Abstract 20063: C-Reactive Protein Antagonizes Endothelial NO Synthase via FcγRI and Src Kinase-dependent Activation of FcγRIIB
C-reactive protein (CRP) is an acute-phase reactant that is elevated in multiple inflammatory conditions, and it is positively associated with cardiovascular disease risk and endothelial dysfunction. Our prior work in cultured endothelial cells and in mice demonstrated that CRP antagonizes the activation of endothelial NO synthase (eNOS) to cause hypertension and impaired reendothelialization in vivo. This process is mediated by the inhibitory IgG receptor Fcγ receptor IIB (FcγRIIB) and its cytoplasmic immunoreceptor tyrosine-based inhibitory motif (ITIM), which recruits and thereby activates Src homology 2 domain-containing inositol 5′-phosphatase type 1 (SHIP-1) to attenuate PI3 kinase signaling to Akt upstream of eNOS. The molecular basis for CRP activation of FcγRIIB is not known. In this study we determined if it is mediated by the related IgG receptor Fcγ receptor I (FcγRI) and Src kinase. In cultured endothelial cells, blocking antibodies directed against FcγRI or the Src family kinase inhibitor PP2 fully prevented CRP antagonism of insulin- or acetylcholine-induced eNOS activity. In addition, CRP stimulated the activating phosphorylation of Src at Tyr-416, and it increased the phosphorylation of Tyr-292 within the FcγRIIB ITIM in a Src-dependent manner. Furthermore, CRP-induced activation of SHIP-1 downstream of FcRγIIB was Src-dependent. To determine if FcγRI is required for CRP-mediated vascular phenotypes in vivo, mice lacking the γ chain component of FcγRI (FcRγ−/−) were crossed with CRP transgenic mice (TG-CRP) to yield FcRγ+/+;TG-CRP, FcRγ−/−;TG-CRP, and FcRγ+/+ and FcRγ−/− littermates. Compared to wild-type FcRγ+/+ mice, carotid artery reendothelialization after perivascular electric injury, which is eNOS-dependent, was predictably impaired in FcRγ+/+;TG-CRP mice. In contrast, reendothelialization was normal in FcRγ−/−;TG-CRP. Thus, CRP antagonism of eNOS is initiated by the activation of FcγRI, which stimulates Src to increase FcγRIIB ITIM phosphorylation and thereby recruit and activate SHIP-1, and FcγRI is required for CRP to antagonize endothelial monolayer repair in vivo. As such, FcγRI may be a novel therapeutic target for preventing or reversing endothelial dysfunction in the setting of inflammation.
- © 2010 by American Heart Association, Inc.