Role of enteric glial cells in gastric motility in diabetic rats at different stages

Hyperglycemic stress induces oxidative damage of enteric glial cells by triggering redoxosomes/p66SHC activation

OBJECTIVES

Diabetic gastrointestinal dysfunction (DGD) is a serious complication of diabetic mellitus (DM), affecting the enteric nervous system (ENS), particular enteric glial cells (EGCs). This study aimed to elucidate the effects and underlying molecular mechanisms of hyperglycemic stress on EGCs in in vitro and in vivo models of DM.

METHODS

In in vitro studies, enteric glial cell line CRL-2690 was exposed to hyperglycemia stress, and cell viability, cell apoptosis and oxidative damage were assessed. In in vivo studies, STZ-induced diabetic mice were constructed, and cell apoptosis and oxidative damage of EGCs in the duodenum of DM mice were assessed.

RESULTS

The results showed that hyperglycemic stress markedly induced oxidative damage of EGCs in in vitro and in vivo models of DM. This damage was found to be dependent on the activation of redoxosomes, which involved the phosphorylation of SRC and Vav2, the up-regulation of active RAC1-GTP, and the activation of NADPH oxidase (NOX). Moreover, inhibitors of redoxosomes, such as the RAC1 inhibitor NSC23766 and the NOX inhibitor VAS2870, effectively mitigated the hyperglycemic stress-induced oxidative damage of EGCs. Additionally, inhibition of p66SHC, a downstream target of redoxosomes, attenuated oxidative damage of EGCs under hyperglycemic stress.

DISCUSSION

Our findings suggest that the redoxosomes/p66SHC signaling is involved in the oxidative damage of EGCs during the pathological process of DGD. This signaling cascade may represent a potential therapeutic target for the treatment of DGD.

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.

Pathogenesis and management of diabetic gastroparesis: An updated clinically oriented review

BACKGROUND AND AIMS

Diabetic gastroparesis (DGp) is a common and preventable complication of uncontrolled diabetes mellitus (D.M.) and significantly affects the Quality of Life of patients. Diagnosis and management present as a clinical challenge due to the disease's complexity and limited effective therapeutic options. This review aims to comprehensively outline the pathogenesis, diagnosis, and management of diabetic gastroparesis, evaluating evolving approaches to guide clinicians and provide future recommendations.

METHODS

A literature review was conducted on scholarly databases of PubMed, Google Scholar, Scopus and Web of Science encompassing published articles, gray literature and relevant clinical guidelines. Data were synthesized and analyzed to provide a comprehensive overview of diabetic gastroparesis, focusing on pathogenesis, diagnosis, and management.

RESULTS

The review intricately explores the pathogenesis contributing to diabetic gastroparesis, emphasizing autonomic neuropathy, oxidative stress, inflammation, hormonal dysregulation, microbiota alterations, and gastrointestinal neuropathy. Primary management strategies are underscored, including lifestyle modifications, symptom relief, and glycemic control. The discussion encompasses pharmacological and surgical options, highlighting the importance of a multidisciplinary approach involving various healthcare professionals for comprehensive patient care.

CONCLUSION

This review offers a thorough understanding of pathogenesis, diagnosis, and management of diabetic gastroparesis, underlining evolving approaches for clinicians. A multidisciplinary approach is crucial to address both the physical and mental health aspects of diabetes and its complications.

Circular RNA-VPS13A attenuates diabetes-induced enteric glia damage by targeting miR-182/GDNF Axis

Gastrointestinal (GI) complications of diabetes mellitus (DM) significantly impact on patients' quality of life. Enteric glial cells (EGC) are the key cell type of enteric nervous system (ENS), which contributes to the destruction of gut homeostasis in DM. Circular RNAs (circRNAs) are a novel type of RNAs abundant in the eukaryotic transcriptome, which form covalently closed continuous loops. In this study, the contribution of circRNAs to EGC damage in DM is investigated. Transcriptome sequencing analysis and functional study show that circVPS13A is significantly down-regulated in hyperglycemia-treated EGC, and circVPS13A overexpression attenuates EGC damage in both in vitro and in vivo DM models. In vitro mechanistic study using dual-luciferase reporter assay, affinity-isolation assay, fluorescence in situ hybridization (FISH) and immunostaining analysis identify that circVPS13A exerts its protective effect by sponging miR-182 and then up-regulates glial cell line-derived neurotrophic factor (GDNF) expression. In addition, in vivo study confirms that the circVPS13A-miR-182-GDNF network regulation can attenuate hyperglycemia-induced EGC damage of duodenum in streptozotocine (STZ)-induced DM mice. The findings of this study may provide novel insights into the protective role of circVPS13A in DM-associated EGC damage and clues for the development of new therapeutic approaches for the prevention of GI complications of DM.

5/6 nephrectomy affects enteric glial cells and promotes impaired antioxidant defense in the colonic neuromuscular layer

AIMS

Chronic kidney disease (CKD) produces multiple repercussions in the gastrointestinal tract (GIT), such as alterations in motility, gut microbiota, intestinal permeability, and increased oxidative stress. However, despite enteric glial cells (EGC) having important neural and immune features in GIT physiology, their function in CKD remains unknown. The present study investigates colonic glial markers, inflammation, and antioxidant parameters in a CKD model.

MAIN METHODS

A 5/6 nephrectomized rat model was used to induce CKD in rats and Sham-operated animals as a control to suppress. Biochemical measures in plasma and neuromuscular layer such as glutathione peroxidase (GPx) and superoxide dismutase (SOD) activity were carried out. Kidney histopathology was evaluated. Colon morphology analysis and glial fibrillary acid protein (GFAP), connexin-43 (Cx43), nuclear factor-kappa B (NF-κB) p65, and GPx protein expression were performed.

KEY FINDINGS

The CKD group exhibited dilated tubules and tubulointerstitial fibrosis in the reminiscent kidney (p = 0.0002). CKD rats showed higher SOD activity (p = 0.004) in plasma, with no differences in neuromuscular layer (p = 0.9833). However, GPx activity was decreased in the CKD group in plasma (p = 0.013) and neuromuscular layer (p = 0.0338). Morphological analysis revealed alterations in colonic morphometry with inflammatory foci in the submucosal layer and neuromuscular layer straightness in CKD rats (p = 0.0291). In addition, GFAP, Cx43, NF-κBp65 protein expression were increased, and GPx decreased in the neuromuscular layer of the CKD group (p < 0.05).

SIGNIFICANCE

CKD animals present alterations in colonic cytoarchitecture and decreased layer thickness. Moreover, CKD affects the enteric glial network of the neuromuscular layer, associated with decreased antioxidant activity and inflammation.

Brazil Nut (Bertholletia excelsa H.B.K) Retards Gastric Emptying and Modulates Enteric Glial Cells in a Dose-Dependent Manner

BACKGROUND

The role of food and nutrients in the regulation of enteric glial cell functions is unclear. Some foods influence enteric neurophysiology and can affect glial cell functions that include regulation of the intestinal barrier, gastric emptying, and colonic transit. Brazil nuts are the most abundant natural source of selenium, unsaturated fatty acids, fibers, and polyphenols.

OBJECTIVE

The study investigated the effects of a Brazil nut-enriched diet on enteric glial cells and gastrointestinal transit.

METHODS

Two-month-old male Wistar rats were randomized to a standard diet (control group, CG), standard diet containing 5% (wt/wt) Brazil nut (BN5), and standard diet containing 10% (wt/wt) Brazil nut (BN10) (n = 9 per group). After eight weeks, the animals underwent constipation and gastric emptying tests to assess motility. Evaluations of colonic immunofluorescence staining for glial fibrillary acidic protein (GFAP) and myenteric ganglia area were performed.

RESULTS

The BN5 group showed increased weight gain while the BN10 group did not (p < 0.0001). The BN10 group showed higher gastric residue amounts compared to the other groups (p = 0.0008). The colon exhibited an increase in GFAP immunoreactivity in the BN5 group compared to that in the other groups (p = 0.0016), and the BN10 group presented minor immunoreactivity compared to the CG (p = 0.04). The BN10 group presented a minor ganglia area compared to the CG (p = 0.0155).

CONCLUSION

The Brazil nut-enriched diet modified the gastric residual, colonic GFAP immunoreactivity, and myenteric ganglia area after eight weeks in healthy male Wistar rats.

Interactions between the microbiota and enteric nervous system during gut-brain disorders

For the last 20 years, researchers have focused their intention on the impact of gut microbiota in healthy and pathological conditions. This year (2021), more than 25,000 articles can be retrieved from PubMed with the keywords "gut microbiota and physiology", showing the constant progress and impact of gut microbes in scientific life. As a result, numerous therapeutic perspectives have been proposed to modulate the gut microbiota composition and/or bioactive factors released from microbes to restore our body functions. Currently, the gut is considered a primary site for the development of pathologies that modify brain functions such as neurodegenerative (Parkinson's, Alzheimer's, etc.) and metabolic (type 2 diabetes, obesity, etc.) disorders. Deciphering the mode of interaction between microbiota and the brain is a real original option to prevent (and maybe treat in the future) the establishment of gut-brain pathologies. The objective of this review is to describe recent scientific elements that explore the communication between gut microbiota and the brain by focusing our interest on the enteric nervous system (ENS) as an intermediate partner. The ENS, which is known as the "second brain", could be under the direct or indirect influence of the gut microbiota and its released factors (short-chain fatty acids, neurotransmitters, gaseous factors, etc.). Thus, in addition to their actions on tissue (adipose tissue, liver, brain, etc.), microbes can have an impact on local ENS activity. This potential modification of ENS function has global repercussions in the whole body via the gut-brain axis and represents a new therapeutic strategy.

Nerve growth factor and Tropomyosin receptor kinase A are increased in the gastric mucosa of patients with functional dyspepsia

Background

Nerve growth factor (NGF) and enteric glial cells (EGCs) are associated with visceral hypersensitivity and gastrointestinal motility disorder, which may represent the pathogenesis of functional dyspepsia (FD). This study aimed to investigate the expression of NGF, its high affinity receptor tropomyosin receptor kinase A (TrkA) and the EGC activation marker glial fibrillary acidic protein (GFAP) in the gastric mucosa of patients with FD and the association of these proteins with dyspeptic symptoms.

Methods

Gastric mucosal biopsies taken from 27 FD patients (9 epigastric pain syndrome (EPS) patients, 7 postprandial distress syndrome (PDS) patients and 11 EPS overlap PDS patients) and 26 control subjects were used for analysis. The expression of NGF, TrkA and GFAP was examined, and the association of these proteins with dyspeptic symptoms, including epigastric pain, postprandial fullness, early satiation and epigastric burning, was analysed.

Results

The expression levels of NGF, TrkA, and GFAP in the gastric mucosa were significantly higher in the EPS group, the PDS group, and the EPS overlap PDS group than in the healthy control group. There was no significant difference between the FD subgroups. TrkA colocalized with GFAP, which indicated that TrkA was localized to EGCs, and the expression of TrkA in EGCs was significantly higher in the FD group than in the control group. Changes in the expression of NGF, TrkA, and GFAP were positively correlated with epigastric pain, postprandial fullness and early satiation but had no significant relationship with epigastric burning.

Conclusions

The increased expression of gastric NGF, TrkA and GFAP might be involved in FD pathophysiology and symptom perception.

Co-expression of caspase-3 or caspase-8 with galanin in the human stomach section affected by carcinoma

Neoplastic process may cause distinct changes in the morphology, i.e. size and number of the neurons of the neuronal plexuses forming the enteric nervous system (ENS) of the human intestine. Moreover, it was also reported that these changes were not directly associated with apoptosis. Thus, the main aim of this study was to determine the atrophic changes of myenteric plexuses (MPs) in the vicinity of cancer invasion and the potential reason which may be responsible for these changes if they occur. Tissue samples from the stomach were collected from ten patients which undergo organ resection due to cancer diagnosis. Samples were taken from the margin of cancer invasion and from a macroscopically-unchanged part of the stomach wall. Triple-immunofluorescence staining of the 10-µm-thick cryostat sections was used to visualize the co-expression of caspase-3 (CASP3) or caspase-8 (CASP8) with galanin (GAL) in the MPs of ENS. Microscopic observations of MPs located closely to gastric cancer invasion showed that they were significantly smaller than plexuses located distally. The percentage of neurons containing CASP3 within MPs located close to cancer-affected regions of the stomach was higher, while containing CASP8 was lower compared to the unchanged regions. Additionally, elevated high expression of CASP3 or CASP8 in the neurons from MPs was accompanied by a decreased expression of GAL. To our knowledge, this is the first report describing the decomposition of MPs within cancer-affected human stomach wall and the possible role of apoptosis in this process.

Pathophysiology and management of diabetic gastroenteropathy

Polyneuropathy is a common complication to diabetes. Neuropathies within the enteric nervous system are associated with gastroenteropathy and marked symptoms that severely reduce quality of life. Symptoms are pleomorphic but include nausea, vomiting, dysphagia, dyspepsia, pain, bloating, diarrhoea, constipation and faecal incontinence. The aims of this review are fourfold. First, to provide a summary of the pathophysiology underlying diabetic gastroenteropathy. Secondly to give an overview of the diagnostic methods. Thirdly, to provide clinicians with a focussed overview of current and future methods for pharmacological and nonpharmacological treatment modalities. Pharmacological management is categorised according to symptoms arising from the upper or lower gut as well as sensory dysfunctions. Dietary management is central to improvement of symptoms and is discussed in detail, and neuromodulatory treatment modalities and other emerging management strategies for diabetic gastroenteropathy are discussed. Finally, we propose a diagnostic/investigation algorithm that can be used to support multidisciplinary management.

Enteric glial cell activation protects enteric neurons from damage due to diabetes in part via the promotion of neurotrophic factor release

BACKGROUND

Diabetes can result in pathological changes to enteric nervous system. Our aim was to test the dynamic changes of enteric neurons and identify the role of enteric glial cells (EGCs) in regulating enteric neuron expression in diabetic rats.

METHODS

A single injection of streptozotocin (STZ) was used to establish diabetic rats. Animals were randomly distributed into diabetic 1-, 4-, 8-, and 16-week groups, as well as age-matched control groups. The PGP9.5- and glial fibrillary acidic protein (GFAP)-immunopositive cells were quantified by immunohistochemistry. The protein levels of PGP9.5, ChAT, nNOS, S-100β, and c-fos were determined by western blotting. The levels of nerve growth factor (NGF), neurotrophin 3 (NT-3), and glial cell-derived neurotrophic factor (GDNF) were tested by ELISA.

KEY RESULTS

An increase in blood glucose and a decrease in body weight were observed following STZ administration. PGP9.5 expression did not change in the diabetic ileum. However, ChAT increased after 16 weeks, and nNOS decreased after 8 and 16 weeks in the ilea of diabetic rats. The absence of degeneration of enteric neurons during the acute stage of the disease could be the consequence of the up-regulation of GFAP, S-100β, and c-fos. Moreover, the content of NGF, NT-3, and GDNF in the ileum increased by varying degrees after 1 and/or 4 weeks of diabetes. Using 2 co-culture models of EGCs and SH-SY5Y cells in a high glucose condition, the supportive role of EGCs was further confirmed.

CONCLUSIONS & INFERENCES

Enteric glial cell activation can protect enteric neurons from damage due to diabetes in the acute stage of the disease, in part via the promotion of neurotrophin release.

Enteric Glial Dysfunction Evoked by Apolipoprotein E Deficiency Contributes to Delayed Gastric Emptying

BACKGROUND AND AIM

Diabetes is the main cause of gastroparesis accompanying decreased neuronal nitric oxide synthase (nNOS) in myenteric ganglia of the stomach. Decreased nNOS expression in the stomach also results from defects in apolipoprotein E (ApoE), which is secreted by astrocytes and has neuroprotective effects on the central nervous system. However, the roles of ApoE and enteric glial cells on gastric motility are uncertain. In this study, ApoE and enteric glial cell alterations in gastroparesis were investigated.

METHODS

Type 2 diabetic (db/db) mice and ApoE-knockout mice were analyzed. Gastric emptying was measured using the ¹³C acetic acid breath test. Expression levels of the pan-neuronal marker, protein gene product 9.5 (PGP 9.5), and glial marker, glial fibrillary acidic protein (GFAP) were examined by immunohistochemistry. Neural stem cells (NSCs) were injected into the gastric antral wall of ApoE-knockout mice.

RESULTS

Delayed gastric emptying was observed in 27% of db/db mice with significant decreases in serum ApoE levels and GFAP expression in the gastric antrum. Gastric emptying was also delayed in ApoE-knockout mice, with a significant decrease in GFAP expression, but no change in PGP 9.5 expression. Transplantation of NSCs improved gastric emptying in ApoE-knockout mice through supplementation of GFAP-positive cells.

CONCLUSIONS

Our results suggest that decreased enteric glial cells in ApoE-knockout mice are crucial for development of delayed gastric emptying, and NSC transplantation is effective in restoring myenteric ganglia and gastric motility.

Pathogenesis of diabetic gastrointestinal dysfunction

Diabetic gastrointestinal dysfunction is a common complication in patients with diabetes mellitus. Most of the symptoms are related to impaired gastrointestinal function. The pathogenesis and etiology of diabetic gastroenteropathy are complex, involving the parasympathetic and sympathetic nervous systems, enteric neurons, smooth muscle cells, the network of interstitial cells of Cajal, cholinergic receptors and neuronal nitric oxide synthase. This article reviews the pathogenesis of diabetic gastrointestinal dysfunction.

Diabetic gastrointestinal motility disorders and the role of enteric nervous system: current status and future directions

BACKGROUND

Gastrointestinal manifestations of diabetes are common and a source of significant discomfort and disability. Diabetes affects almost every part of gastrointestinal tract from the esophagus to the rectum and causes a variety of symptoms including heartburn, nausea, vomiting, abdominal pain, diarrhea and constipation. Understanding the underlying mechanisms of diabetic gastroenteropathy is important to guide development of therapies for this common problem. Over recent years, the data regarding the pathophysiology of diabetic gastroenteropathy is expanding. In addition to autonomic neuropathy causing gastrointestinal disturbances the role of enteric nervous system is becoming more evident.

PURPOSE

In this review, we summarize the reported alterations in enteric nervous system including enteric neurons, interstitial cells of Cajal and neurotransmission in diabetic animal models and patients. We also review the possible underlying mechanisms of these alterations, with focus on oxidative stress, growth factors and diabetes induced changes in gastrointestinal smooth muscle. Finally, we will discuss recent advances and potential areas for future research related to diabetes and the ENS such as gut microbiota, micro-RNAs and changes in the microvasculature and endothelial dysfunction.

Synchronized dual pulse gastric electrical stimulation induces activation of enteric glial cells in rats with diabetic gastroparesis

Objective. The aims of this study were to investigate the effects of synchronized dual pulse gastric electrical stimulation (SGES) on gastric motility in different periods for diabetic rats and try to explore the possible mechanisms of the effects. Methods. Forty-six rats were used in the study. Gastric slow waves were recorded at baseline, 7-14-day diabetes and 56-63-day diabetes before and after stimulation and the age-matched control groups. SGES-60 mins and SGES-7 days (60 mins/day) were performed to test the effects on gastric motility and to evaluate glial marker S100B expression in stomach. Results. (1) Gastric emptying was accelerated in 7-14-day diabetes and delayed in 56-63-day diabetes. (2) The S100B expression in 56-63-day diabetes decreased and the ultrastructure changed. (3) The age-associated loss of EGC was observed in 56-63-day control group. (4) SGES was able to not only accelerate gastric emptying but also normalize gastric slow waves. (5) The S100B expression increased after SGES and the ultrastructure of EGC was partially restored. The effect of SGES-7 days was superior to SGES-60 mins. Conclusions. Delayed gastric emptying due to the growth of age may be related to the EGC inactivation. The effects of the SGES on gastric motility may be associated with EGC activation.