Role of substance P in the regulation of glucose metabolism via insulin signaling-associated pathways

Substance P (SP), encoded by the tachykinin 1 (Tac1) gene, is the most potent tachykinin ligand for the high-affinity neurokinin-1 receptor (NK-1R). We previously reported that NK-1R-deficient mice show less weight gain and reduced circulating levels of leptin and insulin in response to a high-fat diet (HFD) and demonstrated the presence of functional NK-1R in isolated human preadipocytes. Here we assessed the effects of SP on weight gain in response to HFD and determined glucose metabolism in Tac1-deficient (Tac1(-/-)) mice. The effect of SP on the expression of molecules that may predispose to reduced glucose uptake was also determined in isolated human mesenteric, omental, and sc preadipocytes. We show that although weight accumulation in response to HFD was similar between Tac1(-/-) mice and wild-type littermates, Tac1(-/-) mice demonstrated lower glucose and leptin and increased adiponectin blood levels and showed improved responses to insulin challenge after HFD. SP stimulated phosphorylation of c-Jun N-terminal kinase, protein kinase C, mammalian target of rapamycin, and inhibitory serine insulin receptor substrate-1 phosphorylation in human preadipocytes in vitro. Preincubation of human mesenteric preadipocytes with the protein kinase C pseudosubstrate inhibitor reduced insulin receptor substrate 1 phosphorylation in response to SP. Lastly, SP also induced insulin receptor substrate-1 phosphorylation in mature human sc adipocytes. Our results demonstrate an important role for SP in adipose tissue responses and obesity-associated pathologies. These novel SP effects on molecules that enhance insulin resistance at the adipocyte level may reflect an important role for this peptide in the pathophysiology of type 2 diabetes.

The neurotensin receptor-1 promotes tumor development in a sporadic but not an inflammation-associated mouse model of colon cancer

Neurotensin receptor-1 (NTR-1) is overexpressed in colon cancers and colon cancer cell lines. Signaling through this receptor stimulates proliferation of colonocyte-derived cell lines and promotes inflammation and mucosal healing in animal models of colitis. Given the causal role of this signaling pathway in mediating colitis and the importance of inflammation in cancer development, we tested the effects of NTR-1 in mouse models of inflammation-associated and sporadic colon cancer using NTR-1-deficient (Ntsr1(-) (/-)) and wild-type (Ntsr1(+/+)) mice. In mice treated with azoxymethane (AOM) to model sporadic cancer, NTR-1 had a significant effect on tumor development with Ntsr1(+/+) mice developing over twofold more tumors than Ntsr1(-) (/-) mice (p = 0.04). There was no effect of NTR-1 on the number of aberrant crypt foci or tumor size, suggesting that NT/NTR-1 signaling promotes the conversion of precancerous cells to adenomas. Interestingly, NTR-1 status did not affect tumor development in an inflammation-associated cancer model where mice were treated with AOM followed by two cycles of 5% dextran sulfate sodium (DSS). In addition, colonic molecular and histopathologic analyses were performed shortly after a single cycle of DSS. NTR-1 status did not affect colonic myeloperoxidase activity or histopathologic scores for damage and inflammation. However, Ntsr1(-) (/-) mice were more resistant to DSS-induced mortality (p = 0.01) and had over twofold higher colonic expression levels of Il6 and Cxcl2 (p < 0.04), cytokines known to promote tumor development. These results represent the first direct demonstration that targeted disruption of the Ntsr1 gene reduces susceptibility to colon tumorigenesis.

Neuropeptide - adipose tissue communication and intestinal pathophysiology

Until recently, fat was considered a relatively inactive tissue serving only as a depot for the storage of excess lipid around the body. Over the last decade, however, several studies have established fat as a metabolically active endocrine organ able to affect human pathophysiology at multiple levels. During this time adipose tissue has been shown to produce a number of hormones and inflammatory mediators collectively termed as adipokines. These molecules have been shown to be involved in the etiology of a number of inflammation-associated pathological conditions ranging from atherosclerosis and hypertension to diabetes and cancer. Despite the close physical association of abdominal fat and the intestine in the visceral cavity and the significant paracrine functions now attributed to adipose tissue, very little is known on the potential interactions between these tissues as they may relate to intestinal homeostasis. Considering the dramatic alterations in mesenteric fat depot size and placement during at least one intestinal disease, Crohn's disease, the potential involvement of fat tissue in the development as well as the progression of this and other pathological conditions should be considered. In this review we discuss the latest knowledge on neuropeptide-adipose tissue communication and the potential changes such interaction may induce in intra-abdominal fat tissue physiology. Finally we will discuss evidence on the potential pathways by which such changes in fat physiology may affect the development and progress of intestinal pathological conditions such as inflammatory bowel disease.

Cathelicidin signaling via the Toll-like receptor protects against colitis in mice

BACKGROUND & AIMS

Cathelicidin (encoded by Camp) is an antimicrobial peptide in the innate immune system. We examined whether macrophages express cathelicidin in colons of mice with experimental colitis and patients with inflammatory bowel disease, and we investigated its signaling mechanisms.

METHODS

Quantitative, real-time, reverse-transcription polymerase chain reaction (PCR), bacterial 16S PCR, immunofluorescence, and small interfering RNA (siRNA) analyses were performed. Colitis was induced in mice using dextran sulfate sodium (DSS); levels of cathelicidin were measured in human primary monocytes.

RESULTS

Expression of cathelicidin increased in the inflamed colonic mucosa of mice with DSS-induced colitis compared with controls. Cathelicidin expression localized to mucosal macrophages in inflamed colon tissues of patients and mice. Exposure of human primary monocytes to Escherichia coli DNA induced expression of Camp messenger RNA, which required signaling by extracellular signal-regulated kinase (ERK); expression was reduced by siRNAs against Toll-like receptor (TLR)9 and MyD88. Intracolonic administration of bacterial DNA to wild-type mice induced expression of cathelicidin in colons of control mice and mice with DSS-induced colitis. Colon expression of cathelicidin was significantly reduced in TLR9(-/-) mice with DSS-induced colitis. Compared with wild-type mice, Camp(-/-) mice developed a more severe form of DSS-induced colitis, particularly after intracolonic administration of E coli DNA. Expression of cathelicidin from bone marrow-derived immune cells regulated DSS induction of colitis in transplantation studies in mice.

CONCLUSIONS

Cathelicidin protects against induction of colitis in mice. Increased expression of cathelicidin in monocytes and experimental models of colitis involves activation of TLR9-ERK signaling by bacterial DNA. This pathway might be involved in the pathogenesis of ulcerative colitis.

Neurotensin signaling activates microRNAs-21 and -155 and Akt, promotes tumor growth in mice, and is increased in human colon tumors

BACKGROUND & AIMS

Neurotensin promotes inflammation and colon cancer via the neurotensin-1 receptor (NTR1). MicroRNAs (miR) regulate protein synthesis by degrading or preventing translation of mRNAs. We analyzed expression of 365 different microRNAs by human colonic epithelial cells (NCM460) after activation of NTR1.

METHODS

We performed microarray analysis of mRNA expression by neurotensin-stimulated NCM460 cells that overexpressed NTR1. Nuclear factor-κB (NF-κB) binding sites were identified and tumorigenesis was assessed using soft agar assays and xenograft analysis of severe combined immunodeficiency mice. Targets of neurotensin-regulated microRNAs were identified via bioinformatic, real-time polymerase chain reaction, and immunoblot analyses. We analyzed RNA samples from human normal colon and tumor samples.

RESULTS

Neurotensin stimulated differential expression of 38 microRNAs, including miR-21 and miR-155, which have been associated with tumor growth and contain NF-κB binding sites. Neurotensin expression increased colony formation by HCT-116 cells. Blocking miR-21 and/or miR-155 prevented colony formation (P < .001). In mice, intraperitoneal administration of neurotensin increased the growth rate of HCT-116 xenograft tumors; blocking miR-21 and/or miR-155 slowed this tumor growth. Neurotensin activated Akt in HCT-116 cells; this effect was inhibited by blocking miR-21 and/or miR-155 (P < .001). Neurotensin activated AKT through miR-155-mediated suppression of the phosphatase protein phosphatase 2A catalytic subunit alpha (PPP2CA). Levels of phosphatase and tensin homolog (PTEN) and suppressor of cytokine signaling 1 (SOCS1) mRNA, potential targets of miR-21 and miR-155, respectively, were down-regulated by these miRs. Levels of NTR1, miR-21, and miR-155 increased significantly in human colon tumor samples, compared with normal tissues, whereas PPP2CA, SOCS1, and PTEN mRNAs were reduced significantly.

CONCLUSIONS

NTR1 activation stimulates expression of miR-21 and miR-155 in colonocytes, via Akt and NF-κB, to down-regulate PTEN and SOCS1 and promote growth of tumors in mice. Levels of NTR1, miR-21, and miR-155 increase in human colon tumor samples and correlate with tumor stage.

Substance P induces CCN1 expression via histone deacetylase activity in human colonic epithelial cells

We have shown that substance P (SP) and its neurokinin-1 receptor (NK-1R) regulate intestinal angiogenesis by increasing expression of protein CYR61 (the cysteine-rich angiogenic inducer 61, or CCN1) in colonic epithelial cells. However, the mechanism involved in SP-induced CCN1 expression has not been studied, and the outcome of increased CCN1 expression in the development of colitis is not fully understood. Because histone deacetylase (HDAC) modulates transcription of several genes involved in inflammation, we investigated participation of HDAC in SP-induced CCN1 expression in human colonic epithelial NCM460 cells overexpressing NK-1R (NCM460-NK-1R) and in primary colonocytes. SP increased HDAC activity with deacetylation and dephosphorylation of nucleosome protein histone H3 in NCM460-NK-1R and/or primary colonocytes. Histone deacetylation and dephosphorylation was observed in colonic mucosa from irritable bowel disease patients. Similarly, colonic mucosal tissues from mice exposed to dextran sulfate sodium showed histone H3 deacetylation and dephosphorylation and increased HDAC activity that was reversed by the NK-1R antagonist CJ-12255. SP-induced increased CCN1 expression in NCM460-NK-1R cells was abolished by pharmacological HDAC inhibition. HDAC overexpression activated basal and SP-induced CCN1 promoter activity. Intracolonic CCN1 overexpression significantly ameliorated dextran sulfate sodium-induced colitis, with reduction of proinflammatory cytokine expression in mice. Thus, SP-mediated CCN1 expression in the inflamed human and mouse colon involves increased HDAC activity. Our results strongly suggest that increased CCN1 expression may be involved in mucosal healing during colitis.

Role of astrocytes and altered regulation of spinal glutamatergic neurotransmission in stress-induced visceral hyperalgesia in rats

Glutamate (Glu) is the primary excitatory neurotransmitter in the central nervous system and plays a critical role in the neuroplasticity of nociceptive networks. We aimed to examine the role of spinal astroglia in the modulation of glutamatergic neurotransmission in a model of chronic psychological stress-induced visceral hyperalgesia in male Wistar rats. We assessed the effect of chronic stress on different glial Glu control mechanisms in the spinal cord including N-methyl-d-aspartate receptors (NMDARs), glial Glu transporters (GLT1 and GLAST), the Glu conversion enzyme glutamine synthetase (GS), and glial fibrillary acidic protein (GFAP). We also tested the effect of pharmacological inhibition of NMDAR activation, of extracellular Glu reuptake, and of astrocyte function on visceral nociceptive response in naive and stressed rats. We observed stress-induced decreased expression of spinal GLT1, GFAP, and GS, whereas GLAST expression was upregulated. Although visceral hyperalgesia was blocked by pharmacological inhibition of spinal NMDARs, we observed no stress effects on NMDAR subunit expression or phosphorylation. The glial modulating agent propentofylline blocked stress-induced visceral hyperalgesia, and blockade of GLT1 function in control rats resulted in enhanced visceral nociceptive response. These findings provide evidence for stress-induced modulation of glia-controlled spinal Glu-ergic neurotransmission and its involvement in chronic stress-induced visceral hyperalgesia. The findings reported in this study demonstrate a unique pattern of stress-induced changes in spinal Glu signaling and metabolism associated with enhanced responses to visceral distension.

The effects of acute and chronic psychological stress on bladder function in a rodent model

OBJECTIVE

Psychological stress plays a role in the exacerbation of functional lower urinary tract disorders, such as painful bladder syndrome and overactive bladder. To better understand the mechanism underlying this relationship, we characterized changes in micturition, anxiety-related behavior, and bladder pathology in rats exposed to repeated water avoidance (WA) stress.

METHODS

Twenty-four Wistar rats were subjected to WA stress or sham. Immediately after acute (day 1) and chronic (day 10) stress or sham, rats were placed in a metabolic cage for a 2-hour voiding behavior assessment. Voiding parameters were compared with baseline values obtained before stress. Four animals from each group were sacrificed on day 10 and bladders harvested for histologic and gene expression studies. The remaining 8 animals per group underwent repeated voiding assessment every 3 days for 1 month followed by 10 days of repeat WA stress or sham. Bladder histology and gene expression were studied.

RESULTS

Rats exposed to WA stress developed a significant increase in micturition frequency and decrease in latency to void, voiding interval, and volume of first void compared with sham and baseline. Alterations in micturition persisted for approximately 1 month. Stressed rats showed increased fecal pellet excretion and anxiety-like behavior. In addition, bladder specimens from stressed animals revealed increased angiogenesis, and increased total and activated mast cells.

CONCLUSION

In rats, repeated psychological stress results in lasting alterations in micturition frequency, interval, and volume. This rodent model may represent a valid tool for studying syndromes characterized by increased urinary frequency.

Host S-nitrosylation inhibits clostridial small molecule-activated glucosylating toxins

The global prevalence of severe Clostridium difficile infection highlights the profound clinical significance of clostridial glucosylating toxins. Virulence is dependent on the autoactivation of a toxin cysteine protease, which is promoted by the allosteric cofactor inositol hexakisphosphate (InsP(6)). Host mechanisms that protect against such exotoxins are poorly understood. It is increasingly appreciated that the pleiotropic functions attributed to nitric oxide (NO), including host immunity, are in large part mediated by S-nitrosylation of proteins. Here we show that C. difficile toxins are S-nitrosylated by the infected host and that S-nitrosylation attenuates virulence by inhibiting toxin self-cleavage and cell entry. Notably, InsP(6)- and inositol pyrophosphate (InsP(7))-induced conformational changes in the toxin enabled host S-nitrosothiols to transnitrosylate the toxin catalytic cysteine, which forms part of a structurally conserved nitrosylation motif. Moreover, treatment with exogenous InsP(6) enhanced the therapeutic actions of oral S-nitrosothiols in mouse models of C. difficile infection. Allostery in bacterial proteins has thus been successfully exploited in the evolutionary development of nitrosothiol-based innate immunity and may provide an avenue to new therapeutic approaches.

Substance P (SP)-neurokinin-1 receptor (NK-1R) alters adipose tissue responses to high-fat diet and insulin action

Peripheral administration of a specific neurokinin-1 receptor (NK-1R) antagonist to mice leads to reduced weight gain and circulating levels of insulin and leptin after high-fat diet (HFD). Here, we assessed the contribution of substance P (SP) and NK-1R in diet-induced obesity using NK-1R deficient [knockout (KO)] mice and extended our previous findings to show the effects of SP-NK-1R interactions on adipose tissue-associated insulin signaling and glucose metabolic responses. NK-1R KO and wild-type (WT) littermates were fed a HFD for 3 wk, and obesity-associated responses were determined. Compared with WT, NK-1 KO mice show reduced weight gain and circulating levels of leptin and insulin in response to HFD. Adiponectin receptor mRNA levels are higher in mesenteric fat and liver in NK-1 KO animals compared with WT, after HFD. Mesenteric fat from NK-1R KO mice fed with HFD has reduced stress-activated protein kinase/c-Jun N-terminal kinase and protein kinase C activation compared with WT mice. After glucose challenge, NK-1R KO mice remove glucose from the circulation more efficiently than WT and pair-fed controls, suggesting an additional peripheral effect of NK-1R-mediated signaling on glucose metabolism. Glucose uptake experiments in isolated rat adipocytes showed that SP directly inhibits insulin-mediated glucose uptake. Our results further establish a role for SP-NK-1R interactions in adipose tissue responses, specifically as they relate to obesity-associated pathologies such as glucose intolerance and insulin resistance. Our results highlight this pathway as an important therapeutic approach for type 2 diabetes.

Activation of corticotropin-releasing factor receptor 2 mediates the colonic motor coping response to acute stress in rodents

BACKGROUND & AIMS

Corticotropin-releasing factor receptor-1 (CRF(1)) mediates the stress-induced colonic motor activity. Less is known about the role of CRF(2) in the colonic response to stress.

METHODS

We studied colonic contractile activity in rats and CRF(2)-/-, CRF-overexpressing, and wild-type mice using still manometry; we analyzed defecation induced by acute partial-restraint stress (PRS), and/or intraperitoneal injection of CRF ligands. In rats, we monitored activation of the colonic longitudinal muscle myenteric plexus (LMMP) neurons and localization of CRF(1) and CRF(2) using immunohistochemical and immunoblot analyses. We measured phosphorylation of extracellular signal-regulated kinase 1/2 by CRF ligands in primary cultures of LMMP neurons (PC-LMMPn) and cyclic adenosine monophosphate (cAMP) production in human embryonic kidney-293 cells transfected with CRF(1) and/or CRF(2).

RESULTS

In rats, a selective agonist of CRF(2) (urocortin 2) reduced CRF-induced defecation (>50%), colonic contractile activity, and Fos expression in the colonic LMMP. A selective antagonist of CRF(2) (astressin(2)-B) increased these responses. Urocortin 2 reduced PRS-induced colonic contractile activity in wild-type and CRF-overexpressing mice, whereas disruption of CRF(2) increased PRS-induced colonic contractile activity and CRF-induced defecation. CRF(2) colocalized with CRF(1) and neuronal nitric oxide synthase in the rat colon, LMMP, and PC-LMMPn. CRF-induced phosphorylation of extracellular signal-regulated kinase in PC-LMMPn; this was inhibited or increased by a selective antagonist of CRF(1) (NBI35965) or astressin(2)-B, respectively. The half maximal effective concentration, EC(50), for the CRF-induced cAMP response was 8.6 nmol/L in human embryonic kidney-293 cells that express only CRF(1); this response was suppressed 10-fold in cells that express CRF(1) and CRF(2).

CONCLUSIONS

In colon tissues of rodents, CRF(2) activation inhibits CRF(1) signaling in myenteric neurons and the stress-induced colonic motor responses. Disruption of CRF(2) function impairs colonic coping responses to stress.

[Recent advances in Saccharomyces boulardii research]

This review summarizes the probiotic mechanisms of action of Saccharomyces boulardii (S. boulardii) against inflammatory and non-inflammatory diarrheal conditions. S. boulardii is distributed in lyophilized form in many countries and used for the prevention of diarrhea in children and adults, including Clostridium difficile (C. difficile) associated infection. The main mechanisms of action of S. boulardii include inhibition of activities of bacterial pathogenic products, trophic effects on the intestinal mucosa, as well as modification of host signaling pathways involved in inflammatory and non-inflammatory intestinal diseases. S. boulardii inhibits production of pro-inflammatory cytokines by inhibiting main regulators of inflammation, including nuclear factor κB (NF-κB), and mitogen-activated protein kinases (MAP kinases), ERK1/2 and p38, but stimulates production of anti-inflammatory molecules such as peroxisome proliferator-activated receptor-gamma (PPAR-γ). Moreover, S. boulardii suppresses bacterial infection by inhibiting adhesion and/or overgrowth of bacteria, produces a serine protease that cleaves C. difficile toxin A, and stimulates antibody production against this toxin. Furthermore, S. boulardii may interfere with pathogenesis of Inflammatory Bowel Disease (IBD) by acting on T cells and acts in diarrheal conditions by improving the fecal biostructure in patients with diarrhea. These diverse mechanisms exerted by S. boulardii provide molecular clues for its effectiveness in diarrheal diseases and intestinal inflammatory conditions with an inflammatory component.

Insulin-like growth factor-1 receptor transactivation modulates the inflammatory and proliferative responses of neurotensin in human colonic epithelial cells

Neurotensin (NT) is a gastrointestinal neuropeptide that modulates intestinal inflammation and healing by binding to its high-affinity receptor NTR1. The dual role of NT in inflammation and healing is demonstrated in models of colitis induced by Clostridium difficile toxin A and dextran sulfate sodium, respectively, and involves NF-κB-dependent IL-8 expression and EGF receptor-mediated MAPK activation in human colonocytes. However, the detailed signaling pathways involved in these responses remain to be elucidated. We report here that NT/NTR1 coupling in human colonic epithelial NCM460 cells activates tyrosine phosphorylation of the insulin-like growth factor-1 receptor (IGF-1R) in a time- and dose-dependent manner. NT also rapidly induces Src tyrosine phosphorylation, whereas pretreatment of cells with the Src inhibitor PP2 before NT exposure decreases NT-induced IGF-1R phosphorylation. In addition, inhibition of IGF-1R activation by either its specific antagonist AG1024 or siRNA against IGF-1 significantly reduces NT-induced IL-8 expression and NF-κB-dependent reporter gene expression. Pretreatment with AG1024 also inhibits Akt activation and apoptosis induced by NT. Silencing of Akt expression by siRNA also substantially attenuates NT-induced IL-8 promoter activity and NF-κB-dependent reporter gene expression. This is the first report to indicate that NT transactivates IGF-1R and that this response is linked to Akt phosphorylation and NF-κB activation, contributing to both pro-inflammatory and tissue repair signaling pathways in response to NT in colonic epithelial cells. We propose that IGF-1R activation represents a previously unrecognized key pathway involved in the mechanisms by which NT and NTR1 modulate colonic inflammation and inflammatory bowel disease.

Corticotropin-releasing factor regulates TLR4 expression in the colon and protects mice from colitis

BACKGROUND & AIMS

Defects in the colonic innate immune response have been associated with inflammatory bowel disease (IBD). Corticotropin-releasing hormone (CRH, or corticotropin-releasing factor [CRF]) is a neuropeptide that mediates the stress response in humans, is an immunomodulatory factor with proinflammatory effects, and regulates transcription of Toll-like receptors (TLR)-2 and TLR4. We investigated the role of CRF in an innate immunity-dependent mouse model of IBD.

METHODS

Crh(-/-) and wild-type (Crh(+/+)) mice, which are glucocorticoid insufficient, were given dextran sodium sulfate in their drinking water to induce colitis; in some experiments, mice were also given glucocorticoids. Phenotypes of mice were compared; tissues were analyzed by histology and for expression of immune mediators.

RESULTS

Crh(-/-) mice had more colonic inflammation than Crh(+/+) mice, characterized by reduced numbers of crypts and severe epithelial damage and ulcerations. Colonic tissue levels of the proinflammatory factors interleukin-12 and prostaglandin E(2) were increased in the Crh(-/-) mice. Colons of Crh(-/-) mice expressed lower levels of Tlr4 than wild-type mice before, but not after, colitis was induced. Administration of glucocorticoid at low levels did not prevent Crh(-/-) mice from developing severe colitis. Crh(-/-) mice were unable to recover from acute colitis, as indicated by their increased death rate.

CONCLUSIONS

Mice deficient in CRF down-regulate TLR4 and are more susceptible to dextran sodium sulfate-induced colitis. CRF has anti-inflammatory effects in innate immunity-dependent colitis and its recovery phase; these are independent of glucocorticoid administration. CRF might therefore be developed as a therapeutic target for patients with IBD.

Substance P modulates colitis-associated fibrosis

Substance P (SP) and the neurokinin-1 receptor (NK-1R) are involved in the development of colitis and mucosal healing after colonic inflammation. We studied whether SP modulates colonic fibrosis by using a chronic model of trinitrobenzenesulfonic acid (TNBS)-induced colitis in wild-type (WT) and NK-1R-deficient (NK-1R KD) mice. We found increased mRNA expression levels of collagen, vimentin, and the fibrogenic factors transforming growth factor β1 and insulin-like growth factor 1 in the chronically inflamed colons of WT mice treated with repeated intracolonic TNBS administrations. Fibrosis in TNBS-treated mice was also evident immunohistochemically by collagen deposition in the colon. Treatment of TNBS-exposed WT mice with the NK-1R antagonist CJ-12255 reduced colonic inflammation, colonic fibrosis, fibroblast accumulation, and expression levels of the fibrogenic factors. NK-1R knockout mice chronically exposed to TNBS had similar colonic inflammation compared with WT, but reduced colonic fibrosis, fibroblast accumulation, and expression levels of fibrogenic factors. Immunohistochemical staining also showed co-localization of NK-1R with fibroblasts in inflamed colons of mice and in colonic mucosa of patients with Crohn's disease. Exposure of human colonic CCD-18Co fibroblasts to SP (10 nmol/L) increased cell migration. SP stimulated collagen synthesis in CCD-18Co fibroblasts in the presence of transforming growth factor β1 and insulin-like growth factor 1, and this effect was reduced by Akt inhibition. Thus, SP, via NK-1R, promotes intestinal fibrogenesis after chronic colitis by stimulating fibrotic responses in fibroblasts.

TRIF mediates Toll-like receptor 5-induced signaling in intestinal epithelial cells

Toll-like receptors (TLRs) associate with adaptor molecules (MyD88, Mal/TIRAP, TRAM, and TRIF) to mediate signaling of host-microbial interaction. For instance, TLR4 utilizes the combination of both Mal/TIRAP-MyD88 (MyD88-dependent pathway) and TRAM-TRIF (MyD88-independent pathway). However, TLR5, the specific receptor for flagellin, is known to utilize only MyD88 to elicit inflammatory responses, and an involvement of other adaptor molecules has not been suggested in TLR5-dependent signaling. Here, we found that TRIF is involved in mediating TLR5-induced nuclear factor κB (NFκB) and mitogen-activated protein kinases (MAPKs), specifically JNK1/2 and ERK1/2, activation in intestinal epithelial cells. TLR5 activation by flagellin permits the physical interaction between TLR5 and TRIF in human colonic epithelial cells (NCM460), whereas TLR5 does not interact with TRAM upon flagellin stimulation. Both primary intestinal epithelial cells from TRIF-KO mice and TRIF-silenced NCM460 cells significantly reduced flagellin-induced NFκB (p105 and p65), JNK1/2, and ERK1/2 activation compared with control cells. However, p38 activation by flagellin was preserved in these TRIF-deficient cells. TRIF-KO intestinal epithelial cells exhibited substantially reduced inflammatory cytokine (keratinocyte-derived cytokine, macrophage inflammatory protein 3α, and IL-6) expression upon flagellin, whereas control cells from TRIF-WT mice showed robust cytokine expression by flagellin. Compare with TRIF-WT mice, TRIF-KO mice were resistant to in vivo intestinal inflammatory responses: flagellin-mediated exacerbation of colonic inflammation and dextran sulfate sodium-induced experimental colitis. We conclude that in addition to MyD88, TRIF mediates TLR5-dependent responses and, thereby regulates inflammatory responses elicited by flagellin/TLR5 engagement. Our findings suggest an important role of TRIF in regulating host-microbial communication via TLR5 in the gut epithelium.

TRIF mediates Toll-like receptor 5-induced signaling in intestinal epithelial cells

Toll-like receptors (TLRs) associate with adaptor molecules (MyD88, Mal/TIRAP, TRAM, and TRIF) to mediate signaling of host-microbial interaction. For instance, TLR4 utilizes the combination of both Mal/TIRAP-MyD88 (MyD88-dependent pathway) and TRAM-TRIF (MyD88-independent pathway). However, TLR5, the specific receptor for flagellin, is known to utilize only MyD88 to elicit inflammatory responses, and an involvement of other adaptor molecules has not been suggested in TLR5-dependent signaling. Here, we found that TRIF is involved in mediating TLR5-induced nuclear factor κB (NFκB) and mitogen-activated protein kinases (MAPKs), specifically JNK1/2 and ERK1/2, activation in intestinal epithelial cells. TLR5 activation by flagellin permits the physical interaction between TLR5 and TRIF in human colonic epithelial cells (NCM460), whereas TLR5 does not interact with TRAM upon flagellin stimulation. Both primary intestinal epithelial cells from TRIF-KO mice and TRIF-silenced NCM460 cells significantly reduced flagellin-induced NFκB (p105 and p65), JNK1/2, and ERK1/2 activation compared with control cells. However, p38 activation by flagellin was preserved in these TRIF-deficient cells. TRIF-KO intestinal epithelial cells exhibited substantially reduced inflammatory cytokine (keratinocyte-derived cytokine, macrophage inflammatory protein 3α, and IL-6) expression upon flagellin, whereas control cells from TRIF-WT mice showed robust cytokine expression by flagellin. Compare with TRIF-WT mice, TRIF-KO mice were resistant to in vivo intestinal inflammatory responses: flagellin-mediated exacerbation of colonic inflammation and dextran sulfate sodium-induced experimental colitis. We conclude that in addition to MyD88, TRIF mediates TLR5-dependent responses and, thereby regulates inflammatory responses elicited by flagellin/TLR5 engagement. Our findings suggest an important role of TRIF in regulating host-microbial communication via TLR5 in the gut epithelium.

Clostridium difficile toxin A decreases acetylation of tubulin, leading to microtubule depolymerization through activation of histone deacetylase 6, and this mediates acute inflammation

Clostridium difficile toxin A is known to cause actin disaggregation through the enzymatic inactivation of intracellular Rho proteins. Based on the rapid and severe cell rounding of toxin A-exposed cells, we speculated that toxin A may be involved in post-translational modification of tubulin, leading to microtubule instability. In the current study, we observed that toxin A strongly reduced α-tubulin acetylation in human colonocytes and mouse intestine. Fractionation analysis demonstrated that toxin A-induced α-tubulin deacetylation yielded monomeric tubulin, indicating the presence of microtubule depolymerization. Inhibition of the glucosyltransferase activity against Rho proteins of toxin A by UDP-2',3'-dialdehyde significantly abrogated toxin A-induced α-tubulin deacetylation. In colonocytes treated with trichostatin A (TSA), an inhibitor of the HDAC6 tubulin deacetylase, toxin A-induced α-tubulin deacetylation and loss of tight junction were completely blocked. Administration of TSA also attenuated proinflammatory cytokine production, mucosal damage, and epithelial cell apoptosis in mouse intestine exposed to toxin A. These results suggest that toxin A causes microtubule depolymerization by activation of HDAC6-mediated tubulin deacetylation. Indeed, blockage of HDAC6 by TSA markedly attenuates α-tubulin deacetylation, proinflammatory cytokine production, and mucosal damage in a toxin A-induced mouse enteritis model. Tubulin deacetylation is an important component of the intestinal inflammatory cascade following toxin A-mediated Rho inactivation in vitro and in vivo.

The anticancer effect of probiotic Bacillus polyfermenticus on human colon cancer cells is mediated through ErbB2 and ErbB3 inhibition

A wealth of data implicates that ErbB receptors have essential roles in tumor development. Probiotic bacteria are known to exert an anticancer activity in animal studies. Bacillus polyfermenticus (B.P.), a probiotic bacterium, has been clinically used for a variety of gastrointestinal disorders in East Asia. Here, we investigated the effect of B.P. on the growth of tumors and its putative mechanism of actions. Conditioned medium of B.P. cultures (B.P. CM) inhibited the growth of human colon cancer cells including HT-29, DLD-1 and Caco-2 cells. Moreover, B.P. CM suppressed colony formation of HT-29 cells cultured on soft agar and reduced carcinogen-induced colony formation of normal colonocytes. Furthermore, data from the mouse xenograft model of human colon cancer cells showed reduced tumor size in B.P. CM-injected mice when compared to E. coli conditioned medium-injected mice. Exposure of B.P. CM to HT-29 cells for 24 hr, 48 hr and 2 weeks reduced ErbB2 and ErbB3 protein expression as well as mRNA levels. Moreover, cyclin D1 expression that is required for ErbB-dependent cell transformation was decreased by B.P. CM. Furthermore, transcription factor E2F-1 that regulates cyclin D1 expression was also decreased by B.P. CM. These results show that B.P. inhibits tumor growth and its anticancer activity occurs, at least in part, through suppressing ErbB2 and ErbB3. Taken together, our study suggests that this probiotic may be clinically used as a prophylactic treatment to prevent colon cancer development.

Corticotropin-releasing hormone family of peptides regulates intestinal angiogenesis

BACKGROUND & AIMS

The corticotrophin-releasing hormone (CRH) family of peptides modulates intestinal inflammation and the CRH receptor 2 (CRHR2) suppresses postnatal angiogenesis in mice. We investigated the functions of CRHR1 and CRHR2 signaling during intestinal inflammation and angiogenesis.

METHODS

The activities of CRHR1 and CRHR2 were disrupted by genetic deletion in mice or with selective antagonists. A combination of in vivo, ex vivo, and in vitro measures of angiogenesis were used to determine their activity. CRHR1(-/-) mice and CRHR2(-/-) mice with dextran sodium sulfate-induced colitis were analyzed in comparison with wild-type littermates (controls).

RESULTS

Colitis was significantly reduced in mice in which CRHR1 activity was disrupted by genetic deletion or with an antagonist, determined by analyses of survival rate, weight loss, histological scores, and cytokine production. Inflammation was exacerbated in mice in which CRHR2 activity was inhibited by genetic deletion or with an antagonist, compared with controls. The inflamed intestines of CRHR1(-/-) mice had reduced microvascular density and expression of vascular endothelial growth factor (VEGF)-A, whereas the intestines of CRHR2(-/-) mice had increased angiogenesis and VEGF-A levels. An antagonist of VEGFR2 activity alleviated colitis in CRHR2(-/-) mice. Ex vivo aortic vessel outgrowth was reduced when CRHR1 was deficient but increased when CRHR2 was deficient. The CRHR1 preferred agonist CRH stimulated tube formation, proliferation, and migration of cultured intestinal microvascular endothelial cells by phosphorylating Akt, whereas the specific CRHR2 agonist Urocortin III had opposite effects.

CONCLUSION

CRHR1 promotes intestinal inflammation, as well as endogenous and inflammatory angiogenesis whereas CRHR2 inhibits these activities.

TRIF modulates TLR5-dependent responses by inducing proteolytic degradation of TLR5

Proteolytic modification of pattern recognition receptors and their signaling adaptor molecules has recently emerged as an essential cellular event to regulate immune and inflammatory responses. Here we show that the TIR domain containing adaptor-inducing interferon-beta (TRIF), an adaptor molecule mediating TLR3 signaling and MyD88-independent signaling of TLR4, plays an inhibitory role in TLR5-elicited responses by inducing proteolytic degradation of TLR5. TRIF overexpression in human embryonic kidney (HEK293) and human colonic epithelial (NCM460) cells abolishes the cellular protein level of TLR5, whereas it does not alter TLR5 mRNA level. Thus, TRIF overexpression dramatically suppresses flagellin/TLR5-deriven NFkappaB activation in NCM460 cells. TRIF-induced TLR5 protein degradation is completely inhibited in the presence of pan-caspase inhibitor (benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone), whereas several specific inhibitors against cathepsin B, reactive oxygen species, or ubiquitin-mediated proteasome activity fail to suppress this degradation. These results indicate that TRIF-induced caspase activity causes TLR5 protein degradation. In addition, we identify that the C terminus of TRIF and extracellular domain of TLR5 are required for TRIF-induced TLR5 degradation. Furthermore, TRIF-induced proteolytic degradation is extended to TLR3, TLR6, TLR7, TLR8, TLR9, and TLR10, whereas the cellular level of TLR1, TLR2, and TLR4 is not affected by TRIF overexpression. These results suggest that, in addition to mediating TLR3- or TLR4-induced signaling as an adaptor molecule, TRIF can participate in proteolytic modification of certain members of TLRs to modulate the functionality of TLRs at post-translational level. Collectively, our findings propose a potential inhibitory role of TRIF at least in regulating host-microbial communication via TLR5 in colonic epithelial cells.

The angiogenic effect of probiotic Bacillus polyfermenticus on human intestinal microvascular endothelial cells is mediated by IL-8

Angiogenesis is required for wound healing and repair, but dysregulated angiogenesis is involved in gastrointestinal inflammation. Bacillus polyfermenticus (B.P.) is a probiotic bacterium clinically used for a variety of intestinal disorders in East Asia. Here we investigated the effect of B.P. on angiogenesis of human intestinal microvascular endothelial cells (HIMECs) and wound healing in intestinal mucosa. Exposure of HIMECs to the conditioned medium of B.P. cultures (B.P. CM) increased cell migration, permeability, and tube formation. Production of the proangiogenic cytokine IL-8 was increased by B.P. CM, and neutralizing antibodies against IL-8 or IL-8 receptor CXCR2 reduced tube formation as well as actin stress fiber formation. B.P. CM also increased NF-kappaB activation, and inhibitors of NF-kappaB suppressed B.P. CM-induced tube formation and IL-8 production. Furthermore, B.P. facilitated recovery of mice from colitis as shown by increased body weight and reduced rectal bleeding and histological severity. B.P. also increased angiogenesis and mouse IL-8 production in the mucosal layer. Collectively, these results show that B.P. increases angiogenesis of HIMECs in a NF-kappaB/IL-8/CXCR2-dependent manner. Moreover, B.P. promotes angiogenesis in the mucosa during recovery of mice from colitis, suggesting that this probiotic may be clinically used to facilitate intestinal wound healing.

Review article: anti-inflammatory mechanisms of action of Saccharomyces boulardii

BACKGROUND

Saccharomyces boulardii, a well-studied probiotic, can be effective in inflammatory gastrointestinal diseases with diverse pathophysiology, such as inflammatory bowel disease (IBD), and bacterially mediated or enterotoxin-mediated diarrhoea and inflammation.

AIM

To discuss the mechanisms of action involved in the intestinal anti-inflammatory action of S. boulardii.

METHODS

Review of the literature related to the anti-inflammatory effects of this probiotic.

RESULTS

Several mechanisms of action have been identified directed against the host and pathogenic microorganisms. S. boulardii and S. boulardii secreted-protein(s) inhibit production of proinflammatory cytokines by interfering with the global mediator of inflammation nuclear factor kappaB, and modulating the activity of the mitogen-activated protein kinases ERK1/2 and p38. S. boulardii activates expression of peroxisome proliferator-activated receptor-gamma (PPAR-gamma) that protects from gut inflammation and IBD. S. boulardii also suppresses 'bacteria overgrowth' and host cell adherence, releases a protease that cleaves C. difficile toxin A and its intestinal receptor and stimulates antibody production against toxin A. Recent results indicate that S. boulardii may interfere with IBD pathogenesis by trapping T cells in mesenteric lymph nodes.

CONCLUSIONS

The multiple anti-inflammatory mechanisms exerted by S. boulardii provide molecular explanations supporting its effectiveness in intestinal inflammatory states.