| Atherosclerosis is a leading cause of mortality and morbidity in industrialized communities. A central feature of the oxidative hypothesis for the development of atherosclerosis is the oxidative modification of low density lipoproteins (LDL) forming oxidized LDL (oxLDL). This concept is derived from many studies that have demonstrated the pro-atherogenic properties of oxLDL. However, more recent studies have suggested that the role of oxLDL in atherogenesis is more complex and that low levels of oxidation of LDL may in fact stimulate anti-atherogenic responses. Conflicting data have been presented that suggest oxLDL can initiate deleterious effects in EC, leading to cytotoxicity, but also stimulate signaling pathways that are cytoprotective, the latter may be considered as a novel adaptive pathway by which cells respond to oxLDL. OxLDL can regulate vascular EC function by modulating specific signaling pathways. In the context of atherogenesis, important examples include those pertaining to leukocyte adhesion, cell death, and migration. The mechanisms that may protect EC from oxidative damage are largely unknown. Preliminary studies by our laboratory and others have shown that oxLDL stimulates signaling pathways in EC that increase the concentration of the endogenous antioxidant glutathione (GSH) via transcriptional up-regulation of the enzyme glutamate-cysteine ligase (GCL). However, the mechanisms of oxLDL induction of GSH are not well defined. GSH is a low-molecular thiol-containing tripeptide constitutively synthesized in animal and plant cells often in the millimolar range functioning as a vital intra- and extra-cellular protective antioxidant. It is therefore hypothesized that low levels of non-toxic lipid oxidation products serve a cytoprotective function by activating signaling pathways, including the synthesis of endogenous GSH in EC through transcriptional regulation of GCL. The hypothesis will be tested by pursuit of the following specific aims: (1) to determine that oxLDL induction of GSH biosynthesis is through transcriptional regulation of GCL in human endothelial cells, (2) to define the role of mitogen activated protein-kinases in the signaling mechanisms involved in GSH induction and cell death or survival by oxLDL in EC, and (3) to investigate the effect of oxLDL on the conditions conducive to cell death in EC and the role that mitochondria play in this process. |
