Abstract 14406: CD36 Facilitate Macrophage Phagocytosis Through Mitochondrial ROS During Initiation of Atherosclerosis

Abstract

Introduction: Macrophage-mediated phagocytosis is essential for tissue homeostasis but abnormal phagocytosis may lead to metabolic defect and chronic inflammation. Macrophage-derived lipid-laden foam cell is a hallmark of the early stages of atherosclerosis. However, phagocytosis efficiency in foam cells is not well explored. We previously showed that oxLDL/CD36 signaling in macrophages promoted mitochondrial reactive oxygen species (mtROS) production, foam cell formation, and facilitated diet-induced atherosclerosis. The aim of this study is to investigate the role of CD36-mediated mtROS production in phagocytosis during the early stages of atherosclerosis. Methods and Results: We conducted flow cytometry-based phagocytosis assays using E. coli bioparticles conjugated with pH-sensitive pHrodo® dyes. Utilizing peritoneal murine macrophages, we showed that pre-treatment of oxLDL, but not native LDL or HDL, stimulated phagocytosis efficiency in a dose- and time-dependent manner. However, CD36 deficiency in macrophages attenuated oxLDL-stimulated phagocytosis by ~50%. Reducing mtROS levels either by MitoTempo, a mtROS scavenger, or using MCAT macrophages, which overexpress human catalase in the mitochondria, also significantly decreased oxLDL-stimulated phagocytosis in vitro. To explore the physiological relevance, we conducted in vivo phagocytosis assay by IV injection of pHrodo bioparticles into ApoE -/- and ApoE -/- /CD36 -/- mice after chow or high fat diet (HFD) for 6 weeks. We found that aortic F4/80 + /TREM + foamy macrophages from ApoE -/- mice on HFD showed 1.5-fold increase in phagocytosis compared with those from ApoE -/- mice on chow diet. CD36 deficiency in ApoE -/- mice blocked the HFD-induced phagocytosis in aortic foamy macrophages. Moreover, we investigated the phagocytosis of apoptotic cells (efferocytosis) by macrophages and showed that mtROS-induction is critical for efficient efferocytosis in vivo. Conclusions: OxLDL stimulates macrophage phagocytosis, which is dependent on CD36. CD36-mediated mtROS production is essential for aortic macrophage phagocytosis and may play a role in foam cell formation during the initiation of atherosclerosis.