Dataset Information

Astragalus polysaccharide stimulates glucose uptake in L6 myotubes through AMPK activation and AS160/TBC1D4 phosphorylation.

ABSTRACT:

Aim

To establish the mechanism responsible for the stimulation of glucose uptake by Astragalus polysaccharide (APS), extracted from Astragalus membranaceus Bunge, in L6 myotubes in vitro.

Methods

APS-stimulated glucose uptake in L6 myotubes was measured using the 2-deoxy-[(3)H]-D-glucose method. The adenine nucleotide contents in the cells were measured by HPLC. The phosphorylation of AMP-activated protein kinase (AMPK) and Akt substrate of 160 kDa (AS160) was examined using Western blot analysis. The cells transfected with 4P mutant AS160 (AS160-4P) were constructed using gene transfer approach.

Results

Treatment of L6 myotubes with APS (100-1600 ?g/mL) significantly increased glucose uptake in time- and concentration-dependent manners. The maximal glucose uptake was reached in the cells treated with APS (400 ?g/mL) for 36 h. The APS-stimulated glucose uptake was significantly attenuated by pretreatment with Compound C, a selective AMPK inhibitor or in the cells overexpressing AS160-4P. Treatment of L6 myotubes with APS strongly promoted the activation of AMPK. We further demonstrated that either Ca(2+)/calmodulin-dependent protein kinase kinase ? (CaMKK?) or liver kinase B1 (LKB1) mediated APS-induced activation of AMPK in L6 myotubes, and the increased cellular AMP: ATP ratio was also involved. Treatment of L6 myotubes with APS robustly enhanced the phosphorylation of AS160, which was significantly attenuated by pretreatment with Compound C.

Conclusion

Our results demonstrate that APS stimulates glucose uptake in L6 myotubes through the AMP-AMPK-AS160 pathway, which may contribute to its hypoglycemic effect.

SUBMITTER: Liu J

PROVIDER: S-EPMC4086491 | biostudies-literature | 2013 Jan

REPOSITORIES: biostudies-literature

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Publications

Astragalus polysaccharide stimulates glucose uptake in L6 myotubes through AMPK activation and AS160/TBC1D4 phosphorylation.

Liu Jian J Zhang Jing-fang JF Lu Jin-zhi JZ Zhang De-ling DL Li Ke K Su Ke K Wang Jing J Zhang Ye-min YM Wang Nian N Yang Si-Tu ST Bu Lang L Ou-Yang Jing-ping JP

Acta pharmacologica Sinica 20121029 1

<h4>Aim</h4>To establish the mechanism responsible for the stimulation of glucose uptake by Astragalus polysaccharide (APS), extracted from Astragalus membranaceus Bunge, in L6 myotubes in vitro.<h4>Methods</h4>APS-stimulated glucose uptake in L6 myotubes was measured using the 2-deoxy-[(3)H]-D-glucose method. The adenine nucleotide contents in the cells were measured by HPLC. The phosphorylation of AMP-activated protein kinase (AMPK) and Akt substrate of 160 kDa (AS160) was examined using Weste ...[more]

PMID: 23103623

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Project description:BackgroundType 2 Diabetes mellitus (T2DM) is a major risk factor for cardiovascular disease and associated with poor outcome after myocardial infarction (MI). In T2DM, cardiac metabolic flexibility, i.e. the switch between carbohydrates and lipids as energy source, is disturbed. The RabGTPase-activating protein TBC1D4 represents a crucial regulator of insulin-stimulated glucose uptake in skeletal muscle by controlling glucose transporter GLUT4 translocation. A human loss-of-function mutation in TBC1D4 is associated with impaired glycemic control and elevated T2DM risk. The study's aim was to investigate TBC1D4 function in cardiac substrate metabolism and adaptation to MI.MethodsCardiac glucose metabolism of male Tbc1d4-deficient (D4KO) and wild type (WT) mice was characterized using in vivo [18F]-FDG PET imaging after glucose injection and ex vivo basal/insulin-stimulated [3H]-2-deoxyglucose uptake in left ventricular (LV) papillary muscle. Mice were subjected to cardiac ischemia/reperfusion (I/R). Heart structure and function were analyzed until 3 weeks post-MI using echocardiography, morphometric and ultrastructural analysis of heart sections, complemented by whole heart transcriptome and protein measurements.ResultsTbc1d4-knockout abolished insulin-stimulated glucose uptake in ex vivo LV papillary muscle and in vivo cardiac glucose uptake after glucose injection, accompanied by a marked reduction of GLUT4. Basal cardiac glucose uptake and GLUT1 abundance were not changed compared to WT controls. D4KO mice showed mild impairments in glycemia but normal cardiac function. However, after I/R D4KO mice showed progressively increased LV endsystolic volume and substantially increased infarction area compared to WT controls. Cardiac transcriptome analysis revealed upregulation of the unfolded protein response via ATF4/eIF2α in D4KO mice at baseline. Transmission electron microscopy revealed largely increased extracellular matrix (ECM) area, in line with decreased cardiac expression of matrix metalloproteinases of D4KO mice.ConclusionsTBC1D4 is essential for insulin-stimulated cardiac glucose uptake and metabolic flexibility. Tbc1d4-deficiency results in elevated cardiac endoplasmic reticulum (ER)-stress response, increased deposition of ECM and aggravated cardiac damage following MI. Hence, impaired TBC1D4 signaling contributes to poor outcome after MI.

Dataset Information

Astragalus polysaccharide stimulates glucose uptake in L6 myotubes through AMPK activation and AS160/TBC1D4 phosphorylation.

Aim

Methods

Results

Conclusion

Publications

Astragalus polysaccharide stimulates glucose uptake in L6 myotubes through AMPK activation and AS160/TBC1D4 phosphorylation.

Similar Datasets

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