Iron metabolism in inflammation has been mostly characterized in macrophages exposed to pathogens or inflammatory conditions, mimicked by the combined action of LPS and IFN-c (M1 polarization). However, macrophages can undergo an alternative type of activation stimulated by Th2 cytokines, and acquire a role in cell growth and tissue repair control (M2 polarization). We characterized the expression of genes related to iron homeostasis in fully differentiated unpolarized (M0), M1 and M2 human macrophages. The molecular signature of the M1 macrophages showed changes in gene expression (ferroportin repression and H ferritin induction) that favour iron sequestration in the reticuloendothelial system, a hallmark of inflammatory disorders, whereas the M2 macrophages had an expression profile (ferroportin upregulation and the downregulation of H ferritin and heme oxygenase) that enhanced iron release. The conditioned media from M2 macrophages promoted cell proliferation more efficiently than those of M1 cells and the effect was blunted by iron chelation. The role of ferroportin-mediated iron release was demonstrated by the absence of differences from the media of macrophages of a patient with loss of function ferroportin mutation. The distinct regulation of iron homeostasis in M2 macrophages provides insights into their role under pathophysiological conditions. Key words: Immune system . Iron . Polarized macrophages IntroductionMacrophages play a critical role in body iron homeostasis by recovering iron from old red blood cells and returning it to the circulation for binding to transferrin, which delivers the metal to the cells that need it for various functions, thus contributing more than 80% to daily iron turnover [1][2][3].Iron retention in the reticuloendothelial system is the main response of body iron homeostasis to inflammation and is regarded as a host's attempt to withhold iron from the invading pathogens [4]. This restricts iron availability for erythroid progenitor cells and may contribute toward causing the common condition of inflammation-related anaemia [1,5,6]. Increased iron retention within inflammatory macrophages is due to increased iron uptake and decreased iron export [7], and is favoured by the induction of the iron storage protein ferritin (Ft) [8,9]. The blockade of macrophage iron release is mainly due to the interaction between the acute phase protein hepcidin and the iron exporter ferroportin (Fpn) [1][2][3], as the increase in circulating hepcidin triggered by inflammatory cytokines causes the internalization and degradation of Fpn [10], the exporter of non-heme iron [11], thus blocking iron release from macrophages.Macrophage Fpn is also negatively regulated at transcriptional and post-transcriptional levels by inflammatory mediators [12][13][14]. It is still unknown whether the inflammatory response affects the feline leukemia virus, subgroup C, receptor that exports heme from macrophages [15] and whether the heme transporter HRG1 proteins play a role in macrophage iron metabolism [16]. O...

Nitric oxide (NO) is a free radical product of cell metabolism that plays diverse and important roles in the regulation of cellular function. S-Nitrosylation is emerging as a specific and fundamental posttranslational protein modification for the transduction of NO bioactivity, but very little is known about its physiological functions in plants. We investigated the molecular mechanism for S-nitrosylation of peroxiredoxin II E (PrxII E) from Arabidopsis thaliana and found that this posttranslational modification inhibits the hydroperoxide-reducing peroxidase activity of PrxII E, thus revealing a novel regulatory mechanism for peroxiredoxins. Furthermore, we obtained biochemical and genetic evidence that PrxII E functions in detoxifying peroxynitrite (ONOO À ), a potent oxidizing and nitrating species formed in a diffusion-limited reaction between NO and O 2 À that can interfere with Tyr kinase signaling through the nitration of Tyr residues. S-Nitrosylation also inhibits the ONOO À detoxification activity of PrxII E, causing a dramatic increase of ONOO À -dependent nitrotyrosine residue formation. The same increase was observed in a prxII E mutant line after exposure to ONOO À , indicating that the PrxII E modulation of ONOO À bioactivity is biologically relevant. We conclude that NO regulates the effects of its own radicals through the S-nitrosylation of crucial components of the antioxidant defense system that function as common triggers for reactive oxygen species-and NO-mediated signaling events.

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The hepatic iron regulator hormone hepcidin consists, in its mature form, of 25 amino acids, but two other isoforms, hepcidin-20 and hepcidin-22, have been reported, whose biological meaning remains poorly understood. We evaluated hepcidin isoforms in sera from 57 control and 54 chronic haemodialysis patients using a quantitative proteomic approach based on SELDI-TOF-MS. Patients had elevated serum levels of both hepcidin-25 and hepcidin-20 as compared to controls (geometric means: 7.52 versus 4.69 nM, and 4.06 versus 1.76 nM, resp., P < .05 for both). The clearance effects of a single dialysis session by different dialysis techniques and membranes were also investigated, showing an average reduction by 51.3% ± 29.2% for hepcidin-25 and 34.2% ± 28.4% for hepcidin-20 but only minor differences among the different dialysis modalities. Measurement of hepcidin isoforms through MS-based techniques can be a useful tool for better understanding of their biological role in hemodialysis patients and other clinical conditions.