Transforming growth factor-β1 modulates the expression of vascular endothelial growth factor by osteoblasts.

Angiogenesis is essential to both normal and pathological bone physiology. Vascular endothelial growth factor (VEGF) has been implicated in angiogenesis, whereas transforming growth factor-β1 (TGF-β1) modulates bone differentiation, matrix formation, and cytokine expression. The purpose of this study was to investigate the relationship between TGF-β1 and VEGF expression in osteoblasts and osteoblast-like cells. Northern blot analysis revealed an early peak of VEGF mRNA (6-fold at 3 h) in fetal rat calvarial cells and MC3T3-E1 osteoblast-like cells after stimulation with TGF-β1 (2.5 ng/ml). The stability of VEGF mRNA in MC3T3-E1 cells was not increased after TGF-β1 treatment. Actinomycin D inhibited the TGF-β1-induced peak in VEGF mRNA, whereas cycloheximide did not. Blockade of TGF-β1 signal transduction via a dominant-negative receptor II adenovirus significantly decreased TGF-β1 induction of VEGF mRNA. Additionally, TGF-β1 induced a dose-dependent increase in VEGF protein expression by MC3T3-E1 cells ( P < 0.01). Dexamethasone similarly inhibited VEGF protein expression. Both TGF-β1 mRNA and VEGF mRNA were concurrently present in rat membranous bone, and both followed similar patterns of expression during rat mandibular fracture healing (mRNA and protein). In summary, TGF-β1-induced VEGF expression by osteoblasts and osteoblast-like cells is a dose-dependent event that may be intimately related to bone development and fracture healing.