Deficiency of bone marrow β3-integrin enhances non-functional neovascularization

beta 3-Integrin is a cell surface adhesion and signalling molecule important in the regulation of tumour angiogenesis. Mice with a global deficiency in beta 3-integrin show increased pathological angiogenesis, most likely due to increased vascular endothelial growth factor receptor 2 expression on beta 3-null endothelial cells. Here we transplanted beta 3-null bone marrow (BM) into wild-type (WT) mice to dissect the role of BM beta 3-integrin deficiency in pathological angiogenesis. Mice transplanted with beta 3-null bone marrow show significantly enhanced angiogenesis in subcutaneous B16F0 melanoma and Lewis lung carcinoma (LLC) cell models and in B16F0 melanoma lung metastasis when compared with tumours grown in mice transplanted with WT bone marrow. The effect of bone marrow beta 3-integrin deficiency was also assessed in the RIPTAg mouse model of pancreatic tumour growth. Again, angiogenesis in mice lacking BM beta 3-integrin was enhanced. However, tumour weight between the groups was not significantly altered, suggesting that the enhanced blood vessel density in the mice transplanted with beta 3-null bone marrow was not functional. Indeed, we demonstrate that in mice transplanted with beta 3-null bone marrow a significant proportion of tumour blood vessels are non-functional when compared with tumour blood vessels in WT-transplanted controls. Furthermore, beta 3-null-transplanted mice showed an increased angiogenic response to VEGF in vivo when compared with WT-transplanted animals. BM beta 3-integrin deficiency affects the mobilization of progenitor cells to the peripheral circulation. We show that VEGF-induced mobilization of endothelial progenitor cells is enhanced in mice transplanted with beta 3-null bone marrow when compared with WT-transplanted controls, suggesting a possible mechanism underlying the increased blood vessel density seen in beta 3-null-transplanted mice. In conclusion, although BM beta 3-integrin is not required for pathological angiogenesis, our studies demonstrate a role for BM beta 3-integrin in VEGF-induced mobilization of bone marrow-derived cells to the peripheral circulation and for the functionality of those vessels in which BM-derived cells become incorporated. Copyright (C) 2009 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.