EPH receptor B2 stimulates human monocyte adhesion and migration independently of its EphrinB ligands

Abstract

The molecular basis of atherosclerosis is not fully understood and mice studies have shown that Ephrins and EPH receptors play a role in the atherosclerotic process. We set out to assess the role for monocytic EPHB2 and its Ephrin ligands in human atherosclerosis and show a role for EPHB2 in monocyte functions independently of its EphrinB ligands. Immunohistochemical staining of human aortic sections at different stages of atherosclerosis showed that EPHB2 and its ligand EphrinB are expressed in atherosclerotic plaques and that expression proportionally increases with plaque severity. Functionally, stimulation with EPHB2 did not affect endothelial barrier function, nor did stimulation with EphrinB1 or EphrinB2 affect monocyte‐endothelial interactions. In contrast, reduced expression of EPHB2 in monocytes resulted in decreased monocyte adhesion to endothelial cells and a decrease in monocyte transmigration, mediated by an altered morphology and a decreased ability to phosphorylate FAK. Our results suggest that EPHB2 expression in monocytes results in monocyte accumulation by virtue of an increase of transendothelial migration, which can subsequently contribute to atherosclerotic plaque progression.

Ephs and Ephrins in Adult Endothelial Biology

“…Besides endothelial cells, Eph receptors and ephrins are also expressed on several leukocytes. For example, primary monocytes and the human monocytic cell line THP-1 cells have been shown to strongly express ephrinA3, ephrinA4, EphB2, EphB3, EphB4 and EphB6 [35,77,81]. A T-lymphocyte cell line was shown to strongly express, among others, ephrinA1, ephrinA3, ephrinA4, ephrinB1, ephrinB2, EphA4, EphB2, EphB3, EphB4 and EphB6 [35,77].…”

“…Pre-incubation with antibodies against ephrinB1/B2 inducing reverse signaling, increased T-cell migration, while a double knockout impaired their migration [93]. Independent of its ephrinB1/B2 ligands, reduction in EphB2 expression in a monocyte cell line induces cytoskeletal changes resulting in decreased monocyte adhesion and migration [81].…”

“…Not only is the expression of ephrins regulated under pro-atherosclerotic conditions such as turbulent flow and exposure to pro-inflammatory cytokines, several studies have also shown expression of ephrins within plaque lesions. For example, ephrinA1, ephrinB1, EphA2, EphA4 and EphB2 have been found in human atherosclerotic plaques [12,81,86,91]. Additionally, ephrinB2 has been found in atherosclerotic lesions but its expression does not significantly differ from expression in relatively normal vessels [24].…”

“…Additional studies have shown a pro-atherosclerotic role for EphA2 and EphB2. In vivo knockout of EphA2 in ApoE-deficient mice showed decreased atherosclerotic lesion formation and less inflammation [87,102], while decreased expression of EphB2 in monocytes results in decreased adhesion and migration of these cells in vitro [81]. While all these studies seem to indicate a potential role, additional research is necessary to show the precise mechanisms of ephrins on the development of atherosclerosis.…”

“…Not only the ephrinA subclass of the ephrin family but also ephrinB family members have been shown to modulate leukocyte–endothelial interactions. For example, a surface coating of ephrinB2 enhances monocyte adhesion [ 90 ], while both soluble ephrinB2 and ephrinB1 had no effect on monocyte adhesion [ 81 , 90 ]. Lymphocyte migration, on the other hand, is diminished when membranes are coated with ephrinB2/B1 [ 83 , 91 ], while preincubation with ephrinB1 or ephrinB2 used as a chemoattractant increased migration [ 21 , 92 ].…”