Induction of FPN1 transcription by MTF-1 reveals a role for ferroportin in transition metal efflux

Asiatic acid ameliorates doxorubicin-induced cardiotoxicity by promoting FPN-mediated iron export and inhibiting ferroptosis

Doxorubicin (DOX), a common chemotherapeutic agent in cancer therapy, is accompanied by pronounced cardiotoxicity. Ferroptosis has been implicated in the pathogenesis and therapeutics of DOX-induced cardiotoxicity (DIC). Asiatic acid (AA), a pentacyclic triterpene from the Chinese medicinal herb Centella asiatica, displays antioxidant, anti-inflammatory, and antiapoptotic activities. In this study, we investigated the beneficial effects of AA against DOX-induced ferroptosis and cardiotoxicity and the underlying mechanisms. A chronic DIC model was established by challenging mice with DOX (5 mg/kg, i.p.) once per week for 4 weeks. Concurrent with DOX insult, the mice were administered AA (25 mg·kg-1·d-1, i.g.). Cardiac function and mechanical properties of isolated cardiomyocytes were evaluated at the end of treatment. We showed that AA administration preserved cardiac function, significantly reduced cardiac injury, and improved cardiomyocyte contractile function in DIC mice. The beneficial effects of AA were causally linked to the inhibition of DOX-induced ferroptosis both in vivo and in vitro. We revealed that AA attenuated DOX-induced iron accumulation in HL-1 cells by increasing FPN-mediated iron export, in a Nrf2-dependent manner. AA upregulated Nrf2 expression and promoted Nrf2 nuclear translocation in DOX-treated HL-1 cells. Moreover, AA-offered benefits against DOX-induced cardiac dysfunction and ferroptosis were abolished by Nrf2 inhibitor ML385 (30 mg·kg-1·d-1, i.p.) administrated 30 min before AA in DIC mice. Our data favor that AA promotes FPN-mediated iron export to inhibit iron overload and ferroptosis in DIC, suggesting its therapeutic potential in the treatment of DIC.

Expression and Functional Analysis of the Metallothionein and Metal-Responsive Transcription Factor 1 in Phascolosoma esculenta under Zn Stress

Metallothioneins (MTs) are non-enzymatic metal-binding proteins widely found in animals, plants, and microorganisms and are regulated by metal-responsive transcription factor 1 (MTF1). MT and MTF1 play crucial roles in detoxification, antioxidation, and anti-apoptosis. Therefore, they are key factors allowing organisms to endure the toxicity of heavy metal pollution. Phascolosoma esculenta is a marine invertebrate that inhabits intertidal zones and has a high tolerance to heavy metal stress. In this study, we cloned and identified MT and MTF1 genes from P. esculenta (designated as PeMT and PeMTF1). PeMT and PeMTF1 were widely expressed in all tissues and highly expressed in the intestine. When exposed to 16.8, 33.6, and 84 mg/L of zinc ions, the expression levels of PeMT and PeMTF1 in the intestine increased first and then decreased, peaking at 12 and 6 h, respectively, indicating that both PeMT and PeMTF1 rapidly responded to Zn stress. The recombinant pGEX-6p-1-MT protein enhanced the Zn tolerance of Escherichia coli and showed a dose-dependent ABTS free radical scavenging ability. After RNA interference (RNAi) with PeMT and 24 h of Zn stress, the oxidative stress indices (MDA content, SOD activity, and GSH content) and the apoptosis indices (Caspase 3, Caspase 8, and Caspase 9 activities) were significantly increased, implying that PeMT plays an important role in Zn detoxification, antioxidation, and anti-apoptosis. Moreover, the expression level of PeMT in the intestine was significantly decreased after RNAi with PeMTF1 and 24 h of Zn stress, which preliminarily proved that PeMTF1 has a regulatory effect on PeMT. Our data suggest that PeMT and PeMTF1 play important roles in the resistance of P. esculenta to Zn stress and are the key factors allowing P. esculenta to endure the toxicity of Zn.

Integrating Transcriptomics and Proteomics to Characterize the Intestinal Responses to Cadmium Exposure Using a Piglet Model

Cadmium (Cd) is a heavy metal element with a wide range of hazards and severe biotoxicity. Since Cd can be easily accumulated in the edible parts of plants, the exposure of humans to Cd is mainly through the intake of Cd-contaminated food. However, the intestinal responses to Cd exposure are not completely characterized. Herein, we simulated laboratory and environmental Cd exposure by feeding the piglets with CdCl2-added rice and Cd-contaminated rice (Cdcr) contained diet, as piglets show anatomical and physiological similarities to humans. Subsequent analysis of the metal element concentrations showed that exposure to the two types of Cd significantly increased Cd levels in piglets. After verifying the expression of major Cd transporters by Western blots, multi-omics further expanded the possible transporters of Cd and found Cd exposure causes wide alterations in the metabolism of piglets. Of significance, CdCl2 and Cdcr exhibited different body distribution and metabolic rewiring, and Cdcr had stronger carcinogenic and diabetes-inducing potential. Together, our results indicate that CdCl2 had a significant difference compared with Cdcr, which has important implications for a more intense study of Cd toxicity.

Cadmium exposure induced neuronal ferroptosis and cognitive deficits via the mtROS-ferritinophagy pathway

Exposure to environmental cadmium (Cd) is known to cause neuronal death and cognitive decline in humans. Ferroptosis, a novel iron-dependent type of regulated cell death, is involved in various neurological disorders. In the present study, Cd exposure triggered ferroptosis in the mouse hippocampus and in the HT22 murine hippocampal neuronal cell line, as indicated by significant increases in ferroptotic marker expression, intracellular iron levels, and lipid peroxidation. Interestingly, ferroptosis of hippocampal neurons in response to Cd exposure relied on the induction of autophagy since the suppression of autophagy by 3-methyladenine (3-MA) and chloroquine (CQ) substantially ameliorated Cd-induced ferroptosis. Furthermore, nuclear receptor coactivator 4 (NCOA4)-mediated degradation of ferritin was required for the Cd-induced ferroptosis of hippocampal neurons, demonstrating that NCOA4 knockdown decreased intracellular iron levels and lipid peroxidation and increased cell survival, following Cd exposure. Moreover, Cd-induced mitochondrial reactive oxygen species (mtROS) generation was essential for the ferritinophagy-mediated ferroptosis of hippocampal neurons. Importantly, pretreatment with the ferroptosis inhibitor ferrostatin-1 (Fer-1) effectively attenuated Cd-induced hippocampal neuronal death and cognitive impairment in mice. Taken together, these findings indicate that ferroptosis is a novel mechanism underlying Cd-induced neurotoxicity and cognitive impairment and that the mtROS-ferritinophagy axis modulates Cd-induced neuronal ferroptosis.

Ferroptosis as a Therapeutic Target in Subarachnoid Hemorrhage

Subarachnoid hemorrhage (SAH) is a cerebrovascular disorder with significant mortality and morbidity. Neural injury in SAH is mediated through a variety of pathophysiological processes. Currently available treatments are either nonspecific in targeting the basic pathophysiological mechanisms that result in neural damage in SAH, or merely focus on vasospasm. Ferroptosis is a type of programmed iron dependent cell death, which has received attention due to its possible role in neural injury in SAH. Herein, we review how intracellular iron overload mediates the production of reactive free radicals and lipid peroxidation through a variety of biochemical pathways in SAH. This in turn results in induction of ferroptosis, as well as exacerbation of vasospasm. We also discuss several therapeutic agents that have been shown to inhibit ferroptosis through targeting different steps of the process. Such agents have proven effective in ameliorating vasospasm, neural damage, and neurobehavioral outcomes in animal models of SAH. Human studies to test the safety and efficacy of intrathecal or parenteral administration of the inhibitors of ferroptosis in improving outcomes of SAH patients are warranted. There are currently a few ongoing clinical trials pursuing this therapeutic concept, the results of which will be critical to determine the value of ferroptosis as a novel therapeutic target in SAH.

From zinc homeostasis to disease progression: Unveiling the neurodegenerative puzzle

Zinc is a crucial trace element in the human body, playing a role in various physiological processes such as oxidative stress, neurotransmission, protein synthesis, and DNA repair. The zinc transporters (ZnTs) family members are responsible for exporting intracellular zinc, while Zrt- and Irt-like proteins (ZIPs) are involved in importing extracellular zinc. These processes are essential for maintaining cellular zinc homeostasis. Imbalances in zinc metabolism have been linked to the development of neurodegenerative diseases. Disruptions in zinc levels can impact the survival and activity of neurons, thereby contributing to the progression of neurodegenerative diseases through mechanisms like cell apoptosis regulation, protein phase separation, ferroptosis, oxidative stress, and neuroinflammation. Therefore, conducting a systematic review of the regulatory network of zinc and investigating the relationship between zinc dysmetabolism and neurodegenerative diseases can enhance our understanding of the pathogenesis of these diseases. Additionally, it may offer new insights and approaches for the treatment of neurodegenerative diseases.

Ferroptosis-related gene MTF-1 as a novel prognostic biomarker in low-grade glioma and its correlation with immune infiltration

Background

Metal-responsive transcription factor-1 performs a necessary position in a range of cancers. It is unknown, though, how the prognosis of patients with low-grade gliomas is related to immune infiltration.

Method

The Cancer Genome Atlas database was used in this investigation to evaluate MTF-1 transcription in low-grade glioma and healthy brain tissues, and immunohistochemistry was used to confirm MTF-1 levels. By using functional enrichment analysis and R software, the putative biological roles and signaling pathways connected to MTF-1 in LGG as well as its prognostic significance were investigated. Further research was done on the connection involving MTF-1 and tumor mutational burden in LGG. Finally, the research evaluated how MTF-1 and immune cell infiltration are related.

Results

We noticed that the WHO grade, 1p/19q codeletion, and older age were all substantially linked with MTF-1 overexpression in low-grade gliomas. OS and disease-specific survival were significantly lowered as a result of MTF-1 transcription. MTF-1 was recognized as an independent OS prognostic predictor with a poor prognosis by multifactorial Cox analysis. Functional enrichment analysis revealed that the primary enrichment pathways were chemical carcinogenesis-receptor activation and the generation of miRNAs implicated in gene suppression by miRNA. Additionally, there was a negative correlation between MTF-1 overexpression and the degree of immune cell infiltration in neutrophils and DC.

Conclusion

MTF-1 may be a novel prognostic biomarker.

Macrophage metallothioneins participate in the antileishmanial activity of antimonials

Host cell functions that participate in the pharmacokinetics and pharmacodynamics (PK/PD) of drugs against intracellular pathogen infections are critical for drug efficacy. In this study, we investigated whether macrophage mechanisms of xenobiotic detoxification contribute to the elimination of intracellular Leishmania upon exposure to pentavalent antimonials (SbV). Primary macrophages from patients with cutaneous leishmaniasis (CL) (n=6) were exposed ex vivo to L. V. panamensis infection and SbV, and transcriptomes were generated. Seven metallothionein (MT) genes, potent scavengers of heavy metals and central elements of the mammalian cell machinery for xenobiotic detoxification, were within the top 20 up-regulated genes. To functionally validate the participation of MTs in drug-mediated killing of intracellular Leishmania, tandem knockdown (KD) of MT2-A and MT1-E, MT1-F, and MT1-X was performed using a pan-MT shRNA approach in THP-1 cells. Parasite survival was unaffected in tandem-KD cells, as a consequence of strong transcriptional upregulation of MTs by infection and SbV, overcoming the KD effect. Gene silencing of the metal transcription factor-1 (MTF-1) abrogated expression of MT1 and MT2-A genes, but not ZnT-1. Upon exposure to SbV, intracellular survival of Leishmania in MTF-1KD cells was significantly enhanced. Results from this study highlight the participation of macrophage MTs in Sb-dependent parasite killing.

Study on the Zinc Nutritional Status and Risk Factors of Chinese 6–18-Year-Old Children

Zinc is an essential micronutrient that is involved in several metabolic processes, especially children’s growth and development. Although many previous studies have evaluated the zinc nutritional status of children, there are very few reports on children aged 6–18 years old. Furthermore, there are few reports on children’s zinc nutrition status based on the Chinese population. According to WHO data, the prevalence of zinc deficiency in Asian countries is rather high and has resulted in high child mortality. In this study, we aimed to comprehensively assess zinc nutritional status and the prevalence of zinc deficiency among children aged 6–18 years in China based on nationally representative cross-sectional data. Subgroup comparisons were made under possible influencing factors. The potential risk factors of zinc deficiency were also discussed. A total of 64,850 children, equally male and female, were recruited from 150 monitoring sites in 31 provinces through stratified random sampling from China National Nutrition and Health Survey of Children and Lactating Mothers (CNNHS 2016–2017). Median and interquartile intervals were used to represent the overall zinc concentration levels and different subgroups. A Chi-square test was used to compare serum zinc levels and the prevalence of zinc deficiency in children under different group variables. In order to study the influencing factors of zinc deficiency, multiple logistic regression was utilized. It was found that the median concentration of serum Zn was 88.39 μg/dL and the prevalence of Zn deficiency was 9.62%. The possible influence factors for Zn deficiency were sex, anemia, nutritional status, city type and income. By conducting a subgroup analysis of the factors, it was found that males; those with anemia, stunting and low income; and children living in rural areas have a higher risk of Zn deficiency. This study offers a comprehensive analysis of Zn nutritional status among Chinese children, which provides reliable data for policy formulation to improve the zinc nutrition status of children.

Elucidating the progress and impact of ferroptosis in hemorrhagic stroke

Hemorrhagic stroke is a devastating cerebrovascular disease with high morbidity and mortality, for which effective therapies are currently unavailable. Based on different bleeding sites, hemorrhagic stroke can be generally divided into intracerebral hemorrhage (ICH) and subarachnoid hemorrhage (SAH), whose pathogenesis share some similarity. Ferroptosis is a recently defined programmed cell deaths (PCDs), which is a critical supplement to the hypothesis on the mechanism of nervous system injury after hemorrhagic stroke. Ferroptosis is characterized by distinctive morphological changes of mitochondria and iron-dependent accumulation of lipid peroxides. Moreover, scientists have successfully demonstrated the involvement of ferroptosis in animal models of ICH and SAH, indicating that ferroptosis is a promising target for hemorrhagic stroke therapy. However, the studies on ferroptosis still faces a serious of technical and theoretical challenges. This review systematically elaborates the role of ferroptosis in the pathogenesis of hemorrhagic stroke and puts forward some opinions on the dilemma of ferroptosis research.

Mitochondrial Iron Metabolism: The Crucial Actors in Diseases

Iron is a trace element necessary for cell growth, development, and cellular homeostasis, but insufficient or excessive level of iron is toxic. Intracellularly, sufficient amounts of iron are required for mitochondria (the center of iron utilization) to maintain their normal physiologic function. Iron deficiency impairs mitochondrial metabolism and respiratory activity, while mitochondrial iron overload promotes ROS production during mitochondrial electron transport, thus promoting potential disease development. This review provides an overview of iron homeostasis, mitochondrial iron metabolism, and how mitochondrial iron imbalances-induced mitochondrial dysfunction contribute to diseases.

The cGAS-STING-autophagy pathway: Novel perspectives in neurotoxicity induced by manganese exposure

Chronic high-level heavy metal exposure increases the risk of developing different neurodegenerative diseases. Chronic excessive manganese (Mn) exposure is known to lead to neurodegenerative diseases. In addition, some evidence suggests that autophagy dysfunction plays an important role in the pathogenesis of various neurodegenerative diseases. Over the past decade, the DNA-sensing receptor cyclic GMP-AMP synthase (cGAS) and its downstream signal-efficient interferon gene stimulator (STING), as well as the molecular composition and regulatory mechanisms of this pathway have been well understood. The cGAS-STING pathway has emerged as a crucial mechanism to induce effective innate immune responses by inducing type I interferons in mammalian cells. Moreover, recent studies have found that Mn²⁺ is the second activator of the cGAS-STING pathway besides dsDNA, and inducing autophagy is a primitive function for the activation of the cGAS-STING pathway. However, overactivation of the immune response can lead to tissue damage. This review discusses the mechanism of neurotoxicity induced by Mn exposure from the cGAS-STING-autophagy pathway. Future work exploiting the cGAS-STING-autophagy pathway may provide a novel perspective for manganese neurotoxicity.

Nano-selenium alleviates cadmium-induced cerebellar injury by activating metal regulatory transcription factor 1 mediated metal response

This study aims to investigate the role of metal regulatory transcription factor 1 (MTF1)-mediated metal response in cadmium (Cd)-induced cerebellar injury, and to evaluate the antagonistic effects of nano-selenium (Nano-Se) against Cd toxicity. A total of 80 chicks (1 d old, male, Hy-Line Variety White) were randomly allocated to 4 treatment groups for 3 months: the control group (fed with a basic diet, n = 20), the Nano-Se group (basic diet with 1 mg/kg nano-Se 1 mg/kg Nano-Se in basic diet, n = 20), the Nano-Se + Cd group (basic diet with 1 mg/kg Nano-Se and 140 mg/kg CdCl₂, n = 20) and the Cd group (basic diet with 140 mg/kg CdCl₂ , n = 20). The results of the experiment showed that the Purkinje cells were significantly decreased with their degradation and indistinct nucleoli after Cd exposure. Moreover, exposure to Cd caused a significant accumulation of Cd and cupper. However, the contents of Se, iron, and zinc were decreased, thereby disturbing the metal homeostasis in the cerebellum. The Cd exposure also resulted in high levels of malondialdehyde (MDA) and down regulation of selenoprotein transcriptome. Furthermore, the expressions of MTF1, metallothionein 1 (MT1), MT2, zinc transporter 3 (ZNT3), ZNT5, ZNT10, zrt, irt-like protein 8 (ZIP8), ZIP10, transferrin (TF), ferroportin 1 (FPN1), ATPase copper transporting beta (ATP7B), and copper uptake protein 1 (CTR1) were inhibited by Cd exposure. However, all these changes were significantly alleviated by the supplementation of Nano-Se. This study proved that Cd could disorder metal homeostasis and induce oxidative stress, whereas Nano-Se could relieve all these negative effects caused by Cd via activating the MTF1-mediated metal response in the cerebellum of chicken.

Emerging Mechanisms and Targeted Therapy of Ferroptosis in Neurological Diseases and Neuro-oncology

Ferroptosis is a novel type of cell death characterized by iron-dependent lipid peroxidation that involves a variety of biological processes, such as iron metabolism, lipid metabolism, and oxidative stress. A growing body of research suggests that ferroptosis is associated with cancer and neurodegenerative diseases, such as glioblastoma, Alzheimer's disease, Parkinson's disease, and stroke. Building on these findings, we can selectively induce ferroptosis for the treatment of certain cancers, or we can treat neurodegenerative diseases by inhibiting ferroptosis. This review summarizes the relevant advances in ferroptosis, the regulatory mechanisms of ferroptosis, the participation of ferroptosis in brain tumors and neurodegenerative diseases, and the corresponding drug therapies to provide new potential targets for its treatment.

Cadmium Accumulation in the Goat Liver and Kidney Is Partially Promoted by the Upregulation of Metal Transporter Genes

Metal transporters, including divalent metal-ion transporter-1 (DMT1), Zrt-/Irt-like protein 8 and 14 (ZIP8 and ZIP14), and ferroportin-1 (FPN1), reportedly participate in cellular cadmium (Cd) uptake, but those in farm animals remain unclarified. This study aimed to examine the growth, plasma biochemical indices, Cd accumulation, and expression of metal transporter genes in the liver, kidney, and muscle of goats exposed to rice paddies contaminated with different levels of Cd. Twenty-four goats were randomly assigned across three dietary treatments: 0.23, 0.63, and 1.07 mg of Cd/kg of dry matter (DM) for 60 days. The results showed that dietary Cd exposure increased (p < 0.05) both Cd accumulation and the mRNA expressions of metal transporter genes (DMT1, ZIP, and FPN1) in the liver and kidney but not in the muscle, suggesting dietary Cd exhibited different deposition rates between goat liver, kidney, and muscle. These outcomes suggest that high levels of dietary Cd stimulated the expression of metal transporter genes and thereby enhanced the uptake and accumulation of Cd in the goat liver and kidney. As such, higher Cd concentrations in the liver and kidney observed with Cd diets could be partly explained by upregulation of metal transport genes expression.

Transcriptome analysis of developing zebrafish (Danio rerio) embryo following exposure to Gaudichaudione H reveals teratogenicity and cardiovascular defects caused by abnormal iron metabolism

Gaudichaudione H (GH), a caged polyprenylated xanthone from Garcinia plants, showed anti-cancer and anti-inflammatory effects in vitro. However, the in vivo toxicity of this compound has never been reported. The present study was aimed to address the toxic effects of Gaudichaudione H using zebrafish embryos and larvae as an in vivo test model. The zebrafish embryos were treated with GH having different concentrations (0, 0.28, 0.38 and 0.57 μg/mL). The results revealed that GH induces significant embryonic mortality, decreased heartbeat, cardiotoxicity, cardiovascular defects, increased apoptosis and decreased hemoglobinization in zebrafish embryos and larvae. According to transcriptome analysis, 1841 genes were significantly differentially expressed (1185 down-regulated and 656 up-regulated) after GH treatment. The main functions of these genes were related to iron metabolism pathways. The toxicity of GH on zebrafish embryonic development and cardiovascular may due to large amounts of downregulated genes involved in metabolic pathways and DEGs related to 'Iron ion binding' and 'Heme binding' functions.

Mitochondrial oxidative stress mediated Fe-induced ferroptosis via the NRF2-ARE pathway

Ferroptosis is a regulated form of cell death induced by iron (Fe)-dependent lipid peroxidation. At present, the underlying molecular mechanisms remain elusive. Herein, we hypothesized that mitochondria and the NRF2 (transcription factor nuclear factor E2-related factor 2) are potential mediators of ferroptosis, considering their well-established involvement in the oxidative stress pathway. We found that a high iron diet increased hepatic iron content and promoted glutathione (GSH) depletion, lipid peroxidation and oxidative stress. Dietary iron overload also decreased mRNA and protein expression levels of glutathione peroxidase 4 (GPX4) and cystine-glutamate antiporter (SLC7A11), and increased mRNA and protein expression of acyl-CoA synthetase long-chain family member 4 (ACSL4), which are all markers of ferroptosis. Consistent with ferroptosis, iron overload promoted lipid peroxidation and the generation of mitochondrial reactive oxygen species (ROS), and decreased the mitochondrial membrane potential (MMP). Pre-treatment with deferoxamine mesylate (DFO, an iron chelator) alleviated ROS generation and lipid peroxidation, indicating a causative link between iron overload and lipid peroxidation. Suppression of mitochondrial oxidative stress attenuated ferroptosis. Experiments with HEK293T cells revealed that Fe-induced ferroptosis involved direct inhibition of NRF2 binding to antioxidant response elements (AREs) within the promoters of the gpx4 and slc7a11 genes, which in turn induced transcriptional silencing. In conclusion, our study provided a direct link between mitochondrial oxidative stress and ferroptosis via the NRF2-ARE pathway.

Hepatic Homeostasis of Metal Ions Following Acute Repeated Stress Exposure in Rats

Essential metals such as copper, iron, and zinc are cofactors in various biological processes including oxygen utilisation, cell growth, and biomolecular synthesis. The homeostasis of these essential metals is carefully controlled through a system of protein transporters involved in the uptake, storage, and secretion. Some metal ions can be transformed by processes including reduction/oxidation (redox) reactions, and correspondingly, the breakdown of metal ion homeostasis can lead to formation of reactive oxygen and nitrogen species. We have previously demonstrated rapid biochemical responses to stress involving alterations in the redox state to generate free radicals and the resultant oxidative stress. However, the effects of stress on redox-active metals including iron and copper and redox-inert zinc have not been well characterised. Therefore, this study aims to examine the changes in these essential metals following exposure to short-term repeated stress, and to further elucidate the alterations in metal homeostasis through expression analysis of different metal transporters. Outbred male Wistar rats were exposed to unrestrained (control), 1 day, or 3 days of 6 h restraint stress (n = 8 per group). After the respective stress treatment, blood and liver samples were collected for the analysis of biometal concentrations and relative gene expression of metal transporter and binding proteins. Exposure to repeated restraint stress was highly effective in causing hepatic redox imbalance. Stress was also shown to induce hepatic metal redistribution, while modulating the mRNA levels of key metal transporters. Overall, this study is the first to characterise the gene expression profile of metal homeostasis following stress and provide insight into the changes occurring prior to the onset of chronic stress conditions.

A detrimental role of NLRP6 in host iron metabolism during Salmonella infection

Maintaining host iron homeostasis is an essential component of nutritional immunity responsible for sequestrating iron from pathogens and controlling infection. Nucleotide-oligomerization domain-like receptors (NLRs) contribute to cytoplasmic sensing and antimicrobial response orchestration. However, it remains unknown whether and how NLRs may regulate host iron metabolism, an important component of nutritional immunity. Here, we demonstrated that NLRP6, a member of the NLR family, has an unconventional role in regulating host iron metabolism that perturbs host resistance to bacterial infection. NLRP6 deficiency is advantageous for maintaining cellular iron homeostasis in both macrophages and enterocytes through increasing the unique iron exporter ferroportin-mediated iron efflux in a nuclear factor erythroid-derived 2–related factor 2 (NRF2)-dependent manner. Additional studies uncovered a novel mechanism underlying NRF2 regulation and operating through NLRP6/AKT interaction and that causes a decrease in AKT phosphorylation, which in turn reduces NRF2 nuclear translocation. In the absence of NLRP6, increased AKT activation promotes NRF2/KEAP1 dissociation via increasing mTOR-mediated p62 phosphorylation and downregulates KEAP1 transcription by promoting FOXO3A phosphorylation. Together, our observations provide new insights into the mechanism of nutritional immunity by revealing a novel function of NLRP6 in regulating iron metabolism, and suggest NLRP6 as a therapeutic target for limiting bacterial iron acquisition.

Effect of zinc depletion/repletion on intestinal iron absorption and iron status in rats

Iron and zinc deficiencies likely coexist in general population. We have previously demonstrated that zinc treatment induces while zinc deficiency inhibits iron absorption in intestinal cell culture models, but this needs to be tested in vivo. In the present study we assessed intestinal iron absorption, iron status (haemoglobin), red blood cell number, plasma ferritin, transferrin receptor, hepcidin) and tissue iron levels in zinc depleted, replete and pair fed control rats. Zinc depletion led to reduction in body weight, tissue zinc levels, intestinal iron absorption, protein and mRNA expression of iron transporters, the divalent metal ion transporter-1, hephaestin and ferroportin, but elevated the intestinal and liver tissue iron levels compared with the pair fed control rats. Zinc repletion led to a significant weight gain compared to zinc deficient rats and normalized the iron absorption, iron transporter expression, tissue iron levels to that of pair fed control rats. Surprisingly, haemoglobin levels and red blood cell number reduced significantly in zinc repleted rats, which could be due to rapid weight gain. Together, these results indicate that whole body zinc status has profound influence on growth, intestinal absorption and systemic utilization of iron, mediated via modulation of iron transporter expression.

Cadmium induced cerebral toxicity via modulating MTF1-MTs regulatory axis

Metal-responsive transcription factor 1 (MTF1) participates in redox homeostasis and heavy metals detoxification via regulating the expression of metal responsive genes. However, the exact role of MTF1 in Cd-induced cerebral toxicity remains unclear. Herein, we explored the mechanism of Cd-elicited cerebral toxicity through modulating MTF1/MTs pathway in chicken cerebrum exposed to different concentrations of Cd (35 mg, 70 mg, and 140 mg/kg CdCl₂) via diet. Notably, cerebral tissues showed varying degrees of microstructural changes under Cd exposure. Cd exposure significantly up-regulated the expression of metal transporters (DMT1, ZIP8, and ZIP10) with concomitant elevated Cd level, as determined by ICP-MS. Cd significantly altered other cerebral biometals concentrations (particularly, Zn, Fe, Se, Cr, Mo, and Pb) and redox balance, resulting in increased cerebral oxidative stress. More importantly, Cd exposure suppressed MTF1 mRNA and nuclear protein levels and its target metal-responsive genes, notably metallothioneins (MT1 and MT2), and Fe and Cu transporter genes (FPN1, ATOX1, and XIAP). Moreover, Cd disrupted the regulation of expression of selenoproteome (particularly, GPxs and SelW), and cerebral Se level. Overall, our data revealed that molecular mechanisms associated with Cd-induced cerebral damage might include over-expression of DMT1, ZIP8 and ZIP10, and suppression of MTF1 and its main target metal-responsive genes as well as several selenoproteins.

MAFG-AS1/MAFG positive feedback loop contributes to cisplatin resistance in bladder urothelial carcinoma through antagonistic ferroptosis

Though promoting ferroptosis can reduce cisplatin resistance in tumor cells, ferroptosis and cisplatin resistance in bladder urothelial carcinoma (BUC) following long non-coding RNAs (lncRNAs) is largely unknown. Here, we found the highly expressed lncRNA MAF transcription factor G antisense RNA 1 (MAFG-AS1) in BUC, and its inhibition increased the sensitivity of BUC cells to cisplatin by promoting ferroptosis. Mechanically, binding to iron chaperone poly(rC)-binding protein 2 (PCBP2) facilitated the recruitments of MAFG-AS1 to deubiquitinase ubiquitin carboxyl-terminal hydrolase isozyme L5 (UCHL5), thus stabilizing PCBP2 protein itself. Then PCBP2 was confirmed to interact with ferroportin 1 (FPN1), an iron export protein, leading to inhibition of ferroptosis. Moreover, the expression of MAFG-AS1 was regulated by the transcriptional factor MAFG. Interestingly, MAFG-AS1 stimulated MAFG transcription by recruiting histone acetyltransferase p300 (EP300) to promote the histone 3 at lysine 27 (H3K27ac) at genomic locus of MAFG, forming a MAFG-AS1/MAFG positive feedback loop. In patient samples, higher expression of MAFG-AS1 and MAFG in BUC tissues was significantly correlated with T status and N status, such that MAFG-AS1, MAFG, and the combination of the two were independent prognostic indicators and chemotherapy sensitivity predictive biomarkers for BUC patients. These findings suggest that inhibition of MAFG-AS1 and MAFG can increase the sensitivity of BUC cells to cisplatin through promoting ferroptosis, indicating the novel chemotherapy sensitivity biomarkers and therapeutic target for BUC.

Effect of the Forth and Fifth Zinc Finger Deletions of MTF-1 on the Expression of Metal Ion Metabolism Related Gene

Metal response element binding transcription factor 1 (MTF-1) is one of the important regulatory proteins involved in the mediation of intracellular metal ion balance, which is zinc dependent. The changes of zinc finger effected its function. MTF-1 mutant 293T cell line was obtained by transferring the vector of MTF-1 4th or 5th mutant zinc finger into 293T cell line that knocked out MTF-1 gene. The results showed that the mutant of 4th zinc finger in MTF-1 protein showed a significant difference on target gene expression compared with 5th zinc finger. Further RNA-seq assay showed that 4th and 5th zinc finger of MTF-1 have a different effect on molecular biological functions, cellular components, and biological process. The mutant of 4th and 5th zinc finger in MTF-1 protein changed different signaling pathways and metal ion metabolism related to genes. The present study evaluated that 4th or 5th mutant zinc finger in MTF-1 gene were associated with the function of MTF-1 protein.

The Role of Copper in the Regulation of Ferroportin Expression in Macrophages

The critical function of ferroportin (Fpn) in maintaining iron homeostasis requires complex and multilevel control of its expression. Besides iron-dependent cellular and systemic control of Fpn expression, other metals also seem to be involved in regulating the Fpn gene. Here, we found that copper loading significantly enhanced Fpn transcription in an Nrf2-dependent manner in primary bone-marrow-derived macrophages (BMDMs). However, prolonged copper loading resulted in decreased Fpn protein abundance. Moreover, CuCl₂ treatment induced Fpn expression in RAW 264.7 macrophages at both the mRNA and protein level. These data suggest that cell-type-specific regulations have an impact on Fpn protein stability after copper loading. Transcriptional suppression of Fpn after lipopolysaccharide (LPS) treatment contributes to increased iron storage inside macrophages and may result in anemia of inflammation. Here, we observed that in both primary BMDMs and RAW 264.7 macrophages, LPS treatment significantly decreased Fpn mRNA levels, but concomitant CuCl₂ stimulation counteracted the transcriptional suppression of Fpn and restored its expression to the control level. Overall, we show that copper loading significantly enhances Fpn transcription in macrophages, while Fpn protein abundance in response to CuCl₂ treatment, depending on macrophage type and factors specific to the macrophage population, can influence Fpn regulation in response to copper loading.

The transfer of trace metals in the soil-plant-arthropod system

Essential and non-essential trace metals are capable of causing toxicity to organisms above a threshold concentration. Extensive research has assessed the behaviour of trace metals in biological and ecological systems, but has typically focused on single organisms within a trophic level and not on multi-trophic transfer through terrestrial food chains. This reinforces the notion of metal toxicity as a closed system, failing to consider one trophic level as a pollution source to another; therefore, obscuring the full extent of ecosystem effects. Given the relatively few studies on trophic transfer of metals, this review has taken a compartment-based approach, where transfer of metals through trophic pathways is considered as a series of linked compartments (soil-plant-arthropod herbivore-arthropod predator). In particular, we consider the mechanisms by which trace metals are taken up by organisms, the forms and transformations that can occur within the organism and the consequences for trace metal availability to the next trophic level. The review focuses on four of the most prevalent metal cations in soil which are labile in terrestrial food chains: Cd, Cu, Zn and Ni. Current knowledge of the processes and mechanisms by which these metals are transformed and moved within and between trophic levels in the soil-plant-arthropod system are evaluated. We demonstrate that the key factors controlling the transfer of trace metals through the soil-plant-arthropod system are the form and location in which the metal occurs in the lower trophic level and the physiological mechanisms of each organism in regulating uptake, transformation, detoxification and transfer. The magnitude of transfer varies considerably depending on the trace metal concerned, as does its toxicity, and we conclude that biomagnification is not a general property of plant-arthropod and arthropod-arthropod systems. To deliver a more holistic assessment of ecosystem toxicity, integrated studies across ecosystem compartments are needed to identify critical pathways that can result in secondary toxicity across terrestrial food-chains.

Gawky modulates MTF-1-mediated transcription activation and metal discrimination

Metal-induced genes are usually transcribed at relatively low levels under normal conditions and are rapidly activated by heavy metal stress. Many of these genes respond preferentially to specific metal-stressed conditions. However, the mechanism by which the general transcription machinery discriminates metal stress from normal conditions and the regulation of MTF-1-meditated metal discrimination are poorly characterized. Using a focused RNAi screening in Drosophila Schneider 2 (S2) cells, we identified a novel activator, the Drosophila gawky, of metal-responsive genes. Depletion of gawky has almost no effect on the basal transcription of the metallothionein (MT) genes, but impairs the metal-induced transcription by inducing the dissociation of MTF-1 from the MT promoters and the deficient nuclear import of MTF-1 under metal-stressed conditions. This suggests that gawky serves as a 'checkpoint' for metal stress and metal-induced transcription. In fact, regular mRNAs are converted into gawky-controlled transcripts if expressed under the control of a metal-responsive promoter, suggesting that whether transcription undergoes gawky-mediated regulation is encrypted therein. Additionally, lack of gawky eliminates the DNA binding bias of MTF-1 and the transcription preference of metal-specific genes. This suggests a combinatorial control of metal discrimination by gawky, MTF-1, and MTF-1 binding sites.

Human ferroportin mediates proton-coupled active transport of iron

As the sole iron exporter in humans, ferroportin controls systemic iron homeostasis through exporting iron into the blood plasma. The molecular mechanism of how ferroportin exports iron under various physiological settings remains unclear. Here we found that purified ferroportin incorporated into liposomes preferentially transports Fe2+ and exhibits lower affinities of transporting other divalent metal ions. The iron transport by ferroportin is facilitated by downhill proton gradients at the same direction. Human ferroportin is also capable of transporting protons, and this activity is tightly coupled to the iron transport. Remarkably, ferroportin can conduct active transport uphill against the iron gradient, with favorable charge potential providing the driving force. Targeted mutagenesis suggests that the iron translocation site is located at the pore region of human ferroportin. Together, our studies enhance the mechanistic understanding by which human ferroportin transports iron and suggest that a combination of electrochemical gradients regulates iron export.

The hypoxia sensitive metal transcription factor MTF-1 activates NCX1 brain promoter and participates in remote postconditioning neuroprotection in stroke

Remote limb ischemic postconditioning (RLIP) is an experimental strategy in which short femoral artery ischemia reduces brain damage induced by a previous harmful ischemic insult. Ionic homeostasis maintenance in the CNS seems to play a relevant role in mediating RLIP neuroprotection and among the effectors, the sodium-calcium exchanger 1 (NCX1) may give an important contribution, being expressed in all CNS cells involved in brain ischemic pathophysiology. The aim of this work was to investigate whether the metal responsive transcription factor 1 (MTF-1), an important hypoxia sensitive transcription factor, may (i) interact and regulate NCX1, and (ii) play a role in the neuroprotective effect mediated by RLIP through NCX1 activation. Here we demonstrated that in brain ischemia induced by transient middle cerebral occlusion (tMCAO), MTF-1 is triggered by a subsequent temporary femoral artery occlusion (FAO) and represents a mediator of endogenous neuroprotection. More importantly, we showed that MTF-1 translocates to the nucleus where it binds the metal responsive element (MRE) located at -23/-17 bp of Ncx1 brain promoter thus activating its transcription and inducing an upregulation of NCX1 that has been demonstrated to be neuroprotective. Furthermore, RLIP restored MTF-1 and NCX1 protein levels in the ischemic rat brain cortex and the silencing of MTF-1 prevented the increase of NCX1 observed in RLIP protected rats, thus demonstrating a direct regulation of NCX1 by MTF-1 in the ischemic cortex of rat exposed to tMCAO followed by FAO. Moreover, silencing of MTF-1 significantly reduced the neuroprotective effect elicited by RLIP as demonstrated by the enlargement of brain infarct volume observed in rats subjected to RLIP and treated with MTF-1 silencing. Overall, MTF-dependent activation of NCX1 and their upregulation elicited by RLIP, besides unraveling a new molecular pathway of neuroprotection during brain ischemia, might represent an additional mechanism to intervene in stroke pathophysiology.

Neuroprotective effects of disubstituted dithiolethione ACDT against manganese-induced toxicity in SH-SY5Y cells

Dithiolethiones are lipophilic, organosulfur compounds that activate the Nrf2 transcription factor causing an upregulation of various phase II antioxidant enzymes. A disubstituted dithiolethione 5-amino-3-thioxo-3H-(1,2) dithiole-4-carboxylic acid ethyl ester (ACDT) retains the functional pharmacophore while also containing modifiable functional groups. Neuroprotection against autoimmune encephalomyelitis in vivo and 6-hydroxy dopamine (a model for Parkinson's disease) in vitro have been previously reported with ACDT. Manganese (Mn) is a metal essential for metabolic processes at low concentrations. Overexposure and accumulation of Mn leads to a neurological condition called manganism which shares pathophysiological sequelae with parkinsonism. Here we hypothesized ACDT to be protective against manganese-induced cytotoxicity. SH-SY5Y human neuroblastoma cells exposed to 300 μM MnCl₂ displayed approximately 50% cell death, and a 24-h pretreatment with 75 μM ACDT significantly reversed this cytotoxicity. ACDT pretreatment was also found to increase total GSH levels (2.18-fold) and the protein levels of NADPH:quinone oxidoreductase-1 (NQO1) enzyme (6.33-fold), indicating an overall increase in the cells' antioxidant defense stores. A corresponding 2.32-fold reduction in the level of Mn-induced reactive oxygen species was also observed in cells pretreated with ACDT. While no changes were observed in the protein levels of apoptotic markers Bax and Bcl-2, pretreatment with 75 μM ACDT led to a 2.09-fold downregulation of ZIP14 import transporter, indicating a potential reduction in the cellular uptake of Mn as an additional neuroprotective mechanism. These effects did not extend to other transporters like the divalent metal transporter 1 (DMT1) or ferroportin. Collectively, ACDT showed substantial neuroprotection against Mn-induced cytotoxicity, opening a path for dithiolethiones as a potential novel therapeutic option against heavy metal neurotoxicity.

Nutritive Manganese and Zinc Overdosing in Aging C. elegans Result in a Metallothionein-Mediated Alteration in Metal Homeostasis

SCOPE

Manganese (Mn) and zinc (Zn) are not only essential trace elements, but also potential exogenous risk factors for various diseases. Since the disturbed homeostasis of single metals can result in detrimental health effects, concerns have emerged regarding the consequences of excessive exposures to multiple metals, either via nutritional supplementation or parenteral nutrition. This study focuses on Mn-Zn-interactions in the nematode Caenorhabditis elegans (C. elegans) model, taking into account aspects related to aging and age-dependent neurodegeneration.

METHODS AND RESULTS

Chronic co-exposure of C. elegans to Mn and Zn increases metal uptake, exceeding levels of single metal exposures. Supplementation with Mn and/or Zn also leads to an age-dependent increase in metal content, a decline in overall mRNA expression, and metal co-supplementation induced expression of target genes involved in Mn and Zn homeostasis, in particular metallothionein 1 (mtl-1). Studies in transgenic worms reveal that mtl-1 played a prominent role in mediating age- and diet-dependent alterations in metal homeostasis. Metal dyshomeostasis is further induced in parkin-deficient nematodes (Parkinson's disease (PD) model), but this did not accelerate the age-dependent dopaminergic neurodegeneration.

CONCLUSIONS

A nutritive overdose of Mn and Zn can alter interactions between essential metals in an aging organism, and metallothionein 1 acts as a potential protective modulator in regulating homeostasis.

Ferroptosis: An emerging therapeutic target in stroke

Stroke is a disastrous neurological disease with high morbidity and mortality. The mechanism of the pathological process is extremely complicated and unclear. Although many basic studies have confirmed molecular mechanism of brain injury after stroke, these studies have not yet translated into treatment and clinical application. Ferroptosis is a form of cell death that is distinct from necrosis, apoptosis, and autophagy morphologically and biochemically and is characterized by iron-dependent accumulation of lipid peroxides. Despite ferroptosis being first identified in cancer cells, it was recently revealed to also be a significant factor in the pathological process of stroke. A better understanding of ferroptosis in stroke may provide us with better therapeutic targets to treat this devastating disease. Here, we systematically summarized the current mechanism of ferroptosis and reviewed the current studies regarding the relationship between ferroptosis and stroke.

Iron Availability in Tissue Microenvironment: The Key Role of Ferroportin

Body iron levels are regulated by hepcidin, a liver-derived peptide that exerts its function by controlling the presence of ferroportin (FPN), the sole cellular iron exporter, on the cell surface. Hepcidin binding leads to FPN internalization and degradation, thereby inhibiting iron release, in particular from iron-absorbing duodenal cells and macrophages involved in iron recycling. Disruption in this regulatory mechanism results in a variety of disorders associated with iron-deficiency or overload. In recent years, increasing evidence has emerged to indicate that, in addition to its role in systemic iron metabolism, FPN may play an important function in local iron control, such that its dysregulation may lead to tissue damage despite unaltered systemic iron homeostasis. In this review, we focus on recent discoveries to discuss the role of FPN-mediated iron export in the microenvironment under both physiological and pathological conditions.

Ferroportin-Dependent Iron Homeostasis Protects against Oxidative Stress-Induced Nucleus Pulposus Cell Ferroptosis and Ameliorates Intervertebral Disc Degeneration In Vivo

Ferroptosis is a specialized form of regulated cell death that is charactered by iron-dependent lethal lipid peroxidation, a process associated with multiple diseases. However, its role in the pathogenesis of intervertebral disc degeneration (IVDD) is rarely investigated. This study is aimed at investigating the role of ferroptosis in oxidative stress- (OS-) induced nucleus pulposus cell (NPC) decline and the pathogenesis of IVDD and determine the underlying regulatory mechanisms. We used tert-butyl hydroperoxide (TBHP) to simulate OS conditions around human NPCs. Flow cytometry and transmission electron microscopy were used to identify ferroptosis, while iron assay kit, Perl's staining, and western blotting were performed to assay the intracellular iron levels. A ferroportin- (FPN-) lentivirus and FPN-siRNA were constructed and used to explore the relationship between FPN, intracellular iron homeostasis, and ferroptosis. Furthermore, hinokitiol, a bioactive compound known to specifically resist OS and restore FPN function, was evaluated for its therapeutic role in IVDD both in vitro and in vivo. The results indicated that intercellular iron overload plays an essential role in TBHP-induced ferroptosis of human NPCs. Mechanistically, FPN dysregulation is responsible for intercellular iron overload under OS. The increase in nuclear translocation of metal-regulatory transcription factor 1 (MTF1) restored the function of FPN, abolished the intercellular iron overload, and protected cells against ferroptosis. Additionally, hinokitiol enhanced the nuclear translocation of MTF1 by suppressing the JNK pathway and ameliorated the progression of IVDD in vivo. Taken together, our results demonstrate that ferroptosis and FPN dysfunction are involved in the NPC depletion and the pathogenesis of IVDD under OS. To the best of our knowledge, this is the first study to demonstrate the protective role of FPN in ferroptosis of NPCs, suggesting its potential used as a novel therapeutic target against IVDD.

Astrocytes in heavy metal neurotoxicity and neurodegeneration

With the industrial development and progressive increase in environmental pollution, the mankind overexposure to heavy metals emerges as a pressing public health issue. Excessive intake of heavy metals, such as arsenic (As), manganese (Mn), mercury (Hg), aluminium (Al), lead (Pb), nickel (Ni), bismuth (Bi), cadmium (Cd), copper (Cu), zinc (Zn), and iron (Fe), is neurotoxic and it promotes neurodegeneration. Astrocytes are primary homeostatic cells in the central nervous system. They protect neurons against all types of insults, in particular by accumulating heavy metals. However, this makes astrocytes the main target for heavy metals neurotoxicity. Intake of heavy metals affects astroglial homeostatic and neuroprotective cascades including glutamate/GABA-glutamine shuttle, antioxidative machinery and energy metabolism. Deficits in these astroglial pathways facilitate or even instigate neurodegeneration. In this review, we provide a concise outlook on heavy metal-induced astrogliopathies and their association with major neurodegenerative disorders. In particular, we focus on astroglial mechanisms of iron-induced neurotoxicity. Iron deposits in the brain are detected in main neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease and amyotrophic lateral sclerosis. Accumulation of iron in the brain is associated with motor and cognitive impairments and iron-induced histopathological manifestations may be considered as the potential diagnostic biomarker of neurodegenerative diseases. Effective management of heavy metal neurotoxicity can be regarded as a potential strategy to prevent or retard neurodegenerative pathologies.

Biology of the iron efflux transporter, ferroportin

Iron, the most common metal in the earth, is also an essential component for almost all living organisms. While these organisms require iron for many biological processes, too much or too little iron itself poses many issues; this is most easily recognized in human beings. The control of body iron levels is thus an important metabolic process which is regulated essentially by controlling the expression, activity and levels of the iron transporter ferroportin. Ferroportin is the only known iron exporter. The function and activity of ferroportin is influenced by its interaction with the iron-regulatory peptide hepcidin, which itself is regulated by many factors. Here we review the current state of understanding of the mechanisms that regulate ferroportin and its function.

Manganese, a Likely Cause of 'Parkinson's in Cirrhosis', a Unique Clinical Entity of Acquired Hepatocerebral Degeneration

With idiopathic Parkinson's disease being a common entity, parkinsonism in acquired hepatocerebral degeneration (AHD) in the context of Manganese (Mn) has gained importance in recent years. An insight into the pathomechanisms behind this disease has been put forth. How can Mn as a divalent metal exert its effect in leading to chronic neurodegenerative disorder? Secondary to decreased excretion in liver cirrhosis, Mn significantly alters the striatal dopaminergic system. Management of this debilitating disease also focuses on different aspects where Mn has been involved in the pathogenesis. We have put forth the details behind Mn effects in Parkinson’s, which will be a guide for better understanding and management of this disease.

A literature search was performed using PubMed as a sole database, and all the articles were peer-reviewed. The author tried to follow the PRISMA guidelines. Inclusion criteria were set for 10 years, with most studies with in the last seven years. All types of study designs were included relevant to the topic, clearly delineating the pathomechanisms of Mn in the disease and also its management. After extensive research, through the PubMed database, we found that Parkinson's disease is one of the neurological complications in advanced liver cirrhosis. Mn is an essential element behind its pathogenesis; it works at different cellular levels to promote neurotoxicity. From its influx to its effects on dopamine transporters (DAT), where it disrupts dopamine homeostasis also altering postsynaptic dopamine (D2) receptors, it disrupts mitochondria and the endoplasmic reticulum (ER) promotes oxidative stress and neuroinflammation. Misfolding of alpha-synuclein (α-Syn) is promoted on chronic exposure to Mn where α-Syn from being neuroprotective becomes neurotoxic. It also alters glutaminergic and gabaergic neurotransmission. In a nutshell, the diversity of its effect on nigrostriatal denervation is challenging. The importance of neuroimaging and various approaches to management is also discussed. AHD, an uncommon entity in advanced liver cirrhosis, needs more awareness so that it can be diagnosed earlier and better therapeutic options can be sought. Our study highlighted Mn mechanisms behind this clinical entity, putting forth grounds for a better understanding of this disease. Advanced research targeting Mn for managing this disease will be revolutionary.

Regulation of Iron Homeostasis and Related Diseases

The liver is the organ for iron storage and regulation; it senses circulating iron concentrations in the body through the BMP-SMAD pathway and regulates the iron intake from food and erythrocyte recovery into the bloodstream by secreting hepcidin. Under iron deficiency, hypoxia, and hemorrhage, the liver reduces the expression of hepcidin to ensure the erythropoiesis but increases the excretion of hepcidin during infection and inflammation to reduce the usage of iron by pathogens. Excessive iron causes system iron overload; it accumulates in never system and damages neurocyte leading to neurodegenerative diseases such as Parkinson's syndrome. When some gene mutations affect the perception of iron and iron regulation ability in the liver, then they decrease the expression of hepcidin, causing hereditary diseases such as hereditary hemochromatosis. This review summarizes the source and utilization of iron in the body, the liver regulates systemic iron homeostasis by sensing the circulating iron concentration, and the expression of hepcidin regulated by various signaling pathways, thereby understanding the pathogenesis of iron-related diseases.

Kinome screen of ferroptosis reveals a novel role of ATM in regulating iron metabolism

Ferroptosis is a specialized iron-dependent cell death that is associated with lethal lipid peroxidation. Modulation of ferroptosis may have therapeutic potential since it has been implicated in various human diseases as well as potential antitumor activities. However, much remains unknown about the underlying mechanisms and genetic determinants of ferroptosis. Given the critical role of kinases in most biological processes and the availability of various kinase inhibitors, we sought to systemically identify kinases essential for ferroptosis. We performed a forward genetic-based kinome screen against ferroptosis in MDA-MB-231 cells triggered by cystine deprivation. This screen identified 34 essential kinases involved in TNFα and NF-kB signaling. Unexpectedly, the DNA damage response serine/threonine kinase ATM (mutated in Ataxia-Telangiectasia) was found to be essential for ferroptosis. The pharmacological or genetic inhibition of ATM consistently rescued multiple cancer cells from ferroptosis triggered by cystine deprivation or erastin. Instead of the canonical DNA damage pathways, ATM inhibition rescued ferroptosis by increasing the expression of iron regulators involved in iron storage (ferritin heavy and light chain, FTH1 and FTL) and export (ferroportin, FPN1). The coordinated changes of these iron regulators during ATM inhibition resulted in a lowering of labile iron and prevented the iron-dependent ferroptosis. Furthermore, we found that ATM inhibition enhanced the nuclear translocation of metal-regulatory transcription factor 1 (MTF1), responsible for regulating expression of Ferritin/FPN1 and ferroptosis protection. Genetic depletion of MTF-1 abolished the regulation of iron-regulatory elements by ATM and resensitized the cells to ferroptosis. Together, we have identified an unexpected ATM-MTF1-Ferritin/FPN1 regulatory axis as novel determinants of ferroptosis through regulating labile iron levels.

Effect of manganese source on manganese absorption and expression of related transporters in the small intestine of broilers

An experiment was conducted to investigate the effect of manganese (Mn) source on Mn absorption and expressions of Mn, amino acid, and peptide transporters in the small intestine of broilers. A total of 320 Mn-deficient 15-day-old Arbor Acres male broilers were randomly assigned to 5 treatments with 8 replicates/treatment and 8 chicks/replicate and fed an Mn-unsupplemented control diet or the control diet supplemented with 110 mg Mn/kg from either MnSO4, or 1 of 3 organic Mn chelates with weak (OW), moderate (OM), or strong (OS) chelation strength for 14 D. The plasma Mn contents were higher (P < 0.03) in supplemental Mn groups than in the control group, in OS group than in OM group, and in OM group than in OW and MnSO4 groups on day 28. Broilers fed diets supplemented with Mn had higher (P < 0.02) duodenal divalent metal transporter 1 (DMT1) and ferroportin 1 (FPN1) mRNA levels and FPN1 protein level on both days 21 and 28 than those fed the control diet. Duodenal DMT1 mRNA and protein levels were higher (P < 0.05) in OM and OS groups than in OW and MnSO4 groups on day 28. The mRNA levels of amino acid transporters [b0, +-type amino acid transporter 1 (B0AT1) and excitatory amino acid transporter 3 (EAAT3)] were higher (P < 0.0005), and peptide transporter 1 was lower (P < 0.04) in the ileum than in the duodenum and jejunum; however, Mn source did not affect (P > 0.05) mRNA levels of amino acid and peptide transporters in the small intestine of broilers. The results from the present study indicate that both DMT1 and FPN1 facilitated Mn absorption, however, the amino acid and peptide transporters might not be involved in the transport of the organic Mn chelates; organic Mn chelates with moderate and strong chelation strength, especially strong chelation strength, showed higher Mn absorption possibly due to enhanced DMT1 expression in the duodenum of broilers.

O-GlcNAcylation-dependent upregulation of HO1 triggers ammonia-induced oxidative stress and senescence in hepatic encephalopathy

BACKGROUND & AIMS

Cerebral oxidative stress plays an important role in the pathogenesis of hepatic encephalopathy (HE), but the underlying mechanisms are incompletely understood. Herein, we analyzed a role of heme oxygenase (HO)1, iron and NADPH oxidase 4 (Nox4) for the induction of oxidative stress and senescence in HE.

METHODS

Gene and protein expression in human post-mortem brain samples was analyzed by gene array and western blot analysis. Mechanisms and functional consequences of HO1 upregulation were studied in NH₄Cl-exposed astrocytes in vitro by western blot, qPCR and super-resolution microscopy.

RESULTS

HO1 and the endoplasmic reticulum (ER) stress marker grp78 were upregulated, together with changes in the expression of multiple iron metabolism-related genes, in post-mortem brain samples from patients with liver cirrhosis and HE. NH₄Cl elevated HO1 protein and mRNA in cultured astrocytes through glutamine synthetase (GS)-dependent upregulation of glutamine/fructose amidotransferases 1/2 (GFAT1/2), which blocked the transcription of the HO1-targeting miR326-3p in a O-GlcNAcylation dependent manner. Upregulation of HO1 by NH₄Cl triggered ER stress and was associated with elevated levels of free ferrous iron and expression changes in iron metabolism-related genes, which were largely abolished after knockdown or inhibition of GS, GFAT1/2, HO1 or iron chelation. NH₄Cl, glucosamine (GlcN) and inhibition of miR326-3p upregulated Nox4, while knockdown of Nox4, GS, GFAT1/2, HO1 or iron chelation prevented NH₄Cl-induced RNA oxidation and astrocyte senescence. Elevated levels of grp78 and O-GlcNAcylated proteins were also found in brain samples from patients with liver cirrhosis and HE.

CONCLUSION

The present study identified glucosamine synthesis-dependent protein O-GlcNAcylation as a novel mechanism in the pathogenesis of HE that triggers oxidative and ER stress, as well as senescence, through upregulation of HO1 and Nox4.

LAY SUMMARY

Patients with liver cirrhosis frequently exhibit hyperammonemia and suffer from cognitive and motoric dysfunctions, which at least in part involve premature ageing of the astrocytes in the brain. This study identifies glucosamine and an O-GlcNAcylation-dependent disruption of iron homeostasis as novel triggers of oxidative stress, thereby mediating ammonia toxicity in the brain.

Salmonella effector SpvB interferes with intracellular iron homeostasis via regulation of transcription factor NRF2

Iron is a necessary nutrient for humans and nearly all bacterial species. During Salmonella infection, macrophages limit the availability of iron to intracellular pathogens in one of the central components of nutritional immunity. However, Salmonella also have mechanisms to interfere with the antimicrobial effect of host iron withdrawal and meet their own nutrient requirements by scavenging iron from the host. Here, we provide what is, to our knowledge, the first report that SpvB, a pSLT-encoded cytotoxic protein whose function is associated with the intracellular stage of salmonellosis, perturbs macrophage iron metabolism, thereby facilitating Salmonella survival and intracellular replication. In investigating the underlying mechanism, we observed that the Salmonella effector SpvB down-regulated nuclear factor erythroid-derived 2-related factor 2 (NRF2), and its C-terminal domain was necessary and sufficient for NRF2 degradation via the proteasome pathway. Decreased NRF2 expression in the nucleus resulted in a decrease in its transcriptional target ferroportin, encoding the sole macrophage iron exporter, thus ultimately decreasing iron efflux and increasing the intracellular iron content. Additionally, SpvB contributes to the pathogenesis of Salmonella including severe serum hypoferremia, increased splenic and hepatic bacterial burden, and inflammatory injury in vivo. Together, our observations uncovered a novel contribution of SpvB to Salmonella pathology via interference with host intracellular iron metabolism.-Yang, S., Deng, Q., Sun, L., Dong, K., Li, Y., Wu, S., Huang, R. Salmonella effector SpvB interferes with intracellular iron homeostasis via regulation of transcription factor NRF2.

Crosstalk of Nrf2 with the Trace Elements Selenium, Iron, Zinc, and Copper

Trace elements, like Cu, Zn, Fe, or Se, are important for the proper functioning of antioxidant enzymes. However, in excessive amounts, they can also act as pro-oxidants. Accordingly, trace elements influence redox-modulated signaling pathways, such as the Nrf2 pathway. Vice versa, Nrf2 target genes belong to the group of transport and metal binding proteins. In order to investigate whether Nrf2 directly regulates the systemic trace element status, we used mice to study the effect of a constitutive, whole-body Nrf2 knockout on the systemic status of Cu, Zn, Fe, and Se. As the loss of selenoproteins under Se-deprived conditions has been described to further enhance Nrf2 activity, we additionally analyzed the combination of Nrf2 knockout with feeding diets that provide either suboptimal, adequate, or supplemented amounts of Se. Experiments revealed that the Nrf2 knockout partially affected the trace element concentrations of Cu, Zn, Fe, or Se in the intestine, liver, and/or plasma. However, aside from Fe, the other three trace elements were only marginally modulated in an Nrf2-dependent manner. Selenium deficiency mainly resulted in increased plasma Zn levels. One putative mediator could be the metal regulatory transcription factor 1, which was up-regulated with an increasing Se supply and downregulated in Se-supplemented Nrf2 knockout mice.

Uptake of Manganese from the Manganese-Lysine Complex in Primary Chicken Intestinal Epithelial Cells

Simple Summary

Manganese (Mn) supplementation is especially necessary to avian species because the absorption of dietary Mn is relatively inefficient in birds. Recently, there has been increasing interest in the use of organic Mn to replace inorganic Mn as dietary Mn supplements in poultry. This study compared the uptake of Mn from Mn-lysine complex (MnLys) and MnSO₄ in the primary chicken intestinal epithelial cells when the Fe, N-ethylmaleimide (a transport system y⁺ inhibitor), or cycloheximide (a transport system b^0,+ activator) added in the culture medium. The results revealed that the uptake of Mn from the MnLys complex not only might be transported through the ionized Mn²⁺ pathway, but also appeared to be transported through the transport systems y⁺ and b^0,+ in the intestine of chickens.

Abstract

Organic manganese (Mn) sources can replace inorganic Mn as dietary Mn supplements in poultry. To compare the uptake of Mn from the Mn-lysine complex (MnLys) and MnSO₄, we first established the primary chicken intestinal epithelial cells (IECs) model and used it to determine Mn uptake. The MnLys increased the uptake of Mn compared to MnSO₄. The uptake of Mn decreased in the IECs with Fe addition in the medium regardless of the Mn sources. The MnLys decreased the Mn²⁺ efflux transporter ferroportin 1 (FPN1) mRNA level but did not influence the Mn²⁺ influx transporter divalent metal transporter 1 (DMT1) mRNA expression when compared to MnSO₄. The results above indicated that the increase of Mn accumulation for MnLys at least partly was due to the decrease of Mn efflux by reduced FPN1 expression. The addition of N-ethylmaleimide, an L-lysine transport system y⁺ inhibitor, decreased the uptake of Mn from MnLys but did not affect the uptake of Mn from MnSO₄. The cycloheximide, as an L-lysine transport system b^0,+ activator, increased the uptake of Mn from MnLys, whereas they did not influence the uptake of Mn from MnSO₄. The MnLys increased the system y⁺ members cationic amino acid transporter (CAT) 1 and CAT2, and system b^0,+ components rBAT and b^0,+AT mRNA expression when compared to MnSO₄. These results suggested that the uptake of MnLys complex might be transported by CAT1/2 and system b^0,+, which was different from the ionized Mn²⁺ uptake pathway. In conclusion, the uptake of Mn from MnLys complex not only might be uptake through the ionized Mn²⁺ pathway, but also appeared to be transported through the CAT1/2 and system b^0,+ in primary chicken IECs.

Iron and Zinc Homeostasis and Interactions: Does Enteric Zinc Excretion Cross-Talk with Intestinal Iron Absorption?

Iron and zinc are essential micronutrients required for growth and health. Deficiencies of these nutrients are highly prevalent among populations, but can be alleviated by supplementation and food fortification. Cross-sectional studies in humans showed positive association of serum zinc levels with hemoglobin and markers of iron status. Dietary restriction of zinc or intestinal specific conditional knock out of ZIP4 (SLC39A4), an intestinal zinc transporter, in experimental animals demonstrated iron deficiency anemia and tissue iron accumulation. Similarly, increased iron accumulation has been observed in cultured cells exposed to zinc deficient media. These results together suggest a potential role of zinc in modulating intestinal iron absorption and mobilization from tissues. Studies in intestinal cell culture models demonstrate that zinc induces iron uptake and transcellular transport via induction of divalent metal iron transporter-1 (DMT1) and ferroportin (FPN1) expression, respectively. It is interesting to note that intestinal cells are exposed to very high levels of zinc through pancreatic secretions, which is a major route of zinc excretion from the body. Therefore, zinc appears to be modulating the iron metabolism possibly via regulating the DMT1 and FPN1 levels. Herein we critically reviewed the available evidence to hypothesize novel mechanism of Zinc-DMT1/FPN1 axis in regulating intestinal iron absorption and tissue iron accumulation to facilitate future research aimed at understanding the yet elusive mechanisms of iron and zinc interactions.

The Emerging Roles of Ferroptosis in Vascular Cognitive Impairment

Vascular cognitive impairment (VCI) is a clinical syndrome that encompasses all forms of cognitive deficits caused by cerebrovascular disease, from mild cognitive impairment to dementia. Vascular dementia, the second most common type of dementia after Alzheimer’s disease (AD), accounts for approximately 20% of dementia patients. Ferroptosis is a recently defined iron-dependent form of cell death, which is distinct from apoptosis, necrosis, autophagy, and other forms of cell death. Emerging evidence suggests that ferroptosis has significant implications in neurological diseases such as stroke, traumatic brain injury, and AD. Additionally, ferroptosis inhibition has an obvious neuroprotective effect and ameliorates cognitive impairment in various animal models. Here, we summarize the underlying mechanisms of ferroptosis and review the close relationship between ferroptosis and VCI.

Manganese-Induced Neurotoxicity: New Insights Into the Triad of Protein Misfolding, Mitochondrial Impairment, and Neuroinflammation

Occupational or environmental exposure to manganese (Mn) can lead to the development of "Manganism," a neurological condition showing certain motor symptoms similar to Parkinson's disease (PD). Like PD, Mn toxicity is seen in the central nervous system mainly affecting nigrostriatal neuronal circuitry and subsequent behavioral and motor impairments. Since the first report of Mn-induced toxicity in 1837, various experimental and epidemiological studies have been conducted to understand this disorder. While early investigations focused on the impact of high concentrations of Mn on the mitochondria and subsequent oxidative stress, current studies have attempted to elucidate the cellular and molecular pathways involved in Mn toxicity. In fact, recent reports suggest the involvement of Mn in the misfolding of proteins such as α-synuclein and amyloid, thus providing credence to the theory that environmental exposure to toxicants can either initiate or propagate neurodegenerative processes by interfering with disease-specific proteins. Besides manganism and PD, Mn has also been implicated in other neurological diseases such as Huntington's and prion diseases. While many reviews have focused on Mn homeostasis, the aim of this review is to concisely synthesize what we know about its effect primarily on the nervous system with respect to its role in protein misfolding, mitochondrial dysfunction, and consequently, neuroinflammation and neurodegeneration. Based on the current evidence, we propose a 'Mn Mechanistic Neurotoxic Triad' comprising (1) mitochondrial dysfunction and oxidative stress, (2) protein trafficking and misfolding, and (3) neuroinflammation.