Simvastatin stimulates chondrogenic phenotype of intervertebral disc cells partially through BMP-2 pathway

Study Design. In vitro experiment to study the effect of simvastatin on rat intervertebral disc (IVD) cells. Objective. To evaluate the time-course effect of simvastatin on the gene expression of bone morphogenetic protein-2 (BMP-2), aggrecan, and collagen type II in rat IVD cells cultured in alginate bead. Role of BMP-2 on the simvastatin-induced chondrogenesis of IVD cells was also investigated. Summary of Background Data. Growth factors including BMP-2 have been found to improve anabolism of IVD cells and have shown promise for the treatment of disc degeneration. Statins is known to increase BMP-2 expression in vitro and stimulate bone formation in vivo. However, it is still unknown whether statins can also increase BMP-2 expression and in turn, stimulate matrix synthesis by IVD cells. Methods. Rat IVD cells (harvested from nucleus pulpusos and inner annular fibrosus) cultured in alginate beads were exposed to different doses of simvastatin. DMMB, and real-time polymerase chain reaction were used to quantify proteoglycan and gene expression of BMP-2, aggrecan and collagen type II, respectively. Noggin or mevalonate was used to investigate the mechanism of the effect of simvastatin on rat IVD cells. Results. Simvastatin significantly upregulated BMP-2 mRNA expression, followed by aggrecan and type II collagen gene expression and proteoglycan content in rat IVD cells. Moderate dose (500 ng/mL) of noggin completely hindered the expression of aggrecan and collagen type II induced by simvastatin on day 7, but not on day 14. The upregulated type II collagen expression was blocked with 3 mu g/mL of noggin on day 14, whereas aggrecan levels remained unchanged. Lastly, simvastatin appeared to facilitate BMP-2, aggrecan, and type II collagen gene expression by inhibiting the production of mevalonate as evidenced that the anabolic effect was completely reversed with the addition of mevalonate. Conclusion. Simvastatin drives a mechanism for promoting chondrogenesis of IVD cells partially mediated by upregulated BMP-2 through the inhibition of mevalonate pathway.