Comparative effects of bone morphogenetic proteins and Sox9 overexpression on extracellular matrix metabolism of bovine nucleus pulposus cells

STUDY DESIGN. An in vitro biologic study of the effects of adenovirus expressing bone morphogenetic proteins (BMPs) and adenovirus expressing Sox9 on extracellular matrix metabolism by bovine nucleus pulposus cells. OBJECTIVE. To compare the effects of recombinant adenoviral vectors expressing various BMPs (2, 3, 4, 5, 7, 8, 10, 11, 12, 13, 14, and 15) and Sox9 on extracellular matrix accumulation by bovine nucleus pulposus cells. SUMMARY OF BACKGROUND DATA. Nucleus pulposus matrix production may be promoted by transducing the cells with genes that permit the sustained expression of growth factors. The choice of the particular factors or BMPs to be studied for these applications has been largely based on the commercial availability of such products. To our knowledge, this study is the first effort to evaluate systematically the relative effectiveness of the various members of the BMP family in promoting intervertebral disc matrix repair. METHODS. Adult bovine nucleus pulposus cells cultured in monolayer were transduced with adenoviruses expressing human BMP-2, 3, 4, 5, 7, 8, 10, 11, 12, 13, 14, and 15, and adenovirus expressing Sox9. Proteoglycan and collagen accumulation, and cell proliferation were measured 6 days after viral transduction. As a positive control, cells were cultured without any exogenous gene in the presence of recombinant human (rh)BMP-7. RESULTS. Nucleus pulposus cells transduced with adenoviruses expressing BMP-2, 3, 4, 5, 7, 8, 10, 13, 15, and Sox9 accumulated more proteoglycans than nucleus pulposus cells transduced with adenovirus expressing green fluorescent protein (control). It is noteworthy that nucleus pulposus cells transduced with adenoviruses expressing BMP-2 and 7 resulted in essentially as great a stimulation of proteoglycan accumulation as nucleus pulposus cells maintained in the presence of rhBMP-7 (adenoviruses expressing BMP-2: 104% increase; adenoviruses expressing BMP-7: 162% increase; and rhBMP-7: 120% increase). Nucleus pulposus cells transduced with BMP-2, 4, 5, 7, 8, 10, 14, 15, and Sox9 accumulated significantly more collagen compared to nucleus pulposus cells transduced with adenovirus expressing green fluorescent protein; adenoviruses expressing BMP-4 and 14 were the most effective (552% and 661% increase, respectively). Nucleus pulposus cells also proliferated, as measured by deoxyribonucleic acid content, when transduced with adenoviruses expressing BMP-2 and 8. CONCLUSIONS. To our knowledge, for the first time, we have shown the relative effectiveness of 12 different BMPs and Sox9 in stimulating proteoglycan and collagen production by nucleus pulposus cells. Adenoviruses expressing BMP-2 and 7 were the most effective in stimulating proteoglycan accumulation, while adenoviruses expressing BMP-4 and 14 were the most effective in stimulating collagen accumulation. To our knowledge, this study is the first to compare the relative effectiveness of various BMPs and Sox9 on extracellular matrix accumulation by nucleus pulposus cells, and could help to develop more efficacious approaches to the treatment of degenerating intervertebral discs.