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Increased systemic glucose tolerance with increased muscle glucose uptake in transgenic mice overexpressing RXR? in skeletal muscle.

ABSTRACT: BACKGROUND: Retinoid X receptor (RXR) ? is a nuclear receptor-type transcription factor expressed mostly in skeletal muscle, and regulated by nutritional conditions. Previously, we established transgenic mice overexpressing RXR? in skeletal muscle (RXR? mice), which showed lower blood glucose than the control mice. Here we investigated their glucose metabolism. METHODOLOGY/PRINCIPAL FINDINGS: RXR? mice were subjected to glucose and insulin tolerance tests, and glucose transporter expression levels, hyperinsulinemic-euglycemic clamp and glucose uptake were analyzed. Microarray and bioinformatics analyses were done. The glucose tolerance test revealed higher glucose disposal in RXR? mice than in control mice, but insulin tolerance test revealed no difference in the insulin-induced hypoglycemic response. In the hyperinsulinemic-euglycemic clamp study, the basal glucose disposal rate was higher in RXR? mice than in control mice, indicating an insulin-independent increase in glucose uptake. There was no difference in the rate of glucose infusion needed to maintain euglycemia (glucose infusion rate) between the RXR? and control mice, which is consistent with the result of the insulin tolerance test. Skeletal muscle from RXR? mice showed increased Glut1 expression, with increased glucose uptake, in an insulin-independent manner. Moreover, we performed in vivo luciferase reporter analysis using Glut1 promoter (Glut1-Luc). Combination of RXR? and PPAR? resulted in an increase in Glut1-Luc activity in skeletal muscle in vivo. Microarray data showed that RXR? overexpression increased a diverse set of genes, including glucose metabolism genes, whose promoter contained putative PPAR-binding motifs. CONCLUSIONS/SIGNIFICANCE: Systemic glucose metabolism was increased in transgenic mice overexpressing RXR?. The enhanced glucose tolerance in RXR? mice may be mediated at least in part by increased Glut1 in skeletal muscle. These results show the importance of skeletal muscle gene regulation in systemic glucose metabolism. Increasing RXR? expression may be a novel therapeutic strategy against type 2 diabetes.

SUBMITTER: Sugita S

PROVIDER: S-EPMC3105070 | biostudies-literature | 2011

REPOSITORIES: biostudies-literature

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Increased systemic glucose tolerance with increased muscle glucose uptake in transgenic mice overexpressing RXRγ in skeletal muscle.

Sugita Satoshi S Kamei Yasutomi Y Akaike Fumiko F Suganami Takayoshi T Kanai Sayaka S Hattori Maki M Manabe Yasuko Y Fujii Nobuharu N Takai-Igarashi Takako T Tadaishi Miki M Oka Jun-ichiro J Aburatani Hiroyuki H Yamada Tetsuya T Katagiri Hideki H Kakehi Saori S Tamura Yoshifumi Y Kubo Hideo H Nishida Kenichi K Miura Shinji S Ezaki Osamu O Ogawa Yoshihiro Y

PloS one 20110531 5

<h4>Background</h4>Retinoid X receptor (RXR) γ is a nuclear receptor-type transcription factor expressed mostly in skeletal muscle, and regulated by nutritional conditions. Previously, we established transgenic mice overexpressing RXRγ in skeletal muscle (RXRγ mice), which showed lower blood glucose than the control mice. Here we investigated their glucose metabolism.<h4>Methodology/principal findings</h4>RXRγ mice were subjected to glucose and insulin tolerance tests, and glucose transporter ex ...[more]

PMID: 21655215

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Project description:ObjectiveAcute administration of the main protein component of high-density lipoprotein, apolipoprotein A-I (ApoA-1), improves glucose uptake in skeletal muscle. The molecular mechanisms mediating this are not known, but in muscle cell cultures, ApoA-1 failed to increase glucose uptake when infected with a dominant-negative AMP-activated protein kinase (AMPK) virus. We therefore investigated whether AMPK is necessary for ApoA-1-stimulated glucose uptake in intact heart and skeletal muscle in vivo.MethodsThe effect of injection with recombinant human ApoA-1 (rApoA-1) on glucose tolerance, glucose-stimulated insulin secretion, and glucose uptake into skeletal and heart muscle with and without block of insulin secretion by injection of epinephrine (0.1 mg/kg) and propranolol (5 mg/kg), were investigated in 8 weeks high-fat diet-fed (60E%) wild-type and AMPKα2 kinase-dead mice in the overnight-fasted state. In addition, the effect of rApoA-1 on glucose uptake in isolated skeletal muscle ex vivo was studied.ResultsrApoA-1 lowered plasma glucose concentration by 1.7 mmol/l within 3 h (6.1 vs 4.4 mmol/l; p < 0.001). Three hours after rApoA-1 injection, glucose tolerance during a 40-min glucose tolerance test (GTT) was improved compared to control (area under the curve (AUC) reduced by 45%, p < 0.001). This was accompanied by an increased glucose clearance into skeletal (+110%; p < 0.001) and heart muscle (+100%; p < 0.001) and an increase in glucose-stimulated insulin secretion 20 min after glucose injection (+180%; p < 0.001). When insulin secretion was blocked during a GTT, rApoA-1 still enhanced glucose tolerance (AUC lowered by 20% compared to control; p < 0.001) and increased glucose clearance into skeletal (+50%; p < 0.05) and heart muscle (+270%; p < 0.001). These improvements occurred to a similar extent in both wild-type and AMPKα2 kinase-dead mice and thus independently of AMPKα2 activity in skeletal- and heart muscle. Interestingly, rApoA-1 failed to increase glucose uptake in isolated skeletal muscles ex vivo.ConclusionsIn conclusion, ApoA-1 stimulates in vivo glucose disposal into skeletal and heart muscle independently of AMPKα2. The observation that ApoA-1 fails to increase glucose uptake in isolated muscle ex vivo suggests that additional systemic effects are required.

Dataset Information

Increased systemic glucose tolerance with increased muscle glucose uptake in transgenic mice overexpressing RXR? in skeletal muscle.

Publications

Increased systemic glucose tolerance with increased muscle glucose uptake in transgenic mice overexpressing RXRγ in skeletal muscle.

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