Several experimental and clinical studies have shown that oxidized low-density lipoprotein and oxidation-sensitive mechanisms are central in the pathogenesis of vascular dysfunction and atherogenesis. Here, we have used p66 ^Shc−/− and WT mice to investigate the effects of high-fat diet on both systemic and tissue oxidative stress and the development of early vascular lesions. To date, the p66 ^Shc−/− mouse is the unique genetic model of increased resistance to oxidative stress and prolonged life span in mammals. Computer-assisted image analysis revealed that chronic 21% high-fat treatment increased the aortic cumulative early lesion area by ≈21% in WT mice and only by 3% in p66 ^Shc−/− mice. Early lesions from p66 ^Shc−/− mice had less content of macrophage-derived foam cells and apoptotic vascular cells, in comparison to the WT. Furthermore, in p66 ^Shc−/− mice, but not WT mice, we found a significant reduction of systemic and tissue oxidative stress (assessed by isoprostanes, plasma low-density lipoprotein oxidizability, and the formation of arterial oxidation-specific epitopes). These results support the concept that p66 ^Shc−/− may play a pivotal role in controlling systemic oxidative stress and vascular diseases. Therefore, p66 ^Shc might represent a molecular target for therapies against vascular diseases.

Apoptosis of arterial cells induced by oxidized low density lipoproteins (OxLDL) is thought to contribute to the progression of atherosclerosis. However, most data on apoptotic effects and mechanisms of OxLDL were obtained with extensively oxidized LDL unlikely to occur in early stages of atherosclerotic lesions. We now demonstrate that mildly oxidized LDL generated by incubation with oxygen radical‐producing xanthine/xanthine oxidase (X/XO) induces apoptosis in primary cultures of human coronary endothelial and SMC, as determined by TUNEL technique, DNA laddering, and FACS analysis. Apoptosis was markedly reduced when X/XO‐LDL was generated in the presence of different oxygen radical scavengers. Apoptotic signals were mediated by intramembrane domains of both Fas and tumor necrosis factor (TNF) receptors I and II. Blocking of Fas ligand (FasL) reduced apoptosis by 50% and simultaneous blocking of FasL and TNF receptors by 70%. Activation of apoptotic receptors was accompanied by an increase of proapoptotic and a decrease in antiapoptotic proteins of the Bcl‐2 family and resulted in marked activation of class I and II caspases. Mildly oxidized LDL also activated MAP and Jun kinases and increased p53 and other transcription factors (ATF‐2, ELK‐1, CREB, AP‐1). Inhibitors of Map and Jun kinase significantly reduced apoptosis. Our results provide the first evidence that OxLDL‐induced apoptosis involves TNF receptors and Jun activation. More important, they demonstrate that even mildly oxidized LDL formed in atherosclerotic lesions may activate a broad cascade of oxygen radical‐sensitive signaling pathways affecting apoptosis and other processes influencing the evolution of plaques. Thus, we suggest that extensive oxidative modifications of LDL are not necessary to influence signal transduction and transcription in vivo .—Napoli, C., Quehenberger, O., de Nigris, F., Abete, P., Glass, C. K., Palinski, W. Mildly oxidized low density lipoprotein activates multiple apoptotic signaling pathways in human coronary cells. FASEB J. 14, 1996–2007 (2000)