Absence of mitochondrial superoxide dismutase results in a murine hemolytic anemia responsive to therapy with a catalytic antioxidant

Iron chelation improves ineffective erythropoiesis and iron overload in myelodysplastic syndrome mice

Myelodysplastic syndrome (MDS) is a heterogeneous group of bone marrow stem cell disorders characterized by ineffective hematopoiesis and cytopenias, most commonly anemia. Red cell transfusion therapy for anemia in MDS results in iron overload, correlating with reduced overall survival. Whether the treatment of iron overload benefits MDS patients remains controversial. We evaluate underlying iron-related pathophysiology and the effect of iron chelation using deferiprone on erythropoiesis in NUP98-HOXD13 transgenic mice, a highly penetrant well-established MDS mouse model. Our results characterize an iron overload phenotype with aberrant erythropoiesis in these mice which was reversed by deferiprone-treatment. Serum erythropoietin levels decreased while erythroblast erythropoietin receptor expression increased in deferiprone-treated MDS mice. We demonstrate, for the first time, normalized expression of the iron chaperones Pcbp1 and Ncoa4 and increased ferritin stores in late-stage erythroblasts from deferiprone-treated MDS mice, evidence of aberrant iron trafficking in MDS erythroblasts. Importantly, erythroblast ferritin is increased in response to deferiprone, correlating with decreased erythroblast ROS. Finally, we confirmed increased expression of genes involved in iron uptake, sensing, and trafficking in stem and progenitor cells from MDS patients. Taken together, our findings provide evidence that erythroblast-specific iron metabolism is a novel potential therapeutic target to reverse ineffective erythropoiesis in MDS.

Haematopoietic development and HSC formation in vitro: promise and limitations of gastruloid models

Haematopoietic stem cells (HSCs) are the most extensively studied adult stem cells. Yet, six decades after their first description, reproducible and translatable generation of HSC in vitro remains an unmet challenge. HSC production in vitro is confounded by the multi-stage nature of blood production during development. Specification of HSC is a late event in embryonic blood production and depends on physical and chemical cues which remain incompletely characterised. The precise molecular composition of the HSC themselves is incompletely understood, limiting approaches to track their origin in situ in the appropriate cellular, chemical and mechanical context. Embryonic material at the point of HSC emergence is limiting, highlighting the need for an in vitro model of embryonic haematopoietic development in which current knowledge gaps can be addressed and exploited to enable HSC production. Gastruloids are pluripotent stem cell-derived 3-dimensional (3D) cellular aggregates which recapitulate developmental events in gastrulation and early organogenesis with spatial and temporal precision. Gastruloids self-organise multi-tissue structures upon minimal and controlled external cues, and are amenable to live imaging, screening, scaling and physicochemical manipulation to understand and translate tissue formation. In this review, we consider the haematopoietic potential of gastruloids and review early strategies to enhance blood progenitor and HSC production. We highlight possible strategies to achieve HSC production from gastruloids, and discuss the potential of gastruloid systems in illuminating current knowledge gaps in HSC specification.

Hematologic cytopenia post CAR T cell therapy: Etiology, potential mechanisms and perspective

Chimeric Antigen-Receptor (CAR) T-cell therapies have shown dramatic efficacy in treating relapsed and refractory cancers, especially B cell malignancies. However, these innovative therapies cause adverse toxicities that limit the broad application in clinical settings. Hematologic cytopenias, one frequently reported adverse event following CAR T cell treatment, are manifested as a disorder of hematopoiesis with decreased number of mature blood cells and subdivided into anemia, thrombocytopenia, leukopenia, and neutropenia, which increase the risk of infections, fatigue, bleeding, fever, and even fatality. Herein, we initially summarized the symptoms, etiology, risk factors and management of cytopenias. Further, we elaborated the cellular and molecular mechanisms underlying the initiation and progression of cytopenias following CAR T cell therapy based on previous studies about acquired cytopenias. Overall, this review will facilitate our understanding of the etiology of cytopenias and shed lights into developing new therapies against CAR T cell-induced cytopenias.

Impact of Superoxide Dismutase Genetic Polymorphism (SOD2 Val16Ala) and Superoxide Dismutase Level on Disease Severity in a Cohort of Egyptian Sickle Cell Disease Patients

Background

Oxidative stress plays a pivotal role in the pathophysiology of sickle cell disease (SCD) and its associated disease complications. Superoxide Dismutases (SODs) are protective enzymes against oxidative stress. SOD2 deficiency results in the accumulation of oxidized red cell proteins, increased rate of hemoglobin oxidation, decreased red cell membrane deformability, and subsequently decreased red cells survival.

Objective

The current study was designed to determine the effect of SOD2 Val16Ala gene polymorphism (rs4880) on SOD2 level and their possible impact on SCD disease severity in a cohort of Egyptian SCD patients.

Methods

Genotyping SOD2 Val16Ala polymorphism by TaqMan allelic discrimination assay for hundred SCD patients and a hundred age-sex matched healthy controls revealed the genotypic and allelic frequencies of the studied polymorphism in the SCD patients were close to that of the controls.

Results

Serum SOD2 level was significantly lower in those having the polymorphic genotypes (p=0.005). SOD2 level inversely correlates with the annual rate of hospitalization (r=-0.023, p= 0.038).

Conclusion

SOD2 Val16Ala polymorphism was associated with low serum SOD2 level that may predict disease severity.

Deficiency of Antioxidative Paraoxonase 2 (Pon2) Leads to Increased Number of Phenotypic LT-HSCs and Disturbed Erythropoiesis

Background

Long-term hematopoietic stem cells (LT-HSCs) reside in bone marrow niches with tightly controlled reactive oxygen species (ROS) levels. ROS increase results into LT-HSC differentiation and stem cell exhaustion. Paraoxonase 2 (PON2) has been shown to be important for ROS control.

Objectives

We investigate the effects of inactivation of the PON2 gene on hematopoietic cell differentiation and activity.

Methods and Results

In young mice with inactivated Pon2 gene (Pon2^−/−, <3 months), we observed an increase of LT-HSCs and a reduced frequency of progenitor cells. In competitive transplantations, young Pon2^−/− BM outcompeted WT BM at early time points. ROS levels were significantly increased in Pon2^−/− whole BM, but not in Pon2^−/− LT-HSCs. In more differentiated stages of hematopoiesis, Pon2 deficiency led to a misbalanced erythropoiesis both in physiologic and stress conditions. In older mice (>9 months), Pon2 depletion caused an increase in LT-HSCs as well as increased levels of granulocyte/macrophage progenitors (GMPs) and myeloid skewing, indicating a premature aging phenotype. No significant changes in ROS levels in old Pon2^−/− LT- and short-term (ST-) HSCs were observed, but a significant reduction of spontaneous apoptotic cell death was measured. RNA-seq analysis in Pon2^−/− LT-HSCs identified overrepresentation of genes involved in the C-X-C chemokine receptor type 4 (Cxcr4) signaling, suggesting compensatory mechanisms to overcome ROS-mediated accelerated aging in hematopoietic progenitor cells.

Conclusions

In summary, our current data indicate that PON2 is involved in the regulation of HSC functions.

Association of serum selenium with anemia-related indicators and risk of anemia

Few studies have examined the association of serum selenium with anemia-related indicators and risk of anemia. We conducted a cross-sectional analysis of 2,902 adults in 2003-2004 National Health and Nutrition Examination Survey database. Multivariable linear and logistic regression models were used to examine the association of serum selenium with anemia-related indicators and risk of anemia. The nonlinear relationship was analyzed using a generalized additive model with the smoothing plot. A total of 1,472 males and 1,430 females with a mean age of 61.94 ± 13.73 years were included. Compared with the lowest quintile, the highest quintile of serum selenium was associated with increased level of serum iron (β = 12.44, 95% confidence interval [CI]: 7.14, 17.75, p < .001), mean corpuscular hemoglobin concentration (MCHC) (β = 0.14, 95%CI: 0.02, 0.26, p = .020), and hemoglobin (β = 0.40, 95%CI: 0.19, 0.61, p < .001), and decreased risk of anemia (odds ratio [OR] = 0.47, 95%CI: 0.28, 0.77, p = .002). Furthermore, smoothed plots suggested the nonlinear relationships between serum selenium and MCHC, hemoglobin level, and risk of anemia. Interestingly, on the left of inflection point, serum selenium was associated with decreased risk of anemia (OR = 0.972, 95%CI: 0.960, 0.985, p < .001), and then, the risk of anemia increased with increasing serum selenium concentration (OR = 1.011, 95%CI: 1.002, 1.021, p = .023). Future large-scale, polycentric prospective studies should be conducted to verify our results.

Pleckstrin-2 is essential for erythropoiesis in β-thalassemic mice, reducing apoptosis and enhancing enucleation

Erythropoiesis involves complex interrelated molecular signals influencing cell survival, differentiation, and enucleation. Diseases associated with ineffective erythropoiesis, such as β-thalassemias, exhibit erythroid expansion and defective enucleation. Clear mechanistic determinants of what make erythropoiesis effective are lacking. We previously demonstrated that exogenous transferrin ameliorates ineffective erythropoiesis in β-thalassemic mice. In the current work, we utilize transferrin treatment to elucidate a molecular signature of ineffective erythropoiesis in β-thalassemia. We hypothesize that compensatory mechanisms are required in β-thalassemic erythropoiesis to prevent apoptosis and enhance enucleation. We identify pleckstrin-2-a STAT5-dependent lipid binding protein downstream of erythropoietin-as an important regulatory node. We demonstrate that partial loss of pleckstrin-2 leads to worsening ineffective erythropoiesis and pleckstrin-2 knockout leads to embryonic lethality in β-thalassemic mice. In addition, the membrane-associated active form of pleckstrin-2 occurs at an earlier stage during β-thalassemic erythropoiesis. Furthermore, membrane-associated activated pleckstrin-2 decreases cofilin mitochondrial localization in β-thalassemic erythroblasts and pleckstrin-2 knockdown in vitro induces cofilin-mediated apoptosis in β-thalassemic erythroblasts. Lastly, pleckstrin-2 enhances enucleation by interacting with and activating RacGTPases in β-thalassemic erythroblasts. This data elucidates the important compensatory role of pleckstrin-2 in β-thalassemia and provides support for the development of targeted therapeutics in diseases of ineffective erythropoiesis.

Hematopoietic Stem Cell Metabolism during Development and Aging

Cellular metabolism in hematopoietic stem cells (HSCs) is an area of intense research interest, but the metabolic requirements of HSCs and their adaptations to their niches during development have remained largely unaddressed. Distinctive from other tissue stem cells, HSCs transition through multiple hematopoietic sites during development. This transition requires drastic metabolic shifts, insinuating the capacity of HSCs to meet the physiological demand of hematopoiesis. In this review, we highlight how mitochondrial metabolism determines HSC fate, and especially focus on the links between mitochondria, endoplasmic reticulum (ER), and lysosomes in HSC metabolism.

Erythrocytes as a preferential target of oxidative stress in blood

Red blood cells (RBC) are specifically differentiated to transport oxygen and carbon dioxide in the blood and they lack most organelles, including mitochondria. The autoxidation of hemoglobin constitutes a major source of reactive oxygen species (ROS). Nitric oxide, which is produced by endothelial nitric oxide synthase (NOS3) or via the hemoglobin-mediated conversion of nitrite, interacts with ROS and results in the production of reactive nitrogen oxide species. Herein we present an overview of anemic diseases that are closely related to oxidative damage. Because the compensation of proteins by means of gene expression does not proceed in enucleated cells, antioxidative and redox systems play more important roles in maintaining the homeostasis of RBC against oxidative insult compared to ordinary cells. Defects in hemoglobin and enzymes that are involved in energy production and redox reactions largely trigger oxidative damage to RBC. The results of studies using genetically modified mice suggest that antioxidative enzymes, notably superoxide dismutase 1 and peroxiredoxin 2, play essential roles in coping with oxidative damage in erythroid cells, and their absence limits erythropoiesis, the life-span of RBC and consequently results in the development of anemia. The degeneration of the machinery involved in the proteolytic removal of damaged proteins appears to be associated with hemolytic events. The ubiquitin-proteasome system is the dominant machinery, not only for the proteolytic removal of damaged proteins in erythroid cells but also for the development of erythropoiesis. Hence, despite the fact that it is less abundant in RBC compared to ordinary cells, the aberrant ubiquitin-proteasome system may be associated with the development of anemic diseases via the accumulation of damaged proteins, as typified in sickle cell disease, and impaired erythropoiesis.

Metabolome Changes during In Vivo Red Cell Aging Reveal Disruption of Key Metabolic Pathways

Understanding the mechanisms for cellular aging is a fundamental question in biology. Normal red blood cells (RBCs) survive for approximately 100 days, and their survival is likely limited by functional decline secondary to cumulative damage to cell constituents, which may be reflected in altered metabolic capabilities. To investigate metabolic changes during in vivo RBC aging, labeled cell populations were purified at intervals and assessed for abundance of metabolic intermediates using mass spectrometry. A total of 167 metabolites were profiled and quantified from cell populations of defined ages. Older RBCs maintained ATP and redox charge states at the cost of altered activity of enzymatic pathways. Time-dependent changes were identified in metabolites related to maintenance of the redox state and membrane structure. These findings illuminate the differential metabolic pathway usage associated with normal cellular aging and identify potential biomarkers to determine average RBC age and rates of RBC turnover from a single blood sample.

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Altered glycolytic, amino acid, and fatty acid metabolism occurs in normal RBC aging

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GSH pools are maintained in spite of age-dependent shifts in enzyme synthesis

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Changes in choline and GPC suggest alterations in membrane lipid metabolism

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Ophthalmate, GPC, and ergothioneine are candidate metabolic clocks for RBC aging

Decoding the role of SOD2 in sickle cell disease

Sickle cell disease (SCD) is an inherited hemoglobinopathy caused by a single point mutation in the β-globin gene. As a consequence, deoxygenated hemoglobin polymerizes triggering red blood cell sickling and hemolysis, vaso-occlusion, and ischemia/reperfusion. Allied to these pathologies is the overproduction of reactive oxygen species driven by hemoglobin Fenton chemistry and peroxidase reactions as well as by secondary activation of vascular oxidases, including NAD(P)H oxidase and xanthine oxidase. In addition, hypoxia, produced by sickle red blood cell occlusion, disrupts mitochondrial metabolism and generates excess superoxide through electron leak from the mitochondrial respiratory chain. Superoxide dismutase 2 (SOD2) is a mitochondrial-specific antioxidant enzyme that dismutates superoxide to hydrogen peroxide, which is then converted to water by catalase and glutathione peroxidase. In SCD, the antioxidant defense system is significantly diminished through decreased expression and activity levels of antioxidant enzymes, including superoxide dismutase, catalase, and glutathione peroxidase. From a translational perspective, genetic variants including a missense variant in SOD2 (valine to alanine at position 16) are present in 45% of people with African ancestry and are associated with increased sickle complications. While it is known that there is an imbalance between oxidative species and antioxidant defenses in SCD, much more investigation is warranted. This review summarizes our current understanding of antioxidant defense systems in SCD, particularly focused on SOD2, and provides insight into challenges and opportunities as the field moves forward.

Evaluation of oxidative stress-related genetic variants for predicting stroke in patients with sickle cell anemia

Overt stroke in adults with sickle cell anemia (SCA) continues to be a major cause of morbidity and mortality, while no evidence-based strategy for prevention has been reached so far. Although transcranial Doppler ultrasonography represents the most important tool for identifying young patients with SCA at risk of primary stroke, strategies for stroke prediction in adulthood remain challenging. Emerging data suggest that oxidative stress may exert a pivotal role in the pathogenesis of ischemic brain injury. Combining these pieces of evidences with the well-known genetic contribution to the development of stroke in SCA, we hypothesized that genetic variants related to the biology of oxidative stress could be used to identify adult patients at higher risk of stroke. Overall, 499 unrelated patients with SCA aged >18 years were genotyped for SOD2 Val16Ala (rs4880), GPX3 T-568C (rs8177404), GPX3 T-518C (rs8177406), GPX3 T-65C (rs8177412), and CAT01 C-262 T (rs1001179) polymorphisms, along with α-thalassemia status and β-globin gene haplotypes. Of these, only the SOD2 Val16Ala polymorphism was associated with stroke. SOD2 Val16Ala polymorphism was independently associated with risk of stroke (odds ratio: 1.98; 95% confidence interval [CI]: 1.18-3.32; P = .009) and with the long-term cumulative incidence of stroke (hazard ratio: 2.24, 95% CI: 1.3-3.9; P = .004). In summary, we provide evidence that oxidative stress-related genetic variants, in particular, the SOD2 Val16Ala polymorphism, may represent a simple and inexpensive alternative for identifying patients at risk of stroke.

Calcium dysregulation mediates mitochondrial and neurite outgrowth abnormalities in SOD2 deficient embryonic cerebral cortical neurons

Mitochondrial superoxide dismutase 2 (SOD2) is a major antioxidant defense enzyme. Here we provide evidence that SOD2 plays critical roles in maintaining calcium homeostasis in newly generated embryonic cerebral cortical neurons, which is essential for normal mitochondrial function and subcellular distribution, and neurite outgrowth. Primary cortical neurons in cultures established from embryonic day 15 SOD2^+/+ and SOD2^-/- mice appear similar during the first 24 h in culture. During the ensuing two days in culture, SOD2^-/- neurons exhibit a profound reduction of neurite outgrowth and their mitochondria become fragmented and accumulate in the cell body. The structural abnormalities of the mitochondria are associated with reduced levels of phosphorylated (S637) dynamin related protein 1 (Drp1), a major mitochondrial fission-regulating protein, whereas mitochondrial fusion regulating proteins (OPA1 and MFN2) are relatively unaffected. Mitochondrial fission and Drp1 dephosphorylation coincide with impaired mitochondrial Ca²⁺ buffering capacity and an elevation of cytosolic Ca²⁺ levels. Treatment of SOD2^-/- neurons with the Ca²⁺ chelator BAPTA-AM significantly increases levels of phosphorylated Drp1, reduces mitochondrial fragmentation and enables neurite outgrowth.

Mutant KLF1 in Adult Anemic Nan Mice Leads to Profound Transcriptome Changes and Disordered Erythropoiesis

Anemic Nan mice carry a mutation (E339D) in the second zinc finger of erythroid transcription factor KLF1. Nan-KLF1 fails to bind a subset of normal KLF1 targets and ectopically binds a large set of genes not normally engaged by KLF1, resulting in a corrupted fetal liver transcriptome. Here, we performed RNAseq using flow cytometric-sorted spleen erythroid precursors from adult Nan and WT littermates rendered anemic by phlebotomy to identify global transcriptome changes specific to the Nan Klf1 mutation as opposed to anemia generally. Mutant Nan-KLF1 leads to extensive and progressive transcriptome corruption in adult spleen erythroid precursors such that stress erythropoiesis is severely compromised. Terminal erythroid differentiation is defective in the bone marrow as well. Principle component analysis reveals two major patterns of differential gene expression predicting that defects in basic cellular processes including translation, cell cycle, and DNA repair could contribute to disordered erythropoiesis and anemia in Nan. Significant erythroid precursor stage specific changes were identified in some of these processes in Nan. Remarkably, however, despite expression changes in large numbers of associated genes, most basic cellular processes were intact in Nan indicating that developing red cells display significant physiological resiliency and establish new homeostatic set points in vivo.

A review of select minerals influencing the haematopoietic process

Micronutrients are indispensable for adequate metabolism, such as biochemical function and cell production. The production of blood cells is named haematopoiesis and this process is highly consuming due to the rapid turnover of the haematopoietic system and consequent demand for nutrients. It is well established that micronutrients are relevant to blood cell production, although some of the mechanisms of how micronutrients modulate haematopoiesis remain unknown. The aim of the present review is to summarise the effect of Fe, Mn, Ca, Mg, Na, K, Co, iodine, P, Se, Cu, Li and Zn on haematopoiesis. This review deals specifically with the physiological requirements of selected micronutrients to haematopoiesis, showing various studies related to the physiological requirements, deficiency or excess of these minerals on haematopoiesis. The literature selected includes studies in animal models and human subjects. In circumstances where these minerals have not been studied for a given condition, no information was used. All the selected minerals have an important role in haematopoiesis by influencing the quality and quantity of blood cell production. In addition, it is highly recommended that the established nutrition recommendations for these minerals be followed, because cases of excess or deficient mineral intake can affect the haematopoiesis process.

Chemotherapy-Induced Tissue Injury: An Insight into the Role of Extracellular Vesicles-Mediated Oxidative Stress Responses

The short- and long-term side effects of chemotherapy limit the maximum therapeutic dose and impair quality of life of survivors. Injury to normal tissues, especially chemotherapy-induced cardiomyopathy, is an unintended outcome that presents devastating health impacts. Approximately half of the drugs approved by the Food and Drug Administration for cancer treatment are associated with the generation of reactive oxygen species, and Doxorubicin (Dox) is one of them. Dox undergoes redox cycling by involving its quinone structure in the production of superoxide free radicals, which are thought to be instrumental to the role it plays in cardiomyopathy. Dox-induced protein oxidation changes protein function, translocation, and aggregation that are toxic to cells. To maintain cellular homeostasis, oxidized proteins can be degraded intracellularly by ubiquitin-proteasome pathway or by autophagy, depending on the redox status of the cell. Alternatively, the cell can remove oxidized proteins by releasing extracellular vesicles (EVs), which can be transferred to neighboring or distant cells, thereby instigating an intercellular oxidative stress response. In this article, we discuss the role of EVs in oxidative stress response, the potential of EVs as sensitive biomarkers of oxidative stress, and the role of superoxide dismutase in attenuating EV-associated oxidative stress response resulting from chemotherapy.

Red Blood Cell Function and Dysfunction: Redox Regulation, Nitric Oxide Metabolism, Anemia

SIGNIFICANCE

Recent clinical evidence identified anemia to be correlated with severe complications of cardiovascular disease (CVD) such as bleeding, thromboembolic events, stroke, hypertension, arrhythmias, and inflammation, particularly in elderly patients. The underlying mechanisms of these complications are largely unidentified. Recent Advances: Previously, red blood cells (RBCs) were considered exclusively as transporters of oxygen and nutrients to the tissues. More recent experimental evidence indicates that RBCs are important interorgan communication systems with additional functions, including participation in control of systemic nitric oxide metabolism, redox regulation, blood rheology, and viscosity. In this article, we aim to revise and discuss the potential impact of these noncanonical functions of RBCs and their dysfunction in the cardiovascular system and in anemia.

CRITICAL ISSUES

The mechanistic links between changes of RBC functional properties and cardiovascular complications related to anemia have not been untangled so far.

FUTURE DIRECTIONS

To allow a better understanding of the complications associated with anemia in CVD, basic and translational science studies should be focused on identifying the role of noncanonical functions of RBCs in the cardiovascular system and on defining intrinsic and/or systemic dysfunction of RBCs in anemia and its relationship to CVD both in animal models and clinical settings. Antioxid. Redox Signal. 26, 718-742.

Erythropoietin-regulated oxidative stress negatively affects enucleation during terminal erythropoiesis

Differentiating erythroblasts are exposed to an oxidative environment. The dynamics of oxidative status during terminal erythropoiesis and how they affect cell differentiation in response to erythropoietin (Epo) are unclear. Here, we show that Epo induces reactive oxygen species (ROS) production in the early stages of terminal erythropoiesis. The levels of ROS correlate with CD71 surface expression and the uptake of iron and transferrin. ROS decreases in the late stages of terminal erythropoiesis, when the cells are preparing for enucleation. Consistently, treatment of erythroblasts with a low dose (5 mM) of N-acetyl-cysteine (NAC), a ROS scavenger, promotes enucleation. However, a high dose (20 mM) of NAC leads to significant cell death. Our study reveals an important function of Epo in regulating the dynamics of oxidative status and enucleation.

Pleiotropic age-dependent effects of mitochondrial dysfunction on epidermal stem cells

Tissue homeostasis declines with age partly because stem/progenitor cells fail to self-renew or differentiate. Because mitochondrial damage can accelerate aging, we tested the hypothesis that mitochondrial dysfunction impairs stem cell renewal or function. We developed a mouse model, Tg(KRT14-cre/Esr1) (20Efu/J) × Sod2 (tm1Smel) , that generates mitochondrial oxidative stress in keratin 14-expressing epidermal stem/progenitor cells in a temporally controlled manner owing to deletion of Sod2, a nuclear gene that encodes the mitochondrial antioxidant enzyme superoxide dismutase 2 (Sod2). Epidermal Sod2 loss induced cellular senescence, which irreversibly arrested proliferation in a fraction of keratinocytes. Surprisingly, in young mice, Sod2 deficiency accelerated wound closure, increasing epidermal differentiation and reepithelialization, despite the reduced proliferation. In contrast, at older ages, Sod2 deficiency delayed wound closure and reduced epidermal thickness, accompanied by epidermal stem cell exhaustion. In young mice, Sod2 deficiency accelerated epidermal thinning in response to the tumor promoter 12-O-tetradecanoylphorbol-13-acetate, phenocopying the reduced regeneration of older Sod2-deficient skin. Our results show a surprising beneficial effect of mitochondrial dysfunction at young ages, provide a potential mechanism for the decline in epidermal regeneration at older ages, and identify a previously unidentified age-dependent role for mitochondria in skin quality and wound closure.

Dimethyl Fumarate Protects Neural Stem/Progenitor Cells and Neurons from Oxidative Damage through Nrf2-ERK1/2 MAPK Pathway

Multiple sclerosis (MS) is the most common multifocal inflammatory demyelinating disease of the central nervous system (CNS). Due to the progressive neurodegenerative nature of MS, developing treatments that exhibit direct neuroprotective effects are needed. Tecfidera™ (BG-12) is an oral formulation of the fumaric acid esters (FAE), containing the active metabolite dimethyl fumarate (DMF). Although BG-12 showed remarkable efficacy in lowering relapse rates in clinical trials, its mechanism of action in MS is not yet well understood. In this study, we reported the potential neuroprotective effects of dimethyl fumarate (DMF) on mouse and rat neural stem/progenitor cells (NPCs) and neurons. We found that DMF increased the frequency of the multipotent neurospheres and the survival of NPCs following oxidative stress with hydrogen peroxide (H₂O₂) treatment. In addition, utilizing the reactive oxygen species (ROS) assay, we showed that DMF reduced ROS production induced by H₂O₂. DMF also decreased oxidative stress-induced apoptosis. Using motor neuron survival assay, DMF significantly promoted survival of motor neurons under oxidative stress. We further analyzed the expression of oxidative stress-induced genes in the NPC cultures and showed that DMF increased the expression of transcription factor nuclear factor-erythroid 2-related factor 2 (Nrf2) at both levels of RNA and protein. Furthermore, we demonstrated the involvement of Nrf2-ERK1/2 MAPK pathway in DMF-mediated neuroprotection. Finally, we utilized SuperArray gene screen technology to identify additional anti-oxidative stress genes (Gstp1, Sod2, Nqo1, Srxn1, Fth1). Our data suggests that analysis of anti-oxidative stress mechanisms may yield further insights into new targets for treatment of multiple sclerosis (MS).

Abnormal erythroid maturation leads to microcytic anemia in the TSAP6/Steap3 null mouse model

Genetic ablation of the ferrireductase STEAP3, also known as TSAP6, leads to severe microcytic and hypochromic red cells with moderate anemia in the mouse. However, the mechanism leading to anemia is poorly understood. Previous results indicate that TSAP6/Steap3 is a regulator of exosome secretion. Using TSAP6/Steap3 knockout mice, we first undertook a comprehensive hematologic characterization of the red cell compartment, and confirmed a dramatic decrease in the volume and hemoglobin content of these erythrocytes. We observed marked anisocytosis as well as the presence of fragmenting erythrocytes. Consistent with these observations, we found by ektacytometry decreased membrane mechanical stability of knockout red cells. However, we were unable to document significant changes in the expression levels of the major skeletal and transmembrane proteins to account for this decrease in the membrane stability. Furthermore, there were no differences in red cell survival between wild type and knockout animals. However, when we monitored erythropoiesis, we found a decreased number of proerythroblasts in the bone marrow of TSAP6/Steap3(-/-) animals. In addition, progression from the proerythroblastic to the orthochromatic stage was affected, with accumulation of cells at the polychromatic stage. Altogether, our findings demonstrate that abnormal erythroid maturation is the main cause of anemia in these mice.

FOXO3-mTOR metabolic cooperation in the regulation of erythroid cell maturation and homeostasis

Ineffective erythropoiesis is observed in many erythroid disorders including β-thalassemia and anemia of chronic disease in which increased production of erythroblasts that fail to mature exacerbate the underlying anemias. As loss of the transcription factor FOXO3 results in erythroblast abnormalities similar to the ones observed in ineffective erythropoiesis, we investigated the underlying mechanisms of the defective Foxo3(-/-) erythroblast cell cycle and maturation. Here we show that loss of Foxo3 results in overactivation of the JAK2/AKT/mTOR signaling pathway in primary bone marrow erythroblasts partly mediated by redox modulation. We further show that hyperactivation of mTOR signaling interferes with cell cycle progression in Foxo3 mutant erythroblasts. Importantly, inhibition of mTOR signaling, in vivo or in vitro enhances significantly Foxo3 mutant erythroid cell maturation. Similarly, in vivo inhibition of mTOR remarkably improves erythroid cell maturation and anemia in a model of β-thalassemia. Finally we show that FOXO3 and mTOR are likely part of a larger metabolic network in erythroblasts as together they control the expression of an array of metabolic genes some of which are implicated in erythroid disorders. These combined findings indicate that a metabolism-mediated regulatory network centered by FOXO3 and mTOR control the balanced production and maturation of erythroid cells. They also highlight physiological interactions between these proteins in regulating erythroblast energy. Our results indicate that alteration in the function of this network might be implicated in the pathogenesis of ineffective erythropoiesis.

Stem cells, redox signaling, and stem cell aging

SIGNIFICANCE

Functional stem cell decline has been postulated to result in loss of maintenance of tissue homeostasis leading to organismal decline and diseases of aging.

RECENT ADVANCES

Recent findings implicate redox metabolism in the control of stem cell pool and stem cell aging. Although reactive oxygen species (ROS) are better known for their damaging properties to DNA, proteins and lipids, recent findings suggest that ROS may also be an integral physiological mediator of cellular signaling in primary cells.

CRITICAL ISSUES

Here we review recent published work on major signaling pathways and transcription factors that are regulated by ROS and mediate ROS regulation of stem cell fate. We will specifically focus on how alterations in this regulation may be implicated in disease and particularly in diseases of stem cell aging. In general, based on the work described here we propose a model in which ROS function as stem cell rheostat.

FUTURE DIRECTIONS

Future work in elucidating how ROS control stem cell cycling, apoptotic machinery, and lineage determination should shed light on mechanisms whereby ROS may control stem cell aging.

Interplay between the pro-oxidant and antioxidant systems and proinflammatory cytokine levels, in relation to iron metabolism and the erythron in depression

As there is strong evidence for inflammation and oxidative stress in depression, the aim of this study was to elucidate the relationship between oxidative imbalance and cellular immune response and to ask whether these processes are linked with iron metabolism in depressed patients. Blood was collected from patients diagnosed with recurrent depressive disorder (n=15) and from healthy controls (n=19). Whole-blood reduced glutathione (GSH), erythrocyte superoxide dismutase (SOD-1), glutathione peroxidase (GPx-1), glutathione reductase, malondialdehyde (MDA), and methemoglobin (MetHb) and plasma H₂O₂ were assayed spectrophotometrically. The serum heme oxygenase 1 (HO-1), cytokine, neopterin, and iron statuses were measured by ELISA. DNA damage was analyzed by comet assay. Serum concentrations of ferritin and soluble transferrin receptor were assayed by ELISA. MetHb saturation was analyzed spectrophotometrically in red blood cell hemolysate. The erythron variables were measured using a hematological analyzer. We observed a significant decrease in GPx-1 and SOD-1 activities and decreased levels of HO-1 and GSH in depressed patients compared to controls. Conversely, compared with controls, we found increased concentrations of MDA and H₂O₂ and more DNA damage in depressed patients. Furthermore, the levels of the proinflammatory cytokine interleukin-6 and of neopterin were increased in depressed patients along with decreased hemoglobin and hematocrit. A strong association between antioxidant defense, cytokine levels, and iron homeostasis was also revealed. These findings show that depression is associated with increased oxidative stress, inflammation, and restrictions on the available iron supply for red blood cell production. Furthermore, decreased antioxidant defense correlates with an increased cellular inflammatory response, whereas both concur with erythron and iron status, the latter explained by significant canonical correlations with the set of free radical scavenging enzymes and proinflammatory enzymes. The strong links between immune function, oxidative stress, and iron homeostasis suggest the presence of a self-sustaining multipathway mechanism that may progressively worsen, i.e., throughout accumulation of oxidative damage, producing the functional and structural consequences associated with depression. Hence, identifying viable therapeutic strategies to tackle oxidative stress and accompanying physiological disturbances, including inflammation and anemia, of chronic disease provides more opportunities for the treatment and, ultimately, prevention of depression.

Erythroid cells generated in the absence of specific β1-integrin heterodimers accumulate reactive oxygen species at homeostasis and are unable to mount effective antioxidant defenses

We have previously reported that β1(Δ/Δ) mice have a markedly impaired response to hemolytic stress, but the mechanisms of this were unclear. In the present study we explored in detail quantitative, phenotypic and functional aspects of erythropoiesis at homeostasis in a large number of animals for each of 3 murine models with specific β1 heterodimer integrin deficiencies. We found that, at homeostasis, β1-deficient mice have a modest uncompensated anemia with ineffective erythropoiesis and decreased red blood cell survival. Mice lacking only α4 integrins (α4β1/α4β7) do not share this phenotype. There is an increased tendency for reactive oxygen species accumulation in β1(Δ/Δ) erythroid cells with decreased anti-oxidant defenses at homeostasis which are exaggerated after stress. Furthermore, expansion of erythroid cells in spleen post-stress is dependent on α5β1, likely through mechanisms activating focal adhesion kinase complexes that are distinct from α4β1-mediated responses. In vivo inhibition of focal adhesion kinase activation partially recapitulates the β1(Δ/Δ) stress response. Mice lacking all α4 and β1 integrins (double knockouts) had, at homeostasis, the most severe phenotype with selective impairment of erythroid responses. The fact that integrins participate in mitigating stress in erythroid cells through redox activation of distinct signaling pathways by specific integrin heterodimers is a link that has not been appreciated until now.

Manganese superoxide dismutase depletion in murine hematopoietic stem cells perturbs iron homeostasis, globin switching, and epigenetic control in erythrocyte precursor cells

Heme synthesis partially occurs in the mitochondrial matrix; thus there is a high probability that enzymes and intermediates important in the production of heme will be exposed to metabolic by-products including reactive oxygen species. In addition, the need for ferrous iron for heme production, Fe/S coordination, and other processes occurring in the mitochondrial matrix suggests that aberrant fluxes of reactive oxygen species in this compartment might perturb normal iron homeostasis. Manganese superoxide dismutase (Sod2) is an antioxidant enzyme that governs steady-state levels of the superoxide in the mitochondrial matrix. Using hematopoietic stem cell-specific conditional Sod2 knockout mice we observed increased superoxide concentrations in red cell progeny, which caused significant pathologies including impaired erythrocytes and decreased ferrochelatase activity. Animals lacking Sod2 expression in erythroid precursors also displayed extramedullary hematopoiesis and systemic iron redistribution. Additionally, the increase in superoxide flux in erythroid precursors caused abnormal gene regulation of hematopoietic transcription factors, globins, and iron-response genes. Moreover, the erythroid precursors also displayed evidence of global changes in histone posttranslational modifications, a likely cause of at least some of the aberrant gene expression noted. From a therapeutic translational perspective, mitochondrially targeted superoxide-scavenging antioxidants partially rescued the observed phenotype. Taken together, our findings illuminate the superoxide sensitivity of normal iron homeostasis in erythrocyte precursors and suggest a probable link between mitochondrial redox metabolism and epigenetic control of nuclear gene regulation during mammalian erythropoiesis.

SOD2 deficiency in hematopoietic cells in mice results in reduced red blood cell deformability and increased heme degradation

Among the three types of super oxide dismutases (SODs) known, SOD2 deficiency is lethal in neonatal mice owing to cardiomyopathy caused by severe oxidative damage. SOD2 is found in red blood cell (RBC) precursors, but not in mature RBCs. To investigate the potential damage to mature RBCs resulting from SOD2 deficiency in precursor cells, we studied RBCs from mice in which fetal liver stem cells deficient in SOD2 were capable of efficiently rescuing lethally irradiated host animals. These transplanted animals lack SOD2 only in hematopoietically generated cells and live longer than SOD2 knockouts. In these mice, approximately 2.8% of their total RBCs in circulation are iron-laden reticulocytes, with numerous siderocytic granules and increased protein oxidation similar to that seen in sideroblastic anemia. We have studied the RBC deformability and oxidative stress in these animals and the control group by measuring them with a microfluidic ektacytometer and assaying fluorescent heme degradation products with a fluorimeter, respectively. In addition, the rate of hemoglobin oxidation in RBCs from these mice and the control group were measured spectrophotometrically. The results show that RBCs from these SOD2-deficient mice have reduced deformability, increased heme degradation products, and an increased rate of hemoglobin oxidation compared with control animals, indicative of increased RBC oxidative stress.

Hematopoietic stem cell regeneration enhanced by ectopic expression of ROS-detoxifying enzymes in transplant mice

High levels of reactive oxygen species (ROS) can exhaust hematopoietic stem cells (HSCs). Thus, maintaining a low state of redox in HSCs by modulating ROS-detoxifying enzymes may augment the regeneration potential of HSCs. Our results show that basal expression of manganese superoxide dismutase (MnSOD) and catalase were at low levels in long-term and short-term repopulating HSCs, and administration of a MnSOD plasmid and lipofectin complex (MnSOD-PL) conferred radiation protection on irradiated recipient mice. To assess the intrinsic role of elevated MnSOD or catalase in HSCs and hematopoietic progenitor cells, the MnSOD or catalase gene was overexpressed in mouse hematopoietic cells via retroviral transduction. The impact of MnSOD and catalase on hematopoietic progenitor cells was mild, as measured by colony-forming units (CFUs). However, overexpressed catalase had a significant beneficial effect on long-term engraftment of transplanted HSCs, and this effect was further enhanced after an insult of low-dose γ-irradiation in the transplant mice. In contrast, overexpressed MnSOD exhibited an insignificant effect on long-term engraftment of transplanted HSCs, but had a significant beneficial effect after an insult of sublethal irradiation. Taken together, these results demonstrate that HSC function can be enhanced by ectopic expression of ROS-detoxifying enzymes, especially after radiation exposure in vivo.

Mitochondrial ABC transporters function: the role of ABCB10 (ABC-me) as a novel player in cellular handling of reactive oxygen species

Mitochondria are one of the major sources of reactive oxygen species (ROS) in the cell. When exceeding the capacity of antioxidant mechanisms, ROS production may lead to different pathologies, such as ischemia-reperfusion injury, neurodegeneration, anemia and ageing. As a consequence of the endosymbiotic origin of mitochondria, eukaryotic cells have developed different transport mechanisms that coordinate mitochondrial function with other cellular compartments. Four mitochondrial ATP-binding cassette (ABC) transporters have been described to date in mammals: ABCB6, ABCB8, ABCB7 and ABCB10. ABCB10 is located in the inner mitochondrial membrane forming homodimers, with the ATP binding domain facing the mitochondrial matrix. ABCB10 expression is highly induced during erythroid differentiation and its overexpression increases hemoglobin synthesis in erythroid cells. However, ABCB10 is also expressed in nonerythroid tissues, suggesting a role not directly related to hemoglobin synthesis. Recent evidence points toward ABCB10 as an important player in the protection from oxidative stress in mammals. In this regard, ABCB10 is required for normal erythropoiesis and cardiac recovery after ischemia-reperfusion, processes intimately related to mitochondrial ROS generation. Here, we review the current knowledge on mitochondrial ABC transporters and ABCB10 and discuss the potential mechanisms by which ABCB10 and its transport activity may regulate oxidative stress. We discuss ABCB10 as a potential therapeutic target for diseases in which increased mitochondrial ROS production and oxidative stress play a major role.

Circulating selenium and carboxymethyl-lysine, an advanced glycation endproduct, are independent predictors of anemia in older community-dwelling adults

OBJECTIVE

To assess whether selenium and carboxymethyl-lysine (CML), two biomarkers of oxidative stress, are independent predictors of anemia in older community-dwelling adults.

METHODS

Plasma levels of selenium, CML, folate, vitamin B12, and testosterone and markers of iron status and inflammation were measured at baseline in 1036 adults at least 65 y old in the Invecchiare in Chianti Study, a population-based cohort study of aging in Tuscany, Italy, and examined in relation to prevalent anemia and incident anemia over 6 y of follow-up.

RESULTS

At enrollment, 11.6% of participants were anemic. Of 472 participants who were non-anemic at enrollment, 72 (15.3%) developed anemia within 6 y of follow-up. At enrollment, plasma CML in the highest quartile (>425 ng/mL) and plasma selenium in the lowest quartile (<66.6 μg/L) predicted incident anemia (hazard ratio 1.67, 95% confidence interval 1.07-2.59, P = 0.02; hazard ratio 1.55, 95% confidence interval 1.01-2.38, P = 0.05, respectively) in a multivariate Cox proportional hazards model that adjusted for age, education, body mass index, cognition, inflammation, red blood cell distribution width, ferritin, vitamin B12, testosterone, and chronic diseases.

CONCLUSION

Elevated plasma CML and low plasma selenium are long-term independent predictors of anemia in older community-dwelling adults. These findings support the idea that oxidative stress contributes to the development of anemia.

The ribosome-related protein, SBDS, is critical for normal erythropoiesis

Although anemia is common in Shwachman- Diamond syndrome (SDS), the underlying mechanism remains unclear. We asked whether SBDS, which is mutated in most SDS patients, is critical for erythroid development. We found that SBDS expression is high early during erythroid differentiation. Inhibition of SBDS in CD34(+) hematopoietic stem cells and early progenitors (HSC/Ps) and K562 cells led to slow cell expansion during erythroid differentiation. Induction of erythroid differentiation resulted in markedly accelerated apoptosis in the knockdown cells; however, proliferation was only mildly reduced. The percentage of cells entering differentiation was not reduced. Differentiation also increased the oxidative stress in SBDS-knockdown K562 cells, and antioxidants enhanced the expansion capability of differentiating SBDS-knockdown K562 cells and colony production of SDS patient HSC/Ps. Erythroid differentiation also resulted in reduction of all ribosomal subunits and global translation. Furthermore, stimulation of global translation with leucine improved the erythroid cell expansion of SBDS-knockdown cells and colony production of SDS patient HSC/Ps. Leucine did not reduce the oxidative stress in SBDS-deficient K562 cells. These results demonstrate that SBDS is critical for normal erythropoiesis. Erythropoietic failure caused by SBDS deficiency is at least in part related to elevated ROS levels and translation insufficiency because antioxidants and leucine improved cell expansion.

Telomere, DNA damage, and oxidative stress in stem cell aging

"Stem cell aging" is a novel concept that developed together with the advances of stem cell biology, especially the sophisticated prospectively isolation and characterization of multipotent somatic tissue stem cells. Although being immortal in principle, stem cells can also undergo aging processes and potentially contribute to organismal aging. The impact of an age-dependent decline of stem cell function weighs differently in organs with high or low rates of cell turnover. Nonetheless, most of the organ systems undergo age-dependent loss of homeostasis and functionality, and emerging evidence showed that this has to do with the aging of resident stem cells in the organ systems. The mechanisms of stem cell aging and its real contribution to human aging remain to be defined. Many antitumor mechanisms protect potential malignant transformation of stem cell by inducing apoptosis or senescence but simultaneously provoke stem cell aging. In this review, we try to discuss several concept of stem cell aging and summarize recent progression on the molecular mechanisms of stem cell aging.

LYL-1 deficiency induces a stress erythropoiesis

OBJECTIVE

LYL-1 is a transcription factor containing a basic helix-loop-helix motif closely related to SCL/TAL-1, a regulator of erythroid differentiation. Because LYL-1 is expressed in erythroid cell populations, we addressed its role in erythropoiesis using knockin mice.

MATERIALS AND METHODS

Erythropoiesis of LYL-1(-/-) mice was studied by progenitor assays, flow cytometry, reconstitution assays, and functional tests. Expression of LYL-1, SCL, and GATA-1 was assessed at messenger RNA level by quantitative reverse transcription polymerase chain reaction.

RESULTS

LYL-1(-/-) mice displayed decreased erythropoiesis with a partial arrest in differentiation, and enhanced apoptosis associated with decreased Bcl-x(L) expression in the bone marrow (BM). In addition, LYL-1(-/-) BM cells were severely impaired in their abilities to reconstitute the erythroid lineage in competitive assays, suggesting a cell autonomous abnormality of erythropoiesis. In parallel, erythroid progenitor and precursor cells were significantly increased in the spleen of LYL-1(-/-) mice. Expression of LYL-1 was differentially regulated during maturation of erythroblasts and strikingly different between spleen- and BM-derived erythroblasts. Expression of LYL-1 decreased during erythroid differentiation in the spleen whereas it increased in the BM to reach the same level in mature erythroblasts as in the soleen. Loss of Lyl-1 expression was accompanied with an increase of SCL/TAL-1 and GATA-1 transcripts in spleen but not in BM-derived erythroblasts. Furthermore, phenylhydrazine-induced stress erythropoiesis was elevated in LYL-1(-/-) mice and mutant BM and spleen erythroid progenitors were hypersensitive to erythropoietin.

CONCLUSIONS

Taken together, these results suggest that LYL-1 plays a definite role in erythropoiesis, albeit with different effects in BM specifically regulating basal erythropoiesis, and spleen, controlling stress-induced erythropoiesis.

SOD2 deficient erythroid cells up-regulate transferrin receptor and down-regulate mitochondrial biogenesis and metabolism

Background

Mice irradiated and reconstituted with hematopoietic cells lacking manganese superoxide dismutase (SOD2) show a persistent hemolytic anemia similar to human sideroblastic anemia (SA), including characteristic intra-mitochondrial iron deposition. SA is primarily an acquired, clonal marrow disorder occurring in individuals over 60 years of age with uncertain etiology.

Methodology/Principal Findings

To define early events in the pathogenesis of this murine model of SA, we compared erythroid differentiation of Sod2^-/- and normal bone marrow cells using flow cytometry and gene expression profiling of erythroblasts. The predominant transcriptional differences observed include widespread down-regulation of mitochondrial metabolic pathways and mitochondrial biogenesis. Multiple nuclear encoded subunits of complexes I-IV of the electron transport chain, ATP synthase (complex V), TCA cycle and mitochondrial ribosomal proteins were coordinately down-regulated in Sod2^-/- erythroblasts. Despite iron accumulation within mitochondria, we found increased expression of transferrin receptor, Tfrc, at both the transcript and protein level in SOD2 deficient cells, suggesting deregulation of iron delivery. Interestingly, there was decreased expression of ABCb7, the gene responsible for X-linked hereditary SA with ataxia, a component required for iron-sulfur cluster biogenesis.

Conclusions/Significance

These results indicate that in erythroblasts, mitochondrial oxidative stress reduces expression of multiple nuclear genes encoding components of the respiratory chain, TCA cycle and mitochondrial protein synthesis. An additional target of particular relevance for SA is iron:sulfur cluster biosynthesis. By decreasing transcription of components of cluster synthesis machinery, both iron utilization and regulation of iron uptake are impacted, contributing to the sideroblastic phenotype.

The familial Parkinson's disease gene DJ-1 (PARK7) is expressed in red cells and plays a role in protection against oxidative damage

The antioxidant enzyme manganese superoxide dismutase (SOD2) serves as the primary defense against mitochondrial superoxide. Impaired SOD2 activity in murine hematopoietic cells affects erythroid development, resulting in anemia characterized by intra-mitochondrial iron deposition, reticulocytosis and shortened red cell life span. Gene expression profiling of normal and SOD2 deficient erythroblasts identified the Parkinson's disease locus DJ-1 (Park7) as a differentially expressed transcript. To investigate the role of DJ-1 in hematopoietic cell development and protection against oxidative stress caused by Sod2 loss, we evaluated red cell parameters, reticulocyte count, red cell turnover and reactive oxygen species production in DJ-1 knockout animals and chimeric animals lacking both SOD2 and DJ-1 in hematopoietic cells generated by fetal liver transplantation. We also investigated DJ-1 protein expression in primary murine erythroid and erythroleukemia cells (MEL). Loss of DJ-1 exacerbates the phenotype of SOD2 deficiency, increasing reticulocyte count and decreasing red cell survival. Using MEL cells, we show that DJ-1 is up-regulated at the protein level during erythroid differentiation. These results indicate that DJ-1 plays a physiologic role in protection of erythroid cells from oxidant damage, a function unmasked in the context of oxidative stress.

Pro-inflammatory cytokine-mediated anemia: regarding molecular mechanisms of erythropoiesis

Anemia of cancer and chronic inflammatory diseases is a frequent complication affecting quality of life. For cancer patients it represents a particularly bad prognostic. Low level of erythropoietin is considered as one of the causes of anemia in these pathologies. The deficiency in erythropoietin production results from pro-inflammatory cytokines effect. However, few data is available concerning molecular mechanisms involved in cytokine-mediated anemia. Some recent publications have demonstrated the direct effect of pro-inflammatory cytokines on cell differentiation towards erythroid pathway, without erythropoietin defect. This suggested that pro-inflammatory cytokine-mediated signaling pathways affect erythropoietin activity. They could interfere with erythropoietin-mediated signaling pathways, inducing early apoptosis and perturbing the expression and regulation of specific transcription factors involved in the control of erythroid differentiation. In this review we summarize the effect of tumor necrosis factor (TNF)α, TNF-related apoptosis-inducing ligand (TRAIL), and interferon (IFN)-γ on erythropoiesis with a particular interest for molecular feature.

Redox regulation of multidrug resistance in cancer chemotherapy: molecular mechanisms and therapeutic opportunities

The development of multidrug resistance to cancer chemotherapy is a major obstacle to the effective treatment of human malignancies. It has been established that membrane proteins, notably multidrug resistance (MDR), multidrug resistance protein (MRP), and breast cancer resistance protein (BCRP) of the ATP binding cassette (ABC) transporter family encoding efflux pumps, play important roles in the development of multidrug resistance. Overexpression of these transporters has been observed frequently in many types of human malignancies and correlated with poor responses to chemotherapeutic agents. Evidence has accumulated showing that redox signals are activated in response to drug treatments that affect the expression and activity of these transporters by multiple mechanisms, including (a) conformational changes in the transporters, (b) regulation of the biosynthesis cofactors required for the transporter's function, (c) regulation of the expression of transporters at transcriptional, posttranscriptional, and epigenetic levels, and (d) amplification of the copy number of genes encoding these transporters. This review describes various specific factors and their relevant signaling pathways that are involved in the regulation. Finally, the roles of redox signaling in the maintenance and evolution of cancer stem cells and their implications in the development of intrinsic and acquired multidrug resistance in cancer chemotherapy are discussed.

Oxidative stress in the regulation of normal and neoplastic hematopoiesis

Recent evidence suggests that oxidative stress contributes significantly to the regulation of hematopoietic cell homeostasis. In particular, red blood cells and hematopoietic stem cells are highly sensitive to deregulated accumulation of reactive oxygen species (ROS). Unchecked ROS accumulation often leads to hemolysis, that is, to destruction and shortened life span of red blood cells. In addition, the process of erythroid cell formation is sensitive to ROS accumulation. Similarly, ROS buildup in hematopoietic stem cells compromises their function as a result of potential damage to their DNA leading to loss of quiescence and alterations of hematopoietic stem cell cycling. These abnormalities may lead to accelerated aging of hematopoietic stem cells or to hematopoietic malignancies.

UCP2 modulates cell proliferation through the MAPK/ERK pathway during erythropoiesis and has no effect on heme biosynthesis

UCP2, an inner membrane mitochondrial protein, has been implicated in bioenergetics and reactive oxygen species (ROS) modulation. High levels of UCP2 mRNA were recently found in erythroid cells where UCP2 is hypothesized to function as a facilitator of heme synthesis and iron metabolism by reducing ROS production. We examined UCP2 protein expression and role in mice erythropoiesis in vivo. UCP2 was mainly expressed at early stages of erythroid maturation when cells are not fully committed in heme synthesis. Iron incorporation into heme was unaltered in reticulocytes from UCP2-deficient mice. Although heme synthesis was not influenced by UCP2 deficiency, mice lacking UCP2 had a delayed recovery from chemically induced hemolytic anemia. Analysis of progenitor cells from bone marrow and fetal liver both in vitro and in vivo revealed that UCP2 deficiency results in a significant decrease in cell proliferation at the erythropoietin-dependent phase of erythropoiesis. This was accompanied by reduction in the phosphorylated form of ERK, a ROS-dependent cytosolic regulator of cell proliferation. Analysis of ROS in UCP2 null erythroid cells revealed altered distribution of ROS, resulting in decreased cytosolic and increased mitochondrial ROS. Restoration of the cytosol oxidative state of erythroid progenitor cells by the pro-oxidant Paraquat reversed the effect of UCP2 deficiency on cell proliferation in in vitro differentiation assays. Together, these results indicate that UCP2 is a regulator of erythropoiesis and suggests that inhibition of UCP2 function may contribute to the development of anemia.

An unexpected functional link between lysosomal thiol reductase and mitochondrial manganese superoxide dismutase

Gamma interferon-inducible thiol reductase (GILT) is an enzyme involved in the initial steps of antigen processing and presentation. Recently we have shown that GILT is also expressed in mouse T cells, where it exerts an inhibitory role on T cell activation. In this study, we identified mitochondrial manganese superoxide dismutase (SOD2) as one of the key intermediaries affected by GILT expression in fibroblasts. Expression and activity of SOD2 is reduced in the absence of GILT because of reduced SOD2 protein stability. The forced increase in SOD2 expression in the absence of GILT restores fibroblast proliferation to wild-type levels. Thus, GILT appears to have a fundamental role in cellular proliferation mediated through its influence on SOD2 protein activity and expression.

Foxo3 is required for the regulation of oxidative stress in erythropoiesis

Erythroid cells accumulate hemoglobin as they mature and as a result are highly prone to oxidative damage. However, mechanisms of transcriptional control of antioxidant defense in erythroid cells have thus far been poorly characterized. We observed that animals deficient in the forkhead box O3 (Foxo3) transcription factor died rapidly when exposed to erythroid oxidative stress-induced conditions, while wild-type mice showed no decreased viability. In view of this striking finding, we investigated the potential role of Foxo3 in the regulation of ROS in erythropoiesis. Foxo3 expression, nuclear localization, and transcriptional activity were all enhanced during normal erythroid cell maturation. Foxo3-deficient erythrocytes exhibited decreased expression of ROS scavenging enzymes and had a ROS-mediated shortened lifespan and evidence of oxidative damage. Furthermore, loss of Foxo3 induced mitotic arrest in erythroid precursor cells, leading to a significant decrease in the rate of in vivo erythroid maturation. We identified ROS-mediated upregulation of p21(CIP1/WAF1/Sdi1) (also known as Cdkn1a) as a major contributor to the interference with cell cycle progression in Foxo3-deficient erythroid precursor cells. These findings establish an essential nonredundant function for Foxo3 in the regulation of oxidative stress, cell cycle, maturation, and lifespan of erythroid cells. These results may have an impact on the understanding of human disorders in which ROS play a role.

Mitochondrial oxidative stress causes hyperphosphorylation of tau

Age-related neurodegenerative disease has been mechanistically linked with mitochondrial dysfunction via damage from reactive oxygen species produced within the cell. We determined whether increased mitochondrial oxidative stress could modulate or regulate two of the key neurochemical hallmarks of Alzheimer's disease (AD): tau phosphorylation, and beta-amyloid deposition. Mice lacking superoxide dismutase 2 (SOD2) die within the first week of life, and develop a complex heterogeneous phenotype arising from mitochondrial dysfunction and oxidative stress. Treatment of these mice with catalytic antioxidants increases their lifespan and rescues the peripheral phenotypes, while uncovering central nervous system pathology. We examined sod2 null mice differentially treated with high and low doses of a catalytic antioxidant and observed striking elevations in the levels of tau phosphorylation (at Ser-396 and other phospho-epitopes of tau) in the low-dose antioxidant treated mice at AD-associated residues. This hyperphosphorylation of tau was prevented with an increased dose of the antioxidant, previously reported to be sufficient to prevent neuropathology. We then genetically combined a well-characterized mouse model of AD (Tg2576) with heterozygous sod2 knockout mice to study the interactions between mitochondrial oxidative stress and cerebral Ass load. We found that mitochondrial SOD2 deficiency exacerbates amyloid burden and significantly reduces metal levels in the brain, while increasing levels of Ser-396 phosphorylated tau. These findings mechanistically link mitochondrial oxidative stress with the pathological features of AD.

Pathogenic mitochondrial DNA-induced respiration defects in hematopoietic cells result in anemia by suppressing erythroid differentiation

Anemia is a symptom in patients with Pearson syndrome caused by the accumulation of mutated mitochondrial DNA (mtDNA). Such mutated mtDNAs have been detected in patients with anemia. This suggested that respiration defects due to mutated mtDNA are responsible for the anemia. However, there has been no convincing experimental evidence to confirm the pathophysiological relation between respiration defects in hematopoietic cells and expression of anemia. We address this issue by transplanting bone marrow cells carrying pathogenic mtDNA with a large-scale deletion (DeltamtDNA) into normal mice. The bone marrow-transplanted mice carried high proportion of DeltamtDNA only in hematopoietic cells, and resultant the mice suffered from macrocytic anemia. They show abnormalities of erythroid differentiation and weak erythropoietic response to a stressful condition. These observations suggest that hematopoietic cell-specific respiration defects caused by mtDNAs with pathogenic mutations are responsible for anemia by inducing abnormalities in erythropoiesis.

Elevated oxidative stress in erythrocytes due to a SOD1 deficiency causes anaemia and triggers autoantibody production

Reactive oxygen species are involved in the aging process and diseases. Despite the important role of Cu/Zn SOD (superoxide dismutase) encoded by SOD1, SOD1-/- mice appear to grow normally under conventional breeding conditions. In the present paper we report on a novel finding showing a distinct connection between oxidative stress in erythrocytes and the production of autoantibodies against erythrocytes in SOD1-/- mice. Evidence is presented to show that SOD1 is primarily required for maintaining erythrocyte lifespan by suppressing oxidative stress. A SOD1 deficiency led to an increased erythrocyte vulnerability by the oxidative modification of proteins and lipids, resulting in anaemia and compensatory activation of erythropoiesis. The continuous destruction of oxidized erythrocytes appears to induce the formation of autoantibodies against certain erythrocyte components, e.g. carbonic anhydrase II, and the immune complex is deposited in the glomeruli. The administration of an antioxidant, N-acetylcysteine, suppressed erythrocyte oxidation, ameliorated the anaemia, and inhibited the production of autoantibodies. These data imply that a high level of oxidative stress in erythrocytes increases the production of autoantibodies, possibly leading to an autoimmune response, and that the intake of antioxidants would prevent certain autoimmune responses by maintaining an appropriate redox balance in erythrocytes.

Molecular pathogenesis and therapy of polycythemia induced in mice by JAK2 V617F

Background

A somatic activating mutation (V617F) in the JAK2 tyrosine kinase was recently discovered in the majority of patients with polycythemia vera (PV), and some with essential thrombocythemia (ET) and chronic idiopathic myelofibrosis. However, the role of mutant JAK2 in disease pathogenesis is unclear.

Methods and Findings

We expressed murine JAK2 WT or V617F via retroviral bone marrow transduction/transplantation in the hematopoietic system of two different inbred mouse strains, Balb/c and C57Bl/6 (B6). In both strains, JAK2 V617F, but not JAK2 WT, induced non-fatal polycythemia characterized by increased hematocrit and hemoglobin, reticulocytosis, splenomegaly, low plasma erythropoietin (Epo), and Epo-independent erythroid colonies. JAK2 V617F also induced leukocytosis and neutrophilia that was much more prominent in Balb/c mice than in B6. Platelet counts were not affected in either strain despite expression of JAK2 V617F in megakaryocytes and markedly prolonged tail bleeding times. The polycythemia tended to resolve after several months, coincident with increased spleen and marrow fibrosis, but was resurrected by transplantation to secondary recipients. Using donor mice with mutations in Lyn, Hck, and Fgr, we demonstrated that the polycythemia was independent of Src kinases. Polycythemia and reticulocytosis responded to treatment with imatinib or a JAK2 inhibitor, but were unresponsive to the Src inhibitor dasatinib.

Conclusions

These findings demonstrate that JAK2 V617F induces Epo-independent expansion of the erythroid lineage in vivo. The fact that the central erythroid features of PV are recapitulated by expression of JAK2 V617F argues that it is the primary and direct cause of human PV. The lack of thrombocytosis suggests that additional events may be required for JAK2 V617F to cause ET, but qualitative platelet abnormalities induced by JAK2 V617F may contribute to the hemostatic complications of PV. Despite the role of Src kinases in Epo signaling, our studies predict that Src inhibitors will be ineffective for therapy of PV. However, we provide proof-of-principle that a JAK2 inhibitor should have therapeutic effects on the polycythemia, and perhaps myelofibrosis and hemostatic abnormalities, suffered by MPD patients carrying the JAK2 V617F mutation.

SOD2-deficiency sideroblastic anemia and red blood cell oxidative stress

Iron overload is a feature of an array of human disorders such as sideroblastic anemias, a heterogeneous group of erythropoietic disorders without identified cause in most cases. However, sideroblastic anemias appear to result from a disturbance at the interface between mitochondrial function and iron metabolism. A defining feature is excessive iron deposition within mitochondria of developing red cells, the consequences of which are an increase in cellular free radicals production, increased damage to proteins, and reduced cell survival. Because of its mitochondrial location, superoxide dismutase (SOD2) is the principal defense against the toxicity of superoxide anions generated by the oxidative phosphorylation. We have used hematopoietic stem cell transplantation to study blood cells lacking SOD2. We became interested in the role SOD2 plays in the metabolism of superoxide anions during erythroid development, as anemia is the major phenotype in transplanted animals. Our exploration of this model suggests that oxidative stress-and in particular, mitochondrial- derived oxidants-plays an important role in the pathogenesis of the human disorder, sideroblastic anemia. Here we review the relation between mitochondrial dysfunction and sideroblastic anemia, describe several methods for assessing oxidative damage to mature or developing red cells, present data on, and discuss the potential of antioxidant therapy for this disorder.