Glial-derived neurotrophic factor regulates intestinal epithelial barrier function and inflammation and is therapeutic for murine colitis

Neurotrophic Factors Protect the Intestinal Barrier from Rotavirus Insult in Mice

Human and mouse studies have shown that rotavirus infection is associated with low inflammation and unaffected intestinal barrier at the time of diarrhea, properties different from most bacterial and inflammatory diseases of the gut. We showed by in vitro, ex vivo, and in vivo experiments that neurotrophic factors and 5-HT have barrier protective properties during rotavirus insult. These observations advance our understanding of how the gut barrier is protected against rotavirus and suggest that rotavirus affects the gut barrier differently from bacteria. This is the first report to show that neurotrophic factors contribute to maintain the gut epithelial barrier during viral insult.

Increased intestinal permeability has been proposed as a mechanism of rotavirus-induced diarrhea. Studies with humans and mice have, however, shown that rotavirus leaves intestinal permeability unaffected or even reduced during diarrhea, in contrast to most bacterial infections. Gastrointestinal permeability is regulated by the vagus nerve and the enteric nervous system, which is composed of neurons and enteric glial cells (EGCs). We investigated whether the vagus nerve, serotonin (5-HT), EGCs, and neurotropic factors contribute to maintaining gut barrier homeostasis during rotavirus infection. Using subdiaphragmatic vagotomized and 5-HT₃ receptor knockout mice, we found that the unaffected epithelial barrier during rotavirus infection is independent of the vagus nerve but dependent on 5-HT signaling through enteric intrinsic 5-HT₃ receptors. Immunofluorescence analysis showed that rotavirus-infected enterocytes were in close contact with EGCs and enteric neurons and that the glial cell-derived neurotrophic factor (GDNF) was strongly upregulated in enterocytes of infected mice. Moreover, rotavirus and 5-HT activated EGCs (P < 0.001). Using Ussing chambers, we found that GDNF and S-nitrosoglutathione (GSNO) led to denser epithelial barriers in small intestinal resections from noninfected mice (P < 0.01) and humans (P < 0.001) and that permeability was unaffected in rotavirus-infected mice. GSNO made the epithelial barrier denser in Caco-2 cells by increasing the expression of the tight junction protein zona occludens 1 (P < 0.001), resulting in reduced passage of fluorescein isothiocyanate dextran (P < 0.05) in rotavirus-infected monolayers. This is the first report to show that neurotropic factors contribute to maintaining the gut epithelial barrier during viral insult.

Neurotrophic factor GDNF regulates intestinal barrier function in inflammatory bowel disease

Impaired intestinal epithelial barrier (IEB) function with loss of desmosomal junctional protein desmoglein 2 (DSG2) is a hallmark in the pathogenesis of inflammatory bowel disease (IBD). While previous studies have reported that glial cell line-derived neurotrophic factor (GDNF) promotes IEB function, the mechanisms are poorly understood. We hypothesized that GDNF is involved in the loss of DSG2, resulting in impaired IEB function as seen in IBD. In the inflamed intestine of patients with IBD, there was a decrease in GDNF concentrations accompanied by a loss of DSG2, changes of the intermediate filament system, and increased phosphorylation of p38 MAPK and cytokeratins. DSG2-deficient and RET-deficient Caco2 cells revealed that GDNF specifically recruits DSG2 to the cell borders, resulting in increased DSG2-mediated intercellular adhesion via the RET receptor. Challenge of Caco2 cells and enteroids with proinflammatory cytokines as well as dextran sulfate sodium-induced (DSS-induced) colitis in C57Bl/6 mice led to impaired IEB function with reduced DSG2 mediated by p38 MAPK-dependent phosphorylation of cytokeratins. GDNF blocked all inflammation-induced changes in the IEB. GDNF attenuates inflammation-induced impairment of IEB function caused by the loss of DSG2 through p38 MAPK-dependent phosphorylation of cytokeratin. The reduced GDNF in patients with IBD indicates a disease-relevant contribution to the development of IEB dysfunction.

Molecular Mechanisms Underlying How Sialyllactose Intervention Promotes Intestinal Maturity by Upregulating GDNF Through a CREB-Dependent Pathway in Neonatal Piglets

Sialylated milk oligosaccharides (SMOs) have a multifunctional health benefit, yet the molecular details underlying their potential role in modulating intestinal maturation remains unknown. To test the hypothesis that sialyllactose (SL) may mediate intestinal maturation and function through controlling neuronal function, studies were carried out where the diet of postnatal piglets was supplemented with a mixture of 3'- and 6'-sialyllactose from postnatal day 3 to 38. Gene transcription pathways regulating enteric nervous system function, polysialic acid (polySia) synthesis, and cell proliferation were quantified. Our new findings show that SL intervention: (1) upregulated the level of gene and protein expression of the glial-derived neurotrophic factor (GDNF) in the ileum; (2) upregulated phosphorylation of the cAMP responsive element-binding protein (CREB), the downstream target of GDNF signaling pathway; (3) promoted cell proliferation based on an increase in the number and density of Ki-67 positive cells in the crypts; (4) increased the crypt width in the ileum by 10%, while gene markers for the functional cells were not affected; (5) upregulated mRNA expression level of ST8Sia IV, a key polysialyltransferase responsible for synthesis of polySia-NCAM; (6) reduced the incidence and severity of diarrhea. These results show that SL promotes intestinal maturation in neonatal piglets by upregulating GDNF, synthesis of polySia and CREB-interactive pathway.

p300/CBP-associated factor promotes autophagic degradation of δ-catenin through acetylation and decreases prostate cancer tumorigenicity

δ-Catenin shares common binding partners with β-catenin. As acetylation and deacetylation regulate β-catenin stability, we searched for histone acetyltransferases (HATs) or histone deacetylases (HDACs) affecting δ-catenin acetylation status and protein levels. We showed that p300/CBP-associated factor (PCAF) directly bound to and acetylated δ-catenin, whereas several class I and class II HDACs reversed this effect. Unlike β-catenin, δ-catenin was downregulated by PCAF-mediated acetylation and upregulated by HDAC-mediated deacetylation. The HDAC inhibitor trichostatin A attenuated HDAC1-mediated δ-catenin upregulation, whereas HAT or autophagy inhibitors, but not proteasome inhibitors, abolished PCAF-mediated δ-catenin downregulation. The results suggested that PCAF-mediated δ-catenin acetylation promotes its autophagic degradation in an Atg5/LC3-dependent manner. Deletions or point mutations identified several lysine residues in different δ-catenin domains involved in PCAF-mediated δ-catenin downregulation. PCAF overexpression in prostate cancer cells markedly reduced δ-catenin levels and suppressed cell growth and motility. PCAF-mediated δ-catenin downregulation inhibited E-cadherin processing and decreased the nuclear distribution of β-catenin, resulting in the suppression of β-catenin/LEF-1-mediated downstream effectors. These data demonstrate that PCAF downregulates δ-catenin by promoting its autophagic degradation and suppresses δ-catenin-mediated oncogenic signals.

The novel insight into anti-inflammatory and anxiolytic effects of psychobiotics in diabetic rats: possible link between gut microbiota and brain regions

PURPOSE

Type 2 diabetes mellitus (T2DM) was associated with gut microbial impairment (dysbiosis) and neurological and behavioral disorders. The role of the gut-brain axis in the management of many diseases including T2DM has been the focus of much research activity in the recent years. However, a wide knowledge gap exists about the gut microbial effects on the function of glia cells. Hence, the present study was aimed to examine the effects of psychobatics on dysbiosis and glia cells function in enteric and central nervous system with an inflammatory insight in T2DM.

METHODS

Thirty rats were treated by Lactobacillus (L.) plantarum, inulin, or their combination (synbiotic) for 8 weeks after inducing T2DM. Fecal sample was collected to evaluate gut microbial composition. Then, the rats were sacrificed, and the colon, amygdala, and prefrontal cortex (PFC) were studied.

RESULTS

T2DM resulted in dysbiosis and increased levels of glial cell-derived neurotrophic factor (GDNF), glial fibrillary acidic protein (GFAP), and inflammatory markers (IL-17, IL-6, and TLR-2) in the colon and brain. However, concurrent supplementation of L. plantarum and inulin could improve the gut microbial composition as well as reduce the levels of inflammatory cytokines. While the administration of L. plantarum led to a significant decrease in TLR-2 as well as GDNF and GFAP only in the amygdala, the synbiotic intake could make such changes in the colon, amygdala, and PFC.

CONCLUSIONS

Our findings demonstrated an innovative approach to the beneficial effects of psychobiotics in neuroinflammation and behavioral performance through gut microbiota changes, focusing on possible role of glial cells in gut-brain axis.

Unexpected Roles for the Second Brain: Enteric Nervous System as Master Regulator of Bowel Function

At the most fundamental level, the bowel facilitates absorption of small molecules, regulates fluid and electrolyte flux, and eliminates waste. To successfully coordinate this complex array of functions, the bowel relies on the enteric nervous system (ENS), an intricate network of more than 500 million neurons and supporting glia that are organized into distinct layers or plexi within the bowel wall. Neuron and glial diversity, as well as neurotransmitter and receptor expression in the ENS, resembles that of the central nervous system. The most carefully studied ENS functions include control of bowel motility, epithelial secretion, and blood flow, but the ENS also interacts with enteroendocrine cells, influences epithelial proliferation and repair, modulates the intestinal immune system, and mediates extrinsic nerve input. Here, we review the many different cell types that communicate with the ENS, integrating data about ENS function into a broader view of human health and disease. In particular, we focus on exciting new literature highlighting relationships between the ENS and its lesser-known interacting partners.

Rat enteric glial cells express novel isoforms of Interleukine-7 regulated during inflammation

BACKGROUND

Neuroimmune interactions are essential to maintain gut homeostasis and prevent intestinal disorders but so far, the impact of enteric glial cells (EGC) on immune cells remains a relatively unexplored area of research. As a dysregulation of critical cytokines such as interleukine-7 (IL-7) was suggested to exacerbate gut chronic inflammation, we investigated whether EGC could be a source of IL-7 in the gastrointestinal tract.

METHODS

Expression of IL-7 in the rat enteric nervous system was analyzed by immunochemistry and Q-PCR. IL-7 variants were cloned and specific antibodies against rat IL-7 isoforms were raised to characterize their expression in the submucosal plexus. IL-7 isoforms were produced in vitro to analyze their impact on T-cell survival.

KEY RESULTS

Neurons and glial cells of the rat enteric nervous system expressed IL-7 at both mRNA and protein levels. Novel rat IL-7 isoforms with distinct C-terminal parts were detected. Three of these isoforms were found in EGC or in both enteric neurons and EGC. Exposure of EGC to pro-inflammatory cytokines (IL-1β and/or TNFα) induced an upregulation of all IL-7 isoforms. Interestingly, time-course and intensity of the upregulation varied according to the presence or absence of exon 5a in IL-7 variants. Functional analysis on T lymphocytes revealed that only canonical IL-7 protects T cells from cell death.

CONCLUSIONS AND INFERENCES

IL-7 and its variants are expressed by neurons and glial cells in the enteric nervous system. Their distinct expression and upregulation in inflammatory conditions suggest a role in gut homeostasis which could be critical in case of chronic inflammatory diseases.

IL-33/ST2 Axis in Organ Fibrosis

Interleukin 33 (IL-33) is highly expressed in barrier sites, acting via the suppression of tumorigenicity 2 receptor (ST2). IL-33/ST2 axis has long been known to play a pivotal role in immunity and cell homeostasis by promoting wound healing and tissue repair. However, it is also involved in the loss of balance between extensive inflammation and tissue regeneration lead to remodeling, the hallmark of fibrosis. The aim of the current review is to critically evaluate the available evidence regarding the role of the IL-33/ST2 axis in organ fibrosis. The role of the axis in tissue remodeling is better understood considering its crucial role reported in organ development and regeneration. Generally, the IL-33/ST2 signaling pathway has mainly anti-inflammatory/anti-proliferative effects; however, chronic tissue injury is responsible for pro-fibrogenetic responses. Regarding pulmonary fibrosis mature IL-33 enhances pro-fibrogenic type 2 cytokine production in an ST2- and macrophage-dependent manner, while full-length IL-33 is also implicated in the pulmonary fibrotic process in an ST2-independent, Th2-independent fashion. In liver fibrosis, evidence indicate that when acute and massive liver damage occurs, the release of IL-33 might act as an activator of tissue-protective mechanisms, while in cases of chronic injury IL-33 plays the role of a hepatic fibrotic factor. IL-33 signaling has also been involved in the pathogenesis of acute and chronic pancreatitis. Moreover, IL-33 could be used as an early marker for ulcer-associated activated fibroblasts and myofibroblast trans-differentiation; thus one cannot rule out its potential role in inflammatory bowel disease-associated fibrosis. Similarly, the upregulation of the IL-33/ST2 axismay contribute to tubular cell injury and fibrosis via epithelial to mesenchymal transition (EMT) of various cell types in the kidneys. Of note, IL-33 exerts a cardioprotective role via ST2 signaling, while soluble ST2 has been demonstrated as a marker of myocardial fibrosis. Finally, IL-33 is a crucial cytokine in skin pathology responsible for abnormal fibroblast proliferation, leukocyte infiltration and morphologic differentiation of human endothelial cells. Overall, emerging data support a novel contribution of the IL-33/ST2 pathway in tissue fibrosis and highlight the significant role of the Th2 pattern of immune response in the pathophysiology of organ fibrosis.

Neurotrophic factors in enteric physiology and pathophysiology

Neurotrophic factors are traditionally recognized for their roles in differentiation, growth, and survival of specific neurons in the central and peripheral nervous system. Some neurotrophic factors are essential for the development and migration of the enteric nervous system along the fetal and post-natal gut. Over the last two decades, several non-developmental functions of neurotrophic factors have been characterized. In the adult gastrointestinal tract, neurotrophic factors regulate gut sensation, motility, epithelial barrier function, and protect enteric neurons and glial cells from damaging insults in the microenvironment of the gut. In this issue of Neurogastroenterology and Motility, Fu et al demonstrate that brain-derived neurotrophic factor plays a role in the pathogenesis of distention-induced abdominal pain in bowel obstruction. In light of this interesting finding, this mini-review highlights some of the recent advances in understanding of the physiological and pathophysiological roles of neurotrophic factors in the adult gut.

The Intestinal Stem Cell Niche: Homeostasis and Adaptations

The intestinal epithelium is a rapidly renewing cellular compartment. This constant regeneration is a hallmark of intestinal homeostasis and requires a tightly regulated balance between intestinal stem cell (ISC) proliferation and differentiation. Since intestinal epithelial cells directly contact pathogenic environmental factors that continuously challenge their integrity, ISCs must also actively divide to facilitate regeneration and repair. Understanding niche adaptations that maintain ISC activity during homeostatic renewal and injury-induced intestinal regeneration is therefore a major and ongoing focus for stem cell biology. Here, we review recent concepts and propose an active interconversion of the ISC niche between homeostasis and injury-adaptive states that is superimposed upon an equally dynamic equilibrium between active and reserve ISC populations.

The multiple faces of inflammatory enteric glial cells: is Crohn's disease a gliopathy?

Gone are the days when enteric glial cells (EGC) were considered merely satellites of enteric neurons. Like their brain counterpart astrocytes, EGC express an impressive number of receptors for neurotransmitters and intercellular messengers, thereby contributing to neuroprotection and to the regulation of neuronal activity. EGC also produce different soluble factors that regulate neighboring cells, among which are intestinal epithelial cells. A better understanding of EGC response to an inflammatory environment, often referred to as enteric glial reactivity, could help define the physiological role of EGC and the importance of this reactivity in maintaining gut functions. In chronic inflammatory disorders of the gut such as Crohn's disease (CD) and ulcerative colitis, EGC exhibit abnormal phenotypes, and their neighboring cells are dysfunctional; however, it remains unclear whether EGC are only passive bystanders or active players in the pathophysiology of both disorders. The aim of the present study is to review the physiological roles and properties of EGC, their response to inflammation, and their role in the regulation of the intestinal epithelial barrier and to discuss the emerging concept of CD as an enteric gliopathy.

HIV-1 Tat-induced diarrhea is improved by the PPARalpha agonist, palmitoylethanolamide, by suppressing the activation of enteric glia

Background

Diarrhea is a severe complication in HIV-1-infected patients with Trans-activator of transcription (HIV-1 Tat) protein being recognized as a major underlying cause. Beside its direct enterotoxic effects, Tat protein has been recently shown to affect enteric glial cell (EGC) activity. EGCs regulate intestinal inflammatory responses by secreting pro-inflammatory molecules; nonetheless, they might also release immune-regulatory factors, as palmytoilethanolamide (PEA), which exerts anti-inflammatory effects by activating PPARα receptors. We aimed at clarifying whether EGCs are involved in HIV-1 Tat-induced diarrhea and if PEA exerts antidiarrheal activity.

Methods

Diarrhea was induced by intracolonic administration of HIV-1 Tat protein in rats at day 1. PEA alone or in the presence of peroxisome proliferator-activated receptor (PPAR) antagonists was given intraperitoneally from day 2 to day 7. S100B, iNOS, NF-kappaB, TLR4 and GFAP expression were evaluated in submucosal plexi, while S100B and NO levels were measured in EGC submucosal plexi lysates, respectively. To verify whether PEA effects were PPARα-mediated, PPARα^−/− mice were also used. After 7 days from diarrhea induction, endogenous PEA levels were measured in submucosal plexi homogenates deriving from rats and PPARα^−/− mice.

Results

HIV-1 Tat protein induced rapid onset diarrhea alongside with a significant activation of EGCs. Tat administration significantly increased all hallmarks of neuroinflammation by triggering TLR4 and NF-kappaB activation and S100B and iNOS expression. Endogenous PEA levels were increased following HIV-1 Tat exposure in both wildtype and knockout animals. In PPARα^−/− mice, PEA displayed no effects. In wildtype rats, PEA, via PPARα-dependent mechanism, resulted in a significant antidiarrheal activity in parallel with marked reduction of EGC-sustained neuroinflammation.

Conclusions

EGCs mediate HIV-1 Tat-induced diarrhea by sustaining the intestinal neuroinflammatory response. These effects are regulated by PEA through a selective PPARα-dependent mechanism. PEA might be considered as an adjuvant therapy in HIV-1-induced diarrhea.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1126-4) contains supplementary material, which is available to authorized users.

Inhibition of miR-142-5P ameliorates disease in mouse models of experimental colitis

BACKGROUND

MicroRNAs (miRNAs) are epigenetically involved in regulating gene expression. They may be of importance in the pathogenesis of inflammatory bowel disease (IBD). The aim of this study was to determine the role of miRNAs by their specific blocking in the CD4+CB45RBhi T-cell transfer model of chronic experimental colitis.

METHODS

Colitis caused by transfer of WT CD4+CD45RBhi T cells in severe combined immunodeficiency (SCID) mice shares many features with human IBD. Colonic miRNA expression levels were measured at three time points in colitic mice, where a time-dependent upregulation of multiple miRNAs was seen. To inhibit these miRNAs, specific locked-nucleic-acid-modified (LNA) oligonucleotides were administered in further experiments at the moment the mice demonstrated the first signs of colitis. As controls, PBS and a scrambled sequence of anti-miRNA were used. Genome-wide expression analyses were also performed in order to detect candidate target genes of miR-142-5p, of which inhibition resulted in most effective amelioration of colitis.

RESULTS

Anti-miR-142-5p reduced colitis and related wasting disease when administered in the T-cell transfer model, reflected in reduced weight loss and a lower disease activity index (DAI). In further validation experiments we also observed a higher survival rate and less colonic histological inflammation in the antagomir-treated mice. Moreover, by genome-wide expression analyses, we found downstream activation of the anti-inflammatory IL10RA pathway, including three genes also found in the top-20 candidate target genes of miR-142-5p.

CONCLUSION

In conclusion, CD4+CD45RBhi-transfer colitis induces miR-142-5p. Blocking miR-142-5p reduced colitis and prevented wasting disease, possibly by activation of the IL10RA pathway.

IL-33 and the intestine: The good, the bad, and the inflammatory

Interleukin-33 (IL-33) is a member of the IL-1 cytokine family that has been widely studied since its discovery in 2005 for its dichotomous functions in homeostasis and inflammation. IL-33, along with its receptor suppression of tumorigenicity 2 (ST2), has been shown to modulate both the innate and adaptive immune system. Originally, the IL-33/ST2 signaling axis was studied in the context of inducing type 2 immune responses with the expression of ST2 by T helper 2 (T_H2) cells. However, the role of IL-33 is not limited to T_H2 responses. Rather, IL-33 is a potent activator of T_H1 cells, group 2 innate lymphoid cells (ILC2s), regulatory T (Treg) cells, and CD8⁺ T cells. The intestine is uniquely important in this discussion, as the intestinal epithelium is distinctively positioned to interact with both pathogens and the immune cells housed in the mucosa. In the intestine, IL-33 is expressed by the pericryptal fibroblasts and its expression is increased particularly in disease states. Moreover, IL-33/ST2 signaling aberrancy is implicated in the pathogenesis of inflammatory bowel disease (IBD). Accordingly, for this review, we will focus on the role of IL-33 in the regulation of intestinal immunity, involvement in intestinal disease, and implication in potential therapeutics.

Enteric glial-mediated enhancement of intestinal barrier integrity is compromised by morphine

BACKGROUND

The opioid epidemic is a growing concern, and emerging evidence suggests that morphine use may be associated with sepsis. Enteric glial cells (EGCs) are the most numerous cell type in the enteric nervous system and regulate gastrointestinal function through the production of trophic factors, including glial-derived neurotrophic factor (GDNF). We sought to determine the effect of morphine on enteric glia and hypothesized that morphine contributes to EGC dysfunction and increased gut permeability.

MATERIALS AND METHODS

Rat intestinal epithelial cells (IECs) and EGC lines were purchased from ATCC. Immunocytochemistry was used to evaluate the impact of EGCs on IEC barrier proteins and detect the μ-opioid receptor. Co-culture assays were used to determine the effect of EGCs, GDNF, and morphine on barrier integrity. Quantitative polymerase chain reaction and western blotting were performed to determine the impact of morphine in GDNF production. Transepithelial resistance of IEC-6 cell monolayers was measured in the presence of EGC-conditioned media (EGC-CM) and morphine treated EGC-CM using electrical cell impedance sensing.

RESULTS

EGC-CM enhanced tight junction organization in IECs. IEC barrier integrity was enhanced when co-cultured with unstimulated EGCs or with GDNF alone; this barrier protective effect was lost with morphine-treated EGCs. GDNF RNA and protein expression were decreased by morphine treatment. Transepithelial resistance was decreased in IEC confluent monolayers when exposed to morphine-treated EGC-CM compared with control.

CONCLUSIONS

Morphine compromises intestinal epithelial cell barrier function through a mechanism which appears to involve GDNF. Further studies are warranted to delineate the role of enteric glial cell function in opioid signaling and sepsis.

Effect of enteric nervous system on intestinal epithelial barrier in inflammatory bowel disease

Both enteric nervous system and intestinal epithelial barrier are vital components to ensure gut homeostasis. Recent studies have shown the implications of their close relationship for gut health and disease. By secreting neurotransmitters, the enteric nervous system plays an important role in regulating the epithelial barrier function. Meanwhile, communicating largely through the vagal nerve, the central nervous system could also interact with the intestinal epithelium through the enteric nervous system. Although the etiology and pathogenesis of inflammatory bowel disease remain elusive, increasing evidence has shown that the dysregulation of enteric nervous system affects both epithelial integrity and barrier function, which contributes to the occurrence and development of inflammatory bowel disease. This review will summarize the current knowledge regarding the effect of enteric nervous system on intestinal epithelial barrier and its implication in the development of inflammatory bowel disease.

Enteric glia: the most alimentary of all glia

Glia (from Greek γλοία meaning 'glue') pertains to non-neuronal cells in the central (CNS) and peripheral nervous system (PNS) that nourish neurons and maintain homeostasis. In addition, glia are now increasingly appreciated as active regulators of numerous physiological processes initially considered exclusively under neuronal regulation. For instance, enteric glia, a collection of glial cells residing within the walls of the intestinal tract, regulate intestinal motility, a well-characterized reflex controlled by enteric neurons. Enteric glia also interact with various non-neuronal cell types in the gut wall such as enterocytes, enteroendocrine and immune cells and are therefore emerging as important local regulators of diverse gut functions. The intricate molecular mechanisms that govern glia-mediated regulation are beginning to be discovered, but much remains unknown about the functions of enteric glia in health and disease. Here we present a current view of the enteric glia and their regulatory roles in gastrointestinal (GI) (patho)physiology; from GI motility and epithelial barrier function to enteric neuroinflammation.

Concentration of Glial Cell Line-Derived Neurotrophic Factor Positively Correlates with Symptoms in Functional Dyspepsia

BACKGROUND

In patients with functional dyspepsia (FD), mild duodenal inflammation correlates with increased mucosal permeability. Enteric glial cells can produce glial cell line-derived neurotrophic factor (GDNF) to repair disrupted epithelial barrier function.

AIMS

We examined the role of duodenal GDNF in FD pathophysiology and its association with dyspeptic symptoms.

METHODS

Duodenal biopsies taken from FD patients and control subjects were used for analysis. GDNF protein expression and localization were examined. Cellular infiltration of eosinophils and mast cells was measured. We also examined the intercellular space between the adjacent epithelial cells at the apical junction complex using transmission electron microscopy.

RESULTS

In FD patients, expression of GDNF protein was significantly increased compared with controls, 107.3 (95.3-136.7) versus 49.3 (38.0-72.6) pg/mg protein (median (interquartile range), p = 0.006), respectively. GDNF was localized in enteric glial cells, eosinophils, and epithelial cells. The number of eosinophils was significantly greater in FD patients than in controls, 1039 (923-1181) versus 553 (479-598) cells/mm² (p = 0.021), respectively. The intercellular space was dilated at the adherent junction in FD patients compared to control patients, 32.4 (29.8-34.8) versus 22.0 (19.9-26.1) nm (p = 0.002), respectively. Intercellular distance positively correlated with the frequency of postprandial fullness and early satiation (p = 0.001, r = 0.837 and p = 0.009, r = 0.693, respectively). Expression of GDNF correlated with epigastric burning (p = 0.041, r = 0.552).

CONCLUSIONS

Increased expression of duodenal GDNF might be involved in FD pathophysiology and symptom perception.

Enteric glial cells: An emerging key player in intestinal homeostasis modulation under physiological and pathological conditions

The intestine contains multiple components including epithelial cells, microbiome as well as various neuroendocrine pathways, all of which are essential for maintaining dynamic mucosal homeostasis through complex interactions among different components in the gastrointestinal tract. Beyond the basic neurosupportive and neurotrophic effects, growing evidence reveals the key role of enteric glial cells (EGCs) in the modulation of bowel movement, nutrient absorption and secretion, intestinal immunity as well as barrier function. As well, abnormally activated EGCs are believed to be a vital player in the pathogenesis of a variety of diseases including inflammatory bowel disease, intestinal barrier dysfunction and infections. Here we provide a brief overview of recent research progress about the precise role and the molecule mechanisms of EGCs in modulating intestinal homeostasis, and highlight the critical role of EGC in various intestinal diseases.

GDNF From Human Periodontal Ligament Cells Treated With Pro-Inflammatory Cytokines Promotes Neurocytic Differentiation of PC12 Cells

Glial cell line-derived neurotrophic factor (GDNF) is known to mediate multiple biological activities such as promotion of cell motility and proliferation, and morphogenesis. However, little is known about its effects on periodontal ligament (PDL) cells. Recently, we reported that GDNF expression is increased in wounded rat PDL tissue and human PDL cells (HPDLCs) treated with pro-inflammatory cytokines. Here, we investigated the associated expression of GDNF and the pro-inflammatory cytokine interleukin-1 beta (IL-1β) in wounded PDL tissue, and whether HPDLCs secrete GDNF which affects neurocytic differentiation. Rat PDL cells near the wounded area showed intense immunoreactions against an anti-GDNF antibody, where immunoreactivity was also increased against an anti-IL-1β antibody. Compared with untreated cells, HPDLCs treated with IL-1β or tumor necrosis factor-alpha showed an increase in the secretion of GDNF protein. Conditioned medium of IL-1β-treated HPDLCs (IL-1β-CM) increased neurite outgrowth of PC12 rat adrenal pheochromocytoma cells. The expression levels of two neural regeneration-associated genes, growth-associated protein-43 (Gap-43), and small proline-rich repeat protein 1A (Sprr1A), were also upregulated in IL-1β-CM-treated PC12 cells. These stimulatory effects of IL-1β-CM were significantly inhibited by a neutralizing antibody against GDNF. In addition, U0126, a MEK inhibitor, inhibited GDNF-induced neurite outgrowth of PC12 cells. These findings suggest that an increase of GDNF in wounded PDL tissue might play an important role in neural regeneration probably via the MEK/ERK signaling pathway. J. Cell. Biochem. 118: 699-708, 2017. © 2016 Wiley Periodicals, Inc.

Neuroimmunomodulation in the Gut: Focus on Inflammatory Bowel Disease

Intestinal immunity is finely regulated by several concomitant and overlapping mechanisms, in order to efficiently sense external stimuli and mount an adequate response of either tolerance or defense. In this context, a complex interplay between immune and nonimmune cells is responsible for the maintenance of normal homeostasis. However, in certain conditions, the disruption of such an intricate network may result in intestinal inflammation, including inflammatory bowel disease (IBD). IBD is believed to result from a combination of genetic and environmental factors acting in concert with an inappropriate immune response, which in turn interacts with nonimmune cells, including nervous system components. Currently, evidence shows that the interaction between the immune and the nervous system is bidirectional and plays a critical role in the regulation of intestinal inflammation. Recently, the maintenance of intestinal homeostasis has been shown to be under the reciprocal control of the microbiota by immune mechanisms, whereas intestinal microorganisms can modulate mucosal immunity. Therefore, in addition to presenting the mechanisms underlying the interaction between immune and nervous systems in the gut, here we discuss the role of the microbiota also in the regulation of neuroimmune crosstalk involved in intestinal homeostasis and inflammation, with potential implications to IBD pathogenesis.

The glial cell-line derived neurotrophic factor: a novel regulator of intestinal barrier function in health and disease

Regulation of the intestinal epithelial barrier is a differentiated process, which is profoundly deranged in inflammatory bowel diseases. Recent data provide evidence that the glial cell line-derived neurotrophic factor (GDNF) is critically involved in intestinal epithelial wound healing and barrier maturation and exerts antiapoptotic effects under certain conditions. Furthermore, not only the enteric nervous system, but also enterocytes synthesize GDNF in significant amounts, which points to a potential para- or autocrine signaling loop between enterocytes. Apart from direct effects of GDNF on enterocytes, an immunomodulatory role of this protein has been previously assumed because of a significant reduction of inflammation in a model of chronic inflammatory bowel disease after application of GDNF. In this review we summarize the current knowledge of GDNF on intestinal epithelial barrier regulation and discuss the novel role for GDNF as a regulator of intestinal barrier functions in health and disease.

Enteric glial cells: Powerful guardian of intestinal epithelial barrier in inflammatory bowel disease

The intestinal epithelium constitutes a physical and functional barrier between the external environment and the host organism. Once the integrity of this barrier is disrupted, inflammatory disorders and tissue injury are initiated and perpetuated. Beneath the intestinal epithelial cells lies a population of astrocyte-like cells that are known as enteric glia cells (EGCs). They play a key role in maintaining the homeostasis and integrity of intestinal epithelial barrier by secretion of some mediators and modulation of enteric neuronal activities. In this review, we will describe the functional roles of enteric glia cells in the intestinal barrier, and highlight the protective action of EGCs in inflammatory bowel disease.

Role of glial cell line-derived neurotrophic factor in intestinal inflammatory diseases

Glial cell line-derived neurotrophic factor (GDNF), a member of the neurotrophic factor family, promotes the survival, proliferation, migration, differentiation, and axonal growth of intestinal neurons. With studies on the role that enteric glia cells (EGCs) play in intestinal inflammation, GDNF has come into vision as an anti-inflammatory factor in the gut. Recent studies have gradually witnessed that, besides the role in protecting the intestinal epithelial barrier, GDNF plays an important part in a variety of protective mechanisms against intestinal inflammation, and has become the focus of numerous defense mechanisms in intestinal inflammation. GDNF also plays a very important role in the occurrence and development of intestinal inflammatory diseases. This review summarizes the results of recent studies in this field to fully discuss the roles of GDNF in the occurrence and development of intestinal inflammatory diseases.

Enteric glia: A new player in inflammatory bowel diseases

In addition to the well-known involvement of macrophages and neutrophils, other cell types have been recently reported to substantially contribute to the onset and progression of inflammatory bowel diseases (IBD). Enteric glial cells (EGC) are the equivalent cell type of astrocyte in the central nervous system (CNS) and share with them many neurotrophic and neuro-immunomodulatory properties. This short review highlights the role of EGC in IBD, describing the role played by these cells in the maintenance of gut homeostasis, and their modulation of enteric neuronal activities. In pathological conditions, EGC have been reported to trigger and support bowel inflammation through the specific over-secretion of S100B protein, a pivotal neurotrophic factor able to induce chronic inflammatory changes in gut mucosa. New pharmacological tools that may improve the current therapeutic strategies for inflammatory bowel diseases (IBD), lowering side effects (i.e. corticosteroids) and costs (i.e. anti-TNFα monoclonal antibodies) represent a very important challenge for gastroenterologists and pharmacologists. Novel drugs capable to modulate enteric glia reactivity, limiting the pro-inflammatory release of S100B, may thus represent a significant innovation in the field of pharmacological interventions for inflammatory bowel diseases.

Glial cell line-derived neurotrophic factor promotes barrier maturation and wound healing in intestinal epithelial cells in vitro

Recent data suggest that neurotrophic factors from the enteric nervous system are involved in intestinal epithelial barrier regulation. In this context the glial cell line-derived neurotrophic factor (GDNF) was shown to affect gut barrier properties in vivo directly or indirectly by largely undefined processes in a model of inflammatory bowel disease (IBD). We further investigated the potential role and mechanisms of GDNF in the regulation of intestinal barrier functions. Immunostaining of human gut specimen showed positive GDNF staining in enteric neuronal plexus and in enterocytes. In Western blots of the intestinal epithelial cell lines Caco2 and HT29B6, significant amounts of GDNF were detected, suggesting that enterocytes represent an additional source of GDNF. Application of recombinant GDNF on Caco2 and HT29B6 cells for 24 h resulted in significant epithelial barrier stabilization in monolayers with immature barrier functions. Wound-healing assays showed a significantly faster closure of the wounded areas after GDNF application. GDNF augmented cAMP levels and led to significant inactivation of p38 MAPK in immature cells. Activation of p38 MAPK signaling by SB-202190 mimicked GDNF-induced barrier maturation, whereas the p38 MAPK activator anisomycin blocked GDNF-induced effects. Increasing cAMP levels had adverse effects on barrier maturation, as revealed by permeability measurements. However, increased cAMP augmented the proliferation rate in Caco2 cells, and GDNF-induced proliferation of epithelial cells was abrogated by the PKA inhibitor H89. Our data show that enterocytes represent an additional source of GDNF synthesis. GDNF contributes to wound healing in a cAMP/PKA-dependent manner and promotes barrier maturation in immature enterocytes cells by inactivation of p38 MAPK signaling.

Wild jujube polysaccharides protect against experimental inflammatory bowel disease by enabling enhanced intestinal barrier function

Dietary polysaccharides provide various beneficial effects for our health. We investigated the protective effects of wild jujube (Ziziphus jujuba Mill. var. spinosa (Bunge) Hu ex H. F. Chou) sarcocarp polysaccharides (WJPs) against experimental inflammatory bowel disease (IBD) by enabling enhanced intestinal barrier function. Colitis was induced in rats by the intrarectal administration of TNBS. We found that WJPs markedly ameliorated the colitis severity, including less weight loss, decreased disease activity index scores, and improved mucosal damage in colitis rats. Moreover, WJPs suppressed the inflammatory response via attenuation of TNF-α, IL-1β, IL-6 and MPO activity in colitis rats. And then, to determine the effect of WJPs on the intestinal barrier, we measured the effect of WJPs on the transepithelial electrical resistance (TER) and FITC-conjugated dextran permeability in Caco-2 cell stimulation with TNF-α. We further demonstrated that the alleviation of WJPs to colon injury was associated with barrier function by assembly of tight junction proteins. Moreover, the effect of WJPs on TER was eliminated by the specific inhibitor of AMPK. AMPK activity was also up-regulated by WJPs in Caco-2 cell stimulation with TNF-α and in colitis rats. This study demonstrates that WJPs protect against IBD by enabling enhanced intestinal barrier function involving the activation of AMPK.

δ-Catenin, a Wnt/β-catenin modulator, reveals inducible mutagenesis promoting cancer cell survival adaptation and metabolic reprogramming

Mutations of Wnt/β-catenin signaling pathway has essential roles in development and cancer. Although β-catenin and adenomatous polyposis coli (APC) gene mutations are well established and are known to drive tumorigenesis, discoveries of mutations in other components of the pathway lagged, which hinders the understanding of cancer mechanisms. Here we report that δ-catenin (gene designation: CTNND2), a primarily neural member of the β-catenin superfamily that promotes canonical Wnt/β-catenin/LEF-1-mediated transcription, displays exonic mutations in human prostate cancer and promotes cancer cell survival adaptation and metabolic reprogramming. When overexpressed in cells derived from prostate tumor xenografts, δ-catenin gene invariably gives rise to mutations, leading to sequence disruptions predicting functional alterations. Ectopic δ-catenin gene integrating into host chromosomes is locus nonselective. δ-Catenin mutations promote tumor development in mouse prostate with probasin promoter (ARR2PB)-driven, prostate-specific expression of Myc oncogene, whereas mutant cells empower survival advantage upon overgrowth and glucose deprivation. Reprogramming energy utilization accompanies the downregulation of glucose transporter-1 and poly (ADP-ribose) polymerase cleavage while preserving tumor type 2 pyruvate kinase expression. δ-Catenin mutations increase β-catenin translocation to the nucleus and hypoxia-inducible factor 1α (HIF-1α) expression. Therefore, introducing δ-catenin mutations is an important milestone in prostate cancer metabolic adaptation by modulating β-catenin and HIF-1α signaling under glucose shortage to amplify its tumor-promoting potential.

Enteric nervous system abnormalities are present in human necrotizing enterocolitis: potential neurotransplantation therapy

Introduction

Intestinal dysmotility following human necrotizing enterocolitis suggests that the enteric nervous system is injured during the disease. We examined human intestinal specimens to characterize the enteric nervous system injury that occurs in necrotizing enterocolitis, and then used an animal model of experimental necrotizing enterocolitis to determine whether transplantation of neural stem cells can protect the enteric nervous system from injury.

Methods

Human intestinal specimens resected from patients with necrotizing enterocolitis (n = 18), from control patients with bowel atresia (n = 8), and from necrotizing enterocolitis and control patients undergoing stoma closure several months later (n = 14 and n = 6 respectively) were subjected to histologic examination, immunohistochemistry, and real-time reverse-transcription polymerase chain reaction to examine the myenteric plexus structure and neurotransmitter expression. In addition, experimental necrotizing enterocolitis was induced in newborn rat pups and neurotransplantation was performed by administration of fluorescently labeled neural stem cells, with subsequent visualization of transplanted cells and determination of intestinal integrity and intestinal motility.

Results

There was significant enteric nervous system damage with increased enteric nervous system apoptosis, and decreased neuronal nitric oxide synthase expression in myenteric ganglia from human intestine resected for necrotizing enterocolitis compared with control intestine. Structural and functional abnormalities persisted months later at the time of stoma closure. Similar abnormalities were identified in rat pups exposed to experimental necrotizing enterocolitis. Pups receiving neural stem cell transplantation had improved enteric nervous system and intestinal integrity, differentiation of transplanted neural stem cells into functional neurons, significantly improved intestinal transit, and significantly decreased mortality compared with control pups.

Conclusions

Significant injury to the enteric nervous system occurs in both human and experimental necrotizing enterocolitis. Neural stem cell transplantation may represent a novel future therapy for patients with necrotizing enterocolitis.

Enteric glial cells and their role in the intestinal epithelial barrier

The intestinal epithelium constitutes a physical and functional barrier between the external environment and the host organism. It is formed by a continuous monolayer of intestinal epithelial cells maintained together by intercellular junctional complex, limiting access of pathogens, toxins and xenobiotics to host tissues. Once this barrier integrity is disrupted, inflammatory disorders and tissue injury are initiated and perpetuated. Beneath the intestinal epithelial cells lies a population of astrocyte-like cells that are known as enteric glia. The morphological characteristics and expression markers of these enteric glia cells were identical to the astrocytes of the central nervous system. In the past few years, enteric glia have been demonstrated to have a trophic and supporting relationship with intestinal epithelial cells. Enteric glia lesions and/or functional defects can be involved in the barrier dysfunction. Besides, factors secreted by enteric glia are important for the regulation of gut barrier function. Moreover, enteric glia have an important impact on epithelial cell transcriptome and induce a shift in epithelial cell phenotype towards increased cell adhesion and cell differentiation. Enteric glia can also preserve epithelial barrier against intestinal bacteria insult. In this review, we will describe the current body of evidence supporting functional roles of enteric glia on intestinal barrier.

GDNF is involved in the barrier-inducing effect of enteric glial cells on intestinal epithelial cells under acute ischemia reperfusion stimulation

Acute intestinal ischemia reperfusion (IR) injury is often associated with intestinal epithelial barrier (IEB) dysfunction. Enteric glial cells (EGCs) play an essential role in maintaining the integrity of IEB functions. However, the precise mechanism of EGCs under IR stimulation remains unclear. Here, we report that EGCs are closely involved in the modulation of IEB functions in response to IR challenge. The intestinal IR treatment led to the significant upregulation of the EGC activation marker, glial fibrillary acidic protein, accompanied by the increasing abundance of glial-derived neurotrophic factor (GDNF) and inducible nitric oxidase (iNOS) proteins, which was also confirmed in in vitro hypoxia reoxygenation (HR) tests. Co-culturing with EGCs attenuated the tight junctional abnormalities, blocked the downregulation of ZO-1 and occludin protein expression, and relieved the decrease of permeability of intestinal epithelial cell (IEC) monolayers under HR treatment. Furthermore, exogenous GDNF administration displays the barrier-protective effects similar to EGCs against HR stimulation, while RNA interference-mediated knockdown of GDNF significantly inhibited the protective capability of EGCs. The expression of both GDNF and iNOS proteins of EGCs was significantly upregulated by co-culturing with IECs, which was further increased by HR treatment. Interestingly, through inhibiting iNOS activity, the barrier-protective effect of EGCs was influenced in normal condition but enhanced in HR condition. These results suggest that GDNF plays an important role in the barrier-protective mechanism of activated EGCs under IR stimulation, whereas EGCs (via iNOS release) are also involved in intestinal inflammation response, which may contribute to IEB damage induced by IR injury.

Multifunctional activity of a small tellurium redox immunomodulator compound, AS101, on dextran sodium sulfate-induced murine colitis

Inflammatory bowel diseases (IBDs) are a group of idiopathic, chronic immune-mediated diseases characterized by an aberrant immune response, including imbalances of inflammatory cytokine production and activated innate and adaptive immunity. Selective blockade of leukocyte migration into the gut is a promising strategy for the treatment of IBD. This study explored the effect of the immunomodulating tellurium compound ammonium trichloro (dioxoethylene-o,o') tellurate (AS101) on dextran sodium sulfate (DSS)-induced murine colitis. Both oral and intraperitoneal administration of AS101 significantly reduced clinical manifestations of IBD. Colonic inflammatory cytokine levels (IL-17 and IL-1β) were significantly down-regulated by AS101 treatment, whereas IFN-γ was not affected. Neutrophil and α4β7(+) macrophage migration into the tissue was inhibited by AS101 treatment. Adhesion of mesenteric lymph node cells to mucosal addressin cell adhesion molecule (MAdCAM-1), the ligand for α4β7 integrin, was blocked by AS101 treatment both in vitro and in vivo. DSS-induced destruction of colonic epithelial barrier/integrity was prevented by AS101, via up-regulation of colonic glial-derived neurotrophic factor, which was found previously to regulate the intestinal epithelial barrier through activation of the PI3K/AKT pathway. Indeed, the up-regulation of glial-derived neurotrophic factor by AS101 was associated with increased levels of colonic pAKT and BCL-2 and decreased levels of BAX. Furthermore, AS101 treatment reduced colonic permeability to Evans blue and decreased colonic TUNEL(+) cells. Our data revealed multifunctional activities of AS101 in the DSS-induced colitis model via anti-inflammatory and anti-apoptotic properties. We suggest that treatment with the small, nontoxic molecule AS101 may be an effective early therapeutic approach for controlling human IBD.

Role of enteric glial cells in inflammatory bowel disease

The etiology and pathogenesis of inflammatory bowel disease are currently unknown. It is generally believed that persistent intestinal infection, intestinal mucosal barrier defect, intestinal mucosal immune dysregulation and genetic and environmental factors together contribute to the pathogenesis of inflammatory bowel disease. Several studies have demonstrated that enteric glial cells play an important role in maintaining the integrity of intestinal mucosal barrier. Enteric glial cell deficiency in mice leads to the destruction of integrity of intestinal mucosal barrier, increases mucosal permeability, and results in intestinal inflammation, hemorrhage and necrosis. This article discusses the role of enteric glial cells in the occurrence and development of inflammatory bowel disease.

Glial-derived neurotrophic factor reduces inflammation and improves delayed colonic transit in rat models of dextran sulfate sodium-induced colitis

BACKGROUND

Intestinal inflammation is well known to cause gut dysmotility through the effects on the enteric nervous system. Glial-derived neurotrophic factor (GDNF) has been demonstrated to have anti-inflammatory effects and neuronal protective actions. The aim of this study was to investigate whether the GDNF could improve inflammation-induced gut dysmotility.

METHODS

Recombinant adenoviral vectors encoding GDNF (Ad-GDNF) were administered intracolonically in experimental colitis induced by dextran sulfate sodium (DSS). The disease activity index (DAI) and histological score were measured. Colonic transit was measured by using phenol red and assessed with the geometric center. PGP 9.5 immunostaining was used to examine the number and distribution of enteric neurons. The expression of tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and myeloperoxidase (MPO) activity were measured by ELISA assay. The expression of Akt, caspase-3, bcl-2 and PGP 9.5 was analyzed by western blot assay.

RESULTS

A significant neuronal cell loss and a significant delay in colonic transit accompanied with the neuronal loss following inflammation were observed. GDNF prevented partially the loss of enteric neurons and ameliorated significantly experimental colitis and delayed colonic transit by, at least in part, down-regulation of TNF-α and IL-1β expression, decrease of infiltration of leukocytes, and inhibition of neuronal cell apoptosis.

CONCLUSIONS

GDNF reduces inflammation and improves delayed colonic transit in DSS-induced colitis. GDNF may be a useful therapeutic agent for the treatment of gut dysmotility in patients with UC.

Toll-like receptor 2 regulates intestinal inflammation by controlling integrity of the enteric nervous system

BACKGROUND & AIMS

In the intestines, Toll-like receptor 2 (TLR2) mediates immune responses to pathogens and regulates epithelial barrier function; polymorphisms in TLR2 have been associated with inflammatory bowel disease phenotype. We assessed the effects of TLR2 signaling on the enteric nervous system (ENS) in mice.

METHODS

TLR2 distribution and function in the ileal neuromuscular layer of mice were determined by immunofluorescence, cytofluorimetric analysis, immunoprecipitation, and immunoblot analyses. We assessed morphology and function of the ENS in Tlr2(-/-) mice and in mice with wild-type Tlr2 (wild-type mice) depleted of intestinal microbiota, using immunofluorescence, immunoblot, and gastrointestinal motility assays. Levels and signaling of glial cell line-derived neurotrophic factor (GDNF) were determined using quantitative reverse transcriptase polymerase chain reaction, immunohistochemistry, and immunoprecipitation analyses. Colitis was induced by administration of dextran sulfate sodium or 2,4 dinitrobenzensulfonic acid to Tlr2(-/-) mice after termination of GDNF administration.

RESULTS

TLR2 was expressed in enteric neurons, glia, and smooth muscle cells of the intestinal wall. Tlr2(-/-) mice had alterations in ENS architecture and neurochemical profile, intestinal dysmotility, abnormal mucosal secretion, reduced levels of GDNF in smooth muscle cells, and impaired signaling via Ret-GFRα1. ENS structural and functional anomalies were completely corrected by administration of GDNF to Tlr2(-/-) mice. Wild-type mice depleted of intestinal microbiota had ENS defects and GDNF deficiency, similar to Tlr2(-/-) mice; these defects were partially restored by administration of a TLR2 agonist. Tlr2(-/-) mice developed more severe colitis than wild-type mice after administration of dextran sulfate sodium or 2,4 dinitrobenzensulfonic acid; colitis was not more severe if Tlr2(-/-) mice were given GDNF before dextran sulfate sodium or 2,4 dinitrobenzensulfonic acid.

CONCLUSIONS

In mice, TLR2 signaling regulates intestinal inflammation by controlling ENS structure and neurochemical coding, along with intestinal neuromuscular function. These findings provide information as to how defective TLR2 signaling in the ENS affects inflammatory bowel disease phenotype in humans.

The digestive neuronal-glial-epithelial unit: a new actor in gut health and disease

The monolayer of columnar epithelial cells lining the gastrointestinal tract--the intestinal epithelial barrier (IEB)--is the largest exchange surface between the body and the external environment. The permeability of the IEB has a central role in the regulation of fluid and nutrient intake as well as in the control of the passage of pathogens. The functions of the IEB are highly regulated by luminal as well as internal components, such as bacteria or immune cells, respectively. Evidence indicates that two cell types of the enteric nervous system (ENS), namely enteric neurons and enteric glial cells, are potent modulators of IEB functions, giving rise to the novel concept of a digestive 'neuronal-glial-epithelial unit' akin to the neuronal-glial-endothelial unit in the brain. In this Review, we summarize findings demonstrating that the ENS is a key regulator of IEB function and is actively involved in pathologies associated with altered barrier function.

Targeting α-7 nicotinic acetylcholine receptor in the enteric nervous system: a cholinergic agonist prevents gut barrier failure after severe burn injury

We have previously shown that vagal nerve stimulation prevents intestinal barrier loss in a model of severe burn injury in which injury was associated with decreased expression and altered localization of intestinal tight junction proteins. α-7 Nicotinic acetylcholine receptor (α-7 nAchR) has been shown to be necessary for the vagus nerve to modulate the systemic inflammatory response, but the role of α-7 nAchR in mediating gut protection remained unknown. We hypothesized that α-7 nAchR would be present in the gastrointestinal tract and that treatment with a pharmacological agonist of α-7 nAchR would protect against burn-induced gut barrier injury. The effects of a pharmacological cholinergic agonist on gut barrier integrity were studied using an intraperitoneal injection of nicotine 30 minutes after injury. Intestinal barrier integrity was examined by measuring permeability to 4-kDa fluorescein isothiocyanate-dextran and by examining changes in expression and localization of the intestinal tight junction proteins occludin and ZO-1. Nicotine injection after injury prevented burn-induced intestinal permeability and limited histological gut injury. Treatment with nicotine prevented decreased expression and altered localization of occludin and ZO-1, as seen in animals undergoing burn alone. Defining the interactions among the vagus nerve, the enteric nervous system, and the intestinal epithelium may lead to development of targeted therapeutics aimed at reducing gut barrier failure and intestinal inflammation after severe injury.

Expression and effects of glial cell line-derived neurotrophic factor on periodontal ligament cells

AIM

To investigate Glial cell line-derived neurotrophic factor (GDNF) expression in normal and wounded rat periodontal ligament (PDL) and the effects of GDNF on human PDL cells (HPDLCs) migration and extracellular matrix expression in HPDLCs.

MATERIAL AND METHODS

The expression of GDNF and GDNF receptors was examined by immunocyto/histochemical analyses. Gene expression in HPDLCs treated with GDNF, interleukin-1 beta (IL-1β), or tumour necrosis factor-alpha (TNF-α) was quantified by quantitative RT-PCR (qRT-PCR). In addition, we examined the migratory effect of GDNF on HPDLCs.

RESULTS

GDNF was expressed in normal rat PDL and cultured HPDLCs. HPDLCs also expressed GDNF receptors. In wounded rat PDL, GDNF expression was up-regulated. QRT-PCR analysis revealed that IL-1β and TNF-α significantly increased the expression of GDNF in HPDLCs. Furthermore, GDNF induced migration of HPDLCs, which was blocked by pre-treatment with the peptide including Arg-Gly-Asp (RGD) sequence, or neutralizing antibodies against integrin αVβ3 or GDNF. Also, GDNF up-regulated expression of bone sialoprotein (BSP) and fibronectin in HPDLCs.

CONCLUSIONS

GDNF expression is increased in rat wounded PDL tissue and HPDLCs treated with pro-inflammatory cytokines. GDNF enhances the expression of BSP and fibronectin, and migration in an RGD-dependent manner via the integrin αVβ3. These findings suggest that GDNF may contribute to wound healing in PDL tissue.

Hyperbaric oxygen therapy: can it prevent irradiation-induced necrosis?

Radiosurgery is an important non-invasive procedure for the treatment of tumors and vascular malformations. However, in addition to killing target tissues, cranial irradiation induces damage to adjacent healthy tissues leading to neurological deterioration in both pediatric and adult patients, which is poorly understood and insufficiently treatable. To minimize irradiation damage to healthy tissue, not the optimal therapeutic irradiation dose required to eliminate the target lesion is used but lower doses. Although the success rate of irradiation surgery is about 95%, 5% of patients suffer problems, most commonly neurological, that are thought to be a direct consequence of irradiation-induced inflammation. Although no direct correlation has been demonstrated, the appearance and disappearance of inflammation that develops following irradiation commonly parallel the appearance and disappearance of neurological side effects that are associated with the neurological function of the irradiated brain regions. These observations have led to the hypothesis that brain inflammation is causally related to the observed neurological side effects. Studies indicate that hyperbaric oxygen therapy (HBOT) applied after the appearance of irradiation-induced neurological side effects reduces the incidence and severity of those side effects. This may result from HBOT reducing inflammation, promoting angiogenesis, and influencing other cellular functions thereby suppressing events that cause the neurological side effects. However, it would be significantly better for the patient if rather than waiting for neurological side effects to become manifest they could be avoided. This review examines irradiation-induced neurological side effects, methods that minimize or resolve those side effects, and concludes with a discussion of whether HBOT applied following irradiation, but before manifestation of neurological side effects may prevent or reduce the appearance of irradiation-induced neurological side effects.

NGF and nitrosative stress in patients with Huntington's disease

INTRODUCTION

Huntington's disease (HD) is a neurodegenerative genetic disorder caused by expansion of polyglutamine repeats in the huntingtin gene and characterised by the loss of striatal and cortical neurons. Few studies to date have focussed on peripheral neurotrophic-factor levels in patients with HD.

OBJECTIVE

To measure plasma NGF levels in Huntington's disease and investigate their correlation with disease intensity.

MATERIALS AND METHODS

Nineteen patients with HD and nineteen age- and sex-matched healthy subjects took part in this cross-sectional study. Plasma levels of NGF, BDNF, GDNF, nitrotyrosine, and myeloperoxidase (MPO) were measured; lactate dehydrogenase (LDH) levels were determined and white blood cell (WBC) counts were evaluated.

RESULTS

NGF levels were significantly lower, nitrotyrosine levels were higher and LDH activity was greater in HD patients than in healthy subjects. There was no significant difference in MPO levels or WBC counts, whereas the MPO/WBC ratio was considerably higher in HD patients. The data obtained suggested that biochemical and haematological changes correlated with disease severity.

CONCLUSION

NGF levels are lower in HD patients than in healthy subjects. However, further research is required to confirm the role of NGF in HD.

Diet-induced obesity has neuroprotective effects in murine gastric enteric nervous system: involvement of leptin and glial cell line-derived neurotrophic factor

Nutritional factors can induce profound neuroplastic changes in the enteric nervous system (ENS), responsible for changes in gastrointestinal (GI) motility. However, long-term effects of a nutritional imbalance leading to obesity, such as Western diet (WD), upon ENS phenotype and control of GI motility remain unknown. Therefore, we investigated the effects of WD-induced obesity (DIO) on ENS phenotype and function as well as factors involved in functional plasticity. Mice were fed with normal diet (ND) or WD for 12 weeks. GI motility was assessed in vivo and ex vivo. Myenteric neurons and glia were analysed with immunohistochemical methods using antibodies against Hu, neuronal nitric oxide synthase (nNOS), Sox-10 and with calcium imaging techniques. Leptin and glial cell line-derived neurotrophic factor (GDNF) were studied using immunohistochemical, biochemical or PCR methods in mice and primary culture of ENS. DIO prevented the age-associated decrease in antral nitrergic neurons observed in ND mice. Nerve stimulation evoked a stronger neuronal Ca(2+) response in WD compared to ND mice. DIO induced an NO-dependent increase in gastric emptying and neuromuscular transmission in the antrum without any change in small intestinal transit. During WD but not ND, a time-dependent increase in leptin and GDNF occurred in the antrum. Finally, we showed that leptin increased GDNF production in the ENS and induced neuroprotective effects mediated in part by GDNF. These results demonstrate that DIO induces neuroplastic changes in the antrum leading to an NO-dependent acceleration of gastric emptying. In addition, DIO induced neuroplasticity in the ENS is likely to involve leptin and GDNF.

Iridoid glycosides fraction of Folium syringae leaves modulates NF-κB signal pathway and intestinal epithelial cells apoptosis in experimental colitis

BACKGROUND AND AIMS

Iridoid glycosides (IG), the major active fraction of F. syringae leaves has been demonstrated to have strong anti-inflammatory properties to ulcerative colitis (UC) in our previous study. The aim of this study was to investigate whether IG modulates the inflammatory response in experimental colitis at the level of NF-κB signal pathway and epithelial cell apoptosis.

METHODS

UC in rats was induced by administration with dextran sulfate sodium (DSS) in drinking water. The inflammatory damage was assessed by disease activity index (DAI), macroscopic findings, histology and myeloperoxidase (MPO) activity. The effect of IG on pro-inflammatory cytokines TNF-α, IL-8, COX-2 and regulatory peptide TGF-β1 was measured. Epithelial cell apoptosis and the protein and mRNA expressions of Fas/FasL, Bcl-2/Bax, caspase-3, NF-κB p65, IκBα, p-IκBα and IKKβ were detected by TUNEL method, immunohistochemistry, Western blotting and real-time quantitative PCR, respectively.

RESULTS

IG significantly ameliorated macroscopic damage and histological changes, reduced the activity of MPO, and strongly inhibited epithelial cell apoptosis. Moreover, IG markedly depressed TNF-α, IL-8, COX-2 and TGF-β1 levels in the colon tissues in a dose-dependent manner. Furthermore, IG significantly blocked of NF-κB signaling by inhibiting IκBα phosphorylation/degradation and IKKβ activity, down-regulated the protein and mRNA expressions of Fas/FasL, Bax and caspase-3, and activated Bcl-2 in intestinal epithelial cells.

CONCLUSIONS

These results demonstrated for the first time that IG possessed marked protective effects on experimental colitis through inhibition of epithelial cell apoptosis and blockade of NF-κB signal pathway.

Caspase-3 cleavage links delta-catenin to the novel nuclear protein ZIFCAT

δ-Catenin is an Armadillo protein of the p120-catenin subfamily capable of modulating cadherin stability, small GTPase activity, and nuclear transcription. From yeast two-hybrid screening of a human embryonic stem cell cDNA library, we identified δ-catenin as a potential interacting partner of the caspase-3 protease, which plays essential roles in apoptotic as well as non-apoptotic processes. Interaction of δ-catenin with caspase-3 was confirmed using cleavage assays conducted in vitro, in Xenopus apoptotic extracts, and in cell line chemically induced contexts. The cleavage site, a highly conserved caspase consensus motif (DELD) within Armadillo repeat 6 of δ-catenin, was identified through peptide sequencing. Cleavage thus generates an amino-terminal (residues 1-816) and carboxyl-terminal (residues 817-1314) fragment, each containing about half of the central Armadillo domain. We found that cleavage of δ-catenin both abolishes its association with cadherins and impairs its ability to modulate small GTPases. Interestingly, 817-1314 possesses a conserved putative nuclear localization signal that may facilitate the nuclear targeting of δ-catenin in defined contexts. To probe for novel nuclear roles of δ-catenin, we performed yeast two-hybrid screening of a mouse brain cDNA library, resolving and then validating interaction with an uncharacterized KRAB family zinc finger protein, ZIFCAT. Our results indicate that ZIFCAT is nuclear and suggest that it may associate with DNA as a transcriptional repressor. We further determined that other p120 subfamily catenins are similarly cleaved by caspase-3 and likewise bind ZIFCAT. Our findings potentially reveal a simple yet novel signaling pathway based upon caspase-3 cleavage of p120-catenin subfamily members, facilitating the coordinate modulation of cadherins, small GTPases, and nuclear functions.

S100B protein, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor in human milk

Background

Human milk contains a wide variety of nutrients that contribute to the fulfillment of its functions, which include the regulation of newborn development. However, few studies have investigated the concentrations of S100B protein, brain-derived neurotrophic factor (BDNF), and glial cell line-derived neurotrophic factor (GDNF) in human milk. The associations of the concentrations of S100B protein, BDNF, and GDNF with maternal factors are not well explored.

Methodology/Principal Findings

To investigate the concentrations of S100B protein, BDNF, and GDNF in human milk and characterize the maternal factors associated with their levels in human milk, human milk samples were collected at days 3, 10, 30, and 90 after parturition. Levels of S100B protein, BDNF, and GDNF, and their mRNAs in the samples were detected. Then, these concentrations were compared with lactation and other maternal factors. S100B protein levels in human milk samples collected at 3, 10, 30, and 90 d after parturition were 1249.79±398.10, 1345.05±539.16, 1481.83±573.30, and 1414.39±621.31 ng/L, respectively. On the other hand, the BDNF concentrations in human milk samples were 10.99±4.55, 13.01±5.88, 13.35±6.43, and 2.83±5.47 µg/L, while those of GDNF were 10.90±1.65, 11.38±1., 11.29±3.10, and 11.40±2.21 g/L for the same time periods. Maternal post-pregnancy body mass index was positively associated with S100B levels in human milk (r = 0.335, P = 0.030<0.05). In addition, there was a significant correlation between the levels of S100B protein and BDNF (z = 2.09, P = 0.037<0.05). Delivery modes were negatively associated with the concentration of GDNF in human milk.

Conclusions

S100B protein, BDNF, and GDNF are present in all samples of human milk, and they may be responsible for the long term effects of breast feeding.

Can "functional" constipation be considered as a form of enteric neuro-gliopathy?

Constipation has been traditionally viewed and classified as a functional or idiopathic disorder. However, evidence has been accumulating that suggests how constipation might be considered as due to abnormalities of the enteric nervous system, since alterations of this system, not evident in conventional histological examination, may be present in these patients. These abnormalities often consist in decrease or loss of the enteric glial cells, a pathological finding present in most types of constipation so far investigated. In this article we will discuss these evidences, and will try to consider constipation no more as a simple functional or idiopathic disorder but as a form of enteric neuro-gliopathy.