Evidence of a Myenteric Plexus Barrier and Its Macrophage-Dependent Degradation During Murine Colitis: Implications in Enteric Neuroinflammation

Interaction between nutritional factors and the enteric nervous system in inflammatory bowel diseases

The enteric nervous system (ENS) is a highly conserved, yet complicated network of neurons and glial cells located throughout the gut wall that controls digestive processes and gastrointestinal (GI) homeostasis. The intestinal epithelium, the immune system, and the gut microbiota are just a few examples of the cellular networks that the ENS interacts with on a variety of levels to maintain GI function. The presence or absence of nutrients in the intestinal lumen may cause short- and/or long-term changes in neurotransmitter expression, excitability, and neuronal survival, which ultimately affect gut motility, secretion, and permeability. Hence, the ENS should be identified as a key factor in initiating coordinated responses to nutrients. In this review we summarize current knowledge on nutrient-dependent ENS activity and how ENS secondary to nutrition may affect likelihood of developing inflammatory bowel disease. Our findings highlight that nutrients interact with enteroendocrine cells in the gut, triggering hormone secretion that plays a crucial role in signaling food-related information to the brain and regulating metabolic processes such as feeding behavior, insulin secretion, and energy balance; however, the complex interactions between nutrients, the ENS, and the immune system require further research to understand their contributions to GI disorders and potential therapeutic applications in treating obesity and metabolic diseases. Lay Summary: The enteric nervous system (ENS) controls digestion and interacts with nutrients in the gut to regulate processes like gut movement and hormone release, affecting metabolism and overall gut health. This review highlights the need for further research on how nutrient-ENS interactions contribute to conditions like inflammatory bowel disease, obesity, and metabolic disorders.

Toll-like receptor 4 deficiency ameliorates experimental ileitis and enteric neuropathy: Involvement of nitrergic and 5-hydroxytryptaminergic neurotransmission

BACKGROUND AND PURPOSE

Inflammatory bowel disease (IBD) patients display genetic polymorphisms in toll-like receptor 4 (TLR4) genes, contributing to dysregulate enteric nervous system (ENS) circuits with increased levels of 5-HT and alteration of the neuroimmune crosstalk. In this study, we investigated the impact of TLR4 signalling on mouse ENS dysfunction caused by dextran sulphate sodium (DSS)-induced ileitis.

EXPERIMENTAL APPROACH

Male C57BL/6J (wild-type [WT]) and TLR4-/- mice (10 ± 2 weeks old) received 2% DSS in drinking water for 5 days and then were switched to 3-day regular drinking water. Histological analysis and proinflammatory cytokine mRNA levels were assessed in ileal samples. Gut motility was evaluated by changes in transit of a fluorescent-labelled marker and isometric neuromuscular responses of ileal full-thickness segments to receptor and non-receptor-mediated stimuli. Alterations in ENS architecture were assessed by confocal immunohistochemistry in longitudinal muscle-myenteric plexus whole-mount preparations.

KEY RESULTS

In WT mice, DSS treatment caused delayed gastrointestinal transit, ileal myenteric neurodegeneration, reactive gliosis and release of proinflammatory cytokines. Enhanced cholinergic and tachykinergic excitatory tone, increased inducible nitric oxide synthase (iNOS)-mediated relaxation, and changes in 5-HT2A and 5-HT3 receptor-mediated responses were observed during ileitis in WT mice. TLR4 deficiency reversed most of the functional and morphological abnormalities.

CONCLUSION AND IMPLICATIONS

Our results demonstrate that TLR4 activity influences the severity of ileitis, neuroglial plasticity, gut motility, and nitrergic and 5-HTergic neurotransmissions. The neuroimmune interaction between TLR4 and 5-HT observed in our study appears to be a potential pharmacological target to treat ENS dysfunction implicated in IBD onset/progression.

The interrelationship between intestinal immune cells and enteric α-synuclein in the progression of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder primarily characterized by motor impairment, resulting from the accumulation of α-synuclein and neuronal cell death in the substantia nigra of the midbrain. Emerging evidence suggests that α-synuclein aggregation may originate in the enteric nervous system (ENS) and subsequently propagate to the brain via the vagus nerve. Clinical observations, such as prodromal gastrointestinal dysfunction in PD patients and the increased incidence of PD among individuals with inflammatory bowel disease, support the hypothesis that abnormal intestinal inflammation may contribute to the onset of motor dysfunction and neuropathology in PD. This review examines recent findings on the interplay between intestinal immune cells and α-synuclein aggregation within the framework of gut-originated PD pathogenesis. It begins by discussing evidence linking dysbiosis and intestinal inflammation to α-synuclein aggregation in the ENS. Additionally, it explores the potential role of intestinal immune cells in influencing enteric neurons and α-synuclein aggregation, furthering the understanding of PD development.

Functional analysis of antigen presentation by enteric glial cells during intestinal inflammation

The Enteric Nervous System is composed of a vastly interconnected network of neurons and glial cells that coordinate to regulate homeostatic gut function including intestinal motility, nutrient sensing, and mucosal barrier immunity. Enteric Glial Cells (EGCs) are a heterogeneous cell population located throughout the gastrointestinal tract and have well described roles in regulating intestinal immune responses. Enteric Glial Cells have been suggested to act as nonconventional antigen presenting cells via the Major Histocompatibility Complex II (MHC II), though this has not been confirmed functionally. Here, we investigate the capability of EGCs to present antigen on MHC I and MHC II using in vitro antigen presentation assays performed with primary murine EGC cultures. We found that EGCs are capable of functional antigen presentation on MHC I, including antigen cross-presentation, but are not capable of functional antigen presentation on MHC II. We also determined EGC cell surface MHC I and MHC II expression levels by flow cytometry during intestinal inflammation during Dextran Sodium Sulfate-induced colitis or acute Toxoplasma gondii infection. We found that EGCs upregulate MHC I during acute T. gondii infection and induce low-level MHC II expression. These findings suggest that EGCs may be important in the regulation of CD8+ T cell responses via MHC I mediated antigen (cross) presentation but may not be relevant for MHC II-mediated antigen presentation.

Macrophage-induced enteric neurodegeneration leads to motility impairment during gut inflammation

Current studies pictured the enteric nervous system and macrophages as modulators of neuroimmune processes in the inflamed gut. Expanding this view, we investigated the impact of enteric neuron-macrophage interactions on postoperative trauma and subsequent motility disturbances, i.e., postoperative ileus. In the early postsurgical phase, we detected strong neuronal activation, followed by transcriptional and translational signatures indicating neuronal death and synaptic damage. Simultaneously, our study revealed neurodegenerative profiles in macrophage-specific transcriptomes after postoperative trauma. Validating the role of resident and monocyte-derived macrophages, we depleted macrophages by CSF-1R-antibodies and used CCR2-/- mice, known for reduced monocyte infiltration, in POI studies. Only CSF-1R-antibody-treated animals showed decreased neuronal death and lessened synaptic decay, emphasizing the significance of resident macrophages. In human gut samples taken early and late during abdominal surgery, we substantiated the mouse model data and found reactive and apoptotic neurons and dysregulation in synaptic genes, indicating a species' overarching mechanism. Our study demonstrates that surgical trauma activates enteric neurons and induces neurodegeneration, mediated by resident macrophages, introducing neuroprotection as an option for faster recovery after surgery.

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.

The role of macrophage polarization in ulcerative colitis and its treatment

Macrophages have great plasticity. Typically, there are two of activated macrophages: M1 macrophages and M2 macrophages. Of them, M1 macrophages play a major role in responses that are pro-inflammatory, while M2 macrophages play an important part in responses that are anti-inflammatory. Ulcerative colitis (UC) is a chronic, non-specific inflammatory disease of the intestine. The pathophysiology and course of UC are significantly influenced by the inflammatory response triggered by macrophage activation. M1 is a possible cause of increased inflammation in UC whereas M2 has a significant function in the healing of inflammation. The polarization imbalance of intestinal M1/M2 macrophages is closely linked to UC. Thus, by suppressing M1 polarization, encouraging M2 polarization, and reestablishing macrophage polarization balance, the treatment of UC based on macrophage polarization is beneficial for UC. Not only chemical drugs, but also traditional Chinese medicine compounds and herbal extracts have been shown to restore the balance of macrophage polarization, providing a new idea in the treatment of UC.

Resolving Resident Colonic Muscularis Macrophage Diversity and Plasticity During Colitis

BACKGROUND

Immune cell populations in the intestinal muscularis propria during colitis are poorly resolved. Maintaining homeostasis in this niche is critical, highlighted by the poorer prognosis of inflammatory bowel disease associated with muscularis propria inflammation.

METHODS

This study utilizes single-cell RNA sequencing to survey the immune cell populations within the muscularis propria of normal colon and dextran sodium sulfate-induced colitis. Findings are validated by immunohistochemistry, flow cytometry and cell-lineage tracing in vivo, and in vitro assays with muscularis macrophages (MMφ).

RESULTS

In naïve conditions, transcriptional duality is observed in MMφs with 2 major subpopulations: conventional resident Cx3cr1+ MMφs and Lyve1+ MMφs. The Lyve1+ population is phagocytic and expresses several known MMφ markers in mouse and human, confirming their identity as a bona fide MMφ subset. Single-cell transcriptomics indicate that resident MMφs are retained during colitis and exhibit plasticity toward an inflammatory profile. Lyve1+ MMφs, which express anti-inflammatory marker CD163, are absent during colitis, as confirmed by flow cytometry. In contrast, lineage tracing finds that resident Cx3cr1+ MMφs remain during colitis and are not completely replaced by the inflammatory infiltrating monocytes. In vitro studies provide biological evidence of the plasticity of resident Cx3cr1+ MMφs in response to lipopolysaccharide (LPS), mirroring transcriptional observations in vivo of their inflammatory plasticity. Potential markers for colitic MMφs, validated in animal models and in individuals with ulcerative colitis, are identified.

CONCLUSIONS

Our findings contribute to the understanding of the immune system in the muscularis propria niche during colitis by resolving the heterogeneity and origins of colitic MMφs.

Prevention of colon enlargement by TNF-α antagonist in a streptozotocin-induced diabetic rat model

PURPOSE

We investigated the effect of tumor necrosis factor (TNF)-α antagonist on the structure and function of the streptozotocin-nicotinamide (STZ-NA)-induced diabetic rat colon.

METHODS

Thirty rats were divided into normal control (NC), diabetic control (DC), and diabetic etanercept (DE) groups. The DE group was injected with etanercept twice a week. Blood glucose, body weight, fecal pellet, colonic transit time, and plasma TNF-α were measured. The colon was dissected out, followed by weight and length measurements. Toluidine blue and Verhoeff's staining, immunohistochemistry for TNF-α, RAGE, iNOS, arginase, and western blot for RAGE were performed on the colonic tissue.

RESULTS

Administration of TNF-α antagonist had no significant effect on the body weight and blood glucose level of the diabetic groups. However, the DE group had a shorter and lighter colon and less coarse and less dense collagen fibers in the submucosal layer than the DC group. Weaker immunoreactivity of TNF-α, RAGE, iNOS, and arginase I was observed in colon tissue sections of the DE groups compared with the DC group. Although the etanercept effect on colonic function was not significantly different, the preventive effect size of etanercept on colon remodeling was considerably large, as shown by calculated-Cohen's d>0.8.

CONCLUSIONS

TNF-α signaling in the colonic tissue of diabetic rats has a strong effect on tissue remodeling, leading to colon enlargement. TNF-α antagonists may be beneficial in preventing diabetic-related pathology in the colon in combination with anti-diabetic drugs.

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.

From bench to bedside: an interdisciplinary journey through the gut-lung axis with insights into lung cancer and immunotherapy

This comprehensive review undertakes a multidisciplinary exploration of the gut-lung axis, from the foundational aspects of anatomy, embryology, and histology, through the functional dynamics of pathophysiology, to implications for clinical science. The gut-lung axis, a bidirectional communication pathway, is central to understanding the interconnectedness of the gastrointestinal- and respiratory systems, both of which share embryological origins and engage in a continuous immunological crosstalk to maintain homeostasis and defend against external noxa. An essential component of this axis is the mucosa-associated lymphoid tissue system (MALT), which orchestrates immune responses across these distant sites. The review delves into the role of the gut microbiome in modulating these interactions, highlighting how microbial dysbiosis and increased gut permeability ("leaky gut") can precipitate systemic inflammation and exacerbate respiratory conditions. Moreover, we thoroughly present the implication of the axis in oncological practice, particularly in lung cancer development and response to cancer immunotherapies. Our work seeks not only to synthesize current knowledge across the spectrum of science related to the gut-lung axis but also to inspire future interdisciplinary research that bridges gaps between basic science and clinical application. Our ultimate goal was to underscore the importance of a holistic understanding of the gut-lung axis, advocating for an integrated approach to unravel its complexities in human health and disease.

Lonicerin alleviates intestinal myenteric neuron injury induced by hypoxia/reoxygenation treated macrophages by downregulating EZH2

Intestinal ischemia-reperfusion (IR) injury is a common gastrointestinal disease that induces severe intestinal dysfunction. Intestinal myenteric neurons participate in maintaining the intestinal function, which will be severely injured by IR. Macrophages are widely reported to be involved in the pathogenesis of organ IR injury, including intestine, which is activated by NLRP3 signaling. Lonicerin (LCR) is a natural extracted monomer with inhibitory efficacy against the NLRP3 pathway in macrophages. The present study aims to explore the potential protective function of LCR in intestinal IR injury. Myenteric neurons were extracted from mice. RAW 264.7 cells were stimulated by H/R with or without 10 μM and 30 μM LCR. Remarkable increased release of IL-6, MCP-1, and TNF-α were observed in H/R treated RAW 264.7 cells, along with an upregulation of NLRP3, cleaved-caspase-1, IL-1β, and EZH2, which were sharply repressed by LCR. Myenteric neurons were cultured with the supernatant collected from each group. Markedly decreased neuron number and shortened length of neuron axon were observed in the H/R group, which were signally reversed by LCR. RAW 264.7 cells were stimulated by H/R, followed by incubated with 30 μM LCR with or without pcDNA3.1-EZH2. The inhibition of LCR on NLRP3 signaling in H/R treated RAW 264.7 cells was abolished by EZH2 overexpression. Furthermore, the impact of LCR on neuron number and neuron axon length in myenteric neurons in the H/R group was abated by EZH2 overexpression. Collectively, LCR alleviated intestinal myenteric neuron injury induced by H/R treated macrophages via downregulating EZH2.

Overview of pro-inflammatory and pro-survival components in neuroinflammatory signalling and neurodegeneration

Neurodegenerative diseases (NDDs) are identified by the progressive deterioration of neurons and a subsequent decline in cognitive function, creating an enormous burden on the healthcare system globally. Neuroinflammation is an intricate procedure that initiates the immune response in the central nervous system (CNS) and significantly impacts the expansion of NDDs. This study scrutinizes the complicated interaction between neuronal degeneration and neuroinflammation, with an appropriate emphasis on their reciprocal impacts. It also describes how neuroinflammatory reactions in NDDs are controlled by activating certain pro-inflammatory transcription factors, including p38 MAPK, FAF1, Toll-like receptors (TLRs), and STAT3. Alternatively, it evaluates the impact of pro-survival transcription factors, such as the SOCS pathway, YY1, SIRT1, and MEF2, which provide neuroprotective protection against damage triggered by neuroinflammation. Moreover, we study the feasibility of accommodating drug repositioning as a therapeutic approach for treating neuroinflammatory disorders. This suggests the use of existing medications for novel utilization in the treatment of NDDs. Furthermore, the study intends to reveal novel biomarkers of neuroinflammation that contribute fundamental observation for the initial detection and diagnosis of these disorders. This study aims to strengthen therapy interference and augment patient outcomes by combining ongoing data and evaluating novel therapeutic and diagnostic approaches. The goal is to devote the growth of an effective strategy to reducing the impact of neuroinflammation on neuronal protection in NDDs.

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

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

Molecular mechanisms of enteric neuropathies in high-fat diet feeding and diabetes

BACKGROUND

Obesity and diabetes are associated with altered gastrointestinal function and with the development of abdominal pain, nausea, diarrhea, and constipation among other symptoms. The enteric nervous system (ENS) regulates gastrointestinal motility. Enteric neuropathies defined as damage or loss of enteric neurons can lead to motility disorders.

PURPOSE

Here, we review the molecular mechanisms that drive enteric neurodegeneration in diabetes and obesity, including signaling pathways leading to neuronal cell death, oxidative stress, and microbiota alteration. We also highlight potential approaches to treat enteric neuropathies including antioxidant therapy to prevent oxidative stress-induced damage and the use of stem cells.

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

Introduction

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

Methods

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

Results

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

Discussion

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

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.

The interplay between the microbiota and opioid in the treatment of neuropathic pain

Neuropathic pain (NP) is characterized by its complex and multifactorial nature and limited responses to opioid therapy; NP is associated with risks of drug resistance, addiction, difficulty in treatment cessation, and psychological disorders. Emerging research on gut microbiota and their metabolites has demonstrated their effectiveness in alleviating NP and augmenting opioid-based pain management, concurrently mitigating the adverse effects of opioids. This review addresses the following key points: (1) the current advances in gut microbiota research and the challenges in using opioids to treat NP, (2) the reciprocal effects and benefits of gut microbiota on NP, and (3) the interaction between opioids with gut microbiota, as well as the benefits of gut microbiota in opioid-based treatment of NP. Through various intricate mechanisms, gut microbiota influences the onset and progression of NP, ultimately enhancing the efficacy of opioids in the management of NP. These insights pave the way for further pragmatic clinical research, ultimately enhancing the efficacy of opioid-based pain management.

Histological Image-based Ensemble Model to Identify Myenteric Plexitis and Predict Endoscopic Postoperative Recurrence in Crohn's Disease: A Multicentre, Retrospective Study

BACKGROUND AND AIMS

Myenteric plexitis is correlated with postoperative recurrence of Crohn's disease when relying on traditional statistical methods. However, comprehensive assessment of myenteric plexus remains challenging. This study aimed to develop and validate a deep learning system to predict postoperative recurrence through automatic screening and identification of features of the muscular layer and myenteric plexus.

METHODS

We retrospectively reviewed 205 patients who underwent bowel resection surgery from two hospitals. Patients were divided into a training cohort [n = 108], an internal validation cohort [n = 47], and an external validation cohort [n = 50]. A total of 190 960 patches from 278 whole-slide images of surgical specimens were analysed using the ResNet50 encoder, and 6144 features were extracted after transfer learning. We used five robust algorithms to construct classification models. The performances of the models were evaluated based on the area under the receiver operating characteristic curve [AUC] in three cohorts.

RESULTS

The stacking model achieved satisfactory accuracy in predicting postoperative recurrence of CD in the training cohort (AUC: 0.980; 95% confidence interval [CI] 0.960-0.999), internal validation cohort [AUC: 0.908; 95% CI 0.823-0.992], and external validation cohort [AUC: 0.868; 95% CI 0.761-0.975]. The accuracy for identifying the severity of myenteric plexitis was 0.833, 0.745, and 0.694 in the training, internal validation and external validation cohorts, respectively.

CONCLUSIONS

Our work initially established an interpretable stacking model based on features of the muscular layer and myenteric plexus extracted from histological images to identify the severity of myenteric plexitis and predict postoperative recurrence of CD.

Characterizing enteric neurons in dopamine transporter (DAT)-Cre reporter mice reveals dopaminergic subtypes with dual-transmitter content

The enteric nervous system (ENS) comprises a complex network of neurons whereby a subset appears to be dopaminergic although the characteristics, roles, and implications in disease are less understood. Most investigations relating to enteric dopamine (DA) neurons rely on immunoreactivity to tyrosine hydroxylase (TH)-the rate-limiting enzyme in the production of DA. However, TH immunoreactivity is likely to provide an incomplete picture. This study herein provides a comprehensive characterization of DA neurons in the gut using a reporter mouse line, expressing a fluorescent protein (tdTomato) under control of the DA transporter (DAT) promoter. Our findings confirm a unique localization of DA neurons in the gut and unveil the discrete subtypes of DA neurons in this organ, which we characterized using both immunofluorescence and single-cell transcriptomics, as well as validated using in situ hybridization. We observed distinct subtypes of DAT-tdTomato neurons expressing co-transmitters and modulators across both plexuses; some of them likely co-releasing acetylcholine, while others were positive for a slew of canonical DAergic markers (TH, VMAT2 and GIRK2). Interestingly, we uncovered a seemingly novel population of DA neurons unique to the ENS which was ChAT/DAT-tdTomato-immunoreactive and expressed Grp, Calcb, and Sst. Given the clear heterogeneity of DAergic gut neurons, further investigation is warranted to define their functional signatures and decipher their implication in disease.

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

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

Bone marrow-derived mesenchymal stem cells mitigate chronic colitis and enteric neuropathy via anti-inflammatory and anti-oxidative mechanisms

Current treatments for inflammatory bowel disease (IBD) are often inadequate due to limited efficacy and toxicity, leading to surgical resection in refractory cases. IBD's broad and complex pathogenesis involving the immune system, enteric nervous system, microbiome, and oxidative stress requires more effective therapeutic strategies. In this study, we investigated the therapeutic potential of bone marrow-derived mesenchymal stem cell (BM-MSC) treatments in spontaneous chronic colitis using the Winnie mouse model which closely replicates the presentation and inflammatory profile of ulcerative colitis. The 14-day BM-MSC treatment regimen reduced the severity of colitis, leading to the attenuation of diarrheal symptoms and recovery in body mass. Morphological and histological abnormalities in the colon were also alleviated. Transcriptomic analysis demonstrated that BM-MSC treatment led to alterations in gene expression profiles primarily downregulating genes related to inflammation, including pro-inflammatory cytokines, chemokines and other biomarkers of inflammation. Further evaluation of immune cell populations using immunohistochemistry revealed a reduction in leukocyte infiltration upon BM-MSC treatment. Notably, enteric neuronal gene signatures were the most impacted by BM-MSC treatment, which correlated with the restoration of neuronal density in the myenteric ganglia. Moreover, BM-MSCs exhibited neuroprotective effects against oxidative stress-induced neuronal loss through antioxidant mechanisms, including the reduction of mitochondrial-derived superoxide and attenuation of oxidative stress-induced HMGB1 translocation, potentially relying on MSC-derived SOD1. These findings suggest that BM-MSCs hold promise as a therapeutic intervention to mitigate chronic colitis by exerting anti-inflammatory effects and protecting the enteric nervous system from oxidative stress-induced damage.

Myenteric Plexus Immune Cell Infiltrations and Neurotransmitter Expression in Crohn's Disease and Ulcerative Colitis

BACKGROUND AND AIMS

Pain is a cardinal symptom in inflammatory bowel disease [IBD]. An important structure in the transduction of pain signalling is the myenteric plexus [MP]. Nevertheless, IBD-associated infiltration of the MP by immune cells lacks in-depth characterisation. Herein, we decipher intra- and periganglionic immune cell infiltrations in Crohn´s disease [CD] and ulcerative colitis [UC] and provide a comparison with murine models of colitis.

METHODS

Full wall specimens of surgical colon resections served to examine immune cell populations by either conventional immuno-histochemistry or immunofluorescence followed by either bright field or confocal microscopy. Results were compared with equivalent examinations in various murine models of intestinal inflammation.

RESULTS

Whereas the MP morphology was not significantly altered in IBD, we identified intraganglionic IBD-specific B cell- and monocyte-dominant cell infiltrations in CD. In contrast, UC-MPs were infiltrated by CD8+ T cells and revealed a higher extent of ganglionic cell apoptosis. With regard to the murine models of intestinal inflammation, the chronic dextran sulphate sodium [DSS]-induced colitis model reflected CD [and to a lesser extent UC] best, as it also showed increased monocytic infiltration as well as a modest B cell and CD8+ T cell infiltration.

CONCLUSIONS

In CD, MPs were infiltrated by B cells and monocytes. In UC, mostly CD8+ cytotoxic T cells were found. The chronic DSS-induced colitis in the mouse model reflected best the MP-immune cell infiltrations representative for IBD.

Probiotics and microbial metabolites maintain barrier and neuromuscular functions and clean protein aggregation to delay disease progression in TDP43 mutation mice

Amyotrophic lateral sclerosis (ALS) is a neuromuscular disease. The ALS mice expressing human mutant of transactive response DNA binding protein of 43 kDa (hmTDP43) showed intestinal dysfunction before neuromuscular symptoms. We hypothesize that restoring the intestinal and microbial homeostasis with a bacterial metabolite or probiotics delays the ALS disease onset. We investigate the pathophysiological changes in the intestine and neurons, intestinal and blood-brain barriers, and inflammation during the ALS progression. We then cultured enteric glial cells (EGCs) isolated from TDP43 mice for mechanistic studies. TDP43 mice had significantly decreased intestinal mobility, increased permeability, and weakened muscle, compared with the age-matched wild-type mice. We observed increased hmTDP43 and Glial fibrillary acidic protein (GFAP), and decreased expression of α-smooth muscle actin (α-SMA), tight junction proteins (ZO-1 and Claudin-5) in the colon, spinal cord, and brain in TDP43 mice. TDP43 mice had reduced Butyryl-coenzyme A CoA transferase, decreased butyrate-producing bacteria Butyrivibrio fibrisolvens, and increased Bacteroides fragilis, compared to the WT mice. Serum inflammation cytokines (IL-6, IL-17, and IFN-γ) and LPS were elevated in TDP43 mice. EGCs from TDP43 mice showed aggregation of hmTDP43 associated with increased GFAP and ionized calcium-binding adaptor molecule (IBA1, a microglia marker). TDP43 mice treated with butyrate or probiotic VSL#3 had significantly increased rotarod time, increased intestinal mobility and decreased permeability, compared to the untreated group. Butyrate or probiotics treatment decreased the expression of GFAP, TDP43, and increased α-SMA, ZO-1, and Claudin-5 in the colon, spinal cord, and brain. Also, butyrate or probiotics treatment enhanced the Butyryl-coenzyme A CoA transferase, Butyrivibrio fibrisolvens, and reduced inflammatory cytokines in TDP43 mice. The TDP43 EGCs treated with butyrate or probiotics showed reduced GFAP, IBA1, and TDP43 aggregation. Restoring the intestinal and microbial homeostasis by beneficial bacteria and metabolites provide a potential therapeutic strategy to treat ALS.

The critical role of muscularis macrophages in modulating the enteric nervous system function and gastrointestinal motility

Macrophages are the originators of inflammatory compounds, phagocytic purifiers in their local environment, and wound healing protectors in oxidative environments. They are molded by the tissue milieu they inhabit, with gastrointestinal (GI) muscularis macrophages (MMs) being a prime example. MMs are located in the muscular layer of the GI tract and contribute to muscle repair and maintenance of GI motility. MMs are often in close proximity to the enteric nervous system, specifically near the enteric neurons and interstitial cells of Cajal (ICCs). Consequently, the anti-inflammatory function of MMs corresponds to the development and maintenance of neural networks in the GI tract. The capacity of MMs to shift from anti-inflammatory to proinflammatory states may contribute to the inflammatory aspects of various GI diseases and disorders such as diabetic gastroparesis or postoperative ileus, functional disorders such as irritable bowel syndrome, and organic diseases such as inflammatory bowel disease. We reviewed the current knowledge of MMs and their influence on neighboring cells due to their important role in the GI tract.

Depletion of muscularis macrophages ameliorates inflammation-driven dysmotility in murine colitis model

Previously, the presence of a blood-myenteric plexus barrier and its disruption was reported in experimentally induced colitis via a macrophage-dependent process. The aim of this study is to reveal how myenteric barrier disruption and subsequent neuronal injury affects gut motility in vivo in a murine colitis model. We induced colitis with dextran sulfate sodium (DSS), with the co-administration of liposome-encapsulated clodronate (L-clodronate) to simultaneously deplete blood monocytes contributing to macrophage infiltration in the inflamed muscularis of experimental mice. DSS-treated animals receiving concurrent L-clodronate injection showed significantly decreased blood monocyte numbers and colon muscularis macrophage (MM) density compared to DSS-treated control (DSS-vehicle). DSS-clodronate-treated mice exhibited significantly slower whole gut transit time than DSS-vehicle-treated animals and comparable to that of controls. Experiments with oral gavage-fed Evans-blue dye showed similar whole gut transit times in DSS-clodronate-treated mice as in control animals. Furthermore, qPCR-analysis and immunofluorescence on colon muscularis samples revealed that factors associated with neuroinflammation and neurodegeneration, including Bax1, Hdac4, IL-18, Casp8 and Hif1a are overexpressed after DSS-treatment, but not in the case of concurrent L-clodronate administration. Our findings highlight that MM-infiltration in the muscularis layer is responsible for colitis-associated dysmotility and enteric neuronal dysfunction along with the release of mediators associated with neurodegeneration in a murine experimental model.

New insights into muscularis macrophages in the gut: from their origin to therapeutic targeting

Muscularis macrophages, as the most abundant immune cells in the intestinal muscularis externa, exhibit tissue protective phenotype in the steady state. Owing to tremendous advances in technology, we now know the fact that muscularis macrophages are a heterogeneous population of cells which could be divided into different functional subsets depending on their anatomic niches. There is emerging evidence showing that these subsets, through molecular interactions with their neighbours, take part in a wide range of physiological and pathophysiological processes in the gut. In this review, we summarize recent progress (particularly over the past 4 years) on distribution, morphology, origin and functions of muscularis macrophages and, where possible, the characteristics of specific subsets in response to the microenvironment they occupy, with particular emphasis on their role in muscular inflammation. Furthermore, we also integrate their role in inflammation-related gastrointestinal disorders, such as post-operative ileus and diabetic gastroparesis, in order to propose future therapeutic strategies.

Erythritol aggravates gut inflammation and anxiety-like behavioral disorders induced by acute dextran sulfate sodium administration in mice

Erythritol is a widely used sugar substitute in food and beverages with beneficial and detrimental roles in obesity and cardiovascular diseases, respectively; however, its influence on inflammatory bowel disease (IBD) and related behavioral disorders is not well understood. Here, we found that erythritol exacerbated gut inflammation by promoting macrophage infiltration and inducing M1 macrophage polarization, thus increasing gut leakage during colitis triggered by acute dextran sulfate sodium (DSS) treatment. Increased gut permeability can cause neuroinflammation and anxiety-like behavioral disorders. In conclusion, our results revealed a negative role for erythritol in gut inflammation and anxiety-like behavioral disorders induced by erythritol administration in a mouse model of acute colitis, suggesting that erythritol intake control may be necessary for IBD treatment.

Procyanidin improves experimental colitis by regulating macrophage polarization

BACKGROUND

Inflammatory bowel disease (IBD) is a chronic disease with an unclear pathogenesis for which successful treatments are still lacking. It has been reported that procyanidin, a natural antioxidant, relieves colitis, but the specific mechanism is elusive.

PURPOSE

Our present study was designed to investigate the effects of procyanidin on colitis and the regulation of the M1 macrophage phenotype and related signaling pathways.

METHODS

In vivo, we used two classic colitis models to observe the effect of procyanidin on macrophage polarization. In vitro, we further validated the therapeutic effect of procyanidin in the RAW264.7 cell line and peritoneal macrophages.

RESULTS

The current findings provide new evidence that procyanidin ameliorated dextran sulfate sodium (DSS)-induced colitis by preventing the polarization of macrophages to the M1 type and downregulating the levels of proinflammatory factors in cells. We also showed that procyanidin prevented lipopolysaccharide (LPS)-induced elevation of inflammatory cytokines and the activation of proinflammatory macrophages, which was achieved by activating the STAT3 and NF-κB pathways.

CONCLUSIONS

This is the first study to demonstrate that procyanidin alleviates experimental colitis by inhibiting the polarization of proinflammatory macrophages. These data reveal new ideas for the pathogenesis and treatment of inflammatory diseases.

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

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

Enteric glia at center stage of inflammatory bowel disease

Although our understanding of the pathophysiology of inflammatory bowel disease (IBD) is increasing, the expanding body of knowledge does not simplify the equation but rather reveals diverse, interconnected, and complex mechanisms in IBD. In addition to immune overactivation, defects in intestinal epithelial barrier (IEB) functioning, dysbiosis, and structural and functional abnormalities of the enteric nervous system are emerging as new elements contributing to the development of IBD. In addition to molecular changes in IBD, enteric glia from patients with Crohn's disease (CD) exhibits the inability to strengthen the IEB; these defects are not observed in patients with ulcerative colitis. In addition, there is a growing body of work describing that enteric glia interacts with not only enterocytes and enteric neurons but also other local cellular neighbours. Thus, because of their functions as connectors and regulators of immune cells, IEB, and microbiota, enteric glia could be the keystone of digestive homeostasis that is lacking in patients with CD.

Vasculature in the mouse colon and spatial relationships with the enteric nervous system, glia, and immune cells

The distribution, morphology, and innervation of vasculature in different mouse colonic segments and layers, as well as spatial relationships of the vasculature with the enteric plexuses, glia, and macrophages are far from being complete. The vessels in the adult mouse colon were stained by the cardiovascular perfusion of wheat germ agglutinin (WGA)-Alexa Fluor 448 and by CD31 immunoreactivity. Nerve fibers, enteric glia, and macrophages were immunostained in the WGA-perfused colon. The blood vessels entered from the mesentery to the submucosa and branched into the capillary networks in the mucosa and muscularis externa. The capillary net formed anastomosed rings at the orifices of mucosa crypts, and the capillary rings surrounded the crypts individually in the proximal colon and more than two crypts in the distal colon. Microvessels in the muscularis externa with myenteric plexus were less dense than in the mucosa and formed loops. In the circular smooth muscle layer, microvessels were distributed in the proximal, but not the distal colon. Capillaries did not enter the enteric ganglia. There were no significant differences in microvascular volume per tissue volume between the proximal and distal colon either in the mucosa or muscularis externa containing the myenteric plexus. PGP9.5-, tyrosine hydroxylase-, and calcitonin gene-related peptide (CGRP)-immunoreactive nerve fibers were distributed along the vessels in the submucosa. In the mucosa, PGP9.5-, CGRP-, and vasoactive intestinal peptide (VIP)-immunoreactive nerves terminated close to the capillary rings, while cells and processes labeled by S100B and glial fibrillary acidic protein were distributed mainly in the lamina propria and lower portion of the mucosa. Dense Iba1 immunoreactive macrophages were closely adjacent to the mucosal capillary rings. There were a few macrophages, but no glia in apposition to microvessels in the submucosa and muscularis externa. In conclusion, in the mouse colon, (1) the differences in vasculature between the proximal and distal colon were associated with the morphology, but not the microvascular amount per tissue volume in the mucosa and muscle layers; (2) the colonic mucosa contained significantly more microvessels than the muscularis externa; and (3) there were more CGRP and VIP nerve fibers found close to microvessels in the mucosa and submucosa than in the muscle layers.

Mini-review: Interaction between intestinal microbes and enteric glia in health and disease

Enteric glia are a unique population of peripheral neuroglia associated with the enteric nervous system (ENS) throughout the digestive tract. The emerging data from the latest glial biology studies unveiled enteric glia as a heterogenic population with plastic and adaptative abilities that display phenotypic and functional changes upon distinct extrinsic cues. This aspect is essential in the dynamic signaling that enteric glia engage with neurons and other neighboring cells within the intestinal wall, such as epithelial, endocrine, and immune cells to maintain local homeostasis. Likewise, enteric glia sense signals from luminal microbes, although the extent of this active communication is still unclear. In this minireview, we discuss the recent findings that support glia-microbes crosstalk in the intestine in health and disease, pointing out the critical aspects that require further investigation.

Cell-penetrating TLR inhibitor peptide alleviates ulcerative colitis by the functional modulation of macrophages

Toll-like receptors (TLRs) have a crucial role not only in triggering innate responses against microbes but in orchestrating an appropriate adaptive immunity. However, deregulated activation of TLR signaling leads to chronic inflammatory conditions such as inflammatory bowel disease (IBD). In this study, we evaluated the immunomodulatory potential of a TLR inhibitor in the form of a cell-penetrating peptide using an ulcerative colitis animal model. A peptide derived from the TIR domain of the TLR adaptor molecule TIRAP that was conjugated with a cell-penetrating sequence (cpTLR-i) suppressed the induction of pro-inflammatory cytokines such as TNF-α and IL-1β in macrophages. In DSS-induced colitis mice, cpTLR-i treatment ameliorated colitis symptoms, colonic tissue damage, and mucosal inflammation. Intriguingly, cpTLR-i attenuated the induction of TNF-α-expressing proinflammatory macrophages while promoting that of regulatory macrophages expressing arginase-1 and reduced type 17 helper T cell (Th17) responses in the inflamed colonic lamina propria. An in vitro study validated that cpTLR-i enhanced the differentiation of monocyte-driven macrophages into mature macrophages with a regulatory phenotype in a microbial TLR ligand-independent manner. Furthermore, the cocultivation of CD4 T cells with macrophages revealed that cpTLR-i suppressed the activation of Th17 cells through the functional modulation of macrophages. Taken together, our data show the immunomodulatory potential of the TLR inhibitor peptide and suggest cpTLR-i as a novel therapeutic candidate for the treatment of IBD.

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.

Acute Exposure to Pyridostigmine Bromide Disrupts Cholinergic Myenteric Neuroimmune Function in Mice

Gulf War Illness (GWI) results from chemical exposure during the Gulf War, with notable impacts on gastrointestinal motility. Due to the limited demographic impacted by this ailment, an in-depth investigation of the GWI has yielded little regarding the underlying pathophysiological mechanisms. Here, the hypothesis that exposure to pyridostigmine bromide (PB) results in severe enteric neuro-inflammation, that cascades to disruptions in colonic motility, is tested. The analyses are performed on male C57BL/6 mice that are treated with physiologically similar doses of PB given to GW veterans. When colonic motility is assessed, GWI colons have significantly reduced forces in response to acetylcholine or electrical field stimulation. GWI is also accompanied by high levels of pro-inflammatory cytokines and chemokines, associated with increased numbers of CD40⁺ pro-inflammatory macrophages within the myenteric plexus. Enteric neurons responsible for mediating colonic motility reside within the myenteric plexus, and PB exposure reduced their numbers. Significant smooth muscle hypertrophy is also observed due to increased inflammation. Together, the results show that PB exposure caused functional and anatomical dysfunction, promoting impaired motility within the colon. Achieving a greater understanding of the mechanisms of GWI will allow more refinement in therapeutic options that improve veterans' quality of life.

Divergent regulation of basement membrane trafficking by human macrophages and cancer cells

Macrophages and cancer cells populations are posited to navigate basement membrane barriers by either mobilizing proteolytic enzymes or deploying mechanical forces. Nevertheless, the relative roles, or identity, of the proteinase -dependent or -independent mechanisms used by macrophages versus cancer cells to transmigrate basement membrane barriers harboring physiologically-relevant covalent crosslinks remains ill-defined. Herein, both macrophages and cancer cells are shown to mobilize membrane-anchored matrix metalloproteinases to proteolytically remodel native basement membranes isolated from murine tissues while infiltrating the underlying interstitial matrix ex vivo. In the absence of proteolytic activity, however, only macrophages deploy actomyosin-generated forces to transmigrate basement membrane pores, thereby providing the cells with proteinase-independent access to the interstitial matrix while simultaneously exerting global effects on the macrophage transcriptome. By contrast, cancer cell invasive activity is reliant on metalloproteinase activity and neither mechanical force nor changes in nuclear rigidity rescue basement membrane transmigration. These studies identify membrane-anchored matrix metalloproteinases as key proteolytic effectors of basement membrane remodeling by macrophages and cancer cells while also defining the divergent invasive strategies used by normal and neoplastic cells to traverse native tissue barriers.

Macrophages in the gut: Masters in multitasking

The gastrointestinal tract has the important task of absorbing nutrients, a complex process that requires an intact barrier allowing the passage of nutrients but that simultaneously protects the host against invading microorganisms. To maintain and regulate intestinal homeostasis, the gut is equipped with one of the largest populations of macrophages in the body. Here, we will discuss our current understanding of intestinal macrophage heterogeneity and describe their main functions in the different anatomical niches of the gut during steady state. In addition, their role in inflammatory conditions such as infection, inflammatory bowel disease, and postoperative ileus are discussed, highlighting the roles of macrophages in immune defense. To conclude, we describe the interaction between macrophages and the enteric nervous system during development and adulthood and highlight their contribution to neurodegeneration in the context of aging and diabetes.

Telocytes and Macrophages in the Gut: From Morphology to Function. Do the Two Cell Types Interact with Each Other? Which Helps Which?

Telocytes and macrophages are ubiquitous cells located in loose connective tissues and share the same mesenchymal origin. Despite these common elements, depending on where they reside, these two cell types are profoundly different in terms of their morphology and functions. The purpose of this review is to provide an update on the knowledge regarding telocytes and macrophages in the gut, where their presence and significance have long been underestimated or misunderstood. The focus will be on the possibility that these two cell types interact with each other and on the potential meaning of these interactions. Based on the complexity of the topic, the variety of possible methodological approaches and the expertise of the author, the point of view in the discussion of the literature data will be mainly morphological. Furthermore, considering the relatively recent period in which these cell types have acquired a primary role in gastrointestinal functions, the attention will be greatly confined to those articles published in the last decade. The microbiota, another main protagonist in this context, will be mentioned only in passing. It is hoped that this review, although not exhaustive, will highlight the importance of macrophages and telocytes in the complex mechanisms that ensure intestinal functions.

Astrocyte Cell Surface Antigen 2 and Other Potential Cell Surface Markers of Enteric glia in the Mouse Colon

Enteric glia regulate gut functions in health and disease through diverse interactions with neurons and immune cells. Intracellular localization of traditional markers of enteric glia such as GFAP, s100b, and Sox10 makes them incompatible for studies that require antigen localization at the cell surface. Thus, new tools are needed for probing the heterogeneous roles of enteric glia at the protein, cell, and functional levels. Here we selected several cell surface antigens including Astrocyte Cell Surface Marker 2 (ACSA2), Cluster of differentiation 9 (CD9), lysophosphatidic acid receptor 1 (LPAR1), and Proteolipid protein 1 (PLP1) as potential markers of enteric glia. We tested their specificity for enteric glia using published single-cell/-nuclei and glia-specific translating mRNA enriched transcriptome datasets, immunolabeling, and flow cytometry. The data show that ACSA2 is a specific marker of mucosal and myenteric glia while other markers are suitable for identifying all subpopulations of enteric glia (LPAR1), glia and immune cells (CD9), or are not suitable for cell-surface labeling (PLP1). These new tools will be useful for future work focused on understanding specific glial functions in health and disease.Summary StatementThis study identifies astrocyte cell surface antigen 2 as a novel marker of myenteric glia in the intestine. This, in combination with other markers identified in this study, could be used for selective targeting of enteric glia.

Targeted Drug Delivery for the Treatment of Blood Cancers

Blood cancers are a type of liquid tumor which means cancer is present in the body fluid. Multiple myeloma, leukemia, and lymphoma are the three common types of blood cancers. Chemotherapy is the major therapy of blood cancers by systemic administration of anticancer agents into the blood. However, a high incidence of relapse often happens, due to the low efficiency of the anticancer agents that accumulate in the tumor site, and therefore lead to a low survival rate of patients. This indicates an urgent need for a targeted drug delivery system to improve the safety and efficacy of therapeutics for blood cancers. In this review, we describe the current targeting strategies for blood cancers and recently investigated and approved drug delivery system formulations for blood cancers. In addition, we also discuss current challenges in the application of drug delivery systems for treating blood cancers.

Neurons, Macrophages, and Glia: The Role of Intercellular Communication in the Enteric Nervous System

Neurons of the enteric nervous system (ENS) are the primary controllers of gastrointestinal functions. Although the ENS has been the central focus of research areas such as motility, this has now expanded to include the modulatory roles that non-neuronal cells have on neuronal function. This review discusses how enteric glia (EGC) and resident muscularis macrophages (mMacs) influence ENS communication. It highlights how the understanding of neuroglia interactions has extended beyond EGCs responding to exogenously applied neurotransmitters. Proposed mechanisms for neuron-EGC and glio-glia communication are discussed. The significance of these interactions is evidenced by gut functions that rely on these processes. mMacs are commonly known for their roles as immune cells which sample and respond to changes in the tissue environment. However, a more recent theory suggests that mMacs and enteric neurons are mutually dependent for their maintenance and function. This review summarizes the supportive and contradictory evidence for this theory, including potential mechanisms for mMac-neuron interaction. The need for a more thorough classification scheme to define how the "state" of mMacs relates to neuron loss or impaired function in disease is discussed. Despite the growing literature suggesting EGCs and mMacs have supportive or modulatory roles in ENS communication and gut function, conflicting evidence from different groups suggests more investigation is required. A broader understanding of why enteric neurons may need assistance from EGCs and mMacs in neurotransmission is still missing.

The effect of macrophage polarization on the expression of the oxytocin signalling system in enteric neurons

BACKGROUND

The aim of the current study was to investigate the effect of macrophage polarization on the expression of oxytocin (OT) and the oxytocin receptor (OTR) in enteric neurons.

METHODS

In this study, we used a classic colitis model and D-mannose model to observe the correlation between macrophage polarization and OT signalling system. In order to further demonstrate the effect of macrophages, we examined the expression of OT signalling system after depletion of macrophages.

RESULTS

The data showed that, in vitro, following polarization of macrophages to the M1 type by LPS, the macrophage supernatant contained proinflammatory cytokines (IL-1β, IL-6 and TNF-α) that inhibited the expression of OT and OTR in cultured enteric neurons; following macrophage polarization to the M2 type by IL4, the macrophage supernatant contained anti-inflammatory cytokines (TGF-β) that promoted the expression of OT and OTR in cultured enteric neurons. Furthermore, M1 macrophages decreased the expression of the OT signalling system mainly through STAT3/NF-κB pathways in cultured enteric neurons; M2 macrophages increased the expression of the OT signalling system mainly through activation of Smad2/3 and inhibition of the expression of Peg3 in cultured enteric neurons. In a colitis model, we demonstrated that macrophages were polarized to the M1 type during the inflammatory phase, with significant decreased in the expression of OT and OTR. When macrophages were polarized to the M2 type during the recovery phase, OT and OTR expression increased significantly. In addition, we found that D-mannose increased the expression of OT and OTR through polarization of macrophages to the M2 type.

CONCLUSIONS

This is the first study to demonstrate that macrophage polarization differentially regulates the expression of OT and OTR in enteric neurons.