Macrophage-expressed Neuropilin 2 promotes plaque formation in ApoE knockout mice and is essential for pro-inflammatory macrophage polarisation and gene expression.

Abstract

AimsAtherosclerosis is a chronic inflammatory disease causing the narrowing of arteries, leading to ischaemic heart disease. It is characterised by the subendothelial retention, and modification, of lipoproteins by macrophages, highly plastic cells which undergo polarisation to a pro-inflammatory phenotype in response to cytokines and other environmental stimuli. Neuropilin-2 (NRP2) is a cell-surface co-receptor with essential roles in angiogenesis and axonal guidance, that is also expressed by macrophages. However, the role of NRP2 in macrophage function in the development of atherosclerosis has not been studied. Methods and resultsThe role of NRP2 in modulating macrophage polarisation and signalling was assessed using functional assays and transcriptome analysis in macrophages obtained from mice with macrophage-specific deletion of Nrp2 (Nrp2-KOMac,EYFP). These mice were further crossed with pro-atherogenic Apolipoprotein E-deficient mice to produce Nrp2-KOMac,Apoe-/-,EYFP mice, which were fed a high-fat diet (HFD) for 16 weeks. Plaque formation and composition were characterised using chemical and immuno-staining. NRP2 was significantly upregulated upon differentiation of bone marrow progenitors into bone marrow derived macrophages (BMDM), and further upregulated by pro-inflammatory polarisation. Transcriptome analysis revealed that inflammatory signalling pathway genes, and genes regulating monocyte chemotaxis, were downregulated in Nrp2-KOMac,EYFP BMDMs. HFD-induced plaque development was significantly reduced in Nrp2-KOMac,Apoe-/-,EYFP mice. Additionally, plaques from those mice displayed features consistent with increased plaque stability, including reduced necrotic core area, plaque lipid content and increased cap thickness. ConclusionsMacrophage-derived NRP2 is proatherogenic, likely resulting from its ability to positively regulate pro-inflammatory pathways and macrophage migration. Targeting NRP2 expressed on the surface of macrophages could therefore offer a novel therapeutic approach for reducing the disease burden associated with atherosclerosis.