Abstract 18783: Contrasting Roles Of E2F2 And E2F3 in Endothelial Cell Growth and Ischemic Angiogenesis

Abstract

Background: Endothelial cell (EC) growth is essential for angiogenesis and ischemic tissue repair. The E2F family of transcription factors are master regulators of genes responsible for cell-cycle regulation; however, the specific roles of individual E2Fs in ECs are largely unknown. Here, we investigated the roles of E2F2 and E2F3 in EC growth, angiogenesis, and their functional impact on limb ischemia and myocardial infarction (MI). Methods and Results: We generated an endothelial-specific E2F3-deficient mouse strain, Tie2-Cre;E2F3 fl/fl (EndoE2F3 Δ / Δ ). The animals were embryonic lethal with a penetrance equivalent to the global E2F3-knockout mice (live birth at ∼8% of the expected frequency). The survived EndoE2F3 Δ / Δ mice grew to adulthood relatively normally, however, developed limb and toe necrosis (25% and 50%, respectively) after surgically-induced hindlimb ischemia and displayed a larger infarct size and worsened LV EF than Tie2-Cre;E2F3 +/+ littermates after surgical MI. Notably, in the ischemic tissues, the capillary density and rate of EC proliferation (BrdU staining) were significant lower in EndoE2F3 Δ / Δ mice than in the controls. In contrast, E2F2 -/- mice displayed better functional parameters after the surgical injuries and an increase in local vessel density and EC proliferation as compared to WT littermates. Ex vivo aortic ring assays confirmed that microvessel outgrowth was impaired in EndoE2F3 Δ / Δ explants, however, enhanced in E2F2 -/- explants. We then evaluated the roles of E2F2 and E2F3 on EC proliferation in vitro . ECs were isolated from lungs of the genetic mice, with E2F3 fl/fl ECs being transduced with Adeno-Cre/GFP or Adeno-GFP. The E2F3 fl/fl /AdenoCre-GFP ECs exhibited a dramatically lowered growth rate and reduced DNA synthesis than E2F3 fl/fl /AdenoGFP ECs. Furthermore, the expression of E2F target genes, including CyclinA, Cdc2, Cyclin D, B-Myb, DHFR and Cdc6, was significantly downregulated in E2F3 fl/fl /AdenoCre-GFP ECs. In contrast, E2F2 -/- ECs displayed an increased rate of cell growth, DNA synthesis and the expression of E2F-regulated genes. Conclusions: E2F3 promotes while E2F2 suppresses ischemic tissue repair via reciprocal regulation of cell-cycle gene expression, EC proliferation and angiogenesis.