title: Inhibition of PI-3 kinase/Akt/mTOR, but not calcineurin signaling, reverses insulin-like growth factor I-induced protection against glucose toxicity in cardiomyocyte contractile function.
abstract: Insulin-like growth factor-I (IGF-1) ameliorates cardiac dysfunction in diabetes although the mechanism of action remains poorly understood. This study examined the role of PI-3 kinase/Akt/mammalian target of rapamycin (mTOR) and calcineurin pathways in cardiac effects of IGF-1 against glucose toxicity. Adult rat ventricular myocytes were cultured for 8 h with either normal (NG, 5.5 mM) or high (HG, 25.5 mM) glucose, in the presence or absence of IGF-1 (10-500 nM), the PI-3 kinase/Akt inhibitor LY294002 (10 microM), the mTOR inhibitor rapamycin (20 microM) or the calcineurin inhibitors cyclosporin A (5 microM) or FK506 (10 mg/l). Mechanical properties were evaluated using an IonOptix MyoCam system. HG depressed peak shortening (PS), reduced maximal velocity of shortening/relengthening (+/- dl/dt) and prolongs time-to-90% relengthening (TR90), which were abolished by IGF-1 (100 and 500 nM). Interestingly, the IGF-1-elicited protective effect against HG was nullified by either LY294002 or rapamycin, but not by cyclosporine A or FK506. None of the inhibitors affected cell mechanics. Western blot analysis indicated that HG and IGF-1 stimulated phosphorylation of Akt and mTOR. HG also activated p70s6k and suppressed GSK-3beta phosphorylation. However, the HG-induced alterations in phosphorylation of Akt, mTOR, p70s6k and GSK-3beta were significantly reversed by IGF-1. Protein expression of Akt, mTOR, p70s6k, GSK-3beta, SERCA2a and phospholamban was unaffected by HG, IGF-1 or rapamycin. Rapamycin significantly enhanced Akt phosphorylation whereas it inhibited mTOR phosphorylation. Collectively, our data suggest that IGF-1 may provide cardiac protection against glucose in part through a PI-3 kinase/Akt/mTOR/ p70s6k-dependent and calcineurin-independent pathway.
authors.affiliation: Division of Pharmaceutical Sciences and Center for Cardiovascular Research and Alternative Medicine, University of Wyoming, Laramie, Wyoming 82071, USA.
authors.forename: Shi-Yan
authors.initials: SY
authors.lastname: Li
authors.forename: Cindy X
authors.initials: CX
authors.lastname: Fang
authors.forename: Nicholas S
authors.initials: NS
authors.lastname: Aberle
authors.forename: Bonnie H
authors.initials: BH
authors.lastname: Ren
authors.forename: Asli F
authors.initials: AF
authors.lastname: Ceylan-Isik
authors.forename: Jun
authors.initials: J
authors.lastname: Ren
mesh_terms: D000818:Animals; D065095:Calcineurin Inhibitors; D000252:Calcium-Transporting ATPases / Q000378:metabolism; D002478:Cells, Cultured; D002867:Chromones / Q000494:pharmacology; D016572:Cyclosporine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000009:adverse effects / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D009025:Morpholines / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism; D051381:Rats; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D015398:Signal Transduction / Q000187:drug effects*; D020123:Sirolimus / Q000494:pharmacology; D013268:Stimulation, Chemical; D058570:TOR Serine-Threonine Kinases; D016559:Tacrolimus / Q000494:pharmacology
chemical_list: D065095:Calcineurin Inhibitors; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D000081082:Phosphoinositide-3 Kinase Inhibitors; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D007334:Insulin-Like Growth Factor I; D016572:Cyclosporine; D011494:Protein Kinases; C546845:mTOR protein, rat; D058570:TOR Serine-Threonine Kinases; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000252:Calcium-Transporting ATPases; D005947:Glucose; D020123:Sirolimus; D016559:Tacrolimus