Fermented Tea Improves Glucose Intolerance in Mice by Enhancing Translocation of Glucose Transporter 4 in Skeletal Muscle

The antihyperglycemic effects of tea are well documented. However; the effects of fermented tea on the translocation of glucose transporter 4 (GLUT4), the major glucose transporter for glucose uptake in the postprandial period, in skeletal muscle and the underlying molecular mechanisms are not fully understood. This study investigated the translocation of GLUT4 and its related signaling pathways in skeletal muscle of male ICR mice given fermented tea. Intake of oolong, black, or pu-erh tea for 7 days enhanced GLUT4 translocation to the plasma membrane of skeletal muscle. Each type of fermented tea stimulated the phosphorylation of phosphoinositide 3-kinase (PI3K), Akt/protein kinase B, and AMP-activated protein kinase (AMPK). Fermented tea also increased the protein expression of insulin receptor. These results strongly suggest that fermented tea activates both PI3K/Akt- and AMPK-dependent signaling pathways to induce GLUT4 translocation and increases the expression of insulin receptor to improve glucose intolerance.