Modified LDLs induce proliferation-mediated death of human vascular endothelial cells through MAPK pathway

The ability of modified low-density lipoptoteins ( LDLs) to induce both proliferation and death of endothelial cells is considered to be a mechanism of early atherosclerosis development. We previously showed that carbamylated LDL ( cLDL) induces human coronary artery endothelial cell ( HCAEC) death in vitro. This effect is similar to the atherogenic action of oxidized LDL ( oxLDL) that induces the proliferation and death of endothelial cells. The present study was designed to analyze a potential proliferative effect of cLDL and whether proliferation caused by modified LDLs is related to cell death. Cultured HCAECs were exposed to different concentrations of modified LDL or native LDL for varying periods of time. Cell proliferation measured by bromodeoxyuridine incorporation and S-phase analysis was dose-dependently increased in the presence of cLDL ( 6.25-200 mu g/ml). The proliferation induced by cLDL or oxLDL was associated with cell death and increased phosphorylation of extracellular signal-regulated kinase ( ERK) and c-Jun NH2-terminal kinase ( JNK). Inhibition of cLDL- or oxLDL-induced proliferation by aphidicolin ( 1 mu g/ml) was protective against both short-term cell death measured by lactate dehydrogenase release into the medium and long-term cell viability visualized by cell multiplication. Inhibition of ERK phosphorylation led to a significant decrease of DNA synthesis and cell rescue from injury by modified LDLs, while inhibition of JNK phosphorylation had an only partial rescue effect without involvement in cell proliferation. These data are the first evidence that endothelial cell death induced by cLDL or oxLDL is mediated by cell proliferation through the mitogen-activated protein kinase pathway.