Complement Protein C1q Regulation of Macrophage Metabolic Pathways

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Complement Protein C1q Regulation of Macrophage Metabolic Pathways PROJECT SUMMARY Atherosclerosis is a chronic inflammatory disorder which in early stages is characterized by the migration of macrophages and modified lipoproteins into the arterial walls, leading to the formation and apoptosis of macrophage foam cells. In late stages of disease, insufficient apoptotic foam cell removal by macrophages leads to their secondary necrosis and plaque development. Plaque damage by pro-inflammatory cytokines, proteases and oxygen radicals can lead to clinical complications such as myocardial infarction and ischemic stroke. Thus, macrophage foam cell survival, cholesterol removal, and inflammation are key factors in progression of this disease. Complement pathway activation by innate immune protein C1q has been shown to promote disease progression. However, studies in C1q-deficient mice suggest a protective role for C1q in the early atherosclerotic lesion. In addition to complement activation, C1q can directly opsonize targets and interacts with phagocytes leading to increased phagocytic responses and reduced inflammatory cytokine signaling. Macrophages can synthesize C1q and therefore C1q may be localized in macrophage-rich tissues, such as the early atherosclerotic lesion, in the absence of other complement components needed for complement activation. Therefore, our central hypothesis is that complement-independent actions of C1q program protective, anti-atherosclerotic macrophage responses in atherosclerosis. Recent studies have identified a number of potentially beneficial mechanisms of C1q on macrophage survival, efferocytosis, cholesterol metabolism, and inflammatory polarization in vitro and in vivo models of atherosclerosis. The goal of this project is to investigate pathways and biological relevance of C1q modulation of cholesterol metabolism, and to determine for the first time if there is a role for C1q in mitochondrial metabolism in macrophage foam cells. Specific aims are: 1: Investigate C1q modulation of lipid metabolism in macrophages and microglia. We will test the hypothesis that C1q modulation of LXR-activating lipids 24-OHC, 25-OHC, and desmosterol are involved in macrophage foam cell survival, efferocytosis and polarization. Lipidomic analysis will be performed in primary human M0, M1, or M2 polarized macrophage foam cells and murine microglia ±C1q. Survival, efferocytosis, and polarization assays will be performed in specific pathway-deficient or knocked-down macrophages to identify their relative importance in these biological responses. Specific Aim 2: Investigate C1q modulation of macrophage metabolic programming. We will test the hypothesis that C1q modulation of mitochondrial metabolism and autophagy are involved in macrophage foam cell survival, efferocytosis, and polarization. Changes to mitochondrial respiration, glycolysis and superoxide production will be measured in human monocyte-derived macrophages during ingestion of oxLDL ±C1q. Similar studies will be performed in murine bone marrow-derived macrophages from wild-type or C1q-deficient mice to investigate autocrine vs. paracrine actions of C1q. Assays will be repeated in macrophages ingesting oxLDL ±C1q in the presence of autophagy (or other metabolic pathway) inhibitors, or cultured in high glucose environment to identify involvement of metabolic pathways in these biological responses. Overall, these studies aim to explore the dual role that C1q plays in atherosclerosis, and should assist in identifying novel molecular pathways for therapeutic targeting.