Abstract 407: Modulation of Delta-Like Ligand-4 Signaling Improves Myocardial Revascularization Following Coronary Ischemia

Abstract

Delta-like ligand-4 (DLL4) is an arterial-specific Notch ligand and balanced signaling by DLL4 is required for functional neovascularization. We hypothesized that modest inhibition of DLL4 signaling improves myocardial revascularization following coronary ischemia. Myocardial infarction was induced by ligation of mid-left anterior descending (LAD) artery via rapid left thoracotomy in 6-8 week-old male mice with inducible endothelial-specific knockout or overexpression of DLL4. DLL4 silencing in homozygous mice on the day of or 5 days prior to LAD ligation resulted in significant reduction in revascularization. At four weeks, explanted hearts showed 1.8-fold fewer vessels in LAD territory, 3-fold greater myocardial hypoxia, 1.7-fold larger fibrotic scar and 17% increased perfusion defect in the left ventricle (LV) by scintigraphy. CT angiography confirmed fewer collateral vessels. Echocardiography showed increased LV dilation (37% higher end-diastolic volume) and 12% greater reduction in ejection fraction (EF) compared to baseline (all p<0.001). Overexpression of DLL4 showed a similarly worse outcome. Conversely, partial DLL4 knockout in heterozygous animals resulted in improved outcomes in all parameters. For translational application, animals were systemically administered 1.5mg/kg or 3mg/kg DLL4-Fc intraperitoneally three times a week beginning the day of ligation. RT-PCR analysis of downstream molecules confirmed that systemic DLL4-Fc partially inhibits Notch signaling in endothelial cells in the ischemic LV. When LAD was ligated very proximally, DLL4-Fc improved survival. With mid-LAD ligation, DLL4-Fc induced a dose-dependent increase in number of CD 31-positive vessels and by CT angiography. There was a dose-dependent reduction in hypoxic myocardial area, scar burden, and scintigraphic perfusion defect. DLL4-Fc treated mice had lower end-diastolic LV volume and preserved or improved EF. In an ischemia-reperfusion model, DLL4-Fc increased the number of vessels in the ischemic zone. Our data suggests that balanced DLL4 signaling is crucially required for myocardial angiogenic recovery following coronary ischemia. Modulation of DLL4 signaling has translational therapeutic potential.