Bacillus polyfermenticus ameliorates colonic inflammation by promoting cytoprotective effects in colitic mice

Although human consumption of Bacillus polyfermenticus provides several health benefits, the probiotic effect of this bacterium against colonic inflammation has not yet, to our knowledge, been studied. Therefore, we induced colitis in mice by oral or intrarectal administration of dextran sodium sulfate (DSS) or trinitrobenzenosulfonic acid (TNBS), respectively, and investigated the effect of B. polyfermenticus on colitis. We found that mice treated with DSS or TNBS along with B. polyfermenticus had reduced mortality and severity of colitis (weight loss, diarrhea, and mucosal damages) than mice treated with DSS or TNBS alone. B. polyfermenticus also reduced the expression of inflammatory molecules, including chemokine (C-X-C motif) ligand 1, intercellular adhesion molecule, and tumor necrosis factor-alpha, but enhanced the expression of the antiinflammatory cytokine interleukin-10 in the inflamed mouse colon. Moreover, B. polyfermenticus suppressed apoptosis both in vivo in inflamed colonic mucosa and in vitro in colonic epithelial cells stimulated with apoptosis-inducing agents (FasL or Clostridium difficile Toxin A) when the apoptotic response was determined by a terminal deoxynucleotidyl transferase dUTP nick end labeling assay and cleavage of poly(ADP-ribose) polymerase or caspase-3, respectively. Treating colonic epithelial cells with B. polyfermenticus-conditioned medium (BPCM) enhanced cell proliferation and induced the phosphoinositide 3-kinases/Akt signaling pathway, suggesting that this bacterium can promote epithelial cell proliferation. BPCM also promoted the migration of colonic epithelial cells. These data suggest that B. polyfermenticus ameliorates colonic inflammation by suppressing apoptosis and promoting epithelial cell proliferation and migration.

Activation of phosphatidylinositol 3-kinase/protein kinase B by corticotropin-releasing factor in human monocytes

Corticotropin-releasing factor (CRF) exerts proinflammatory effects in peripheral tissues, whereas the intracellular pathways mediating these effects have not been completely characterized yet. We have previously shown that CRF induces nuclear factor-kappaB DNA-binding activity in mouse and human leukocytes. Here we demonstrate that in the human monocytic THP-1 cells, CRF activates the phosphatidylinositol 3-kinase (PI3K)/Akt and ERK1/2 pathways. These effects of CRF are mediated by corticotropin-releasing factor receptor 2 (CRF2), as suggested by their abolishment after treatment with the specific CRF2 antagonist, astressin 2B. The CRF-mediated PI3K/Akt activation induces cell survival as suggested by the stimulation of the antiapoptotic factor Bcl-2. ERK1/2 activation results in up-regulation of IL-8 expression, an effect inhibited by the CRF-induced activation of PI3K/Akt. These studies demonstrate novel effects of CRF in human monocytes mediated by the activation of PI3K/Akt. Moreover, they reveal pathway-specific effects of the CRF/CRF2 system in chemokine activation and cell survival that may be of importance for the development of novel therapeutics for inflammatory diseases.

Saccharomyces boulardii inhibits EGF receptor signaling and intestinal tumor growth in Apc(min) mice

BACKGROUND & AIMS

Saccharomyces boulardii (Sb) is a probiotic yeast with anti-inflammatory and anti-microbial activities and has been used for decades in the prevention and treatment of a variety of human gastrointestinal disorders. We reported previously that Sb modulates host inflammatory responses through down-regulation of extracellular signal-regulated kinase (Erk)1/2 activities both in vitro and in vivo. The aim of this study was to identify upstream mediators responsible for extracellular signal-regulated kinase (Erk)1/2 inactivation and to examine the effects of Sb on tumor development in Apc(Min) mice.

METHODS

Signaling studies of colon cancer cells were done by western blot. Cell proliferation was measured by MTS and BrdU assay. Apoptosis was examined by flow cytometry, tunel assay and caspase assay. Apc(Min) mice were orally given Sb for 9 weeks before sacrifice for tumor analysis.

RESULTS

We found that the epidermal growth factor receptor (EGFR) was deactivated upon exposure to Sb, leading to inactivation of both the EGFR-Erk and EGFR-Akt pathways. In human colonic cancer cells, Sb prevented EGF-induced proliferation, reduced cell colony formation, and promoted apoptosis. HER-2, HER-3, and insulin-like growth factor-1 receptor were also found to be inactivated by Sb. Oral intake of Sb reduced intestinal tumor growth and dysplasia in C57BL/6J Min/+ (Apc(Min)) mice.

CONCLUSIONS

Thus, in addition to its anti-inflammatory effects, Sb inhibits EGFR and other receptor tyrosine kinase signaling and thereby may also serve a novel therapeutic or prophylactic role in intestinal neoplasia.

Clostridium difficile toxin A binds colonocyte Src causing dephosphorylation of focal adhesion kinase and paxillin

Clostridium difficile toxin A impairs tight junction function of colonocytes by glucosylation of Rho family proteins causing actin filament disaggregation and cell rounding. We investigated the effect of toxin A on focal contact formation by assessing its action on focal adhesion kinase (FAK) and the adapter protein paxillin. Exposure of NCM460 human colonocytes to toxin A for 1 h resulted in complete dephosphorylation of FAK and paxillin, while protein tyrosine phosphatase activity was reduced. Blockage of toxin A-associated glucosyltransferase activity by co-incubation with UDP-2'3' dialdehyde did not reduce toxin A-induced FAK and paxillin dephosphorylation. GST-pull down and in vitro kinase activity experiments demonstrated toxin A binding directly to the catalytic domain of Src with suppression of its kinase activity. Direct binding of toxin A to Src, independent of any effect on protein tyrosine phosphatase or Rho glucosylation, inhibits Src kinase activity followed by FAK/paxillin inactivation. These mechanisms may contribute to toxin A inhibition of colonocyte focal adhesion that occurs in human colonic epithelium exposed to toxin A.

Substance P promotes expansion of human mesenteric preadipocytes through proliferative and antiapoptotic pathways

White adipose tissue is intimately involved in the regulation of immunity and inflammation. We reported that human mesenteric preadipocytes express the substance P (SP)-mediated neurokinin-1 receptor (NK-1R), which signals proinflammatory responses. Here we tested the hypothesis that SP promotes proliferation and survival of human mesenteric preadipocytes and investigated responsible mechanism(s). Preadipocytes were isolated from mesenteric fat biopsies during gastric bypass surgery. Proliferative and antiapoptotic responses were delineated in 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS), bromodeoxyuridine (BrdU), caspase-3, and TUNEL assays, as well as Western immunoanalysis. SP (10(-7) M) increased MTS and proliferation (BrdU) and time dependently (15-30 min) induced Akt, EGF receptor, IGF receptor, integrin alphaVbeta3, phosphatidylinositol 3-kinase, and PKC-theta phosphorylation. Furthermore, pharmacological antagonism of Akt and PKC-theta activation significantly attenuated SP-induced preadipocyte proliferation. Exposure of preadipocytes to the proapoptotic Fas ligand (FasL, 100 microM) resulted in nuclear DNA fragmentation (TUNEL assay), as well as increased cleaved poly (ADP-ribose) polymerase, cleaved caspase-7, and caspase-3 expression. Cotreatment with SP almost completely abolished these responses in a NK-1R-dependent fashion. SP (10(-7) M) also time dependently stimulated expression 4E binding protein 1 and phosphorylation of p70 S6 kinase, which increased protein translation efficiency. SP increases preadipocyte viability, reduces apoptosis, and stimulates proliferation, possibly via cell cycle upregulation and increased protein translation efficiency. SP-induced proliferative and antiapoptotic pathways in fat depots may contribute to development of the creeping fat and inflammation characteristic of Crohn's disease.

Role of spinal microglia in visceral hyperalgesia and NK1R up-regulation in a rat model of chronic stress

BACKGROUND & AIMS

Chronic psychological stress is associated with visceral hyperalgesia and increased expression of spinal NK1 receptors (NK1Rs). We aimed to identify the role of spinal microglia in this process.

METHODS

Male Wistar rats were exposed to water avoidance (WA) or sham stress 1 hour each day for 10 days and given daily injections of minocycline, the p38 inhibitor SB203580, or saline. Phosphorylation levels of the kinase p38 (P-p38), the microglia marker OX42, NK1R, and IkappaBalpha were assessed by immunoblotting and/or immunostaining of spinal samples collected at day 11. The visceromotor response to colorectal distention at baseline and following WA were also assayed in rats given injections of minocycline, SB203580, or vehicle. The effects of fractalkine were assessed on the visceromotor response in rats exposed to minocycline or vehicle.

RESULTS

P-p38 protein levels and immunoreactivity were increased in stressed rats and colocalized with OX42-positive cells and neurons in the dorsal horn. This increase was reversed by minocycline or SB203580 exposure. Stress-induced increased NK1R expression was blocked by minocycline but not SB203580. WA-induced decreased IkappaBalpha expression was blocked by minocycline and SB203580. WA-induced hyperalgesia was blocked by minocycline and SB203580 intrathecally. Fractalkine-induced hyperalgesia was blocked by minocycline.

CONCLUSIONS

This is the first demonstration that stress-induced activation of spinal microglia has a key role in visceral hyperalgesia and associated spinal NK1R up-regulation.

Neuropeptides, mesenteric fat, and intestinal inflammation

The ability of fat tissue cells to produce proinflammatory cytokines and the concept that obesity represents a low-grade inflammatory response have been well documented during the past decade. The effects of fat-mediated inflammation on metabolic pathologies have also been drawing increasing interest. However, very little is known on the potential effects of adipose tissue in the pathophysiology of gastrointestinal diseases with an inflammatory component, such as inflammatory bowel disease (IBD). The development of large fat masses around the inflamed intestine during Crohn's disease makes this tissue a candidate for more intense investigation in studies aiming to gain insights into the pathogenesis and progress of the disease. Furthermore, neuropeptides act in many cases in a proinflammatory manner and are shown to participate in the pathogenesis of intestinal inflammation in animal models of IBD. However, the potential of these molecules to interact with fat cells in the context of IBD has not been investigated. In this review the authors' most recent data related to the effects of neuropeptides on noninflammatory fat tissue components are described. In addition, a discussion to associate neuropeptide-induced, adipose tissue-mediated responses with the generation of intestinal inflammatory conditions such as Crohn's disease is included.

Substance P, obesity, and gut inflammation

PURPOSE OF REVIEW

The purpose of this review is to present recent data on the effects of substance P on the development of two common pathological conditions, namely obesity and gut inflammation, and elucidate the role of this neuropeptide as a potential regulator between increased adiposity and exacerbated inflammatory responses during inflammatory bowel disease.

RECENT FINDINGS

We present data that demonstrate a role for substance P in both obesity and inflammatory bowel disease and investigate potential effects on fat tissue that may influence the progression of intestinal inflammation. More specifically, we discuss new evidence for direct effects of substance P on fat tissue that determine fat depot size and overall weight in mice and analyze some of the potential mechanisms. Furthermore, we present data that describe changes in the intestinal sensory innervation, in particular substance P-positive innervation, during gut inflammation and new direct evidence of the effects of preestablished obesity in the outcome of experimental inflammation of the colon in mice. In the end we propose a link between the role of substance P in the promotion of obesity and the potential consequences on inflammatory bowel disease.

SUMMARY

We propose that substance P may promote fat tissue expansion either centrally or peripherally and thus create a proinflammatory environment (as is the case with obesity) which may in turn affect the progression (exacerbate) of gut inflammation. Further studies are required on the effects of 'creeping fat' in inflammatory bowel disease in order to decipher the role of this type of fat-depot expansion in the development of the disease.

Melanin-concentrating hormone (MCH) modulates C difficile toxin A-mediated enteritis in mice

OBJECTIVE

Melanin-concentrating hormone (MCH) is a hypothalamic orexigenic neuropeptide that regulates energy balance. However, the distribution of MCH and its receptor MCHR1 in tissues other than brain suggested additional, as yet unappreciated, roles for this neuropeptide. Based on previous paradigms and the presence of MCH in the intestine as well as in immune cells, its potential role in gut innate immune responses was examined.

METHODS

In human intestinal xenografts grown in mice, changes in the expression of MCH and its receptors following treatment with Clostridium difficile toxin A, the causative agent of antibiotic-associated diarrhoea in hospitalised patients, were examined. In colonocytes, the effect of C difficile toxin A treatment on MCHR1 expression, and of MCH on interleukin 8 (IL8) expression was examined. MCH-deficient mice and immunoneutralisation approaches were used to examine the role of MCH in the pathogenesis of C difficile toxin A-mediated acute enteritis.

RESULTS

Upregulation of MCH and MCHR1 expression was found in the human intestinal xenograft model, and of MCHR1 in colonocytes following exposure to toxin A. Treatment of colonocytes with MCH resulted in IL8 transcriptional upregulation, implying a link between MCH and inflammatory pathways. In further support of this view, MCH-deficient mice developed attenuated toxin A-mediated intestinal inflammation and secretion, as did wild-type mice treated with an antibody against MCH or MCHR1.

CONCLUSION

These findings signify MCH as a mediator of C difficile-associated enteritis and possibly of additional gut pathogens. MCH may mediate its proinflammatory effects at least in part by acting on epithelial cells in the intestine.

Toll-like receptor 5 engagement modulates tumor development and growth in a mouse xenograft model of human colon cancer

BACKGROUND & AIMS

Toll-like receptor (TLR)-dependent signaling was proposed as immunotherapeutic targets against invading pathogens and tumorigenesis. Here, we investigated whether TLR5-dependent signaling modulates colonic tumor development in mouse xenograft model of human colon cancer.

METHODS

The expression of myeloid differentiation factor 88 (MyD88) or TLR5 was stably knocked down in human colon cancer cells (DLD-1). Nude mice were subcutaneously implanted with MyD88-knocked down (KD), TLR5-KD, or control cells (n = 16) to examine the pathophysiology of tumor xenografts. Protein microarray assessed the differential expression of cytokines in these tumors. Leukocyte infiltration and tumor angiogenesis were assessed by immunohistochemistry with antibodies against neutrophil (Gr-1, 7/4) or macrophage-specific antigens (CD68, F4-80) and the vascular endothelial cell marker CD31, respectively. Tumor xenografts from DLD-1 cells were treated with flagellin (5.0 microg/kg, 1 injection/every 2 days for 3 weeks), and tumor regression and histopathology were examined.

RESULTS

Lack of MyD88 or TLR5 expression dramatically enhanced tumor growth and inhibited tumor necrosis in mouse xenografts of human colon cancer. In contrast, TLR5 activation by peritumoral flagellin treatment substantially increased tumor necrosis, leading to significant tumor regression. Tumors from MyD88-KD or TLR5-KD cells revealed the reduced production of neutrophil attracting chemokines (epithelial cell-derived neutrophil-activating peptide-78, macrophage-inflammatory protein alpha, and interleukin-8). Consequently, neutrophil infiltration was dramatically diminished in MyD88- or TLR5-KD xenografts, whereas tumor-associated macrophage infiltration or angiogenesis was not changed.

CONCLUSIONS

TLR5 engagement by flagellin mediates innate immunity and elicits potent antitumor activity, indicating that TLR5-dependent signaling could be a potential immunotherapeutic target to modulate colonic tumors.

Substance P-mediated expression of the pro-angiogenic factor CCN1 modulates the course of colitis

Substance P (SP) regulates important intestinal functions, such as mucosal permeability, motility, chloride secretion, and inflammation via the neurokinin-1 receptor (NK-1R). Previous reports showed that vascularization and expression of angiogenic factors are evident in the colonic mucosa of rats with colitis and patients with inflammatory bowel disease. Here we determined whether SP is associated with angiogenesis. Human NCM460 colonocytes stably transfected with the human NK-1R (NCM460-NK-1R cells) and mice with dextran sodium sulfate-induced colitis were used. We found that expression of the angiogenic factor CCN1 was increased in the colons of patients with Crohn's disease and ulcerative colitis. Mucosal extracts from inflammatory bowel disease patients induced human intestinal microvascular endothelial cell migration that was inhibited by blockade of CCN1 and its receptor integrin alphavbeta3. Both the degree of angiogenesis and CCN1 expression were elevated in the colons of mice with dextran sodium sulfate-induced colitis, which was reduced by treatment with the NK-1R antagonist CJ-12255. SP also increased CCN1 expression in NCM460-NK-1R colonocytes. SP exposure to human intestinal microvascular endothelial cells co-cultured with NCM460-NK-1R cells induced angiogenic activity that was inhibited by CCN1 silencing. In addition, intracolonic overexpression of CCN1 induced angiogenesis in mouse colon. Thus, SP mediates angiogenesis via CCN1 during colitis.

Corticotropin-releasing hormone deficiency is associated with reduced local inflammation in a mouse model of experimental colitis

CRH, the hypothalamic component of the hypothalamic-pituitary adrenal axis, attenuates inflammation through stimulation of glucocorticoid release, whereas peripherally expressed CRH acts as a proinflammatory mediator. CRH is expressed in the intestine and up-regulated in patients with ulcerative colitis. However, its pathophysiological significance in intestinal inflammatory diseases has just started to emerge. In a mouse model of acute, trinitrobenzene sulfonic acid-induced experimental colitis, we demonstrate that, despite low glucocorticoid levels, CRH-deficient mice develop substantially reduced local inflammatory responses. These effects were shown by histological scoring of tissue damage and neutrophil infiltration. At the same time, CRH deficiency was found to be associated with higher serum leptin and IL-6 levels along with sustained anorexia and weight loss, although central CRH has been reported to be a strong appetite suppressor. Taken together, our results support an important proinflammatory role for CRH during mouse experimental colitis and possibly in inflammatory bowel disease in humans. Moreover, the results suggest that CRH is involved in homeostatic pathways that link inflammation and metabolism.

Gastrin-mediated interleukin-8 and cyclooxygenase-2 gene expression: differential transcriptional and posttranscriptional mechanisms

BACKGROUND & AIMS

Gastrin induces the expression of cyclooxygenase (COX)-2 and interleukin (IL)-8; however, the mechanism(s), especially in gastric epithelial cells, is not well understood. Here, we have determined the intracellular mechanisms mediating gastrin-dependent gene expression.

METHODS

AGS-E human gastric cancer cell line stably expressing cholecystokinin-2 receptor was treated with amidated gastrin-17. Real-time polymerase chain reaction, Western blot, and enzyme-linked immunosorbent assay were performed to determine COX-2 and IL-8 expression and Akt, Erk, and p38 phosphorylation. Gene promoter activity was determined by luciferase assay. Electrophoretic mobility shift assay analysis was performed for nuclear factor kappaB (NF-kappaB) and activator protein-1 activity. RNA stability was determined after actinomycin D treatment. HuR localization was determined by immunocytochemistry.

RESULTS

Gastrin induced COX-2 and IL-8 expression in AGS-E cells, which was inhibited by phosphatidylinositol 3' kinase (PI3K) and p38 inhibitors. Gastrin-mediated Akt activation was observed to be downstream of p38. IL-8 expression was dependent on COX-2-mediated prostaglandin E(2) synthesis. In the presence of an NF-kappaB inhibitor MG132, IL-8 transcription was inhibited, but not that of COX-2. This was confirmed after knockdown of the p65 RelA subunit of NF-kappaB. Further studies showed that COX-2 gene transcription is regulated by activator protein-1. Gastrin increased the stability of both COX-2 and IL-8 messenger RNA (mRNA) in a p38-dependent manner, the half-life increasing from 31 minutes to 8 hours and approximately 4 hours, respectively. Gastrin, through p38 activity, also enhanced HuR expression, nucleocytoplasmic translocation, and enhanced COX-2 mRNA binding.

CONCLUSIONS

Gastrin differentially induces COX-2 and IL-8 expression at the transcriptional and posttranscriptional levels by PI3K and p38 mitogen-activated protein kinase pathways, respectively.

Substance P as a novel anti-obesity target

BACKGROUND & AIMS

Substance P (SP) is an 11-amino acid peptide that belongs to the tachykinin family of peptides. SP acts in the brain and in the periphery as a neuropeptide, neurotransmitter, and hormone affecting diverse physiologic pathways, mainly via its high-affinity neurokinin-1 receptor (NK-1R). Its presence in the hypothalamus and other areas of the brain that regulate feeding as well as in the stomach and small intestine prompted us to investigate its role on appetite control and energy balance.

METHODS

CJ 012,255 (CJ), a SP antagonist that binds to NK-1R, was injected into lean, diet-induced obese (DIO), and genetically obese (ob/ob) mice, and its effects on body weight, adiposity, and insulin sensitivity were investigated.

RESULTS

CJ administration prevented weight gain and accumulation of fat after 2 weeks of high-fat feeding, whereas similar CJ treatment in obese mice (following 3 months of high-fat diet) resulted in weight loss, reduction in adiposity, and improvement of insulin sensitivity, in part because of inhibition of food intake. The effects of SP in the control of energy balance are, at least in part, leptin independent because CJ treatment was also effective in leptin-deficient mice. Peripheral SP administration resulted in a mild, dose-dependent increase in food intake, evident 3 hours post-SP injection.

CONCLUSIONS

CJ reduces appetite and promotes weight loss in mice. We speculate that NK-1R antagonists, already tested in clinical trials for various diseases, may represent a potential target against obesity.

Obesity, innate immunity and gut inflammation

PURPOSE OF REVIEW

The purpose of this review is to present recent data on how obesity-associated conditions may affect innate immunity and its role in the development of gut inflammation.

RECENT FINDINGS

Here we present studies that demonstrate the participation of adipose tissue components in the generation of inflammation. More specifically, we describe increases in the release of proinflammatory cytokines during obesity as well as the expression of receptors involved in innate immune responses by adipocytes. Furthermore, we present data on the involvement of adipose tissue-specific molecules (adipokines) in the generation of an environment that is favorable for diseases with an immune cause and in some cases (leptin) directly contribute to the development of inflammatory bowel disease. Finally, we present evidence supporting a putative association between obesity and gut inflammation through the link of inflammation with angiogenesis and neovascularization and the favorable conditions created for these responses in obesity.

SUMMARY

We believe that obesity-related systemic changes may create conditions that predispose to the development of gut inflammation or even worsen the progression of ongoing disease.

Urocortin II mediates pro-inflammatory effects in human colonocytes via corticotropin-releasing hormone receptor 2alpha

BACKGROUND/AIMS

Urocortin II (UcnII) is a neuropeptide that binds with high affinity to the corticotropin-releasing hormone receptor 2 (CRHR2) in peripheral tissues. UcnII is synthesised in the intestine, but its role in human intestinal inflammation is largely unknown.

METHODS

Responses of human colonic epithelial cells expressing CRHR2 to stimulation by UcnII were measured using ELISA, western blot analysis, real-time reverse transcription-PCR (RT-PCR) and interleukin (IL)8 promoter activity. Expression levels of CRHR2 and UcnII in human colitis were determined by immunofluorescence and real-time RT-PCR in mucosal biopsies from patients with Crohn's and ulcerative colitis, and in human intestinal xenografts after exposure to Clostridium difficile toxin A.

RESULTS

It is reported here that expression of CRHR2 mRNA and protein in human colonic epithelial cells (HT-29) are increased by exposure to C difficile toxin A or tumour necrosis factor (TNF)alpha. Stimulation of non-transformed NCM460 colonocytes overexpressing CRHR2alpha receptor with UcnII resulted in a time- and concentration-dependent increase in IL8 production. UcnII stimulation also led to activation of nuclear factor-kappaB (NF-kappaB) and mitogen-acivated protein (MAP) kinase in these cells, as evidenced by degradation of IkappaBalpha and phosphorylation of the p65 subunit of NF-kappaB and extracellularly regulated kinase (ERK) 1/2. Furthermore, expression of UcnII and CRHR2 mRNA was increased in mucosal samples of patients with inflammatory bowel disease, and after exposure of human intestinal xenografts to C difficile toxin A.

CONCLUSIONS

These results suggest that UcnII has pro-inflammatory effects in human intestinal cells via the CRHR2alpha receptor and may play an important role in the pathophysiology of colitis in humans.

Inflammation and apoptosis in Clostridium difficile enteritis is mediated by PGE2 up-regulation of Fas ligand

BACKGROUND & AIMS

Clostridium difficile toxin A causes acute inflammation and fluid secretion in experimental animals and patients with C difficile infection. We previously reported that toxin A increased cyclooxygenase-2/prostaglandin E(2) (PGE(2)) expression and apoptosis in human colonocytes. Here, we assessed the role of secreted PGE(2) in inflammation and enterocyte apoptosis in toxin A enteritis.

METHODS

Effects of PGE(2) and PGE(2) blockade on toxin A-induced apoptosis of human colonocytes (NCM460) and of PGE(2) or toxin A on the Fas ligand (FasL) induction were analyzed by flow cytometry and Western blot. Functional activity of elevated FasL on colonocytes was assessed by coculture of colonocytes with Fas bearing Jurkat T cells. The involvement of PGE(2)-dependent Fas/FasL activation in toxin A enteritis was further assessed in either scid or FasL and Fas deficient mice.

RESULTS

Inhibition of cyclooxygenase-2 by NS-398 and of PGE(2) using a blocking antibody markedly attenuated apoptosis in colonocytes exposed to toxin A. Enhanced expression and release of FasL followed PGE(2) or toxin A exposure in vivo and in vitro and also was significantly attenuated by treatment with NS-398 and PGE(2) blocking antibody. PGE(2) acting through an EP1 receptor activated nuclear factor-kappaB, which induced transcription of FasL. Toxin A enteritis was accompanied by increased cellular infiltration, fluid secretion, and mucosal damage in control mice, but this response was markedly reduced in both Fas(-/-) and FasL(-/-) mice.

CONCLUSIONS

Toxin A enteritis involves release of PGE(2), which activates the Fas/FasL system, causing enterocyte apoptosis and inflammation.

Role of neuropeptides in inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic, relapsing condition involving complex interactions between genes and the environment. The mechanisms triggering the initial attack and relapses, however, are not well understood. In the past several years the enteric nervous system (ENS) has been implicated in the pathophysiology of IBD. Both the ENS and the central nervous system (CNS) can amplify or modulate aspects of intestinal inflammation through secretion of neuropeptides that serve as a link between the ENS and CNS. Neuropeptides are defined as any peptide released from the nervous system that serves as an intercellular signaling molecule. Neuropeptides thought to play a potentially key role in IBD include substance P, corticotropin-releasing hormone, neurotensin, vasoactive intestinal peptide, mu-opioid receptor agonists, and galanin. This review focuses on the role of these neuropeptides in the pathophysiology of IBD and discusses the cell types and mechanisms involved in this process. The available evidence that neuropeptide blockade may be considered a therapeutic approach in both Crohn's disease and ulcerative colitis will also be discussed.

Functional consequences of alteration of N-linked glycosylation sites on the neurokinin 1 receptor

The neurokinin 1 receptor (NK1R), a G protein-coupled receptor involved in diverse functions including pain and inflammation, has two putative N-linked glycosylation sites, Asn-14 and Asn-18. We studied the role of N-linked glycosylation in the functioning of the NK1R by constructing three receptor mutants: two single mutants (Asn --> Gln-14 and Asn --> Gln-18) and a double mutant, lacking both glycosylation sites. Using a lentiviral transfection system, the mutants were stably transfected into NCM 460 cells, a nontransformed human colonic epithelial cell line. We observed that the magnitude of glycosylation as estimated by changes in gel migration depends on the number of glycosylation sites available, with the wild-type receptor containing the greatest amount of glycosylation. All mutant receptors were able to bind to substance P and neurokinin A ligand with similar affinities; however, the double mutant, nonglycosylated NK1R showed only half the B(max) of the wild-type NK1R. In terms of receptor function, the ablation of both N-linked glycosylation sites did not have a profound effect on the receptors' abilities to activate the MAP kinase families (p42/p44, JNK, and p38), but did affect SP-induced IL-8 secretion. All mutants were able to internalize, but the kinetics of internalization of the double mutant receptor was more rapid, when compared with wild-type NK1R. Therefore, glycosylation of NK1R may stabilize the receptor in the plasma membrane. These results contribute to the ongoing elucidation of the role of glycosylation in G protein-coupled receptors and the study of the neurokinin receptors in particular.

Protease-activated receptor 2, dipeptidyl peptidase I, and proteases mediate Clostridium difficile toxin A enteritis

BACKGROUND & AIMS

We studied the role of protease-activated receptor 2 (PAR(2)) and its activating enzymes, trypsins and tryptase, in Clostridium difficile toxin A (TxA)-induced enteritis.

METHODS

We injected TxA into ileal loops in PAR(2) or dipeptidyl peptidase I (DPPI) knockout mice or in wild-type mice pretreated with tryptase inhibitors (FUT-175 or MPI-0442352) or soybean trypsin inhibitor. We examined the effect of TxA on expression and activity of PAR(2) and trypsin IV messenger RNA in the ileum and cultured colonocytes. We injected activating peptide (AP), trypsins, tryptase, and p23 in wild-type mice, some pretreated with the neurokinin 1 receptor antagonist SR140333.

RESULTS

TxA increased fluid secretion, myeloperoxidase activity in fluid and tissue, and histologic damage. PAR(2) deletion decreased TxA-induced ileitis, reduced luminal fluid secretion by 20%, decreased tissue and fluid myeloperoxidase by 50%, and diminished epithelial damage, edema, and neutrophil infiltration. DPPI deletion reduced secretion by 20% and fluid myeloperoxidase by 55%. In wild-type mice, FUT-175 or MPI-0442352 inhibited secretion by 24%-28% and tissue and fluid myeloperoxidase by 31%-71%. Soybean trypsin inhibitor reduced secretion to background levels and tissue myeloperoxidase by up to 50%. TxA increased expression of PAR(2) and trypsin IV in enterocytes and colonocytes and caused a 2-fold increase in Ca(2+) responses to PAR(2) AP. AP, tryptase, and trypsin isozymes (trypsin I/II, trypsin IV, p23) caused ileitis. SR140333 prevented AP-induced ileitis.

CONCLUSIONS

PAR(2) and its activators are proinflammatory in TxA-induced enteritis. TxA stimulates existing PAR(2) and up-regulates PAR(2) and activating proteases, and PAR(2) causes inflammation by neurogenic mechanisms.

Neurotensin stimulates expression of early growth response gene-1 and EGF receptor through MAP kinase activation in human colonic epithelial cells

Neurotensin (NT) is a highly expressed gastrointestinal (GI) neuropeptide, which modulates GI motility, secretion and cell growth as well as intestinal inflammation. Since EGF receptor is highly expressed in human colon cancer cells, we sought to examine whether NT stimulation contributes to the EGFR overexpression using nontransformed colonocyte NCM460 cells. The results show that NT treatment caused a significant increase in EGFR protein expression and gene transcription. Pretreatment with MAP kinase pathway inhibitor PD98059 blocked NT-induced EGFR expression. As the EGFR promoter has a functional Egr-1 site, previously shown to mediate its transcription in response to hypoxia, we examined the role of Egr-1 in the NT response. We first show that NT stimulated Egr-1 expression, which can be inhibited by PD98059. We also determined whether NT increases Egr-1 binding to its site within the EGFR promoter. The data indicate that NT enhanced the amount of Egr-1 binding to the EGFR Egr-1 site and that this binding was significantly decreased by PD98059. To verify that Egr-1 mediated NT-induced EGFR transcription, Egr-1 siRNA was used to knock down its expression. The data show that transfection of Egr-1 siRNA significantly inhibited NT-stimulated EGFR transcription. Together, our results suggest that NT can stimulate MAP kinase-mediated Egr-1 and EGFR gene expression in human colonocytes. Our results may be relevant to the mechanisms by which NT participates in the development of colon cancer.

Enteric glia regulate intestinal barrier function and inflammation via release of S-nitrosoglutathione

BACKGROUND & AIMS

Barrier functions across epithelia and endothelia are essential for homeostatic tissue regulation. Astroglia interact with cerebral endothelia to maintain the blood-brain barrier. Whether similar interactions between astrocyte-like enteric glia and epithelia regulate intestinal barrier function is not known.

METHODS

Fluorescent permeability markers were used to measure intestinal barrier function in vivo after conditional ablation of enteric glia in transgenic mice. Enteric glial cell regulation of epithelial barrier integrity then was modeled in vitro using coculture. Glial-derived barrier-inducing factors were characterized using size-exclusion chromatography and mass spectrometry. Epithelial barrier integrity was assessed by transepithelial resistance readings and by quantitative measurement of tight-junction-associated protein expression by quantitative polymerase chain reaction and Western blot.

RESULTS

We show that ablation of enteric glial cells in transgenic mice causes intestinal mucosal barrier dysfunction, resulting in inflammation. Glial-derived s-nitrosoglutathione (GSNO) was identified as a potent inducer of mucosal barrier function in vitro and in vivo and of attenuated tissue inflammation after ablation of enteric glia in transgenic mice. GSNO regulation of mucosal barrier function was associated directly with an increased expression of perijunctional F-actin and tight-junction-associated proteins zonula occludens-1 and occludin. GSNO also significantly restored mucosal barrier function in colonic biopsy specimens from patients with Crohn's disease, a well-described inflammatory permeability disorder associated with enteric glial-cell disruption.

CONCLUSIONS

Enteric glia therefore share the ability of astrocytes to regulate tight-junction integrity, and cellular interactions comparable with those maintaining blood-brain barrier function also regulate epithelial permeability at mucosal surfaces.

Immunomodulatory properties of substance P: the gastrointestinal system as a model

Communication between nerves and immune and inflammatory cells of the small and large intestine plays a major role in the modulation of several intestinal functions, including intestinal motility, ion transport, and mucosal permeability. Neuroimmune interactions at intestinal sites have been associated with the pathophysiology of infectious and enterotoxin-mediated diarrhea and intestinal inflammation, including inflammatory bowel disease (IBD). During the past 20 years the neuropeptide substance P (SP) has been identified as an important mediator in the development and progress of intestinal inflammation by binding to its high-affinity neurokinin-1 receptor (NK-1R). This peptide, released from enteric nerves, sensory neurons, and inflammatory cells of the lamina propria during intestinal inflammation, participates in gut inflammation by interacting, directly or indirectly, with NK-1R expressed on nerves, epithelial cells, and immune and inflammatory cells, such as mast cells, macrophages, and T cells. SP-dependent activation of these cells leads to the release of cytokines and chemokines as well as other neuropeptides that modulate diarrhea, inflammation, and motility associated with the pathophysiology of several intestinal disease states. The recent development of specific nonpeptide NK-1R antagonists and NK-1R-deficient mice helped us understand the functional importance of the SP-NK-1R system in mediating intestinal neuroimmune interactions and to identify the particular cells and signaling pathways involved in this response. This review summarizes our understanding on the immunomodulatory properties of SP and its receptor in the intestinal tract with particular focus on their involvement in intestinal physiology as well as in the pathophysiology of several intestinal disease states at the in vivo and cell signaling level.

Substance P mediates antiapoptotic responses in human colonocytes by Akt activation

We examined the hypothesis that substance P (SP) and the neurokinin-1 receptor (NK-1R), both in vitro and in vivo, promote mucosal healing during recovery from colitis by stimulating antiapoptotic pathways in human colonic epithelial cells. For the in vitro experiments, human nontransformed NCM460 colonocytes stably transfected with NK-1R (NCM460-NK-1R cells) were exposed to SP, and cell viability assays, TUNEL assays, and Western blot analyses were used to detect apoptotic and antiapoptotic pathways. SP exposure of NCM460-NK-1R colonocytes stimulated phosphorylation of the antiapoptotic molecule Akt and inhibited tamoxifen-induced cell death and apoptosis evaluated by the cell viability assay and poly(ADP-ribose) polymerase cleavage, respectively. SP-induced phosphorylation of Akt and cleavage of poly(ADP-ribose) polymerase were inhibited by blockade of integrin alphaVbeta3, Jak2, and activation of phosphatidylinositol 3-kinase. For the in vivo experiments, C57BL/6 mice, administered 5% dextran sulfate (DSS) dissolved in tap water for 5 days followed by a 5-day recovery period, were treated with the NK-1R antagonist CJ-12,255 or vehicle. Vehicle-treated mice showed increased colonic Akt phosphorylation and apoptosis compared with mice that received no DSS. In contrast, daily i.p. administration of CJ-12,255 for 5 days post-DSS suppressed Akt activation, exacerbated colitis, and enhanced apoptosis, and pharmacologic inhibition of Akt, either alone or together with CJ-12,255, produced a similar effect. Thus, SP, through NK-1R, possesses antiapoptotic effects in the colonic mucosa by activating Akt, which prevents apoptosis and mediates tissue recovery during colitis.

Identification of depot-specific human fat cell progenitors through distinct expression profiles and developmental gene patterns

Anatomically separate fat depots differ in size, function, and contribution to pathological states, such as the metabolic syndrome. We isolated preadipocytes from different human fat depots to determine whether the basis for this variation is partly attributable to differences in inherent properties of fat cell progenitors. We found that genome-wide expression profiles of primary preadipocytes cultured in parallel from abdominal subcutaneous, mesenteric, and omental fat depots were distinct. Interestingly, visceral fat was not homogeneous. Preadipocytes from one of the two main visceral depots, mesenteric fat, had an expression profile closer to that of subcutaneous than omental preadipocytes, the other main visceral depot. Expression of genes that regulate early development, including homeotic genes, differed extensively among undifferentiated preadipocytes isolated from different fat depots. These profiles were confirmed by real-time PCR analysis of preadipocytes from additional lean and obese male and female subjects. We made preadipocyte strains from single abdominal subcutaneous and omental preadipocytes by expressing telomerase. Depot-specific developmental gene expression profiles persisted for 40 population doublings in these strains. Thus, human fat cell progenitors from different regions are effectively distinct, consistent with different fat depots being separate mini-organs.