Induction of apoptosis before shedding of human intestinal epithelial cells

Executioner caspases 3 and 7 are dispensable for intestinal epithelium turnover and homeostasis at steady state

Historically, programmed cell death by apoptosis is considered crucial for proper intestinal organogenesis and gut homeostasis. To challenge this concept, we generated caspase-3 and -7 double knockout mice specifically in intestinal epithelial cells (IECs). However, absence of apoptosis in IECs elicits neither morphological and inflammatory changes nor intestinal dysbiosis during gut homeostasis at steady state. This demonstrates the robustness of intestinal homeostasis at steady state for the absence of caspase-3/7 and shows that in contrast to caspase-8, which keeps necroptosis and associated inflammation in check, caspase-3/7–dependent apoptosis of IECs in homeostatic conditions is dispensable for normal intestinal development, immune cell composition, and microbiome control.

Apoptosis is widely believed to be crucial for epithelial cell death and shedding in the intestine, thereby shaping the overall architecture of the gastrointestinal tract, but also regulating tolerance induction, pinpointing a role of apoptosis intestinal epithelial cell (IEC) turnover and maintenance of barrier function, and in maintaining immune homeostasis. To experimentally address this concept, we generated IEC-specific knockout mice that lack both executioner caspase-3 and caspase-7 (Casp3/7^ΔIEC), which are the converging point of the extrinsic and intrinsic apoptotic pathway. Surprisingly, the overall architecture, cellular landscape, and proliferation rate remained unchanged in these mice. However, nonapoptotic cell extrusion was increased in Casp3/7^ΔIEC mice, compensating apoptosis deficiency, maintaining the same physiological level of IEC shedding. Microbiome richness and composition stayed unaffected, bearing no sign of dysbiosis. Transcriptome and single-cell RNA sequencing analyses of IECs and immune cells revealed no differences in signaling pathways of differentiation and inflammation. These findings demonstrate that during homeostasis, apoptosis per se is dispensable for IEC turnover at the top of intestinal villi intestinal tissue dynamics, microbiome, and immune cell composition.

Evidence that Clostridium perfringens Enterotoxin-Induced Intestinal Damage and Enterotoxemic Death in Mice Can Occur Independently of Intestinal Caspase-3 Activation

Clostridium perfringens enterotoxin (CPE) is responsible for the gastrointestinal symptoms of C. perfringens type A food poisoning and some cases of nonfoodborne gastrointestinal diseases, such as antibiotic-associated diarrhea. In the presence of certain predisposing medical conditions, this toxin can also be absorbed from the intestines to cause enterotoxemic death. CPE action in vivo involves intestinal damage, which begins at the villus tips. The cause of this CPE-induced intestinal damage is unknown, but CPE can induce caspase-3-mediated apoptosis in cultured enterocyte-like Caco-2 cells. Therefore, the current study evaluated whether CPE activates caspase-3 in the intestines and, if so, whether this effect is required for the development of intestinal tissue damage or enterotoxemic lethality. Using a mouse ligated small intestinal loop model, CPE was shown to cause intestinal caspase-3 activation in a dose- and time-dependent manner. Most of this caspase-3 activation occurred in epithelial cells shed from villus tips. However, CPE-induced caspase-3 activation occurred after the onset of tissue damage. Furthermore, inhibition of intestinal caspase-3 activity did not affect the onset of intestinal tissue damage. Similarly, inhibition of intestinal caspase-3 activity did not reduce CPE-induced enterotoxemic lethality in these mice. Collectively, these results demonstrate that caspase-3 activation occurs in the CPE-treated intestine but that this effect is not necessary for the development of CPE-induced intestinal tissue damage or enterotoxemic lethality.

Structural control of caspase-generated glutamyl-tRNA synthetase by appended noncatalytic WHEP domains

Aminoacyl-tRNA synthetases are ubiquitous, evolutionarily conserved enzymes catalyzing the conjugation of amino acids onto cognate tRNAs. During eukaryotic evolution, tRNA synthetases have been the targets of persistent structural modifications. These modifications can be additive, as in the evolutionary acquisition of noncatalytic domains, or subtractive, as in the generation of truncated variants through regulated mechanisms such as proteolytic processing, alternative splicing, or coding region polyadenylation. A unique variant is the human glutamyl-prolyl-tRNA synthetase (EPRS) consisting of two fused synthetases joined by a linker containing three copies of the WHEP domain (termed by its presence in tryptophanyl-, histidyl-, and glutamyl-prolyl-tRNA synthetases). Here, we identify site-selective proteolysis as a mechanism that severs the linkage between the EPRS synthetases in vitro and in vivo Caspase action targeted Asp-929 in the third WHEP domain, thereby separating the two synthetases. Using a neoepitope antibody directed against the newly exposed C terminus, we demonstrate EPRS cleavage at Asp-929 in vitro and in vivo Biochemical and biophysical characterizations of the N-terminally generated EPRS proteoform containing the glutamyl-tRNA synthetase and most of the linker, including two WHEP domains, combined with structural analysis by small-angle neutron scattering, revealed a role for the WHEP domains in modulating conformations of the catalytic core and GSH-S-transferase-C-terminal-like (GST-C) domain. WHEP-driven conformational rearrangement altered GST-C domain interactions and conferred distinct oligomeric states in solution. Collectively, our results reveal long-range conformational changes imposed by the WHEP domains and illustrate how noncatalytic domains can modulate the global structure of tRNA synthetases in complex eukaryotic systems.

The evolutionary trade-off between stem cell niche size, aging, and tumorigenesis

Many epithelial tissues within multicellular organisms are continually replenished by small independent populations of stem cells largely responsible for maintaining tissue homeostasis. These continually dividing populations are subject to mutations that can lead to tumorigenesis but also contribute to aging. Mutations accumulate in stem cell niches and change the rate of cell division and differentiation; the pace of this process and the fate of specific mutations depend strongly on niche population size. Here, we create a mathematical model of the intestinal stem cell niche, crypt system, and epithelium. We calculate the expected effect of fixed mutations in stem cell niches and their effect on tissue homeostasis throughout the intestinal epithelium over organismal lifetime. We find that, due to the small population size of stem cell niches, mutations predominantly fix via genetic drift and decrease stem cell fitness, leading to niche and tissue attrition, and contributing to organismal aging. We also explore mutation accumulation at various stem cell niche sizes and demonstrate that an evolutionary trade-off exists between niche size, tissue aging, and the risk of tumorigenesis. Further, mouse and human niches exist at a size that minimizes the probability of tumorigenesis, at the expense of accumulating deleterious mutations due to genetic drift. Finally, we show that the trade-off between the probability of tumorigenesis and the extent of aging depends on whether or not mutational effects confer a selective advantage in the stem cell niche.

CD8αβ+ γδ T Cells: A Novel T Cell Subset with a Potential Role in Inflammatory Bowel Disease

γδ T cells have been attributed a wide variety of functions, which in some cases may appear as contradictory. To better understand the enigmatic biology of γδ T cells it is crucial to define the constituting subpopulations. γδ T cells have previously been categorized into two subpopulations: CD8αα⁺ and CD8^- cells. In this study we have defined and characterized a novel subset of human γδ T-cells expressing CD8αβ. These CD8αβ⁺ γδ T cells differed from the previously described γδ T cell subsets in several aspects, including the degree of enrichment within the gut mucosa, the activation status in blood, the type of TCRδ variant used in blood, and small but significant differences in their response to IL-2 stimulation. Furthermore, the novel subset expressed cytotoxic mediators and CD69, and produced IFN-γ and TNF-α. In patients with active inflammatory bowel disease the mucosal frequencies of CD8αβ⁺ γδ T cells were significantly lower as compared with healthy controls, correlated negatively with the degree of disease activity, and increased to normal levels as a result of anti-TNF-α therapy. In conclusion, our results demonstrate that CD8αβ⁺ γδ T cells constitute a novel lymphocyte subset, which is strongly enriched within the gut and may play an important role in gut homeostasis and mucosal healing in inflammatory bowel disease.

The role of cell location and spatial gradients in the evolutionary dynamics of colon and intestinal crypts

BACKGROUND

Colon and intestinal crypts serve as an important model system for adult stem cell proliferation and differentiation. We develop a spatial stochastic model to study the rate of somatic evolution in a normal crypt, focusing on the production of two-hit mutants that inactivate a tumor suppressor gene. We investigate the effect of cell division pattern along the crypt on mutant production, assuming that the division rate of each cell depends on its location.

RESULTS

We find that higher probability of division at the bottom of the crypt, where the stem cells are located, leads to a higher rate of double-hit mutant production. The optimal case for delaying mutations occurs when most of the cell divisions happen at the top of the crypt. We further consider an optimization problem where the "evolutionary" penalty for double-hit mutant generation is complemented with a "functional" penalty that assures that fully differentiated cells at the top of the crypt cannot divide.

CONCLUSION

The trade-off between the two types of objectives leads to the selection of an intermediate division pattern, where the cells in the middle of the crypt divide with the highest rate. This matches the pattern of cell divisions obtained experimentally in murine crypts.

REVIEWERS

This article was reviewed by David Axelrod (nominated by an Editorial Board member, Marek Kimmel), Yang Kuang and Anna Marciniak-Czochra. For the full reviews, please go to the Reviewers' comments section.

Regulation of antiapoptotic and cytoprotective pathways in colonic epithelial cells in ulcerative colitis

Ulcerative colitis is an inflammatory bowel disease involving the colon resulting in bloody diarrhea and increased risk of colorectal cancer in certain patient subgroups. Increased apoptosis in the epithelial cell layer causes increased permeability, especially during flares; this leads to translocation of luminal pathogens resulting in a continued inflammatory drive. The present work investigates how epithelial apoptosis is regulated in ulcerative colitis. The main results are that Fas mediated apoptosis is inhibited during flares of ulcerative colitis, probably by an upregulation of cellular inhibitor of apoptosis protein 2 (cIAP2) and cellular FLICE-like inhibitory protein. cIAP2 is upregulated in regenerative epithelial cells both in ulcerative colitis and in experimental intestinal wounds. Inhibition of cIAP2 decreases wound healing in vitro possibly through inhibition of migration. Altogether, it is shown that epithelial cells in ulcerative colitis responds to the hostile microenvironment by activation of cytoprotective pathways that tend to counteract the cytotoxic effects of inflammation. However, the present studies also show that epithelial cells produce increased amounts of reactive oxygen species during stimulation with tumor necrosis factor-α and interferon-γ resulting in DNA instability. The combined effect of increased DNA-instability and decreased apoptosis responses could lead to neoplasia.

Induction of Apoptosis in Intestinal Toxicity to a Histone Deacetylase Inhibitor in a Phase I Study with Pelvic Radiotherapy

Purpose

When integrating molecularly targeted compounds in radiotherapy, synergistic effects of the systemic agent and radiation may extend the limits of patient tolerance, increasing the demand for understanding the pathophysiological mechanisms of treatment toxicity. In this Pelvic Radiation and Vorinostat (PRAVO) study, we investigated mechanisms of adverse effects in response to the histone deacetylase (HDAC) inhibitor vorinostat (suberoylanilide hydroxamic acid, SAHA) when administered as a potential radiosensitiser.

Materials and Methods

This phase I study for advanced gastrointestinal carcinoma was conducted in sequential patient cohorts exposed to escalating doses of vorinostat combined with standard-fractionated palliative radiotherapy to pelvic target volumes. Gene expression microarray analysis of the study patient peripheral blood mononuclear cells (PBMC) was followed by functional validation in cultured cell lines and mice treated with SAHA.

Results

PBMC transcriptional responses to vorinostat, including induction of apoptosis, were confined to the patient cohort reporting dose-limiting intestinal toxicities. At relevant SAHA concentrations, apoptotic features (annexin V staining and caspase 3/7 activation, but not poly-(ADP-ribose)-polymerase cleavage) were observed in cultured intestinal epithelial cells. Moreover, SAHA-treated mice displayed significant weight loss.

Conclusion

The PRAVO study design implemented a strategy to explore treatment toxicity caused by an HDAC inhibitor when combined with radiotherapy and enabled the identification of apoptosis as a potential mechanism responsible for the dose-limiting effects of vorinostat. To the best of our knowledge, this is the first report deciphering mechanisms of normal tissue adverse effects in response to an HDAC inhibitor within a combined-modality treatment regimen.

Cryosectioning the intestinal crypt-villus axis: an ex vivo method to study the dynamics of epigenetic modifications from stem cells to differentiated cells

The intestinal epithelium is a particularly attractive biological adult model to study epigenetic mechanisms driving adult stem cell renewal and cell differentiation. Since epigenetic modifications are dynamic, we have developed an original ex vivo approach to study the expression and epigenetic profiles of key genes associated with either intestinal cell pluripotency or differentiation by isolating cryosections of the intestinal crypt-villus axis. Gene expression, DNA methylation and histone modifications were studied by qRT-PCR, methylation-specific PCR and micro-chromatin immunoprecipitation, respectively. Using this approach, it was possible to identify segment-specific methylation and chromatin profiles. We show that (i) expression of intestinal stem cell markers (Lgr5, Ascl2) exclusively in the crypt is associated with active histone marks, (ii) promoters of all pluripotency genes studied and transcription factors involved in intestinal cell fate (Cdx2) harbour a bivalent chromatin pattern in the crypts and (iii) expression of differentiation markers (Muc2, Sox9) along the crypt-villus axis is associated with DNA methylation. Hence, using an original model of cryosectioning along the crypt-villus axis that allows in situ detection of dynamic epigenetic modifications, we demonstrate that regulation of pluripotency and differentiation markers in healthy intestinal mucosa involves different and specific epigenetic mechanisms.

Proteinase-activated receptor 2 (PAR2) decreases apoptosis in colonic epithelial cells

Mucosal biopsies from inflamed colon of inflammatory bowel disease patients exhibit elevated epithelial apoptosis compared with those from healthy individuals, disrupting mucosal homeostasis and perpetuating disease. Therapies that decrease intestinal epithelial apoptosis may, therefore, ameliorate inflammatory bowel disease, but treatments that specifically target apoptotic pathways are lacking. Proteinase-activated receptor-2 (PAR2), a G protein-coupled receptor activated by trypsin-like serine proteinases, is expressed on intestinal epithelial cells and stimulates mitogenic pathways upon activation. We sought to determine whether PAR2 activation and signaling could rescue colonic epithelial (HT-29) cells from apoptosis induced by proapoptotic cytokines that are increased during inflammatory bowel disease. The PAR2 agonists 2-furoyl-LIGRLO (2f-LI), SLIGKV and trypsin all significantly reduced cleavage of caspase-3, -8, and -9, poly(ADP-ribose) polymerase, and the externalization of phosphatidylserine after treatment of cells with IFN-γ and TNF-α. Knockdown of PAR2 with siRNA eliminated the anti-apoptotic effect of 2f-LI and increased the sensitivity of HT-29 cells to cytokine-induced apoptosis. Concurrent inhibition of both MEK1/2 and PI3K was necessary to inhibit PAR2-induced survival. 2f-LI was found to increase phosphorylation and inactivation of pro-apoptotic BAD at Ser(112) and Ser(136) by MEK1/2 and PI3K-dependent signaling, respectively. PAR2 activation also increased the expression of anti-apoptotic MCL-1. Simultaneous knockdown of both BAD and MCL-1 had minimal effects on PAR2-induced survival, whereas single knockdown had no effect. We conclude that PAR2 activation reduces cytokine-induced epithelial apoptosis via concurrent stimulation of MEK1/2 and PI3K but little involvement of MCL-1 and BAD. Our findings represent a novel mechanism whereby serine proteinases facilitate epithelial cell survival and may be important in the context of colonic healing.

Effect of montmorillonite powder and mesalazine on intestinal epithelial cell apoptosis in rats with ulcerative colitis

AIM: To assess the effect of montmorillonite powder (Smecta) and mesalazine, alone or in combination, on intestinal epithelial cell apoptosis in rats with 2,4,6-trinitrobenzene sulfonic acid (TNBS) induced colitis.

METHODS: Eighty-two male SD rats were randomly divided into a normal group, a model group and three intervention groups including Smecta group, mesalazine group, and mesalazine plus Smecta group. Ulcerative colitis (UC) was induced in rats by the TNBS/ethanol method. The model group was daily treated with normal saline, and the intervention groups were intragastrically treated with Smecta, mesalazine, mesalazine plus Smecta, respectively. Rats were killed on days 5 and 12 after treatment to collect colon specimens. Terminal-deoxynucleoitidyl transferase mediated nick end labeling (TUNEL) method was used to assay intestinal cell apoptosis rate.

RESULTS: The rats treated with TNBS/ethanol had diarrhea with bloody stools and weight loss 24 h after model creation. Light and electronic microscopic analyses showed large mucosal ulceration area accompanied by neutrophil infiltration, damaged gland structural and decreased goblet cells. Compared with the normal group, intestinal epithelial cell apoptosis rates in the model group and three intervention groups were significantly increased on days 5 and 12 (H₅ = 439.78, H₁₂ = 84.03, P = 0.000). Compared with the model group, intestinal epithelial cell apoptosis rates in the three intervention groups were significantly lower on days 5 and 12 (P = 0.000). The apoptosis rates in the combination group were more significantly lower than those in the two monotherapy groups (P = 0.000). The apoptosis rates in the three intervention groups on day 12 were more significantly lower than those on day 5 (P = 0.000).

CONCLUSION: Intestinal epithelial cell apoptosis is involved in the pathogenesis of UC. Montmorillonite powder combined with mesalazine therapy has a synergistic inhibitory effect on apoptosis. The inhibitory effect on apoptosis is better on day 12 than on day 5.

Pleiotropic functions of TNF-α in the regulation of the intestinal epithelial response to inflammation

An important function of intestinal epithelial cells (IECs) is to maintain the integrity of the mucosal barrier. Inflammation challenges the integrity of the mucosal barrier and the intestinal epithelium needs to adapt to a multitude of signals in order to perform the complex process of maintenance and restitution of its barrier function. Dysfunctions in epithelial barrier integrity and restoration contribute to the pathogenesis of inflammatory bowel diseases (IBDs) such as Crohn's disease and ulcerative colitis. Mucosal healing has developed to a significant treatment goal in IBD. In this review, we would like to highlight physiologic and pathologic adaptations of the intestinal epithelium to inflammation, exemplified by its responses to TNF-α. A large body of literature exists that highlights the diverse effects of this cytokine on IECs. TNF-α modulates intestinal mucus secretion and constitution. TNF-α stimulation modulates paracellular flow via tight junctional control. TNF-α induces intracellular signaling cascades that determine significant cell fate decisions such as survival, cell death or proliferation. TNF-α impacts epithelial wound healing in ErbB- and Wnt-dependent pathways while also importantly guiding immune cell attraction and function. We selected important studies from recent years with a focus on functional in vivo data providing crucial insights into the complex process of intestinal homeostasis.

Altered transcription of murine genes induced in the small bowel by administration of probiotic strain Lactobacillus rhamnosus HN001

Lactobacillus rhamnosus HN001 is a probiotic strain reported to increase resistance to epithelium-adherent and -invasive intestinal pathogens in experimental animals. To increase understanding of the relationship between strain HN001 and the bowel, transcription of selected genes in the mucosa of the murine small bowel was measured. Mice previously naive to lactobacilli (Lactobacillus-free mice) were examined after daily exposure to HN001 in drinking water. Comparisons were made to results from matched Lactobacillus-free mice. Infant and adult mice were investigated to provide a temporal view of gene expression in response to exposure to HN001. Genes sgk1, angptl4, and hspa1b, associated with the apoptosis pathway, were selected for investigation by reverse transcription-quantitative PCR on the basis of a preliminary duodenal DNA microarray screen. Normalized to gapdh gene transcription, these three genes were upregulated after 6 to 10 days exposure of adult mice to HN001. Angptl4 was shown by immunofluorescence to be upregulated in duodenal epithelial cells of mucosal samples. Epithelial cell migration was faster in HN001-exposed mice than in the Lactobacillus-free controls. Transcriptional responses in infant mice differed according to bowel region and age. For example, sgk1 was upregulated in duodenal, jejunal, and ileal mucosa of mice less than 25 days old, whereas angptl4 and hspa1b were upregulated at 10 days in the duodenum but downregulated in the jejunal mucosa until mice were 25 days old. Overall, the results provide links between a probiotic strain, mucosal gene expression, and host phenotype, which may be useful in delineating mechanisms of probiotic action.

Removal of luminal content protects the small intestine during hemorrhagic shock but is not sufficient to prevent lung injury

The small intestine plays a key role in the pathogenesis of multiple organ failure following circulatory shock. Current results show that reduced perfusion of the small intestine compromises the mucosal epithelial barrier, and the intestinal contents (including pancreatic digestive enzymes and partially digested food) can enter the intestinal wall and transport through the circulation or mesenteric lymph to other organs such as the lung. The extent to which the luminal contents of the small intestine mediate tissue damage in the intestine and lung is poorly understood in shock. Therefore, rats were assigned to three groups: No-hemorrhagic shock (HS) control and HS with or without a flushed intestine. HS was induced by reducing the mean arterial pressure (30 mmHg; 90 min) followed by return of shed blood and observation (3 h). The small intestine and lung were analyzed for hemorrhage, neutrophil accumulation, and cellular membrane protein degradation. After HS, animals with luminal contents had increased neutrophil accumulation, bleeding, and destruction of E-cadherin in the intestine. Serine protease activity was elevated in mesenteric lymph fluid collected from a separate group of animals subjected to intestinal ischemia/reperfusion. Serine protease activity was elevated in the plasma after HS but was detected in lungs only in animals with nonflushed lumens. Despite removal of the luminal contents, lung injury occurred in both groups as determined by elevated neutrophil accumulation, permeability, and lung protein destruction. In conclusion, luminal contents significantly increase intestinal damage during experimental HS, suggesting transport of luminal contents across the intestinal wall should be minimized.

Cdx1 and Cdx2 exhibit transcriptional specificity in the intestine

The caudal-related homeodomain transcription factors Cdx1 and Cdx2 are expressed in the developing endoderm with expression persisting into adulthood. Cdx1^−/− mutants are viable and fertile and display no overt intestinal phenotype. Cdx2 null mutants are peri-implantation lethal; however, conditional mutation approaches have revealed that Cdx2 is required for patterning the intestinal epithelium and specification of the colon. Cdx2 is also necessary for homeostasis of the intestinal tract in the adult, where Cdx1 and Cdx2 appear to functionally overlap in the distal colon, but not during intestinal development. Cdx1 and Cdx2 exhibit complete overlap of expression in the intestine, although they differ in their relative levels, with Cdx1 maximal in the distal colon and Cdx2 peaking in the proximal cecum. Moreover, Cdx1 protein is graded along the crypt-villus axis, being abundant in the crypts and diminishing towards the villi. Cdx2 is expressed uniformly along this axis, but is differentially phosphorylated; the functional relevance of these expression domains and phosphorylation is currently unknown. Cdx1 and Cdx2 have been suggested to exhibit functional specificity in the intestinal tract. In the present study, using cell-based models, we found that relative to Cdx1, Cdx2 was significantly less potent at effecting a transcriptional response from the Cdx1 promoter, a known Cdx target gene. We subsequently assessed this relationship in vivo using a “gene swap” approach and found that Cdx2 cannot substitute for Cdx1 in this autoregulatory loop. This is in marked contrast with the ability of Cdx2 to support Cdx1 expression and function in paraxial mesoderm and vertebral patterning, thus providing novel in vivo evidence of context-dependent transcriptional specificity between these transcription factors.

Proteasome inhibition of pathologic shedding of enterocytes to defend barrier function requires X-linked inhibitor of apoptosis protein and nuclear factor κB

BACKGROUND & AIMS

Although we are beginning to understand where, when, and how intestinal epithelial cells are shed, physiologically, less is understood about alterations in cell fate during minimally invasive epithelial infections. We used a piglet model of Cryptosporidium parvum infection to determine how elimination of infected enterocytes is balanced with the need to maintain barrier function.

METHODS

We studied the effects of enterocyte shedding by C parvum-infected ileum on barrier function ex vivo with Ussing chambers. The locations and activities of caspase-3, nuclear factor κB (NF-κB), and inhibitor of apoptosis proteins (IAP) were assayed by enzyme-linked immunosorbent assay, immunoblot, and tissue immunoreactivity analyses and using specific pharmacologic inhibitors. The location, specificity, and magnitude of enterocyte shedding were quantified using special stains and light microscopy.

RESULTS

Infection with C parvum activated apoptotic signaling pathways in enterocytes that resulted in cleavage of caspase-3. Despite caspase-3 cleavage, enterocyte shedding was confined to villus tips, coincident with apoptosis, and observed more frequently in infected cells. Epithelial expression of X-linked inhibitor of apoptosis protein (XIAP), activation of NF-κB, and proteasome activity were required for control of cell shedding and barrier function. The proteasome blocked activity of caspase-3; this process was mediated by expression of XIAP, which bound to cleaved caspase-3.

CONCLUSIONS

We have identified a pathway by which villus epithelial cells are maintained during C parvum infection. Loss of barrier function is reduced by active retention of infected enterocytes until they reach the villus tip. These findings might be used to promote clearance of minimally invasive enteropathogens, such as by increasing the rate of migration of epithelial cells from the crypt to the villus tip.

BCL-2 modifying factor (BMF) is a central regulator of anoikis in human intestinal epithelial cells

BCL-2 modifying factor (BMF) is a sentinel considered to register damage at the cytoskeleton and to convey a death signal to B-cell lymphoma 2. B-cell lymphoma 2 is neutralized by BMF and thereby facilitates cytochrome C release from mitochondria. We investigated the role of BMF for intestinal epithelial cell (IEC) homeostasis. Acute colitis was induced in Bmf-deficient mice (Bmf(-/-)) with dextran sulfate sodium. Colonic crypt length in Bmf(-/-) mice was significantly increased as compared with WT mice. Dextran sulfate sodium induced less signs of colitis in Bmf(-/-) mice, as weight loss was reduced compared with the WT. Primary human IEC exhibited increased BMF in the extrusion zone. Quantitative PCR showed a significant up-regulation of BMF expression after initiation of anoikis in primary human IEC. BMF was found on mitochondria during anoikis, as demonstrated by Western blot analysis. RNAi mediated knockdown of BMF reduced the number of apoptotic cells and led to reduced caspase 3 activity. A significant increase in phospho-AKT was determined after RNAi treatment. BMF knockdown supports survival of IEC. BMF is induced in human IEC by the loss of cell attachment and is likely to play an important role in the regulation of IEC survival.

Norovirus non-structural protein p20 leads to impaired restitution of epithelial defects by inhibition of actin cytoskeleton remodelling

OBJECTIVE

Norovirus is the most common cause of acute gastroenteritis in humans worldwide. Typical symptoms are vomiting, nausea and severe watery diarrhea. Because of the lack of cell lines susceptible to human norovirus infection, pathomechanisms and replication cycle are largely unknown. Here, we address the issue of how norovirus infection could lead to epithelial barrier dysfunction.

MATERIAL AND METHODS

Expression of the non-structural norovirus protein p20 in the epithelial cell line HT-29/B6 was activated through a tetracycline sensitive promoter. Tight junction proteins were studied by Western blot and confocal laser scanning microscopy. Apoptoses were detected in TUNEL stainings. Epithelial restitution was monitored by conductance scanning after induction of single cell lesions.

RESULTS

Changes in the expression or localization of the tight junction proteins occludin and/or claudin-1, -2,- 3, -4, -5, -7 and -8 could be ruled out to mediate epithelial barrier modulation. Cell motility was also unaltered by p20. Investigation of epithelial apoptosis revealed an accumulation of apoptic cells in epithelial monolayers after induction of p20 expression. In epithelial cell restitution assays, an arrest was identified in p20 expressing cells. Fluorescence microscopy revealed an inability for condensation and redistribution of cellular actin, which led to a reduced transepithelial electrical resistance.

CONCLUSIONS

Functional data for norovirus protein p20 suggest a role in modulation of the actin cytoskeleton leading to barrier dysfunction through impairment of restitution of epithelial defects.

Dissemination of invasive Salmonella via bacterial-induced extrusion of mucosal epithelia

Salmonella enterica is an intracellular bacterial pathogen that resides and proliferates within a membrane-bound vacuole in epithelial cells of the gut and gallbladder. Although essential to disease, how Salmonella escapes from its intracellular niche and spreads to secondary cells within the same host, or to a new host, is not known. Here, we demonstrate that a subpopulation of Salmonella hyperreplicating in the cytosol of epithelial cells serves as a reservoir for dissemination. These bacteria are transcriptionally distinct from intravacuolar Salmonella. They are induced for the invasion-associated type III secretion system and possess flagella; hence, they are primed for invasion. Epithelial cells laden with these cytosolic bacteria are extruded out of the monolayer, releasing invasion-primed and -competent Salmonella into the lumen. This extrusion mechanism is morphologically similar to the process of cell shedding required for turnover of the intestinal epithelium. In contrast to the homeostatic mechanism, however, bacterial-induced extrusion is accompanied by an inflammatory cell death characterized by caspase-1 activation and the apical release of IL-18, an important cytokine regulator of gut inflammation. Although epithelial extrusion is obviously beneficial to Salmonella for completion of its life cycle, it also provides a mechanistic explanation for the mucosal inflammation that is triggered during Salmonella infection of the gastrointestinal and biliary tracts.

How bacteria-induced apoptosis of intestinal epithelial cells contributes to mucosal inflammation

The life cycle of an intestinal epithelial cell is terminated by apoptosis and/or cell shedding. Apoptotic deletion of epithelial cells from the intact intestinal mucosa is not accompanied by detectable inflammatory response or loss of barrier function. But increased permeability of the epithelial barrier and increased apoptotic rates of epithelial cells have been reported for patients suffering from inflammatory bowel disease. Microbiota can both induce or inhibit apoptosis of intestinal epithelial cells thus contribute to mucosal inflammation or support epithelial integrity respectively. Bacteria-mediated cytokine secretion and altered cell signalling are central to epithelial injury. Tumor necrosis factor (TNF) secreted after exposure to invasive bacteria induces both apoptosis and cell shedding. TNF is the major target gene of the transcription factor nuclear factor-kappa B with both pro- and anti-apoptotic effects. Autophagy promotes both cell survival and “autophagic” cell death. If autophagy is directed against microbes it is termed xenophagy. Inhibition of xenophagy has been shown to decrease cell survival. Endoplasmic reticulum (ER) stress causes misfolded proteins to accumulate in the ER lumen. It was suggested that ER stress and autophagy may interact within intestinal epithelial cells. Apoptosis in response to infection may be well proposed by the host to delete infected epithelial cells or could be a strategy of microbial pathogens to escape from exhausted cells to invade deeper mucosal layers for a prolonged bacterial colonization.

Loss of Toll-like receptor 2 and 4 leads to differential induction of endoplasmic reticulum stress and proapoptotic responses in the intestinal epithelium under conditions of chronic inflammation

Toll-like receptors (TLRs) play an important role in the recognition of microbial molecular patterns of infectious and commensal bacteria and their expression in various tissues including the intestinal epithelium orchestration of the innate and adaptive immune defense mechanisms. Changes in the TLR signaling pathways due to host genetic predispositions may turn a physiological response into a pathological situation including failure of bacterial clearance and development of chronic inflammation. The aim of this study was to characterize the role of TLR2 or TLR4 deficiency in epithelial cell stress responses under noninflamed and inflamed conditions using TLR-deficient mice and TLR(-/-) cross-bred IL-10-deficient mice as a model for genetically driven experimental colitis. Primary intestinal epithelial cells (IEC) were isolated from specific-pathogen-free wild-type, TLR2-, TLR4-, IL-10-, IL-10XTLR2- and IL-10XTLR4-deficient mice at the age of 1, 8, and 16 weeks. Histopathological analysis showed absence of tissue pathology (score 0-12) in distal colon sections of TLR2- and TLR4-deficient mice. In addition, TLR2- but not TLR4-deficient mice cross-bred to the IL-10-deficient background develop moderate colitis, suggesting different effects of these pattern recognition receptors in regulating disease mechanisms. Proteome analysis revealed significantly regulated proteins associated with endoplasmic reticulum (ER) and mitochondrial stress responses in the epithelium. In contrast to TLR2(-/-) and IL-10XTLR2(-/-) mice, the induction of the ER-associated chaperone grp-78 was dissociated from the activation of proapoptotic caspase 3 cleavage in noninflamed TLR4(-/-) and IL10XTLR4(-/-) mice. These results suggest that ER-associated cellular stress responses play an important role in epithelial cells homeostasis leading to beneficial but also deleterious effects. We hypothesize that ER stress-associated processes in the absence of TLR2 and TLR4 differentially affect host responses and epithelial functions under conditions of genetically driven chronic intestinal inflammation.

Primary human colonic epithelial cells are transiently protected from anoikis by a Src-dependent mechanism

Complete loss of cell anchorage triggers apoptosis in primary human colonic epithelial cells (CEC), a phenomenon known as anoikis. Besides the induction of pro-apoptotic events, activation of survival pathways was observed in detached intestinal epithelial cell lines, providing a transient apoptosis protection. However, nothing is known about molecular mechanisms protecting primary CEC from anoikis. In this study intact CEC crypts were isolated and kept in suspension, a condition which leads to the loss of cell-cell anchorage and induces anoikis. To reconstitute cell-cell contacts, cells were centrifuged to form cell aggregates. Induction of apoptosis was assessed by caspase-3 activity assay; activation of survival pathways was analyzed by Western blot. Immediately after loss of cell anchorage a rapid activation of survival proteins was observed before active caspase-3 could be detected. Src hyperactivation significantly contributed to transient protection from anoikis in CEC because its inhibition reversed the protecting effect of re-establishment of cell contacts. Basal levels of active Src in CEC from patients with inflammatory bowel disease were markedly reduced compared to control patients. These results demonstrate that loss of cell anchorage activates survival pathways in primary human CEC providing transient anoikis protection. Src is an important mediator of this mechanism and therefore constitutes a key regulatory molecule coordinating survival signals mediated by cell adhesion in primary human CEC.

Histoplanimetrical study on the relationship between cellular kinetics of epithelial cells and proliferation of indigenous bacteria in the rat colon

The aim of this study was to clarify the regulatory effects of epithelial kinetics on indigenous bacterial proliferation in the large intestine. The lifespan, migration speed and proliferation rate of crypt epithelial cells in the initial 20% of the colon (proximal colon) and the 50% of the colon (middle colon) in bromodeoxyuridine-administrated rats were histoplanimetrically and chronologically compared. The proximal colon possessed well-developed mucosal folds and a large amount of indigenous bacteria which filled the crypt lumen, whereas no folds or bacteria were found to occupy the crypt lumen in the middle colon. The cell lifespans were 32.2, 42.5 and 33.6 hr in the apical and the basal parts of the mucosal folds of the proximal colon, and in the middle colon, respectively. The migration speeds were 4.2, 2.1 and 3.3 microm/hr, respectively, while the appearance frequencies of proliferating cell nuclear antigen (PCNA)-positive crypt epithelial cells were 35.0, 24.6 and 33.8%. These findings suggest that the lifespan was shortened and the migration speed increased in the most luminal mucosa of colon, contributing to the elimination of the adhered bacteria from the most luminal mucosa. By contrast, the elongation of the lifespan and deceleration of the migration of epithelial cells in the basal parts of the mucosal folds might contribute to reliable settlement of indigenous bacteria, resulting in the maintenance of a large amount of indigenous bacteria in the lumen of the proximal colon.

The epidemiology and pathogenesis of neoplasia in the small intestine

PURPOSE

The mucosa of the small intestine encompasses about 90% of the luminal surface area of the digestive system, but only 2% of the total annual gastrointestinal cancer incidence in the United States.

METHODS

The remarkable contrast in age-standardized cancer incidence between the small and large intestine has been reviewed with respect to the cell type patterns, demographic features, and molecular characteristics of neoplasms.

RESULTS

Particularly noteworthy is the predominance of adenocarcinoma in the colon, which exceeds 98% of the total incidence by cell type, in contrast to that of 30% to 40% in the small intestine, resulting in an age-standardized ratio of rates exceeding 50-fold. The prevalence of adenomas and carcinomas is most prominent in the duodenum and proximal jejunum. The positive correlation in global incidence rates of small and large intestinal neoplasms and the reciprocal increases in risk of second primary adenocarcinomas suggest that there are common environmental risk factors. The pathophysiology of Crohn inflammatory bowel disease and the elevated risk of adenocarcinoma demonstrate the significance of the impaired integrity of the mucosal barrier and of aberrant immune responses to luminal indigenous and potentially pathogenic microorganisms.

CONCLUSION

In advancing a putative mechanism for the contrasting mucosal susceptibilities of the small and large intestine, substantial differences are underscored in the diverse taxonomy, concentration and metabolic activity of anaerobic organisms, rate of intestinal transit, changing pH, and the enterohepatic recycling and metabolism of bile acids. Experimental and epidemiologic studies are cited that suggest that the changing microecology, particularly in the colon, is associated with enhanced metabolic activation of ingested and endogenously formed procarcinogenic substrates.

Constitutive CXCL12 expression induces anoikis in colorectal carcinoma cells

BACKGROUND & AIMS

CXCL12 and CXCR4 signaling plays critical roles in development, homeostasis, and tumor metastasis. Previously, we have shown that epigenetic silencing of CXCL12 in colorectal and mammary carcinomas promotes metastasis. Anoikis is an essential process of colonic epithelial turnover and limits the metastatic progression of carcinoma. We sought to determine the role for anoikis in limiting tumor metastasis following reexpression of CXCL12 in human colorectal carcinoma cells.

METHODS

Tumor formation and metastasis of colonic carcinoma cells was monitored using in vivo bioluminescence imaging. Anoikis was defined by using caspase-3/7, focal adhesion kinase (FAK) and p130Cas cleavage, DNA fragmentation, and cell survival assays. Phosphorylation of extracellular-regulated kinase-1/2 (ERK1/2) was monitored by immunoblot and immunohistochemistry, and activity was inhibited by using U0126.

RESULTS

Constitutive expression of CXCL12 in human colorectal carcinoma cells reduced orthotopic tumor formation and inhibited metastasis in severe combined immunodeficient mice. Further, CXCL12 expression induced apoptosis specifically in nonadherent colorectal carcinoma cells. Apoptotic cell death was preceded by hypophosphorylation and cleavage of FAK and p130Cas, leading to increased cellular detachment in culture, and depended on alterations in the extracellular matrix. Similar to in vivo colonic epithelium, CXCL12-induced anoikis of carcinoma cells depended on basal ERK1/2 activation.

CONCLUSIONS

These data significantly expand the current paradigm of chemokine signaling in carcinogenesis by showing that endogenous CXCL12, in marked contrast to exogenous ligand, inhibits tumor metastasis through increased anoikis. Altered ERK1/2 signaling provides a mechanism for the dichotomy between the physiologic and pathophysiologic roles of CXCL12-CXCR4 signaling in the intestinal epithelium.

Simian immunodeficiency virus-induced intestinal cell apoptosis is the underlying mechanism of the regenerative enteropathy of early infection

The enteropathic manifestations of the human immunodeficiency virus (HIV) and the simian immunodeficiency virus (SIV) in late infection are usually due to infection by other microbes, but in early infection the viruses themselves cause an enteropathy by heretofore undetermined mechanisms. Here we report that SIV induces massive apoptosis of intestinal epithelial cells lining the small and large bowel, thus identifying apoptosis as the driving force behind the regenerative pathology of early infection. We found that apoptosis of gut epithelium paralleled the previously documented apoptosis and massive depletion of CD4 T cells in gut lamina propria, triggered by established mechanisms of gut epithelial cell apoptosis and, at peak, possibly by virus interactions with GPR15/Bob, an intestinal epithelial cell-associated alternative coreceptor for SIV and HIV-1. Apoptosis in early SIV infection is thus the common theme of the pathological processes that quickly afflict the innate as well as adaptive arms of the gut immune system.

Effect of raloxifene treatment on osteocyte apoptosis in postmenopausal women

Increased osteocyte apoptosis, as the result of estrogen deficiency, could play a role in the decrease of bone mass and bone strength seen in postmenopausal osteoporosis. We investigated whether treatment with raloxifene of postmenopausal women with osteoporosis affects osteocyte apoptosis. Transiliac bone biopsies were obtained from 26 osteoporotic women at baseline and after 2 years of treatment with placebo or raloxifene. Immunohistochemical detection of cleaved caspase-3 was performed on sections from nondecalcified bone biopsies to visualize apoptosis. In the trabecular bone total osteocytes, positively stained osteocytes and empty lacunae were counted and percent positive cells and percent empty lacunae determined. Statistical evaluation was performed by Wilcoxon's paired t-test and Spearman's rank correlations. There was no significant difference in percentage positive osteocytes between baseline and follow-up biopsies in both the placebo and the raloxifene groups. The percentage empty lacunae increased significantly in the placebo group (11.20 +/- 1.43 vs. 9.00 +/- 2.25, P = 0.014) but not in the raloxifene group. At baseline in both groups combined, there was a negative correlation between indices of bone remodeling and the percentage positive osteocytes (bone formation rate/bone volume r = -0.67, P = 0.001). We found no direct evidence for an effect of raloxifene treatment on osteocyte apoptosis, but small effects of raloxifene treatment cannot be excluded. The percent of apoptotic osteocytes was dependent on the level of bone remodeling in an individual.

Cell-cell contacts prevent anoikis in primary human colonic epithelial cells

BACKGROUND & AIMS

Colonic epithelial cells (CECs) receive important survival signals from the extracellular matrix and undergo detachment-induced apoptosis (anoikis) as soon as they lose their cell-matrix anchorage. In contrast to the established role of cell-matrix contact, the role of cell-cell contacts as a physiologic survival factor for CECs is less clear.

METHODS

Intact CEC crypts gently centrifuged to form a cell aggregate in which cell-cell contacts were maintained. Induction of apoptosis was assessed by Western Blot analysis, colorimetric assays, DNA electrophoresis, 4',6-diamidino-2-phenylindole staining, and flow cytometry. Activation of survival pathways was analyzed by Western blot. The role of mitogen-activated protein kinase/extracellular signal-regulated kinase (MEK)/extracellular signal-regulated kinase (Erk)1/2, epidermal growth factor receptor, phosphatidylinositol 3-kinase (PI3-K), and Src signaling was investigated using specific inhibitors.

RESULTS

Despite a complete loss of cell-matrix adhesion after CEC isolation, activation of caspases was blocked and anoikis was prevented when cell-cell contacts were preserved. CECs with preserved cell-cell contacts exhibited a rapid dephosphorylation of focal adhesion kinase. Aggregated CECs had stable levels of active beta-catenin and phosphorylated Akt, Erk1/2, and epidermal growth factor receptor, but CECs undergoing anoikis rapidly degraded beta-catenin and dephosphorylated Akt. Inhibition of Src- and PI3-K-dependent signaling reversed the antiapoptotic effect of cell-cell contact preservation, while inhibition of the MEK pathway had no effect.

CONCLUSIONS

Integrity of cell-cell contacts compensates for the loss of cell-matrix contact-mediated survival signals in CECs and prevents apoptosis. Cell-cell contact-triggered CEC survival involves antiapoptotic signaling through beta-catenin-, Src-, and PI3-K/Akt- but not through MEK- and focal adhesion kinase-dependent pathways.

5-aminosalicylic acid enhances anchorage-independent colorectal cancer cell death

Resistance to anoikis, the cell death triggered by the loss of anchorage to the substratum, is an essential prerequisite in the proliferation and diffusion of colorectal cancer (CRC) cells. We examined whether 5-aminosalicylic acid (5-ASA), a drug that seems to reduce the risk of colitis-associated CRC, enhances CRC cell anoikis. To this end, Colo205 cells were treated with 5-ASA in the presence or absence of inhibitors of caspases (zVAD-fmk) and reactive oxygen species (ROS). We demonstrate that 5-ASA enhances Colo205 cell death. Although 5-ASA induces dissipation of mitochondrial transmembrane potential and caspase-3 activation, zVAD-fmk does not completely prevent the 5-ASA-induced cell death. 5-ASA also enhances the synthesis of ROS. However, inhibitors of ROS reduce the fraction of 5-ASA-induced Colo205 cell death but do not confer protection. In contrast, the 5-ASA-mediated Colo205 cell death is preventable by Bcl-2 over-expression. These data suggest a mechanism by which 5-ASA interferes with colon carcinogenesis.

Crypt dynamics and colorectal cancer: advances in mathematical modelling

Mathematical modelling forms a key component of systems biology, offering insights that complement and stimulate experimental studies. In this review, we illustrate the role of theoretical models in elucidating the mechanisms involved in normal intestinal crypt dynamics and colorectal cancer. We discuss a range of modelling approaches, including models that describe cell proliferation, migration, differentiation, crypt fission, genetic instability, APC inactivation and tumour heterogeneity. We focus on the model assumptions, limitations and applications, rather than on the technical details. We also present a new stochastic model for stem-cell dynamics, which predicts that, on average, APC inactivation occurs more quickly in the stem-cell pool in the absence of symmetric cell division. This suggests that natural niche succession may protect stem cells against malignant transformation in the gut. Finally, we explain how we aim to gain further understanding of the crypt system and of colorectal carcinogenesis with the aid of multiscale models that cover all levels of organization from the molecular to the whole organ.

Distribution of E-cadherin and β-catenin in relation to cell maturation and cell extrusion in rat and mouse small intestines

In the small intestines, cell renewal from stem cells present in the crypts is balanced by cell extrusion from the tips of the villi. The mechanism by which extrusion occurs is unknown. Recent in vitro data suggested that loss of E-cadherin could contribute to cell extrusion and induction of programmed cell death (PCD) in mouse small intestinal epithelium. We have studied if this also occurs in the intact rodent small intestine. Our results confirm that extruded cells are negative for E-cadherin. However, loss of the E-cadherin-interacting protein beta-catenin preceded both extrusion and loss of E-cadherin. Thus, all extruded cells as well as all cells in the process of extrusion lacked staining for beta-catenin. Moreover, almost 80% of all cells undergoing programmed cell death, as detected by the TUNEL reaction, lacked beta-catenin whereas over 70% of such cells were positive for E-cadherin. However, most cells lacking beta-catenin did not display signs of PCD as detected by the TUNEL method or by staining for active caspase-3. Therefore, these results suggest that loss of beta-catenin precedes the onset of programmed cell death, loss of E-cadherin and extrusion from the villi.

Restitution of single-cell defects in the mouse colon epithelium differs from that of cultured cells

Integrity of colon epithelium is of crucial importance and, as small defects occur constantly, rapid repair (restitution) is essential. To investigate the mechanism of restitution, single-cell lesions were induced in mouse colonic surface epithelia by iontophoretic injection of Ca2+. Closure of the resulting defects was monitored using confocal laser scanning microscopy (CLSM), and functional sealing by electrophysiological techniques. Restitution was evaluated as the time constant tau of the exponential decrease in conductance of an induced leak and amounted to 0.28 min under control conditions. After 4 min, the leak was completely sealed. Repair was thus considerably faster than in previously investigated HT-29/B6 cells (tau=5.73 min). As in cultured cells, cytochalasin D delayed restitution in native colon epithelia (tau=0.69 min), indicating the involvement of actin in the healing process; however, no accumulation of actin surrounding the lesion was detected. Long-term incubation of epithelia with IFN-gamma alone or in combination with TNF-alpha increased tau to 0.49 and 0.59 min, respectively. In contrast to cultured cells, TNF-alpha alone did not affect restitution. A brief (<10 min) exposure to the sterile filtered supernatant of hemolytic E. coli O4 cultures did not affect the morphology of the epithelium, but delayed restitution. In CLSM studies, defects were still clearly visible 4 min after the onset of lesion induction. The supernatant of a nonhemolytic E. coli O4 mutant did not exhibit this effect. In conclusion, single-cell defects in native colon cause functional leaks that seal faster than in cell cultures. Proinflammatory cytokines and pathogenic bacteria delay restitution. This suggests a key role of very small lesions at the onset of pathogenic processes in the intestine.

Lactoferrin-enhanced anoikis: a defense against neonatal necrotizing enterocolitis

Enteral nutrition with human milk lowers the incidence of necrotizing enterocolitis in preterm human infants. Lactoferrin, the major whey protein in human milk, has many functions related to host defense against bacterial infection. Here, we hypothesize that lactoferrin also helps terminate bacterial invasion of enterocytes via a detachment-induced apoptosis called anoikis. Death of infected epithelia by anoikis prevents local spread of bacterial pathogens because the bacteria are trapped within the cell. Such infected, apoptotic and sloughed epithelia also cannot infect the lower gastrointestinal tract, and the epithelia exit the body in the stool. Currently, anoikis is a phenomenon related to the renewal of enterocytes, and it is not recognized as an anti-bacterial host defense. We suggest that anoikis of infected enterocytes is a process in which lactoferrin plays an important role. In a pilot study in which neonatal rats were pre-treated with intra-gastric recombinant human lactoferrin, we found evidence of epithelia with anoikis in ileal fluid after enteric infection. This finding was rarely seen in infected neonatal rats without pre-treatment with lactoferrin. Quantitative analysis of intestinal lavage specimens and quantitative stereology of apoptotic epithelia in this model will be required to verify the theory. We propose that oral use of recombinant human lactoferrin might have these hypothesized and other anti-bacterial effects in preterm infants, and hence, this protein might prevent necrotizing enterocolitis in preterm infants who cannot take human milk.

Programmed cell death and cell extrusion in rat duodenum: a study of expression and activation of caspase-3 in relation to C-jun phosphorylation, DNA fragmentation and apoptotic morphology

The small intestinal epithelium is continuously renewed through a balance between cell division and cell loss. How this balance is achieved is uncertain. Thus, it is unknown to what extent programmed cell death (PCD) contributes to intestinal epithelial cell loss. We have used a battery of techniques detecting the events associated with PCD in order to better understand its role in the turnover of the intestinal epithelium, including modified double- and triple-staining techniques for simultaneously detecting multiple markers of PCD in individual cells. Only a partial correlation between TUNEL positivity for DNA fragmentation, c-jun phosphorylation on serine-63, positivity for activated caspase-3 and apoptotic morphology was observed. Our results show that DNA fragmentation does not invariably correlate to activation of caspase-3. Moreover, many cells were found to activate caspase-3 early in the process of extrusion, but did not acquire an apoptotic nuclear morphology until late during the extrusion process. These observations show that the lack of consensus between different methods for detecting PCD may be explained both by different timing of appearance of PCD markers and, additionally, by the occurrence of different forms of PCD during the normal turnover of cells on small intestinal villi.

Harnessing the gut to treat diabetes

The gut contains one of the largest stem cell populations in the body, yet has been largely overlooked as a source of potentially therapeutic cells. The stem cells reside in the crypts located at the base of the protruding villi, reproduce themselves, and repopulate the gut lining as differentiated cells are sloughed off into the lumen. Some studies have demonstrated that gut stem cells can be isolated and maintained in culture, but the field is currently hampered by the lack of clear markers for these cells. Nevertheless, the relative accessibility of the cells and the similar pathways of differentiation of both intestinal and pancreatic endocrine cells make the gut an attractive potential source of cells to treat diabetes. In particular, it may be possible to recapitulate islet development by the introduction of specific factors to gut stem cells. Alternatively, gut endocrine cells might be coaxed to produce insulin and secrete it into the blood in a meal-responsive manner. Several investigations support the feasibility of both approaches as novel potential therapies for diabetes. Utilizing a patient's own gut cells to re-establish endogenous meal-regulated insulin secretion could represent an attractive approach to ultimately cure diabetes.

Evidence for increased apoptosis of duodenal intraepithelial lymphocytes in cow's milk sensitive enteropathy

OBJECTIVES

Enterocyte apoptosis induced by activated intraepithelial lymphocytes (IELs) is increased in celiac disease (CD). A lesser increment in intraepithelial lymphocytes associated with normal villous structure is also characteristic of cow's milk sensitive enteropathy (CMSE), but no information is available about the apoptosis rate of this condition.

METHODS

Endoscopic biopsy samples of 21 children with untreated CMSE were compared with samples from 15 children with CD and 18 controls. Apoptosis was analyzed using the TUNEL technique and the M30 antibody from duodenal bulb and mid-duodenum samples. Ki-67 was used to detect the proliferation rate and CD3(+) to count the overall number of T lymphocytes.

RESULTS

In the mid-duodenum, CMSE patients showed a significantly increased intraepithelial and lamina propria density of TUNEL(+) cells, but no difference in the density of M30(+) epithelial cells was seen compared with controls. In CD subjects, TUNEL(+) counts in mid-duodenal villous epithelium were increased. CD3(+) intraepithelial lymphocytes were increased in both CMSE and CD and correlated with TUNEL(+) and M30(+) counts among all patients. No increase in proliferation rate was seen in CMSE, and no significant correlations between apoptosis and proliferation rates were detected.

CONCLUSIONS

The observed increase in TUNEL(+) counts and the absence of any increase in M30(+) cells suggest that the apoptosis rate of intraepithelial lymphocytes, but not of enterocytes, is increased in the small IELs in CMSE. However, the number of intraepithelial lymphocytes is still elevated in CMSE, indicating that a disturbance of homeostasis of intraepithelial lymphocytes is important in its pathogenesis.

Genistein inhibits intestinal cell proliferation in piglets

Currently 15% of U.S. infants are fed soy formulas that contain up to 14 mg of genistein equivalents/L. Our goal was to investigate the impact of dietary genistein on intestinal development. Piglets (n=8/group) were fed sow milk replacer (MR), MR+1 mg/L of genistein (LG), or MR+14 mg/L of genistein (HG) for 10 d. Formula intake, weight gain, and intestinal length and weight were similar in all groups. Average serum genistein concentration in the HG group was similar to that of soy formula-fed infants. No significant effects of genistein on enterocyte apoptosis, lactase, and sucrase activities or electrophysiologic measures were observed in jejunum or ileum. Jejunal and ileal villus heights were not significantly different, but the percentage of proliferating cell nuclear antigen-positive jejunal crypt cells in the HG was reduced 50% compared with that in MR and LG (p=0.001), indicating decreased proliferation. Enterocyte migration distance in the HG group tended to be 20% less (p=0.1) than LG or MR. Jejunal estrogen receptor beta mRNA expression in HG was half of that in LG (p=0.05), but neither was significantly different from MR. In conclusion, genistein at the level present in soy infant formula is bioactive in the small intestine and results in reduced enterocyte proliferation and migration. The lack of effect of genistein on nutrient transport and enzyme activity suggests that the impact of genistein is greater on proliferating versus differentiated intestinal cells.

The Salmonella effector protein SopB protects epithelial cells from apoptosis by sustained activation of Akt

Invasion of epithelial cells by Salmonella enterica is mediated by bacterial "effector" proteins that are delivered into the host cell by a type III secretion system. Although primarily known for their roles in actin rearrangements and membrane ruffling, translocated effectors also affect host cell processes that are not directly associated with invasion. Here, we show that SopB/SigD, an effector with phosphoinositide phosphatase activity, has anti-apoptotic activity in Salmonella-infected epithelial cells. Salmonella induced the sustained activation of Akt/protein kinase B, a pro-survival kinase, in a SopB-dependent manner. Failure to activate Akt resulted in increased levels of apoptosis after infection with a sopB deletion mutant (DeltasopB). Furthermore, cells infected with wild type bacteria, but not the DeltasopB strain, were protected from camptothecin-induced cleavage of caspase-3 and subsequent apoptosis. The anti-apoptotic activity of SopB was dependent on its phosphatase activity, because a catalytically inactive mutant was unable to protect cells from the effects of camptothecin. Finally, small interfering RNA was used to demonstrate the essential role of Akt in SopB-mediated protection against apoptosis. These results provide new insights into the mechanisms of apoptosis and highlight how bacterial effectors can intercept signaling pathways to manipulate host responses.

Differential subcellular targeting of PKC-epsilon in response to pharmacological or ischemic stimuli in intestinal epithelia

Ischemia is the central pathogenic factor underlying a spectrum of intestinal disorders. The study of the cellular signaling responses to ischemic stress in nonepithelial cells has progressed substantially in the previous several years, but little is known about the response in epithelial cells. Unique features of the epithelial response to ischemic stress suggest differential regulation with regards to signaling. The PKC family of proteins has been implicated in ischemic stress in nonepithelial systems. The role of PKC isoforms in chemical ischemia in intestinal epithelial cells is evaluated in this study. Additionally, the phosphorylation of the F-actin cross-linking protein myristoylated alanine-rich C kinase substrate (MARCKS) is also studied. Chemical ischemia resulted in the transient activation of only the isoform PKC-epsilon as detected by translocation employing the subcellular fractionation technique. The pharmacological agonists phorbol 12-myristate 13-acetate and carbachol also led to the translocation of PKC-epsilon. By immunofluoresence, MARCKS is noted to be located at the lateral membrane under control conditions. In response to carbachol, MARCKS translocates to the cytosol, indicating its phosphorylation, which is additionally confirmed biochemically. Consistent with this observation, carbachol induces the translocation of PKC-epsilon to proximity with MARCKS at the lateral membrane. In response to chemical ischemia, MARCKS fails to translocate and phosphorylation does not increase. Additionally, the translocation of PKC-epsilon is not to the lateral membrane but rather basally. The data suggest that the differential translocation of PKC-epsilon in response to pharmacological agonists versus ischemic stress may lead to different effects on downstream targets.

DRO1, a gene down-regulated by oncogenes, mediates growth inhibition in colon and pancreatic cancer cells

Neoplastic progression in human tissues appears to be paralleled by a series of genetic and epigenetic alterations. In human colorectal cancers, defect Wnt/beta-catenin/T-cell factor and RAS/RAF signaling pathways have a major contributing role in tumor initiation and progression. To date, much of the research on the consequences of beta-catenin activation has been focused on genes whose expression is believed to be activated by beta-catenin-associated T-cell factor-dependent transcription. Little is known about genes whose expression may be down-regulated secondary to beta-catenin activation. Using a subtractive suppression hybridization approach, we identified a gene with markedly decreased expression in rat RK3E epithelial cells neoplastically transformed by beta-catenin. Because expression of this gene was also down-regulated in RK3E transformed by several other oncogenes, the gene was named DRO1 for "down-regulated by oncogenes 1." Compared with corresponding normal tissues, DRO1 expression was found to be very reduced in colon and pancreatic cancer cell lines as well as in most colorectal cancer specimens. The predicted DRO1 protein contains three repetitive elements with significant similarity to the carboxyl-terminal regions of the predicted proteins from DRS/SRPX/ETX1 and SRPUL genes, suggesting the existence of a new protein family. Ectopic expression of DRO1 in neoplastically transformed RK3E or colorectal and pancreatic cancer cell lines lacking endogenous DRO1 expression resulted in substantial inhibition of growth properties. DRO1 was found to suppress anchorage independent growth and to sensitize cells to anoikis and CD95-induced apoptosis. Our findings suggest that inhibition of DRO1 expression may be an important event in the development of colorectal and pancreatic cancers.

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Human intestinal epithelial cell survival and anoikis. Differentiation state-distinct regulation and roles of protein kinase B/Akt isoforms

We have shown previously that human intestinal epithelial cell survival and anoikis are distinctively regulated according to the state of differentiation. Here we analyzed the roles of protein kinase B/Akt isoforms in such differentiation state distinctions. Anoikis was induced in undifferentiated and differentiated enterocytes by inhibition of focal adhesion kinase (Fak; pharmacologic inhibition or overexpression of dominant-negative mutants) or beta1 integrins (antibody blocking) or by maintaining cells in suspension. Expression/activation parameters of Akt isoforms (Akt-1, Akt-2, and Akt-3) and Fak were analyzed. Activity of Akt isoforms was also blocked by inhibition of phosphatidylinositol 3-kinase or by overexpression of dominant-negative mutants. Here we report the following. 1) The expression/activation levels of Akt-1 increase overall during enterocytic differentiation, and those of Akt-2 decrease, whereas Akt-3 is not expressed. 2) Akt-1 activation is dependent on beta1 integrins/Fak signaling, regardless of the differentiation state. 3) Akt-2 activation is dependent on beta1 integrins/Fak signaling in undifferentiated cells only. 4) Activation of Akt-1 is phosphatidylinositol 3-kinase-dependent, whereas that of Akt-2 is not. 5) Akt-2 does not promote survival or apoptosis/anoikis. 6) Akt-1 is essential for survival. 7) Akt-2 cannot substitute for Akt-1 in the suppression of anoikis. Hence, the expression and regulation of Akt isoforms show differentiation state-specific distinctions that ultimately reflect upon their selective implication in the mediation of human intestinal epithelial cell survival. These data provide new insights into the synchronized regulation of cell survival/death that is required in the dynamic renewal process of tissues such as the intestinal epithelium.

Ultrastructural study shows morphologic features of apoptosis and para-apoptosis in megakaryocytes from patients with idiopathic thrombocytopenic purpura

To investigate whether altered megakaryocyte morphology contributes to reduced platelet production in idiopathic thrombocytopenic purpura (ITP), ultrastructural analysis of megakaryocytes was performed in 11 ITP patients. Ultrastructural abnormalities compatible with (para-)apoptosis were present in 78% +/- 14% of ITP megakaryocytes, which could be reversed by in vivo treatment with prednisone and intravenous immunoglobulin. Immunohistochemistry of bone marrow biopsies of ITP patients with extensive apoptosis showed an increased number of megakaryocytes with activated caspase-3 compared with normal (28% +/- 4% versus 0%). No difference, however, was observed in the number of bone marrow megakaryocyte colony-forming units (ITP, 118 +/- 93/105 bone marrow cells; versus controls, 128 +/- 101/105 bone marrow cells; P =.7). To demonstrate that circulating antibodies might affect megakaryocytes, suspension cultures of CD34+ cells were performed with ITP or normal plasma. Morphology compatible with (para-)apoptosis could be induced in cultured megakaryocytes with ITP plasma (2 of 10 samples positive for antiplatelet autoantibodies). Finally, the plasma glycocalicin index, a parameter of platelet and megakaryocyte destruction, was increased in ITP (57 +/- 70 versus 0.7 +/- 0.2; P =.009) and correlated with the proportion of megakaryocytes showing (para-) apoptotic ultrastructure (P =.02; r = 0.7). In conclusion, most ITP megakaryocytes show ultrastructural features of (para-) apoptosis, probably due to action of factors present in ITP plasma.

Human intestinal epithelial crypt cell survival and death: Complex modulations of Bcl-2 homologs by Fak, PI3-K/Akt-1, MEK/Erk, and p38 signaling pathways

To investigate the mechanisms responsible for survival and apoptosis/anoikis in normal human intestinal epithelial crypt cells, we analyzed the roles of various signaling pathways and cell adhesion on the expression of six Bcl-2 homologs (Bcl-2, Bcl-XL, Mcl-1, Bax, Bak, Bad) in the well established HIEC-6 cell model. Pharmacological inhibitors and/or dominant-negative constructs were used to inhibit focal adhesion kinase (Fak) and p38 isoforms, as well as the phosphatidylinositol 3'-kinase (PI3-K)/Akt-1 and mitogen-activated protein kinase [MAPK] kinase (MEK)/extracellular regulated kinases (Erk) pathways. Cell adhesion was disrupted by antibody-inhibition of integrin binding or forced cell suspension. The activation levels of studied kinase pathways were also analyzed. Herein, we report that beta1 integrins, Fak, and the PI3-K/Akt-1 pathway, but not beta4 integrins or the MEK/Erk pathway, are crucial for the survival of HIEC-6 cells. Conversely, p38beta, but not p38alpha or gamma, is required for the induction of apoptosis/anoikis in HIEC-6 cells. However, each of the signaling molecules/pathways analyzed were found to affect distinctively the individual expression of the Bcl-2 homologs studied. For example, the inhibition of the PI3-K/Akt-1 pathway down-regulated Bcl-XL, Mcl-1, and Bad, while at the same time up-regulating Bax, whereas the inhibition of Fak up-regulated both Bax and Bak, down-regulated Bad, and did not affect the other Bcl-2 homologs analyzed. These results indicate that integrins, Fak, PI3-K/Akt-1, MEK/Erk, and p38 isoforms perform distinct roles in the regulation of HIEC-6 cell survival and/or death. In addition, our data show that the functions performed by these molecules/pathways in promoting cell survival or apoptosis/anoikis translate into complex, differential modulations of individual Bcl-2 homologs.

General suitability of techniques for in situ detection of apoptosis in small intestinal epithelium

The present study was designed to evaluate different techniques for the in situ detection of apoptosis in human and rat small intestinal epithelium. The techniques included light microscopy (LM) and transmission electron microscopy (TEM) observation of epoxy resin-embedded tissue, scanning electron microscopy (SEM), TUNEL assay, and antibodies directed against caspase cleavage products of caspase 3, cytokeratin 18 (CK 18), and apoptotic single-strand DNA (ssDNA). All techniques, if the labeling was positive, showed apoptotic cells exclusively at the villus tip. LM and TEM were the most reliable and revealed morphological signs typical of cells that have died via apoptosis. SEM indicated the extension of the process. The antibody recognizing cleaved caspase 3 could be considered an appropriate marker for apoptotic epithelial cells in human and rat small intestine. However, the majority of epithelial cells lining the proximal small intestinal villus contained only low levels of intact CK 18. Therefore, sufficient amounts of cleaved CK 18 for immunohistochemical detection were not generated during apoptosis, rendering the application of the antibody inappropriate. The antibody detecting formamide-denatured ssDNA in apoptotic cells was both suitable and reliable; however, the particular staining procedure used compromised the tissue preservation. In comparison to this, the TUNEL assay was less reliable. Although it was performed with a commercially available ready-to-use kit, its application conditions had to be adjusted for each specimen on the basis of the findings produced by other techniques.

Progress on isolation and short-term ex-vivo culture of highly purified non-apoptotic human intestinal epithelial cells (IEC)

Intestinal epithelial cells (IEC) form the largest surface of the human body and are of pivotal importance to digest and absorb nutrients. Furthermore these cells play a critical role shielding the organism against microorganisms and toxins present in the intestinal lumen. It is therefore not surprising that a large group of researchers take great interest in the study of these cells. However, to date it is a challenge to purify viable primary human intestinal epithelial cells and it has been even more fastidious to maintain IEC in culture ex-vivo as IEC undergo apoptosis within hours due to loss of cell anchorage ('anoikis') following the isolation process. Over recent years the authors aimed to continuously improve the isolation technique for primary IEC, allowing a simple, effective and rapid isolation of highly purified non-apoptotic human IEC. In this study the newly improved method is presented and applied to establish ex-vivo cultures of highly purified, fully viable primary IEC displaying important functional properties, making these cells amenable for ex-vivo research on primary human intestinal epithelial cells.