Abstract 18384: Hypoxia-Induced FOXC2 Expression in Human Endothelial Cells is Dependent on the MEK and PI3K Pathways

Abstract

FoxC2, a member of the Forkhead box (Fox) transcription factor family, is critical for vascular formation during embryonic development and tumor progression; however, the role of Foxc2 in pathological neovascularization involving ischemic conditions remains largely unknown. To test the hypothesis that FoxC2 is induced and required for hypoxia-induced angiogenesis, in vitro culture of human umbilical vein endothelial cells (HUVECs) under hypoxia and a myocardial infarction (MI) mouse model were employed. FoxC2 expression in both experimental systems was subsequently assessed. Levels of FOXC2 mRNA were transiently increased in HUVECs after 1 hour of hypoxia. Treatment of a mitogen-activated protein kinase kinase (MEK) 1/2 inhibitor (U0126) and a phosphatidylinositide 3-kinases inhibitor (LY 294002) significantly blocked hypoxia-induced FOXC2 expression, whereas culture with a MEK1 inhibitor (PD 98059) did not. Consistent with the in vitro observation, expression of Foxc2 was upregulated in ischemic myocardial tissue of murine hearts in a time-dependent manner from day 1 to day 7 after surgically induced MI. We next examined whether Foxc2 deficiency could influence neovascularization and cardiac repair after MI. Echocardiographic measurements of left ventricular ejection fractions and fractional shortening were reduced in heterozygous Foxc2 null mutant (Foxc2+/-) mice after MI compared to wild-type mice, whereas cardiac fibrosis was increased in Foxc2+/- mice. Most significantly, Foxc2+/- mice had a drastic reduction in capillary vessel formation in the ischemic border zone after MI compared to wild-type mice. Collectively, FoxC2 is transiently induced in vascular endothelial cells in vitro under hypoxia and in ischemic murine hearts after MI, and it is essential for neovascularization during ischemic cardiac repair after MI.