Gene Expression Profiling Reveals Platelet-Derived Growth Factor Receptor Alpha as a Target of Cell Contact-Dependent Gene Regulation in an Endothelial Cell–Osteoblast Co-culture Model

Angiogenesis plays an important role in bone development, repair, and remodelling. Neovascularization is furthermore a crucial step in bone tissue engineering because implantation of voluminous grafts without sufficient vascularity results in hypoxic cell death of the engineered tissue. We have previously described a co-cultivation system of human primary osteoblasts and human primary endothelial cells that was developed to improve neovascularization in bone tissue–engineering applications. In our present study, we have performed complementary deoxyribonucleic acid microarray analysis to analyze putative changes in osteoblastic gene expression upon co-cultivation of osteoblasts and endothelial cells. Transcriptional profiling revealed upregulation of 79 genes and downregulation of 62 genes in osteoblasts after co-cultivation with endothelial cells. To verify the microarray data, quantitative real-time reverse transcriptase polymerase chain reaction was carried out on selected genes. The expression of the plateletderived growth factor receptor alpha gene in osteoblasts was analyzed in more detail, revealing that a cell contact–dependent mechanism, and not paracrine-acting diffusible factors, mediates the downregulation of this receptor in osteoblasts upon co-cultivation with endothelial cells. In summary, the data demonstrate complex gene-regulation mechanisms between endothelial cells and osteoblasts that are likely to play a role in bone morphogenesis.