title: Chronic treatment with insulin-like growth factor I enhances myocyte contraction by upregulation of Akt-SERCA2a signaling pathway.
abstract: Chronic treatment with insulin-like growth factor I (IGF-I) improves contractile function in congestive heart failure and ischemic cardiomyopathy. The present study investigated the effect of chronic treatment with IGF-I on intrinsic myocyte function and the role of the phosphatidylinositol (PI)3-kinase-Akt-sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA)2a signaling cascade in these responses. Myocytes were isolated from 23 adult rats and cultured with and without IGF-I (10(-6) M). After 48 h of treatment, myocyte function was evaluated. IGF-I increased contractile function (percent contraction, 7.7 +/- 0.3% vs. 4.5 +/- 0.3%; P < 0.01) and accelerated relaxation time (time for 70% relengthening, 81 +/- 4 vs. 106 +/- 5 ms; P < 0.05) compared with untreated myocytes [control (Con)]. The enhanced function was associated with an increase in Ca(2+) transients assessed by fura-2 (340/380 nm; IGF-I, 0.42 +/- 0.02 vs. Con, 0.25 +/- 0.01; P < 0.01). The PI3-kinase inhibitor LY-249002 (10(-9) M) abolished the enhanced function caused by IGF-I. IGF-I increased both Akt and SERCA2a protein levels 2.5- and 4.8-fold, respectively, compared with those of Con (P < 0.01); neither phospholamban nor calsequestrin was affected. To evaluate whether the SERCA2a protein was directly mediated by Akt-SERCA2a signaling, IGF-I-induced changes in the SERCA2a protein were compared in myocytes transfected with adenovirus harboring either constitutively active Akt [multiplicity of infection (MOI), 15] or dominant negative Akt (dnAkt; MOI, 15). The ability of IGF-I to upregulate the SERCA2a protein in myocytes transfected with active Akt was absent in dnAkt myocytes. Taken together, our findings indicate that chronic treatment with IGF-I enhances intrinsic myocyte function and that this effect is due to an enhancement in intracellular Ca(2+) handling, secondary to the activation of the PI3-kinase-Akt-SERCA2a signaling cascade.
authors.affiliation: Section of Cardiology, Advocate Illinois Masonic Medical Center, Chicago, IL 60657, USA. kimso@uic.edu
authors.forename: Song-Jung
authors.initials: SJ
authors.lastname: Kim
authors.forename: Maha
authors.initials: M
authors.lastname: Abdellatif
authors.forename: Sharat
authors.initials: S
authors.lastname: Koul
authors.forename: George J
authors.initials: GJ
authors.lastname: Crystal
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects*; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002155:Calsequestrin; D002316:Cardiotonic Agents / Q000494:pharmacology*; D002352:Carrier Proteins / Q000378:metabolism; D002478:Cells, Cultured; D005822:Genetic Vectors; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D009200:Myocardial Contraction / Q000187:drug effects*; D032383:Myocytes, Cardiac / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases / Q000378:metabolism*; D014162:Transfection; D015854:Up-Regulation; D000099211:Phospholamban
chemical_list: D002135:Calcium-Binding Proteins; D002155:Calsequestrin; D002316:Cardiotonic Agents; D002352:Carrier Proteins; D007334:Insulin-Like Growth Factor I; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D051057:Proto-Oncogene Proteins c-akt; D053498:Sarcoplasmic Reticulum Calcium-Transporting ATPases; D000099211:Phospholamban; C506948:Atp2a2 protein, rat; C057137:Casq1 protein, rat