Abstract 5427: Regulation of Arterial Branching Morphogenesis by Notch Ligand Delta-like 1

Abstract

Arterial development and homeostasis are regulated by genetic factors and hemodynamic forces but how hemodynamic forces shape arterial branching morphogenesis and whether there is cross-talk to genetic programms is largely unknown. Here we show that the Notch ligand Delta-like 1 (Dll1) is regulated by hemodynamic forces to regulate arterial branching morphogenesis and adult arterial phenotype in vivo. RESULTS: The onset of Dll1 expression was observed in fetal arteries at embryonic day E12.5, concurrent with the establishment of proper arterial circulation. Dll1 expression was restricted to endothelial cells (EC) of arteries and absent in veins or capillaries. Arterial branching morphogenesis in the developing retinal vasculature was significantly reduced in Dll1+/− mice, which lacked arterial branches forming the secondary vascular plexus. To test the influence of hemodynamic forces on Dll1 expression we exposed human aortic EC to cyclic stretch in vitro (10 and 15%), which upregulated Dll1 mRNA and protein levels and activated Notch target gene expression of Hes1 in a time-dependent manner. Dll1 regulation by hemodynamic forces had a strong impact on the branching phenotype of adult coronary arteries. Whole-mount ink perfusion and SMA-stained ventricular cross sections demonstrated significant rarefication of small, medium and large coronary arteries of Dll1+/− mice (p<0.01), while the number of microvessels was significantly increased (p<0.01). Quantification of the perfusion territory of the left descending coronary artery (LAD) by Evans blue perfusion revealed a significantly reduced perfusion territory in Dll1+/− mice (37±5% of wt, p<0.01), consistent with a regulation of coronary branching and extension by Dll1. Notably, while body size was normal, heart weight and LV dimensions were reduced in Dll1+/− mice, but EF was increased to maintain a normal stroke volume and cardiac output. To test whether hemodynamic forces regulate Dll1 expression in vivo we occluded the LAD and performed Dll1 stainings in sections 24hrs after occlusion, which revealed downregulation of EC Dll1. CONCLUSION: Hemodynamic forces regulate Dll1 which regulates arterial branching morphogenesis during development and postnatal life.