Distinct growth hormone receptor signaling modes regulate skeletal muscle development and insulin sensitivity in mice.
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ABSTRACT:
SUBMITTER: Mavalli MD
PROVIDER: S-EPMC2964973 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Our previous studies showed that loss-of-function mutation of growth hormone releasing hormone (GHRH) results in increased longevity and enhanced insulin sensitivity in mice. However, the details of improved insulin action and tissue-specific insulin signaling are largely unknown in this healthy-aging mouse model. We conducted hyperinsulinemic-euglycemic clamp to investigate mechanisms underlying enhanced insulin sensitivity in growth hormone (GH) deficient mice. Further, we assessed in vivo tissue-specific insulin activity via activation of PI3K-AKT and MAPK-ERK1/2 cascades using western blot. Clamp results showed that the glucose infusion rate required for maintaining euglycemia was much higher in GHRH-/- mice compared to WT controls. Insulin-mediated glucose production was largely suppressed, whereas glucose uptake in skeletal muscle and brown adipose tissue were significant enhanced in GHRH-/- mice compared to WT controls. Enhanced capacity of insulin-induced activation of the PI3K-AKT and MAPK-ERK1/2 signaling were observed in a tissue-specific manner in GHRH-/- mice. Enhanced systemic insulin sensitivity in long-lived GHRH-/- mice is associated with differential activation of insulin signaling cascades among various organs. Improved action of insulin in the insulin sensitive tissues is likely to mediate the prolonged longevity and healthy-aging effects of GH deficiency in mice.
| S-EPMC7585079 | biostudies-literature
Project description:Growth hormone (GH) participates in the postnatal regulation of skeletal muscle growth, although the mechanism of action is unclear. Here we show that the mass of skeletal muscles lacking GH receptors is reduced because of a decrease in myofiber size with normal myofiber number. GH signaling controls the size of the differentiated myotubes in a cell-autonomous manner while having no effect on size, proliferation, and differentiation of the myoblast precursor cells. The GH hypertrophic action leads to an increased myonuclear number, indicating that GH facilitates fusion of myoblasts with nascent myotubes. NFATc2, a transcription factor regulating this phase of fusion, is required for GH action because GH is unable to induce hypertrophy of NFATc2-/- myotubes. Finally, we provide three lines of evidence suggesting that GH facilitates cell fusion independent of insulin-like growth factor 1 (IGF-1) up-regulation. First, GH does not regulate IGF-1 expression in myotubes; second, GH action is not mediated by a secreted factor in conditioned medium; third, GH and IGF-1 hypertrophic effects are additive and rely on different signaling pathways. Taken together, these data unravel a specific function of GH in the control of cell fusion, an essential process for muscle growth.
| S-EPMC1456062 | biostudies-literature
Project description:Skeletal muscle insulin resistance is a key component of the etiology of type 2 diabetes. Caloric restriction (CR) enhances the sensitivity of skeletal muscle to insulin. However, the molecular signals within skeletal muscle linking CR to improved insulin action remain largely unknown. Recently, the mammalian ortholog of Sir2, sirtuin 1 (Sirt1), has been identified as a potential transducer of perturbations in cellular energy flux into subsequent metabolic adaptations, including modulation of skeletal muscle insulin action. Here, we have demonstrated that CR increases Sirt1 deacetylase activity in skeletal muscle in mice, in parallel with enhanced insulin-stimulated phosphoinositide 3-kinase (PI3K) signaling and glucose uptake. These adaptations in skeletal muscle insulin action were completely abrogated in mice lacking Sirt1 deacetylase activity. Mechanistically, Sirt1 was found to be required for the deacetylation and inactivation of the transcription factor Stat3 during CR, which resulted in decreased gene and protein expression of the p55?/p50? subunits of PI3K, thereby promoting more efficient PI3K signaling during insulin stimulation. Thus, these data demonstrate that Sirt1 is an integral signaling node in skeletal muscle linking CR to improved insulin action, primarily via modulation of PI3K signaling.
| S-EPMC3204844 | biostudies-other
Project description:Aims/hypothesisSkeletal muscle accounts for >80% of insulin-stimulated glucose uptake; dysfunction of this process underlies insulin resistance and type 2 diabetes. Insulin sensitivity is impaired in mice deficient in the double C2 domain β (DOC2B) protein, while whole-body overexpression of DOC2B enhances insulin sensitivity. Whether insulin sensitivity in the skeletal muscle is affected directly by DOC2B or is secondary to an effect on other tissues is unknown; the underlying molecular mechanisms also remain unclear.MethodsHuman skeletal muscle samples from non-diabetic or type 2 diabetic donors were evaluated for loss of DOC2B during diabetes development. For in vivo analysis, new doxycycline-inducible skeletal-muscle-specific Doc2b-overexpressing mice fed standard or high-fat diets were evaluated for insulin and glucose tolerance, and insulin-stimulated GLUT4 accumulation at the plasma membrane (PM). For in vitro analyses, a DOC2B-overexpressing L6-GLUT4-myc myoblast/myotube culture system was coupled with an insulin resistance paradigm. Biochemical and molecular biology methods such as site-directed mutagenesis, co-immunoprecipitation and mass spectrometry were used to identify the molecular mechanisms linking insulin stimulation to DOC2B.ResultsWe identified loss of DOC2B (55% reduction in RNA and 40% reduction in protein) in the skeletal muscle of human donors with type 2 diabetes. Furthermore, inducible enrichment of DOC2B in skeletal muscle of transgenic mice enhanced whole-body glucose tolerance (AUC decreased by 25% for female mice) and peripheral insulin sensitivity (area over the curve increased by 20% and 26% for female and male mice, respectively) in vivo, underpinned by enhanced insulin-stimulated GLUT4 accumulation at the PM. Moreover, DOC2B enrichment in skeletal muscle protected mice from high-fat-diet-induced peripheral insulin resistance, despite the persistence of obesity. In L6-GLUT4-myc myoblasts, DOC2B enrichment was sufficient to preserve normal insulin-stimulated GLUT4 accumulation at the PM in cells exposed to diabetogenic stimuli. We further identified that DOC2B is phosphorylated on insulin stimulation, enhancing its interaction with a microtubule motor protein, kinesin light chain 1 (KLC1). Mutation of Y301 in DOC2B blocked the insulin-stimulated phosphorylation of DOC2B and interaction with KLC1, and it blunted the ability of DOC2B to enhance insulin-stimulated GLUT4 accumulation at the PM.Conclusions/interpretationThese results suggest that DOC2B collaborates with KLC1 to regulate insulin-stimulated GLUT4 accumulation at the PM and regulates insulin sensitivity. Our observation provides a basis for pursuing DOC2B as a novel drug target in the muscle to prevent/treat type 2 diabetes.
| S-EPMC6451670 | biostudies-literature
Project description:Downregulation of endothelial Sirtuin1 (Sirt1) in insulin resistant states contributes to vascular dysfunction. Furthermore, Sirt1 deficiency in skeletal myocytes promotes insulin resistance. Here, we show that deletion of endothelial Sirt1, while impairing endothelial function, paradoxically improves skeletal muscle insulin sensitivity. Compared to wild-type mice, male mice lacking endothelial Sirt1 (E-Sirt1-KO) preferentially utilize glucose over fat, and have higher insulin sensitivity, glucose uptake, and Akt signaling in fast-twitch skeletal muscle. Enhanced insulin sensitivity of E-Sirt1-KO mice is transferrable to wild-type mice via the systemic circulation. Endothelial Sirt1 deficiency, by inhibiting autophagy and activating nuclear factor-kappa B signaling, augments expression and secretion of thymosin beta-4 (Tβ4) that promotes insulin signaling in skeletal myotubes. Thus, unlike in skeletal myocytes, Sirt1 deficiency in the endothelium promotes glucose homeostasis by stimulating skeletal muscle insulin sensitivity through a blood-borne mechanism, and augmented secretion of Tβ4 by Sirt1-deficient endothelial cells boosts insulin signaling in skeletal muscle cells.
| S-EPMC10495425 | biostudies-literature
Project description:ObjectiveSkeletal muscle AMP-activated protein kinase (AMPK) is important for regulating glucose homeostasis, mitochondrial content and exercise capacity. R419 is a mitochondrial complex-I inhibitor that has recently been shown to acutely activate AMPK in myotubes. Our main objective was to examine whether R419 treatment improves insulin sensitivity and exercise capacity in obese insulin resistant mice and whether skeletal muscle AMPK was important for mediating potential effects.MethodsGlucose homeostasis, insulin sensitivity, exercise capacity, and electron transport chain content/activity were examined in wildtype (WT) and AMPK β1β2 muscle-specific null (AMPK-MKO) mice fed a high-fat diet (HFD) with or without R419 supplementation.ResultsThere was no change in weight gain, adiposity, glucose tolerance or insulin sensitivity between HFD-fed WT and AMPK-MKO mice. In both HFD-fed WT and AMPK-MKO mice, R419 enhanced insulin tolerance, insulin-stimulated glucose disposal, skeletal muscle 2-deoxyglucose uptake, Akt phosphorylation and glucose transporter 4 (GLUT4) content independently of alterations in body mass. In WT, but not AMPK-MKO mice, R419 improved treadmill running capacity. Treatment with R419 increased muscle electron transport chain content and activity in WT mice; effects which were blunted in AMPK-MKO mice.ConclusionsTreatment of obese mice with R419 improved skeletal muscle insulin sensitivity through a mechanism that is independent of skeletal muscle AMPK. R419 also increases exercise capacity and improves mitochondrial function in obese WT mice; effects that are diminished in the absence of skeletal muscle AMPK. These findings suggest that R419 may be a promising therapy for improving whole-body glucose homeostasis and exercise capacity.
| S-EPMC4563030 | biostudies-literature
Project description:Aims/hypothesisHomozygous staggerer (sg/sg) mice, which have decreased and dysfunctional Ror? (also known as Rora) expression in all tissues, display a lean and dyslipidaemic phenotype. They are also resistant to (high fat) diet-induced obesity. We explored whether retinoic acid receptor-related orphan receptor (ROR) ? action in skeletal muscle was involved in the regulation of glucose metabolism.MethodsWe used a three-armed genomic approach, including expression profiling, ingenuity analysis and quantitative PCR validation to identify the signalling pathway(s) in skeletal muscle that are perturbed in sg/sg mice. Moreover, western analysis, functional insulin and glucose tolerance tests, and ex vivo glucose uptake assays were used to phenotypically characterise the impact of aberrant v-AKT murine thymoma viral oncogene homologue (AKT) signalling.ResultsHomozygous and heterozygous (sg/sg and sg/+) animals exhibited decreased fasting blood glucose levels, mildly improved glucose tolerance and increased insulin sensitivity. Illumina expression profiling and bioinformatic analysis indicated the involvement of ROR? in metabolic disease and phosphatidylinositol 3-kinase-AKT signalling. Quantitative PCR and western analysis validated increased AKT2 (mRNA and protein) and phosphorylation in sg/sg mice in the basal state. This was associated with increased expression of Tbc1d1 and Glut4 (also known as Slc2a4) mRNA and protein. Finally, in agreement with the phenotype, we observed increased (absolute) levels of AKT and phosphorylated AKT (in the basal and insulin stimulated states), and of (ex vivo) glucose uptake in skeletal muscle from sg/sg mice relative to wild-type littermates.Conclusions/interpretationWe propose that Ror? plays an important role in regulation of the AKT2 signalling cascade, which controls glucose uptake in skeletal muscle.
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Project description:Both glucose and free fatty acids (FFAs) are used as fuel sources for energy production in a living organism. Compelling evidence supports a role for excess fatty acids synthesized in intramuscular space or dietary intermediates in the regulation of skeletal muscle function. Excess FFA and lipid droplets leads to intramuscular accumulation of lipid intermediates. The resulting downregulation of the insulin signaling cascade prevents the translocation of glucose transporter to the plasma membrane and glucose uptake into skeletal muscle, leading to metabolic disorders such as type 2 diabetes. The mechanisms underlining metabolic dysfunction in skeletal muscle include accumulation of intracellular lipid derivatives from elevated plasma FFAs. This paper provides a review of the molecular mechanisms underlying insulin-related signaling pathways after excess accumulation of lipids.
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Project description:Protein kinase C (PKC)? has been shown to be increased in liver in obesity and plays an important role in the development of hepatic insulin resistance in both mice and humans. In the current study, we explored the role of PKC? in skeletal muscle in the control of insulin sensitivity and glucose metabolism by generating mice in which PKC? was deleted specifically in muscle using Cre-lox recombination. Deletion of PKC? in muscle improved insulin signaling in young mice, especially at low insulin doses; however, this did not change glucose tolerance or insulin tolerance tests done with pharmacological levels of insulin. Likewise, in young mice, muscle-specific deletion of PKC? did not rescue high-fat diet-induced insulin resistance or glucose intolerance. However, with an increase in age, PKC? levels in muscle increased, and by 6 to 7 months of age, muscle-specific deletion of PKC? improved whole-body insulin sensitivity and muscle insulin resistance and by 15 months of age improved the age-related decline in whole-body glucose tolerance. At 15 months of age, M-PKC?KO mice also exhibited decreased metabolic rate and lower levels of some proteins of the OXPHOS complex suggesting a role for PKC? in the regulation of mitochondrial mass at older age. These data indicate an important role of PKC? in the regulation of insulin sensitivity and mitochondrial homeostasis in skeletal muscle with aging.
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Project description:The ADAMTS9 rs4607103 C allele is one of the few gene variants proposed to increase the risk of type 2 diabetes through an impairment of insulin sensitivity. We show that the variant is associated with increased expression of the secreted ADAMTS9 and decreased insulin sensitivity and signaling in human skeletal muscle. In line with this, mice lacking Adamts9 selectively in skeletal muscle have improved insulin sensitivity. The molecular link between ADAMTS9 and insulin signaling was characterized further in a model where ADAMTS9 was overexpressed in skeletal muscle. This selective overexpression resulted in decreased insulin signaling presumably mediated through alterations of the integrin ?1 signaling pathway and disruption of the intracellular cytoskeletal organization. Furthermore, this led to impaired mitochondrial function in mouse muscle-an observation found to be of translational character because humans carrying the ADAMTS9 risk allele have decreased expression of mitochondrial markers. Finally, we found that the link between ADAMTS9 overexpression and impaired insulin signaling could be due to accumulation of harmful lipid intermediates. Our findings contribute to the understanding of the molecular mechanisms underlying insulin resistance and type 2 diabetes and point to inhibition of ADAMTS9 as a potential novel mode of treating insulin resistance.
| S-EPMC6385758 | biostudies-literature