Redistribution of intracellular calcium and its effect on apoptosis in macrophages: Induction by oxidized LDL.
Calcium signaling, as a key to early step of the elementary intracellular events, has been implicated in controlling the development of atherosclerosis. We have shown previously that oxidized low density lipoprotein OxLDL-induced spatiotemporal increases of intracellular free calcium ([Ca(2+)](i)) in the early formation of macrophage foam cells. Here, we evaluated how spatiotemporal redistribution of intracellular calcium occurs and would affect OxLDL-induced apoptosis. Confocal laser scanning microscopy and flow cytometry showed the time-dependent increase of mitochondrial Ca(2+) ([Ca(2+)](m)) in acute and chronic exposure of U937-derived macrophages to OxLDL (100 microg/ml). Independent of the presence or absence of external Ca(2+), OxLDL-induced a peak of [Ca(2+)](m) in acute exposure, whose amplitude in the absence of extracellular Ca(2+) was obviously lower than the presence of extracellular Ca(2+). In addition, the thapsigargin-mediated increase of [Ca(2+)](i), through endoplasmic reticulum (ER) Ca(2+) pump depletion, was obviously reduced by 1-h pretreatment of OxLDL. OxLDL also caused a time-dependent opening of mitochondrial permeability transition pores (PTPs). EGTA/AM, an intracellular Ca(2+) chelator, significantly reduced OxLDL-induced apoptosis and failed to prevent OxLDL-induced necrosis at 6h. In contrast to control cells, chelation of cytosolic Ca(2+) by EGTA/AM at 6h did not completely reverse OxLDL-induced apoptosis. OxLDL stimulated depolarization of mitochondrial membrane potential (Deltapsi) in time-dependent manner. Our data demonstrated that OxLDL-induced spatiotemporal Ca(2+) redistribution in appropriate organelles and mediated Ca(2+)-dependent apoptosis in relation to depolarization of Deltapsi. These findings suggested that manipulation of the intracellular calcium balance may be a useful strategy to limit the loss of macrophages in early atherosclerosis.
Deng
Tongle
T
Department of Biomedical Engineering, Zhejiang University, Hangzhou 310027, PR China.
Zhang
Le
L
Ge
Yakun
Y
Lu
Min
M
Zheng
Xiaoxiang
X
D017209:Apoptosis / Q000187:drug effects*; D020013:Calcium Signaling / Q000187:drug effects*; D002454:Cell Differentiation / Q000187:drug effects; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D008077:Lipoproteins, LDL / Q000494:pharmacology*; D008264:Macrophages / Q000166:cytology / Q000187:drug effects*; D008564:Membrane Potentials / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects; D033681:Mitochondrial Membrane Transport Proteins / Q000187:drug effects; D051336:Mitochondrial Membranes / Q000187:drug effects / Q000502:physiology; D000083162:Mitochondrial Permeability Transition Pore; D009336:Necrosis; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D020298:U937 Cells / Q000166:cytology / Q000187:drug effects
D016895:Culture Media, Serum-Free; D008077:Lipoproteins, LDL; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; C099252:oxidized low density lipoprotein; D004533:Egtazic Acid; D019284:Thapsigargin; C046770:EGTA acetoxymethyl ester; D013755:Tetradecanoylphorbol Acetate