Project description:Liver-expressed antimicrobial peptide 2 (LEAP2) is an endogenous antagonist and inverse agonist of the growth hormone secretagogue receptor 1a (GHS-R1a), exhibiting opposing effects on cell signaling, feeding, and hormonal secretion compared to ghrelin. However, despite an emerging interest in LEAP2’s physiology and pharmacology, its endocrine regulation remains unclear. Here, we show that plasma LEAP2 levels decrease significantly upon supraphysiological glucagon infusions during pancreatic somatostatin clamps in humans and that a hypercaloric diet and a sedentary lifestyle for two weeks impair this effect. Moreover, in patients with obesity and type 2 diabetes, plasma LEAP2 levels decrease significantly following glucagon infusion. Additionally, we find that postprandial upregulation of LEAP2 in mice is insulin-dependent. In the postprandial state, insulin receptor antagonism offsets the upregulation of hepatic Leap2expression and plasma LEAP2 levels. Finally, we show that insulin and glucagon receptor-expressing hepatocytes are the primary source of hepatic LEAP2 expression. This coincides with a putative enhancer-like signature bound by insulin- and glucagon-regulated transcription factors at the LEAP2 locus in the liver. Collectively, these findings implicate insulin and glucagonin the regulation of LEAP2 and highlight the need for further investigations into the endocrine mechanisms both upstream and downstream of LEAP2.
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: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 analysis identified 122 genes displaying responses to insulin and/or glucagon administration in the liver of WT male mice. Of 122 genes, 75 genes responded in a insulin-selected manner, 29 genes in a glucagon-selected manner, and 18 genes were regulated by both of insulin and glucagon 60 min after stimulation with each hormone. Insulin upregulated expression of 45 genes including Btg2, Ddit4, and Rasgef1b, downregulated 30 genes such as Arrdc3 Rgs16, and Txnip. Glucagon upregulated expression of 15 genes including Chordc1 and Gck, and downregulated expression of 14 genes such as Mt2 and Lcn2. Seventeen genes showed transcriptional upregulation in response to both insulin and glucagon including Hspa1b, Nr4a1 Trp53inp1, and one gene, Orm2, displayed downregulation after stimulation of insulin or glucagon.
Project description:Glucagon is secreted from pancreatic α-cells, and hypersecretion (hyperglucagonemia) contributes to diabetic hyperglycemia. Molecular heterogeneity in hyperglucagonemia is poorly investigated. By screening human plasma by high-resolution-proteomics, we identified several glucagon variants among which proglucagon 1-61 (PG 1-61) appears to be the most abundant form. PG 1-61 was secreted in obese subjects before and as well after gastric bypass surgery with protein and fat as the main drivers for secretion before surgery, but glucose after. Studies in hepatocytes and in β-cells demonstrated that PG 1-61 dose-dependently increased levels of cAMP, through the glucagon receptor, and increased insulin secretion and protein levels of enzymes regulating glycogenolysis and gluconeogenesis. As a consequence, PG 1-61 increased blood glucose and plasma insulin and decreased plasma levels of amino acids in vivo. Glucagon variants, such as PG 1-61, may contribute to glucose regulation by stimulating hepatic glucose production and insulin secretion.
Project description:Glucagon serves as an important regulatory hormone for regulating blood glucose concentrations with tight feedback control with insulin and glucose. There are critical gaps in our understanding of glucagon kinetics, pancreatic α cell function and intra-islet feedback network that are disrupted in type 1 diabetes. This is important for translational research applications of evolving dual-hormone (insulin+glucagon) closed-loop artificial pancreas algorithms and their usage in type 1 diabetes. Thus, it is important to accurately measure glucagon kinetics in vivo and to develop robust models of glucose-insulin-glucagon interplay that could inform next generation of artificial pancreas algorithms.
Project description:Glucagon supports glucose homeostasis by stimulating hepatic gluconeogenesis, in part by promoting the uptake and conversion of amino acids into gluconeogenic precursors. Genetic disruption or pharmacologic inhibition of glucagon signaling results in elevated plasma amino acids, and compensatory glucagon hypersecretion involving expansion of pancreatic α-cell mass. Regulation of pancreatic α- and β-cell growth has drawn a lot of attention because of potential therapeutic implications. Recent findings indicate that hyperaminoacidemia triggers pancreatic α-cell proliferation via an mTOR-dependent pathway. We confirm and extend these findings by demonstrating that glucagon pathway blockade selectively increases expression of the sodium-coupled neutral amino acid transporter Slc38a5 in a subset of highly proliferative α-cells, and that Slc38a5 is critical for the pancreatic response to glucagon pathway blockade; most notably, mice deficient in Slc38a5 exhibit markedly decreased α-cell hyperplasia to glucagon pathway blockade-induced hyperaminoacidemia. These results show that Slc38a5 is a key component of the feedback circuit between glucagon receptor signaling in the liver and amino acid-dependent regulation of pancreatic α-cell mass in mice.
Project description:The phosphorylation state of human HA-tagged-SIK2, adenovirally introduced in murine hepatocytes (C57/BL/6 strain) was analysed in unstimulated and in response to glucagon- or insulin- treated conditions. Background:- LKB1 is a master kinase that regulates metabolism and growth through AMPK and 12 other closely-related kinases. Liver-specific ablation of LKB1 causes increased glucose production in hepatocytes in vitro and hyperglycaemia in fasting mice in vivo. The salt-inducible kinases (SIK1, 2 and 3), members of the AMPK-related kinase family, play a key role as gluconeogenic suppressor downstream of LKB1 in the liver. A selective SIK inhibitor (HG-9-91-01) promotes dephosphorylation of transcriptional co-activators CRTC2/3 resulting in enhanced gluconeogenic gene expression and glucose production in hepatocytes, an effect that is abolished when an HG-9-91-01-insensitive-mutant-SIK is introduced or LKB1 is ablated. Although SIK2 was proposed as a key regulator of insulin-mediated suppression of gluconeogenesis, we provide genetic evidence that liver-specific ablation of SIK2 alone has no effect on gluconeogenesis and insulin does not modulate SIK2 phosphorylation/activity. Collectively, we demonstrate that the LKB1-SIK pathway functions as a key gluconeogenic gatekeeper in the liver.