to the N-terminal 40 amino acids of BI-1. Knockdown of BI-1 resulted in the loss of NleH's antiapoptotic activity. These results indicate that NleH effectors are inhibitors of apoptosis that may act through BI-1 to carry out their cytoprotective function.

Loss of hepatocyte-nuclear-factor-4alpha affects colonic ion transport and causes chronic inflammation resembling inflammatory bowel disease in mice

BACKGROUND

Hnf4alpha, an epithelial specific transcriptional regulator, is decreased in inflammatory bowel disease and protects against chemically-induced colitis in mice. However, the precise role of this factor in maintaining normal inflammatory homeostasis of the intestine remains unclear. The aim of this study was to evaluate the sole role of epithelial Hnf4alpha in the maintenance of gut inflammatory homeostasis in mice.

METHODOLOGY/PRINCIPAL FINDINGS

We show here that specific epithelial deletion of Hnf4alpha in mice causes spontaneous chronic intestinal inflammation leading to focal areas of crypt dropout, increased cytokines and chemokines secretion, immune cell infiltrates and crypt hyperplasia. A gene profiling analysis in diseased Hnf4alpha null colon confirms profound genetic changes in cell death and proliferative behaviour related to cancer. Among the genes involved in the immune protection through epithelial barrier function, we identify the ion transporter claudin-15 to be down-modulated early in the colon of Hnf4alpha mutants. This coincides with a significant decrease of mucosal ion transport but not of barrier permeability in young animals prior to the manifestation of the disease. We confirm that claudin-15 is a direct Hnf4alpha gene target in the intestinal epithelial context and is down-modulated in mouse experimental colitis and inflammatory bowel disease.

CONCLUSION

Our results highlight the critical role of Hnf4alpha to maintain intestinal inflammatory homeostasis during mouse adult life and uncover a novel function for Hnf4alpha in the regulation of claudin-15 expression. This establishes Hnf4alpha as a mediator of ion epithelial transport, an important process for the maintenance of gut inflammatory homeostasis.

Reduced colonic apoptosis in mice overexpressing bovine growth hormone occurs through changes in several kinase pathways

OBJECTIVE

Growth hormone (GH) has antiapoptotic effects in several cell lines, including human colonic adenocarcinoma cells. In addition, it has been reported that patients with acromegaly have reduced apoptosis in colonic mucosa. The aim of the study was to investigate colonic apoptosis and underlying molecular mechanisms in transgenic mice overexpressing bovine GH (Acro) aged 3 months (young) or 9 months (elder).

DESIGN AND METHODS

Apoptosis in colonic epithelial cells was evaluated by TUNEL and Annexin V; expression of pro- and anti-apoptotic proteins was assessed by Western blot. GH action was blocked treating Acro with a selective GH receptor antagonist.

RESULTS

Young and elder Acro had lower colonic apoptosis [driven by GH through p38, p44/42 and PI3 kinase pathways], than littermate controls; changes were abolished by treating Acro with a selective GH receptor antagonist. The effects of GH were consistent with an anti-apoptotic phenotype (reduced cytosolic cytochrome-c, Bad and Bax and increased Bcl-2, and Bcl-XL level) leading to lower activation of caspase-9 and caspase-3. Changes in apoptotic proteins reversed after treatment with a GH receptor antagonist, suggesting a direct effect of GH. In addition, antiapoptotic phenotype of Acro had a protective role against doxorubicin-induced apoptosis.

CONCLUSIONS

Our results suggest that GH leads to increased and reduced levels of anti- and pro-apoptotic proteins, respectively, lowering apoptosis in either young or elder transgenic animals through activation of several kinase pathways.

The cereal type in feed influences gut wall morphology and intestinal immune cell infiltration in broiler chickens

In broiler chickens, a diet where the major cereal types are wheat, rye and/or barley has a lower digestibility compared with a diet in which maize is the major cereal type. In the present study, the effects of two different dietary cereal types, maizev.wheat/rye, on host factors (inflammation and gut integrity) and gut microbiota composition were studied. In addition, the effects of low-dose Zn-bacitracin supplementation were examined. Broilers given a wheat/rye-based diet showed more villus fusion, a thinner tunica muscularis, more T-lymphocyte infiltration, higher amount of immune cell aggregates in the mucosa, more and larger goblet cells and more apoptosis of epithelial cells in the mucosa than those given a maize-based diet. Adding Zn-bacitracin generally reversed these alterations. The microbiota composition was analysed by the use of terminal-restriction fragment length polymorphism, showing changes in the microbiota composition depending on the cereal type used in the diets. The effect of the change of cereal type on the gut microbiota composition was larger than that of Zn-bacitracin supplementation. In conclusion, a wheat/rye-based diet evoked mucosal damage, an alteration in the composition of the microbiota and an inflammatory bowel type of condition.

Transglutaminases in inflammation and fibrosis of the gastrointestinal tract and the liver

Transglutaminases are a family of eight currently known calcium-dependent enzymes that catalyze the cross-linking or deamidation of proteins. They are involved in important biological processes such as wound healing, tissue repair, fibrogenesis, apoptosis, inflammation and cell-cycle control. Therefore, they play important roles in the pathomechanisms of autoimmune, inflammatory and degenerative diseases, many of which affect the gastrointestinal system. Transglutaminase 2 is prominent, since it is central to the pathogenesis of celiac disease, and modulates inflammation and fibrosis in inflammatory bowel and chronic liver diseases. This review highlights our present understanding of transglutaminase function in gastrointestinal and liver diseases and therapeutic strategies that target transglutaminase activities.

Contribution of intestinal epithelial cells to innate immunity of the human gut--studies on polarized monolayers of colon carcinoma cells

The aim was to establish an in vitro model for studies of innate defence mechanisms of human intestinal epithelium. Ultrastructural characterization and determination of mRNA expression levels for apical glycocalyx and mucous components showed that polarized, tight monolayers of the colon carcinoma cell lines T84 and Caco2 acquire the features of mature- and immature columnar epithelial cells, respectively. Polarized monolayers were challenged with non-pathogenic Gram+ and Gram- bacteria from the apical side and the proinflammatory cytokines interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) from the basolateral side. Immune responses were estimated as changes in mRNA expression levels for the mucous component mucin-2 (MUC2), the glycocalyx components carcinoembryonic antigen (CEA), CEA-related cell adhesion molecule-1 (CEACAM1), CEACAM6, CEACAM7 and MUC3, the antimicrobial factors human beta-defensin-1 (hBD1), hBD2, hBD3 and lysozyme, the chemokine IL-8 and the cytokines IL-6 and TNF-alpha. Tight monolayer cells were generally unresponsive to bacterial challenge, but increased their hBD2 levels when challenged with Bacillus megaterium. T84 cells also increased their TNF-alpha levels upon bacterial challenge. Tight monolayer cells responded to cytokine challenge suggesting awareness of basolateral attack. TNF-alpha induced significantly increased levels of IL-8 and TNF-alpha itself in both cell lines suggesting recruitment and activation of immune cells in the underlying mucosa in vivo. Cytokine challenge also increased levels of CEACAM1, which includes two functionally different forms, CEACAM1-L and CEACAM1-S. In T84 cells, IFN-gamma was selective for CEACAM1-L while TNF-alpha upregulated both forms. Increased CEACAM1 expression may influence epithelial function and communication between epithelial cells and intraepithelial lymphocytes.

Enhanced expression of resistin-like molecule beta in human colon cancer and its clinical significance

Previous studies have indicated that resistin-like molecule beta (RELM beta), an intestinal goblet cell-specific protein, is markedly increased in the intestinal tumors of min mice and over-expressed in a human colon cancer cell line. We hypothesized that RELM beta might be enhanced in human colon cancer. The aim of this study was to examine the clinical importance of RELM beta expression in colon cancer patients and to correlate its expression with various clinicopathological parameters, upstream regulatory molecule expression, tumor proliferative capacity, and patients' survival. Of the 80 colon cancer patients studied, 65 (81.25%) tested positive for RELM beta, mainly in the cytoplasm of colon mucosa. Contrasting sharply with the strongly RELM beta-positive tumors, normal colon mucous membrane was negative or weakly positive. RELM beta positivity in colon cancer was correlated with histological grade of differentiation and lymph node metastasis, but not with age, gender, tumor location and size, tumor infiltration, Dukes' stage, liver metastasis, and venous invasion. RELM beta expression was significantly correlated with the expression of transcription factor CDX-2 (P < 0.01) but not with that of proliferative index Ki-67 (P > 0.05). The mean postoperative survival time (2.76 years) of RELM beta-positive patients was significantly longer than that (1.26 years) of RELM beta-negative patients (P = 0.032). These findings support evidence of the enhanced RELM beta expression in colon cancer patients and suggest that further investigation is warranted to explore the role of RELM beta in colon cancer.

Genetic analysis of Drosophila melanogaster susceptibility to intestinal Vibrio cholerae infection

We previously demonstrated that Vibrio cholerae is able to colonize the intestine of the fly to produce a lethal infection. Here we present the results of a genetic screen undertaken to identify factors that alter susceptibility of the fly to intestinal V. cholerae infection. In this model of infection, the Eiger/Wengen signalling pathway protects the fly against infection. Furthermore, mutations within the IMD signalling pathway increase resistance to intestinal V. cholerae infection and increase programmed cell death within the intestinal epithelium during infection. We propose that programmed cell death protects the intestinal epithelium against V. cholerae infection and therefore that the fly may serve as a useful model in which to study modulation of intestinal epithelial cell survival by commensal and pathogenic intestinal bacteria as well as the pathological processes leading to erosion of the intestinal epithelium and intestinal malignancy.

Enteral and parenteral nutrition distinctively modulate intestinal permeability and T cell function in vitro

BACKGROUND

Nutritional support is an established element of therapy for various indications. However, its impact on the mucosal barrier function is not well understood.

AIM OF THE STUDY

We investigated the influence of EN and PN on intestinal epithelial cells and peripheral blood (PBMC) and lamina propria mononuclear cells (LPMC), all of which are involved in the mucosal defense against bacterial translocation and systemic inflammation.

METHODS

Integrity of epithelial cells was measured as transepithelial electrical resistance (TER) of confluent Caco-2 monolayers in the presence of 1% EN, PN and a parenteral amino acid mixture (AM). To determine wound healing capacities, an established migration model with IEC-6 cells was used. Furthermore, we investigated apoptosis, cell activation, proliferation and cytokine secretion of Caco-2, HT29 and of stimulated PBMC and LPMC cultured with or without 1 and 5% EN, AM or PN.

RESULTS

We demonstrated that EN, AM and PN promoted the integrity of the epithelial monolayer and reconstituted epithelial cell continuity TGF-beta-dependently and -independently. Interestingly, only PN induced apoptosis and decreased the mitochondrial membrane potential. The activation status of PBMC was significantly reduced by EN and AM. Specifically, EN leads to an increased apoptosis rate, inhibited cell cycle progression and increased pro-inflammatory cytokine secretion. Both EN and PN reduced the activation status and the release of pro- and anti-inflammatory cytokines.

CONCLUSIONS

Our study provides evidence that by promoting wound healing and regulating T cell function, EN, AM, and PN potently interact with the intestinal barrier and immune system, thus justifying its use in diseases accompanied by impaired mucosal barrier function.

Inhibition of apoptosis in Bacteroides fragilis enterotoxin-stimulated intestinal epithelial cells through the induction of c-IAP-2

Enterotoxigenic Bacteroides fragilis produces an approximately 20-kDa heat-labile enterotoxin (BFT) that plays an essential role in generating mucosal inflammation. Although it is well known that proinflammatory signals are expressed in BFT-stimulated intestinal epithelial cells, cell death processes have not been elucidated. BFT induced apoptosis in HT-29 cells, but the apoptosis was first apparent 36 h after stimulation. During the early period of BFT stimulation, expression of cellular inhibitor of apoptosis protein-2 (c-IAP2) increased, and inhibition of c-IAP2 augmented the apoptotic cell death. Inhibition of BFT-induced COX-2 expression decreased prostaglandin E(2) (PGE(2)) production, which led not only to a decrease of c-IAP2 activity but also to an enhancement of DNA fragmentation in the early period of BFT stimulation. Furthermore, apoptosis inhibition through PGE(2) and c-IAP2 was mainly regulated by a p38 mitogen-activated protein kinase (MAPK). These results suggest that the inhibition of apoptosis may be mediated by a sequential pathway, including MAPK, COX-2, PGE(2) and c-IAP2, in the early period of stimulation. The delay in the onset of epithelial cell apoptosis after enterotoxigenic B. fragilis infection may be important to the host since it can provides sufficient time for epithelial cells to generate signals for the activation of mucosal inflammation and it may increase the chances of bacterial colonization.

B1 integrin/Fak/Src signaling in intestinal epithelial crypt cell survival: integration of complex regulatory mechanisms

The molecular determinants which dictate survival and apoptosis/anoikis in human intestinal crypt cells remain to be fully understood. To this effect, the roles of beta1 integrin/Fak/Src signaling to the PI3-K/Akt-1, MEK/Erk, and p38 pathways, were investigated. The regulation of six Bcl-2 homologs (Bcl-2, Mcl-1, Bcl-X(L), Bax, Bak, Bad) was likewise analyzed. We report that: (1) Anoikis causes a down-activation of Fak, Src, Akt-1 and Erk1/2, a loss of Fak-Src association, and a sustained/enhanced activation of p38beta, which is required as apoptosis/anoikis driver; (2) PI3-K/Akt-1 up-regulates the expression of Bcl-X(L) and Mcl-1, down-regulates Bax and Bak, drives Bad phosphorylation (both serine112/136 residues) and antagonizes p38beta activation; (3) MEK/Erk up-regulates Bcl-2, drives Bad phosphorylation (serine112 residue), but does not antagonize p38bactivation; (4) PI3-K/Akt-1 is required for survival, whereas MEK/Erk is not; (5) Src acts as a cornerstone in the engagement of both pathways by beta1 integrins/Fak, and is crucial for survival; and (6) beta1 integrins/Fak and/or Src regulate Bcl-2 homologs as both PI3-K/Atk-1 and MEK/Erk combined. Hence, beta1 integrin/Fak/Src signaling translates into integrated mediating functions of p38beta activation and regulation of Bcl-2 homologs by PI3-K/Akt-1 and MEK/Erk, consequently determining their requirement (or not) for survival.

The hydroxylase inhibitor dimethyloxalylglycine is protective in a murine model of colitis

BACKGROUND & AIMS

Prolyl and asparaginyl hydroxylases are key oxygen-sensing enzymes that confer hypoxic sensitivity to transcriptional regulatory pathways including the hypoxia inducible factor 1 (HIF-1) and nuclear factor-kappaB (NF-kappaB). Knockout of either HIF-1 or (IKKbeta-dependent) NF-kappaB pathways in intestinal epithelial cells promotes inflammatory disease in murine models of colitis. Both HIF-1 and NF-kappaB pathways are repressed by the action of hydroxylases through the hydroxylation of key regulatory molecules.

METHODS

In this study we have investigated the effects of the hydroxylase inhibitor dimethyloxalylglycine (DMOG) on Caco-2 intestinal epithelial cells in vitro and in a dextran sodium sulfate-induced model of murine colitis.

RESULTS

DMOG induces both HIF-1 and NF-kappaB activity in cultured intestinal epithelial cells, and is profoundly protective in dextran-sodium sulfate colitis in a manner that is at least in part reflected by the development of an anti-apoptotic phenotype in intestinal epithelial cells, which we propose reduces epithelial barrier dysfunction.

CONCLUSIONS

These data show that hydroxylase inhibitors such as DMOG represent a new strategy for the treatment of inflammatory bowel disease.

Subclinical Rejection in the Initial Postoperative Period in Small Intestinal Transplantation: A Negative Influence on Graft Survival

BACKGROUND

Subclinical rejection (SCR) is a known entity in various solid organ transplants but not in intestinal transplantation.

METHODS

The purpose of this study is to characterize the presence and effect of SCR in small intestinal transplantation (Itx). A total of 151 patients who underwent Itx and maintained a functioning graft for at least 3 months after Itx were investigated. The clinicopathological characteristics associated with a SCR episode within 3 months after Itx were analyzed. Cox regression with the landmark method (the landmark time being 3 months after Itx) was used for the analyses of overall graft survival and cause-specific hazard rate of SCR.

RESULTS

A total of 2744 small intestinal transplant biopsies within 3 months after Itx were available for retrospective evaluation; 171 cases (6.2%) were determined as SCR and 78 patients (51.7%) experienced SCR episode within 3 months after Itx. Adult patients were associated with a significantly higher occurrence of a SCR episode (P=0.001). Overall graft survival at 5 years posttransplant for patients experiencing SCR within 3 months posttransplant and for patients without SCR was 37.2% and 60.2%, respectively (P=0.009). Cause-specific hazard rate analysis showed that a SCR episode was associated with a significantly higher hazard rate of death due to infection (P=0.005).

CONCLUSIONS

A SCR episode in the initial postoperative period of Itx is a significant factor for unfavorable graft prognosis, likely representing alloimmune injury ultimately resulting in patient morbidity due to infection.

Differential roles of HIC-5 isoforms in the regulation of cell death and myotube formation during myogenesis

Hic-5 is a LIM-Only member of the paxillin superfamily of focal adhesion proteins. It has been shown to regulate a range of biological processes including: senescence, tumorigenesis, steroid hormone action, integrin signaling, differentiation, and apoptosis. To better understand the roles of Hic-5 during development, we initiated a detailed analysis of Hic-5 expression and function in C(2)C(12) myoblasts, a well-established model for myogenesis. We have found that: (1) myoblasts express at least 6 distinct Hic-5 isoforms; (2) the two predominant isoforms, Hic-5alpha and Hic-5beta, are differentially expressed during myogenesis; (3) any experimentally induced change in Hic-5 expression results in a substantial increase in apoptosis during differentiation; (4) ectopic expression of Hic-5alpha is permissive to differentiation while expression of either Hic-5beta or antisense Hic-5 blocks myoblast fusion but not chemodifferentiation; (5) Hic-5 localizes to focal adhesions in C(2)C(12) myoblasts and perturbation of Hic-5 leads to defects in cell spreading; (6) alterations in Hic-5 expression interfere with the normal dynamics of laminin expression; and (7) ectopic laminin, but not fibronectin, can rescue the Hic-5-induced blockade of myoblast survival and differentiation. Our data demonstrate differential roles for individual Hic-5 isoforms during myogenesis and support the hypothesis that Hic-5 mediates these effects via integrin signaling.

Apoptosis in skeletal muscle and its relevance to atrophy

Apoptosis is necessary for maintaining the integrity of proliferative tissues, such as epithelial cells of the gastrointestinal system. The role of apoptosis in post mitotic tissues, such as skeletal muscle, is less well defined. Apoptosis during muscle atrophy occurs in both myonuclei and other muscle cell types. Apoptosis of myonuclei likely contributes to the loss of muscle mass, but the mechanisms underlying this process are largely unknown. Caspase-dependent as well as -independent pathways have been implicated and the mode by which atrophy is induced likely determines the apoptotic mechanisms that are utilized. It remains to be determined whether a decrease in apoptosis will alleviate atrophy and distinct research strategies may be required for different causes of skeletal muscle loss.