Linkage of cytosolic peroxiredoxin 2 to erythrocyte membrane imposed by hydrogen peroxide-induced oxidative stress

Modulation of Antioxidant Enzyme Expression of In Vitro Culture-Derived Reticulocytes

The regulation of reactive oxygen species (ROS) in red blood cells (RBCs) is crucial for maintaining functionality and lifespan. Indeed, dysregulated ROS occurs in haematological diseases such as sickle cell disease and β-thalassaemia. In order to combat this, RBCs possess high levels of protective antioxidant enzymes. We aimed to further boost RBC antioxidant capacity by overexpressing peroxiredoxin (Prxs) and glutathione peroxidase (GPxs) enzymes. Multiple antioxidant enzyme cDNAs were individually overexpressed in expanding immortalised erythroblasts using lentivirus, including Prx isoforms 1, 2, and 6 and GPx isoforms 1 and 4. Enhancing Prx protein expression proved straightforward, but GPx overexpression required modifications. For GPx4, these modifications included adding a SECIS element in the 3'UTR, the removal of a mitochondrial-targeting sequence, and removing putative ubiquitination sites. Culture-derived reticulocytes exhibiting enhanced levels of Prx and GPx antioxidant proteins were successfully engineered, demonstrating a novel approach to improve RBC resilience to oxidative stress. Further work is needed to explore the activity of these proteins and their impact on RBC metabolism, but this strategy shows promise for improving RBC function in physiological and pathological contexts and during storage for transfusion. Enhancing the antioxidant capacity of reticulocytes has exciting promise for developing culture-derived RBCs with enhanced resistance to oxidative damage and offers new therapeutic interventions in diseases with elevated oxidative stress.

Hereditary Spherocytosis with Mitochondrial Retention, Increased Oxidative Stress, and Alterations to Bioactive Membrane Lipids

The clinical course for Hereditary Spherocytosis (HS) patients is highly varied, even within families with identical driving mutations. Here, we describe four siblings with HS attributed to an unreported SPTB mutation. All patients displayed an increased fraction of mitochondria-positive erythrocytes. This was associated with increased reactive oxygen species (ROS) generation and alteration to alterations to bioactive membrane lipids associated with oxidant stress. Given the early promise for mitophagy-inducing agents in sickle cell disease and ready availability of antioxidants, this concept warrants continued exploration as a disease-modifying factor and a potential target for therapy.

Peroxiredoxins in erythrocytes: far beyond the antioxidant role

The red blood cells (RBCs) are essential to transport oxygen (O2) and nutrients throughout the human body. Changes in the structure or functioning of the erythrocytes can lead to several deficiencies, such as hemolytic anemias, in which an increase in reactive oxidative species generation is involved in the pathophysiological process, playing a significant role in the severity of several clinical manifestations. There are important lines of defense against the damage caused by oxidizing molecules. Among the antioxidant molecules, the enzyme peroxiredoxin (Prx) has the higher decomposition power of hydrogen peroxide, especially in RBCs, standing out because of its abundance. This review aimed to present the recent findings that broke some paradigms regarding the three isoforms of Prxs found in RBC (Prx1, Prx2, and Prx6), showing that in addition to their antioxidant activity, these enzymes may have supplementary roles in transducing peroxide signals, as molecular chaperones, protecting from membrane damage, and maintenance of iron homeostasis, thus contributing to the overall survival of human RBCs, roles that seen to be disrupted in hemolytic anemia conditions.

Degradation of band3 and PRDX2 in erythrocytes during severe acute GVHD

We investigated the proteins of erythrocytes from stem cell transplantation patients and found decreased expression of band3 and C-terminal-truncated peroxiredoxin 2 (PRDX2) only during severe graft-versus-host disease (GVHD), using time-of-flight mass spectrometry (TOF-MS) analysis and Western blotting. During the same period, PRDX2 dimerization and calpain-1 activation were observed, indicating severe oxidative stress. We also found a putative cleavage site for calpain-1 in the C-terminal-truncated site of PRDX2. Decreased band3 expression impairs the plasticity and stability of erythrocytes, and C-terminal-truncated PRDX2 induces irreversible dysfunction of antioxidant activity. These effects may exacerbate microcirculation disorders and the progression of organ dysfunction.

Peroxiredoxin 2: An Important Element of the Antioxidant Defense of the Erythrocyte

Peroxiredoxin 2 (Prdx2) is the third most abundant erythrocyte protein. It was known previously as calpromotin since its binding to the membrane stimulates the calcium-dependent potassium channel. Prdx2 is present mostly in cytosol in the form of non-covalent dimers but may associate into doughnut-like decamers and other oligomers. Prdx2 reacts rapidly with hydrogen peroxide (k > 10⁷ M^-1 s^-1). It is the main erythrocyte antioxidant that removes hydrogen peroxide formed endogenously by hemoglobin autoxidation. Prdx2 also reduces other peroxides including lipid, urate, amino acid, and protein hydroperoxides and peroxynitrite. Oxidized Prdx2 can be reduced at the expense of thioredoxin but also of other thiols, especially glutathione. Further reactions of Prdx2 with oxidants lead to hyperoxidation (formation of sulfinyl or sulfonyl derivatives of the peroxidative cysteine). The sulfinyl derivative can be reduced by sulfiredoxin. Circadian oscillations in the level of hyperoxidation of erythrocyte Prdx2 were reported. The protein can be subject to post-translational modifications; some of them, such as phosphorylation, nitration, and acetylation, increase its activity. Prdx2 can also act as a chaperone for hemoglobin and erythrocyte membrane proteins, especially during the maturation of erythrocyte precursors. The extent of Prdx2 oxidation is increased in various diseases and can be an index of oxidative stress.

Inhibition of erythrocyte's catalase, glutathione peroxidase or peroxiredoxin 2 - Impact on cytosol and membrane

Catalase (CAT), glutathione peroxidase (GPx) and Prx2 (peroxiredoxin 2) are the main antioxidant enzymatic defenses of erythrocytes. They prevent and minimize oxidative injuries in red blood cell (RBC) components, which are continuously exposed to oxidative stress (OS). The crosstalk between CAT, GPx and Prx2 is still not fully disclosed, as well as why these typically cytoplasmic enzymes bind to the RBC membrane. Our aim was to understand the interplay between CAT, GPx and Prx2 in the erythrocyte's cytosol and membrane. Under specific (partial) inhibition of each enzyme and increasing H₂O₂-induced OS conditions, we evaluated the enzyme activities and amounts, the binding of CAT, GPx and Prx2 to RBC membrane, and biomarkers of OS, such as the reduced and oxidized glutathione levels, thiobarbituric acid reactive substances (TBARS) levels, membrane bound hemoglobin and total antioxidant status. Our results support the hypothesis that when high levels of H₂O₂ get within the erythrocyte, CAT is the main player in the antioxidant protection of the cell, while Prx2 and GPx have a less striking role. Moreover, we found that CAT, appears to have more importance in the antioxidant protection of cytoplasm than of the membrane components, since when the activity of CAT is disturbed, GPx and Prx2 are both activated in the cytosol and mobilized to the membrane. In more severe OS conditions, the antioxidant activity of GPx is more significant at the membrane, as we found that GPx moves from the cytosol to the membrane, probably to protect it from lipid peroxidation.

p97 dysfunction underlies a loss of quality control of damaged membrane proteins and promotes oxidative stress and sickling in sickle cell disease

Sickling is the central pathogenic process of sickle cell disease (SCD), one of the most prevalent inherited hemolytic disorders. Having no easy access to antioxidants in the cytosol, elevated levels of reactive oxygen species (ROS) residing at the plasma membrane in sickle red blood cells (sRBCs) easily oxidize membrane proteins and thus contribute to sickling. Although the ubiquitin-proteasome system (UPS) is essential to rapidly clear ROS-damaged membrane proteins and maintain cellular homeostasis, the function and regulatory mechanism of the UPS for their clearance in sRBCs remains unidentified. Elevated levels of polyubiquitinated membrane-associated proteins in human sRBCs are reported here. High throughput and untargeted proteomic analyses of membrane proteins immunoprecipitated by ubiquitin antibodies detected elevated levels of ubiquitination of a series of proteins including cytoskeletal proteins, transporters, ROS-related proteins, and UPS machinery components in sRBCs. Polyubiquitination of membrane-associated catalase was increased in sRBCs, associated with decreased catalase activity and elevated ROS. Surprisingly, shuttling of p97 (ATP-dependent valosin-containing chaperone protein), a key component of the UPS to shuttle polyubiquitinated proteins from the membrane to cytosol for proteasomal degradation, was significantly impaired, resulting in significant accumulation of p97 along with polyubiquitinated proteins in the membrane of human sRBCs. Functionally, inhibition of p97 directly promoted accumulation of polyubiquitinated membrane-associated proteins, excessive ROS levels, and sickling in response to hypoxia. Overall, we revealed that p97 dysfunction underlies impaired UPS and contributes to oxidative stress in sRBCs.

Copper(ii) complexes with terpene derivatives of ethylenediamine: synthesis, and antibacterial, antifungal and antioxidant activity

The synthesis of new chiral copper(ii) complexes with terpene derivatives of ethylenediamine and the results of studying their antibacterial, antifungal and antioxidant activity in vitro are discussed. All studied copper complexes (1-4) showed significantly higher antifungal activity against the strains of C. albicans, S. salmonicolor and P. notatum compared to the activity of the clinical antifungal drug amphotericin. High antibacterial activity of copper complexes with terpene derivatives of ethylenediamine was revealed against the S. aureus (MRSA) strain, which is resistant to the reference antibiotic ciprofloxacin. Using various test systems, a comparative assessment of the antioxidant activity (AOA) of the synthesized copper complexes and the ligands was carried out. The salen-type complex 4, which has the highest AOA in the model of initiated oxidation of a substrate containing animal lipids, was superior to other copper complexes in the ability to protect erythrocytes under conditions of H2O2-induced hemolysis.

Innate Variability in Physiological and Omics Aspects of the Beta Thalassemia Trait-Specific Donor Variation Effects

The broad spectrum of beta-thalassemia (βThal) mutations may result in mild reduction (β ⁺⁺), severe reduction (β ⁺) or complete absence (β ⁰) of beta-globin synthesis. βThal heterozygotes eligible for blood donation are "good storers" in terms of red blood cell (RBC) fragility, proteostasis and redox parameters of storage lesion. However, it has not been examined if heterogeneity in genetic backgrounds among βThal-trait donors affects their RBC storability profile. For this purpose, a paired analysis of physiological and omics parameters was performed in freshly drawn blood and CPD/SAGM-stored RBCs donated by eligible volunteers of β ⁺⁺ (N = 4), β ⁺ (N = 9) and β ⁰ (N = 2) mutation-based phenotypes. Compared to β ⁺, β ⁺⁺ RBCs were characterized by significantly lower RDW and HbA₂ but higher hematocrit, MCV and NADPH levels in vivo. Moreover, they had lower levels of reactive oxygen species and markers of oxidative stress, already from baseline. Interestingly, their lower myosin and arginase membrane levels were accompanied by increased cellular fragility and arginine values. Proteostasis markers (proteasomal activity and/or chaperoning-protein membrane-binding) seem to be also diminished in β ⁺⁺ as opposed to the other two phenotypic groups. Overall, despite the low number of samples in the sub-cohorts, it seems that the second level of genetic variability among the group of βThal-trait donors is reflected not only in the physiological features of RBCs in vivo, but almost equally in their storability profiles. Mutations that only slightly affect the globin chain equilibrium direct RBCs towards phenotypes closer to the average control, at least in terms of fragility indices and proteostatic dynamics.

Peroxiredoxins-The Underrated Actors during Virus-Induced Oxidative Stress

Enhanced production of reactive oxygen species (ROS) triggered by various stimuli, including viral infections, has attributed much attention in the past years. It has been shown that different viruses that cause acute or chronic diseases induce oxidative stress in infected cells and dysregulate antioxidant its antioxidant capacity. However, most studies focused on catalase and superoxide dismutases, whereas a family of peroxiredoxins (Prdx), the most effective peroxide scavengers, were given little or no attention. In the current review, we demonstrate that peroxiredoxins scavenge hydrogen and organic peroxides at their physiological concentrations at various cell compartments, unlike many other antioxidant enzymes, and discuss their recycling. We also provide data on the regulation of their expression by various transcription factors, as they can be compared with the imprint of viruses on transcriptional machinery. Next, we discuss the involvement of peroxiredoxins in transferring signals from ROS on specific proteins by promoting the oxidation of target cysteine groups, as well as briefly demonstrate evidence of nonenzymatic, chaperone, functions of Prdx. Finally, we give an account of the current state of research of peroxiredoxins for various viruses. These data clearly show that Prdx have not been given proper attention despite all the achievements in general redox biology.

Global analysis of erythroid cells redox status reveals the involvement of Prdx1 and Prdx2 in the severity of beta thalassemia

β-thalassemia is a worldwide distributed monogenic red cell disorder, characterized by an absent or reduced beta globin chain synthesis. The unbalance of alpha-gamma chain and the presence of pathological free iron promote severe oxidative damage, playing crucial a role in erythrocyte hemolysis, exacerbating ineffective erythropoiesis and decreasing the lifespan of red blood cells (RBC). Catalase, glutathione peroxidase and peroxiredoxins act together to protect RBCs from hydrogen peroxide insult. Among them, peroxiredoxins stand out for their overall abundance and reactivity. In RBCs, Prdx2 is the third most abundant protein, although Prdxs 1 and 6 isoforms are also found in lower amounts. Despite the importance of these enzymes, Prdx1 and Prdx2 may have their peroxidase activity inactivated by hyperoxidation at high hydroperoxide concentrations, which also promotes the molecular chaperone activity of these proteins. Some studies have demonstrated the importance of Prdx1 and Prdx2 for the development and maintenance of erythrocytes in hemolytic anemia. Now, we performed a global analysis comparatively evaluating the expression profile of several antioxidant enzymes and their physiological reducing agents in patients with beta thalassemia intermedia (BTI) and healthy individuals. Furthermore, increased levels of ROS were observed not only in RBC, but also in neutrophils and mononuclear cells of BTI patients. The level of transcripts and the protein content of Prx1 were increased in reticulocyte and RBCs of BTI patients and the protein content was also found to be higher when compared to beta thalassemia major (BTM), suggesting that this peroxidase could cooperate with Prx2 in the removal of H₂O₂. Furthermore, Prdx2 production is highly increased in RBCs of BTM patients that present high amounts of hyperoxidized species. A significant increase in the content of Trx1, Srx1 and Sod1 in RBCs of BTI patients suggested protective roles for these enzymes in BTI patients. Finally, the upregulation of Nrf2 and Keap1 transcription factors found in BTI patients may be involved in the regulation of the antioxidant enzymes analyzed in this work.

Neutrophil Elastase Inhibitors and Chronic Kidney Disease

End-stage renal disease (ESRD), the last stage of chronic kidney disease (CKD), is characterized by chronic inflammation and oxidative stress. Neutrophils are the front line cells that mediate an inflammatory response against microorganisms as they can migrate, produce reactive oxygen species (ROS), secrete neutrophil serine proteases (NSPs), and release neutrophil extracellular traps (NETs). Serine proteases inhibitors regulate the activity of serine proteases and reduce neutrophil accumulation at inflammatory sites. This review intends to relate the role of neutrophil elastase in CKD and the effects of neutrophil elastase inhibitors in predicting or preventing inflammation.

Peroxiredoxin 2, glutathione peroxidase, and catalase in the cytosol and membrane of erythrocytes under H2O2-induced oxidative stress

Erythrocytes are continuously exposed to risk of oxidative injury due to oxidant oxygen species. To prevent damage, they have antioxidant agents namely, catalase (Cat), glutathione peroxidase (GPx), and peroxiredoxin 2 (Prx2). Our aim was to contribute to a better understanding of the interplay between Prx2, Cat, and GPx under H2O2-induced oxidative stress, by studying their changes in the red blood cell cytosol and membrane, in different conditions. These three enzymes were quantified by immunoblotting. Malondialdehyde, that is, lipoperoxidation (LPO) in the erythrocyte membrane, and membrane-bound hemoglobin (MBH) were evaluated, as markers of oxidative stress. We also studied the erythrocyte membrane protein profile, to estimate how oxidative stress affects the membrane protein structure. We showed that under increasing H2O2 concentrations, inhibition of the three enzymes with or without metHb formation lead to the binding of Prx2 and GPx (but not Cat) to the erythrocyte membrane. Prx2 was detected mainly in its oxidized form and the linkage of metHb to the membrane seems to compete with the binding of Prx2. Catalase played a major role in protecting erythrocytes from high exogenous flux of H2O2, since whenever Cat was active there were no significant changes in any of the studied parameters. When only Cat was inhibited, Prx2 and GPx were unable to prevent H2O2-induced oxidative stress resulting in increasing MBH and membrane LPO. Additionally, the inhibition of one or more of these enzymes induced changes in the anchor/linker proteins of the junctional complexes of the membrane cytoskeleton-lipid bilayer, which might lead to membrane destabilization.

Identification of human erythrocyte cytosolic proteins associated with plasma membrane during thermal stress

The influence of thermal stress on the association between human erythrocyte membranes and cytosolic proteins was studied by exposing erythrocyte suspensions and whole blood to different elevated temperatures. Membranes and cytosolic proteins from unheated and heat-stressed erythrocytes were analyzed by electrophoresis, followed by mass spectrometric identification. Four major (carbonic anhydrase I, carbonic anhydrase II, peroxiredoxin VI, flavin reductase) and some minor (heat shock protein 90α, heat shock protein 70, α-enolase, peptidylprolyl cis-trans isomerase A) cytosolic proteins were found to be associated with the erythrocyte membrane in response to in vitro thermal stress. Unlike the above proteins, catalase and peroxiredoxin II were associated with membranes from unheated erythrocytes, and their content increased in the membrane following heat stress. The heat-induced association of cytosolic proteins was restricted to the Triton shells (membrane skeleton/cytoskeleton). Similar results were observed when Triton shells derived from unheated erythrocyte membranes were incubated with an unheated erythrocyte cytosolic fraction at elevated temperatures. This is a first report on the association of cytosolic catalase, α-enolase, peroxiredoxin VI, peroxiredoxin II and peptidylprolyl cis-trans isomerase A to the membrane or membrane skeleton of erythrocytes under heat stress. From these results, it is concluded that specific cytosolic proteins are translocated to the membrane in human erythrocytes exposed to heat stress and they may play a novel role as erythrocyte membrane protectors under stress by stabilizing the membrane skeleton through their interactions with skeletal proteins.

Role of peroxiredoxin-2 in protecting RBCs from hydrogen peroxide-induced oxidative stress

The role of peroxiredoxin-2 (PRDX2) in preventing hydrogen peroxide-induced oxidative stress in the red blood cell was investigated by comparing blood from PRDX2 knockout mice with superoxide dismutase-1 (SOD1) knockout and control mice. Loss of PRDX2 increased basal levels of methemoglobin and heme degradation (a marker for oxidative stress), and reduced red blood cell deformability. In vitro incubation under normoxic conditions, both with and without inhibition of catalase, resulted in a lag phase during which negligible heme degradation occurred followed by a more rapid rate of heme degradation in the absence of PRDX2. The appreciable basal increase in heme degradation for PRDX2 knockout mice, together with the lag during in vitro incubation, implies that PRDX2 neutralizes hydrogen peroxide generated in vivo under the transient hypoxic conditions experienced as the cells pass through the microcirculation.

Potentially antigenic RBC membrane proteins in dogs with primary immune-mediated hemolytic anemia

BACKGROUND

Primary immune-mediated hemolytic anemia (IMHA) is an important cause of morbidity and mortality in dogs. The mechanisms underlying autoimmune reactivity remain poorly understood.

OBJECTIVE

The aim of this study was to identify membrane proteins of RBCs that could be antigenic in dogs with primary IMHA.

METHODS

Antibodies were eluted with xylene from RBCs of 12 dogs with IMHA, 4 dogs with anemia due to causes other than IMHA, and 2 healthy dogs. Pooled RBC membrane proteins were prepared from blood of 17 healthy dogs. The eluted antibodies were then analyzed by immunoblotting for interactions with the pooled membrane proteins and autologous plasma. Bands present in the 12 dogs with IMHA but not in the 6 other dogs were considered potential autoantigens and were identified by liquid chromatography followed by tandem mass spectrometry.

RESULTS

RBC eluates from all 18 dogs had reactivity against band 3 protein. Antibodies to 6 additional proteins were uniquely identified in dogs with IMHA. Reactivity to calpain, complement component 3, and peroxiredoxin 2 was identified in 8, 8, and 4 of the 12 samples, respectively, from dogs with IMHA, but in none of the samples from the 6 dogs without IMHA.

CONCLUSIONS

Detection of universal immune reactivity against band 3 protein probably indicates recognition of senescent RBC. Proteins uniquely recognized by antibodies in dogs with IMHA are involved in oxidative stress and apoptosis (calpain), inflammation (complement), and scavenging of reactive oxygen species (peroxiredoxin 2). It remains to be determined if these proteins are important in initiating autoimmunity or if immunoglobulins targeting these proteins develop during IMHA.

In-depth analysis of cysteine oxidation by the RBC proteome: advantage of peroxiredoxin II knockout mice

Peroxiredoxin II (Prdx II, a typical 2-Cys Prdx) has been originally isolated from erythrocytes, and its structure and peroxidase activity have been adequately studied. Mice lacking Prdx II proteins had heinz bodies in their peripheral blood, and morphologically abnormal cells were detected in the dense red blood cell (RBC) fractions, which contained markedly higher levels of reactive oxygen species (ROS). In this study, a labeling experiment with the thiol-modifying reagent biotinylated iodoacetamide (BIAM) in Prdx II-/- mice revealed that a variety of RBC proteins were highly oxidized. To identify oxidation-sensitive proteins in Prdx II-/- mice, we performed RBC comparative proteome analysis in membrane and cytosolic fractions by nano-UPLC-MSE shotgun proteomics. We found oxidation-sensitive 54 proteins from 61 peptides containing cysteine oxidation, and analyzed comparative expression pattern in healthy RBCs of Prdx II+/+ mice, healthy RBCs of Prdx II-/- mice, and abnormal RBCs of Prdx II-/- mice. These proteins belonged to cellular functions related with RBC lifespan maintain, such as cytoskeleton, stress-induced proteins, metabolic enzymes, signal transduction, and transporters. Furthermore, protein networks among identified oxidation-sensitive proteins were analyzed to associate with various diseases. Consequently, we expected that RBC proteome might provide clues to understand redox-imbalanced diseases.

Peroxiredoxin-2 as a candidate biomarker to test oxidative stress levels of stored red blood cells under blood bank conditions

BACKGROUND

Several researches on aging red blood cells (RBCs)--performed both in vivo and under blood bank conditions--revealed that RBC membrane proteins undergo a number of irreversible alterations, mainly due to oxidative stress. The individuation of proteins to be used as indicators of irreversible RBC injury and to be proposed as candidate biomarkers of oxidative damage or aging status during blood storage is therefore of great interest.

STUDY DESIGN AND METHODS

Based on this purpose we performed proteomic analysis of the membranes of RBCs during various storage periods under blood bank conditions. Changes in protein composition of RBC membranes were monitored as a function of the storage period by means of polyacrylamide gel electrophoresis coupled with immunoblotting and mass spectrometry analyses.

RESULTS

During storage, a progressive linkage of typical cytosolic proteins to the membrane was detected, including both antioxidant and metabolic enzymes (such as catalase, peroxiredoxin-2 [Prx2], and 2,3-bisphosphoglycerate-mutase), as well as nonreducible cross-linkings of probably oxidized or denatured hemoglobin. This phenomenon was unequivocally related to oxidative stress, since storage of RBCs under anaerobic conditions showed a suppression of these protein recruitments to the membrane.

CONCLUSION

The detailed analysis of these protein associations to the membrane of aged RBCs allowed Prx2 to be suggested as a potential RBC oxidative stress marker for the sake of developing new approaches in quality assurance of blood components.

Comparative proteomics reveals deficiency of NHE-1 (Slc9a1) in RBCs from the beta-adducin knockout mouse model of hemolytic anemia

Hemolytic anemia is one of the most common inherited disorders. To identify candidate proteins involved in hemolytic anemia pathophysiology, we utilized a label-free comparative proteomic approach to detect differences in RBCs from normal and beta-adducin (Add2) knock-out mice. We detected 7 proteins that were decreased and 48 proteins that were increased in the beta-adducin knock-out RBC ghost. Since hemolytic anemias are characterized by reticulocytosis, we compared reticulocyte-enriched samples from phenylhydrazine-treated mice with mature RBCs from untreated mice. Label-free analysis identified 47 proteins that were increased in the reticulocyte-enriched samples and 21 proteins that were decreased. Among the proteins increased in Add2 knockout RBCs, only 11 were also found increased in reticulocytes. Among the proteins decreased in Add2 knockout RBCs, beta- and alpha-adducin showed the greatest intensity difference, followed by NHE-1 (Slc9a1), the sodium-hydrogen exchanger. We verified these mass spectrometry results by immunoblot. This is the first example of a deficiency of NHE-1 in hemolytic anemia and suggests new insights into the mechanisms leading to fragile RBCs. Our use of label-free comparative proteomics to make this discovery demonstrates the usefulness of this approach as opposed to metabolic or chemical isotopic labeling of mice.

Oxidative stress-dependent oligomeric status of erythrocyte peroxiredoxin II (PrxII) during storage under standard blood banking conditions

Although biochemical properties of 2-Cys peroxiredoxins have been extensively studied in various cell lines and organisms, redox-induced structural transitions of peroxiredoxin II (PrxII) in human erythrocytes certainly warrant further investigation. In this work, cytosol and membrane ghosts of both fresh erythrocytes (cells obtained just after blood collection) and 28-day stored erythrocytes were analyzed by proteomics tools. We demonstrated that in fresh red blood cells PrxII exhibits four different oligomeric states in cytosol, whereas no PrxII complexes are in the membrane. The highest molecular weight PrxII protein complex (440 kDa) was proven to derive from the association between tetrameric catalase (CAT, 232 kDa) and decameric PrxII, whereas oligomers at 140, 100 and 67 kDa resulted to be homo-polymeric complexes composed of variable copies of PrxII monomeric subunits. Interestingly, the 440 kDa complex contained both reduced and oxidized (disulphide-linked dimers) PrxII decamers. Upon oxidative stress (28-day storage), the PrxII oligomers at 100 kDa in the cytosol disappeared and the CAT-PrxII hetero-oligomeric complex at 440 kDa is converted to a higher molecular weight structure (480 kDa) due to the presence therein of cross-linked species of PrxII and hemoglobin. More interestingly, oxidized red cell membranes contained the CAT-PrxII complex detected in 0-day cytosol as a consequence of protein recruitments induced by oxidative stress, however it showed a greater percentage of PrxII dimers. Finally, since the adoption of distinct PrxII structures is known to be closely related to different functions, peroxidase activity assays were performed demonstrating a positive reaction for oligomers at 440 kDa (both in cytosol and membrane compartment) and at 140 kDa. Our results contribute to clarify structural and functional switching of peroxiredoxin II in erythrocytes, thus possibly opening new scenarios in the biological roles played by this protein in defense mechanisms against oxidative stress, especially with the reference to red cell storage lesions.