Hypoxia and upregulation of hypoxia-inducible factor 1{alpha} stimulate venous thrombus recanalization.

OBJECTIVE: Angiogenic factors are expressed within thrombus during resolution, but the primary stimulus for neovascularization is unknown. Our aims were to determine whether (1) hypoxia and hypoxia-inducible factor 1α (HIF1α) are induced in resolving thrombus, (2) this stimulates angiogenic factor production, and (3) upregulating HIF1α enhances thrombus resolution and vein recanalization. METHODS AND
RESULTS: Oxygen tension in the thrombus was negatively correlated with HIF1α levels (Spearman correlation [RS] = -0.77, P<0.0001), whereas HIF1α levels positively correlated with vascular endothelial growth factor (VEGF) expression (Pearson correlation [R] = 0.85, P<0.0005), during resolution in a murine model. HIF1α (P<0.005), VEGF (P<0.005), and VEGF receptor 1 (VEGFR1) (P<0.05) expression was 2-fold greater in the thrombus of mice treated with the prolyl hydroxylase domain inhibitor L-mimosine compared with controls. The levels of 13 other HIF1-mediated angiogenic factors were also increased. Thrombus weight (P<0.001) and volume (P<0.05) were reduced by a third in l-mimosine-treated mice compared with controls, whereas vein recanalization (P<0.005) and thrombus neovascularization (P<0.001) were 2-fold greater, and this was associated with increased inflammatory cell content.
CONCLUSIONS: Hypoxia and HIF1α are induced in the naturally resolving thrombus and correlate with increased angiogenic factor expression. Upregulation of HIF1α enhances thrombus resolution and vein recanalization. HIF1α may represent a novel target for treatments that promote resolution and recanalization and reduce the incidence of post-thrombotic syndrome.