Differences in vulnerability of neurons and astrocytes to heme oxygenase-1 modulation: Implications for mitochondrial ferritin

Vitamin K2 (MK-7) attenuates LPS-induced acute lung injury via inhibiting inflammation, apoptosis, and ferroptosis

Acute lung injury (ALI) is a life-threatening disease that has received considerable critical attention in the field of intensive care. This study aimed to explore the role and mechanism of vitamin K2 (VK2) in ALI. Intraperitoneal injection of 7 mg/kg LPS was used to induce ALI in mice, and VK2 injection was intragastrically administered with the dose of 0.2 and 15 mg/kg. We found that VK2 improved the pulmonary pathology, reduced myeloperoxidase (MPO) activity and levels of TNF-α and IL-6, and boosted the level of IL-10 of mice with ALI. Moreover, VK2 played a significant part in apoptosis by downregulating and upregulating Caspase-3 and Bcl-2 expressions, respectively. As for further mechanism exploration, we found that VK2 inhibited P38 MAPK signaling. Our results also showed that VK2 inhibited ferroptosis, which manifested by reducing malondialdehyde (MDA) and iron levels, increasing glutathione (GSH) level, and upregulated and downregulated glutathione peroxidase 4 (GPX4) and heme oxygenase-1 (HO-1) expressions, respectively. In addition, VK2 also inhibited elastin degradation by reducing levels of uncarboxylated matrix Gla protein (uc-MGP) and desmosine (DES). Overall, VK2 robustly alleviated ALI by inhibiting LPS-induced inflammation, apoptosis, ferroptosis, and elastin degradation, making it a potential novel therapeutic candidate for ALI.

CHEX-seq detects single-cell genomic single-stranded DNA with catalytical potential

Genomic DNA (gDNA) undergoes structural interconversion between single- and double-stranded states during transcription, DNA repair and replication, which is critical for cellular homeostasis. We describe "CHEX-seq" which identifies the single-stranded DNA (ssDNA) in situ in individual cells. CHEX-seq uses 3'-terminal blocked, light-activatable probes to prime the copying of ssDNA into complementary DNA that is sequenced, thereby reporting the genome-wide single-stranded chromatin landscape. CHEX-seq is benchmarked in human K562 cells, and its utilities are demonstrated in cultures of mouse and human brain cells as well as immunostained spatially localized neurons in brain sections. The amount of ssDNA is dynamically regulated in response to perturbation. CHEX-seq also identifies single-stranded regions of mitochondrial DNA in single cells. Surprisingly, CHEX-seq identifies single-stranded loci in mouse and human gDNA that catalyze porphyrin metalation in vitro, suggesting a catalytic activity for genomic ssDNA. We posit that endogenous DNA enzymatic activity is a function of genomic ssDNA.

Myelinated axons are the primary target of hemin-mediated oxidative damage in a model of the central nervous system

Iron released from oligodendrocytes during demyelination or derived from haemoglobin breakdown products is believed to amplify oxidative tissue injury in multiple sclerosis (MS). However, the pathophysiological significance of iron-containing haemoglobin breakdown products themselves is rarely considered in the context of MS and their cellular specificity and mode of action remain unclear. Using myelinating cell cultures, we now report the cytotoxic potential of hemin (ferriprotoporphyrin IX chloride), a major degradation product of haemoglobin, is 25-fold greater than equimolar concentrations of free iron in myelinating cultures; a model that reproduces the complex multicellular environment of the CNS. At low micro molar concentrations (3.3 - 10 μM) we observed hemin preferentially binds to myelin and axons to initiate a complex detrimental response that results in targeted demyelination and axonal loss but spares neuronal cell bodies, astrocytes and the majority of oligodendroglia. Demyelination and axonal loss in this context are executed by a combination of mechanisms that include iron-dependent peroxidation by reactive oxygen species (ROS) and ferroptosis. These effects are microglial-independent, do not require any initiating inflammatory insult and represent a direct effect that compromises the structural integrity of myelinated axons in the CNS. Our data identify hemin-mediated demyelination and axonal loss as a novel mechanism by which intracerebral degradation of haemoglobin may contribute to lesion development in MS.

Beneficial and Detrimental Roles of Heme Oxygenase-1 in the Neurovascular System

Heme oxygenase (HO) has both beneficial and detrimental effects via its metabolites, including carbon monoxide (CO), biliverdin or bilirubin, and ferrous iron. HO-1 is an inducible form of HO that is upregulated by oxidative stress, nitric oxide, CO, and hypoxia, whereas HO-2 is a constitutive form that regulates vascular tone and homeostasis. In brains injured by trauma, ischemia-reperfusion, or Alzheimer’s disease (AD), the long-term expression of HO-1 can be detected, which can lead to cytotoxic ferroptosis via iron accumulation. In contrast, the transient induction of HO-1 in the peri-injured region may have regenerative potential (e.g., angiogenesis, neurogenesis, and mitochondrial biogenesis) and neurovascular protective effects through the CO-mediated signaling pathway, the antioxidant properties of bilirubin, and the iron-mediated ferritin synthesis. In this review, we discuss the dual roles of HO-1 and its metabolites in various neurovascular diseases, including age-related macular degeneration, ischemia-reperfusion injury, traumatic brain injury, Gilbert’s syndrome, and AD.

Dysregulation of a Heme Oxygenase-Synuclein Axis in Parkinson Disease

α-Synuclein is a key driver of the pathogenesis of Parkinson disease (PD). Heme oxygenase-1 (HO-1), a stress protein that catalyzes the conversion of heme to biliverdin, carbon monoxide and free ferrous iron, is elevated in PD-affected neural tissues and promotes iron deposition and mitochondrial dysfunction in models of the disease, pathways also impacted by α-synuclein. Elevated expression of human HO-1 in astrocytes of GFAP.HMOX1 transgenic mice between 8.5 and 19 months of age elicits a parkinsonian phenotype characterized by nigrostriatal hypodopaminergia, locomotor incoordination and overproduction of neurotoxic native S129-phospho-α-synuclein. Two microRNAs (miRNA) known to regulate α-synuclein, miR-153 and miR-223, are significantly decreased in the basal ganglia of GFAP.HMOX1 mice. Serum concentrations of both miRNAs progressively decline in wild-type (WT) and GFAP.HMOX1 mice between 11 and 18 months of age. Moreover, circulating levels of miR-153 and miR-223 are significantly lower, and erythrocyte α-synuclein concentrations are increased, in GFAP.HMOX1 mice relative to WT values. MiR-153 and miR-223 are similarly decreased in the saliva of PD patients compared to healthy controls. Upregulation of glial HO-1 may promote parkinsonism by suppressing miR-153 and miR-223, which, in turn, enhance production of neurotoxic α-synuclein. The aim of the current review is to explore the link between HO-1, α-synuclein and PD, evaluating evidence derived from our laboratory and others. HO-1, miR-153 and miR-223 and α-synuclein may serve as potential biomarkers and targets for disease-modifying therapy in idiopathic PD.

Activation of Nrf2 by methylene blue is associated with the neuroprotection against MPP+ induced toxicity via ameliorating oxidative stress and mitochondrial dysfunction

The neuropathological hallmark of Parkinson's disease (PD) is the preferential loss of dopaminergic neurons in the substantia nigra and presence of Lewy bodies in the dying neurons. Though specific molecular mechanisms for the neurodegeneration remains to be clarified, mitochondrial dysfunction and increased oxidative stress are major players associated with PD pathogenesis and these pathogenic mechanisms can be reproduced in cells and animals by application of various neurotoxins such as MPP⁺. In this study, we attempted to determine the neuroprotective effects of methylene blue (MB) against 1-methyl-4-phenylpyridinium (MPP⁺)-induced neurotoxicity, and to elucidate its action mechanism. We observed that MB attenuated MPP⁺-induced apoptotic cell death in SH-SY5Y cells and the mescencephalic dopaminergic neurons. In addition, MB protected the cells against MPP⁺-induced oxidative stress and mitochondrial dysfunction as evidenced by restoration of mitochondrial complex I activity and ATP levels, and attenuation of oxidative stress. Moreover, we demonstrated that MB induced antioxidant molecules, and activated Nrf2 pathway through AKT activation. These results indicate that MB protects the neurons from MPP⁺-induced toxicity through activation of antioxidant system, thereby reducing the oxidative stress and mitochondrial impairment, implying the potential use of MB in the treatment of neurodegenerative diseases such as PD.

HO-1-mediated ferroptosis as a target for protection against retinal pigment epithelium degeneration

Oxidative stress-mediated retinal pigment epithelium (RPE) degeneration plays a vital role in retinal degeneration with irreversible visual impairment, most notably in age-related macular degeneration (AMD), but a key pathogenic factor and the targeted medical control remain controversial and unclear. In this work, by sophisticated high-throughput sequencing and biochemistry investigations, the major pathologic processes during RPE degeneration in the sodium iodate-induced oxidative stress model has been identified to be heme oxygenase-1 (HO-1)-regulated ferroptosis, which is controlled by the Nrf2–SLC7A11–HO-1 hierarchy, through which ferrous ion accumulation and lethal oxidative stress cause RPE death and subsequently photoreceptor degeneration. By direct knockdown of HO-1 or using HO-1 inhibitor ZnPP, the specific inhibition of HO-1 overexpression has been determined to significantly block RPE ferroptosis. In mice, treatment with ZnPP effectively rescued RPE degeneration and achieved superior therapeutic effects: substantial recovery of the retinal structure and visual function. These findings highlight that targeting HO-1-mediated RPE ferroptosis could serve as an effectively retinal-protective strategy for retinal degenerative diseases prevention, including AMD.

Iron homeostasis and disorders revisited in the sepsis

Sepsis is a life-threatening condition caused by a dysregulated host-response to inflammation, although it currently lacks a fully elucidated pathobiology. Iron is a crucial trace element that is essential for fundamental processes in both humans and bacteria. During sepsis, iron metabolism is altered, including increased iron transport and uptake into cells and decreased iron export. The intracellular sequestration of iron limits its availability to circulating pathogens, which serves as a conservative strategy against the pathogens. Although iron retention has been showed to have protective protect effects, an increase in labile iron may cause oxidative injury and cell death (e.g., pyroptosis, ferroptosis) as the condition progresses. Moreover, iron disorders are substantial and correlate with the severity of sepsis. This also suggests that iron may be useful as a diagnostic marker for evaluating the severity and predicting the outcome of the disease. Further knowledge about these disorders could help in evaluating how drugs targeting iron homeostasis can be optimally applied to improve the treatment of patients with sepsis. Here, we present a comprehensive review of recent advances in the understanding of iron metabolism, focusing on the regulatory mechanisms and iron-mediated injury in sepsis.

Importance of Heme Oxygenase-1 in Gastrointestinal Cancers: Functions, Inductions, Regulations, and Signaling

INTRODUCTION : Colorectal cancer (CRC) is one of the important gastrointestinal tract tumors. Heme is mainly absorbed in the colon and induces nitrosamine formation, genotoxicity,  and oxidative stress, and increases the risk of CRC.

MATERIALS AND METHODS

Information was collected from articles on Scopus, Google Scholar, and PubMed.

RESULTS

Heme can irritate intestinal epithelial cells and increases the proliferation of colonic mucosa. Heme can be considered as a carcinogenic agent for CRC induction. In typical situations, Heme Oxygenase-1 (HO-1) is expressed at low concentration in the gastrointestinal tract, but its expression is elevated during lesion and inflammation. Based on the multiple reports, the impact of HO-1 on tumor growth is related to the cancer cell type. Increased HO-1 levels were also indicated in different human and animal malignancies, possibly through its contribution to tumor cell growth, metastasis, expression of angiogenic factors, and resistance to chemotherapy. Recent studies noted that HO-1 can act as an immunomodulator that suppresses immune cell maturation, activation, and infiltration. It also inhibits apoptosis through CO production that leads to p53 suppression. The upregulation of HO-1 significantly increases the endurance of colon cancer cell lines. Therefore, it is supposed that HO-1 inhibitors could become a novel antitumor agent. Lactobacillus rhamnosus and its metabolites can activate Nrf2 and improves anti-oxidant levels along with upregulation of its objective genes like HO-1, and downregulation of NF-κB which reduce phosphorylated TNF-α, IL-1β, and PAI-1.

CONCLUSION

The precise mechanism accountable for the anti-inflammatory features of HO-1 is not completely understood; nevertheless, the CO signaling function associated with the antioxidant property shown by bilirubin possibly will play an act in the improvement of inflammation.

The Chemical Basis of Intracerebral Hemorrhage and Cell Toxicity With Contributions From Eryptosis and Ferroptosis

Intracerebral hemorrhage (ICH) is a particularly devastating event both because of the direct injury from space-occupying blood to the sequelae of the brain exposed to free blood components from which it is normally protected. Not surprisingly, the usual metabolic and energy pathways are overwhelmed in this situation. In this review article, we detail the complexity of red blood cell degradation, the contribution of eryptosis leading to hemoglobin breakdown into its constituents, the participants in that process, and the points at which injury can be propagated such as elaboration of toxic radicals through the metabolism of the breakdown products. Two prominent products of this breakdown sequence, hemin, and iron, induce a variety of pathologies including free radical damage and DNA breakage, which appear to include events independent from typical oxidative DNA injury. As a result of this confluence of damaging elements, multiple pathways of injury, cell death, and survival are likely engaged including ferroptosis (which may be the same as oxytosis but viewed from a different perspective) and senescence, suggesting that targeting any single cause will likely not be a sufficient strategy to maximally improve outcome. Combination therapies in addition to safe methods to reduce blood burden should be pursued.

Systematic Surveys of Iron Homeostasis Mechanisms Reveal Ferritin Superfamily and Nucleotide Surveillance Regulation to be Modified by PINK1 Absence

Iron deprivation activates mitophagy and extends lifespan in nematodes. In patients suffering from Parkinson’s disease (PD), PINK1-PRKN mutations via deficient mitophagy trigger iron accumulation and reduce lifespan. To evaluate molecular effects of iron chelator drugs as a potential PD therapy, we assessed fibroblasts by global proteome profiles and targeted transcript analyses. In mouse cells, iron shortage decreased protein abundance for iron-binding nucleotide metabolism enzymes (prominently XDH and ferritin homolog RRM2). It also decreased the expression of factors with a role for nucleotide surveillance, which associate with iron-sulfur-clusters (ISC), and are important for growth and survival. This widespread effect included prominently Nthl1-Ppat-Bdh2, but also mitochondrial Glrx5-Nfu1-Bola1, cytosolic Aco1-Abce1-Tyw5, and nuclear Dna2-Elp3-Pold1-Prim2. Incidentally, upregulated Pink1-Prkn levels explained mitophagy induction, the downregulated expression of Slc25a28 suggested it to function in iron export. The impact of PINK1 mutations in mouse and patient cells was pronounced only after iron overload, causing hyperreactive expression of ribosomal surveillance factor Abce1 and of ferritin, despite ferritin translation being repressed by IRP1. This misregulation might be explained by the deficiency of the ISC-biogenesis factor GLRX5. Our systematic survey suggests mitochondrial ISC-biogenesis and post-transcriptional iron regulation to be important in the decision, whether organisms undergo PD pathogenesis or healthy aging.

Hepcidin-to-Ferritin Ratio Is Decreased in Astrocytes With Extracellular Alpha-Synuclein and Iron Exposure

Astrocytes are the most abundant glial cells in the central nervous system (CNS). As indispensable elements of the neurovascular unit, they are involved in the inflammatory response and disease-associated processes. Alpha-synuclein (α-syn) is released into the extracellular space by neurons and can be internalized by adjacent astrocytes, which activates glial cells to induce neuroinflammation. We were interested in whether astrocyte-mediated neuroinflammation is modulated by intracellular iron status and extracellular α-syn. Our results showed that recombinant α-syn (1 μg/ml and 5 μg/ml) treatment for 24 h did not affect the expression of the iron transporters divalent metal transporter 1 (DMT1) and ferroportin 1 (FPN1), nor those of iron regulatory protein (IRP) 1 or IRP2. Several proinflammatory cytokines, including tumor necrosis factor-α (TNF-α), interleukin (IL)-1β, and IL-6 exhibited up-regulated mRNA levels in 5 μg/ml α-syn-treated astrocytes. TNF-α release was increased, indicating that inflammatory responses were triggered in these cells. Pretreatment with the iron-overload reagent ferric ammonium citrate (FAC, 100 μmol/L) for 24 h had no effects on mRNA levels and release of proinflammatory cytokines. Inflammatory responses triggered by α-syn were not affected by iron overload. The iron chelator desferrioxamine (DFO, 100 μmol/L) exerted suppressive effects on TNF-α mRNA levels, although no change was observed for TNF-α release. Hepcidin mRNA levels were down-regulated significantly in astrocytes co-treated with FAC and α-syn, although independent treatment with either FAC or α-syn did not alter hepcidin levels. In contrast, hepcidin mRNA levels were up-regulated in DFO and α-syn co-treated cells. As expected, ferritin protein levels were up-regulated or down-regulated with FAC or DFO treatment, respectively. Following the up-regulation of ferritin mediated by α-syn, hepcidin-to-ferritin levels were indicative of modulatory effects in α-syn-treated astrocytes with altered iron status. Therefore, we propose that the hepcidin-to-ferritin ratio is indicative of a detrimental response in primary cultured astrocytes experiencing iron and extracellular α-syn.

The Role of Astrocytes in the Central Nervous System Focused on BK Channel and Heme Oxygenase Metabolites: A Review

Astrocytes outnumber neurons in the human brain, and they play a key role in numerous functions within the central nervous system (CNS), including glutamate, ion (i.e., Ca²⁺, K⁺) and water homeostasis, defense against oxidative/nitrosative stress, energy storage, mitochondria biogenesis, scar formation, tissue repair via angiogenesis and neurogenesis, and synapse modulation. After CNS injury, astrocytes communicate with surrounding neuronal and vascular systems, leading to the clearance of disease-specific protein aggregates, such as β-amyloid, and α-synuclein. The astrocytic big conductance K⁺ (BK) channel plays a role in these processes. Recently, potential therapeutic agents that target astrocytes have been tested for their potential to repair the brain. In this review, we discuss the role of the BK channel and antioxidant agents such as heme oxygenase metabolites following CNS injury. A better understanding of the cellular and molecular mechanisms of astrocytes’ functions in the healthy and diseased brains will greatly contribute to the development of therapeutic approaches following CNS injury, such as Alzheimer’s disease, Parkinson’s disease, and stroke.

Iron in Neurodegeneration - Cause or Consequence?

Iron dyshomeostasis can cause neuronal damage to iron-sensitive brain regions. Neurodegeneration with brain iron accumulation reflects a group of disorders caused by iron overload in the basal ganglia. High iron levels and iron related pathogenic triggers have also been implicated in sporadic neurodegenerative diseases including Alzheimer’s disease (AD), Parkinson’s disease (PD), and multiple system atrophy (MSA). Iron-induced dyshomeostasis within vulnerable brain regions is still insufficiently understood. Here, we summarize the modes of action by which iron might act as primary or secondary disease trigger in neurodegenerative disorders. In addition, available treatment options targeting brain iron dysregulation and the use of iron as biomarker in prodromal stages are critically discussed to address the question of cause or consequence.

Mitochondrial superoxide generation induces a parkinsonian phenotype in zebrafish and huntingtin aggregation in human cells

Superoxide generation by mitochondria respiratory complexes is a major source of reactive oxygen species (ROS) which are capable of initiating redox signaling and oxidative damage. Current understanding of the role of mitochondrial ROS in health and disease has been limited by the lack of experimental strategies to selectively induce mitochondrial superoxide production. The recently-developed mitochondria-targeted redox cycler MitoParaquat (MitoPQ) overcomes this limitation, and has proven effective in vitro and in Drosophila. Here we present an in vivo study of MitoPQ in the vertebrate zebrafish model in the context of Parkinson's disease (PD), and in a human cell model of Huntington's disease (HD). We show that MitoPQ is 100-fold more potent than non-targeted paraquat in both cells and in zebrafish in vivo. Treatment with MitoPQ induced a parkinsonian phenotype in zebrafish larvae, with decreased sensorimotor reflexes, spontaneous movement and brain tyrosine hydroxylase (TH) levels, without detectable effects on heart rate or atrioventricular coordination. Motor phenotypes and TH levels were partly rescued with antioxidant or monoaminergic potentiation strategies. In a HD cell model, MitoPQ promoted mutant huntingtin aggregation without increasing cell death, contrasting with the complex I inhibitor rotenone that increased death in cells expressing either wild-type or mutant huntingtin. These results show that MitoPQ is a valuable tool for cellular and in vivo studies of the role of mitochondrial superoxide generation in redox biology, and as a trigger or co-stressor to model metabolic and neurodegenerative disease phenotypes.

Neurotoxicity Linked to Dysfunctional Metal Ion Homeostasis and Xenobiotic Metal Exposure: Redox Signaling and Oxidative Stress

SIGNIFICANCE

Essential metals such as copper, iron, manganese, and zinc play a role as cofactors in the activity of a wide range of processes involved in cellular homeostasis and survival, as well as during organ and tissue development. Throughout our life span, humans are also exposed to xenobiotic metals from natural and anthropogenic sources, including aluminum, arsenic, cadmium, lead, and mercury. It is well recognized that alterations in the homeostasis of essential metals and an increased environmental/occupational exposure to xenobiotic metals are linked to several neurological disorders, including neurodegeneration and neurodevelopmental alterations. Recent Advances: The redox activity of essential metals is key for neuronal homeostasis and brain function. Alterations in redox homeostasis and signaling are central to the pathological consequences of dysfunctional metal ion homeostasis and increased exposure to xenobiotic metals. Both redox-active and redox-inactive metals trigger oxidative stress and damage in the central nervous system, and the exact mechanisms involved are starting to become delineated.

CRITICAL ISSUES

In this review, we aim to appraise the role of essential metals in determining the redox balance in the brain and the mechanisms by which alterations in the homeostasis of essential metals and exposure to xenobiotic metals disturb the cellular redox balance and signaling. We focus on recent literature regarding their transport, metabolism, and mechanisms of toxicity in neural systems.

FUTURE DIRECTIONS

Delineating the specific mechanisms by which metals alter redox homeostasis is key to understand the pathological processes that convey chronic neuronal dysfunction in neurodegenerative and neurodevelopmental disorders. Antioxid. Redox Signal. 28, 1669-1703.

A review on heme oxygenase-1 induction: is it a necessary evil

Heme oxygenase-1 (HO-1) is considered to be the main protein in diseases arising as a result of oxidative and inflammatory insults. Tremendous research has been carried out on HO-1 since years, pertaining its cytoprotective effect against oxidative injury and other cellular stresses. HO-1, by regulating intracellular levels of pro-oxidant heme, or by other benefits of its by-products such as carbon monoxide (CO) and biliverdin (BV) had become an important candidate protein to be up-regulated to combat diverse stressful events. Although the beneficial effects of HO-1 induction have been reported in a number of cells and tissues, a growing body of evidence indicates that this increased HO-1 expression may lead to the progression of several diseases such as neurodegeneration, carcinogenesis. But it is not clear, what accounts for the increased expression of HO-1 in cells and tissues. The observed friendly role of HO-1 in a wide range of stress conditions since times is now doubtful. Therefore, more studies are needed to elucidate the exact role of HO-1 in various stressful events. Being more concise, elucidating the effect of HO-1 up-regulation on critical genes involved in particular diseases such as cancer will help to a larger extent to comprehend the exact role of HO-1. This review will assist in understanding the dual role (protective and detrimental) of HO-1 and the signaling pathway involved and will help in unraveling the doubtful role of HO-1 induction.

Astroglial DJ-1 over-expression up-regulates proteins involved in redox regulation and is neuroprotective in vivo

DJ-1, a Parkinson's disease-associated protein, is strongly up-regulated in reactive astrocytes in Parkinson's disease. This is proposed to represent a neuronal protective response, although the mechanism has not yet been identified. We have generated a transgenic zebrafish line with increased astroglial DJ-1 expression driven by regulatory elements from the zebrafish GFAP gene. Larvae from this transgenic line are protected from oxidative stress-induced injuries as caused by MPP⁺, a mitochondrial complex I inhibitor shown to induce dopaminergic cells death. In a global label-free proteomics analysis of wild type and transgenic larvae exposed to MPP⁺, 3418 proteins were identified, in which 366 proteins were differentially regulated. In particular, we identified enzymes belonging to primary metabolism to be among proteins affected by MPP⁺ in wild type animals, but not affected in the transgenic line. Moreover, by performing protein profiling on isolated astrocytes we showed that an increase in astrocytic DJ-1 expression up-regulated a large group of proteins associated with redox regulation, inflammation and mitochondrial respiration. The majority of these proteins have also been shown to be regulated by Nrf2. These findings provide a mechanistic insight into the protective role of astroglial up-regulation of DJ-1 and show that our transgenic zebrafish line with astrocytic DJ-1 over-expression can serve as a useful animal model to understand astrocyte-regulated neuroprotection associated with oxidative stress-related neurodegenerative disease.

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Increases astrocytic proteins linked to oxidative stress regulation & inflammation.

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Protects from MPP⁺-induced changes in central metabolism and protein nitrosylation.

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Protects from MPP⁺-induced tyrosine hydroxylase loss and motor deficits.

HACE1 is essential for astrocyte mitochondrial function and influences Huntington disease phenotypes in vivo

Oxidative stress is a prominent feature of Huntington disease (HD), and we have shown previously that reduced levels of hace1 (HECT domain and Ankyrin repeat containing E3 ubiquitin protein ligase 1) in patient striatum may contribute to the pathogenesis of HD. Hace1 promotes the stability of Nrf2 and thus plays an important role in antioxidant response mechanisms, which are dysfunctional in HD. Moreover, hace1 overexpression mitigates mutant huntingtin (mHTT)-induced oxidative stress in vitro through promotion of the Nrf2 antioxidant response. Here, we show that the genetic ablation of hace1 in the YAC128 mouse model of HD accelerates motor deficits and exacerbates cognitive and psychiatric phenotypes in vivo. We find that both the expression of mHTT and the ablation of hace1 alone are sufficient to cause deficits in astrocytic mitochondrial respiration. We confirm the crucial role of hace1 in astrocytes in vivo, since its ablation is sufficient to cause dramatic astrogliosis in wild-type FVB/N mice. Astrogliosis is not observed in the presence of mHTT but a strong dysregulation in the expression of astrocytic markers in HACE1-/- x YAC128 striatum suggests an additive effect of mHTT expression and hace1 loss on this cell type. HACE1-/- x YAC128 mice and primary cells derived from these animals therefore provide model systems that will allow for the further dissection of Nrf2 pathways and astrocyte dysfunction in the context of HD.

Astroglial and microglial contributions to iron metabolism disturbance in Parkinson's disease

Understandings of the disturbed iron metabolism in Parkinson's disease (PD) are largely from the perspectives of neurons. Neurodegenerative processes in PD trigger universal and conserved astroglial dysfunction and microglial activation. In this review, we start with astroglia and microglia in PD with an emphasis on their roles in spreading α-synuclein pathology, and then focus on their contributions in iron metabolism under normal conditions and the diseased state of PD. Elevated iron in the brain regions affects glial features, meanwhile, glial effects on neuronal iron metabolism are largely dependent on their releasing factors. These advances might be valuable for better understanding and modulating iron metabolism disturbance in PD.

"Pumping iron"-how macrophages handle iron at the systemic, microenvironmental, and cellular levels

Macrophages reside in virtually every organ. First arising during embryogenesis, macrophages replenish themselves in the adult through a combination of self-renewal and influx of bone marrow-derived monocytes. As large phagocytic cells, macrophages participate in innate immunity while contributing to tissue-specific homeostatic functions. Among the key metabolic tasks are senescent red blood cell recycling, free heme detoxification, and provision of iron for de novo hemoglobin synthesis. While this systemic mechanism involves the shuttling of iron between spleen, liver, and bone marrow through the concerted function of defined macrophage populations, similar circuits appear to exist within the microenvironment of other organs. The high turnover of iron is the prerequisite for continuous erythropoiesis and tissue integrity but challenges macrophages’ ability to maintain cellular iron homeostasis and immune function.

This review provides a brief overview of systemic, microenvironmental, and cellular aspects of macrophage iron handling with a focus on exciting and unresolved questions in the field.