Caffeine modulates phosphorylation of insulin receptor substrate-1 and impairs insulin signal transduction in rat skeletal muscle

Egawa T, Tsuda S, Ma X, Hamada T, Hayashi T. Caffeine modulates phosphorylation of insulin receptor substrate-1 and impairs insulin signal transduction in rat skeletal muscle. J Appl Physiol 111: 1629-1636, 2011. First published September 22, 2011; doi:10.1152/japplphysiol.00249.2011.-Caffeine decreases insulin sensitivity and insulin-stimulated glucose transport in skeletal muscle; however, the precise mechanism responsible for this deleterious effect is not understood fully. We investigated the effects of incubation with caffeine on insulin signaling in rat epitrochlearis muscle. Caffeine (>= 1 mM, >= 15 min) suppressed insulin-stimulated insulin receptor substrate (IRS)-1 Tyr(612) phosphorylation in a dose- and time-dependent manner. These responses were associated with inhibition of the insulin-stimulated phosphorylation of phosphatidylinositol 3-kinase (PI3K) Tyr(458), Akt Ser(473), and glycogen synthase kinase-3 beta Ser(9) and with inhibition of insulin-stimulated 3-O-methyl-D-glucose (3MG) transport but not with inhibition of the phosphorylation of insulin receptor-beta Tyr(1158/62/63). Furthermore, caffeine enhanced phosphorylation of IRS-1 Ser(307) and an IRS-1 Ser(307) kinase, inhibitor-kappa B kinase (IKK)-alpha/beta Ser(176/180). Blockade of IKK/IRS-1 Ser(307) by caffeic acid ameliorated the caffeine-induced downregulation of IRS-1 Tyr(612) phosphorylation and 3MG transport. Caffeine also increased the phosphorylation of IRS-1 Ser(789) and an IRS-1 Ser(789) kinase, 5'-AMP-activated protein kinase (AMPK). However, inhibition of IRS-1 Ser(789) and AMPK phosphorylation by dantrolene did not rescue the caffeine-induced downregulation of IRS-1 Tyr(612) phosphorylation or 3MG transport. In addition, caffeine suppressed the phosphorylation of insulin-stimulated IRS-1 Ser(636/639) and upstream kinases, including the mammalian target of rapamycin and p70S6 kinase. Intravenous injection of caffeine at a physiological dose (5 mg/kg) in rats inhibited the phosphorylation of insulin-stimulated IRS-1 Tyr(612) and Akt Ser(473) in epitrochlearis muscle. Our results indicate that caffeine inhibits insulin signaling partly through the IKK/IRS-1 Ser(307) pathway, via a Ca2+- and AMPK-independent mechanism in skeletal muscle.