Upregulation of macrophage-specific functions by oxidized LDL: lysosomal degradation-dependent and -independent pathways.
Formation of foam cells from macrophages, which are formed by the differentiation of blood-borne monocytes, is a critical early event in atherogenesis. To examine how pre-exposure of monocytes to modified proteins, such as oxLDL, influences their differentiation to macrophages, an in vitro model system using isolated PBMC maintained in culture in the presence of oxLDL was used. Pretreatment of monocytes with oxLDL caused a faster rate of expression of macrophage-specific functions and loss of monocyte-specific functions compared to unmodified LDL. The effect of oxidation of lipid component of LDL by CuSO(4) and its protein component by HOCl, on mo-mϕ differentiation was studied by monitoring the upregulation of macrophage-specific functions, particularly MMP-9. Chloroquine, a lysosomal degradation blocker, significantly reversed the effect mediated by CuSO(4) oxLDL, indicating the involvement of lysosomal degradation products, while no such effect was observed in HOCl oxLDL-treated cells, indicating the existence of a pathway independent of its lysosomal degradation products. Reversal of the effect of oxLDL by NAC and Calphostin C, an inhibitor of PKC, suggested the activation of RO-mediated signaling pathways. Use of inhibitors of signaling pathways showed that CuSO(4) oxLDL upregulated mϕ-specific MMP-9 through p38 MAPK and Akt-dependent pathways, while HOCl oxLDL utilized ERK ½ and Akt. Further analysis showed the activation of PPARγ and AP-1 in CuSO(4) oxLDL, while HOCl-oxLDL-mediated effect involved NFκB and AP-1. These results suggest that lipid oxLDL- and protein oxLDL-mediated upregulation of mo-mϕ-specific functions involve lysosomal degradation-dependent and -independent activation of intracellular signaling pathways.
Department of Biochemistry, University of Kerala, Kariavattom, Trivandrum 695 581, India.
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Radhika
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Sudhakaran
D000111:Acetylcysteine / Q000494:pharmacology; D002454:Cell Differentiation / Q000187:drug effects; D002478:Cells, Cultured; D002738:Chloroquine / Q000494:pharmacology; D002867:Chromones / Q000494:pharmacology; D019327:Copper Sulfate / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D007093:Imidazoles / Q000494:pharmacology; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D008077:Lipoproteins, LDL / Q000494:pharmacology / Q000502:physiology*; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D020778:Matrix Metalloproteinase 2 / Q000378:metabolism; D020780:Matrix Metalloproteinase 9 / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D016328:NF-kappa B / Q000378:metabolism; D009281:Naphthalenes / Q000494:pharmacology; D010084:Oxidation-Reduction; D047495:PPAR gamma / Q000235:genetics / Q000378:metabolism; D059748:Proteolysis; D011725:Pyridines / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects; D018808:Transcription Factor AP-1 / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects; D015854:Up-Regulation
D002867:Chromones; D004791:Enzyme Inhibitors; D005419:Flavonoids; D016166:Free Radical Scavengers; D007093:Imidazoles; D008077:Lipoproteins, LDL; D009025:Morpholines; D016328:NF-kappa B; D009281:Naphthalenes; D047495:PPAR gamma; D011725:Pyridines; D018808:Transcription Factor AP-1; C099252:oxidized low density lipoprotein; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D002738:Chloroquine; C522361:MMP2 protein, human; D020778:Matrix Metalloproteinase 2; C579270:MMP9 protein, human; D020780:Matrix Metalloproteinase 9; C058819:calphostin C; D019327:Copper Sulfate; C093642:SB 203580; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D000111:Acetylcysteine