ABSTRACT
We used a novel approach of cytostatically induced leucocyte depletion and subsequent reconstitution with leucocytes deprived of classical (inflammatory/Gr1(hi) ) or non-classical (resident/Gr1(lo) ) monocytes to dissect their differential role in atheroprogression under high-fat diet (HFD). Apolipoprotein E-deficient (Apoe(-/-) ) mice lacking classical but not non-classical monocytes displayed reduced lesion size and macrophage and apoptotic cell content. Conversely, HFD induced a selective expansion of classical monocytes in blood and bone marrow. Increased CXCL1 levels accompanied by higher expression of its receptor CXCR2 on classical monocytes and inhibition of monocytosis by CXCL1-neutralization indicated a preferential role for the CXCL1/CXCR2 axis in mobilizing classical monocytes during hypercholesterolemia. Studies correlating circulating and lesional classical monocytes in gene-deficient Apoe(-/-) mice, adoptive transfer of gene-deficient cells and pharmacological modulation during intravital microscopy of the carotid artery revealed a crucial function of CCR1 and CCR5 but not CCR2 or CX3 CR1 in classical monocyte recruitment to atherosclerotic vessels. Collectively, these data establish the impact of classical monocytes on atheroprogression, identify a sequential role of CXCL1 in their mobilization and CCR1/CCR5 in their recruitment.
Subject(s)
Aortic Diseases/immunology , Atherosclerosis/immunology , Carotid Artery Diseases/immunology , Chemotaxis, Leukocyte , Monocytes/immunology , Receptors, Chemokine/metabolism , Adoptive Transfer , Animals , Aorta/immunology , Aorta/metabolism , Aorta/pathology , Aortic Diseases/etiology , Aortic Diseases/genetics , Aortic Diseases/metabolism , Aortic Diseases/pathology , Apolipoproteins E/deficiency , Apolipoproteins E/genetics , Apoptosis , Atherosclerosis/etiology , Atherosclerosis/genetics , Atherosclerosis/metabolism , Atherosclerosis/pathology , Carotid Arteries/immunology , Carotid Arteries/metabolism , Carotid Arteries/pathology , Carotid Artery Diseases/etiology , Carotid Artery Diseases/genetics , Carotid Artery Diseases/metabolism , Carotid Artery Diseases/pathology , Chemokine CXCL1/metabolism , Diet, High-Fat , Disease Models, Animal , Disease Progression , Leukocyte Count , Leukocyte Reduction Procedures , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Monocytes/classification , Monocytes/transplantation , Receptors, CCR1/metabolism , Receptors, CCR5/metabolism , Receptors, Chemokine/deficiency , Receptors, Chemokine/genetics , Receptors, Interleukin-8B/metabolism , Signal Transduction , Time FactorsABSTRACT
RATIONALE: Neutrophils have been reported to contribute to early atherosclerotic lesion formation. Mechanisms of neutrophil-driven atherosclerosis remain unclear so far. OBJECTIVE: Investigation of the role of the neutrophil granule protein cathelicidin (CRAMP in mouse, LL37 in human) in atherosclerosis. METHODS AND RESULTS: Compared to Apoe(-/-) mice, Cramp(-/-) Apoe(-/-) mice exhibit reduced lesion sizes with lower macrophage numbers. In atherosclerotic aortas, we could detect CRAMP specifically in neutrophils, but not in monocytes or macrophages. By use of intravital microscopy, CRAMP was found to be deposited by activated neutrophils on inflamed endothelium of large arteries. In this location cathelicidins promote adhesion of classical monocytes and neutrophils, but not nonclassical monocytes in a formyl-peptide receptor-dependent manner. CONCLUSIONS: Cathelicidins promote atherosclerosis by enhancement of the recruitment of inflammatory monocytes.