Morphological and molecular characterization of human hamstrings shows that tendon features are not influenced by donor age

Purpose: Age-related modifications of tendons, such as reduced tenocyte proliferation and modified extracellular matrix (ECM) turnover, have been previously described, but results are often incomplete and discordant. The aim of this study was to investigate, using morphological and molecular methods, the effect of ageing on human tendons and tenocytes, especially focusing on the collagen turnover pathways, in order to understand how the ageing process could influence tendon biology and structure. Methods: Morphological analysis was performed on fragments from human semitendinosus and gracilis tendons harvested from 10 adult (mean age 41.8 ± 13.3 years) and 6 aged healthy patients (mean age 72.7 ± 7.0 years) by haematoxylin and eosin, Sirius red and Alcian blue staining. The expression of genes and proteins involved in collagen turnover and focal adhesions was assessed by real-time PCR, slot blot and zymography in cultured tenocytes. Cytoskeleton arrangement was studied by immunofluorescence and cell migration by wound healing assay. Results: The structure and composition of ECM in ageing tendons are preserved as well as the expression of genes and proteins involved in collagen turnover pathways. Although morphological analysis revealed that ageing tenocytes tended to an impaired migration potential and that actin filaments are occasionally shorter and randomly distributed, the expression of proteins involved in focal adhesion formation is preserved. Conclusion: Results of this study suggest that the structure of ageing tendons is preserved and that ageing tenocytes maintain their ability for ECM remodelling, supporting the hypothesis that ageing tendons maintain their biomechanical properties. The biological reliability of aged tendons has a clinical relevance, supporting the use of tendon autografts also in the elderly patients. Since the common and successful orthopaedic procedure of anterior cruciate ligament reconstruction using either autografts or allografts is becoming more common in older age groups, these findings suggest that the donor age would not significantly influence the clinical outcome.