title: 15(S)-Lipoxygenase-1 associates with neutral lipid droplets in macrophage foam cells: evidence of lipid droplet metabolism.
abstract: 15(S)-lipoxygenase-1 (15-LO-1) was present in the whole-cell homogenate of an acute human monocytic leukemia cell line (THP-1). Additionally, 15-LO-1 was detected on neutral lipid droplets isolated from THP-1 foam cells. To investigate if 15-LO-1 is active on lipid droplets, we used the mouse leukemic monocytic macrophage cell line (RAW 264.7), which are stably transfected with human 15-LO-1. The RAW 15-LO-1 cells were incubated with acetylated low density lipoprotein to generate foam cells. 15(S)-hydroxyeicosatetraenoic acid [15(S)-HETE], the major 15-LO-1 metabolite of arachidonic acid, was produced in the 15-LO-1 RAW but not in the mock transfected cells when incubated with arachidonic acid. Lipid droplets were isolated from the cells and incubated with arachidonic acid, and production of 15(S)-HETE was measured over 2 h. 15(S)-HETE was produced in the incubations with the lipid droplets, and this production was attenuated when the lipid droplet fraction was subjected to enzyme inactivation through heating. Efflux of 15(S)-HETE from cholesteryl ester-enriched 15-LO RAW cells, when lipid droplets are present, was significantly reduced compared with that from cells enriched with free cholesterol (lipid droplets are absent). We propose that 15-LO-1 is present and functional on cytoplasmic neutral lipid droplets in macrophage foam cells, and these droplets may act to accumulate the anti-inflammatory lipid mediator 15(S)-HETE.
authors.affiliation: Division of Gastroenterology and Nutrition, The Children's Hospital of Philadelphia, Philadelphia, PA, USA. weibel@email.chop.edu
authors.forename: Ginny L
authors.initials: GL
authors.lastname: Weibel
authors.forename: Michelle R
authors.initials: MR
authors.lastname: Joshi
authors.forename: Cong
authors.initials: C
authors.lastname: Wei
authors.forename: Sandra R
authors.initials: SR
authors.lastname: Bates
authors.forename: Ian A
authors.initials: IA
authors.lastname: Blair
authors.forename: George H
authors.initials: GH
authors.lastname: Rothblat
mesh_terms: D001093:Arachidonate 15-Lipoxygenase / Q000378:metabolism*; D005487:Foam Cells / Q000378:metabolism*; D006801:Humans; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry*; D014407:Tumor Cells, Cultured
chemical_list: D008055:Lipids; C515716:ALOX15 protein, human; D001093:Arachidonate 15-Lipoxygenase