Hypochlorous acid-modified extracellular matrix contributes to the behavioral switching of human coronary artery smooth muscle cells

The extracellular matrix (ECM) influences the structure and function of the arterial wall and modulates the behavior of vascular cells through ECM-cell interactions. Alterations to the ECM have been implicated in multiple pathological processes, including atherosclerosis which is characterized by low-grade chronic inflammation and the infiltration and proliferation of smooth muscle cells during disease development. Considerable evidence has been presented for a role for inflammation-derived oxidation in atherogenesis, with enzymatically-active myeloperoxidase (MPO), elevated levels of 3-chlorotyrosine (a biomarker of MPO-catalyzed damage) and oxidized ECM materials detected in advanced human atherosclerotic lesions. Whether oxidant-modified ECM contributes to the altered behavior of smooth muscle cells is however unclear. This study therefore investigated the effects of hypochlorous acid (HOCl), a major MPO-derived oxidant, on the structure of the native ECM synthesized by human coronary artery smooth muscle cells (HCAMSCs) and whether modified ECM proteins affected HCASMC adhesion, proliferation and gene expression. Exposure of native HCASMC-derived ECM to reagent HOCl or a MPO-Cl--H2O2 system resulted in extensive ECM modifications as evidenced by the loss of antibody recognition of epitopes on type IV collagen, laminin, versican and fibronectin. Oxidation of HCASMC ECM markedly reduced HCASMC adhesion to matrix components, but facilitated subsequent proliferation in vitro. Multiple genes were upregulated in HCASMCs in response to HOCl-modified HCASMC-ECM including interleukin-6 (IL-6), fibronectin (FN1) and matrix-metalloproteinases (MMPs). These data reveal a mechanism through which inflammation-induced ECM-modification may contribute to the behavioral switching of HCASMCs, a key process in plaque formation during the development of atherosclerosis.