Metabolic kinetics of proteoglycans by embryonic chick sternal cartilage in culture

Explant cultures of embryonic chick sternum have been widely studied, but t he kinetics of biosynthesis of proteoglycans by this tissue in culture has not been characterized, Caudal cartilaginous portions of 16-day-old embryon ic chick sterna were cultured for 8 days. Histological examination showed t hat the fresh cartilage contained morphologically homogenous chondrocytes, which were embedded in a uniform extracellular matrix. After culture for 8 days, the histological appearance of the explant remained unchanged but the tissue increased in size with time as indicated by a progressive increase in DNA content and in the content of glycosaminoglycan and collagen. Rates of degradation and release from the tissue of proteoglycans labeled in ovo with S-35 were first order during culture, as were the unlabeled proteoglyc ans. Proteoglycan synthesis was high during the first 2 days of culture, an d this then gradually decreased from this high level during the following 2 days. Synthesis was then maintained at a constant level for the remainder of the culture period. After culture for 2 and 7 days, the proteoglycans sy nthesized by the explants were identical to the preexisting proteoglycans i n hydrodynamic size, glycosaminoglycan chain size, and ability to form aggr egates. These findings suggest that the embryonic chick sterna maintained a stable cartilage phenotype during the extended culture periods. The initia l rapid rate of matrix turnover was probably attributable to an adaptation of the tissue to ex ovo culture conditions and the subsequent maintenance o f cellular activities at a lower level indicated the establishment of a ste ady-state rate of metabolism. (C) 1999 Academic Press.