During inflammation, myeloperoxidase (MPO) released by circulating leukocytes accumulates within the subendothelial matrix by binding to and transcytosing the endothelium. Oxidative reactions catalyzed by subendothelial-localized MPO are implicated as a key cause of endothelial dysfunction in inflammatory vascular diseases. Whilst the subendothelial matrix is a reactive target for MPO-derived oxidants in disease, the functional implications of oxidative matrix modification for the endothelium are largely unknown. Here we show that hypochlorous acid (HOCl) produced by endothelial-transcytosed MPO oxidizes the subendothelial matrix, involving covalent crosslinking of the adhesive matrix protein fibronectin. Real-time biosensor and live cell imaging studies showed that HOCl-mediated matrix oxidation triggers rapid membrane retraction from the substratum and adjacent cells (de-adhesion). This de-adhesion was linked with the alteration of Tyr-118 phosphorylation of paxillin, a key focal adhesion-dependent signaling process, as well as Rho kinase-dependent myosin light chain-2 phosphorylation. De-adhesion dynamics were dependent on the contractile state of cells, with myosin II inhibition with blebbistatin markedly attenuating the rate of membrane retraction. Rho kinase inhibition with Y-27632 also conferred protection, but not during the initial phase of membrane retraction, which was driven by pre-existing actomyosin tensile stress. Notably, diversion of MPO from HOCl production by thiocyanate and nitrite attenuated de-adhesion and associated signaling responses, despite the latter substrate supporting MPO-catalyzed fibronectin nitration. This study indicates that HOCl-mediated matrix oxidation by subendothelial MPO deposits may play an important and previously unrecognized role in altering endothelial adhesion, signaling and integrity during inflammatory vascular disorders.
- extracellular matrix,
- endothelial dysfunction,
- redox signaling,
- free radicals
Available at: http://works.bepress.com/thuan-thai/1/