Heterogenous distribution of ferroportin-containing neurons in mouse brain

Exploring Potential Mechanisms Accounting for Iron Accumulation in the Central Nervous System of Patients with Alzheimer's Disease

Elevated levels of iron occur in both cortical and subcortical regions of the CNS in patients with Alzheimer's disease. This accumulation is present early in the disease process as well as in more advanced stages. The factors potentially accounting for this increase are numerous, including: (1) Cells increase their uptake of iron and reduce their export of iron, as iron becomes sequestered (trapped within the lysosome, bound to amyloid β or tau, etc.); (2) metabolic disturbances, such as insulin resistance and mitochondrial dysfunction, disrupt cellular iron homeostasis; (3) inflammation, glutamate excitotoxicity, or other pathological disturbances (loss of neuronal interconnections, soluble amyloid β, etc.) trigger cells to acquire iron; and (4) following neurodegeneration, iron becomes trapped within microglia. Some of these mechanisms are also present in other neurological disorders and can also begin early in the disease course, indicating that iron accumulation is a relatively common event in neurological conditions. In response to pathogenic processes, the directed cellular efforts that contribute to iron buildup reflect the importance of correcting a functional iron deficiency to support essential biochemical processes. In other words, cells prioritize correcting an insufficiency of available iron while tolerating deposited iron. An analysis of the mechanisms accounting for iron accumulation in Alzheimer's disease, and in other relevant neurological conditions, is put forward.

Iron homeostasis and post-hemorrhagic hydrocephalus: a review

Iron physiology is regulated by a complex interplay of extracellular transport systems, coordinated transcriptional responses, and iron efflux mechanisms. Dysregulation of iron metabolism can result in defects in myelination, neurotransmitter synthesis, and neuronal maturation. In neonates, germinal matrix-intraventricular hemorrhage (GMH-IVH) causes iron overload as a result of blood breakdown in the ventricles and brain parenchyma which can lead to post-hemorrhagic hydrocephalus (PHH). However, the precise mechanisms by which GMH-IVH results in PHH remain elusive. Understanding the molecular determinants of iron homeostasis in the developing brain may lead to improved therapies. This manuscript reviews the various roles iron has in brain development, characterizes our understanding of iron transport in the developing brain, and describes potential mechanisms by which iron overload may cause PHH and brain injury. We also review novel preclinical treatments for IVH that specifically target iron. Understanding iron handling within the brain and central nervous system may provide a basis for preventative, targeted treatments for iron-mediated pathogenesis of GMH-IVH and PHH.

Ferroportin1 in the brain

Despite years of research, it remains unclear why certain brain regions of patients with neurodegenerative diseases (NDs) have abnormally high levels of iron, although it has long been suggested that disrupted expression of iron-metabolizing proteins due to genetic or non-genetic factors is responsible for the enhancement in brain iron contents. In addition to the increased expression of cell-iron importers lactoferrin (lactotransferrin) receptor (LfR) in Parkinson's disease (PD) and melanotransferrin (p97) in Alzheimer's disease (AD), some investigations have suggested that cell-iron exporter ferroportin 1 (Fpn1) may be also associated with the elevated iron observed in the brain. The decreased expression of Fpn1 and the resulting decrease in the amount of iron excreted from brain cells has been thought to be able to enhance iron levels in the brain in AD, PD and other NDs. Cumulative results also suggest that the reduction of Fpn1 can be induced by hepcidin-dependent and -independent pathways. In this article, we discuss the current understanding of Fpn1 expression in the brain and cell lines of rats, mice and humans, with emphasis on the potential involvement of reduced Fpn1 in brain iron enhancement in patients with AD, PD and other NDs.

Upregulation of brain hepcidin in prion diseases

Accumulation of redox-active iron in human sporadic Creutzfeldt-Jakob disease (sCJD) brain tissue and scrapie-infected mouse brains has been demonstrated previously. Here, we explored whether upregulation of local hepcidin secreted within the brain is the underlying cause of iron accumulation and associated toxicity. Using scrapie-infected mouse brains, we demonstrate transcriptional upregulation of hepcidin relative to controls. As a result, ferroportin (Fpn), the downstream effector of hepcidin and the only known iron export protein was downregulated, and ferritin, an iron storage protein was upregulated, suggesting increased intracellular iron. A similar transcriptional and translational upregulation of hepcidin, and decreased expression of Fpn and an increase in ferritin expression was observed in sCJD brain tissue. Further evaluation in human neuroblastoma cells (M17) exposed to synthetic mini-hepcidin showed downregulation of Fpn, upregulation of ferritin, and an increase in reactive oxygen species (ROS), resulting in cytotoxicity in a dose-dependent manner. Similar effects were noted in primary neurons isolated from mouse brain. As in M17 cells, primary neurons accumulated ferritin and ROS, and showed toxicity at five times lower concentration of mini-hepcidin. These observations suggest that upregulation of brain hepcidin plays a significant role in iron accumulation and associated neurotoxicity in human and animal prion disorders.

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.

Iron Dyshomeostasis Participated in Rat Hippocampus Toxicity Caused by Aluminum Chloride

Aluminum (Al) alters iron regulatory factors content and leads to the changes in iron-related proteins causing iron accumulation. But limited evidence ascertains this hypothesis. Therefore, our experiment was conducted and four groups of male Wistar rats were orally administrated of 0, 50, 150, and 450 mg/kg BW/d aluminum chloride (AlCl₃) for 90 days by drinking water, respectively. The cognitive function, pathological lesion of hippocampus, oxidative stress, as well as iron-related proteins and iron regulatory factors expression were detected. The results showed that AlCl₃ remarkably induced the oxidative stress and pathological lesion in the hippocampus and impaired the learning-memory ability. The contents of Al and iron increased in all AlCl₃-exposed groups. Meanwhile, the increased divalent metal transporter 1 (DMT1) expression enhanced iron import and the decreased ferroportin 1 (Fpn1) expression reduced iron export in AlCl₃-exposed groups. The iron accumulated and ferritin heavy chains (Fth) expression decreased in all AlCl₃-exposed groups led to an increase in free iron. The study also showed that iron regulatory factor iron regulatory protein 2 (IRP2) was decreased and hepcidin was increased in AlCl₃-exposed groups. The results indicated that AlCl₃ induces iron dyshomeostasis presenting as iron accumulation, the disordered expression of iron import, export, store, and regulatory proteins in rat hippocampus accompanied with oxidative stress, pathological lesion, and impaired learning-memory ability.

Pulse magnetization elicits differential gene expression in the central nervous system of the Caribbean spiny lobster, Panulirus argus

Diverse animals use Earth's magnetic field to guide their movements, but the neural and molecular mechanisms underlying the magnetic sense remain enigmatic. One hypothesis is that particles of the mineral magnetite (Fe₃O₄) provide the basis of magnetoreception. Here we examined gene expression in the central nervous system of a magnetically sensitive invertebrate, the Caribbean spiny lobster (Panulirus argus), after applying a magnetic pulse known to alter magnetic orientation behavior. Numerous genes were differentially expressed in response to the pulse, including 647 in the brain, 1256 in the subesophageal ganglion, and 712 in the thoracic ganglia. Many such genes encode proteins linked to iron regulation, oxidative stress, and immune response, consistent with possible impacts of a magnetic pulse on magnetite-based magnetoreceptors. Additionally, however, altered expression also occurred for numerous genes with no apparent link to magnetoreception, including genes encoding proteins linked to photoreception, carbohydrate and hormone metabolism, and other physiological processes. Overall, the results are consistent with the magnetite hypothesis of magnetoreception, yet also reveal that in spiny lobsters, a strong pulse altered expression of > 10% of all expressed genes, including many seemingly unrelated to sensory processes. Thus, caution is required when interpreting the effects of magnetic pulses on animal behavior.

Epigenetic Regulation of Ferroportin in Primary Cultures of the Rat Blood-Brain Barrier

Ferroportin plays an essential role for iron transport through the blood-brain barrier (BBB), which is formed by brain capillary endothelial cells (BCECs). To maintain the integrity of the BBB, the BCECs gain support from pericytes and astrocytes, which together with neurons form the neurovascular unit (NVU). The objectives of the present study were to investigate ferroportin expression in primary cells of the NVU and to determine if ferroportin mRNA (Fpn) expression is epigenetically regulated. Primary rat BCECs, pericytes, astrocytes, and neurons all expressed ferroportin mRNA at varying levels, with BCECs exhibiting the highest expression of Fpn, peaking when co-cultured but examined separately from astrocytes. Conversely, Fpn expression was lowest in isolated astrocytes, which correlated with high DNA methylation in their Slc40a1 promoter. To provide further evidence for epigenetic regulation, mono-cultured BCECs, pericytes, and astrocytes were treated with the histone deacetylase inhibitors valproic acid (VPA) and sodium butyrate (SB), which significantly increased Fpn and ferroportin protein in BCECs and pericytes. Furthermore, ⁵⁹Fe export from BCECs was elevated after treatment with VPA. In conclusion, we present first time evidence stating that Fpn expression is epigenetically regulated in BCECs, which may have implications for pharmacological induction of iron transport through the BBB.

Prenatal Ethanol Exposure Misregulates Genes Involved in Iron Homeostasis Promoting a Maladaptation of Iron Dependent Hippocampal Synaptic Transmission and Plasticity

Prenatal ethanol exposure (PAE) induces behavioral maladptations in offspring, including a deficit in memory formation which is part of the umbrella sign of fetal alcohol spectrum disorder. Clinical and preclinical studies have shown that iron depletion exacerbates cognitive problems in offspring exposed to ethanol in utero and that PAE promotes dysregulation in brain iron homeostasis. However, the mechanisms underlying brain iron dysregulation and neuronal activity defects in adolescent offspring of PAE are unclear and poorly understand. Here, we used a PAE rat model to analyze messenger RNA (mRNA) and protein expression of iron homeostasis genes such as transferrin receptor (TfR), divalent metal transporter (DMT1), ferroportin (FPN1), and ferritin (FT) in brain areas associated with memory formation such as the prefrontal cortex (PFC), ventral tegmental area, and hippocampus. Interestingly, we found that 21 day old PAE rats have higher mRNA expression of DMT1 in the PFC, and TfR in the hippocampus, compared to control animals. In contrast FPN has lower mRNA expression in the PFC, and FT and FPN1 have lower expression in the hippocampus. In agreement with these results, we found a 1.5–2 fold increase of TfR and DMT1 protein levels both in the hippocampus and the PFC. Additionally, using an electrophysiological approach, we found that in hippocampal slices from PAE rats, iron treatment decreased long-term potentiation (LTP), but not AMPAR basal transmission (AMPAR fEPSP). In contrast, in control slices Fe-NTA did not affect LTP but decreased significantly the AMPAR fEPSP. Meanwhile, iron chelation with deferiprone decreased AMPAR transmission in PAE and control slices and decreased LTP only in controls slices. These results suggest that PAE affects iron homeostasis of specific brain areas—PFC and hippocampus—which could be involved in maladaptive cognition observed in this animal model.

Haemoglobin scavenging in intracranial bleeding: biology and clinical implications

Haemoglobin is released into the CNS during the breakdown of red blood cells after intracranial bleeding. Extracellular free haemoglobin is directly neurotoxic. Haemoglobin scavenging mechanisms clear haemoglobin and reduce toxicity; these mechanisms include erythrophagocytosis, haptoglobin binding of haemoglobin, haemopexin binding of haem and haem oxygenase breakdown of haem. However, the capacity of these mechanisms is limited in the CNS, and they easily become overwhelmed. Targeting of haemoglobin toxicity and scavenging is, therefore, a rational therapeutic strategy. In this Review, we summarize the neurotoxic mechanisms of extracellular haemoglobin and the peculiarities of haemoglobin scavenging pathways in the brain. Evidence for a role of haemoglobin toxicity in neurological disorders is discussed, with a focus on subarachnoid haemorrhage and intracerebral haemorrhage, and emerging treatment strategies based on the molecular pathways involved are considered. By focusing on a fundamental biological commonality between diverse neurological conditions, we aim to encourage the application of knowledge of haemoglobin toxicity and scavenging across various conditions. We also hope that the principles highlighted will stimulate research to explore the potential of the pathways discussed. Finally, we present a consensus opinion on the research priorities that will help to bring about clinical benefits.

Brain iron transport

Brain iron is a crucial participant and regulator of normal physiological activity. However, excess iron is involved in the formation of free radicals, and has been associated with oxidative damage to neuronal and other brain cells. Abnormally high brain iron levels have been observed in various neurodegenerative diseases, including neurodegeneration with brain iron accumulation, Alzheimer's disease, Parkinson's disease and Huntington's disease. However, the key question of why iron levels increase in the relevant regions of the brain remains to be answered. A full understanding of the homeostatic mechanisms involved in brain iron transport and metabolism is therefore critical not only for elucidating the pathophysiological mechanisms responsible for excess iron accumulation in the brain but also for developing pharmacological interventions to disrupt the chain of pathological events occurring in these neurodegenerative diseases. Numerous studies have been conducted, but to date no effort to synthesize these studies and ideas into a systematic and coherent summary has been made, especially concerning iron transport across the luminal (apical) membrane of the capillary endothelium and the membranes of different brain cell types. Herein, we review key findings on brain iron transport, highlighting the mechanisms involved in iron transport across the luminal (apical) as well as the abluminal (basal) membrane of the blood-brain barrier, the blood-cerebrospinal fluid barrier, and iron uptake and release in neurons, oligodendrocytes, astrocytes and microglia within the brain. We offer suggestions for addressing the many important gaps in our understanding of this important topic, and provide new insights into the potential causes of abnormally increased iron levels in regions of the brain in neurodegenerative disorders.

Iron Pathophysiology in Stroke

Ischemic and hemorrhagic stroke are the common types of stroke that lead to brain injury neurological deficits and mortality. All forms of stroke remain a serious health issue, and there is little successful development of drugs for treating stroke. Incomplete understanding of stroke pathophysiology is considered the main barrier that limits this research progress. Besides mitochondria and free radical-producing enzymes, labile iron is an important contributor to oxidative stress. Although iron regulation and metabolism in cerebral stroke are not fully understood, much progress has been achieved in recent years. For example, hepcidin has recently been recognized as the principal regulator of systemic iron homeostasis and a bridge between inflammation and iron regulation. This review discusses recent research progress in iron pathophysiology following cerebral stroke, focusing molecular regulation of iron metabolism and potential treatment targets.

The Role of Iron in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder characterized by the degeneration of motor neurons in the motor cortex, brainstem, and spinal cord. The etiology and pathogenesis of this devastating disease remain largely unknown. Increasing evidence suggests that iron accumulation is involved in the onset and progression of ALS. In this review, we discuss the regulation of iron homoeostasis in the brain, the misregulation of iron homeostasis in ALS, and its possible roles in the mechanism of the disease. Finally, we summarize the recent progress and problems with respect to iron chelator therapies on ALS, aiming to propose a new therapeutic strategy to ameliorate the progression of the disease.

The Dual Role of Hepcidin in Brain Iron Load and Inflammation

Hepcidin is the major regulator of systemic iron metabolism, while the role of this peptide in the brain has just recently been elucidated. Studies suggest a dual role of hepcidin in neuronal iron load and inflammation. This is important since neuronal iron load and inflammation are pathophysiological processes frequently associated with neurodegeneration. Furthermore, manipulation of hepcidin activity has recently been used to recover neuronal damage due to brain inflammation in animal models and cultured cells. Therefore, understanding the mechanistic insights of hepcidin action in the brain is important to uncover its role in treating neuronal damage in neurodegenerative diseases.

Iron-mediated oxidative cell death is a potential contributor to neuronal dysfunction induced by neonatal hemolytic hyperbilirubinemia

The review article discusses current knowledge of iron-mediated oxidative cell death (ferroptosis) and its potential role in the pathogenesis of neuronal dysfunction induced by neonatal hemolytic hyperbilirubinemia. The connection between metabolic conditions related to hemolysis (iron and bilirubin overload) and iron-induced lipid peroxidation is highlighted. Neurotoxicity of iron and bilirubin is associated with their release from destructed erythrocytes in response to hemolytic disease. Iron overload initiates lipid peroxidation through the reactive oxygen species production resulting to oxidative damage to cells. Excessive loading of immature brain cells by iron-induced formation of reactive oxygen species contributes to the development of various neurodevelopmental disorders. The causal relationship between iron overload and susceptibility of brain cells to oxidative damage by ferroptosis appears to be associated not only with the amount of redox-active iron involved in oxidative cell damage but also with the degree of maturity of the neonatal brain. Neuronal dysfunction induced by neonatal hemolytic disease can represent a specific model of ferroptosis. The mechanism by which iron overload triggers ferroptosis is not completely explained. However, hemolysis of neonatal red blood cells appears to be a determining factor. Potential therapeutic strategy with iron-chelating agents to inhibit ferroptosis has a promising future in postnatal care.

The Ferroxidase Hephaestin But Not Amyloid Precursor Protein is Required for Ferroportin-Supported Iron Efflux in Primary Hippocampal Neurons

Iron efflux in mammalian cells is mediated by the ferrous iron exporter ferroportin (Fpn); Fpn plasma membrane localization and function are supported by a multicopper ferroxidase and/or the soluble amyloid precursor protein (sAPP). Fpn and APP are ubiquitously expressed in all cell types in the central nervous system including neurons. In contrast, neuronal ferroxidase(s) expression has not been well characterized. Using primary cultures of hippocampal neurons, we examined the molecular mechanism of neuronal Fe efflux in detail. Developmental increases of Fpn, APP, and the ferroxidase hephaestin (Hp) were observed in hippocampal neurons. Iron efflux in these neurons depended on the level of Fpn localized at the cell surface; as noted, Fpn stability is supported by ferroxidase activity, an enzymatic activity that is required for Fe efflux. Iron accumulation increases and iron efflux decreases in Hp knockout neurons. In contrast, suppression of endogenous APP by RNAi knockdown does not affect surface Fpn stability or Fe efflux. These data support the model that the neuronal ferroxidase Hp plays a unique role in support of Fpn-mediated Fe efflux in primary hippocampal neurons. Our data also demonstrate that Hp ferroxidase activity relies on copper bioavailability, which suggests neuronal iron homeostasis will be modulated by cellular copper status.

Nucleic acid oxidative damage in Alzheimer's disease-explained by the hepcidin-ferroportin neuronal iron overload hypothesis?

There is strong literature support for brain metal dysregulation, oxidative stress and oxidative damage to neurons in Alzheimer's disease (AD); these processes begin early and continue throughout the disease. Here, we review current knowledge on metal dysregulation and nucleic acid oxidative damage in AD (we also include new data demonstrating increased RNA and DNA oxidative damage in hippocampus from individuals having suffered from degenerative (e.g. AD) and psychological diseases: 8-oxo-7,8-dihydroguanine (8-oxoGua) levels as determined by HPLC-EC-UV were particularly elevated in RNA and heterogeneously distributed among adjacent regions versus the control). Whereas neuronal iron accumulation occurs in aging, neuronal iron levels further increase in AD accompanied by oxidative damage, decreased copper levels, amyloid plaque formation and brain inflammation. The 'hepcidin-ferroportin iron overload' AD hypothesis links these processes together and is discussed here. Moreover, we find that most existing transgenic animal AD models only partly involve these processes, rather they are often limited to expression of mutated amyloid beta protein precursor (AbetaPP), presenilin, tau or apolipoprotein E proteins although a few models appear more relevant than others. Relevant models are likely to be crucial for refining and testing this hypothesis as well as developing new drugs.

Iron Regulation of Pancreatic Beta-Cell Functions and Oxidative Stress

Dietary advice is the cornerstone in first-line treatment of metabolic diseases. Nutritional interventions directed at these clinical conditions mainly aim to (a) improve insulin resistance by reducing energy-dense macronutrient intake to obtain weight loss and (b) reduce fluctuations in insulin secretion through avoidance of rapidly absorbable carbohydrates. However, even in the majority of motivated patients selected for clinical trials, massive efforts using this approach have failed to achieve lasting efficacy. Less attention has been given to the role of micronutrients in metabolic diseases. Here, we review the evidence that highlights (a) the importance of iron in pancreatic beta-cell function and dysfunction in diabetes and (b) the integrative pathophysiological effects of tissue iron levels in the interactions among the beta cell, gut microbiome, hypothalamus, innate and adaptive immune systems, and insulin-sensitive tissues. We propose that clinical trials are warranted to clarify the impact of dietary or pharmacological iron reduction on the development of metabolic disorders.

Distribution of manganese and other biometals in flatiron mice

Flatiron (ffe) mice display features of “ferroportin disease” or Type IV hereditary hemochromatosis. While it is known that both Fe and Mn metabolism are impaired in flatiron mice, the effects of ferroportin (Fpn) deficiency on physiological distribution of these and other biometals is unknown. We hypothesized that Fe, Mn, Zn and/or Cu distribution would be altered in ffe/+ compared to wild-type (+/+) mice. ICP-MS analysis showed that Mn, Zn and Cu levels were significantly reduced in femurs from ffe/+ mice. Bone deposits reflect metal accumulation, therefore these data indicate that Mn, Zn and Cu metabolism are affected by Fpn deficiency. The observations that muscle Cu, lung Mn, and kidney Cu and Zn levels were reduced in ffe/+ mice support the idea that metal metabolism is impaired. While all four biometals appeared to accumulate in brains of flatiron mice, significant gender effects were observed for Mn and Zn levels in male ffe/+ mice. Metals were higher in olfactory bulbs of ffe/+ mice regardless of gender. To further study brain metal distribution, ⁵⁴MnCl₂ was administered by intravenous injection and total brain ⁵⁴Mn was measured over time. At 72 h, ⁵⁴Mn was significantly greater in brains of ffe/+ mice compared to +/+ mice while blood ⁵⁴Mn was cleared to the same levels by 24 h. Taken together, these results indicate that Fpn deficiency decreases Mn trafficking out of the brain, alters body Fe, Mn, Zn and Cu levels, and promotes metal accumulation in olfactory bulbs.

Ferroportin deficiency impairs manganese metabolism in flatiron mice

We examined the physiologic role of ferroportin (Fpn) in manganese (Mn) export using flatiron (ffe/+) mice, a genetic model of Fpn deficiency. Blood (0.0123 vs. 0.0107 mg/kg; P = 0.0003), hepatic (1.06 vs. 0.96 mg/kg; P = 0.0125), and bile Mn levels (79 vs. 38 mg/kg; P = 0.0204) were reduced in ffe/+ mice compared to +/+ controls. Erythrocyte Mn-superoxide dismutase was also reduced at 6 (0.154 vs. 0.096, P = 0.0101), 9 (0.131 vs. 0.089, P = 0.0162), and 16 weeks of age (0.170 vs. 0.090 units/mg protein/min; P < 0.0001). (54)Mn uptake after intragastric gavage was markedly reduced in ffe/+ mice (0.0187 vs. 0.0066% dose; P = 0.0243), while clearance of injected isotope was similar in ffe/+ and +/+ mice. These values were compared to intestinal absorption of (59)Fe, which was significantly reduced in ffe/+ mice (8.751 vs. 3.978% dose; P = 0.0458). The influence of the ffe mutation was examined in dopaminergic SH-SY5Y cells and human embryonic HEK293T cells. While expression of wild-type Fpn reversed Mn-induced cytotoxicity, ffe mutant H32R failed to confer protection. These combined results demonstrate that Fpn plays a central role in Mn transport and that flatiron mice provide an excellent genetic model to explore the role of this exporter in Mn homeostasis. -

Naotaifang extract treatment results in increased ferroportin expression in the hippocampus of rats subjected to cerebral ischemia

The expression of Ferroportin (Fpn) was examined at different time points in rats following focal cerebral ischemia treated with or without the traditional Chinese medicine Naotaifang. Initially, rats were randomly divided into 2, 6, 12, 24 and 72 h groups following middle cerebral artery occlusion (MCAO) and the mRNA and protein level of Fpn was detected by immunohistochemistry and reverse transcription polymerase chain reaction (RT‑PCR) at the above time points. Secondly, the rats were randomly divided into five groups as follows: Sham surgery group, model group, low‑dose group (3 g/kg NTE), medium dose group (9 g/kg NTE) and the high‑dose group (27 g/kg NTE). After 3 days of corresponding therapy by intragastric administration once a day, the regional cerebral ischemia model was reproduced by the MCAO suture method. On the third day, the neurological behavior of the rats was analyzed by neurobehavioral assessment. Fpn in the hippocampal CA2 region was measured by immunohistochemistry and the mRNA level of Fpn was detected by RT‑PCR. Expression of Fpn in the hippocampal CA2 region reached a peak 12 h after surgery (P<0.05, compared with the model group). The high‑dose group (27 g/kg NTE) exhibited a lower neurological behavior score (P<0.05) and a higher level of expression of Fpn at the mRNA and protein level compared with the sham surgery group and model group (P<0.05). Dysregulation of intracellular iron balance is possibly a new mechanism underlying cerebral ischemia. NTE can protect the neuronal population in the hippocampal CA2 region by adjusting the expression of Fpn to balance iron levels following cerebral ischemia.

The role of iron in brain ageing and neurodegenerative disorders

SUMMARY

In the CNS, iron in several proteins is involved in many important processes such as oxygen transportation, oxidative phosphorylation, myelin production, and the synthesis and metabolism of neurotransmitters. Abnormal iron homoeostasis can induce cellular damage through hydroxyl radical production, which can cause the oxidation and modification of lipids, proteins, carbohydrates, and DNA. During ageing, different iron complexes accumulate in brain regions associated with motor and cognitive impairment. In various neurodegenerative diseases, such as Alzheimer's disease and Parkinson's disease, changes in iron homoeostasis result in altered cellular iron distribution and accumulation. MRI can often identify these changes, thus providing a potential diagnostic biomarker of neurodegenerative diseases. An important avenue to reduce iron accumulation is the use of iron chelators that are able to cross the blood-brain barrier, penetrate cells, and reduce excessive iron accumulation, thereby affording neuroprotection.

Iron transport across the blood-brain barrier: development, neurovascular regulation and cerebral amyloid angiopathy

There are two barriers for iron entry into the brain: (1) the brain-cerebrospinal fluid (CSF) barrier and (2) the blood-brain barrier (BBB). Here, we review the literature on developmental iron accumulation by the brain, focusing on the transport of iron through the brain microvascular endothelial cells (BMVEC) of the BBB. We review the iron trafficking proteins which may be involved in the iron flux across BMVEC and discuss the plausible mechanisms of BMVEC iron uptake and efflux. We suggest a model for how BMVEC iron uptake and efflux are regulated and a mechanism by which the majority of iron is trafficked across the developing BBB under the direct guidance of neighboring astrocytes. Thus, we place brain iron uptake in the context of the neurovascular unit of the adult brain. Last, we propose that BMVEC iron is involved in the aggregation of amyloid-β peptides leading to the progression of cerebral amyloid angiopathy which often occurs prior to dementia and the onset of Alzheimer's disease.

Iron deposits in the chronically inflamed central nervous system and contributes to neurodegeneration

Neurodegenerative disorders are characterized by the presence of inflammation in areas with neuronal cell death and a regional increase in iron that exceeds what occurs during normal aging. The inflammatory process accompanying the neuronal degeneration involves glial cells of the central nervous system (CNS) and monocytes of the circulation that migrate into the CNS while transforming into phagocytic macrophages. This review outlines the possible mechanisms responsible for deposition of iron in neurodegenerative disorders with a main emphasis on how iron-containing monocytes may migrate into the CNS, transform into macrophages, and die out subsequently to their phagocytosis of damaged and dying neuronal cells. The dying macrophages may in turn release their iron, which enters the pool of labile iron to catalytically promote formation of free-radical-mediated stress and oxidative damage to adjacent cells, including neurons. Healthy neurons may also chronically acquire iron from the extracellular space as another principle mechanism for oxidative stress-mediated damage. Pharmacological handling of monocyte migration into the CNS combined with chelators that neutralize the effects of extracellular iron occurring due to the release from dying macrophages as well as intraneuronal chelation may denote good possibilities for reducing the deleterious consequences of iron deposition in the CNS.

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.