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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2009;29:837.)
© 2009 American Heart Association, Inc.

Integrative Physiology/Experimental Medicine

Overexpression of Human 15(S)-Lipoxygenase-1 in RAW Macrophages Leads to Increased Cholesterol Mobilization and Reverse Cholesterol Transport

Ginny L. Weibel; Michelle R. Joshi; Eric T. Alexander; Peijuan Zhu; Ian A. Blair; George H. Rothblat

From the Division of Gastroenterology and Nutrition (G.L.W., M.R.J., E.T.A., G.H.R.), The Children’s Hospital of Philadelphia, and the Centers for Cancer Pharmacology and Excellence in Environmental Toxicology (P.Z., I.A.B.), University of Pennsylvania School of Medicine.

Correspondence to Ginny L. Weibel, The Children’s Hospital of Philadelphia, 3615 Civic Center Blvd, ARC1102, Philadelphia, PA 19104-4399. E-mail weibel{at}email.chop.edu

Objective— The purpose of this study was to determine the effect of 15-lipoxygenase-1 (15-LO-1) on cholesterol mobilization from macrophages.

Methods and Results— Overexpression of human 15-LO-1 in RAW mouse macrophages led to enhanced cholesterol efflux, increased cholesteryl ester (CE) hydrolysis, and increased reverse cholesterol transport (RCT). Efflux studies comparing 15-LO-1 overexpressing cells to mock-transfected RAW macrophages resulted in a 3- to 7-fold increase in cholesterol efflux to apolipoprotein A-I and a modest increase in efflux to HDL. Additional experiments revealed an increase in mRNA and protein levels of ABCA1 and ABCG1 in the RAW expressing 15-LO-1 compared to controls. Efforts to examine whether the arachidonic acid metabolite of 15-LO-1, (15S)-hydroxyeicosatetraenoic acid (HETE), was responsible for the enhanced efflux revealed this eicosanoid metabolite did not play a role. Enhanced steryl ester hydrolysis was observed in 15-LO-1 overexpressing cells suggesting that the CE produced in the 15-LO-1 expressing cells was readily mobilized. To measure RCT, RAW macrophages overexpressing 15-LO-1 or mock-transfected cells were cholesterol enriched by exposure to acetylated low-density lipoprotein and [³H]-cholesterol. These macrophages were injected into wild-type animals and RCT was measured as a percent of injected dose of ³H appearing in the feces at 48 hours. We found 7% of the injected ³H in the feces of mice that received macrophages overexpressing 15-LO-1 and 4% in the feces of mice that received mock-transfected cells.

Conclusions— These data are consistent with a model in which overexpression of human 15-LO-1 in RAW macrophages promotes RCT through increased CE hydrolysis and ABCA1-mediated cholesterol efflux.

Key Words: macrophage • lipoxygenase • reverse cholesterol transport • ABCA-1

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