Fatty acids liberated from high-density lipoprotein phospholipids by endothelial-derived lipase are incorporated into lipids in HepG2 cells

Abstract

We previously reported that endothelial-derived lipase (EDL) efficiently hydrolyses high-density-lipoprotein-derived phosphatidycholine (HDL-PC). In the present study, we assessed the ability of EDL to supply HepG2 cells with non-esterified fatty acids (NEFA) liberated from HDL-phospholipids. For this purpose, HepG2 cells infected with adenovirus encoding human EDL (EDL-Ad), or with control β-galactosidase-expressing adenovirus (LacZ-Ad), were incubated with 14C-HDL-PC. The analysis of the cellular lipids by TLC revealed that EDL overexpression led to an increase in the amount of cellular 14C-lipids, whereby the label was mainly incorporated into phospholipids and triacylglycerols (TAG). Cells expressing mutant enzymically inactive EDL (MUT-EDL-Ad) contained similar amounts of 14C-TAG but higher amounts of 14C-phosphatidylcholine (PC) compared with LacZ-Ad-infected cells. The co-expression of CD36 augmented the EDL-mediated accumulation of 14C-lipids in HEK-293 cells. The quadrupole MS analysis of the cellular lipids revealed an increased content of PC and TAG in EDL-expressing HepG2 cells compared with MUT-EDL-Ad-expressing and control cells. However, the MUT-EDL-Ad-expressing cells contained more PC than control cells. Additionally, EDL overexpression led to a 2-fold decrease in the amount of fatty acid synthase mRNA and, in turn, a slightly, but significantly, decreased rate of fatty acid (FA) synthesis in HepG2 cells. In the present study, we show for the first time that EDL efficiently supplies HepG2 cells with NEFA derived from HDL-PL, thus affecting cellular lipid composition and FA synthesis.