Trace Element Distribution in Flatiron Mice, a Genetic Model of Human Ferroportin Disease

Ferroportin (Fpn; SLC40A1) is a metal exporter involved in the assimilation of dietary iron (Fe) and manganese (Mn). Accumulating evidence suggest it also may function in the transport of additional metals, including copper (Cu) and zinc (Zn). Patients with mutations in the Fpn gene develop hereditary hemochromatosis (HH) type 4, also called “ferroportin disease”, which is associated with Fe‐loading and restricted erythropoiesis. Flatiron ( ffe ) mice have deficiency in Fpn and provide the first genetic model that fully recapitulates human ferroportin disease. While the role of Fpn in Fe metabolism has been established and its influence on Mn homeostasis begins to be appreciated, relatively little is known about the potential impact of Fpn on the distribution of other metals or how ferroportin disease might alter trace element metabolism. Therefore, we characterized the distribution of Mn, Fe, Zn, and Cu in flatiron mice. Tissues, erythrocytes, and plasma from flatiron mice and wild‐type control ( +/+) mice at 15 weeks of age were analyzed for trace element by inductively coupled plasma mass spectrometry (ICP‐MS). Ffe/+ mice had reduced hematocrit values (47.2 vs. 49.80 %; P =0.01) and higher non‐heme Fe levels in both liver (151.9 vs. 112.9 μg/mL; P= 0.025) and spleen (587.0 vs. 571.6 μg/mL; P= 0.0002) compared to +/+ mice. These data confirm the Fe deficiency and Fe loading phenotype of flatiron mouse associated with ferroportin disease. Mn associated with red blood cells was significantly reduced in ffe/+ mice compared to +/+ mice (2.5 vs. 2.9 μg/L, P =0.011). Mn (0.596 vs. 0.788 mg/kg; P =0.002), Zn (61.079 vs. 77.840 mg/kg; P =0.008), and Cu (0.716 vs. 0.941 mg/kg; P =0.008) levels were reduced in femurs from ffe/+ mice compared to +/+ mice. Because bone deposits reflect metal accumulation, these data indicate that Mn, Zn and Cu metabolism are altered by Fpn deficiency. Lung Mn (0.153 vs. 0.180 mg/kg; P =0.01), and kidney Cu (24.0 vs. 48.0 mg/kg; P =0.002) and kidney Zn (7.5 vs. 10.5 mg/kg; P =0.018) were reduced in ffe/+ mice compared to +/+ mice. Interestingly, Mn and Fe levels were higher in olfactory bulbs of ffe/+ mice compared to +/+ controls (0.650 vs . 0.162; P =0.0006 and 20.4 vs . 7.58 mg/kg; P =0.05 respectively). To further study brain metal distribution, 54 MnCl 2 was administered by intravenous injection and total brain 54 Mn was measured over time. By 72 h post‐intravenous injection, brain 54 Mn was increased in ffe/+ mice compared to +/+ mice (0.809 vs. 0.502 % dose; P= 0.04), but blood 54 Mn was reduced to the same level at 24 and 72 h in both groups of mice. Taken together, these results indicate that Fpn deficiency alters body Fe, Mn, Zn and Cu levels, decreases Mn trafficking out of the brain, and promotes brain metal accumulation in the flatiron mouse model of “ferroportin disease”. These findings highlight the importance of Fpn function in trace element homeostasis, and implicate metal dyshomeostasis in patients with ferroportin disease. Support or Funding Information This work was supported by grants from the U.S. National Institute of Health (NIH) to Y.A.S (K99ES024340) and M.W.R (R01ES0146380). This study was supported in part by funding from the HSPH‐NIEHS Center for Environmental Health (ES2).