Project description:Glucagon and insulin are counter-regulatory pancreatic hormones that precisely control blood glucose homeostasis1. Type 2 diabetes mellitus (T2DM) is characterized by inappropriately elevated blood glucagon2-5 levels as well as insufficient glucose stimulated insulin secretion (GSIS) by pancreatic ß-cells6. Early in the pathogenesis of T2DM, hyperglucagonemia is observable antecedent to ß-cell dysfunction7-9; and in mice, liver-specific activation of glucagon receptor-dependent signaling results in impaired GSIS10. However, the mechanistic relationship between hyperglucagonemia, hepatic glucagon action, and ß-cell dysfunction remains poorly understood. Here we show that glucagon action stimulates hepatic production of the neuropeptide kisspeptin1, which acts in an endocrine manner on ß-cells to suppress GSIS. In vivo glucagon administration acutely stimulates hepatic kisspeptin1 production, and kisspeptin1 is increased in livers from humans with T2DM and from mouse models of diabetes mellitus. Synthetic kisspeptin1 potently suppresses GSIS in vivo and in vitro from normal isolated islets, which express the kisspeptin1 receptor Kiss1R. Administration of a Kiss1R antagonist in diabetic Leprdb/db mice potently augments GSIS and reduces glycemia. Our observations indicate in the pathogenesis of T2DM an endocrine mechanism sequentially linking hyperglucagonemia via hepatic kisspeptin1 production to impaired insulin secretion. In addition, our findings suggest Kiss1R antagonism as a therapeutic avenue to improve ß-cell function in T2DM. Total RNA from L-Δprkar1a KO mice compared to control D-glucose mice
Project description:Pancreatic b-cell failure in type 2 diabetes is associated with functional abnormalities of insulin secretion and deficits of b-cell mass. It’s unclear how one begets the other. We have shown that loss of b-cell mass can be ascribed to impaired FoxO1 function in different models of diabetes. Here we show that ablation of the three FoxO genes (1, 3a, and 4) in mature b-cells results in early-onset, maturity onset diabetes of the young (MODY)-like diabetes, with signature abnormalities of the MODY networks of Hnf4a, Hnf1a, and Pdx1. Transcriptome and functional analyses reveal that FoxO-deficient b-cells are metabolically inflexible, i.e., they preferentially utilize lipids rather than carbohydrates as source of acetyl-CoA for mitochondrial oxidative phosphorylation. This results in impaired ATP generation, and reduced Ca2+-dependent insulin secretion. When viewed in the context of prior data illustrating a role of FoxO1 in b-cell dedifferentiation, the present findings define a seamless FoxO-dependent mechanism linking the twin abnormalities of b-cell function in diabetes. We used microarrays to detail the change of gene expression in pancreatic beta cells after knocking out FoxO1,3 and 4. Primary islets were isolated from pancretic beta cell- specific triple FoxO(1,3, and 4) KO and their littermates control (WT) mice. Gene expression was analyzed by microarray.
Project description:Glucagon and insulin are counter-regulatory pancreatic hormones that precisely control blood glucose homeostasis1. Type 2 diabetes mellitus (T2DM) is characterized by inappropriately elevated blood glucagon2-5 levels as well as insufficient glucose stimulated insulin secretion (GSIS) by pancreatic ß-cells6. Early in the pathogenesis of T2DM, hyperglucagonemia is observable antecedent to ß-cell dysfunction7-9; and in mice, liver-specific activation of glucagon receptor-dependent signaling results in impaired GSIS10. However, the mechanistic relationship between hyperglucagonemia, hepatic glucagon action, and ß-cell dysfunction remains poorly understood. Here we show that glucagon action stimulates hepatic production of the neuropeptide kisspeptin1, which acts in an endocrine manner on ß-cells to suppress GSIS. In vivo glucagon administration acutely stimulates hepatic kisspeptin1 production, and kisspeptin1 is increased in livers from humans with T2DM and from mouse models of diabetes mellitus. Synthetic kisspeptin1 potently suppresses GSIS in vivo and in vitro from normal isolated islets, which express the kisspeptin1 receptor Kiss1R. Administration of a Kiss1R antagonist in diabetic Leprdb/db mice potently augments GSIS and reduces glycemia. Our observations indicate in the pathogenesis of T2DM an endocrine mechanism sequentially linking hyperglucagonemia via hepatic kisspeptin1 production to impaired insulin secretion. In addition, our findings suggest Kiss1R antagonism as a therapeutic avenue to improve ß-cell function in T2DM.
Project description:The activity of pancreatic islets’ insulin-producing β-cells is closely regulated by systemic cues and, locally, by adjacent islet hormone-producing “non-β-cells” (namely α-, δ- and γ-cells). Still, it is unclear whether the presence of the non-β-cells is a requirement for accurate insulin secretion. Here, we generated and studied a mouse model in which adult islets are exclusively composed of β-cells, and human pseudoislets containing only primary β-cells. Mice lacking non-β-cells had optimal blood glucose regulation. They exhibited enhanced glucose tolerance, insulin sensitivity and restricted body weight gain under high-fat diet. The insulin secretion dynamics in islets composed of only β-cells was like in intact islets, both in homeostatic conditions and upon extreme insulin demand. Similarly, human β-cell pseudoislets retained the glucose-regulated mitochondrial respiration, insulin secretion and exendin-4 responses of human islets comprising all four cell types. Together, the findings indicate that non-β-cells are dispensable for blood glucose homeostasis and β-cell function. This is particularly relevant in diabetes, where non-β-cells become dysfunctional and worsen the disease’s pathophysiology. These results support efforts aimed at developing diabetes treatments by generating β-like cell clusters devoid of non-β-cells, as for example from human embryonic stem cells and/or by in situ conversion of non-β-cells into insulin producers.
Project description:Hyperinsulinemia often precedes type 2 diabetes but its role in disease progression is unknown. Palmitoylation, a protein modification implicated in regulated exocytosis, is reversed by acyl-protein thioesterase 1 (APT1). We found altered APT1 biology in pancreatic islets from humans with type 2 diabetes, and APT1 knockdown in nondiabetic human islets caused insulin hypersecretion. Chow fed global and islet specific APT1 knockout mice had enhanced glucose tolerance due to islet autonomous increased glucose-stimulated insulin secretion. APT1 deficiency did not affect islet calcium dynamics but prolonged insulin granule fusion. Using palmitoylation proteomics, we identified Scamp1 as an APT1 substrate that localized to insulin secretory granules. Knockdown of Scamp1 caused insulin hypersecretion. APT1 deficient insulinoma cells subjected to nutrient excess had increased apoptosis, and expression of a mutated Scamp1 incapable of being palmitoylated in APT1 deficient cells rescued insulin hypersecretion and nutrient induced apoptosis. Compared to APT1 sufficient controls, high fat fed islet specific APT1 knockout mice and global APT1 deficient db/db mice showed increased -cell failure. These findings suggest that the depalmitoylation enzyme APT1 is regulated in human islets, and that APT1 deficiency causes insulin hypersecretion leading to -cell failure, modeling the evolution of some forms of human type 2 diabetes.
Project description:Pancreatic b-cell failure in type 2 diabetes is associated with functional abnormalities of insulin secretion and deficits of b-cell mass. It’s unclear how one begets the other. We have shown that loss of b-cell mass can be ascribed to impaired FoxO1 function in different models of diabetes. Here we show that ablation of the three FoxO genes (1, 3a, and 4) in mature b-cells results in early-onset, maturity onset diabetes of the young (MODY)-like diabetes, with signature abnormalities of the MODY networks of Hnf4a, Hnf1a, and Pdx1. Transcriptome and functional analyses reveal that FoxO-deficient b-cells are metabolically inflexible, i.e., they preferentially utilize lipids rather than carbohydrates as source of acetyl-CoA for mitochondrial oxidative phosphorylation. This results in impaired ATP generation, and reduced Ca2+-dependent insulin secretion. When viewed in the context of prior data illustrating a role of FoxO1 in b-cell dedifferentiation, the present findings define a seamless FoxO-dependent mechanism linking the twin abnormalities of b-cell function in diabetes. We used microarrays to detail the change of gene expression in pancreatic beta cells after knocking out FoxO1,3 and 4.
Project description:To identify novel disease genes for type 2 diabetes (T2D) we generated two backcross populations of obese and diabetes-susceptible New Zealand Obese (NZO) with the two lean mouse strains 129P2 and C3H/FeJ. Subsequent whole-genome linkage scan revealed 36 novel quantitative trait loci (QTL) for T2D-associated traits. The strongest association with blood glucose (12 cM, LOD 13.3) and plasma insulin (17 cM, LOD 4.8) was detected on proximal chromosome 7 (designated Cdp7prox) exclusively in the NZOxC3H crossbreeding, suggesting that the causal gene is unique for the C3H genome. Introgression of the critical C3H fragment into the genetic NZO background by generating recombinant congenic strains (RCS) and metabolic phenotyping validated the phenotype. For the detection of candidate genes in the critical region (30-46 Mb) we used a combined approach of haplotype- and gene expression analysis to search for C3H-specific gene variants in the pancreatic islets, which appeared as the most likely target tissue for the QTL. Only the two genes Potassium-transporting ATPase alpha chain 1 (Atp4a) and Ribonuclease P protein subunit p29 (Pop4) fulfilled the criteria from our candidate gene approaches. The knockdown of both genes in MIN6 cells led to a decreased glucose-stimulated insulin secretion (GSIS), indicating a stimulating role of both genes in insulin secretion, thereby likely contributing to the phenotype linked to Cdp7prox. In conclusion, our combined- and comparative-cross analysis approach has successfully led to the identification of two novel diabetes susceptibility genes and thus has proven to be a powerful tool for the discovery of novel disease genes.
Project description:To identify effector genes of pancreatic beta cell failure, we integrated analyses of FoxO1 regulated genes with ChIPseq and RNAseq, super-enhancers, and human type 2 diabetes GWAS loci.