Impact of Endothelial Lipase on Cholesterol Efflux Capacity of Serum and High-density Lipoprotein

Irene Schilcher,Madalina Duta-Mare,Sabine Kern,Gunther Marsche,Andelko Hrzenjak,Saša Frank,Tatjana Stojakovic,Dagmar Kratky,Hubert Scharnagl,Thomas O Eichmann

doi:10.1038/s41598-017-12882-7

Abstract

Endothelial lipase (EL) is a potent modulator of the structural and functional properties of HDL. Impact of EL on cholesterol efflux capacity (CEC) of serum and isolated HDL is not well understood and apparently contradictory data were published. Here, we systematically examined the impact of EL on composition and CEC of serum and isolated HDL, in vitro and in vivo, using EL-overexpressing cells and EL-overexpressing mice. CEC was examined in a validated assay using 3H-cholesterol labelled J774 macrophages. In vitro EL-modification of serum resulted in complex alterations, including enrichment of serum with lipid-free/-poor apoA-I, decreased size of human (but not mouse) HDL and altered HDL lipid composition. EL-modification of serum increased CEC, in line with increased lipid-free/-poor apoA-I formation. In contrast, CEC of isolated HDL was decreased likely through altered lipid composition. In contrast to in vitro results, EL-overexpression in mice markedly decreased HDL-cholesterol and apolipoprotein A-I serum levels associated with a decreased CEC of serum. HDL lipid composition was altered, but HDL particle size and CEC were not affected. Our study highlights the multiple and complex effects of EL on HDL composition and function and may help to clarify the seemingly contradictory data found in published articles.

Highlights

The best-studied atheroprotective activity of high-density lipoprotein (HDL) is the promotion of reverse cholesterol transport (RCT)
Inconclusive are the results from studies addressing the impact of Endothelial lipase (EL) overexpression on cholesterol efflux capacity (CEC) of mouse serum; while in one study the adenovirus-mediated EL overexpression in human apolipoprotein AI transgenic mice markedly augmented the CEC of serum[15], exactly the opposite was found in mice in which EL overexpression was achieved by profurin-overexpression-mediated furin inhibition[16]
Human (h) serum was modified with HepG2 cells overexpressing human EL or with empty virus (EV)transduced control HepG2 cells (Supplementary Fig. S1) followed by measurements of CEC of serum and isolated HDL in 3H-cholesterol labeled J774 macrophages under basal conditions or following ABCA1 upregulation

Summary

Introduction

The best-studied atheroprotective activity of high-density lipoprotein (HDL) is the promotion of reverse cholesterol transport (RCT). Inconclusive are the results from studies addressing the impact of EL overexpression on cholesterol efflux capacity (CEC) of mouse serum; while in one study the adenovirus-mediated EL overexpression in human apolipoprotein (apo) AI transgenic mice markedly augmented the CEC of serum[15], exactly the opposite was found in mice in which EL overexpression was achieved by profurin-overexpression-mediated furin inhibition[16]. Genetic inactivation of EL resulted in increased HDL cholesterol levels and increased CEC of apolipoprotein B-depleted serum (apoB-DS)[5]. Because of the inconclusive data from literature and the lack of data on the impact of EL overexpression on the CEC of human serum, we studied the impact of EL on CEC of serum, apoB-DS and HDL generated in vitro and in vivo

Methods

Results

Conclusion