Alterations of Prostanoid Expression and Intestinal Epithelial Barrier Functions in Ileus

INTRODUCTION

Intestinal manipulation (IM)-induced inflammation could contribute to postoperative ileus (POI) pathophysiology via the modulation of prostanoid pathways. To identify the prostanoids involved, we aimed to characterize the profile of prostanoids and their synthesis enzyme expression in a murine model of POI and to determine whether the altered prostanoids could contribute to POI.

METHODS

Four or 14 h after IM in mice, gastrointestinal (GI) motility and intestinal epithelial barrier (IEB) permeability were assessed in vivo and ex vivo in Ussing chambers. Using high sensitivity liquid chromatography-tandem mass spectrometry, we characterized the tissue profile of polyunsaturated fatty acid metabolites in our experimental model. Finally, we evaluated in vivo the effects of the prostanoids studied upon IM-induced gut dysfunctions.

RESULTS

We first showed that 14 h after IM was significantly faster than jejunal transit at 4 h post-IM, although it remained significantly increased compared to the control. In contrast, we showed that IM-induced inflammation increase in jejunum permeability was similar after four and 14 h. We next showed that expression of prostacyclin synthase and hemopoietic prostaglandin-D synthase mRNA and their products were significantly reduced 14 h after IM as compared to controls. Furthermore, 15-deoxy-delta 12,14-Prostaglandin J2 reduced the IM-induced inflammation increase in IEB permeability but had no effect on GI motility. In contrast, PGI2 increased IM-induced IEB permeability and motility dysfunctions.

CONCLUSIONS

Arachidonic acid derivative contributes differentially to GI dysfunction in POI. The decrease of 15-deoxy-delta 12,14-Prostaglandin J2 levels induced by IM could contribute to impaired GI dysfunctions in POI and could be considered as putative therapeutic targets to restore barrier dysfunctions associated with POI.

Role of ICAM-1 in the Adhesion of T Cells to Enteric Glia: Perspectives in the Formation of Plexitis in Crohn's Disease

BACKGROUND & AIMS

The presence of myenteric plexitis in the proximal resection margins is a predictive factor of early postoperative recurrence in Crohn's disease. To decipher the mechanisms leading to their formation, T-cell interactions with enteric neural cells were studied in vitro and in vivo.

METHODS

T cells close to myenteric neural cells were retrospectively quantified in ileocolonic resections from 9 control subjects with cancer and 20 patients with Crohn's disease. The mechanisms involved in T-cell adhesion were then investigated in co-cultures of T lymphocytes with enteric glial cells (glia). Finally, the implication of adhesion molecules in the development of plexitis and colitis was studied in vitro but also in vivo in Winnie mice.

RESULTS

The mean number of T cells close to glia, but not neurons, was significantly higher in the myenteric ganglia of relapsing patients with Crohn's disease (2.42 ± 0.5) as compared with controls (0.36 ± 0.08, P = .0007). Co-culture experiments showed that exposure to proinflammatory cytokines enhanced T-cell adhesion to glia and increased intercellular adhesion molecule-1 (ICAM-1) expression in glia. We next demonstrated that T-cell adhesion to glia was inhibited by an anti-ICAM-1 antibody. Finally, using the Winnie mouse model of colitis, we showed that the blockage of ICAM-1/lymphocyte function-associated antigen-1 (LFA-1) with lifitegrast reduced colitis severity and decreased T-cell infiltration in the myenteric plexus.

CONCLUSIONS

Our present work argues for a role of glia-T-cell interaction in the development of myenteric plexitis through the adhesion molecules ICAM-1/LFA-1 and suggests that deciphering the functional consequences of glia-T-cell interaction is important to understand the mechanisms implicated in the development and recurrence of Crohn's disease.

Propionibacterium freudenreichii CIRM-BIA 129 mitigates colitis through S layer protein B-dependent epithelial strengthening

The growing incidence of human diseases involving inflammation and increased gut permeability makes the quest for protective functional foods more crucial than ever. Propionibacterium freudenreichii (P. freudenreichii) is a beneficial bacterium used in the dairy and probiotic industries. Selected strains exert anti-inflammatory effects, and the present work addresses whether the P. freudenreichii CIRM-BIA129, consumed daily in a preventive way, could protect mice from acute colitis induced by dextran sodium sulfate (DSS), and more precisely, whether it could protect from intestinal epithelial breakdown induced by inflammation. P. freudenreichii CIRM-BIA129 mitigated colitis severity and inhibited DSS-induced permeability. It limited crypt length reduction and promoted the expression of zonula occludens-1 (ZO-1), without reducing interleukin-1β mRNA (il-1β) expression. In vitro, P. freudenreichii CIRM-BIA129 prevented the disruption of a Caco-2 monolayer induced by proinflammatory cytokines. It increased transepithelial electrical resistance (TEER) and inhibited permeability induced by inflammation, along with an increased ZO-1 expression. Extracellular vesicles (EVs) from P. freudenreichii CIRM-BIA129, carrying the surface layer protein (SlpB), reproduced the protective effect of P. freudenreichii CIRM-BIA129. A mutant strain deleted for slpB (ΔslpB), or EVs from this mutant strain, had lost their protective effects and worsened both DSS-induced colitis and inflammation in vivo. These results shown that P. freudenreichii CIRM-BIA129 daily consumption has the potential to greatly alleviate colitis symptoms and, particularly, to counter intestinal epithelial permeability induced by inflammation by restoring ZO-1 expression through mechanisms involving S-layer protein B. They open new avenues for the use of probiotic dairy propionibacteria and/or postbiotic fractions thereof, in the context of gut permeability.NEW & NOTEWORTHY Propionibacterium freudenreichii reduces dextran sodium sulfate (DSS)-induced intestinal permeability in vivo. P. freudenreichii does not inhibit inflammation but damages linked to inflammation. P. freudenreichii inhibits intestinal epithelial breakdown through S-layer protein B. The protective effects of P. freudenreichii depend on S-layer protein B. Extracellular vesicles from P. freudenreichii CB 129 mimic the protective effect of the probiotic.

Are LRRK2 mysteries lurking in the gut?

Gut-brain axis and inflammation are two hot topics in Parkinson's disease (PD). In this setting, the leucine-rich repeat kinase 2 (LRRK2) gene, which encodes the eponym protein, has attracted much attention. LRRK2 is not only the gene most commonly associated with Parkinson's disease but also a susceptibility gene for Crohn's disease (CD), thereby suggesting that it may sit at the crossroads of gastrointestinal inflammation, Parkinson's, and Crohn's disease. In contrast to the accumulated data on LRRK2 in the central nervous system (CNS), research on LRRK2 in the digestive tract is still in its infancy, and the scope of the present review article is therefore to review existing studies on LRRK2 in the gastrointestinal tract in both physiological and pathological conditions. In light of current data on LRRK2 in the gastrointestinal tract, we discuss if LRRK2 could be or not regarded as a molecular link between gut inflammation, Parkinson's disease, and Crohn's disease, and we suggest directions for future research.

Enteric glia at center stage of inflammatory bowel disease

Although our understanding of the pathophysiology of inflammatory bowel disease (IBD) is increasing, the expanding body of knowledge does not simplify the equation but rather reveals diverse, interconnected, and complex mechanisms in IBD. In addition to immune overactivation, defects in intestinal epithelial barrier (IEB) functioning, dysbiosis, and structural and functional abnormalities of the enteric nervous system are emerging as new elements contributing to the development of IBD. In addition to molecular changes in IBD, enteric glia from patients with Crohn's disease (CD) exhibits the inability to strengthen the IEB; these defects are not observed in patients with ulcerative colitis. In addition, there is a growing body of work describing that enteric glia interacts with not only enterocytes and enteric neurons but also other local cellular neighbours. Thus, because of their functions as connectors and regulators of immune cells, IEB, and microbiota, enteric glia could be the keystone of digestive homeostasis that is lacking in patients with CD.

Tau expression and phosphorylation in enteroendocrine cells

Background and objective

There is mounting evidence to suggest that the gut-brain axis is involved in the development of Parkinson's disease (PD). In this regard, the enteroendocrine cells (EEC), which faces the gut lumen and are connected with both enteric neurons and glial cells have received growing attention. The recent observation showing that these cells express alpha-synuclein, a presynaptic neuronal protein genetically and neuropathologically linked to PD came to reinforce the assumption that EEC might be a key component of the neural circuit between the gut lumen and the brain for the bottom-up propagation of PD pathology. Besides alpha-synuclein, tau is another key protein involved in neurodegeneration and converging evidences indicate that there is an interplay between these two proteins at both molecular and pathological levels. There are no existing studies on tau in EEC and therefore we set out to examine the isoform profile and phosphorylation state of tau in these cells.

Methods

Surgical specimens of human colon from control subjects were analyzed by immunohistochemistry using a panel of anti-tau antibodies together with chromogranin A and Glucagon-like peptide-1 (two EEC markers) antibodies. To investigate tau expression further, two EEC lines, namely GLUTag and NCI-H716 were analyzed by Western blot with pan-tau and tau isoform specific antibodies and by RT-PCR. Lambda phosphatase treatment was used to study tau phosphorylation in both cell lines. Eventually, GLUTag were treated with propionate and butyrate, two short chain fatty acids known to sense EEC, and analyzed at different time points by Western blot with an antibody specific for tau phosphorylated at Thr205.

Results

We found that tau is expressed and phosphorylated in EEC in adult human colon and that both EEC lines mainly express two tau isoforms that are phosphorylated under basal condition. Both propionate and butyrate regulated tau phosphorylation state by decreasing its phosphorylation at Thr205.

Conclusion and inference

Our study is the first to characterize tau in human EEC and in EEC lines. As a whole, our findings provide a basis to unravel the functions of tau in EEC and to further investigate the possibility of pathological changes in tauopathies and synucleinopathies.

d-Serine agonism of GluN1-GluN3 NMDA receptors regulates the activity of enteric neurons and coordinates gut motility

The enteric nervous system (ENS) is a complex network of diverse molecularly defined classes of neurons embedded in the gastrointestinal wall and responsible for controlling the major functions of the gut. As in the central nervous system, the vast array of ENS neurons is interconnected by chemical synapses. Despite several studies reporting the expression of ionotropic glutamate receptors in the ENS, their roles in the gut remain elusive. Here, by using an array of immunohistochemistry, molecular profiling and functional assays, we uncover a new role for d-serine (d-Ser) and non-conventional GluN1-GluN3 N-methyl d-aspartate receptors (NMDARs) in regulating ENS functions. We demonstrate that d-Ser is produced by serine racemase (SR) expressed in enteric neurons. By using both in situ patch clamp recording and calcium imaging, we show that d-Ser alone acts as an excitatory neurotransmitter in the ENS independently of the conventional GluN1-GluN2 NMDARs. Instead, d-Ser directly gates the non-conventional GluN1-GluN3 NMDARs in enteric neurons from both mouse and guinea-pig. Pharmacological inhibition or potentiation of GluN1-GluN3 NMDARs had opposite effects on mouse colonic motor activities, while genetically driven loss of SR impairs gut transit and fluid content of pellet output. Our results demonstrate the existence of native GluN1-GluN3 NMDARs in enteric neurons and open new perspectives on the exploration of excitatory d-Ser receptors in gut function and diseases.

Crosstalk between omega-6 oxylipins and the enteric nervous system: Implications for gut disorders?

The enteric nervous system (ENS) continues to dazzle scientists with its ability to integrate signals, from the outside as well as from the host, to accurately regulate digestive functions. Composed of neurons and enteric glial cells, the ENS interplays with numerous neighboring cells through the reception and/or the production of several types of mediators. In particular, ENS can produce and release n-6 oxylipins. These lipid mediators, derived from arachidonic acid, play a major role in inflammatory and allergic processes, but can also regulate immune and nervous system functions. As such, the study of these n-6 oxylipins on the digestive functions, their cross talk with the ENS and their implication in pathophysiological processes is in full expansion and will be discussed in this review.

Maternal prebiotic supplementation impacts colitis development in offspring mice

Background and aims

Maternal diet plays a key role in preventing or contributing to the development of chronic diseases, such as obesity, allergy, and brain disorders. Supplementation of maternal diet with prebiotics has been shown to reduce the risk of food allergies and affect the intestinal permeability in offspring later in life. However, its role in modulating the development of other intestinal disorders, such as colitis, remains unknown. Therefore, we investigated the effects of prebiotic supplementation in pregnant mice on the occurrence of colitis in their offspring.

Materials and methods

Offspring from mothers, who were administered prebiotic galacto-oligosaccharides and inulin during gestation or fed a control diet, were subjected to three cycles of dextran sulphate sodium (DSS) treatment to induce chronic colitis, and their intestinal function and disease activity were evaluated. Colonic remodelling, gut microbiota composition, and lipidomic and transcriptomic profiles were also assessed.

Results

DSS-treated offspring from prebiotic-fed mothers presented a higher disease score, increased weight loss, and increased faecal humidity than those from standard diet-fed mothers. DSS-treated offspring from prebiotic-fed mothers also showed increased number of colonic mucosal lymphocytes and macrophages than the control group, associated with the increased colonic concentrations of resolvin D5, protectin DX, and 14-hydroxydocosahexaenoic acid, and modulation of colonic gene expression. In addition, maternal prebiotic supplementation induced an overabundance of eight bacterial families and a decrease in the butyrate caecal concentration in DSS-treated offspring.

Conclusion

Maternal prebiotic exposure modified the microbiota composition and function, lipid content, and transcriptome of the colon of the offspring. These modifications did not protect against colitis, but rather sensitised the mice to colitis development.

LRRK2 expression in normal and pathologic human gut and in rodent enteric neural cell lines

Leucine-rich repeat kinase 2 (LRRK2) gene, which is the gene most commonly associated with Parkinson's disease (PD), is also a susceptibility gene for Crohn's disease, thereby suggesting that LRRK2 may sit at the crossroads of gastrointestinal inflammation, Parkinson's, and Crohn's disease. LRRK2 protein has been studied intensely in both CNS neurons and in immune cells, but there are only few studies on LRRK2 in the enteric nervous system (ENS). LRRK2 is present in ENS ganglia and the existing studies on LRRK2 expression in colonic biopsies from PD subjects have yielded conflicting results. Herein, we propose to extend these findings by studying in more details LRRK2 expression in the ENS. LRRK2 expression was evaluated in full thickness segments of colon of 16 Lewy body, 12 non-Lewy body disorders cases, and 3 non-neurodegenerative controls and in various enteric neural cell lines. We showed that, in addition to enteric neurons, LRRK2 is constitutively expressed in enteric glial cells in both fetal and adult tissues. LRRK2 immunofluorescence intensity in the myenteric ganglia was not different between Lewy body and non-Lewy body disorders. Additionally, we identified the cAMP pathway as a key signaling pathway involved in the regulation of LRRK2 expression and phosphorylation in the enteric glial cells. Our study is the first detailed characterization of LRRK2 in the ENS and the first to show that enteric glial cells express LRRK2. Our findings provide a basis to unravel the functions of LRRK2 in the ENS and to further investigate the pathological changes in enteric synucleinopathies.

Inflammatory bowel disease therapeutic strategies by modulation of the microbiota: how and when to introduce pre-, pro-, syn-, or postbiotics?

Inflammatory bowel diseases (IBD), a heterogeneous group of inflammatory conditions that encompass both ulcerative colitis and Crohn's disease, represent a major public health concern. The etiology of IBD is not yet fully understood and no cure is available, with current treatments only showing long-term effectiveness in a minority of patients. A need to increase our knowledge on IBD pathophysiology is growing, to define preventive measures, to improve disease outcome, and to develop new effective and lasting treatments. IBD pathogenesis is sustained by aberrant immune responses, associated with alterations of the intestinal epithelial barrier (IEB), modifications of the enteric nervous system, and changes in microbiota composition. Currently, most of the treatments target the inflammation and the immune system, but holistic approaches targeting lifestyle and diet improvements are emerging. As dysbiosis is involved in IBD pathogenesis, pre-, pro-, syn-, and postbiotics are used/tested to reduce the inflammation or strengthen the IEB. The present review will resume these works, pointing out the stage of life, the duration, and the environmental conditions that should go along with microbiota or microbiota-derived treatments.

Intestinal Epithelial AMPK Deficiency Causes Delayed Colonic Epithelial Repair in DSS-Induced Colitis

Dysfunctions in the intestinal barrier, associated with an altered paracellular pathway, are commonly observed in inflammatory bowel disease (IBD). The AMP-activated protein kinase (AMPK), principally known as a cellular energy sensor, has also been shown to play a key role in the stabilization and assembly of tight junctions. Here, we aimed to investigate the contribution of intestinal epithelial AMPK to the initiation, progression and resolution of acute colitis. We also tested the hypothesis that protection mediated by metformin administration on intestinal epithelium damage required AMPK activation. A dextran sodium sulfate (DSS)-induced colitis model was used to assess disease progression in WT and intestinal epithelial cell (IEC)-specific AMPK KO mice. Barrier integrity was analyzed by measuring paracellular permeability following dextran-4kDa gavage and pro-inflammatory cytokines and tight junction protein expression. The deletion of intestinal epithelial AMPK delayed intestinal injury repair after DSS exposure and was associated with a slower re-epithelization of the intestinal mucosa coupled with severe ulceration and inflammation, and altered barrier function. Following intestinal injury, IEC AMPK KO mice displayed a lower goblet cell counts with concomitant decreased Muc2 gene expression, unveiling an impaired restitution of goblet cells and contribution to wound healing process. Metformin administration during the recovery phase attenuated the severity of DSS-induced colitis through improvement in intestinal repair capacity in both WT and IEC AMPK KO mice. Taken together, these findings demonstrate a critical role for IEC-expressed AMPK in regulating mucosal repair and epithelial regenerative capacity following acute colonic injury. Our studies further underscore the therapeutic potential of metformin to support repair of the injured intestinal epithelium, but this effect is conferred independently of intestinal epithelial AMPK.

PGI2 Inhibits Intestinal Epithelial Permeability and Apoptosis to Alleviate Colitis

BACKGROUND & AIMS

Inflammatory bowel diseases (IBDs) that encompass both ulcerative colitis and Crohn's disease are a major public health problem with an etiology that has not been fully elucidated. There is a need to improve disease outcomes and preventive measures by developing new effective and lasting treatments. Although polyunsaturated fatty acid metabolites play an important role in the pathogenesis of several disorders, their contribution to IBD is yet to be understood.

METHODS

Polyunsaturated fatty acids metabolite profiles were established from biopsy samples obtained from Crohn's disease, ulcerative colitis, or control patients. The impact of a prostaglandin I₂ (PGI₂) analog on intestinal epithelial permeability was tested in vitro using Caco-2 cells and ex vivo using human or mouse explants. In addition, mice were treated with PGI₂ to observe dextran sulfate sodium (DSS)-induced colitis. Tight junction protein expression, subcellular location, and apoptosis were measured in the different models by immunohistochemistry and Western blotting.

RESULTS

A significant reduction of PGI₂ in IBD patient biopsies was identified. PGI₂ treatment reduced colonic inflammation, increased occludin expression, decreased caspase-3 cleavage and intestinal permeability, and prevented colitis development in DSS-induced mice. Using colonic explants from mouse and human control subjects, the staurosporine-induced increase in paracellular permeability was prevented by PGI₂. PGI₂ also induced the membrane location of occludin and reduced the permeability observed in colonic biopsies from IBD patients.

CONCLUSIONS

The present study identified a PGI₂ defect in the intestinal mucosa of IBD patients and demonstrated its protective role during colitis.

Tau in the gut, does it really matter?

The enteric nervous system plays a critical role in the regulation of gastrointestinal tract functions and is often referred to as the 'second brain' because it shares many features with the central nervous system. These similarities include among others a large panel of neurotransmitters, a large population of glial cells and a susceptibility to neurodegeneration. This close homology between the central and enteric nervous systems suggests that a disease process affecting the central nervous system could also involve its enteric counterpart. This was already documented in Parkinson's disease, the most common synucleinopathy, in which alpha-synuclein deposits are reported in the enteric nervous system in the vast majority of patients. Tau is another key protein involved in neurodegenerative disorders of the brain. Whether changes in tau also occur in the enteric nervous system during gut or brain disorders has just begun to be explored. The scope of the present article is therefore to review existing studies on the expression and phosphorylation pattern of tau in the enteric nervous system under physiological and pathological conditions and to discuss the possible occurrence of 'enteric tauopathies'.

Deletion of intestinal epithelial AMP-activated protein kinase alters distal colon permeability but not glucose homeostasis

Objective

The intestinal epithelial barrier (IEB) restricts the passage of microbes and potentially harmful substances from the lumen through the paracellular space, and rupture of its integrity is associated with a variety of gastrointestinal disorders and extra-digestive diseases. Increased IEB permeability has been linked to disruption of metabolic homeostasis leading to obesity and type 2 diabetes. Interestingly, recent studies have uncovered compelling evidence that the AMP-activated protein kinase (AMPK) signaling pathway plays an important role in maintaining epithelial cell barrier function. However, our understanding of the function of intestinal AMPK in regulating IEB and glucose homeostasis remains sparse.

Methods

We generated mice lacking the two α1 and α2 AMPK catalytic subunits specifically in intestinal epithelial cells (IEC AMPK KO) and determined the physiological consequences of intestinal-specific deletion of AMPK in response to high-fat diet (HFD)-induced obesity. We combined histological, functional, and integrative analyses to ascertain the effects of gut AMPK loss on intestinal permeability in vivo and ex vivo and on the development of obesity and metabolic dysfunction. We also determined the impact of intestinal AMPK deletion in an inducible mouse model (i-IEC AMPK KO) by measuring IEB function, glucose homeostasis, and the composition of gut microbiota via fecal 16S rRNA sequencing.

Results

While there were no differences in in vivo intestinal permeability in WT and IEC AMPK KO mice, ex vivo transcellular and paracellular permeability measured in Ussing chambers was significantly increased in the distal colon of IEC AMPK KO mice. This was associated with a reduction in pSer425 GIV phosphorylation, a marker of leaky gut barrier. However, the expression of tight junction proteins in intestinal epithelial cells and pro-inflammatory cytokines in the lamina propria were not different between genotypes. Although the HFD-fed AMPK KO mice displayed suppression of the stress polarity signaling pathway and a concomitant increase in colon permeability, loss of intestinal AMPK did not exacerbate body weight gain or adiposity. Deletion of AMPK was also not sufficient to alter glucose homeostasis or the acute glucose-lowering action of metformin in control diet (CD)- or HFD-fed mice. CD-fed i-IEC AMPK KO mice also presented higher permeability in the distal colon under homeostatic conditions but, surprisingly, this was not detected upon HFD feeding. Alteration in epithelial barrier function in the i-IEC AMPK KO mice was associated with a shift in the gut microbiota composition with higher levels of Clostridiales and Desulfovibrionales.

Conclusions

Altogether, our results revealed a significant role of intestinal AMPK in maintaining IEB integrity in the distal colon but not in regulating glucose homeostasis. Our data also highlight the complex interaction between gut microbiota and host AMPK.

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Deletion of intestinal AMPKα1 and α2 suppresses the stress-polarity signaling (SPS) pathway.

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Loss of the SPS pathway is associated with increased paracellular permeability in the distal colon.

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Intestinal AMPK is dispensable for the acute glucose-lowering action of metformin.

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Loss of intestinal AMPK alters the gut microbiota composition.

Tau accumulates in Crohn's disease gut

A sizeable body of evidence has recently emerged to suggest that gastrointestinal (GI) inflammation might be involved in the development of Parkinson's disease (PD). There is now strong epidemiological and genetical evidence linking PD to inflammatory bowel diseases and we recently demonstrated that the neuronal protein alpha-synuclein, which is critically involved in PD pathophysiology, is upregulated in inflamed segments of Crohn's colon. The microtubule associated protein tau is another neuronal protein critically involved in neurodegenerative disorders but, in contrast to alpha-synuclein, no data are available about its expression and phosphorylation patterns in inflammatory bowel diseases. Here, we examined the expression levels of tau isoforms, their phosphorylation profile and truncation in colon biopsy specimens from 16 Crohn's disease (CD) and 6 ulcerative colitis (UC) patients and compared them to samples from 16 controls. Additional experiments were performed in full thickness segments of colon of five CD and five control subjects, in primary cultures of rat enteric neurons and in nuclear factor erythroid 2-related factor (Nrf2) knockout mice. Our results show the upregulation of two main human tau isoforms in the enteric nervous system (ENS) in CD but not in UC. This upregulation was not transcriptionally regulated but instead likely resulted from a decrease in protein clearance via an Nrf2 pathway. Our findings, which provide the first detailed characterization of tau in CD, suggest that the key proteins involved in neurodegenerative disorders such as alpha-synuclein and tau, might also play a role in CD.

Neonatal Consumption of Oligosaccharides Greatly Increases L-Cell Density without Significant Consequence for Adult Eating Behavior

Oligosaccharides (OS) are commonly added to infant formulas, however, their physiological impact, particularly on adult health programming, is poorly described. In adult animals, OS modify microbiota and stimulate colonic fermentation and enteroendocrine cell (EEC) activity. Since neonatal changes in microbiota and/or EEC density could be long-lasting and EEC-derived peptides do regulate short-term food intake, we hypothesized that neonatal OS consumption could modulate early EECs, with possible consequences for adult eating behavior. Suckling rats were supplemented with fructo-oligosaccharides (FOS), beta-galacto-oligosaccharides/inulin (GOS/In) mix, alpha-galacto-oligosaccharides (αGOS) at 3.2 g/kg, or a control solution (CTL) between postnatal day (PND) 5 and 14/15. Pups were either sacrificed at PND14/15 or weaned at PND21 onto standard chow. The effects on both microbiota and EEC were characterized at PND14/15, and eating behavior at adulthood. Very early OS supplementation drastically impacted the intestinal environment, endocrine lineage proliferation/differentiation particularly in the ileum, and the density of GLP-1 cells and production of satiety-related peptides (GLP-1 and PYY) in the neonatal period. However, it failed to induce any significant lasting changes on intestinal microbiota, enteropeptide secretion or eating behavior later in life. Overall, the results did not demonstrate any OS programming effect on satiety peptides secreted by L-cells or on food consumption, an observation which is a reassuring outlook from a human perspective.

Acute inflammation down-regulates alpha-synuclein expression in enteric neurons

The protein alpha-synuclein whose expression is strongly implicated in Parkinson's disease (PD) is not only expressed in the CNS but also in the enteric nervous system (ENS). The growing body of evidence suggesting that gastrointestinal inflammation is involved in the development of PD led us to investigate the effects of inflammation on alpha-synuclein expression in primary culture of rat ENS and in mice with dextran sulfate sodium-induced colitis. Using western blot and qPCR, we found that both lipopolysaccharide and a combination of tumor necrosis factor-α and interleukin 1-β decreased the expression levels of alpha-synuclein in primary culture of rat ENS, an effect that was prevented in the presence of the p38 inhibitors SB203580 and BIRB 796. Lipopolysaccharide and tumor necrosis factor-α/interleukin 1-β had no effect on alpha-synuclein expression in primary culture of rat CNS and in human erythroid leukemia cells. In mice, acute but not chronic dextran sulfate sodium-induced colitis was associated with a decreased expression of colonic alpha-synuclein. As a whole, our findings indicate that acute inflammatory insults down-regulate alpha-synuclein expression in the ENS via a p38 pathway. They provide new insights into the widely discussed concepts of alpha-synuclein expression and aggregation in the ENS in PD and raise issues about the possible role of gastrointestinal inflammation in the development of PD. OPEN SCIENCE BADGES: This article has received a badge for *Open Materials* because it provided all relevant information to reproduce the study in the manuscript. The complete Open Science Disclosure form for this article can be found at the end of the article. More information about the Open Practices badges can be found at https://cos.io/our-services/open-science-badges/.

Characterisation of tau in the human and rodent enteric nervous system under physiological conditions and in tauopathy

Tau is normally a highly soluble phosphoprotein found predominantly in neurons. Six different isoforms of tau are expressed in the adult human CNS. Under pathological conditions, phosphorylated tau aggregates are a defining feature of neurodegenerative disorders called tauopathies. Recent findings have suggested a potential role of the gut-brain axis in CNS homeostasis, and therefore we set out to examine the isoform profile and phosphorylation state of tau in the enteric nervous system (ENS) under physiological conditions and in tauopathies. Surgical specimens of human colon from controls, Parkinson's disease (PD) and progressive supranuclear palsy (PSP) patients were analyzed by Western Blot and immunohistochemistry using a panel of anti-tau antibodies. We found that adult human ENS primarily expresses two tau isoforms, localized in the cell bodies and neuronal processes. We did not observe any difference in the enteric tau isoform profile and phosphorylation state between PSP, PD and control subjects. The htau mouse model of tauopathy also expressed two main isoforms of human tau in the ENS, and there were no apparent differences in ENS tau localization or phosphorylation between wild-type and htau mice. Tau in both human and mouse ENS was found to be phosphorylated but poorly susceptible to dephosphorylation with lambda phosphatase. To investigate ENS tau phosphorylation further, primary cultures from rat enteric neurons, which express four isoforms of tau, were pharmacologically manipulated to show that ENS tau phosphorylation state can be regulated, at least in vitro. Our study is the first to characterize tau in the rodent and human ENS. As a whole, our findings provide a basis to unravel the functions of tau in the ENS and to further investigate the possibility of pathological changes in enteric neuropathies and tauopathies.

The multiple faces of inflammatory enteric glial cells: is Crohn's disease a gliopathy?

Gone are the days when enteric glial cells (EGC) were considered merely satellites of enteric neurons. Like their brain counterpart astrocytes, EGC express an impressive number of receptors for neurotransmitters and intercellular messengers, thereby contributing to neuroprotection and to the regulation of neuronal activity. EGC also produce different soluble factors that regulate neighboring cells, among which are intestinal epithelial cells. A better understanding of EGC response to an inflammatory environment, often referred to as enteric glial reactivity, could help define the physiological role of EGC and the importance of this reactivity in maintaining gut functions. In chronic inflammatory disorders of the gut such as Crohn's disease (CD) and ulcerative colitis, EGC exhibit abnormal phenotypes, and their neighboring cells are dysfunctional; however, it remains unclear whether EGC are only passive bystanders or active players in the pathophysiology of both disorders. The aim of the present study is to review the physiological roles and properties of EGC, their response to inflammation, and their role in the regulation of the intestinal epithelial barrier and to discuss the emerging concept of CD as an enteric gliopathy.

Glioplasticity in irritable bowel syndrome

BACKGROUND

Growing evidence indicates a wide array of cellular remodeling in the mucosal microenvironment during irritable bowel syndrome (IBS), which possibly contributes to pathophysiology and symptom generation. Here, we investigated whether enteric glial cells (EGC) may be altered, and which factors/mechanisms lead to these changes.

METHODS

Colonic mucosal biopsies of IBS patients (13 IBS-Constipation [IBS-C]; 10 IBS-Diarrhea [IBS-D]; 11 IBS-Mixed [IBS-M]) and 24 healthy controls (HC) were analyzed. Expression of S100β and GFAP was measured. Cultured rat EGC were incubated with supernatants from mucosal biopsies, then proliferation and Ca²⁺ response to ATP were analyzed using flow cytometry and Ca²⁺ imaging. Histamine and histamine 1-receptor (H1R) involvement in the effects of supernatant upon EGC was analyzed.

KEY RESULTS

Compared to HC, the mucosal area immunoreactive for S100β was significantly reduced in biopsies of IBS patients, independently of the IBS subtype. IBS-C supernatants reduced EGC proliferation and IBS-D and IBS-M supernatants reduced Ca²⁺ response to ATP in EGC. EGC expressed H1R and the effects of supernatant upon Ca²⁺ response to ATP in EGC were blocked by pyrilamine and reproduced by histamine via H1R. IBS supernatants reduced mRNA expression of connexin-43. The S100β-stained area was negatively correlated with the frequency and intensity of pain and bloating.

CONCLUSION AND INFERENCES

Changes in EGC occur in IBS, involving mucosal soluble factors. Histamine, via activation of H1R-dependent pathways, partly mediates altered Ca²⁺ response to ATP in EGC. These changes may contribute to the pathophysiology and the perception of pain and bloating in patients with IBS.

Modulation of VIPergic phenotype of enteric neurons by colonic biopsy supernatants from patients with inflammatory bowel diseases: Involvement of IL-6 in Crohn's disease

BACKGROUND

Neuroplastic changes in the enteric nervous system (ENS) observed during IBD might participate in physiopathological processes. Vasoactive intestinal polypeptide has been shown to be involved in intestinal inflammation and barrier functions. We aimed to investigate the modulation of VIP expression in colonic biopsies of IBD patient, the ability of soluble factors from biopsies to reproduce in vitro these modulations and identify soluble factors responsible.

METHODS

VIP and cytokines mRNA expressions were assessed in colonic biopsies of healthy subjects (HS) and IBD patients from inflamed (I) and non-inflamed areas (NI). Supernatants (SUP) of biopsies were applied to primary culture of ENS and VIP and cytokines mRNA expressions were assessed. The role of cytokines in SUP induced changes in VIP expression was evaluated.

KEY RESULTS

VIP mRNA expression was lower in biopsies of patients with Crohn's disease (CD) than Ulcerative Colitis (UC) but unchanged as compared to HS. VIP mRNA and protein expression were lower in primary culture of ENS incubated with SUP-CD than with SUP-UC. Furthermore, in CD but not UC, SUP-I reduced VIP expression in the ENS as compared to SUP-NI. Next, IL-6 but not IL-5, IL-10, IL-17, IFN-γ or TNF-α reduced VIP expression in the ENS. Finally, in CD, SUP-I incubated with anti-IL-6 antibody increased VIP expression as compared to SUP-I alone.

CONCLUSIONS & INFERENCES

Mucosal soluble factors from IBD induce VIP neuroplastic changes in the ENS. IL-6 was identified as a putative soluble factor responsible in part for changes in VIP expression in CD.

Biochemical analysis of α-synuclein extracted from control and Parkinson's disease colonic biopsies

Lewy bodies and neurites, the pathological hallmarks found in the brain of Parkinson's disease (PD) patients, are primarily composed of aggregated and hyperphosphorylated alpha-synuclein. The observation that alpha-synuclein inclusions are also found in the gut of the vast majority of parkinsonian patients has led to an increasing number of studies aimed at developing diagnostic procedures based on the detection of pathological alpha-synuclein in gastrointestinal biopsies. The previous studies, which have all used immunohistochemistry for the detection of alpha-synuclein, have provided conflicting results. In the current survey, we used a different approach by analyzing the immunoreactivity pattern of alpha-synuclein separated by one- and two-dimensional electrophoresis, in colonic biopsies from PD subjects and healthy individuals. We did not observe any differences between controls and PD in the expression levels, phosphorylation or aggregation status of alpha-synuclein. Overall, our study suggests that the two biochemical methods tested here are not adequate for the prediction of PD using gastrointestinal biopsies. Further studies, using other biochemical approaches, are warranted to test whether there exists specific forms of pathological alpha-synuclein that distinguish PD from control subjects.

The arachidonic acid metabolite 11β-ProstaglandinF2α controls intestinal epithelial healing: deficiency in patients with Crohn's disease

In healthy gut enteric glial cells (EGC) are essential to intestinal epithelial barrier (IEB) functions. In Crohn's Disease (CD), both EGC phenotype and IEB functions are altered, but putative involvement of EGC in CD pathogenesis remains unknown and study of human EGC are lacking. EGC isolated from CD and control patients showed similar expression of glial markers and EGC-derived soluble factors (IL6, TGF-β, proEGF, GSH) but CD EGC failed to increase IEB resistance and healing. Lipid profiling showed that CD EGC produced decreased amounts of 15-HETE, 18-HEPE, 15dPGJ2 and 11βPGF2α as compared to healthy EGC. They also had reduced expression of the L-PGDS and AKR1C3 enzymes. Produced by healthy EGC, the 11βPGF2 activated PPARγ receptor of intestinal epithelial cells to induce cell spreading and IEB wound repair. In addition to this novel healing mechanism our data show that CD EGC presented impaired ability to promote IEB functions through defect in L-PGDS-AKR1C3-11βPGF2α dependent pathway.

Distinct expression of interleukin (IL)-36α, β and γ, their antagonist IL-36Ra and IL-38 in psoriasis, rheumatoid arthritis and Crohn's disease

Interleukin (IL)-36α, IL-36β and IL-36γ are expressed highly in skin and are involved in the pathogenesis of psoriasis, while the antagonists IL-36Ra or IL-38, another potential IL-36 inhibitor, limit uncontrolled inflammation. The expression and role of IL-36 cytokines in rheumatoid arthritis (RA) and Crohn's disease (CD) is currently debated. Here, we observed that during imiquimod-induced mouse skin inflammation and in human psoriasis, expression of IL-36α, γ and IL-36Ra, but not IL-36β and IL-38 mRNA, was induced and correlated with IL-1β and T helper type 17 (Th17) cytokines (IL-17A, IL-22, IL-23, CCL20). In mice with collagen-induced arthritis and in the synovium of patients with RA, IL-36α, β, γ, IL-36Ra and IL-38 were all elevated and correlated with IL-1β, CCL3, CCL4 and macrophage colony-stimulating factor (M-CSF), but not with Th17 cytokines. In the colon of mice with dextran sulphate sodium-induced colitis and in patients with CD, only IL-36α, γ and IL-38 were induced at relatively low levels and correlated with IL-1β and IL-17A. We suggest that only a minor subgroup of patients with RA (17-29%) or CD (25%) had an elevated IL-36 agonists/antagonists ratio, versus 93% of patients with psoriasis. By immunohistochemistry, IL-36 cytokines were produced by various cell types in skin, synovium and colonic mucosa such as keratinocytes, CD68⁺ macrophages, dendritic/Langerhans cells and CD79α⁺ plasma cells. In primary cultures of monocytes or inflammatory macrophages (M1), IL-36β and IL-36Ra were produced constitutively, but IL-36α, γ and IL-38 were produced after lipopolysaccharide stimulation. These distinct expression profiles may help to explain why only subgroups of RA and CD patients have a potentially elevated IL-36 agonists/antagonists ratio.

Defects in 15-HETE Production and Control of Epithelial Permeability by Human Enteric Glial Cells From Patients With Crohn's Disease

BACKGROUND & AIMS

Enteric glial cells (EGCs) produce soluble mediators that regulate homeostasis and permeability of the intestinal epithelial barrier (IEB). We investigated the profile of polyunsaturated fatty acid (PUFA) metabolites produced by EGCs from rats and from patients with Crohn's disease (CD), compared with controls, along with the ability of one of these metabolites, 15-hydroxyeicosatetraenoic acid (15-HETE), to regulate the permeability of the IEB.

METHODS

We isolated EGCs from male Sprague-Dawley rats, intestinal resections of 6 patients with CD, and uninflamed healthy areas of intestinal tissue from 6 patients who underwent surgery for colorectal cancer (controls). EGC-conditioned media was analyzed by high-sensitivity liquid-chromatography tandem mass spectrometry to determine PUFA signatures. We used immunostaining to identify 15-HETE-producing enzymes in EGCs and tissues. The effects of human EGCs and 15-HETE on permeability and transepithelial electrical resistance of the IEB were measured using Caco-2 cells; effects on signal transduction proteins were measured with immunoblots. Levels of proteins were reduced in Caco-2 cells using short-hairpin RNAs or proteins were inhibited pharmacologically. Rats were given intraperitoneal injections of 15-HETE or an inhibitor of 15-lipoxygenase (the enzyme that produces 15-HETE); colons were collected and permeability was measured.

RESULTS

EGCs expressed 15-lipoxygenase-2 and produced high levels of 15-HETE, which increased IEB resistance and reduced IEB permeability. 15-HETE production was reduced in EGCs from patients with CD compared with controls. EGCs from patients with CD were unable to reduce the permeability of the IEB; the addition of 15-HETE restored permeability to levels of control tissues. Inhibiting 15-HETE production in rats increased the permeability of the IEB in colon tissues. We found that 15-HETE regulates IEB permeability by inhibiting an adenosine monophosphate-activated protein kinase and increasing expression of zonula occludens-1.

CONCLUSIONS

Enteric glial cells from patients with CD have reduced production of 15-HETE, which controls IEB permeability by inhibiting adenosine monophosphate-activated protein kinase and increasing expression of zonula occludens-1.

Activation of the prostaglandin D2 metabolic pathway in Crohn's disease: involvement of the enteric nervous system

Background

Recent works provide evidence of the importance of the prostaglandin D2 (PGD2) metabolic pathway in inflammatory bowel diseases. We investigated the expression of PGD2 metabolic pathway actors in Crohn’s disease (CD) and the ability of the enteric nervous system (ENS) to produce PGD2 in inflammatory conditions.

Methods

Expression of key actors involved in the PGD2 metabolic pathway and its receptors was analyzed using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) in colonic mucosal biopsies of patients from three groups: controls, quiescent and active CD patients. To determine the ability of the ENS to secrete PGD2 in proinflammatory conditions, Lipocalin-type prostaglandin D synthase (L-PGDS) expression by neurons and glial cells was analyzed by immunostaining. PGD2 levels were determined in a medium of primary culture of ENS and neuro-glial coculture model treated by lipopolysaccharide (LPS).

Results

In patients with active CD, inflamed colonic mucosa showed significantly higher COX2 and L-PGDS mRNA expression, and significantly higher PGD2 levels than healthy colonic mucosa. On the contrary, peroxysome proliferator-activated receptor Gamma (PPARG) expression was reduced in inflamed colonic mucosa of CD patients with active disease. Immunostaining showed that L-PGDS was expressed in the neurons of human myenteric and submucosal plexi. A rat ENS primary culture model confirmed this expression. PGD2 levels were significantly increased on primary culture of ENS treated with LPS. This production was abolished by AT-56, a specific competitive L-PGDS inhibitor. The neuro-glial coculture model revealed that each component of the ENS, ECG and neurons, could contribute to PGD2 production.

Conclusions

Our results highlight the activation of the PGD2 metabolic pathway in Crohn’s disease. This study supports the hypothesis that in Crohn’s disease, enteric neurons and glial cells form a functional unit reacting to inflammation by producing PGD2.

Modulation of lipopolysaccharide-induced neuronal response by activation of the enteric nervous system

BACKGROUND

Evidence continues to mount concerning the importance of the enteric nervous system (ENS) in controlling numerous intestinal functions in addition to motility and epithelial functions. Nevertheless, little is known concerning the direct participation of the ENS in the inflammatory response of the gut during infectious or inflammatory insults. In the present study we analyzed the ENS response to bacterial lipopolysaccharide, in particular the production of a major proinflammatory cytokine, tumor necrosis factor-alpha (TNF-α).

METHODS

TNF-α expression (measured by qPCR, quantitative Polymerase Chain Reaction) and production (measured by ELISA) were measured in human longitudinal muscle-myenteric plexus (LMMP) and rat ENS primary cultures (rENSpc). They were either treated or not treated with lipopolysaccharide (LPS) in the presence or not of electrical field stimulation (EFS). Activation of extracellular signal-regulated kinase (ERK) and 5'-adenosine monophosphate-activated protein kinase (AMPK) pathways was analyzed by immunocytochemistry and Western blot analysis. Their implications were studied using specific inhibitors (U0126, mitogen-activated protein kinase kinase, MEK, inhibitor and C compound, AMPK inhibitor). We also analyzed toll-like receptor 2 (TLR2) expression and interleukin-6 (IL-6) production after LPS treatment simultaneously with EFS or TNF-α-neutralizing antibody.

RESULTS

Treatment of human LMMP or rENSpc with LPS induced an increase in TNF-α production. Activation of the ENS by EFS significantly inhibited TNF-α production. This regulation occurred at the transcriptional level. Signaling analyses showed that LPS induced activation of ERK but not AMPK, which was constitutively activated in rENSpc neurons. Both U0126 and C compound almost completely prevented LPS-induced TNF-α production. In the presence of LPS, EFS inhibited the ERK and AMPK pathways. In addition, we demonstrated using TNF-α-neutralizing antibody that LPS-induced TNF-α production increased TLR2 expression and reduced IL-6 production.

CONCLUSIONS

Our results show that LPS induced TNF-α production by enteric neurons through activation of the canonical ERK pathway and also in an AMPK-dependent manner. ENS activation through the inhibition of these pathways decreased TNF-α production, thereby modulating the inflammatory response induced by endotoxin.

Enteric glial cells: recent developments and future directions

Since their discovery at the end of the 19th century, enteric glial cells (EGCs), the major cellular component of the enteric nervous system, have long been considered mere supportive cells for neurons. However, recent evidence has challenged this view and highlighted their central role in the regulation of gut homeostasis as well as their implication in digestive and extradigestive diseases. In this review, we summarize emerging concepts as to how EGCs regulate neuromediator expression, exert neuroprotective roles, and even act as neuronal as well as glial progenitors in the enteric nervous system. A particularly crucial property of EGCs is their ability to maintain the integrity of the intestinal epithelial barrier, a role that may have important clinical implications not only for digestive diseases, such as postoperative ileus and inflammatory bowel diseases, but also for extradigestive diseases, such as Parkinson disease or obesity. EGCs could also contribute directly to disease processes (eg, inflammation) by their ability to secrete chemokines/cytokines in response to bacterial or inflammatory challenges. Defining the pleiotropic roles exerted by EGCs may reveal better knowledge and help develop new targeted therapeutic options for a variety of gastrointestinal diseases.

Smooth muscle specific Rac1 deficiency induces hypertension by preventing p116RIP3-dependent RhoA inhibition

Background

Increasing evidence implicates overactivation of RhoA as a critical component of the pathogenesis of hypertension. Although a substantial body of work has established that Rac1 functions antagonize RhoA in a broad range of physiological processes, the role of Rac1 in the regulation of vascular tone and blood pressure is not fully elucidated.

Methods and Results

To define the role of Rac1 in vivo in vascular smooth muscle cells (vSMC), we generated smooth muscle (SM)‐specific Rac1 knockout mice (SM‐Rac1‐KO) and performed radiotelemetric blood pressure recordings, contraction measurements in arterial rings, vSMC cultures and biochemical analyses. SM‐Rac1‐KO mice develop high systolic blood pressure sensitive to Rho kinase inhibition by fasudil. Arteries from SM‐Rac1‐KO mice are characterized by a defective NO‐dependent vasodilation and an overactivation of RhoA/Rho kinase signaling. We provide evidence that Rac1 deletion‐induced hypertension is due to an alteration of cGMP signaling resulting from the loss of Rac1‐mediated control of type 5 PDE activity. Consequently, cGMP‐dependent phosphorylation and binding of RhoA with its inhibitory partner, the phosphatase‐RhoA interacting protein (p116^RIP3), are decreased.

Conclusions

Our data reveal that the depletion of Rac1 in SMC decreases cGMP‐dependent p116^RIP3/RhoA interaction and the subsequent inhibition of RhoA signaling. Thus, we unveil an in vivo role of Rac1 in arterial blood pressure regulation and a new pathway involving p116^RIP3 that contributes to the antagonistic relationship between Rac1 and RhoA in vascular smooth muscle cells and their opposite roles in arterial tone and blood pressure.

Enteric GFAP expression and phosphorylation in Parkinson's disease

Enteric glial cells (EGCs) are in many respects similar to astrocytes of the central nervous system and express similar proteins including glial fibrillary acidic protein (GFAP). Changes in GFAP expression and/or phosphorylation have been reported during brain damage or central nervous system degeneration. As in Parkinson's disease (PD) the enteric neurons accumulate α-synuclein, and thus are showing PD-specific pathological features, we undertook the present survey to study whether the enteric glia in PD become reactive by assessing the expression and phosphorylation levels of GFAP in colonic biopsies. Twenty-four PD, six progressive supranuclear palsy (PSP), six multiple system atrophy (MSA) patients, and 21 age-matched healthy controls were included. The expression levels and the phosphorylation state of GFAP were analyzed in colonic biopsies by western blot. Additional experiments were performed using real-time PCR for a more precise analysis of the GFAP isoforms expressed by EGCs. We showed that GFAPκ was the main isoform expressed in EGCs. As compared to control subjects, patients with PD, but not PSP and MSA, had significant higher GFAP expression levels in their colonic biopsies. The phosphorylation level of GFAP at serine 13 was significantly lower in PD patients compared to control subjects. By contrast, no change in GFAP phosphorylation was observed between PSP, MSA and controls. Our findings provide evidence that enteric glial reaction occurs in PD and further reinforce the role of the enteric nervous system in the initiation and/or the progression of the disease. We showed that GFAP is over-expressed and hypophosphorylated in the enteric glial cells (EGCs) of Parkinson's disease (PD) patients as compared to healthy subjects and patients with atypical parkinsonism (MSA, multiple system atrophy and PSP, progressive supranuclear palsy). Our findings provide evidence that enteric glial reaction occurs in PD but not in PSP and MSA and further reinforce the role of the enteric nervous system in the pathophysiology of PD.

Endogenous regulation of visceral pain via production of opioids by colitogenic CD4(+) T cells in mice

BACKGROUND & AIMS

A dysregulated response of CD4(+) T cells against the microbiota contributes to the development of inflammatory bowel disease. Effector CD4(+) T cells, generated in response to microbe-derived antigens, can reduce somatic inflammatory pain through the local release of opioids. We investigated whether colitogenic CD4(+) T cells that accumulate in the inflamed colon also produce opioids and are able to counteract inflammation-induced visceral pain in mice.

METHODS

Colitis was induced via transfer of naive CD4(+)CD45RB(high) T cells to immune-deficient mice or by administration of dextran sulfate sodium. Mice without colitis were used as controls. Samples of colon tissue were collected, and production of opioids by immune cells from inflamed intestine was assessed by quantitative polymerase chain reaction and cytofluorometry analyses. The role of intestinal opioid tone in inflammation-induced visceral hypersensitivity was assessed by colorectal distention.

RESULTS

In mice with T cell- or dextran sulfate sodium-induced colitis, colitogenic CD4(+) T cells (T-helper 1 and Th17 cells) accumulated in the inflamed intestine and expressed a high level of endogenous opioids. In contrast, macrophages and epithelial cells did not express opioids; opioid synthesis in the myenteric plexus was not altered on induction of inflammation. In mice with colitis, the local release of opioids by colitogenic CD4(+) T cells led to significant reduction of inflammation-associated visceral hypersensitivity.

CONCLUSIONS

In mice, colitogenic Th1 and Th17 cells promote intestinal inflammation and colonic tissue damage but have simultaneous opioid-mediated analgesic activity, thereby reducing abdominal pain.

Characterization of human, mouse, and rat cultures of enteric glial cells and their effect on intestinal epithelial cells

BACKGROUND

Enteric glial cells (EGC) are major regulators of neuronal and intestinal epithelial cell (IEC) functions. Simple isolation methods of EGC, especially human tissues, remain scarce and limit their study. We present herein a method to isolate EGC and we characterize EGC phenotype and their functional impact on IEC.

METHODS

Longitudinal muscle and myenteric plexus preparations of rat, mouse, or human intestine were obtained by microdissection. After mechanical and enzymatic dissociation, individual ganglionic or interganglionic structures were seeded into plates, maintained in culture several weeks and passaged up to 4 times. Purity of cultures was assessed by immunocytochemistry using antibodies against glial fibrillary acidic protein (GFAP), S100β and Sox10 or smooth muscle actin. Effects of adenosine triphosphate (ATP) on intracellular Ca²⁺ signaling in EGC were studied. Co-cultures of EGC with IEC line, Caco-2, were performed for 2-6 days to analyze their impact on monolayer resistance, cell proliferation, and cell spreading.

KEY RESULTS

More than 80% of DAPI-positive cells were GFAP, S100β, and Sox10-immunoreactive. EGC expressed these glial markers over 4 consecutive passages, and the majority of them responded to ATP by an increase in intracellular Ca²⁺ concentration. In addition, rat, mouse, and human EGC increased intestinal barrier resistance, IEC size, and reduced IEC number.

CONCLUSIONS & INFERENCES

We have developed a simple method to isolate and culture human, rat, or mouse EGC. EGC exhibit similar functional properties on the intestinal barrier independently of the species. This study sets the basis for exploring glial biology and functions in human health and diseases.

The digestive neuronal-glial-epithelial unit: a new actor in gut health and disease

The monolayer of columnar epithelial cells lining the gastrointestinal tract--the intestinal epithelial barrier (IEB)--is the largest exchange surface between the body and the external environment. The permeability of the IEB has a central role in the regulation of fluid and nutrient intake as well as in the control of the passage of pathogens. The functions of the IEB are highly regulated by luminal as well as internal components, such as bacteria or immune cells, respectively. Evidence indicates that two cell types of the enteric nervous system (ENS), namely enteric neurons and enteric glial cells, are potent modulators of IEB functions, giving rise to the novel concept of a digestive 'neuronal-glial-epithelial unit' akin to the neuronal-glial-endothelial unit in the brain. In this Review, we summarize findings demonstrating that the ENS is a key regulator of IEB function and is actively involved in pathologies associated with altered barrier function.

AMPK Alpha 1-Induced RhoA Phosphorylation Mediates Vasoprotective Effect of Estradiol

Objective—

Estradiol (E2) mediates numerous beneficial effects assigned to estrogens, but whereas mechanisms have been described at the endothelial level, direct effects on vascular smooth muscle cells (VSMC) are poorly documented. As evidence accumulates regarding the role of RhoA in vascular pathophysiology and the benefit of RhoA-Rho associated protein kinase (Rock) pathway inhibition, we analyzed if E2 could inhibit it in VSMC.

Methods and Results—

We show that in VSMC, E2 inhibits the RhoA-Rock pathway in a time- and concentration-dependent manner. The inhibition of RhoA-Rock pathway results from E2-induced phosphorylation of the Ser188 of RhoA. Using pharmacological, transfection, and in vitro phosphorylation experiments, we demonstrate that AMP-activated protein kinase subunit alpha 1 (AMPKα1) is activated by estrogen receptor stimulation and catalyzes RhoA phosphorylation induced by E2. Ex vivo, ovariectomy leads to an increase in the amplitude of phenylephrine- or serotonine-induced contractions of aortic rings in wild-type mice but not in AMPKα1-knock-out mice or E2-supplemented animals. These functional effects were correlated with a reduced level of RhoA phosphorylation in the aorta of ovariectomized female, male, and AMPKα1 knock-out mice.

Conclusion—

Our work thus defines AMPKα1 as (1) a new kinase for RhoA and (2) a new mediator of the vasoprotective effects of estrogen.

n-3 polyunsaturated fatty acids in the maternal diet modify the postnatal development of nervous regulation of intestinal permeability in piglets

The intestinal epithelial barrier (IEB) plays a key role in the maintenance of gut homeostasis and the development of the immune system in newborns. The enteric nervous system (ENS), a key regulator of gastrointestinal functions, has been shown to be modulated by nutritional factors. However, it remains currently unknown whether maternal diet, in particular n-3 polyunsaturated fatty acids (n-3PUFAs), can impact upon the IEB in newborn piglets and whether the ENS is involved in this effect. Sows received either a control diet (lard based) or an n-3PUFA diet (linseed oil based) during gestation and lactation. Intestinal paracellular permeability was assessed in Ussing chambers on piglets at birth, 3, 7, 14, 21 and 28 postnatal days (PND). Basal jejunal permeability increased significantly and similarly in both groups until PND14 and decreased thereafter. However, at PND28, permeability was higher in n-3PUFA animals as compared to controls. In addition, a vasoactive intestinal peptide (VIP) receptor antagonist increased paracellular permeability in controls but not in n-3PUFA piglets. Conversely, atropine and hexamethonium decreased paracellular permeability in the n-3PUFA group but not in the control group. Moreover, the n-3PUFA diet increased the proportion of choline acetyltransferase (ChAT)-immunoreactive (IR) neurons and decreased the proportion of VIP-IR neurons in the submucosal plexus of piglet jejunum compared to controls. In addition, in primary culture of rat ENS, we showed that 20:5n-3 but not 18:3n-3 increased the proportion of ChAT-IR neurons and decreased the proportion of VIP-IR neurons. In conclusion, supplementation of the maternal diet with n-3PUFAs modified intestinal permeability probably via diet-induced neuroplastic changes in the ENS of newborn piglets.

Enteric glia protect against Shigella flexneri invasion in intestinal epithelial cells: a role for S-nitrosoglutathione

BACKGROUND

Enteric glial cells (EGCs) are important regulators of intestinal epithelial barrier (IEB) functions. EGC-derived S-nitrosoglutathione (GSNO) has been shown to regulate IEB permeability. Whether EGCs and GSNO protect the IEB during infectious insult by pathogens such as Shigella flexneri is not known.

METHODS

S flexneri effects were characterised using in vitro coculture models of Caco-2 cells and EGCs (or GSNO), ex vivo human colonic mucosa, and in vivo ligated rabbit intestinal loops. The effect of EGCs on S flexneri-induced changes in the invasion area and the inflammatory response were analysed by combining immunohistochemical, ELISA and PCR methods. Expression of small G-proteins was analysed by western blot. Expression of ZO-1 and localisation of bacteria were analysed by fluorescence microscopy.

RESULTS

EGCs significantly reduced barrier lesions and inflammatory response induced by S flexneri in Caco-2 monolayers. The EGC-mediated effects were reproduced by GSNO, but not by reduced glutathione, and pharmacological inhibition of pathways involved in GSNO synthesis reduced EGC protecting effects. Furthermore, expression of Cdc42 and phospho-PAK in Caco-2 monolayers was significantly reduced in the presence of EGCs or GSNO. In addition, changes in ZO-1 expression and distribution induced by S flexneri were prevented by EGCs and GSNO. Finally, GSNO reduced S flexneri-induced lesions of the IEB in human mucosal colonic explants and in a rabbit model of shigellosis.

CONCLUSION

These results highlight a major protective function of EGCs and GSNO in the IEB against S flexneri attack. Consequently, this study lays the scientific basis for using GSNO to reduce barrier susceptibility to infectious or inflammatory challenge.

Protective role of the antidiabetic drug metformin against chronic experimental pulmonary hypertension

BACKGROUND AND PURPOSE

Pulmonary arterial hypertension (PAH) is associated with increased contraction and proliferation of pulmonary vascular smooth muscle cells. The anti-diabetic drug metformin has been shown to have relaxant and anti-proliferation properties. We thus examined the effect of metformin in PAH.

EXPERIMENTAL APPROACH

Metformin effects were analysed in hypoxia- and monocrotaline-induced PAH in rats. Ex vivo and in vitro analyses were performed in lungs, pulmonary artery rings and cells.

KEY RESULTS

In hypoxia- and monocrotaline-induced PAH, the changes in mean pulmonary arterial pressure and right heart hypertrophy were nearly normalized by metformin treatment (100 mg.kg(-1).day(-1)). Pulmonary arterial remodelling occurring in both experimental models of PAH was also inhibited by metformin treatment. In rats with monocrotaline-induced PAH, treatment with metformin significantly increased survival. Metformin increased endothelial nitric oxide synthase phosphorylation and decreased Rho kinase activity in pulmonary artery from rats with PAH. These effects are associated with an improvement of carbachol-induced relaxation and reduction of phenylephrine-induced contraction of pulmonary artery. In addition, metformin inhibited mitogen-activated protein kinase activation and strongly reduced pulmonary arterial cell proliferation during PAH. In vitro, metformin directly inhibited pulmonary artery smooth muscle cell growth.

CONCLUSIONS AND IMPLICATIONS

Metformin protected against PAH, regardless of the initiating stimulus. This protective effect may be related to its anti-remodelling property involving improvement of endothelial function, vasodilatory and anti-proliferative actions. As metformin is currently prescribed to treat diabetic patients, assessment of its use as a therapy against PAH in humans should be easier.

Angiotensin II induces RhoA activation through SHP2-dependent dephosphorylation of the RhoGAP p190A in vascular smooth muscle cells

Angiotensin II (ANG II) is a major regulator of blood pressure that essentially acts through activation of ANG II type 1 receptor (AT1R) of vascular smooth muscle cells (VSMC). AT1R activates numerous intracellular signaling pathways, including the small G protein RhoA known to control several VSMC functions. Nevertheless, the mechanisms leading to RhoA activation by AT1R are unknown. RhoA activation can result from activation of RhoA exchange factor and/or inhibition of Rho GTPase-activating protein (GAP). Here we hypothesize that a RhoGAP could participate to RhoA activation induced by ANG II in rat aortic VSMC. The knockdown of the RhoGAP p190A by small interfering RNA (siRNA) abolishes the activation of RhoA-Rho kinase pathway induced after 5 min of ANG II (0.1 microM) stimulation in rat aortic VSMC. We then show that AT1R activation induces p190A dephosphorylation and inactivation. In addition, expression of catalytically inactive or phosphoresistant p190A mutants increases the basal activity of RhoA-Rho kinase pathway, whereas phosphomimetic mutant inhibits early RhoA activation by ANG II. Using siRNA and mutant overexpression, we then demonstrate that the tyrosine phosphatase SHP2 is necessary for 1) maintaining p190A basally phosphorylated and activated by the tyrosine kinase c-Abl, and 2) inducing p190A dephosphorylation and RhoA activation in response to AT1R activation. Our work then defines p190A as a new mediator of RhoA activation by ANG II in VSMC.

Ste20-Related Kinase SLK Phosphorylates Ser188 of RhoA to Induce Vasodilation in Response to Angiotensin II Type 2 Receptor Activation

The small G protein Rho signaling pathways are recognized as major regulators of cardiovascular functions, and activation of Rho proteins appears to be a common component for the pathogenesis of hypertension and vascular proliferative disorders. Recent evidence suggests that modulation of Rho protein signaling by phosphorylation of Rho proteins provides an additional simple mechanism for coordinating Rho protein functions. Phosphorylation of RhoA by cAMP- or cGMP-activated kinase on Ser188 induces cytosolic sequestration of RhoA through increased interaction with guanine dissociation inhibitor, thereby resulting in inhibition of RhoA-dependent functions. Here we show that stimulation of angiotensin II (Ang II) type 2 receptor (AT 2 R) in vascular smooth muscle cells induces Ser188 phosphorylation of RhoA independently of cAMP- or cGMP-activated kinase. We identify the Ser/Thr kinase Ste20-related kinase SLK as a new kinase phosphorylating RhoA on Ser188. Activation of the signaling cascade involving Src homology 2 domain–containing protein-tyrosine phosphatase 1, casein kinase II and SLK is responsible for RhoA phosphorylation and inhibition of RhoA-mediated arterial contraction induced by AT 2 R activation. These results thus identify the molecular mechanism linking AT 2 R to RhoA inhibition and vasodilation.

Urotensin II and atherosclerosis

Urotensin II, through its interaction with its UT receptor, is a potent vasoactive peptide in humans and in several animal models. Recent studies have demonstrated elevated plasma U-II levels in patients with atherosclerosis and coronary artery disease. U-II is expressed in endothelial cells, smooth muscle cells and infiltrating macrophages of atherosclerotic human coronary arteries. UT receptor expression is up-regulated by inflammatory stimuli. Activation of UT receptor by U-II stimulates endothelial and smooth muscle cell proliferation and monocytes chemotaxis. Therefore, in addition to its primary vasoactive effect, these observations suggest a role of U-II and UT receptor in the initiation and/or progression of atherosclerosis.

Urotensin II is a new chemotactic factor for UT receptor-expressing monocytes

Urotensin II (U-II), a vasoactive cyclic neuropeptide which activates the G protein-coupled receptor UT receptor, exerts various cardiovascular effects and may play a role in the pathophysiology of atherosclerosis. In this study, we report that the UT receptor is expressed and functional on human PBMC and rat splenocytes. PBMC surface expression of the UT receptor was mainly found in monocytes and NK cells, also in a minority of B cells, but not in T cells. Stimulation of monocytes with LPS increased UT receptor mRNA and protein expression. Cloning and functional characterization of the human UT receptor gene promoter revealed the presence of NF-kappaB-binding sites involved in the stimulation of UT receptor gene expression by LPS. Activation of the UT receptor by U-II induced chemotaxis with maximal activity at 10 and 100 nM. This U-II effect was restricted to monocytes. Analysis of the signaling pathway involved indicated that U-II-mediated chemotaxis was related to RhoA and Rho kinase activation and actin cytoskeleton reorganization. The present results thus identify U-II as a chemoattractant for UT receptor-expressing monocytes and indicate a pivotal role of the RhoA-Rho kinase signaling cascade in the chemotaxis induced by U-II.