Abstract 349: Overexpression of Tie2-Promoted Activated Fibroblast Growth Factor Receptor 2 in Endothelial Cells Enhances Mature Neovascularization via Akt Signaling Pathway in Mice Hindlimb Ischemia
Introduction: Fibroblast growth factor (FGF) is a potent angiogenic mediator that stimulates cell proliferation, migration, and differentiation through binding to membrane-associated tyrosine kinase receptors (FGFR), whereas the pathophysiological role of FGFR signaling in endothelial cells (ECs) has not been fully elucidated.
Methods and Results: We surgically induced hindlimb ischemia in transgenic mice overexpressing activated human FGFR2 linked to the Tie2 promoter (Tie2-FGFR-Tg) and studied the mechanisms for FGFR-mediated capillarization and arteriogenesis in association with Tie2-FGFR-mediated mobilization of EC progenitors. Laser Doppler imaging revealed a markedly increased recovery of blood perfusion in ischemic limbs of Tie2-FGFR-Tg mice (32% increase at Week 4), compared with wild-type mice. Although basal CD31+ capillary and αSMA+ arteriole numbers were not different between these mice, ischemia-induced capillarization and arteriogenesis in Tie2-FGFR-Tg mice was significantly increased to 1.2-fold and 1.6-fold of wild-type mice (p<0.001). There was no significant difference in a basal and ischemia-induced increase in circulating CD45-/Flk-1+ endothelial-linkaged progenitor cells between these mice. In contrast, cultured ECs from Tie2-FGFR-Tg mice showed a marked increase in VEGF-induced migratory capacity and tube formation by 1.9-fold and 2.0-fold over wild-type mice (p<0.001). Moreover, serum-deprivation-induced EC apoptosis was significantly inhibited (40%, p<0.001) in Tie2-FGFR-Tg mice. Western blot analysis showed that Akt phophorylation in ECs was significantly increased in Tie2-FGFR-Tg mice, and these in vitro pro-angiogenic activities were significantly inhibited by phospho-inositide-3 kinase inhibitor, LY294002. Notably, migratory activity of cultured vascular smooth muscle cells (VSMCs) from wild-type mice was significantly enhanced in conditioned medium from hypoxic Tie2-FGFR-Tg ECs.
Conclusion: The present data demonstrate that FGF signaling augments neovessel formation via Akt activation in resident ECs in the ischemic regions. Moreover, activated FGF signaling accelerates the paracrine effect on recruitment of VSMCs, resulting in the formation of mature vascular networks.