Esterified Cholesterol Accumulation Induced by Aggregated LDL Uptake in Human Vascular Smooth Muscle Cells Is Reduced by HMG-CoA Reductase Inhibitors

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Abstract
Abstract —Vascular smooth muscle cell (VSMC) proliferation is a key event in the development of atherosclerotic lesions. VSMCs synthesize extracellular matrix, where low density lipoproteins (LDLs) are trapped and become aggregated (agLDL). The objective of this study was to investigate the cholesterol uptake and accumulation triggered by agLDL in comparison with native LDL (nLDL) on unstimulated and platelet-derived growth factor–stimulated human aortic VSMCs and the role of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors on these processes. Esterified cholesterol (EC) accumulation induced by agLDL in VSMCs was correlated with the degree of aggregation and concentration. The EC content of VSMCs treated with 100 μg/mL of agLDL (80% aggregated) increased ≈70-fold over that in VSMCs incubated with the same concentration of nLDL. Whereas nLDL-derived EC was increased approximately twofold in platelet-derived growth factor–stimulated VSMCs, there was no effect of platelet-derived growth factor (10 −9 mol/L) on the uptake of agLDL. The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor simvastatin (5 μmol/L) reduced EC accumulation derived from agLDL uptake by 58% and 35% in platelet-derived growth factor—stimulated and unstimulated VSMCs, respectively. This inhibition was overcome by geranylgeraniol (10 μmol/L) and partially by farnesol (10 μmol/L). Fluorescence microscopy of the cellular internalization of agLDL labeled with the fluorochrome 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine demonstrated that simvastatin reduces EC accumulation derived from agLDL by inhibiting its endocytosis and that the effect is completely reversed by geranygeraniol. These results indicate that agLDLs are rapidly internalized by human VSMCs and that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors modulate EC accumulation. These data suggest a possible mechanism by which statins could contribute to the passivation and stabilization of actively growing atherosclerotic lesions.