Differential gene expression by Osterix knockdown in mouse chondrogenic ATDC5 cells

Osterix (Osx) is a transcription factor required for osteoblast differentiation during intramembranous and endochondral ossification. Recently, several reports have described novel functions of Osx in chondrocyte differentiation. In an in vitro study, in which the effects of Osx gene silencing were examined in mouse chondrogenic ATDC5 cells, chondrocyte marker genes were found to be expressionally downregulated and chondrocyte differentiation reduced. On the other hand, in vivo studies based on chondrocyte-specific Osx knockouts demonstrated impaired endochondral bone formation with delayed chondrocyte differentiation and reduced cartilage matrix ossification. However, little is known about the mechanism or targets of Osx involved in the control of chondrocyte differentiation. Here, we attempted to high-density of Affymetrix GeneChip microarray to investigate global gene expression profile changes caused by Osx knockdown in ATDC5 chondrocytes. The mRNA expressions of 112 genes were significantly modified by Osx knockdown: 68 genes were upregulated and 44 genes downregulated. Functional categories of gene expression classified by gene ontology demonstrated that genes related to cell adhesion, development, and signal transduction were highly affected by Osx knockdown. The expressions of differential genes, such as Sfrp2, Sema3a, Nox4, Rgs4, Zfp521, Has2, Sox6, Scn2a1, Sirpa, and Thbs2, were validated by quantitative real-time PCR. This study shows that expression profiling can be used to identify genes that are transcriptionally modified following Osx knockdown and to reveal the molecular mechanism of chondrocyte differentiation regulated by Osx.