Induction of cystine transport activity in mouse peritoneal macrophages by bacterial lipopolysaccharide

Exploiting ferroptosis vulnerabilities in cancer

Ferroptosis is a distinct lipid peroxidation-dependent form of necrotic cell death. This process has been increasingly contemplated as a new target for cancer therapy because of an intrinsic or acquired ferroptosis vulnerability in difficult-to-treat cancers and tumour microenvironments. Here we review recent advances in our understanding of the molecular mechanisms that underlie ferroptosis and highlight available tools for the modulation of ferroptosis sensitivity in cancer cells and communication with immune cells within the tumour microenvironment. We further discuss how these new insights into ferroptosis-activating pathways can become new armouries in the fight against cancer.

Ferroptosis resists intracellular Vibrio splendidus AJ01 mediated by ferroportin in sea cucumber Apostichopus japonicus

Ferroptosis, a kind of programmed cell death, is characterized with iron-dependent lipid ROS buildup, which is considered as an important cellular immunity in resisting intracellular bacterial infection in mammalian macrophages. In this process, lipid ROS oxidizes the bacterial biofilm to inhibit intracellular bacteria. However, the function of ferroptosis in invertebrate remains unknown. In this study, the existence of ferroptosis in Apostichopus japonicus coelomocytes was confirmed, and its antibacterial mechanism was investigated. First, our results indicated that the expression of glutathione peroxidase (AjGPX4) was significantly inhibited by 0.21-fold (p < 0.01) after injecting A. japonicus with the ferroptosis inducer RSL3, and the contents of MDA (3.93-fold, p < 0.01), ferrous iron (1.40-fold, p < 0.01), and lipid ROS (3.10-fold, p < 0.01) were all significantly increased under this condition and simultaneously accompanied with mitochondrial contraction and disappearance of cristae, indicating the existence of ferroptosis in the coelomocytes of A. japonicus. Subsequently, the contents of ferrous iron (1.40-fold, p < 0.05), MDA (2.10-fold, p < 0.01), ROS (1.70-fold, p < 0.01), and lipid ROS (2.50-fold, p < 0.01) were all significantly increased, whereas the mitochondrial membrane potential and GSH/GSSG were markedly decreased by 0.68-fold (p < 0.05) and 0.69-fold (p < 0.01) under Vibrio splendidus (AJ01) infection. This process could be reversed by the iron-chelating agent deferoxamine mesylate, which indicated that AJ01 could induce coelomocytic ferroptosis. Moreover, the results demonstrated that the intracellular AJ01 load was clearly decreased to 0.49-fold (p < 0.05) and 0.06-fold (p < 0.01) after treating coelomocytes with RSL3 and ferrous iron, which indicated that enhanced ferroptosis could inhibit bacterial growth. Finally, subcellular localization demonstrated that ferrous iron efflux protein ferroportin (AjFPN) and intracellular AJ01 were co-localized in coelomocytes. After AjFPN interference (0.58-fold, p < 0.01), the signals of ferrous iron and lipid ROS levels in intracellular AJ01 were significantly reduced by 0.38-fold (p < 0.01) and 0.48-fold (p < 0.01), indicating that AjFPN was an important factor in the introduction of ferroptosis into intracellular bacteria. Overall, our findings indicated that ferroptosis could resist intracellular AJ01 infection via AjFPN. These findings provide a novel defense mechanism for aquatic animals against intracellular bacterial infection.

Widespread S-persulfidation in activated macrophages as a protective mechanism against oxidative-inflammatory stress

Acute inflammatory responses often involve the production of reactive oxygen and nitrogen species by innate immune cells, particularly macrophages. How activated macrophages protect themselves in the face of oxidative-inflammatory stress remains a long-standing question. Recent evidence implicates reactive sulfur species (RSS) in inflammatory responses; however, how endogenous RSS affect macrophage function and response to oxidative and inflammatory insults remains poorly understood. In this study, we investigated the endogenous pathways of RSS biogenesis and clearance in macrophages, with a particular focus on exploring how hydrogen sulfide (H2S)-mediated S-persulfidation influences macrophage responses to oxidative-inflammatory stress. We show that classical activation of mouse or human macrophages using lipopolysaccharide and interferon-γ (LPS/IFN-γ) triggers substantial production of H2S/RSS, leading to widespread protein persulfidation. Biochemical and proteomic analyses revealed that this surge in cellular S-persulfidation engaged ∼2% of total thiols and modified over 800 functionally diverse proteins. S-persulfidation was found to be largely dependent on the cystine importer xCT and the H2S-generating enzyme cystathionine γ-lyase and was independent of changes in the global proteome. We further investigated the role of the sulfide-oxidizing enzyme sulfide quinone oxidoreductase (SQOR), and found that it acts as a negative regulator of S-persulfidation. Elevated S-persulfidation following LPS/IFN-γ stimulation or SQOR inhibition was associated with increased resistance to oxidative stress. Upregulation of persulfides also inhibited the activation of the macrophage NLRP3 inflammasome and provided protection against inflammatory cell death. Collectively, our findings shed light on the metabolism and effects of RSS in macrophages and highlight the crucial role of persulfides in enabling macrophages to withstand and alleviate oxidative-inflammatory stress.

Ironing out the role of ferroptosis in immunity

Ferroptosis is a type of regulated cell death that drives the pathophysiology of many diseases. Oxidative stress is detectable in many types of regulated cell death, but only ferroptosis involves lipid peroxidation and iron dependency. Ferroptosis originates and propagates from several organelles, including the mitochondria, endoplasmic reticulum, Golgi, and lysosomes. Recent data have revealed that immune cells can both induce and undergo ferroptosis. A mechanistic understanding of how ferroptosis regulates immunity is critical to understanding how ferroptosis controls immune responses and how this is dysregulated in disease. Translationally, more work is needed to produce ferroptosis-modulating immunotherapeutics. This review focuses on the role of ferroptosis in immune-related diseases, including infection, autoimmune diseases, and cancer. We discuss how ferroptosis is regulated in immunity, how this regulation contributes to disease pathogenesis, and how targeting ferroptosis may lead to novel therapies.

Role of solute carrier transporters in regulating dendritic cell maturation and function

Dendritic cells (DCs) are specialized antigen-presenting cells that initiate and regulate innate and adaptive immune responses. Solute carrier (SLC) transporters mediate diverse physiological functions and maintain cellular metabolite homeostasis. Recent studies have highlighted the significance of SLCs in immune processes. Notably, upon activation, immune cells undergo rapid and robust metabolic reprogramming, largely dependent on SLCs to modulate diverse immunological responses. In this review, we explore the central roles of SLC proteins and their transported substrates in shaping DC functions. We provide a comprehensive overview of recent studies on amino acid transporters, metal ion transporters, and glucose transporters, emphasizing their essential contributions to DC homeostasis under varying pathological conditions. Finally, we propose potential strategies for targeting SLCs in DCs to bolster immunotherapy for a spectrum of human diseases.

Deciphering the link: ferroptosis and its role in glioma

Glioma, as the most frequently occurring primary malignancy in the central nervous system, significantly impacts patients' quality of life and cognitive abilities. Ferroptosis, a newly discovered form of cell death, is characterized by significant iron accumulation and lipid peroxidation. This process is fundamentally dependent on iron. Various factors inducing ferroptosis can either directly or indirectly influence glutathione peroxidase, leading to reduced antioxidant capabilities and an increase in lipid reactive oxygen species (ROS) within cells, culminating in oxidative cell death. Recent research indicates a strong connection between ferroptosis and a range of pathophysiological conditions, including tumors, neurological disorders, ischemia-reperfusion injuries, kidney damage, and hematological diseases. The regulation of ferroptosis to intervene in the progression of these diseases has emerged as a major area of interest in etiological research and therapy. However, the exact functional alterations and molecular mechanisms underlying ferroptosis remain to be extensively studied. The review firstly explores the intricate relationship between ferroptosis and glioma, highlighting how ferroptosis contributes to glioma pathogenesis and how glioma cells may resist this form of cell death. Then, we discuss recent studies that have identified potential ferroptosis inducers and inhibitors, which could serve as novel therapeutic strategies for glioma. We also examine the current challenges in targeting ferroptosis in glioma treatment, including the complexity of its regulation and the need for precise delivery methods. This review aims to provide a comprehensive overview of the current state of research on ferroptosis in glioma, offering insights into future therapeutic strategies and the broader implications of this novel cell death pathway in cancer biology.

Organelle-Mediated Dissipative Self-Assembly of Peptides in Living Cells

Implementing dissipative assembly in living systems is meaningful for creation of living materials or even artificial life. However, intracellular dissipative assembly remains scarce and is significantly impeded by the challenges lying in precisely operating chemical reaction cycles under complex physiological conditions. Here, we develop organelle-mediated dissipative self-assembly of peptides in living cells fueled by GSH, via the design of a mitochondrion-targeting and redox-responsive hexapeptide. While the hexapeptide undergoes efficient redox-responsive self-assembly, the addition of GSH into the peptide solution in the presence of mitochondrion-biomimetic liposomes containing hydrogen peroxide allows for transient assembly of peptides. Internalization of the peptide by LPS-stimulated macrophages leads to the self-assembly of the peptide driven by GSH reduction and the association of the peptide assemblies with mitochondria. The association facilitates reversible oxidation of the reduced peptide by mitochondrion-residing ROS and thereby dissociates the peptide from mitochondria to re-enter the cytoplasm for GSH reduction. The metastable peptide-mitochondrion complexes prevent the thermodynamically equilibrated self-assembly, thus establishing dissipative assembly of peptides in stimulated macrophages. The entire dissipative self-assembling process allows for elimination of elevated ROS and decrease of pro-inflammatory cytokine expression. Creating dissipative self-assembling systems assisted by internal structures provides new avenues for the development of living materials or medical agents in the future.

Reactive Oxygen Species and Ferroptosis at the Nexus of Inflammation and Colon Cancer

Significance: Reactive oxygen species (ROS) are essential in maintaining normal intestinal physiology. Inflammatory bowel disease (IBD) is a relapsing chronic inflammatory disease of the intestine that is a major risk factor for colorectal cancer (CRC). Excess ROS are widely implicated in intestinal inflammation and cancer. Recent Advances: Clinical data have shown that targeting ROS broadly does not yield improved outcomes in IBD and CRC. However, selectively limiting oxidative damage may improve the efficacy of ROS targeting. An accumulation of lipid ROS induces a novel oxidative cell death pathway known as ferroptosis. A growing body of evidence suggests that ferroptosis is relevant to both IBD and CRC. Critical Issues: We propose that inhibition of ferroptosis will improve disease severity in IBD, whereas activating ferroptosis will limit CRC progression. Data from preclinical models suggest that methods of modulating ferroptosis have been successful in attenuating IBD and CRC. Future Directions: The etiology of IBD and progression of IBD to CRC are still unclear. Further understanding of ferroptosis in intestinal diseases will provide novel therapies. Ferroptosis is highly linked to inflammation, cell metabolism, and is cell-type dependent. Further research in assessing the inflammatory and tumor microenvironment in the intestine may provide novel vulnerabilities that can be targeted. Antioxid. Redox Signal. 39, 551-568.

MAT1A Suppression by the CTBP1/HDAC1/HDAC2 Transcriptional Complex Induces Immune Escape and Reduces Ferroptosis in Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) remains a significant health burden globally due to its high prevalence and morbidity. C-terminal-binding protein 1 (CTBP1) is a transcriptional corepressor that modulates gene transcription by interacting with transcription factors or chromatin-modifying enzymes. High CTBP1 expression has been associated with the progression of various human cancers. In this study, bioinformatics analysis suggested the existence of a CTBP1/histone deacetylase 1 (HDAC1)/HDAC2 transcriptional complex that regulates the expression of methionine adenosyltransferase 1A (MAT1A), whose loss has been associated with ferroptosis suppression and HCC development. Thus, this study aims to investigate the interactions between the CTBP1/HDAC1/HDAC2 complex and MAT1A and their roles in HCC progression. First, high expression of CTBP1 was observed in HCC tissues and cells, where it promoted HCC cell proliferation and mobility while inhibiting cell apoptosis. CTBP1 interacted with HDAC1 and HDAC2 to suppress the MAT1A transcription, and silencing of either HDAC1 or HDAC2 or overexpression of MAT1A led to the inhibition of cancer cell malignancy. In addition, MAT1A overexpression resulted in increased S-adenosylmethionine levels, which promoted ferroptosis of HCC cells directly or indirectly by increasing CD8+ T-cell cytotoxicity and interferon-γ production. In vivo, MAT1A overexpression suppressed growth of CTBP1-induced xenograft tumors in mice while enhancing immune activity and inducing ferroptosis. However, treatment with ferrostatin-1, a ferroptosis inhibitor, blocked the tumor-suppressive effects of MAT1A. Collectively, this study reveals that the CTBP1/HDAC1/HDAC2 complex-induced MAT1A suppression is liked to immune escape and reduced ferroptosis of HCC cells.

The epigenetic regulatory mechanisms of ferroptosis and its implications for biological processes and diseases

Ferroptosis is a form of regulated cell death triggered by the iron-dependent peroxidation of phospholipids. Interactions of iron and lipid metabolism factors jointly promote ferroptosis. Ferroptosis has been demonstrated to be involved in the development of various diseases, such as tumors and degenerative diseases (e.g., aortic dissection), and targeting ferroptosis is expected to be an effective strategy for the treatment of these diseases. Recent studies have shown that the regulation of ferroptosis is affected by multiple mechanisms, including genetics, epigenetics, posttranscriptional modifications, and protein posttranslational modifications. Epigenetic changes have garnered considerable attention due to their importance in regulating biological processes and potential druggability. There have been many studies on the epigenetic regulation of ferroptosis, including histone modifications (e.g., histone acetylation and methylation), DNA methylation, and noncoding RNAs (e.g., miRNAs, circRNAs, and lncRNAs). In this review, we summarize recent advances in research on the epigenetic mechanisms involved in ferroptosis, with a description of RNA N6-methyladenosine (m6A) methylation included, and the importance of epigenetic regulation in biological processes and ferroptosis-related diseases, which provides reference for the clinical application of epigenetic regulators in the treatment of related diseases by targeting ferroptosis.

The crosslinks between ferroptosis and autophagy in asthma

Autophagy is an evolutionarily conserved cellular process capable of degrading various biological molecules and organelles via the lysosomal pathway. Ferroptosis is a type of oxidative stress-dependent regulated cell death associated with the iron accumulation and lipid peroxidation. The crosslinks between ferroptosis and autophagy have been focused on since the dependence of ferroptosis on autophagy was discovered. Although the research and theories on the relationship between autophagy and ferroptosis remain scattered and fragmented, the crosslinks between these two forms of regulated cell death are closely related to the treatment of various diseases. Thereof, asthma as a chronic inflammatory disease has a tight connection with the occurrence of ferroptosis and autophagy since the crosslinked signal pathways may be the crucial regulators or exactly regulated by cells and secretion in the immune system. In addition, non-immune cells associated with asthma are also closely related to autophagy and ferroptosis. Further studies of cross-linking asthma inflammation with crosslinked signaling pathways may provide us with several key molecules that regulate asthma through specific regulators. The crosslinks between autophagy and ferroptosis provide us with a new perspective to interpret and understand the manifestations of asthma, potential drug discovery targets, and new therapeutic options to effectively intervene in the imbalance caused by abnormal inflammation in asthma. Herein, we introduce the main molecular mechanisms of ferroptosis, autophagy, and asthma, describe the role of crosslinks between ferroptosis and autophagy in asthma based on their common regulatory cells or molecules, and discuss potential drug discovery targets and therapeutic applications in the context of immunomodulatory and symptom alleviation.

Identification of ferroptosis‑associated genes in chronic kidney disease

Ferroptosis serves a pivotal role in developing chronic kidney disease (CKD). The present study aimed to detect and confirm the relevance of potential ferroptosis-related genes in CKD using bioinformatics and experimentation strategies. The original GSE15072 mRNA expression dataset was retrieved from the Gene Expression Omnibus database. Subsequently, the potential differentially expressed genes associated with ferroptosis of CKD were screened using R software. Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) pathway enrichment analyses, correlation analysis and protein-protein interactions (PPI) were performed for differentially expressed ferroptosis-associated genes (DFGs). Lastly, the expression levels of the top nine DFGs were measured in the kidney tissue of Adriamycin-induced CKD rats and healthy controls via reverse transcription-quantitative (RT-q)PCR analysis. Overall, 49 DFGs among 21 patients with CKD and nine healthy controls were identified. GO and KEGG enrichment analyses demonstrated that these DFGs were primarily involved in 'ferroptosis' and 'mitophagy'. PPI findings indicated that these ferroptosis-associated genes interacted with one another. RT-qPCR of CKD tissue from the rat model revealed that STAT3, MAPK14, heat shock protein (HSP)A5, MTOR and solute carrier family 2 member 1 (SLC2A1) mRNA levels in CKD were upregulated. Overall, 49 potential ferroptosis-associated genes of CKD were identified via bioinformatics analyses. STAT3, MAPK14, HSPA5, MTOR and SLC2A1 may influence CKD onset by regulating ferroptosis. The present results add to the existing body of knowledge about CKD and may be useful in the treatment of CKD.

Is depression the missing link between inflammatory mediators and cancer?

Patients with cancer are at greater risk of developing depression in comparison to the general population and this is associated with serious adverse effects, such as poorer quality of life, worse prognosis and higher mortality. Although the relationship between depression and cancer is now well established, a common underlying pathophysiological mechanism between the two conditions is yet to be elucidated. Existing theories of depression, based on monoamine neurotransmitter system dysfunction, are insufficient as explanations of the disorder. Recent advances have implicated neuroinflammatory mechanisms in the etiology of depression and it has been demonstrated that inflammation at a peripheral level may be mirrored centrally in astrocytes and microglia serving to promote chronic levels of inflammation in the brain. Three major routes to depression in cancer in which proinflammatory mediators are implicated, seem likely. Activation of the kynurenine pathway involving cytokines, increases tryptophan catabolism, resulting in diminished levels of serotonin which is widely acknowledged as being the hallmark of depression. It also results in neurotoxic effects on brain regions thought to be involved in the evolution of major depression. Proinflammatory mediators also play a crucial role in impairing regulatory glucocorticoid mediated feedback of the hypothalamic-pituitary-adrenal axis, which is activated by stress and considered to be involved in both depression and cancer. The third route is via the glutamatergic pathway, whereby glutamate excitotoxicity may lead to depression associated with cancer. A better understanding of the mechanisms underlying these dysregulated and other newly emerging pathways may provide a rationale for therapeutic targeting, serving to improve the care of cancer patients.

Targeting ferroptosis as a vulnerability in cancer

Ferroptosis is an iron-dependent form of regulated cell death that is triggered by the toxic build-up of lipid peroxides on cellular membranes. In recent years, ferroptosis has garnered enormous interest in cancer research communities, partly because it is a unique cell death modality that is mechanistically and morphologically different from other forms of cell death, such as apoptosis, and therefore holds great potential for cancer therapy. In this Review, we summarize the current understanding of ferroptosis-inducing and ferroptosis defence mechanisms, dissect the roles and mechanisms of ferroptosis in tumour suppression and tumour immunity, conceptualize the diverse vulnerabilities of cancer cells to ferroptosis, and explore therapeutic strategies for targeting ferroptosis in cancer.

Nutritional and Metabolic Control of Ferroptosis

Ferroptosis is a type of regulated cell death characterized by an excessive lipid peroxidation of cellular membranes caused by the disruption of the antioxidant defense system and/or an imbalanced cellular metabolism. Ferroptosis differentiates from other forms of regulated cell death in that several metabolic pathways and nutritional aspects, including endogenous antioxidants (such as coenzyme Q₁₀, vitamin E, and di/tetrahydrobiopterin), iron handling, energy sensing, selenium utilization, amino acids, and fatty acids, directly regulate the cells' sensitivity to lipid peroxidation and ferroptosis. As hallmarks of ferroptosis have been documented in a variety of diseases, including neurodegeneration, acute organ injury, and therapy-resistant tumors, the modulation of ferroptosis using pharmacological tools or by metabolic reprogramming holds great potential for the treatment of ferroptosis-associated diseases and cancer therapy. Hence, this review focuses on the regulation of ferroptosis by metabolic and nutritional cues and discusses the potential of nutritional interventions for therapy by targeting ferroptosis. Expected final online publication date for the Annual Review of Nutrition, Volume 42 is August 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Soluble Carrier Transporters and Mitochondria in the Immunometabolic Regulation of Macrophages

Significance: Immunometabolic regulation of macrophages is a growing area of research across many fields. Here, we review the contribution of solute carriers (SLCs) in regulating macrophage metabolism. We also highlight key mechanisms that regulate SLC function, their effects on mitochondrial activity, and how these intracellular activities contribute to macrophage fitness in health and disease. Recent Advances: SLCs serve as a major drug absorption pathway and represent a novel category of therapeutic drug targets. SLC dynamics affect cellular nutritional sensors, such as AMP-activated protein kinase and mammalian target of rapamycin, and consequently alter the cellular metabolism and mitochondrial dynamics within macrophages to adapt to a new functional phenotype. Critical Issues: SLC function affects macrophage phenotype, but their mechanisms of action and how their functions contribute to host health remain incompletely defined. Future Directions: Few studies focus on the impact of solute transporters on macrophage function. Identifying which SLCs are present in macrophages and determining their functional roles may reveal novel therapeutic targets with which to treat metabolic and inflammatory diseases. Antioxid. Redox Signal. 36, 906-919.

Metabolite transporters as regulators of macrophage polarization

Macrophages are myeloid immune cells, present in virtually all tissues which exhibit considerable functional plasticity and diversity. Macrophages are often subdivided into two distinct subsets described as classically activated (M1) and alternatively activated (M2) macrophages. It has recently emerged that metabolites regulate the polarization and function of macrophages by altering metabolic pathways. These metabolites often cannot freely pass the cell membrane and are therefore transported by the corresponding metabolite transporters. Here, we reviewed how glucose, glutamate, lactate, fatty acid, and amino acid transporters are involved in the regulation of macrophage polarization. Understanding the interactions among metabolites, metabolite transporters, and macrophage function under physiological and pathological conditions may provide further insights for novel drug targets for the treatment of macrophage-associated diseases. In Brief Recent studies have shown that the polarization and function of macrophages are regulated by metabolites, most of which cannot pass freely through biofilms. Therefore, metabolite transporters required for the uptake of metabolites have emerged seen as important regulators of macrophage polarization and may represent novel drug targets for the treatment of macrophage-associated diseases. Here, we summarize the role of metabolite transporters as regulators of macrophage polarization.

Cystine-glutamate antiporter deletion accelerates motor recovery and improves histological outcomes following spinal cord injury in mice

xCT is the specific subunit of System xc-, an antiporter importing cystine while releasing glutamate. Although xCT expression has been found in the spinal cord, its expression and role after spinal cord injury (SCI) remain unknown. The aim of this study was to characterize the role of xCT on functional and histological outcomes following SCI induced in wild-type (xCT+/+) and in xCT-deficient mice (xCT−/−). In the normal mouse spinal cord, slc7a11/xCT mRNA was detected in meningeal fibroblasts, vascular mural cells, astrocytes, motor neurons and to a lesser extent in microglia. slc7a11/xCT gene and protein were upregulated within two weeks post-SCI. xCT−/− mice recovered muscular grip strength as well as pre-SCI weight faster than xCT+/+ mice. Histology of xCT−/− spinal cords revealed significantly more spared motor neurons and a higher number of quiescent microglia. In xCT−/− mice, inflammatory polarization shifted towards higher mRNA expression of ym1 and igf1 (anti-inflammatory) while lower levels of nox2 and tnf-a (pro-inflammatory). Although astrocyte polarization did not differ, we quantified an increased expression of lcn2 mRNA. Our results show that slc7a11/xCT is overexpressed early following SCI and is detrimental to motor neuron survival. xCT deletion modulates intraspinal glial activation by shifting towards an anti-inflammatory profile.

Role of Ferroptosis in Lung Diseases

Ferroptosis is a new type of programmed cell death characterized by intracellular iron accumulation and lipid peroxidation that leads to oxidative stress and cell death. The metabolism of iron, lipids, and amino acids and multiple signalling pathways precisely regulate the process of ferroptosis. Emerging evidence has demonstrated that ferroptosis participates in the occurrence and progression of various pathological conditions and diseases, such as infections, neurodegeneration, tissue ischaemia-reperfusion injury and immune diseases. Recent studies have also indicated that ferroptosis plays a critical role in the pathogenesis of acute lung injury, chronic obstructive pulmonary disease, pulmonary fibrosis, pulmonary infection and asthma. Herein, we summarize the latest knowledge on the regulatory mechanism of ferroptosis and its association with iron, lipid and amino acid metabolism as well as several signalling pathways. Furthermore, we review the contribution of ferroptosis to the pathogenesis of lung diseases and discuss ferroptosis as a novel therapeutic target for various lung diseases.

Ferroptosis: mechanisms, biology and role in disease

The research field of ferroptosis has seen exponential growth over the past few years, since the term was coined in 2012. This unique modality of cell death, driven by iron-dependent phospholipid peroxidation, is regulated by multiple cellular metabolic pathways, including redox homeostasis, iron handling, mitochondrial activity and metabolism of amino acids, lipids and sugars, in addition to various signalling pathways relevant to disease. Numerous organ injuries and degenerative pathologies are driven by ferroptosis. Intriguingly, therapy-resistant cancer cells, particularly those in the mesenchymal state and prone to metastasis, are exquisitely vulnerable to ferroptosis. As such, pharmacological modulation of ferroptosis, via both its induction and its inhibition, holds great potential for the treatment of drug-resistant cancers, ischaemic organ injuries and other degenerative diseases linked to extensive lipid peroxidation. In this Review, we provide a critical analysis of the current molecular mechanisms and regulatory networks of ferroptosis, the potential physiological functions of ferroptosis in tumour suppression and immune surveillance, and its pathological roles, together with a potential for therapeutic targeting. Importantly, as in all rapidly evolving research areas, challenges exist due to misconceptions and inappropriate experimental methods. This Review also aims to address these issues and to provide practical guidelines for enhancing reproducibility and reliability in studies of ferroptosis. Finally, we discuss important concepts and pressing questions that should be the focus of future ferroptosis research.

Astrocytes release glutamate via cystine/glutamate antiporter upregulated in response to increased oxidative stress related to sporadic amyotrophic lateral sclerosis

A vast body of evidence implicates increased oxidative stress and extracellular glutamate accumulation in the pathomechanism of sporadic amyotrophic lateral sclerosis (ALS). Cystine/glutamate antiporter (xCT) carries extracellular cystine uptake and intracellular glutamate release (cystine/glutamate exchange) in the presence of oxidative stress. The aim of the present study was to determine the involvement of xCT in ALS. Immunohistochemical observations in the spinal cord sections demonstrated that xCT was mainly expressed in astrocytes, with staining more intense in 12 sporadic ALS patients as compared to 12 age-matched control individuals. Western blot and densitometric analyses of the spinal cord samples revealed that the relative value of xCT/β-actin optical density ratio was significantly higher in the ALS group as compared to the control group. Next, we conducted cell culture experiments using a human astrocytoma-derived cell line (1321N1) and a mouse motor neuron/neuroblastoma hybrid cell line (NSC34). In 1321N1 cells, the normalized xCT expression levels in cell lysates were significantly increased by H₂ O₂ treatment. Glutamate concentrations in 1321 N1 cell culture-conditioned media were significantly elevated by H₂ O₂ treatment, and the H₂ O₂ -driven elevations were completely canceled by the xCT inhibitor erastin pretreatment. In motor neuron-differentiated NSC34 cells (NSC34d cells), both the normalized xCT expression levels in the cell lysates and glutamate concentrations in the cell-conditioned media were constant with or without H₂ O₂ treatment. The present results provide in vivo and in vitro evidence that astrocytes upregulate xCT expression to release glutamate in response to increased oxidative stress associated with ALS, contributing to extracellular glutamate accumulation.

The Metabolic Underpinnings of Ferroptosis

Acute or chronic cellular stress resulting from aberrant metabolic and biochemical processes may trigger a pervasive non-apoptotic form of cell death, generally known as ferroptosis. Ferroptosis is unique among the different cell death modalities, as it has been mostly linked to pathophysiological conditions and because several metabolic pathways, such as (seleno)thiol metabolism, fatty acid metabolism, iron handling, mevalonate pathway, and mitochondrial respiration, directly impinge on the cells' sensitivity toward lipid peroxidation and ferroptosis. Additionally, key cellular redox systems, such as selenium-dependent glutathione peroxidase 4 and the NAD(P)H/ferroptosis suppressor protein-1/ubiquinone axis, are at play that constantly surveil and neutralize oxidative damage to cellular membranes. Since this form of cell death emerges to be the root cause of a number of diseases and since it offers various pharmacologically tractable nodes for therapeutic intervention, there has been overwhelming interest in the last few years aiming for a better molecular understanding of the ferroptotic death process.

An Overview of Nrf2 Signaling Pathway and Its Role in Inflammation

Inflammation is a key driver in many pathological conditions such as allergy, cancer, Alzheimer’s disease, and many others, and the current state of available drugs prompted researchers to explore new therapeutic targets. In this context, accumulating evidence indicates that the transcription factor Nrf2 plays a pivotal role controlling the expression of antioxidant genes that ultimately exert anti-inflammatory functions. Nrf2 and its principal negative regulator, the E3 ligase adaptor Kelch-like ECH- associated protein 1 (Keap1), play a central role in the maintenance of intracellular redox homeostasis and regulation of inflammation. Interestingly, Nrf2 is proved to contribute to the regulation of the heme oxygenase-1 (HO-1) axis, which is a potent anti-inflammatory target. Recent studies showed a connection between the Nrf2/antioxidant response element (ARE) system and the expression of inflammatory mediators, NF-κB pathway and macrophage metabolism. This suggests a new strategy for designing chemical agents as modulators of Nrf2 dependent pathways to target the immune response. Therefore, the present review will examine the relationship between Nrf2 signaling and the inflammation as well as possible approaches for the therapeutic modulation of this pathway.

Metabolite Transporters as Regulators of Immunity

In the past decade, the rise of immunometabolism has fundamentally reshaped the face of immunology. As the functions and properties of many (immuno)metabolites have now been well described, their exchange among cells and their environment have only recently sparked the interest of immunologists. While many metabolites bind specific receptors to induce signaling cascades, some are actively exchanged between cells to communicate, or induce metabolic reprograming. In this review, we give an overview about how active metabolite transport impacts immune cell function and shapes immunological responses. We present some examples of how specific transporters feed into metabolic pathways and initiate intracellular signaling events in immune cells. In particular, we focus on the role of metabolite transporters in the activation and effector functions of T cells and macrophages, as prototype adaptive and innate immune cell populations.

Identification, Expression, and Roles of the Cystine/Glutamate Antiporter in Ocular Tissues

The cystine/glutamate antiporter (system x _c ^-) is composed of a heavy chain subunit 4F2hc linked by a disulphide bond to a light chain xCT, which exchanges extracellular cystine, the disulphide form of the amino acid cysteine, for intracellular glutamate. In vitro research in the brain, kidney, and liver have shown this antiporter to play a role in minimising oxidative stress by providing a source of intracellular cysteine for the synthesis of the antioxidant glutathione. In vivo studies using the xCT knockout mouse revealed that the plasma cystine/cysteine redox couple was tilted to a more oxidative state demonstrating system x_c ^- to also play a role in maintaining extracellular redox balance by driving a cystine/cysteine redox cycle. In addition, through import of cystine, system x_c ^- also serves to export glutamate into the extracellular space which may influence neurotransmission and glutamate signalling in neural tissues. While changes to system x_c ^- function has been linked to cancer and neurodegenerative disease, there is limited research on the roles of system x_c ^- in the different tissues of the eye, and links between the antiporter, aging, and ocular disease. Hence, this review seeks to consolidate research on system x_c ^- in the cornea, lens, retina, and ocular humours conducted across several species to shed light on the in vitro and in vivo roles of xCT in the eye and highlight the utility of the xCT knockout mouse as a tool to investigate the contribution of xCT to age-related ocular diseases.

Solute carrier transporters: the metabolic gatekeepers of immune cells

Solute carrier (SLC) transporters meditate many essential physiological functions, including nutrient uptake, ion influx/efflux, and waste disposal. In its protective role against tumors and infections, the mammalian immune system coordinates complex signals to support the proliferation, differentiation, and effector function of individual cell subsets. Recent research in this area has yielded surprising findings on the roles of solute carrier transporters, which were discovered to regulate lymphocyte signaling and control their differentiation, function, and fate by modulating diverse metabolic pathways and balanced levels of different metabolites. In this review, we present current information mainly on glucose transporters, amino-acid transporters, and metal ion transporters, which are critically important for mediating immune cell homeostasis in many different pathological conditions.

Erastin Inhibits Septic Shock and Inflammatory Gene Expression via Suppression of the NF-κB Pathway

Sepsis is a life-threatening condition that is caused by an abnormal immune response to infection and can lead to tissue damage, organ failure, and death. Erastin is a small molecule capable of initiating ferroptotic cell death in cancer cells. However, the function of erastin in the inflammatory response during sepsis remains unknown. Here, we showed that erastin ameliorates septic shock induced by cecal ligation and puncture or lipopolysaccharides (LPS) in mice, which was associated with a reduced production of inflammatory mediators such as nitric oxide, tumor necrosis factor (TNF)-α, and interleukin (IL)-1β. Pretreatment with erastin in bone marrow-derived macrophages (BMDMs) significantly attenuated the expression of inducible nitric oxide synthase, cyclooxygenase-2, TNF-α, and IL-1β mRNA in response to LPS treatment. Furthermore, we also showed that erastin suppresses phosphorylation of IκB kinase β, phosphorylation and degradation of IκBα, and nuclear translocation of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in LPS-stimulated BMDMs. Our findings suggest that erastin attenuates the inflammatory response by suppressing the NF-κB signaling pathway, resulting in inhibition of sepsis development. This study provides new insights regarding the potential therapeutic properties of erastin in sepsis.

The chemical basis of ferroptosis

Lipid peroxidation underlies the mechanism of oxidative cell death now known as ferroptosis. This modality, distinct from other forms of cell death, has been intensely researched in recent years owing to its relevance in both degenerative disease and cancer. The demonstration that it can be modulated by small molecules in multiple pathophysiological contexts offers exciting opportunities for novel pharmacological interventions. Herein, we introduce the salient features of lipid peroxidation, how it can be modulated by small molecules and what principal aspects require urgent investigation by researchers in the field. The central role of non-enzymatic reactions in the execution of ferroptosis will be emphasized, as these processes have hitherto not been generally considered 'druggable'. Moreover, we provide a critical perspective on the biochemical mechanisms that contribute to cell vulnerability to ferroptosis and discuss how they can be exploited in the design of novel therapeutics.

Corneal opacities in mice exposed to repeated contact procedures during ocular examinations

BACKGROUND

Cystine/glutamate exchanger (xCT) knockout mice are reported to exhibit an oxidative shift in the plasma cystine/cysteine ratio reminiscent of that seen in human plasma of ageing individuals. This suggests that the xCT knockout mouse is a model of accelerated ageing. The aim of this study was to examine the progression of age-related pathologies in the ocular tissues of wild-type mice and compare this to the xCT knockout mice.

METHODS

Wild-type and xCT knockout mice were examined longitudinally or as separate groups of animals at six weeks, three months, six months, nine months, and 12 months of age. All groups of mice were anaesthetised, intraocular pressure measured using the iCare TONOLAB rebound tonometer and eyes examined using the Micron IV system.

RESULTS

While the aim of the study was to determine if xCT knockout mice developed age-related pathologies earlier than wild-type mice, it was inadvertently discovered in the longitudinal cohort of animals, that the eyes developed corneal lesions in both groups of animals by six months of age, which obscured examination of the lens and retina. These lesions were not characteristic of age-related pathologies, but rather due to an external stressor. Lesions in the xCT knockout mice developed at an earlier age compared to wild-type mice, suggesting that loss of xCT exacerbates damage to the cornea, most likely caused by the rebound tonometer. When the same ocular procedures were performed on separate cohorts of mice of specific ages, no corneal lesions were detected for both groups of mice.

CONCLUSIONS

While it may seem advantageous to examine the same cohort of mice to monitor the development of age-related pathologies, the type of ophthalmic tests conducted needs to be carefully considered to avoid introducing pathologies that are inadvertently a result of the examination process itself.

Genetic deletion of xCT attenuates peripheral and central inflammation and mitigates LPS-induced sickness and depressive-like behavior in mice

The communication between the immune and central nervous system (CNS) is affected in many neurological disorders. Peripheral injections of the endotoxin lipopolysaccharide (LPS) are widely used to study this communication: an LPS challenge leads to a biphasic syndrome that starts with acute sickness and is followed by persistent brain inflammation and chronic behavioral alterations such as depressive-like symptoms. In vitro, the response to LPS treatment has been shown to involve enhanced expression of system <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mi>x</mml:mi></mml:mrow> <mml:mrow><mml:mi>c</mml:mi></mml:mrow> <mml:mrow><mml:mo>-</mml:mo></mml:mrow> </mml:msubsup> </mml:math> . This cystine-glutamate antiporter, with xCT as specific subunit, represents the main glial provider of extracellular glutamate in mouse hippocampus. Here we injected male xCT knockout and wildtype mice with a single intraperitoneal dose of 5 mg/kg LPS. LPS-injection increased hippocampal xCT expression but did not alter the mainly astroglial localization of the xCT protein. Peripheral and central inflammation (as defined by cytokine levels and morphological activation of microglia) as well as LPS-induced sickness and depressive-like behavior were significantly attenuated in xCT-deficient mice compared with wildtype mice. Our study is the first to demonstrate the involvement of system <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup><mml:mrow><mml:mi>x</mml:mi></mml:mrow> <mml:mrow><mml:mi>c</mml:mi></mml:mrow> <mml:mrow><mml:mo>-</mml:mo></mml:mrow> </mml:msubsup> </mml:math> in peripheral and central inflammation in vivo and the potential therapeutic relevance of its inhibition in brain disorders characterized by peripheral and central inflammation, such as depression.

Chemical Biology of Hydropersulfides and Related Species: Possible Roles in Cellular Protection and Redox Signaling

SIGNIFICANCE

For >20 years, physiological signaling associated with the endogenous generation of hydrogen sulfide (H₂S) has been of significant interest. Despite its presumed importance, the biochemical mechanisms associated with its actions have not been elucidated. Recent Advances: Recently it has been found that H₂S-related or derived species are highly prevalent in mammalian systems and that these species may be responsible for some, if not the majority, of the biological actions attributed to H₂S. One of the most prevalent and intriguing species are hydropersulfides (RSSH), which can be present at significant levels. Indeed, it appears that H₂S and RSSH are intimately linked in biological systems and likely to be mutually inclusive.

CRITICAL ISSUES

The fact that H₂S and polysulfides such as RSSH are present simultaneously means that the biological actions previously assigned to H₂S can be instead because of the presence of RSSH (or other polysulfides). Thus, it remains possible that hydropersulfides are the biological effectors, and H₂S serves, to a certain extent, as a marker for persulfides and polysulfides. Addressing this possibility will to a large extent be based on the chemistry of these species.

FUTURE DIRECTIONS

Currently, it is known that persulfides possess unique and novel chemical properties that may explain their biological prevalence. However, significantly more work will be required to establish the possible physiological roles of these species. Moreover, an understanding of the regulation of their biosynthesis and degradation will become important topics in piecing together their biology. Antioxid. Redox Signal. 00, 000-000.

The complex roles of STAT3 and STAT5 in maintaining redox balance: Lessons from STAT-mediated xCT expression in cancer cells

STAT3 and STAT5 mediate diverse cellular processes, transcriptionally regulating gene expression and interacting with cytoplasmic proteins. Their canonical activity is stimulated by cytokines/growth factors through JAK-STAT signaling. As targets of oncogenes with intrinsic tyrosine kinase activity, STAT3 and STAT5 become constitutively active in hematologic neoplasms and solid tumors, promoting cell proliferation and survival and modulating redox homeostasis. This review summarizes reactive oxygen species (ROS)-regulated STAT activation and how STATs influence ROS production. ROS-induced effects on post-translational modifications are presented, and STAT3/5-mediated regulation of xCT, a redox-sensitive target up-regulated in numerous cancers, is discussed with regard to transcriptional cross-talk.

Anti-inflammatory effects of the cannabidiol derivative dimethylheptyl-cannabidiol - studies in BV-2 microglia and encephalitogenic T cells

BACKGROUND

Dimethylheptyl-cannabidiol (DMH-CBD), a non-psychoactive, synthetic derivative of the phytocannabinoid cannabidiol (CBD), has been reported to be anti-inflammatory in RAW macrophages. Here, we evaluated the effects of DMH-CBD at the transcriptional level in BV-2 microglial cells as well as on the proliferation of encephalitogenic T cells.

METHODS

BV-2 cells were pretreated with DMH-CBD, followed by stimulation with the endotoxin lipopolysaccharide (LPS). The expression levels of selected genes involved in stress regulation and inflammation were determined by quantitative real-time PCR. In addition, MOG35-55-reactive T cells (TMOG) were cultured with antigen-presenting cells in the presence of DMH-CBD and MOG35-55 peptide, and cell proliferation was determined by measuring [3H]thymidine incorporation.

RESULTS

DMH-CBD treatment downregulated in a dose-dependent manner the mRNA expression of LPS-upregulated pro-inflammatory genes (Il1b, Il6, and Tnf) in BV-2 microglial cells. The expression of these genes was also downregulated by DMH-CBD in unstimulated cells. In parallel, DMH-CBD upregulated the expression of genes related to oxidative stress and glutathione homeostasis such as Trb3, Slc7a11/xCT, Hmox1, Atf4, Chop, and p8 in both stimulated and unstimulated microglial cells. In addition, DMH-CBD dose-dependently inhibited MOG35-55-induced TMOG proliferation.

CONCLUSIONS

The results show that DMH-CBD has similar anti-inflammatory properties to those of CBD. DMH-CBD downregulates the expression of inflammatory cytokines and protects the microglial cells by inducing an adaptive cellular response against inflammatory stimuli and oxidative injury. In addition, DMH-CBD decreases the proliferation of pathogenic activated TMOG cells.

Development of a primary microglia screening assay and its use to characterize inhibition of system xc- by erastin and its analogs

The inflammatory response in the central nervous system involves activated microglia. Under normal conditions they remove damaged neurons by phagocytosis. On the other hand, neurodegenerative diseases are thought to involve chronic microglia activation resulting in release of excess glutamate, proinflammatory cytokines and reactive oxygen species, leading to neuronal death. System x_C^- cystine/glutamate antiporter (SXC), a sodium independent heterodimeric transporter found in microglia and astrocytes in the CNS, imports cystine into the cell and exports glutamate. SXC has been shown to be upregulated in neurodegenerative diseases including multiple sclerosis, ALS, neuroAIDS Parkinson's disease and Alzheimer's disease. Consequently, SXC inhibitors could be of use in the treatment of diseases characterized by neuroinflammation and glutamate excitotoxicity. We report on the optimization of a primary microglia-based assay to screen for SXC inhibitors. Rat primary microglia were activated using lipopolysaccharides (LPS) and glutamate release and cystine uptake were monitored by fluorescence and radioactivity respectively. LPS-induced glutamate release increased with increasing cell density, time of incubation and LPS concentration. Conditions to screen for SXC inhibitors were optimized in 96-well format and subsequently used to evaluate SXC inhibitors. Known SXC inhibitors sulfasalazine, S-4CPG and erastin blocked glutamate release and cystine uptake while R-4CPG, the inactive enantiomer of S-4CPG, failed to inhibit glutamate release or cystine transport. In addition, several erastin analogs were evaluated using primary microglia and found to have EC₅₀ values in agreement with previous studies using established cell lines.

•

Conditions to screen for SXC inhibitors were optimized in 96-well format.

•

Assay enables higher throughput screens for SXC inhibitors with primary microglia.

•

Screening assay was used to evaluate prototype SXC inhibitors and erastin analogs.

Absence of system xc- on immune cells invading the central nervous system alleviates experimental autoimmune encephalitis

BACKGROUND

Multiple sclerosis (MS) is an autoimmune demyelinating disease that affects the central nervous system (CNS), leading to neurodegeneration and chronic disability. Accumulating evidence points to a key role for neuroinflammation, oxidative stress, and excitotoxicity in this degenerative process. System x_c^- or the cystine/glutamate antiporter could tie these pathological mechanisms together: its activity is enhanced by reactive oxygen species and inflammatory stimuli, and its enhancement might lead to the release of toxic amounts of glutamate, thereby triggering excitotoxicity and neurodegeneration.

METHODS

Semi-quantitative Western blotting served to study protein expression of xCT, the specific subunit of system x_c^-, as well as of regulators of xCT transcription, in the normal appearing white matter (NAWM) of MS patients and in the CNS and spleen of mice exposed to experimental autoimmune encephalomyelitis (EAE), an accepted mouse model of MS. We next compared the clinical course of the EAE disease, the extent of demyelination, the infiltration of immune cells and microglial activation in xCT-knockout (xCT^-/-) mice and irradiated mice reconstituted in xCT^-/- bone marrow (BM), to their proper wild type (xCT^+/+) controls.

RESULTS

xCT protein expression levels were upregulated in the NAWM of MS patients and in the brain, spinal cord, and spleen of EAE mice. The pathways involved in this upregulation in NAWM of MS patients remain unresolved. Compared to xCT^+/+ mice, xCT^-/- mice were equally susceptible to EAE, whereas mice transplanted with xCT^-/- BM, and as such only exhibiting loss of xCT in their immune cells, were less susceptible to EAE. In none of the above-described conditions, demyelination, microglial activation, or infiltration of immune cells were affected.

CONCLUSIONS

Our findings demonstrate enhancement of xCT protein expression in MS pathology and suggest that system x_c^- on immune cells invading the CNS participates to EAE. Since a total loss of system x_c^- had no net beneficial effects, these results have important implications for targeting system x_c^- for treatment of MS.

Genomic analysis of xCT-mediated regulatory network: Identification of novel targets against AIDS-associated lymphoma

Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiological agent of primary effusion lymphoma (PEL), a rapidly progressing malignancy mostly arising in HIV-infected patients. Even under conventional chemotherapy, PEL continues to portend nearly 100% mortality within several months, which urgently requires novel therapeutic strategies. We have previously demonstrated that targeting xCT, an amino acid transporter for cystine/glutamate exchange, induces significant PEL cell apoptosis through regulation of multiple host and viral factors. More importantly, one of xCT selective inhibitors, Sulfasalazine (SASP), effectively prevents PEL tumor progression in an immune-deficient xenograft model. In the current study, we use Illumina microarray to explore the profile of genes altered by SASP treatment within 3 KSHV⁺ PEL cell-lines, and discover that many genes involved in oxidative stress/antioxidant defense system, apoptosis/anti-apoptosis/cell death, and cellular response to unfolded proteins/topologically incorrect proteins are potentially regulated by xCT. We further validate 2 downstream candidates, OSGIN1 (oxidative stress-induced growth inhibitor 1) and XRCC5 (X-ray repair cross-complementing protein 5), and evaluate their functional relationship with PEL cell survival/proliferation and chemoresistance, respectively. Together, our data indicate that targeting these novel xCT-regulated downstream genes may represent a promising new therapeutic strategy against PEL and/or other AIDS-related lymphoma.

Interleukin 1β Regulation of the System xc- Substrate-specific Subunit, xCT, in Primary Mouse Astrocytes Involves the RNA-binding Protein HuR

System xc(-) is a heteromeric amino acid cystine/glutamate antiporter that is constitutively expressed by cells of the CNS, where it functions in the maintenance of intracellular glutathione and extracellular glutamate levels. We recently determined that the cytokine, IL-1β, increases the activity of system xc(-) in CNS astrocytes secondary to an up-regulation of its substrate-specific light chain, xCT, and that this occurs, in part, at the level of transcription. However, an in silico analysis of the murine xCT 3'-UTR identified numerous copies of adenine- and uridine-rich elements, raising the possibility that undefined trans-acting factors governing mRNA stability and translation may also contribute to xCT expression. Here we show that IL-1β increases the level of mRNA encoding xCT in primary cultures of astrocytes isolated from mouse cortex in association with an increase in xCT mRNA half-life. Additionally, IL-1β induces HuR translocation from the nucleus to the cytoplasm. RNA immunoprecipitation analysis reveals that HuR binds directly to the 3'-UTR of xCT in an IL-1β-dependent manner. Knockdown of endogenous HuR protein abrogates the IL-1β-mediated increase in xCT mRNA half-life, whereas overexpression of HuR in unstimulated primary mouse astrocytes doubles the half-life of constitutive xCT mRNA. This latter effect is accompanied by an increase in xCT protein levels, as well as a functional increase in system xc(-) activity. Altogether, these data support a critical role for HuR in mediating the IL-1β-induced stabilization of astrocyte xCT mRNA.

A Cytotoxic, Co-operative Interaction Between Energy Deprivation and Glutamate Release From System xc- Mediates Aglycemic Neuronal Cell Death

The astrocyte cystine/glutamate antiporter (system xc(-)) contributes substantially to the excitotoxic neuronal cell death facilitated by glucose deprivation. The purpose of this study was to determine the mechanism by which this occurred. Using pure astrocyte cultures, as well as, mixed cortical cell cultures containing both neurons and astrocytes, we found that neither an enhancement in system xc(-) expression nor activity underlies the excitotoxic effects of aglycemia. In addition, using three separate bioassays, we demonstrate no change in the ability of glucose-deprived astrocytes--either cultured alone or with neurons--to remove glutamate from the extracellular space. Instead, we demonstrate that glucose-deprived cultures are 2 to 3 times more sensitive to the killing effects of glutamate or N-methyl-D-aspartate when compared with their glucose-containing controls. Hence, our results are consistent with the weak excitotoxic hypothesis such that a bioenergetic deficiency, which is measureable in our mixed but not astrocyte cultures, allows normally innocuous concentrations of glutamate to become excitotoxic. Adding to the burgeoning literature detailing the contribution of astrocytes to neuronal injury, we conclude that under our experimental paradigm, a cytotoxic, co-operative interaction between energy deprivation and glutamate release from astrocyte system xc(-) mediates aglycemic neuronal cell death.

Exploratory Clinical Investigation of (4S)-4-(3-18F-Fluoropropyl)-L-Glutamate PET of Inflammatory and Infectious Lesions

We explored system [Formula: see text] transporter activity and the detection of inflammatory or infectious lesions using (4S)-4-(3-(18)F-fluoropropyl)-l-glutamate ((18)F-FSPG) PET.

METHODS

In 10 patients with various inflammatory or infectious diseases, as many as 5 of the largest lesions were selected as reference lesions. (18)F-FSPG images were assessed visually and quantitatively. Expression levels of xCT, CD44, and surface markers of inflammatory cells were evaluated by immunohistochemistry.

RESULTS

(18)F-FSPG PET detected all reference lesions. (18)F-FSPG uptake in sarcoidosis was significantly higher than that in nonsarcoidosis. The lesion-to-blood-pool SUV ratio for (18)F-FSPG was comparable to that for (18)F-FDG in sarcoidosis. In nonsarcoidosis, however, it was significantly lower. In 5 patients with available tissue samples, the SUVmax for (18)F-FSPG and CD163 were negatively correlated (ρ = -0.872, P = 0.054).

CONCLUSION

(18)F-FSPG PET may detect inflammatory lesions when activated macrophages or monocytes are present, such as in sarcoidosis.

Main path and byways: non-vesicular glutamate release by system xc(-) as an important modifier of glutamatergic neurotransmission

System xc(-) is a cystine/glutamate antiporter that exchanges extracellular cystine for intracellular glutamate. Cystine is intracellularly reduced to cysteine, a building block of GSH. As such, system xc(-) can regulate the antioxidant capacity of cells. Moreover, in several brain regions, system xc(-) is the major source of extracellular glutamate. As such this antiporter is able to fulfill key physiological functions in the CNS, while evidence indicates it also plays a role in certain brain pathologies. Since the transcription of xCT, the specific subunit of system xc(-), is enhanced by the presence of reactive oxygen species and inflammatory cytokines, system xc(-) could be involved in toxic extracellular glutamate release in neurological disorders that are associated with increased oxidative stress and neuroinflammation. System xc(-) has also been reported to contribute to the invasiveness of brain tumors and, as a source of extracellular glutamate, could participate in the induction of peritumoral seizures. Two independent reviews (Pharmacol. Rev. 64, 2012, 780; Antioxid. Redox Signal. 18, 2013, 522), approached from a different perspective, have recently been published on the functions of system xc(-) in the CNS. In this review, we highlight novel achievements and insights covering the regulation of system xc(-) as well as its involvement in emotional behavior, cognition, addiction, neurological disorders and glioblastomas, acquired in the past few years. System xc(-) constitutes an important source of extrasynaptic glutamate in the brain. By modulating the tone of extrasynaptic metabotropic or ionotropic glutamate receptors, it affects excitatory neurotransmission, the threshold for overexcitation and excitotoxicity and, as a consequence, behavior. This review describes the current knowledge of how system xc(-) is regulated and involved in physiological as well as pathophysiological brain functioning.

Lack of effect of Theiler's murine encephalomyelitis virus infection on system xc⁻

Changes in the expression of xCT, the specific subunit of system xc(-) or the cystine/glutamate antiporter, have been associated with several neurological disorders and system xc(-) was recently proposed as a potential target for the development of new treatment strategies for multiple sclerosis (MS). In this study we used Theiler's murine encephalomyelitis virus (TMEV) infection, both in vitro and in vivo, as a model to further evaluate the involvement of system xc(-) in MS. Protein levels of xCT, as well as activity of system xc(-) were unaffected in RAW264.7 macrophages after infection with the demyelinating DA strain of TMEV. Also, protein expression of xCT remained stable in spinal cord and brain of FVB mice 1-2 and 6 weeks after intracranial injection of the DA strain of TMEV. These results demonstrate that TMEV infection of macrophages or FVB mice has no effect on system xc(-) and as such cannot be used as a model to study the involvement of system xc(-) in MS.

xCT, not just an amino-acid transporter: a multi-functional regulator of microbial infection and associated diseases

Expression of xCT, a component of the x_c^– amino-acid transporter, is essential for the uptake of cystine required for intracellular glutathione (GSH) synthesis and maintenance of the intracellular redox balance. Therefore, xCT plays an important role not only in the survival of somatic and immune cells, but also in other aspects of tumorigenesis, including the growth and malignant progression of cancer cells, resistance to anticancer drugs, and protection of normal cells against oxidative damage induced by carcinogens. xCT also functions as a factor required for infection by Kaposi’s sarcoma-associated herpesvirus (KSHV), the causative agent of Kaposi’s sarcoma (KS) and other lymphoproliferative diseases associated with HIV/AIDS. In spite of these advances, our understanding of the role of xCT in the pathogenesis of infectious diseases is still limited. Therefore, this review will summarize recent findings about the functions of xCT in diseases associated with microbial (bacterial or viral) infections, in particular KSHV-associated malignancies. We will also discuss the remaining questions, future directions, as well as evidence that supports the potential benefits of exploring system x_c^– as a target for prevention and clinical management of microbial diseases and cancer.

A novel transcription mechanism activated by ethanol: induction of Slc7a11 gene expression via inhibition of the DNA-binding activity of transcriptional repressor octamer-binding transcription factor 1 (OCT-1)

Solute carrier family 7, member 11 (Slc7a11) is a plasma membrane cystine/glutamate exchanger that provides intracellular cystine to produce glutathione, a major cellular antioxidant. Oxidative and endoplasmic reticulum stresses up-regulate Slc7a11 expression by activation of nuclear factor erythroid 2-related factor 2 and transcription factor 4. This study examined the effect of ethanol on Slc7a11 expression and the underlying mechanism involved. Treatment of mouse hepatic stellate cells with ethanol significantly increased Slc7a11 mRNA and protein levels. Deletion of a 20-bp DNA sequence between -2044 to -2024 upstream of the transcription start site significantly increased basal activity and completely abolished the ethanol-induced activity of the Slc7a11 promoter. This deletion did not affect Slc7a11 promoter activity induced by oxidative or endoplasmic reticulum stress. DNA sequence analysis revealed a binding motif for octamer-binding transcription factor 1 (OCT-1) in the deleted fragment. Mutation of this OCT-1 binding motif resulted in a similar effect as the deletion experiment, i.e. it increased the basal promoter activity and abolished the response to ethanol. Ethanol exposure significantly inhibited OCT-1 binding to the Slc7a11 promoter region, although it did not alter OCT-1 mRNA and protein levels. OCT-1 reportedly functions as either a transcriptional enhancer or repressor, depending on the target genes. Results from this study suggest that OCT-1 functions as a repressor on the Slc7a11 promoter and that ethanol inhibits OCT-1 binding to the Slc7a11 promoter, thereby increasing Slc7a11 expression. Taken together, inhibition of the DNA binding activity of transcriptional repressor OCT-1 is a mechanism by which ethanol up-regulates Slc711 expression.