Macrophage expressed CD36 promotes plaque vulnerability in atherosclerosis

Abstract

Abstract Background Atherosclerosis is characterised by a chronic lipid-driven inflammation that accounts for the majority of deaths worldwide. CD36 is an immunoregulatory scavenger receptor at the interface of lipid metabolism and inflammation that is critically involved in atherogenesis. However, due to the lack of cell-specific in vivo models the exact role of CD36 on macrophages in atherosclerosis remains unknown to date. Purpose Here we aimed to evaluate the role of macrophage expressed CD36 in atherogenesis. Approach & Results: To screen for a potential role of macrophage expressed CD36 in atherosclerosis we assessed CD36 gene expression across different leukocyte populations in single-cell-RNA Sequencing (scRNAseq) data from atherosclerotic LDLR-/- mice. Here, we identified macrophages as the main CD36 expressing cell type. In line, CD36 protein expression in aortic cell suspensions from LDLR-/- mice was significantly higher in macrophages compared to B and T cells as assessed by flow cytometry. To assess the role of macrophage expressed CD36 in atherogenesis, we generated macrophage specific CD36 deficient mice on an atherosclerotic prone LDLR deficient (LDLR-/-) background. CD36fl/fl-CXC3R1Cre LDLR-/- mice (termed iMΦ-CD36) and CD36fl/fl-CXC3R1Wt LDLR-/- controls (termed CD36fl/fl) were injected with tamoxifen for 5 consecutive days and placed on a high cholesterol diet for 16 weeks to induce atherogenesis. At harvest the aortic root was obtained from whole heart, embedded in OCT, cut and stained with Oil Red O staining for histological analyses of atherosclerotic lesions. Macrophages were differentiated from isolated bone marrow cells for in vitro assessment of ROS production and oxLDL uptake. Notably, Macrophage-specific CD36 deficiency did not affect atherosclerotic lesion size but substantially reduced the necrotic core area indicating ameliorated plaque vulnerability. In vitro, macrophage CD36 deficiency ameliorated ROS production and facilitated oxLDL uptake. Further, macrophage-specific CD36 deficiency reduced circulating MCP-1 levels. To interrogate a potential role of CD36 in human atherosclerosis, human atherosclerotic plaques were studies by scRNAseq. Similar to our observations in mice, cellular CD36 expression was highest in human macrophages/monocytes. Further pathway analysis revealed that CD36-expressing macrophages exhibited a significantly more pro-inflammatory gene signature than CD36-negative macrophages. Down this line, CD36 expression was significantly higher in unstable carotid plaques compared to stable lesions indicating that CD36 expression correlates with plaque vulnerability in humans. Conclusion All in all, our data indicates a pro-inflammatory role of macrophage expressed CD36 in murine and human atherosclerosis. These findings suggest that targeting CD36 on macrophages may represent a potential target for anti-atherosclerotic therapy.