Induction of fibrillin-2 and periostin expression in Osterix-knockdown MC3T3-E1 cells

Osteoporosis is the most common age-related bone disease that is characterized by an imbalance between osteoblasts for bone formation and osteoclasts for bone resorption. Anti-catabolic drugs have been developed to inhibit osteoclast activity and to prevent bone loss in osteoporosis. However, because it is difficult to increase bone mass in osteoporotic bone, it would be beneficial to simultaneously enhance osteoblast function and thus form bone. Osterix (Osx) is an essential transcription factor for osteoblast differentiation. To date, many studies have focused on discovering Osx target genes and on increasing osteoblast differentiation. However, Osx targets and the mechanisms controlling osteoblast differentiation, are not well known. Here, we generated stable Osx-knockdown cell lines by employing shRNA in MC3T3-E1 osteoblastic cells. Stable Osx-knockdown osteoblasts exhibited a significant reduction in cell differentiation and nodule formation, which was similar to the reduced osteoblast activity observed in an Osx-deficient mouse model. Using an Affymetrix GeneChip microarray, we determined the differential gene expression profile in response to Osx knockdown, which provided insight into molecular mechanisms underlying osteoblast differentiation. Of 2743 genes with roles in cell differentiation, 15 were upregulated and 2 were downregulated in Osx-knockdown osteoblasts. In particular, the expression of fibrillin-2 and periostin was significantly increased in Osx-knockdown osteoblasts compared to that in control cells, as validated by RT-PCR and quantitative real-time PCR. Finally, this study showed differential gene expression profiles for Osx-mediated osteoblast differentiation, suggesting that fibrillin-2 and periostin will be target candidates of Osx in osteoblast differentiation.