The expression and role of Fas ligand in intestinal inflammation

Enteric Nervous System in Neonatal Necrotizing Enterocolitis

BACKGROUND

The pathophysiology of necrotizing enterocolitis (NEC) is not clear, but increasing information suggests that the risk and severity of NEC may be influenced by abnormalities in the enteric nervous system (ENS).

OBJECTIVE

The purpose of this review was to scope and examine the research related to ENS-associated abnormalities that have either been identified in NEC or have been noted in other inflammatory bowel disorders (IBDs) with histopathological abnormalities similar to NEC. The aim was to summarize the research findings, identify research gaps in existing literature, and disseminate them to key knowledge end-users to collaborate and address the same in future studies.

METHODS

Articles that met the objectives of the study were identified through an extensive literature search in the databases PubMed, EMBASE, and Scopus.

RESULTS

The sources identified through the literature search revealed that: (1) ENS may be involved in NEC development and post-NEC complications, (2) NEC development is associated with changes in the ENS, and (3) NEC-associated changes could be modulated by the ENS.

CONCLUSION

The findings from this review identify the enteric nervous as a target in the development and progression of NEC. Thus, factors that can protect the ENS can potentially prevent and treat NEC and post-NEC complications. This review serves to summarize the existing literature and highlights a need for further research on the involvement of ENS in NEC.

Targeting Enteric Neurons and Plexitis for the Management of Inflammatory Bowel Disease

Ulcerative colitis (UC) and Crohn's disease (CD) are pathological conditions with an unknown aetiology that are characterised by severe inflammation of the intestinal tract and collectively referred to as inflammatory bowel disease (IBD). Current treatments are mostly ineffective due to their limited efficacy or toxicity, necessitating surgical resection of the affected bowel. The management of IBD is hindered by a lack of prognostic markers for clinical inflammatory relapse. Intestinal inflammation associates with the infiltration of immune cells (leukocytes) into, or surrounding the neuronal ganglia of the enteric nervous system (ENS) termed plexitis or ganglionitis. Histological observation of plexitis in unaffected intestinal regions is emerging as a vital predictive marker for IBD relapses. Plexitis associates with alterations to the structure, cellular composition, molecular expression and electrophysiological function of enteric neurons. Moreover, plexitis often occurs before the onset of gross clinical inflammation, which may indicate that plexitis can contribute to the progression of intestinal inflammation. In this review, the bilateral relationships between the ENS and inflammation are discussed. These include the effects and mechanisms of inflammation-induced enteric neuronal loss and plasticity. Additionally, the role of enteric neurons in preventing antigenic/pathogenic insult and immunomodulation is explored. While all current treatments target the inflammatory pathology of IBD, interventions that protect the ENS may offer an alternative avenue for therapeutic intervention.

Loss of BID Delays FASL-Induced Cell Death of Mouse Neutrophils and Aggravates DSS-Induced Weight Loss

Neutrophils are key players in the early defense against invading pathogens. Due to their potent effector functions, programmed cell death of activated neutrophils has to be tightly controlled; however, its underlying mechanisms remain unclear. Fas ligand (FASL/CD95L) has been shown to induce neutrophil apoptosis, which is accelerated by the processing of the BH3-only protein BH3 interacting domain death agonist (BID) to trigger mitochondrial apoptotic events, and been attributed a regulatory role during viral and bacterial infections. Here, we show that, in accordance with previous works, mouse neutrophils underwent caspase-dependent apoptosis in response to FASL, and that this cell death was significantly delayed upon loss of BID. However, pan-caspase inhibition failed to protect mouse neutrophils from FASL-induced apoptosis and caused a switch to RIPK3-dependent necroptotic cell death. Intriguingly, such a switch was less evident in the absence of BID, particularly under inflammatory conditions. Delayed neutrophil apoptosis has been implicated in several auto-inflammatory diseases, including inflammatory bowel disease. We show that neutrophil and macrophage driven acute dextran sulfate sodium (DSS) induced colitis was slightly more aggravated in BID-deficient mice, based on significantly increased weight loss compared to wild-type controls. Taken together, our data support a central role for FASL > FAS and BID in mouse neutrophil cell death and further underline the anti-inflammatory role of BID.

Neuroimmunomodulation in the Gut: Focus on Inflammatory Bowel Disease

Intestinal immunity is finely regulated by several concomitant and overlapping mechanisms, in order to efficiently sense external stimuli and mount an adequate response of either tolerance or defense. In this context, a complex interplay between immune and nonimmune cells is responsible for the maintenance of normal homeostasis. However, in certain conditions, the disruption of such an intricate network may result in intestinal inflammation, including inflammatory bowel disease (IBD). IBD is believed to result from a combination of genetic and environmental factors acting in concert with an inappropriate immune response, which in turn interacts with nonimmune cells, including nervous system components. Currently, evidence shows that the interaction between the immune and the nervous system is bidirectional and plays a critical role in the regulation of intestinal inflammation. Recently, the maintenance of intestinal homeostasis has been shown to be under the reciprocal control of the microbiota by immune mechanisms, whereas intestinal microorganisms can modulate mucosal immunity. Therefore, in addition to presenting the mechanisms underlying the interaction between immune and nervous systems in the gut, here we discuss the role of the microbiota also in the regulation of neuroimmune crosstalk involved in intestinal homeostasis and inflammation, with potential implications to IBD pathogenesis.

Experimental evidence and mathematical modeling of thermal effects on human colonic smooth muscle contractility

It has been shown, in animal models, that gastrointestinal tract (GIT) motility is influenced by temperature; nevertheless, the basic mechanism governing thermal GIT smooth muscle responses has not been fully investigated. Studies based on physiologically tuned mathematical models have predicted that thermal inhomogeneity may induce an electrochemical destabilization of peristaltic activity. In the present study, the effect of thermal cooling on human colonic muscle strip (HCMS) contractility was studied. HCMSs were obtained from disease-free margins of resected segments for cancer. After removal of the mucosa and serosa layers, strips were mounted in separate chambers. After 30 min, spontaneous contractions developed, which were measured using force displacement transducers. Temperature was changed every hour (37, 34, and 31°C). The effect of cooling was analyzed on mean contractile activity, oscillation amplitude, frequency, and contraction to ACh (10(-5) M). At 37°C, HCMSs developed a stable phasic contraction (~0.02 Hz) with a significant ACh-elicited mean contractile response (31% and 22% compared with baseline in the circular and longitudinal axis, respectively). At a lower bath temperature, higher mean contractile amplitude was observed, and it increased in the presence of ACh (78% and 43% higher than the basal tone in the circular and longitudinal axis, respectively, at 31°C). A simplified thermochemomechanical model was tuned on experimental data characterizing the stress state coupling the intracellular Ca(2+) concentration to tissue temperature. In conclusion, acute thermal cooling affects colonic muscular function. Further studies are needed to establish the exact mechanisms involved to better understand clinical consequences of hypothermia on intestinal contractile activity.

Interaction of dietary fatty acids with tumour necrosis factor family cytokines during colon inflammation and cancer

Intestinal homeostasis is precisely regulated by a number of endogenous regulatory molecules but significantly influenced by dietary compounds. Malfunction of this system may result in chronic inflammation and cancer. Dietary essential n-3 polyunsaturated fatty acids (PUFAs) and short-chain fatty acid butyrate produced from fibre display anti-inflammatory and anticancer activities. Both compounds were shown to modulate the production and activities of TNF family cytokines. Cytokines from the TNF family (TNF- α, TRAIL, and FasL) have potent inflammatory activities and can also regulate apoptosis, which plays an important role in cancer development. The results of our own research showed enhancement of apoptosis in colon cancer cells by a combination of either docosahexaenoic acid (DHA) or butyrate with TNF family cytokines, especially by promotion of the mitochondrial apoptotic pathway and modulation of NF κ B activity. This review is focused mainly on the interaction of dietary PUFAs and butyrate with these cytokines during colon inflammation and cancer development. We summarised recent knowledge about the cellular and molecular mechanisms involved in such effects and outcomes for intestinal cell behaviour and pathologies. Finally, the possible application for the prevention and therapy of colon inflammation and cancer is also outlined.

Serum m 30 levels reflects ulcerative colitis activity

BACKGROUND

Apoptosis plays a role in epithelial and mucosal injury, which is 1 of the mechanisms in the pathogenesis of ulcerative colitis. Apoptotic cells increase as a result of injured mucosa in ulcerative colitis and serum M 30 levels increase in epithelial cell apoptosis. In this study, we aimed to evaluate the relation between M 30 serum levels and ulcerative colitis activity.

METHODS

Eighty patients with ulcerative colitis and 40 healthy controls were enrolled into the study. The patient group consisted of 31 extensive colitis, 30 left-sided colitis, and 19 proctitis. The activity of ulcerative colitis was determined with clinical and endoscopic findings. Serum M 30 levels, acute phase reactants, and biochemical tests were analyzed in all subjects.

RESULTS

Serum M 30 levels in patients with active ulcerative colitis were significantly higher when compared with the healthy controls (165.6 ± 60.6 and 129.6 ± 37.4; P = 0.003). Serum M 30 levels in active left-sided colitis patients was significantly higher when compared with patients in remission phase (180.6 ± 58.5, 141.5 ± 35.4; P = 0.044). When we exclude patients with ulcerative proctitis, M 30 levels in active ulcerative colitis patients were significantly higher than that the patients in remission phase (174.0 ± 63.5, 135.0 ± 29.9; P = 0.017).

CONCLUSIONS

We found that M 30 levels increase in patients with active ulcerative colitis. Our findings support the role of apoptosis demonstrated by serum M 30 levels in the pathogenesis of active ulcerative colitis.

Trp53 deficiency protects against acute intestinal inflammation

The p53 protein has not only important tumor suppressor activity but also additional immunological and other functions, whose nature and extent are just beginning to be recognized. In this article, we show that p53 has a novel inflammation-promoting action in the intestinal tract, because loss of p53 or the upstream activating kinase, ATM, protects against acute intestinal inflammation in murine models. Mechanistically, deficiency in p53 leads to increased survival of epithelial cells and lamina propria macrophages, higher IL-6 expression owing to enhanced glucose-dependent NF-κB activation, and increased mucosal STAT3 activation. Blockade or loss of IL-6 signaling reverses the protective effects of p53 deficiency. Conversely, IL-6 treatment protects against acute colitis in a manner dependent on STAT3 signaling and induction of cytoprotective factors in epithelial cells. Together, these results indicate that p53 promotes inflammation in the intestinal tract through suppression of epithelium-protective factors, thus significantly expanding the spectrum of physiological and immunological p53 activities unrelated to cancer formation.

Butyrate suppresses colonic inflammation through HDAC1-dependent Fas upregulation and Fas-mediated apoptosis of T cells

Butyrate, an intestinal microbiota metabolite of dietary fiber, has been shown to exhibit protective effects toward inflammatory diseases such as ulcerative colitis (UC) and inflammation-mediated colorectal cancer. Recent studies have shown that chronic IFN-γ signaling plays an essential role in inflammation-mediated colorectal cancer development in vivo, whereas genome-wide association studies have linked human UC risk loci to IFNG, the gene that encodes IFN-γ. However, the molecular mechanisms underlying the butyrate-IFN-γ-colonic inflammation axis are not well defined. Here we showed that colonic mucosa from patients with UC exhibit increased signal transducer and activator of transcription 1 (STAT1) activation, and this STAT1 hyperactivation is correlated with increased T cell infiltration. Butyrate treatment-induced apoptosis of wild-type T cells but not Fas-deficient (Fas(lpr)) or FasL-deficient (Fas(gld)) T cells, revealing a potential role of Fas-mediated apoptosis of T cells as a mechanism of butyrate function. Histone deacetylase 1 (HDAC1) was found to bind to the Fas promoter in T cells, and butyrate inhibits HDAC1 activity to induce Fas promoter hyperacetylation and Fas upregulation in T cells. Knocking down gpr109a or slc5a8, the genes that encode for receptor and transporter of butyrate, respectively, resulted in altered expression of genes related to multiple inflammatory signaling pathways, including inducible nitric oxide synthase (iNOS), in mouse colonic epithelial cells in vivo. Butyrate effectively inhibited IFN-γ-induced STAT1 activation, resulting in inhibition of iNOS upregulation in human colon epithelial and carcinoma cells in vitro. Our data thus suggest that butyrate delivers a double-hit: induction of T cell apoptosis to eliminate the source of inflammation and suppression of IFN-γ-mediated inflammation in colonic epithelial cells, to suppress colonic inflammation.

Iridoid glycosides fraction of Folium syringae leaves modulates NF-κB signal pathway and intestinal epithelial cells apoptosis in experimental colitis

BACKGROUND AND AIMS

Iridoid glycosides (IG), the major active fraction of F. syringae leaves has been demonstrated to have strong anti-inflammatory properties to ulcerative colitis (UC) in our previous study. The aim of this study was to investigate whether IG modulates the inflammatory response in experimental colitis at the level of NF-κB signal pathway and epithelial cell apoptosis.

METHODS

UC in rats was induced by administration with dextran sulfate sodium (DSS) in drinking water. The inflammatory damage was assessed by disease activity index (DAI), macroscopic findings, histology and myeloperoxidase (MPO) activity. The effect of IG on pro-inflammatory cytokines TNF-α, IL-8, COX-2 and regulatory peptide TGF-β1 was measured. Epithelial cell apoptosis and the protein and mRNA expressions of Fas/FasL, Bcl-2/Bax, caspase-3, NF-κB p65, IκBα, p-IκBα and IKKβ were detected by TUNEL method, immunohistochemistry, Western blotting and real-time quantitative PCR, respectively.

RESULTS

IG significantly ameliorated macroscopic damage and histological changes, reduced the activity of MPO, and strongly inhibited epithelial cell apoptosis. Moreover, IG markedly depressed TNF-α, IL-8, COX-2 and TGF-β1 levels in the colon tissues in a dose-dependent manner. Furthermore, IG significantly blocked of NF-κB signaling by inhibiting IκBα phosphorylation/degradation and IKKβ activity, down-regulated the protein and mRNA expressions of Fas/FasL, Bax and caspase-3, and activated Bcl-2 in intestinal epithelial cells.

CONCLUSIONS

These results demonstrated for the first time that IG possessed marked protective effects on experimental colitis through inhibition of epithelial cell apoptosis and blockade of NF-κB signal pathway.

The effects of glucagon-like peptide 2 on enteric neurons in intestinal inflammation

BACKGROUND

Intestinal inflammation alters the structure and function of the enteric nervous system (ENS). Glucagon-like peptide 2 (GLP-2) reduces intestinal inflammation and has trophic effects on isolated neurons. This study examined the effects of GLP-2 treatment on the submucosal plexus of rat colon in the trinitrobenzene sulfonic acid (TNBS) model of colitis.

METHODS

After administration of TNBS or saline/ethanol for controls, animals were allocated to treatment with GLP-2 (50 μg kg⁻¹ day⁻¹, s.c.) or sham injection of vehicle, twice daily. Animals were monitored, following clinical parameters, and killed on day 5. The number of neuronal cell bodies per ganglion was quantified using immunohistochemistry on submucosal whole mount preparations, with further characterization of specific subpopulations using antibodies against vasoactive intestinal polypeptide (VIP), neuronal nitric oxide synthase (nNOS), and enteric glial cells with glial fibrillary acid protein and S100.

KEY RESULTS

Glucagon-like peptide 2 treatment was associated with a significant amelioration of weight loss, and reduced neutrophil infiltration and microscopic colitis scores in the TNBS animals. Inflammation resulted in a loss of enteric neurons in submucosal ganglia; GLP-2 treatment restored the enteric neuronal populations to normal. In control, non-inflamed animals, GLP-2 treatment increased the number of VIP expressing neurons per ganglion; in TNBS-treated animals, GLP-2 prevented an inflammation-induced reduction in the numbers of VIP expressing neurons per ganglion. Glucagon-like peptide 2 did not change the numbers of nNOS neurons or enteric glial cells in either the control, or inflamed state.

CONCLUSIONS & INFERENCES

These findings show that GLP-2 increased the number of VIP expressing neurons in normal animals, and prevents the inflammation-induced loss of neurons in the colonic submucosal ganglia, with an increase in the proportion of VIP expressing neurons. They suggest that GLP-2 may have a role in protecting or regulating the circuitry of the ENS under basal and inflamed states.

Peroxisome proliferator-activated receptor-alpha modulates the anti-inflammatory effect of glucocorticoids in a model of inflammatory bowel disease in mice

Glucocorticoids (GCs) are effective anti-inflammatory agents widely used in therapeutic approach to treatment of inflammatory bowel disease (IBD). Previous results suggest that peroxisome proliferator-activated receptor [alpha] (PPAR-[alpha]), an intracellular transcription factor activated by fatty acids, plays a role in control of inflammation. With the aim to characterize the role of PPAR-[alpha] in GC-mediated anti-inflammatory activity, we tested the efficacy of dexamethasone (DEX), a synthetic GC specific for GR, in an experimental model of IBD induced by dinitrobenzene sulfonic acid, comparing mice lacking PPAR-[alpha] (PPAR-[alpha]KO) with wild-type (WT) mice. Results indicate that DEX-mediated anti-inflammatory activity is weakened in PPAR-[alpha]KO mice as compared with WT controls. In particular, DEX was less effective in PPAR-[alpha]KO compared with WT mice, as evaluated by inhibition of proinflammatory cytokines production, cell migration, oxidative stress, apoptosis, and colon injury. These results indicate that PPAR-[alpha] can contribute to the anti-inflammatory activity of GCs in IBD.

Inflammation and inflammatory agents activate protein kinase C epsilon translocation and excite guinea-pig submucosal neurons

BACKGROUND & AIMS

Properties of enteric neurons are transformed by inflammation and protein kinase C (PKC) isoforms are involved both in long-term changes in enteric neurons, and in transducing the effects of substances released during inflammation. We investigated roles of PKCepsilon in submucosal neurons by studying translocation in response to inflammatory mediators, effects on neuron excitability, and the changes in PKCepsilon distribution in a trinitrobenzene sulphonate model of ileitis.

METHODS

Immunohistochemical detection and analysis of association with membrane and cytosolic fractions, and Western blot analysis of cytosolic and particulate fractions were used to quantify translocation. Electrophysiology methods were used to measure effects on neuron excitability.

RESULTS

All submucosal neurons were immunoreactive for the novel PKC, PKCepsilon, and direct PKC activators, phorbol 12,13-dibutyrate, ingenol 3,20-dibenzoate, and the PKCepsilon-specific activator, transactivator of transduction-Psiepsilon receptor for activated C kinase, all caused PKCepsilon translocation from cytoplasm to surfaces of the neurons. Electrophysiologic studies showed that the stimulant of novel PKCs, ingenol (1 micromol/L), increased excitability of all neurons. Stimulation of protease-activated receptors caused PKCepsilon translocation selectively in vasoactive intestinal peptide secretomotor neurons, whereas a neurokinin 3 tachykinin receptor agonist caused translocation in neuropeptide Y and calretinin neurons. In all cases translocation was reduced significantly by a PKCepsilon-specific translocation inhibitor peptide. Increased PKCepsilon at the plasma membrane occurred in all neurons 6-7 days after an inflammatory stimulus.

CONCLUSIONS

Major targets for PKCepsilon include ion channels near the plasma membrane. PKCepsilon is likely to have a significant role in controlling the excitability of submucosal neurons and is probably an intermediate in causing hyperexcitability after inflammation.

Loss of functional Fas ligand enhances intestinal tumorigenesis in the Min mouse model

Fas ligand (FasL/CD95L), a member of the tumor necrosis factor family, interacts with a specific receptor Fas, ultimately leading to cell death. Tumor expression of FasL has been proposed to aid in immune evasion through a "Fas counterattack" mechanism but has also been described as a proinflammatory factor. Here, we tested the role of FasL in a mouse model of spontaneous tumor development. We used the Min mouse in which multiple benign polyps develop in the intestine due to a mutation in the Apc tumor suppressor gene. Mutant mice deficient in functional FasL, termed gld/gld, were crossed to Min mice to generate tumor-prone animals lacking functional FasL. Comparison of FasL-deficient versus proficient Min mice revealed a significant increase in polyp number in the gld/gld mice. We next assessed immune cell infiltration into adenomas. There was no difference in the number of either lymphocytes or macrophages; however, the number of tumor-infiltrating neutrophils was 3-fold lower in the gld/gld specimens compared with controls. Neutrophil migration in vitro was stimulated by wild-type but not mutant FasL. In a nontumor-bearing colitis model in vivo, neutrophil recruitment to the intestine was also reduced in gld/gld mice. Although the Fas counterattack hypothesis suggests that the absence of FasL would result in increased immune-mediated tumor elimination, the opposite is true in the Min model with lack of functional FasL associated with reduced neutrophil influx and increased tumor development. Thus, the proinflammatory rather than counterattack role of tumor FasL is more relevant.

Melatonin modulates signal transduction pathways and apoptosis in experimental colitis

Various evidences have documented that the pineal secretory product melatonin exerts an important anti-inflammatory effect in different experimental models including colitis. The aim of the present study was to evaluate whether melatonin regulates the inflammatory response of experimental colitis in rats at the level of signal transduction pathway. Colitis was induced by intracolonic instillation of dinitrobenzene sulfonic acid (DNBS). Four days after DNBS administration, a substantial increase of colon TNF-alpha production was associated with the colon damage. In DNBS-treated rats, the colon injury correlated with a significant rise of apoptosis (evaluated by TUNEL coloration) which was associated with a significant increased expression of proapoptotic Bax and decreased colon content of antiapoptotic Bcl-2. This inflammatory response was also related to activation of nuclear factor-kappaB (NF-kappaB) and phosphorylation of c-Jun as well as FAS ligand expression in the colon. Treatment with melatonin (15 mg/kg daily i.p.) was associated with a remarkable amelioration of colonic disrupted architecture as well as a significant reduction of TNF-alpha. Melatonin also reduced the NF-kappaB activation and phosphorylation of c-Jun as well as the Fas ligand expression in the colon. Furthermore, melatonin reduced the expression of Bax and prevented the loss of Bcl-2 proteins as well as the presence of apoptotic cells caused by DNBS. The results of this study show that melatonin administration exerts beneficial effects in inflammatory bowel disease by modulating signal transduction pathways.

Effects of gastrointestinal inflammation on enteroendocrine cells and enteric neural reflex circuits

Inflammation of the gastrointestinal (GI) tract has pronounced effects on GI function. Many of the functions of the GI tract are subject to neural regulation by the enteric nervous system (ENS) and its extrinsic connections. Therefore, it is possible that inflammatory effects on the ENS contribute to altered function during GI inflammation. The reflex circuitry of the ENS is comprised of sensory transducers in the mucosa (enteroendocrine cells), afferent neurons, interneurons and motor neurons. This review focuses on recent data that describe inflammation-induced changes to the ENS and mucosal enteroendocrine cells. Studies of tissues from patients with inflammatory bowel disease (IBD) and from animal models of IBD have demonstrated marked changes in mucosal enteroendocrine cell signaling. These changes, which have been studied most intensely in 5-HT-containing enterochromaffin cells, involve changes in the number of cells, their signaling molecule content or their means of signal termination. Morphological evidence of enteric neuropathy during inflammation has been obtained from human samples and animal models of IBD. The neuropathy can reduce the number of enteric neurons in the inflamed region and is often accompanied by a change in the neurochemical coding of enteric neurons, both in the inflamed region and at distant sites. Electrophysiological recordings have been made from enteric neurons in inflamed regions of the colon of animal models of IBD. These studies have consistently found that inflammation increases excitability of intrinsic primary afferent neurons and alters synaptic transmission to interneurons and motor neurons. These data set the stage for a comprehensive examination of the role of altered neuronal and enteroendocrine cell signaling in symptom generation during GI inflammation.