Transfer of phosphatidylcholine, phosphatidylethanolamine and sphingomyelin from low- and high-density lipoprotein to human platelets.
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).
Engelmann
B
B
Physiologisches Institut, Universität München, Germany.
Kögl
C
C
Kulschar
R
R
Schaipp
B
B
D001693:Biological Transport, Active / Q000187:drug effects; D001792:Blood Platelets / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008074:Lipoproteins / Q000097:blood*; D008075:Lipoproteins, HDL / Q000097:blood; D008077:Lipoproteins, LDL / Q000097:blood; D010196:Pancreatic Elastase / Q000494:pharmacology; D010713:Phosphatidylcholines / Q000097:blood; D010714:Phosphatidylethanolamines / Q000097:blood; D010743:Phospholipids / Q000097:blood*; D015398:Signal Transduction; D013109:Sphingomyelins / Q000097:blood
D008074:Lipoproteins; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D010743:Phospholipids; D013109:Sphingomyelins; D010196:Pancreatic Elastase