A New Model for Specific Visualization of Skin Graft Neoangiogenesis Using Flt1-tdsRed BAC Transgenic Mice

Background: Neovascularization plays a critical role in skin graft survival. Up to date, the lack of specificity to solely track the newly sprouting blood vessels has remained a limiting factor in skin graft transplantation models. Therefore, the authors developed a new model by using Flt1-tdsRed BAC transgenic mice. Flt1 is a vascular endothelial growth factor receptor expressed by sprouting endothelial cells mediating neoangiogenesis. The authors determined whether this model reliably visualizes neovascularization by quantifying tdsRed fluorescence in the graft over 14 days. Methods: Cross-transplantation of two full-thickness 1 x 1-cm dorsal skin grafts was performed between 6- to 8-week-old male Flt1 mice and KSN/Slc nude mice (n = 5). The percentage of graft area occupied by tdsRed fluorescence in the central and lateral areas of the graft on days 3, 5, 9, and 14 was determined using confocal-laser scanning microscopy. Results: Flt1(+) endothelial cells migrating from the transgenic wound bed into the nude graft were first visible in the reticular dermis of the graft center on day 3 (0.5 +/- 0.1; p < 0.05). Peak neovascularization was observed on day 9 in the lateral and central parts, increasing by 2- to 4-fold (4.6 +/- 0.8 and 4.2 +/- 0.9; p < 0.001). Notably, some limited neoangiogenesis was displayed within the Flt grafts on nude mice, particularly in the center. No neovascularization was observed from the wound margins. Conclusion: The ability of the Flt1-tdsRed transgenic mouse model to efficiently identify the origin of the skin-graft vasculature and visualize graft neovascularization over time suggests its potential utility for developing techniques that promote graft neovascularization.