Objective: To determine whether articular chondrocytes express growth factor genes delivered by adenoviral vectors and whether expression of these genes influences matrix synthesis in the presence and absence of interleukin-1 (IL-1).
Methods: Monolayer cultures of rabbit articular chondrocytes were infected with recombinant adenovirus carrying genes encoding the following growth factors: insulin-like growth factor 1 (IGF-1), transforming growth factor beta1 (TGFbeta1), and bone morphogenetic protein 2 (BMP-2). As a control, cells were transduced with the lac Z gene. Cultures were also treated with each growth factor supplied as a protein. Levels of gene expression were noted, and the synthesis of proteoglycan, collagen, and noncollagenous proteins was measured by radiolabeling. Collagen was typed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. The effects of growth factor gene transfer on proteoglycan synthesis in the presence of IL-1 were also measured.
Results: The expression of all transgenes was high following adenoviral transduction. Proteoglycan synthesis was stimulated approximately 8-fold by the BMP-2 gene and 2-3-fold by the IGF-1 gene. The effects of BMP-2 and IGF-1 genes were additive upon cotransduction. Synthesis of collagen and noncollagenous proteins, in contrast, was most strongly stimulated by the IGF-1 gene. In each case, collagen typing confirmed the synthesis of type II collagen. IL-1 suppressed proteoglycan synthesis by 50-60%. IGF-1 and TGFbeta genes restored proteoglycan synthesis to control levels in the presence of IL-1. The BMP-2 gene, in contrast, elevated proteoglycan synthesis beyond control levels in the presence of IL-1.
Conclusion: Transfer of growth factor genes to articular chondrocytes can greatly increase matrix synthesis in vitro, even in the presence of the inflammatory cytokine IL-1. This result encourages the further development of gene therapy for the repair of damaged cartilage.