Nogo-B Is Essential For Macrophage Dependent Inflammatory Arteriogenesis And Angiogenesis

Nogo-B, a member of the reticulon 4 family of proteins, is the dominant isoform expressed in endothelial, vascular smooth muscle and inflammatory cells. We previously have shown Nogo-B plays a critical role in vascular remodeling after injury in vivo . In mice and rabbits, neointimal expansion of injured blood vessels is associated with a marked reduction in Nogo-B, and, in humans, the loss of Nogo-B correlates with stenotic lesions and plaque rupture. However, the role of Nogo-B in regulating arteriogenesis or angiogenesis is not known. In the present study, we investigated the role of Nogo-B in arteriogenesis/angiogenesis using a mouse hindlimb ischemia model in Nogo-A/B KO (NgKO) and wild-type (WT) littermate control mice. Nogo-B mRNA and protein levels increased in the ischemic leg relative to the contralateral leg in WT. Hindlimb ischemia reduces tissue perfusion by 80% followed by a complete recovery of flow to pre-surgical values in WT after 4 weeks. In NgKO, there was a marked decrease in blood flow recovery post-ischemia, which was accompanied by a reduction in capillary density (assessed by isolectin staining), a decrease in smooth muscle/pericyte recruitment and an impaired collateral artery remodeling (assessed by quantitative angiography) compared to WT. Blood vessel formation and remodeling during ischemia requires coordination of the inflammatory response with regulated gene expression that promotes blood vessel assembly. Thus, we assessed the presence of tissue macrophages (F4/80 immunochemistry) 3 days after ischemia and found a 76% reduction of F4/80 positive cells in ischemic tissue in NgKO compared to WT. Mechanistically, the impaired recruitment of tissue macrophages was associated with reduced spreading, impairment of chemotaxis in response to monocyte chemokines compared to WT cells (76±4 vs. 113±8 cells/field in NgKO vs. WT), but not adhesion, of isolated bone marrow derived monocytes from NgKO compared to controls. Moreover, NgKO macrophage demonstrated impaired Rac activation, translocation and cytoskeletal organization upon stimulation of with chemokines. In conclusion, our data suggests that endogenous Nogo coordinates macrophage mediated inflammation with angiogenesis, arteriogenesis and blood flow control.