Endothelial lipase releases saturated and unsaturated fatty acids of high density lipoprotein phosphatidylcholine.
We assessed the ability of endothelial lipase (EL) to hydrolyze the sn-1 and sn-2 fatty acids (FAs) from HDL phosphatidylcholine. For this purpose, reconstituted discoidal HDLs (rHDLs) that contained free cholesterol, apolipoprotein A-I, and either 1-palmitoyl-2-oleoylphosphatidylcholine, 1-palmitoyl-2-linoleoylphosphatidylcholine, or 1-palmitoyl-2-arachidonylphosphatidylcholine were incubated with EL- and control (LacZ)-conditioned media. Gas chromatography analysis of the reaction mixtures revealed that both the sn-1 (16:0) and sn-2 (18:1, 18:2, and 20:4) FAs were liberated by EL. The higher rate of sn-1 FA cleavage compared with sn-2 FA release generated corresponding sn-2 acyl lyso-species as determined by MS analysis. EL failed to release sn-2 FA from rHDLs containing 1-O-1'-hexadecenyl-2-arachidonoylphosphatidylcholine, whose sn-1 position contained a nonhydrolyzable alkyl ether linkage. The lack of phospholipase A(2) activity of EL and its ability to liberate [(14)C]FA from [(14)C]lysophosphatidylcholine (lyso-PC) led us to conclude that EL-mediated deacylation of phosphatidylcholine (PC) is initiated at the sn-1 position, followed by the release of the remaining FA from the lyso-PC intermediate. Thin-layer chromatography analysis of cellular lipids obtained from EL-overexpressing cells revealed a pronounced accumulation of [(14)C]phospholipid and [(14)C]triglyceride upon incubation with 1-palmitoyl-2-[1-(14)C]linoleoyl-PC-labeled HDL(3), indicating the ability of EL to supply cells with unsaturated FAs.
Gauster
M
M
Institute of Molecular Biology and Biochemistry, Center of Molecular Medicine, Medical University Graz, Harrachgasse 21/III, Graz A-8010, Austria.
Rechberger
G
G
Sovic
A
A
Hörl
G
G
Steyrer
E
E
Sattler
W
W
Frank
S
S
D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D005231:Fatty Acids, Unsaturated / Q000378:metabolism*; D006801:Humans; D008049:Lipase / Q000378:metabolism*; D008075:Lipoproteins, HDL / Q000378:metabolism*; D008245:Lysophospholipase / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism*
D005231:Fatty Acids, Unsaturated; D008075:Lipoproteins, HDL; D010713:Phosphatidylcholines; C410382:LIPG protein, human; D008049:Lipase; D008245:Lysophospholipase