15(S)-lipoxygenase-1 associates with neutral lipid droplets in macrophage foam cells: evidence of lipid droplet metabolism

Ginny L. Weibel, Michelle R. Joshi, Cong Wei, Sandra R. Bates, Ian A. Blair, and George H. Rothblat

GI/Nutrition - Lipid Research, The Children's Hospital of Philadelphia, Philadelphia, PA 19104-4399

Corresponding Author: weibel{at}email.chop.edu

15(S)-lipoxygenase-1 (15-LO-1) was present in the whole cell homogenate of THP-1 human macrophages. 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 RAW murine macrophages, which are stably transfected with human 15-LO-1. The RAW 15-LO-1 cells were incubated with acetylated low density lipoprotein (acLDL) 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 2h. 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 to 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.

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