title: Apposite insulin-like growth factor (IGF) receptor glycosylation is critical to the maintenance of vascular smooth muscle phenotype in the presence of factors promoting osteogenic differentiation and mineralization.
abstract: Vascular calcification is strongly linked with increased morbidity and mortality from cardiovascular disease. Vascular calcification is an active cell-mediated process that involves the differentiation of vascular smooth muscle cells (VSMCs) to an osteoblast-like phenotype. Several inhibitors of this process have been identified, including insulin-like growth factor-I (IGF-I). In this study, we examined the role of the IGF receptor (IGFR) and the importance of IGFR glycosylation in the maintenance of the VSMC phenotype in the face of factors known to promote osteogenic conversion. IGF-I (25 ng/ml) significantly protected VSMCs from β-glycerophosphate-induced osteogenic differentiation (p < 0.005) and mineral deposition (p < 0.01). Mevalonic acid depletion (induced by 100 nm cerivastatin) significantly inhibited these IGF protective effects (p < 0.01). Mevalonic acid depletion impaired IGFR processing, decreased the expression of mature IGFRs at the cell surface, and inhibited the downstream activation of Akt and MAPK. Inhibitors of N-linked glycosylation (tunicamycin, deoxymannojirimycin, and deoxynojirimycin) also markedly attenuated the inhibitory effect of IGF-I on β-glycerophosphate-induced mineralization (p < 0.05) and activation of Akt and MAPK. These results demonstrate that alterations in the glycosylation of the IGFR disrupt the ability of IGF-I to protect against the osteogenic differentiation and mineralization of VSMCs by several interrelated mechanisms: decreased IGFR processing, reduced IGFR cell-surface expression, and reduced downstream signaling via the Akt and MAPK pathways. IGF-I thus occupies a critical position in the maintenance of normal VSMC phenotype and protection from factors known to stimulate vascular calcification.
authors: Imaging, Genomics, and Proteomics Group, School of Cancer and Enabling Sciences, University of Manchester, Oxford Road, Manchester M13 9PY, United Kingdom. kirk.siddals@manchester.ac.uk
authors: Kirk W
authors: KW
authors: Siddals
authors: Justine
authors: J
authors: Allen
authors: Smeeta
authors: S
authors: Sinha
authors: Ann E
authors: AE
authors: Canfield
authors: Philip A
authors: PA
authors: Kalra
authors: J Martin
authors: JM
authors: Gibson
mesh_terms: D017485:1-Deoxynojirimycin / Q000494:pharmacology; D000818:Animals; D000998:Antiviral Agents / Q000494:pharmacology; D001011:Aorta / Q000378:metabolism; D002417:Cattle; D002454:Cell Differentiation; D005994:Glycerophosphates / Q000737:chemistry; D006031:Glycosylation; D006801:Humans; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000494:pharmacology; D020935:MAP Kinase Signaling System; D008798:Mevalonic Acid / Q000378:metabolism; D008954:Models, Biological; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D010012:Osteogenesis; D010641:Phenotype; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D017451:Receptors, Somatomedin / Q000378:metabolism*; D014415:Tunicamycin / Q000494:pharmacology
chemical_list: D000998:Antiviral Agents; D005994:Glycerophosphates; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D017451:Receptors, Somatomedin; D014415:Tunicamycin; D017485:1-Deoxynojirimycin; D017526:Receptor, IGF Type 1; D008798:Mevalonic Acid; C031463:beta-glycerophosphoric acid