Objective: Although apolipoprotein E3 (apoE3) is known to be atheroprotective, its mechanisms of protection in endothelial cells remain unclear.
Methods and results: Cultured human aortic endothelial cells were stimulated with tumor necrosis factor (TNF)-alpha in the presence of human recombinant apoE3 solubilized in dimyristoyl phosphatidylcholine liposomes. Using flow cytometry and real-time polymerase chain reaction, a significant increase of inflammatory cell adhesion proteins (vascular cell adhesion molecule-1 and E-Selectin), and MCP-1, interleukin-8, and intercellular adhesion molecule-1 gene expression was observed within 5 hours of TNF-alpha exposure, which was markedly attenuated in cells coincubated with apoE3. Treatment with apoE4 resulted in increased inflammatory gene expression relative to either TNF treatment alone or TNF + apoE3 treatment. NO synthase inhibition experiments demonstrated NO to be an active participant in the actions of both TNF and apoE. To clarify the role of NO, dose-response experiments were performed with 0.03 to 300 micromol/L DEA-NONOate. Using flow cytometry and real-time polymerase chain reaction, a modulatory role of NO in TNF-induced endothelial cell activation was observed.
Conclusions: These data suggest a role of vascular wall apoE3 to balance the intracellular redox state in injured endothelial cells via NO-dependent pathways.