Angiotensin II suppresses osteoblastic differentiation and mineralized nodule formation via AT₁ receptor in ROS17/2.8 cells

Introduction: Angiotensin II (Ang II) not only regulates systemic blood pressure through a vasoconstrictive effect, but also promotes bone resorption. We recently reported that Ang II (10^-6 M) stimulated the production of matrix metalloproteinases via the AT₁ receptor in osteoblastic ROS17/2.8 cells, but suppressed alkaline phosphatase activity. However, the roles of Ang II in osteoblastic differentiation and the function of osteogenesis in osteoblasts are unclear. Therefore, we examined the effect of Ang II on the expression of osteogenesis-related transcription factors and extracellular matrix (ECM) proteins, as well as mineralized nodule formation in ROS17/2.8 cells. Material and methods: ROS17/2.8 cells were cultured with 0 (control) or 10^-6 M Ang II in the presence or absence of the AT₁ receptor blocker losartan. Mineralized nodule formation was detected by Alizarin Red staining. Gene and protein expression levels of transcription factors and ECM proteins were determined using real-time PCR and Western blotting, respectively. Results: Runx2, Msx2, and osteocalcin expression significantly decreased with Ang II compared to the control, whereas AJ18 expression significantly increased. Osterix, Dlx5, type I collagen, bone sialoprotein, and osteopontin expression was unaffected. Mineralized nodule formation and calcium content in mineralized nodules decreased with Ang II. Losartan blocked suppressive or stimulatory effects of Ang II on Runx2, Msx2, osteocalcin, and AJ18 expression. Conclusions: These results suggest that Ang II suppresses osteoblastic differentiation by altering the expression of osteogenesis-related transcription factors via the AT₁ receptor and the function of osteogenesis in ROS17/2.8 cells.