Enteric glia regulate gut motility in health and disease

GDNF's Role in Mitigating Intestinal Reactive Gliosis and Inflammation to Improve Constipation and Depressive Behavior in Rats with Parkinson's disease

Constipation is a common symptom in patients with Parkinson's disease (PD) and is often associated with depression. Enteric glial cells (EGCs) are crucial for regulating intestinal inflammation and colon motility, and their activation can lead to the death of intestinal neurons. Glial cell line-derived neurotrophic factor (GDNF) has been recognized for its neuroprotective properties in various neurological disorders, including PD. This study explores the potential of GDNF in alleviating intestinal reactive gliosis and inflammation, thereby improving constipation and depressive behavior in a rat model of PD. A PD model was established via unilateral stereotaxic injection of 6-hydroxydopamine (6-OHDA). Five weeks post-injury, AAV5-GDNF (2 ~ 5 × 10^11) was intraperitoneally injected into experimental and control rats. Fecal moisture percentage (FMP) and colonic propulsion rate (CPPR) were used to evaluate colon motility. Colon-related inflammation and colonic epithelial morphology were assessed, and depressive behavior was analyzed one week before sampling. PD rats exhibited reduced colonic motility and GDNF expression, along with increased EGC reactivity and elevated levels of pro-inflammatory cytokines IL-1, IL-6, and TNF-α. Additionally, there was an up-regulation of CX43 and a decrease in PGP 9.5 expression. The intraperitoneal injection of AAV-GDNF significantly protected colonic neurons by inhibiting EGC activation and down-regulating CX43. This treatment also led to a notable reduction in depressive-like symptoms in PD rats with constipation. GDNF effectively reduces markers of reactive gliosis and inflammation, and promotes the survival of colonic neurons, and improves colonic motility in PD rats by regulating CX43 activity. Furthermore, GDNF treatment alleviates depressive behavior, suggesting that GDNF or its agonists could be promising therapeutic agents for managing gastrointestinal and neuropsychiatric symptoms associated with PD.

The gut-brain and gut-macrophage contribution to gastrointestinal dysfunction with systemic inflammation

The gastrointestinal tract is one of the main organs affected during systemic inflammation and disrupted gastrointestinal motility is a major clinical manifestation. Many studies have investigated the involvement of neuroimmune interactions in regulating colonic motility during localized colonic inflammation, i.e., colitis. However, little is known about how the enteric nervous system and intestinal macrophages contribute to dysregulated motility during systemic inflammation. Given that systemic inflammation commonly results from the innate immune response against bacterial infection, we mimicked bacterial infection by administering lipopolysaccharide (LPS) to rats and assessed colonic motility using ex vivo video imaging techniques. We utilized the Cx3cr1-Dtr rat model of transient depletion of macrophages to investigate the role of intestinal macrophages in regulating colonic motility during LPS infection. To investigate the role of inhibitory enteric neurotransmission on colonic motility following LPS, we applied the nitric oxide synthase inhibitor, Nω-nitro-L-arginine (NOLA). Our results confirmed an increase in colonic contraction frequency during LPS-induced systemic inflammation. However, neither the depletion of intestinal macrophages, nor the suppression of inhibitory enteric nervous system activity impacted colonic motility disruption during inflammation. This implies that the interplay between the enteric nervous system and intestinal macrophages is nuanced, and complex, and further investigation is needed to clarify their joint roles in colonic motility.

Stroke Alters the Function of Enteric Neurons to Impair Smooth Muscle Relaxation and Dysregulates Gut Transit

BACKGROUND

Gut dysmotility is common after ischemic stroke, but the mechanism underlying this response is unknown. Under homeostasis, gut motility is regulated by the neurons of the enteric nervous system that control contractile/relaxation activity of muscle cells in the gut wall. More recently, studies of gut inflammation revealed interactions of macrophages with enteric neurons are also involved in modulating gut motility. However, whether poststroke gut dysmotility is mediated by direct signaling to the enteric nervous system or indirectly via inflammatory macrophages is unknown.

METHODS AND RESULTS

We examined these hypotheses by using a clinically relevant permanent intraluminal midcerebral artery occlusion experimental model of stroke. At 24 hours after stroke, we performed in vivo and ex vivo gut motility assays, flow cytometry, immunofluorescence, and transcriptomic analysis. Stroke-induced gut dysmotility was associated with recruitment of muscularis macrophages into the gastrointestinal tract and redistribution of muscularis macrophages away from myenteric ganglia. The permanent intraluminal midcerebral artery occlusion model caused changes in gene expression in muscularis macrophages consistent with an altered phenotype. While the size of myenteric ganglia after stroke was not altered, myenteric neurons from post-permanent intraluminal midcerebral artery occlusion mice showed a reduction in neuronal nitric oxide synthase expression, and this response was associated with enhanced intestinal smooth muscle contraction ex vivo. Finally, chemical sympathectomy with 6-hydroxydopamine prevented the loss of myenteric neuronal nitric oxide synthase expression and stroke-induced slowed gut transit.

CONCLUSIONS

Our findings demonstrate that activation of the sympathetic nervous system after stroke is associated with reduced neuronal nitric oxide synthase expression in myenteric neurons, resulting in impaired smooth muscle relaxation and dysregulation of gut transit.

Brazil Nut-Enriched Diet Modulates Enteric Glial Cells and Gut Microbiota in an Experimental Model of Chronic Kidney Disease

Introduction: Chronic kidney disease (CKD) promotes gut dysbiosis, and enteric glial reactivity, a feature of intestinal inflammation. Brazil nut modulated enteric glial profile in healthy animals and could modulate these cells in 5/6 nephrectomized rats.Methods: A 5/6 nephrectomy-induced CKD and Sham-operated rats were divided as follows: CKD and Sham received a standard diet and CKD-BN and Sham-BN received a 5% Brazil nut enriched-diet. The protein content of glial fibrillary acid protein (GFAP), enteric glial marker, and GPx protein content and activity were assessed in the colon. The major phyla of gut microbiota were assessed.Results: CKD-BN group presented a decrease in GFAP content (p = 0.0001). The CKD-BN group modulated the abundance of Firmicutes, increasing its proportion compared to the CKD group. The CKD-BN group showed increased GPx activity in the colon (p = 0.0192), despite no significant difference in protein content.Conclusion: Brazil nut-enriched diet consumption decreased enteric glial reactivity and modulated gut microbiota in the CKD experimental model.

From the Gut to the Brain: The Role of Enteric Glial Cells and Their Involvement in the Pathogenesis of Parkinson's Disease

The brain-gut axis has been identified as an important contributor to the physiopathology of Parkinson's disease. In this pathology, inflammation is thought to be driven by the damage caused by aggregation of α-synuclein in the brain. Interestingly, the Braak's theory proposes that α-synuclein misfolding may originate in the gut and spread in a "prion-like" manner through the vagus nerve into the central nervous system. In the enteric nervous system, enteric glial cells are the most abundant cellular component. Several studies have evaluated their role in Parkinson's disease. Using samples obtained from patients, cell cultures, or animal models, the studies with specific antibodies to label enteric glial cells (GFAP, Sox-10, and S100β) seem to indicate that activation and reactive gliosis are associated to the neurodegeneration produced by Parkinson's disease in the enteric nervous system. Of interest, Toll-like receptors, which are expressed on enteric glial cells, participate in the triggering of immune/inflammatory responses, in the maintenance of intestinal barrier integrity and in the configuration of gut microbiota; thus, these receptors might contribute to Parkinson's disease. External factors like stress also seem to be relevant in its pathogenesis. Some authors have studied ways to reverse changes in EGCs with interventions such as administration of Tryptophan-2,3-dioxygenase inhibitors, nutraceuticals, or physical exercise. Some researchers point out that beyond being activated during the disease, enteric glial cells may contribute to the development of synucleinopathies. Thus, it is still necessary to further study these cells and their role in Parkinson's disease.

Glial cell alterations in diabetes-induced neurodegeneration

Type 2 diabetes mellitus is a global epidemic that due to its increasing prevalence worldwide will likely become the most common debilitating health condition. Even if diabetes is primarily a metabolic disorder, it is now well established that key aspects of the pathogenesis of diabetes are associated with nervous system alterations, including deleterious chronic inflammation of neural tissues, referred here as neuroinflammation, along with different detrimental glial cell responses to stress conditions and neurodegenerative features. Moreover, diabetes resembles accelerated aging, further increasing the risk of developing age-linked neurodegenerative disorders. As such, the most common and disabling diabetic comorbidities, namely diabetic retinopathy, peripheral neuropathy, and cognitive decline, are intimately associated with neurodegeneration. As described in aging and other neurological disorders, glial cell alterations such as microglial, astrocyte, and Müller cell increased reactivity and dysfunctionality, myelin loss and Schwann cell alterations have been broadly described in diabetes in both human and animal models, where they are key contributors to chronic noxious inflammation of neural tissues within the PNS and CNS. In this review, we aim to describe in-depth the common and unique aspects underlying glial cell changes observed across the three main diabetic complications, with the goal of uncovering shared glial cells alterations and common pathological mechanisms that will enable the discovery of potential targets to limit neuroinflammation and prevent neurodegeneration in all three diabetic complications. Diabetes and its complications are already a public health concern due to its rapidly increasing incidence, and thus its health and economic impact. Hence, understanding the key role that glial cells play in the pathogenesis underlying peripheral neuropathy, retinopathy, and cognitive decline in diabetes will provide us with novel therapeutic approaches to tackle diabetic-associated neurodegeneration.

Dietary ingredient change induces a transient MyD88-dependent mucosal enteric glial cell response and promotes obesity

OBJECTIVE

Consumption of a modern Western-type high-fat low-fiber diet increases the risk of obesity. However, how a host responds to such a diet, especially during the early period of dietary transition from a previous low-fat and fiber-rich diet, remains poorly explored.

METHODS

Wild-type C57BL/6 mice were fed a normal chow diet or a high-fat diet. Enteric glial cell (EGC) activation was detected through quantitative real-time PCR (qRT-PCR), immunoblotting and immunohistology analysis. Fluorocitrate or genetic deletion of glial fibrillary acidic protein (GFAP)-positive glial-intrinsic myeloid differentiation factor 88 (Myd88) was used to inhibit EGC activation, and the effect of a high-fat diet on obesity was further investigated. The role of MYD88-dependent sensing of commensal products in adipocyte was observed to analyze the effect of obesity.

RESULTS

A dietary shift from a normal chow diet to a high-fat diet in mice induced a transient early-phase emergence of a GFAP-positive EGC network in the lamina propria of the ileum, accompanied with an increase in glial-derived neurotrophic factor production. Inhibition of glial cell activity blocked this response. GFAP-positive glial Myd88 knockout mice gained less body weight after high-fat diet (HFD) feeding than littermate controls. In contrast, adipocyte deletion of Myd88 in mice had no effect on weight gain but instead exacerbated glucose intolerance. Furthermore, short-term fluorocitrate intervention during HFD feeding attenuated body weight gain.

CONCLUSIONS

Our findings indicate that EGCs are early responders to intestinal ecosystem changes and the GFAP-positive glial Myd88 signaling participates in regulating obesity.

Enteric glia promote visceral hypersensitivity during inflammation through intercellular signaling with gut nociceptors

Inflammation in the intestines causes abdominal pain that is challenging to manage. The terminals of sensory neurons innervating the gut are surrounded by glia. Here, using a mouse model of acute colitis, we found that enteric glia contribute to visceral pain by secreting factors that sensitized sensory nerves innervating the gut in response to inflammation. Acute colitis induced a transient increase in the production of proinflammatory cytokines in the intestines of male and female mice. Of these, IL-1β was produced in part by glia and augmented the opening of the intercellular communication hemichannel connexin-43 in glia, which made normally innocuous stimuli painful in female mice. Chemogenetic glial activation paired with calcium imaging in nerve terminals demonstrated that glia sensitized gut-innervating nociceptors only under inflammatory conditions. This inflammatory, glial-driven visceral hypersensitivity involved an increased abundance of the enzyme COX-2 in glia, resulting in greater production and release of prostaglandin E2 that activated EP4 receptors on sensory nerve terminals. Blocking EP4 receptors reduced nociceptor sensitivity in response to glial stimulation in tissue samples from colitis-model mice, and impairing glial connexin-43 reduced visceral hypersensitivity induced by IL-1β in female mice. The findings suggest that therapies targeting enteric glial-neuron signaling might alleviate visceral pain caused by inflammatory disorders.

Impaired cecal motility and secretion alongside expansion of gut-associated lymphoid tissue in the Nlgn3R451C mouse model of autism

Individuals with Autism Spectrum Disorder (ASD; autism) commonly present with gastrointestinal (GI) illness in addition to core diagnostic behavioural traits. The appendix, or cecum in mice, is important for GI homeostasis via its function as a key site for fermentation and a microbial reservoir. Even so, the role of the appendix and cecum in autism-associated GI symptoms remains uninvestigated. Here, we studied mice with an autism-associated missense mutation in the post-synaptic protein neuroligin-3 (Nlgn3R451C), which impacts brain and enteric neuronal activity. We assessed for changes in cecal motility using a tri-cannulation video-imaging approach in ex vivo preparations from wild-type and Nlgn3R451C mice. We investigated cecal permeability and neurally-evoked secretion in wild-type and Nlgn3R451C tissues using an Ussing chamber set-up. The number of cecal patches in fresh tissue samples were assessed and key immune populations including gut macrophages and dendritic cells were visualised using immunofluorescence. Nlgn3R451C mice displayed accelerated cecal motor complexes and reduced cecal weight in comparison to wildtype littermates. Nlgn3R451C mice also demonstrated reduced neurally-evoked cecal secretion in response to the nicotinic acetylcholine receptor agonist 1,1-dimethyl-4-phenylpiperazinium (DMPP), but permeability was unchanged. We observed an increase in the number of cecal patches in Nlgn3R451C mice, however the cellular morphologies of key immune populations studied were not significantly altered. We show that the R451C nervous system mutation leads to cecal dysmotility, impaired secretion, and neuro-immune alterations. Together, these results suggest that the R451C mutation disrupts the gut-brain axis with GI dysfunction in autism.

Calcineurin B1 Deficiency Reduces Proliferation, Increases Apoptosis, and Alters Secretion in Enteric Glial Cells of Mouse Small Intestine in Culture

To investigate the roles of calcineurin (CN) in glial cells, we previously generated conditional knockout (CKO) mice lacking CNB1 in glial cells. Because these CKO mice showed dysfunction and inflammation of the small intestine in addition to growth impairment and postweaning death, we have focused on enteric glial cells (EGCs) in the small intestine. In this study, we examined the effects of CNB1 deficiency on the proliferation and survival of EGCs and the expression and secretion of EGC-derived substances in culture to reveal the mechanisms of how CNB1 deficiency leads to dysfunction and inflammation of the small intestine. In primary myenteric cultures of the small intestine, EGCs from the CKO mice showed reduced proliferation and increased apoptosis compared with EGCs from control mice. In purified EGC cultures from the CKO mice, Western blot analysis showed increased expression of S100B, iNOS, GFAP, and GDNF, and increased phosphorylation of NF-κB p65. In the supernatants of purified EGC cultures from the CKO mice, ELISA showed reduced secretion of TGF-β1. In contrast, GDNF secretion was not altered in purified EGC cultures from the CKO mice. Furthermore, treatment with an S100B inhibitor partially rescued the CKO mice from growth impairment and postweaning death in vivo. In conclusion, CNB1 deficiency leads to reduced proliferation and increased apoptosis of EGCs and abnormal expression and secretion of EGC-derived substances, which may contribute to dysfunction and inflammation of the small intestine.

Quantitative Spatial Analysis of Neuroligin-3 mRNA Expression in the Enteric Nervous System Reveals a Potential Role in Neuronal-Glial Synapses and Reduced Expression in Nlgn3R451C Mice

Mutations in the Neuroligin-3 (Nlgn3) gene are implicated in autism spectrum disorder (ASD) and gastrointestinal (GI) dysfunction, but cellular Nlgn3 expression in the enteric nervous system remains to be characterised. We combined RNAScope in situ hybridization and immunofluorescence to measure Nlgn3 mRNA expression in cholinergic and VIP-expressing submucosal neurons, nitrergic and calretinin-containing myenteric neurons and glial cells in both WT and Nlgn3^R451C mutant mice. We measured Nlgn3 mRNA neuronal and glial expression via quantitative three-dimensional image analysis. To validate dual RNAScope/immunofluorescence data, we interrogated available single-cell RNA sequencing (scRNASeq) data to assess for Nlgn3, Nlgn1, Nlgn2 and their binding partners, Nrxn1-3, MGDA1 and MGDA2, in enteric neural subsets. Most submucosal and myenteric neurons expressed Nlgn3 mRNA. In contrast to other Nlgns and binding partners, Nlgn3 was strongly expressed in enteric glia, suggesting a role for neuroligin-3 in mediating enteric neuron-glia interactions. The autism-associated R451C mutation reduces Nlgn3 mRNA expression in cholinergic but not in VIPergic submucosal neurons. In the myenteric plexus, Nlgn3 mRNA levels are reduced in calretinin, nNOS-labelled neurons and S100 β -labelled glia. We provide a comprehensive cellular profile for neuroligin-3 expression in ileal neuronal subpopulations of mice expressing the R451C autism-associated mutation in Nlgn3, which may contribute to the understanding of the pathophysiology of GI dysfunction in ASD.

Mini-review: Intercellular communication between enteric glia and neurons

The enteric nervous system is a dense network of enteric neurons and glia housed in the gastrointestinal tract. This system is responsible for performing several functions that enable digestion as well as maintaining gut homeostasis through diverse signaling processes including those that arise from interactions with the immune system. Bidirectional communication between enteric neurons and enteric glia has gained increased attention for playing essential roles in enteric nervous system function. Neuronal mediators such as neurotransmitters stimulate enteric glia and subsequent gliotransmission processes refine neuronal signaling during intestinal motor control. In this mini-review, we present and discuss the basis of intercellular signaling between neurons and glia in the enteric nervous system and the relevance of these interactions to gut function.

Global cerebral ischemia followed by long-term reperfusion promotes neurodegeneration, oxidative stress, and inflammation in the small intestine in Wistar rats

AIMS

Brain ischemia and reperfusion may occur in several clinical conditions that have high rates of mortality and disability, compromising an individual's quality of life. Brain injury can affect organs beyond the brain, such as the gastrointestinal tract. The present study investigated the effects of cerebral ischemia on the ileum and jejunum during a chronic reperfusion period by examining oxidative stress, inflammatory parameters, and the myenteric plexus in Wistar rats.

MAIN METHODS

Ischemia was induced by the four-vessel occlusion model for 15 min with 52 days of reperfusion. Oxidative stress and inflammatory markers were evaluated using biochemical techniques. Gastrointestinal transit time was evaluated, and immunofluorescence techniques were used to examine morpho-quantitative aspects of myenteric neurons.

KEY FINDINGS

Brain ischemia and reperfusion promoted inflammation, characterized by increases in myeloperoxidase and N-acetylglycosaminidase activity, oxidative stress, and lipid hydroperoxides, decreases in superoxide dismutase and catalase activity, a decrease in levels of reduced glutathione, neurodegeneration in the gut, and slow gastrointestinal transit.

SIGNIFICANCE

Chronic ischemia and reperfusion promoted a slow gastrointestinal transit time, oxidative stress, and inflammation and neurodegeneration in the small intestine in rats. These findings indicate that the use of antioxidant and antiinflammatory molecules even after a long period of reperfusion may be useful to alleviate the consequences of this pathology.

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.

Role of enteric glia and microbiota-gut-brain axis in parkinson disease pathogenesis

The microbiota-gut-brain axis or simple gut-brain axis (GBA) is a complex and interactive bidirectional communication network linking the gut to the brain. Alterations in the composition of the gut microbiome have been linked to GBA dysfunction, central nervous system (CNS) inflammation, and dopaminergic degeneration, as those occurring in Parkinson's disease (PD). Besides inflammation, the activation of brain microglia is known to play a central role in the damage of dopaminergic neurons. Inflammation is attributed to the toxic effect of aggregated α-synuclein, in the brain of PD patients. It has been suggested that the α-synuclein misfolding might begin in the gut and spread "prion-like", via the vagus nerve into the lower brainstem and ultimately to the midbrain, known as the Braak hypothesis. In this review, we discuss how the microbiota-gut-brain axis and environmental influences interact with the immune system to promote a pro-inflammatory state that is involved in the initiation and progression of misfolded α-synuclein proteins and the beginning of the early non-motor symptoms of PD. Furthermore, we describe a speculative bidirectional model that explains how the enteric glia is involved in the initiation and spreading of inflammation, epithelial barrier disruption, and α-synuclein misfolding, finally reaching the central nervous system and contributing to neuroinflammatory processes involved with the initial non-motor symptoms of PD.

Effect of old age on the subpopulations of enteric glial cells in human descending colon

Old age is associated with a higher incidence of lower bowel conditions such as constipation. Recent evidence suggest that colonic motility may be influenced by enteric glial cells (EGCs). Little is known about the effect of aging on the subpopulation of EGCs in the human colon. We assessed and compared the pattern of distribution of EGCs in adult and elderly human colon. Human descending colon were obtained from 23 cancer patients comprising of adults (23-63 years; 6 male, 7 female) and elderly (66-81 year; 6 male, 4 female). Specimens were serially-sectioned and immunolabeled with anti-Sox-10, anti-S100 and anti-GFAP for morphometric analysis. Standardized procedures were utilized to ensure unbiased counting and densitometric evaluation of EGCs. The number of Sox-10 immunoreactive (IR) EGCs were unaltered with age in both the myenteric plexus (MP) (respectively, in adult and elderly patients, 1939 ± 82 and 1760 ± 44/mm length; p > .05) and submucosal plexus; there were no apparent differences between adult males and females. The density of S100-IR EGCs declined among the elderly in the circular muscle and within the MP per ganglionic area. In the adult colon, there were more S100-IR EGCs distributed in the circular muscle per unit area than the Taenia coli. There was little or no GFAP-IR EGCs in both adult and elderly colon. We concluded that aging of the human descending colon does not result in a loss of Sox-10-IR EGCs in the MP and SMP but reduces S100-IR EGCs density within the musculature. This alteration in myenteric EGCs density with age may contribute to colonic dysfunction.

Vagus Nerve Stimulation: A Personalized Therapeutic Approach for Crohn's and Other Inflammatory Bowel Diseases

Inflammatory bowel diseases, including Crohn's disease and ulcerative colitis, are incurable autoimmune diseases characterized by chronic inflammation of the gastrointestinal tract. There is increasing evidence that inappropriate interaction between the enteric nervous system and central nervous system and/or low activity of the vagus nerve, which connects the enteric and central nervous systems, could play a crucial role in their pathogenesis. Therefore, it has been suggested that appropriate neuroprosthetic stimulation of the vagus nerve could lead to the modulation of the inflammation of the gastrointestinal tract and consequent long-term control of these autoimmune diseases. In the present paper, we provide a comprehensive overview of (1) the cellular and molecular bases of the immune system, (2) the way central and enteric nervous systems interact and contribute to the immune responses, (3) the pathogenesis of the inflammatory bowel disease, and (4) the therapeutic use of vagus nerve stimulation, and in particular, the transcutaneous stimulation of the auricular branch of the vagus nerve. Then, we expose the working hypotheses for the modulation of the molecular processes that are responsible for intestinal inflammation in autoimmune diseases and the way we could develop personalized neuroprosthetic therapeutic devices and procedures in favor of the patients.

Functional Intraregional and Interregional Heterogeneity between Myenteric Glial Cells of the Colon and Duodenum in Mice

Enteric glia are a unique population of peripheral neuroglia that regulate homeostasis in the enteric nervous system (ENS) and intestinal functions. Despite existing in functionally diverse regions of the gastrointestinal tract, enteric glia have been approached scientifically as a homogeneous group of cells. This assumption is at odds with the functional specializations of gastrointestinal organs and recent data suggesting glial heterogeneity in the brain and ENS. Here, we used calcium imaging in transgenic mice of both sexes expressing genetically encoded calcium sensors in enteric glia and conducted contractility studies to investigate functional diversity among myenteric glia in two functionally distinct intestinal organs: the duodenum and the colon. Our data show that myenteric glia exhibit regionally distinct responses to neuromodulators that require intercellular communication with neurons to differing extents in the duodenum and colon. Glia regulate intestinal contractility in a region-specific and pathway-specific manner, which suggests regionally diverse engagement of enteric glia in local motor patterns through discrete signaling pathways. Further, functional response profiles delineate four unique subpopulations among myenteric glia that are differentially distributed between the colon and duodenum. Our findings support the conclusion that myenteric glia exhibit both intraregional and interregional heterogeneity that contributes to region-specific mechanisms that regulate digestive functions. Glial heterogeneity adds an unexpected layer of complexity in peripheral neurocircuits, and understanding the specific functions of specialized glial subtypes will provide new insight into ENS physiology and pathophysiology.SIGNIFICANCE STATEMENT Enteric glia modulate gastrointestinal functions through intercellular communication with enteric neurons. Whether heterogeneity exists among neuron-glia interactions in the digestive tract is not understood. Here, we show that myenteric glia display regional heterogeneity in their responses to neuromodulators in the duodenum and the colon, which are functionally distinct organs. Glial-mediated control of intestinal motility is region and pathway specific. Four myenteric glial subtypes are present within a given gut region that are differently distributed between gut regions. These data provide functional and regional insights into enteric circuit specificity in the adult enteric nervous system.

P2X7 receptor blockade decreases inflammation, apoptosis, and enteric neuron loss during Clostridioides difficile toxin A-induced ileitis in mice

BACKGROUND

Clostridioides difficile (C. difficile) is the most common pathogen causing health care-associated infections. C. difficile TcdA and TcdB have been shown to activate enteric neurons; however, what population of these cells is more profoundly influenced and the mechanism underlying these effects remain unknown.

AIM

To characterize a specific population of TcdA-affected myenteric neurons and investigate the role of the P2X7 receptor in TcdA-induced ileal inflammation, cell death, and the changes in the enteric nervous system in mice.

METHODS

Swiss mice were used to model TcdA-induced ileitis in ileal loops exposed to TcdA (50 μg/Loop) for 4 h. To investigate the role of the P2X7 receptor, Brilliant Blue G (50 mg/kg, i.p.), which is a nonspecific P2X7 receptor antagonist, or A438079 (0.7 μg/mouse, i.p.), which is a competitive P2X7 receptor antagonist, were injected one hour prior to TcdA challenge. Ileal samples were collected to analyze the expression of the P2X7 receptor (by quantitative real-time polymerase chain reaction and immunohistochemistry), the population of myenteric enteric neurons (immunofluorescence), histological damage, intestinal inflammation, cell death (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling), neuronal loss, and S100B synthesis (immunohistochemistry).

RESULTS

TcdA upregulated (P < 0.05) the expression of the P2X7 receptor gene in the ileal tissues, increasing the level of this receptor in myenteric neurons compared to that in control mice. Comparison with the control mice indicated that TcdA promoted (P < 0.05) the loss of myenteric calretinin+ (Calr) and choline acetyltransferase+ neurons and increased the number of nitrergic+ and Calr+ neurons expressing the P2X7 receptor. Blockade of the P2X7 receptor decreased TcdA-induced intestinal damage, cytokine release [interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor-α], cell death, enteric neuron loss, and S100B synthesis in the mouse ileum.

CONCLUSION

Our findings demonstrated that TcdA induced the upregulation of the P2X7 receptor, which promoted enteric neuron loss, S100B synthesis, tissue damage, inflammation, and cell death in the mouse ileum. These findings contribute to the future directions in understanding the mechanism involved in intestinal dysfunction reported in patients after C. difficile infection.

5/6 nephrectomy affects enteric glial cells and promotes impaired antioxidant defense in the colonic neuromuscular layer

AIMS

Chronic kidney disease (CKD) produces multiple repercussions in the gastrointestinal tract (GIT), such as alterations in motility, gut microbiota, intestinal permeability, and increased oxidative stress. However, despite enteric glial cells (EGC) having important neural and immune features in GIT physiology, their function in CKD remains unknown. The present study investigates colonic glial markers, inflammation, and antioxidant parameters in a CKD model.

MAIN METHODS

A 5/6 nephrectomized rat model was used to induce CKD in rats and Sham-operated animals as a control to suppress. Biochemical measures in plasma and neuromuscular layer such as glutathione peroxidase (GPx) and superoxide dismutase (SOD) activity were carried out. Kidney histopathology was evaluated. Colon morphology analysis and glial fibrillary acid protein (GFAP), connexin-43 (Cx43), nuclear factor-kappa B (NF-κB) p65, and GPx protein expression were performed.

KEY FINDINGS

The CKD group exhibited dilated tubules and tubulointerstitial fibrosis in the reminiscent kidney (p = 0.0002). CKD rats showed higher SOD activity (p = 0.004) in plasma, with no differences in neuromuscular layer (p = 0.9833). However, GPx activity was decreased in the CKD group in plasma (p = 0.013) and neuromuscular layer (p = 0.0338). Morphological analysis revealed alterations in colonic morphometry with inflammatory foci in the submucosal layer and neuromuscular layer straightness in CKD rats (p = 0.0291). In addition, GFAP, Cx43, NF-κBp65 protein expression were increased, and GPx decreased in the neuromuscular layer of the CKD group (p < 0.05).

SIGNIFICANCE

CKD animals present alterations in colonic cytoarchitecture and decreased layer thickness. Moreover, CKD affects the enteric glial network of the neuromuscular layer, associated with decreased antioxidant activity and inflammation.

Brazil Nut (Bertholletia excelsa H.B.K) Retards Gastric Emptying and Modulates Enteric Glial Cells in a Dose-Dependent Manner

BACKGROUND

The role of food and nutrients in the regulation of enteric glial cell functions is unclear. Some foods influence enteric neurophysiology and can affect glial cell functions that include regulation of the intestinal barrier, gastric emptying, and colonic transit. Brazil nuts are the most abundant natural source of selenium, unsaturated fatty acids, fibers, and polyphenols.

OBJECTIVE

The study investigated the effects of a Brazil nut-enriched diet on enteric glial cells and gastrointestinal transit.

METHODS

Two-month-old male Wistar rats were randomized to a standard diet (control group, CG), standard diet containing 5% (wt/wt) Brazil nut (BN5), and standard diet containing 10% (wt/wt) Brazil nut (BN10) (n = 9 per group). After eight weeks, the animals underwent constipation and gastric emptying tests to assess motility. Evaluations of colonic immunofluorescence staining for glial fibrillary acidic protein (GFAP) and myenteric ganglia area were performed.

RESULTS

The BN5 group showed increased weight gain while the BN10 group did not (p < 0.0001). The BN10 group showed higher gastric residue amounts compared to the other groups (p = 0.0008). The colon exhibited an increase in GFAP immunoreactivity in the BN5 group compared to that in the other groups (p = 0.0016), and the BN10 group presented minor immunoreactivity compared to the CG (p = 0.04). The BN10 group presented a minor ganglia area compared to the CG (p = 0.0155).

CONCLUSION

The Brazil nut-enriched diet modified the gastric residual, colonic GFAP immunoreactivity, and myenteric ganglia area after eight weeks in healthy male Wistar rats.

Enteric neuroimmune interactions coordinate intestinal responses in health and disease

The enteric nervous system (ENS) of the gastrointestinal (GI) tract interacts with the local immune system bidirectionally. Recent publications have demonstrated that such interactions can maintain normal GI functions during homeostasis and contribute to pathological symptoms during infection and inflammation. Infection can also induce long-term changes of the ENS resulting in the development of post-infectious GI disturbances. In this review, we discuss how the ENS can regulate and be regulated by immune responses and how such interactions control whole tissue physiology. We also address the requirements for the proper regeneration of the ENS and restoration of GI function following the resolution of infection.

Altered interaction between enteric glial cells and mast cells in the colon of women with irritable bowel syndrome

BACKGROUND

Enteric glial cells (EGC) and mast cells (MC) are intimately associated with gastrointestinal physiological functions. We aimed to investigate EGC-MC interaction in irritable bowel syndrome (IBS), a gut-brain disorder linked to increased intestinal permeability, and MC.

METHODS

Parallel approaches were used to quantify EGC markers in colonic biopsies from healthy controls (HC) and patients with IBS. Data were correlated with MC, vasoactive intestinal polypeptide (VIP) and VIP receptors (VPAC1/VPAC2) expressions, and bacterial translocation through biopsies mounted in Ussing chambers. In addition, we investigated the effects of EGC mediators on colonic permeability and the pharmacological-induced responses of EGC and MC cell lines.

KEY RESULTS

Immunofluorescence of IBS colonic mucosa, as well as Western blotting and ELISA of IBS biopsy lysates, revealed increased glial fibrillary intermediate filament (GFAP) expression, indicating EGC activation. Mucosal GFAP correlated with increased MC and VPAC1⁺ MC numbers and decreased VIP⁺ MC, which seemed to control bacterial translocation in HC. In the contrary, EGC activation in IBS correlated with less MC and VPAC1⁺ MC numbers, and more VIP⁺ MC. In vitro, MC and EGC cell lines showed intracellular calcium responses to each other's mediators. Furthermore, EGC mediators prevented VIP-induced MC degranulation, while MC mediators induced a reactive EGC phenotype. In Ussing chambers, EGC mediators decreased paracellular passage through healthy colonic biopsies.

CONCLUSIONS & INFERENCES

Findings suggest the involvement of EGC and MC in the control of barrier function in the human colon and indicate a potential EGC-MC interaction that seems altered in IBS, with detrimental consequences to colonic permeability. Altogether, results suggest that imbalanced EGC-MC communication contributes to the pathophysiology of IBS.

S100B Inhibition Attenuates Intestinal Damage and Diarrhea Severity During Clostridioides difficile Infection by Modulating Inflammatory Response

The involvement of the enteric nervous system, which is a source of S100B, in Clostridioides difficile (C. difficile) infection (CDI) is poorly understood although intestinal motility dysfunctions are known to occur following infection. Here, we investigated the role of S100B in CDI and examined the S100B signaling pathways activated in C. difficile toxin A (TcdA)- and B (TcdB)-induced enteric glial cell (EGC) inflammatory response. The expression of S100B was measured in colon tissues and fecal samples of patients with and without CDI, as well as in colon tissues from C. difficile-infected mice. To investigate the role of S100B signaling in IL-6 expression induced by TcdA and TcdB, rat EGCs were used. Increased S100B was found in colonic biopsies from patients with CDI and colon tissues from C. difficile-infected mice. Patients with CDI-promoted diarrhea exhibited higher levels of fecal S100B compared to non-CDI cases. Inhibition of S100B by pentamidine reduced the synthesis of IL-1β, IL-18, IL-6, GMCSF, TNF-α, IL-17, IL-23, and IL-2 and downregulated a variety of NFκB-related genes, increased the transcription (SOCS2 and Bcl-2) of protective mediators, reduced neutrophil recruitment, and ameliorated intestinal damage and diarrhea severity in mice. In EGCs, TcdA and TcdB upregulated S100B-mediated IL-6 expression via activation of RAGE/PI3K/NFκB. Thus, CDI appears to upregulate colonic S100B signaling in EGCs, which in turn augment inflammatory response. Inhibition of S100B activity attenuates the intestinal injury and diarrhea caused by C. difficile toxins. Our findings provide new insight into the role of S100B in CDI pathogenesis and opens novel avenues for therapeutic interventions.

Nitric Oxide: From Gastric Motility to Gastric Dysmotility

It is known that nitric oxide (NO) plays a key physiological role in the control of gastrointestinal (GI) motor phenomena. In this respect, NO is considered as the main non-adrenergic, non-cholinergic (NANC) inhibitory neurotransmitter responsible for smooth muscle relaxation. Moreover, many substances (including hormones) have been reported to modulate NO production leading to changes in motor responses, further underlying the importance of this molecule in the control of GI motility. An impaired NO production/release has indeed been reported to be implicated in some GI dysmotility. In this article we wanted to focus on the influence of NO on gastric motility by summarizing knowledge regarding its role in both physiological and pathological conditions. The main role of NO on regulating gastric smooth muscle motor responses, with particular reference to NO synthases expression and signaling pathways, is discussed. A deeper knowledge of nitrergic mechanisms is important for a better understanding of their involvement in gastric pathophysiological conditions of hypo- or hyper-motility states and for future therapeutic approaches. A possible role of substances which, by interfering with NO production, could prove useful in managing such motor disorders has been advanced.

The intestinal luminal sources of α-synuclein: a gastroenterologist perspective

Parkinson's disease is characterized by nonmotor/motor dysfunction, midbrain dopaminergic neuronal death, and α-synuclein (aSN) deposits. The current hypothesis is that aSN accumulates in the enteric nervous system to reach the brain. However, invertebrate, vertebrate, and nutritional sources of aSN reach the luminal compartment. Submitted to local amyloidogenic forces, the oligomerized proteins' cargo can be sensed and sampled by a specialized mucosal cell to be transmitted to the adjacent enteric nervous system, starting their upward journey to the brain. The present narrative review extends the current mucosal origin of Parkinson's disease, presenting the possibility that the disease starts in the intestinal lumen. If substantiated, eliminating the nutritional sources of aSN (eg, applying a vegetarian diet) might revolutionize the currently used dopaminergic pharmacologic therapy.

Zebrafish: A Model Organism for Studying Enteric Nervous System Development and Disease

The Enteric Nervous System (ENS) is a large network of enteric neurons and glia that regulates various processes in the gastrointestinal tract including motility, local blood flow, mucosal transport and secretion. The ENS is derived from stem cells coming from the neural crest that migrate into and along the primitive gut. Defects in ENS establishment cause enteric neuropathies, including Hirschsprung disease (HSCR), which is characterized by an absence of enteric neural crest cells in the distal part of the colon. In this review, we discuss the use of zebrafish as a model organism to study the development of the ENS. The accessibility of the rapidly developing gut in zebrafish embryos and larvae, enables in vivo visualization of ENS development, peristalsis and gut transit. These properties make the zebrafish a highly suitable model to bring new insights into ENS development, as well as in HSCR pathogenesis. Zebrafish have already proven fruitful in studying ENS functionality and in the validation of novel HSCR risk genes. With the rapid advancements in gene editing techniques and their unique properties, research using zebrafish as a disease model, will further increase our understanding on the genetics underlying HSCR, as well as possible treatment options for this disease.

Neuroglia in Psychiatric Disorders

In the twentieth century, neuropsychiatric disorders have been perceived solely from a neurone-centric point of view, which considers neurones as the key cellular elements of pathological processes. This dogma has been challenged thanks to the better comprehension of the brain functioning, which, even if far from being complete, has revealed the complexity of interactions that exist between neurones and neuroglia. Glial cells represent a highly heterogeneous population of cells of neural (astroglia and oligodendroglia) and non-neural (microglia) origin populating the central nervous system. The variety of glia reflects the innumerable functions that glial cells perform to support functions of the nervous system. Aberrant execution of glial functions contributes to the development of neuropsychiatric pathologies. Arguably, all types of glial cells are implicated in the neuropathology; however, astrocytes have received particular attention in recent years because of their pleiotropic functions that make them decisive in maintaining cerebral homeostasis. This chapter describes the multiple roles of astrocytes in the healthy central nervous system and discusses the diversity of astroglial responses in neuropsychiatric disorders suggesting that targeting astrocytes may represent an effective therapeutic strategy.

Neuromechanism of acupuncture regulating gastrointestinal motility

Acupuncture has been used in China for thousands of years and has become more widely accepted by doctors and patients around the world. A large number of clinical studies and animal experiments have confirmed that acupuncture has a benign adjustment effect on gastrointestinal (GI) movement; however, the mechanism of this effect is unclear, especially in terms of neural mechanisms, and there are still many areas that require further exploration. This article reviews the recent data on the neural mechanism of acupuncture on GI movements. We summarize the neural mechanism of acupuncture on GI movement from four aspects: acupuncture signal transmission, the sympathetic and parasympathetic nervous system, the enteric nervous system, and the central nervous system.

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

The role played by adenosine A_2B receptors (A_2BRs) in the regulation of enteric glial cell (EGC) functions remains unclear. This study was aimed at investigating the involvement of A_2BRs in the control of EGC functions in a model of obesity. C57BL/6 mice were fed with standard diet (SD) or high fat diet (HFD) for eight weeks. Colonic tachykininergic contractions were recorded in the presence of BAY60-6583 (A_2BRs agonist), MRS1754 (A_2BRs antagonist), and the gliotoxin fluorocitrate. Immunofluorescence distribution of HuC/D, S100β, and A_2BRs was assessed in whole mount preparations of colonic myenteric plexus. To mimic HFD, EGCs were incubated in vitro with palmitate (PA) and lipopolysaccharide (LPS), in the absence or in the presence of A_2BR ligands. Toll-like receptor 4 (TLR4) expression was assessed by Western blot analysis. Interleukin-1β (IL-1β), substance P (SP), and glial cell derived neurotrophic factor (GDNF) release were determined by enzyme-linked immunosorbent assay (ELISA) assays. MRS1754 enhanced electrically evoked tachykininergic contractions of colonic preparations from HFD mice. BAY60-6583 decreased the evoked tachykininergic contractions, with higher efficacy in HFD mice. Such effects were blunted upon incubation with fluorocitrate. In in vitro experiments on EGCs, PA and LPS increased TLR4 expression as well as IL-1β, GDNF, and SP release. Incubation with BAY60-6583 reduced TLR4 expression as well as IL-1β, GDNF, and SP release. Such effects were blunted by MRS1754. The present results suggest that A_2BRs, expressed on EGCs, participate in the modulation of enteric inflammation and altered tachykininergic responses associated with obesity, thus representing a potential therapeutic target.

Glial mitochondrial function and dysfunction in health and neurodegeneration

Mitochondria play essential metabolic roles in neural cells. Mitochondrial dysfunction has profound effects on the brain. In primary mitochondrial diseases, mutations that impair specific oxidative phosphorylation (OXPHOS) proteins or OXPHOS assembly factors lead to isolated biochemical defects and a heterogeneous group of clinical phenotypes, including mitochondrial encephalopathies. A broader defect of OXPHOS function, due to mutations in proteins involved in mitochondrial DNA maintenance, mitochondrial biogenesis, or mitochondrial tRNAs can also underlie severe mitochondrial encephalopathies. While primary mitochondrial dysfunction causes rare genetic forms of neurological disorders, secondary mitochondrial dysfunction is involved in the pathophysiology of some of the most common neurodegenerative disorders, including Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis. Many studies have investigated mitochondrial function and dysfunction in bulk central nervous system (CNS) tissue. However, the interpretation of these studies has been often complicated by the extreme cellular heterogeneity of the CNS, which includes many different types of neurons and glial cells. Because neurons are especially dependent on OXPHOS for ATP generation, mitochondrial dysfunction is thought to be directly involved in cell autonomous neuronal demise. Despite being metabolically more flexible than neurons, glial mitochondria also play an essential role in the function of the CNS, and have adapted specific metabolic and mitochondrial features to support their diversity of functions. This review analyzes our current understanding and the gaps in knowledge of mitochondrial properties of glia and how they affect neuronal functions, in health and disease.

Dysbiosis-Associated Enteric Glial Cell Immune-Activation and Redox Imbalance Modulate Tight Junction Protein Expression in Gulf War Illness Pathology

About 14% of veterans who suffer from Gulf war illness (GWI) complain of some form of gastrointestinal disorder but with no significant markers of clinical pathology. Our previous studies have shown that exposure to GW chemicals resulted in altered microbiome which was associated with damage associated molecular pattern (DAMP) release followed by neuro and gastrointestinal inflammation with loss of gut barrier integrity. Enteric glial cells (EGC) are emerging as important regulators of the gastrointestinal tract and have been observed to change to a reactive phenotype in several functional gastrointestinal disorders such as IBS and IBD. This study is aimed at investigating the role of dysbiosis associated EGC immune-activation and redox instability in contributing to observed gastrointestinal barrier integrity loss in GWI via altered tight junction protein expression. Using a mouse model of GWI and in vitro studies with cultured EGC and use of antibiotics to ensure gut decontamination we show that exposure to GW chemicals caused dysbiosis associated change in EGCs. EGCs changed to a reactive phenotype characterized by activation of TLR4-S100β/RAGE-iNOS pathway causing release of nitric oxide and activation of NOX2 since gut sterility with antibiotics prevented this change. The resulting peroxynitrite generation led to increased oxidative stress that triggered inflammation as shown by increased NLRP-3 inflammasome activation and increased cell death. Activated EGCs in vivo and in vitro were associated with decrease in tight junction protein occludin and selective water channel aquaporin-3 with a concomitant increase in Claudin-2. The tight junction protein levels were restored following a parallel treatment of GWI mice with a TLR4 inhibitor SsnB and butyric acid that are known to decrease the immunoactivation of EGCs. Our study demonstrates that immune-redox mechanisms in EGC are important players in the pathology in GWI and may be possible therapeutic targets for improving outcomes in GWI symptom persistence.

Regulation of intestinal epithelial barrier by and dysfunction of intestinal glial cells

The enteric glia is an important component of the enteric nervous system and forms a broad network in the mucosa of the gastrointestinal tract. Enteric glial cells (EGC) are located in all layers of the intestinal wall and respond to neurotransmitters and neuromodulators through signal transduction pathways. The enteric nervous system interacts with resident glial cells in the gut, and there is increasing evidence that EGC are involved in the regulation of epithelial function. Epithelial cells have important absorption and secretion functions and are also involved in the formation of intestinal epithelial barrier. Studies have found that the enteric glia is not only involved in the regulation of gastrointestinal motility and epithelial barrier function, but also in the formation of cellular molecular bridges between intestinal neurons, enteroendocrine cells, immune cells, and epithelial cells. This article reviews the recent progress in the understanding of the role of EGC in the intestinal barrier and defense functions.

Calcineurin B1 Deficiency in Glial Cells Reduces Gastrointestinal Motility and Results in Maldigestion and/or Malabsorption in Mice

Calcineurin is a Ca²⁺/calmodulin-dependent protein phosphatase abundantly expressed in the nervous system. To investigate the roles of calcineurin in glial cells, we previously generated glial calcineurin B1-conditional knockout (CKO) mice and found that these mice displayed dysfunction of enteric glial cells, mucosal degeneration and inflammation in the small intestine, and growth retardation and postweaning death, suggesting a novel role of calcineurin in enteric glial cells. Although these findings raised a possibility that abnormalities in calcineurin B1-deficient enteric glial cells may cause dysregulation of gastrointestinal motility and result in maldigestion and/or malabsorption in the CKO mice, these issues remain to be elucidated. In the present study, we showed that gastrointestinal motility was reduced in the CKO mice. Degeneration of mucosal epithelium was observed in the small intestine. Glucose levels were decreased in serum, whereas starch, glucose, and lipid levels were increased in feces. Thus, calcineurin B1 deficiency in glial cells reduces gastrointestinal motility, induces mucosal epithelium degeneration in the small intestine, and results in maldigestion and/or malabsorption in mice, further supporting the important role of calcineurin in enteric glial cells.

Enteric Glia: S100, GFAP, and Beyond

Since several years, the enteric nervous system (ENS) is getting more and more in the focus of gastrointestinal research. While the main interest was credited for years to the enteric neurons and their functional properties, less attention has been paid on the enteric glial cells (EGCs). Although the similarity of EGCs to central nervous system (CNS) astrocytes has been demonstrated a long time ago, EGCs were investigated in more detail only recently. Similar to the CNS, there is not "the" EGC, but also a broad range of diversity. Based on morphology and protein expression, such as glial fibrillary acidic protein (GFAP), S100, or Proteolipid-protein-1 (PLP1), several distinct glial types can be differentiated. Their heterogeneity in morphology, localization, and transcription as well as interaction with surrounding cells indicate versatile functional properties of these cells for gut function in health and disease. Although NG2 is found in a subset of CNS glial cells, it did not colocalize with the glial marker S100 or GFAP in the ENS. Instead, it in part colocalize with PDGFRα, as it does in the CNS, which do stain fibroblast-like cells in the gastrointestinal tract. Moreover, there seem to be species dependent differences. While GFAP is always found in the rodent ENS, this is completely different for the human gut. Only the compromised human ENS shows a significant amount of GFAP-positive glial cells. So, in general we can conclude that the EGC population is species specific and as complex as CNS glia. Anat Rec, 302:1333-1344, 2019. © 2019 Wiley Periodicals, Inc.

Identification of neuropeptide y in superior cervical ganglion neurons that project to the oesophagus - A combined immunohistochemical labelling and retrograde tracing study in pigs

Neuropeptide Y (NPY) is a neuronal active substance taking part in the regulation of gastrointestinal (GI) tract activity. This study used retrograde neuronal tracing and immunofluorescence methods to analyse NPY-positive neurons located in superior cervical ganglion and supplying the cervical oesophagus in the pig. The presence of NPY was observed in 30% of all neurons supplying the part of oesophagus studied. Probably the number of Fast Blue (FB) positive cells depends on the area of the wall injected with FB and the fragment of oesophagus studied. Therefore, the obtained results indicate that the described peptide is an important factor in the extrinsic innervation of this part of the GI tract.

Acute Toxoplasma gondii infection alters the number of neurons and the proportion of enteric glial cells in the duodenum in Wistar rats

BACKGROUND

Toxoplasma gondii infection can occur through the ingestion of raw meat that contains tissue cysts or food that contains oocysts. Through the ingestion of oocysts, the parasite crosses the intestinal barrier, where the enteric nervous system is located. The objective was to investigate the kinetics of neuronal and glial responses during acute T. gondii infection.

METHODS

We used 45 Wistar rats that were divided into a control group and infected groups that were evaluated at 6, 12, 24, 48, 72 hours, 7 days, 10 days, and 15 days after infection. The rats received 5000 sporulated oocysts of the parasite orally. To detect neurons and enteric glia cells, the myenteric and submucosal plexuses of the duodenum underwent double-labeling immunohistochemical techniques to evaluate HuC/HuD and S100, HuC/HuD and ChAT, and HuC/HuD and nNOS.

KEY RESULTS

We observed a reduction of the total neuron population in the submucosal plexus 72 hours after infection. Cholinergic neurons decreased in the submucosal plexus 15 days after infection, and nitrergic neurons decreased in the myenteric plexus 72 hours after infection. A decrease in the number of glial cells was observed 7 days after infection in the submucosal plexus, and an increase in the enteric glial cell (EGC)/neuron ratio was found in both plexuses 48 hours after infection.

CONCLUSIONS AND INFERENCES

We found decrease of neurons and increase in the EGC/neuron ratio in both plexuses caused by acute T. gondii infection, with major alterations 72 hours after oral infection. The number of cholinergic neurons decreased in the submucosal plexus, and the number of nitrergic neurons decreased in the myenteric plexus. A decrease in the number of enteric glial cells was observed in the submucosal plexus, and an increase in the enteric glial cell/neuron ratio was observed in both ganglionate plexuses of the duodenum.

The Concept of Neuroglia

Neuroglia represent a diverse population of non-neuronal cells in the nervous systems, be that peripheral, central, enteric or autonomic nervous system. Arguably, these cells represent about half of the volume of the human brain. This volumetric ratio, and by extension glia to neurone ratio, not only widely differ depending on the size of the animal species brain and its positioning on the phylogenetic tree, but also vary between the regions of an individual brain. Neuroglia derived from a dual origin (ectoderm and mesodermal) and in an assorted morphology, yet their functional traits can be mainly classified into being keepers of homeostasis (water, ions, neurotransmitters, metabolites, fuels, etc.) and defenders (e.g., against microbial organisms, etc.) of the nervous system. As these capabilities go awry, neuroglia ultimately define their fundamental role in most, if not, all neuropathologies. This concept presented in this chapter serves as a general introduction into the world of neuroglia and subsequent topics covered by this book.

Neuro-immune regulation of mucosal physiology

Mucosal barriers constitute major body surfaces that are in constant contact with the external environment. Mucosal sites are densely populated by a myriad of distinct neurons and immune cell types that sense, integrate and respond to multiple environmental cues. In the recent past, neuro-immune interactions have been reported to play central roles in mucosal health and disease, including chronic inflammatory conditions, allergy and infectious diseases. Discrete neuro-immune cell units act as building blocks of this bidirectional multi-tissue cross-talk, ensuring mucosal tissue health and integrity. Herein, we will focus on reciprocal neuro-immune interactions in the airways and intestine. Such neuro-immune cross-talk maximizes sensing and integration of environmental aggressions, which can be considered an important paradigm shift in our current views of mucosal physiology and immune regulation.

Enteric glia: Diversity or plasticity?

Glial cells of the enteric nervous system correspond to a unique glial lineage distinct from other central and peripheral glia, and form a vast and abundant network spreading throughout all the layers of the gastrointestinal wall. Research over the last two decades has demonstrated that enteric glia regulates all major gastrointestinal functions via multiple bi-directional crosstalk with enteric neurons and other neighboring cell types. Recent studies propose that enteric glia represents a heterogeneous population associated with distinct localization within the gut wall, phenotype and activity. Compelling evidence also indicates that enteric glial cells are capable of plasticity leading to phenotypic changes whose pinnacle so far has been shown to be the generation of enteric neurons. While alterations of the glial network have been heavily incriminated in the development of gastrointestinal pathologies, enteric glial cells have also recently emerged as an active player in gut-brain signaling. Therefore, the development of tools and techniques to better appraise enteric glia heterogeneity and plasticity will undoubtedly unveil critical regulatory mechanisms implicated in gut health and disease, as well as disorders of the gut-brain axis.

Clostridium difficile-related postinfectious IBS: a case of enteroglial microbiological stalking and/or the solution of a conundrum?

Post-infectious irritable bowel syndrome is a well-defined pathological entity that develops in about one-third of subjects after an acute infection (bacterial, viral) or parasitic infestation. Only recently it has been documented that an high incidence of post-infectious irritable bowel syndrome occurs after Clostridium difficile infection. However, until now it is not known why in some patients recovered from this infection the gastrointestinal disturbances persist for months or years. Based on our in vitro studies on enteric glial cells exposed to the effects of C. difficile toxin B, we hypothesize that persistence of symptoms up to the development of irritable bowel syndrome might be due to a disturbance/impairment of the correct functions of the enteroglial intestinal network.

Interaction of Human Enterochromaffin Cells with Human Enteric Adenovirus 41 Leads to Serotonin Release and Subsequent Activation of Enteric Glia Cells

Human adenovirus 41 (HAdV-41) causes acute gastroenteritis in young children. The main characteristics of HAdV-41 infection are diarrhea and vomiting. Nevertheless, the precise mechanism of HAdV-41-induced diarrhea is unknown, as a suitable small-animal model has not been described. In this study, we used the human midgut carcinoid cell line GOT1 to investigate the effect of HAdV-41 infection and the individual HAdV-41 capsid proteins on serotonin release by enterochromaffin cells and on enteric glia cell (EGC) activation. We first determined that HAdV-41 could infect the enterochromaffin cells. Immunofluorescence staining revealed that the cells expressed HAdV-41-specific coxsackievirus and adenovirus receptor (CAR); flow cytometry analysis supported these findings. HAdV-41 infection of the enterochromaffin cells induced serotonin secretion dose dependently. In contrast, control infection with HAdV-5 did not induce serotonin secretion in the cells. Confocal microscopy studies of enterochromaffin cells infected with HAdV-41 revealed decreased serotonin immunofluorescence compared to that in uninfected cells. Incubation of the enterochromaffin cells with purified HAdV-41 short fiber knob and hexon proteins increased the serotonin levels in the harvested cell supernatant significantly. HAdV-41 infection could also activate EGCs, as shown in the significantly altered expression of glia fibrillary acidic protein (GFAP) in EGCs incubated with HAdV-41. The EGCs were also activated by serotonin alone, as shown in the significantly increased GFAP staining intensity. Likewise, EGCs were activated by the cell supernatant of HAdV-41-infected enterochromaffin cells.IMPORTANCE The nonenveloped human adenovirus 41 causes diarrhea, vomiting, dehydration, and low-grade fever mainly in children under 2 years of age. Even though acute gastroenteritis is well described, how human adenovirus 41 causes diarrhea is unknown. In our study, we analyzed the effect of human adenovirus 41 infection on human enterochromaffin cells and found it stimulates serotonin secretion in the cells, which is involved in regulation of intestinal secretion and gut motility and can also activate enteric glia cells, which are found in close proximity to enterochromaffin cells in vivo This disruption of gut barrier homeostasis as maintained by these cells following human adenovirus 41 infection might be a mechanism in enteric adenovirus pathogenesis in humans and could indicate a possible serotonin-dependent cross talk between human adenovirus 41, enterochromaffin cells, and enteric glia cells.

The Gut Microbiome Feelings of the Brain: A Perspective for Non-Microbiologists

Objectives: To comprehensively review the scientific knowledge on the gut-brain axis. Methods: Various publications on the gut-brain axis, until 31 July 2017, were screened using the Medline, Google, and Cochrane Library databases. The search was performed using the following keywords: "gut-brain axis", "gut-microbiota-brain axis", "nutrition microbiome/microbiota", "enteric nervous system", "enteric glial cells/network", "gut-brain pathways", "microbiome immune system", "microbiome neuroendocrine system" and "intestinal/gut/enteric neuropeptides". Relevant articles were selected and reviewed. Results: Tremendous progress has been made in exploring the interactions between nutrients, the microbiome, and the intestinal, epithelium-enteric nervous, endocrine and immune systems and the brain. The basis of the gut-brain axis comprises of an array of multichannel sensing and trafficking pathways that are suggested to convey the enteric signals to the brain. These are mediated by neuroanatomy (represented by the vagal and spinal afferent neurons), the neuroendocrine-hypothalamic-pituitary-adrenal (HPA) axis (represented by the gut hormones), immune routes (represented by multiple cytokines), microbially-derived neurotransmitters, and finally the gate keepers of the intestinal and brain barriers. Their mutual and harmonious but intricate interaction is essential for human life and brain performance. However, a failure in the interaction leads to a number of inflammatory-, autoimmune-, neurodegenerative-, metabolic-, mood-, behavioral-, cognitive-, autism-spectrum-, stress- and pain-related disorders. The limited availability of information on the mechanisms, pathways and cause-and-effect relationships hinders us from translating and implementing the knowledge from the bench to the clinic. Implications: Further understanding of this intricate field might potentially shed light on novel preventive and therapeutic strategies to combat these disorders. Nutritional approaches, microbiome manipulations, enteric and brain barrier reinforcement and sensing and trafficking modulation might improve physical and mental health outcomes.

Combining thioridazine and loratadine for the treatment of gastrointestinal tumor

In 2015, the American Society of Clinical Oncology announced that strategies of using combination therapies have been indicated to be effective against many types of cancer. In the present study, thioridazine (THZ) was used in a combination therapy with loratadine (LOR) to target gastrointestinal tumor, with the aim of investigating whether combined therapy was superior to monotherapy in its antitumor effects. The antiproliferative effects on CT26.WT and MFC cells were analyzed using cell-counting kit-8 assay, and synergistic effect was assessed by combination index (Fig. 1). Annexin V and propidium iodide staining indicated the combination therapy was able to induce apoptosis and that this may be mediated via caspase-3, -9 and poly (ADP-ribose) polymerase (PARP) (Fig. 2). Antitumor activity was also evaluated in CT26.WT xenografts in BALB/c mice (Fig. 3). Furthermore, as expected, combination therapy was able to successfully inhibit the phosphoinositide 3-kinase/Akt/mammalian target of rapamycin signaling pathway (Fig. 4). These findings suggest that the combination therapy with THZ and LOR may provide a promising therapy for gastrointestinal cancer.