title: Increase in tendon protein synthesis in response to insulin-like growth factor-I is preserved in elderly men.
abstract: Insulin-like growth factor-I (IGF-I) is known to be an anabolic factor in tendon, and the systemic levels are reduced with aging. However, it is uncertain how tendon fibroblasts are involved in tendon aging and how aging cells respond to IGF-I. The purpose of this study was to investigate the in vivo IGF-I stimulation of tendon protein synthesis in elderly compared with young men. We injected IGF-I in the patellar tendons of young (n = 11, 20-30 yr of age) and old (n = 11, 66-75 yr of age) men, and the acute fractional synthesis rate (FSR) of tendon protein was measured with the stable isotope technique and compared with the contralateral side (injected with saline as control). We found that tendons injected with IGF-I had significantly higher protein FSR compared with controls (old group: 0.018 ± 0.015 vs. 0.008 ± 0.008, young group: 0.016 ± 0.009 vs. 0.009 ± 0.006%/h, mean ± SE, P < 0.01). This increase in protein synthesis was seen in both young and old men, with no differences between age groups. The old group had markedly lower serum IGF-I levels compared with young (165 ± 17 vs. 281 ± 27 ng/ml, P < 0.01). In conclusion, local IGF-I stimulated tendon protein synthesis in both young and old men, despite lower systemic IGF-I levels in the old group. This could indicate that the changed phenotype in aging tendon is not caused by decreased fibroblast function.
authors.affiliation: Department of Orthopedic Surgery, Institute of Sports Medicine, Bispebjerg Hospital and Faculty of Health and Medical Sciences, Center for Healthy Aging, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Rie Harboe
authors.initials: RH
authors.lastname: Nielsen
authors.forename: Lars
authors.initials: L
authors.lastname: Holm
authors.forename: Nikolaj Mølkjær
authors.initials: NM
authors.lastname: Malmgaard-Clausen
authors.forename: Søren
authors.initials: S
authors.lastname: Reitelseder
authors.forename: Katja Maria
authors.initials: KM
authors.lastname: Heinemeier
authors.forename: Michael
authors.initials: M
authors.lastname: Kjaer
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000378:metabolism* / Q000502:physiology*; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D017847:Patellar Ligament / Q000378:metabolism* / Q000502:physiology*; D014176:Protein Biosynthesis / Q000502:physiology*; D055815:Young Adult
chemical_list: D007334:Insulin-Like Growth Factor I
keywords: growth factors; growth hormone; protein turnover; tenocytes