Matrix synthesis in mandibular condylar cartilage of aging mice.

Osteoarthritic (OA) lesions often develop along the articular surface of mandibular condylar cartilage of aging mice. Metabolic activities of chondrocytes in condylar cartilage of newborn to 18-month-old mice were evaluated morphologically and biochemically in vivo and in vitro. In the period between birth and 3 months of age, marked age-dependent reductions in the number of cells per unit area (-56.43%), in DNA (-64.38%) and in glycosaminoglycan (GAG) (-46.32%) contents were observed. In the same time period, protein content remained almost constant. Reduced rates in the incorporation of [3H]thymidine, [3H]leucine and [35S]sulfate between birth and 3 months of age (-81.60%, -25.98% and -67.75%, respectively) were also observed in vitro. Collagen synthesis was similarly reduced, from 38.70% in newborns to 27.86% in 18-month-old animals. Morphology and autoradiography in mandibular cartilage revealed that the reductions of cellularity and of sulfated macromolecular synthesis appeared to be more pronounced along the articular surface. In this region OA lesions were often observed. It may thus be that the combination of reduced sulfated GAGs and the decreased number of cells in this region could result in tissue with architecture that is less suited to withstanding stress and thus more prone to the development of the typical OA lesions that are seen along the articular surfaces of mandibular cartilage in aged mice.