Proteoglycan synthesis and deposition in fetal rat bone

A pulse-labeling approach has been used to study proteoglycan metabolism in fetal rat bone. Pregnant rats were injected with [35S]sulfate and sacrificed 6, 24, or 48 h later. Fetal calvaria were dissected and extracted sequentially with 4 M guanidine hydrochloride and 4 M guanidine hydrochloride/0.5 M ( ethylenedinitrilo )tetraacetic acid (EDTA). With time after injection, the proportion of total incorporated radioactivity decreased in the guanidine pool (corresponding to nonmineralized bone and associated soft tissues) and increased in the guanidine/EDTA pool (mineralized bone). Chromatographic analysis of the proteoglycan species present in these pools after different labeling times indicated that three species of proteoglycan are synthesized in fetal rat calvaria. A large chondroitin sulfate (CS) proteoglycan and a smaller dermatan sulfate (DS) proteoglycan are located in the nonmineralized compartment. A CS proteoglycan similar in size to the DS proteoglycan is initially present in the nonmineralized bone but subsequently is located in the mineralized matrix. A fraction of the small CS proteoglycan is strongly associated with collagen.