BACKGROUND: Endothelial dysfunction and injury are thought to play an important role in progression of coronary-artery-disease (CAD). High-density-lipoprotein from healthy subjects (HDLHealthy) has been proposed to exert endothelial anti-apoptotic effects that may represent an important anti-atherogenic property of the lipoprotein. The present study therefore aimed to compare effects of HDLCAD and HDLHealthy on activation of endothelial anti- and pro-apoptotic pathways and to determine which changes of the lipoprotein are relevant for these processes. METHODS AND RESULTS: HDL was isolated from patients with stable CAD (HDLsCAD), an acute coronary syndrome (HDLACS) and healthy subjects. HDLHealthy induced expression of the endothelial anti-apoptotic Bcl-2 protein Bcl-xL and reduced endothelial cell apoptosis in vitro and in apoE-deficient-mice in vivo. In contrast, HDLsCAD and HDLACS did not inhibit endothelial apoptosis, failed to activate endothelial Bcl-xL and stimulated endothelial pro-apoptotic pathways, in particular p38-MAPK-mediated activation of the pro-apoptotic Bcl-2-protein tBid. Endothelial anti-apoptotic effects of HDLHealthy were observed after inhibition of endothelial nitric-oxide-synthase and after delipidation, but not completely mimicked by apoA-I or reconstituted HDL, suggesting an important role of the HDL-proteome. HDL proteomics analyses and subsequent validations and functional characterizations suggested a reduced clusterin- and increased apoC-III-content of HDLsCAD and HDLACS as mechanisms leading to altered effects on endothelial apoptosis. CONCLUSIONS: The present study demonstrates for the first time that HDLCAD does not activate endothelial anti-apoptotic pathways, but rather stimulates potential endothelial pro-apoptotic pathways. HDL-proteome remodeling plays an important role for these altered functional properties of HDL. These findings provide novel insights into mechanisms leading to altered vascular effects of HDL in coronary disease.