Abstract 379: Potential Protective Effects of Semaphorin3A on Macrophage Function

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Semaphorin3A (SEMA3A) is a secreted member of the Semaphorin family, first found to play a role in axon guidance. Recently many studies revealed immune functions for this protein. However, how SEMA3A may regulate monocyte and macrophage functions associated with atherosclerosis is unknown. An early step in plaque formation is the adhesion of monocytes on activated endothelial cells expressing adhesion molecules. However, we found that 25-100 ng/ml SEMA 3A did not affect the adhesion of monocyes on ICAM-1- or VCAM-1-coated plates. Similarly, stimulation of mouse carotid arteries with SEMA3A in an ex-vivo perfusion system, either administered alone or in conjunction with TNF-α, did not increase adhesiveness of monocytes injected in the intraluminal compartment. Furthermore SEMA3A did not stimulate monocyte migration in a boyden chamber assay. However SEMA3A had significant effects on macrophages, the most abundant cells in the plaque. Inefficient apoptotic cell phagocytosis and macrophage retention in the artery wall are hallmarks of atherosclerosis progression. We found that SEMA3A increased the migration of M2 “wound healing” macrophages more than 4-fold (p<0.05), but had no such effect on M1 “inflammatory” macrophages. Increased M2 migration was associated with phosphorylation of FAK Y397, and could be inhibited by RGD peptide that prevents integrin-matrix interaction and by a blocking antibody targeting the SEMA3A receptor Neuropilin-1. SEMA3A (100ng/ml) also significantly increased phagocytosis of apoptotic cells by M2 macrophages (1.8-fold, p<0.01) but not M1 cells. Interestingly, Sema3A did not affect lipoprotein uptake by macrophages, which characterizes foam cell formation. Finally in an in vivo model of acute inflammation, SEMA3A plasmid pretreatment reduced redness, swelling, and macrophage infiltration associated with LPS injection.In summary, our data suggest that SEMA3A is unlikely to participate in atherosclerotic plaque formation. On the contrary, effects of SEMA3A on macrophage function in vitro and in vivo indicate a potential protective effect in the inflammatory setting.