FcgammaRIIa mediates C-reactive protein-induced inflammatory responses of human vascular smooth muscle cells by activating NADPH oxidase 4.

We investigated the mechanism by which C-reactive protein (CRP) affects pro-inflammatory activities of vascular smooth muscle cells (VSMCs). RT-PCR, flow cytometry, and immunoblotting assays consistently showed the expression of FcgammaRIIa by cultured VSMCs isolated from human coronary arteries. Immunofluorescence staining of human coronary artery plaque showed the co-localization of FcgammaRIIa with alpha-actin(+) VSMCs in atheromatous regions. Confocal microscopic image analysis of H(2)DCFDA-labeled cells showed that CRP induced intracellular reactive oxygen species (ROS) generation by FcgammaRIIa(+) HEK293T cells. Moreover, CRP time- and dose-dependently generated ROS in VSMCs through FcgammaRIIa activation. VSMCs mainly express NADPH oxidase 4 isoform (Nox4), the suppression of which using a specific siRNA completely abolished CRP-induced ROS generation by VSMCs. The downregulation of p22(phox), a component of the active Nox4 complex, by transfecting with specific decoy oligomers and functional blocking of FcgammaRIIa not only inhibited the CRP-induced ROS generation but also reduced the degree of AP-1 and NF-kappaB activation, the production of MCP-1, IL-6, and ET-1, and the apoptotic changes of VSMCs in response to CRP. CRP-induced ROS generation by VSMCs, which requires functional activation of FcgammaRIIa and NADPH oxidase 4, orchestrates pro-inflammatory activities of VSMCs and may eventually promote atherogenesis and plaque rupture.