Antiapoptotic and Proliferative Effects of Low Concentrations of 7β-Hydroxycholesterol in Human Endothelial Cells via ERK Activation
The atherogenic potential of oxidized low-density lipoproteins (oxLDL) has been correlated to their 7β-hydroxycholesterol (7βOHC) content; oxLDLs have a dual effect on endothelial cell viability, inducing apoptosis or proliferation depending on the concentration. Considering that 7βOHC is apoptotic for endothelial cells at concentrations ≧20 µg/ml, a study on the effect of lower concentrations of 7βOHC on human umbilical vein endothelial cells (HUVECs) was undertaken. 7βOHC (1–10 µg/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 [&lt;sup&gt;3&lt;/sup&gt;H]thymidine incorporation, and the reduction of apoptosis, revealed by the decreased caspase-3 activation and annexin V staining. 7βOHC also protected against staurosporine apoptosis. 7βOHC induced an increase in intracellular ROS antagonized by N-acetylcysteine; however, HUVECs treatment with the antioxidant did not inhibit the effects of 7βOHC. 7βOHC 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 7βOHC. The results suggest that 7βOHC promotes HUVECs survival and proliferation by a mechanism independent of ROS production and involving calcium-dependent activation of ERK.