Abstract 621: Vascular Smooth Muscle EphA2 Signaling Regulates Fibrillar Adhesion Formation to Drive Fibronectin Deposition

Abstract

During atherosclerosis, synthetic vascular smooth muscle cells drive development of the fibrous cap through extracellular matrix deposition. Deposition of the provisional matrix protein fibronectin appears to critically regulate fibrous cap development by promoting smooth muscle recruitment and by providing a critical scaffold for assembly of fibrillar collagens. We previously showed that deletion of the receptor tyrosine kinase EphA2 in ApoE knockout mice attenuated plaque size and progression, characterized by a reduction of both smooth muscle content and fibrosis, and we further demonstrated that EphA2 depletion attenuates smooth muscle fibronectin deposition in vitro. Despite this, the mechanisms by which EphA2 regulates smooth muscle matrix deposition remains unknown. Fibronectin fibrillogenesis involves both the formation of α5β1 integrin-rich fibrillar adhesions and contractility-dependent fibronectin unfolding. We now show EphA2 localizes to integrin adhesions and appears to regulate matrix deposition through multiple mechanisms. Knockdown of EphA2 reduces the formation of fibrillar adhesions characterized by a loss of α5β1 integrins and tensin, whereas EphA2 overexpression is sufficient to induce fibrillar adhesion formation in contractile smooth muscle cells. In addition, vascular smooth muscle cells show diminished collagen gel contraction following EphA2 knockdown, and EphA2 depletion significantly reduces smooth muscle myosin light chain phosphorylation, suggesting that EphA2 expression is required to generate the contractive forces required for matrix remodeling in synthetic smooth muscle cells. Together these data identify a novel role for EphA2 in the regulation of smooth muscle matrix deposition through effects on both integrin adhesion structure and cytoskeletal contractility.