EVIDENCE OF A DIRECT ROLE FOR BCL-2 IN THE REGULATION OF ARTICULAR CHONDROCYTE APOPTOSIS UNDER THE CONDITIONS OF SERUM WITHDRAWAL AND RETINOIC ACID TREATMENT

The regulation of chondrocyte apoptosis in articular cartilage may und erlay age-associated changes in cartilage and the development of osteo arthritis. Here we demonstrate the importance of Bcl-2 in regulating a rticular chondrocyte apoptosis in response to both serum withdrawal an d retinoic acid treatment. Both stimuli induced apoptosis of primary h uman articular chondrocytes and a rat chondrocyte cell line as evidenc ed by the formation of DNA ladders. Apoptosis was accompanied by decre ased expression of aggrecan, a chondrocyte specific matrix protein. Th e expression of Bcl-2 was downregulated by both agents based on Northe rn and Western analysis, while the level of Bar expression remained un changed compared to control cells. The importance of Bcl-2 in regulati ng chondrocyte apoptosis was confirmed by creating cell lines overexpr essing sense and antisense Bcl-2 mRNA. Multiple cell lines expressing antisense Bcl-2 displayed increased apoptosis even in the presence of 10% serum as compared to wild-type cells. in contrast, chondrocytes ov erexpressing Bcl-2 were resistant to apoptosis induced by both serum w ithdrawal and retinoic acid treatment. Finally, the expression of Bcl- 3 did not block the decreased aggrecan expression in IRC cells treated with retinoic acid. We conclude that Bcl-2 plays an important role in the maintenance of articular chondrocyte survival and that retinoic a cid inhibits aggrecan expression independent of the apoptotic process. J. Cell. Biochem. 71 :302-309, 1998. (C) 1998 Wiley-Liss, Inc.dagger