Despite considerable knowledge of the biochemistry and cell biology of collagen, little is known about its physiology. We previously demonstrated that in human bone, tendon, ligament and muscle, collagen is synthesized faster than expected and feeding of essential amino acids (EAA) does not stimulate muscle collagen synthesis in young men (Babraj et al 2003a, 2003b). We hypothesized that the concentration of epimysial collagen should be greater in the elderly than the young, due to the faster synthetic rates. We studied two groups of 4 healthy young and elderly men, (28 ± 6 and 70 ± 6 y, BMI 24 ± 3 and 25 ± 4 kg/m2 respectively; all values are means ± SD). The studies had Tayside Ethics Committee approval. The subjects were infused throughout with octreotide and insulin to maintain insulin (∼10 m IU/l) and glucose (∼5 mM) at post-absorptive values; they remained either post-absorptive throughout or ingested 20g of EAA. M. quadriceps was biopsied using a conchotome with 1 % lignocaine anaesthesia. Muscle collagen synthesis was measured as the incorporation over 3 h of leucine after a primed constant infusion of [1-13C]ketoisocaproate. Muscle collagen-derived proline (P) and hydroxyproline (OHP) concentrations were measured by gas chromatography mass spectrometry.The collagen fractional synthetic rate was higher in the elderly than in the young (0.024 ± 0.002 vs. 0.017 ± 0.004 %.h1; P< 0.05, ANOVA) possibly due to increased inflammation as indicated by an increased expression of NFκB. Ingestion of EAA did not stimulate collagen synthesis in either group (0.024 ± 0.003 and 0.016 ± 0.003 %.h-1 respectively). Despite the higher synthetic rate the total concentration of collagen in the elderly and young was similar (9.9 ± 1 vs. 9.5 ± 2 µg.mg-1 wet weight muscle). However the relative abundance of OHP to P in insoluble collagen is lower in the elderly than the young (0.70 ± 0.03 vs. 0.98 ± 0.14 mol.mol-1 respectively, P= 0.09) probably reflecting a decreased stability of the insoluble collagen, in line with the observed increased turnover.
University of Glasgow (2004) J Physiol 557P, PC68
Communications: Muscle collagen synthesis is faster in the elderly, has a different hydroxyproline composition but is unresponsive to feeding.
J.A. Babraj (a),K.Smith (a),D.Cuthbertson (a) and M. Rennie (b)
(a) Molecular Physiology, University of Dundee, Dundee, UK and (b) Graduate Medical School, University of Nottingham, Derby, UK
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Where applicable, experiments conform with Society ethical requirements.