Activation of neuronal P2X7 receptor-pannexin-1 mediates death of enteric neurons during colitis. Nat Med. 2012;18:600-604. [PMID: 22426419 PMCID: PMC3321107 DOI: 10.1038/nm.2679]

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

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

Purinergic control of apical ion conductance by luminal ATP in rat colonic epithelium

ATP, released e.g. after cell damage or during inflammation, can alter ion transport across the intestinal mucosa via stimulation of purinergic receptors in the basolateral as well as in the apical membrane of epithelial cells. When ATP acts from the serosal side, it induces an increase in short-circuit current (Isc) via Cl- secretion across the colonic epithelium. In contrast, mucosal ATP or its derivative, BzATP, predominantly stimulating ionotropic P2X4 and P2X7 receptors, evoke an increase in Isc, which could not be explained by Cl- secretion. The underlying ion currents after stimulation of apical purinergic receptors in rat distal colon are still unclear and were investigated in the present study. Ussing chamber experiments revealed that the Isc induced by mucosal ATP was dependent on the presence of mucosal Ca2+ and inhibited by the K+ channel blocker, Ba2+, indicating the involvement of Ca2+-dependent K+ channels. Blockade of the transepithelial Isc by lanthanides (La3+, Gd3+) suggests that Ca2+ enters the epithelium via nonselective cation channels. Experiments with basolaterally depolarized epithelia confirmed the activation of apical lanthanide-sensitive Na+- and Ca2+-permeable cation channels by ATP. Putative candidates might be TRP channels, from which several subtypes were detected in colonic tissue in RT-PCR experiments. In addition, the activation of an apical Cl- conductance was observed when suitable Cl- concentration gradients were applied. Consequently, mucosal ATP, acting as 'danger signal', stimulates cation and anion channels in the apical membrane to induce a secretory response as part of the local defence mechanism in the intestinal epithelium.

Endocannabinoids regulate enteric neuron-glia networks and visceral hypersensitivity following inflammation through a glial-dependent mechanism

Acute gastrointestinal (GI) inflammation induces neuroplasticity that produces long-lasting changes in gut motor function and pain. The endocannabinoid system is an attractive target to correct pain and dysmotility, but how inflammation changes endocannabinoid control over cellular communication in enteric neurocircuits is not understood. Enteric glia modulate gut neurons that control motility and pain and express monoacylglycerol lipase (MAGL) which controls endocannabinoid availability. We used a combination of in situ calcium imaging, chemogenetics, and selective drugs to study how endocannabinoid mechanisms affect glial responses and subsequent enteric neuron activity in health and following colitis in Wnt1Cre;GCaMP5g-tdT;GFAP::hM3Dq mice. Trpv1Cre;GCaMP5gtdT mice were used to study nociceptor sensitivity and Sox10CreERT2;Mgllf/f mice were used to test the role of glial MAGL in visceral pain. The data show that endocannabinoid signaling regulates neuro-glial signaling in gut neurocircuits in a sexually dimorphic manner. Inhibiting MAGL in healthy samples decreased glial responsiveness but this effect was lost in females following colitis and converted to an excitatory effect in males. Manipulating CB1 and CB2 receptors revealed further sex differences amongst neuro-glia signaling that were impacted following inflammation. Inflammation increased gut nociceptor sensitivity in both sexes but only females exhibited visceral hypersensitivity in vivo. Blocking MAGL normalized nociceptor responses in vitro and deleting glial Mgll in vivo rescued visceral hypersensitivity in females. These results show that sex and inflammation impact endocannabinoid mechanisms that regulate intercellular enteric glia-neuron communication. Further, targeting glial MAGL could provide therapeutic benefits for visceral nociception in a sex-dependent manner.

The role of reactive enteric glia-macrophage interactions in acute and chronic inflammation

Enteric glia are a heterogeneous population of peripheral glia within the enteric nervous system and play pivotal roles in gut homeostasis, tissue integrity, coordination of motility, and intestinal immune responses. Under physiological conditions, they communicate with enteric neurons to control intestinal motility. In contrast, enteric glia undergo reactive changes in response to inflammatory signals during enteric neuroinflammation and participate in immune control. In this state, these glia are called reactive enteric glia, which promote cytokine and chemokine secretion and perpetuate immune cell recruitment, thereby affecting disease progression. Interestingly, reactive glia exhibit a huge plasticity and adapt to or shape the immune environment towards a resolving phenotype during inflammation and neuropathies. Recent studies revealed a bidirectional communication between enteric glia and resident and infiltrating immune cells under healthy conditions and in the context of inflammation-based intestinal disorders and neuropathies. While recent reviews give a superb general overview of enteric glial reactivity, we herein discuss the latest evidence on enteric glial reactivity in two prominent inflammatory conditions: acute postoperative inflammation, resulting in postoperative ileus, and chronic inflammation in inflammatory bowel diseases. We define their plasticity during inflammation and the interplay between reactive enteric glia and intestinal macrophages. Finally, we sketch important questions that should be addressed to clarify further the impact of enteric glial reactivity on intestinal inflammation.

Persistent Activation of the P2X7 Receptor Underlies Chronic Inflammation and Carcinogenic Changes in the Intestine

Aberrant signaling through damage-associated molecular patterns (DAMPs) has been linked to several health disorders, attracting considerable research interest over the last decade. Adenosine triphosphate (ATP), a key extracellular DAMP, activates the purinergic receptor P2X7, which acts as a danger sensor in immune cells and is implicated in distinct biological functions, including cell death, production of pro-inflammatory cytokines, and defense against microorganisms. In addition to driving inflammation mediated by immune and non-immune cells, the persistent release of endogenous DAMPs, including ATP, has been shown to result in epigenetic modifications. In intestinal diseases such as inflammatory bowel disease (IBD) and colorectal cancer (CRC), consequent amplification of the inflammatory response and the resulting epigenetic reprogramming may impact the development of pathological changes associated with specific disease phenotypes. P2X7 is overexpressed in the gut mucosa of patients with IBD, whereas the P2X7 blockade prevents the development of chemically induced experimental colitis. Recent data suggest a role for P2X7 in determining gut microbiota composition. Regulatory mechanisms downstream of the P2X7 receptor, combined with signals from dysbiotic microbiota, trigger intracellular signaling pathways and inflammasomes, intensify inflammation, and foster colitis-associated CRC development. Preliminary studies targeting the ATP-P2X7 pathway have shown favorable therapeutic effects in human IBD and experimental colitis.

A DNA Molecular Logic Circuit for Precise Tumor Identification

Tumor-associated antigens (TAAs) are not exclusively expressed in cancer cells, inevitably causing the "on target, off tumor" effect of molecular recognition tools. To achieve precise recognition of cancer cells, by using protein tyrosine kinase 7 (PTK7) as a model TAA, a DNA molecular logic circuit Aisgc8 was rationally developed by arranging H+-binding i-motif, ATP-binding aptamer, and PTK7-targeting aptamer Sgc8c in a DNA sequence. Aisgc8 output the conformation of Sgc8c to recognize PTK7 on cells in a simulated tumor microenvironment characterized by weak acidity and abundant ATP, but not in a simulated physiological environment. Through in vitro and in vivo results, Aisgc8 demonstrated its ability to precisely recognize cancer cells and, as a result, displayed excellent performance in tumor imaging. Thus, our studies produced a simple and efficient strategy to construct DNA logic circuits, opening new possibilities to develop convenient and intelligent precision diagnostics by using DNA logic circuits.

Dietary Polyphenols and Gut Microbiota Cross-Talk: Molecular and Therapeutic Perspectives for Cardiometabolic Disease: A Narrative Review

The intricate interplay between the gut microbiota and polyphenols has emerged as a captivating frontier in understanding and potentially harnessing the therapeutic potential of these bioactive compounds. Phenolic compounds, renowned for their antioxidant, anti-inflammatory, antidiabetic, and anticancer properties, are subject to intricate transformations within the gut milieu, where the diverse microbial ecosystem exerts profound effects on their metabolism and bioavailability. Conversely, polyphenols exhibit a remarkable capacity to modulate the composition and activity of the gut microbiota, fostering a bidirectional relationship that extends beyond mere nutrient processing. This symbiotic interaction holds significant implications for human health, particularly in cardiometabolic diseases such as diabetes mellitus, metabolic-dysfunction-associated steatotic liver disease, and cardiovascular disease. Through a comprehensive exploration of molecular interactions, this narrative review elucidates the reciprocal dynamics between the gut microbiota and polyphenols, unveiling novel avenues for therapeutic intervention in cardiometabolic disorders. By unravelling the intricate cross-talk between these two entities, this review underscores the multifaceted roles of polyphenols in overall health and the pivotal role of gut microbiota modulation as a promising therapeutic strategy in mitigating the burden of cardiometabolic diseases.

Adenosine triphosphate release inhibitors targeting pannexin1 improve recovery after spinal cord injury

Traumatic spinal cord injury is characterized by immediate and irreversible tissue loss at the lesion site and secondary tissue damage. Secondary injuries should, in principle, be preventable, although no effective treatment options currently exist for patients with acute spinal cord injury. Traumatized tissues release excessive amounts of adenosine triphosphate and activate the P2X purinoceptor 7/pannexin1 complex, which is associated with secondary injury. We investigated the neuroprotective effects of the blue dye Brilliant Blue FCF, a selective inhibitor of P2X purinoceptor 7/pannexin1 that is approved for use as a food coloring, by comparing it with Brilliant Blue G, a P2X7 purinoceptor antagonist, and carbenoxolone, which attenuates P2X purinoceptor 7/pannexin1 function, in a rat spinal cord injury model. Brilliant Blue FCF administered early after spinal cord injury reduced spinal cord anatomical damage and improved motor recovery without apparent toxicity. Brilliant Blue G had the highest effect on this neurological recovery, with Brilliant Blue FCF and carbenoxolone having comparable improvement. Furthermore, Brilliant Blue FCF administration reduced local astrocytic and microglial activation and neutrophil infiltration, and no differences in these histological effects were observed between compounds. Thus, Brilliant Blue FCF protects spinal cord neurons after spinal cord injury and suppresses local inflammatory responses as well as Brilliant Blue G and carbenoxolone.

Unlocking the therapeutic potential of P2X7 receptor: a comprehensive review of its role in neurodegenerative disorders

The P2X7 receptor (P2X7R), an ATP-gated ion channel, has emerged as a crucial player in neuroinflammation and a promising therapeutic target for neurodegenerative disorders. This review explores the current understanding of P2X7R's structure, activation, and physiological roles, focusing on its expression and function in microglial cells. The article examines the receptor's involvement in calcium signaling, microglial activation, and polarization, as well as its role in the pathogenesis of Alzheimer's disease, Parkinson's disease, multiple sclerosis, and amyotrophic lateral sclerosis. The review highlights the complex nature of P2X7R signaling, discussing its potential neuroprotective and neurotoxic effects depending on the disease stage and context. It also addresses the development of P2X7R antagonists and their progress in clinical trials, identifying key research gaps and future perspectives for P2X7R-targeted therapy development. By providing a comprehensive overview of the current state of knowledge and future directions, this review serves as a valuable resource for researchers and clinicians interested in exploring the therapeutic potential of targeting P2X7R for the treatment of neurodegenerative disorders.

Mechanisms of enteric neuropathy in diverse contexts of gastrointestinal dysfunction

The enteric nervous system (ENS) commands moment-to-moment gut functions through integrative neurocircuitry housed in the gut wall. The functional continuity of ENS networks is disrupted in enteric neuropathies and contributes to major disturbances in normal gut activities including abnormal gut motility, secretions, pain, immune dysregulation, and disrupted signaling along the gut-brain axis. The conditions under which enteric neuropathy occurs are diverse and the mechanistic underpinnings are incompletely understood. The purpose of this brief review is to summarize the current understanding of the cell types involved, the conditions in which neuropathy occurs, and the mechanisms implicated in enteric neuropathy such as oxidative stress, toll like receptor signaling, purines, and pre-programmed cell death.

From diversity to disease: unravelling the role of enteric glial cells

Enteric glial cells (EGCs) are an essential component of the enteric nervous system (ENS) and play key roles in gastrointestinal development, homeostasis, and disease. Derived from neural crest cells, EGCs undergo complex differentiation processes regulated by various signalling pathways. Being among the most dynamic cells of the digestive system, EGCs react to cues in their surrounding microenvironment and communicate with various cell types and systems within the gut. Morphological studies and recent single cell RNA sequencing studies have unveiled heterogeneity among EGC populations with implications for regional functions and roles in diseases. In gastrointestinal disorders, including inflammatory bowel disease (IBD), infections and cancer, EGCs modulate neuroplasticity, immune responses and tumorigenesis. Recent evidence suggests that EGCs respond plastically to the microenvironmental cues, adapting their phenotype and functions in disease states and taking on a crucial role. They exhibit molecular abnormalities and alter communication with other intestinal cell types, underscoring their therapeutic potential as targets. This review delves into the multifaceted roles of EGCs, particularly emphasizing their interactions with various cell types in the gut and their significant contributions to gastrointestinal disorders. Understanding the complex roles of EGCs in gastrointestinal physiology and pathology will be crucial for the development of novel therapeutic strategies for gastrointestinal disorders.

Early life adversity promotes gastrointestinal dysfunction through a sex-dependent phenotypic switch in enteric glia

Irritable bowel syndrome and related disorders of gut-brain interaction (DGBI) are common and exhibit a complex, poorly understood etiology that manifests as abnormal gut motility and pain. Risk factors such as biological sex, stressors during critical periods, and inflammation are thought to influence DGBI vulnerability by reprogramming gut-brain circuits, but the specific cells affected are unclear. Here, we used a model of early life stress to understand cellular mechanisms in the gut that produce DGBIs. Our findings identify enteric glia as a key cellular substrate in which stress and biological sex converge to dictate DGBI susceptibility. Enteric glia exhibit sexual dimorphism in genes and functions related to cellular communication, inflammation, and disease susceptibility. Experiencing early life stress has sex-specific effects on enteric glia that cause a phenotypic switch in male glia toward a phenotype normally observed in females. This phenotypic transformation is followed by physiological changes in the gut, mirroring those observed in DGBI in humans. These effects are mediated, in part, by alterations to glial prostaglandin and endocannabinoid signaling. Together, these data identify enteric glia as a cellular integration site through which DGBI risk factors produce changes in gut physiology and suggest that manipulating glial signaling may represent an attractive target for sex-specific therapeutic strategies in DGBIs.

Enteric Nervous System Alterations in Inflammatory Bowel Disease: Perspectives and Implications

The enteric nervous system (ENS), consisting of neurons and glial cells, is situated along the gastrointestinal (GI) tract's wall and plays a crucial role in coordinating digestive processes. Recent research suggests that the optimal functioning of the GI system relies on intricate connections between the ENS, the intestinal epithelium, the immune system, the intestinal microbiome, and the central nervous system (CNS). Inflammatory bowel disease (IBD) encompasses a group of chronic inflammatory disorders, such as Crohn's disease (CD) and ulcerative colitis (UC), characterized by recurring inflammation and damage to the GI tract. This review explores emerging research in the dynamic field of IBD and sheds light on the potential role of ENS alterations in both the etiology and management of IBD. Specifically, we delve into IBD-induced enteric glial cell (EGC) activation and its implications for persistent enteric gliosis, elucidating how this activation disrupts GI function through alterations in the gut-brain axis (GBA). Additionally, we examine IBD-associated ENS alterations, focusing on EGC senescence and the acquisition of the senescence-associated secretory phenotype (SASP). We highlight the pivotal role of these changes in persistent GI inflammation and the recurrence of IBD. Finally, we discuss potential therapeutic interventions involving senotherapeutic agents, providing insights into potential avenues for managing IBD by targeting ENS-related mechanisms. This approach might represent a potential alternative to managing IBD and advance treatment of this multifaceted disease.

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

Background

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

Methods

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

Results

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

Conclusion

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

Caveolin-1 forms a complex with P2X7 receptor and tunes P2X7-mediated ATP signaling in mouse bone marrow-derived macrophages

The ionotropic purinergic P2X7 receptor responds to extracellular ATP and can trigger proinflammatory immune signaling in macrophages. Caveolin-1 (Cav-1) is known to modulate functions of macrophages and innate immunity. However, it is unknown how Cav-1 modulates P2X7 receptor activity in macrophages. We herein examined P2X7 receptor activity and macrophage functions using bone marrow-derived macrophages (BMDMs) from wild-type (WT) and Cav-1 knockout (KO) mice. ATP (1 mM) application caused biphasic increase in cytosolic [Ca2+] and sustained decrease in cytosolic [K+]. A specific P2X7 receptor blocker, A-740003, inhibited the maintained cytosolic [Ca2+] increase and cytosolic [K+] decrease. Total internal reflection fluorescent imaging and proximity ligation assays revealed a novel molecular complex formation between P2X7 receptors and Cav-1 in WT BMDMs that were stimulated with lipopolysaccharides. This molecular coupling was increased by ATP application. Specifically, the ATP-induced Ca2+ influx and K+ efflux through P2X7 receptors were increased in Cav-1 KO BMDMs, even though the total and surface protein levels of P2X7 receptors in WT and Cav-1 KO BMDMs were unchanged. Cell-impermeable dye (TO-PRO3) uptake analysis revealed that macropore formation of P2X7 receptors was enhanced in Cav-1 KO BMDMs. Cav-1 KO BMDMs increased ATP-induced IL-1β secretion, reactive oxygen species production, Gasdermin D (GSDMD) cleavage, and lactate dehydrogenase release indicating pyroptosis. A-740003 completely prevented ATP-induced pyroptosis. In combination, these datasets show that Cav-1 has a negative effect on P2X7 receptor activity in BMDMs and that Cav-1 in macrophages may contribute to finely tuned immune responses by preventing excessive IL-1β secretion and pyroptosis.NEW & NOTEWORTHY In bone marrow-derived macrophages, Cav-1 suppresses the macropore formation of P2X7 receptors through their direct or indirect interactions, resulting in reduced membrane permeability of cations (Ca2+ and K+) and large cell-impermeable dye (TO-PRO3) induced by ATP. Cav-1 also inhibits ATP-induced IL-1β secretion, ROS production, GSDMD cleavage, and pyroptosis. Cav-1 contributes to the maintenance of proper immune responses by finely tuning IL-1β secretion and cell death in macrophages.

Biological functions of connexins in the development of inflammatory bowel disease

Inflammatory bowel disease (IBD) is a group of chronic intestinal inflammatory diseases with unknown etiology. Gap junctions composed of connexins (Cxs) have been recently validated as an important factor in the development of IBD. Under IBD-induced inflammatory response in the gut, gap junctions connect multiple signaling pathways involved in the interaction between inflammatory cells with other intestinal cells, which altogether mediate the development of IBD. This paper is a narrative review aiming to comprehensively elucidate the biological function of connexins, especially the ubiquitously and predominantly expressed Cx43, in the pathogenesis of IBD.

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.

Aberrations in Cell Signaling Quantified in Diabetic Murine Globes after Injury

The corneal epithelium is an avascular structure that has a unique wound healing mechanism, which allows for rapid wound closure without compromising vision. This wound healing mechanism is attenuated in diabetic patients, resulting in poor clinical outcomes and recurrent non-healing erosion. We investigated changes in cellular calcium signaling activity during the wound response in murine diabetic tissue using live cell imaging from both ex vivo and in vitro models. The calcium signaling propagation in diabetic cells was significantly decreased and displayed altered patterns compared to non-diabetic controls. Diabetic cells and tissue display distinct expression of the purinergic receptor, P2X7, which mediates the wound healing response. We speculate that alterations in P2X7 expression, interactions with other proteins, and calcium signaling activity significantly impact the wound healing response. This may explain aberrations in the diabetic wound response.

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.

Sexually Dimorphic Effects of Histamine Degradation by Enteric Glial Histamine N-Methyltransferase (HNMT) on Visceral Hypersensitivity

Histamine is a neuromodulator that affects gut motility and visceral sensitivity through intrinsic and extrinsic neural pathways, yet the mechanisms regulating histamine availability in these pathways remain poorly understood. Here, we show that enteric glia contribute to histamine clearance in the enteric nervous system (ENS) through their expression of the enzyme histamine N-methyltransferase (HNMT). Glial HNMT expression was initially assessed using immunolabeling and gene expression, and functionally tested using CRISPR-Cas9 to create a Cre-dependent conditional Hnmt ablation model targeting glia. Immunolabeling, calcium imaging, and visceromotor reflex recordings were used to assess the effects on ENS structure and visceral hypersensitivity. Immunolabeling and gene expression data show that enteric neurons and glia express HNMT. Deleting Hnmt in Sox10+ enteric glia increased glial histamine levels and altered visceromotor responses to colorectal distension in male mice, with no effect in females. Interestingly, deleting glial Hnmt protected males from histamine-driven visceral hypersensitivity. These data uncover a significant role for glial HNMT in histamine degradation in the gut, which impacts histamine-driven visceral hypersensitivity in a sex-dependent manner. Changes in the capacity of glia to clear histamines could play a role in the susceptibility to developing visceral pain in disorders of the gut-brain interaction.

The Eph/ephrin system symphony of gut inflammation

The extent of gut inflammation depends largely on the gut barrier's integrity and enteric neuroimmune interactions. However, the factors and molecular mechanisms that regulate inflammation-related changes in the enteric nervous system (ENS) remain largely unexplored. Eph/ephrin signaling is critical for inflammatory response, neuronal activation, and synaptic plasticity in the brain, but its presence and function in the ENS have been largely unknown to date. This review discusses the critical role of Eph/ephrin in regulating gut homeostasis, inflammation, neuroimmune interactions, and pain pathways. Targeting the Eph/ephrin system offers innovative treatments for gut inflammation disorders, offering hope for enhanced patient prognosis, pain management, and overall quality of life.

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.

Enteric neuro-immune interactions in intestinal health and disease

The enteric nervous system is an autonomous neuronal circuit that regulates many processes far beyond the peristalsis in the gastro-intestinal tract. This circuit, consisting of enteric neurons and enteric glial cells, can engage in many intercellular interactions shaping the homeostatic microenvironment in the gut. Perhaps the most well documented interactions taking place, are the intestinal neuro-immune interactions which are essential for the fine-tuning of oral tolerance. In the context of intestinal disease, compelling evidence demonstrates both protective and detrimental roles for this bidirectional neuro-immune signaling. This review discusses the different immune cell types that are recognized to engage in neuronal crosstalk during intestinal health and disease. Highlighting the molecular pathways involved in the neuro-immune interactions might inspire novel strategies to target intestinal disease.

Effects of experimental ulcerative colitis on myenteric neurons in P2X7-knockout mice

This study aimed to investigate the distal colon myenteric plexus and enteric glial cells (EGCs) in P2X7 receptor-deficient (P2X7-/-) animals after the induction of experimental ulcerative colitis. 2,4,6-Trinitrobenzene sulfonic acid (TNBS) was injected into the distal colon of C57BL/6 (WT) and P2X7 receptor gene-deficient (P2X7-/-, KO) animals. Distal colon tissues in the WT and KO groups were analyzed 24 h and 4 days after administration. The tissues were analyzed by double immunofluorescence of the P2X7 receptor with neuronal nitric oxide synthase (nNOS)-immunoreactive (ir), choline acetyltransferase (ChAT)-ir, and PGP9.5 (pan neuronal)-ir, and their morphology was assessed by histology. The quantitative analysis revealed 13.9% and 7.1% decreases in the number of P2X7 receptor-immunoreactive (ir) per ganglion in the 24 h-WT/colitis and 4 day-WT/colitis groups, respectively. No reduction in the number of nNOS-ir, choline ChAT-ir, and PGP9.5-ir neurons per ganglion was observed in the 4 day-KO/colitis group. In addition, a reduction of 19.3% in the number of GFAP (glial fibrillary acidic protein)-expressing cells per ganglion was found in the 24 h-WT/colitis group, and a 19% increase in the number of these cells was detected in the 4 day-WT/colitis group. No profile area changes in neurons were observed in the 24 h-WT and 24 h-KO groups. The 4 day-WT/colitis and 4 day-KO/colitis groups showed increases in the profile neuronal areas of nNOS, ChAT, and PGP9.5. The histological analysis showed hyperemia, edema, or cellular infiltration in the 24 h-WT/colitis and 4 day-WT/colitis groups. Edema was observed in the 4 day-KO/colitis group, which showed no histological changes compared with the 24 h-KO/colitis group. We concluded that ulcerative colitis differentially affected the neuronal classes in the WT and KO animals, demonstrating the potential participation and neuroprotective effect of the P2X7 receptor in enteric neurons in inflammatory bowel disease.

BQ788 reveals glial ETB receptor modulation of neuronal cholinergic and nitrergic pathways to inhibit intestinal motility: Linked to postoperative ileus

BACKGROUND AND PURPOSE

ET-1 signalling modulates intestinal motility and inflammation, but the role of ET-1/ETB receptor signalling is poorly understood. Enteric glia modulate normal motility and inflammation. We investigated whether glial ETB signalling regulates neural-motor pathways of intestinal motility and inflammation.

EXPERIMENTAL APPROACH

We studied ETB signalling using: ETB drugs (ET-1, SaTX, BQ788), activity-dependent stimulation of neurons (high K+ -depolarization, EFS), gliotoxins, Tg (Ednrb-EGFP)EP59Gsat/Mmucd mice, cell-specific mRNA in Sox10CreERT2 ;Rpl22-HAflx or ChATCre ;Rpl22-HAflx mice, Sox10CreERT2 ::GCaMP5g-tdT, Wnt1Cre2 ::GCaMP5g-tdT mice, muscle tension recordings, fluid-induced peristalsis, ET-1 expression, qPCR, western blots, 3-D LSM-immunofluorescence co-labelling studies in LMMP-CM and a postoperative ileus (POI) model of intestinal inflammation.

KEY RESULTS

In the muscularis externa ETB receptor is expressed exclusively in glia. ET-1 is expressed in RiboTag (ChAT)-neurons, isolated ganglia and intra-ganglionic varicose-nerve fibres co-labelled with peripherin or SP. ET-1 release provides activity-dependent glial ETB receptor modulation of Ca2+ waves in neural evoked glial responses. BQ788 reveals amplification of glial and neuronal Ca2+ responses and excitatory cholinergic contractions, sensitive to L-NAME. Gliotoxins disrupt SaTX-induced glial-Ca2+ waves and prevent BQ788 amplification of contractions. The ETB receptor is linked to inhibition of contractions and peristalsis. Inflammation causes glial ETB up-regulation, SaTX-hypersensitivity and glial amplification of ETB signalling. In vivo BQ788 (i.p., 1 mg·kg-1 ) attenuates intestinal inflammation in POI.

CONCLUSION AND IMPLICATIONS

Enteric glial ET-1/ETB signalling provides dual modulation of neural-motor circuits to inhibit motility. It inhibits excitatory cholinergic and stimulates inhibitory nitrergic motor pathways. Amplification of glial ETB receptors is linked to muscularis externa inflammation and possibly pathogenic mechanisms of POI.

Structure-Based Design and Synthesis of Stapled 10Panx1 Analogues for Use in Cardiovascular Inflammatory Diseases

Following a rational design, a series of macrocyclic ("stapled") peptidomimetics of 10Panx1, the most established peptide inhibitor of Pannexin1 (Panx1) channels, were developed and synthesized. Two macrocyclic analogues SBL-PX1-42 and SBL-PX1-44 outperformed the linear native peptide. During in vitro adenosine triphosphate (ATP) release and Yo-Pro-1 uptake assays in a Panx1-expressing tumor cell line, both compounds were revealed to be promising bidirectional inhibitors of Panx1 channel function, able to induce a two-fold inhibition, as compared to the native 10Panx1 sequence. The introduction of triazole-based cross-links within the peptide backbones increased helical content and enhanced in vitro proteolytic stability in human plasma (>30-fold longer half-lives, compared to 10Panx1). In adhesion assays, a "double-stapled" peptide, SBL-PX1-206 inhibited ATP release from endothelial cells, thereby efficiently reducing THP-1 monocyte adhesion to a TNF-α-activated endothelial monolayer and making it a promising candidate for future in vivo investigations in animal models of cardiovascular inflammatory disease.

A branching model of lineage differentiation underpinning the neurogenic potential of enteric glia

Glial cells have been proposed as a source of neural progenitors, but the mechanisms underpinning the neurogenic potential of adult glia are not known. Using single cell transcriptomic profiling, we show that enteric glial cells represent a cell state attained by autonomic neural crest cells as they transition along a linear differentiation trajectory that allows them to retain neurogenic potential while acquiring mature glial functions. Key neurogenic loci in early enteric nervous system progenitors remain in open chromatin configuration in mature enteric glia, thus facilitating neuronal differentiation under appropriate conditions. Molecular profiling and gene targeting of enteric glial cells in a cell culture model of enteric neurogenesis and a gut injury model demonstrate that neuronal differentiation of glia is driven by transcriptional programs employed in vivo by early progenitors. Our work provides mechanistic insight into the regulatory landscape underpinning the development of intestinal neural circuits and generates a platform for advancing glial cells as therapeutic agents for the treatment of neural deficits.

Uncovering the Novel Role of NR1D1 in Regulating BNIP3-Mediated Mitophagy in Ulcerative Colitis

BACKGROUND

Ulcerative colitis (UC) is a chronic, incurable condition characterized by mucosal inflammation and intestinal epithelial cell (IEC) damage. The circadian clock gene NR1D1, implicated in UC and the critical mitophagy process for epithelial repair, needs further exploration regarding its role in mitophagy regulation in UC.

METHODS

We created a jet lag mouse model and induced colitis with dextran sulfate sodium (DSS), investigating NR1D1's role. Intestinal-specific Nr1d1 knockout mice were also generated. RNA sequencing, chromatin immunoprecipitation (ChIP), and dual-luciferase reporter assays helped ascertain NR1D1's regulatory effect on BNIP3 expression. The mitochondrial state in IECs was assessed through transmission electron microscopy, while confocal microscopy evaluated mitophagy-associated protein expression in colon tissue and CCD841 cells. Cell apoptosis and reactive oxygen species (ROS) were measured via flow cytometry.

RESULTS

We observed reduced NR1D1 expression in the IECs of UC patients, accentuated under jet lag and DSS exposure in mice. NR1D1 ablation led to disrupted immune homeostasis and declined mitophagy in IECs. NR1D1, usually a transcriptional repressor, was a positive regulator of BNIP3 expression, leading to impaired mitophagy, cellular inflammation, and apoptosis. Administering the NR1D1 agonist SR9009 ameliorated colitis symptoms, primarily by rectifying defective mitophagy.

CONCLUSIONS

Our results suggest that NR1D1 bridges the circadian clock and UC, controlling BNIP3-mediated mitophagy and representing a potential therapeutic target. Its agonist, SR9009, shows promise in UC symptom alleviation.

The Crucial Role of the Interstitial Cells of Cajal in Neurointestinal Diseases

Neurointestinal diseases result from dysregulated interactions between the nervous system and the gastrointestinal (GI) tract, leading to conditions such as Hirschsprung's disease and irritable bowel syndrome. These disorders affect many people, significantly diminishing their quality of life and overall health. Central to GI motility are the interstitial cells of Cajal (ICC), which play a key role in muscle contractions and neuromuscular transmission. This review highlights the role of ICC in neurointestinal diseases, revealing their association with various GI ailments. Understanding the functions of the ICC could lead to innovative perspectives on the modulation of GI motility and introduce new therapeutic paradigms. These insights have the potential to enhance efforts to combat neurointestinal diseases and may lead to interventions that could alleviate or even reverse these conditions.

Recent advances in the structure and activation mechanisms of metabolite-releasing Pannexin 1 channels

Pannexin 1 (PANX1) is a widely expressed large-pore ion channel located in the plasma membrane of almost all vertebrate cells. It possesses a unique ability to act as a conduit for both inorganic ions (e.g. potassium or chloride) and bioactive metabolites (e.g. ATP or glutamate), thereby activating varying signaling pathways in an autocrine or paracrine manner. Given its crucial role in cell-cell interactions, the activity of PANX1 has been implicated in maintaining homeostasis of cardiovascular, immune, and nervous systems. Dysregulation of PANX1 has also been linked to numerous diseases, such as ischemic stroke, seizure, and inflammatory disorders. Therefore, the mechanisms underlying different modes of PANX1 activation and its context-specific channel properties have gathered significant attention. In this review, we summarize the roles of PANX1 in various physiological processes and diseases, and analyze the accumulated lines of evidence supporting diverse molecular mechanisms associated with different PANX1 activation modalities. We focus on examining recent discoveries regarding PANX1 regulations by reversible post-translational modifications, elevated intracellular calcium concentration, and protein-protein interactions, as well as by irreversible cleavage of its C-terminal tail. Additionally, we delve into the caveats in the proposed PANX1 gating mechanisms and channel open-closed configurations by critically analyzing the structural insights derived from cryo-EM studies and the unitary properties of PANX1 channels. By doing so, we aim to identify potential research directions for a better understanding of the functions and regulations of PANX1 channels.

Puerarin Inhibits NLRP3-Caspase-1-GSDMD-Mediated Pyroptosis via P2X7 Receptor in Cardiomyocytes and Macrophages

Diabetic cardiomyopathy (DCM) is a critical complication of long-term chronic diabetes mellitus, and it is characterized by myocardial fibrosis and myocardial hypertrophy. Previous studies have shown that the pyroptosis pathway was significantly activated in DCM and may be related to the P2X7 receptor. However, the role of the P2X7 receptor in the development of DCM with pyroptosis is still unclear. In this study, we aimed to explore the mechanism of puerarin and whether the P2X7 receptor can be used as a new target for puerarin in the treatment of DCM. We adopted systematic pharmacology and bioinformatic approaches to identify the potential targets of puerarin for treating DCM. Additionally, we employed D-glucose-induced H9C2 rat cardiomyocytes and lipopolysaccharide-treated RAW264.7 mouse mononuclear macrophages as the in vitro model on DCM research, which is close to the pathological conditions. The mRNA expression of cytokines in H9C2 cells and RAW264.7 macrophages was detected. The protein expressions of NLRP3, N-GSDMD, cleaved-caspase-1, and the P2X7 receptor were investigated with Western blot analysis. Furthermore, molecular docking of puerarin and the P2X7 receptor was conducted based on CDOCKER. A total of 348 puerarin targets and 4556 diabetic cardiomyopathy targets were detected, of which 218 were cross targets. We demonstrated that puerarin is effective in enhancing cardiomyocyte viability and improving mitochondrial function. In addition, puerarin is efficacious in blocking NLRP3-Caspase-1-GSDMD-mediated pyroptosis in H9C2 cells and RAW264.7 cells, alleviating cellular inflammation. On the other hand, similar experimental results were obtained by intervention with the P2X7 receptor antagonist A740003, suggesting that the protective effects of puerarin are related to the P2X7 receptor. The molecular docking results indicated key binding activity between the P2X7 receptor and puerarin. These findings indicate that puerarin effectively regulated the pyroptosis signaling pathway during DCM, and this regulation was associated with the P2X7 receptor.

Study of the roles of caspase-3 and nuclear factor kappa B in myenteric neurons in a P2X7 receptor knockout mouse model of ulcerative colitis

BACKGROUND

The literature indicates that the enteric nervous system is affected in inflammatory bowel diseases (IBDs) and that the P2X7 receptor triggers neuronal death. However, the mechanism by which enteric neurons are lost in IBDs is unknown.

AIM

To study the role of the caspase-3 and nuclear factor kappa B (NF-κB) pathways in myenteric neurons in a P2X7 receptor knockout (KO) mouse model of IBDs.

METHODS

Forty male wild-type (WT) C57BL/6 and P2X7 receptor KO mice were euthanized 24 h or 4 d after colitis induction by 2,4,6-trinitrobenzene sulfonic acid (colitis group). Mice in the sham groups were injected with vehicle. The mice were divided into eight groups (n = 5): The WT sham 24 h and 4 d groups, the WT colitis 24 h and 4 d groups, the KO sham 24 h and 4 d groups, and the KO colitis 24 h and 4 d groups. The disease activity index (DAI) was analyzed, the distal colon was collected for immunohistochemistry analyses, and immunofluorescence was performed to identify neurons immunoreactive (ir) for calretinin, P2X7 receptor, cleaved caspase-3, total caspase-3, phospho-NF-κB, and total NF-κB. We analyzed the number of calretinin-ir and P2X7 receptor-ir neurons per ganglion, the neuronal profile area (µm²), and corrected total cell fluorescence (CTCF).

RESULTS

Cells double labeled for calretinin and P2X7 receptor, cleaved caspase-3, total caspase-3, phospho-NF-κB, or total NF-κB were observed in the WT colitis 24 h and 4 d groups. The number of calretinin-ir neurons per ganglion was decreased in the WT colitis 24 h and 4 d groups compared to the WT sham 24 h and 4 d groups, respectively (2.10 ± 0.13 vs 3.33 ± 0.17, P < 0.001; 2.92 ± 0.12 vs 3.70 ± 0.11, P < 0.05), but was not significantly different between the KO groups. The calretinin-ir neuronal profile area was increased in the WT colitis 24 h group compared to the WT sham 24 h group (312.60 ± 7.85 vs 278.41 ± 6.65, P < 0.05), and the nuclear profile area was decreased in the WT colitis 4 d group compared to the WT sham 4 d group (104.63 ± 2.49 vs 117.41 ± 1.14, P < 0.01). The number of P2X7 receptor-ir neurons per ganglion was decreased in the WT colitis 24 h and 4 d groups compared to the WT sham 24 h and 4 d groups, respectively (19.49 ± 0.35 vs 22.21 ± 0.18, P < 0.001; 20.35 ± 0.14 vs 22.75 ± 0.51, P < 0.001), and no P2X7 receptor-ir neurons were observed in the KO groups. Myenteric neurons showed ultrastructural changes in the WT colitis 24 h and 4 d groups and in the KO colitis 24 h group. The cleaved caspase-3 CTCF was increased in the WT colitis 24 h and 4 d groups compared to the WT sham 24 h and 4 d groups, respectively (485949 ± 14140 vs 371371 ± 16426, P < 0.001; 480381 ± 11336 vs 378365 ± 4053, P < 0.001), but was not significantly different between the KO groups. The total caspase-3 CTCF, phospho-NF-κB CTCF, and total NF-κB CTCF were not significantly different among the groups. The DAI was recovered in the KO groups. Furthermore, we demonstrated that the absence of the P2X7 receptor attenuated inflammatory infiltration, tissue damage, collagen deposition, and the decrease in the number of goblet cells in the distal colon.

CONCLUSION

Ulcerative colitis affects myenteric neurons in WT mice but has a weaker effect in P2X7 receptor KO mice, and neuronal death may be associated with P2X7 receptor-mediated caspase-3 activation. The P2X7 receptor can be a therapeutic target for IBDs.

Degranulation of Mast Cells as a Target for Drug Development

Mast cells act as key effector cells of inflammatory responses through degranulation. Mast cell degranulation is induced by the activation of cell surface receptors, such as FcεRI, MRGPRX2/B2, and P2RX7. Each receptor, except FcεRI, varies in its expression pattern depending on the tissue, which contributes to their differing involvement in inflammatory responses depending on the site of occurrence. Focusing on the mechanism of allergic inflammatory responses by mast cells, this review will describe newly identified mast cell receptors in terms of their involvement in degranulation induction and patterns of tissue-specific expression. In addition, new drugs targeting mast cell degranulation for the treatment of allergy-related diseases will be introduced.

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.

The enteric nervous system

Of all the organ systems in the body, the gastrointestinal tract is the most complicated in terms of the numbers of structures involved, each with different functions, and the numbers and types of signaling molecules utilized. The digestion of food and absorption of nutrients, electrolytes, and water occurs in a hostile luminal environment that contains a large and diverse microbiota. At the core of regulatory control of the digestive and defensive functions of the gastrointestinal tract is the enteric nervous system (ENS), a complex system of neurons and glia in the gut wall. In this review, we discuss 1) the intrinsic neural control of gut functions involved in digestion and 2) how the ENS interacts with the immune system, gut microbiota, and epithelium to maintain mucosal defense and barrier function. We highlight developments that have revolutionized our understanding of the physiology and pathophysiology of enteric neural control. These include a new understanding of the molecular architecture of the ENS, the organization and function of enteric motor circuits, and the roles of enteric glia. We explore the transduction of luminal stimuli by enteroendocrine cells, the regulation of intestinal barrier function by enteric neurons and glia, local immune control by the ENS, and the role of the gut microbiota in regulating the structure and function of the ENS. Multifunctional enteric neurons work together with enteric glial cells, macrophages, interstitial cells, and enteroendocrine cells integrating an array of signals to initiate outputs that are precisely regulated in space and time to control digestion and intestinal homeostasis.

Intestinal distension orchestrates neuronal activity in the enteric nervous system of adult mice

The enteric nervous system (ENS) regulates the motor, secretory and defensive functions of the gastrointestinal tract. Enteric neurons integrate mechanical and chemical inputs from the gut lumen to generate complex motor outputs. How intact enteric neural circuits respond to changes in the gut lumen is not well understood. We recorded intracellular calcium in live-cell confocal recordings in neurons from intact segments of mouse intestine in order to investigate neuronal response to luminal mechanical and chemical stimuli. Wnt1-, ChAT- and Calb1-GCaMP6 mice were used to record neurons from the jejunum and colon. We measured neuronal calcium response to KCl (75 mM), veratridine (10 μM), 1,1-dimethyl-4-phenylpiperazinium (DMPP; 100 μM) or luminal nutrients (Ensure®), in the presence or absence of intraluminal distension. In the jejunum and colon, distension generated by the presence of luminal content (chyme and faecal pellets, respectively) renders the underlying enteric circuit unresponsive to depolarizing stimuli. In the distal colon, high levels of distension inhibit neuronal response to KCl, while intermediate levels of distension reorganize Ca2+ response in circumferentially propagating slow waves. Mechanosensitive channel inhibition suppresses distension-induced Ca2+ elevations, and calcium-activated potassium channel inhibition restores neuronal response to KCl, but not DMPP in the distended colon. In the jejunum, distension prevents a previously unknown tetrodotoxin-resistant neuronal response to luminal nutrient stimulation. Our results demonstrate that intestinal distension regulates the excitability of ENS circuits via mechanosensitive channels. Physiological levels of distension locally silence or synchronize neurons, dynamically regulating the excitability of enteric neural circuits based on the content of the intestinal lumen. KEY POINTS: How the enteric nervous system of the gastrointestinal tract responds to luminal distension remains to be fully elucidated. Here it is shown that intestinal distension modifies intracellular calcium levels in the underlying enteric neuronal network, locally and reversibly silencing neurons in the distended regions. In the distal colon, luminal distension is integrated by specific mechanosensitive channels and coordinates the dynamics of neuronal activation within the enteric network. In the jejunum, distension suppresses the neuronal calcium responses induced by luminal nutrients. Physiological levels of distension dynamically regulate the excitability of enteric neuronal circuits.

Colonic motility adjustments in acute and chronic DSS-induced colitis

AIMS

Inflammatory bowel disease is recurrent inflammation that affects the gastrointestinal tract causing changes in intestinal motility. The evolution of these changes is not completely understood. The aim of this study was to evaluate anatomical and functional changes in the colon during the development of acute and chronic DSS-induced ulcerative colitis (UC) in C57Bl/6 mice.

MATERIALS AND METHODS

Mice were relocated into 5 groups: control (GC) and groups exposed to DSS 3 % for 2 (DSS2d), 5 (DSS5d) and 7 DSS7d) days (acute UC) or 3 cycles (DSS3C; Chronic UC). Mice were monitored daily. After euthanasia, colonic tissue was assessed with histological, immunofluorescence and colon manometry methods.

KEY FINDINGS

Ulcerative Colitis is a chronic disease characterized by overt inflammation of the colon. Here we investigate whether the morphological changes caused by UC in the colonic wall, in tuft cells and in enteric neurons also promote any alteration in colonic motility patterns. UC Promotes thickening in the colonic wall, fibrosis, reduction in the number of tuft cells and consequently goblet cells also, without promoting neuronal death however there is a change in the chemical code of myenteric neurons. All of these morphological changes were responsible for causing a change in colonic contractions, colonic migration motor complex, total time of gastrointestinal transit and therefore promoting dysmotility. Further studies stimulating a hyperplasia of tuft cells may be the way to try to keep the colonic epithelium healthy, reducing the damage caused by UC.

SIGNIFICANCE

Increasing disease pathology of DSS-induced UC induces structural and neuroanatomical changes and driven damage to cholinergic neurons causes colonic dysmotility, including increase of cholinergic myenteric neurons, followed by variations in the motility pattern of different regions of the colon that taking together characterize colonic dysmotility.

Progress in the relationship between P2X7R and colorectal cancer

Purinergic ligand-gated ion channel 7 receptor (P2X7R) is a nonselective cation channel of the purinergic receptor family. P2X7R is activated by adenosine triphosphate (ATP) and plays a significant role in inflammatory and autoimmune diseases by triggering cellular signal transduction. More importantly, P2X7R is abnormally expressed in many tumor cells and is involved in the progression of various tumor cells. Studies have shown that the irregular expression of P2X7R in colorectal cancer (CRC) can not only indirectly affect the occurrence and development of CRC by promoting inflammatory bowel disease but also directly affect the proliferation and metastasis of CRC cells. P2X7R plays a bidirectional role in cancer induction and inhibition by mediating complex signaling pathways in CRC, and its expression level is closely related to the overall survival of CRC patients. Therefore, P2X7R may be a biomarker and potential therapeutic target for the development and prognosis of CRC. In this paper, we review the research progress on P2X7R in CRC.

Amount of Pannexin 1 in Smooth Muscle Cells Regulates Sympathetic Nerve-Induced Vasoconstriction

BACKGROUND

Panx1 (pannexin 1) forms high conductance channels that secrete ATP upon stimulation. The role of Panx1 in mediating constriction in response to direct sympathetic nerve stimulation is not known. Additionally, it is unknown how the expression level of Panx1 in smooth muscle cells (SMCs) influences α-adrenergic responses. We hypothesized that the amount of Panx1 in SMCs dictates the levels of sympathetic constriction and blood pressure.

METHODS

To test this hypothesis, we used genetically modified mouse models enabling expression of Panx1 in vascular cells to be varied. Electrical field stimulation on isolated arteries and blood pressure were assessed.

RESULTS

Genetic deletion of SMC Panx1 prevented constriction by electric field stimulation of sympathetic nerves. Conversely, overexpression of Panx1 in SMCs using a ROSA26 transgenic model increased sympathetic nerve-mediated constriction. Connexin 43 hemichannel inhibitors did not alter constriction. Next, we evaluated the effects of altered SMC Panx1 expression on blood pressure. To do this, we created mice combining a global Panx1 deletion, with ROSA26-Panx1 under the control of an inducible SMC specific Cre (Myh11). This resulted in mice that could express only human Panx1, only in SMCs. After tamoxifen, these mice had increased blood pressure that was acutely decreased by the Panx1 inhibitor spironolactone. Control mice genetically devoid of Panx1 did not respond to spironolactone.

CONCLUSIONS

These data suggest Panx1 in SMCs could regulate the extent of sympathetic nerve constriction and blood pressure. The results also show the feasibility humanized Panx1-mouse models to test pharmacological candidates.

Activation of Intra-nodose Ganglion P2X7 Receptors Elicit Increases in Neuronal Activity

Vagus nerve innervates several organs including the heart, stomach, and pancreas among others. Somas of sensory neurons that project through the vagal nerve are located in the nodose ganglion. The presence of purinergic receptors has been reported in neurons and satellite glial cells in several sensory ganglia. In the nodose ganglion, calcium depletion-induced increases in neuron activity can be partly reversed by P2X7 blockers applied directly into the ganglion. The later suggest a possible role of P2X7 receptors in the modulation of neuronal activity within this sensory ganglion. We aimed to characterize the response to P2X7 activation in nodose ganglion neurons under physiological conditions. Using an ex vivo preparation for electrophysiological recordings of the neural discharges of nodose ganglion neurons, we found that treatments with ATP induce transient neuronal activity increases. Also, we found a concentration-dependent increase in neural activity in response to Bz-ATP (ED₅₀ = 0.62 mM, a selective P2X7 receptor agonist), with a clear desensitization pattern when applied every ~ 30 s. Electrophysiological recordings from isolated nodose ganglion neurons reveal no differences in the responses to Bz-ATP and ATP. Finally, we showed that the P2X7 receptor was expressed in the rat nodose ganglion, both in neurons and satellite glial cells. Additionally, a P2X7 receptor negative allosteric modulator decreased the duration of Bz-ATP-induced maximal responses without affecting their amplitude. Our results show the presence of functional P2X7 receptors under physiological conditions within the nodose ganglion of the rat, and suggest that ATP modulation of nodose ganglion activity may be in part mediated by the activation of P2X7 receptors.

Macrophages and glia are the dominant P2X7-expressing cell types in the gut nervous system-No evidence for the role of neuronal P2X7 receptors in colitis

The blockade or deletion of the pro-inflammatory P2X7 receptor channel has been shown to reduce tissue damage and symptoms in models of inflammatory bowel disease, and P2X7 receptors on enteric neurons were suggested to mediate neuronal death and associated motility changes. Here, we used P2X7-specific antibodies and nanobodies, as well as a bacterial artificial chromosome transgenic P2X7-EGFP reporter mouse model and P2rx7^-/- controls to perform a detailed analysis of cell type-specific P2X7 expression and possible overexpression effects in the enteric nervous system of the distal colon. In contrast to previous studies, we did not detect P2X7 in neurons but found dominant expression in glia and macrophages, which closely interact with the neurons. The overexpression of P2X7 per se did not induce significant pathological effects. Our data indicate that macrophages and/or glia account for P2X7-mediated neuronal damage in inflammatory bowel disease and provide a refined basis for the exploration of P2X7-based therapeutic strategies.

Effects of probenecid and brilliant blue G on rat enteric glial cells following intestinal ischemia and reperfusion

The P2X7 receptor participates in several intracellular events and acts with the pannexin-1 channel. This study examined the effects of probenecid (PB) and brilliant blue G (BBG), which are antagonists of the pannexin-1 channel and P2X7 receptor, respectively, on rat ileum enteric glial cells after on ischemia and reperfusion. The ileal vessels were occluded for 45 min with nontraumatic vascular tweezers, and reperfusion was performed for periods of 24 h and 14 and 28 days. After ischemia (IR groups), the animals were treated with BBG (BG group) or PB (PB group). The double-labeling results demonstrated the following: the P2X7 receptor was present in enteric glial cells (S100β) and enteric neurons positive for HuC/D; enteric glial cells exhibited different phenotypes; some enteric glial cells were immunoreactive to only S100β or GFAP; and the pannexin-1 channel was present in enteric glial cells (GFAP). Density (in cells/cm²) analyses showed that the IR group exhibited a decrease in the number of cells immunoreactive for the P2X7 receptor, pannexin-1, and HuC/D and that treatment with BBG or PB resulted in the recovery of the numbers of these cells. The number of glial cells (S100β and GFAP) was higher in the IR group, and the treatments decreased the number of these cells to the normal value. However, the PB group did not exhibit recovery of S100β-positive glia. The cell profile area (μm²) of S100β-positive enteric glial cells decreased to the normal value after BBG treatment, whereas no recovery was observed in the PB group. The ileum contractile activity was decreased in the IR group and returned to baseline in the BG and PB groups. BBG and PB can effectively induce the recovery of neurons and glia cells and are thus potential therapeutic agents in the treatment of gastrointestinal tract diseases.

Inhibition of PANX1 Channels Reduces the Malignant Properties of Human High-Risk Neuroblastoma

Pannexin 1 (PANX1) is expressed in many tissue types including tissues of neural origin. Neuroblastoma (NB) is a neural crest-derived malignancy mainly occurring in children. The majority of NB patients present with high-risk disease for which current therapies are ineffective. Here, we show that while PANX1 is expressed in NB of all stages, high PANX1 expression in high-risk NB is associated with a reduced survival probability. PANX1 channel inhibition using probenecid (PBN) or carbenoxolone (CBX) reduced the proliferation of our panel of high-risk NB cell lines. We show that expression of the Y10F PANX1 mutant, which cannot be phosphorylated on tyrosine 10 and acts in a dominant-negative manner, curtailed NB cell proliferation. Furthermore, PBN and CBX treatment halted the growth of NB spheroids and in some cases triggered the regression of established NB spheroids. Finally, both drugs reduced the progression of high-risk NB in vivo. Together our data indicate that PANX1 channels regulate human NB malignant properties and that the use of PBN or CBX may provide a new therapeutic approach for high-risk NB.

Oxidative Stress-Induced HMGB1 Translocation in Myenteric Neurons Contributes to Neuropathy in Colitis

High-mobility group box 1 (HMGB1) is a damage-associated molecular pattern released by dying cells to stimulate the immune response. During cell death, HMGB1 is translocated from the nucleus to the cytoplasm and passively released. High levels of secreted HMGB1 are observed in the faeces of inflammatory bowel disease (IBD) patients, indicating its role in IBD pathophysiology and potential as a non-invasive IBD biomarker. HMGB1 is important in regulating neuronal damage in the central nervous system; its pathological activity is intertwined with oxidative stress and inflammation. In this study, HMGB1 expression in the enteric nervous system and its relevance to intestinal neuroinflammation is explored in organotypic cultures of the myenteric plexus exposed to oxidative stimuli and in Winnie mice with spontaneous chronic colitis. Oxidative stimuli induced cytoplasmic translocation of HMGB1 in myenteric neurons in organotypic preparations. HMGB1 translocation correlated with enteric neuronal loss and oxidative stress in the myenteric ganglia of Winnie mice. Inhibition of HMGB1 by glycyrrhizic acid ameliorated HMGB1 translocation and myenteric neuronal loss in Winnie mice. These data highlight modulation of HMGB1 signalling as a therapeutic strategy to reduce the consequences of enteric neuroinflammation in colitis, warranting the exploration of therapeutics acting on the HMGB1 pathway as an adjunct treatment with current anti-inflammatory agents.

Continued P2X7 activation leads to mitochondrial fission and compromising microglial phagocytosis after subarachnoid haemorrhage

Subarachnoid haemorrhage (SAH) has a high rate of disability and mortality. Extremely damaging molecules, including adenosine triphosphate (ATP), are released from extravasated red blood cells and nerve cells, which activate microglia and induce sterile tissue injury and organ dysfunction. P2X purinoceptor 7 (P2X7) is one of the most important purine receptors on the microglial surface and is involved in the proinflammatory activation of microglia. While P2X7 can also affect microglial phagocytosis, the mechanism is not clear. Here, we demonstrated that microglial phagocytosis is progressively impaired under continued BzATP exposure and P2X7 activation. Furthermore, we found that P2X7 activation leads to increased intracellular Ca²⁺ levels and activates Calcineurin, which dephosphorylates dynamin-related protein 1 (DRP1) S637. The dephosphorylation of DRP1 at S637 leads to increased mitochondrial fission and decreased mitochondrial function, which may be responsible for the decreased microglial phagocytosis. Finally, we pharmacologically inhibited P2X7 activation in mice, which resulted in rescue of mitochondrial function and decreased microglial proliferation, but improved phagocytosis after SAH. Our study confirmed that P2X7 activation after SAH leads to the impairment of microglial phagocytosis through mitochondrial fission and verified that P2X7 inhibition restores microglial phagocytosis both in vitro and in vivo.

The Long-Term Pannexin 1 Ablation Produces Structural and Functional Modifications in Hippocampal Neurons

Enhanced activity and overexpression of Pannexin 1 (Panx1) channels contribute to neuronal pathologies such as epilepsy and Alzheimer's disease (AD). The Panx1 channel ablation alters the hippocampus's glutamatergic neurotransmission, synaptic plasticity, and memory flexibility. Nevertheless, Panx1-knockout (Panx1-KO) mice still retain the ability to learn, suggesting that compensatory mechanisms stabilize their neuronal activity. Here, we show that the absence of Panx1 in the adult brain promotes a series of structural and functional modifications in the Panx1-KO hippocampal synapses, preserving spontaneous activity. Compared to the wild-type (WT) condition, the adult hippocampal neurons of Panx1-KO mice exhibit enhanced excitability, a more complex dendritic branching, enhanced spine maturation, and an increased proportion of multiple synaptic contacts. These modifications seem to rely on the actin-cytoskeleton dynamics as an increase in the actin polymerization and an imbalance between the Rac1 and the RhoA GTPase activities were observed in Panx1-KO brain tissues. Our findings highlight a novel interaction between Panx1 channels, actin, and Rho GTPases, which appear to be relevant for synapse stability.

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.

Intrauterine exposure to oxidative stress induces caspase-1-dependent enteric nerve cell pyroptosis

PURPOSE

This study determined whether oxidative stress causes the developmental abnormalities of the enteric nervous system during the embryonic period.

METHODS

Using the test results of tissue specimens of children with Hirschsprung disease (HSCR), we established a pregnant rat model of oxidative stress and a cellular oxidative stress model to conduct related molecular, cellular, and histopathological experiments for exploration and validation.

RESULTS

The results of the quantitative real-time polymerase chain reaction assay indicated overexpression of pyroptosis markers (NLRP3, ASC, and caspase-1) in HSCR lesions and newborn pups in the oxidative stress group (treated with D-galactose). The expression of cathepsin D was significantly decreased in intestinal tissues of newborn pups in the oxidative stress group compared to the control group. Reactive oxygen species scavengers (N-acetyl-cysteine, NAC), the caspase-1 inhibitor (VX-765), and the NLRP3 siRNA could reverse the release of LDH, decrease the number of propidium iodide stained cells, and reduce the percentage of TUNEL/caspase-3 double-positive cells in the H₂O₂-treated group.

CONCLUSION

Oxidative stress can induce the death of enteric nerve cells by activating caspase-1-dependent pyroptosis through NLRP3 inflammasomes, which may contribute to abnormal enteric nervous system development.