LOCALIZATION OF HYALURONIC-ACID IN HUMAN ARTICULAR-CARTILAGE

To demonstrate localization of hyaluronic acid (HA) in articular carti lage of the human femur, biotinylated HA-binding region, which specifi cally binds HA molecules, was applied to the tissue. In sections fixed by 2% paraformaldehyde-2% glutaraldehyde, HA staining was detected in lamina splendens and chondrocytes in the middle zone. By pretreatment with trypsin, intense HA staining appeared in the extracellular matri x of the deep zone and weak staining in the superficial and middle zon es. Moreover, pre-treatment with chondroitinase ABC (CHase ABC) intens ely enhanced the stainability for HA in the superficial and middle zon es and weakly in the deeper zone. Combined pre-treatment of trypsin wi th CHase ABC abolished intra- and extracellular staining for HA in all zones. By microbiochemical study, the concentrations of HA and dermat an sulfate were high in the middle zone, whereas those of chondroitin sulfate and keratan sulfate were high in the deep zone. These results suggest that HA is abundantly synthesized in and secreted from the cho ndrocytes, particularly in the middle zone, whereas it is largely mask ed by proteoglycan constituents in the extracellular matrix.