The role of Zn²⁺-sensing receptor GPR39 on glucose homeostasis and incretin regulation was assessed in enteroendocrine L- and K-cells. Anti-hyperglycaemic, insulinotropic and incretin secreting properties of Zn²⁺ were explored in normal, diabetic and incretin receptor knockout mice. Compared to intraperitoneal injection, oral administration of Zn²⁺ (50 μmol/kg body weight) with glucose (18 mmol/kg) in lean mice reduced the glycaemic excursion by 25–34% (p < 0.05–p < 0.001) and enhanced glucose-induced insulin release by 46–48% (p < 0.05–p < 0.01). In diabetic mice, orally administered Zn²⁺ lowered glucose by 24–31% (p < 0.01) and augmented insulin release by 32% (p < 0.01). In glucagon like peptide-1 (GLP-1) receptor knockout mice, Zn²⁺ reduced glucose by 15–28% (p < 0.05–p < 0.01) and increased insulin release by 35–43% (p < 0.01). In contrast Zn²⁺ had no effect on responses of glucose-dependent insulinotropic polypeptide (GIP) receptor knockout mice. Consistent with this, Zn²⁺ had no effect on circulating total GLP-1 whereas GIP release was stimulated by 26% (p < 0.05) in lean mice. Immunocytochemistry demonstrated GPR39 expression on mouse enteroendocrine L- and K-cells, GLUTag cells and pGIP/Neo STC-1 cells. Zn²⁺ had a direct effect on GIP secretion from pGIPneo STC-1 cells, increasing GIP secretion by 1.3-fold. GPR39 is expressed on intestinal L- and K-cells, and stimulated GIP secretion plays an integral role in mediating enhanced insulin secretion and glucose tolerance following oral administration of Zn²⁺. This suggests development of potent and selective GPR39 agonists as a therapeutic approach for diabetes.

Aims/hypothesis: Roux-en-Y gastric bypass surgery (RYGB) frequently results in remission of type 2 diabetes as well as exaggerated secretion of glucagon-like peptide-1 (GLP-1). Here, we assessed RYGB-induced transcriptomic alterations in the small intestine and investigated how they were related to the regulation of GLP-1 production and secretion in vitro and in vivo. Methods: Human jejunal samples taken perisurgically and 1 year post RYGB (n=13) were analysed by RNA-seq. Guided by bioinformatics analysis we targeted four genes involved in cholesterol biosynthesis, which we confirmed to be expressed in human L cells, for potential involvement in GLP-1 regulation using siRNAs in GLUTag and STC-1 cells. Gene expression analyses, GLP-1 secretion measurements, intracellular calcium imaging and RNA-seq were performed in vitro. OGTTs were performed in C57BL/6j and iScd1^−/− mice and immunohistochemistry and gene expression analyses were performed ex vivo. Results: Gene Ontology (GO) analysis identified cholesterol biosynthesis as being most affected by RYGB. Silencing or chemical inhibition of stearoyl-CoA desaturase 1 (SCD1), a key enzyme in the synthesis of monounsaturated fatty acids, was found to reduce Gcg expression and secretion of GLP-1 by GLUTag and STC-1 cells. Scd1 knockdown also reduced intracellular Ca²⁺ signalling and membrane depolarisation. Furthermore, Scd1 mRNA expression was found to be regulated by NEFAs but not glucose. RNA-seq of SCD1 inhibitor-treated GLUTag cells identified altered expression of genes implicated in ATP generation and glycolysis. Finally, gene expression and immunohistochemical analysis of the jejunum of the intestine-specific Scd1 knockout mouse model, iScd1^−/−, revealed a twofold higher L cell density and a twofold increase in Gcg mRNA expression. Conclusions/interpretation: RYGB caused robust alterations in the jejunal transcriptome, with genes involved in cholesterol biosynthesis being most affected. Our data highlight SCD as an RYGB-regulated L cell constituent that regulates the production and secretion of GLP-1. Graphical

Context: Statin use is associated with increased risk of type 2 diabetes (T2D) and mild hyperglycemia. The underlying mechanisms are not well studied, and the effect of statin treatment on glucagon-like peptide 1 (GLP-1) secretion or production is unknown. Objective: This work aimed to assess the effects of rosuvastatin on GLP-1 secretion and production. Methods: We performed association studies in the Malmö Diet and Cancer study cardiovascular cohort (MDCS-CC) reexamination cohort, in vitro investigations using GLUTag cells and acute and chronic studies in female, normoglycemic C57Bl/6j mice. Results: Studies in the MDCS-CC reexamination cohort (n = 3734) revealed that in individuals without T2D, statin usage was associated with higher fasting glucose-dependent insulinotropic peptide (GIP), insulin, glucose, glucagon, and homeostatic model assessment of insulin resistance, but not GLP-1. However, in patients with T2D, statin usage was associated with higher fasting GLP-1 levels. Rosuvastatin treatment or 3-hydroxy-3-methyl-glutaryl-coenzyme A reductase (Hmgcr) knockdown (KD) reduced GLP-1 secretion and increased Gcg messenger RNA in GLUTag cells. Rosuvastatin acutely reduced postprandial GLP-1 secretion, whereas chronic rosuvastatin treatment in mice caused hyperglycemia and increased postprandial GLP-1 levels. The acute effect of Hmgcr KD on GLP-1 secretion could be mimicked by targeting intracellular cholesterol using a PCSK9 inhibitor. Finally, transcriptomic alterations induced by rosuvastatin were limited to genes involved in cholesterol biosynthesis. Conclusion: We have established HMGCR as a regulator of GLP-1 secretion and provide a plausible explanation for the clinically observed mild hyperglycemia associated with statin use. Given the negative acute effect on GLP-1 secretion, monitoring of blood glucose levels is recommended after prescribing rosuvastatin.