Phosphate enhances reactive oxygen species production and suppresses osteoblastic differentiation

Phosphate has been shown to work as a signaling molecule in several cells including endothelial cells and chondrocytes. However, it is largely unknown how phosphate affects osteoblastic cells. In the present study, we investigated the effects of phosphate on reactive oxygen species (ROS) production and osteoblastic differentiation in murine osteoblastic MC3T3-E1 cells. Phosphate increased production of ROS in MC3T3-E1 cells and the inhibitors of sodium-phosphate cotransporter and NADPH oxidase suppressed ROS production by phosphate. Silencing Nox1 and Nox4 also inhibited the increase of ROS by phosphate. Phosphate also decreased alkaline phosphatase activity induced by bone morphogenetic protein 2 and this inhibition was abrogated by an inhibitor of NADPH oxidase. Furthermore, phosphate decreased the expression of osteoblastic marker genes in MC3T3-E1 cells. These results indicate that phosphate suppresses osteoblastic differentiation at least in part by enhancing ROS production in MC3T3-E1 cells.