title: The role of insulin-like-growth factor binding protein 2 (IGFBP2) and phosphatase and tensin homologue (PTEN) in the regulation of myoblast differentiation and hypertrophy.
abstract: The complex actions of the insulin-like-growth factor binding proteins (IGFBPs) in skeletal muscle are becoming apparent, with IGFBP2 being implicated in skeletal muscle cell proliferation and differentiation (Ernst et al., 1992; Sharples et al., 2010). Furthermore, PTEN signalling has been linked to IGFBP2 action in other cell types by co-ordinating downstream Akt signalling, a known modulator of myoblast differentiation. The present study therefore aimed to determine the interaction between IGFBP2 and PTEN on myoblast differentiation. It has previously been established that C2C12 cells have high IGFBP2 gene expression upon transfer to low serum media, and that expression reduces rapidly as cells differentiate over 72 h [1]. Wishing to establish a potential role for IGFBP2 in this model, a neutralising IGFBP2 antibody was administered to C2C12 myoblasts upon initiation of differentiation. Myoblasts subsequently displayed reduced morphological differentiation (myotube number), biochemical differentiation (creatine kinase) and myotube hypertrophy (myotube area) with an early reduction in Akt phosphorylation. Knock-down of phosphatase and tensin homologue (PTEN) using siRNA in the absence of the neutralising antibody did not improve differentiation or hypertrophy vs. control conditions, however, in the presence of the neutralising IGFBP2 antibody, differentiation was restored and importantly hypertrophy exceeded that of control levels. Overall, these data suggest that; 1) reduced early availability of IGFBP2 can inhibit myoblast differentiation at later time points, 2) knock-down of PTEN levels can restore myoblast differentiation in the presence of neutralising IGFBP2 antibody, and 3) PTEN inhibition acts as a potent inducer of myotube hypertrophy when the availability of IGFBP2 is reduced in C2C12 myoblasts.
authors.affiliation: Stem Cell, Ageing and Molecular Physiology (SCAMP) Unit, Research Institute for Sport and Exercise Sciences (RISES), School of Sport and Exercise Sciences, Liverpool John Moores University, Tom Reilly Building, Byrom Street, Liverpool, UK. a.p.sharples@googlemail.com
authors.forename: Adam P
authors.initials: AP
authors.lastname: Sharples
authors.forename: Nasser
authors.initials: N
authors.lastname: Al-Shanti
authors.forename: David C
authors.initials: DC
authors.lastname: Hughes
authors.forename: Mark P
authors.initials: MP
authors.lastname: Lewis
authors.forename: Claire E
authors.initials: CE
authors.lastname: Stewart
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002454:Cell Differentiation; D002478:Cells, Cultured; D003402:Creatine Kinase / Q000378:metabolism; D005434:Flow Cytometry; D006984:Hypertrophy / Q000378:metabolism*; D007124:Immunoenzyme Techniques; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000276:immunology / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D051379:Mice; D032448:Myoblasts, Skeletal / Q000166:cytology* / Q000378:metabolism; D051059:PTEN Phosphohydrolase / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D010641:Phenotype; D010766:Phosphorylation; D012333:RNA, Messenger / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D060888:Real-Time Polymerase Chain Reaction; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D018971:Insulin-Like Growth Factor Binding Protein 2; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D003402:Creatine Kinase; D051059:PTEN Phosphohydrolase