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 underlay age-associated changes in cartilage and the development of osteoarthritis. Here we demonstrate the importance of Bcl-2 in regulating articular chondrocyte apoptosis in response to both serum withdrawal and retinoic acid treatment. Both stimuli induced apoptosis of primary human articular chondrocytes and a rat chondrocyte cell line as evidenced by the formation of DNA ladders. Apoptosis was accompanied by decreased expression of aggrecan, a chondrocyte specific matrix protein. The expression of Bcl-2 was downregulated by both agents based on Northern and Western analysis, while the level of Bax expression remained unchanged compared to control cells. The importance of Bcl-2 in regulating chondrocyte apoptosis was confirmed by creating cell lines overexpressing 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 overexpressing Bcl-2 were resistant to apoptosis induced by both serum withdrawal and retinoic acid treatment. Finally, the expression of Bcl-2 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 acid inhibits aggrecan expression independent of the apoptotic process.
Laboratory of Biological Chemistry, Gerontology Research Center, National Institute on Aging, NIH, Baltimore, Maryland 21224, USA.
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L
Feng
P
P
Precht
R
R
Balakir
W E
WE
Horton
D000368:Aged; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001769:Blood; D002358:Cartilage, Articular / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology*; D011817:Rabbits; D051381:Rats; D014212:Tretinoin / Q000494:pharmacology*
D019253:Proto-Oncogene Proteins c-bcl-2; D014212:Tretinoin