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Background & Aims: To date, it is unclear how environmental factors influence Crohn's disease (CD) risk and how they interact with biological processes. This study investigates the association between environmental exposures and CD risk and evaluates their association with pre-disease biomarkers., Methods: We studied 4289 healthy first-degree relatives (FDRs) of patients with CD from the Crohn's and Colitis Canada - Genetic, Environmental, Microbial (CCC-GEM) project. Regression models identified environmental factors associated with future CD onset and their association with pre-disease biological factors, including altered intestinal permeability measured by urinary fractional excretion of lactulose to mannitol ratio (LMR); gut inflammation via fecal calprotectin (FCP) levels; and fecal microbiome composition through 16S rRNA sequencing., Results: Over a 5.62-year median follow-up, 86 FDRs developed CD. Living with a dog between ages 5 and 15 (hazard ratio [HR], 0.62; 95% confidence interval [CI], 0.40-0.96; P = .034), and living with a large family size in the first year of life (HR, 0.43; 95% CI, 0.21-0.85; P = .016) were associated with decreased CD risk, whereas having a bird at the time of recruitment (HR, 2.78; 95% CI, 1.36-5.68; P = .005) was associated with an increased CD risk. Furthermore, living with a dog was associated with reduced LMR, altered relative abundance of multiple bacterial genera, and increased Chao1 diversity, whereas bird owners had higher FCP levels. Large family during participants' first year of life was associated with altered microbiota composition without affecting FCP or LMR., Conclusion: This study identifies environmental variables associated with CD risk. These variables were also associated with altered barrier function, subclinical inflammation, and gut microbiome composition shifts, suggesting potential roles in CD pathogenesis., (Copyright © 2024 AGA Institute. Published by Elsevier Inc. All rights reserved.)

Inflammatory bowel disease (IBD) is a painful chronic gastrointestinal disease associated with diminished quality of life. No research documents IBD body pain or the associations of pain patterns to outcomes. Objectives were to map patient body pain areas and examine the associations between pain patterns with depression, catastrophizing, pain severity, and quality of life. A cross-sectional survey was collected from consecutive tertiary-care IBD clinic patients ( n = 255). Patients were classified into three pain pattern groups (No Pain; Localized Pain Only; and Widespread Pain) with more than 40% reporting widespread pain. The Localized Pain Only and Widespread Pain groups reported pain in the abdomen, the uterus/testes, vagina/penis, bladder, and pelvis/buttock areas. The body area most often reported was the anterior abdomen for the Localized Pain Only and Widespread Pain groups, with additional endorsement of lower back and anterior thigh and knees for the Widespread Pain group. The pain versus no pain patients reported greater depressive symptoms, catastrophizing, and diminished quality of life. Patients reported a variety of pain patterns during clinic visits. Widespread pain is associated with greatest pain and poorest psychosocial outcomes., (Copyright © 2022 Society of Gastroenterology Nurses and Associates.)

Importance: Clostridium difficile infection (CDI) is a major burden in health care and community settings. CDI recurrence is of particular concern because of limited treatment options and associated clinical and infection control issues. Fecal microbiota transplantation (FMT) is a promising, but not readily available, intervention., Objective: To determine whether frozen-and-thawed (frozen, experimental) FMT is noninferior to fresh (standard) FMT in terms of clinical efficacy among patients with recurrent or refractory CDI and to assess the safety of both types of FMT., Design, Setting, and Participants: Randomized, double-blind, noninferiority trial enrolling 232 adults with recurrent or refractory CDI, conducted between July 2012 and September 2014 at 6 academic medical centers in Canada., Interventions: Patients were randomly allocated to receive frozen (n = 114) or fresh (n = 118) FMT via enema., Main Outcomes and Measures: The primary outcome measures were clinical resolution of diarrhea without relapse at 13 weeks and adverse events. Noninferiority margin was set at 15%., Results: A total of 219 patients (n = 108 in the frozen FMT group and n = 111 in the fresh FMT group) were included in the modified intention-to-treat (mITT) population and 178 (frozen FMT: n = 91, fresh FMT: n = 87) in the per-protocol population. In the per-protocol population, the proportion of patients with clinical resolution was 83.5% for the frozen FMT group and 85.1% for the fresh FMT group (difference, -1.6% [95% CI, -10.5% to ∞]; P = .01 for noninferiority). In the mITT population the clinical resolution was 75.0% for the frozen FMT group and 70.3% for the fresh FMT group (difference, 4.7% [95% CI, -5.2% to ∞]; P < .001 for noninferiority). There were no differences in the proportion of adverse or serious adverse events between the treatment groups., Conclusions and Relevance: Among adults with recurrent or refractory CDI, the use of frozen compared with fresh FMT did not result in worse proportion of clinical resolution of diarrhea. Given the potential advantages of providing frozen FMT, its use is a reasonable option in this setting., Trial Registration: clinicaltrials.gov Identifier:NCT01398969.

Intestinal inflammation causes initial axonal degeneration and neuronal death but subsequent axon outgrowth from surviving neurons restores innervation density to the target smooth muscle cells. Elsewhere, the pro-inflammatory cytokines TNFα and IL-1β cause neurotoxicity, leading us to test their role in promoting enteric neuron death. In a rat coculture model, TNFα or IL-1β did not affect neuron number but did promote significant neurite outgrowth to twofold that of control by 48 h, while other cytokines (e.g., IL-4, TGFβ) were without effect. TNFα or IL-1β activated the NFκB signaling pathway, and inhibition of NFκB signaling blocked the stimulation of neurite growth. However, nuclear translocation of NFκB in smooth muscle cells but not in adjacent neurons suggested a dominant role for smooth muscle cells. TNFα or IL-1β sharply increased both mRNA and protein for GDNF, while the neurotrophic effects of TNFα or IL-1β were blocked by the RET-receptor blocker vandetanib. Conditioned medium from cytokine-treated smooth muscle cells mimicked the neurotrophic effect, inferring that TNFα and IL-1β promote neurite growth through NFκB-dependent induction of glial cell line-derived neurotrophic factor (GDNF) expression in intestinal smooth muscle cells. In vivo, TNBS-colitis caused early nuclear translocation of NFκB in smooth muscle cells. Conditioned medium from the intact smooth muscle of the inflamed colon caused a 2.5-fold increase in neurite number in cocultures, while Western blotting showed a substantial increase in GDNF protein. Pro-inflammatory cytokines promote neurite growth through upregulation of GDNF, a novel process that may facilitate re-innervation of smooth muscle cells and a return to homeostasis following initial damage.

Heat shock proteins (Hsps) are highly conserved proteins that play a role in cytoprotection and maintaining intestinal homeostasis. Glutamine is essential for the optimal induction of intestinal epithelial Hsp expression, but its mechanisms of action are incompletely understood. Glutamine is a substrate for polyamine synthesis and stimulates the activity of ornithine decarboxylase (ODC), a key enzyme for polyamine synthesis, in intestinal epithelial cells. Thus we investigated whether polyamines (putrescine, spermidine, or spermine) and their precursor ornithine mediate the induction of Hsp expression in IEC-18 rat intestinal epithelial cells. As previously observed, glutamine was required for heat stress induction of Hsp70 and Hsp25, although it had little effect under basal conditions. Under conditions of glutamine depletion, supplementation of ornithine or polyamines restored the heat-induced expression of Hsp70 and Hsp25. When ODC was inhibited by α-difluoromethylornithine (DFMO), an irreversible ODC inhibitor, the heat stress induction of Hsp70 and Hsp25 was decreased significantly, even in the presence of glutamine. Ornithine, polyamines, and DFMO did not modify the nuclear localization of heat shock transcription factor 1 (HSF-1). However, DFMO dramatically reduced glutamine-dependent HSF-1 binding to an oligonucleotide with heat shock elements (HSE), which was increased by glutamine. In addition, exogenous polyamines recovered the DNA-binding activity. These results indicate that polyamines play a critical role in the glutamine-dependent induction of the intestinal epithelial heat shock response through facilitation of HSF-1 binding to HSE.

Background & Aims: The roles of intestinal Toll-like receptors (TLR) in the pathogenesis of colitis are not known. TLR2 and TLR4 appear to protect against dextran sodium sulfate-induced colitis by promoting mucosal integrity, but it is not clear whether this method of protection occurs in other models of colitis. We investigated the roles of TLR2 and TLR4 and the cell types that express these receptors during infectious colitis., Methods: We generated chimeric mice with TLR2(-/-) or TLR4(-/-) bone marrow and infected them with the bacterial pathogen Citrobacter rodentium. We assessed their susceptibility to colitis and the mechanisms of TLR-mediated mucosal integrity., Results: TLR2-expressing tissue resident cells prevented lethal colitis, whereas TLR4-dependent inflammatory responses of hematopoietic cells mediated intestinal damage. TLR2 expression protected against intestinal damage by maintaining epithelial barrier function and inducing expression of interleukin (IL)-11 from tissue resident cells in the muscularis mucosae, concurrent with epithelial activation of the transcription factor STAT3. Addition of exogenous IL-11 protected against the lethal colitis in TLR2-deficient mice via STAT3 activation in intestinal epithelial cells., Conclusions: TLR2-dependent cytoprotective responses from tissue resident cells maintain mucosal integrity against the ultimately lethal TLR4-dependent inflammatory responses of hematopoietic cells. Whereas TLR2 protects against various noxious agents, the role of TLR4 during colitis can be either protective or damaging, depending on the stimulus. Therefore, therapeutics that reduce innate immunity (TLR2 signaling in particular) may not be beneficial to patients with colitis; they could worsen symptoms. Therapies that stimulate cytoprotective responses, like IL-11, could have benefits for patients with colitis., (Copyright © 2010 AGA Institute. Published by Elsevier Inc. All rights reserved.)

Background & Aims: Glutamine plays a protective role in intestinal cells during physiologic stress; however, the protection mechanisms are not fully understood. Autophagy functions in bulk degradation of cellular components, but has been recognized recently as an important mechanism for cell survival under conditions of stress. We therefore sought to see if glutamine's actions involve the induction of autophagy in intestinal cells and, if so, the mechanisms that underlie this action., Methods: Formation of microtubule-associated protein light chain 3 (LC3)-phospholipid conjugates (LC3-II) in rat intestinal epithelial IEC-18 cells and human colonic epithelial Caco-2(BBE) cells was determined by Western blotting and localized by confocal microscopy. Activation of mammalian target of rapamycin (mTOR) pathway, mitogen-activated protein (MAP) kinases, caspase-3, and poly (ADP-ribose) polymerase were monitored by Western blotting., Results: Glutamine increased LC3-II as well as the number of autophagosomes. Glutamine-induced LC3-II formation was paralleled by inactivation of mTOR and p38 MAP kinase pathways, and inhibition of mTOR and p38 MAP kinase allowed LC3-II induction in glutamine-deprived cells. Under glutamine starvation, LC3-II recovery after heat stress or the increase under oxidative stress was blunted significantly. Glutamine depletion increased caspase-3 and poly (ADP-ribose) polymerase activity after heat stress, which was inhibited by treatment with inhibitors of mTOR and p38 MAP kinase., Conclusions: Glutamine induces autophagy under basal and stressed conditions, and prevents apoptosis under heat stress through its regulation of the mTOR and p38 MAP kinase pathways. We propose that glutamine contributes to cell survival during physiologic stress by induction of autophagy.

Persistent infection with Helicobacter pylori confers an increased risk for the development of gastric cancer. However, the exact mechanisms whereby this bacterium causes carcinogenesis have not been completely elucidated. Recent evidence indicates that aberrant activation of the signal transducers and activators of transcription 3 (STAT3) signaling pathway may play a role in gastric carcinogenesis. Therefore, we hypothesized that H. pylori infection modulates STAT3 signaling, favoring gastric cancer development. In epithelial cells infected with H. pylori, STAT3 was activated, as assessed by immunoblotting for phosphorylated STAT3, immunofluorescence of translocated STAT3, fluorescence recovery after photobleaching, and luciferase activation in transfected cells. Activation was dependent on translocation but not phosphorylation of cytotoxin-associated gene A (CagA) in host cells. Activation seemed to be receptor-mediated because preincubation of cells with the interleukin-6 (IL-6) receptor superantagonist sant7 or inhibition of gp130 by a monoclonal antibody prevented H. pylori-mediated STAT3 activation. However, activation was not related to autocrine activation by IL-6 or IL-11. CagA+ wild-type H. pylori, but not the noncarcinogenic cagA- mutant, activated STAT3 in gastric epithelial cells in vivo in the gerbil model of H. pylori-mediated gastric carcinogenesis. Collectively, these results indicate that H. pylori CagA activates the STAT3 signaling pathway in vitro and in vivo, providing a potential mechanism by which chronic H. pylori infection promotes the development of gastric cancer.

Interleukin-11 (IL-11) displays epithelial cytoprotective effects during intestinal injury. Antiapoptotic effects of IL-11 have been described, yet mechanisms remain unclear. Fas/CD95 death receptor signaling is upregulated in ulcerative colitis, leading to mucosal breakdown. We hypothesized that IL-11 inhibits Fas ligand (FasL)-mediated apoptosis in intestinal epithelia. Cell death was monitored in IEC-18 cells by microscopy, caspase and poly(ADP-ribose) polymerase cleavage, mitochondrial release of cytochrome c, and abundance of cytoplasmic oligonucleosomal DNA. RT-PCR was used to monitor Fas, cIAP1, cIAP2, XIAP, cFLIP, survivin, and Bcl-2 family members. Fas membrane expression was detected by immunoblot. Inhibitors of JAK2, phosphatidylinositol 3-kinase (PI3-kinase), Akt 1, MEK1 and MEK2, and p38 MAPK were used to delineate IL-11's antiapoptotic mechanisms. IL-11 did not alter Fas expression. Pretreatment with IL-11 for 24 h before FasL reduced cytoplasmic oligonucleosomal DNA by 63.2%. IL-11 also attenuated caspase-3, caspase-9, and poly(ADP-ribose) polymerase cleavage without affecting expression of activated caspase-8 p20 or cytochrome c release. IL-11 did not affect mRNA expression of the candidate antiapoptotic genes. The MEK1 and MEK2 inhibitors U-0126 and PD-98059 significantly attenuated the protection of IL-11 against caspase-3 and caspase-9 cleavage and cytoplasmic oligonucleosomal DNA accumulation. Although Akt inhibition reversed IL-11-mediated effects on caspase cleavage, it did not reverse the protective effects of IL-11 by DNA ELISA. We conclude that IL-11-dependent MEK1 and MEK2 signaling inhibits FasL-induced apoptosis. The lack of reversal of the IL-11 effect on DNA cleavage by Akt inhibition, despite antagonism of caspase cleavage, suggests that IL-11 inhibits caspase-independent cell death signaling by FasL in a MEK-dependent manner.

Glutamine is considered a nonessential amino acid; however, it becomes conditionally essential during critical illness when consumption exceeds production. Glutamine may modulate the heat shock/stress response, an important adaptive cellular response for survival. Glutamine increases heat induction of heat shock protein (Hsp) 25 in both intestinal epithelial cells (IEC-18) and mesenchymal NIH/3T3 cells, an effect that is neither glucose nor serum dependent. Neither arginine, histidine, proline, leucine, asparagine, nor tyrosine acts as physiological substitutes for glutamine for heat induction of Hsp25. The lack of effect of these amino acids was not caused by deficient transport, although some amino acids, including glutamate (a major direct metabolite of glutamine), were transported poorly by IEC-18 cells. Glutamate uptake could be augmented in a concentration- and time-dependent manner by increasing either media concentration and/or duration of exposure. Under these conditions, glutamate promoted heat induction of Hsp25, albeit not as efficiently as glutamine. Further evidence for the role of glutamine conversion to glutamate was obtained with the glutaminase inhibitor 6-diazo-5-oxo-l-norleucine (DON), which inhibited the effect of glutamine on heat-induced Hsp25. DON inhibited phosphate-dependent glutaminase by 75% after 3 h, decreasing cell glutamate. Increased glutamine/glutamate conversion to glutathione was not involved, since the glutathione synthesis inhibitor, buthionine sulfoximine, did not block glutamine's effect on heat induction of Hsp25. A large drop in ATP levels did not appear to account for the diminished Hsp25 induction during glutamine deficiency. In summary, glutamine is an important amino acid, and its requirement for heat-induced Hsp25 supports a role for glutamine supplementation to optimize cellular responses to pathophysiological stress.

Although short-chain fatty acid (SCFA)-induced heat shock protein 25 (Hsp25) is associated with increased cellular resistance to injury, withdrawal of lumenal butyrate in vivo is associated with intestinal epithelial injury and apoptosis. Recognizing that SCFA-dependent posttranslational modification of Hsp25 may involve altered Hsp25 phosphorylation, we hypothesized that butyrate regulates Hsp25 phosphorylation and secondarily affects cellular responses to apoptosis-inducing agents. Intestinal epithelial crypt IEC-18 cells were treated with butyrate, propionate, or the histone deacetylase inhibitor trichostatin A for 6-24 h. Immunolocalization of Hsp25 was examined by confocal laser microscopy. Hsp25 phosphorylation was characterized using two-dimensional isoelectric focusing gel electrophoresis. Hsp25 accumulation in cytoskeletal- and mitochondrial-enriched fractions was examined by immunoblotting. The activation of p38 MAP kinase was determined using phospho-specific antibodies and MAPKAPK 2 kinase assays. The effects of SCFA on apoptosis were studied by ELISA detection of cleaved DNA and using antibodies recognizing cleaved caspase-3. Five-millimolar butyrate induced no significant injury to IEC-18 cells. Hsp25 did not accumulate in Triton X-100-insoluble cytoskeletal fractions with butyrate treatment but did localize to mitochondria in a p38 MAP kinase-dependent manner. Hsp25 phosphorylation was induced by butyrate, propionate, and trichostatin A. Butyrate-mediated changes in Hsp25 phosphorylation coincide with the activation of the p38 MAP kinase and MAPKAPK 2. Butyrate, propionate, and low-dose trichostatin A confer significant protection from camptothecin-induced apoptosis, which was not reversed by the p38 inhibitor SB203580. We conclude that butyrate-mediated phosphorylation of Hsp25 is associated with significant resistance to apoptosis, which appears to be independent of p38-mediated targeting of Hsp25 to mitochondria.

Background & Aims: During physiologic stress, L-glutamine becomes conditionally essential. Its deficiency results in altered epithelial barrier competence, bacterial translocation, and decreased survival. L-glutamine may attenuate these effects by modulating heat shock protein expression, a well-described effect in vitro. We sought to characterize L-glutamine-dependent transcriptional regulation in heat-shocked intestinal cells and to determine its physiologic relevance., Methods: IEC-18 and H4 intestinal cells were used. Heat shock protein 72 (Hsp72) gene expression was determined by Northern blotting and luciferase assays. Heat shock factor-1 (HSF-1) activation was assessed by electromobility shift assay, Western blotting, and HSF-1 minimal promoters. Phosphorylation and trimerization of HSF-1 were determined by immunoprecipitation and native nonreducing gradient polyacrylamide gel electrophoresis (PAGE). Camptothecin-induced apoptosis was monitored using caspase-3 and poly (ADP-ribose) polymerase [PARP]-specific antibodies and DNA Elisa +/- Hsp72 siRNA., Results: L-glutamine specifically augmented Hsp72 transcript abundance and HSF-1 DNA binding during heat shock. No glutamine-dependent differences in HSF-1 phosphorylation, trimerization, nuclear localization during heat shock, or HSF-1 minimal promoter activity were observed. Nevertheless, the presence of L-glutamine was an important determinant of wild-type Hsp72 promoter transcriptional activation. Reduced Hsp72 was associated with increased camptothecin-induced caspase-3 and PARP cleavage in glutamine-deficient cells. siRNA treated cells were less resistant to camptothecin., Conclusions: Taken together, the data suggest that glutamine does not affect the classical pathway of HSF-1 activation and that glutamine-dependent upstream trans -factor binding elsewhere in the Hsp72 promoter or coactivator recruitment may determine Hsp72 abundance. L-glutamine potentiation of Hsp72 is associated with increased epithelial resistance to apoptotic injury.

Background and Aims: The extent and severity of mucosal injury in inflammatory bowel diseases are determined by the disequilibrium between 2 opposing processes: reparative and cytoprotective mechanisms vs. inflammation-induced injury. Probiotics may provide clinical benefit by ameliorating colitis; however, their mechanisms of action remain largely unknown. Our objective was to investigate microbial-epithelial interactions that could explain the beneficial therapeutic effects of probiotics., Methods: The effect of VSL#3-conditioned media on the nuclear factor-kappaB pathway in young adult mouse colonic epithelial cells was assessed by using monocyte chemoattractant protein-1 enzyme-linked immunosorbent assays; IkappaBalpha, IkappaBbeta, and p105 immunoblot analysis; and nuclear factor-kappaB luciferase reporter gene and proteasome assays. Effects on heat shock proteins were determined by electrophoretic mobility shift assay and immunoblot for heat shock proteins 25 and 72 in young adult mouse colonic cells. Cytoprotection against oxidant injury was determined by chromium 51 release and filamentous and globular actin assays., Results: VSL#3 produces soluble factors that inhibit the chymotrypsin-like activity of the proteasome in gut epithelial cells. Proteasome inhibition is an early event that begins almost immediately after exposure of the epithelial cells to the probiotic-conditioned media. In addition, these bacteria inhibit the proinflammatory nuclear factor-kappaB pathway through a mechanism different from the type III secretory mechanisms described for other nonpathogenic enteric flora. They also induce the expression of cytoprotective heat shock proteins in intestinal epithelial cells., Conclusions: The resulting inhibition of nuclear factor-kappaB and increased expression of heat shock proteins may account for the anti-inflammatory and cytoprotective effects reported for probiotics and may be a novel mechanism of microbial-epithelial interaction. These effects seem to be mediated through the common unifying mechanism of proteasome inhibition.

Protection of colonic epithelial integrity and function is critical, because compromises in mucosal functions can lead to adverse and potentially life-threatening effects. The gut flora may contribute to this protection, in part, through the sustained induction of cytoprotective heat shock proteins (HSPs) in surface colonocytes. In this study, we investigated whether Escherichia coli LPS mediates bacteria-induced HSP by using cultured young adult mouse colon (YAMC) cells, an in vitro model of the colonic epithelium. E. coli LPS led to an epithelial cell-type specific induction of HSP25 in a time- and concentration-dependent manner, an effect that did not involve changes in HSP72. YAMC cells expressed the toll-like receptors (TLR)2 and TLR4 but not the costimulatory CD14 molecule. Whereas LPS stimulated both the p38 and ERK1/2 but not the stress-activated protein kinase/c-Jun NH(2)-terminal kinase, signaling pathways in the YAMC cells, all three were stimulated in RAW macrophage cells (in which no LPS-induced HSP25 expression was observed). The p38 inhibitor SB-203580 and the MAP kinase kinase-1 inhibitor PD-98059 inhibited HSP25 induction by LPS. LPS treatment also conferred protection against actin depolymerization induced by the oxidant monochloramine. The HSP25 dependence of the LPS protective effect was outlined in inhibitor studies and through adenovirus-mediated overexpression of HSP25. In conclusion, LPS may be an important mediator of enteric bacteria-induced expression of intestinal epithelial HSP25, an effect that may contribute to filamentous actin stabilization under physiological as well as pathophysiological conditions and thus protection of colonic epithelial integrity.

Background & Aims: The mechanisms of interleukin-11 (IL-11) cytoprotection in intestinal epithelial injury are largely unknown. IL-11 protects barrier integrity during oxidant stress, a common endpoint of numerous types of intestinal injury including ischemia and immune-mediated inflammation. Because heat shock proteins (hsp) are cytoprotective in intestinal epithelia, we hypothesized that IL-11-conferred cytoprotection is mediated by inducible hsps., Methods: IL-11 receptor (IL-11R) activation was determined using phospho-specific antibodies to STAT3. IL-11 induction of hsp72 and hsp25 was determined by immunoblot in IEC-18 crypt and young adult mouse colon colonic epithelial cells. Epithelial resistance to oxidant injury by monochloramine was determined by (51)Cr release. Stable hsp anti-sense IEC-18 cell clones were obtained by electroporation and hygromycin B selection. The IL-11 effect on hsp25 distribution was characterized by analysis of Triton x-100 insoluble fractions, 2-D isoelectric focusing gels, and confocal microscopy., Results: IL-11R signaling was detected in all cells under study. IL-11 induces hsp25 in an intestinal epithelial-specific manner that significantly preserves cellular viability in the presence of monochloramine. This effect was significantly reversed in intestinal epithelia stably expressing anti-sense to hsp25. IL-11 induced a shift of hsp25 to Triton x-100 insoluble fractions containing cytoskeletal elements, which was not associated with altered hsp25 phosphorylation. The shift was not paralleled by increased hsp25 co-localization with F-actin by confocal microscopy., Conclusions: The induction of hsp25 by IL-11 confers epithelial-specific cytoprotection that is independent of phosphorylation-dependent co-localization of hsp25 to F-actin, thereby contributing to the protective effects of IL-11 in models of intestinal epithelial injury.

We determined whether the cytoprotective heat shock protein HSP72 protects against the injurious effects of Clostridium difficile toxin A (TxA) on intestinal epithelial cells. Colonic epithelial Caco-2/bbe (C2) cells were stably transfected with HSP72 antisense (C2AS) or vector only (C2VC), resulting in low and high HSP72 expression, respectively. Measurements of epithelial barrier integrity, mitochondrial function, and apoptosis activation were assessed after TxA exposure. HSP72 and RhoA interactions were evaluated with immunoprecipitations. In C2AS cells, TxA was associated with a greater decrease in transepithelial resistance (TER), an increase in [(3)H]mannitol flux, and increased dissociation of perijunctional actin. Although HSP72 binds RhoA, it failed to prevent RhoA glucosylation. TxA caused a more rapid decrease in ATP, release of cytochrome c, and activation of caspase-9 in C2AS cells. To determine whether ATP depletion decreases TER, we treated cells with antimycin A, which caused a decline in TER. We conclude that HSP72 may protect intestinal epithelial cells from TxA-mediated damage through several mechanisms, including actin stabilization, mitochondrial protection, and inhibition of apoptosis activation, but not by prevention of RhoA glucosylation.

The translation of mRNA constitutes the first step in the synthesis of a functional protein. The polypeptide chain is subsequently folded into the appropriate three-dimensional configuration and undergoes a variety of processing steps before being converted into its active form. These processing steps are intimately related to the cellular events that occur in the endoplasmic reticulum and Golgi compartments, and determine the sorting and transport of different proteins to their appropriate destinations within the cell. While the regulation of gene expression occurs primarily at the level of transcription, the expression of many genes can also be controlled at the level of translation. Most proteins can be regulated in response to extracellular signals. In addition, intracellular protein levels can be controlled by differential rates of protein degradation. Thus, the regulation of both the amounts and activities of intracellular proteins ultimately determines all aspects of cell behaviour.

The transcription of DNA into RNA is the primary level at which gene expression is controlled in eukaryotic cells. Eukaryotic gene transcription involves several different RNA polymerases that interact with a host of transcription factors to initiate transcription. Genes that encode proteins are transcribed into messenger RNA (mRNA) by RNA polymerase II. Ribosomal RNAs (rRNAs) and transfer RNAs (tRNAs) are transcribed by RNA polymerase I and III, respectively. The production of each mRNA in human cells involves complex interactions of proteins (ie, trans-acting factors) with specific sequences on the DNA (ie, cis-acting elements). Cis-acting elements are short base sequences adjacent to or within a particular gene. While the regulation of transcription is a pivotal step in the control of gene expression, a variety of molecular events, collectively known as 'RNA processing' add an additional level of control of gene expression in eukaryotic cells. (Pour le résumé, voir page suivante)

Progress in the basic sciences of cell and molecular biology has provided an exciting dimension that has translated into clinically relevant information in every medical subspecialty. Importantly, the application of recombinant DNA technology has played a major role in unravelling the intricacies related to the molecular pathophysiology of disease. This series of review articles constitutes a framework for the integration of the database of new information into the core knowledge base of concepts related to the pathogenesis of gastrointestinal disorders and liver disease. The goal of this series of three articles is to review the basic principles of eukaryotic gene expression. The first article examines the role of DNA in directing the flow of genetic information in eukaryotic cells.