Oxidized low density lipoprotein and very low density lipoprotein enhance expression of monocyte chemoattractant protein-1 in rabbit peritoneal exudate macrophages

Abstract

The migration of monocytes into arterial subendothelial space is one of the earliest events in atherogenesis. Monocyte chemoattractant protein 1 (MCP-1) is a potent monocyte chemoattractant. The purpose of this work was to examine whether oxidized low density lipoprotein (OX-LDL) and very low density lipoprotein (OX-VLDL) have any effect on the expression of MCP-1 mRNA and protein in rabbit peritoneal exudate macrophages. The total RNA was extracted from the macrophages after 24 h exposure to LDL, VLDL, OX-LDL, and OX-VLDL, respectively, and the media (LDL-CM, VLDL-CM, OX-LDL-CM and OX-VLDL-CM) conditioned by the macrophages exposed to the above-mentioned lipoproteins were collected. The MCP-1 mRNA expression in macrophages was examined by Northern blot analysis. Meanwhile, MCP-1 protein in the conditioned media was determined by sandwich ELISA. The chemotactic activity of the conditioned media for monocytes was determined by micropore filter assay. The results revealed that the macrophages can express MCP-1, and 24 h exposure to OX-LDL and OX-VLDL induced a 3.2-fold and a 3.4-fold increase in MCP-1 mRNA expression in macrophages and a 2.2-fold and a 2.5-fold increase in the level of MCP-1 protein in the conditioned media, respectively. However, 24 h exposure to LDL and VLDL only induced a slight increase in the expression of MCP-1 mRNA and protein in macrophages. Furthermore, the migration distance of monocyte induced by OX-LDL-CM and OX-VLDL-CM was longer than that induced by LDL-CM and VLDL-CM, as well as by CM. We conclude that the macrophages can express MCP-1, and OX-LDL and OX- VLDL induce stronger MCP-1 expression. It suggests that macrophages may amplify the recruitment of monocytes into subendothelial space, and OX-LDL and OX-VLDL may play an important role in the pathogenesis of atherosclerosis through enhancing the MCP-1 expression in macrophages.