Qualitative changes in human osteoarthritic hip cartilage proteoglycan synthesis during long-term explant culture

Cartilage explants from 14 human osteoarthritic (OA) femoral heads synthesize 4 subpopulations of proteoglycan (PG) based on hydrodynamic size on Sepharose CL-2B (Kav: I, 0.05; II, 0.28; III, 0.68; IV, 0.9-1.0). A detailed analysis of newly synthesized PG monomer from each PG subpopulation was made during protracted (20 days vs. 1 day) explant culture of the cartilage specimens. Subpopulations I and II--high-density PG each eluted off Sepharose CL-2B as a unimodal peak, Kav, 0.2-0.25. High-density PG from subpopulation II appeared as a broad polydisperse symmetrical peak. Subpopulation IV eluted as 2 peaks; a minor peak of large size, and a major peak, Kav, 0.9. Large pore composite polyacrylamide gel electrophoresis (CAPAGE) of intact PG monomer (fraction D1D1) resolved at least 2 discrete PG subpopulations as constituents of both subpopulations I and II. Subpopulations III and IV PG monomer consisted of several heterogeneous subpopulations. The size of the high-density PG from subpopulations I and II decreased with time-in-culture. No significant differences were found in the average glycosaminoglycan (GAG) chain size (Kav, 0.65 on Sepharose CL-6B) or in susceptibility to chondroitinase ABC or AC-II (both 80%) in subpopulations I, II and III high density PG as a function of time-in-culture. The average GAG chain length of subpopulation IV high density PG (Kav, 0.75-0.9) was significantly shorter than the high-density PG of other subpopulations. Variations in the average GAG length and chondroitinase susceptibility did not appear to underly the smaller size of subpopulations I and II high-density PG with culture age. By contrast, keratanase susceptibility of subpopulations I and II high-density PG increased as a function of culture time.