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.

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.

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.

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.

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.

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.

A new mechanism of POCD caused by sevoflurane in mice: cognitive impairment induced by cross-dysfunction of iron and glucose metabolism.

Sevoflurane (Sev) is a commonly used anesthetic in hospitals that can cause neurotoxicity. Postoperative cognitive dysfunction (POCD) is a common clinical problem induced by some anesthetics. However, the exact mechanism of neurotoxicity induced by Sev is unclear. Here we studied a new mechanism of POCD induced by Sev. We treated 15-month-old mice with 2% Sev for 6 hours, and we had found that Sev causes POCD. Using isobaric tags for relative and absolute quantitation (iTRAQ), we found that the transporter and the metabolism of carbohydrates and inorganic ions were involved in the cognitive impairment induced by Sev. Using synchrotron radiation micro-X-ray fluorescence (µ-XRF), we showed that Sev caused the iron overload in the brain of 15-month-old mice. Subsequently, excessive iron led to oxidative stress and impaired mitochondrial function that further led to glucose metabolism disorder and reduced ATP production by regulating the expression of key enzyme genes or proteins including G6Pase, Pck1, and Cs. Meanwhile, Sev also inhibited the oxygen consumption rate and glucose absorption by downregulating the expression of glucose transporter 1 in cerebral vascular endothelial cells. The cross-dysfunction of iron and glucose metabolism caused the apoptosis in the cortex and hippocampus through Bcl2/Bax pathway. In conclusion, the data here showed a new mechanism that Sev caused apoptosis by cross-dysregulation of iron and glucose metabolism and induced energy stress in mice. Maintaining iron and glucose metabolism homeostasis may play an important role in cognitive impairment induced by Sev.

Ferritinophagy-Mediated Ferroptosis Involved in Paraquat-Induced Neurotoxicity of Dopaminergic Neurons: Implication for Neurotoxicity in PD.

Parkinson's disease (PD) is a progressive nervous system disorder. Until now, the molecular mechanism of its occurrence is not fully understood. Paraquat (PQ) was identified as a neurotoxicant and is linked to increased PD risk and PD-like neuropathology. Ferroptosis is recognized as a new form of regulated cell death. Here, we revealed a new underlying mechanism by which ferritinophagy-mediated ferroptosis is involved in PD induced by PQ. The effect of PQ on movement injury in mice was investigated by the bar fatigue and pole-climbing test. SH-SY5Y human neuroblastoma cells were used to evaluate the mechanism of ferroptosis. Our results showed that PQ induced movement injury by causing the decrease in tyrosine hydroxylase in mice. In vitro, PQ significantly caused the iron accumulation in cytoplasm and mitochondria through ferritinophagy pathway induced by NCOA4. Iron overload initiated lipid peroxidation through 12Lox, further inducing ferroptosis by producing lipid ROS. PQ downregulated SLC7A11 and GPX4 expression and upregulated Cox2 expression significantly, which were important markers in ferroptosis. Fer-1, an inhibitor of ferroptosis, could significantly ameliorate the ferroptosis induced by PQ. Meanwhile, Bcl2, Bax, and p-38 were involved in apoptosis induced by PQ. In conclusion, ferritinophagy-mediated ferroptosis pathway played an important role in PD occurrence. Bcl2/Bax and P-p38/p38 pathways mediated the cross-talk between ferroptosis and apoptosis induced by PQ. These data further demonstrated the complexity of PD occurrence. The inhibition of the ferroptosis and apoptosis together may be a new strategy for the prevention of neurotoxicity or PD in the future.

Effect of sevoflurane on iron homeostasis and toxicity in the brain of mice.

Sevoflurane (Sev), a commonly used volatile anesthetic, could induce nerve damage and cognitive deficiency. Oxidative stress induced by iron overload promotes nerve damage and cell apoptosis in the brain. This study revealed a new toxic mechanism of Sev to the brain occurred through the dysfunction of iron metabolism. Twelve-month-old C57BL/6 mice were randomly assigned to the following three groups: control group; 2% Sev (6 h) group; and Sev plus iron deficiency group. Iron levels and iron metabolism-related proteins and apoptosis-related factors in hippocampus and cortex tissues were detected by using synchrotron radiation micro-X-ray fluorescence (µ-XRF) and western blotting. Our results showed that a decline in cognitive function was observed in mice treated with Sev. Sev significantly induced iron accumulation through upregulating ferritin and downregulating transferrin receptor 1 which involved in ferroportin1 (Fpn1)/hepcidin pathway and increasing reactive oxygen species (ROS) and malondialdehyde (MDA) content of hippocampus and cortex. Sev aggravated BACE1 expression and Aß accumulation. Changes in the ratio of Bcl2/Bax and Tau/p-Tau intensified the cell apoptosis in hippocampus and cortex tissues. Interestingly, the cognitive deficiency and neurotoxicity induced by Sev could be ameliorated significantly by feeding a low-iron diet to mice prior to anesthesia. The data uncovered a new lesion mechanism of Sev from the role of iron metabolism. This study also suggested that the reduction in iron levels could protect the brain against neurological damage induced by Sev.

Nrf2 knockout altered brain iron deposition and mitigated age-related motor dysfunction in aging mice.

The transcription factor NF-E2-related factor 2 (Nrf2) is a central regulator of cellular antioxidant and detoxification response. The association between Nrf2 activity and iron-related oxidative stress in neurodegenerative diseases has been studied, and Nrf2 was found to transcriptionally regulate the expression of iron transporters and ferroptosis-related factors. However, the role of Nrf2 in age-related motor dysfunction and its link to iron metabolism dysregulation in brain have not been fully elucidated. In this study, with different ages of Nrf2 knockout (KO) and wild type (WT) mice, we investigated the effects of Nrf2 deficiency on brain oxidative stress, iron metabolism and the motor coordination ability of mice. In contrast to the predicted neuroprotective role of Nrf2 in oxidative stress-related diseases, we found that Nrf2 KO remarkably improved the motor coordination of aged mice, which was associated with the reduced ROS level and decreased apoptosis of dopaminergic neurons in substantia nigra (SN) of 18-month-old Nrf2 KO mice. With high-iron and Parkinson's disease (PD) mouse models, we revealed that Nrf2 KO prevented the deposition of brain iron, particularly in SN and striatum, which may subsequently delay motor dysfunction in aged mice. The regulation of Nrf2 KO on brain iron metabolism was likely mediated by decreasing the ferroportin 1 (FPN1) level on brain microvascular endothelial cells, thus hindering the process of iron entry into the brain. Nrf2 may be a potential therapeutic target in age-related motor dysfunction diseases for its role in regulating brain iron homeostasis.

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 overexpression in astrocytes alters brain iron metabolism and protects against amyloid-ß induced brain damage in mice.

Progressive iron accumulation in the brain and iron-induced oxidative stress are considered to be one of the initial causes of Alzheimer's disease (AD), and modulation of brain iron level shows promise for its treatment. Hepcidin expressed by astrocytes has been speculated to regulate iron transport across the blood-brain barrier (BBB) and control the whole brain iron load. Whether increasing the expression of astrocyte hepcidin can reduce brain iron level and relieve AD symptoms has yet to be studied. Here, we overexpressed hepcidin in astrocytes of the mouse brain and challenged the mice with amyloid-ß25-35 (Aß25-35) by intracerebroventricular injection. Our results revealed that hepcidin overexpression in astrocytes significantly ameliorated Aß25-35-induced cell damage in both the cerebral cortex and hippocampus. This protective role was also attested by behavioral tests of the mice. Our data further demonstrated that astrocyte-overexpressed hepcidin could decrease brain iron level, possibly by acting on ferroportin 1 (FPN1) on the brain microvascular endothelial cells (BMVECs), which in turn reduced Aß25-35-induced oxidative stress and apoptosis, and ultimately protected cells from damage. This study provided in vivo evidences of the important role of astrocyte hepcidin in the regulation of brain iron metabolism and protection against Aß-induced cortical and hippocampal damages and implied its potential in the treatment of oxidative stress-related brain disorders.

Astrocyte hepcidin ameliorates neuronal loss through attenuating brain iron deposition and oxidative stress in APP/PS1 mice.

Iron overload in the brain and iron-induced oxidative damage have been considered to play key roles in the pathogenesis of Alzheimer's disease (AD). Hepcidin is a peptide that regulates systemic iron metabolism by interacting with iron exporter ferroportin 1 (FPN1). Studies have indicated that the astrocyte hepcidin could regulate brain iron intake at the blood-brain barrier and injection of hepcidin into brain attenuated iron deposition in the brain. However, whether overexpression of hepcidin in astrocytes of APP/PS1 transgenic mice can alleviate AD symptoms by reducing iron deposition has not been evaluated. In this study, we overexpressed hepcidin in astrocytes of APP/PS1 mice and investigated its effects on ß-amyloid (Aß) aggregation, neuronal loss, iron deposition and iron-induced oxidative damages. Our results showed that the elevated expression of astrocyte hepcidin in APP/PS1 mice significantly improved their cognitive decline, and partially alleviated the formation of Aß plaques in cortex and hippocampus. Further investigations revealed that overexpression of hepcidin in astrocytes significantly reduced iron levels in cortex and hippocampus of APP/PS1 mice, especially iron content in neurons, which led to the reduction of iron accumulation-induced oxidative stress and neuroinflammation, and finally decreased neuronal cell death in the cortex and hippocampus of APP/PS1 mice. This study demonstrated that overexpression of hepcidin in astrocytes of APP/PS1 mice could partially alleviate AD symptoms and delay the pathological process of AD.

Nrf2 knockout dysregulates iron metabolism and increases the hemolysis through ROS in aging mice.

AIMS: Dysregulation of iron homeostasis in the body causes a variety of diseases. Iron deficiency leads to anemia, whereas iron overload aggravates cellular oxidative stress. Nuclear factor erythroid-2-related factor 2 (Nrf2) is a protein that is activated in the nucleus and turns on the production of antioxidant enzymes, protecting cell against oxidative damage. This study aimed to investigate whether Nrf2 gene knockout influences iron homeostasis in aging mice. MATERIALS AND METHODS: Iron content and iron metabolism-related proteins were assessed in different organs and blood serum of the 18 month-old Nrf2 knockout (Nrf2-/-) mice in comparison with the wild-type (WT) mice. KEY FINDINGS: Results showed that the iron contents in spleen and liver all increased, and expression levels of iron transporters were altered in Nrf2-/- mice. In particularly, we found that the expression of iron export protein ferroportin 1 (Fpn1) in liver, spleen and small intestine all decreased in Nrf2-/- mice, which might account for the deposition of iron in different organs and the increased ROS. Surprisingly, we found that the serum iron level of Nrf2-/- mice did not decrease, but increased significantly even when the iron absorption at small intestine decreased. Our further investigation revealed that the increase of serum iron was due to the release of iron from the hemolysis of erythrocytes, which caused by the increased ROS level in red blood cells of the Nrf2-/- mice. SIGNIFICANCE: These findings provide a more comprehensive understanding of the important role of Nrf2 in the regulation of systemic iron metabolism.

Sevoflurane anesthesia during pregnancy in mice induces cognitive impairment in the offspring by causing iron deficiency and inhibiting myelinogenesis.

Maternal anesthetic exposure during pregnancy is associated with an increased risk of cognitive impairment in offspring. The balance of cerebral iron metabolism is essential for the development of brain tissue. Iron deficiency affects the myelinogenesis and nerve tissue development, especially in fetus or infant, which has a key role in cognitive function. We aimed to investigate whether maternal sevoflurane (Sev) exposure caused cognitive impairment in offspring through inducing iron deficiency and inhibiting myelinogenesis. Pregnant mice (gestation stage day 14) were treated with 2% Sev for 6 h. Cognitive function of offspring mice was determined by the Morris water maze and Context fear conditioning test. Iron levels were assayed by Perl's iron staining and synchrotron imaging. Hippocampus and cortex tissues or cerebral microvascular endothelial cells of offspring mice (postnatal day 35) were harvested and subjected to Western blot and/or immunhistochemistry to assess ferritin, transferrin receptor 1(TfR1), Ferroportin-1 (FpN1), myelin basic protein (MBP), tight junction protein ZO-1, occludin, and claudin-5 levels. Beginning with postnatal day 30, the offspring were treated with iron therapy for 30 days, and the indicators above were tested. Our results showed Sev dramatically decreased the iron levels of brain and impaired cognitive function in offspring mice. Sev decreased the expression of heavy chain ferritin (FtH), light chain ferritin (FtL), MBP, ZO-1, occludin, claudin-5, and FpN1, and increased TfR1 in hippocampus and cortex or cerebral microvascular endothelial cells of offspring mice, indicating that Sev caused the iron deficiency and impaired the myelinogenesis in the brain of offspring. Interestingly, iron therapy prompted the myelinogenesis and improved impaired cognitive function at postnatal day 60. Our research uncovered a new mechanism which showed that iron deficiency induced by Sev and myelin formation disorder due to decreased iron of brain may be an important risk factor for cognitive impairment in offspring. It was necessary for offspring to be supplied iron supplement whose mother suffered exposure to sevoflurane during pregnancy.