CXCL4 downregulates the atheroprotective hemoglobin receptor CD163 in human macrophages.
BACKGROUND
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.


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.
Gleissner
Christian A
CA
Division of Inflammation Biology, La Jolla Institute for Allergy & Immunology, La Jolla, CA 92037, USA. christian.gleissner@med.uni-heidelberg.de
Shaked
Iftach
I
Erbel
Christian
C
Böckler
Dittmar
D
Katus
Hugo A
HA
Ley
Klaus
K
D000818:Animals; D015703:Antigens, CD / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D015214:Antigens, Differentiation, Myelomonocytic / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D001057:Apolipoproteins E / Q000235:genetics / Q000378:metabolism; D050197:Atherosclerosis / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D051547:Heme Oxygenase-1 / Q000096:biosynthesis / Q000235:genetics; D006454:Hemoglobins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009000:Monocytes / Q000378:metabolism; D010978:Platelet Factor 4 / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D011956:Receptors, Cell Surface / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D051116:Receptors, Scavenger / Q000819:agonists / Q000096:biosynthesis* / Q000235:genetics; D000098902:CD163 Antigen; D000097382:CD68 Molecule
D015703:Antigens, CD; D015214:Antigens, Differentiation, Myelomonocytic; D001057:Apolipoproteins E; D051547:Heme Oxygenase-1; D006454:Hemoglobins; D010978:Platelet Factor 4; D011956:Receptors, Cell Surface; D051116:Receptors, Scavenger; D000098902:CD163 Antigen; C067980:CD68 antigen, human; D000097382:CD68 Molecule