Targeted Loss of GHR Signaling in Mouse Skeletal Muscle Protects Against High-Fat Diet–Induced Metabolic Deterioration

Division of Endocrinology, Diabetes, and Bone Diseases, Department of Medicine, Mount Sinai School of Medicine, New York, New York, USA.
Diabetes (Impact Factor: 8.1). 01/2012; 61(1):94-103. DOI: 10.2337/db11-0814
Source: PubMed


Growth hormone (GH) exerts diverse tissue-specific metabolic effects that are not revealed by global alteration of GH action. To study the direct metabolic effects of GH in the muscle, we specifically inactivated the growth hormone receptor (ghr) gene in postnatal mouse skeletal muscle using the Cre/loxP system (mGHRKO model). The metabolic state of the mGHRKO mice was characterized under lean and obese states. High-fat diet feeding in the mGHRKO mice was associated with reduced adiposity, improved insulin sensitivity, lower systemic inflammation, decreased muscle and hepatic triglyceride content, and greater energy expenditure compared with control mice. The obese mGHRKO mice also had an increased respiratory exchange ratio, suggesting increased carbohydrate utilization. GH-regulated suppressor of cytokine signaling-2 (socs2) expression was decreased in obese mGHRKO mice. Interestingly, muscles of both lean and obese mGHRKO mice demonstrated a higher interleukin-15 and lower myostatin expression relative to controls, indicating a possible mechanism whereby GHR signaling in muscle could affect liver and adipose tissue function. Thus, our study implicates skeletal muscle GHR signaling in mediating insulin resistance in obesity and, more importantly, reveals a novel role of muscle GHR signaling in facilitating cross-talk between muscle and other metabolic tissues.

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Available from: Gary J Schwartz
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    • "Standard rat fodder [license No. SCXK (Guangdong Province, China) 2003-0002; Guangdong supervison No. 2008D002] was provided by the Medical Laboratory Animal Center of Guangdong Province in China. Pregnant rats subjected to dietary restriction were utilized to establish the SGA rat model [17]. Rats were randomly housed in standard rat cages at a 2∶1 female-to-male ratio. "
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    ABSTRACT: Objective Insulin resistance has been observed in individuals born small for gestational age (SGA) with catch-up growth (CUG), yet the mechanisms involved remain unclear. This study examined the role of GH and insulin signaling crosstalk in insulin resistance of SGA rats with CUG. Design and Methods SGA rats were developed by dietary restriction in pregnant rats. GH receptor inhibition was performed on four-week old CUG-SGA and AGA rats. Phosphorylation of IRS-1, AKT, and ERK, and expression of SOCS3 in the skeletal muscle were determined via immunoblot analysis at baseline and after insulin stimulation in CUG-SGA, NCUG-SGA and AGA groups. Results Compared to AGA controls, phosphorylation of IRS-1 and AKT in response to insulin stimulation in CUG-SGA rats was significantly blunted (P<0.05), and phosphorylation of ERK at baseline was dramatically activated (P<0.05). SOCS3 expression was significantly increased in CUG-SGA compared to AGA (P = 0.001) and NCUG-SGA (P = 0.006) rats, and was significantly suppressed following GHR inhibition (P<0.05). Furthermore, phosphorylation of IRS-1 and AKT in response to insulin stimulation increased after GHR inhibition (P<0.05). Conclusions Insulin resistance in CUG-SGA rats is associated with impairment of IRS-1-PI3K-AKT signaling, which may result from GH signaling-induced up-regulation of SOCS3.
    Full-text · Article · Jun 2014 · PLoS ONE
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    • "We have previously shown that loss of GHR signaling in the skeletal muscle in the mGHRKO mice is associated with a marked protection from the development of HFD-induced insulin resistance, as assessed by several parameters. In addition, the HFD-fed mGHRKO mice had a higher RER in the light phase under conditions of ad libitum feeding, indicative of greater whole-body carbohydrate utilization [8]. This indicated that lipid oxidation is suppressed in the mGHRKO mice, and we explored this hypothesis in this study. "
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    ABSTRACT: Growth hormone (GH) stimulates whole-body lipid oxidation, but its regulation of muscle lipid oxidation is not clearly defined. Mice with a skeletal muscle-specific knockout of the GH receptor (mGHRKO model) are protected from high fat diet (HFD)-induced insulin resistance and display increased whole-body carbohydrate utilization. In this study we used the mGRHKO mice to investigate the role of muscle GHR signaling on lipid oxidation under regular chow (RC)- and HFD- fed conditions, and in response to fasting. Expression of lipid oxidation genes was analyzed by real-time PCR in the muscles of RC- and HFD- fed mice, and after 24 h fasting in the HFD-fed mice. Expression of lipid oxidation genes was lower in the muscles of the mGHRKO mice relative to the controls, irrespective of diet. However, in response to 24 h fasting, the HFD-fed mGHRKO mice displayed up-regulation of lipid oxidation genes similar to the fasted controls. When subjected to treadmill running challenge, the HFD-fed mGHRKO mice demonstrated increased whole-body lipid utilization. Additionally, under fasted conditions, the adipose tissue of the mGHRKO mice displayed increased lipolysis as compared to both the fed mGHRKO as well as the fasted control mice. Our data show that muscle GHR signaling regulates basal lipid oxidation, but not the induction of lipid oxidation in response to fasting. We further demonstrate that muscle GHR signaling is involved in muscle-adipose tissue cross-talk; however the mechanisms mediating this remain to be elucidated.
    Full-text · Article · Sep 2012 · PLoS ONE
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    ABSTRACT: GH receptor (GHR) gene-disrupted mice (GHR-/-) have provided countless discoveries as to the numerous actions of GH. Many of these discoveries highlight the importance of GH in adipose tissue. For example GHR-/- mice are insulin sensitive yet obese with preferential enlargement of the sc adipose depot. GHR-/- mice also have elevated levels of leptin, resistin, and adiponectin, compared with controls leading some to suggest that GH may negatively regulate certain adipokines. To help clarify the role that GH exerts specifically on adipose tissue in vivo, we selectively disrupted GHR in adipose tissue to produce Fat GHR Knockout (FaGHRKO) mice. Surprisingly, FaGHRKOs shared only a few characteristics with global GHR-/- mice. Like the GHR-/- mice, FaGHRKO mice are obese with increased total body fat and increased adipocyte size. However, FaGHRKO mice have increases in all adipose depots with no improvements in measures of glucose homeostasis. Furthermore, resistin and adiponectin levels in FaGHRKO mice are similar to controls (or slightly decreased) unlike the increased levels found in GHR-/- mice, suggesting that GH does not regulate these adipokines directly in adipose tissue in vivo. Other features of FaGHRKO mice include decreased levels of adipsin, a near-normal GH/IGF-1 axis, and minimal changes to a large assortment of circulating factors that were measured such as IGF-binding proteins. In conclusion, specific removal of GHR in adipose tissue is sufficient to increase adipose tissue and decrease circulating adipsin. However, removal of GHR in adipose tissue alone is not sufficient to increase levels of resistin or adiponectin and does not alter glucose metabolism.
    No preview · Article · Jan 2013 · Molecular Endocrinology
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