Abstract 646: Isoform-Specific Dysregulation of Endothelin Converting Enzyme-1 and Hypertension in E2F2-Deficient Mice
Introduction: E2F family of transcription factors play a pivotal role in cell cycle regulation but the cardiovascular specific role for one of its members, E2F2, is not well defined. Recent studies have revealed that a polymorphism in Endothelin Converting Enzyme-1b (ECE-1b) promoter (C-338A), which is strongly associated with blood pressure (BP) values in hypertensive women, is located at a E2F consensus site and increases the promoter affinity specifically for E2F2. Since ECE-1b has been shown to negatively regulate other active ECE-1 isoforms, we investigated the consequences of E2F2 deficiency on vascular response to ET precursor and BP in E2F2-null mice.
Methods and Results: The arterial BP of E2F2-null mice (6 month old) were measured by tail cuff method. It was significantly higher in E2F2-null mice (102.2±4.02 mmHg) compared to that of WT littermates (91.8±2.81 mmHg) (n=16, P<0.05). Aortic ring assay was performed using endothelial-intact aortas isolated from E2F2-null mice and WT littermates to assess the ECE-1 bioactivity. While KCL (30 mM)- or Phenonephrine (10-9-3x10-6M)-induced contraction and Acetylcholine (10-9-10-6M)-induced relaxation were similar between the two groups, the E2F2-null aortas demonstrated a significantly increased contractile response to Big ET (2.7x10-7 M to 2.1x10-6 M). At maxmum dose, E2F2-null aorta contracted to 80.0±18.81 vs. 26.5±6.77 by WT aorta (% Contraction /KCl, n=4, P<0.05), indicating a specific increase in ECE-1 activity due to the loss of E2F2. To confirm that the increased ECE-1 activity in E2F2-null mice is due to a specific regulation of ECE-1b promoter by E2F2, bovine aortic endothelial cells were co-transfected with E2F2 and ECE-1b promoter plasmids and luciferase reporter assay was performed. Overexpression of E2F2 significantly increased the native form, but not the (C-338A) polymorphic form, of ECE-1b promoter activity (28.7 vs. 1.9 fold induction, P<0.001), suggesting that E2F2 activates ECE-1b and that this polymorphism may blunt E2F2-induced ECE-1b expression to increase ECE-1 bioactivity.
Conclusion: We provide genetic evidence that E2F2 regulates ECE-1b expression and vascular contraction. Deregulated E2F2 activity therefore may contribute to the pathogenesis of hypertension.