Necrosis and apoptosis induced by oxidized low density lipoproteins occur through two calcium‐dependent pathways in lymphoblastoid cells

Abstract

Oxidized low density lipoproteins (LDL) elicit in cultured lymphoblastoid cell lines a delayed and sustained calcium rise followed by a progressive of DNA fragmentation, endogenous proteolysis, and morphological features of necrosis and apoptosis. All these events were blocked by chelating the calcium of the culture medium by EGTA, thus suggesting that the two types of cell death induced by oxidized LDL (necrosis and apoptosis) were subsequent to the rise in calcium. The protease inhibitors leupeptin and antipain were able to block (at least in part) the endogenous proteolysis and the necrotic process, but exhibited no effect on apoptosis and DNA fragmentation. At the opposite, aurintricarboxylic acid and spermine (inhibitors of DNA degradation by endonucleases) inhibit DNA fragmentation and morphological apoptosis, but not endogenous proteolysis and necrosis. These data suggest that cell death induced by oxidized LDL occurs through two calcium-dependent processes triggering 1) on one hand, proteolysis and subsequently necrosis characterized by the loss of cell membrane integrity; and 2) on the other hand, internucleosomal DNA cleavage and subsequently morphological apoptosis. The RNA or protein synthesis inhibitors, actinomycin D and cycloheximide, were completely ineffective in preventing endogenous proteolysis, DNA fragmentation, necrosis, and apoptosis induced by oxidized LDL. The subclassification of the type of apoptosis elicited by oxidized LDL is discussed.

HDLs inhibit endoplasmic reticulum stress and autophagic response induced by oxidized LDLs

“…We previously reported that oxLDLs-induced apoptosis results from a deregulation of the cytosolic Ca 2 þ homeostasis, characterized by a delayed and intense Ca 2 þ rise occurring several hours after the beginning of the pulse with oxLDLs. 5,8 Interestingly, HoyerHansen et al 14 demonstrate that a rise in free cytosolic Ca 2 þ is a potent inducer of autophagy which suggests that apoptosis and autophagy share many of the same regulators. The rise in cytosolic Ca 2 þ triggered by oxLDLs was completely blocked in cells pre-treated by HDLs (Figure 8a).…”

“…1 Oxidized LDLs (oxLDLs) exhibit a variety of atherogenic properties including foam cell formation, inflammatory response, cell proliferation at low concentration and apoptosis at higher concentration 1,2 OxLDLs may alter the fragile balance between survival and death of vascular cells, thereby, leading to plaque instability and finally to atherothrombotic events. 3,4 The proapoptotic effects of oxLDLs are mediated through a complex sequence of signaling events that lead to the activation of several caspase-dependent or caspase-independent apoptotic pathways 2,5,6 Previously, we reported that treatment of human vascular endothelial and smooth muscle cells with oxLDLs or 7-ketocholesterol (a major oxysterol in oxLDLs) causes an increase in cytosolic Ca 2 þ through TRPC1 channels that triggers a proteolytic cascade involving Ca 2 þ -dependent calpains, Bid cleavage and cytochrome c release, leading finally to caspase-3 activation and apoptosis. [7][8][9] Recently, we have reported that oxLDLs induced the unfolded protein response (UPR) and triggered endoplasmic reticulum (ER) stress.…”

Alteration of the Sphingomyelin/Ceramide Pathway Is Associated with Resistance of Human Breast Carcinoma MCF7 Cells to Tumor Necrosis Factor-α-mediated Cytotoxicity

“…The mean value of quadruplicate was used for analysis. Quantitative DNA fragmentation was determined as described previously (28). TNF-or ceramide-treated and untreated cells (1 ϫ 10 6 ) were pelleted and washed in PBS.…”

Phenolic antioxidants trolox and caffeic acid modulate the oxidized LDL‐induced EGF‐receptor activation

“…OxLDL induce a variety of biological e ects potentially involved in atherogenesis, such as foam cells and fatty streak formation, alterations in gene expression, cell migration, motility and contractility, cell proliferation, cell viability, local immune response, vasomotor tone (Witztum & Steinberg, 1991;Hajjar & Haberland, 1997). These biological responses are triggered by oxidized lipids contained in oxLDL that alter the activity of various cellular signalling pathways (Hajjar & Haberland, 1997), for instance calcium (Escargueil-Blanc et al, 1994), phospholipase D (Natarajan et al, 1995(Natarajan et al, ), trimericet al 1996, EGF-receptor (EGFR) (Suc et al, 1998), PI3-kinase (Martens et al, 1998), PPARgamma (Nagy et al, 1998), rho-kinase (Essler et al 1999).…”