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

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Abstract
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, (15 S )-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 [ 3 H]-cholesterol. These macrophages were injected into wild-type animals and RCT was measured as a percent of injected dose of 3 H appearing in the feces at 48 hours. We found 7% of the injected 3 H 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.

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