Aged bovine chondrocytes display a diminished capacity to produce a collagen-rich, mechanically functional cartilage extracellular matrix

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Abstract
Most fundamental studies in cartilage tissue engineering investigate the ability of chondrocytes from young animals to produce cartilaginous matrix under various conditions, while current clinical applications such as autologous chondrocyte implantation, use chondrocytes from donors that are decades past skeletal maturity. Previous investigations have suggested that several characteristics of primary chondrocytes are age-dependent but none have quantified cell proliferation, proteoglycan synthesis and accumulation, collagen synthesis and accumulation, compressive and tensile mechanical properties in order to examine the effects of donor age on all of these parameters. We enzymatically isolated primary bovine chondrocytes from fetal, young and aged animals and cultured these cells in agarose gels to assess the above-mentioned properties. We found that fetal and young (but still skeletally mature i.e. 18-month-old bovine) chondrocytes behaved similarly, while aged chondrocytes (5- to 7-year-old bovine) displayed diminished proliferation ( approximately 2x less), a slightly reduced proteoglycan accumulation per cell ( approximately 20%), and significantly less collagen accumulation per cell ( approximately 55%) compared to the younger cells. Histological observations and mechanical properties supported these findings, where a particularly significant reduction in tensile stiffness produced by aged chondrocytes compared to younger cells was observed. Our findings suggest that donor age is an important factor in determining the outcome and potential success when tissue-engineered cartilage is produced from articular chondrocytes. More specifically, primary chondrocytes from aged donors may not possess sufficient capacity to produce the extracellular matrix that is required for a mechanically resilient tissue.

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