Proteoglycan synthesis during intramembranous bone regeneration following avulsive wounding in guinea pig long bones

Information on proteoglycan synthesis by bone cells and tissue is largely limited to studies of developing fetal bone. The present investigation focuses on proteoglycan synthesis during the intramembranous type of bone regeneration seen within avulsive (puncture-type) defects placed in guinea pig tibiae. [35S] Sulfate-labeled proteoglycans were extracted from tissue within regenerating tibial avulsive defects seven days following surgical wounding and also from xiphisternal cartilage utilized as an internal control. Labeled proteoglycans in 4M guanidine HCl extracts of regenerating bone and cartilage were purified by DEAE-Sephacel chromatography and further analyzed by chromatography and appropriate enzyme digestions. Regenerating bone tissue contained a proteoglycan relatively small in size (Kav = 0.56 following chromatography on Sepharose CL-2B) compared to proteoglycan from xiphisternal cartilage (Kav = 0.17). Alkaline borohydride treatment degraded this bone proteoglycan (Kav = 0.4 on Sepharose CL-6B), indicating an average molecular weight of glycosaminoglycan chains approximating 50,000. Enzymatic digestions followed by Sepharose CL-6B chromatography showed that glycosaminoglycan side chains of regenerating bone proteoglycan contained dermatan sulfate, with 60% chondroitinase AC II-resistant but chondroitinase ABC-sensitive material. This bone proteoglycan did not interact with hyaluronic acid to form aggregates under conditions where such aggregates were formed by xiphisternal cartilage proteoglycan. The regenerating bone proteoglycans are therefore similar to other bone proteoglycans in hydrodynamic size and glycosaminoglycan chain size, but differ in the per cent of iduronic acid within glycosaminoglycan side chains. This guinea pig bone proteoglycan may be associated with the large mesenchymal cell population noted histologically within the bone defects at seven days of regeneration.