Abstract 898: Notch Signaling In The Arterial Endothelium Determines Postnatal Arteriogenesis
Introduction: Arteriogenesis by growth of preexisting collaterals is critical for the rescue of ischemic tissue. Activation of Notch signaling by the Notch ligand Delta-like 1 (Dll1) is essential for postnatal arteriogenesis. However, it is currently unknown whether Notch activation alone is sufficient for arteriogenesis. Furthermore, the location where Notch signaling exerts its function in this context is unclear. We hypothesized that Notch activation in the arterial endothelium enhances arteriogenesis, while loss of Dll1 in arterial endothelium impairs arteriogenesis.
Methods and Results: To modulate Notch signaling specifically in postnatal arterial endothelium we generated transgenic mice with tamoxifen-sensitive Cre under control of the Bmx promotor crossed with either conditional alleles for Dll1 to inhibit Notch (Bmx-Dll1) or a conditional transgene of constitutive active Notch intracellular domain (Bmx-NICD). Reporter gene studies with RosaR26-lacZ mice confirmed selective Cre activity in the arterial endothelium. Arteriogenesis was evaluated in a mouse model of hind limb ischemia (HLI) by femoral artery ligation after tamoxifen treatment. Histomorphometry of collaterals showed increase of lumen and wall thickness in wildtype mice (baseline: lumen 25±2 μm, wall 8±2 μm, HLI: lumen 45±5 μm, wall 11±2 μm, n=6, p <0.05). However, in Bmx-Dll1 dimensions remained unchanged after ligation (bl: l 24±3 μm, w 9±2 μm, HLI: l 28±2 μm, w 10±1 μm, n=6, p <0.05), indicating that loss of endothelial Dll1 leads to defective arteriogenesis. In many tissue sections from Bmx-Dll1 mice collaterals were obliterated. In contrast arterial growth in Bmx-NICD was increased (bl: l 26±3 μm, w 9±2 μm, HLI: l 70±10 μm, w 14±2 μm, n=6, p <0.05), indicating that activation of endothelial Notch enhances physiological arteriogenesis. Invading perivascular cells were observed in all groups, suggesting that their homing is not regulated by endothelial Notch activity.
Conclusion: Modulation of endothelial Notch activity in arteries regulates arterial growth. These results suggest a therapeutic potential of Notch activation to enhance arteriogenesis in ischemic disease.