title: Distinct capillary density and progression promoted by vascular endothelial growth factor-A homodimers and heterodimers.
abstract: The aim of this study was to characterize the capillary density, progression and persistence of new capillaries induced by different isoforms of vascular endothelial growth factor (VEGF)-A. They were produced and purified using the same protocol and assessed in the same experimental model, the rabbit cornea assay. Monogenic homodimers for VEGF121 and VEGF165 together with the heterodimer VEGF121/165 were tested as slow release polymer pellets implanted into the avascular rabbit cornea and examined up to 18 days post-implantation. The implants consistently stimulated angiogenesis in the absence of inflammation. The VEGF121 isoform produced the strongest increase of new capillary vessels which rapidly and persistently progressed into the corneal stroma. VEGF165 promoted the growth of a smaller number of capillaries which ten-ded to regress over time. Heterodimers of VEGF121/165 produced intermediate in vivo activities between the two homodimers. In vitro endothelial cell proliferation, mobilization and adhesion were promoted by all VEGF isoforms under serum-free or serum-reduced conditions with the same order of potency. Anti-soluble KDR (sKDR) antibody completely inhibited the effects of all the isoforms. These results indicate that monogenic homodimer preparations of VEGF121 and VEGF165 can display distinct biological effects which are functionally retained after the heterodimeric assembly of VEGF121 and VEGF165. The observed different biological behavior of the VEGF isoforms reveals the possibility that in vivo the assembly of dimers derived from splicing of a single gene may yield molecules with either different matrix or receptor interaction, stability or diffusion rate according to specific needs.