Polarization dictates iron handling by inflammatory and alternatively activated macrophages

Abstract

The online version of this article has a Supplementary Appendix. BackgroundMacrophages play a key role in iron homeostasis. In peripheral tissues, they are known to polarize into classically activated (or M1) macrophages and alternatively activated (or M2) macrophages. Little is known on whether the polarization program influences the ability of macrophages to store or recycle iron and the molecular machinery involved in the processes. Design and MethodsInflammatory/M1 and alternatively activated/M2 macrophages were propagated in vitro from mouse bone-marrow precursors and polarized in the presence of recombinant interferon-γ or interleukin-4. We characterized and compared their ability to handle radioactive iron, the characteristics of the intracellular iron pools and the expression of molecules involved in internalization, storage and export of the metal. Moreover we verified the influence of iron on the relative ability of polarized macrophages to activate antigen-specific T cells. ResultsM1 macrophages have low iron regulatory protein 1 and 2 binding activity, express high levels of ferritin H, low levels of transferrin receptor 1 and internalize -albeit with low efficiencyiron only when its extracellular concentration is high. In contrast, M2 macrophages have high iron regulatory protein binding activity, express low levels of ferritin H and high levels of transferrin receptor 1. M2 macrophages have a larger intracellular labile iron pool, effectively take up and spontaneously release iron at low concentrations and have limited storage ability. Iron export correlates with the expression of ferroportin, which is higher in M2 macrophages. M1 and M2 cells activate antigen-specific, MHC class II-restricted T cells. In the absence of the metal, only M1 macrophages are effective. ConclusionsCytokines that drive macrophage polarization ultimately control iron handling, leading to the differentiation of macrophages into a subset which has a relatively sealed intracellular iron content (M1) or into a subset endowed with the ability to recycle the metal (M2).Key words: macrophages, iron, inflammation. 95(11):1814-1822 doi:10.3324/haematol.2010 This is an open-access paper. Polarization dictates iron handling by inflammatory and alternatively activated macrophages. Haematologica Polarization dictates iron handling by inflammatory and alternatively activated macrophages

Highly Dynamic Transcriptional Signature of Distinct Macrophage Subsets during Sterile Inflammation, Resolution, and Tissue Repair

“…Iron capture protects against iron-mediated toxicity (40). This is in agreement with the described iron retention phenotype of M1 macrophages (41), which also has been described in early regenerating muscle (42). It has been shown that chelatable iron release from disrupted muscle tissue represents the major cause for the oxidative stress that aggravates muscle destruction (43).…”

Role of iron overload-induced macrophage apoptosis in the pathogenesis of peritoneal endometriosis

“…Hepcidin-mediated Fpn down-regulation has been reported to result in iron accumulation in M1 macrophages, which may contribute to wound healing or chronic inflammation (Recalcati et al 2012). By contrast, immunosuppressive M2 macrophages resolve inflammation and promote parasite killing, angiogenesis, wound healing, matrix remodeling, and tumor growth by increasing the availability of extracellular iron and polarized Th2 responses (Brunelli & Rovere-Querini 2008, Corna et al 2010, Gaetano et al 2010, Recalcati et al 2010 The inflammatory peritoneal environment characterizes macrophage polarization toward the M2 phenotype expressing markers of alternative activation, particularly high levels of scavenger receptors, CD163 and CD206, which are involved in the export of hemederived iron and removal of inflammatory mediators respectively (Smith et al 2012, Capobianco & RovereQuerini 2013. Impaired ability of peritoneal macrophages to dispose apoptotic endometrial remnants and defective scavenging heme-bound iron, resulting from cyclic progesterone withdrawal, may activate macrophages recruited at sites of local hypoxia and tissue stress (Capobianco & Rovere-Querini 2013).…”

“…The differential expression of proteins involved in iron metabolism can affect the functional polarization of macrophages into classically activated M1 and alternatively activated M2 phenotypes (Cairo et al 2011, Recalcati et al 2012. The iron retention-prone M1 macrophages are characterized by up-regulated iron storage ferritin (FtH) that is accompanied by the down-regulation of transferrin receptor 1 (TfR1) and iron exporter ferroportin (Fpn) due to decreased activity of the iron regulatory protein 2 (IREB2 (IRP2)), a primary regulator of iron homeostasis within the cell, which in turn limits the labile iron pool (LIP) to protect themselves from oxidative damage (Corna et al 2010, Recalcati et al 2010. These cells perform several effector functions, including bacteriostatic activity, secretion of pro-inflammatory cytokines, immunostimulation, and tumor suppression, by inducing a polarized Th1 response (Gaetano et al 2010, Recalcati et al 2012.…”

Transplanted Mesoangioblasts Require Macrophage IL-10 for Survival in a Mouse Model of Muscle Injury

“…Lysis of total muscles was also performed on muscles from untreated healthy mice. Samples were homogenized, and 1 mg of extracted RNA/sample was used for first-strand synthesis of cDNA as described (51). Each cDNA sample was amplified in duplicate on a real-time PCR system (7900HT Fast Real-Time PCR System; Applied Biosystems).…”

“…Satellite cells were isolated as described (50). Polarized macrophages were propagated as described (51). Briefly, after 7 d of culture in aMEM (Life Technologies, Invitrogen) containing 10% FCS in the presence of 100 ng/ml recombinant murine M-CSF (R&D Systems), bone marrow-derived macrophages from C57BL/6 female mice were differentiated into IFN-g macrophages (IFN-g-Mf) or into IL-10 macrophages (IL-10-Mf) when cultured for an additional 2 d with 50 ng/ml recombinant murine IFN-g (Peprotech) or for an additional 4 d with 10 ng/ml recombinant murine IL-10 (R&D Systems), respectively.…”