Prolonged Glucagon Exposure Rewires Lipid Oxidation and Drives Diabetic Kidney Disease Progression
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ABSTRACT:
PROVIDER: PRJNA1067109 | ENA |
REPOSITORIES: ENA
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Project description:Diabetic kidney disease (DKD) is the leading cause of end-stage kidney disease (ESKD), and few treatment options are available today to prevent the progressive loss of renal function. Tubular abnormalities may precede glomerular pathology early and indicate the functional progression of DKD, however, pathological mechanisms that initiate tubular abnormalities are poorly understood. Here, we found that glucagon receptor (Gcgr) is specifically and highly expressed in proximal tubular cells (PTEC) of kidney. Glucagon injection exacerbated lipid accumulation, glycogen content, inflammation, fibrosis, and renal injury, along with morphology changes on proximal tubules, podocytes, glomerular basement membrane (GBM), and mitochondria in the early phase of DKD mice. Whereas, the specific knockdown or knockout of Gcgr in PTEC of kidney almost completely halted the development of DKD. In contrary to the effect of short-term glucagon stimulation on fatty acid oxidation, long-term glucagon exposure led to glucagon reversal in PTEC, which is characterized by reduced energy production and promoted lipogenesis, and this effect was through the Gcgr-PKA-Creb-mTOR pathway. Accordingly, anti-GCGR antibody treatment greatly blocked the pathogenesis of DKD induced by both type 2 and type 1 diabetes. Thus, our results revealed a novel role of glucagon/GCGR signaling in PTEC lipogenesis and DKD, and Gcgr would be a promising therapeutic drug target for the treatment of DKD.
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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.
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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.
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Project description:Diabetes is characterized by hyperglycemia, loss of functional islet beta cell mass, deficiency of glucose-lowering insulin, and persistent alpha cell secretion of gluconeogenic glucagon. Still, no therapies that target these underlying processes are available. We therefore performed high-throughput screening of 300,000 compounds and extensive medicinal chemistry optimization and here report the discovery of SRI-37330, an orally bioavailable, non-toxic small molecule, which effectively rescued mice from streptozotocin- and obesity-induced (db/db) diabetes. Interestingly, in rat cells and in mouse and human islets, SRI-37330 inhibited expression and signaling of thioredoxin-interacting protein, which we have previously found to be elevated in diabetes and to have detrimental effects on islet function. In addition, SRI-37330 treatment inhibited glucagon secretion and function, reduced hepatic glucose production, and reversed hepatic steatosis. Thus, these studies describe a newly designed chemical compound that, compared to currently available therapies, may provide a distinct and effective approach to treating diabetes.
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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.
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Project description:Appropriate glucagon secretion from pancreatic alpha cells in response to hypoglycemia is an important component of maintaining glucose homeostasis. Dysregulated glucagon secretion leads to the delayed recovery from a hypoglycemic attack in type 1 diabetes patients which can be lethal. Although elucidating the precise mechanism of glucagon secretion in hypoglycemia is warranted, the underlying mechanism remains poorly understood.The present study provides evidence of the role of autophagy in glucagon secretion in hypoglycemia by demonstrating that autophagy regulates adrenergic stimulation of glucagon secretion downstream of beta2 adrenergic receptor. First, from the analyses of T1D human islets and the published database of scRNA-seq of T1D human alpha cells, we described autophagy pathways altered in T1D alpha cells. Second, we generated alpha cell-specific Atg7KO mice (alphaAtg7KO) and clarified that the lack of autophagy in alpha cells impairs the reactive glucagon secretion in acute hypoglycemia. Third, to interrogate the molecular mechanism of autophagy-mediated glucagon regulation, we analyzed top genes downregulated inT1D and T2D alpha cells and found the expression of beta2 adrenergic receptor showed significant down-regulation in T1D alpha cells. We confirmed the decreased expression of beta2 adrenergic receptor in alpha cells of the T1D pancreas section, the islets of alphaAtg7KO mice, and a murine alpha cell line with stable knockdown of Atg7. Furthermore, in vivo and ex vivo studies of alphaAtg7KO mice exhibited that lack of autophagy led to the loss of stimulatory effect of beta2-adrenergic signaling on glucagon secretion. Finally, we established the Atg7 knockdown model in sorted human alpha cells and confirmed the effect of autophagy on the expression of the beta2 adrenergic receptor. Together, our study provides novel insights into the regulatory role of autophagy in glucagon secretion in response to hypoglycemia and provides therapeutic options to achieve stable glycemic control in T1D patients.
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