title: Oxidized low-density lipoprotein stimulates macrophage 18F-FDG uptake via hypoxia-inducible factor-1α activation through Nox2-dependent reactive oxygen species generation.
abstract: For (18)F-FDG PET to be widely used to monitor atherosclerosis progression and therapeutic response, it is crucial to better understand how macrophage glucose metabolism is influenced by the atherosclerotic microenvironment and to elucidate the molecular mechanisms of this response. Oxidized low-density lipoprotein (oxLDL) is a key player in atherosclerotic inflammation that promotes macrophage recruitment, activation, and foam cell formation. We thus explored the effect of oxLDL on macrophage (18)F-FDG uptake and investigated the underlying molecular mechanism including the roles of hypoxia-inducible factor-1α (HIF-1α) and reactive oxygen species (ROS).
  
  
  METHODS
  RAW264.7 macrophages were stimulated with native LDL, oxLDL, or lipopolysaccharide. Cells were assessed for (18)F-FDG uptake, lactate production, membrane glucose transporter 1 (GLUT1) expression, and hexokinase activity. ROS generation, Nox expression, and HIF-1α activity were also measured.
  
  
  RESULTS
  oxLDL (20 μg/mL) induced a 17.5 ± 1.7-fold increase in macrophage (18)F-FDG uptake by 24 h, which was accompanied by increased lactate production, membrane GLUT1 expression, and hexokinase activity. oxLDL-stimulated (18)F-FDG uptake was completely blocked by inhibitors of Src or phosphoinositide 3-kinase. ROS generation was increased to 262.4% ± 17.9% of controls by oxLDL, and N-acetyl-l-cysteine completely abrogated both oxLDL-induced ROS production and (18)F-FDG uptake. oxLDL increased Nox2 expression, and nicotinamide adenine dinucleotide phosphate oxidase inhibition totally blocked increased ROS generation and (18)F-FDG uptake by oxLDL. Finally, there was a clear ROS-dependent increase of HIF-1α accumulation by oxLDL, and silencing of HIF-1α completely abolished the metabolic effect of oxLDL.
  
  
  CONCLUSIONS
  oxLDL is a strong stimulator of macrophage (18)F-FDG uptake and glycolysis through upregulation of GLUT1 and hexokinase. This metabolic response is mediated by Nox2-dependent ROS generation that promotes HIF-1α activation.
authors.affiliation: Department of Nuclear Medicine, Ajou University School of Medicine, Suwon, Korea; and.
authors.forename: Su Jin
authors.initials: SJ
authors.lastname: Lee
authors.affiliation: Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Cung Hoa
authors.initials: CH
authors.lastname: Thien Quach
authors.affiliation: Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Kyung-Ho
authors.initials: KH
authors.lastname: Jung
authors.affiliation: Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Jin-Young
authors.initials: JY
authors.lastname: Paik
authors.affiliation: Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Jin Hee
authors.initials: JH
authors.lastname: Lee
authors.affiliation: Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Jin Won
authors.initials: JW
authors.lastname: Park
authors.affiliation: Department of Nuclear Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea khnm.lee@samsung.com.
authors.forename: Kyung-Han
authors.initials: KH
authors.lastname: Lee
mesh_terms: D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D018450:Disease Progression; D019788:Fluorodeoxyglucose F18 / Q000378:metabolism; D051272:Glucose Transporter Type 1 / Q000378:metabolism; D006593:Hexokinase / Q000378:metabolism; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000378:metabolism*; D019344:Lactic Acid / Q000737:chemistry; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008264:Macrophages / Q000000981:diagnostic imaging / Q000378:metabolism*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases / Q000378:metabolism*; D011877:Radionuclide Imaging; D019275:Radiopharmaceuticals; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D051272:Glucose Transporter Type 1; C497442:HIF1A protein, human; C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D008077:Lipoproteins, LDL; D008562:Membrane Glycoproteins; D019275:Radiopharmaceuticals; D017382:Reactive Oxygen Species; C495677:SLC2A1 protein, human; C495678:Slc2a1 protein, mouse; C099252:oxidized low density lipoprotein; D019788:Fluorodeoxyglucose F18; D019344:Lactic Acid; C056558:CYBB protein, human; C488842:Cybb protein, mouse; D000074662:NADPH Oxidase 2; D019255:NADPH Oxidases; D006593:Hexokinase
keywords: 18F-FDG; HIF-1α; PET; macrophage; oxidized LDL; reactive oxygen species