Protein kinase C activation induces phosphatidylserine exposure on red blood cells

Signaling mechanisms in red blood cells: A view through the protein phosphorylation and deformability

Intracellular signaling mechanisms in red blood cells (RBCs) involve various protein kinases and phosphatases and enable rapid adaptive responses to hypoxia, metabolic requirements, oxidative stress, or shear stress by regulating the physiological properties of the cell. Protein phosphorylation is a ubiquitous mechanism for intracellular signal transduction, volume regulation, and cytoskeletal organization in RBCs. Spectrin-based cytoskeleton connects integral membrane proteins, band 3 and glycophorin C to junctional proteins, ankyrin and Protein 4.1. Phosphorylation leads to a conformational change in the protein structure, weakening the interactions between proteins in the cytoskeletal network that confers a more flexible nature for the RBC membrane. The structural organization of the membrane and the cytoskeleton determines RBC deformability that allows cells to change their ability to deform under shear stress to pass through narrow capillaries. The shear stress sensing mechanisms and oxygenation-deoxygenation transitions regulate cell volume and mechanical properties of the membrane through the activation of ion transporters and specific phosphorylation events mediated by signal transduction. In this review, we summarize the roles of Protein kinase C, cAMP-Protein kinase A, cGMP-nitric oxide, RhoGTPase, and MAP/ERK pathways in the modulation of RBC deformability in both healthy and disease states. We emphasize that targeting signaling elements may be a therapeutic strategy for the treatment of hemoglobinopathies or channelopathies. We expect the present review will provide additional insights into RBC responses to shear stress and hypoxia via signaling mechanisms and shed light on the current and novel treatment options for pathophysiological conditions.

Rosmarinic Acid Elicits Calcium-Dependent and Sucrose-Sensitive Eryptosis and Hemolysis through p38 MAPK, CK1α, and PKC

BACKGROUND

Rosmarinic acid (RA) possesses promising anticancer potential, but further development of chemotherapeutic agents is hindered by their toxicity to off-target tissue. In particular, chemotherapy-related anemia is a major obstacle in cancer therapy, which may be aggravated by hemolysis and eryptosis. This work presents a toxicity assessment of RA in human RBCs and explores associated molecular mechanisms.

METHODS

RBCs isolated from healthy donors were treated with anticancer concentrations of RA (10-800 μM) for 24 h at 37 °C, and hemolysis and related markers were photometrically measured. Flow cytometry was used to detect canonical markers of eryptosis, including phosphatidylserine (PS) exposure by annexin-V-FITC, intracellular Ca2+ by Fluo4/AM, cell size by FSC, and oxidative stress by H2DCFDA. Ions and pH were assessed by an ion-selective electrode, while B12 was detected by chemiluminescence.

RESULTS

RA elicited concentration-dependent hemolysis with AST and LDH release but rescued the cells from hypotonic lysis at sub-hemolytic concentrations. RA also significantly increased annexin-V-positive cells, which was ameliorated by extracellular Ca2+ removal and isosmotic sucrose. Furthermore, a significant increase in Fluo4-positive cells and B12 content and a decrease in FSC and extracellular pH with KCl efflux were noted upon RA treatment. Hemolysis was augmented by blocking KCl efflux and was blunted by ATP, SB203580, staurosporin, D4476, isosmotic urea, and PEG 8000.

CONCLUSIONS

RA stimulates Ca2+-dependent and sucrose-sensitive hemolysis and eryptosis characterized by PS exposure, Ca2+ accumulation, loss of ionic regulation, and cell shrinkage. These toxic effects were mediated through energy deprivation, p38 MAPK, protein kinase C, and casein kinase 1α.

Desipramine induces eryptosis in human erythrocytes, an effect blunted by nitric oxide donor sodium nitroprusside and N-acetyl-L-cysteine but enhanced by Calcium depletion

Background: Desipramine a representative of tricyclic antidepressants (TCAs) promotes recovery of depressed patients by inhibition of reuptake of neurotransmitters serotonin (SER) and norepinephrine (NE) in the presynaptic membrane by directly blocking their respective transporters SERT and NET.Aims: To study the effect of desipramine on programmed erythrocyte death (eryptosis) and explore the underlying mechanisms.Methods: Phosphatidylserine (PS) exposure on the cell surface as marker of cell death was estimated from annexin-V-binding, cell volume from forward scatter in flow cytometry. Hemolysis was determined photometrically, and intracellular glutathione [GSH]i from high performance liquid chromatography.Results: Desipramine dose-dependently significantly enhanced the percentage of annexin-V-binding cells and didn´t impact glutathione (GSH) synthesis. Desipramine-induced eryptosis was significantly reversed by pre-treatment of erythrocytes with either nitric oxide (NO) donor sodium nitroprusside (SNP) or N-acetyl-L-cysteine (NAC). The highest inhibitory effect was obtained by using both inhibitors together. Calcium (Ca2+) depletion aggravated desipramine-induced eryptosis. Changing the order of treatment, i.e. desipramine first followed by inhibitors, could not influence the inhibitory effect of SNP or NAC.Conclusion: Antidepressants-caused intoxication can be treated by SNP and NAC, respectively. B) Patients with chronic hypocalcemia should not be treated with tricyclic anti-depressants or their dose should be noticeably reduced.

Casein kinase 1α mediates eryptosis: a review

Eryptosis is a coordinated non-lytic cell death of erythrocytes characterized by cell shrinkage, cell membrane scrambling, Ca²⁺ influx, ceramide accumulation, oxidative stress, activation of calpain and caspases. Physiologically, it aims at removing damaged or aged erythrocytes from circulation. A plethora of diseases are associated with enhanced eryptosis, including metabolic diseases, cardiovascular pathology, renal and hepatic diseases, hematological disorders, systemic autoimmune pathology, and cancer. This makes eryptosis and eryptosis-regulating signaling pathways a target for therapeutic interventions. This review highlights the eryptotic signaling machinery containing several protein kinases and its small molecular inhibitors with a special emphasis on casein kinase 1α (CK1α), a serine/threonine protein kinase with a broad spectrum of activity. In this review article, we provide a critical analysis of the regulatory role of CK1α in eryptosis, highlight triggers of CK1α-mediated suicidal death of red blood cells, cover the knowledge gaps in understanding CK1α-driven eryptosis and discover the opportunity of CK1α-targeted pharmacological modulation of eryptosis. Moreover, we discuss the directions of future research focusing on uncovering crosstalks between CK1α and other eryptosis-regulating kinases and pathways.

Identification of radiation responsive RBC membrane associated proteins (RMAPs) in whole-body γ-irradiated New Zealand white rabbits

This study is aimed to identify radiation-responsive RBC Membrane Associated Proteins (RMAPs) in Rabbits in vivo. Male New Zealand White rabbits were exposed to a single acute total body γ-radiation dose of 2 Gy at a dose rate of 0.746 Gy/min. Following this, at early time points of 6 h till the 7 d, RMAPs were collected and analyzed by MALDI-TOF-MS. Bioinformatics analysis was conducted to explore the biological functions of these proteins. Based on fold change, radiation responsiveness, GO, pathway enrichment, and hub position in the PPI network, we identified seven RMAPs as potential biomarker candidates viz., PVALB, PRKCB, GPD1, CP2G1, CSNK2B, ATP1B1, TPI1. As per KEGG enrichment, most of the proteins were implicated in cellular radiation response, oxidative damage, DNA repair, apoptosis, immune response, and cell signaling. This study forms the foundation for RMAPs-based Proteomic strategies for high throughput radiation bio-dosimetry for triage in the case of a radiological/nuclear incident.

Eryptosis as a New Insight in Malaria Pathogenesis

Eryptosis is a programmed cell death-like process that occurs in red blood cells. Although the red blood cells are anucleated, there are similarities between eryptosis and apoptosis, such as increased calcium efflux, calpain activation, phosphatidylserine exposure, cell blebbing and cell shrinkage. Eryptosis occurs physiologically in red blood cells, as a consequence of the natural senescence process of these cells, but it can also be stimulated in pathological situations such as metabolic syndromes, uremic syndromes, polycythemia vera, anemias such as sickle cell anemia and thalassemia, and infectious processes including Plasmodium infection. Infection-induced eryptosis is believed to contribute to damage caused by Plasmodium, but it’s still a topic of debate in the literature. In this review, we provided an overview of eryptosis mechanisms and its possible pathogenic role in malaria.

Eryptosis: Programmed Death of Nucleus-Free, Iron-Filled Blood Cells

Human erythrocytes are organelle-free cells packaged with iron-containing hemoglobin, specializing in the transport of oxygen. With a total number of approximately 25 trillion cells per individual, the erythrocyte is the most abundant cell type not only in blood but in the whole organism. Despite their low complexity and their inability to transcriptionally upregulate antioxidant defense mechanisms, they display a relatively long life time, of 120 days. This ensures the maintenance of tissue homeostasis where the clearance of old or damaged erythrocytes is kept in balance with erythropoiesis. Whereas the regulatory mechanisms of erythropoiesis have been elucidated over decades of intensive research, the understanding of the mechanisms of erythrocyte clearance still requires some refinement. Here, we present the main pathways leading to eryptosis, the programmed death of erythrocytes, with special emphasis on Ca²⁺ influx, the generation of ceramide, oxidative stress, kinase activation, and iron metabolism. We also compare stress-induced erythrocyte death with erythrocyte ageing and clearance, and discuss the similarities between eryptosis and ferroptosis, the iron-dependent regulated death of nucleated blood cells. Finally, we focus on the pathologic consequences of deranged eryptosis, and discuss eryptosis in the context of different infectious diseases, e.g., viral or parasitic infections, and hematologic disorders.

Human erythrocytes, nuclear factor kappaB (NFκB) and hydrogen sulfide (H2S) - from non-genomic to genomic research

Enucleated mature human erythrocytes possess NFĸBs and their upstream kinases. There is a negative correlation between eryptosis (cell death of erythrocytes) and the amount of NFĸB subunits p50 and Rel A (p65). This finding is based on the fact that young erythrocytes have the highest levels of NFĸBs and the lowest eryptosis rate, while in old erythrocytes the opposite ratio prevails. Human erythrocytes (hRBCs) effectively control the homeostasis of the cell membrane permeable anti-inflammatory signal molecule hydrogen sulfide (H2S). They endogenously produce H2S via both non-enzymic (glutathione-dependent) and enzymic processes (mercaptopyruvate sulfur transferase-dependent). They uptake H2S from diverse tissues and very effectively degrade H2S via methemoglobin (Hb-Fe3+)-catalyzed oxidation. Interestingly, a reciprocal correlation exists between the intensity of inflammatory diseases and endogenous levels of H2S. H2S deficiency has been observed in patients with diabetes, psoriasis, obesity, and chronic kidney disease (CKD). Furthermore, endogenous H2S deficiency results in impaired renal erythropoietin (EPO) production and EPO-dependent erythropoiesis. In general we can say: dynamic reciprocal interaction between tumor suppressor and oncoproteins, orchestrated and sequential activation of pro-inflammatory NFĸB heterodimers (RelA-p50) and the anti-inflammatory NFĸB-p50 homodimers for optimal inflammation response, appropriate generation, subsequent degradation of H2S etc., are prerequisites for a functioning cell and organism. Diseases arise when the fragile balance between different signaling pathways that keep each other in check is permanently disturbed. This work deals with the intact anti-inflammatory hRBCs and their role as guarantors to maintain the redox status in the physiological range, a basis for general health and well-being.

Relationship between oxidant-antioxidant status and hypercoagulobility indices in children with iron deficiency anaemia

Oxidative stress is a potential mechanism involved in the pathogenesis of iron deficiency anaemia (IDA). Although a tendency for hypercoagulability has been reported in IDA, its underlying mechanism is yet to be elucidated. This study investigated the probable relationship between oxidative stress and hypercoagulability in children with IDA. This study included 57 children diagnosed with IDA (IDA group) between October 2016 and October 2017 in addition to 48 healthy children (control group). The maximum clot firmness (MCF) index, and clot formation time (CFT) index, which are indicators of hypercoagulability in rotational thromboelastometry assays [intrinsic TEM (INTEM) and extrinsic TEM (EXTEM)] derived from our previous study, were recorded. Total oxidant status (TOS), total antioxidant capacity (TAC) and oxidative stress index (OSI) were analysed from serum samples of the individuals. In IDA group, OSI and TOS levels were higher and TAC level was lower compared to the control group (P < 0.001, for all). The EXTEM and INTEM MCF in the IDA group was higher than in the control group, while the INTEM CFT was lower than in the control group (P < 0.001, P < 0.001, P < 0.05, published data).TOS and OSI had a negative correlation with INTEM CFT (r:-0.361, P < 0.001 and r:-0.333, P = 0.001) and a positive correlation with INTEM MCF (r:+0.420, P < 0.001 and r:+0.367, P < 0.001) and EXTEM MCF (r:+0.476, P < 0.001 and r:+0.403, P < 0.001). However, TAC demonstrated no correlation with CFT and MCF index. The oxidant-antioxidant balance is disrupted in favour of oxidative stress in children with IDA. In addition, TOS and OSI, which are parameters of oxidative stress, are correlated with CFT and MCF indices. Oxidative stress appears to be an important factor for the development of tendency to hypercoagulability in IDA.

The specific PKC-α inhibitor chelerythrine blunts costunolide-induced eryptosis

Costunolide, a natural sesquiterpene lactone, has multiple pharmacological activities such as neuroprotection or induction of apoptosis and eryptosis. However, the effects of costunolide on pro-survival factors and enzymes in human erythrocytes, e.g. glutathione and glucose-6-phosphate dehydrogenase (G6PDH) respectively, have not been studied yet. Our aim was to determine the mechanisms underlying costunolide-induced eryptosis and to reverse this process. Phosphatidylserine exposure was estimated from annexin-V-binding, cell volume from forward scatter in flow cytometry, and intracellular glutathione [GSH]_i from high performance liquid chromatography. The oxidized status of intracellular glutathione and enzyme activities were measured by spectrophotometry. Treatment of erythrocytes with costunolide dose-dependently enhanced the percentage of annexin-V-binding cells, decreased the cell volume, depleted [GSH]_i and completely inhibited G6PDH activity. The effects of costunolide on annexin-V-binding and cell volume were significantly reversed by pre-treatment of erythrocytes with the specific PKC-α inhibitor chelerythrine. The latter, however, had no effect on costunolide-induced GSH depletion. Costunolide induces eryptosis, depletes [GSH]_i and inactivates G6PDH activity. Furthermore, our study reveals an inhibitory effect of chelerythrine on costunolide-induced eryptosis, indicating a relationship between costunolide and PKC-α. In addition, chelerythrine acts independently of the GSH depletion. Understanding the mechanisms of G6PDH inhibition accompanied by GSH depletion should be useful for development of anti-malarial therapeutic strategies or for synthetic lethality-based approaches to escalate oxidative stress in cancer cells for their sensitization to chemotherapy and radiotherapy.

Pathophysiological Relevance of Renal Medullary Conditions on the Behaviour of Red Cells From Patients With Sickle Cell Anaemia

Red cells from patients with sickle cell anaemia (SCA) contain the abnormal haemoglobin HbS. Under hypoxic conditions, HbS polymerises and causes red cell sickling, a rise in intracellular Ca²⁺ and exposure of phosphatidylserine (PS). These changes make sickle cells sticky and liable to lodge in the microvasculature, and so reduce their lifespan. The aim of the present work was to investigate how the peculiar conditions found in the renal medulla - hypoxia, acidosis, lactate, hypertonicity and high levels of urea - affect red cell behaviour. Results show that the first four conditions all increased sickling and PS exposure. The presence of urea at levels found in a healthy medulla during antidiuresis, however, markedly reduced sickling and PS exposure and would therefore protect against red cell adherence. Loss of the ability to concentrate urine, which occurs in sickle cell nephropathy would obviate this protective effect and may therefore contribute to pathogenesis.

Anhydroecgonine methyl ester, a cocaine pyrolysis product, contributes to cocaine-induced rat primary hippocampal neuronal death in a synergistic and time-dependent manner

Crack cocaine users are simultaneously exposed to volatilized cocaine and to its main pyrolysis product, anhydroecgonine methyl ester (AEME). Although the neurotoxic effects of cocaine have been extensively studied, little is known about AEME or its combination. We investigated cell death processes using rat primary hippocampal cells exposed to cocaine (2 mM), AEME (1 mM) and their combination (C + A), after 1, 3, 6 and 12 h. Cocaine increased LC3 I after 6 h and LC3 II after 12 h, but reduced the percentage of cells with acid vesicles, suggesting failure in the autophagic flux, which activated the extrinsic apoptotic pathway after 12 h. AEME neurotoxicity did not involve the autophagic process; rather, it activated caspase-9 after 6 h and caspase-8 after 12 h leading to a high percentage of cells in early apoptosis. C + A progressively reduced the percentage of undamaged cells, starting after 3 h; it activated both apoptotic pathways after 6 h, and was more neurotoxic than cocaine and AEME alone. Also, C + A increased the phosphorylation of p62 after 12 h, but there was little difference in LC3 I or II, and a small percentage of cells with acid vesicles at all time points investigated. In summary, the present study provides new evidence for the neurotoxic mechanism and timing response of each substance alone and in combination, indicating that AEME is more than just a biological marker for crack cocaine consumption, as it may intensify and hasten cocaine neurotoxicity.

Phosphatidylserine inside out: a possible underlying mechanism in the inflammation and coagulation abnormalities of COVID-19

The rapid ability of SARS-CoV-2 to spread among humans, along with the clinical complications of coronavirus disease 2019-COVID-19, have represented a significant challenge to the health management systems worldwide. The acute inflammation and coagulation abnormalities appear as the main causes for thousands of deaths worldwide. The intense inflammatory response could be involved with the formation of thrombi. For instance, the presence of uncleaved large multimers of von Willebrand (vWF), due to low ADAMTS13 activity in plasma could be explained by the inhibitory action of pro-inflammatory molecules such as IL-1β and C reactive protein. In addition, the damage to endothelial cells after viral infection and/or activation of endothelium by pro-inflammatory cytokines, such as IL-1β, IL-6, IFN-γ, IL-8, and TNF-α induces platelets and monocyte aggregation in the vascular wall and expression of tissue factor (TF). The TF expression may culminate in the formation of thrombi, and activation of cascade by the extrinsic pathway by association with factor VII. In this scenario, the phosphatidylserine-PtdSer exposure on the outer leaflet of the cell membrane as consequence of viral infection emerges as another possible underlying mechanism to acute immune inflammatory response and activation of coagulation cascade. The PtdSer exposure may be an important mechanism related to ADAM17-mediated ACE2, TNF-α, EGFR and IL-6R shedding, and the activation of TF on the surface of infected endothelial cells. In this review, we address the underlying mechanisms involved in the pathophysiology of inflammation and coagulation abnormalities. Moreover, we introduce key biochemical and pathophysiological concepts that support the possible participation of PtdSer exposure on the outer side of the SARS-CoV-2 infected cells membrane, in the pathophysiology of COVID-19. Video Abstract.

Yoda1 and phosphatidylserine exposure in red cells from patients with sickle cell anaemia

Phosphatidylserine (PS) exposure is increased in red cells from sickle cell anaemia (SCA) patients. Externalised PS is prothrombotic and attractive to phagocytes and activated endothelial cells and thus contributes to the anaemic and ischaemic complications of SCA. The mechanism of PS exposure remains uncertain but it can follow increased intracellular Ca²⁺ concentration ([Ca²⁺]_i). Normally, [Ca²⁺]_i is maintained at very low levels but in sickle cells, Ca²⁺ permeability is increased, especially following deoxygenation and sickling, mediated by a pathway sometimes called P_sickle. The molecular identity of P_sickle is also unclear but recent work has implicated the mechanosensitive channel, PIEZO1. We used Yoda1, an PIEZO1 agonist, to investigate its role in sickle cells. Yoda1 caused an increase in [Ca²⁺]_i and PS exposure, which was inhibited by its antagonist Dooku1 and the PIEZO1 inhibitor GsMTx4, consistent with functional PIEZO1. However, PS exposure did not necessitate an increase in [Ca²⁺]_i. Two PKC inhibitors were also tested, chelerytherine chloride and calphostin C. Both reduced PS exposure whilst chelerytherine chloride also reduced Yoda1-induced increases in [Ca²⁺]_i. Findings are therefore consistent with the presence of PIEZO1 in sickle cells, able to mediate Ca²⁺ entry but that PKC was also involved in both Ca²⁺ entry and PS exposure.

Status update on iRhom and ADAM17: It's still complicated

Several membrane-bound proteins with a single transmembrane domain are subjected to limited proteolysis at the cell surface. This cleavage leads to the release of their biologically active ectodomains, which can trigger different signalling pathways. In many cases, this ectodomain shedding is mediated by members of the family of a disintegrins and metalloproteinases (ADAMs). ADAM17 in particular is responsible for the cleavage of several proinflammatory mediators, growth factors, receptors and adhesion molecules. Due to its direct involvement in the release of these signalling molecules, ADAM17 can be positively and negatively involved in various physiological processes as well as in inflammatory, fibrotic and malignant pathologies. This central role of ADAM17 in a variety of processes requires strict multi-level regulation, including phosphorylation, various conformational changes and endogenous inhibitors. Recent research has shown that an early, crucial control mechanism is interaction with certain adapter proteins identified as iRhom1 and iRhom2, which are pseudoproteases of the rhomboid superfamily. Thus, iRhoms have also a decisive influence on physiological and pathophysiological signalling processes regulated by ADAM17. Their characteristic gene expression profiles, the specific consequences of gene knockouts and finally the occurrence of disease-associated mutations suggest that iRhom1 and iRhom2 undergo different gene regulation in order to fulfil their function in different cell types and are therefore only partially redundant. Therefore, there is not only interest in ADAM17, but also in iRhoms as therapeutic targets. However, to exploit the therapeutic potential, the regulation of ADAM17 activity and in particular its interaction with iRhoms must be well understood.

Amyloid β peptide affects erythrocyte morphology: Role of intracellular signaling pathways

BACKGROUND

Circulating red blood cells (RBCs) undergo aging, a fundamental physiological phenomenon that regulates their turnover.

OBJECTIVE

Understanding the role of Aβ in the cross talk between cell signalling pathways and modulation of the cell structural and biomechanical properties occurring in RBCs during aging.

METHODS

The morphological pattern has been monitored using Atomic Force Microscopy (AFM) imaging and measuring the RBCs' plasma membrane roughness employed as a morphological parameter capable to provide information on the structure and integrity of the membrane-skeleton.

RESULTS

We show that treatment with Aβ accelerates the occurrence of morphological and biochemical aging markers in human RBC and influences the cell metabolism. Biochemical data demonstrate that contemporaneously to morphological alterations, Aβ triggers: (i) metabolic alterations and (ii) a complex signaling pathway involving caspase 3, protein kinase C and nitric oxide derived metabolites.

CONCLUSIONS

our study provides a comprehensive picture in which Aβ treatment of RBC induces changes in specific cell signalling events and/or metabolic pathways, in turns affecting the membrane-cytoskeleton interaction and the membrane integrity.

Multiscale Simulations of Biological Membranes: The Challenge To Understand Biological Phenomena in a Living Substance

Biological membranes are tricky to investigate. They are complex in terms of molecular composition and structure, functional over a wide range of time scales, and characterized by nonequilibrium conditions. Because of all of these features, simulations are a great technique to study biomembrane behavior. A significant part of the functional processes in biological membranes takes place at the molecular level; thus computer simulations are the method of choice to explore how their properties emerge from specific molecular features and how the interplay among the numerous molecules gives rise to function over spatial and time scales larger than the molecular ones. In this review, we focus on this broad theme. We discuss the current state-of-the-art of biomembrane simulations that, until now, have largely focused on a rather narrow picture of the complexity of the membranes. Given this, we also discuss the challenges that we should unravel in the foreseeable future. Numerous features such as the actin-cytoskeleton network, the glycocalyx network, and nonequilibrium transport under ATP-driven conditions have so far received very little attention; however, the potential of simulations to solve them would be exceptionally high. A major milestone for this research would be that one day we could say that computer simulations genuinely research biological membranes, not just lipid bilayers.

Manipulating Eryptosis of Human Red Blood Cells: A Novel Antimalarial Strategy?

Malaria is a major global health burden, affecting over 200 million people worldwide. Resistance against all currently available antimalarial drugs is a growing threat, and represents a major and long-standing obstacle to malaria eradication. Like many intracellular pathogens, Plasmodium parasites manipulate host cell signaling pathways, in particular programmed cell death pathways. Interference with apoptotic pathways by malaria parasites is documented in the mosquito and human liver stages of infection, but little is known about this phenomenon in the erythrocytic stages. Although mature erythrocytes have lost all organelles, they display a form of programmed cell death termed eryptosis. Numerous features of eryptosis resemble those of nucleated cell apoptosis, including surface exposure of phosphatidylserine, cell shrinkage and membrane ruffling. Upon invasion, Plasmodium parasites induce significant stress to the host erythrocyte, while delaying the onset of eryptosis. Many eryptotic inducers appear to have a beneficial effect on the course of malaria infection in murine models, but major gaps remain in our understanding of the underlying molecular mechanisms. All currently available antimalarial drugs have parasite-encoded targets, which facilitates the emergence of resistance through selection of mutations that prevent drug-target binding. Identifying host cell factors that play a key role in parasite survival will provide new perspectives for host-directed anti-malarial chemotherapy. This review focuses on the interrelationship between Plasmodium falciparum and the eryptosis of its host erythrocyte. We summarize the current knowledge in this area, highlight the different schools of thoughts and existing gaps in knowledge, and discuss future perspectives for host-directed therapies in the context of antimalarial drug discovery.

Oxidative stress, eryptosis and anemia: a pivotal mechanistic nexus in systemic diseases

The average lifespan of circulating erythrocytes usually exceeds hundred days. Prior to that, however, erythrocytes may be exposed to oxidative stress in the circulation which could cause injury and trigger their suicidal death or eryptosis. Oxidative stress activates Ca²⁺ -permeable nonselective cation channels in the cell membrane, thus, stimulating Ca²⁺ entry and subsequent cell membrane scrambling resulting in phosphatidylserine exposure and activation of Ca²⁺ -sensitive K⁺ channels leading to K⁺ exit, hyperpolarization, Cl^- exit, and ultimately cell shrinkage due to loss of KCl and osmotically driven water. While the mechanistic link between oxidative stress and anemia remains ill-defined, several diseases such as diabetes, hepatic failure, malignancy, chronic kidney disease and inflammation have been identified to display both increased oxidative stress as well as eryptosis. Recent compelling evidence suggests that oxidative stress is an important perpetrator in accelerating erythrocyte loss in different systemic conditions and an underlying mechanism for anemia associated with these pathological states. In the present review, we discuss the role of oxidative stress in reducing erythrocyte survival and provide novel insights into the possible use of antioxidants as putative antieryptotic and antianemic agents in a variety of systemic diseases.

Morphological changes induced in erythrocyte by amyloid beta peptide and glucose depletion: A combined atomic force microscopy and biochemical study

Circulating red blood cells (RBCs) undergo aging, a fundamental physiological phenomenon that regulates their turnover. We show that treatment with beta amyloid peptide 1-42 (Aβ) accelerates the occurrence of morphological and biochemical aging markers in human RBCs and influences the cell metabolism leading to intracellular ATP depletion. The morphological pattern has been monitored using Atomic Force Microscopy (AFM) imaging and measuring the RBCs' plasma membrane roughness employed as a morphological parameter capable to provide information on the structure and integrity of the membrane-skeleton. Results evidence that Aβ boosts the development of crenatures and proto-spicules simultaneously to acceleration in the weakening of the cell-cytoskeleton contacts and to the induction of peculiar nanoscale features on the cell membrane. Incubation in the presence of glucose can remove all but the latter Aβ-induced effects. Biochemical data demonstrate that contemporaneously to morphological and structural alterations, Aβ and glucose depletion trigger a complex signaling pathway involving caspase 3, protein kinase C (PKC) and nitric oxide derived metabolites. As a whole, the collected data revealed that, the damaging path induced by Aβ in RBC provide a sequence of morphological and functional intermediates following one another along RBC life span, including: (i) an acceleration in the development of shape alteration typically observed along the RBC's aging; (ii) the development of characteristic membrane features on the plasma membrane and (iii) triggering a complex signaling pathway involving caspase 3, PKC and nitric oxide derived metabolites.

Erythrocyte's aging in microgravity highlights how environmental stimuli shape metabolism and morphology

The determination of the function of cells in zero-gravity conditions is a subject of interest in many different research fields. Due to their metabolic unicity, the characterization of the behaviour of erythrocytes maintained in prolonged microgravity conditions is of particular importance. Here, we used a 3D-clinostat to assess the microgravity-induced modifications of the structure and function of these cells, by investigating how they translate these peculiar mechanical stimuli into modifications, with potential clinical interest, of the biochemical pathways and the aging processes. We compared the erythrocyte's structural parameters and selected metabolic indicators that are characteristic of the aging in microgravity and standard static incubation conditions. The results suggest that, at first, human erythrocytes react to external stimuli by adapting their metabolic patterns and the rate of consumption of the cell resources. On longer timeframes, the cells translate even small differences in the environment mechanical solicitations into structural and morphologic features, leading to distinctive morphological patterns of aging.

Avenues to molecular imaging of dying cells: Focus on cancer

Successful treatment of cancer patients requires balancing of the dose, timing, and type of therapeutic regimen. Detection of increased cell death may serve as a predictor of the eventual therapeutic success. Imaging of cell death may thus lead to early identification of treatment responders and nonresponders, and to “patient‐tailored therapy.” Cell death in organs and tissues of the human body can be visualized, using positron emission tomography or single‐photon emission computed tomography, although unsolved problems remain concerning target selection, tracer pharmacokinetics, target‐to‐nontarget ratio, and spatial and temporal resolution of the scans. Phosphatidylserine exposure by dying cells has been the most extensively studied imaging target. However, visualization of this process with radiolabeled Annexin A5 has not become routine in the clinical setting. Classification of death modes is no longer based only on cell morphology but also on biochemistry, and apoptosis is no longer found to be the preponderant mechanism of cell death after antitumor therapy, as was earlier believed. These conceptual changes have affected radiochemical efforts. Novel probes targeting changes in membrane permeability, cytoplasmic pH, mitochondrial membrane potential, or caspase activation have recently been explored. In this review, we discuss molecular changes in tumors which can be targeted to visualize cell death and we propose promising biomarkers for future exploration.

Effects of Plant Sterols or β-Cryptoxanthin at Physiological Serum Concentrations on Suicidal Erythrocyte Death

The eryptotic and hemolytic effects of a phytosterol (PS) mixture (β-sitosterol, campesterol, stigmasterol) or β-cryptoxanthin (β-Cx) at physiological serum concentration and their effect against oxidative stress induced by tert-butylhydroperoxide (tBOOH) (75 and 300 μM) were evaluated. β-Cryptoxanthin produced an increase in eryptotic cells, cell volume, hemolysis, and glutathione depletion (GSH) without ROS overproduction and intracellular Ca²⁺ influx. Co-incubation of both bioactive compounds protected against β-Cx-induced eryptosis. Under tBOOH stress, PS prevented eryptosis, reducing Ca²⁺ influx, ROS overproduction and GSH depletion at 75 μM, and hemolysis at both tBOOH concentrations. β-Cryptoxanthin showed no cytoprotective effect. Co-incubation with both bioactive compounds completely prevented hemolysis and partially prevented eryptosis as well as GSH depletion induced by β-Cx plus tBOOH. Phytosterols at physiological serum concentrations help to prevent pro-eryptotic and hemolytic effects and are promising candidate compounds for ameliorating eryptosis-associated diseases.

The Action of Red Cell Calcium Ions on Human Erythrophagocytosis in Vitro

In the present work we have studied in vitro the effect of increasing red cell Ca²⁺ ions on human erythrophagocytosis by peripheral monocyte-derived autologous macrophages. In addition, the relative contribution to phagocytosis of phosphatidylserine exposure, autologous IgG binding, complement deposition and Gárdos channel activity was also investigated. Monocytes were obtained after ficoll-hypaque fractionation and induced to transform by adherence to glass coverslips, for 24 h at 37°C in a RPMI medium, containing 10% fetal calf serum. Red blood cells (RBC) were loaded with Ca²⁺ using 10 μM A23187 and 1 mM Ca-EGTA buffers, in the absence of Mg²⁺. Ca²⁺-loaded cells were transferred to above coverslips and incubated for 2 h at 37°C under various experimental conditions, after which phagocytosis was assessed by light microscopy. Confirming earlier findings, phagocytosis depended on internal Ca²⁺. Accordingly; it was linearly raised from about 2–15% by increasing the free Ca²⁺ content of the loading solution from 0.5 to 20 μM, respectively. Such a linear increase was virtually doubled by the presence of 40% autologous serum. At 7 μM Ca²⁺, the phagocytosis degree attained with serum was practically equal to that obtained with either 2 mg/ml affinity-purified IgG or 40% IgG-depleted serum. However, phagocytosis was reduced to levels found with Ca²⁺ alone when IgG-depleted serum was inactivated by heat, implying an involvement of complement. On the other hand, phagocytosis in the absence of serum was markedly reduced by preincubating macrophages with phosphatidylserine-containing liposomes. In contrast, a similar incubation in the presence of serum affected it partially whereas employing liposomes made only of phosphatidylcholine essentially had no effect. Significantly, the Gárdos channel inhibitors clotrimazole (2 μM) and TRAM-34 (100 nM) fully blocked serum-dependent phagocytosis. These findings show that a raised internal Ca²⁺ promotes erythrophagocytosis by independently triggering phosphatidylserine externalization, complement deposition and IgG binding. Serum appeared to stimulate phagocytosis in a way dependent on Gárdos activity. It seems likely that Ca²⁺ promoted IgG-binding to erythrocytes via Gárdos channel activation. This can be an important signal for clearance of senescent human erythrocytes under physiological conditions.

Protein kinase C mediates caspase 3 activation: A role for erythrocyte morphology changes

We have previously showed that morphological alterations in Red Blood Cells (RBCs) are correlated to an impaired eNOS enzymatic activity and a concomitant reduced NO derived metabolites formation. Here we extend our previous observations, reporting that RBC morphology is regulated by a series of specific cell signaling events linked to Protein Kinase C (PKC)-mediated activation of caspase 3. Pretreatment of RBCs with the PKC inhibitor chelerythrine, prior to the addition of phorbol-12-myristate-13-acetate (PMA), an activator of PKC, blocks the appearance of the morphology alterations and the sustained decrease in nitrates and nitrites levels induced by PMA. Inhibition of PKC also completely inhibits PMA mediated caspase-3 activation. On the other hand, caspase 3 inhibition, lessens the PMA induced-effects on the appearance of RBC morphology alterations, although it enhances PMA-mediated effects on nitric oxide (NO) derived metabolites levels. These data demonstrate that PKC-mediated activation of caspase 3 is an integral and essential part of signaling pathway in RBCs, that may be a regulatory factor of RBC mechanical properties, through regulation of NO metabolism.

Phosphatidylserine exposure is required for ADAM17 sheddase function

ADAM17, a prominent member of the 'Disintegrin and Metalloproteinase' (ADAM) family, controls vital cellular functions through cleavage of transmembrane substrates. Here we present evidence that surface exposure of phosphatidylserine (PS) is pivotal for ADAM17 to exert sheddase activity. PS exposure is tightly coupled to substrate shedding provoked by diverse ADAM17 activators. PS dependency is demonstrated in the following: (a) in Raji cells undergoing apoptosis; (b) in mutant PSA-3 cells with manipulatable PS content; and (c) in Scott syndrome lymphocytes genetically defunct in their capacity to externalize PS in response to intracellular Ca(2+) elevation. Soluble phosphorylserine but not phosphorylcholine inhibits substrate cleavage. The isolated membrane proximal domain (MPD) of ADAM17 binds to PS but not to phosphatidylcholine liposomes. A cationic PS-binding motif is identified in this domain, replacement of which abrogates liposome-binding and renders the protease incapable of cleaving its substrates in cells. We speculate that surface-exposed PS directs the protease to its targets where it then executes its shedding function.

[BRAIN FOCAL ISCHEMIA-REPERFUSION CAUSES A DECREASED RESISTANCE OF ERYTHROCYTES FROM VENOUS BLOOD TO ACID HEMOLYSIS, WHICH IS PREVENTED BY ECDYSTERONE]

We investigated the resistance of erythrocytes from rat brain venous blood to acid hemolysis in the dynamics of brain ischemic period (15, 30, 45 and 60 min), as well as in the early (5 min) and distant (24h) period of brain reperfusion. Brain ischemia-reperfusion was made in rats that received ecdysterone (standartized extract of Serratula coronata) within 18 days (per os, 1 mg/kg). Analysis of the kinetic curves of acid hemolysis showed a pronounced (60 times, from 1.45 to 85.85% at 60 min of brain ischemia and at 5 min of brain reperfusion, respectively) increase of unstable erythrocytes that hemolyzed easily (< 2.5 min). In the preconditioned rats, this increase was only 8-fold. During the period of brain ischemia, with a maximum at 15th minute, in the venous blood from brain the diene conjugates (DK) pools increased from 2.40 to 9.48 ng/mg protein and LTC4 pools increased from 1.49 to 5.98 pmol/mg protein. Even more pools of DC and LTC4 were increased at 5th min of brain reperfusion. In animals received ecdysterone, during ischemia and early reperfusion period, both pools of DC and LTC4 in venous blood were lower than that in the controls. The latter implies a possible antiradical mechanism of the protective effect of ecdysterone.

VDR gene polymorphisms impact on anemia at 2 weeks of anti-HCV therapy: a possible mechanism for early RBV-induced anemia

OBJECTIVES

Vitamin D receptors (VDR) bind calcitriol and modulate several physiological systems through genomic and nongenomic pathways. Calcitriol stimulates store-operated channels Ca²⁺ influx by translocation of the caveolar VDR to the plasma membrane. Intracellular Ca²⁺ levels in erythrocytes control biophysical properties and an increase in its concentration can deregulate membrane composition, cell volume, glycolytic enzymes regulation, redox state, and cell clearance.We evaluated the role of single nucleotide polymorphisms in ITPA, CYP27B1, CYP24A1, and VDR genes in the prediction of ribavirin-induced anemia in HCV-1/2/3/4 patients at 2 and 4 weeks of treatment.

PATIENTS AND METHODS

Two hundred and twenty-five patients treated with ribavirin and pegylated interferon-α were genotyped by real-time PCR.

RESULTS

BMI at baseline more than 30 kg/m² [P=0.013, odds ratio (OR): 10.95, 95% confidence interval (CI): 1.66-74.21], alanine aminotransferase at baseline more than 37 IU/l (P=0.020, OR: 0.26, 95% CI: 0.09-0.81), and the VDR BsmI AA profile (P=0.003, OR: 5.09, 95% CI: 1.72-15.05) were anemia-predictive factors at 2 weeks of therapy. At week 4, the ITPA rs6051702 AC/CC profile (P=0.001, OR: 0.19, 95% CI: 0.07-0.51) was the only factor that could predict this side effect.

CONCLUSION

The BsmI AA genotype is a predictive factor of 2-week anemia and it could be related to a VDR-enhanced activity, and thus an increased calcium influx, resulting in the deregulation of the Ca²⁺-dependent signaling, which can lead to erythrocytes hemolysis. This rapid mechanism could be responsible for the development of early anemia.These results indicate for the first time the strong, significant, and independent role of VDR in the early development of ribavirin-induced anemia and confirm the ITPA function in the prediction of anemia at week 4.

Ankyrin exposure induced by activated protein kinase C plays a potential role in erythrophagocytosis

BACKGROUND

In physiological and pathological conditions activated protein kinace C (PKC) has been observed in the erythrocytes. Externalization of ankyrin followed by Arg-Gly-Asp (RGD)/integrin recognition also triggers erythrophagocytosis. In the present study, to test whether activated PKC is associated with ankyrin exposure in erythrophagocytosis.

METHODS

Phorbol 12-myristate-13-acetate (PMA)-induced PKC activation and ankyrin phosphorylation were tested, and under different treatment conditions the subpopulation of erythrocytes with ankyrin exposure and the levels of intracellular calcium were analyzed by flow cytometry.

RESULTS

Results showed that treatment of erythrocytes with PMA in a calcium-containing buffer led to ankyrin exposure. In the absence of extracellular calcium, no ankyrin exposure was observed. PKC inhibition with calphostin C, a blocker of the PMA binding site, completely prevented the calcium entry, protein phosphorylation and ankyrin exposure. PKC inhibition with chelerythrine chloride, an inhibitor of the active site, diminished the level of ankyrin-exposing cells and ankyrin phosphorylation; however it even led to a higher percentage of cells with increased levels of calcium than with PMA treatment alone. Although PKC was activated and ankyrin phosphorylation occurred, no ankyrin exposure was observed in the absence of extracellular calcium.

CONCLUSION

Analyses of results suggested that PMA induces calcium influx into the erythrocytes, leading to the activation of calcium-dependent enzymes and the phosphorylation of membrane proteins, ultimately inducing ankyrin exposure and erythrophagocytosis. This study may provide insights into the molecular mechanisms of removing aged or diseased erythrocytes.

Activation of protein kinase C by phorbol ester increases red blood cell scramblase activity and external phosphatidylserine

Externalization of phosphatidylserine (PS) is thought to contribute to sickle cell disease (SCD) pathophysiology. The red blood cell (RBC) aminophospholipid translocase (APLT) mediates the transport of PS from the outer to the inner RBC membrane leaflet to maintain an asymmetric distribution of PL, while phospholipid scramblase (PLSCR) equilibrates PL across the RBC membrane, promoting PS externalization. We previously identified an association between PS externalization level and PLSCR activity in sickle RBC under basal conditions. Other studies showed that activation of protein kinase C (PKC) by PMA (phorbol-12-myristate-13-acetate) causes increased external PS on RBC. Therefore, we hypothesized that PMA-activated PKC stimulates PLSCR activity in RBC and thereby contributes to increased PS externalization. In the current studies, we show that PMA treatment causes immediate and variable PLSCR activation and subsequent PS externalization in control and sickle RBC. While TfR+ sickle reticulocytes display some endogenous PLSCR activity, we observed a robust activation of PLSCR in sickle reticulocytes treated with PMA. The PKC inhibitor, chelerythrine (Chel), significantly inhibited PMA-dependent PLSCR activation and PS externalization. Chel also inhibited endogenous PLSCR activity in sickle reticulocytes. These data provide evidence that PKC mediates PS externalization in RBC through activation of PLSCR.

Alterations of red cell membrane properties in neuroacanthocytosis

Neuroacanthocytosis (NA) refers to a group of heterogenous, rare genetic disorders, namely chorea acanthocytosis (ChAc), McLeod syndrome (MLS), Huntington’s disease-like 2 (HDL2) and pantothenate kinase associated neurodegeneration (PKAN), that mainly affect the basal ganglia and are associated with similar neurological symptoms. PKAN is also assigned to a group of rare neurodegenerative diseases, known as NBIA (neurodegeneration with brain iron accumulation), associated with iron accumulation in the basal ganglia and progressive movement disorder. Acanthocytosis, the occurrence of misshaped erythrocytes with thorny protrusions, is frequently observed in ChAc and MLS patients but less prevalent in PKAN (about 10%) and HDL2 patients. The pathological factors that lead to the formation of the acanthocytic red blood cell shape are currently unknown. The aim of this study was to determine whether NA/NBIA acanthocytes differ in their functionality from normal erythrocytes. Several flow-cytometry-based assays were applied to test the physiological responses of the plasma membrane, namely drug-induced endocytosis, phosphatidylserine exposure and calcium uptake upon treatment with lysophosphatidic acid. ChAc red cell samples clearly showed a reduced response in drug-induced endovesiculation, lysophosphatidic acid-induced phosphatidylserine exposure, and calcium uptake. Impaired responses were also observed in acanthocyte-positive NBIA (PKAN) red cells but not in patient cells without shape abnormalities. These data suggest an “acanthocytic state” of the red cell where alterations in functional and interdependent membrane properties arise together with an acanthocytic cell shape. Further elucidation of the aberrant molecular mechanisms that cause this acanthocytic state may possibly help to evaluate the pathological pathways leading to neurodegeneration.

Inhibition of the prothrombinase complex on red blood cells by heparin and covalent antithrombin-heparin complex

The role of red blood cells (RBCs) in coagulation is not well understood. Overt exposure of phosphatidylserine on surfaces of RBCs provide docking sites for formation of the prothrombinase complex, which further aids in amplification of coagulation leading to subsequent thrombosis. No studies to date have evaluated heparin inhibition of the RBC-prothrombinase system. Therefore, this study examines the ability of heparin and a covalent antithrombin-heparin complex (ATH) to inhibit the RBC-prothrombinase system. Discontinuous inhibition assays were performed to obtain k₂ values for inhibition of free or prothrombinase-bound Xa by antithrombin and unfractionated heparin (AT + UFH) versus ATH. In addition, components of the complex (prothrombin, RBCs or Va) were excluded prior to reaction with inhibitors to investigate potential mechanisms involved. Inhibition of thrombin generation, fibrinogen conversion and plasma clotting by the RBC-prothrombinase system was also examined. Protection of Xa was observed for AT + UFH and not for ATH reactions. Inhibition rates for ATH were significantly faster when compared with AT + UFH results. The greatest impact on Xa inhibition was observed from factor Va omission for both inhibitors. ATH inhibited thrombin generation, fibrinogen conversion and plasma clotting better compared with AT + UFH. This study determined potential control of coagulation contributed by RBCs. Moreover, greater control of coagulation is achieved by covalently linking heparin to AT.

Prothrombin activation in blood coagulation: the erythrocyte contribution to thrombin generation

Prothrombin activation can proceed through the intermediates meizothrombin or prethrombin-2. To assess the contributions that these 2 intermediates make to prothrombin activation in tissue factor (Tf)-activated blood, immunoassays were developed that measure the meizothrombin antithrombin (mTAT) and α-thrombin antithrombin (αTAT) complexes. We determined that Tf-activated blood produced both αTAT and mTAT. The presence of mTAT suggested that nonplatelet surfaces were contributing to approximately 35% of prothrombin activation. Corn trypsin inhibitor-treated blood was fractionated to yield red blood cells (RBCs), platelet-rich plasma (PRP), platelet-poor plasma (PPP), and buffy coat. Compared with blood, PRP reconstituted with PPP to a physiologic platelet concentration showed a 2-fold prolongation in the initiation phase and a marked decrease in the rate and extent of αTAT formation. Only the addition of RBCs to PRP was capable of normalizing αTAT generation. FACS on glycophorin A-positive cells showed that approximately 0.6% of the RBC population expresses phosphatidylserine and binds prothrombinase (FITC Xa·factor Va). These data indicate that RBCs participate in thrombin generation in Tf-activated blood, producing a membrane that supports prothrombin activation through the meizothrombin pathway.

Reduced PKC α Activity Induces Senescent Phenotype in Erythrocytes

The molecular mechanism mediating expression of senescent cell antigen-aggregated or cleaved band 3 and externalized phosphatidylserine (PS) on the surface of aged erythrocytes and their premature expression in certain anemias is not completely elucidated. The erythrocytes with these surface modifications undergo macrophage-mediated phagocytosis. In this study, the role of protein kinase C (PKC) isoforms in the expression of these surface modifications was investigated. Inhibition of PKC α by 30 μM rottlerin (R30) and 2.3 nM Gö 6976 caused expression of both the senescent cell marker-externalized PS measured by FACS analysis and aggregated band 3 detected by western blotting. In contrast to this observation, but in keeping with literature, PKC activation by phorbol-12-myristate-13-acetate (PMA) also led to the expression of senescence markers. We explain this antithesis by demonstrating that PMA-treated cells show reduction in the activity of PKC α, thereby simulating inhibition. The reduction in PKC α activity may be attributed to the known downregulation of PMA-activated PKC α, caused by its membrane translocation and proteolysis. We demonstrate membrane translocation of PKC α in PMA-treated cells to substantiate this inference. Thus loss of PKC α activity either by inhibition or downregulation can cause surface modifications which can trigger erythrophagocytosis.

Regulation of phosphatidylserine exposure in red blood cells

The exposure of phosphatidylserine (PS) on the outer membrane leaflet of red blood cells (RBCs) serves as a signal for eryptosis, a mechanism for the RBC clearance from blood circulation. The process of PS exposure was investigated as function of the intracellular Ca(2+) content and the activation of PKCα in human and sheep RBCs. Cells were treated with lysophosphatidic acid (LPA), 4-bromo-A23187, or phorbol-12 myristate-13 acetate (PMA) and analysed by flow cytometry, single cell fluorescence video imaging, or confocal microscopy. For human RBCs, no clear correlation existed between the number of cells with an elevated Ca(2+) content and PS exposure. Results are explained by three different mechanisms responsible for the PS exposure in human RBCs: (i) Ca(2+)-stimulated scramblase activation (and flippase inhibition) by LPA, 4-bromo-A23187, and PMA; (ii) PKC activation by LPA and PMA; and (iii) enhanced lipid flop caused by LPA. In sheep RBCs, only the latter mechanism occurs suggesting absence of scramblase activity.

Procoagulant and prothrombotic activation of human erythrocytes by phosphatidic acid

Increased phosphatidic acid (PA) and phospholipase D (PLD) activity are frequently observed in various disease states including cancers, diabetes, sepsis, and thrombosis. Previously, PA has been regarded as just a precursor for lysophosphatidic acid (LPA) and diacylglycerol (DAG). However, increasing evidence has suggested independent biological activities of PA itself. In the present study, we demonstrated that PA can enhance thrombogenic activities in human erythrocytes through phosphatidylserine (PS) exposure in a Ca2+-dependent manner. In freshly isolated human erythrocytes, treatment of PA or PLD induced PS exposure. PA-induced PS exposure was not attenuated by inhibitors of phospholipase A2or phosphatidate phosphatase, which converts PA to LPA or DAG. An intracellular Ca2+increase and the resultant activation of Ca2+-dependent PKC-α appeared to underlie the PA-induced PS exposure through the activation of scramblase. A marginal decrease in flippase activity was also noted, contributing further to the maintenance of exposed PS on the outer membrane. PA-treated erythrocytes showed strong thrombogenic activities, as demonstrated by increased thrombin generation, endothelial cell adhesion, and erythrocyte aggregation. Importantly, these procoagulant activations by PA were confirmed in a rat in vivo venous thrombosis model, where PA significantly enhanced thrombus formation. In conclusion, these results suggest that PA can induce thrombogenic activities in erythrocytes through PS exposure, which can increase thrombus formation and ultimately contribute to the development of cardiovascular diseases.

Altered phosphorylation of cytoskeleton proteins in sickle red blood cells: the role of protein kinase C, Rac GTPases, and reactive oxygen species

The small Rho GTPases Rac1 and Rac2 regulate actin structures and mediate reactive oxygen species (ROS) production via NADPH oxidase in a variety of cells. We have demonstrated that deficiency of Rac1 and Rac2 GTPases in mice disrupts the normal hexagonal organization of the RBC cytoskeleton and reduces erythrocyte deformability. This is associated with increased phosphorylation of adducin at Ser-724, (corresponding to Ser-726 in human erythrocytes), a domain target of protein kinase C (PKC). PKC phosphorylates adducin and leads to decreased F-actin capping and dissociation of spectrin from actin, implicating a significant role of such phosphorylation in cytoskeletal remodeling. We evaluated adducin phosphorylation in erythrocytes from patients with sickle cell disease and found it consistently increased at Ser-726. In addition, ROS concentration is elevated in sickle erythrocytes by 150-250% compared to erythrocytes from normal control individuals. Here, we review previous studies demonstrating that altered phosphorylation of erythrocyte cytoskeletal proteins and increased ROS production result in disruption of cytoskeleton stability in healthy and sickle cell erythrocytes. We discuss in particular the known and potential roles of protein kinase C and the Rac GTPases in these two processes.

Current knowledge about the functional roles of phosphorylative changes of membrane proteins in normal and diseased red cells

With the advent of proteomic techniques the number of known post-translational modifications (PTMs) affecting red cell membrane proteins is rapidly growing but the understanding of their role under physiological and pathological conditions is incompletely established. The wide range of hereditary diseases affecting different red cell membrane functions and the membrane modifications induced by malaria parasite intracellular growth represent a unique opportunity to study PTMs in response to variable cellular stresses. In the present review, some of the major areas of interest in red cell membrane research have been considered as modifications of erythrocyte deformability and maintenance of the surface area, membrane transport alterations, and removal of diseased and senescent red cells. In all mentioned research areas the functional roles of PTMs are prevalently restricted to the phosphorylative changes of the more abundant membrane proteins. The insufficient information about the PTMs occurring in a large majority of the red membrane proteins and the general lack of mass spectrometry data evidence the need of new comprehensive, proteomic approaches to improve the understanding of the red cell membrane physiology.

Tin triggers suicidal death of erythrocytes

Suicidal erythrocyte death or eryptosis is characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine (PS) exposure at the erythrocyte surface. Triggers of eryptosis include increase in cytosolic Ca(2+) activity, formation of ceramide and energy depletion. Excessive eryptosis contributes to several anemic conditions. Intoxication with inorganic tin(II) may lead to anemia. The present study therefore explored whether tin influences eryptosis. To this end, erythrocytic phosphatidylserine exposure was estimated from annexin V-binding, cell volume from forward scatter, cytosolic Ca(2+) activity from Fluo3 fluorescence, ceramide formation from binding of fluorescent antibodies and cytosolic ATP utilizing a luciferin-luciferase assay kit. Under control conditions, eryptosis was observed in less than 5% of the erythrocytes. Exposure to tin (1-100 microm) significantly increased the percentage of PS-exposing erythrocytes and decreased cell volume. The effect was paralleled by an increase in the cytosolic Ca(2+) concentration, ceramide formation and a decrease of intracellular ATP concentration. In conclusion, tin triggers eryptosis, an effect at least partially due to Ca(2+ )entry, ceramide formation and ATP depletion. The effect could contribute to tin-induced anemia.

Mitochondrial defects lie at the basis of neutropenia in Barth syndrome

PURPOSE OF REVIEW

Barth syndrome (BTHS) is a mitochondrial disorder characterized by neutropenia, among other defects. As yet, the correlation between the mitochondrial defect in BTHS and the neutropenia observed in these patients is unclear. In this review, we hope to shed some light upon the correlation between the metabolic properties of neutrophil mitochondria and their susceptibility to the defects observed in BTHS.

RECENT FINDINGS

BTHS neutrophils avidly expose phosphatidyl serine, a phospholipid that is normally restrained to the inner leaflet of the plasma membrane. Although phosphatidyl serine exposure is usually considered to be a marker for apoptosis, BTHS neutrophils have no other apoptotic features and function normally. It has recently become clear that the respiratory chain in all BTHS tissues lacks super-complex organization, leading to inefficient electron transport. In neutrophils, the super-complex organization of the respiratory chain is disturbed by default, even in healthy individuals. Further disturbance in BTHS patients may lie at the basis of their neutropenia.

SUMMARY

It seems unlikely that neutropenia in BTHS is caused by apoptosis of the myeloid precursor cells or end-stage neutrophils. Instead, mitochondria-derived reactive oxygen species may act as signaling intermediates that trigger phosphatidyl serine exposure. This, in turn, appears to lead to increased clearance of neutrophils by tissue macrophages.

Erythrocyte programmed cell death

Eryptosis, the suicidal death of erythrocytes, is characterised by cell shrinkage, membrane blebbing and cell membrane phospholipid scrambling with phosphatidylserine exposure at the cell surface. Phosphatidylserine-exposing erythrocytes are recognised by macrophages, which engulf and degrade the affected cells. Reported triggers of eryptosis include osmotic shock, oxidative stress, energy depletion, ceramide, prostaglandin E(2), platelet activating factor, hemolysin, listeriolysin, paclitaxel, chlorpromazine, cyclosporine, methylglyoxal, amyloid peptides, anandamide, Bay-5884, curcumin, valinomycin, aluminium, mercury, lead and copper. Diseases associated with accelerated eryptosis include sepsis, malaria, sickle-cell anemia, beta-thalassemia, glucose-6-phosphate dehydrogenase (G6PD)-deficiency, phosphate depletion, iron deficiency, hemolytic uremic syndrome and Wilsons disease. Eryptosis may be inhibited by erythropoietin, adenosine, catecholamines, nitric oxide (NO) and activation of G-kinase. Most triggers of eryptosis except oxidative stress are effective without activation of caspases. Their signalling involves formation of prostaglandin E(2) with subsequent activation of cation channels and Ca2+ entry and/or release of platelet activating factor (PAF) with subsequent activation of sphingomyelinase and formation of ceramide. Ca2+ and ceramide stimulate scrambling of the cell membrane. Ca2+ further activates Ca2+-sensitive K+ channels leading to cellular KCl loss and cell shrinkage and stimulates the protease calpain resulting in degradation of the cytoskeleton. Eryptosis allows defective erythrocytes to escape hemolysis. On the other hand, excessive eryptosis favours the development of anemia. Thus, a delicate balance between proeryptotic and antieryptotic mechanisms is required to maintain an adequate number of circulating erythrocytes and yet avoid noneryptotic death of injured erythrocytes.

Microparticles in stored red blood cells: an approach using flow cytometry and proteomic tools

BACKGROUND AND OBJECTIVES

Microparticles (MPs) are small phospholipid vesicles of less than 1 microm, shed in blood flow by various cell types. These MPs are involved in several biological processes and diseases. MPs have also been detected in blood products; however, their role in transfused patients is unknown. The purpose of this study was to characterize those MPs in blood bank conditions.

MATERIALS AND METHODS

Qualitative and quantitative experiments using flow cytometry or proteomic techniques were performed on MPs derived from erythrocytes concentrates. In order to count MPs, they were either isolated by various centrifugation procedures or counted directly in erythrocyte concentrates.

RESULTS

A 20-fold increase after 50 days of storage at 4 degrees C was observed (from 3370 +/- 1180 MPs/microl at day 5 to 64 850 +/- 37 800 MPs/microl at day 50). Proteomic analysis revealed changes of protein expression comparing MPs to erythrocyte membranes. Finally, the expression of Rh blood group antigens was shown on MPs generated during erythrocyte storage.

CONCLUSIONS

Our work provides evidence that storage of red blood cell is associated with the generation of MPs characterized by particular proteomic profiles. These results contribute to fundamental knowledge of transfused blood products.

Advances in clinical research in sickle cell disease

Sickle cell disease continues to cause significant morbidity and mortality despite increases in life expectancy. This review looks at recent translational research in sickle cell disease, covering the red cell membrane, the vascular endothelium, local and systemic inflammation and the potentially pivotal role of nitric oxide as a key regulator of sickle cell complications. Clinical research reviewed includes pulmonary hypertension, which is emerging as a particularly deadly scourge of adults with any haemolytic anaemia, and newer insights into older, more established complications and treatments, such as red cell transfusions, the need for and use of iron chelation and avascular necrosis. Finally, recent studies about those factors that affect the day-to-day lives of persons with sickle cell disease, pain and neuropsychiatric functioning, are discussed.

Regulated externalization of phosphatidylserine at the cell surface: implications for apoptosis

The regulated loss of plasma membrane phosphatidylserine (PS) asymmetry is critical to many biological processes. In particular, the appearance of PS at the cell surface, a hallmark of apoptosis, prepares the dying cell for engulfment and elimination by phagocytes. While it is well established that PS externalization is regulated by activation of a calcium-dependent phospholipid scramblase activity in concert with inactivation of the aminophospholipid translocase, there is no evidence indicating that these processes are triggered and regulated by apoptotic regulatory mechanisms. Using a novel model system, we show that PS externalization is inducible, reversible, and independent of cytochrome c release, caspase activation, and DNA fragmentation. Additional evidence is presented indicating that the outward movement of plasma membrane PS requires sustained elevation in cytosolic Ca2+ in concert with inactivation of the aminophospholipid translocase and is inhibited by calcium channel blockers.