EXPRESSION OF PARATHYROID HORMONE-RELATED PROTEIN IN RAT ARTICULAR-CARTILAGE

Expression and localization of parathyroid hormone-related protein (PT HrP) in rat articular cartilage during fetal and postnatal periods wer e investigated by immunohistochemistry and in situ hybridization. PHTr P displayed distinct distribution and intensity of staining at differe nt ages. In fetal (18-day-old) and young (3-week-old) rats, articular chondrocytes expressed abundant PTHrP throughout the entire thickness of cartilage. In contrast, in 60-week-old rats, PTHrP was expressed in a few articular chondrocytes of superficial and middle layers. Regula tion of PTHrP and PTH/PTHrP receptor mRNA was also studied in cultured rat articular chondrocytes. Northern blot analysis revealed that both transforming growth factor-beta (TGF-beta), an important stimulator f or chondrocyte proliferation and differentiation, and 10% fetal bovine serum (FBS) stimulated the expression of PTHrP mRNA with down-regulat ion of its receptor mRNA. In contrast, 12-O-tetradecanoylphorbol-13-ac etate (TPA) down-regulated the expression of receptor without changes of PTHrP mRNA level. These results suggest that the changes in abundan ce and localization of PTHrP and its receptor may be directly involved in the cell growth and differentiation of articular cartilage.