EphA2 Expression Regulates Inflammation and Fibroproliferative Remodeling in Atherosclerosis

Abstract

Background Atherosclerotic plaque formation results from chronic inflammation and fibroproliferative remodeling in the vascular wall. We previously demonstrated that both human and mouse atherosclerotic plaques show elevated expression of EphA2, a guidance molecule involved in cell-cell interactions and tumorigenesis. Methods Here, we assessed EphA2's role in atherosclerosis by deleting EphA2 in a mouse model of atherosclerosis (Apoe-/-) and by assessing EphA2 function in multiple vascular cell culture models. Following 8-16 weeks Western diet, male and female mice were assessed for atherosclerotic burden in the large vessels, and plasma lipid levels were analyzed. Results Despite enhanced weight gain and plasma lipid levels compared to Apoe-/- controls, EphA2-/-Apoe-/- knockout mice show diminished atherosclerotic plaque formation, characterized by reduced proinflammatory gene expression and plaque macrophage content. While plaque macrophages express EphA2, EphA2 deletion does not affect macrophage phenotype, inflammatory responses, and lipid uptake, and bone marrow chimeras suggest hematopoietic EphA2 deletion does not affect plaque formation. In contrast, endothelial EphA2 knockdown significantly reduces monocyte firm adhesion under flow. In addition, EphA2-/-Apoe-/- mice show reduced progression to advanced atherosclerotic plaques with diminished smooth muscle and collagen content. Consistent with this phenotype, EphA2 shows enhanced expression following smooth muscle transition to a synthetic phenotype, and EphA2 depletion reduces smooth muscle proliferation, mitogenic signaling, and extracellular matrix deposition both in atherosclerotic plaques and in vascular smooth muscle cells in culture. Conclusions Together these data identify a novel role for EphA2 in atherosclerosis, regulating both plaque inflammation and progression to advanced atherosclerotic lesions. Cell culture studies suggest that endothelial EphA2 contributes to atherosclerotic inflammation by promoting monocyte firm adhesion, whereas smooth muscle EphA2 expression may regulate the progression to advanced atherosclerosis by regulating smooth muscle proliferation and extracellular matrix deposition.

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

“…It is acknowledged that Ephrin family members are involved in atherosclerotic related processes, like among others leukocyte chemotaxis, adhesion, and migration, and regulation of atherosclerotic inflammation 12‐14,24 . This is not surprising since EPHA2, EPHA8, and EPHB2, are located within the murine Athsq1 atherosclerosis susceptibility locus, 25 which is highly homologous to the premature myocardial infarction susceptibility locus in human 18 that similarly contains EPHA2, EPHA8, and EPHB2.…”

“…Moreover, NGCs have been implicated in leukocyte adhesion and migration, which implies that NGCs are crucial in the initial steps of atherogenesis 10 . Specifically, several studies have shown that members of the Ephrin family are involved in atherosclerosis related processes 10‐15 …”

Guidance Molecules in Vascular Smooth Muscle

“…Soluble EphA receptors either (a) activate reverse signaling on the peripheral nerve, since ephrinA interacts with neurotrophin receptors to enable repulsive cues in retinal axons ( Marler et al, 2010 ) or (b) block forward signaling on the vascular smooth muscle. Experimental models would favor the latter scenario, since EphA2 expression is required for fibronectin deposition ( Hu et al, 2004 ; Finney et al, 2017 ) and fibronectin is hypothesized to guide peripheral nerves on vascular smooth muscle ( Spence and Poole, 1994 ). Furthermore, soluble EphA4 enhances norepinephrine release by the peripheral nerve without affecting norepinephrine uptake by the vascular smooth muscle, suggesting EphA4 treatment does affect peripheral nerve function during reinnervation ( Damon et al, 2010 ).…”

“…In general, expression patterns of each subtype determine receptor-ligand interactions. In vascular smooth muscle cells, EphA2, EphA4, EphA5, and EphA7 are highly expressed in conjunction with ephrinA4 and ephrinA5 ( Finney et al, 2017 ). Additionally, EphB4 and EphB6 are the predominant EphB receptors in smooth muscle, and are co-expressed with ephrinB1, ephrinB2, and ephrinB3 ( Kudo et al, 2007 ; Luo et al, 2012 ).…”

Roles of EphA1/A2 and ephrin‐A1 in cancer

“…The interaction between EphA2 and Progranulin modulates capillary formation in vitro and MAPK signaling pathway . While the EphA1/A2 and ephrin‐A1 system plays roles in physiological settings, it is implicated in pathological circumustances . EphA1 and EphA2 have the highest protein homology (approximately 65% in human) among EphAs.…”