Abstract 1176: Vascular Endothelial Growth Factor Accelerates Neointima Formation Through Flk-1 After Wire Injury In Flt-1 Tyrosine Kinase-deficient Mice
[Background] Vascular endothelial growth factor (VEGF) expression increases in vascular wall after percutaneous coronary intervention in humans, whereas the pathological role of VEGF induction remains to be clarified. We have reported that blockade of endogenous VEGF by soluble VEGF receptor type 1 (sFlt-1) gene transfer inhibits neointima formation after vascular injury in mice, rabbits, and monkeys (Circulation 2004), and hypertensive vascular remodeling in mice (Hypertension 2004). However, it remains to be clarified which of two VEGF receptors (flt-1 and flk-1/KDR) mediates VEGF-dependent neointima formation. Therefore, the aim of this study was to determine the relative contribution of flt-1 versus flk-1 in the pathogenesis of neointima formation after wire injury.
[Methods and results] We used flt-1 tyrosine kinase knockout (Flt-1-TK-KO) mice (C57BL/6J background), which underwent wire injury in femoral arteries. We analyzed neointima formation as intima to media ratio (I/M ratio) 28 days after injury. Neointima formation was comparable between wild type and Flt-1-TK-KO mice (I/M ratio 2.5 ± 0.2 vs. 2.2 ± 0.4, p = 0.50), suggesting the minor role of flt-1. Next, we performed soluble Flt-1 (sFlt-1) gene transfer into Flt-1-TK-KO mice in order to block the effect of endogenous VEGF on flk-1 as well as flt-1. The sFlt-1 gene transfer inhibited neointima formation (I/M ratio 1.4 ± 0.4 vs. 2.8 ± 0.4, p < 0.05) and suppressed macrophage infiltration (50 ± 20 cells/vessel vs. 193 ± 32 cells/vessel, p < 0.01). MCP-1 expression in injured vascular wall was also inhibited. Proliferating cells in neointima evaluated by PCNA staining were also inhibited by sFlt-1 gene transfer (84 ± 13 cells/vessel vs. 126 ± 13 cells/vessel, p < 0.05). In vitro Boyden chamber experiment using abdominal macrophages revealed that VEGF-induced chemotaxis was abrogated in Flt-1-TK-KO mice, whereas MCP-1-induced chemotaxis was comparable with that in wild type mice.
[Conclusions] The present study clearly showed that VEGF accelerates neointima formation through flk-1 but not flt-1 after wire injury in mice. VEGF/flk-1 may contribute to the mechanism of neointima formation by enhancing MCP-1 expression and chemoattracting monocyte/macrophages into injured vascular wall.