Intestinal Epithelial Barrier Maturation by Enteric Glial Cells Is GDNF-Dependent

Anti-inflammatory and glial response maintain normal colon function in trimethyltin-treated rats

Studies on the contribution of enteric neuropathy and intestinal homeostasis to central nervous system degeneration using animal models have reported varying results. Recently, colonic myenteric plexus degeneration was observed in trimethyltin-treated rats. Further characterization of this animal model is necessary to determine its potential for investigating the relationship between the enteric nervous system and central nervous system degeneration. In this study, trimethyltin-treated rats (8 mg/kg body weight, i.p.) were used to measure colonic function, structure, and possible colon abnormalities. The colonic function was assessed by measuring fecal pellet output and transit time. Hematoxylin and eosin staining and immunohistochemistry were performed to evaluate inflammatory profiles and intestinal epithelial cell homeostasis. The expression of mRNA encoding tight junction proteins was quantified with quantitative PCR to determine colon permeability. Histological examination of the colon revealed mucosal immune cell infiltration, crypt damage, and high iNOS and arginase-1 expression in the mucosal layer of trimethyltin-treated rats. At the same time, trimethyltin induced high expression of iNOS, arginase-1, and GFAP and increased cell death in the colonic myenteric plexus. The low cell proliferation and low goblet cell distribution suggested altered intestinal epithelial cell homeostasis in trimethyltin-treated rats. Trimethyltin also upregulated claudin 1 expression. However, normal colon function was preserved. In conclusion, the results show that trimethyltin induces colon inflammation and cell death in the colonic myenteric plexus, and disrupts intestinal epithelial cell homeostasis. However, the balance between anti-inflammatory and pro-inflammatory responses maintains normal colon function in trimethyltin-treated rats.

The role of enteric nervous system and GDNF in depression: Conversation between the brain and the gut

Depression is a debilitating mental disorder that causes a persistent feeling of sadness and loss of interest. Approximately 280 million individuals worldwide suffer from depression by 2023. Despite the heavy medical and social burden imposed by depression, pathophysiology remains incompletely understood. Emerging evidence indicates various bidirectional interplay enable communication between the gut and brain. These interplays provide a link between intestinal and central nervous system as well as feedback from cortical and sensory centers to enteric activities, which also influences physiology and behavior in depression. This review aims to overview the significant role of the enteric nervous system (ENS) in the pathophysiology of depression and gut-brain axis's contribution to depressive disorders. Additionally, we explore the alterations in enteric glia cells (EGCs) and glial cell line-derived neurotrophic factor (GDNF) in depression and their involvement in neuronal support, intestinal homeostasis maintains and immune response activation. Modulating ENS function, EGCs and GDNF level could serve as novel strategies for future antidepressant therapy.

Multi-platform analysis revealed the substance basis and mechanism of Wei-Tong-Xin in ameliorating ENS dysfunction for dyspepsia treatment

ETHNOPHARMACOLOGICAL RELEVANCE

Duodenal motility disorder is a contributing factor to dyspepsia. The traditional Chinese medicine (TCM) formula Wei-Tong-Xin (WTX), originated from the famous ancient Chinese formula "Wan Ying Yuan", has been demonstrated efficacy in alleviating dyspepsia.

AIM OF THE STUDY

The current study aims to elucidate the chemical composition of WTX to establish the pharmacodynamic material basis. On the basis of component, in depth to illuminate the mechanism by which WTX treats dyspepsia via constructing the comprehensive analysis of multi-platform.

MATERIALS AND METHODS

The chemical constituents of WTX were systematically analyzed by UHPLC-Q-TOF-MS/MS data processing methods. Based on this, network pharmacology was employed to predict the mechanism by which WTX improved dyspepsia. The dyspepsia mouse model was constructed, and histopathology as well as intestinal permeability were assessed using H&E staining, PAS staining and FITC-dextran assay. Protein expression was detected using Western blot, immunofluorescence, immunohistochemistry and ELISA kits.

RESULTS

A total of 100 chemical components of WTX were preliminarily identified. Network pharmacological analysis indicated that the therapeutic mechanism of WTX in treating dyspepsia may be related to the regulation of inflammation and oxidative stress-related signaling pathways. In vivo studies showed that WTX mitigated duodenal inflammation and oxidative stress responses, repairing the intestinal mucosal barrier damaged by cisplatin (CIS). Additionally, WTX restored the number of glial cells diminished by inflammatory damage, and ameliorated the serotoninergic neuronal dysfunction caused by insufficient secretion of glia-derived neurotrophic factor (GDNF), and enhanced intestinal transit.

CONCLUSIONS

In this study, a total of 100 components of the WTX extract were identified through literature review and mass spectrometry database search. Utilizing computer technology, in conjunction with pharmacodynamic and mechanistic studies, WTX has been found to restore serotoninergic neuronal function by reducing intestinal mucosal inflammatory and oxidative damage, ultimately promoting intestinal transport and treating dyspepsia.

Enteric glial NLRP3 inflammasome contributes to gut mucosal barrier alterations in a mouse model of diet-induced obesity

AIM

In the present study, we investigated the involvement of NLRP3 inflammasome in the intestinal epithelial barrier (IEB) changes associated with obesity, and its role in the interplay between enteric glia and intestinal epithelial cells (IECs).

METHODS

Wild-type C57BL/6J and NLRP3-KO (-/-) mice were fed with high-fat diet (HFD) or standard diet for 8 weeks. Colonic IEB integrity and inflammasome activation were assessed. Immunolocalization of colonic mucosal GFAP- and NLRP3-positive cells along with in vitro coculture experiments with enteric glial cells (EGCs) and IECs allowed to investigate the potential link between altered IEB, enteric gliosis, and NLRP3 activation.

RESULTS

HFD mice showed increased body weight, altered IEB integrity, increased GFAP-positive glial cells, and NLRP3 inflammasome hyperactivation. HFD-NLRP3-/- mice showed a lower increase in body weight, an improvement in IEB integrity and an absence of enteric gliosis. Coculture experiments showed that palmitate and lipopolysaccharide contribute to IEB damage and promote enteric gliosis with consequent hyperactivation of enteric glial NLRP3/caspase-1/IL-1β signaling. Enteric glial-derived IL-1β release exacerbates the IEB alterations. Such an effect was abrogated upon incubation with anakinra (IL-1β receptor antagonist) and with conditioned medium derived from silenced-NLRP3 glial cells.

CONCLUSION

HFD intake elicits mucosal enteric gliotic processes characterized by a hyperactivation of NLRP3/caspase-1/IL-1β signaling pathway, that contributes to further exacerbate the disruption of intestinal mucosal barrier integrity. However, we cannot rule out the contribution of NLRP3 inflammasome activation from other cells, such as immune cells, in IEB alterations associated with obesity. Overall, our results suggest that enteric glial NLRP3 inflammasome might represent an interesting molecular target for the development of novel pharmacological approaches aimed at managing the enteric inflammation and intestinal mucosal dysfunctions associated with obesity.

Is the enteric nervous system a lost piece of the gut-kidney axis puzzle linked to chronic kidney disease?

The enteric nervous system (ENS) regulates numerous functional and immunological attributes of the gastrointestinal tract. Alterations in ENS cell function have been linked to intestinal outcomes in various metabolic, intestinal, and neurological disorders. Chronic kidney disease (CKD) is associated with a challenging intestinal environment due to gut dysbiosis, which further affects patient quality of life. Although the gut-related repercussions of CKD have been thoroughly investigated, the involvement of the ENS in this puzzle remains unclear. ENS cell dysfunction, such as glial reactivity and alterations in cholinergic signaling in the small intestine and colon, in CKD are associated with a wide range of intestinal pathways and responses in affected patients. This review discusses how the ENS is affected in CKD and how it is involved in gut-related outcomes, including intestinal permeability, inflammation, oxidative stress, and dysmotility.

Extracellular matrix substrates differentially influence enteric glial cell homeostasis and immune reactivity

Introduction

Enteric glial cells are important players in the control of motility, intestinal barrier integrity and inflammation. During inflammation, they switch into a reactive phenotype enabling them to release inflammatory mediators, thereby shaping the inflammatory environment. While a plethora of well-established in vivo models exist, cell culture models necessary to decipher the mechanistic pathways of enteric glial reactivity are less well standardized. In particular, the composition of extracellular matrices (ECM) can massively affect the experimental outcome. Considering the growing number of studies involving primary enteric glial cells, a better understanding of their homeostatic and inflammatory in vitro culture conditions is needed.

Methods

We examined the impact of different ECMs on enteric glial culture purity, network morphology and immune responsiveness. Therefore, we used immunofluorescence and brightfield microscopy, as well as 3' bulk mRNA sequencing. Additionally, we compared cultured cells with in vivo enteric glial transcriptomes isolated from Sox10iCreERT2Rpl22HA/+ mice.

Results

We identified Matrigel and laminin as superior over other coatings, including poly-L-ornithine, different lysines, collagens, and fibronectin, gaining the highest enteric glial purity and most extended glial networks expressing connexin-43 hemichannels allowing intercellular communication. Transcriptional analysis revealed strong similarities between enteric glia on Matrigel and laminin with enrichment of gene sets supporting neuronal differentiation, while cells on poly-L-ornithine showed enrichment related to cell proliferation. Comparing cultured and in vivo enteric glial transcriptomes revealed a 50% overlap independent of the used coating substrates. Inflammatory activation of enteric glia by IL-1β treatment showed distinct coating-dependent gene expression signatures, with an enrichment of genes related to myeloid and epithelial cell differentiation on Matrigel and laminin coatings, while poly-L-ornithine induced more gene sets related to lymphocyte differentiation.

Discussion

Together, changes in morphology, differentiation and immune activation of primary enteric glial cells proved a strong effect of the ECM. We identified Matrigel and laminin as pre-eminent substrates for murine enteric glial cultures. These new insights will help to standardize and improve enteric glial culture quality and reproducibility between in vitro studies in the future, allowing a better comparison of their functional role in enteric neuroinflammation.

Glycyrol Relieves Ulcerative Colitis by Promoting the Fusion of ZO-1 with the Cell Membrane through the Enteric Glial Cells GDNF/RET Pathway

The damage to the mechanical barrier of the intestinal mucosa is the initiating factor and the core link of the progression of ulcerative colitis (UC). Protecting the mechanical barrier of the intestinal mucosa is of great significance for improving the health status of UC patients. ZO-1 is a key scaffold protein of the mechanical barrier of the intestinal mucosa, and its fusion with the membrane of the intestinal epithelium is a necessary condition to maintain the integrity of the mechanical barrier of the intestinal mucosa. Enteric glial cells (EGCs) play an important role in the maintenance of intestinal homeostasis and have become a new target for regulating intestinal health in recent years. In this study, we found that glycyrol (GC), a representative coumarin compound isolated from Licorice (Glycyrrhiza uralensis Fisch, used for medicine and food), can alleviate UC by promoting the production of neurotrophic factor GDNF in mice EGCs. Specifically, we demonstrated that GC promotes the production of GDNF, then activates its receptor RET, promotes ZO-1 fusion with cell membranes, and protects the intestinal mucosal mechanical barrier. The results of this study can provide new ideas for the prevention and treatment of UC.

Organoids in gastrointestinal diseases: from bench to clinic

The etiology of gastrointestinal (GI) diseases is intricate and multifactorial, encompassing complex interactions between genetic predisposition and gut microbiota. The cell fate change, immune function regulation, and microenvironment composition in diseased tissues are governed by microorganisms and mutated genes either independently or through synergistic interactions. A comprehensive understanding of GI disease etiology is imperative for developing precise prevention and treatment strategies. However, the existing models used for studying the microenvironment in GI diseases-whether cancer cell lines or mouse models-exhibit significant limitations, which leads to the prosperity of organoids models. This review first describes the development history of organoids models, followed by a detailed demonstration of organoids application from bench to clinic. As for bench utilization, we present a layer-by-layer elucidation of organoid simulation on host-microbial interactions, as well as the application in molecular mechanism analysis. As for clinical adhibition, we provide a generalized interpretation of organoid application in GI disease simulation from inflammatory disorders to malignancy diseases, as well as in GI disease treatment including drug screening, immunotherapy, and microbial-targeting and screening treatment. This review draws a comprehensive and systematical depiction of organoids models, providing a novel insight into the utilization of organoids models from bench to clinic.

Expression levels and diagnostic value of serum GDNF, CEA and CA199 in patients with colorectal carcinoma

Background

To investigate the expression levels and diagnostic value of glial cell line-derived neurotrophic factor (GDNF), carcinoembryonic antigen (CEA) and carbohydrate antigen199 (CA199) in patients with colorectal carcinoma (CRC).

Methods

50 CRC patients at our hospital from Feb. 2020 to Feb. 2021 were chosen as the malignant group, another 50 patients with benign colonic diseases were chosen as the benign group, and 50 healthy people who came to our hospital for physical examination during the same period were considered as the control group. Fasting peripheral venous blood was taken from all research subjects in the morning and tested by a fully-automated electrochemiluminometer to determine the GDNF, CEA and CA199 levels. The sensitivity and specificity of the combined detection of the three indexes for CRC were analyzed, and the receiver operating characteristic (ROC) curve was plotted to record the area under the curve (AUC).

Results

The malignant group had remarkably higher CEA and CA199 levels (P<0.001) and a lower GDNF level (P<0.001) when compared with the benign and control groups. The sensitivity, specificity, positive predictive value and negative predictive value of the combined detection were 96.0%, 94.0%, 88.9% and 97.9%, respectively. Under combined detection, AUC (95% CI) = 0.950 (0.909-0.991), standard error = 0.021, and P<0.001.

Conclusions

The combined diagnosis of serum GDNF, CEA and CA199 is a reliable method to improve the diagnostic accuracy of CRC, and this strategy can effectively reduce the missed diagnosis rate and has high application value in clinic.

Toll-like receptor 3 signaling drives enteric glial cells against dextran sulfate sodium-induced colitis in mice

The activation of toll-like receptor 3 (TLR3) has been reported to attenuate astrocytes injury in central nervous system, but its effect on enteric glial cells (EGCs) remains unknown. Here, we confirmed that the residence of EGCs was regulated by TLR3 agonist (polyinosinic-polycytidylic acid, PIC) or TLR3/dsRNA complex inhibitor in dextran sulfate sodium (DSS)-induced mice. In vitro, TLR3 signaling prevented apoptosis in EGCs and drove the secretion of EGCs-derived glial cell line-derived neurotrophic factor, 15-hydroxyeicosatetraenoic acid and S-nitrosoglutathione. PIC preconditioning enhanced the protective effects of EGCs against the dysfunction of intestinal epithelial barrier and the development of colitis in DSS-induced mice. Interestingly, PIC stimulation also promoted the effects of EGCs on converting macrophages to an M2-like phenotype and regulating the levels of inflammatory cytokines, including IL-1β, TNF-α and IL-10, in DSS-induced mice. These findings imply that TLR3 signaling in EGCs may provide a potential target for the prevention and treatment of colitis.

Potential biological functions and future perspectives of sialylated milk oligosaccharides

Sialyllactoses (SLs) primarily include sialylated human milk oligosaccharides (HMOs) and bovine milk oligosaccharides (BMOs). First, the safety assessment of 3'-sialyllactose (3'-SL) and 6'-sialyllactose (6'-SL) revealed low toxicity in various animal models and human participants. SLs constitute a unique milk component, highlighting the essential nutrients and bioactive components crucial for infant development, along with numerous associated health benefits for various diseases. This review explores the safety, biosynthesis, and potential biological effects of SLs, with a specific focus on their influence across various physiological systems, including the gastrointestinal system, immune disorders, rare genetic disorders (such as GNE myopathy), cancers, neurological disorders, cardiovascular diseases, diverse cancers, and viral infections, thus indicating their therapeutic potential.

Neuroimmune Connectomes in the Gut and Their Implications in Parkinson's Disease

The gastrointestinal tract is the largest immune organ and it receives dense innervation from intrinsic (enteric) and extrinsic (sympathetic, parasympathetic, and somatosensory) neurons. The immune and neural systems of the gut communicate with each other and their interactions shape gut defensive mechanisms and neural-controlled gut functions such as motility and secretion. Changes in neuroimmune interactions play central roles in the pathogenesis of diseases such as Parkinson's disease (PD), which is a multicentric disorder that is heterogeneous in its manifestation and pathogenesis. Non-motor and premotor symptoms of PD are common in the gastrointestinal tract and the gut is considered a potential initiation site for PD in some cases. How the enteric nervous system and neuroimmune signaling contribute to PD disease progression is an emerging area of interest. This review focuses on intestinal neuroimmune loops such as the neuroepithelial unit, enteric glial cells and their immunomodulatory effects, anti-inflammatory cholinergic signaling and the relationship between myenteric neurons and muscularis macrophages, and the role of α-synuclein in gut immunity. Special consideration is given to the discussion of intestinal neuroimmune connectomes during PD and their possible implications for various aspects of the disease.

Enteric glial cell network function is required for epithelial barrier restitution following intestinal ischemic injury in the early postnatal period

Ischemic damage to the intestinal epithelial barrier, such as in necrotizing enterocolitis or small intestinal volvulus, is associated with higher mortality rates in younger patients. We have recently reported a powerful pig model to investigate these age-dependent outcomes in which mucosal barrier restitution is strikingly absent in neonates but can be rescued by direct application of homogenized mucosa from older, juvenile pigs by a yet-undefined mechanism. Within the mucosa, a postnatally developing network of enteric glial cells (EGCs) is gaining recognition as a key regulator of the mucosal barrier. Therefore, we hypothesized that the developing EGC network may play an important role in coordinating intestinal barrier repair in neonates. Neonatal and juvenile jejunal mucosa recovering from surgically induced intestinal ischemia was visualized by scanning electron microscopy and the transcriptomic phenotypes were assessed by bulk RNA sequencing. EGC network density and glial activity were examined by Gene Set Enrichment Analysis, three-dimensional (3-D) volume imaging, and Western blot and its function in regulating epithelial restitution was assessed ex vivo in Ussing chamber using the glia-specific inhibitor fluoroacetate (FA), and in vitro by coculture assay. Here we refine and elaborate our translational model, confirming a neonatal phenotype characterized by a complete lack of coordinated reparative signaling in the mucosal microenvironment. Furthermore, we report important evidence that the subepithelial EGC network changes significantly over the early postnatal period and demonstrate that the proximity of a specific functional population of EGC to wounded intestinal epithelium contributes to intestinal barrier restitution following ischemic injury.NEW & NOTEWORTHY This study refines a powerful translational pig model, defining an age-dependent relationship between enteric glia and the intestinal epithelium during intestinal ischemic injury and confirming an important role for enteric glial cell (EGC) activity in driving mucosal barrier restitution. This study suggests that targeting the enteric glial network could lead to novel interventions to improve recovery from intestinal injury in neonatal patients.

Sinomenine regulates the cholinergic anti-inflammatory pathway to inhibit TLR4/NF-κB pathway and protect the homeostasis in brain and gut in scopolamine-induced Alzheimer's disease mice

Sinomenine (SIN), an alkaloid extracted from the Chinese herbal medicine Sinomenium acutum, has great potential in anti-inflammatory, immune regulation, analgesic and sedative, and is already a clinical drug for the treatment of rheumatoid arthritis in China. Our previous studies show SIN inhibits inflammation by regulating ɑ7nAChR, a key receptor of cholinergic anti-inflammatory pathway (CAP), which plays an important role in regulating peripheral and central nervous system inflammation. Growing evidence supports the cholinergic dysregulation and inflammatory responses play the key role in the pathogenesis of AD. The intervention effects of SIN on AD by regulating CAP and homeostasis in brain and gut were analyzed for the first time in the present study using scopolamine-induced AD model mice. Behavioral tests were used to assess the cognitive performance. The neurons loss, cholinergic function, inflammation responses, biological barrier function in the mouse brain and intestinal tissues were evaluated through a variety of techniques, and the gut microbiota was detected using 16SrRNA sequencing. The results showed that SIN significantly inhibited the cognitive decline, dysregulation of cholinergic system, peripheral and central inflammation, biological barrier damage as well as intestinal flora disturbance caused by SCOP in mice. More importantly, SIN effectively regulated CAP to suppress the activation of TLR4/NF-κB and protect the homeostasis in brain and gut to alleviate cognitive impairment.

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.

Potential roles of enteric glial cells in Crohn's disease: A critical review

Enteric glial cells in the enteric nervous system are critical for the regulation of gastrointestinal homeostasis. Increasing evidence suggests two-way communication between enteric glial cells and both enteric neurons and immune cells. These interactions may be important in the pathogenesis of Crohn's disease (CD), a chronic relapsing disease characterized by a dysregulated immune response. Structural abnormalities in glial cells have been identified in CD. Furthermore, classical inflammatory pathways associated with CD (e.g., the nuclear factor kappa-B pathway) function in enteric glial cells. However, the specific mechanisms by which enteric glial cells contribute to CD have not been summarized in detail. In this review, we describe the possible roles of enteric glial cells in the pathogenesis of CD, including the roles of glia-immune interactions, neuronal modulation, neural plasticity, and barrier integrity. Additionally, the implications for the development of therapeutic strategies for CD based on enteric glial cell-mediated pathogenic processes are discussed.

β-adrenergic signaling triggers enteric glial reactivity and acute enteric gliosis during surgery

BACKGROUND

Enteric glia contribute to the pathophysiology of various intestinal immune-driven diseases, such as postoperative ileus (POI), a motility disorder and common complication after abdominal surgery. Enteric gliosis of the intestinal muscularis externa (ME) has been identified as part of POI development. However, the glia-restricted responses and activation mechanisms are poorly understood. The sympathetic nervous system becomes rapidly activated by abdominal surgery. It modulates intestinal immunity, innervates all intestinal layers, and directly interfaces with enteric glia. We hypothesized that sympathetic innervation controls enteric glia reactivity in response to surgical trauma.

METHODS

Sox10iCreERT2/Rpl22HA/+ mice were subjected to a mouse model of laparotomy or intestinal manipulation to induce POI. Histological, protein, and transcriptomic analyses were performed to analyze glia-specific responses. Interactions between the sympathetic nervous system and enteric glia were studied in mice chemically depleted of TH+ sympathetic neurons and glial-restricted Sox10iCreERT2/JellyOPfl/+/Rpl22HA/+ mice, allowing optogenetic stimulation of β-adrenergic downstream signaling and glial-specific transcriptome analyses. A laparotomy model was used to study the effect of sympathetic signaling on enteric glia in the absence of intestinal manipulation. Mechanistic studies included adrenergic receptor expression profiling in vivo and in vitro and adrenergic agonism treatments of primary enteric glial cell cultures to elucidate the role of sympathetic signaling in acute enteric gliosis and POI.

RESULTS

With ~ 4000 differentially expressed genes, the most substantial enteric glia response occurs early after intestinal manipulation. During POI, enteric glia switch into a reactive state and continuously shape their microenvironment by releasing inflammatory and migratory factors. Sympathetic denervation reduced the inflammatory response of enteric glia in the early postoperative phase. Optogenetic and pharmacological stimulation of β-adrenergic downstream signaling triggered enteric glial reactivity. Finally, distinct adrenergic agonists revealed β-1/2 adrenoceptors as the molecular targets of sympathetic-driven enteric glial reactivity.

CONCLUSIONS

Enteric glia act as early responders during post-traumatic intestinal injury and inflammation. Intact sympathetic innervation and active β-adrenergic receptor signaling in enteric glia is a trigger of the immediate glial postoperative inflammatory response. With immune-activating cues originating from the sympathetic nervous system as early as the initial surgical incision, adrenergic signaling in enteric glia presents a promising target for preventing POI development.

Enteric glia as a player of gut-brain interactions during Parkinson's disease

The enteric glia has been shown as a potential component of neuroimmune interactions that signal in the gut-brain axis during Parkinson's disease (PD). Enteric glia are a peripheral glial type found in the enteric nervous system (ENS) that, associated with enteric neurons, command various gastrointestinal (GI) functions. They are a unique cell type, with distinct phenotypes and distribution in the gut layers, which establish relevant neuroimmune modulation and regulate neuronal function. Comprehension of enteric glial roles during prodromal and symptomatic phases of PD should be a priority in neurogastroenterology research, as the reactive enteric glial profile, gastrointestinal dysfunction, and colonic inflammation have been verified during the prodromal phase of PD-a moment that may be interesting for interventions. In this review, we explore the mechanisms that should govern enteric glial signaling through the gut-brain axis to understand pathological events and verify the possible windows and pathways for therapeutic intervention. Enteric glia directly modulate several functional aspects of the intestine, such as motility, visceral sensory signaling, and immune polarization, key GI processes found deregulated in patients with PD. The search for glial biomarkers, the investigation of temporal-spatial events involving glial reactivity/signaling, and the proposal of enteric glia-based therapies are clearly demanded for innovative and intestine-related management of PD.

Human organoids are superior to cell culture models for intestinal barrier research

Loss of intestinal epithelial barrier function is a hallmark in digestive tract inflammation. The detailed mechanisms remain unclear due to the lack of suitable cell-based models in barrier research. Here we performed a detailed functional characterization of human intestinal organoid cultures under different conditions with the aim to suggest an optimized ex-vivo model to further analyse inflammation-induced intestinal epithelial barrier dysfunction. Differentiated Caco2 cells as a traditional model for intestinal epithelial barrier research displayed mature barrier functions which were reduced after challenge with cytomix (TNFα, IFN-γ, IL-1ß) to mimic inflammatory conditions. Human intestinal organoids grown in culture medium were highly proliferative, displayed high levels of LGR5 with overall low rates of intercellular adhesion and immature barrier function resembling conditions usually found in intestinal crypts. WNT-depletion resulted in the differentiation of intestinal organoids with reduced LGR5 levels and upregulation of markers representing the presence of all cell types present along the crypt-villus axis. This was paralleled by barrier maturation with junctional proteins regularly distributed at the cell borders. Application of cytomix in immature human intestinal organoid cultures resulted in reduced barrier function that was accompanied with cell fragmentation, cell death and overall loss of junctional proteins, demonstrating a high susceptibility of the organoid culture to inflammatory stimuli. In differentiated organoid cultures, cytomix induced a hierarchical sequence of changes beginning with loss of cell adhesion, redistribution of junctional proteins from the cell border, protein degradation which was accompanied by loss of epithelial barrier function. Cell viability was observed to decrease with time but was preserved when initial barrier changes were evident. In summary, differentiated intestinal organoid cultures represent an optimized human ex-vivo model which allows a comprehensive reflection to the situation observed in patients with intestinal inflammation. Our data suggest a hierarchical sequence of inflammation-induced intestinal barrier dysfunction starting with loss of intercellular adhesion, followed by redistribution and loss of junctional proteins resulting in reduced barrier function with consecutive epithelial death.

Plakophilin 2 regulates intestinal barrier function by modulating protein kinase C activity in vitro

Previous data provided evidence for a critical role of desmosomes to stabilize intestinal epithelial barrier (IEB) function. These studies suggest that desmosomes not only contribute to intercellular adhesion but also play a role as signaling hubs. The contribution of desmosomal plaque proteins plakophilins (PKP) in the intestinal epithelium remains unexplored. The intestinal expression of PKP2 and PKP3 was verified in human gut specimens, human intestinal organoids as well as in Caco2 cells whereas PKP1 was not detected. Knock-down of PKP2 using siRNA in Caco2 cells resulted in loss of intercellular adhesion and attenuated epithelial barrier. This was paralleled by changes of the whole desmosomal complex, including loss of desmoglein2, desmocollin2, plakoglobin and desmoplakin. In addition, tight junction proteins claudin1 and claudin4 were reduced following the loss of PKP2. Interestingly, siRNA-induced loss of PKP3 did not change intercellular adhesion and barrier function in Caco2 cells, while siRNA-induced loss of both PKP2 and PKP3 augmented the changes observed for reduced PKP2 alone. Moreover, loss of PKP2 and PKP2/3, but not PKP3, resulted in reduced activity levels of protein kinase C (PKC). Restoration of PKC activity using Phorbol 12-myristate 13-acetate (PMA) rescued loss of intestinal barrier function and attenuated the reduced expression patterns of claudin1 and claudin4. Immunostaining, proximity ligation assays and co-immunoprecipitation revealed a direct interaction between PKP2 and PKC. In summary, our in vitro data suggest that PKP2 plays a critical role for intestinal barrier function by providing a signaling hub for PKC-mediated expression of tight junction proteins claudin1 and claudin4.

Enteric glial cells aggravate the intestinal epithelial barrier damage by secreting S100β under high-altitude conditions

Damage to the intestinal epithelial barrier (IEB) has been reported under high-altitude (HA) conditions and may be responsible for HA-associated gastrointestinal (GI) disorders. However, this pathogenetic mechanism does not fully explain the GI stress symptoms, such as flatulence and motility diarrhea, which accompany the IEB damage under HA conditions, especially for the people exposed to HA acutely. In the present study, we collected the blood samples from the people who lived at HA and found the concentration of enteric glial cells (EGCs)-associated biomarkers increased significantly. HA mouse model was then established and the results revealed that EGCs were involved in IEB damage. Zona occludens (ZO)-1, occludin, and claudin-1 expression was negatively correlated with that of glial fibrillary acidic protein (GFAP) and S100β under HA conditions. In order to learn more about how EGCs influence IEB, the in vitro EGC and MODE-K hypoxia experiments that used hypoxic stimulation for simulating in vivo exposure to HA was performed. We found that hypoxia increased S100β secretion in EGCs. And MODE-K cells cultured in medium conditioned by hypoxic EGCs showed low ZO-1, occludin, and claudin-1 levels of expression. Furthermore, treatment of MODE-K cells with recombinant mouse S100β resulted in diminished levels of ZO-1, occludin, and claudin-1 expression. Thus, HA exposure induces greater S100β secretion by EGCs, which aggravates the damage to the IEB. This study has revealed a novel mechanism of IEB damage under HA conditions, and suggest that EGCs may constitute a fresh avenue for the avoidance of GI disorders at HA.

Guardians of the gut: influence of the enteric nervous system on the intestinal epithelial barrier

The intestinal mucosal surface forms one of the largest areas of the body, which is in direct contact with the environment. Co-ordinated sensory functions of immune, epithelial, and neuronal cells ensure the timely detection of noxious queues and potential pathogens and elicit proportional responses to mitigate the threats and maintain homeostasis. Such tuning and maintenance of the epithelial barrier is constantly ongoing during homeostasis and its derangement can become a gateway for systemic consequences. Although efforts in understanding the gatekeeping functions of immune cells have led the way, increasing number of studies point to a crucial role of the enteric nervous system in fine-tuning and maintaining this delicate homeostasis. The identification of immune regulatory functions of enteric neuropeptides and glial-derived factors is still in its infancy, but has already yielded several intriguing insights into their important contribution to the tight control of the mucosal barrier. In this review, we will first introduce the reader to the current understanding of the architecture of the enteric nervous system and the epithelial barrier. Next, we discuss the key discoveries and cellular pathways and mediators that have emerged as links between the enteric nervous, immune, and epithelial systems and how their coordinated actions defend against intestinal infectious and inflammatory diseases. Through this review, the readers will gain a sound understanding of the current neuro-immune-epithelial mechanisms ensuring intestinal barrier integrity and maintenance of intestinal homeostasis.

Mini-Review: Enteric glial regulation of the gastrointestinal epithelium

Many enteric glia are located along nerve fibers in the gut mucosa where they form close associations with the epithelium lining the gastrointestinal tract. The gut epithelium is essential for absorbing nutrients, regulating fluid flux, forming a physical barrier to prevent the entry of pathogens and toxins into the host, and participating in immune responses. Disruptions to this epithelium are linked to numerous diseases, highlighting its central importance in maintaining health. Accumulating evidence indicates that glia regulate gut epithelial homeostasis. Observations from glial-epithelial co-cultures in vitro and mouse genetic models in vivo suggest that enteric glia influence several important features of the gut epithelium including barrier integrity, ion transport, and capacity for self-renewal. Here we review the evidence for enteric glial regulation of the intestinal epithelium, with a focus on these three features of its biology.

Enteric nervous system and intestinal epithelial regulation of the gut-brain axis

The gut-brain axis describes a bidirectional interplay within the enteric environment between the intestinal epithelium, the mucosal immune system, and the microbiota with the enteric nervous system. This interplay provides a link between exogenous environmental stimuli such as nutrient sensing, and nervous system function, as well as a mechanism of feedback from cortical and sensory centers of the brain to enteric activities. The intestinal epithelium is one of the human body's largest sources of hormones and neurotransmitters, which have critical effects on neuronal function. The influence of the gut microbiota on these processes appears to be profound; yet to date, it has been insufficiently explored. Disruption of the intestinal microbiota is linked not only to diseases in the gut but also to brain symptomatology, including neurodegenerative and behavioral disorders (Parkinson disease, Alzheimer disease, autism, and anxiety and/or depression). In this review we discuss the cellular wiring of the gut-brain axis, with a particular focus on the epithelial and neuronal interaction, the evidence that has led to our current understanding of the intestinal role in neurologic function, and future directions of research to unravel this important interaction in both health and allergic disease.

Amelioration effect of Lactobacillus plantarum KFY02 on low-fiber diet-induced constipation in mice by regulating gut microbiota

This study aimed to examine the ameliorating effect of Lactobacillus plantarum (LP) KFY02 on low-fiber diet-induced constipation in mice. LP-KFY02 was isolated from the natural fermented yogurt in Korla of Xinjiang. The mice with low-fiber diet-induced constipation in experimental groups were administered 1 × 10⁹ CFU/kg LP-KFY02 (KFY02H) and 1 × 10⁸ CFU/kg LP-KFY02 (KFY02L). After LP-KFY02 treatment with constipation mice, the mice fecal water content, intestinal transit ability and defecation time of constipated mice were improved. The mice fecal flora diversity, abundance and structure of the intestinal flora were regulated to the balanced state. The mice serum levels of gut motility related neuroendocrine factors have been increased, the intestinal mucosal barrier function and gut motility related gene expression were regulated in mice colon tissues. At the same time, the mice colon tissue damage were improved. These parameters in the KFY02H group were close to the normal group. These results suggested that LP-KFY02 could be considered as a potential probiotic to help alleviate low-fiber diet-induced constipation. They also provided a theoretical basis for the study of probiotics to relieve constipation by regulating intestinal flora.

Enteric Glial Cells in Immunological Disorders of the Gut

Enteric glial cells (EGCs) are one of the major cell types of neural crest lineage distributed in the gastrointestinal tract. EGCs represent an integral part of the enteric nervous system (ENS) and significantly outnumber ENS neurons. Studies have suggested that EGCs would exert essential roles in supporting the survival and functions of the ENS neurons. Notably, recent evidence has begun to reveal that EGCs could possess multiple immune functions and thereby may participate in the immune homeostasis of the gut. In this review article, we will summarize the current evidence supporting the potential involvement of EGCs in several important immunological disorders, including inflammatory bowel disease, celiac disease, and autoimmune enteropathy. Further, we highlight critical questions on the immunological aspects of EGCs that warrant future research attention.

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.

The Involvement of Glial Cell-Derived Neurotrophic Factor in Inflammatory Bowel Disease

Inflammatory bowel diseases (IBD) are chronic inflammatory gastrointestinal diseases characterized by dysregulation of the intestinal epithelial barrier (IEB) and intermittent relapses. Recent data show that the glial cell line-derived neurotrophic factor (GDNF) promotes IEB function and wound healing. Apart from protective effects of GDNF on enteric nervous system and IEB, an immunomodulatory role has been assumed. However, it is inconsistent whether GDNF levels are increased or decreased in the inflamed colon of patients with IBD. Furthermore, GDNF is 1 of 3 protein markers associated with relapse in a prospective cohort study in IBD patients with clinically and endoscopically quiescent disease. Additionally, not only enteric glial cells (EGCs), but also intestinal smooth muscle cells and enterocytes synthesize GDNF in significant amounts; in addition, its receptors are expressed in intestinal neurons, EGCs, immune cells and epithelial cells, which points to a potential auto- or paracrine signaling loop between some of these cells. Whether GDNF is involved in IBD-associated fibrosis and colitis-associated colorectal cancer remains to be confirmed. In this review we aim to summarize and discuss the current knowledge on the effects of GDNF and its potential role in the contribution to the pathogenesis of IBD.

Distribution of α-synuclein in normal human jejunum and its relations with the chemosensory and neuroendocrine system

Alpha-synuclein (α-syn) is a presynaptic neuronal protein and its structural alterations play an important role in the pathogenesis of neurodegenerative diseases, such as Parkinson’s disease (PD). It has been originally described in the brain and aggregated α-syn has also been found in the peripheral nerves including the enteric nervous system (ENS) of PD patients. ENS is a network of neurons and glia found in the gut wall which controls gastrointestinal function independently from the central nervous system. Moreover, two types of epithelial cells are crucial in the creation of an interface between the lumen and the ENS: they are the tuft cells and the enteroendocrine cells (EECs). In addition, the abundant enteric glial cells (EGCs) in the intestinal mucosa play a key role in controlling the intestinal epithelial barrier. Our aim was to localize and characterize the presence of α-syn in the normal human jejunal wall. Surgical specimens of proximal jejunum were collected from patients submitted to pancreaticoduodenectomy and intestinal sections underwent immunohistochemical procedure. Alpha-syn has been found both at the level of the ENS and the epithelial cells. To characterize α-syn immunoreactive epithelial cells, we used markers such as choline acetyltransferase (ChAT), useful for the identification of tuft cells. Then we evaluated the co-presence of α-syn with serotonin (5-HT), expressed in EECs. Finally, we used the low-affinity nerve growth factor receptor (p75NTR), to detect peripheral EGCs. The presence of α-syn has been demonstrated in EECs, but not in the tuft cells. Additionally, p75NTR has been highlighted in EECs of the mucosal layer and co-localized with α-syn in EECs but not with ChAT-positive cells. These findings suggest that α-syn could play a possible role in synaptic transmission of the ENS and may contribute to maintain the integrity of the epithelial barrier of the small intestine through EECs.

Glial cell line-derived neurotrophic factor ameliorates dextran sulfate sodium-induced colitis in mice via a macrophage-mediated pathway

Glial cell line-derived neurotrophic factor (GDNF) has been reported to protect mice from intestinal inflammation, but its anti-inflammatory mechanisms are poorly understood. Here we found that there was a downregulation in intestinal expression of GDNF accompanied by an increase of M1 macrophages in dextran sulfate sodium (DSS)-induced colitis in mice. GDNF treatment could facilitate the macrophages polarization towards the M2-like phenotype in DSS-treated mice and LPS-stimulated RAW264.7 cells, and reduce pro-inflammatory cytokines and increase anti-inflammatory cytokines. Mechanistically, the activation of PI3K/AKT pathway might contribute to the regulation of GDNF on macrophage phenotypes and inflammatory response. Moreover, the administration of GDNF significantly ameliorated colitis in DSS-treated mice, but this benefit of GDNF was diminished by macrophage depletion. Therefore, we propose a new mechanism whereby GDNF suppresses DSS-induced colitis in mice via a macrophage-mediated pathway.

Enteric mesenchymal cells support the growth of postnatal enteric neural stem cells

Interplay between embryonic enteric neural stem cells (ENSCs) and enteric mesenchymal cells (EMCs) in the embryonic gut is essential for normal development of the enteric nervous system. Disruption of these interactions underlies the pathogenesis of intestinal aganglionosis in Hirschsprung disease (HSCR). ENSC therapy has been proposed as a possible treatment for HSCR, but whether the survival and development of postnatal-derived ENSCs similarly rely on signals from the mesenchymal environment is unknown and has important implications for developing protocols to expand ENSCs for cell transplantation therapy. Enteric neural crest-derived cells (ENCDCs) and EMCs were cultured from the small intestine of Wnt1-Rosa26-tdTomato mice. EMCs promoted the expansion of ENCDCs 9.5-fold by inducing ENSC properties, including expression of Nes, Sox10, Sox2, and Ngfr. EMCs enhanced the neurosphere-forming ability of ENCDCs, and this persisted after withdrawal of the EMCs. These effects were mediated by paracrine factors and several ligands known to support neural stem cells were identified in EMCs. Using the optimized expansion procedures, neurospheres were generated from small intestine of the Ednrb-/- mouse model of HSCR. These ENSCs had similar proliferative and migratory capacity to Ednrb+/+ ENSCs, albeit neurospheres contained fewer neurons. ENSCs derived from Ednrb-/- mice generated functional neurons with similar calcium responses to Ednrb+/+ ENSCs and survived after transplantation into the aganglionic colon of Ednrb-/- recipients. EMCs act as supporting cells to ENSCs postnatally via an array of synergistically acting paracrine signaling factors. These properties can be leveraged to expand autologous ENSCs from patients with HSCR mutations for therapeutic application.