Purpose: The question of whether adult animals maintain a reservoir of endothelial progenitor cells (EPCs) in the bone marrow that is involved in neovascularization is under investigation. The following study was undertaken to examine the potential contribution of EPCs to the development of choroidal neovascularization (CNV) in adult mice and to examine the role of local expression of vascular endothelial growth factor (VEGF) in this process.
Methods: Lethally irradiated, adult female nude mice were engrafted with whole bone marrow isolated from male transgenic mice expressing LacZ driven by the endothelial specific Tie-2 promoter. Two months, following bone marrow reconstitution, confirmed by quantitative Taqman PCR, an E1-deleted adenoviral vector expressing vascular endothelial growth factor (165) (Ad.VEGF(165)) was injected subretinally to induce CNV, confirmed by collagen IV immunohistochemistry. Bone marrow-derived endothelial cells were detected using either X-gal staining or Y chromosome in situ hybridization. Y chromosome positive cells within the CNV were confirmed to be endothelial cells by lectin staining.
Results: Subretinal Ad.VEGF(165) was capable of inducing CNV. Four-week old lesions were found to contain LacZ expressing cells within the CNV in bone marrow transplanted animals but not in negative control animals. Eighteen percent of all Y chromosome positive cells within the CNV were found to be lectin positive while 27% of all endothelial cells within the CNV were Y chromosome positive.
Conclusion: Engrafted bone marrow-derived EPCs were shown to differentiate into endothelial cells at the site of subretinal VEGF-induced CNV in mice. These results suggest that EPCs contribute to the formation of neovascularization and that subretinal expression of VEGF might play an important role in recruitment of these cells to the site of CNV.