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Expression of the monocyte chemoattractant protein-1 receptor CCR2 is increased in hypercholesterolemia. Differential effects of plasma lipoproteins on monocyte function.

Monocytes are recruited from the circulation into the subendothelial space where they differentiate into mature macrophages and internalize modified lipoproteins to become lipid-laden foam cells. The accumulation of monocytes is mediated by the interaction of locally produced chemoattractant protein-1 (MCP-1) with its receptor CCR2. The objective of the present study is to demonstrate the differential effects of plasma lipoproteins on monocyte CCR2 expression. The CCR2 expression was increased about 2.4-fold in monocytes isolated from hypercholesterolemic patients, compared to monocytes from normal controls. There was a significant correlation between CCR2 expression and plasma low density lipoprotein (LDL). Elevated levels of high density lipoprotein (HDL) blunted and even reverted the effects of LDL on CCR2 expression, both in vivo and in vitro. The causal relationship between plasma lipoproteins and CCR2 expression was further confirmed by modulating the lipoprotein profile. Estrogen supplement therapy decreased plasma LDL cholesterol, increased plasma HDL cholesterol, and reduced CCR2 expression in hypercholesterolemic postmenopausal women, but had no effect on the plasma lipid profile or CCR2 expression in normocholesterolemic subjects. The physiological significance of altered CCR2 expression was tested by chemotaxis assay, and our results demonstrated that treatment of THP-1 monocytes with LDL induced CCR2 expression and substantially enhanced the chemotaxis elicited by MCP-1. Our findings suggest that plasma lipoproteins differentially control monocyte function and that monocytes from hypercholesterolemic subjects are hyperresponsive to chemotactic stimuli. This may increase their accumulation in the vessel wall and accelerate the pathogenic events of atherogenesis.