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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2009;29:1615.)
© 2009 American Heart Association, Inc.

Cell Biology/Signaling

Aggregated LDL in Contact With Macrophages Induces Local Increases in Free Cholesterol Levels That Regulate Local Actin Polymerization

Inna Grosheva; Abigail S. Haka; Chunbo Qin; Lynda M. Pierini; Frederick R. Maxfield

From the Department of Biochemistry, Weill Cornell Medical College, New York.

Correspondence to Frederick R. Maxfield, Department of Biochemistry, Box 63, Weill Cornell Medical College, New York, NY 10065. E-mail FRMaxfie{at}med.cornell.edu

Objective— Interaction of macrophages with aggregated matrix-anchored lipoprotein deposits is an important initial step in atherogenesis. Aggregated lipoproteins require different cellular uptake processes than those used for endocytosis of monomeric lipoproteins. In this study, we tested the hypothesis that engagement of aggregated LDL (agLDL) by macrophages could lead to local increases in free cholesterol levels and that these increases in free cholesterol regulate signals that control cellular actin.

Methods and Results— AgLDL resides for prolonged periods in surface-connected compartments. Although agLDL is still extracellular, we demonstrate that an increase in free cholesterol occurs at sites of contact between agLDL and cells because of hydrolysis of agLDL-derived cholesteryl ester. This increase in free cholesterol causes enhanced actin polymerization around the agLDL. Inhibition of cholesteryl ester hydrolysis results in decreased actin polymerization.

Conclusions— We describe a novel process that occurs during agLDL–macrophage interactions in which local release of free cholesterol causes local actin polymerization, promoting a pathological positive feedback loop for increased catabolism of agLDL and eventual foam cell formation.

Key Words: atherosclerosis • foam cells • surface-connected compartment • Rho GTPases • F-actin