Nielsen RH, Holm L, Malmgaard-Clausen NMl, Reitelseder Sr, Heinemeier KM, Kjaer M. Increase in tendon protein synthesis in response to insulin-like growth factor-I (IGF-I) is preserved in elderly men. Journal of Applied Physiology. http://jap.physiology.org/content/early/2013/11/18/japplphysiol.01084.2013.abstract (Increase in tendon protein synthesis in response to insulin-like growth factor-I (IGF-I) is preserved in elderly men)
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 to young men. We injected IGF-I into the patellar tendons of young (n=11, 20-30 years of age) and old (n=11, 66-75 years of age) men, and the acute fractional synthesis rate (FSR) of tendon protein was measured with the stable isotope technique and compared to the contra lateral side (injected with saline as control). We found that tendons injected with IGF-I had significantly higher protein FSR compared to 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 ± SEM, 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 to 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.
