Downregulation of Hypoxia-Inducible Factor-1 Alpha Reduces Venous Thrombus Resolution

Abstract

Hypoxia-inducible factor-1 (HIF-1)-mediated angiogenic factors, such as vascular endothelial growth factor (VEGF), are induced within venous thrombus during its resolution, but the primary stimulus for VEGF production and thrombus resolution is unknown. Our aim was to determine whether downregulating HIF-1α in the thrombus and vein wall reduces angiogenic factor expression, inflammatory cell infiltration, and thrombus resolution. Thrombus was induced in the inferior vena cava (IVC) of 40 mice. The mice were treated with the HIF-1α inhibitor 2-methoxyestradiol (2ME; intraperitoneal, 150 mg/kg/day) or vehicle control (n = 20/group). HIF-1α, VEGF, and placental growth factor (PLGF) expression in the thrombus and IVC were measured at days 1 and 10 (n = 7/group) by enzyme-linked immunosorbent assay. Thrombus size, neovascularization, recanalization, and macrophage and neutrophil infiltration were also measured at day 10 by image analysis (n = 6/group). The levels of HIF-1α (P < .001), VEGF (P < .001), and PLGF (P < .001), and neutrophil (P < .005) and macrophage (P < .05, Fig 1) infiltration were decreased in the thrombus of mice treated with 2ME compared with vehicle control. The levels of HIF-1α (P < .005), VEGF (P < .005), and PLGF (P < .001), and neutrophil (P < .01) and macrophage (P < .005, Fig 2) infiltration were also decreased in the IVC wall surrounding the thrombus of 2ME-treated mice compared with controls. Thrombus weight (P < .001, Fig 3) and size (P < .02, Fig 4) were increased, while thrombus neovascularization (P < .005, Fig 5) and vein recanalization (P < .005, Fig 6) were decreased in 2ME-treated mice compared with controls. Reducing HIF-1α expression in the thrombus and vein wall reduces angiogenic growth factor expression, inflammatory cell infiltration, and thrombus resolution. These data suggest that HIF-1 activity is an important regulatory mechanism in thrombus resolution.