Epithelial insulin sensitivity as a gatekeeper of the gut barrier

La muqueuse intestinale forme une barrière sélective, qui assure le transport transcellulaire efficace des nutriments tout en excluant rigoureusement le flux paracellulaire de produits bactériens immunostimulants à travers l'épithélium. Au cours du syndrome métabolique, notamment associé au développement d'une insulino-résistance périphérique, l'altération de la perméabilité intestinale est responsable de la translocation d'endotoxines bactériennes dans la circulation systémique, participant ainsi à l'inflammation de bas grade caractéristique de ces pathologies métaboliques. Alors que les mécanismes impliqués dans la perte de l'intégrité intestinale accompagnant le syndrome métabolique sont longtemps restés mal compris, l'hyperglycémie a récemment été considérée comme un candidat de choix. Thaiss et al ont en effet proposé que le transport via GLUT2 et le métabolisme intracellulaire du glucose entraînait dans l'épithélium intestinal une reprogrammation transcriptionnelle interférant avec sa fonction barrière et favorisait la susceptibilité aux infections entériques. L'hyperglycémie étant étroitement associée à la perte d'action de l'insuline, nous avons émis l'hypothèse qu'au-delà de l'hyperglycémie, une signalisation insulinique intestinale défectueuse pourrait constituer un nouvel acteur dans l'altération de l'intégrité intestinale observée au cours du syndrome métabolique. Pour adresser ce point, nous avons alors développé deux modèles murins de résistance à l'insuline : (i) un modèle d'insulino-résistance globale non obèse, par traitement avec un antagoniste du récepteur de l'insuline (S961), (ii) un modèle d'insulino-résistance spécifiquement intestinale sans hyperglycémie concomitante, suite à la délétion inductible du récepteur de l'insuline dans l'épithélium intestinal (IRKOGUT). De façon intéressante, l'absence de signalisation insulinique dans l'intestin entraîne une détérioration significative de la défense antimicrobienne par les cellules Paneth et l'apparition concomitante d'une dysbiose caractérisée par des proportions accrues de Protéobactéries pro-inflammatoires. En conséquence, ce défaut de signalisation s'accompagne d'une augmentation de la susceptibilité à l'infection par des entéro-pathogènes et du contenu fécal en lipocaline 2, un marqueur de l'inflammation intestinale. Par ailleurs, l'analyse des souris IRKOGUT montre que l'insuline contrôle la capacité de renouvellement épithélial, une autre fonction essentielle à l'intégrité intestinale. L'altération de la croissance ex-vivo d'organoides intestinaux et coliques issus de souris IRKOGUT suggère ainsi un défaut de prolifération des cellules souches. En accord avec ces données, la perte de signalisation insulinique dans l'intestin augmente la susceptibilité à la colite aiguë induite par un traitement au DSS, associée à des défauts majeurs de la ré-épithélialisation. L'ensemble de nos données révèle donc que l'insuline est un acteur nouveau de l'intégrité intestinale en contrôlant dans l'épithélium deux composants essentiels de cette barrière : (i) la fonction bactéricide des cellules de Paneth et (ii) les capacités de survie et de prolifération des cellules souches.Intestinal mucosa forms a selective barrier, which ingeniously allows an efficient transcellular transport of nutrients while rigorously excluding the paracellular flow of immune-stimulatory bacterial products across the epithelium. A common feature of metabolic diseases is their association with chronic inflammatory processes in various tissues, as well as an increased general risk of infection. This state of metaflammation is thought to result from impaired intestinal mucosal barrier, leading to the translocation of microbial products into the systemic circulation. While the mechanistic basis for gut leakiness accompanying the metabolic syndrome has long remained poorly understood, recent evidences indicate that gut epithelial glucose metabolism can be considered as a prime candidate. Thaiss et al indeed proposed that hyperglycemic state leads to GLUT2-mediated glucose transport and metabolism in intestinal epithelial cells and drives intraepithelial gene expression reprograming which markedly interferes with homeostatic gut barrier function and favors susceptibility to enteric infection upon the diabesity cascade. Because hyperglycemia and loss of insulin action are often two sides of the same coin, we hypothesize that, beyond hyperglycemia, defective intestinal insulin signaling could directly impair epithelial integrity upon diabetic conditions. To address this point, we developed two murine models of insulin resistance: (i) a model of global insulin resistance not associated with obesity, by treatment with an insulin receptor antagonist (S961), (ii) a model of specific and inducible intestinal insulin resistance that do not display concomitant hyperglycemia, by inducible deletion of the insulin receptor in the intestinal epithelium (IRKOGUT).Loss of intestinal insulin signaling triggered a significant deterioration of antimicrobial defense by Paneth cells, concomitantly with the onset of a significant dysbiosis as characterized by a bloom of pro-inflammatory Proteobacteria. This was accompanied by an increased susceptibility to infection by enteropathogens and enhanced fecal content of lipocalin 2, a marker of intestinal inflammation. Further examination of IRKOGUT mice pinpointed that insulin controls epithelium renewal capacities, another essential component of intestinal integrity. Ex-vivo growth of intestinal and colonic organoids derived from IRKOGUT mice was indeed significantly altered, suggesting defects in stem cell proliferation and survival. Consequently, IRKOGUT mice exhibited a greater susceptibility to acute colitis induced by DSS treatment, with was associated with major defects in re-epithelialization. This study therefore reveals that insulin acts as a gatekeeper of the intestinal by controlling two essential components of the gut epithelial barrier: (i) the bactericidal activity of Paneth cells and (ii) the survival and proliferative capacities of stem cells

Epithelial insulin signalling: A gatekeeper of the gut barrier function?

Accepted abstracts will be published in the Abstract Volume, a supplement issue of Diabetologia, the journal of the EASD. Furthermore abstracts accepted for presentation and discussion will be published on the Association’s website www.easd.org from 1 July 2022.International audienc

Homocysteine-lowering gene therapy rescues signaling pathways in brain of mice with intermediate hyperhomocysteinemia

Hyperhomocysteinemia due to cystathionine beta synthase (CBS) deficiency is associated with diverse cognitive dysfunction. Considering the role of the serine/threonine kinase DYRK1A, not only in developmental defects with life-long structural and functional consequences, but also in multiple neurodegenerative diseases, its protein expression and kinase activity has been analyzed in brain of heterozygous CBS deficient mice and found to be increased. We previously demonstrated that specific liver treatment with an adenovirus expressing Dyrk1A normalizes hepatic DYRK1A level and decreases hyperhomocysteinemia in mice with moderate to intermediate hyperhomocysteinemia. We here use a hepatocyte-specific recombinant adeno-associated viral (AAV) serotype 8-mediated DYRK1A gene therapy (AAV2/8-DYRK1A) to analyze the effect of hepatic Dyrk1A gene transfer on some altered molecular mechanisms in brain of mice with intermediate hyperhomocysteinemia. Our selective hepatic treatment alleviates altered DYRK1A protein level and signaling pathways in brain of mice, the MAPK/ERK and PI3K/Akt pathways initiated by receptor tyrosine kinase, the BDNF dependent TrkB pathway, and NFkB pathway. These results demonstrate the positive effect of AAV2/8-DYRK1A gene transfer on neuropathological and inflammatory processes in brain of mice with intermediate hyperhomocysteinemia

Epithelial insulin signalling: A gatekeeper of the gut barrier function?

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Insulin resistance per se drives early and reversible dysbiosis-mediated gut barrier impairment and bactericidal dysfunction

International audienceA common feature of metabolic diseases is their association with chronic low-grade inflammation. While enhanced gut permeability and systemic bacterial endotoxin translocation have been suggested as key players of this metaflammation, the mechanistic bases underlying these features upon the diabesity cascade remain partly understood. Here, we show in mice that, independently of obesity, the induction of acute and global insulin resistance and associated hyperglycemia, upon treatment with an insulin receptor (IR) antagonist (S961), elicit gut hyperpermeability without triggering systemic inflammatory response. Of note, S961-treated diabetic mice display major defects of gut barrier epithelial functions, such as increased epithelial paracellular permeability and impaired cell-cell junction integrity. We also observed in these mice the early onset of a severe gut dysbiosis, as characterized by the bloom of pro-inflammatory Proteobacteria, and the later collapse of Paneth cells antimicrobial defense. Interestingly, S961 treatment discontinuation is sufficient to promptly restore both the gut microbial balance and the intestinal barrier integrity. Moreover, fecal transplant approaches further confirm that S961-mediated dybiosis contributes at least partly to the disruption of the gut selective epithelial permeability upon diabetic states. Together, our results highlight that insulin signaling is an indispensable gatekeeper of intestinal barrier integrity, acting as a safeguard against microbial imbalance and acute infections by enteropathogens

Neuromedin U is a gut peptide that alters oral glucose tolerance by delaying gastric emptying via direct contraction of the pylorus and vagal-dependent mechanisms

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Gut mucosa alterations and loss of segmented filamentous bacteria in type 1 diabetes are associated with inflammation rather than hyperglycaemia

International audienceObjective Type 1 diabetes (T1D) is an autoimmune disease caused by the destruction of pancreatic β-cells producing insulin. Both T1D patients and animal models exhibit gut microbiota and mucosa alterations, although the exact cause for these remains poorly understood. We investigated the production of key cytokines controlling gut integrity, the abundance of segmented filamentous bacteria (SFB) involved in the production of these cytokines, and the respective role of autoimmune inflammation and hyperglycaemia. Design We used several mouse models of autoimmune T1D as well as mice rendered hyperglycaemic without inflammation to study gut mucosa and microbiota dysbiosis. We analysed cytokine expression in immune cells, epithelial cell function, SFB abundance and microbiota composition by 16S sequencing. We assessed the role of anti-tumour necrosis factor α on gut mucosa inflammation and T1D onset. Results We show in models of autoimmune T1D a conserved loss of interleukin (IL)-17A, IL-22 and IL-23A in gut mucosa. Intestinal epithelial cell function was altered and gut integrity was impaired. These defects were associated with dysbiosis including progressive loss of SFB. Transfer of diabetogenic T-cells recapitulated these gut alterations, whereas induction of hyperglycaemia with no inflammation failed to do so. Moreover, anti-inflammatory treatment restored gut mucosa and immune cell function and dampened diabetes incidence. Conclusion Our results demonstrate that gut mucosa alterations and dysbiosis in T1D are primarily linked to inflammation rather than hyperglycaemia. Anti-inflammatory treatment preserves gut homeostasis and protective commensal flora reducing T1D incidence