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Published on: April 3, 2017
CXCL4 downregulates the atheroprotective hemoglobin receptor CD163 in human macrophages
Christian A Gleissner1, Iftach Shaked, Christian Erbel
1Division of Inflammation Biology, La Jolla Institute for Allergy & Immunology, La Jolla, CA 92037, USA. christian.gleissner@med.uni-heidelberg.de
Insights
Platelet chemokine CXCL4 (chemokine C-X-C motif ligand 4) suppresses CD163 on macrophages, hindering their ability to protect against atherosclerosis. This finding suggests a novel mechanism in the development of cardiovascular disease.
Area of Science:
- Immunology
- Cardiovascular Biology
- Molecular Medicine
Background:
- CXCL4 (chemokine C-X-C motif ligand 4) is a platelet-derived chemokine.
- CXCL4 influences macrophage differentiation from monocytes.
- Reduced atherosclerotic lesions were observed in ApoE(-/-) mice lacking the PF4 gene encoding CXCL4.
Purpose of the Study:
- To investigate the effects of CXCL4 on macrophage differentiation.
- To explore the potential relevance of these effects in atherogenesis.
Main Methods:
- Flow cytometry to analyze surface markers on M-CSF and CXCL4-induced macrophages.
- mRNA and protein analysis for CD163 expression.
- Neutralization studies using heparin and chlorate.
- Analysis of platelet releasate.
- Immunofluorescence of human atherosclerotic plaques.
- Gene expression analysis of PF4 and CD163 in lesions.
Main Results:
- CXCL4 induced macrophages showed a significant absence of CD163.
- CD163 mRNA and protein levels were downregulated by CXCL4, an effect not reversed by M-CSF.
- Heparin neutralized CXCL4's effect, while chlorate inhibited CD163 downregulation.
- CXCL4-differentiated macrophages could not upregulate heme oxygenase-1 in response to hemoglobin-haptoglobin.
- Human atherosclerotic plaques contained both CD163+ and CD163- macrophages, with inverse PF4 and CD163 gene expression.
Conclusions:
- CXCL4 may promote atherogenesis by downregulating CD163 in macrophages.
- This suppression impairs the macrophages' ability to express the atheroprotective enzyme heme oxygenase-1.
- Findings highlight a potential role for CXCL4-mediated CD163 suppression in the pathogenesis of atherosclerosis.
Rationale:
CXCL4 is a platelet-derived chemokine that promotes macrophage differentiation from monocytes. Deletion of the PF4 gene that encodes CXCL4 reduces atherosclerotic lesions in ApoE(-/-) mice.
Objective:
We sought to study effects of CXCL4 on macrophage differentiation with possible relevance for atherogenesis.
Methods And Results:
Flow cytometry for expression of surface markers in macrophage colony-stimulating factor (M-CSF)- and CXCL4-induced macrophages demonstrated virtually complete absence of the hemoglobin scavenger receptor CD163 in CXCL4-induced macrophages. mRNA for CD163 was downregulated as early as 2 hours after CXCL4. CD163 protein reached a minimum after 3 days, which was not reversed by treatment of cells with M-CSF. The CXCL4 effect was entirely neutralized by heparin, which bound CXCL4 and prevented CXCL4 surface binding to monocytes. Pretreatment of cells with chlorate, which inhibits glycosaminoglycan synthesis, strongly inhibited CXCL4-dependent downregulation of CD163. Similar to recombinant CXCL4, releasate from human platelets also reduced CD163 expression. CXCL4-differentiated macrophages were unable to upregulate the atheroprotective enzyme heme oxygenase-1 at the RNA and protein level in response to hemoglobin-haptoglobin complexes. Immunofluorescence of human atherosclerotic plaques demonstrated presence of both CD68+CD163+ and CD68+CD163- macrophages. PF4 and CD163 gene expression within human atherosclerotic lesions were inversely correlated, supporting the in vivo relevance of CXCL4-induced downregulation of CD163.
Conclusions:
CXCL4 may promote atherogenesis by suppressing CD163 in macrophages, which are then unable to upregulate the atheroprotective enzyme heme oxygenase-1 in response to hemoglobin.
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