An Atherogenic Level of Native LDL Increases Endothelial Cell Vulnerability to Shear-Induced Plasma Membrane Wounding and Consequent Release of Basic Fibroblast Growth Factor

We report here that exposure of large vessel EC to clinically relevant, atherogenic levels of native LDL (240 mg cholesterol/dL) increases the incidence and severity of shear-induced EC plasma membrane wound injury in vitro. The proportion of LDL-treated EC that survived mechanical shearing in suspension was significantly less (∼20%; p < 0.005) than that of control, untreated EC. Moreover, the amount of a fluorescent, cytoplasmic wound marker, detected by flow cytometry, in surviving LDL-treated cells was significantly more (∼2 log units; p < 0.005) than that detected in surviving, control EC. Mechanically sheared LDL-treated EC released significantly more (∼2 fold; p < 0.02) bFGF than sheared, control EC. LDL treatment of EC resulted in an increase of ∼60% in membrane-associated cholesterol, and an increase in the cholesterol/phospholipid ratio from 0.6 to 1.3. Fluorescence anisotropy revealed that the plasma membrane fluidity (PMF) of LDL-treated EC was significantly lower than that of control EC. When the PMF of LDL-treated EC was raised using the membrane fluidizing agent, A2C, we observed a significant reduction in EC vulnerability to shear stress, whereas the presence of the membrane ordering agent, PF-68, caused a significant increase in LDL-treated EC vulnerability to shear stress. Our data suggest that LDL-induced increases in EC vulnerability to mechanical stress and consequent bFGF release, may promote EC injury in vivo, and hence promote the initiation of atherogenesis.