The identification of Nogo-B as a novel regulator of vascular cell function and vessel remodeling

While much work has been done to characterize the role of Nogo as an inhibitor of axon regeneration within the central nervous system (CNS), little is known about its peripheral role(s). Through proteomic analysis of highly purified caveolin-1 containing, cholesterol-rich, buoyant membranes, we identify Nogo-B as a component of these membrane subfractions in cultured endothelial cells. We further identify Nogo-B in vascular smooth muscle cells as well as in intact blood vessels, suggesting a vascular role for Nogo-B. Verifying the subcellular localization of Nogo-B, we show through immunofluorescent microscopy and sucrose gradient fractionation that Nogo-B has a predominantly reticular pattern but is also in plasmalemma, partially co-registering with caveolin-1. FAGS analysis and immunofluorescent microscopy of non-permeabilized vascular endothelial and smooth muscle cells with a Nogo antibody against residues 1--18 demonstrate that Nogo-B is on the cell surface with the amino terminus extracellular. Therefore, we examine the role of the amino terminus as a potential functional domain using either glutathione S-transferase or alkaline phosphatase fusion proteins encompassing residues 1--200 (GST Am-Nogo-B or AP Am-Nogo-B). In contrast to the inhibitory action of Nogo-A, the amino terminus of Nogo-B promotes the adhesion, spreading and migration of endothelial cells but inhibits the migration of vascular smooth muscle. As these processes are necessary for vascular remodeling, using a femoral arterial wire injury model, immunohistochemistry of control and injured vessels show that Nogo expression decreases after injury further suggesting a role in vessel remodeling. As direct evidence, vascular injury in Nogo-A/B knockout mice promotes exaggerated neointimal proliferation and adenoviral mediated gene transfer of Nogo-B rescues the abnormal vascular expansion in Nogo-A/B knockout mice. Thus, Nogo-B is a novel regulator of vascular homeostasis and remodeling, broadening the functions identified for this family of proteins.