Biosynthesis and fate of proteoglycans in cartilage and bone during development and mineralization

Subcutaneous implantation of demineralized bone matrix in rats induces migration of host cells into the site and results in the sequential development of cartilage and bone. The biosynthesis and metabolic fate of proteoglycans in the plaques at the bone matrix implantation site were investigated by [³⁵S]sulfate labeling in vivo. ³⁵S-Labeled proteoglycans were extracted with 4 m guanidine HCl and purified by DEAE-Sephacel chromatography. Analysis of proteoglycans on Sepharose CL-2B chromatography showed two major peaks at K_d = 0.28 and 0.68 (peaks I and II, respectively). Peak I proteoglycan has a high buoyant density and contains chondroitin sulfate chains of average M_r = 20,000. Peak II proteoglycan has a lower average buoyant density and contains dermatan sulfate chains of average M_r = 33,000. Throughout the endochondral bone development sequence, peak II proteoglycan predominates. Peak I was low on Day 3, became prominent on Day 7 (approximately 30% of the total radioactivity), and declined after Day 9. The calculated half-lives of peak I and II proteoglycans labeled on Day 7 were about 1.8 and 2.8 days, respectively. After the initiation of osteogenesis, a species of mineral-associated proteoglycan was extracted with a 4 m guanidine HCl solvent containing 0.5 m EDTA. This proteoglycan has a small hydrodynamic size (K_d = 0.38 on Sepharose CL-6B chromatography) and shows a long half-life, about 6 days.