Downregulation of Endothelial Plexin A4 Under Inflammatory Conditions Impairs Vascular Integrity.

Dianne Vreeken,Janine Maria van Gils,Caroline Suzanne Bruikman,Gerard Kornelis Hovingh,Stefan Martinus Leonardus Cox,Huayu Zhang,Zsófia Nagy,Anton Jan van Zonneveld,Wendy Stam,Rudmer Johannes Postma

doi:10.3389/fcvm.2021.633609

Abstract

Objective: Besides hyperlipidemia, inflammation is an important determinant in the initiation and the progression of atherosclerosis. As Neuroimmune Guidance Cues (NGCs) are emerging as regulators of atherosclerosis, we set out to investigate the expression and function of inflammation-regulated NGCs.Methods and results: NGC expression in human monocytes and endothelial cells was assessed using a publicly available RNA dataset. Next, the mRNA levels of expressed NGCs were analyzed in primary human monocytes and endothelial cells after stimulation with IL1β or TNFα. Upon stimulation a total of 14 and 19 NGCs in monocytes and endothelial cells, respectively, were differentially expressed. Since plexin A4 (PLXNA4) was strongly downregulated in endothelial cells under inflammatory conditions, the role of PLXNA4 in endothelial function was investigated. Knockdown of PLXNA4 in endothelial cells markedly impaired the integrity of the monolayer leading to more elongated cells with an inflammatory phenotype. In addition, these cells showed an increase in actin stress fibers and decreased cell-cell junctions. Functional assays revealed decreased barrier function and capillary network formation of the endothelial cells, while vascular leakage and trans-endothelial migration of monocytes was increased.Conclusion: The current study demonstrates that pro-inflammatory conditions result in differential expression of NGCs in endothelial cells and monocytes, both culprit cell types in atherosclerosis. Specifically, endothelial PLXNA4 is reduced upon inflammation, while PLXNA4 maintains endothelial barrier function thereby preventing vascular leakage of fluids as well as cells. Taken together, PLXNA4 may well have a causal role in atherogenesis that deserves further investigation.

Highlights

Atherosclerosis is a slow progressing pathophysiological process that leads to overt clinical manifestations of cardiovascular disease (CVD) [1], which remains the leading cause of death worldwide [2]
In this study we have shown that many Neuroimmune guidance cues (NGCs), in particular several semaphorin family members, are differentially expressed in monocytes and endothelial cells by pro-inflammatory cytokines and that Plexin A4 (PLXNA4) may have a protective role in endothelial barrier function via modulation of the cellular cytoskeleton
Isolated monocytes and endothelial cells from healthy individuals were stimulated with interleukin 1β (IL1β) or tumor necrosis factor α (TNFα) for 5 or 24 h

Summary

Introduction

Atherosclerosis is a slow progressing pathophysiological process that leads to overt clinical manifestations of cardiovascular disease (CVD) [1], which remains the leading cause of death worldwide [2]. Epidemiological, genetic association and intervention studies have shown that inflammation is an important determinant in the initiation and the progression of atherosclerosis as well [1, 4]. Both interleukin 1β (IL1β) and tumor necrosis factor α (TNFα) have been shown to play a critical role in atherogenesis, in vitro as well as in vivo [5, 6]. The importance of IL1β was shown in a large clinical trial where a monoclonal antibody against IL1β reduced the rate of recurrent cardiovascular events in patients that sustained a prior myocardial infarction and showed residual inflammatory risk as assessed by C-reactive protein levels [7]

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Discussion

Conclusion