title: Caffeine modulates phosphorylation of insulin receptor substrate-1 and impairs insulin signal transduction in rat skeletal muscle.
abstract: 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-3β 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-β Tyr(1158/62/63). Furthermore, caffeine enhanced phosphorylation of IRS-1 Ser(307) and an IRS-1 Ser(307) kinase, inhibitor-κB kinase (IKK)-α/β 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 Ca(2+)- and AMPK-independent mechanism in skeletal muscle.
authors.affiliation: Laboratory of Sports and Exercise Medicine, Graduate School of Human and Environmental Studies, Kyoto University, Kyoto, Japan.
authors.forename: Tatsuro
authors.initials: T
authors.lastname: Egawa
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tsuda
authors.forename: Xiao
authors.initials: X
authors.lastname: Ma
authors.forename: Taku
authors.initials: T
authors.lastname: Hamada
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Hayashi
mesh_terms: D000818:Animals; D002110:Caffeine / Q000008:administration & dosage / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D051550:I-kappa B Kinase / Q000378:metabolism; D066298:In Vitro Techniques; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins / Q000737:chemistry / Q000378:metabolism*; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction / Q000187:drug effects*; D014443:Tyrosine / Q000737:chemistry
chemical_list: D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D002110:Caffeine; D014443:Tyrosine; D012694:Serine; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D051550:I-kappa B Kinase