Hepcidin deficiency impairs hippocampal neurogenesis and mediates brain atrophy and memory decline in mice.

BACKGROUND: Hepcidin is the master regulator of iron homeostasis. Hepcidin downregulation has been demonstrated in the brains of Alzheimer's disease (AD) patients. However, the mechanism underlying the role of hepcidin downregulation in cognitive impairment has not been elucidated. METHODS: In the present study, we generated GFAP-Cre-mediated hepcidin conditional knockout mice (HampGFAP cKO) to explore the effect of hepcidin deficiency on hippocampal structure and neurocognition. RESULTS: We found that the HampGFAP cKO mice developed AD-like brain atrophy and memory deficits. In particular, the weight of the hippocampus and the number of granule neurons in the dentate gyrus were significantly reduced. Further investigation demonstrated that the morphological change in the hippocampus of HampGFAP cKO mice was attributed to impaired neurogenesis caused by decreased proliferation of neural stem cells. Regarding the molecular mechanism, increased iron content after depletion of hepcidin followed by an elevated level of the inflammatory factor tumor necrosis factor-α accounted for the impairment of hippocampal neurogenesis in HampGFAP cKO mice. These observations were further verified in GFAP promoter-driven hepcidin knockdown mice and in Nestin-Cre-mediated hepcidin conditional knockout mice. CONCLUSIONS: The present findings demonstrated a critical role for hepcidin in hippocampal neurogenesis and validated the importance of iron and associated inflammatory cytokines as key modulators of neurodevelopment, providing insights into the potential pathogenesis of cognitive dysfunction and related treatments.

Brain iron deficiency and affected contextual fear memory in mice with conditional Ferroportin1 ablation in the brain.

Fear memory is a pivotal biological function by which organisms can predict possible danger to avoid or reduce harm. However, dysregulation of fear memory processing may lead to pathological fear or anxiety and produce serious clinical symptoms, such as post-traumatic stress disorder (PTSD). Iron deficiency (ID) is reported to inhibit the initiation of fear memory. In our study, we found that ferroportin1 (FPN1), the only known cellular iron export protein in mammals, and ablation in neurons and astrocytes caused iron deficiency in the cortex and hippocampus. However, little is known about its role in the development of fear memory. Moreover, direct evidence of the role of FPN1, or the related molecular mechanisms of such a role, in balancing brain iron homeostasis, especially in neuronal cells, is lacking. Herein, we deleted Fpn1 in mouse neurons, using Nestin-cre transgenic mice, and explored the impact on neuronal iron recycling and brain iron homeostasis in the cortex and hippocampus. We investigated the response of the mice to contextual fear and found that formation of fear memory was impeded after neuronal FPN1 depletion. We also found that FPN1 ablation in neurons and astrocytes caused an atypical expression of iron metabolism-related proteins in these two regions: decreased expression of DMT1, Ft-H, and Ft-L, and increased TfR1 expression. In addition, the decreased FPN1 in brain microvascular endothelial cells (BMVECs) also shed light on the cause of the decreased iron delivery to the brain through the blood-brain barrier (BBB). Our research highlights the major role played by FPN1 in brain iron homeostasis and identifies a potential target for the treatment of PTSD.

Hepcidin and iron regulatory proteins coordinately regulate ferroportin 1 expression in the brain of mice.

Iron plays an essential role in various cellular metabolic processes of the body. Maintenance of cellular iron homeostasis is particularly important for keeping the normal functions of the cells. Ferroportin 1 (FPN1) is the currently only known iron exporter on the cell membrane. It has been indicated that the regulation of FPN1 in response to the alteration of iron level mainly involves two processes, posttranscriptional repression by iron regulatory proteins (IRPs) and posttranslational degradation by hepcidin, the major iron-sensing hormone. However, whether there is any communication between the two types of regulations or which one plays dominant role has not been reported. In our study with IRP2-/- mice, we found that knockout of IRP2 increased FPN1 expression in the cerebral cortex of IRP2-/- mice, whereas the upregulation of FPN1 was more significant in IRP1/IRP2 dual knockdown fibroblasts. Interestingly, we found that the knockout of IRP2 severely affected the regulation effect of hepcidin on FPN1 in mouse brain. FPN1 level decreased dramatically in the brain of wild-type mice injected with hepcidin, but it did not decrease much in IRP2 knockout mice. Further investigation disclosed that the compromised hepcidin-FPN1 regulation in IRP2-/- cells was directly dependent on the existence of iron-responsive element (IRE) in FPN1 messenger RNA. These results indicate that IRPs and hepcidin coordinately regulate the FPN1 level in mice. This study will provide a more comprehensive understanding of the regulatory mechanisms of FPN1 expression.

Transcriptomic analysis reveals the molecular mechanism of Alzheimer-related neuropathology induced by sevoflurane in mice.

Anesthetics could induce cognitive dysfunctions, such as Alzheimer's disease in humans or mice. However, the precise molecular mechanism is unclear. Sevoflurane is a common anesthetic widely used in clinical practice. Here, we demonstrated the induction of cognitive dysfunction induced by Sev in mice to corroborate the signaling pathway and the differentially expressed genes (DEGs) followed by analyzing their functions. The cognitive function of mice was measured by the Morris water maze test. Transcriptomic data were annotated with Illumina HiSeq. 2000. Further, the changes in related proteins or genes were analyzed by western blotting and real-time quantitative polymerase chain reaction. Our results showed that Sev could cause a decline in cognitive competence in mice. The transcriptomic data indicated that adding up to 566 genes were upregulated and 1073 genes were downregulated. The genes of Plin4, Lcn2, Lrg1, Foxf1, and Ctla2a were significantly upregulated, while the genes of Arc, Npas4, Egr2, Hes5, and Cdh9 were downregulated dramatically. The Gene Ontology term with the highest enrichment of DEGs are involved in the regulation of cellular and macromolecule metabolism and cation and nucleic acid binding, respectively. The Kyoto encyclopedia of genes and genomes analysis indicated that the mitogen-activated protein kinases (MAPK) pathway was one of the most important metabolic pathways. In addition, the metabolic pathways related to cognitive function, such as the nervous system and neurodegenerative disease showed significant changes. Furthermore, we found that p38, c-Jun N-terminal kinase, and extracellular signal-regulated kinase of the MAPK signaling pathway played important roles in this process. In conclusion, these results provide the first important clues for identifying the DEGs and signaling pathways in the hippocampus due to a Sev-induced cognitive deficiency in mice.

Hypobaric hypoxia regulates iron metabolism in rats.

Intermittent hypobaric hypoxia can produce a protective effect on both the nervous system and non-nervous system tissues. Intermittent hypobaric hypoxia preconditioning has been shown to protect rats from cardiac ischemia-reperfusion injury by decreasing cardiac iron levels and reactive oxygen species (ROS) production, thereby decreasing oxidative stress to achieve protection. However, the specific mechanism underlying the protective effect of hypobaric hypoxia is unclear. To shed light on this phenomenon, we subjected Sprague-Dawley rats to hypobaric hypoxic preconditioning (8 hours/day). The treatment was continued for 4 weeks. We then measured the iron content in the heart, liver, spleen, and kidney. The iron levels in all of the assessed tissues decreased significantly after hypobaric hypoxia treatment, corroborating previous results that hypobaric hypoxia may produce its protective effect by decreasing ROS production by limiting the levels of catalytic iron in the tissue. We next assessed the expression levels of several proteins involved in iron metabolism (transferrin receptor, L-ferritin, and ferroportin1 [FPN1]). The increased transferrin receptor and decreased L-ferritin levels after hypobaric hypoxia were indicative of a low-iron phenotype, while FPN1 levels remained unchanged. We also examined hepcidin, transmembrane serine proteases 6 (TMPRSS6), erythroferrone (ERFE), and erythropoietin (EPO) levels, all of which play a role in the regulation of systemic iron metabolism. The expression of hepcidin decreased significantly after hypobaric hypoxia treatment, whereas the expression of TMPRSS6 and ERFE and EPO increased sharply. Finally, we measured serum iron and total iron binding capacity in the serum, as well as red blood cell count, mean corpuscular volume, hematocrit, red blood cell distribution width SD, and red blood cell distribution width CV. As expected, all of these values increased after the hypobaric hypoxia treatment. Taken together, our results show that hypobaric hypoxia can stimulate erythropoiesis, which systemically draws iron away from nonhematopoietic tissue through decreased hepcidin levels.

Cellular Iron Metabolism and Regulation.

Iron is an essential trace element in the human body, but excess iron is toxic as it contributes to oxidative damage. To keep iron concentration within the optimal physiologic range, iron metabolism at the cellular level and the whole systemic level are tightly regulated. Balance of iron homeostasis depends on the expression levels and activities of iron carriers, iron transporters, and iron regulatory and storage proteins. Divalent metal transporter 1 (DMT1) at the apical membrane of intestinal enterocyte brings in non-heme iron from the diet, whereas ferroportin 1 (FPN1) at the basal membrane exports iron into the circulation. Plasma transferrin (Tf) then carries iron to various tissues and cells. After binding to transferrin receptor 1 (TfR1), the complex is endocytosed into the cell, where iron enters the cytoplasm via DMT1 on the endosomal membrane. Free iron is either utilized in metabolic processes, such as synthesis of hemoglobin and Fe-S cluster, or sequestered in the cytosolic ferritin, serving as a cellular iron store. Excess iron can be exported from the cell via FPN1. The liver-derived peptide hepcidin plays a major regulatory role in controlling FPN1 level in the enterocyte, and thus controls the whole-body iron absorption. Inside the cells, iron regulatory proteins (IRPs) modulate the expressions of DMT1, TfR1, ferritin, and FPN1 via binding to the iron-responsive element (IRE) in their mRNAs. Both the release of hepcidin and the IRP-IRE interaction are coordinated with the fluctuation of the cellular iron level. Therefore, an adequate and steady iron supplement is warranted for the utilization of cells around the body. Investigations on the molecular mechanisms of cellular iron metabolism and regulation could advance the fields of iron physiology and pathophysiology.

Hypobaric Hypoxia Regulates Brain Iron Homeostasis in Rats.

Disruption of iron homeostasis in brain has been found to be closely involved in several neurodegenerative diseases. Recent studies have reported that appropriate intermittent hypobaric hypoxia played a protective role in brain injury caused by acute hypoxia. However, the mechanisms of this protective effect have not been fully understood. In this study, Sprague-Dawley (SD) rat models were developed by hypobaric hypoxia treatment in an altitude chamber, and the iron level and iron related protein levels were determined in rat brain after 4 weeks of treatment. We found that the iron levels significantly decreased in the cortex and hippocampus of rat brain as compared to that of the control rats without hypobaric hypoxia treatment. The expression levels of iron storage protein L-ferritin and iron transport proteins, including transferrin receptor-1 (TfR1), divalent metal transporter 1 (DMT1), and ferroportin1 (FPN1), were also altered. Further studies found that the iron regulatory protein 2 (IRP2) played a dominant regulatory role in the changes of iron hemostasis, whereas iron regulatory protein 1 (IRP1) mainly acted as cis-aconitase. These results, for the first time, showed the alteration of iron metabolism during hypobaric hypoxia in rat models, which link the potential neuroprotective role of hypobaric hypoxia treatment to the decreased iron level in brain. This may provide insight into the treatment of iron-overloaded neurodegenerative diseases. J. Cell. Biochem. 118: 1596-1605, 2017. © 2016 Wiley Periodicals, Inc.

A New Approach to Produce HIV-1 Envelope Trimers: BOTH CLEAVAGE AND PROPER GLYCOSYLATION ARE ESSENTIAL TO GENERATE AUTHENTIC TRIMERS.

The trimeric envelope spike of HIV-1 mediates virus entry into human cells. The exposed part of the trimer, gp140, consists of two noncovalently associated subunits, gp120 and gp41 ectodomain. A recombinant vaccine that mimics the native trimer might elicit entry-blocking antibodies and prevent virus infection. However, preparation of authentic HIV-1 trimers has been challenging. Recently, an affinity column containing the broadly neutralizing antibody 2G12 has been used to capture recombinant gp140 and prepare trimers from clade A BG505 that naturally produces stable trimers. However, this antibody-based approach may not be as effective for the diverse HIV-1 strains with different epitope signatures. Here, we report a new and simple approach to produce HIV-1 envelope trimers. The C terminus of gp140 was attached to Strep-tag II with a long linker separating the tag from the massive trimer base and glycan shield. This allowed capture of nearly homogeneous gp140 directly from the culture medium. Cleaved, uncleaved, and fully or partially glycosylated trimers from different clade viruses were produced. Extensive biochemical characterizations showed that cleavage of gp140 was not essential for trimerization, but it triggered a conformational change that channels trimers into correct glycosylation pathways, generating compact three-blade propeller-shaped trimers. Uncleaved trimers entered aberrant pathways, resulting in hyperglycosylation, nonspecific cross-linking, and conformational heterogeneity. Even the cleaved trimers showed microheterogeneity in gp41 glycosylation. These studies established a broadly applicable HIV-1 trimer production system as well as generating new insights into their assembly and maturation that collectively bear on the HIV-1 vaccine design.

Quantum dots-hemin: Preparation and application in the absorption of heme iron.

The absorption mechanism of heme iron remains unclear due to the limit of labeling techniques. Quantum dots (QDs) are powerful fluorescent probes resistant to photobleaching, however, there is no data about the application of QDs in heme iron absorption. Herein, we prepared hemin-coated CdSe/ZnS (QDs-hemin), and studied their absorption in vitro and in vivo. Results showed that QDs-hemin had uniform particle sizes, physiological stability and high joint efficiency. Moreover, QDs-hemin could be successfully absorbed gradually into the duodenum with the time using synchrotron radiation micro X-ray fluorescence and confocal laser scanning microscopy. Furthermore, QDs-hemin were observed to degrade in lysosomes, and their absorption was blocked by Heme Carrier Protein 1 (HCP1) antibody and HCP1 siRNA. All the results demonstrate that QDs can be a good tracer for heme iron and that HCP1 pathway is critical and predominant over the endocytosis pathway in the absorption mechanism.

Designing a soluble near full-length HIV-1 gp41 trimer.

The HIV-1 envelope spike is a trimer of heterodimers composed of an external glycoprotein gp120 and a transmembrane glycoprotein gp41. gp120 initiates virus entry by binding to host receptors, whereas gp41 mediates fusion between viral and host membranes. Although the basic pathway of HIV-1 entry has been extensively studied, the detailed mechanism is still poorly understood. Design of gp41 recombinants that mimic key intermediates is essential to elucidate the mechanism as well as to develop potent therapeutics and vaccines. Here, using molecular genetics and biochemical approaches, a series of hypotheses was tested to overcome the extreme hydrophobicity of HIV-1 gp41 and design a soluble near full-length gp41 trimer. The two long heptad repeat helices HR1 and HR2 of gp41 ectodomain were mutated to disrupt intramolecular HR1-HR2 interactions but not intermolecular HR1-HR1 interactions. This resulted in reduced aggregation and improved solubility. Attachment of a 27-amino acid foldon at the C terminus and slow refolding channeled gp41 into trimers. The trimers appear to be stabilized in a prehairpin-like structure, as evident from binding of a HR2 peptide to exposed HR1 grooves, lack of binding to hexa-helical bundle-specific NC-1 mAb, and inhibition of virus neutralization by broadly neutralizing antibodies 2F5 and 4E10. Fusion to T4 small outer capsid protein, Soc, allowed display of gp41 trimers on the phage nanoparticle. These approaches for the first time led to the design of a soluble gp41 trimer containing both the fusion peptide and the cytoplasmic domain, providing insights into the mechanism of entry and development of gp41-based HIV-1 vaccines.

Iron overload suppresses hippocampal neurogenesis in adult mice: Implication for iron dysregulation-linked neurological diseases.

AIMS: Adult hippocampal neurogenesis is an important player in brain homeostasis and its impairment participates in neurological diseases. Iron overload has emerged as an irreversible factor of brain aging, and is also closely related to degenerative disorders, including cognitive dysfunction. However, whether brain iron overload alters hippocampal neurogenesis has not been reported. We investigated the effect of elevated iron content on adult hippocampal neurogenesis and explored the underlying mechanism. METHODS: Mouse models with hippocampal iron overload were generated. Neurogenesis in hippocampus and expression levels of related molecules were assessed. RESULTS: Iron accumulation in hippocampus remarkably impaired the differentiation of neural stem cells, resulting in a significant decrease in newborn neurons. The damage was possibly attributed to iron-induced downregulation of proprotein convertase furin and subsequently decreased maturation of brain-derived neurotrophic factor (BDNF), thus contributing to memory decline and anxiety-like behavior of mice. Supportively, knockdown of furin indeed suppressed hippocampal neurogenesis, while furin overexpression restored the impairment. CONCLUSION: These findings demonstrated that iron overload damaged hippocampal neurogenesis likely via iron-furin-BDNF pathway. This study provides new insights into potential mechanisms on iron-induced neurotoxicity and the causes of neurogenesis injury and renders modulating iron homeostasis and furin expression as novel therapeutic strategies for treatment of neurological diseases.

Cellular iron depletion enhances behavioral rhythm by limiting brain Per1 expression in mice.

AIMS: Disturbances in the circadian rhythm are positively correlated with the processes of aging and related neurodegenerative diseases, which are also associated with brain iron accumulation. However, the role of brain iron in regulating the biological rhythm is poorly understood. In this study, we investigated the impact of brain iron levels on the spontaneous locomotor activity of mice with altered brain iron levels and further explored the potential mechanisms governing these effects in vitro. RESULTS: Our results revealed that conditional knockout of ferroportin 1 (Fpn1) in cerebral microvascular endothelial cells led to brain iron deficiency, subsequently resulting in enhanced locomotor activity and increased expression of clock genes, including the circadian locomotor output cycles kaput protein (Clock) and brain and muscle ARNT-like 1 (Bmal1). Concomitantly, the levels of period circadian regulator 1 (PER1), which functions as a transcriptional repressor in regulating biological rhythm, were decreased. Conversely, the elevated brain iron levels in APP/PS1 mice inhibited autonomous rhythmic activity. Additionally, our findings demonstrate a significant decrease in serum melatonin levels in Fpn1cdh5 -CKO mice compared with the Fpn1flox/flox group. In contrast, APP/PS1 mice with brain iron deposition exhibited higher serum melatonin levels than the WT group. Furthermore, in the human glioma cell line, U251, we observed reduced PER1 expression upon iron limitation by deferoxamine (DFO; iron chelator) or endogenous overexpression of FPN1. When U251 cells were made iron-replete by supplementation with ferric ammonium citrate (FAC) or increased iron import through transferrin receptor 1 (TfR1) overexpression, PER1 protein levels were increased. Additionally, we obtained similar results to U251 cells in mouse cerebellar astrocytes (MA-c), where we collected cells at different time points to investigate the rhythmic expression of core clock genes and the impact of DFO or FAC treatment on PER1 protein levels. CONCLUSION: These findings collectively suggest that altered iron levels influence the circadian rhythm by regulating PER1 expression and thereby modulating the molecular circadian clock. In conclusion, our study identifies the regulation of brain iron levels as a potential new target for treating age-related disruptions in the circadian rhythm.

Transmembrane serine protease 6, a novel target for inhibition of neuronal tumor growth.

Transmembrane serine protease 6 (Tmprss6) has been correlated with the occurrence and progression of tumors, but any specific molecular mechanism linking the enzyme to oncogenesis has remained elusive thus far. In the present study, we found that Tmprss6 markedly inhibited mouse neuroblastoma N2a (neuro-2a) cell proliferation and tumor growth in nude mice. Tmprss6 inhibits Smad1/5/8 phosphorylation by cleaving the bone morphogenetic protein (BMP) co-receptor, hemojuvelin (HJV). Ordinarily, phosphorylated Smad1/5/8 binds to Smad4 for nuclear translocation, which stimulates the expression of hepcidin, ultimately decreasing the export of iron through ferroportin 1 (FPN1). The decrease in cellular iron levels in neuro-2a cells with elevated Tmprss6 expression limited the availability of the metal forribo nucleotide reductase activity, thereby arresting the cell cycle prior to S phase. Interestingly, Smad4 promoted nuclear translocation of activating transcription factor 3 (ATF3) to activate the p38 mitogen-activated protein kinases signaling pathway by binding to ATF3, inducing apoptosis of neuro-2a cells and inhibiting tumor growth. Disruption of ATF3 expression significantly decreased apoptosis in Tmprss6 overexpressed neuro-2a cells. Our study describes a mechanism whereby Tmprss6 regulates the cell cycle and apoptosis. Thus, we propose Tmprss6 as a candidate target for inhibiting neuronal tumor growth.

Iron Metabolism, Redox Balance and Neurological Diseases.

Iron is essential for life, and the dysregulation of iron homeostasis can lead to severe pathological changes in the neurological system [...].

Brain Iron Metabolism, Redox Balance and Neurological Diseases.

The incidence of neurological diseases, such as Parkinson's disease, Alzheimer's disease and stroke, is increasing. An increasing number of studies have correlated these diseases with brain iron overload and the resulting oxidative damage. Brain iron deficiency has also been closely linked to neurodevelopment. These neurological disorders seriously affect the physical and mental health of patients and bring heavy economic burdens to families and society. Therefore, it is important to maintain brain iron homeostasis and to understand the mechanism of brain iron disorders affecting reactive oxygen species (ROS) balance, resulting in neural damage, cell death and, ultimately, leading to the development of disease. Evidence has shown that many therapies targeting brain iron and ROS imbalances have good preventive and therapeutic effects on neurological diseases. This review highlights the molecular mechanisms, pathogenesis and treatment strategies of brain iron metabolism disorders in neurological diseases.

CHIR99021 Maintenance of the Cell Stemness by Regulating Cellular Iron Metabolism.

CHIR99021 is an aminopyrimidine derivative, which can efficiently inhibit the activity of glycogen synthesis kinase 3α (GSK-3α) and GSK-3ß. As an essential component of stem cell culture medium, it plays an important role in maintaining cell stemness. However, the mechanism of its role is not fully understood. In the present study, we first found that removal of CHIR99021 from embryonic stem cell culture medium reduced iron storage in mouse embryonic stem cells (mESCs). CHIR99021-treated Neuro-2a cells led to an upregulation of ferritin expression and an increase in intracellular iron levels, along with GSK3ß inhibition and Wnt/GSK-3ß/ß-catenin pathway activation. In addition, iron treatment activated the classical Wnt pathway by affecting the expression of ß-catenin in the Neuro-2a cells. Our data link the role of iron in the maintenance of cell stemness via the Wnt/GSK-3ß/ß-catenin signaling pathway, and identify intermediate molecules, including Steap1, Bola2, and Kdm6bos, which may mediate the upregulation of ferritin expression by CHIR99021. These findings reveal novel mechanisms of the maintenance of cell stemness and differentiation and provide a theoretical basis for the development of new strategies in stem cell treatment in disease.

Ferrodifferentiation regulates neurodevelopment via ROS generation.

Iron is important for life, and iron deficiency impairs development, but whether the iron level regulates neural differentiation remains elusive. In this study, with iron-regulatory proteins (IRPs) knockout embryonic stem cells (ESCs) that showed severe iron deficiency, we found that the Pax6- and Sox2-positive neuronal precursor cells and Tuj1 fibers in IRP1-/-IRP2-/- ESCs were significantly decreased after inducing neural differentiation. Consistently, in vivo study showed that the knockdown of IRP1 in IRP2-/- fetal mice remarkably affected the differentiation of neuronal precursors and the migration of neurons. These findings suggest that low intracellular iron status significantly inhibits neurodifferentiation. When supplementing IRP1-/-IRP2-/- ESCs with iron, these ESCs could differentiate normally. Further investigations revealed that the underlying mechanism was associated with an increase in reactive oxygen species (ROS) production caused by the substantially low level of iron and the down-regulation of iron-sulfur cluster protein ISCU, which, in turn, affected the proliferation and differentiation of stem cells. Thus, the appropriate amount of iron is crucial for maintaining normal neural differentiation that is termed ferrodifferentiation.

The emerging role of furin in neurodegenerative and neuropsychiatric diseases.

Furin is an important mammalian proprotein convertase that catalyzes the proteolytic maturation of a variety of prohormones and proproteins in the secretory pathway. In the brain, the substrates of furin include the proproteins of growth factors, receptors and enzymes. Emerging evidence, such as reduced FURIN mRNA expression in the brains of Alzheimer's disease patients or schizophrenia patients, has implicated a crucial role of furin in the pathophysiology of neurodegenerative and neuropsychiatric diseases. Currently, compared to cancer and infectious diseases, the aberrant expression of furin and its pharmaceutical potentials in neurological diseases remain poorly understood. In this article, we provide an overview on the physiological roles of furin and its substrates in the brain, summarize the deregulation of furin expression and its effects in neurodegenerative and neuropsychiatric disorders, and discuss the implications and current approaches that target furin for therapeutic interventions. This review may expedite future studies to clarify the molecular mechanisms of furin deregulation and involvement in the pathogenesis of neurodegenerative and neuropsychiatric diseases, and to develop new diagnosis and treatment strategies for these diseases.

Hippocampal Iron Accumulation Impairs Synapses and Memory via Suppressing Furin Expression and Downregulating BDNF Maturation.

Brain iron overload is positively correlated with the pathogenesis of Alzheimer's disease (AD). However, the role of iron in AD pathology is not completely understood. Furin is the first identified mammalian proprotein convertase that catalyzes the proteolytic maturation of large numbers of prohormones and proproteins. The correlation between altered furin expression and AD pathology has been suggested, but the underlying mechanism remains to be clarified. Here, we found that the expression of furin in the hippocampus of Alzheimer's model APP/PS1 mice was significantly reduced, and we demonstrated that the reduction of furin was directly caused by hippocampal iron overload using wild-type mice with intrahippocampal injection of iron. In cultured neuronal cells, this suppression effect was observed as transcriptional inhibition. Regarding the changes of furin-mediated activities caused by hippocampal iron overload, we found that the maturation of brain-derived neurotrophic factor (BDNF) was impeded and the expression levels of synaptogenesis-related proteins were downregulated, leading to cognitive decline. Furthermore, iron chelation or furin overexpression in the hippocampus of APP/PS1 mice increased furin expression, restored synapse plasticity, and ameliorated cognitive decline. Therefore, the inhibitory effect of hippocampal iron accumulation on furin transcription may be an important pathway involved in iron-mediated synapse damage and memory loss in AD. This study provides new insights into the molecular mechanisms of the toxic effects of iron in neurons and AD pathophysiology and renders furin as a potential target for treatment of iron overload-related neurodegenerative diseases.

Astrocyte-derived hepcidin controls iron traffic at the blood-brain-barrier via regulating ferroportin 1 of microvascular endothelial cells.

Brain iron dysregulation associated with aging is closely related to motor and cognitive impairments in neurodegenerative diseases. The regulation of iron traffic at the blood-brain barrier (BBB) is crucial to maintain brain iron homeostasis. However, the specific mechanism has not been clarified in detail. Using various conditional gene knockout and overexpression mice, as well as cell co-culture of astrocyte and bEND.3 in the transwell, we found that astrocyte hepcidin knockdown increased the expression of ferroportin 1 (FPN1) of brain microvascular endothelial cells (BMVECs), and that it also induced brain iron overload and cognitive decline in mice. Moreover, BMVECs FPN1 knockout decreased iron contents in the cortex and hippocampus. Furthermore, hepcidin regulates the level of FPN1 of BMVECs with conditional gene overexpression in vivo and in vitro. Our results revealed that astrocytes responded to the intracellular high iron level and increased the secretion of hepcidin, which in turn diminished iron uptake at BBB from circulation through directly regulating FPN1 of BMVECs. Our results demonstrate that FPN1 of BMVECs is a gateway for iron transport into the brain from circulation, and the controller of this gateway is hepcidin secreted by astrocyte at its endfeet through physical contact with BMVECs. This regulation is indeed the major checkpoint for iron transport from the blood circulation to the brain. This study delineates the pathway and regulation of iron entry into the brain, providing potential therapeutic targets for iron dysregulation-related neurological diseases.