Abstract 17503: E2F1 Stabilizes P53 and Suppresses Neovascularization in the Ischemic Myocardium
Introduction: Insufficient neovascularization contributes to the pathogenesis of ischemic heart disease and limits cardiac tissue preservation and regeneration. The E2F family of transcription factors play a central role in cell-cycle control therefore provides an ideal target for therapeutic modulation of vascular growth.
Objective: To investigate the role of E2F1 in cardiac neovascularization following myocardial infarction (MI).
Methods and Results: We induced MI in wild-type (WT) and E2F1−/− mice by ligating the LAD coronary artery. At day 28 post-MI, E2F1−/− mice exhibited a significantly smaller infarct size (Masson's Trichrome staining, p<0.01, n=15) and a greater vessel density in the infarct border area (lectin perfusion and staining, p<0.01, n=5). We then analyzed angiogenic factors in the ischemic myocardium. Notably, E2F1−/− mice expressed a significantly higher level of VEGF mRNA (qRT-PCR) and protein (Western blotting) than WT mice (p<0.01, n=5, at day 5 post-MI). In vitro, hypoxia treatment (0.5% O2 for 24h) induced VEGF mRNA expression to a higher level in E2F1−/− cardiac fibroblasts than in WT control cells (p<0.01, n=3). Overexpression of E2F1 suppressed the hypoxia-induced VEGF promoter activity in WT cells, interestingly, not in p53−/− cells, suggesting that p53 is required for E2F1 to suppress VEGF transcription. Hypoxia treatment increased the level of both E2F1 and p53 proteins; overexpression of E2F1 further enhanced the p53 accumulation. After WT and E2F1−/− fibroblasts were treated with hypoxia for 6h, pulsed with cyclohexamide and returned to normoxia, the p53 protein level declined gradually in WT cells, however, significantly faster in E2F1−/− cells (p<0.01 at 1, 2, and 4h, n=4), confirming that E2F1 enhances p53 protein stability. Furthermore, co-immunoprecipitation experiments indicated that hypoxia treatment induces physical association of endogenous E2F1 and p53 and that the N-terminus (amino acids 1–109) of E2F1 is essential for the association.
Conclusions: E2F1 inhibits cardiac neovascularization through E2F1:p53 interaction and repression of VEGF expression. Targeting E2F1 or E2F1:p53 interaction (e.g., by E2F1 N-terminal peptide) may protect heart from ischemic injury.
- © 2010 by American Heart Association, Inc.