Dioxin-Sensitive Proteins in Differentiating Osteoblasts: Effects on Bone Formation In Vitro

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is an endocrinedisrupting environmental pollutant which affects bone tissue, although the mechanistic basis of this action is far from clear. We adopted a proteome approach to investigate the disturbance of osteogenesis evoked by TCDD in an in vitro osteoblast differentiation model of rat mesenchymal stem cells. Eighteen individual proteins showed a significant change in abundance as results of ten days of TCDD exposure, at which time mRNA changes in osteoblast differentiation markers were also observed. These proteins were mostly involved in cytoskeleton organization and biogenesis, actin filament-based processes, protein transport, and folding. The alteration in cell architecture and increase in cell adhesion were confirmed by confocal microscopy. The TCDDinduced decrease in the expression of calcium-binding proteins may interfere with osteoblast calcium deposition, which was in fact reduced by TCDD. This is the first report investigating, at the protein expression level, the effect of TCDD during osteoblastic differentiation. Interestingly, MetaCore pathway analysis grouped the majority of these proteins around two principal nodes (c-fos and c-myc) suggesting that they may participate in the transcriptional activation of key pathways in TCDD-driven inhibition of osteoblast differentiation. Our findings provide evidence of new molecular players in the effects of TCDD on bone development.