Characterization of monocyte chemoattractant proteins and CC chemokine receptor 2 expression during atherogenesis in apolipoprotein E-null mice

Abstract

Aim: We aimed to investigate the expression of monocyte chemoattractant proteins (MCPs) and their cognate receptor CC chemokine receptor 2 (CCR2) in aortas of apolipoprotein E-null (apoE -/-) mice during atherogenesis as well as the possible transcription pathway involved in the early induction of MCP-1 in vascular smooth muscle cells (VSMCs) in vivo. Methods: Atherosclerotic lesion development, aortic MCPs and CCR2 mRNA expression as well as the cellular localization of MCP-1, CCR2 and MCP-1 related transcription factors in atherosclerotic lesions were analyzed in apoE -/- mice fed a high fat and cholesterol diet. Results: MCP-1 and CCR2 mRNA expression was significantly induced during early atherogenesis and peaked after 10 and 12 weeks of diet, respectively, whereas MCP-2 and MCP-3 mRNA expression elevated in the late phases of lesion development. Immunostaining revealed that early MCP-1 expression was localized to VSMCs and that, in advanced lesions, both neointimal VSMCs and intimal macrophages expressed high levels of MCP-1. During the early (0 and 4 weeks of diet) induction of MCP-1 in VSMCs, the regulatory activator protein-1 (AP-1) proteins c-Jun and c-Fos were highly expressed and observed within the VSMCs nuclei, whereas nuclear factor-κB (NF-κB) protein p65 was only observed within the nuclei of VSMCs after 4 weeks of diet. CCR2 was also identified on intimal macrophages, endothelial cells and VSMCs in advanced lesions. Conclusion: This study provides fundamental information on the expression kinetics of MCPs and CCR2 during atherogenesis and indicates that the earliest induction of MCP-1 in VSMCs of apoE -/-mice appears to correlate with AP-1 but not NF-κB regulatory pathways.