Project description:Glucagon receptor deficient liver during postnatal development: fig S5a-S5c in Solloway et al. livers from ko and wt GCGR mice at various developmental stages
Project description:Blockade of the glucagon receptor (GCGR) has been shown to improve glycemic control. However, this therapeutic approach also brings side effects, such as α-cell hyperplasia and hyperglucagonemia, and the mechanisms underlying these side effects remain elusive. Here, we conduct single-cell transcriptomic sequencing of islets from male GCGR knockout (GCGR-KO) mice. Our analysis confirms the elevated expression of Gcg in GCGR-KO mice, along with enhanced glucagon secretion at single-cell level. Notably, Vgf (nerve growth factor inducible) is specifically upregulated in α cells of GCGR-KO mice. Inhibition of VGF impairs the formation of glucagon immature secretory granules and compromises glucagon maturation, lead to reduced α-cell hypersecretion of glucagon. We further demonstrate that activation of both mTOR-STAT3 and ERK-CREB pathways, induced by elevated circulation amino acids, is responsible for upregulation of Vgf and Gcg expression following glucagon receptor blockade. Thus, our findings elucidate a previously unappreciated molecular mechanism underlying hyperglucagonemia in GCGR blockade.
Project description:Gene expression of liver tissue from db/db untreated (6x replicates) and db/db treated with 5mg/kg of 3c7.v44 mAb (6x replicates). Anti-GCGR antibody treatment in db/db mice: fig 2b in Solloway et al.
Project description:Glucagon receptor (GCGR) is a potential target for diabetes therapy. Several emerging GCGR antagonism-based therapies are under pre-clinical and clinical development. However, the GCGR antagonism as well as GCGR deficient animal accompanied with α-cell hyperplasia and hyperglucagonemia, which may limit the application of GCGR antagonism. To better understand the physiological changes in the α cells during the GCGR disruption, we performed the single cell sequencing of α cells isolated from control and gcgr-/- zebrafish. We found that α cells in gcgr-/- zebrafish dramatically increased glucagon (both gcga and gcgb) expression, we also found that several transcriptional factors that regulate glucagon expression were also increased. Based on the sequencing data, we further experimentally confirmed that gcgr-/- up-regulated glucagon mRNA level by in situ hybridization, and the gcgr-/- increased glucagon promoter activity indicated by reporter line Tg(gcga: GFP). Moreover, our results also revealed that α cells increased glucagon granule population and glucagon level in gcgr-/- zebrafish. These data suggested that hyperglucagonemia in the organism of GCGR antagonism not only contributed by the α-cell hyperplasia but also contributed by the increased glucagon expression and secretion from α cells. Our study provided more comprehensive understanding of physiological changes of α-cell during the GCGR disruption.
Project description:Co-agonists at the glucagon-like peptide-1/glucagon receptors (GLP1R/GCGR) show promise as treatments for metabolic dysfunction-associated steatotic liver disease (MASLD). Unlike GLP1, glucagon directly acts on the liver to reduce fat content. To date most metabolic studies have looked at heavily GLP1R-biased co-agonists and have not distinguished weight-loss versus weight loss-independent effects. We demonstrate that 24 days’ treatment with Dicretin, a GLP1/GCGR co-agonist with high potency at the GCGR, in mice with hepatic steatosis secondary to diet-induced obesity leads to superior reduction of hepatic lipid content when compared to Semaglutide or equivalent weight loss by calorie restriction. Hepatic transcriptomic and metabolomic profiling demonstrated many changes that were unique to Dicretin-treated mice: some known targets of glucagon signalling and others with as yet unclear physiological significance. Our study supports the development of GLP1/GCGR co-agonists for treatment of MASLD and related conditions.
Project description:Glucagon and glucagon-like peptide-1 (GLP-1) are hormones involved in energy homeostasis. GLP-1 receptor (GLP-1R) agonism reduces food intake and delays gastric emptying, and glucagon receptor (GCGR) agonism increases energy expenditure by thermogenesis. BI 456906 is a subcutaneous, once-weekly injectable dual GLP-1R/GCGR agonist in development for the treatment of obesity or non-alcoholic steatohepatitis. Here we show that BI 456906 is a potent dual agonist with an extended half-life in human plasma. Key GLP-1R-mediated mechanisms of reduced food intake, delayed gastric emptying and improved glucose tolerance were confirmed in GLP-1R knockout mice. GCGR activity was confirmed by reduced plasma amino acids, increased hepatic expression of nicotinamide N-methyltransferase and increased energy expenditure. BI 456906 produced greater bodyweight reductions than maximally efficacious semaglutide doses and modulated gene expression, including genes involved in amino acid metabolism. BI 456906 is a potent dual agonist that produces bodyweight-lowering effects through both GLP-1R and GCGR agonism.
Project description:Glucagon, an essential regulator of glucose and lipid metabolism, also promotes weight loss, in part through potentiation of fibroblast-growth factor 21 (FGF21) secretion. However, FGF21 is only a partial mediator of metabolic actions ensuing from GcgR-activation, prompting us to search for additional pathways. Intriguingly, chronic GcgR agonism increases plasma bile acid levels. We hypothesized that GcgR agonism regulates energy metabolism, at least in part, through farnesoid X receptor (FXR). To test this hypothesis, we studied whole body and liver-specific FXR knockout (FXR∆liver) mice. Chronic GcgR agonist (IUB288) administration in diet-induced obese (DIO) Gcgr, Fgf21 and Fxr whole body or liver-specific knockout (∆liver) mice failed to reduce body weight (BW) when compared to wildtype (WT) mice. IUB288 increased energy expenditure and respiration in DIO WT mice, but not FXR∆liver mice. GcgR agonism increased [14C]-palmitate oxidation in hepatocytes isolated from WT mice in a dose-dependent manner, an effect blunted in hepatocytes from FXR∆liver mice. Our data clearly demonstrate that control of whole body energy expenditure by GcgR agonism requires intact FXR signaling in the liver. This heretofore-unappreciated aspect of glucagon biology has implications for the use of GcgR agonism in the therapy of metabolic disorders.