title: Low density lipoproteins inhibit the Na+/H+ antiport in human platelets via activation of p38MAP kinase.
abstract: Low density lipoproteins (LDL) inhibit the Na+/H+ antiport and thereby sensitize platelet towards agonist. However, mechanisms underlying the suppressing effect of LDL on Na+/H+ exchange are unclear. We here show that the lowering of intracellular pH and the suppression of the sodium propionate-induced Na+/H+ exchange in the presence of LDL are abolished by SKF86002, a selective inhibitor of p38MAP kinase (p38MAPK). The inhibitory effect of LDL on Na+/H+ exchange was mimicked by H2O2, which directly activates p38MAPK. Exposure of platelets to LDL or H2O2 led to phosphorylation of p38MAPK, its upstream regulator MAP kinase kinase 3/6 (MKK 3/6), and its downstream target heat shock protein 27 (HSP27), and this effect was abrogated in SKF86002-pretreated platelets. In addition, both LDL and H2O2 produced the SKF86002-sensitive phosphorylation of an oligopeptide encompassing p38MAPK phosphorylation sequence derived from NHE-1, a major Na+/H+ exchanger in platelets. We further show that the sensitizing effects of LDL on the thrombin-induced platelet activation, as reflected by aggregation and granule secretion, are abolished in cells pretreated with SKF86002. We conclude that activation of p38MAPK is required for the inhibitory effect of LDL on Na+/H+ antiport and thereby for LDL-dependent sensitization in human platelets.
authors.affiliation: Institut für Klinische Chemie und Laboratoriumsmedizin, Universitätsklinikum Münster, Albert Schweizer Str. 33, D-48129 Münster, Germany. nofer@uni-muenster.de
authors.forename: Jerzy-Roch
authors.initials: JR
authors.lastname: Nofer
authors.forename: Christian
authors.initials: C
authors.lastname: Noll
authors.forename: Renata
authors.initials: R
authors.lastname: Feuerborn
authors.forename: Gerd
authors.initials: G
authors.lastname: Assmann
authors.forename: Martin
authors.initials: M
authors.lastname: Tepel
mesh_terms: D001792:Blood Platelets / Q000201:enzymology* / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007093:Imidazoles / Q000494:pharmacology; D008077:Lipoproteins, LDL / Q000378:metabolism / Q000502:physiology*; D048371:MAP Kinase Kinase 3 / Q000378:metabolism; D048669:MAP Kinase Kinase 6 / Q000378:metabolism; D020935:MAP Kinase Signaling System; D009842:Oligopeptides / Q000737:chemistry; D010455:Peptides / Q000737:chemistry; D010766:Phosphorylation; D011422:Propionates / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000378:metabolism*; D013844:Thiazoles / Q000494:pharmacology; D013917:Thrombin / Q000378:metabolism; D013997:Time Factors; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D007093:Imidazoles; D008077:Lipoproteins, LDL; D009842:Oligopeptides; D010455:Peptides; D011422:Propionates; D017923:Sodium-Hydrogen Exchangers; D013844:Thiazoles; C069139:growth factor-activatable Na-H exchanger NHE-1; C052026:6-(4-fluorophenyl)-2,3-dihydro-5-(4-pyridinyl)imidazo(2,1-b)thiazole; D006861:Hydrogen Peroxide; C514135:sodium propionate; D048051:p38 Mitogen-Activated Protein Kinases; D048371:MAP Kinase Kinase 3; D048669:MAP Kinase Kinase 6; C482566:MAP2K6 protein, human; D013917:Thrombin; C029658:propionic acid