Targeting miR-124/Ferroportin signaling ameliorated neuronal cell death through inhibiting apoptosis and ferroptosis in aged intracerebral hemorrhage murine model

Incidence of intracerebral hemorrhage (ICH) and brain iron accumulation increases with age. Excess iron accumulation in brain tissues post‐ICH induces oxidative stress and neuronal damage. However, the mechanisms underlying iron deregulation in ICH, especially in the aged ICH model have not been well elucidated. Ferroportin1 (Fpn) is the only identified nonheme iron exporter in mammals to date. In our study, we reported that Fpn was significantly upregulated in perihematomal brain tissues of both aged ICH patients and mouse model. Fpn deficiency induced by injecting an adeno‐associated virus (AAV) overexpressing cre recombinase into aged Fpn‐floxed mice significantly worsened the symptoms post‐ICH, including hematoma volume, cell apoptosis, iron accumulation, and neurologic dysfunction. Meanwhile, aged mice pretreated with a virus overexpressing Fpn showed significant improvement of these symptoms. Additionally, based on prediction of website tools, expression level of potential miRNAs in ICH tissues and results of luciferase reporter assays, miR‐124 was identified to regulate Fpn expression post‐ICH. Higher serum miR‐124 levels were correlated with poor neurologic scores of aged ICH patients. Administration of miR‐124 antagomir enhanced Fpn expression and attenuated iron accumulation in aged mice model. Both apoptosis and ferroptosis, but not necroptosis, were regulated by miR‐124/Fpn signaling manipulation. Our study demonstrated the critical role of miR‐124/Fpn signaling in iron metabolism and neuronal death post‐ICH in aged murine model. Thus, Fpn upregulation or miR‐124 inhibition might be promising therapeutic approachs for this disease.

A structural model of human ferroportin and of its iron binding site

A structural model of human ferroportin has been built using two Escherichia coli proteins belonging to the major facilitator superfamily of transporters. A potential iron binding site was identified in the inward-open conformation of the model, and its relevance was tested through measurement of iron export of HEK293T cells expressing wild-type or mutated ferroportin. Aspartates 39 and 181 were found to be essential for the transport ability of the protein. Noteworthy, the D181V mutation is naturally found in type 4 hemochromatosis with reticuloendothelial system iron retention phenotype. The outward-open conformation of ferroportin was also predicted, and showed that significant conformational changes must occur in the inward- to outward-open transition of ferroportin. In particular, putative iron ligands move several ångströms away from each other, leading to the logical conclusion that the iron binding site is not occupied by the metal in the outward-open conformation of ferroportin.

Long-term aerobic exercise increases redox-active iron through nitric oxide in rat hippocampus

Adult hippocampus is highly vulnerable to iron-induced oxidative stress. Aerobic exercise has been proposed to reduce oxidative stress but the findings in the hippocampus are conflicting. This study aimed to observe the changes of redox-active iron and concomitant regulation of cellular iron homeostasis in the hippocampus by aerobic exercise, and possible regulatory effect of nitric oxide (NO). A randomized controlled study was designed in the rats with swimming exercise treatment (for 3 months) and/or an unselective inhibitor of NO synthase (NOS) (L-NAME) treatment. The results from the bleomycin-detectable iron assay showed additional redox-active iron in the hippocampus by exercise treatment. The results from nonheme iron content assay, combined with the redox-active iron content, showed increased storage iron content by exercise treatment. NOx (nitrate plus nitrite) assay showed increased NOx content by exercise treatment. The results from the Western blot assay showed decreased ferroportin expression, no changes of TfR1 and DMT1 expressions, increased IRP1 and IRP2 expression, increased expressions of eNOS and nNOS rather than iNOS. In these effects of exercise treatment, the increased redox-active iron content, storage iron content, IRP1 and IRP2 expressions were completely reversed by L-NAME treatment, and decreased ferroportin expression was in part reversed by L-NAME. L-NAME treatment completely inhibited increased NOx and both eNOS and nNOS expression in the hippocampus. Our findings suggest that aerobic exercise could increase the redox-active iron in the hippocampus, indicating an increase in the capacity to generate hydroxyl radicals through the Fenton reactions, and aerobic exercise-induced iron accumulation in the hippocampus might mainly result from the role of the endogenous NO.

Pro-inflammatory cytokine-mediated ferroportin down-regulation contributes to the nigral iron accumulation in lipopolysaccharide-induced Parkinsonian models

Pro-inflammatory cytokines induced by inflammation and iron accumulation in the substantia nigra (SN) have been implicated in the pathogenesis of Parkinson's disease (PD). In the present study, we aimed to investigate the relationship between inflammation and iron accumulation in a lipopolysaccharide (LPS)-induced Parkinsonian rat model. The activation of glial cells and elevated levels of pro-inflammatory cytokines were observed in the SN of LPS models, accompanied by iron deposits in the same region. Moreover, ferroportin (Fpn), the only channel for iron export, was down-regulated. SH-SY5Y dopaminergic cells were pre-incubated with conditioned media enriched in pro-inflammatory cytokines, and abnormal iron deposits and a drop of Fpn were observed. The expression of heme oxygenase-1 (HO-1) was also upregulated in vivo and in vitro. These results suggested that pro-inflammatory cytokines might induce Fpn downregulation, which leads to iron accumulation and dopaminergic neurons' degeneration in PD. HO-1 may also contribute to the iron accumulation in neurons, but its mechanism needs to be further investigated.