Antisense inhibition of osteogenic protein 1 disturbs human articular cartilage integrity.

OBJECTIVE: To delineate the role of endogenous osteogenic protein 1 (OP-1) in human articular cartilage homeostasis via the inhibition of OP-1 gene expression by antisense oligonucleotides.
METHODS: Human adult normal articular cartilage was obtained from the knee and ankle joints of 34 organ donors. Chondrocytes were cultured as tissue explants or isolated cells in alginate or high-density monolayers for 48 hours in the presence of OP-1 antisense or sense oligonucleotides. The effect of OP-1 antisense inhibition was evaluated by reverse transcription-polymerase chain reaction, (35)S incorporation, dimethylmethylene blue assay, histology with Safranin O staining, and immunohistochemistry with anti-proOP-1, anti-mature OP-1, and anti-aggrecan antibodies.
RESULTS: Antisense treatment inhibited OP-1 gene expression by a mean +/- SD of 34 +/- 12% (P < 0.01) in chondrocytes cultured in monolayers and by 77 +/- 27% (P < 0.03) in alginate beads. The inhibition of autocrine OP-1 caused a striking decrease in aggrecan gene expression, in total proteoglycan content accumulated in cartilage matrix, and in the ability of chondrocytes to newly synthesize proteoglycans. OP-1 antisense reduced aggrecan messenger RNA expression by 42 +/- 17% (P < 0.05) and proteoglycan synthesis by 48 +/- 23% (P < 0.01). Histology and immunohistochemistry revealed a dramatic decrease in Safranin O staining and reduced anti-aggrecan staining (primarily in the superficial and middle cartilage layers) with OP-1 antisense treatment.
CONCLUSION: Our results suggest that OP-1 is an important endogenous cartilage factor that regulates matrix integrity and possibly needs to be induced or up-regulated to maintain normal cartilage homeostasis. These findings confirm our hypothesis that a lack of autocrine OP-1 may lead to an elevated susceptibility of chondrocytes to the catabolic processes, thus contributing/promoting cartilage degeneration.