Ephrin-A1/EphA2 modulates vascular smooth muscle cell proliferation in vitro, while VSMC-specific ephrin-A1 deletion is not sufficient to alter arteriosclerosis in vivo

Atherosclerosis, the leading cause of heart attack and stroke, involves plaque formation driven by various cell types, including endothelial cells, immune cells and vascular smooth muscle cells (VSMCs). VSMCs undergo a phenotypic switch from a contractile to a synthetic state, contributing to disease progression. The Eph/ephrin signaling pathway, particularly ephrin-A1 and its receptor EphA2, has been implicated in this phenotypic modulation. Its role in atherosclerosis was explored using in vitro and in vivo models. In plaque-containing arteries, both ephrin-A1 and EphA2 were upregulated compared to plaque-free regions. The phenotypic transition of VSMCs from a contractile to a synthetic state is associated with reduced ephrin-A1 levels, elevated EphA2 expression, and increased cellular proliferation. A consistent expression pattern with low ephrin-A1 and high EphA2 was observed in proliferating cells. Additionally, under pro-proliferative conditions, the non-canonical phosphorylation site S897/898 of EphA2 is phosphorylated in a MEK/ERK/RSK-dependent manner, while the canonical site Y588/589 undergoes autophosphorylation at higher ephrin-A1 levels. These in vitro findings suggest an anti-proliferative, potentially anti-atherogenic role for ephrin-A1 in VSMCs. This hypothesis was further examined in ApoE-KO mice using a conditional VSMC-specific ephrin-A1 knockout. Surprisingly, neither high-fat diet-induced atherosclerosis nor wire injury-induced stenosis differed between ephrin-A1-deficient and wild-type mice, implying functional compensation by other ephrin ligands. The present findings highlight significant roles for the Eph/ephrin system in VSMC biology and plaque development. However, its effects appear to be multimodal, influenced by the interplay between various cell types and distinct members of the Eph/ephrin family.