Toll-like receptor 4-mediated enteric glia loss is critical for the development of necrotizing enterocolitis

Digging deeper into necrotizing enterocolitis: bridging clinical, microbial, and molecular perspectives

Necrotizing Enterocolitis (NEC) is a severe, life-threatening inflammatory condition of the gastrointestinal tract, especially affecting preterm infants. This review consolidates evidence from various biomedical disciplines to elucidate the complex pathogenesis of NEC, integrating insights from clinical, microbial, and molecular perspectives. It emphasizes the modulation of NEC-associated inflammatory pathways by probiotics and novel biologics, highlighting their therapeutic potential. We further critically examine dysbiotic alterations within the gut microbiota, with a particular focus on imbalances in bacterial and viral communities, which may contribute to the onset of NEC. The intricate interactions among toll-like receptor 4 (TLR4), microvascular integrity, immune activation, and the inflammatory milieu are meticulously summarized, offering a sophisticated understanding of NEC pathophysiology. This academic review aims to enhance the etiological comprehension of NEC, promote the development of targeted therapeutic interventions, and impart the significant impact of perinatal factors on the formulation of preventive and curative strategies for the disease.

Necrotizing enterocolitis: specific human milk oligosaccharides prevent enteric glia loss and hypomotility

BACKGROUND

Necrotizing enterocolitis (NEC) is mediated by toll-like receptor 4 (TLR4)-induced inflammation and is preceded by reduced intestinal motility. Human milk oligosaccharides (HMOs) are non-digestible components of breast milk that prevent NEC in preclinical models. We now hypothesize that HMOs can reduce the risk of NEC through restoration of intestinal motility and reduced TLR4-mediated inflammation.

METHODS

NEC was induced in C57-BL/6 mice through the combination of formula gavage, hypoxia, and oral administration of NEC stool. Mice were administered either 2'-FL (5 g/L), 6'-SL (5 g/L), or a blend of 5 specific HMOs (5 g/L) containing 2'-FL (2.606 g/L), 3'-FL (0.652 g/L), LNT (1.304 g/L), 3'-SL (0.174 g/L), and 6'-SL (0.260 g/L). Gastrointestinal motility was assessed by 70 Kd FITC-dextran transit time. Enteric glia were quantified by immunohistochemistry and qRT-PCR expression.

RESULTS

Administration of either 2'-FL, 6'-SL, or HMO blend significantly attenuated NEC severity and reversed intestinal hypomotility. HMOs prevented enteric glia loss and regulated key genes critical for enteric glia maintenance, attenuated pro-apoptotic genes, and increased anti-apoptotic genes in vitro, resulting in a reduction in apoptosis. Strikingly, HMOs reduced LPS-TLR4-induced NFκB signaling and ROS generation in enteric glia.

CONCLUSIONS

HMOs protect against NEC at least in part through protective effects on inflammation and the enteric nervous system.

IMPACT

This study sheds light on the role of certain human milk oligosaccharides in a clinically relevant mouse model of NEC and adds additional insights into their underlying mechanism of action by revealing a protective effect on the enteric nervous system. These results reveal that HMOs prevent the loss of enteric glia in NEC and influence the expression of genes that regulate enteric glia maintenance. HMOs also limit TLR4-NFkB signaling, providing an additional mechanism of enteric glia maintenance.

Persistent Post-Recovery Hyperinflammation of Necrotizing Enterocolitis Is Ameliorated by 5-ASA Treatment

Background: Necrotizing enterocolitis (NEC) is the leading gastrointestinal cause of death of premature neonates. We have previously shown that this hyperinflammatory state persists even post-recovery. We hypothesize that recovered patients with NEC will have a decreased hyperinflammatory response when the anti-inflammatory medication mesalamine (5-ASA) is administered even when exposed to in vitro NEC induction. Methods: Enteroids were generated and subjected to in vitro NEC induction. One half were subjected to 5-ASA treatment. Tumor necrosis factor-alpha (TNF-α) and interleukin 8 (IL-8) were evaluated via RT-qPCR. Mice underwent in vivo NEC induction, one group was given 5-ASA 50 mg/kg 12 h before the start of NEC induction. The intestine was harvested and assessed for hyperinflammatory markers and histological grading was performed. Results: Recovered NEC enteroids treated with 5-ASA during NEC induction show a significant decrease in inflammatory markers compared with control (p = 0.0014 TNF-α, downtrend IL-8). Active NEC enteroids treated with 5-ASA during in vitro NEC induction show a significant decrease in TNF-α RT-qPCR (p = 0.0443) and IL-8 RT-qPCR (p = 0.0265). In mice that received 5-ASA 50 mg/kg before in vivo NEC induction, there is a significant decrease in both TNF-α (p = 0.0114) and IL-8 (p = 0.0051). Conclusion: Enteroids and mice exposed to 5-ASA have a significant decrease in inflammatory markers. This decrease despite NEC induction in both enteroids and mice may demonstrate the impact that anti-inflammatory agents could have on treatment for NEC. This could be important given the robust hyperinflammatory response to a second hit after recovery and may impact the trajectory of an illness post-recovery from NEC.

Enteric glia regulate Paneth cell secretion and intestinal microbial ecology

Glial cells of the enteric nervous system (ENS) interact closely with the intestinal epithelium and secrete signals that influence epithelial cell proliferation and barrier formation in vitro. Whether these interactions are important in vivo, however, is unclear because previous studies reached conflicting conclusions (Prochera and Rao, 2023). To better define the roles of enteric glia in steady state regulation of the intestinal epithelium, we characterized the glia in closest proximity to epithelial cells and found that the majority express the gene Proteolipid protein 1 (PLP1) in both mice and humans. To test their functions using an unbiased approach, we genetically depleted PLP1+ cells in mice and transcriptionally profiled the small and large intestines. Surprisingly, glial loss had minimal effects on transcriptional programs and the few identified changes varied along the gastrointestinal tract. In the ileum, where enteric glia had been considered most essential for epithelial integrity, glial depletion did not drastically alter epithelial gene expression but caused a modest enrichment in signatures of Paneth cells, a secretory cell type important for innate immunity. In the absence of PLP1+ glia, Paneth cell number was intact, but a subset appeared abnormal with irregular and heterogenous cytoplasmic granules, suggesting a secretory deficit. Consistent with this possibility, ileal explants from glial-depleted mice secreted less functional lysozyme than controls with corresponding effects on fecal microbial composition. Collectively, these data suggest that enteric glia do not exert broad effects on the intestinal epithelium but have an essential role in regulating Paneth cell function and gut microbial ecology.

The Double-Edged Sword: The Complex Function of Enteric Glial Cells in Neurodegenerative Diseases

Over the past two decades, a growing number of studies have been conducted on the role of bidirectional communication through the gut-brain axis in the development of neurodegenerative diseases. These studies were driven by the curious fact that all of these diseases present varying degrees of intestinal involvement included in their wide range of symptoms. A population of cells belonging to the ENS, called enteric glial cells (EGCs), appears to actively participate in this communication between the intestine and the brain, but acting in a dualistic manner, sometimes in reactive gliosis releasing inflammatory mediators, sometimes promoting homeostasis and resilience in the face of inflammatory injuries. To date, the intracellular mechanisms that define the transcriptional profile expressed in EGCs in each situation have not yet been elucidated. This review proposes a discussion on: (1) the complex role of distinct phenotypes of enteric glial cells involved in neurodegenerative diseases, such as Parkinson's disease (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), Huntington's disease (HD) and multiple sclerosis (MS); and (2) innovative strategies such as IDO/TDO inhibitors, Brazil nuts, caffeic acid, polyphenols, among others, that act on EGCs and have the potential to treat neurodegenerative diseases.

Enteric Glia

Enteric glia are a unique type of peripheral neuroglia that accompany neurons in the enteric nervous system (ENS) of the digestive tract. The ENS displays integrative neural circuits that are capable of governing moment-to-moment gut functions independent of input from the central nervous system. Enteric glia are interspersed with neurons throughout these intrinsic gut neural circuits and are thought to fulfill complex roles directed at maintaining homeostasis in the neuronal microenvironment and at neuroeffector junctions in the gut. Changes to glial functions contribute to a wide range of gastrointestinal diseases, but the precise roles of enteric glia in gut physiology and pathophysiology are still under examination. This review summarizes current concepts regarding enteric glial development, diversity, and functions in health and disease.

Short-chain fatty acids in Huntington's disease: Mechanisms of action and their therapeutic implications

Huntington's disease (HD) is a progressive neurodegenerative disorder characterized by motor dysfunction, cognitive decline, and emotional instability, primarily resulting from the abnormal accumulation of mutant huntingtin protein. Growing research highlights the role of intestinal microbiota and their metabolites, particularly short-chain fatty acids (SCFAs), in modulating HD progression. SCFAs, including acetate, propionate, and butyrate, are produced by gut bacteria through dietary fiber fermentation and are recognized for their neuroprotective properties. Evidence suggests that SCFAs regulate neuroinflammation, neuronal communication, and metabolic functions within the central nervous system (CNS). In HD, these compounds may support neuronal health, reduce oxidative stress, and enhance blood-brain barrier (BBB) integrity. Their mechanisms of action involve binding to G-protein-coupled receptors (GPCRs) and modulating gene expression through epigenetic pathways, underscoring their therapeutic potential. This analysis examines the significance of SCFAs in HD, emphasizing the gut-brain axis and the benefits of dietary interventions aimed at modifying gut microbiota composition and promoting SCFA production. Further research into these pathways may pave the way for novel HD management strategies and improved therapeutic outcomes.

Platelet-rich plasma improves cyclophosphamide-induced interstitial cystitis in rat models through the toll-like receptor 4/nuclear factor-kappa B signalling pathway

OBJECTIVE

To investigate the therapeutic effect of platelet-rich plasma (PRP) on a cyclophosphamide (CYP)-induced interstitial cystitis (IC) rat model.

METHODS

A CYP-induced IC rat model (75 mg/kg every 3 days, with a total of five injections) was used to evaluate the therapeutic effects of PRP. Here, PRP was administered via bladder irrigation (every 2 days, with a total of three irrigations), and bladder tissue was analysed for inflammation and histological changes. The toll-like receptor 4 (TLR4)/nuclear factor-kappa B (NF-κB) signalling pathway was assessed using real-time quantitative polymerase chain reaction and ribonucleic acid sequencing. In addition, lipopolysaccharide (LPS)-induced SV-HUC-1 cells (10 μg/LPS and 2.5 mM adenosine triphosphate) were employed to investigate the inflammatory response and the effects of PRP on the TLR4/NF-κB signalling pathway.

RESULTS

The PRP treatment significantly improved the bladder tissue condition in the CYP-induced IC rat model, as evidenced by reduced inflammation and histological damage. The damage and shedding of the superficial epithelium of the bladder mucosa were notably decreased following PRP bladder instillation. Importantly, the expression of ZO-1, a key marker of epithelial integrity, was upregulated in PRP-treated rats, indicating enhanced bladder epithelial function. High-throughput analysis revealed that PRP alleviated bladder mucosal injury in the IC rat model through the TLR4/NF-κB signalling pathway. In LPS-induced SV-HUC-1 cells, PRP treatment also increased ZO-1 expression, decreased CDH1 expression and regulated the TLR4/NF-κB signalling pathway.

CONCLUSION

Platelet-rich plasma treatment may improve the expression of ZO-1 and CDH1 in urinary epithelium in vitro by mediating the TLR4/NF-κB pathway, which is effective in the treatment of IC.

Piezo1 promotes the progression of necrotizing enterocolitis by activating the Ca2(+)/CaMKII-dependent pathway

Necrotizing enterocolitis (NEC) is a devastating inflammatory bowel necrosis of preterm infants with limited therapeutic approaches. Mounting evidence supports the role of Piezo1, namely, a widely distributed mechanosensor in intestinal epithelial cells (IECs), in intestinal inflammation but its underlying mechanism in the development of NEC remains unexplored. In this study, we demonstrated that Piezo1 expression was higher in preterm infants with lower gestational age. C57BL/6J mice wherein Piezo1 was deleted in IECs (villin-specific Piezo1 knockout mice; Piezo1flox/floxVillinCre+) and Piezo1flox/flox littermates were subjected to induce NEC, and Piezo1 knockout regulated the intestinal barrier function, restricted cytokines secretion, and diminished the inflammatory response in NEC mouse models. Piezo1 elevated cytosolic Ca2+ levels and activated Ca2+/calmodulin-dependent protein kinase II (CaMKII) to promote the CaMKII/NF-κB interaction and NF-κB activation in vitro. Finally, the effects of a CaMKII inhibitor, KN93, were evaluated both in vitro and in vivo in NEC models, and the functions of Piezo1 in IECs were suppressed partially by KN93. In this study, we characterise the undefined role of Piezo1 in the development of NEC, which may partially be attributed to the differential role of calcium under pathophysiological conditions.

Bifidobacterium bifidum CCFM1163 alleviates cathartic colon by activating the BDNF-TrkB-PLC/IP3 pathway to reconstruct the intestinal nerve and barrier

Introduction: Cathartic colon (CC) is a type of slow-transit constipation caused by a patient's long-term use of irritating laxatives. Probiotics play a crucial role in managing constipation. Objectives: This study aims to identify probiotics that can alleviate CC and explore their specific mechanisms of action. Methods: The CC-model was constructed using senna leaf extract. Bifidobacterium bifidum was applied to the mice for intervention. Relevant marker changes were then examined using ELISA and RT-qPCR. Furthermore, 16S rDNA sequencing was utilized for functional prediction of intestinal microorganisms, while GC-MS analysis was performed to determine the content of short-chain fatty acids (SCFAs) in feces. Results: Senna damages the intestinal nerve and the intestinal barrier while inducing CC. In contrast, Bifidobacterium bifidum CCFM1163 may enhance the brain-derived neurotrophic factor (BDNF) expression in the colon by altering the intestinal microbiota composition (e.g., increasing Lactobacillus and Bacteroides, and decreasing Faecalibaculum) and by elevating SCFA levels (e.g., acetic and isobutyric acid). Subsequently, elevated BDNF expression activates the BDNF-tyrosine kinase receptor B-phospholipase C/inositol trisphosphate (BDNF-TrkB-PLC/IP3) pathway, which upregulates the gene expression of Uchl1, S100β, and Acta2; repairs the enteric nervous system-interstitial cells of Cajal-smooth muscle cells (ENS-ICC-SMC) network; upregulates the gene expression of Ocln and Tjp1; improves intestinal permeability in CC mice; and modulates the immune response by upregulating Tlr4, downregulating Il1b, and upregulating Il10, ultimately alleviating CC. Conclusion: Bifidobacterium bifidum CCFM1163 was identified as a probiotic that can promote BDNF expression in the colon, activate the BDNF-TrkB-PLC/IP3 signaling pathway, and effectively alleviate CC.

Quantitative Proteomic Analysis Identifying and Evaluating TRAF6 and IL-8 as Potential Diagnostic Biomarkers in Neonatal Patients with Necrotizing Enterocolitis

Necrotizing enterocolitis (NEC) is a common gastrointestinal complication in premature infants, resulting in high morbidity and mortality, and its early detection is crucial for accurate treatment and outcome prediction. Extensive research has demonstrated a clear correlation between NEC and extremely low birth weight, degree of preterm, formula feeding, infection, hypoxic/ischemic damage, and intestinal dysbiosis. The development of noninvasive biomarkers of NEC from stool, urine, and serum has attracted a great deal of interest because to these clinical connections and the quest for a deeper knowledge of disease pathophysiology. Therefore, this study aims to identify protein expression patterns in NEC and discover innovative diagnostic biomarkers. In this study, we recruited five patients diagnosed with NEC and paired necrotic segments of intestinal tissue with adjacent normal segments of intestine to form experimental and control groups. Quantitative proteomics tandem mass tagging (TMT) labeling technique was used to detect and quantify the proteins, and the expression levels of the candidate biomarkers in the intestinal tissues were further determined by quantitative polymerase chain reaction (RT-qPCR), Western blot analysis, Immunofluorescence methods and enzyme-linked immunosorbent assay (ELISA). A total of 6880 proteins were identified and quantified in patients with NEC. A significant disparity in protein expression was observed between necrotic and normal segments of intestinal tissue in NEC patients. A total of 55 proteins were found to be upregulated, and 40 proteins were found to be downregulated in NEC patients when using a p-value of < 0.05, and an absolute fold change of > 1.2 for analysis. GO function enrichment analysis showed the positive regulation of significant biological processes such as mitochondrial organization, vasoconstriction, rRNA catabolism, fluid shear stress response, and glycerol ether biosynthesis processes. Enrichment analysis also revealed essential functions such as ligand-gated ion channel activity, potassium channel activity, ligand-gated cation channel activity, ligand-gated ion channel activity, and ligand-gated channel activity, including molecular functions such as ligand-gated ion channel activity and mitotic events in this comparative group. Significant changes were found in endomembrane protein complex, membrane fraction, mitochondrial membrane fraction, membrane components, membrane intrinsic components, and other localized proteins. Additional validation of intestinal tissue and serum revealed a substantial increase in TRAF6 (tumor necrosis factor receptor-associated factor 6) and IL-8(Interleukin-8, CXCL8). The quantitative proteomic TMT method can effectively detect proteins with differential expression in the intestinal tissues of NEC patients. Proteins TRAF6 and CXCL8/IL-8 are significantly upregulated in the intestinal tissues and serum samples of patients and may serve as valuable predictor factors for NEC's early diagnosis.

Detection of an intestinal cell DNA methylation signature in blood samples from neonates with necrotizing enterocolitis

BACKGROUND

Necrotizing enterocolitis (NEC) is an often fatal intestinal injury that primarily affects preterm infants for which screening tools are lacking. We performed a pilot analysis of DNA methylation in peripheral blood samples from preterm infants with and without NEC to identify potential NEC biomarkers.

METHODS

Peripheral blood samples were collected from infants at NEC diagnosis (n = 15) or from preterm controls (n = 13). Targeted genome-wide analysis was performed to identify DNA methylation differences between cases and controls.

RESULTS

Broad differences between NEC cases and controls were identified in distinct genomic elements. Differences between surgical NEC cases and controls were frequently associated with inflammation. Deconvolution analysis to identify cell type-specific DNA signatures revealed increases in ileal, vascular endothelial, and cardiomyocyte cell type proportions and decreases in colonic and neuronal cell type proportions in blood from NEC cases relative to controls.

CONCLUSIONS

We identified marked differences in DNA methylation of peripheral blood samples from preterm infants with and without NEC. Increased ileal cell-specific methylation signatures in the blood of infants with NEC relative to controls, with a marked increase seen in surgical cases, provides rationale for further analysis of intestinal DNA methylation signatures as biomarkers of NEC.

The Physiology of Enteric Glia

Enteric glia are the partners of neurons in the enteric nervous system throughout the gastrointestinal tract. Roles fulfilled by enteric glia are diverse and contribute to maintaining intestinal homeostasis through interactions with neurons, immune cells, and the intestinal epithelium. Glial influences optimize physiological gut processes such as intestinal motility and epithelial barrier integrity through actions that regulate the microenvironment of the enteric nervous system, the activity of enteric neurons, intestinal epithelial functions, and immune response. Changes to glial phenotype in disease switch glial functions and contribute to intestinal inflammation, dysmotility, pain, neuroplasticity, and tumorigenesis. This review summarizes current concepts regarding the physiological roles of enteric glial cells and their potential contributions to gut disease. The discussion is focused on recent evidence that suggests important glial contributions to gastrointestinal health and pathophysiology.

Bifidobacterium bifidum CCFM1359 alleviates intestinal motility disorders through the BDNF-TrkB pathway

Intestinal motility disorder is characterised by abnormal intestinal motility function, often resulting in symptoms such as diarrhoea and constipation. Probiotics are increasingly recognised as an effective treatment for gastrointestinal disorders, including intestinal motility disorders. In this study, we used senna extract to induce an animal model of intestinal dysfunction characterised by BDNF downregulation. By assessing relevant indicators of intestinal dyskinesia, we found that Bifidobacterium bifidum CCFM1359 effectively alleviated the dyskinesia. However, this alleviating effect was nullified when a TrkB receptor inhibitor was introduced, suggesting that Bifidobacterium bifidum CCFM1359 operates through the BDNF-TrkB pathway. Further analysis revealed that Bifidobacterium bifidum CCFM1359 likely exerts its beneficial effects by regulating intestinal microecology (increasing the relative abundance of Bifidobacterium bifidum and valeric acid content while decreasing Faecalibacterium and butyric acid content), reducing intestinal inflammation (upregulating the anti-inflammatory factor IL-10 and downregulating pro-inflammatory factors TNF-α and IL-1β), and remodelling intestinal nerves (upregulating S100β and the excitatory neurotransmitter ACh, while downregulating the inhibitory neurotransmitter nNOS). This study provides a theoretical basis for using probiotics to alleviate intestinal motility disorders.

Estrogen Alleviates Oxidative Bowel Injury and Neuroinflammation in Necrotizing Enterocolitis

INTRODUCTION

High mortality and morbidity of neonates with necrotizing enterocolitis (NEC) necessitates the investigation of novel therapies to improve outcomes. It was aimed to elucidate the potential therapeutic effect of estrogen receptor agonists on NEC-induced intestinal and brain injury in rats.

METHODS

Sprague-Dawley pups of both sexes were separated from their mothers at postnatal 5th d. Feeding with formula along with a single session of hypoxia was applied to induce NEC, while control pups were kept with their mothers. The NEC rats received either vehicle, estrogen receptor α (ERα) agonist propyl pyrazole triol (1 mg/kg/day), ERβ agonist diarylpropionitrile (1 mg/kg/day), or 17β-estradiol (1 mg/kg/day) during maternal separation. All pups were decapitated on postnatal 9th d to collect intestinal and brain tissue samples.

RESULTS

Elevation in proinflammatory cytokines, apoptosis, and microscopically and biochemically evident oxidative injury in both the intestinal and brain tissues were observed in NEC-induced pups. In both the intestinal and brain tissues, nerve growth factor and brain-derived neurotrophic factor protein levels were depleted, expressions of both the ESR1 and ESR2 genes were downregulated, while treatment with 17β-estradiol or ER agonists alleviated extent of oxidative injury of the intestines and brain tissue, upregulated nerve growth factor, brain-derived neurotrophic factor, and ER gene expressions, abolished NEC-induced decrease in claudin-3 expression, increased the survival rates, improved the clinical states of the survived pups at varying degrees.

CONCLUSIONS

Activation of estrogen signaling by receptor agonists alleviated NEC-induced intestinal and cerebral injury, implicating that estrogen agonists could be regarded as promising preventive/therapeutic agents for NEC.

Butyrate protects the intestinal barrier by upregulating Fut2 expression via MEK4-JNK signaling pathway activation

BACKGROUND

Necrotizing enterocolitis (NEC) is a severe gastrointestinal inflammatory disease in neonates. Fucosyltransferase 2 (Fut2) regulates intestinal epithelial cell fucosylation. In this study, we aimed to investigate butyrate-mediated upregulation of Fut2 expression and the underlying mechanisms.

METHODS

In vivo and in vitro models were established. SP600125 was used to inhibit the MEK4-JNK pathway, and anisomycin was used to activate the MEK4-JNK pathway. Fut2, occludin, and ZO-1 expressions were assessed. Furthermore, intestinal permeability was analyzed by FITC-Dextran. The expression of proteins in the MEK-4-JNK pathway was examined by western blotting.

RESULTS

In vivo, the addition of exogenous butyrate notably upregulated Fut2, occludin, and ZO-1 expressions and reduced intestinal permeability in mice with NEC. Butyrate may increase the phosphorylation of MEK4, JNK, and c-jun, which are key components of the MEK4-JNK pathway. Additionally, SP600125 inhibited their phosphorylation, which was reversed by anisomycin treatment. In vitro, butyrate substantially increased occludin and ZO-1 expressions. Butyrate considerably increased Fut2 expression and markedly upregulated p-MEK4, p-JNK, and p-c-jun expressions. SP600125 administration decreased their expressions, while anisomycin administration increased their expressions.

CONCLUSION

Butyrate upregulated Fut2 expression via activation of the MEK4-JNK pathway, improved intestinal barrier integrity, and protected neonatal mice from NEC.

IMPACT

We found that exogenous butyrate could improve intestinal barrier integrity and protect against NEC in neonatal mice. Our data showed that exogenous butyrate supplementation upregulated Fut2 expression by activating the MEK4-JNK pathway. Our study provides novel insights into the pathogenesis of NEC, thereby laying an experimental foundation for future clinical research on the use of butyrate in NEC treatment.

Photoacoustic imaging for non-invasive assessment of biomarkers of intestinal injury in experimental necrotizing enterocolitis

BACKGROUND

Necrotizing enterocolitis (NEC) is an often-lethal disease of the premature infant intestinal tract, exacerbated by significant diagnostic difficulties. In NEC, the intestine exhibits hypoperfusion and dysmotility, contributing to disease pathogenesis. However, these features cannot be accurately and quantitively assessed with current imaging modalities. We have previously demonstrated the ability of photoacoustic imaging (PAI) to non-invasively assess intestinal tissue oxygenation and motility in a healthy neonatal rat model.

METHODS

In this first-in-disease application, we evaluated NEC using PAI to assess intestinal health biomarkers in an experimental model of NEC. NEC was induced in neonatal rats from birth to 4-days. Healthy breastfed (BF) and NEC rat pups were imaged at 2- and 4-days.

RESULTS

Intestinal tissue oxygen saturation was measured with PAI, and NEC pups showed significant decreases at 2- and 4-days. Ultrasound and PAI cine recordings were used to capture intestinal peristalsis and contrast agent transit within the intestine. Intestinal motility, assessed using computational intestinal deformation analysis, demonstrated significant reductions in both early and established NEC. NEC damage was confirmed with histology and dysmotility was confirmed by small intestinal transit assay.

CONCLUSION

This preclinical study presents PAI as an emerging diagnostic imaging modality for intestinal disease assessment in premature infants.

IMPACT

Necrotizing enterocolitis (NEC) is a devastating intestinal disease affecting premature infants with significant mortality. NEC presents significant clinical diagnostic difficulties, with limited diagnostic confidence complicating timely and effective interventional efforts. This study is an important foundational first-in-disease preclinical study that establishes the utility for PAI to detect changes in intestinal tissue oxygenation and intestinal motility with NEC disease induction and progression. This study demonstrates the feasibility and exceptional promise for the use of PAI to non-invasively assess oxygenation and motility in the healthy and diseased infant intestine.

Enteric glia regulate Paneth cell secretion and intestinal microbial ecology

Glial cells of the enteric nervous system (ENS) interact closely with the intestinal epithelium and secrete signals that influence epithelial cell proliferation and barrier formation in vitro. Whether these interactions are important in vivo, however, is unclear because previous studies reached conflicting conclusions [1]. To better define the roles of enteric glia in steady state regulation of the intestinal epithelium, we characterized the glia in closest proximity to epithelial cells and found that the majority express PLP1 in both mice and humans. To test their functions using an unbiased approach, we genetically depleted PLP1+ cells in mice and transcriptionally profiled the small and large intestines. Surprisingly, glial loss had minimal effects on transcriptional programs and the few identified changes varied along the gastrointestinal tract. In the ileum, where enteric glia had been considered most essential for epithelial integrity, glial depletion did not drastically alter epithelial gene expression but caused a modest enrichment in signatures of Paneth cells, a secretory cell type important for innate immunity. In the absence of PLP1+ glia, Paneth cell number was intact, but a subset appeared abnormal with irregular and heterogenous cytoplasmic granules, suggesting a secretory deficit. Consistent with this possibility, ileal explants from glial-depleted mice secreted less functional lysozyme than controls with corresponding effects on fecal microbial composition. Collectively, these data suggest that enteric glia do not exert broad effects on the intestinal epithelium but have an essential role in regulating Paneth cell function and gut microbial ecology.

Reduced enteric BDNF-TrkB signaling drives glucocorticoid-mediated GI dysmotility

Stress affects gastrointestinal (GI) function causing dysmotility, especially in disorders of gut-brain interactions (DGBI) patients. GI motility is regulated by the enteric nervous system (ENS), suggesting that stress alters ENS biology to cause dysmotility. While stress increases glucocorticoid levels through the hypothalamus-pituitary-adrenal axis, how glucocorticoids affect GI motility is not known. Glucocorticoid signaling reduces expression of specific transcriptional isoforms of brain-derived neurotrophic factor (BDNF) in the central nervous system, altering signaling through its receptor Tropomyosin-related kinase B (TrkB) to cause behavioral defects. However, since the nature of ENS-specific Bdnf isoforms and their response to glucocorticoids remains unknown, we are limited in studying how stress impacts the ENS to cause dysmotility. Here, in male and female mice, we establish that stress-responsive Bdnf isoforms that are transcriptionally regulated at exons 4 and 6 represent >85% of all Bdnf isoforms in the post-natal ENS, and that Bdnf and Ntrk2 (TrkB) are expressed by enteric neurons. We further show using male mice dosed with a synthetic glucocorticoid receptor (GR) agonist dexamethasone (Dexa), that increased glucocorticoid signaling in ENS significantly reduces the expression of Bdnf transcripts and protein and that it significantly reduces GI motility. Finally, by using HIOC, a specific synthetic agonist of TrkB, we observe that HIOC treatment significantly improved GI motility of a cohort of Dexa-treated male mice, when compared to Dexa-treated and HIOC-untreated mice. Our results implicate BDNF- TrkB signaling in the etiology of stress-associated dysmotility and suggest that TrkB is a putative therapeutic target for dysmotility in DGBI patients.

Multi-strain probiotic administration decreases necrotizing enterocolitis severity and alters the epigenetic profile in mice

BACKGROUND

Probiotic administration may decrease the incidence of necrotizing enterocolitis (NEC) through mechanisms that are largely unknown. We investigated the effects of probiotics on intestinal epigenetics and assessed their effects on intestinal inflammation and motility using both ileum-predominant and combined ileo-colitis mouse NEC models.

METHODS

C57BL/6 J mice were gavage-fed a multi-strain probiotic from postnatal days 3-11, consisting of B. infantis, B. lactis, and S. thermophilus. From p8, mice were exposed to ileo-colitis NEC involving formula containing NEC bacteria and 0.5% DSS. DNA methylation was measured using the Infinium Methylation Assay. Gastrointestinal motility was assessed by 70 Kd FITC-dextran transit time. Probiotic colonization was measured in probiotic-fed mice by qPCR.

RESULTS

Probiotic administration caused significant changes in the small intestine's epigenetic signature, a reduction in NEC severity, and improved intestinal motility. The effects of probiotics were more pronounced in the ileo-colitis NEC model.

CONCLUSIONS

These findings shed light on the role of probiotics in two clinically relevant models of NEC, add additional insights into their underlying mechanism of action, and reveal unanticipated epigenetic modifications to the intestinal mucosa after their use.

IMPACT

These findings shed light on the role of multi-strain probiotics in two clinically relevant animal models of NEC, and add additional insights into their underlying mechanism of action This study provides a new, clinically relevant model for the study of NEC including administration of 0.5% DSS, to include ileal dominant and ileo-colonic dominant phenotypes of the disease. These results reveal that clinically relevant strains of probiotic bacteria can exert epigenetic effects on the small intestine in mice, and can attenuate the epigenetic changes induced by NEC.

Indigenous gut microbiota constitutively drive release of ciliary neurotrophic factor from mucosal enteric glia to maintain the homeostasis of enteric neural circuits

It has recently become clear that the gut microbiota influence intestinal motility, intestinal barrier function, and mucosal immune function; therefore, the gut microbiota are deeply involved in the maintenance of intestinal homeostasis. The effects of the gut microbiota on the enteric nervous system (ENS) in the adult intestine, however, remain poorly understood. In the current study, we investigated the effects of the gut microbiota on the ENS. Male C57BL/6 SPF mice at 12 weeks of age were given a cocktail of four antibiotics (ABX) orally to induce dysbiosis (ABX mice). As early as six hours after ABX administration, the weight of the cecum of ABX mice increased to be significantly greater than that of vehicle-treated animals; moreover, ABX-induced dysbiosis reduced the density of enteric nerve fibers (marked by tubulin-β3 immunoreactivity) in the lamina propria of the proximal colon to approximately 60% that of control. TAK242, a TLR4 antagonist, significantly lowered the nerve fiber density in the lamina propria of the proximal colonic mucosa to approximately 60% that of vehicle-treated SPF mice. We thus developed and tested the hypothesis that mucosal glia expressing TLR4 are activated by enteric bacteria and release neurotrophic factors that contribute to the maintenance of enteric neural circuits. Neurotrophic factors in the mucosa of the SPF mouse proximal colon were examined immunohistochemically. Ciliary neurotrophic factor (CNTF) was abundantly expressed in the lamina propria; most of the CNTF immunoreactivity was observed in mucosal glia (marked by S100β immunoreactivity). Administration of CNTF (subcutaneously, 0.3 mg/kg, 3 doses, 2 hours apart) to ABX mice significantly increased mucosal nerve fiber density in the ABX mouse proximal colon to nearly control levels. The effect of CNTF on enteric mucosal nerve fibers was examined in isolated preparations of proximal colon of ABX mice. As it did in vivo, exposure to CNTF in vitro significantly increased enteric mucosal nerve fiber density in the ABX-treated colon. In conclusion, our evidence suggests that gut microbiota constitutively activate TLR4 signaling in enteric mucosal glia, which secrete CNTF in response. The resulting bacterial-driven glial release of CNTF helps to maintain the integrity of enteric mucosal nerve fibers.

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.

Impact of Enteric Nervous Cells on Irritable Bowel Syndrome: Potential Treatment Options

Irritable bowel syndrome (IBS) is a condition that significantly impacts the lifestyle, health, and habits of numerous individuals worldwide. Its diagnosis and classification are based on the Rome criteria, updated periodically to reflect new research findings in this field. IBS can be classified into different types based on symptoms, each with distinct treatment approaches and some differences in their pathophysiology. The exact pathological background of IBS remains unclear, with many aspects still unknown. Recent research developments suggest that disorders in the brain-gut-microbiota axis are key contributors to the symptoms and severity of IBS. The central nervous system (CNS) interacts bidirectionally with intestinal processes within the lumen and the intestinal wall, with the autonomic nervous system, particularly the vagus nerve, playing an important role. However, the enteric nervous system (ENS) is also crucial in the pathophysiological pathway of IBS. The apeline-corticotropin-releasing factor (CRF)-toll-like receptor 4 (TLR4) signaling route via enteric glia and serotonin production in enteroendocrine cells at the enteric barrier are among the most well-understood new findings that affect IBS through the ENS. Additionally, the microbiota regulates neuronal signals, modifying enteric function by altering the number of enteric bacteria and other mechanisms. Given the limited therapeutic options currently available, it is essential to identify new treatment targets, with the brain-gut axis, particularly the enteric nervous system, being a promising focus. This study aims to delineate the molecular mechanisms that induce IBS and to suggest potential targets for future research and treatment of this potentially debilitating disease.

ELP1, the Gene Mutated in Familial Dysautonomia, Is Required for Normal Enteric Nervous System Development and Maintenance and for Gut Epithelium Homeostasis

Familial dysautonomia (FD) is a rare sensory and autonomic neuropathy that results from a mutation in the ELP1 gene. Virtually all patients report gastrointestinal (GI) dysfunction and we have recently shown that FD patients have a dysbiotic gut microbiome and altered metabolome. These findings were recapitulated in an FD mouse model and moreover, the FD mice had reduced intestinal motility, as did patients. To understand the cellular basis for impaired GI function in FD, the enteric nervous system (ENS; both female and male mice) from FD mouse models was analyzed during embryonic development and adulthood. We show here that not only is Elp1 required for the normal formation of the ENS, but it is also required in adulthood for the regulation of both neuronal and non-neuronal cells and for target innervation in both the mucosa and in intestinal smooth muscle. In particular, CGRP innervation was significantly reduced as was the number of dopaminergic neurons. Examination of an FD patient's gastric biopsy also revealed reduced and disoriented axons in the mucosa. Finally, using an FD mouse model in which Elp1 was deleted exclusively from neurons, we found significant changes to the colon epithelium including reduced E-cadherin expression, perturbed mucus layer organization, and infiltration of bacteria into the mucosa. The fact that deletion of Elp1 exclusively in neurons is sufficient to alter the intestinal epithelium and perturb the intestinal epithelial barrier highlights a critical role for neurons in regulating GI epithelium homeostasis.

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

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

Immunological aspects of necrotizing enterocolitis models: a review

Necrotizing enterocolitis (NEC) is one of the most devasting diseases affecting preterm neonates. However, despite a lot of research, NEC's pathogenesis remains unclear. It is known that the pathogenesis is a multifactorial process, including (1) a pathological microbiome with abnormal bacterial colonization, (2) an immature immune system, (3) enteral feeding, (3) an impairment of microcirculation, and (4) possibly ischemia-reperfusion damage to the intestine. Overall, the immaturity of the mucosal barrier and the increased expression of Toll-like receptor 4 (TLR4) within the intestinal epithelium result in an intestinal hyperinflammation reaction. Concurrently, a deficiency in counter-regulatory mediators can be seen. The sum of these processes can ultimately result in intestinal necrosis leading to very high mortality rates of the affected neonates. In the last decade no substantial advances in the treatment of NEC have been made. Thus, NEC animal models as well as in vitro models have been employed to better understand NEC's pathogenesis on a cellular and molecular level. This review will highlight the different models currently in use to study immunological aspects of NEC.

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.

The Novel MFG-E8-derived Oligopeptide, MOP3, Improves Outcomes in a Preclinical Murine Model of Neonatal Sepsis

INTRODUCTION

Neonatal sepsis is a devastating inflammatory condition that remains a leading cause of morbidity and mortality. Milk fat globule-EGF-factor VIII (MFG-E8) is a glycoprotein that reduces inflammation, whereas extracellular cold-inducible RNA binding protein (eCIRP) worsens inflammation. This study aimed to determine the therapeutic potential of a novel MFG-E8-derived oligopeptide 3 (MOP3) designed to clear eCIRP and protect against inflammation, organ injury, and mortality in neonatal sepsis.

METHODS

C57BL6 mouse pups were injected intraperitoneally with cecal slurry (CS) and treated with MOP3 (20 μg/g) or vehicle. 10 h after injection, blood, lungs, and intestines were collected for analyses, and in a 7-day experiment, pups were monitored for differences in mortality.

RESULTS

MOP3 treatment protected septic pups from inflammation by reducing eCIRP, IL-6, TNFα, and LDH. MOP3 reduced lung and intestinal inflammation and injury as assessed by reductions in tissue mRNA levels of inflammatory markers, histopathologic injury, and apoptosis in lung and intestines. MOP3 also significantly improved 7-day overall survival for CS-septic mouse pups compared to vehicle (75% vs. 46%, respectively).

CONCLUSION

Deriving from MFG-E8 and designed to clear eCIRP, MOP3 protects against sepsis-induced inflammation, organ injury, and mortality in a preclinical model of neonatal sepsis, implicating it as an exciting potential new therapeutic.

LEVEL OF EVIDENCE

Level 1.

Chromatin as alarmins in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a severe gastrointestinal disease primarily affecting premature neonates, marked by poorly understood pro-inflammatory signaling cascades. Recent advancements have shed light on a subset of endogenous molecular patterns, termed chromatin-associated molecular patterns (CAMPs), which belong to the broader category of damage-associated molecular patterns (DAMPs). CAMPs play a crucial role in recognizing pattern recognition receptors and orchestrating inflammatory responses. This review focuses into the realm of CAMPs, highlighting key players such as extracellular cold-inducible RNA-binding protein (eCIRP), high mobility group box 1 (HMGB1), cell-free DNA, neutrophil extracellular traps (NETs), histones, and extracellular RNA. These intrinsic molecules, often perceived as foreign, have the potential to trigger immune signaling pathways, thus contributing to NEC pathogenesis. In this review, we unravel the current understanding of the involvement of CAMPs in both preclinical and clinical NEC scenarios. We also focus on elucidating the downstream signaling pathways activated by these molecular patterns, providing insights into the mechanisms that drive inflammation in NEC. Moreover, we scrutinize the landscape of targeted therapeutic approaches, aiming to mitigate the impact of tissue damage in NEC. This in-depth exploration offers a comprehensive overview of the role of CAMPs in NEC, bridging the gap between preclinical and clinical insights.

Bidirectional communication of the gut-brain axis: new findings in Parkinson's disease and inflammatory bowel disease

Parkinson's disease (PD) and inflammatory bowel disease (IBD) are the two chronic inflammatory diseases that are increasingly affecting millions of people worldwide, posing a major challenge to public health. PD and IBD show similarities in epidemiology, genetics, immune response, and gut microbiota. Here, we review the pathophysiology of these two diseases, including genetic factors, immune system imbalance, changes in gut microbial composition, and the effects of microbial metabolites (especially short-chain fatty acids). We elaborate on the gut-brain axis, focusing on role of gut microbiota in the pathogenesis of PD and IBD. In addition, we discuss several therapeutic strategies, including drug therapy, fecal microbiota transplantation, and probiotic supplementation, and their potential benefits in regulating intestinal microecology and relieving disease symptoms. Our analysis will provide a new understanding and scientific basis for the development of more effective therapeutic strategies for these diseases.

Qingda granule alleviates cerebral ischemia/reperfusion injury by inhibiting TLR4/NF-κB/NLRP3 signaling in microglia

ETHNOPHARMACOLOGICAL RELEVANCE

Qingda granule (QDG) is effective for treating hypertension and neuronal damage after cerebral ischemia/reperfusion. However, the anti-neuroinflammatory effect of QDG on injury due to cerebral ischemia/reperfusion is unclear.

AIM OF THE STUDY

The objective was to evaluate the effectiveness and action of QDG in treating neuroinflammation resulting from cerebral ischemia/reperfusion-induced injury.

MATERIALS AND METHODS

Network pharmacology was used to predict targets and pathways of QDG. An in vivo rat model of middle cerebral artery occlusion/reperfusion (MCAO/R) as well as an in vitro model of LPS-stimulated BV-2 cells were established. Magnetic resonance imaging (MRI) was used to quantify the area of cerebral infarction, with morphological changes in the brain being assessed by histology. Immunohistochemistry (IHC) was used to assess levels of the microglial marker IBA-1 in brain tissue. Bioplex analysis was used to measure TNF-α, IL-1β, IL-6, and MCP-1 in sera and in BV-2 cell culture supernatants. Simultaneously, mRNA levels of these factors were examined using RT-qPCR analysis. Proteins of the TLR4/NF-κB/NLRP3 axis were examined using IHC in vivo and Western blot in vitro, respectively. While NF-κB translocation was assessed using immunofluorescence.

RESULTS

The core targets of QDG included TNF, NF-κB1, MAPK1, MAPK3, JUN, and TLR4. QDG suppressed inflammation via modulation of TLR4/NF-κB signaling. In addition, our in vivo experiments using MCAO/R rats demonstrated the therapeutic effect of QDG in reducing brain tissue infarction, improving neurological function, and ameliorating cerebral histopathological damage. Furthermore, QDG reduced the levels of TNF-α, IL-1β, IL-6, and MCP-1 in both sera from MCAO/R rats and supernatants from LPS-induced BV-2 cells, along with a reduction in the expression of the microglia biomarker IBA-1, as well as that of TLR4, MyD88, p-IKK, p-IκBα, p-P65, and NLRP3 in MCAO/R rats. In LPS-treated BV-2 cells, QDG downregulated the expression of proinflammatory factors and TLR4/NF-κB/NLRP3 signaling-related proteins. Additionally, QDG reduced translocation of NF-κB to the nucleus in both brains of MCAO/R rats and LPS-induced BV-2 cells. Moreover, the combined treatment of the TLR4 inhibitor TAK242 and QDG significantly reduced the levels of p-P65, NLRP3, and IL-6.

CONCLUSIONS

QDG significantly suppressed neuroinflammation by inhibiting the TLR4/NF-κB/NLRP3 axis in microglia. This suggests potential for QDG in treating ischemia stroke.

Colitis-Induced Small Intestinal Hypomotility Is Dependent on Enteroendocrine Cell Loss in Mice

BACKGROUND & AIMS

The abdominal discomfort experienced by patients with colitis may be attributable in part to the presence of small intestinal dysmotility, yet mechanisms linking colonic inflammation with small-bowel motility remain largely unexplored. We hypothesize that colitis results in small intestinal hypomotility owing to a loss of enteroendocrine cells (EECs) within the small intestine that can be rescued using serotonergic-modulating agents.

METHODS

Male C57BL/6J mice, as well as mice that overexpress (EECOVER) or lack (EECDEL) NeuroD1+ enteroendocrine cells, were exposed to dextran sulfate sodium (DSS) colitis (2.5% or 5% for 7 days) and small intestinal motility was assessed by 70-kilodalton fluorescein isothiocyanate-dextran fluorescence transit. EEC number and differentiation were evaluated by immunohistochemistry, terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling staining, and quantitative reverse-transcriptase polymerase chain reaction. Mice were treated with the 5-hydroxytryptamine receptor 4 agonist prucalopride (5 mg/kg orally, daily) to restore serotonin signaling.

RESULTS

DSS-induced colitis was associated with a significant small-bowel hypomotility that developed in the absence of significant inflammation in the small intestine and was associated with a significant reduction in EEC density. EEC loss occurred in conjunction with alterations in the expression of key serotonin synthesis and transporter genes, including Tph1, Ddc, and Slc6a4. Importantly, mice overexpressing EECs revealed improved small intestinal motility, whereas mice lacking EECs had worse intestinal motility when exposed to DSS. Finally, treatment of DSS-exposed mice with the 5-hydroxytryptamine receptor 4 agonist prucalopride restored small intestinal motility and attenuated colitis.

CONCLUSIONS

Experimental DSS colitis induces significant small-bowel dysmotility in mice owing to enteroendocrine loss that can be reversed by genetic modulation of EEC or administering serotonin analogs, suggesting novel therapeutic approaches for patients with symptomatic colitis.

Key roles of glial cells in the encephalopathy of prematurity

Across the globe, approximately one in 10 babies are born preterm, that is, before 37 weeks of a typical 40 weeks of gestation. Up to 50% of preterm born infants develop brain injury, encephalopathy of prematurity (EoP), that substantially increases their risk for developing lifelong defects in motor skills and domains of learning, memory, emotional regulation, and cognition. We are still severely limited in our abilities to prevent or predict preterm birth. No longer just the "support cells," we now clearly understand that during development glia are key for building a healthy brain. Glial dysfunction is a hallmark of EoP, notably, microgliosis, astrogliosis, and oligodendrocyte injury. Our knowledge of glial biology during development is exponentially expanding but hasn't developed sufficiently for development of effective neuroregenerative therapies. This review summarizes the current state of knowledge for the roles of glia in infants with EoP and its animal models, and a description of known glial-cell interactions in the context of EoP, such as the roles for border-associated macrophages. The field of perinatal medicine is relatively small but has worked passionately to improve our understanding of the etiology of EoP coupled with detailed mechanistic studies of pre-clinical and human cohorts. A primary finding from this review is that expanding our collaborations with computational biologists, working together to understand the complexity of glial subtypes, glial maturation, and the impacts of EoP in the short and long term will be key to the design of therapies that improve outcomes.

More than nutrition: Therapeutic potential and mechanism of human milk oligosaccharides against necrotizing enterocolitis

Human milk is the most valuable source of nutrition for infants. The structure and function of human milk oligosaccharides (HMOs), which are key components of human milk, have long been attracting particular research interest. Several recent studies have found HMOs to be efficacious in the prevention and treatment of necrotizing enterocolitis (NEC). Additionally, they could be developed in the future as non-invasive predictive markers for NEC. Based on previous findings and the well-defined functions of HMOs, we summarize potential protective mechanisms of HMOs against neonatal NEC, which include: modulating signal receptor function, promoting intestinal epithelial cell proliferation, reducing apoptosis, restoring intestinal blood perfusion, regulating microbial prosperity, and alleviating intestinal inflammation. HMOs supplementation has been demonstrated to be protective against NEC in both animal studies and clinical observations. This calls for mass production and use of HMOs in infant formula, necessitating more research into the safety of industrially produced HMOs and the appropriate dosage in infant formula.

Sodium humate ameliorates LPS-induced liver injury in mice by inhibiting TLR4/NF-κB and activating NRF2/HO-1 signaling pathways

BACKGROUND

Acute liver damage is a type of liver disease that has a significant global occurrence and a lack of successful treatment and prevention approaches. Sodium humate (HNa), a natural organic substance, has extensive applications in traditional Chinese medicine due to its antibacterial, anti-diarrheal, and anti-inflammatory characteristics. The purpose of this research was to examine the mitigating impacts of HNa on liver damage induced by lipopolysaccharide (LPS) in mice.

METHODS AND RESULTS

A total of 30 female mice were randomly assigned into Con, Mod, L-HNa, M-HNa, and H-HNa groups. Mice in the Con and Mod groups were gavaged with PBS, whereas L-HNa, M-HNa, and H-HNa groups mice were gavaged with 0.1%, 0.3%, and 0.5% HNa, daily. On day 21, Mod, L-HNa, M-HNa, and H-HNa groups mice were challenged with LPS (10 mg/kg). We discovered that pretreatment with HNa improved liver pathological damage and inflammation by inhibiting the toll-like receptor 4 (TLR4)/nuclear factor kappa-B (NF-κB) signaling pathway, enhancing the polarization of liver M2 macrophages, and reducing the levels of inflammatory cytokines. Our further study found that pretreatment with HNa enhanced the liver ability to combat oxidative stress and reduced hepatocyte apoptosis by activating the nuclear factor erythroid-2-related factor 2 (NRF2)/heme oxygenase-1 (HO-1) signaling pathway and enhancing the activities of antioxidant enzymes.

CONCLUSIONS

In conclusion, HNa could alleviate LPS-induced liver damage through inhibiting TLR4/NF-κB and activating NRF2/HO-1 signaling pathways. This study is the first to discover the therapeutic effects of HNa on liver damage induced by LPS.

Despite Recovery from Necrotizing Enterocolitis Infants Retain a Hyperinflammatory Response to Injury

Background

Necrotizing enterocolitis (NEC) is the leading gastrointestinal cause of death of premature neonates. NEC is associated with prematurity, a hyperinflammatory response, and dysregulation of intestinal barrier function. We hypothesize that patients with NEC will have, and continue to have after recovery, an increased hyperinflammatory intestinal response compared to those patients without NEC.

Methods

Neonates with NEC, those that have recovered from NEC, and those without NEC undergoing intestinal resections had specimens collected and snap frozen or generated into enteroids. The enteroids were treated with 100ug/mL lipopolysaccharide (LPS) and subjected to 24 hr of hypoxia together, then compared with untreated controls. Expression of Tumor Necrosis Factor (TNF-α) and interleukin 8 (IL-8) were evaluated via RT-qPCR and ELISA to measure inflammatory response. ANOVA determined statistical significance (p<0.05).

Results

There was no difference in inflammatory markers in recovered NEC tissue compared to non-NEC tissue on RTqPCR (p=0.701 TNF-α and 0.861 IL-8). However, recovered NEC enteroids demonstrate elevated levels of inflammatory markers after treatment compared to non-NEC enteroids after treatment on RTqPCR (p=0.0485 TNF-α, p=0.0057 IL-8) and ELISA (p=0.0354 TNF-α, p=0.0011 IL-8). Recovered NEC enteroids that underwent treatment demonstrated increased inflammatory markers compared to recovered NEC enteroids without treatment on RTqPCR (p=0.0045 TNF-α, p=0.0002 IL-8) and ELISA (p=0.034 TNF-α, p=0.0002 IL-8) suggesting a heightened inflammatory response to a second hit.

Conclusion

Intestinal tissue resected from neonates with NEC has an elevated hyperinflammatory response compared to neonates recovered from NEC and neonates without NEC. Enteroids generated from patients that have recovered from NEC have a heightened inflammatory response in response to NEC inducing stimuli compared to controls. This tendency towards an increased hyperinflammatory state may be correlated with an infant's proclivity to develop NEC and demonstrates the significance of a second hit on this tissue creating a heightened inflammatory response. This could be correlated with the impact and trajectory of an illness post recovery from NEC.

Protective effects of sodium humate on the intestinal barrier damage of Salmonella Typhimurium-challenged broilers

Salmonella Typhimurium (S. Typhimurium) infections can lead to severe intestinal damage and reduce growth performance in broilers. Thus, this study examined the potential mitigating impact of sodium humate (HNa) on intestinal barrier damage resulting from S. Typhimurium infection in broilers. A total of 320 1-day-old Arbor Acres broilers were randomly assigned into 5 treatments with 8 replicates. On d 22-24, broilers in the CON group were challenged with 1 ml of PBS, while broilers in the other groups were challenged with 1 ml of 3 × 109 CFU/ml S. Typhimurium, daily. Dietary administration with 4 g/kg of HNa increased (P < 0.05) the final body weight, jejunal secretory immunoglobulin A (sIgA), total antioxidant capacity (T-AOC), total superoxide dismutase (T-SOD), and catalase (CAT) levels as compared with the MOD group broilers. Furthermore, HNa alleviated intestinal barrier damage by increasing villus height (VH), upregulating protein expression of Occludin, Claudin-1, and zonula occludens-1 (ZO-1), inhibiting toll-like receptor 4 (TLR4)/nuclear factor kappa-B (NF-κB) signaling pathway activation, and decreasing the secretion of inflammatory cytokines (P < 0.05). Collectively, the present study showed that HNa mitigated intestinal barrier damage induced by S. Typhimurium infection in broilers.

Gut Microbiota as a Modifier of Huntington's Disease Pathogenesis

Huntingtin (HTT) protein is expressed in most cell lineages, and the toxicity of mutant HTT in multiple organs may contribute to the neurological and psychiatric symptoms observed in Huntington's disease (HD). The proteostasis and neurotoxicity of mutant HTT are influenced by the intracellular milieu and responses to environmental signals. Recent research has highlighted a prominent role of gut microbiota in brain and immune system development, aging, and the progression of neurological disorders. Several studies suggest that mutant HTT might disrupt the homeostasis of gut microbiota (known as dysbiosis) and impact the pathogenesis of HD. Dysbiosis has been observed in HD patients, and in animal models of the disease it coincides with mutant HTT aggregation, abnormal behaviors, and reduced lifespan. This review article aims to highlight the potential toxicity of mutant HTT in organs and pathways within the microbiota-gut-immune-central nervous system (CNS) axis. Understanding the functions of Wild-Type (WT) HTT and the toxicity of mutant HTT in these organs and the associated networks may elucidate novel pathogenic pathways, identify biomarkers and peripheral therapeutic targets for HD.

Microbial sensing in the intestine

The gut microbiota plays a key role in host health and disease, particularly through their interactions with the immune system. Intestinal homeostasis is dependent on the symbiotic relationships between the host and the diverse gut microbiota, which is influenced by the highly co-evolved immune-microbiota interactions. The first step of the interaction between the host and the gut microbiota is the sensing of the gut microbes by the host immune system. In this review, we describe the cells of the host immune system and the proteins that sense the components and metabolites of the gut microbes. We further highlight the essential roles of pattern recognition receptors (PRRs), the G protein-coupled receptors (GPCRs), aryl hydrocarbon receptor (AHR) and the nuclear receptors expressed in the intestinal epithelial cells (IECs) and the intestine-resident immune cells. We also discuss the mechanisms by which the disruption of microbial sensing because of genetic or environmental factors causes human diseases such as the inflammatory bowel disease (IBD).

Photoacoustic Imaging for Non-Invasive Assessment of Physiological Biomarkers of Intestinal Injury in Experimental Necrotizing Enterocolitis

Background

Necrotizing enterocolitis (NEC) is an often-lethal disease of the premature infants' intestinal tract that is exacerbated by significant difficulties in early and accurate diagnosis. In NEC disease, the intestine often exhibits hypoperfusion and dysmotility, which contributes to advanced disease pathogenesis. However, these physiological features cannot be accurately and quantitively assessed within the current constraints of imaging modalities frequently used in the clinic (plain film X-ray and ultrasound). We have previously demonstrated the ability of photoacoustic imaging (PAI) to non-invasively and quantitively assess intestinal tissue oxygenation and motility in a healthy neonatal rat model. As a first-in-disease application, we evaluated NEC pathogenesis using PAI to assess intestinal health biomarkers in a preclinical neonatal rat experimental model of NEC.

Methods

NEC was induced in neonatal rat pups from birth to 4 days old via hypertonic formula feeding, full-body hypoxic stress, and lipopolysaccharide administration to mimic bacterial colonization. Healthy breastfed (BF) controls and NEC rat pups were imaged at 2- and 4-days old. Intestinal tissue oxygen saturation was measured with PAI imaging for oxy- and deoxyhemoglobin levels. To measure intestinal motility, ultrasound and co-registered PAI cine recordings were used to capture intestinal peristalsis motion and contrast agent (indocyanine green) transit within the intestinal lumen. Additionally, both midplane two-dimensional and volumetric three-dimensional imaging acquisitions were assessed for oxygenation and motility.

Results

NEC pups showed a significant decrease of intestinal tissue oxygenation as compared to healthy BF controls at both ages (2-days old: 55.90% +/- 3.77% vs 44.12% +/- 7.18%; 4-days old: 56.13% +/- 3.52% vs 38.86% +/- 8.33%). Intestinal motility, assessed using a computational intestinal deformation analysis, demonstrated a significant reduction in the intestinal motility index in both early (2-day) and established (4-day) NEC. Extensive NEC damage was confirmed with histology and dysmotility was confirmed by small intestinal transit assay.

Conclusions

This study presents PAI as a successful emerging diagnostic imaging modality for both intestinal tissue oxygenation and intestinal motility disease hallmarks in a rat NEC model. PAI presents enormous significance and potential for fundamentally changing current clinical paradigms for detecting and monitoring intestinal pathologies in the premature infant.

New insights into intestinal macrophages in necrotizing enterocolitis: the multi-functional role and promising therapeutic application

Necrotizing enterocolitis (NEC) is an inflammatory intestinal disease that profoundly affects preterm infants. Currently, the pathogenesis of NEC remains controversial, resulting in limited treatment strategies. The preterm infants are thought to be susceptible to gut inflammatory disorders because of their immature immune system. In early life, intestinal macrophages (IMφs), crucial components of innate immunity, demonstrate functional plasticity and diversity in intestinal development, resistance to pathogens, maintenance of the intestinal barrier, and regulation of gut microbiota. When the stimulations of environmental, dietary, and bacterial factors interrupt the homeostatic processes of IMφs, they will lead to intestinal disease, such as NEC. This review focuses on the IMφs related pathogenesis in NEC, discusses the multi-functional roles and relevant molecular mechanisms of IMφs in preterm infants, and explores promising therapeutic application for NEC.

Persistent Proclivity to a Proinflammatory State in a Human Enteroid Model of Necrotizing Enterocolitis

Background: Necrotizing enterocolitis (NEC) is a devastating disease of premature neonates with substantial morbidity and mortality. Necrotizing enterocolitis is associated with prematurity, a hyperinflammatory response, and dysregulation of intestinal barrier function. We hypothesize that patients with NEC will have an increased hyperinflammatory intestinal response compared with those without NEC. Patients and Methods: Enteroids were generated from intestinal tissue from neonates undergoing resection. They were treated with 100 mcg/mL lipopolysaccharide (LPS), subjected to 24 hours of hypoxia inducing experimental NEC, then compared with untreated controls. Expression of tumor necrosis factor (TNF-α) and interleukin 8 (IL-8) were evaluated via reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR) and enzyme-linked immunosorbent assay (ELISA) to measure inflammatory response. Analysis of variance (ANOVA) determined statistical significance (p < 0.05). Results: Treated NEC-derived enteroids expressed significantly higher levels of IL-8 (RT-qPCR, p = 0.003; ELISA, p = 0.0002) compared with untreated NEC-derived enteroids with an increase in inflammatory marker concentration in those with a greater degree of prematurity (ELISA, p = 0.0015). A higher level of IL-8 was seen in NEC-derived enteroids compared with control after treatment (RT-qPCR, p = 0.024). Tumor necrosis factor-α levels were elevated in treated NEC-derived enteroids compared with untreated NEC-derived enteroids (RT-qPCR, p = 0.006; ELISA, p = 0.002) and compared with treated non-NEC-derived enteroids (RT-qPCR, p = 0.025; ELISA, p < 0.0001). Conclusions: Enteroids generated from neonates with NEC have an elevated hyperinflammatory response in response to NEC-inducing stimuli compared with controls. Enteroids generated from neonates with NEC with a greater degree of prematurity have a larger increase in inflammatory markers. This tendency toward a hyperinflammatory state may be correlated with an infant's proclivity to develop NEC and further demonstrates the hyperinflammatory state of prematurity.

Intervention effects and related mechanisms of glycyrrhizic acid on zebrafish with Hirschsprung-associated enterocolitis

BACKGROUND

The prevention and treatment of Hirschsprung-associated enterocolitis (HAEC) is a serious challenge in pediatric surgery. Exploring the mechanism of HAEC is conducive to the prevention of this disease.

AIM

To explore the possible mechanism of glycyrrhizic acid (GA) and its therapeutic effect on HAEC.

METHODS

We developed a model of enteritis induced by trinitrobenzenesulfonic acid (TNBS) in zebrafish, and treated it with different concentrations of GA. We analyzed the effect of GA on the phenotype and inflammation of zebrafish.

RESULTS

After treatment with TNBS, the area of the intestinal lumen in zebrafish was significantly increased, but the number of goblet cells in the intestinal lumen was significantly reduced, but these did not increase the mortality of zebrafish, indicating that the zebrafish enteritis model was successfully developed. Different concentrations of GA protected zebrafish with enteritis. In particular, high concentrations of GA were important for the prevention and control of HAEC because it significantly reduced the intestinal luminal area, increased the number of goblet cells in the intestinal lumen, and reduced the levels of interleukin (IL)-1β and IL-8.

CONCLUSION

GA significantly reduced the intestinal luminal area, increased the number of intestinal goblet cells, and decreased IL-1β and IL-8 in zebrafish, and is important for prevention and control of HAEC.

Edaravone Improved Behavioral Abnormalities, Alleviated Oxidative Stress Inflammation, and Metabolic Homeostasis Pathways in Depression

Depression is one of the main factors affecting our daily performance. Among many putative compounds with effect on behavioral and pathophysiological alterations in depression, edaravone (EDV) demonstrates antioxidant and free radical scavenging properties. To investigate possible antidepressive and anxiolytic-like effects of EDV, Wistar rats were randomly divided into six groups: (1) control; (2) EDV (6 mg/kg); (3) post weaning social isolation (PWSI); (4) PWSI+EDV (1.5 mg/kg); (5) PWSI+EDV (3 mg/kg); and (6) PWSI+EDV (6 mg/kg). After the series of behavioral tests, animals were sacrificed, and their hippocampi were dissected for further biochemical and gene expression assays. Our results showed that treatment with 3 and 6 mg/kg EDV after social isolation would improve anxiety, depressive and anhedonic-like behavior in OFT, EPM, FST, and splash tests. In addition, treatment at the aforementioned doses achieved to recover total cellular antioxidant and GSH level. These effects were accompanied with the suppressive effect of EDV on MDA and PCO levels. EDV treatment also modulated the expression of AMPK, Tlr-4, BDNF, nNOS, and iNOS genes. The treatment with 3 and 6 mg/kg EDV would lead to the recovery of behavioral impairments, cellular free radical surge that could be in correlation with the effect of this substance on immune system response, improved energy production system, and more efficacy in the recovery of neural tissue. In conclusion, EDV ameliorates depressive-like disorder by modulating neuroinflammation, energy production, and neural tissue recovery.

Human milk oligosaccharides reduce necrotizing enterocolitis-induced neuroinflammation and cognitive impairment in mice

Necrotizing enterocolitis (NEC) is the leading cause of morbidity and mortality in premature infants. One of the most devastating complications of NEC is the development of NEC-induced brain injury, which manifests as impaired cognition that persists beyond infancy and which represents a proinflammatory activation of the gut-brain axis. Given that oral administration of the human milk oligosaccharides (HMOs) 2'-fucosyllactose (2'-FL) and 6'-sialyslactose (6'-SL) significantly reduced intestinal inflammation in mice, we hypothesized that oral administration of these HMOs would reduce NEC-induced brain injury and sought to determine the mechanisms involved. We now show that the administration of either 2'-FL or 6'-SL significantly attenuated NEC-induced brain injury, reversed myelin loss in the corpus callosum and midbrain of newborn mice, and prevented the impaired cognition observed in mice with NEC-induced brain injury. In seeking to define the mechanisms involved, 2'-FL or 6'-SL administration resulted in a restoration of the blood-brain barrier in newborn mice and also had a direct anti-inflammatory effect on the brain as revealed through the study of brain organoids. Metabolites of 2'-FL were detected in the infant mouse brain by nuclear magnetic resonance (NMR), whereas intact 2'-FL was not. Strikingly, the beneficial effects of 2'-FL or 6'-SL against NEC-induced brain injury required the release of the neurotrophic factor brain-derived neurotrophic factor (BDNF), as mice lacking BDNF were not protected by these HMOs from the development of NEC-induced brain injury. Taken in aggregate, these findings reveal that the HMOs 2'-FL and 6'-SL interrupt the gut-brain inflammatory axis and reduce the risk of NEC-induced brain injury.NEW & NOTEWORTHY This study reveals that the administration of human milk oligosaccharides, which are present in human breast milk, can interfere with the proinflammatory gut-brain axis and prevent neuroinflammation in the setting of necrotizing enterocolitis, a major intestinal disorder seen in premature infants.

Sodium Humate-Derived Gut Microbiota Ameliorates Intestinal Dysfunction Induced by Salmonella Typhimurium in Mice

Salmonella is a foodborne pathogen that is one of the main causes of gastroenteric disease in humans and animals. As a natural organic substance, sodium humate (HNa) possesses antibacterial, antidiarrheal, and anti-inflammatory properties. However, it is unclear whether the HNa and HNa-derived microbiota exert alleviative effects on Salmonella enterica serovar Typhimurium-induced enteritis. We found that treatment with HNa disrupted the cell wall of S. Typhimurium and decreased the virulence gene expression. Next, we explored the effect of HNa presupplementation on S. Typhimurium-induced murine enteritis. The results revealed that HNa ameliorated intestinal pathological damage. In addition, we observed that presupplementation with HNa enhanced intestinal barrier function via modulating gut microbiota, downregulating toll-like receptor 4 (TLR4)/nuclear factor kappa-B (NF-κB) and NOD-like receptor protein 3 (NLRP3) signaling pathways, regulating intestinal mucosal immunity, and enhancing tight junction protein expression. To further validate the effect of HNa-derived microbiota on S. Typhimurium-induced enteritis, we performed fecal microbiota transplantation and found that HNa-derived microbiota also alleviated S. Typhimurium-induced intestinal damage. It is noteworthy that both HNa and HNa-derived microbiota improved the liver injury caused by S. Typhimurium infection. Collectively, this is the first study to confirm that HNa could alleviate S. Typhimurium-induced enteritis in a gut microbiota-dependent manner. This study provides a new perspective on HNa as a potential drug to prevent and treat salmonellosis. IMPORTANCE Salmonella Typhimurium is an important zoonotic pathogen, widely distributed in nature. S. Typhimurium is one of the leading causes of foodborne illnesses worldwide, and more than 350,000 people died from Salmonella infection each year, which poses a substantial risk to public health and causes a considerable economic loss. Here, we found that the S. Typhimurium infection caused severe intestinal and liver damage. In addition, we first found that sodium humate (HNa) and HNa-derived gut microbiota can alleviate S. Typhimurium infection-induced intestinal damage. These findings extend the knowledge about the public health risk and pathogenic mechanisms of S. Typhimurium.

New insights into the pathogenesis of necrotizing enterocolitis and the dawn of potential therapeutics

Necrotizing enterocolitis (NEC) is a devastating gastrointestinal disorder in premature infants that causes significant morbidity and mortality. Research efforts into the pathogenesis of NEC have discovered a pivotal role for the gram-negative bacterial receptor, Toll-like receptor 4 (TLR4), in its development. TLR4 is activated by dysbiotic microbes within the intestinal lumen, which leads to an exaggerated inflammatory response within the developing intestine, resulting in mucosal injury. More recently, studies have identified that the impaired intestinal motility that occurs early in NEC has a causative role in disease development, as strategies to enhance intestinal motility can reverse NEC in preclinical models. There has also been broad appreciation that NEC also contributes to significant neuroinflammation, which we have linked to the effects of gut-derived pro-inflammatory molecules and immune cells which activate microglia in the developing brain, resulting in white matter injury. These findings suggest that the management of the intestinal inflammation may secondarily be neuroprotective. Importantly, despite the significant burden of NEC on premature infants, these and other studies have provided a strong rationale for the development of small molecules with the capability of reducing NEC severity in pre-clinical models, thus guiding the development of specific anti-NEC therapies. This review summarizes the roles of TLR4 signaling in the premature gut in the pathogenesis of NEC, and provides insights into optimal clinical management strategies based upon findings from laboratory studies.

Bugs and the barrier: A review of the gut microbiome and intestinal barrier in necrotizing enterocolitis

Necrotizing enterocolitis (NEC) is a devastating gastrointestinal disease that affects premature neonates. It frequently results in significant morbidity and mortality for those affected. Years of research into the pathophysiology of NEC have revealed it to be a variable and multifactorial disease. However, there are risk factors associated with NEC including low birth weight, prematurity, intestinal immaturity, alterations in microbial colonization, and history of rapid or formula based enteral feeds (Fig. 1).^1-3 An accepted generalization of the pathogenesis of NEC includes a hyperresponsive immune reaction to insults such as ischemia, starting formula feeds, or alterations in the microbiome with pathologic bacterial colonization and translocation. This reaction causes a hyperinflammatory response disrupting the normal intestinal barrier, allowing abnormal bacterial translocation and ultimately sepsis.^1,2,4 This review will focus specifically on the interactions with the microbiome and intestinal barrier function in NEC.

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.

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.