Antiapoptotic and Proliferative Effects of Low Concentrations of 7 beta-Hydroxycholesterol in Human Endothelial Cells via ERK Activation

The atherogenic potential of oxidized low-density lipoproteins (oxLDL) has been correlated to their 7beta-hydroxycholesterol (7betaOHC) content; oxLDLs have a dual effect on endothelial cell viability, inducing apoptosis or proliferation depending on the concentration. Considering that 7betaOHC is apoptotic for endothelial cells at concentrations >/=20 mug/ml, a study on the effect of lower concentrations of 7betaOHC on human umbilical vein endothelial cells (HUVECs) was undertaken. 7betaOHC (1-10 mug/ml) increased 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction of growth-factor-deprived HUVECs. This effect was due to the increased cell proliferation, determined by [(3)H]thymidine incorporation, and the reduction of apoptosis, revealed by the decreased caspase-3 activation and annexin V staining. 7betaOHC also protected against staurosporine apoptosis. 7betaOHC induced an increase in intracellular ROS antagonized by N-acetylcysteine; however, HUVECs treatment with the antioxidant did not inhibit the effects of 7betaOHC. 7betaOHC produced an increase in extracellular signal-regulated kinase (ERK) phosphorylation that was blocked by inhibitors of store-operated calcium entry 2-aminoethoxydiphenyl borate and gadolinium. MEK inhibition with PD98059 or U0126 as well as store-operated calcium entry inhibition antagonized the effect of 7betaOHC. The results suggest that 7betaOHC promotes HUVECs survival and proliferation by a mechanism independent of ROS production and involving calcium-dependent activation of ERK.