Fasting Increases Iron Export by Modulating Ferroportin 1 Expression Through the Ghrelin/GHSR1α/MAPK Pathway in the Liver

Abstract Background: The liver is the metabolic organ considered to contribute the most to maintaining body iron homeostasis and is a regulator of body adaptation to fasting. Our previous studies implied a negative relationship between iron and ghrelin in both mice and humans and indicated that ghrelin was able to increase ferroportin 1 (Fpn1) expression in the spleen and macrophages through the GHSR/MAPK pathway. However, it remains to be explored whether fasting or ghrelin has a functional effect on iron homeostasis in the liver.Methods: In this study, we examined the roles of fasting and ghrelin in modulating the protein expression of Fpn1, transferrin receptor 1 (TfR1), and ferritin light chain (Ft-L), as well as the mRNA expression of ghrelin, hepcidin, ghrelin O-acyltransferase (GOAT) and growth hormone secretagogue receptor 1 alpha (GHSR1α) in mouse liver and cultured hepatocytes.Results: Our in vivo results suggested that fasting significantly upregulated the mRNA expression of ghrelin, GOAT and GHSR1α as well as the protein levels of ghrelin, Fpn1 and Ft-L, but not TfR1, in mouse liver. Meanwhile, in cultured hepatocytes, ghrelin significantly increased the protein expression of Fpn1 but not Ft-L and TfR1 and significantly enhanced ERK phosphorylation. Furthermore, the pretreatment of cultured hepatocytes with either a pERK inhibitor or a GHSR1α antagonist abolished the effects of ghrelin on Fpn1 expression and ERK phosphorylation.Conclusions: Our findings confirmed that fasting increases iron export in the liver by upregulating Fpn1 expression through the ghrelin/GHSR1α/MAPK signaling pathway.

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Abstract 12425: Sirt2 Mediated-Deacetylation Regulates Cellular Iron Homeostasis

Circulation ◽

10.1161/circ.130.suppl_2.12425 ◽

2014 ◽

Vol 130 (suppl_2) ◽

Author(s):

Xiaoyan Yang ◽

Athanassios Vassilopoulos ◽

Seong-Hoon Park ◽

David Gius ◽

Hossein Ardehali

Keyword(s):

Iron Content ◽

Iron Homeostasis ◽

Underlying Mechanism ◽

Heme Iron ◽

Iron Storage ◽

Cellular Iron ◽

Non Heme Iron ◽

Ferroportin 1 ◽

Cellular Iron Homeostasis ◽

Iron Export

Background: Sirtuins (SIRTs) are NAD+-dependent deacetylases and critical regulators of energy metabolism and response to oxidative stress in the heart. Iron is essential for these processes but is toxic when present in excess. Thus, SIRTs may regulate iron levels to ensure adequate supply of this element for their biological functions. SIRT2 is among the least characterized SIRTs and is mainly present in the cytoplasm. We hypothesized that SIRT2 might be required for cellular iron homeostasis. Methods and Results: Iron content was significantly lower in SIRT2-/- mouse embryonic fibroblasts (MEFs) compared to SIRT2+/+ MEFs (non-heme iron: 0.073 vs. 0.060 nmol/μg protein, p=0.02). Gene expression of ferroportin-1 (FPN1), the major cellular iron exporter, was significantly increased in SIRT2-/- MEFs. Similarly, silencing SIRT2 in HepG2 cells decreased cellular iron levels and increased FPN1 expression, indicating that enhanced FPN1 in SIRT2 knockout or knockdown condition increases iron export and reduces cellular iron. To investigate the underlying mechanism, we focused our studies on nuclear factor (erythroid-derived 2)-like 2 (Nrf2), a known regulator of FPN1. Our results demonstrated that Nrf2 is upregulated and translocates into the nucleus in SIRT2-/- MEFs and knocking down Nrf2 in SIRT2-/- MEFs reverses iron deficiency and FPN1 expression. Furthermore, Nrf2 is acetylated by P300/CBP and can be deacetylated by SIRT2. Finally, to confirm the role of SIRT2 in iron regulation, cellular heme and non-heme iron in the heart (major iron-consuming organ) and liver (major iron-storage organ) were measured in wild type (WT) and SIRT2-/- mice. Heme and non-heme iron content were significantly decreased in SIRT2-/- mouse livers compared to WT livers (heme: 2.25 vs. 1.65 nmol/mg protein, p=0.002; non-heme iron: 0.073 vs. 0.064 nmol/μg protein, p=0.03). Furthermore, heme levels were also significant decreased in the heart, while non-heme iron was not significantly altered. Conclusions: Our results suggest that SIRT2 regulates cellular iron homeostasis by deacetylating NRF2 and altering iron export through FPN1.

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Iron Export through the Transporter Ferroportin 1 Is Modulated by the Iron Chaperone PCBP2

Journal of Biological Chemistry ◽

10.1074/jbc.m116.721936 ◽

2016 ◽

Vol 291 (33) ◽

pp. 17303-17318 ◽

Cited By ~ 59

Author(s):

Izumi Yanatori ◽

Des R. Richardson ◽

Kiyoshi Imada ◽

Fumio Kishi

Keyword(s):

Mammalian Cells ◽

Basolateral Membrane ◽

Intracellular Iron ◽

Divalent Metal Transporter 1 ◽

Divalent Metal Transporter ◽

Metal Transporter ◽

Cellular Iron ◽

Ferroportin 1 ◽

Iron Chaperone ◽

Iron Export

Ferroportin 1 (FPN1) is an iron export protein found in mammals. FPN1 is important for the export of iron across the basolateral membrane of absorptive enterocytes and across the plasma membrane of macrophages. The expression of FPN1 is regulated by hepcidin, which binds to FPN1 and then induces its degradation. Previously, we demonstrated that divalent metal transporter 1 (DMT1) interacts with the intracellular iron chaperone protein poly(rC)-binding protein 2 (PCBP2). Subsequently, PCBP2 receives iron from DMT1 and then disengages from the transporter. In this study, we investigated the function of PCBP2 in iron export. Mammalian genomes encode four PCBPs (i.e. PCBP1–4). Here, for the first time, we demonstrated using both yeast and mammalian cells that PCBP2, but not PCBP1, PCBP3, or PCBP4, binds with FPN1. Importantly, iron-loaded, but not iron-depleted, PCBP2 interacts with FPN1. The PCBP2-binding domain of FPN1 was identified in its C-terminal cytoplasmic region. The silencing of PCBP2 expression suppressed FPN1-dependent iron export from cells. These results suggest that FPN1 exports iron received from the iron chaperone PCBP2. Therefore, it was found that PCBP2 modulates cellular iron export, which is an important physiological process.

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