Abstract 260: Apolipoprotein A-I Binding Protein Regulates Macrophage Polarization in Atherosclerosis

Abstract

Our laboratory recently demonstrated that Apolipoprotein A-I Binding Protein (AIBP), an evolutionarily conserved intracellular and secreted protein, mediates cholesterol efflux from endothelial cells, which in turn disrupts lipid rafts and limits angiogenic signaling. Since lipid rafts are implicated in multiple cell signal cascades, to better understand the in vivo role of AIBP our laboratory has generated Apoa1bp -/- mice. The Apoa1bp -/- mice exhibit increased levels of inflammatory cytokines, and have an increased content of M1 macrophages in white adipose tissue in comparison to wild type mice when challenged with a high fat diet. Since AIBP accelerates cholesterol efflux from macrophages to HDL, and vascular lipid accumulation and inflammation are key factors in atherosclerosis, we hypothesized that AIBP is atheroprotective by suppressing macrophage lipid accumulation and inflammatory M1 macrophage polarization. Immunohistochemistry shows that AIBP is present in atherosclerotic lesion macrophages. However, elicited macrophages lacking AIBP expression do not exhibit any impairment in their ability to polarize to M1, suggesting that deficiency in secreted extracellular AIBP may be responsible for the M1 phenotype observed in Apoa1bp -/- mice. Indeed, treating macrophages with recombinant AIBP prior to polarization resulted in suppression of M1 polarization. In a high-cholesterol diet feeding experiment, Apoa1bp -/- Ldlr -/- mice had increased M1 macrophage content in their aorta and aortic root atherosclerotic lesions, as determined by FACS and immunohistochemistry, respectively. In conclusion, AIBP is an important negative regulator of macrophage polarization and lipid accumulation. A better understanding of AIBP’s regulatory functions in the context of atherosclerosis will provide new mechanistic insights and targeted therapies.