Retention of aggregated LDL by cultured human coronary artery endothelial cells

Aggregated LDL (AgLDL) accumulates within the subendothelial space of developing atherosclerotic lesions. We were interested to learn whether endothelial cells can interact with AgLDL. Incubation of endothelial cells with AgLDL resulted in apparent cholesterol retention. Microscopic examination revealed that cholesterol retention resulted mainly from endothelial cell surface attachment of AgLDL. Little AgLDL entered endothelial cells consistent with the small amount of endothelial cell degradation of AgLDL. Although endothelial cell retention of AgLDL was inhibited by LDL, AgLDL retention was not blocked by lactoferrin, C7 anti-LDL receptor monoclonal antibody, or receptor-associated protein, suggesting that LDL receptor family members did not mediate this retention. Surface retention of AgLDL depended on microtubule function and could be regulated by the protein kinase C activator, PMA. Treatment of endothelial cells with PMA either before or during, but not after incubation with AgLDL, inhibited retention of AgLDL. Our findings show that endothelial cells can retain AgLDL but internalize and metabolize little of this AgLDL. Thus, it is unlikely that endothelial cells can transport AgLDL out of atherosclerotic lesions, but it is likely that retention of AgLDL affects endothelial function.