Ferroportin-1 is a ‘nuclear'-negative acute-phase protein in rat liver: a comparison with other iron-transport proteins

Abstract

Liver is the central organ of iron metabolism. During acute-phase-response (APR), serum iron concentration rapidly decreases. The current study aimed to compare expression and localization of iron transport protein ferroportin-1 (Fpn-1) and of other iron import proteins after experimental tissue damage induced by injecting turpentine oil in the hind limbs of rats and mice. Serum and spleen iron concentration decreased with an increase in total liver, cytoplasmic and nuclear iron concentration. In liver, mRNA amount of Fpn-1, Fpn-1a, Fpn-1b, HFE, hemojuvelin (HJV) and hephaestin (heph) genes showed a rapid decrease. Hepcidin, divalent metal transporter-1 (DMT-1), transferrin (Tf) and Tf-receptor-1 (TfR1), TfR-2 (TfR2) gene expression was increased. Western blot analysis of liver tissue lysate confirmed the changes observed at mRNA level. In spleen, a rapid decrease in gene expression of Fpn-1, Fpn-1a, Fpn-1b, DMT-1, Tf, TfR1 and TfR2, and an increase in hepcidin was observed. Immunohistochemistry of DMT-1 and TfR2 were mainly detected in the nucleus of rat liver and spleen, whereas TfR1 was clearly localized in the plasma membrane. Fpn-1 was mostly found in the nuclei of liver cells, whereas in spleen, the protein was mainly detected in the cell membrane. Western blot analysis of liver fractions confirmed immunohistochemical results. In livers of wild-type mice, gene expression of Fpn-1, Fpn-1a and Fpn-1b was downregulated, whereas hepcidin gene expression was increased. In contrast, these changes were less pronounced in IL-6ko-mice. Cytokine (IL-6, IL-1b and TNF-a) treatment of rat hepatocytes showed a downregulation of Fpn-1, Fpn-1a and Fpn-1b, and upregulation of hepcidin gene expression. Moreover, western blot analysis of cell lysate of IL-6-treated hepatocytes detected, as expected, an increase of a2-macroglobulin (positive acute-phase protein), whereas albumin (negative acute-phase protein) and Fpn-1 were downregulated. Our results demonstrate that liver behaves as a 'sponge' for iron under acute-phase conditions, and Fpn-1 behaves as a negative acute-phase protein in rat hepatocytes mainly, but not exclusively, because of the effect of IL-6. These changes could explain iron retention in the cytoplasm and in the nucleus of hepatocytes during APR. The liver is the central organ for iron metabolism. 1 Liver cells (hepatocytes) take up iron absorbed from the diet, and Kupffer cells take up iron from aged erythrocytes and distribute it to different organs. Iron is an important co-factor for oxygen transport, heme and non-heme iron proteins, electron transfer, neurotransmitter synthesis, myelin production, energy metabolism and mitochondrial function, as well as for the production of reactive-oxygen species. 2,3 As a result, its metabolism is tightly regulated. Iron homeostasis is controlled by a large group of iron-regulatory proteins. The absorption of dietary iron begins with its transport across the duodenal brush-border membrane mediated by the duodenal metal transporter-1 (DMT-1), the major iron transporte...

Copper chelation and interleukin-6 proinflammatory cytokine effects on expression of different proteins involved in iron metabolism in HepG2 cell line

“…However, independent of post-translational regulation, our data show that IL-6 reduces Fpn1 mRNA. These results are consistent with published data, which demonstrated that IL-6 is able to downregulate Fpn1 levels in the HepG2 cell line [48] and upregulate the mRNA level of sCp [46, 47]. We demonstrate that the GPI-Cp isoform is also upregulated and the protein level of the two isoforms follow the same behaviour.…”

Daily propranolol administration reduces persistent injury-associated anemia after severe trauma and chronic stress

“…Also, in vitro hepatocytes treated with interleukin-6 reduced liver ferroportin by 90% at 24 hours. 11 In this study, daily propranolol use following LCHS and LCHS/CS significantly improved liver ferroportin expression. Ferroportin expression is impacted by inflammatory states such as severe trauma and chronic stress as well as hemorrhagic shock.…”

“…Seven days following LCHS and LCHS/CS, liver ferroportin expression was decreased and this finding correlated with decreased iron levels after trauma. 12 Similarly, Naz et al 11 demonstrated a 30–50% decrease in liver ferroportin expression at 24 hours in a rodent model of tissue injury. Also, in vitro hepatocytes treated with interleukin-6 reduced liver ferroportin by 90% at 24 hours.…”

“…6, 10 IL-6 increases liver hepcidin, the main regulator of iron homeostasis that alters iron availability. 10 , 11 The true incidence of iron deficiency or functional iron deficiency in trauma patients is unknown. 12 While the etiology of anemia following trauma is multifactorial, the assessment of iron restriction is challenging to define in the context of persistent inflammation.…”

“…18 , 19 Transferrin, a plasma glycoprotein, has a high affinity for iron and transports it to other tissues. 11, 20 Following blood loss, the maturation of erythroid cells are necessary for production of red blood cells and developing erythrocytes have high iron demand. 21, 22 The uptake of iron in erythroid cells is mediated by transferrin and its receptor, transferrin receptor-1 (TFR-1).…”