Transduced bovine articular chondrocytes affect the metabolism of cocultured nucleus pulposus cells in vitro:: Implications for chondrocyte transplantation into the intervertebral disc

Study Design. Biologic study on the effects of coculture of bovine articular chondrocytes transduced ex vivo with genes expressing bone morphogenetic proteins (BMPs) on nucleus pulposus (NP) cells. Objective. To evaluate the effects of bovine articular chondrocytes transduced with adenoviruses expressing various BMPs on proteoglycan and collagen production, and cellular proliferation of NP cells in vitro. Summary of Background Data. Matrix synthesis by intervertebral disc cells is promoted by exposing the cells to growth factors or delivering genes that permit sustained expression of growth factors. We propose a novel therapeutic approach involving delivery of autologous chondrocytes, transduced ex vivo with bioactive proteins, to provide both the cells and proteins required to stimulate disc healing. Methods. Adult bovine articular chondrocytes were transduced with adenoviruses (Ads) expressing either BMP-2, 4, 5, 7, 10, or 13 and plated as monolayers. Bovine NP cells encapsulated in alginate beads were cocultured, floating in the medium. Proteoglycan and collagen accumulation, and NP cell proliferation were measured after 6 days of coculture. As a positive control, beads were cocultured with articular chondrocytes in the presence of rhBMP-7. Results: NP cells cocultered with articular chondrocytes transduced with BMPs-2, 4, 7, and 10 accumulated significantly (P = 0.05) more proteoglycan than when cocultured with chondrocytes transduced with AdGFP ( control) [AdBMP-2: 23.6%; AdBMP-4: 27.0%; AdBMP-7: 129.1%; AdBMP-10: 102.1% increases respectively]. Collagen accumulation was significantly (P < 0.05) increased by NP cells cocultured with articular chondrocytes transduced with BMPs-2, 4, 5, and 7. [AdBMP-2: 104.6%; AdBMP-4: 40.6%; AdBMP-5: 58.6%; AdBMP-7: 55.5% increases respectively]. NP cells proliferated when cocultured with articular chondrocytes transduced with AdBMP-2 and -7. Conclusions: Bovine NP cells are stimulated to produce proteoglycans and collagen when exposed to chondrocytes transduced with genes for various BMPs. If applied to the treatment of disc degeneration, this strategy could provide the disc with not only metabolically active chondrocytes but also promote matrix replenishment by stimulating native NP cells.