Black Tea Polyphenols Promotes GLUT4 Translocation through Both PI3K-and AMPK-dependent Pathways in Skeletal Muscle Cells

Abstract

We previously reported that the intake of black tea promotes translocation of the insulin-sensitive glucose transporter (GLUT) 4 in skeletal muscle. In this study, we investigated whether black tea polyphenols (BTP) promote GLUT4 translocation in L6 myotubes. BTP promoted glucose uptake accompanied by GLUT4 translocation in L6 myotubes. As the molecular mechanism, BTP induced the phosphorylation of insulin receptor substrate-1, atypical protein kinase C, Akt Thr308, Akt substrate 160, and AMP-activated protein kinase (AMPK), but did not affect that of Akt Ser473. BTP increased glycogen accumulation through inactivation of glycogen synthase kinase 3β (GSK-3β). Theaflavin, one of the major components in black tea, also promoted the glucose uptake accompanied by GLUT4 translocation observed with BTP in L6 myotubes. These results indicate that BTP activates both PI3K- and AMPK-dependent pathways to promote GLUT4 translocation and glycogen accumulation in skeletal muscle cells. Moreover, theaflavin is one of the active components in BTP.