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Transfer of phosphatidylcholine, phosphatidylethanolamine and sphingomyelin from low- and high-density lipoprotein to human platelets.

ABSTRACT: Following a 1 h incubation of human platelets with low-density lipoprotein (LDL) labelled in the apoprotein fraction (125I-apoB) or in phospholipid fractions [14C-labelled phosphatidylcholine (PC), phosphatidylethanolamine (PE) or sphingomyelin (SM)], the percentage of total 14C associated with the cells was about 3-fold higher than the percentage of 125I. Differences in temperature sensitivity also indicated differential interactions of phospholipids and apoprotein with platelets. In order to assess the amount of [14C]phospholipid transferred from LDL or high-density lipoprotein (HDL) to the cells, the quantity of bound lipoproteins was estimated by adding an excess of unlabelled lipoprotein, or by selectively degrading LDL- and HDL-associated [14C]PC and [14C]PE with phospholipase C. Incubation of platelets with LDL or HDL containing pyrenedecanoic acid-labelled PC or SM (py-PC, py-SM) increased pyrene monomer fluorescence, indicating incorporation of the phospholipids into platelets. With HDl as donor, incorporation of py-SM was greater than uptake of py-PC. Pretreating platelets with elastase dose-dependently inhibited uptake of py-SM and py-PC. Treatment of cells with phospholipase C indicated that the uptake of [14C]PC by platelets, and not the binding of lipoproteins to the cells, was partially inhibited by elastase. In conclusion, LDL and HDL rapidly deliver SM, PC and PE to platelets. Incorporation of LDL-derived phospholipids into platelets is unlikely to be mediated by endocytosis of lipoprotein particles. The uptake of the two choline-containing phospholipids appears to require the presence of specialized platelet membrane protein(s).

SUBMITTER: Engelmann B

PROVIDER: S-EPMC1217275 | biostudies-other | 1996 May

REPOSITORIES: biostudies-other

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Project description:BackgroundPlasmalogens are either phosphatidylcholine (PC P) or phosphatidylethanolamine (PE P) glycerophospholipids containing a vinyl ether moiety in sn-1-position and an esterified fatty acid in sn-2 position. Multiple functions have been proposed, including reservoir of precursors for inflammatory mediators, modulation of membrane fluidity, and anti-oxidative properties. They could therefore play a role under conditions of metabolic stress. Especially enzymatically modified LDL (eLDL) and oxidatively modified LDL (oxLDL) represent modifications of LDL that are taken up by macrophages in atherosclerotic plaques. The aim of this study was to analyze plasmalogen related effects of eLDL and oxLDL in human monocyte derived macrophages, as well as the effects of HDL3 mediated deloading.MethodsElutriated monocytes from nine healthy donors were differentiated in vitro for four days. Macrophages were then loaded with native LDL, eLDL and oxLDL for 24h and subsequently deloaded with HDL3 for another 24h. Lipidomic and transcriptomic profiles were obtained.ResultsLoading of macrophages with eLDL and oxLDL led to a transient but strong elevation of lysophosphatidylcholine (LPC) most likely through direct uptake. Only eLDL induced increased levels of total PC, presumably through an induction of PC synthesis. On the other hand treatment with oxLDL led to a significant increase in PC P. Analysis of individual lipid species showed lipoprotein and saturation specific effects for LPC, PC P and PE P species. Membrane fluidity was decreased by the large amount of FC contained in the lipoproteins, as indicated by a lower PC to FC ratio after lipoprotein loading. In contrast the observed changes in the saturated to mono-unsaturated fatty acid (SFA to MUFA) and saturated to poly-unsaturated fatty acid (SFA to PUFA) ratios in PE P could represent a cellular reaction to counteract this effect by producing more fluid membranes. Transcriptomic analysis showed considerable differences between eLDL and oxLDL treated macrophages. As a common feature of both lipoproteins we detected a strong downregulation of pathways for endogenous lipid synthesis as well as for exogenous lipid uptake. Deloading with HDL3 had only minor effects on total lipid class as well as on individual lipid species levels, most of the time not reaching significance. Interestingly treatment with HDL3 had no effect on membrane fluidity under these conditions, although incubation with HDL3 was partially able to counteract the oxLDL induced transcriptomic effects. To investigate the functional effect of lipoprotein treatment on macrophage polarization we performed surface marker flow cytometry. Under our experimental conditions oxLDL was able to partially shift the surface marker pattern towards a pro-inflammatory M1-like phenotype. This is consistent with the consumption of arachidonic acid containing PE P species in oxLDL treated cells, presumably for the synthesis of inflammatory mediators.SummaryOur findings provide novel data on the lipoprotein induced, lipidomic and transcriptomic changes in macrophages. This can help us better understand the development of metabolic, inflammatory diseases as well as improve our background knowledge on lipid biomarkers in serum.

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Transfer of phosphatidylcholine, phosphatidylethanolamine and sphingomyelin from low- and high-density lipoprotein to human platelets.

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