PB0930 - HIF-1 Inhibition Reduces Venous Thrombosis in a Murine Polycythemia Vera Model

Background: Twenty-five percent of polycythemia vera (PV) patients will have a thrombotic event after their PV diagnosis. Somatically acquired activating JAK2V617F mutations underly nearly all PV and result in quantitative and qualitative blood cell changes. Aberrant JAK2 signaling results in stabilization of hypoxia-inducible factors (HIF), creating a state of “pseudo-hypoxia.” Hypoxia has long been implicated in venous thrombosis (VT). We previously reported that neutrophils from PV patients have increased HIF-mediated gene expression which positively correlated with neutrophil tissue factor (TF) gene expression and thrombosis history.

Aims: We aimed to study the effect of increased HIF stabilization on VT in PV and to determine the effect of HIF on TF expression.

Methods: Transgenic JAK2 V617F (VF) and wild type littermate (WT) mice were pre-treated with the HIF-1 inhibitor echinomycin 10ug/kg daily for 5 days and then subjected to inferior vena cava (IVC) stenosis. At 24 hours, blood was collected from supra-renal IVC for complete blood count and resulting thrombi were gently extruded from the IVC, weighed, and snap frozen. Western blotting was performed on the soluble protein fraction of thrombi for TF expression. In a separate set of echinomycin-treated mice, spleens were collected for mRNA analysis of HIF-mediated gene expression.

Results: VF mice have increased expression of HIF-1 mediated genes as compared to WT (Figure 1). Echinomycin treatment reduced HIF-1 mediated gene expression without affecting peripheral blood cell counts (Figure 1). VF mice had significantly larger venous thrombi than WT littermates (Figure 2). Echinomycin treatment of VF mice resulted in significant reduction of thrombus weight compared to vehicle treated controls and significant attenuation of TF protein expression in venous thrombi (Figure 2).

Conclusion(s): HIF-1 contributes to increased VT in VF mice, at least in part by increasing thrombus TF expression. This finding highlights the importance of qualitative cellular changes to thrombosis risk in PV.