Introduction: Atherosclerosis is a systemic inflammatory disease, characterized by the accumulation of macrophages in the vascular wall. Neuroimmune guidance cues (NGCs), originally identified to regulate neuronal and vascular patterning, are significant players in leukocyte trafficking. We set out to investigate the expression of NGCs and their receptors in human endothelial cells and monocytes under pro-atherogenic conditions and to clarify their function in atherosclerosis-related processes. 

Methods: Expression of NGC genes in human primary monocytes and endothelial cells cultured in the absence or presence of TNFα or IL1β was determined using RT-PCR. Immunohistochemical staining to determine protein expression of PLXNA4 in human aortic sections with varying stages of atherosclerosis are currently conducted. In vitro silencing of PLXNA4 in endothelial cells enabled us to investigate the role of PLXNA4 in endothelial function and monocyte migration. 

Results: Several NGCs are significantly up- or downregulated under pro-atherogenic conditions. A particularly interesting concurrent downregulation occurred in the receptor PLXNA4 in endothelial cells and its ligand SEMA3A in monocytes. In vitro, silencing of endothelial PLXNA4 markedly induced an inflammatory elongated morphological change. Indeed, endothelial cells with reduced PLXNA4 displayed increased expression of ICAM1, impaired barrier function and increased RAC1 activity. Importantly, we observed an increase in transendothelial monocyte migration with reduced endothelial PLXNA4 expression.  

Conclusion: We show that PLXNA4 has important anti-inflammatory properties. Loss of PLXNA4 affects endothelial integrity and monocyte transendothelial migration. These studies provide novel insights into the immune-modulatory roles of semaphorin ligands and their plexin receptors in atherosclerosis.

01 - DOWNREGULATION OF ENDOTHELIAL PLXNA4 UNDER PRO-ATHEROSCLEROTIC CONDITIONS DIMINISHES VASCULAR INTEGRITY ENABLING MONOCYTE TRANSENDOTHELIAL MIGRATION