The Guanine-Nucleotide Exchange Factor SGEF Plays a Crucial Role in the Formation of Atherosclerosis

Thomas Samson,Jaap D Van Buul,Erik N Bakker,Timo K Van Den Berg,Jeffrey Kroon,Christopher Welch,Klaus Hahn,Keith Burridge,Hanke L Matlung,Claire Doerschuk,Lisa Sharek,Christian Schulz

doi:10.1371/journal.pone.0055202

Abstract

The passage of leukocytes across the endothelium and into arterial walls is a critical step in the development of atherosclerosis. Previously, we showed in vitro that the RhoG guanine nucleotide exchange factor SGEF (Arhgef26) contributes to the formation of ICAM-1-induced endothelial docking structures that facilitate leukocyte transendothelial migration. To further explore the in vivo role of this protein during inflammation, we generated SGEF-deficient mice. When crossed with ApoE null mice and fed a Western diet, mice lacking SGEF showed a significant decrease in the formation of atherosclerosis in multiple aortic areas. A fluorescent biosensor revealed local activation of RhoG around bead-clustered ICAM-1 in mouse aortic endothelial cells. Notably, this activation was decreased in cells from SGEF-deficient aortas compared to wild type. In addition, scanning electron microscopy of intimal surfaces of SGEF−/− mouse aortas revealed reduced docking structures around beads that were coated with ICAM-1 antibody. Similarly, under conditions of flow, these beads adhered less stably to the luminal surface of carotid arteries from SGEF −/− mice. Taken together, these results show for the first time that a Rho-GEF, namely SGEF, contributes to the formation of atherosclerosis by promoting endothelial docking structures and thereby retention of leukocytes at athero-prone sites of inflammation experiencing high shear flow. SGEF may therefore provide a novel therapeutic target for inhibiting the development of atherosclerosis.

Highlights

Atherosclerosis is characterized by the successive influx of proinflammatory monocytes and lymphocytes into the arterial wall resulting in localized inflammation, accumulation of lipids, fibrosis and cell death
We found that ICAM-1 clustering on endothelial cells relocates the Rho guanine nucleotide exchange factor (GEF) SGEF (Arhgef-26) to the plasma membrane where it leads to activation of the Rho family GTPase RhoG [5]
Examining the interaction of beads coated with antibodies against ICAM-1, we find that initial adhesion of the beads to the walls of isolated arteries is identical in the SGEF null mice, exposure to flow dislodges more beads from SGEF null than from wildtype arteries

Summary

Introduction

Atherosclerosis is characterized by the successive influx of proinflammatory monocytes and lymphocytes into the arterial wall resulting in localized inflammation, accumulation of lipids, fibrosis and cell death. RhoG activation contributes to the formation of actin rich protrusions on the dorsal surface of endothelial cells [5], known as transmigratory cups or docking structures [6;7] These cups are thought to serve as intermediate docking structures that provide mechanical support for adhered leukocytes before transmigration (reviewed in [8;9]). Examining the interaction of beads coated with antibodies against ICAM-1, we find that initial adhesion of the beads to the walls of isolated arteries is identical in the SGEF null mice, exposure to flow dislodges more beads from SGEF null than from wildtype arteries Consistent with these results, the SGEF null vessels and endothelial cells reveal lower RhoG activation and decreased docking structure formation than their wildtype counterparts. Our results suggest that the reduced formation of docking structure in mice lacking SGEF contributes to the decreased susceptibility of these mice to develop atherosclerosis

Methods

Results

Conclusion