Characterization of proteoglycans synthesized by different layers of adult human femoral head cartilage.

Full thickness human femoral head cartilage fragments were labeled in vitro with 35S-SO4 and 3H-proline and cut tangentially to the surface in a cryostat. Sixteen-micrometer thick sections were pooled from four zones: I (0-160 microns); II (160-480 microns); III (480-960 microns); and IV (> 960 microns). The pooled sections were extracted with 4 M guanidinium chloride solvent and the extracts and 35S-labeled proteoglycans (35S-PGs) were characterized. The superficial layer gave lowest extraction yields and the deep layers gave the highest yields. The highest specific activity (dpm/mg of dry weight) of 35S-SO4 labeling was in zones II and III and that of [3H] proline in zone I. The superficial layer I also contained: (1) the highest proportions of 35S-PG monomers of small hydrodynamic size and low buoyant density; (2) an increased proportion of hydrodynamically small 35S-PG monomers; (3) the smallest proportion of endogenously reassociated 35S-PG aggregates, although similar proportions of 35S-PG monomers extracted from all layers interacted with exogenous hyaluronan (HA); and (4) the more heterogeneous population of 35S-glycosaminoglycan (GAG) side chains with respect to their size, although their chemical compositions were similar in all layers. In addition, extracted 35S-PGs had shorter GAG chains than the residual nonextracted molecules and were enriched in chondroitin-6 sulfate whereas residual/non-extracted 35S-PGs were enriched in chondroitin-4 sulfate. The extraction yields of keratan sulfate (KS)-enriched 35S-PGs also decreased with the depth of tissue, though the overall 35S-KS chain content varied little with depth of tissue, being slightly higher in the deepest zone IV.