Peroxidized cholesterol in low density lipoprotein: Negative effects on human endothelial cells and atherogenic...

Oxidative stress associated with atherogenesis is often accompanied by fatty acid streak and foam cell formation due to uncontrolled oxidation of cholesterol (Ch) and other unsaturated lipids. We hypothesized that under persistent oxidative stress and elevated Ch conditions, Ch hydroperoxides (ChOOHs) are the most cytotoxic Ch metabolites delivered with oxidized low-density lipoprotein (oxLDL). We further hypothesized that in addition to macrophages, LDL-bearing ChOOHs can damage endothelial cells (ECs), leading to cellular accumulation of Ch oxidation products (ChOX) as well as Ch itself. We tested our hypotheses, focusing on the lower ends of EC susceptibility to ChOX-LDL damage. We used acetylated LDL (AcLDL) which, like parental LDL, is recognized by EC scavenger receptors. Among the ChOXs studied, 7-hydroperoxy-Ch (7-OOH) in AcLDL was taken up most rapidly by ECs, followed by 7 = O and 7-OH; however, 7-OOH was the most cytotoxic. Interestingly, sub-lethal doses of AcLDL-borne 7-OOH (but not other ChOXs) significantly stimulated EC proliferation. We confirmed 7-OOH's cytotoxic role by knocking down or overexpressing seleno-peroxidase GPx4, the only enzyme capable of direct ChOOH detoxification in situ. StAR family proteins are known to mediate intracellular Ch transport: StarD1 in mitochondria and StarD4 in cytosol. In this study, we found that transport of AcLDL-borne 7-OOH can also be StAR-mediated, StarD1 knockdown causing a much greater inhibitory effect than StarD4 knockdown. Collectively, our findings provide new evidence for mitochondrial site-specific cytotoxicity of ldl-borne 7-OOH in vascular endothelial cells and demonstrate the protective role of endogenous GPx4 in mitigating this damage.