Vascular endothelial growth factor (VEGF) has been indicated to play a role during endochondral ossification by stimulation of blood vessel invasion into hypertrophic cartilage resulting in its replacement by trabecular bone. We could demonstrate a dose-dependent chemoattractive effect of VEGF-A and PIGF-1, but not VEGF-E or VEGF-C, on human mesenchymal progenitor cells. Quantitative realtime PCR revealed the expression of VEGFR-I (Flt-1), VEGFR-2 (KDR/Flk-1), and VEGFR-3 (Flt-4), which markedly declined during osteogenic differentiation. In addition, expression of neuropilin-1 and -2 was detected by RT-PCR. In an in vitro kinase assay, we could demonstrate activation of VEGFR-I and VEGFR-2 upon stimulation with specific ligands. These findings are consistent with the idea that the chemotactic effect of VEGF-A on MPC is mediated via VEGFR-1, and that VEGF-A and PIGF-1, have a functional role for recruitment of osteoprogenitor cells in the course of endochondral bone formation or remodeling. (c) 2005 Elsevier Inc. All rights reserved.