Glial A2B Adenosine Receptors Modulate Abnormal Tachykininergic Responses and Prevent Enteric Inflammation Associated with High Fat Diet-Induced Obesity

Global research status and trends of enteric glia: a bibliometric analysis

Background

Enteric glia are essential components of the enteric nervous system. Previously believed to have a passive structural function, mounting evidence now suggests that these cells are indispensable for maintaining gastrointestinal homeostasis and exert pivotal influences on both wellbeing and pathological conditions. This study aimed to investigate the global status, research hotspots, and future directions of enteric glia.

Methods

The literature on enteric glia research was acquired from the Web of Science Core Collection. VOSviewer software (v1.6.19) was employed to visually represent co-operation networks among countries, institutions, and authors. The co-occurrence analysis of keywords and co-citation analysis of references were conducted using CiteSpace (v6.1.R6). Simultaneously, cluster analysis and burst detection of keywords and references were performed.

Results

A total of 514 publications from 36 countries were reviewed. The United States was identified as the most influential country. The top-ranked institutions were University of Nantes and Michigan State University. Michel Neunlist was the most cited author. "Purinergic signaling" was the largest co-cited reference cluster, while "enteric glial cells (EGCs)" was the cluster with the highest number of co-occurring keywords. As the keyword with the highest burst strength, Crohns disease was a hot topic in the early research on enteric glia. The burst detection of keywords revealed that inflammation, intestinal motility, and gut microbiota may be the research frontiers.

Conclusion

This study provides a comprehensive bibliometric analysis of enteric glia research. EGCs have emerged as a crucial link between neurons and immune cells, attracting significant research attention in neurogastroenterology. Their fundamental and translational studies on inflammation, intestinal motility, and gut microbiota may promote the treatment of some gastrointestinal and parenteral disorders.

Gene expression alterations of purinergic signaling components in obesity-associated intestinal low-grade inflammation in type 2 diabetes

Intestinal low-grade inflammation induced by a high-fat diet has been found to detonate chronic systemic inflammation, which is a hallmark of obesity, and precede the apparition of insulin resistance, a key factor for developing type 2 diabetes (T2D). Aberrant purinergic signaling pathways have been implicated in the pathogenesis of inflammatory bowel disease and other gastrointestinal diseases. However, their role in the gut inflammation associated with obesity and T2D remains unexplored. C57BL/6 J mice were fed a cafeteria diet for 21 weeks and received one injection of streptozotocin in their sixth week into the diet. The gene expression profile of purinergic signaling components in colon tissue was assessed by RT-qPCR. Compared to control mice, the treated group had a significant reduction in colonic length and mucosal and muscular layer thickness accompanied by increased NF-κB and IL-1β mRNA expression. Furthermore, colonic P2X2, P2X7, and A3R gene expression levels were lower, while the P2Y2, NT5E, and ADA expression levels increased. In conclusion, these data suggest that these purinergic signaling components possibly play a role in intestinal low-grade inflammation associated with obesity and T2D and thus could represent a novel therapeutic target for the treatment of the metabolic complications related to these diseases.

Pathological Remodeling of the Gut Barrier as a Prodromal Event of High-Fat Diet-Induced Obesity

Intestinal barrier alterations represent a primum movens in obesity and related intestinal dysfunctions. However, whether gut barrier remodeling represents prodromal events in obesity before weight gain, metabolic alterations, and systemic inflammation remains unclear. Herein, we examined morphologic changes in the gut barrier in a mouse model of high-fat diet (HFD) since the earliest phases of diet assumption. C57BL/6J mice were fed with standard diet (SD) or HFD for 1, 2, 4, or 8 weeks. Remodeling of intestinal epithelial barrier, inflammatory infiltrate, and collagen deposition in the colonic wall was assessed by histochemistry and immunofluorescence analysis. Obese mice displayed increased body and epididymal fat weight along with increased plasma resistin, IL-1β, and IL-6 levels after 8 weeks of HFD. Starting from 1 week of HFD, mice displayed (1) a decreased claudin-1 expression in lining epithelial cells, (2) an altered mucus in goblet cells, (3) an increase in proliferating epithelial cells in colonic crypts, (4) eosinophil infiltration along with an increase in vascular P-selectin, and (5) deposition of collagen fibers. HFD intake is associated with morphologic changes in the large bowel at mucosal and submucosal levels. In particular, the main changes include alterations in the mucous layer and intestinal epithelial barrier integrity and activation of mucosal defense-enhanced fibrotic deposition. These changes represent early events occurring before the development of obesity condition that could contribute to compromising the intestinal mucosal barrier and functions, opening the way for systemic dissemination.

Activation of GABA receptor attenuates intestinal inflammation by modulating enteric glial cells function through inhibiting NF-κB pathway

AIMS

Emerging research indicates that γ-aminobutyric acid (GABA) provides substantial benefits during enteritis. Nevertheless, GABA signaling roles on enteric glial cells (EGCs) remain unknown. The study's objective was to evaluate the underlying mechanisms of GABA signaling on EGCs in vitro and in vivo.

MAIN METHODS

We established LPS-induced mouse models and stimulated EGCs with LPS to mimic intestinal inflammation, and combined GABA, GABAA receptor (GABAAR) or GABAB receptor (GABABR) agonists to explore the exact mechanisms of GABA signaling.

KEY FINDINGS

EGCs were immunopositive for GAD65, GAD67, GAT1, GABAARα1, GABAARα3, and GABABR1, indicating GABAergic and GABAceptive properties. GABA receptor activation significantly inhibited the high secretions of proinflammatory factors in EGCs upon LPS stimulation. Interestingly, we found that EGCs express immune-related molecules such as CD16, CD32, CD80, CD86, MHC II, iNOS, Arg1, and CD206, thus establishing their characterization of E1 and E2 phenotype. EGCs exposed to LPS mainly acted as E1 phenotype, whereas GABABR activation strongly promoted EGCs polarization into E2 phenotype. Transcriptome analysis of EGCs indicated that GABA, GABAAR or GABABR agonists treatment participated in various biological processes, however all of these treatments exhibit inhibitory effects on NF-κB pathway. Notably, in LPS-induced mice, activation of GABABR mitigated intestinal damage through modulating inflammatory factors expressions, strengthening sIgA and IgG levels, inhibiting NF-κB pathway and facilitating EGCs to transform into E2 phenotype.

SIGNIFICANCE

These data demonstrate that the anti-inflammatory actions of GABA signaling system offer in enteritis via regulating EGCs-polarized function through impeding NF-κB pathway, thus providing potential targets for intestinal inflammatory diseases.

Mini-review: Enteric glial cell reactions to inflammation and potential therapeutic implications for GI diseases, motility disorders, and abdominal pain

Enteric glial cells are emerging as critical players in the regulation of intestinal motility, secretion, epithelial barrier function, and gut homeostasis in health and disease. Enteric glia react to intestinal inflammation by converting to a 'reactive glial phenotype' and enteric gliosis, contributing to neuroinflammation, enteric neuropathy, bowel motor dysfunction and dysmotility, diarrhea or constipation, 'leaky gut', and visceral pain. The focus of the minireview is on the impact of inflammation on enteric glia reactivity in response to diverse insults such as intestinal surgery, ischemia, infections (C. difficile infection, HIV-Tat-induced diarrhea, endotoxemia and paralytic ileus), GI diseases (inflammatory bowel diseases, diverticular disease, necrotizing enterocolitis, colorectal cancer) and functional GI disorders (postoperative ileus, chronic intestinal pseudo-obstruction, constipation, irritable bowel syndrome). Significant progress has been made in recent years on molecular pathogenic mechanisms of glial reactivity and enteric gliosis, resulting in enteric neuropathy, disruption of motility, diarrhea, visceral hypersensitivity and abdominal pain. There is a growing number of glial molecular targets with therapeutic implications that includes receptors for interleukin-1 (IL-1R), purines (P2X2R, A2BR), PPARα, lysophosphatidic acid (LPAR1), Toll-like receptor 4 (TLR4R), estrogen-β receptor (ERβ) adrenergic α-2 (α-2R) and endothelin B (ETBR), connexin-43 / Colony-stimulating factor 1 signaling (Cx43/CSF1) and the S100β/RAGE signaling pathway. These exciting new developments are the subject of the minireview. Some of the findings in pre-clinical models may be translatable to humans, raising the possibility of designing future clinical trials to test therapeutic application(s). Overall, research on enteric glia has resulted in significant advances in our understanding of GI pathophysiology.

Enteric Glia and Brain Astroglia: Complex Communication in Health and Disease along the Gut-Brain Axis

Several studies have provided interesting evidence about the role of the bidirectional communication between the gut and brain in the onset and development of several pathologic conditions, including inflammatory bowel diseases (IBDs), neurodegenerative diseases, and related comorbidities. Indeed, patients with IBD can experience neurologic disorders, including depression and cognitive impairment, besides typical intestinal symptoms. In parallel, patients with neurodegenerative disease, such as Parkinson disease and Alzheimer disease, are often characterized by the occurrence of functional gastrointestinal disorders. In this context, enteric glial cells and brain astrocytes are emerging as pivotal players in the initiation/maintenance of neuroinflammatory responses, which appear to contribute to the alterations of intestinal and neurologic functions observed in patients with IBD and neurodegenerative disorders. The present review was conceived to provide a comprehensive and critical overview of the available knowledge on the morphologic, molecular, and functional changes occurring in the enteric glia and brain astroglia in IBDs and neurologic disorders. In addition, our intent is to identify whether such alterations could represent a common denominator involved in the onset of comorbidities associated with the aforementioned disorders. This might help to identify putative targets useful to develop novel pharmacologic approaches for the therapeutic management of such disturbances.

Dietary Supplement, Containing the Dry Extract of Curcumin, Emblica and Cassia, Counteracts Intestinal Inflammation and Enteric Dysmotility Associated with Obesity

Intestinal epithelial barrier (IEB) impairment and enteric inflammation are involved in the onset of obesity and gut-related dysmotility. Dietary supplementation with natural plant extracts represents a useful strategy for the management of body weight gain and systemic inflammation associated with obesity. Here, we evaluate the efficacy of a food supplement containing the dry extract of Curcumin, Emblica and Cassia in counteracting enteric inflammation and motor abnormalities in a mouse model of obesity, induced by a high-fat diet (HFD). Male C57BL/6 mice, fed with standard diet (SD) or HFD, were treated with a natural mixture (Curcumin, Emblica and Cassia). After 8 weeks, body weight, BMI, liver and spleen weight, along with metabolic parameters and colonic motor activity were evaluated. Additionally, plasma LBP, fecal calprotectin, colonic levels of MPO and IL-1β, as well as the expression of occludin, TLR-4, MYD88 and NF-κB were investigated. Plant-based food supplement administration (1) counteracted the increase in body weight, BMI and metabolic parameters, along with a reduction in spleen and liver weight; (2) showed strengthening effects on the IEB integrity; and (3) reduced enteric inflammation and oxidative stress, as well as ameliorated the colonic contractile dysfunctions. Natural mixture administration reduced intestinal inflammation and counteracted the intestinal motor dysfunction associated with obesity.

Involvement of enteric glial cells in colonic motility in a rat model of irritable bowel syndrome with predominant diarrhea

The enteric nervous system (ENS) is one of the important systems that regulate gastrointestinal function. The ENS is made up of enteric glial cells (EGCs) and neurons. For a long time, it was believed that the function of EGCs was only to give structural support to neurons. However, recent evidence indicates EGCs are involved in most gut functions, including the development and plasticity of the ENS, epithelial barrier, and motility. However, it remains unclear whether EGCs have the potential to modify colonic motility following irritable bowel syndrome (IBS) with predominant diarrhea (IBS-D). This study aimed to investigate changes in EGCs during IBS-D and assessed the effects of manipulating EGCs. An IBS-D rat model was constructed using acetic acid and restraint stress, and DL-fluorocitric acid (FC), an inhibitor of EGCs, was administered. The changes in EGCs and colonic motility were studied by employing techniques comprising morphological, molecular biological and functional experiments. The results showed significant activation of EGCs in the myenteric plexus (MP) of the IBS-D-induced rat colon with accelerated colonic motility. FC significantly reduced the activation of EGCs and colonic motility caused by acetic acid and restraint stress. Hypercontraction of the colon caused by IBS-D may be associated with activation of EGCs in the MP of the colon and this was prevented by FC. Therefore, regulating colon hypercontraction through interference with the activation of EGCs has significant prospects for clinical application to alleviate diarrhea in patients with IBS-D.

Adenosine receptors differentially mediate enteric glial cell death induced by Clostridioides difficile Toxins A and B

Increased risk of intestinal dysfunction has been reported in patients after Clostridioides difficile infection (CDI). Enteric glial cells (EGCs), a component of the enteric nervous system (ENS), contribute to gut homeostasis. Previous studies showed that adenosine receptors, A2A and A2B, modulate inflammation during CDI. However, it is unknown how these receptors can modulate the EGC response to the C. difficile toxins (TcdA and TcdB). We investigated the effects of these toxins on the expression of adenosine receptors in EGCs and the role of these receptors on toxin-induced EGC death. Rat EGCs line were incubated with TcdA or TcdB alone or in combination with adenosine analogues 1h prior to toxins challenge. After incubation, EGCs were collected to evaluate gene expression (adenosine receptors and proinflammatory markers) and cell death. In vivo, WT, A2A, and A2B KO mice were infected with C. difficile, euthanized on day 3 post-infection, and cecum tissue was processed. TcdA and TcdB increased A2A and A3 transcripts, as well as decreased A2B. A2A agonist, but not A2A antagonist, decreased apoptosis induced by TcdA and TcdB in EGCs. A2B blocker, but not A2B agonist, diminished apoptosis in EGCs challenged with both toxins. A3 agonist, but not A3 blocker, reduced apoptosis in EGCs challenged with TcdA and TcdB. Inhibition of protein kinase A (PKA) and CREB, both involved in the main signaling pathway driven by activation of adenosine receptors, decreased EGC apoptosis induced by both toxins. A2A agonist and A2B antagonist decreased S100B upregulation induced by C. difficile toxins in EGCs. In vivo, infected A2B KO mice, but not A2A, exhibited a decrease in cell death, including EGCs and enteric neuron loss, compared to infected WT mice, reduced intestinal damage and decreased IL-6 and S100B levels in cecum. Our findings indicate that upregulation of A2A and A3 and downregulation of A2B in EGCs and downregulation of A2B in intestinal tissues elicit a protective response against C. difficile toxins. Adenosine receptors appear to play a regulatory role in EGCs death and proinflammatory response induced by TcdA and TcdB, and thus may be potential targets of intervention to prevent post-CDI intestinal dysmotility.

High-fat diet induces intestinal mucosal barrier dysfunction in ulcerative colitis: emerging mechanisms and dietary intervention perspective

The incidence of ulcerative colitis (UC) is increasing worldwide, but its pathogenesis remains largely unclear. The intestinal mucosa is a barrier that maintains the stability of the body's internal environment, and dysfunction of this barrier leads to the occurrence and aggravation of UC. A high-fat diet (HFD) contains more animal fat and low fiber, and accumulating evidence has shown that long-term intake of an HFD is associated with UC. The mechanism linking an HFD with intestinal mucosal barrier disruption is multifactorial, and it typically involves microbiota dysbiosis and altered metabolism of fatty acids, bile acids, and tryptophan. Dysbiosis-induced metabolic changes can enhance intestinal permeability through multiple pathways. These changes modulate the programmed death of intestinal epithelial cells, inhibit the secretion of goblet cells and Paneth cells, and impair intercellular interactions. Gut metabolites can also induce intestinal immune imbalance by stimulating multiple proinflammatory signaling pathways and decreasing the effect of anti-inflammatory immune cells. In this review, we critically analyze the molecular mechanisms by which an HFD disrupts the intestinal mucosal barrier (IMB) and contributes to the development of UC. We also discuss the application and future direction of dietary intervention in the treatment of the IMB and prevention of UC.

Preliminary Evidence of the Potent and Selective Adenosine A2B Receptor Antagonist PSB-603 in Reducing Obesity and Some of Its Associated Metabolic Disorders in Mice

The adenosine A2A and A2B receptors are promising therapeutic targets in the treatment of obesity and diabetes since the agonists and antagonists of these receptors have the potential to positively affect metabolic disorders. The present study investigated the link between body weight reduction, glucose homeostasis, and anti-inflammatory activity induced by a highly potent and specific adenosine A2B receptor antagonist, compound PSB-603. Mice were fed a high-fat diet for 14 weeks, and after 12 weeks, they were treated for 14 days intraperitoneally with the test compound. The A1/A2A/A2B receptor antagonist theophylline was used as a reference. Following two weeks of treatment, different biochemical parameters were determined, including total cholesterol, triglycerides, glucose, TNF-α, and IL-6 blood levels, as well as glucose and insulin tolerance. To avoid false positive results, mouse locomotor and spontaneous activities were assessed. Both theophylline and PSB-603 significantly reduced body weight in obese mice. Both compounds had no effects on glucose levels in the obese state; however, PSB-603, contrary to theophylline, significantly reduced triglycerides and total cholesterol blood levels. Thus, our observations showed that selective A2B adenosine receptor blockade has a more favourable effect on the lipid profile than nonselective inhibition.

High-fat diets on the enteric nervous system: Possible interactions and mechanisms underlying dysmotility

Obesity is a chronic disease that affects various physiological systems. Among them, the gastrointestinal tract appears to be a main target of this disease. High-fat diet (HFD) animal models can help recapitulate the classic signs of obesity and present a series of gastrointestinal alterations, mainly dysmotility. Because intestinal motility is governed by the enteric nervous system (ENS), enteric neurons, and glial cells have been studied in HFD models. Given the importance of the ENS in general gut physiology, this review aims to discuss the relationship between HFD-induced neuroplasticity and gut dysmotility observed in experimental models. Furthermore, we highlight components of the gut environment that might influence enteric neuroplasticity, including gut microbiota, enteric glio-epithelial unit, serotonin release, immune cells, and disturbances such as inflammation and oxidative stress.

Anti-inflammatory Effects of Novel P2X4 Receptor Antagonists, NC-2600 and NP-1815-PX, in a Murine Model of Colitis

The pharmacological blockade of P2X4 receptors has shown potential benefits in the management of several immune/inflammatory diseases. However, data regarding the involvement of P2X4 receptors in the pathophysiological mechanisms of action in intestinal inflammation are not well defined. We aimed to evaluate the anti-inflammatory effects of two novel and selective P2X4 receptor antagonists, NC-2600 and NP-1815-PX, and characterize the molecular mechanisms of their action in a murine model of 2,4-dinitrobenzene sulfonic acid (DNBS)-induced colitis. These two drugs and dexamethasone (DEX) were administered orally for 6 days, immediately after the manifestation of DNBS. The body weight decrease, resulting from colitis, was attenuated by NC-2600 and NP-1815-PX, but not DEX. However, all three drugs attenuated the increase in spleen weight and ameliorated macroscopic and microscopic colonic tissue damage. Furthermore, all three compounds decreased tissue IL-1β levels and caspase-1 expression and activity. Colonic tissue increase of tumor necrosis factor was downregulated by DEX, while both NC-2600 and NP-1815-PX were ineffective. The reduction of occludin associated with colitis was ameliorated by NC-2600 and NP-1815-PX, but not DEX. In THP-1 cells, lipopolysaccharide and ATP upregulated IL-1β release and NLRP3, caspase-1, caspase-5, and caspase-8 activity, but not of caspase-4. These changes were prevented by NC-2600 and NP-1815-PX treatment. For the first time, the above findings show that the selective inhibition of P2X4 receptors represents a viable approach to manage bowel inflammation via the inhibition of NLRP3 inflammasome signaling pathways.

Enteric α-synuclein impairs intestinal epithelial barrier through caspase-1-inflammasome signaling in Parkinson's disease before brain pathology

Bowel inflammation, impaired intestinal epithelial barrier (IEB), and gut dysbiosis could represent early events in Parkinson’s disease (PD). This study examined, in a descriptive manner, the correlation among enteric α-synuclein, bowel inflammation, impairments of IEB and alterations of enteric bacteria in a transgenic (Tg) model of PD before brain pathology. Human A53T α-synuclein Tg mice were sacrificed at 3, 6, and 9 months of age to evaluate concomitance of enteric inflammation, IEB impairments, and enteric bacterial metabolite alterations during the early phases of α-synucleinopathy. The molecular mechanisms underlying the interplay between α-synuclein, activation of immune/inflammatory responses and IEB alterations were investigated with in vitro experiments in cell cultures. Tg mice displayed an increase in colonic levels of IL-1β, TNF, caspase-1 activity and enteric glia activation since 3 months of age. Colonic TLR-2 and zonulin-1 expression were altered in Tg mice as compared with controls. Lipopolysaccharide levels were increased in Tg animals at 3 months, while fecal butyrate and propionate levels were decreased. Co-treatment with lipopolysaccharide and α-synuclein promoted IL-1β release in the supernatant of THP-1 cells. When applied to Caco-2 cells, the THP-1-derived supernatant decreased zonulin-1 and occludin expression. Such an effect was abrogated when THP-1 cells were incubated with YVAD (caspase-1 inhibitor) or when Caco-2 were incubated with anakinra, while butyrate incubation did not prevent such decrease. Taken together, early enteric α-synuclein accumulation contributes to compromise IEB through the direct activation of canonical caspase-1-dependent inflammasome signaling. These changes could contribute both to bowel symptoms as well as central pathology.

Palmitoylethanolamide Counteracts Enteric Inflammation and Bowel Motor Dysfunctions in a Mouse Model of Alzheimer's Disease

Palmitoylethanolamide (PEA), an endogenous lipid mediator, is emerging as a promising pharmacological agent in multiple neurodegenerative disorders for its anti-inflammatory and neuroprotective properties. However, its effects on enteric inflammation and colonic dysmotility associated with Alzheimer’s disease (AD) are lacking. This study was designed to investigate the beneficial effect of PEA administration in counteracting the enteric inflammation and relieving the bowel motor dysfunctions in an AD mouse model, SAMP8 mice. In addition, the ability of PEA in modulating the activation of enteric glial cells (EGCs), pivotally involved in the pathophysiology of bowel dysfunctions associated with inflammatory conditions, has also been examined. SAMP8 mice at 4 months of age were treated orally with PEA (5 mg/kg/day) for 2 months. SAMR1 animals were employed as controls. At the end of treatment, parameters dealing with colonic motility, inflammation, barrier integrity and AD protein accumulation were evaluated. The effect of PEA on EGCs was tested in cultured cells treated with lipopolysaccharide (LPS) plus β-amyloid 1–42 (Aβ). SAMP8 treated with PEA displayed: 1) an improvement of in vitro colonic motor activity, citrate synthase activity and intestinal epithelial barrier integrity and 2) a decrease in colonic Aβ and α-synuclein (α-syn) accumulation, S100-β expression as well as enteric IL-1β and circulating LPS levels, as compared with untreated SAMP8 mice. In EGCs, treatment with PEA counteracted the increment of S100-β, TLR-4, NF-κB p65 and IL-1β release induced by LPS and Aβ. These results suggest that PEA, under a condition of cognitive decline, prevents the enteric glial hyperactivation, reduces AD protein accumulation and counteracts the onset and progression of colonic inflammatory condition, as well as relieves intestinal motor dysfunctions and improves the intestinal epithelial barrier integrity. Therefore, PEA represents a viable approach for the management of the enteric inflammation and motor contractile abnormalities associated with AD.

Influence of Tilia tomentosa Moench Extract on Mouse Small Intestine Neuromuscular Contractility

Functional gastrointestinal disorders (FGIDs) are characterized by abdominal pain, bloating and bowel disturbances. FGID therapy is primarily symptomatic, including treatment with herbal remedies. Flower extract of Tilia tomentosa Moench (TtM) is occasionally used as an anti-spasmodic in popular medicine. Since its effect on intestinal response is unknown, we evaluated the influence of TtM extract on small intestine contractility. Ileal preparations from C57BL/6J mice were mounted in organ baths to assess changes in muscle tension, following addition of TtM extract (0.5–36 μg/mL) or a vehicle (ethanol). Changes in contractile response to receptor- and non-receptor-mediated stimuli were assessed in ileal preparations pretreated with 12 μg/mL TtM. Alterations in the enteric nervous system neuroglial network were analyzed by confocal immunofluorescence. Increasing addition of TtM induced a marked relaxation in ileal specimens compared to the vehicle. Pretreatment with TtM affected cholinergic and tachykininergic neuromuscular contractions as well as K⁺-induced smooth muscle depolarization. Following incubation with TtM, a significant reduction in non-adrenergic non-cholinergic-mediated relaxation sensitive to Nω-Nitro-L-arginine methyl ester hydrochloride (pan-nitric oxide synthase inhibitor) was found. In vitro incubation of intestinal specimens with TtM did not affect the myenteric plexus neuroglial network. Our findings show that TtM-induced intestinal relaxation is mediated by nitric oxide pathways, providing a pharmacological basis for the use of TtM in FGIDs.

NLRP3 at the crossroads between immune/inflammatory responses and enteric neuroplastic remodelling in a mouse model of diet-induced obesity

BACKGROUND AND PURPOSE

Enteric neurogenic/inflammation contributes to bowel dysmotility in obesity. We examined the role of NLRP3 in colonic neuromuscular dysfunctions in mice with high-fat diet (HFD)-induced obesity.

EXPERIMENTAL APPROACH

Wild-type C57BL/6J and NLRP3-KO (Nlrp3^-/- ) mice were fed with HFD or standard diet for 8 weeks. The activation of inflammasome pathways in colonic tissues from obese mice was assessed. The role of NLRP3 in in vivo colonic transit and in vitro tachykininergic contractions and substance P distribution was evaluated. The effect of substance P on NLRP3 signalling was tested in cultured cells.

KEY RESULTS

HFD mice displayed increased body and epididymal fat weight, cholesterol levels, plasma resistin levels and plasma and colonic IL-1β levels, colonic inflammasome adaptor protein apoptosis-associated speck-like protein containing caspase-recruitment domain (ASC) and caspase-1 mRNA expression and ASC immunopositivity in macrophages. Colonic tachykininergic contractions were enhanced in HFD mice. HFD NLRP3^-/- mice developed lower increase in body and epididymal fat weight, cholesterol levels, systemic and bowel inflammation. In HFD Nlrp3^-/- mice, the functional alterations of tachykinergic pathways and faecal output were normalized. In THP-1 cells, substance P promoted IL-1β release. This effect was inhibited upon incubation with caspase-1 inhibitor or NK₁ antagonist and not observed in ASC^-/- cells.

CONCLUSION AND IMPLICATIONS

In obesity, NLRP3 regulates an interplay between the shaping of enteric immune/inflammatory responses and the activation of substance P/NK₁ pathways underlying the onset of colonic dysmotility. Identifying NLRP3 as a therapeutic target for the treatment of bowel symptoms related to obesity.

Dopamine Transporter Genetic Reduction Induces Morpho-Functional Changes in the Enteric Nervous System

Antidopaminergic gastrointestinal prokinetics are indeed commonly used to treat gastrointestinal motility disorders, although the precise role of dopaminergic transmission in the gut is still unclear. Since dopamine transporter (DAT) is involved in several brain disorders by modulating extracellular dopamine in the central nervous system, this study evaluated the impact of DAT genetic reduction on the morpho-functional integrity of mouse small intestine enteric nervous system (ENS). In DAT heterozygous (DAT^+/-) and wild-type (DAT^+/+) mice (14 ± 2 weeks) alterations in small intestinal contractility were evaluated by isometrical assessment of neuromuscular responses to receptor and non-receptor-mediated stimuli. Changes in ENS integrity were studied by real-time PCR and confocal immunofluorescence microscopy in longitudinal muscle-myenteric plexus whole-mount preparations (). DAT genetic reduction resulted in a significant increase in dopamine-mediated effects, primarily via D1 receptor activation, as well as in reduced cholinergic response, sustained by tachykininergic and glutamatergic neurotransmission via NMDA receptors. These functional anomalies were associated to architectural changes in the neurochemical coding and S100β immunoreactivity in small intestine myenteric plexus. Our study provides evidence that genetic-driven DAT defective activity determines anomalies in ENS architecture and neurochemical coding together with ileal dysmotility, highlighting the involvement of dopaminergic system in gut disorders, often associated to neurological conditions.

Enteric Glia at the Crossroads between Intestinal Immune System and Epithelial Barrier: Implications for Parkinson Disease

Over recent years, several investigations have suggested that Parkinson’s disease (PD) can be regarded as the consequence of a bowel disorder. Indeed, gastrointestinal symptoms can occur at all stages of this neurodegenerative disease and in up to a third of cases, their onset can precede the involvement of the central nervous system. Recent data suggest that enteric glial cells (EGCs) may play a major role in PD-related gastrointestinal disturbances, as well as in the development and progression of the central disease. In addition to their trophic and structural functions, EGCs are crucial for the homeostatic control of a wide range of gastrointestinal activities. The main purpose of this review was to provide a detailed overview of the role of EGCs in intestinal PD-associated alterations, with particular regard for their participation in digestive and central inflammation as well as the dynamic interactions between glial cells and intestinal epithelial barrier. Accumulating evidence suggests that several pathological intestinal conditions, associated with an impairment of barrier permeability, may trigger dysfunctions of EGCs and their shift towards a proinflammatory phenotype. The reactive gliosis is likely responsible for PD-related neuroinflammation and the associated pathological changes in the ENS. Thus, ameliorating the efficiency of mucosal barrier, as well as avoiding IEB disruption and the related reactive gliosis, might theoretically prevent the onset of PD or, at least, counteract its progression.

Role of enteric glial cells in intestinal function and intestinal diseases

Enteric glial cells, as a key component of the intestinal nervous system, not only have the function of nutrition and supporting intestinal neurons, but also participate in the regulation of various intestinal functions. Abnormal activation of enteric glial cells may also be one of the important pathogenic factors for inflammatory bowel disease, intestinal infection, intestinal obstruction, colon cancer, and other intestinal diseases. At present, the role of enteric glial cells in the occurrence and development of digestive system diseases remains to be elucidated. This paper reviews the research progress in this area.