Cobalt Hexacyanoferrate Nanocatalysts Combat Acute Lung Injury via Ferroptosis-Based Regulation of Iron Homeostasis and Antioxidant Defenses

HFE and transferrin receptor 2 (TFR2) are membrane proteins integral to mammalian iron homeostasis and associated with human hereditary hemochromatosis. Here we demonstrate that HFE and TFR2 interact in cells, that this interaction is not abrogated by disease-associated mutations of HFE and TFR2, and that TFR2 competes with TFR1 for binding to HFE. We propose a new model for the mechanism of iron status sensing that results in the regulation of iron homeostasis.

Iron is a vital cofactor for enzymes essential to many biological processes, yet in excess, it poses a danger to all living organisms. In order to ensure survival and proliferation under fluctuating environmental iron levels, bacteria evolve sophisticated regulatory systems to maintain iron homeostasis. Unlike master regulator Fur, a large portion of other players remains poorly defined. Here, we characterized the physiological impacts of atypical phosphorylation-independent response regulator SsoR of Shewanella oneidensis, a γ-proteobacterium renowned for metabolic versatility. By combining transcriptomics, proteomics, and transposon screening, we discovered that the SsoR loss impairs growth and decreases cytochrome c content under iron-limited conditions. Further investigations revealed that the defects can be attributed to lowered heme and iron levels, a consequence of elevated Fur production. Together, our findings suggest that SsoR and Fur constitute a derepressing-inhibiting oscillation system in maintaining iron homeostasis, providing a new composite view of regulator dynamics during the regulation of iron homeostasis in bacteria.IMPORTANCEShewanella comprises a large group of bacteria that are ubiquitous, ecologically widespread, and metabolically versatile, having enormous potential in biotechnology, environmental remediation, and energy production. These characteristics and applications are crucially determined by a myriad of iron-containing proteins, whose activity depends on the intricate regulation of iron homeostasis. Our study reveals that a derepressing-inhibiting oscillation system composed of Fur and atypical phosphorylation-independent response regulator SsoR plays a key role in the regulation of iron homeostasis at the transcription level. The loss of either results in altered production of the other, leading to disruption of iron homeostasis, which is harmful to the cell, especially under iron-limited conditions. This study deepens our understanding of the interacting dynamics of multiple regulators in iron homeostasis.

Iron is an essential micronutrient for plants and animals, and plants are a major source of iron for humans. Therefore, understanding the regulation of iron homeostasis in plants is critical. We identified a T-DNA insertion mutant, yellow and sensitive to iron-deficiency 1 (yid1), that was hypersensitive to iron deficiency, containing a reduced amount of iron. YID1 encodes the Arabidopsis Mediator complex subunit MED16. We demonstrated that YID1/MED16 interacted with another subunit, MED25. MED25 played an important role in regulation of iron homeostasis by interacting with EIN3 and EIL1, two transcription factors in ethylene signaling associated with regulation of iron homeostasis. We found that the transcriptome in yid1 and med25 mutants was significantly affected by iron deficiency. In particular, the transcription levels of FIT, IRT1 and FRO2 were reduced in the yid1 and med25 mutants under iron-deficient conditions. The finding that YID1/MED16 and MED25 positively regulate iron homeostasis in Arabidopsis increases our understanding of the complex transcriptional regulation of iron homeostasis in plants.

Hydroponically grown 12-day-old rice (Oryza sativa L. cv. BRRI dhan47) seedlings were exposed to 150mM NaCl alone and combined with 0.5mM MnSO4. Salt stress resulted in disruption of ion homeostasis by Na+ influx and K+ efflux. Higher accumulation of Na+ and water imbalance under salinity caused osmotic stress, chlorosis, and growth inhibition. Salt-induced ionic toxicity and osmotic stress consequently resulted in oxidative stress by disrupting the antioxidant defense and glyoxalase systems through overproduction of reactive oxygen species (ROS) and methylglyoxal (MG), respectively. The salt-induced damage increased with the increasing duration of stress. However, exogenous application of manganese (Mn) helped the plants to partially recover from the inhibited growth and chlorosis by improving ionic and osmotic homeostasis through decreasing Na+ influx and increasing water status, respectively. Exogenous application of Mn increased ROS detoxification by increasing the content of the phenolic compounds, flavonoids, and ascorbate (AsA), and increasing the activities of monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), superoxide dismutase (SOD), and catalase (CAT) in the salt-treated seedlings. Supplemental Mn also reinforced MG detoxification by increasing the activities of glyoxalase I (Gly I) and glyoxalase II (Gly II) in the salt-affected seedlings. Thus, exogenous application of Mn conferred salt-stress tolerance through the coordinated action of ion homeostasis and the antioxidant defense and glyoxalase systems in the salt-affected seedlings.

Changes in expressions of up- and downstream thiol cascade were studied in leaves of Phaseolus vulgaris L. cv. VL-63 and its mutant, pvsod1 (deficient in superoxide dismutase activity) under 50 μM sodium arsenate (As), As + l-buthionine-sulfoximine (BSO) and As + BSO + Sodium hydrosulfide (NaHS)-treatments for 10 days. Main objective was to investigate the functional relationship between hydrogen sulfide (H2S) and glutathione (GSH) in regulation of sulfate transporters and cysteine metabolisms as up-stream thiol components and GSH, phytochelatins (PCs) and antioxidant defense response as downstream cascade under As-exposure. As treatment alone initiated coordinated inductions of sulfate transport, biosynthesis of cysteine, GSH, and PCs, and GSH-mediated antioxidant defense in the pvsod1 mutant. At As + BSO, GSH synthesis was blocked, resulting in significantly low GSH redox pool and steep decline in GSH-dependent antioxidant capacity of both the genotypes. However, unlike VL-63, cysteine-degradation pathway was induced in pvsod1 mutant, resulting in significant accumulation of endogenous H2S. The H2S-surge in the pvsod1 mutant stimulated ascorbate-dependent antioxidant defense and catalases and regulated O-acetylserine (thiol)lyase activity, preventing overaccumulation of H2O2 and free cysteine, respectively. No As-induced oxidative stress symptom was observed in the mutant. This trend was maintained at As + BSO + NaHS treatment, also. In contrast, failure to induce entire cascade from sulfate transport to downstream antioxidant defense led to onset of As-induced oxidative damage in VL-63 plant. Results revealed dual roles of H2S as (a) stimulator of GSH-independent antioxidant defense and (b) regulator of cysteine homeostasis through its metabolic diversion during As-exposure and blockage of GSH biosynthesis.

BackgroundHfe disruption in mouse leads to experimental hemochromatosis by a mechanism that remains elusive. Affymetrix GeneChip® Mouse Genome 430 2.0 microarrays and bioinformatics tools were used to characterize patterns of gene expression in the liver and the duodenum of wild-type and Hfe-deficient B6 and D2 mice (two inbred mouse strains with divergent iron loading severity in response to Hfe disruption), to clarify the mechanisms of Hfe action, and to identify potential modifier genes.ResultsWe identified 1,343 transcripts that were upregulated or downregulated in liver and 370 in duodenum of Hfe-/- mice, as compared to wild-type mice of the same genetic background. In liver, Hfe disruption upregulated genes involved in antioxidant defense, reflecting mechanisms of hepatoprotection activated by iron overload. Hfe disruption also downregulated the expression of genes involved in fatty acid β-oxidation and cholesterol catabolism, and of genes participating in mitochondrial iron traffic, suggesting a link between Hfe and the mitochondrion in regulation of iron homeostasis. These latter alterations may contribute to the inappropriate iron deficiency signal sensed by the duodenal enterocytes of these mice, and the subsequent upregulation of the genes encoding the ferrireductase Dcytb and several iron transporters or facilitators of iron transport in the duodenum. In addition, for several genes differentially expressed between B6 and D2 mice, expression was regulated by loci overlapping with previously mapped Hfe-modifier loci.ConclusionThe expression patterns identified in this study contribute novel insights into the mechanisms of Hfe action and potential candidate genes for iron loading severity.

A strong mechanistic link between the regulation of iron homeostasis and oxygen sensing is evident in the lung, where both systems must be properly controlled to maintain lung function. Imbalances in pulmonary iron homeostasis are frequently associated with respiratory diseases, such as chronic obstructive pulmonary disease and with lung cancer. However, the underlying mechanisms causing alterations in iron levels and the involvement of iron in the development of lung disorders are incompletely understood. Here, we review current knowledge about the regulation of pulmonary iron homeostasis, its functional importance, and the link between dysregulated iron levels and lung diseases. Gaining greater knowledge on how iron contributes to the pathogenesis of these diseases holds promise for future iron-related therapeutic strategies.

BMP-SMAD signalling plays a crucial role in numerous biological processes including embryonic development and iron homeostasis. Dysregulation of the iron-regulatory hormone hepcidin is associated with many clinical iron-related disorders. We hypothesised that molecules which mediate BMP-SMAD signalling play important roles in the regulation of iron homeostasis and variants in these proteins may be potential genetic modifiers of iron-related diseases. We examined the role of endofin, a SMAD anchor, and show that knockdown of endofin in liver cells inhibits basal and BMP-induced hepcidin expression along with other BMP-regulated genes, ID1 and SMAD7. We show for the first time, the in situ interaction of endofin with SMAD proteins and significantly reduced SMAD phosphorylation with endofin knockdown, suggesting that endofin modulates hepcidin through BMP-SMAD signalling. Characterisation of naturally occurring SNPs show that mutations in the conserved FYVE domain result in mislocalisation of endofin, potentially affecting downstream signalling and modulating hepcidin expression. In conclusion, we have identified a hitherto unrecognised link, endofin, between the BMP-SMAD signalling pathway, and the regulation of hepcidin expression and iron homeostasis. This study further defines the molecular network involved in iron regulation and provides potential targets for the treatment of iron-related disorders.

Iron homeostasis is highly regulated in organisms across evolutionary time scale as iron is essential for various cellular processes. In a computational screen, we identified the Yap/bZIP domain family in Candida clade genomes. Cap2/Hap43 is essential for C. albicans growth under iron-deprivation conditions and for virulence in mouse. Cap2 has an amino-terminal bipartite domain comprising a fungal-specific Hap4-like domain and a bZIP domain. Our mutational analyses showed that both the bZIP and Hap4-like domains perform critical and independent functions for growth under iron-deprivation conditions. Transcriptome analysis conducted under iron-deprivation conditions identified about 16% of the C. albicans ORFs that were differentially regulated in a Cap2-dependent manner. Microarray data also suggested that Cap2 is required to mobilize iron through multiple mechanisms; chiefly by activation of genes in three iron uptake pathways and repression of iron utilizing and iron storage genes. The expression of HAP2, HAP32, and HAP5, core components of the HAP regulatory complex was induced in a Cap2-dependent manner indicating a feed-forward loop. In a feed-back loop, Cap2 repressed the expression of Sfu1, a negative regulator of iron uptake genes. Cap2 was coimmunoprecipitated with Hap5 from cell extracts prepared from iron-deprivation conditions indicating an in vivo association. ChIP assays demonstrated Hap32-dependent recruitment of Hap5 to the promoters of FRP1 (Cap2-induced) and ACO1 (Cap2-repressed). Together our data indicates that the Cap2-HAP complex functions both as a positive and a negative regulator to maintain iron homeostasis in C. albicans.

Soil salinity is a major environmental problem that negatively affects crop yield in arid and semi-arid areas of the world. Salinity stress suppresses seed germination and inhibits plant growth by causing physiological alterations such as ion toxicity, nutrient imbalance, membrane disorganization, and inhibition of water uptake. Nitric oxide (NO) is an important signaling molecule, regulating a broad spectrum of developmental and physiological processes in plants under normal as well as in environmental stress conditions. Several lines of evidence indicate NO involvement in regulation of various plant responses such as photosynthesis, antioxidant defense, osmolyte accumulation, protein modifications, and gene expression under salinity stress. Investigations on NO in plants have centered around three main topics: (i) its source of production, (ii) physiological and molecular effects of exogenous NO treatments, and (iii) elucidation of signal transduction pathways. The biological source of endogenous NO in animals is well documented and understood; however, the origin of NO production in plants is poorly understood. Nitrate reductase and nitric oxide synthase are the two widely reported sources of endogenous NO production in plants under salt-stress conditions. The interaction of NO with components of cell signaling (cGMP, cADP-ribose, mitogen-activated protein kinases (MAPK), and Ca2+) and NO-mediated modification of proteins by post-translational modifications (S-nitrosylation and tyrosine nitration) are considered as crucial mechanisms for regulating the physiological responses in plants under salinity stress. The fundamental knowledge of NO production, sensing, and transduction in plants is largely unknown or inadequately characterized. In view of this, an attempt has been made to describe recent advances in NO biosynthesis, signaling, and function in plants under salinity stress. Moreover, the impact of endogenously synthesized and exogenously supplied NO on regulating ion homeostasis, osmolyte accumulation, antioxidant defense, and photosynthesis has also been discussed.

Distinct regulation of iron homeostasis in rat heart and liver in response to systemic iron deficiency

Sex differences in metabolism and cardiometabolic disease risk are well described. Because estrogen action is thought to underlie female-biased protection of immunometabolism and cardiometabolic health, we selectively deleted the estrogen receptor alpha (ERa, encoded by Esr1) from myeloid cells of mice to understand the impact of estrogen action on macrophage function. Our previous findings in other glucoregulatory cell types point to an important role of ERa in the control of mitochondrial form and function. Mitochondria play a critical role in innate immunity, and disruption of mitochondrial function is linked to the pathogenesis of cardiometabolic disease. In addition to a primary role in energy production, mitochondria are central in the regulation of iron homeostasis, a critical process governing immune cell function. Myeloid-specific Esr1 knockout mice (MACER) showed increased diet-induced glucose intolerance, insulin resistance, adiposity, and atherosclerotic lesion area compared with f/f controls. A key phenotype of MACER mice was marked accumulation of iron in liver, spleen, gonadal white adipose tissue, and bone marrow-derived macrophages compared with f/f controls. Specifically, iron accumulated in mitochondria from macrophages within tissues of MACER mice. Iron accumulation was linked with alteration of mitochondrial inner and outer membrane morphology and mtDNA replication machinery, and associated with increased transferrin receptor (Tfrc) expression and cellular inflammation driven by interleukin-1-β. We utilized chromatin immunoprecipitation approaches to identify novel ERa-regulated chromatin structures and target genes that modulate immunometabolism of macrophages. Our findings indicate that Esr1 is critical in the regulation of mitochondrial metabolism and iron homeostasis in macrophages, and the action of ERa is critical for the protection against inflammation and cardiometabolic-related disease. Disclosure H.Iwasaki: None. B.K.Leyva: None. A.Ma: None. N.L.Yang: None. P.H.Tran: None. Z.Zhou: None. A.L.Hevener: None. Funding National Institutes of Health (DK128957)

The key metabolic intermediate lactate can increase expression of the liver-derived peptide hepcidin, the central regulator of body iron homeostasis. A new paper by Liu et al. shows that lactate achieves this by binding to and activating soluble adenylyl cyclase, thereby increasing cellular cyclic adenosine monophosphate (cAMP) (cAMP) and enhancing signaling through the bone morphogenetic protein (BMP) pathway to modulate hepcidin expression.

HFE, the protein that is mutated in hereditary haemochromatosis, binds to the transferrin receptor (TfR). Here we show that wild-type HFE and TfR localize in endosomes and at the basolateral membrane of a polarized duodenal epithelial cell line, whereas the primary haemochromatosis HFE mutant, and another mutant with impaired TfR-binding ability accumulate in the ER/Golgi and at the basolateral membrane, respectively. Levels of the iron-storage protein ferritin are greatly reduced and those of TfR are slightly increased in cells expressing wild-type HFE, but not in cells expressing either mutant. Addition of an endosomal-targeting sequence derived from the human low-density lipoprotein receptor (LDLR) to the TfR-binding-impaired mutant restores its endosomal localization but not ferritin reduction or TfR elevation. Thus, binding to TfR is required for transport of HFE to endosomes and regulation of intracellular iron homeostasis, but not for basolateral surface expression of HFE.

Iron is essential for many biological processes, including oxygen delivery, and its supply is tightly regulated. Hepcidin, a small peptide synthesized in the liver, is a key regulator of iron absorption and homeostasis in mammals. Hepcidin production is increased by iron overload and decreased by anemia and hypoxia; but the molecular mechanisms that govern the hepcidin response to these stimuli are not known. Here we establish that the von Hippel-Lindau/hypoxia-inducible transcription factor (VHL/HIF) pathway is an essential link between iron homeostasis and hepcidin regulation in vivo. Through coordinate downregulation of hepcidin and upregulation of erythropoietin and ferroportin, the VHL-HIF pathway mobilizes iron to support erythrocyte production.