Reactive Oxygen Species Play an Essential Role in IGF-I Signaling and IGF-I-Induced Myocyte Hypertrophy in C2C12 Myocytes

Abstract

IGF-I induces skeletal muscle hypertrophy by stimulating protein synthesis and suppressing the protein degradation pathway; the downstream signaling pathways Akt-mammalian target of rapamycin (mTOR)-p70-kDA-S6-kinase (p70S6K), and Forkhead box O1 (FoxO1) play essential roles in this regulation. Reactive oxygen species (ROS) modulate the signaling of various growth factors via redox regulation. However, the role of ROS in IGF-I signaling is not fully understood. In this study, we investigated whether ROS regulate the signaling and biological action of IGF-I in C2C12 myocytes. We found that IGF-I induces ROS in C2C12 myocytes. While treatment with H(2)O(2) significantly enhanced IGF-I-induced phosphorylation of the IGF-I receptor (IGF-IR), IGF-IR phosphorylation was markedly attenuated when cells were treated with antioxidants. The downstream signaling pathway, Akt-mTOR-p70S6K was subsequently down-regulated. Furthermore, the phosphorylation of FoxO1 by IGF-I decreased concomitantly with the restoration of the expression of its target genes, Atrogin-1 and muscle RING finger 1, which are related to muscle atrophy. Nox4 knockdown, which is reportedly to produce ROS in insulin signaling, attenuated IGF-I-induced IGF-IR phosphorylation, indicating that Nox4 is involved in the regulation of IGF-I signaling. Importantly, antioxidant treatments inhibited IGF-I-induced myocyte hypertrophy, demonstrating that ROS are necessary for IGF-I-induced myocyte hypertrophy in vitro. These results indicate that ROS play an essential role in the signaling and biological action of IGF-I in C2C12 myocytes.

Alterations in Redox Homeostasis in the Elite Endurance Athlete

“…Furthermore, RNS and ROS serve as important signalling molecules in mitochondrial biogenesis [6] and glucose transport [7,8], and possibly muscle hypertrophy [9]. Indeed, the modification of ROS metabolism in a number of human exercise studies through the use of pharmaceutical doses of antioxidant vitamins has blunted the expected physiological response to the exercise bout [10] and the adaptation to the exercise stimulus in some [6,8], but not all studies [11][12][13][14].…”

Growth Hormone Prevents the Memory Deficit Caused by Oxidative Stress in Early Neurodegenerative Stage in Rats

“…Ozone inhalation itself caused increases in the IGF-I expression and Akt phosphorylation at 7 and 15 days, probably to prevent cell death caused by oxidative stress in dentate gyrus. Previous studies that shown ROS are capable to activate IGF-I and Akt [22,25,26]. In this sense, the IGF and Akt activation might modulate the cell survival or death in an oxidativestress in a dependent manner [26][27][28][29].…”

(Pro)renin receptor in skeletal muscle is involved in the development of insulin resistance associated with postinfarct heart failure in mice

“…For transient transfection, C2C12 cells were seeded onto six-well polycarbonate plates at a density of 5 ϫ 10 4 cells/well and transfected 6 h later with 50 nM small interfering (si)RNA against mouse NOX2 (sense, 5=-CGGUGACAAUGAGAACGAAtt-3=, antisense, 5=-UUCGUUCUCAUUGUCACCGat-3=) and mouse angiotensinogen (Agt) (sense, 5=-CGCAUGUACAAGAUGCUGAtt-3=, antisense, 5=-UCAGCAUCUUGUACAUGCGga-3=), or a control scrambled siRNA in antibiotic-free medium plus 10% FBS using Lipofectamine RNAiMAX Reagent (Invitrogen, Carlsbad, CA) according to the manufacturer's instructions (15). All siRNAs were purchased from Ambion (Austin, TX).…”