Objectives: Altered enteroendocrine cell (EEC) function in obesity and type 2 diabetes is not fully understood. Understanding the transcriptional program that controls EEC differentiation is important because some EEC types harbor significant therapeutic potential for type 2 diabetes. Methods: EEC isolation from jejunum of obese individuals with (ObD) or without (Ob) type 2 diabetes was obtained with a new method of cell sorting. EEC transcriptional profiles were established by RNA-sequencing in a first group of 14 Ob and 13 ObD individuals. EEC lineage and densities were studied in the jejunum of a second independent group of 37 Ob, 21 ObD and 22 non obese (NOb) individuals. Results: The RNA seq analysis revealed a distinctive transcriptomic signature and a decreased differentiation program in isolated EEC from ObD compared to Ob individuals. In the second independent group of ObD, Ob and NOb individuals a decreased GLP-1 cell lineage and GLP-1 maturation from proglucagon, were observed in ObD compared to Ob individuals. Furthermore, jejunal density of GLP-1-positive cells was significantly reduced in ObD compared to Ob individuals. Conclusions: These results highlight that the transcriptomic signature of EEC discriminate obese subjects according to their diabetic status. Furthermore, type 2 diabetes is associated with reduced GLP-1 cell differentiation and proglucagon maturation leading to low GLP-1-cell density in human obesity. These mechanisms could account for the decrease plasma GLP-1 observed in metabolic diseases.

With the continuous rise in the worldwide prevalence of obesity and type 2 diabetes, developing therapies regulating body weight and glycemia has become a matter of great concern. Among the current treatments, evidence now shows that the use of intestinal hormone analogs (e.g., GLP1 analogs and others) helps to control glycemia and reduces body weight. Indeed, intestinal endocrine cells produce a large variety of hormones regulating metabolism, including appetite, digestion, and glucose homeostasis. Herein, we discuss how the enteroendocrine system is affected by local environmental and metabolic signals. These signals include those arising from unbalanced diet, gut microbiota, and the host metabolic organs and their complex cross-talk with the intestinal barrier integrity.

Metformin is the first line therapy recommended for type 2 diabetes. However, the precise mechanism of action remains unclear and up to a quarter of patients show some degree of intolerance to the drug, with a similar number showing poor response to treatment, limiting its effectiveness. A better understanding of the mechanism of action of metformin may improve its clinical use. SLC2A2 (GLUT2) is a transmembrane facilitated glucose transporter, with important roles in the liver, gut and pancreas. Our group previously identified single nucleotide polymorphisms in the human SLC2A2 gene, which were associated with reduced transporter expression and an improved response to metformin treatment. The aims of this study were to model Slc2a2 deficiency and measure the impact on glucose homoeostasis and metformin response in mice. We performed extensive metabolic phenotyping and 2-deoxy-2-[¹⁸F]fluoro-d-glucose ([¹⁸F]FDG)-positron emission tomography (PET) analysis of gut glucose uptake in high-fat diet-fed (HFD) mice with whole-body reduced Slc2a2 (Slc2a2^+/-) and intestinal Slc2a2 KO, to assess the impact of metformin treatment. Slc2a2 partial deficiency had no major impact on body weight and insulin sensitivity, however mice with whole-body reduced Slc2a2 expression (Slc2a2^+/-) developed an age-related decline in glucose homoeostasis (as measured by glucose tolerance test) compared to wild-type (Slc2a2^+/+) littermates. Glucose uptake into the gut from the circulation was enhanced by metformin exposure in Slc2a2^+/+ animals fed HFD and this action of the drug was significantly higher in Slc2a2^+/- animals. However, there was no effect of specifically knocking-out Slc2a2 in the mouse intestinal epithelial cells. Overall, this work identifies a differential metformin response, dependent on expression of the SLC2A2 glucose transporter, and also adds to the growing evidence that metformin efficacy includes modifying glucose transport in the gut. We also describe a novel and important role for this transporter in maintaining efficient glucose homoeostasis during ageing.

Carbohydrates and sweeteners are detected by the sweet taste receptor in enteroendocrine cells (EECs). This receptor is coupled to the gustducin G-protein, which α-subunit is encoded by GNAT3 gene. In intestine, the activation of sweet taste receptor triggers a signaling pathway leading to GLP-1 secretion, an incretin hormone. In metabolic diseases, GLP-1 concentration and incretin effect are reduced while partly restored after Roux-en-Y gastric bypass (RYGB). We wondered if the decreased GLP-1 secretion in metabolic diseases is caused by an intestinal defect in sweet taste transduction pathway. In our RNA-sequencing of EECs, GNAT3 expression is decreased in patients with obesity and type 2 diabetes compared with normoglycemic obese patients. This prompted us to explore sweet taste signaling pathway in mice with metabolic deteriorations. During obesity onset in mice, Gnat3 expression was downregulated in EECs. After metabolic improvement with enterogastro anastomosis surgery in mice (a surrogate of the RYGB in humans), the expression of Gnat3 increased in the new alimentary tract and glucose-induced GLP-1 secretion was improved. To evaluate if high-fat diet-induced dysbiotic intestinal microbiota could explain the changes in the expression of sweet taste α-subunit G-protein, we performed a fecal microbiota transfer in mice. However, we could not conclude if dysbiotic microbiota impacted or not intestinal Gnat3 expression. Our data highlight that metabolic disorders were associated with altered gene expression of sweet taste signaling in intestine. This could contribute to impaired GLP-1 secretion that is partly rescued after metabolic improvement. NEW & NOTEWORTHY Our data highlighted 1) the sweet taste transduction pathway in EECs plays pivotal role for glucose homeostasis at least at gene expression level; 2) metabolic disorders lead to altered gene expression of sweet taste signaling pathway in intestine contributing to impaired GLP-1 secretion; and 3) after surgical intestinal modifications, increased expression of GNAT3, encoding α-gustducin contributed to metabolic improvement.

The Goto-Kakizaki (GK) rat is a type 2 diabetes model with a defective beta-cell mass detectable in late fetal development. Diminished IGF-2 production seems to be involved in this effect. Herein, we analyzed the effect of maternal food-restriction on the beta-cell mass of GK fetuses and the involvement of the IGF system, highly responsive to nutritional status in this process. To this end, in undernourished GK fetuses (U-GK), we measured serum GH/IGF levels, beta-cell mass, replication and differentiation, and IGF-1/-2 protein content in liver and pancreas tissue. Pregnant GK females were food restricted (65% restriction) during the last week of gestation. Our results show that maternal malnutrition ameliorates beta-cell mass in U-GK fetuses and a specific pancreatic IGF-2 increase may be instrumental in this effect. Further studies are needed to determine whether maternal undernutrition is sufficient to delay or decrease the risk of the GK rat for developing diabetes.

Objectives Obesity and type 2 diabetes (T2D) are associated with altered secretion of enteroendocrine hormones, including the glucagon-like peptide-1 (GLP-1). The mechanisms underlying this dysregulation remain poorly understood, partly due to the rarity of enteroendocrine cells (EECs) and technical difficulties in humans. Our aim was to generate an in vitro human jejunal enteroids (HJEs) derived from individuals with obesity and T2D as a simplified intestinal epithelium in a controlled environment, in order to explore GLP-1 secretion in metabolic diseases. Subjects and methods HJEs were obtained from jejunum fragments sampled during gastric bypass surgery in individuals with severe obesity and normoglycemia (Ob, n = 12), prediabetes (ObPreD, n = 12), or T2D (ObD, n = 10). HJEs were characterized through gene and protein expression analyses and immunofluorescence. To promote the EEC lineage, HJEs were treated with the Notch pathway inhibitor DAPT. Active GLP-1 secretion was assessed by ELISA. Results HJEs were successfully generated whatever the metabolic group Ob, ObPreD, ObD, exhibiting epithelial cell lineages and expressing critical genes involved in GLP-1 cell lineage, biosynthesis, and secretion. HJEs secreted active GLP-1 in response to both low and high glucose concentrations, regardless of subject metabolic status. However, HJEs from individuals with severe obesity and T2D exhibited a reduced capacity to release GLP-1 in response to high glucose concentrations compared to those from individuals with severe obesity or with obesity and prediabetes. Conclusions HJEs represent a robust human-derived model to investigate EEC function and GLP-1 secretion in metabolic diseases. While HJEs retain functional GLP-1-producing cells, their secretory capacity is impaired in the presence of T2D, confirming functional endocrine alterations. These findings support the use of HJEs in preclinical studies targeting enteroendocrine dysfunction.