Inhibition of phosphatidylinositol 3-kinase causes cell death in rat osteoblasts through inactivation of Akt.

Previous evidences indicated that phosphatidylinositol 3-kinase (PI3-kinase) is an important regulatory molecule that is involved in the cell growth and survival, and inhibition of the PI3-kinase activity enhances apoptotic cell death. However, the relationship between PI3-kinase activity and osteoblasts, capable of new bone formation, remained unknown. In the present study, pharmacological inhibitor of PI3-kinase LY294002 was used to observe the role of the PI3-kinase in the growth of rat osteoblasts. To identify its molecular mechanism, Western blots analysis and immunocytochemistry were applied to examine changes of Akt phosphorylation and its distribution. Our data showed that inhibition of PI3-kinase activity significantly triggered the decrease of cell growth, cell apoptosis and loss of mitochondrial membrane potential (Deltapsi(m)). Osteoblastic dysfunction stimulated by LY294002 was accompanied by inactivation of Akt and its redistribution. In all these results demonstrated that inhibition of PI3-kinase induced apoptotic cell death, which was mediated by inactivation of Akt pathway in rat osteoblasts.