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Classical and intermediate monocytes scavenge non-transferrin-bound iron and damaged erythrocytes
David Haschka, … , Guenter Weiss, Piotr Tymoszuk
David Haschka, … , Guenter Weiss, Piotr Tymoszuk
Published April 18, 2019
Citation Information: JCI Insight. 2019;4(8):e98867. https://doi.org/10.1172/jci.insight.98867.
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Research Article Immunology Metabolism

Classical and intermediate monocytes scavenge non-transferrin-bound iron and damaged erythrocytes

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Abstract

Myelomonocytic cells are critically involved in iron turnover as aged RBC recyclers. Human monocytes are divided in 3 subpopulations of classical, intermediate, and nonclassical cells, differing in inflammatory and migratory phenotype. Their functions in iron homeostasis are, however, unclear. Here, we asked whether the functional diversity of monocyte subsets translates into differences in handling physiological and pathological iron species. By microarray data analysis and flow cytometry we identified a set of iron-related genes and proteins upregulated in classical and, in part, intermediate monocytes. These included the iron exporter ferroportin (FPN1), ferritin, transferrin receptor, putative transporters of non-transferrin-bound iron (NTBI), and receptors for damaged erythrocytes. Consequently, classical monocytes displayed superior scavenging capabilities of potentially toxic NTBI, which were augmented by blocking iron export via hepcidin. The same subset and, to a lesser extent, the intermediate population, efficiently cleared damaged erythrocytes in vitro and mediated erythrophagocytosis in vivo in healthy volunteers and patients having received blood transfusions. To summarize, our data underline the physiologically important function of the classical and intermediate subset in clearing NTBI and damaged RBCs. As such, these cells may play a nonnegligible role in iron homeostasis and limit iron toxicity in iron overload conditions.

Authors

David Haschka, Verena Petzer, Florian Kocher, Christoph Tschurtschenthaler, Benedikt Schaefer, Markus Seifert, Sieghart Sopper, Thomas Sonnweber, Clemens Feistritzer, Tara L. Arvedson, Heinz Zoller, Reinhard Stauder, Igor Theurl, Guenter Weiss, Piotr Tymoszuk

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Figure 1

Differential expression of iron-related genes in human monocyte subsets.

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Differential expression of iron-related genes in human monocyte subsets....
Monocyte subset-specific differences in expression of iron metabolism–related genes were analyzed in 3 whole-genome microarray studies using ANOVA, as described in Methods, Supplemental Figure 1A, and Supplemental Table 1 (GSE25913: n = 4, GSE66936: n = 4, and E-MEXP-2544: n = 3 healthy monocyte donors). Genes proving significant in at least 2 studies were further investigated. (A) Relationship among monocyte populations in terms of iron-related gene expression was visualized with principal coordinate analysis. Expression values for the entire iron-related gene set in each study were transformed to Z-scores and used to calculate Pearson’s distance between human monocyte samples in a 2-dimensional space. Each point represents 1 sample. Red: classical monocytes; gray: intermediate monocytes; blue: nonclassical monocytes. (B) Venn diagram showing significantly regulated iron-related genes.

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