Soy β-conglycinin improves glucose uptake in skeletal muscle and ameliorates hepatic insulin resistance in Goto-Kakizaki rats

Abstract

Although the underlying mechanism is unclear, β-conglycinin (βCG), the major component of soy proteins, regulates blood glucose levels. Here, we hypothesized that consumption of βCG would normalize blood glucose levels by ameliorating insulin resistance and stimulating glucose uptake in skeletal muscles. To test our hypothesis, we investigated the antidiabetic action of βCG in spontaneously diabetic Goto-Kakizaki (GK) rats. Our results revealed that plasma adiponectin levels and adiponectin receptor 1 messenger RNA expression in skeletal muscle were higher in βCG-fed rats than in casein-fed rats. Phosphorylation of adenosine monophosphate-activated protein kinase (AMP kinase) but not phosphatidylinositol-3 kinase was activated in βCG-fed GK rats. Subsequently, βCG increased translocation of glucose transporter 4 to the plasma membrane. Unlike the results in skeletal muscle, the increase in adiponectin receptor 1 did not lead to AMP kinase activation in the liver of βCG-fed rats. The down-regulation of sterol regulatory element-binding factor 1, which is induced by low insulin levels, promoted the increase in hepatic insulin receptor substrate 2 expression. Based on these findings, we concluded that consumption of soy βCG improves glucose uptake in skeletal muscle via AMP kinase activation and ameliorates hepatic insulin resistance and that these actions may help normalize blood glucose levels in GK rats.

Keywords: AMP kinase; AMP-activated protein kinase; ANOVA; Adiponectin; Adipor1; Adipor2; Blood glucose; ELISA; FFA; Fasn; GLUT4; Goto-Kakizaki rat; HOMA-IR; IL-6; Insulin; Insulin resistance; Irs1; Irs2; PI3K; Pparc1α; Pparα; Scd1; Srebf1; Stat3; Tsc1; UCP3; adiponectin receptor 1; adiponectin receptor 2; analysis of variance; enzyme-linked immunosorbent assay; fatty acid synthase; free fatty acid; glucose transporter 4; homeostasis model assessment of insulin resistance; insulin receptor substrate 1; insulin receptor substrate 2; interleukin 6; mRNA; mTORC1; mechanistic target of rapamycin complex 1; messenger RNA; peroxisome proliferator–activated receptor gamma coactivator 1 α; peroxisome proliferator–activated receptor α; phosphatidylinositol-3 kinase; signal transducer and activator of transcription 3; stearoyl-coenzyme A desaturase 1; sterol regulatory element-binding transcription factor 1; tuberous sclerosis 1; uncoupling protein 3; β-Conglycinin; β-conglycinin; βCG.