Altered VEGF-A and receptor mRNA expression profiles, and identification of VEGF144 in foetal rat calvaria cells, in coculture with microvascular endothelial cells.

摘要

Cellular proliferation and differentiation during angiogenesis and osteogenesis require the communication of different cell types through growth factors and their receptors. Vascular endothelial growth factor (VEGF-A) plays an important role in osteoblast and endothelial cell intercommunication. We have investigated the effect of monocultures and indirect coculture of foetal rat calvarial (FRC) osteoblasts and microvascular endothelial cells (ECs) on nodule formation, proliferation, and mRNA-expression of VEGF-A and its receptors during culturing. Despite increased nodule formation in the presence of dexamethasone (Dex) in monocultures, the number of nodules and alkaline phosphatise activity were decreased in cocultured FRCs. VEGF mRNA expression over the differentiation period showed the expression of most Vegf isoforms is biphasic in both FRCs and ECs, whereas receptor expression was quite variable; however, that of Np-2 in FRCs increased steadily and significantly from 8?h to 14 days after an initial drop in expression. Significant changes in the proportion of Vegfa by Day 14 were noted mainly in the matrix-bound variants Vegf144 and Vegf188 in ECs and osteoblasts, respectively. Less striking results were seen in the expression of the soluble isoforms in either cell type. These results have identified expression of Vegf144 in osteoblasts, suggesting a possible autocrine and/or paracrine role that is affecting osteoblast mineralisation along with Vegf188, as well as possible early roles of these isoforms in initial cell attachment. Further study of VEGF expression in coculture and Vegf144 will lead to better understanding of its role in cell-cell communication and bone development.