Retinoic acid induced proteoglycan release and cartilage resorption in rat bone cultures are age dependent and inhibited by EDTA

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Abstract
In explanted humeri of late fetal rats, retinoic acid was found to induce the release of proteoglycan followed by cartilage resorption. Tissue breakdown, which was demonstrated by losses of DNA, RNA, and protein, coincided with the appearance of necrotic cells. In control humeri chondrocytes were the main cell type, but in humeri treated for 4 days with retinoic acid the surviving cells were chondroblastlike. Sensitivity of proteoglycan release and tissue breakdown to retinoic acid decreased with age. The proteinase inhibitors cysteine, Trasylol, and soya and lima bean trypsin inhibitors did not antagonize the effects of retinoic acid. Phenylmethanesulfonyl fluoride suppressed cartilage resorption more effectively than proteoglycan release, while pepstatin merely suppressed cartilage resorption. The inhibition by EDTA of both the release of proteoglycan and cartilage resorption induced by retinoic acid was dose dependent. Zn2+ abolished these effects, whereas Mn2+ only relieved the release of proteoglycan induced by retinoic acid; this indicates that these two effects of retinoic acid are not necessarily linked. In view of our recent demonstration that the release of proteoglycan induced by retinoic acid requires RNA and protein synthesis, we suggest that the degradation of proteoglycans in response to retinoic acid is dependent upon continued synthesis of metalloproteinases.