An age-related decline in chondrocyte production of OP-1 (BMP-7) may contribute to cartilage loss in osteoarthritis. This study was designed to determine if increased methylation of the OP-1 promoter might serve as a mechanism for the age-related decline in OP-1 expression.
Human articular chondrocytes were isolated from cartilage obtained after death from tissue donors (ages 19-86 years) without a known history of arthritis. DNA was obtained from isolated chondrocytes in primary culture and analyzed for OP-1 promoter methylation by PCR after bisulfite treatment. Cultured cells were treated with the DNA methyltransferase inhibitor 5-azacytidine and OP-1 production was measured in the media by ELISA. RNA was isolated to measure expression of IGF-1, the IGF-1 receptor, aggrecan, and OP-1 by real-time PCR.
Methylation of the OP-1 promoter was detected in chondrocytes isolated from tissue obtained from older adults and there was a positive correlation between age and OP-1 methylation status (n=22, R2=0.277, p=0.014). Inhibition of methylation in cultured cells with 5-azacytidine increased chondrocyte production of OP-1 protein and increased the expression of the IGF-1, the IGF-1 receptor, aggrecan, and OP-1 genes but not GAPDH.
Age-related methylation of the OP-1 promoter may contribute to a decrease in OP-1 production in cartilage and a decrease in expression of OP-1 responsive genes such as IGF-1, the IGF-1 receptor, and aggrecan.