Abstract MP27: Endothelial Nogo-B Modulates Ischemia Induced Collateral Artery Remodeling

Abstract

Nogo-B, a member of the reticulon 4 family of proteins, is the dominant isoform expressed in endothelial cells (EC). We have shown that Nogo-B is necessary for blood flow recovery in ischemia. Mice lacking Nogo-B exhibit reduced arteriogenesis and angiogenesis that are linked to a decrease in macrophage infiltration and inflammatory gene expression in vivo. However, whether endothelial Nogo-B regulates arteriogenesis and/or angiogenesis is unknown. We generated an inducible EC-specific mouse overexpressing Nogo-B (Ng ECtg ) and investigated the arteriogenesis and angiogenesis in limb ischemia. Ischemia increased endothelial and serum Nogo-B expression. Blood flow recovery was markedly diminished after femoral artery ligation (FAL) in Ng ECtg compared to WT mice, in association with lower collateral density accessed by micro-CT arteriography. There was no reduction in capillary density or decrease in smooth muscle/pericyte and macrophage recruitment in Ng ECtg mice, suggesting EC Nogo-B overexpression regulates arteriogenesis but not angiogenesis. While Ng ECtg mice have normal number of native collateral artery, the early remodeling of the collateral artery was impaired after ischemia. Furthermore, in line with impaired remodeling, Ng ECtg mice have decreased functional (exercise) hyperemia response in the non-ischemic limb in vivo, and resistant arteries from Ng ECtg have diminished flow induced vasodilatation ex vivo compared to WT mice. Moreover, endothelial reconstitution of Nogo-B in global Nogo knockout background (NogoKO ECrc ) restored blood flow recovery after ischemia in vivo, further suggesting the EC specific function of Nogo-B in arteriogenesis. Mechanistically, we have shown that EC isolated from Ng ECtg mice have decreased nitric oxide release. Nogo-B overexpression negatively regulates eNOS phosphorylation, expression and golgi localization in EC. Future parabiosis study is warranted to elucidate the contribution of paracrine or EC intrinsic Nogo-B in modulating arteriogenesis and angiogenesis. In conclusion, our data showed for the first time that endothelial Nogo-B plays important roles in regulating collateral artery remodeling and blood flow through, at least in part, regulating NO bioavailability.