Deoxygenation affects tyrosine phosphoproteome of red cell membrane from patients with sickle cell disease

Phosphoproteomics and morphology of stored human red blood cells treated by protein tyrosine phosphatases inhibitor

ABSTRACT

The process of protein phosphorylation is involved in numerous cell functions. In particular, phosphotyrosine (pY) has been reported to play a role in red blood cell (RBC) functions, including the cytoskeleton organization. During their storage before transfusion, RBCs suffer from storage lesions that affect their energy metabolism and morphology. This study investigated the relationship between pY and the storage lesions. To do so, RBCs were treated (in the absence of calcium) with a protein tyrosine phosphatase inhibitor (orthovanadate [OV]) to stimulate phosphorylation and with 3 selective kinase inhibitors (KIs). Erythrocyte membrane proteins were studied by western blot analyses and phosphoproteomics (data are available via ProteomeXchange with identifier PXD039914) and cell morphology by digital holographic microscopy. The increase of pY triggered by OV treatment (inducing a global downregulation of pS and pT) disappeared during the storage. Phosphoproteomic analysis identified 609 phosphoproteins containing 1752 phosphosites, of which 41 pY were upregulated and 2 downregulated by OV. After these phosphorylation processes, the shape of RBCs shifted from discocytes to spherocytes, and the addition of KIs partially inhibited this transition. The KIs modulated either pY or pS and pT via diverse mechanisms related to cell shape, thereby affecting RBC morphology. The capacity of RBCs to maintain their function is central in transfusion medicine, and the presented results contribute to a better understanding of RBC biology.

Rapid degradation of protein tyrosine phosphatase 1B in sickle cells: Possible contribution to sickle cell membrane weakening

Although both protein tyrosine phosphatases and kinases are constitutively active in healthy human red blood cells (RBCs), the preponderance of phosphatase activities maintains the membrane proteins in a predominantly unphosphorylated state. We report here that unlike healthy RBCs, proteins in sickle cells are heavily tyrosine phosphorylated, raising the question regarding the mechanism underpinning this tyrosine phosphorylation. Upon investigating possible causes, we observe that protein tyrosine phosphatase 1B (PTP1B), the major erythrocyte tyrosine phosphatase, is largely digested to a lower molecular weight fragment in sickle cells. We further find that the resulting truncated form of PTP1B is significantly less active than its intact counterpart, probably accounting for the intense tyrosine phosphorylation of Band 3 in sickle erythrocytes. Because this tyrosine phosphorylation of Band 3 promotes erythrocyte membrane weakening that causes release of both membrane vesicles and cell free hemoglobin that in turn initiates vaso-occlusive events, we conclude that cleavage of PTP1B could contribute to the symptoms of sickle cell disease. We further posit that methods to inhibit proteolysis of PTP1B could mitigate symptoms of the disease.

Early-stage culprit in protein misfolding diseases investigated using electrochemical parameters: New insights over peptide-membrane interactions

The dysfunctioning of β-cells caused by the unspecific misfolding of the human islet amyloid polypeptide (hIAPP) at the membrane results in type 2 diabetes mellitus. Here, we report for the first time, the early-stage interaction of hIAPP oligomers on the DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine) lipid membrane using electrochemical parameters. Electrochemical techniques are better than other techniques to detect hIAPP at significantly lower concentrations. The surface level interactions between the peptide (hIAPP) and lipid membrane (DMPC) were investigated using atomic force microscopy (AFM), confocal microscopy (CM) and electrochemical techniques such as Tafel polarization, cyclic voltammetry (CV), differential pulse voltammetry (DPV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS). Inserting IAPP into the fluid domains results in breaking the lipid-to-lipid interaction, leading to restriction of membrane mobility. The S_Lateral values of the liposome and IAPP co-solubilized liposome indicates the cooperative insertion of IAPP. Further, a new method of immobilizing a membrane to the gold surface has been employed, resulting in an electrical contact with the buffer, preventing the direct utilization of a steady-state voltage across the bilayer. The electrochemical studies revealed that the charge transfer resistance decreased for 3-mercaptopropanoic acid modified gold (MPA-Au) electrode coated with the liposome and after the addition of IAPP, followed by an increase in the capacitance. The present study has opened up new dimensions to the understanding of peptide-membrane interactions and shows different experimental approaches for the future researchers in this domain.

Tyrosine Phosphorylation Modulates Peroxiredoxin-2 Activity in Normal and Diseased Red Cells

Peroxiredoxin-2 (Prx2) is the third most abundant cytoplasmic protein in red blood cells. Prx2 belongs to a well-known family of antioxidants, the peroxiredoxins (Prxs), that are widely expressed in mammalian cells. Prx2 is a typical, homodimeric, 2-Cys Prx that uses two cysteine residues to accomplish the task of detoxifying a vast range of organic peroxides, H₂O₂, and peroxynitrite. Although progress has been made on functional characterization of Prx2, much still remains to be investigated on Prx2 post-translational changes. Here, we first show that Prx2 is Tyrosine (Tyr) phosphorylated by Syk in red cells exposed to oxidation induced by diamide. We identified Tyr-193 in both recombinant Prx2 and native Prx2 from red cells as a specific target of Syk. Bioinformatic analysis suggests that phosphorylation of Tyr-193 allows Prx2 conformational change that is more favorable for its peroxidase activity. Indeed, Syk-induced Tyr phosphorylation of Prx2 enhances in vitro Prx2 activity, but also contributes to Prx2 translocation to the membrane of red cells exposed to diamide. The biologic importance of Tyr-193 phospho-Prx2 is further supported by data on red cells from a mouse model of humanized sickle cell disease (SCD). SCD is globally distributed, hereditary red cell disorder, characterized by severe red cell oxidation due to the pathologic sickle hemoglobin. SCD red cells show Tyr-phosphorylated Prx2 bound to the membrane and increased Prx2 activity when compared to healthy erythrocytes. Collectively, our data highlight the novel link between redox related signaling and Prx2 function in normal and diseased red cells.

Oxidation Impacts the Intracellular Signaling Machinery in Hematological Disorders

The dynamic coordination between kinases and phosphatases is crucial for cell homeostasis, in response to different stresses. The functional connection between oxidation and the intracellular signaling machinery still remains to be investigated. In the last decade, several studies have highlighted the role of reactive oxygen species (ROS) as modulators directly targeting kinases, phosphatases, and downstream modulators, or indirectly acting on cysteine residues on kinases/phosphatases resulting in protein conformational changes with modulation of intracellular signaling pathway(s). Translational studies have revealed the important link between oxidation and signal transduction pathways in hematological disorders. The intricate nature of intracellular signal transduction mechanisms, based on the generation of complex networks of different types of signaling proteins, revealed the novel and important role of phosphatases together with kinases in disease mechanisms. Thus, therapeutic approaches to abnormal signal transduction pathways should consider either inhibition of overactivated/accumulated kinases or homeostatic signaling resetting through the activation of phosphatases. This review discusses the progress in the knowledge of the interplay between oxidation and cell signaling, involving phosphatase/kinase systems in models of globally distributed hematological disorders.

Signaling Response to Transient Redox Stress in Human Isolated T Cells: Molecular Sensor Role of Syk Kinase and Functional Involvement of IL2 Receptor and L-Selectine

Reactive oxygen species (ROS) are central effectors of inflammation and play a key role in cell signaling. Previous reports have described an association between oxidative events and the modulation of innate immunity. However, the role of redox signaling in adaptive immunity is still not well understood. This work is based on a novel investigation of diamide, a specific oxidant of sulfhydryl groups, and it is the first performed in purified T cell tyrosine phosphorylation signaling. Our data show that ex vivo T cells respond to –SH group oxidation with a distinctive tyrosine phosphorylation response and that these events elicit specific cellular responses. The expression of two essential T-cell receptors, CD25 and CD62L, and T-cell cytokine release is also affected in a specific way. Experiments with Syk inhibitors indicate a major contribution of this kinase in these phenomena. This pilot work confirms the presence of crosstalk between oxidation of cysteine residues and tyrosine phosphorylation changes, resulting in a series of functional events in freshly isolated T cells. Our experiments show a novel role of Syk inhibitors in applying their anti-inflammatory action through the inhibition of a ROS-generated reaction.

Current challenges in the management of patients with sickle cell disease - A report of the Italian experience

Sickle cell disease (SCD) is an inherited red blood cell disorder caused by a structural abnormality of hemoglobin called sickle hemoglobin (HbS). Clinical manifestations of SCD are mainly characterized by chronic hemolysis and acute vaso-occlusive crisis, which are responsible for severe acute and chronic organ damage. SCD is widespread in sub-Saharan Africa, in the Middle East, Indian subcontinent, and some Mediterranean regions. With voluntary population migrations, people harboring the HbS gene have spread globally. In 2006, the World Health Organization recognized hemoglobinopathies, including SCD, as a global public health problem and urged national health systems worldwide to design and establish programs for the prevention and management of SCD. Herein we describe the historical experience of the network of hemoglobinopathy centers and their approach to SCD in Italy, a country where hemoglobinopathies have a high prevalence and where SCD, associated with different genotypes including ß-thalassemia, is present in the native population.

New Therapeutic Options for the Treatment of Sickle Cell Disease

Sickle cell disease (SCD; ORPHA232; OMIM # 603903) is a chronic and invalidating disorder distributed worldwide, with high morbidity and mortality. Given the disease complexity and the multiplicity of pathophysiological targets, development of new therapeutic options is critical, despite the positive effects of hydroxyurea (HU), for many years the only approved drug for SCD. New therapeutic strategies might be divided into (1) pathophysiology-related novel therapies and (2) innovations in curative therapeutic options such as hematopoietic stem cell transplantation and gene therapy. The pathophysiology related novel therapies are: a) Agents which reduce sickling or prevent sickle red cell dehydration; b) Agents targeting SCD vasculopathy and sickle cell-endothelial adhesive events; c) Anti-oxidant agents. This review highlights new therapeutic strategies in SCD and discusses future developments, research implications, and possible innovative clinical trials.

Erythrocyte and platelet proteomics in hematological disorders

Erythrocytes undergo ineffective erythropoesis, hemolysis, and premature eryptosis in sickle cell disease and thalassemia. Abnormal hemoglobin variants associated with hemoglobinopathy lead to vesiculation, membrane instability, and loss of membrane asymmetry with exposal of phosphatidylserine. This potentiates thrombin generation resulting in activation of the coagulation cascade responsible for subclinical phenotypes. Platelet activation also results in the release of microparticles, which express and transfer functional receptors from platelet membrane, playing key roles in vascular reactivity and activation of intracellular signaling pathways. Over the last decade, proteomics had proven to be an important field of research in studies of blood and blood diseases. Blood cells and its fluidic components have been proven to be easy systems for studying differential expressions of proteins in hematological diseases encompassing hemoglobinopathies, different types of anemias, myeloproliferative disorders, and coagulopathies. Proteomic studies of erythrocytes and platelets reported from several groups have highlighted various factors that intersect the signaling networks in these anucleate systems. In this review, we have elaborated on the current scenario of anucleate blood cell proteomes in normal and diseased individuals and the cross-talk between the two major constituent cell types of circulating blood.

Band 3 Erythrocyte Membrane Protein Acts as Redox Stress Sensor Leading to Its Phosphorylation by p (72) Syk

In erythrocytes, the regulation of the redox sensitive Tyr phosphorylation of band 3 and its functions are still partially defined. A role of band 3 oxidation in regulating its own phosphorylation has been previously suggested. The current study provides evidences to support this hypothesis: (i) in intact erythrocytes, at 2 mM concentration of GSH, band 3 oxidation, and phosphorylation, Syk translocation to the membrane and Syk phosphorylation responded to the same micromolar concentrations of oxidants showing identical temporal variations; (ii) the Cys residues located in the band 3 cytoplasmic domain are 20-fold more reactive than GSH; (iii) disulfide linked band 3 cytoplasmic domain docks Syk kinase; (iv) protein Tyr phosphatases are poorly inhibited at oxidant concentrations leading to massive band 3 oxidation and phosphorylation. We also observed that hemichromes binding to band 3 determined its irreversible oxidation and phosphorylation, progressive hemolysis, and serine hyperphosphorylation of different cytoskeleton proteins. Syk inhibitor suppressed the phosphorylation of band 3 also preventing serine phosphorylation changes and hemolysis. Our data suggest that band 3 acts as redox sensor regulating its own phosphorylation and that hemichromes leading to the protracted phosphorylation of band 3 may trigger a cascade of events finally leading to hemolysis.

Fluorescence assay of the interaction between hemoglobin and the cytoplasmic domain of erythrocyte membrane band 3

Oxygen tension has emerged as a potent regulator of multiple erythrocyte properties, including glucose metabolism, cell volume, ATP release, and cytoskeletal organization. Because hemoglobin (Hb)(1) binds to the cytoplasmic domain of band 3 (cdb3) in an oxygen dependent manner, with deoxyHb exhibiting significantly greater affinity for cdb3 than oxyHb, the deoxyHb-cdb3 interaction has been hypothesized to constitute the molecular switch for all O2-controlled erythrocyte processes. In this study, we describe a rapid and accurate method for quantitating the interaction of deoxyHb binding to cdb3. For this purpose, enhanced green fluorescent protein (eGFP) is fused to the COOH-terminus of cdb3, and the binding of Hb to the NH2-terminus of cdb3-eGFP is quantitated by Hb-mediated quenching of cdb3-eGFP fluorescence. As expected, the intensity of cdb3-eGFP fluorescence decreases only slightly following addition of oxyHb. However, upon deoxygenation of the same Hb-cdb3 solution, the fluorescence decreases dramatically (i.e. confirming that deoxyHb exhibits much greater affinity for cdb3 than oxyHb). Using this fluorescence quenching method, we not only confirm previously established characteristics of the Hb-cdb3 interaction, but also establish an assay that can be exploited to screen for inhibitors of the sickle Hb-cdb3 interaction that accelerates sickle Hb polymerization.

Targeted quantitative phosphoproteomic analysis of erythrocyte membranes during blood bank storage

One of the hallmarks of blood bank stored red blood cells (RBCs) is the irreversible transition from a discoid to a spherocyte-like morphology with membrane perturbation and cytoskeleton disorders. Therefore, identification of the storage-associated modifications in the protein-protein interactions between the cytoskeleton and the lipid bilayer may contribute to enlighten the molecular mechanisms involved in the alterations of mechanical properties of stored RBCs. Here we report the results obtained analyzing RBCs after 0, 21 and 35 days of storage under standard blood banking conditions by label free mass spectrometry (MS)-based experiments. We could quantitatively measure changes in the phosphorylation level of crucial phosphopeptides belonging to β-spectrin, ankyrin-1, α-adducin, dematin, glycophorin A and glycophorin C proteins. Data have been validated by both western blotting and pseudo-Multiple Reaction Monitoring (MRM). Although each phosphopeptide showed a distinctive trend, a sharp increase in the phosphorylation level during the storage duration was observed. Phosphopeptide mapping and structural modeling analysis indicated that the phosphorylated residues localize in protein functional domains fundamental for the maintenance of membrane structural integrity. Along with previous morphological evidence acquired by electron microscopy, our results seem to indicate that 21-day storage may represent a key point for the molecular processes leading to the erythrocyte deformability reduction observed during blood storage. These findings could therefore be helpful in understanding and preventing the morphology-linked mechanisms responsible for the post-transfusion survival of preserved RBCs.

T cell tyrosine phosphorylation response to transient redox stress

Reactive Oxygen Species (ROS) are crucial to multiple biological processes involved in the pathophysiology of inflammation, and are also involved in redox signaling responses. Although previous reports have described an association between oxidative events and the modulation of innate immunity, a role for redox signaling in T cell mediated adaptive immunity has not been described yet. This work aims at assessing if T cells can sense redox stress through protein sulfhydryl oxidation and respond with tyrosine phosphorylation changes. Our data show that Jurkat T cells respond to -SH group oxidation with specific tyrosine phosphorylation events. The release of T cell cytokines TNF, IFNγ and IL2 as well as the expression of a number of receptors are affected by those changes. Additionally, experiments with spleen tyrosine kinase (Syk) inhibitors showed a major involvement of Syk in these responses. The experiments described herein show a link between cysteine oxidation and tyrosine phosphorylation changes in T cells, as well as a novel mechanism by which Syk inhibitors exert their anti-inflammatory activity through the inhibition of a response initiated by ROS.

Abnormal red cell features associated with hereditary neurodegenerative disorders: the neuroacanthocytosis syndromes

PURPOSE OF REVIEW

This review discusses the mechanisms involved in the generation of thorny red blood cells (RBCs), known as acanthocytes, in patients with neuroacanthocytosis, a heterogenous group of neurodegenerative hereditary disorders that include chorea-acanthocytosis (ChAc) and McLeod syndrome (MLS).

RECENT FINDINGS

Although molecular defects associated with neuroacanthocytosis have been identified recently, their pathophysiology and the related RBC abnormalities are largely unknown. Studies in ChAc RBCs have shown an altered association between the cytoskeleton and the integral membrane protein compartment in the absence of major changes in RBC membrane composition. In ChAc RBCs, abnormal Lyn kinase activation in a Syk-independent fashion has been reported recently, resulting in increased band 3 tyrosine phosphorylation and perturbation of the stability of the multiprotein band 3-based complexes bridging the membrane to the spectrin-based membrane skeleton. Similarly, in MLS, the absence of XK-protein, which is associated with the spectrin-actin-4.1 junctional complex, is associated with an abnormal membrane protein phosphorylation state, with destabilization of the membrane skeletal network resulting in generation of acanthocytes.

SUMMARY

A novel mechanism in generation of acanthocytes involving abnormal Lyn activation, identified in ChAc, expands the acanthocytosis phenomenon toward protein-protein interactions, controlled by phosphorylation-related abnormal signaling.

The novel role of peroxiredoxin-2 in red cell membrane protein homeostasis and senescence

Peroxiredoxin-2 (Prx2), a typical two-cysteine peroxiredoxin, is the third most abundant protein in red cells. Although progress has been made in the functional characterization of Prx2, its role in red cell membrane protein homeostasis is still under investigation. Here, we studied Prx2(-/-) mouse red cells. The absence of Prx2 promotes (i) activation of the oxidative-induced Syk pathway; (ii) increased band 3 Tyr phosphorylation, with clustered band 3; and (iii) increased heat shock protein (HSP27 and HSP70) membrane translocation. This was associated with enhanced in vitro erythrophagocytosis of Prx2(-/-) red cells and reduced Prx2(-/-) red cell survival, indicating the possible role of Prx2 membrane recruitment in red cell aging and in the clearance of oxidized hemoglobin and damaged proteins through microparticles. Indeed, we observed an increased release of microparticles from Prx2(-/-) mouse red cells. The mass spectrometric analysis of erythroid microparticles found hemoglobin chains, membrane proteins, and HSPs. To test these findings, we treated Prx2(-/-) mice with antioxidants in vivo. We observed that N-acetylcysteine reduced (i) Syk activation, (ii) band 3 clusterization, (iii) HSP27 membrane association, and (iv) erythroid microparticle release, resulting in increased Prx2(-/-) mouse red cell survival. Thus, we propose that Prx2 may play a cytoprotective role in red cell membrane protein homeostasis and senescence.

Performance of a novel sieving matrix of poly(vinyl alcohol)/acrylamide copolymer in electrophoretic separations of high molecular weight proteins from red cell membrane

The analysis of high molecular weight (HMW) proteins from complex mixtures is still a challenge in proteomics. This work introduces a novel hydrogel obtained by the copolymerization of an allyl-PVA derivative with acrylamide and bisacrylamide and applies this matrix to the electrophoretic separation of HMW proteins. By inducing gelation of polyacrylamide in the presence of variable amounts of allyl-PVA, it is possible to control and vary the average gel porosity. This gel is easy to produce and handle and offers the advantage of being highly mechanically resistant and macroporous. The new matrix was tested in mono-dimensional separations of complex protein mixtures extracted from red cell membranes with different detergents. The improved performance of this macroporous matrix allowed to identify new proteins by MS and immunoblot analysis using specific antibodies. In particular, the resolution of proteins ranging in size between 97 and 279 kDa was greatly improved here compared to standard polyacrylamide gels, suggesting that this matrix can be a useful tool in routine analysis of HMW proteins in cell biology.

Oxidative stress and β-thalassemic erythroid cells behind the molecular defect

β-thalassemia is a worldwide distributed monogenic red cell disorder, characterized by the absence or reduced β-globin chain synthesis. Despite the extensive knowledge of the molecular defects causing β-thalassemia, less is known about the mechanisms responsible for the associated ineffective erythropoiesis and reduced red cell survival, which sustain anemia of β-thalassemia. The unbalance of alpha-gamma chain and the presence of pathological free iron promote a severe red cell membrane oxidative stress, which results in abnormal β-thalassemic red cell features. These cells are precociously removed by the macrophage system through two mechanisms: the removal of phosphatidylserine positive cells and through the natural occurring antibody produced against the abnormally clustered membrane protein band 3. In the present review we will discuss the changes in β-thalassemic red cell homeostasis related to the oxidative stress and its connection with production of microparticles and with malaria infection. The reactive oxygen species (ROS) are also involved in ineffective erythropoiesis of β-thalassemia through still partially known pathways. Novel cytoprotective systems such as ASHP, eIF2α, and peroxiredoxin-2 have been suggested to be important against ROS in β-thalassemic erythropoiesis. Finally, we will discuss the results of the major in vitro and in vivo studies with antioxidants in β-thalassemia.

Calcium in red blood cells-a perilous balance

Ca2+ is a universal signalling molecule involved in regulating cell cycle and fate, metabolism and structural integrity, motility and volume. Like other cells, red blood cells (RBCs) rely on Ca2+ dependent signalling during differentiation from precursor cells. Intracellular Ca2+ levels in the circulating human RBCs take part not only in controlling biophysical properties such as membrane composition, volume and rheological properties, but also physiological parameters such as metabolic activity, redox state and cell clearance. Extremely low basal permeability of the human RBC membrane to Ca2+ and a powerful Ca2+ pump maintains intracellular free Ca2+ levels between 30 and 60 nM, whereas blood plasma Ca2+ is approximately 1.8 mM. Thus, activation of Ca2+ uptake has an impressive impact on multiple processes in the cells rendering Ca2+ a master regulator in RBCs. Malfunction of Ca2+ transporters in human RBCs leads to excessive accumulation of Ca2+ within the cells. This is associated with a number of pathological states including sickle cell disease, thalassemia, phosphofructokinase deficiency and other forms of hereditary anaemia. Continuous progress in unravelling the molecular nature of Ca2+ transport pathways allows harnessing Ca2+ uptake, avoiding premature RBC clearance and thrombotic complications. This review summarizes our current knowledge of Ca2+ signalling in RBCs emphasizing the importance of this inorganic cation in RBC function and survival.

Red blood cell metabolism under prolonged anaerobic storage

Oxygen dependent modulation of red blood cell metabolism is a long investigated issue. However, the recent introduction of novel mass spectrometry-based approaches lends itself to implement our understanding of the effects of red blood cell prolonged exposure to anaerobiosis. Indeed, most of the studies conducted so far have addressed the short term issue, while the limited body of literature covering a 42 days storage period only takes into account a handful of metabolic parameters (ATP, DPG, glucose, glyceraldehyde 3-phosphate, and lactate). We hereby performed a mass spectrometry-based untargeted metabolomics analysis in order to highlight metabolic species in erythrocyte concentrates stored anaerobically in SAGM additive solutions for up to 42 days, by testing cells on a weekly basis. We could confirm previous evidence about long term anaerobiosis promoting glycolytic metabolism in RBCs and prolonging the conservation of high energy phosphate reservoirs and purine homeostasis. In parallel, we evidenced that, in contrast to aerobic storage, anaerobiosis impairs erythrocyte capacity to cope with oxidative stress by blocking metabolic diversion towards the pentose phosphate pathway, which negatively affects glutathione homeostasis. Therefore, although oxidative stress was less sustained than in aerobically stored counterparts, oxidative stress markers still accumulate over anaerobic storage progression.

Sickle hemoglobin disturbs normal coupling among erythrocyte O2 content, glycolysis, and antioxidant capacity

Energy metabolism in RBCs is characterized by O2-responsive variations in flux through the Embden Meyerhof pathway (EMP) or the hexose monophosphate pathway (HMP). Therefore, the generation of ATP, NADH, and 2,3-DPG (EMP) or NADPH (HMP) shift with RBC O2 content because of competition between deoxyhemoglobin and key EMP enzymes for binding to the cytoplasmic domain of the Band 3 membrane protein (cdB3). Enzyme inactivation by cdB3 sequestration in oxygenated RBCs favors HMP flux and NADPH generation (maximizing glutathione-based antioxidant systems). We tested the hypothesis that sickle hemoglobin disrupts cdB3-based regulatory protein complex assembly, creating vulnerability to oxidative stress. In RBCs from patients with sickle cell anemia, we demonstrate in the present study constrained HMP flux, NADPH, and glutathione recycling and reduced resilience to oxidative stress manifested by membrane protein oxidation and membrane fragility. Using a novel, inverted membrane-on-bead model, we illustrate abnormal (O2-dependent) association of sickle hemoglobin to RBC membrane that interferes with sequestration/inactivation of the EMP enzyme GAPDH. This finding was confirmed by immunofluorescent imaging during RBC O2 loading/unloading. Moreover, selective inhibition of inappropriately dispersed GAPDH rescues antioxidant capacity. Such disturbance of cdB3-based linkage between O2 gradients and RBC metabolism suggests a novel mechanism by which hypoxia may influence the sickle cell anemia phenotype.

Proteomic analysis of ERK1/2-mediated human sickle red blood cell membrane protein phosphorylation

BACKGROUND

In sickle cell disease (SCD), the mitogen-activated protein kinase (MAPK) ERK1/2 is constitutively active and can be inducible by agonist-stimulation only in sickle but not in normal human red blood cells (RBCs). ERK1/2 is involved in activation of ICAM-4-mediated sickle RBC adhesion to the endothelium. However, other effects of the ERK1/2 activation in sickle RBCs leading to the complex SCD pathophysiology, such as alteration of RBC hemorheology are unknown.

RESULTS

To further characterize global ERK1/2-induced changes in membrane protein phosphorylation within human RBCs, a label-free quantitative phosphoproteomic analysis was applied to sickle and normal RBC membrane ghosts pre-treated with U0126, a specific inhibitor of MEK1/2, the upstream kinase of ERK1/2, in the presence or absence of recombinant active ERK2. Across eight unique treatment groups, 375 phosphopeptides from 155 phosphoproteins were quantified with an average technical coefficient of variation in peak intensity of 19.8%. Sickle RBC treatment with U0126 decreased thirty-six phosphopeptides from twenty-one phosphoproteins involved in regulation of not only RBC shape, flexibility, cell morphology maintenance and adhesion, but also glucose and glutamate transport, cAMP production, degradation of misfolded proteins and receptor ubiquitination. Glycophorin A was the most affected protein in sickle RBCs by this ERK1/2 pathway, which contained 12 unique phosphorylated peptides, suggesting that in addition to its effect on sickle RBC adhesion, increased glycophorin A phosphorylation via the ERK1/2 pathway may also affect glycophorin A interactions with band 3, which could result in decreases in both anion transport by band 3 and band 3 trafficking. The abundance of twelve of the thirty-six phosphopeptides were subsequently increased in normal RBCs co-incubated with recombinant ERK2 and therefore represent specific MEK1/2 phospho-inhibitory targets mediated via ERK2.

CONCLUSIONS

These findings expand upon the current model for the involvement of ERK1/2 signaling in RBCs. These findings also identify additional protein targets of this pathway other than the RBC adhesion molecule ICAM-4 and enhance the understanding of the mechanism of small molecule inhibitors of MEK/1/2/ERK1/2, which could be effective in ameliorating RBC hemorheology and adhesion, the hallmarks of SCD.

Computational identification of phospho-tyrosine sub-networks related to acanthocyte generation in neuroacanthocytosis

Acanthocytes, abnormal thorny red blood cells (RBC), are one of the biological hallmarks of neuroacanthocytosis syndromes (NA), a group of rare hereditary neurodegenerative disorders. Since RBCs are easily accessible, the study of acanthocytes in NA may provide insights into potential mechanisms of neurodegeneration. Previous studies have shown that changes in RBC membrane protein phosphorylation state affect RBC membrane mechanical stability and morphology. Here, we coupled tyrosine-phosphoproteomic analysis to topological network analysis. We aimed to predict signaling sub-networks possibly involved in the generation of acanthocytes in patients affected by the two core NA disorders, namely McLeod syndrome (MLS, XK-related, Xk protein) and chorea-acanthocytosis (ChAc, VPS13A-related, chorein protein). The experimentally determined phosphoproteomic data-sets allowed us to relate the subsequent network analysis to the pathogenetic background. To reduce the network complexity, we combined several algorithms of topological network analysis including cluster determination by shortest path analysis, protein categorization based on centrality indexes, along with annotation-based node filtering. We first identified XK- and VPS13A-related protein-protein interaction networks by identifying all the interactomic shortest paths linking Xk and chorein to the corresponding set of proteins whose tyrosine phosphorylation was altered in patients. These networks include the most likely paths of functional influence of Xk and chorein on phosphorylated proteins. We further refined the analysis by extracting restricted sets of highly interacting signaling proteins representing a common molecular background bridging the generation of acanthocytes in MLS and ChAc. The final analysis pointed to a novel, very restricted, signaling module of 14 highly interconnected kinases, whose alteration is possibly involved in generation of acanthocytes in MLS and ChAc.

Erythrocyte membrane changes of chorea-acanthocytosis are the result of altered Lyn kinase activity

Acanthocytic RBCs are a peculiar diagnostic feature of chorea-acanthocytosis (ChAc), a rare autosomal recessive neurodegenerative disorder. Although recent years have witnessed some progress in the molecular characterization of ChAc, the mechanism(s) responsible for generation of acanthocytes in ChAc is largely unknown. As the membrane protein composition of ChAc RBCs is similar to that of normal RBCs, we evaluated the tyrosine (Tyr)-phosphorylation profile of RBCs using comparative proteomics. Increased Tyr phosphorylation state of several membrane proteins, including band 3, β-spectrin, and adducin, was noted in ChAc RBCs. In particular, band 3 was highly phosphorylated on the Tyr-904 residue, a functional target of Lyn, but not on Tyr-8, a functional target of Syk. In ChAc RBCs, band 3 Tyr phosphorylation by Lyn was independent of the canonical Syk-mediated pathway. The ChAc-associated alterations in RBC membrane protein organization appear to be the result of increased Tyr phosphorylation leading to altered linkage of band 3 to the junctional complexes involved in anchoring the membrane to the cytoskeleton as supported by coimmunoprecipitation of β-adducin with band 3 only in ChAc RBC-membrane treated with the Lyn-inhibitor PP2. We propose this altered association between membrane skeleton and membrane proteins as novel mechanism in the generation of acanthocytes in ChAc.

Oxidative stress modulates heme synthesis and induces peroxiredoxin-2 as a novel cytoprotective response in β-thalassemic erythropoiesis

BACKGROUND

β-thalassemic syndromes are inherited red cell disorders characterized by severe ineffective erythropoiesis and increased levels of reactive oxygen species whose contribution to β-thalassemic anemia is only partially understood.

DESIGN AND METHODS

We studied erythroid precursors from normal and β-thalassemic peripheral CD34(+) cells in two-phase liquid culture by proteomic, reverse transcriptase polymerase chain reaction and immunoblot analyses. We measured intracellular reactive oxygen species, heme levels and the activity of δ-aminolevulinate-synthase-2. We exposed normal cells and K562 cells with silenced peroxiredoxin-2 to H(2)O(2) and generated a recombinant peroxiredoxin-2 for kinetic measurements in the presence of H(2)O(2) or hemin.

RESULTS

In β-thalassemia the increased production of reactive oxygen species was associated with down-regulation of heme oxygenase-1 and biliverdin reductase and up-regulation of peroxiredoxin-2. In agreement with these observations in β-thalassemic cells we found decreased heme levels related to significantly reduced activity of the first enzyme of the heme pathway, δ-aminolevulinate synthase-2 without differences in its expression. We demonstrated that the activity of recombinant δ-aminolevulinate synthase-2 is inhibited by both reactive oxygen species and hemin as a protective mechanism in β-thalassemic cells. We then addressed the question of the protective role of peroxiredoxin-2 in erythropoiesis by exposing normal cells to oxidative stress and silencing peroxiredoxin-2 in human erythroleukemia K562 cells. We found that peroxiredoxin-2 expression is up-regulated in response to oxidative stress and required for K562 cells to survive oxidative stress. We then showed that peroxiredoxin-2 binds heme in erythroid precursors with high affinity, suggesting a possible multifunctional cytoprotective role of peroxiredoxin-2 in β-thalassemia.

CONCLUSIONS

In β-thalassemic erythroid cells the reduction of δ-aminolevulinate synthase-2 activity and the increased expression of peroxiredoxin-2 might represent two novel stress-response protective systems.