SP1/TGF-β1/SMAD2 pathway is involved in angiogenesis during osteogenesis

The relationship between osteoblasts and angiogenesis is vital for bone regeneration, especially mandibular and maxillary bones. Transforming growth factor β1 (TGF-β1) and vascular endothelial growth factor (VEGF) are closely related to angiogenesis; however, the regulatory mechanism between them remains unknown. The present study aimed to reveal this mechanism to provide novel insight for development of potential therapeutic opportunities. Western blotting and reverse transcription-quantitative PCR was used to assess the protein and mRNA expression levels in MC3T3-E1 preosteoblast cells and HUVECs, ELISAs were used to detect the expression levels of secreted VEGF, MTT assays were used to assess the viability of the cells, migratory ability was assessed using Transwell assays, angiogenesis assays were used to analyze the formation of blood vessels, and TGF-β1 regulation was confirmed using a dual-luciferase reporter assay. The overexpression of specificity protein 1 (SP1) or TGF-β1 increased VEGF expression levels and secretion, and promoted angiogenesis of co-cultured HUVECs. SP1 also promoted SMAD2 phosphorylation. These effects of SP1 were all reversed by the TGF-β1 inhibitor. The VEGF inhibitor bevacizumab also reduced the SP1/TGF-β1/SMAD2 pathway-induced angiogenesis of preosteoblasts. In conclusion, it was demonstrated that SP1 promoted TGF-β1 expression, activated the SMAD2 pathway and induced VEGF secretion, which may enhance angiogenic processes in preosteoblasts.