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Gut Jul 2021Intestinal resident macrophages are at the front line of host defence at the mucosal barrier within the gastrointestinal tract and have long been known to play a crucial... (Review)
Review
Intestinal resident macrophages are at the front line of host defence at the mucosal barrier within the gastrointestinal tract and have long been known to play a crucial role in the response to food antigens and bacteria that are able to penetrate the mucosal barrier. However, recent advances in single-cell RNA sequencing technology have revealed that resident macrophages throughout the gut are functionally specialised to carry out specific roles in the niche they occupy, leading to an unprecedented understanding of the heterogeneity and potential biological functions of these cells. This review aims to integrate these novel findings with long-standing knowledge, to provide an updated overview on our understanding of macrophage function in the gastrointestinal tract and to speculate on the role of specialised subsets in the context of homoeostasis and disease.
Topics: Blood Vessels; Cellular Microenvironment; Humans; Intestinal Mucosa; Intestines; Macrophages; Muscle, Smooth; Neurons; Peyer's Patches; Phagocytosis; Submucous Plexus
PubMed: 33384336
DOI: 10.1136/gutjnl-2020-323121 -
Anatomical Record (Hoboken, N.J. : 2007) Aug 2019The enteric nervous system (ENS) controls gastrointestinal key functions and is mainly characterized by two ganglionated plexus located in the gut wall: the myenteric... (Review)
Review
The enteric nervous system (ENS) controls gastrointestinal key functions and is mainly characterized by two ganglionated plexus located in the gut wall: the myenteric plexus and the submucous plexus. The ENS harbors a high number and diversity of enteric neurons and glial cells, which generate neuronal circuitry to regulate intestinal physiology. In the past few years, the pivotal role of enteric neurons in the underlying mechanism of several intestinal diseases was revealed. Intestinal diseases are associated with neuronal death that could in turn compromise intestinal functionality. Enteric neurogenesis and regeneration is therefore a crucial aspect within the ENS and could be revealed not only during embryogenesis and early postnatal periods, but also in the adulthood. Enteric glia and/or enteric neural precursor/progenitor cells differentiate into enteric neurons, both under homeostatic and pathologic conditions beyond the perinatal period. The unique role of the intestinal microbiota and serotonin signaling in postnatal and adult neurogenesis has been shown by several studies in health and disease. In this review article, we will mainly focus on different recent studies, which advanced the concept of postnatal and adult ENS neurogenesis. Moreover, we will discuss the key factors and underlying mechanisms, which promote enteric neurogenesis. Finally, we will shortly describe neurogenesis of transplanted enteric neural progenitor cells. Anat Rec, 302:1345-1353, 2019. © 2019 Wiley Periodicals, Inc.
Topics: Animals; Enteric Nervous System; Gastrointestinal Microbiome; Humans; Longevity; Neurodegenerative Diseases; Neurogenesis; Serotonin; Signal Transduction
PubMed: 30950581
DOI: 10.1002/ar.24124 -
Physiological Reports Feb 2021Obesity is associated with the development of insulin resistance (IR) and type-2 diabetes mellitus (T2DM); however, not all patients with T2DM are obese. The... (Comparative Study)
Comparative Study
BACKGROUND
Obesity is associated with the development of insulin resistance (IR) and type-2 diabetes mellitus (T2DM); however, not all patients with T2DM are obese. The Goto-Kakizaki (GK) rat is an experimental model of spontaneous and non-obese T2DM. There is evidence that the intestine contributes to IR development in GK animals. This information prompted us to investigate small intestine remodeling in this animal model.
METHODS
Four-month-old male Wistar (control) and GK rats were utilized for the present study. After removing the small intestine, the duodenum, proximal jejunum, and distal ileum were separated. We then measured villi and muscular and mucosa layer histomorphometry, goblet cells abundance, total myenteric and submucosal neuron populations, and inflammatory marker expression in the small intestinal segments and intestinal transit of both groups of animals.
KEY RESULTS
We found that the GK rats exhibited decreased intestinal area (p < 0.0001), decreased crypt depth in the duodenum (p = 0.01) and ileum (p < 0.0001), increased crypt depth in the jejunum (p < 0.0001), longer villi in the jejunum and ileum (p < 0.0001), thicker villi in the duodenum (p < 0.01) and ileum (p < 0.0001), thicker muscular layers in the duodenum, jejunum, and ileum (p < 0.0001), increased IL-1β concentrations in the duodenum and jejunum (p < 0.05), and increased concentrations of NF-κB p65 in the duodenum (p < 0.01), jejunum and ileum (p < 0.05). We observed high IL-1β reactivity in the muscle layer, myenteric neurons, and glial cells of the experimental group. GK rats also exhibited a significant reduction in submucosal neuron density in the jejunum and ileum, ganglionic hypertrophy in all intestinal segments studied (p < 0.0001), and a slower intestinal transit (about 25%) compared to controls.
CONCLUSIONS
The development of IR and T2DM in GK rats is associated with small intestine remodeling that includes marked alterations in small intestine morphology, local inflammation, and reduced intestinal transit.
Topics: Animals; Blood Glucose; Cytokines; Diabetes Mellitus, Type 2; Disease Models, Animal; Duodenum; Gastrointestinal Transit; Ileum; Inflammation Mediators; Insulin Resistance; Intestine, Small; Jejunum; Male; Myenteric Plexus; Rats, Wistar; Submucous Plexus; Rats
PubMed: 33580916
DOI: 10.14814/phy2.14755 -
STAR Protocols Mar 2022The myenteric plexus is located between the longitudinal and circular layers of muscularis externa in the gastrointestinal tract. It contains a large network of enteric...
The myenteric plexus is located between the longitudinal and circular layers of muscularis externa in the gastrointestinal tract. It contains a large network of enteric neurons that form the enteric nervous system (ENS) and control intestinal functions, such as motility and nutrient sensing. This protocol describes the method for physical separation (peeling) of muscularis and submucosal layers of the mouse intestine. Subsequently, the intestinal layers are then processed for flow cytometry and/or immunofluorescence analysis. For complete details on the use and execution of this profile, please refer to Ahrends et al. (2021).
Topics: Animals; Flow Cytometry; Fluorescent Antibody Technique; Gastrointestinal Tract; Mice; Mice, Inbred C57BL; Myenteric Plexus; Submucous Plexus
PubMed: 35146454
DOI: 10.1016/j.xpro.2022.101157 -
World Journal of Gastroenterology Dec 2021The enteric nervous system (ENS) consists of thousands of small ganglia arranged in the submucosal and myenteric plexuses, which can be negatively affected by Crohn's... (Review)
Review
The enteric nervous system (ENS) consists of thousands of small ganglia arranged in the submucosal and myenteric plexuses, which can be negatively affected by Crohn's disease and ulcerative colitis - inflammatory bowel diseases (IBDs). IBDs are complex and multifactorial disorders characterized by chronic and recurrent inflammation of the intestine, and the symptoms of IBDs may include abdominal pain, diarrhea, rectal bleeding, and weight loss. The P2X7 receptor has become a promising therapeutic target for IBDs, especially owing to its wide expression and, in the case of other purinergic receptors, in both human and model animal enteric cells. However, little is known about the actual involvement between the activation of the P2X7 receptor and the cascade of subsequent events and how all these activities associated with chemical signals interfere with the functionality of the affected or treated intestine. In this review, an integrated view is provided, correlating the structural organization of the ENS and the effects of IBDs, focusing on cellular constituents and how therapeutic approaches through the P2X7 receptor can assist in both protection from damage and tissue preservation.
Topics: Animals; Colitis, Ulcerative; Enteric Nervous System; Humans; Inflammatory Bowel Diseases; Receptors, Purinergic P2X7; Submucous Plexus
PubMed: 35046620
DOI: 10.3748/wjg.v27.i46.7909 -
Journal of Neurogastroenterology and... Jan 2021The interstitial cells of Cajal (ICC) are located within and around the digestive tract's muscle layers. They function as intestinal muscle pacemakers and aid in the...
BACKGROUND/AIMS
The interstitial cells of Cajal (ICC) are located within and around the digestive tract's muscle layers. They function as intestinal muscle pacemakers and aid in the modification of enteric neurotransmission. The appendix's unique position requires an appropriate contraction pattern of its muscular wall to adequately evacuate its contents. We investigated the development and distribution of nervous structures and ICC in the human fetal appendix.
METHODS
Specimens were exposed to anti-c-kit (CD117) antibodies to investigate ICC differentiation. Enteric plexuses were examined using anti-neuron-specific enolase, and the differentiation of smooth muscle cells was studied with anti-desmin antibodies.
RESULTS
During weeks 13-14, numerous myenteric plexus ganglia form an almost uninterrupted sequence throughout the body and apex of the appendix. Fewer ganglia were present at the submucosal border of the circular muscle layer and within this layer. A large number of ganglia appear within the circular and longitudinal muscle layers in a later fetal period. The first ICC subtypes noted were of the myenteric plexus and the submucous plexus. In the later fetal period, the number of intramuscular ICC markedly rises, and this subtype becomes predominant.
CONCLUSIONS
The ICC and nervous structure distribution in the human fetal appendix are significantly different from all other parts of the small and large intestine. The organization of ICC and the enteric nervous system provides the basis for the specific contraction pattern of the muscular wall of the appendix.
PubMed: 33380557
DOI: 10.5056/jnm20100 -
Cell and Tissue Research Apr 2022We investigated the distributions and targets of nitrergic neurons in the rat stomach, using neuronal nitric oxide synthase (NOS) immunohistochemistry and nicotinamide...
We investigated the distributions and targets of nitrergic neurons in the rat stomach, using neuronal nitric oxide synthase (NOS) immunohistochemistry and nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemistry. Nitrergic neurons comprised similar proportions of myenteric neurons, about 30%, in all gastric regions. Small numbers of nitrergic neurons occurred in submucosal ganglia. In total, there were ~ 125,000 neuronal nitric oxide synthase (nNOS) neurons in the stomach. The myenteric cell bodies had single axons, type I morphology and a wide range of sizes. Five targets were identified, the longitudinal, circular and oblique layers of the external muscle, the muscularis mucosae and arteries within the gastric wall. The circular and oblique muscle layers had nitrergic fibres throughout their thickness, while the longitudinal muscle was innervated at its inner surface by fibres of the tertiary plexus, a component of the myenteric plexus. There was a very dense innervation of the pyloric sphincter, adjacent to the duodenum. The muscle strands that run between mucosal glands rarely had closely associated nNOS nerve fibres. Both nNOS immunohistochemistry and NADPH histochemistry showed that nitrergic terminals did not provide baskets of terminals around myenteric neurons. Thus, the nitrergic neuron populations in the stomach supply the muscle layers and intramural arteries, but, unlike in the intestine, gastric interneurons do not express nNOS. The large numbers of nNOS neurons and the density of innervation of the circular muscle and pyloric sphincter suggest that there is a finely graded control of motor function in the stomach by the recruitment of different numbers of inhibitory motor neurons.
Topics: Animals; Myenteric Plexus; Neurons; Nitric Oxide; Nitric Oxide Synthase; Nitric Oxide Synthase Type I; Rats; Stomach; Submucous Plexus
PubMed: 35146560
DOI: 10.1007/s00441-022-03594-0 -
Cells May 2024Intestinal homeostasis results from the proper interplay among epithelial cells, the enteric nervous system (ENS), interstitial cells of Cajal (ICCs), smooth muscle... (Review)
Review
Intestinal homeostasis results from the proper interplay among epithelial cells, the enteric nervous system (ENS), interstitial cells of Cajal (ICCs), smooth muscle cells, the immune system, and the microbiota. The disruption of this balance underpins the onset of gastrointestinal-related diseases. The scarcity of models replicating the intricate interplay between the ENS and the intestinal epithelium highlights the imperative for developing novel methods. We have pioneered a sophisticated tridimensional in vitro technique, coculturing small intestinal organoids with myenteric and submucosal neurons. Notably, we have made significant advances in (1) refining the isolation technique for culturing the myenteric plexus, (2) enhancing the isolation of the submucosal plexus-both yielding mixed cultures of enteric neurons and glial cells from both plexuses, and (3) subsequently co-culturing myenteric and submucosal neurons with small intestinal organoids. This co-culture system establishes neural innervations with intestinal organoids, allowing for the investigation of regulatory interactions in the context of gastrointestinal diseases. Furthermore, we have developed a method for microinjecting the luminal space of small intestinal organoids with fluorescently labeled compounds. This technique possesses broad applicability such as the assessment of intestinal permeability, transcytosis, and immunocytochemical and immunofluorescence applications. This microinjection method could be extended to alternative experimental setups, incorporating bacterial species, or applying treatments to study ENS-small intestinal epithelium interactions. Therefore, this technique serves as a valuable tool for evaluating the intricate interplay between neuronal and intestinal epithelial cells (IECs) and shows great potential for drug screening, gene editing, the development of novel therapies, the modeling of infectious diseases, and significant advances in regenerative medicine. The co-culture establishment process spans twelve days, making it a powerful asset for comprehensive research in this critical field.
Topics: Animals; Organoids; Coculture Techniques; Mice; Myenteric Plexus; Intestine, Small; Submucous Plexus; Gastrointestinal Tract; Neurons
PubMed: 38786037
DOI: 10.3390/cells13100815 -
Neurogastroenterology and Motility Aug 2021Intravenous administration of adeno-associated virus (AAV) can be used as a noninvasive approach to trace neuronal morphology and links. AAV-PHP.S is a variant of AAV9...
BACKGROUND
Intravenous administration of adeno-associated virus (AAV) can be used as a noninvasive approach to trace neuronal morphology and links. AAV-PHP.S is a variant of AAV9 that effectively transduces the peripheral nervous system. The objective was to label randomly and sparsely enteric plexus in the mouse colon using AAV-PHP.S with a tunable two-component multicolor vector system and digitally trace individual neurons and nerve fibers within microcircuits in three dimensions (3D).
METHODS
A vector system including a tetracycline inducer with a tet-responsive element driving three separate fluorophores was packaged in the AAV-PHP.S capsid. The vectors were injected retro-orbitally in mice, and the colon was harvested 3 weeks after. Confocal microscopic images of enteric plexus were digitally segmented and traced in 3D using Neurolucida 360, neuTube, or Imaris software.
KEY RESULTS
The transduction of multicolor AAV vectors induced random sparse spectral labeling of soma and neurites primarily in the myenteric plexus of the proximal colon, while neurons in the submucosal plexus were occasionally transduced. Digital tracing in 3D showed various types of wiring, including multiple conjunctions of one neuron with other neurons, neurites en route, and endings; clusters of neurons in close apposition between each other; axon-axon parallel conjunctions; and intraganglionic nerve endings consisting of multiple nerve endings and passing fibers. Most of digitally traced neuronal somas were of small or medium in size.
CONCLUSIONS & INFERENCES
The multicolor AAV-PHP.S-packaged vectors enabled random sparse spectral labeling and revealed complexities of enteric microcircuit in the mouse proximal colon. The techniques can facilitate digital modeling of enteric micro-circuitry.
Topics: Animals; Colon; Dependovirus; Enteric Nervous System; Female; Gene Transfer Techniques; Green Fluorescent Proteins; Male; Mice; Submucous Plexus
PubMed: 33094876
DOI: 10.1111/nmo.14014 -
Neurogastroenterology and Motility Dec 2022Alterations in gastrointestinal (GI) function and the gut-brain axis are associated with progression and pathology of Alzheimer's Disease (AD). Studies in AD animal...
BACKGROUND
Alterations in gastrointestinal (GI) function and the gut-brain axis are associated with progression and pathology of Alzheimer's Disease (AD). Studies in AD animal models show that changes in the gut microbiome and inflammatory markers can contribute to AD development in the central nervous system (CNS). Amyloid-beta (Aβ) accumulation is a major AD pathology causing synaptic dysfunction and neuronal death. Current knowledge of the pathophysiology of AD in enteric neurons is limited, and whether Aβ accumulation directly disrupts enteric neuron function is unknown.
METHODS
In 6-month-old 5xFAD (transgenic AD) and wildtype (WT) male and female mice, GI function was assessed by colonic transit in vivo; propulsive motility and GI smooth muscle contractions ex vivo; electrochemical detection of enteric nitric oxide release in vitro, and changes in myenteric neuromuscular transmission using smooth muscle intracellular recordings. Expression of Aβ in the brain and colonic myenteric plexus in these mice was determined by immunohistochemistry staining and ELISA assay.
KEY RESULTS
At 6 months, 5xFAD mice did not show significant changes in GI motility or synaptic neurotransmission in the small intestine or colon. 5xFAD mice, but not WT mice, showed abundant Aβ accumulation in the brain. Aβ accumulation was undetectable in the colonic myenteric plexus of 5xFAD mice.
CONCLUSIONS
5xFAD AD mice are not a robust model to study amyloidosis in the gut as these mice do not mimic myenteric neuronal dysfunction in AD patients with GI dysmotility. An AD animal model with enteric amyloidosis is required for further study.
Topics: Female; Male; Animals; Mice; Amyloidosis; Synaptic Transmission; Neurons; Submucous Plexus; Myenteric Plexus; Disease Models, Animal
PubMed: 36458522
DOI: 10.1111/nmo.14439