Oxidized LDL accumulation suppresses glycolysis and attenuates the macrophage inflammatory response by diverting transcription from the HIF-1a to the Nrf2 pathway
Lipid accumulation in macrophages (Mfs) is a hallmark of atherosclerosis, yet how lipid accumulation affects inflammatory responses through rewiring of Mf metabolism is poorly understood. We modeled lipid accumulation in cultured wild type mouse thioglycolate-elicited peritoneal Mfs and bone marrow-derived Mfs with conditional (Lys2-Cre) or complete genetic deficiency of Vhl, Hif1a, Nos2 and Nfe2l2. Transfection studies employed RAW264.7 cells. Mfs were cultured for 24 hours with oxidized LDL (oxLDL) or cholesterol and then were stimulated with LPS. Transcriptomics revealed that oxLDL accumulation in Mfs down-regulated inflammatory, hypoxia and cholesterol metabolism pathways, while antioxidant pathway, fatty acid oxidation and ABC family proteins were up-regulated. Metabolomics and extracellular metabolic flux assays showed that oxLDL accumulation suppressed LPS-induced glycolysis. Intracellular lipid accumulation in Mfs impaired LPS-induced inflammation by reducing both HIF-1a stability and transactivation capacity; thus, the phenotype was not rescued in Vhl-/- Mfs. Intracellular lipid accumulation in Mfs also enhanced LPS-induced Nrf2-mediated antioxidative defense that destabilizes HIF-1a, and Nrf2-deficient Mfs resisted the inhibitory effects of lipid accumulation on glycolysis and inflammatory gene expression. Furthermore, oxLDL shifted NADPH consumption from HIF-1a- to Nrf2-regulated apoenzymes. Thus, we postulate that repurposing NADPH consumption from HIF-1a to Nrf2 transcriptional pathways is critical in modulating inflammatory responses in Mfs with accumulated intracellular lipid. The relevance of our in vitro models was established by comparative transcriptomic analyses, which revealed that Mfs cultured with oxLDL and stimulated with LPS shared similar inflammatory and metabolic profiles with foamy Mfs derived from the atherosclerotic mouse and human aorta. Overall design: To investigate the effects of oxLDL loading on the transcriptome of mouse peritoneal macrophages before and after LPS stimulation.   Control and OxLDL-loaded peritoneal macrophages before and after stimulation with LPS; 3 replicates per sample.