Transforming growth factor-beta3 induced apoptosis of osteoblasts

Exogenous application of transforming growth factor-beta3 (Tgf-beta3) cytokine has been shown to inhibit cranial suture fusion in wild-type murine models and in craniosynostotic rabbits. It is necessary to establish the mechanism by which Tgf-beta3 inhibits the cranial suture fusion before this can be considered for therapeutic applications. It has been speculated that Tgf-beta3-induced suture maintenance is possibly mediated by upregulation of apoptosis and decreased levels of cell proliferation. Objective:This study was designed to determine the effects of Tgf-beta3 on the apoptosis of osteoblasts and to understand the signaling pathways that mediate the control of Tgf-beta3-mediated apoptosis of osteoblasts. Methods: Mouse osteoblast-like MC3T3-E1 cells were synchronized at G1 phase by serum starvation. Once synchronized, osteoblasts were treated with 1 nM Tgf-beta3 for 24 to 48 hours. Controls received 10% FBS (fetal bovine serum). Cells were collected and stained with Propidium Iodide for cell cycle analysis and apoptosis assay by BD FACSArray Bioanalyzer. Results: Tgf-beta3 induced cell cycle arrest in MC3T3-E1 cells and nearly 94.9% cells remained at G1 state after 24 hours. After 48 hours, 11.4 % of osteoblasts treated with Tgf-beta3 were apoptotic which was almost 9 times that of cells treated with FBS only. Conclusion: Tgf-beta3 induced cell cycle arrest and apoptosis of osteoblasts, which may have inhibited the fusion of Tgf-beta3-treated cranial sutures.