Ferroportin Deficiency Decreases Manganese Accumulation in the brain after Olfactory Manganese Exposure

Abstract

Manganese (Mn) is both essential, yet toxic when present in excessive amounts. In particular, accumulation of Mn in the brain produces neurotoxic effects, disrupting motor function and behavior. A significant route of entry is uptake of airborne Mn, since this metal is efficiently transported into the brain through the nasal epithelium. Ferroportin (Fpn; SLC40A1) can function in the transport of Mn in addition to iron (Fe). Our previous studies have shown that Fpn deficiency impaired Mn metabolism in flatiron (ffe/+) mice, a genetic model of human “ferroportin disease”. Our recent studies have further shown that Fpn deficiency alters body Mn levels, and promotes brain Mn accumulation in flatiron mice, suggesting that toxicity related to Mn exposure could be modified by deficiency of Fpn export function. Therefore, we characterized the impact of Fpn deficiency on Mn accumulation in the brain after olfactory Mn exposure. Ffe/+ mice and wild‐type control (+/+) mice were intranasally instilled with MnCl2 (5 mg/kg) daily for 3 weeks. Mn and Fe levels in the blood, liver, and microdissected brain tissues were determined using inductively coupled plasma mass spectrometry (ICP‐MS). Flatiron mice had reduced blood Fe levels (532.3 vs. 475.5 mg/kg; P=0.0107) and higher Fe levels in liver (44.54 vs. 56.91 mg/kg; P=0.0481) compared to +/+ mice. These data confirm the Fe deficiency and loading phenotype of flatiron mouse associated with ferroportin disease. Blood Mn levels were significantly reduced in flatiron mice compared to +/+ mice (0.0315 vs. 0.0353 mg/kg, P=0.0332). These data agree with our previous findings of the Mn deficiency phenotype of flatiron mouse. Mn instillation increased Mn levels in the liver, which were not affected by Fpn deficiency (Mn X FFE interaction effect; P=0.0369). Flatiron mice showed higher Mn levels in most brain regions, including the olfactory bulbs (0.224 vs. 0.001 mg/kg, P < 0.0001), prefrontal cortex (0.273 vs. 0.163 mg/kg), hippocampus (0.230 vs. 0.180 mg/kg), cerebellum (0.196 vs. 0.172 mg/kg), and brain stem (0.253 vs. 0.174 mg/kg) compared to +/+ mice. Mn instillation increased Mn levels in brain regions, including olfactory bulbs (Mn effect, P=0.0013), cortex (Mn effect, P=0.0092), and midbrain (Mn effect, P=0.0033) compared with vehicle control. Interestingly, Mn‐instilled flatiron mice had significantly reduced Mn levels in the olfactory bulbs (FFE effect, P=0.0013), and most brain regions including the cortex, midbrain, hippocampus, and cerebellum compared to Mn‐instilled +/+ mice. Furthermore, Mn‐instilled flatiron mice displayed reduced Fe levels in the olfactory bulbs (FFE effect, P=0.0013) and elevated Fe levels in prefrontal cortex (FFE effect, P=0.0078) compared to Mn‐instilled +/+ mice. Taken together, these results indicate that olfactory Mn exposure decreases brain Mn accumulation in flatiron mice. These findings further suggest that Fpn deficiency reduces susceptibility to neurotoxicity induced by inhaled Mn.