title: Apoptotic pathways involved in U937 cells exposed to LDL oxidized by hypochlorous acid.
abstract: Oxidized low-density lipoproteins (oxLDL) play a critical role in atherogenesis. One oxidative pathway of LDL involves myeloperoxidase, which catalyzes the production of hypochlorous acid (HOCl) in monocytes. We investigated the apoptotic mechanism induced by oxLDL, generated by HOCl treatment of native LDL, in human monocytic U937 cell line. The involvement of the mitochondrial apoptotic pathway was analyzed in Bcl-2-overexpressing clones, generated from U937 cells. HOCl-oxLDL induced in U937 cells (i) a marked caspase-dependent increase of apoptosis, (ii) a loss of mitochondrial membrane potential, (iii) a specific activation of caspase-2, -3, -8, and -9, and (iv) a similar degree of apoptosis in presence or absence of anti-Fas and anti-TNF-R1 antibodies. Moreover, the degree of HOCl-oxLDL-induced caspase-3 and -8 activation, and apoptosis was significantly reduced in U937/Bcl-2 cells, with no activation of caspase-9. By contrast, Cu-oxLDL-mediated apoptosis in U937 cells involved exclusively the mitochondrial pathway. In conclusion, the mechanism of HOCl-oxLDL-induced apoptosis in monocytic U937 cells involves the two pathways of apical caspase activation: (i) death receptor-mediated caspase-8 and (ii) mitochondria-mediated caspase-9. This converges in the activation of executing caspases, including caspase-3, and apoptosis. The interference of Bcl-2 overexpression with HOCl-oxLDL-induced apoptosis suggests the importance of mitochondrial involvement in this apoptotic mechanism.
authors.affiliation: Laboratory of Biochemistry A, Necker Hospital, Paris, France. stephanie.vicca@nck.ap-hop-paris.fr
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Vicca
authors.forename: Ziad A
authors.initials: ZA
authors.lastname: Massy
authors.forename: Carole
authors.initials: C
authors.lastname: Hennequin
authors.forename: Djamel
authors.initials: D
authors.lastname: Rihane
authors.forename: Tilman B
authors.initials: TB
authors.lastname: Drüeke
authors.forename: Bernard
authors.initials: B
authors.lastname: Lacour
mesh_terms: D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D006801:Humans; D006997:Hypochlorous Acid / Q000737:chemistry*; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D008264:Macrophages / Q000166:cytology / Q000187:drug effects; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D010084:Oxidation-Reduction; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D020298:U937 Cells; D019014:fas Receptor / Q000378:metabolism
chemical_list: D000590:Amino Acid Chloromethyl Ketones; D061945:Caspase Inhibitors; D008077:Lipoproteins, LDL; D019253:Proto-Oncogene Proteins c-bcl-2; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone; D019014:fas Receptor; C099252:oxidized low density lipoprotein; D006997:Hypochlorous Acid; D020169:Caspases