Abstract 19046: RBC-Macrophage Inflammatory Axis: Potential Role in Atherosclerosis

Abstract

Background: Red blood cells (RBC) modulate vasoreactivity, serve as a reservoir for chemokines via binding to Duffy antigen receptor for chemokines (DARC), and contribute to the pathology of atherosclerotic plaque rupture, suggesting a broad role in vascular pathophysiology. High fat diet (HFD) is known to negatively impact vascular function and modify RBC membrane composition, but how this affects RBC chemokine binding, and interaction with macrophages and blood vessels, is unknown. Methods and Results: RBC from C57BL/6J mice fed chow diet (chow RBC) or 60% HFD (HFD RBC) for 16 weeks were collected and studied in vitro and in vivo. Reactive oxygen species (DCFH fluorescence) and phosphatidylserine externalization (annexin V binding), a potential signal for RBC phagocytosis, were increased ~1.5 fold (p<0.05) in HFD RBC compared to chow RBC. HFD RBC released ~1.5 fold more monocyte chemoattractant protein-1 (MCP-1) (p<0.05) compared to chow RBC upon addition of heparin to disrupt DARC binding. In a transwell system, HFD RBC, as compared with chow RBC, produced a significant increase in the migration of thioglycollate-elicited macrophages through an endothelial monolayer (p<0.05). Incubation of HFD RBC with murine macrophages demonstrated a ~1.5 fold (p<0.05) increase in phagocytosis compared to chow RBC; upon their internalization by macrophages, HFD RBC more potently upregulated transcription of major pro-inflammatory chemokines Il-1b, Ccl3, and Cxcl2. As compared with chow RBC, exposure of murine aortic segments to HFD RBC under orbital shear conditions led to enhanced endothelial activation as evidenced by increased adhesion of labeled murine macrophages to the aortic endothelium (p<0.05). Finally, when labeled and injected in vivo, HFD RBC exhibited a ~3 fold (p<0.05) increase in splenic phagocytosis as compared with chow RBC. Conclusion: HFD profoundly impact RBC biology, inducing oxidative stress, altering membrane phospholipid display, and increasing chemokine release, phagocytosis by macrophages, and macrophage-blood vessel interactions. These novel findings suggest that RBC may play an important role in transducing vascular inflammation, and thus contributing to atherosclerosis, during HFD.