Vascular defects in gain‐of‐function fps/fes transgenic mice correlate with PDGF‐ and VEGF‐induced activation of mutant Fps/Fes kinase in endothelial cells

Background: Fps/Fes is a cytoplasmic tyrosine kinase that is abundantly expressed in the myeloid, endothelial, epithelial, neuronal and platelet lineages. Genetic manipulation in mice has uncovered potential roles for this kinase in hematopoiesis, innate immunity, inflammation and angiogenesis. Objective: We have utilized a genetic approach to explore the role of Fps/Fes in angiogenesis. Methods: A hypervascular line of mice generated by expression of a ‘gain‐of‐function’ human fps/fes transgene (fpsMF) encoding a myristoylated variant of Fps (MFps) was used in these studies. The hypervascular phenotype of this line was extensively characterized by intravital microscopy and biochemical approaches. Results: fpsMF mice exhibited 1.6–1.7‐fold increases in vascularity which was attributable to increases in the number of secondary vessels. Vessels were larger, exhibited varicosities and disorganized patterning, and were found to have defects in histamine‐induced permeability. Biochemical characterization of endothelial cell (EC) lines derived from fpsMF mice revealed that MFps was hypersensitive to activation by vascular endothelial growth factor (VEGF) and platelet‐derived growth factor (PDGF). Conclusions: MFps mediates enhanced sensitization to VEGF and PDGF signaling in ECs. We propose that this hypersensitization contributes to excessive angiogenic signaling and that this underlies the observed hypervascular phenotype of fpsMF mice. These phenotypes recapitulate important aspects of the vascular defects observed in both VEGF and angiopoietin‐1 transgenic mice. The fps/fes proto‐oncogene product therefore represents a novel player in the regulation of angiogenesis, and the fpsMF line of mice constitutes a unique new murine model for the study of this process.