Oxidized LDL attenuates apoptosis in monocytic cells by activating ERK signaling

Low concentrations of oxidized low density lipoprotein ( OxLDL) are cytoprotective for phagocytes, although the underlying mechanisms remain unclear. We investigated signaling pathways used by OxLDL to attenuate apoptosis in monocytic cells. OxLDL at 25-50 mu g/ml inhibited staurosporine-induced apoptosis in THP-1 cells and mouse peritoneal macrophages, and it was cytoprotective in human primary monocytes upon serum withdrawal. Attenuated cell demise was reversed by blocking extracellular signal-regulated kinase (ERK) signaling. Translocation of cytochrome c to the cytosol was attenuated by OxLDL, which again demanded ERK signaling. Analysis of Bcl-2 family proteins revealed phosphorylation of Bad at serine 112 as well as ERK-dependent inhibition of Mcl-1 degradation. Although the formation of reactive oxygen species (ROS) is an established signal generated by OxLDL, ROS scavengers did not interfere with cell protection by OxLDL.