The glucagon receptor is required for the adaptive metabolic response to fasting.
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ABSTRACT:
SUBMITTER: Longuet C
PROVIDER: S-EPMC2593715 | biostudies-literature | 2008 Nov
REPOSITORIES: biostudies-literature
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The glucagon receptor is required for the adaptive metabolic response to fasting.
Longuet Christine C Sinclair Elaine M EM Maida Adriano A Baggio Laurie L LL Maziarz Marlena M Charron Maureen J MJ Drucker Daniel J DJ
Cell metabolism 20081101 5
Glucagon receptor (Gcgr) signaling maintains hepatic glucose production during the fasting state; however, the importance of the Gcgr for lipid metabolism is unclear. We show here that fasted Gcgr-/- mice exhibit a significant increase in hepatic triglyceride secretion and fasting increases fatty acid oxidation (FAO) in wild-type (WT) but not in Gcgr-/- mice. Moreover fasting upregulated the expression of FAO-related hepatic mRNA transcripts in Gcgr+/+ but not in Gcgr-/- mice. Exogenous glucagon ...[more]
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Project description:BackgroundThe gut is a major energy consumer, but a comprehensive overview of the adaptive response to fasting is lacking. Gene-expression profiling, pathway analysis, and immunohistochemistry were therefore carried out on mouse small intestine after 0, 12, 24, and 72 hours of fasting.ResultsIntestinal weight declined to 50% of control, but this loss of tissue mass was distributed proportionally among the gut's structural components, so that the microarrays' tissue base remained unaffected. Unsupervised hierarchical clustering of the microarrays revealed that the successive time points separated into distinct branches. Pathway analysis depicted a pronounced, but transient early response that peaked at 12 hours, and a late response that became progressively more pronounced with continued fasting. Early changes in gene expression were compatible with a cellular deficiency in glutamine, and metabolic adaptations directed at glutamine conservation, inhibition of pyruvate oxidation, stimulation of glutamate catabolism via aspartate and phosphoenolpyruvate to lactate, and enhanced fatty-acid oxidation and ketone-body synthesis. In addition, the expression of key genes involved in cell cycling and apoptosis was suppressed. At 24 hours of fasting, many of the early adaptive changes abated. Major changes upon continued fasting implied the production of glucose rather than lactate from carbohydrate backbones, a downregulation of fatty-acid oxidation and a very strong downregulation of the electron-transport chain. Cell cycling and apoptosis remained suppressed.ConclusionThe changes in gene expression indicate that the small intestine rapidly looses mass during fasting to generate lactate or glucose and ketone bodies. Meanwhile, intestinal architecture is maintained by downregulation of cell turnover.
| S-EPMC2148066 | biostudies-literature
Project description:Glucagon is important for maintaining euglycemia during fasting/starvation, and abnormal glucagon secretion is associated with type 1 and type 2 diabetes; however, the mechanisms of hypoglycemia-induced glucagon secretion are poorly understood. We previously demonstrated that global deletion of mitochondrial uncoupling protein 2 (UCP2(-/-)) in mice impaired glucagon secretion from isolated islets. Therefore, UCP2 may contribute to the regulation of hypoglycemia-induced glucagon secretion, which is supported by our current finding that UCP2 expression is increased in nutrient-deprived murine and human islets. Further to this, we created ?-cell-specific UCP2 knockout (UCP2AKO) mice, which we used to demonstrate that blood glucose recovery in response to hypoglycemia is impaired owing to attenuated glucagon secretion. UCP2-deleted ?-cells have higher levels of intracellular reactive oxygen species (ROS) due to enhanced mitochondrial coupling, which translated into defective stimulus/secretion coupling. The effects of UCP2 deletion were mimicked by the UCP2 inhibitor genipin on both murine and human islets and also by application of exogenous ROS, confirming that changes in oxidative status and electrical activity directly reduce glucagon secretion. Therefore, ?-cell UCP2 deletion perturbs the fasting/hypoglycemic glucagon response and shows that UCP2 is necessary for normal ?-cell glucose sensing and the maintenance of euglycemia.
| S-EPMC3636632 | biostudies-literature
Project description:Background The gut is a major energy consumer, but a comprehensive overview of the adaptive response to fasting is lacking. Gene-expression profiling, pathway analysis, and immunohistochemistry were therefore carried out on mouse small intestine after 0, 12, 24, and 72 hours of fasting. Results Intestinal weight declined to 50% of control, but this loss of tissue mass was distributed proportionally among the gut’s structural components, so that the microarrays’ tissue base remained unaffected. Unsupervised hierarchical clustering of the microarrays revealed that the successive time points separated into distinct branches. Pathway analysis depicted a pronounced, but transient early response that peaked at 12 hours, and a late response that became progressively more pronounced with continued fasting. Early changes in gene expression were compatible with a cellular deficiency in glutamine and metabolic adaptations directed at glutamine conservation, inhibition of pyruvate oxidation, stimulation of glutamate catabolism via aspartate and phosphoenolpyruvate to lactate, and enhanced fatty-acid oxidation and ketone-body synthesis. In addition, the expression of key genes involved in cell cycling and apoptosis was suppressed. At 24 hours of fasting, many of the early adaptive changes abated. Major changes upon continued fasting implied the production of glucose rather than lactate from carbohydrate backbones, a downregulation of fatty-acid oxidation and a very strong downregulation of the electron-transport chain. Cell cycling and apoptosis remained suppressed. Conclusion The changes in gene expression indicate that the small intestine rapidly looses mass during fasting to generate lactate or glucose and ketone bodies. Meanwhile, intestinal architecture is maintained by downregulation of cell turnover. Keywords: fasting response, time course
2007-11-12 | GSE8019 | GEO
Project description:Background; The gut is a major energy consumer, but a comprehensive overview of the adaptive response to fasting is lacking. Gene-expression profiling, pathway analysis, and immunohistochemistry were therefore carried out on mouse small intestine after 0, 12, 24, and 72 hours of fasting. Results; Intestinal weight declined to 50% of control, but this loss of tissue mass was distributed proportionally among the gutâs structural components, so that the microarraysâ tissue base remained unaffected. Unsupervised hierarchical clustering of the microarrays revealed that the successive time points separated into distinct branches. Pathway analysis depicted a pronounced, but transient early response that peaked at 12 hours, and a late response that became progressively more pronounced with continued fasting. Early changes in gene expression were compatible with a cellular deficiency in glutamine and metabolic adaptations directed at glutamine conservation, inhibition of pyruvate oxidation, stimulation of glutamate catabolism via aspartate and phosphoenolpyruvate to lactate, and enhanced fatty-acid oxidation and ketone-body synthesis. In addition, the expression of key genes involved in cell cycling and apoptosis was suppressed. At 24 hours of fasting, many of the early adaptive changes abated. Major changes upon continued fasting implied the production of glucose rather than lactate from carbohydrate backbones, a downregulation of fatty-acid oxidation and a very strong downregulation of the electron-transport chain. Cell cycling and apoptosis remained suppressed. Conclusion; The changes in gene expression indicate that the small intestine rapidly looses mass during fasting to generate lactate or glucose and ketone bodies. Meanwhile, intestinal architecture is maintained by downregulation of cell turnover. Experiment Overall Design: Male FVB mice (Charles River, Maastricht, The Netherlands) were housed at 20-22°C, 50-60% humidity, a 12 hours light/dark cycle, and food and water ad libitum. At 6 weeks of age, mice were fasted by removing chow for up to 72 hours before sacrifice (n = 6 per group). The animals were kept in metabolic cages to prevent the consumption of beddings and were kept warm with an infrared lamp starting at 24h. Experiment Overall Design: All animals were sacrificed between 9:00 and 10:00 a.m. by cervical dislocation. The small intestine was removed quickly in such a way that adherent tissue remained behind. It was opened longitudinally, rinsed in phosphate-buffered saline, blotted, weighed, snap-frozen in liquid N2, and stored at -80°C. We opted to use extracts of full-thickness intestine for gene-expression profiling, because the epithelial component of the murine small intestine comprises over 70% of its volume The suitability of this strategy is underscored by a recent microarray study of transporters in the mouse intestine [Anderle P et al., BMC Genomics 2005, 6: 69.]. In addition, isolation of enterocytes is time-consuming and, hence, entails a risk of mRNA degradation, while mucosal scraping harvests villi more efficiently than crypts , whereas many mRNAs are most abundant in the crypts. Experiment Overall Design: Total intestinal RNA was extracted from frozen tissue with guanidiniumthiocyanate [Chomczynski P, Sacchi N: Analytical Biochemistry 1987, 162: 156-159.], followed by cesium-chloride centrifugation [Glisin V, Crkvenjakov R BC: Biochemistry 1974, 13: 2633-2637.] to avoid contamination with mucus. The quality of RNA was assessed with the RNA 6000 Nano LabChip® Kit in an Agilent 2100 bioanalyzer (Agilent Technologies, Palo Alto, USA). Microarray-based quantification of 8 mRNAs with a 1.3-9.2-fold change in expression was validated by qPCR, as described [58]. mRNA concentration was calculated using the LinReg program [59]. In the absence of reverse transcriptase, the signal was < 0.1% of that in its presence for each primer pair (not shown). Experiment Overall Design: Microarrays. The 60-mer Mouse Development (22K) Oligo Microarray G4120A (Agilent) was used. Three arrays per experimental condition were used. Per microarray, 20 μg mRNA, pooled from 2 intestines, was reverse transcribed with Cy3-labelled dCTP (Perkin Elmer, Boston, USA), using the Agilent Fluorescent Direct Label Kit. Cy5-labeled cDNA produced from RNA pooled from 6 fed animals served as the common reference across all arrays (Figure 1A). Hybridized cDNAs were detected with Agilentâs dual-laser microarray slide scanner. The data were retrieved with Agilentâs Feature Extraction software 6.1.1.
2009-05-13 | E-GEOD-8019 | biostudies-arrayexpress
Project description:The liver plays a key role during fasting to maintain energy homeostasis and euglycemia via metabolic processes mainly orchestrated by the insulin/glucagon ratio. We report here that fasting or calorie restriction protocols in C57BL6 mice promote a marked decrease in the hepatic protein levels of G protein-coupled receptor kinase 2 (GRK2), an important negative modulator of both G protein-coupled receptors (GPCRs) and insulin signaling. Such downregulation of GRK2 levels is liver-specific and can be rapidly reversed by refeeding. We find that autophagy, and not the proteasome, represents the main mechanism implicated in fasting-induced GRK2 degradation in the liver in vivo. Reducing GRK2 levels in murine primary hepatocytes facilitates glucagon-induced glucose production and enhances the expression of the key gluconeogenic enzyme Pck1. Conversely, preventing full downregulation of hepatic GRK2 during fasting using adenovirus-driven overexpression of this kinase in the liver leads to glycogen accumulation, decreased glycemia, and hampered glucagon-induced gluconeogenesis, thus preventing a proper and complete adaptation to nutrient deprivation. Overall, our data indicate that physiological fasting-induced downregulation of GRK2 in the liver is key for allowing complete glucagon-mediated responses and efficient metabolic adaptation to fasting in vivo.
| S-EPMC7184883 | biostudies-literature
Project description:As important as the fasting response is for survival, an inability to shut it down once nutrients become available can lead to exacerbated disease and severe wasting. The liver is central to transitions between feeding and fasting states, with glucagon being a key initiator of the hepatic fasting response. However, the precise mechanisms controlling fasting are not well defined. One potential mediator of these transitions is liver kinase B1 (LKB1), given its role in nutrient sensing. Here, we show LKB1 knockout mice have a severe wasting and prolonged fasting phenotype despite increased food intake. By applying RNA sequencing and intravital microscopy, we show that loss of LKB1 leads to a dramatic reprogramming of the hepatic lobule through robust up-regulation of periportal genes and functions. This is likely mediated through the opposing effect that LKB1 has on glucagon pathways and gene expression. Conclusion: Our findings show that LKB1 acts as a brake to the glucagon-mediated fasting response, resulting in "periportalization" of the hepatic lobule and whole-body metabolic inefficiency. These findings reveal a mechanism by which hepatic metabolic compartmentalization is regulated by nutrient-sensing.
| S-EPMC9315124 | biostudies-literature
Project description:BackgroundImpaired secretion of glucagon-like peptide-1 (GLP-1) among Caucasians contributes to reduced incretin effect in type 2 diabetes mellitus (T2DM) patients. However, studies emanating from East Asia suggested preserved GLP-1 levels in pre-diabetes (pre-DM) and T2DM. We aimed to resolve these conflicting findings by investigating GLP-1 levels during oral glucose tolerance test (OGTT) among Malay, Chinese, and Indian ethnicities with normal glucose tolerance (NGT), pre-DM, and T2DM. The association between total GLP-1 levels, insulin resistance, and insulin sensitivity, and GLP-1 predictors were also analyzed.MethodsA total of 174 subjects were divided into NGT (n=58), pre-DM (n=54), and T2DM (n=62). Plasma total GLP-1 concentrations were measured at 0, 30, and 120 min during a 75-g OGTT. Homeostasis model assessment of insulin resistance (HOMA-IR), HOMA of insulin sensitivity (HOMA-IS), and triglyceride-glucose index (TyG) were calculated.ResultsTotal GLP-1 levels at fasting and 30 min were significantly higher in T2DM compared with pre-DM and NGT (27.18 ± 11.56 pmol/L vs. 21.99 ± 10.16 pmol/L vs. 16.24 ± 7.79 pmol/L, p=0.001; and 50.22 ± 18.03 pmol/L vs. 41.05 ± 17.68 pmol/L vs. 31.44 ± 22.59 pmol/L, p<0.001; respectively). Ethnicity was a significant determinant of AUCGLP-1, with the Indians exhibiting higher GLP-1 responses than Chinese and Malays. Indians were the most insulin resistant, whereas Chinese were the most insulin sensitive. The GLP-1 levels were positively correlated with HOMA-IR and TyG but negatively correlated with HOMA-IS. This relationship was evident among Indians who exhibited augmented GLP-1 responses proportionately to their high insulin-resistant states.ConclusionThis is the first study that showed GLP-1 responses are augmented as IR states increase. Fasting and post-OGTT GLP-1 levels are raised in T2DM and pre-DM compared to that in NGT. This raises a possibility of an adaptive compensatory response that has not been reported before. Among the three ethnic groups, the Indians has the highest IR and GLP-1 levels supporting the notion of an adaptive compensatory secretion of GLP-1.
| S-EPMC9501699 | biostudies-literature
Project description:Starvation elicits a complex adaptive response in an organism. No information on transcriptional regulation of metabolic adaptations is available. We, therefore, studied the gene expression profiles of brain, small intestine, kidney, liver, and skeletal muscle in mice that were subjected to 0-72 h of fasting. Functional-category enrichment, text mining, and network analyses were employed to scrutinize the overall adaptation, aiming to identify responsive pathways, processes, and networks, and their regulation. The observed transcriptomics response did not follow the accepted "carbohydrate-lipid-protein" succession of expenditure of energy substrates. Instead, these processes were activated simultaneously in different organs during the entire period. The most prominent changes occurred in lipid and steroid metabolism, especially in the liver and kidney. They were accompanied by suppression of the immune response and cell turnover, particularly in the small intestine, and by increased proteolysis in the muscle. The brain was extremely well protected from the sequels of starvation. 60% of the identified overconnected transcription factors were organ-specific, 6% were common for 4 organs, with nuclear receptors as protagonists, accounting for almost 40% of all transcriptional regulators during fasting. The common transcription factors were PPAR?, HNF4?, GCR?, AR (androgen receptor), SREBP1 and -2, FOXOs, EGR1, c-JUN, c-MYC, SP1, YY1, and ETS1. Our data strongly suggest that the control of metabolism in four metabolically active organs is exerted by transcription factors that are activated by nutrient signals and serves, at least partly, to prevent irreversible brain damage.
| S-EPMC3091239 | biostudies-literature
Project description:The effects of fasting have been studied extensively, predominantly on isolated processes, within a specific organ. No comprehensive study of the adaptations was available for different organs, let alone interrelating them, which left the understanding of the body’s orchestration of fasting response limited. The gene expression profiles of brain, small intestine, kidney, liver and skeletal muscle were therefore studied in mice subjected to short, moderate and prolonged fasting. Functional category enrichment, network, and text-mining analyses were employed to scrutinize the overall adaptive response, aiming to identify responsive pathways, processes and networks, and their regulation. The implicated processes did not follow the accepted carbohydrate-lipid-protein succession of energy substrates expenditure. Instead, they were activated simultaneously in different organs during the whole duration of fasting. The most prominent changes occurred in lipid and steroid metabolism, especially in the liver and kidney, which showed biochemically similar, orchestrated responses. They were accompanied by suppression of the immune response and cell turnover, particularly in the small intestine, tied in with increased proteolysis in the muscle. Enhanced defence against oxidative damage, obvious in all the organs, was the top reaction of the brain, otherwise shown to be extremely well protected from starvation. The major transcription regulators of fasting response in different organs were FoxO transcription factors, AP-1, p53, cMyc, Sp1, EGF and HNF4α. The revealed interorgan interactions between metabolic, inflammatory and cell turnover responses are essential when designing strategies to treat the starvation affected individuals, while stressing the significance of using complimentary bioinformatics tools in the high-throughput data analysis. 6 week-old male FVB mice were fasted for 0, 12, 24, 48 or 72 hours before sacrifice (N = 5 per group). From each mouse total RNA was isolated from five organs - liver, small intestine, kidney, brain, and calf muscle. Five microarrays per experimental condition (five tissues, five timepoints) were performed. We used a common reference design. The single common-reference sample was a pool of equal amounts of RNA from all the samples investigated, including additional samples from 5 mice that were fasted for 48 hours and supplemented with vitamin B complex after 24 and 36 hours of fasting.
2011-03-09 | E-GEOD-24504 | biostudies-arrayexpress
Project description:Under fasting conditions, increases in circulating glucagon maintain glucose balance by promoting hepatic gluconeogenesis. Triggering of the cAMP pathway stimulates gluconeogenic gene expression through the PKA-mediated phosphorylation of the cAMP response element binding (CREB) protein and via the dephosphorylation of the latent cytoplasmic CREB regulated transcriptional coactivator 2 (CRTC2). CREB and CRTC2 activities are increased in insulin resistance, in which they promote hyperglycemia because of constitutive induction of the gluconeogenic program. The extent to which CREB and CRTC2 are coordinately up-regulated in response to glucagon, however, remains unclear. Here we show that, following its activation, CRTC2 enhances CREB phosphorylation through an association with the protein arginine methyltransferase 5 (PRMT5). In turn, PRMT5 was found to stimulate CREB phosphorylation via increases in histone H3 Arg2 methylation that enhanced chromatin accessibility at gluconeogenic promoters. Because depletion of PRMT5 lowers hepatic glucose production and gluconeogenic gene expression, these results demonstrate how a chromatin-modifying enzyme regulates a metabolic program through epigenetic changes that impact the phosphorylation of a transcription factor in response to hormonal stimuli.
| S-EPMC3670393 | biostudies-literature