The enteric nervous system and the digestive neuronal-glial-epithelial unit

In spite of its apparent simplicity, the digestive tract is probably one of the most complex organs of the human body. The complexity of the digestive functions requires an extremely fine regulation, to direct nutriments towards sites dedicated to absorption, to control their absorption, and protect our body against adverse environmental factors (bacteria, toxins…). All these functions are controlled by a second brain: the enteric nervous system (ENS). Neurons and enteric glial cells, which form the ENS, regulate gastrointestinal motility as well as intestinal barrier functions. The physical proximity of neurons and of glial and epithelial intestinal cells, and especially their inter-regulation have led to the definition of the new concept of neuronal-glial-epithelial unit. The ENS is a key regulator of digestive functions, and is also involved in the development of digestive disordersEn dépit d’une apparente simplicité, le tube digestif est probablement l’un des organes les plus complexes du corps humain. En effet, la complexité des fonctions digestives nécessite une régulation extrêmement fine, permettant à la fois de diriger les nutriments vers les sites spécialisés d’absorption du tube digestif, de contrôler leur absorption, et de protéger notre corps de l’agression par des facteurs environnementaux délétères (bactéries, toxiques…). L’ensemble de ces fonctions est assuré par un véritable deuxième cerveau : le système nerveux entérique (SNE). Les neurones et les cellules gliales entériques qui forment le SNE régulent la motilité digestive, mais aussi les fonctions de barrière de l’épithélium intestinal. La proximité physique des neurones ainsi que des cellules gliales et épithéliales intestinales, mais aussi et surtout leurs inter-régulations nous a permis de définir le nouveau concept d’unité-neuro-glio-épithéliale. Le SNE est un régulateur clef des fonctions digestives et participe également au développement de pathologies digestive

Transglutaminase-dependent RhoA Activation and Depletion by Serotonin in Vascular Smooth Muscle Cells

The small G protein RhoA plays a major role in several vascular processes and cardiovascular disorders. Here we analyze the mechanisms of RhoA regulation by serotonin (5-HT) in arterial smooth muscle. 5-HT (0.1-10 microM) induced activation of RhoA followed by RhoA depletion at 24-72 h. Inhibition of 5-HT1 receptors reduced the early phase of RhoA activation but had no effect on 5-HT-induced delayed RhoA activation and depletion, which were suppressed by the 5-HT transporter inhibitor fluoxetine and the transglutaminase inhibitor monodansylcadaverin and in type 2 transglutaminase-deficient smooth muscle cells. Coimmunoprecipitations demonstrated that 5-HT associated with RhoA both in vitro and in vivo. This association was calcium-dependent and inhibited by fluoxetine and monodansylcadaverin. 5-HT promotes the association of RhoA with the E3 ubiquitin ligase Smurf1, and 5-HT-induced RhoA depletion was inhibited by the proteasome inhibitor MG132 and the RhoA inhibitor Tat-C3. Simvastatin, the Rho kinase inhibitor Y-27632, small interfering RNA-mediated RhoA gene silencing, and long-term 5-HT stimulation induced Akt activation. In contrast, inhibition of 5-HT-mediated RhoA degradation by MG132 prevented 5-HT-induced Akt activation. Long-term 5-HT stimulation also led to the inhibition of the RhoA/Rho kinase component of arterial contraction. Our data provide evidence that 5-HT, internalized through the 5-HT transporter, is transamidated to RhoA by transglutaminase. Transamidation of RhoA leads to RhoA activation and enhanced proteasomal degradation, which in turn is responsible for Akt activation and contraction inhibition. The observation of transamidation of 5-HT to RhoA in pulmonary artery of hypoxic rats suggests that this process could participate in pulmonary artery remodeling and hypertension

Tau expression and phosphorylation in enteroendocrine cells

Background and objectiveThere is mounting evidence to suggest that the gut-brain axis is involved in the development of Parkinson’s disease (PD). In this regard, the enteroendocrine cells (EEC), which faces the gut lumen and are connected with both enteric neurons and glial cells have received growing attention. The recent observation showing that these cells express alpha-synuclein, a presynaptic neuronal protein genetically and neuropathologically linked to PD came to reinforce the assumption that EEC might be a key component of the neural circuit between the gut lumen and the brain for the bottom-up propagation of PD pathology. Besides alpha-synuclein, tau is another key protein involved in neurodegeneration and converging evidences indicate that there is an interplay between these two proteins at both molecular and pathological levels. There are no existing studies on tau in EEC and therefore we set out to examine the isoform profile and phosphorylation state of tau in these cells.MethodsSurgical specimens of human colon from control subjects were analyzed by immunohistochemistry using a panel of anti-tau antibodies together with chromogranin A and Glucagon-like peptide-1 (two EEC markers) antibodies. To investigate tau expression further, two EEC lines, namely GLUTag and NCI-H716 were analyzed by Western blot with pan-tau and tau isoform specific antibodies and by RT-PCR. Lambda phosphatase treatment was used to study tau phosphorylation in both cell lines. Eventually, GLUTag were treated with propionate and butyrate, two short chain fatty acids known to sense EEC, and analyzed at different time points by Western blot with an antibody specific for tau phosphorylated at Thr205.ResultsWe found that tau is expressed and phosphorylated in EEC in adult human colon and that both EEC lines mainly express two tau isoforms that are phosphorylated under basal condition. Both propionate and butyrate regulated tau phosphorylation state by decreasing its phosphorylation at Thr205.Conclusion and inferenceOur study is the first to characterize tau in human EEC and in EEC lines. As a whole, our findings provide a basis to unravel the functions of tau in EEC and to further investigate the possibility of pathological changes in tauopathies and synucleinopathies

Maternal prebiotic supplementation impacts colitis development in offspring mice

Background and aimsMaternal diet plays a key role in preventing or contributing to the development of chronic diseases, such as obesity, allergy, and brain disorders. Supplementation of maternal diet with prebiotics has been shown to reduce the risk of food allergies and affect the intestinal permeability in offspring later in life. However, its role in modulating the development of other intestinal disorders, such as colitis, remains unknown. Therefore, we investigated the effects of prebiotic supplementation in pregnant mice on the occurrence of colitis in their offspring.Materials and methodsOffspring from mothers, who were administered prebiotic galacto-oligosaccharides and inulin during gestation or fed a control diet, were subjected to three cycles of dextran sulphate sodium (DSS) treatment to induce chronic colitis, and their intestinal function and disease activity were evaluated. Colonic remodelling, gut microbiota composition, and lipidomic and transcriptomic profiles were also assessed.ResultsDSS-treated offspring from prebiotic-fed mothers presented a higher disease score, increased weight loss, and increased faecal humidity than those from standard diet-fed mothers. DSS-treated offspring from prebiotic-fed mothers also showed increased number of colonic mucosal lymphocytes and macrophages than the control group, associated with the increased colonic concentrations of resolvin D5, protectin DX, and 14-hydroxydocosahexaenoic acid, and modulation of colonic gene expression. In addition, maternal prebiotic supplementation induced an overabundance of eight bacterial families and a decrease in the butyrate caecal concentration in DSS-treated offspring.ConclusionMaternal prebiotic exposure modified the microbiota composition and function, lipid content, and transcriptome of the colon of the offspring. These modifications did not protect against colitis, but rather sensitised the mice to colitis development

Étude des rôles de la phosphorylation de RhoA (nouveaux partenaires et effet vasoprotecteur de l'estradiol)

RhoA a un rôle crucial dans la régulation des fonctions vasculaires et une suractivation de la protéine a été associée à plusieurs pathologies vasculaires. Notre équipe s intéresse à la régulation de RhoA par phosphorylation, mais ce mécanisme d'inactivation reste encore peu connu. L'objectif de ce travail est donc 1) d identifier de nouvelles kinases responsables de la phosphorylation de RhoA, et 2) d'identifier les partenaires et les régulateurs potentiels de la protéine phosphorylée. Avec ce travail, nous avons mis en évidence une nouvelle kinase de RhoA, l AMPK, qui phosphoryle la protéine sur son résidu sérine en position 188 et est capable d'induire l'inhibition de la voie RhoA-Rock. Nous avons également montré que l estradiol induit la phosphorylation de RhoA et l'inhibition de la voie RhoA-Rock, et que cet effet est médié par l'AMPK. Par la suite, des études de vasoréactivité nous ont permis de mettre en évidence un effet vasoprotecteur de l'estradiol et de l'AMPK. Enfin, l'étude des partenaires de RhoA phosphorylée a permis d'identifier principalement des protéines du cytosquelette mais aussi, M-RIP et Hsp70, dont l étude pourrait permettre de mieux comprendre les conséquences de la phosphorylation de RhoA.NANTES-BU Médecine pharmacie (441092101) / SudocSudocFranceF

Enseignement et formation de troisième cycle

Enseignement et formation de troisième cycl

Enseignement et formation de troisième cycle

Enseignement et formation de troisième cycl

Upregulation of enteric alpha-synuclein as a possible link between inflammatory bowel disease and Parkinson's disease

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