Redox Status of Erythrocytes as an Important Factor in Eryptosis and Erythronecroptosis.

Overall, reactive oxygen species (ROS) signalling significantly contributes to initiation and mo-dulation of multiple regulated cell death (RCD) pathways. Lately, more information has become available about RCD modalities of erythrocytes, including the role of ROS. ROS accumulation has therefore been increasingly recognized as a critical factor involved in eryptosis (apoptosis of erythrocytes) and erythro-necroptosis (necroptosis of erythrocytes). Eryptosis is a Ca2+-dependent apoptosis-like RCD of erythrocytes that occurs in response to oxidative stress, hyperosmolarity, ATP depletion, and a wide range of xenobiotics. Moreover, eryptosis seems to be involved in the pathogenesis of multiple human diseases and pathological processes. Several studies have reported that erythrocytes can also undergo necroptosis, a lytic RIPK1/RIPK3/MLKL-mediated RCD. As an example, erythronecroptosis can occur in response to CD59-specific pore-forming toxins. We have systematically summarized available studies regarding the involvement of ROS and oxidative stress in these two distinct RCDs of erythrocytes. We have focused specifically on cellular signalling pathways involved in ROS-mediated cell death decisions in erythrocytes. Furthermore, we have summarized dysregulation of related erythrocytic antioxidant defence systems. The general concept of the ROS role in eryptotic and necroptotic cell death pathways in erythrocytes seems to be established. However, further studies are required to uncover the complex role of ROS in the crosstalk and interplay between the survival and RCDs of erythrocytes.

Apoptosis and eryptosis: Striking differences on biomembrane level.

The cell plasma membrane plays an essential role in programmed cell death of nucleated cells (apoptosis) and erythrocytes (eryptosis), and its changes due to loss of transmembrane asymmetry are quite similar. However, nucleated cells possess the network of intracellular membranes, which are missing in erythrocytes. Providing comparative studies with series of molecular probes, we observe dramatic differences in membrane lipid order in the course of apoptosis and eryptosis. In contrast to nucleated cells, in which a significant drop of the lipid order in the plasma membrane is observed, the erythrocyte membrane retains the relatively high level of the lipid order. Observation in nucleated cells of significant differences between inner and plasma membranes and detection of apoptotic bodies with different organization suggest that the decrease in the lipid order of their plasma membrane could be at least partially explained by the phospholipid and/or cholesterol exchange between membranes. Such features are absent in erythrocytes.

Genetic deficiency of the tumor suppressor protein p53 influences erythrocyte survival.

The transcription factor p53 suppresses tumor growth by inducing nucleated cell apoptosis and cycle arrest. Because of its influence on primitive erythroid cell differentiation and survival, p53 is an important determinant of erythropoiesis. However, the impact of p53 on the fate of erythrocytes, cells lacking nucleus and mitochondria, during their post-maturation phase in the circulation remained elusive. Erythrocyte survival may be compromised by suicidal erythrocyte death or eryptosis, which is hallmarked by phosphatidylserine translocation and stimulated by increase of cytosolic Ca2+ concentration. Here, we comparatively examined erythrocyte homeostasis in p53-mutant mice (Trp53tm1Tyj/J) and in corresponding WT mice (C57BL/6J) by analyzing eryptosis and erythropoiesis. To this end, spontaneous cell membrane phosphatidylserine exposure and cytosolic Ca2+ concentration were higher in erythrocytes drawn from Trp53tm1Tyj/J mice than from WT mice. Eryptosis induced by glucose deprivation, a pathophysiological cell stressor, was slightly, but significantly more prominent in erythrocytes drawn from Trp53tm1Tyj/J mice as compared to WT mice. The loss of erythrocytes by eryptosis was fully compensated by enhanced erythropoiesis in Trp53tm1Tyj/J mice, as reflected by increased reticulocytosis and abundance of erythroid precursor cells in the bone marrow. Accordingly, erythrocyte number, packed cell volume and hemoglobin were similar in Trp53tm1Tyj/J and WT mice. Taken together, functional p53 deficiency enhances the turnover of circulating erythrocytes by parallel increase of eryptosis and stimulated compensatory erythropoiesis.

Erythropoietin Protects Erythrocytes Against Oxidative Stress-Induced Eryptosis In Vitro.

BACKGROUND: Excessive eryptosis has been found in maintained hemodialysis or peritoneal dialysis patients. Signaling of triggering eryptosis includes oxidative stress, increased cytosolic Ca2+-activity, and ceramide. Erythropoietin (EPO) possesses the property of an antioxidant. The aim of this study was to investigate the ability of hydrogen peroxide (H2O2) on erythrocytes in vitro, and to assess the possible effects of recombinant human erythropoietin (rhEPO) on eryptosis. METHODS: One percent erythrocyte suspension was cultured in vitro in three kinds of media: Control group (Group C), H2O2 group (Group H), and EPO group (Group E). Erythrocytes were sampled at 24 hours and 60 hours. Phosphatidylserine (PS) was estimated with annexin-V, reactive oxygen species (ROS) with 2',7'-dichlorodihydrofuorescein diacetate (DCFDA) and cytosolic Ca2+ activity ([Ca2+]i) with Fluo3. RESULTS: Eryptosis in Group C increased as the incubating time extended (2.05 ± 0.06 at 24 hours, and 10.00 ± 0.08 at 60 hours). Eryptosis increased in Group H compared with Group C (10.86 ± 0.06 at 24 hours, p < 0.01; 12.46 ± 0.14 at 60 hours, p < 0.01, respectively), while it decreased in Group E compared with Group H (8.80 ± 0.08 at 24 hours, p < 0.01; 11.29 ± 0.04 at 60 hours, p < 0.01, respectively). Meanwhile, ROS increased in Group H compared with Group C (9.37 ± 0.04 versus 5.49 ± 0.09 at 24 hours, p < 0.01;19.82 ± 0.05 versus 13.51 ± 0.10 at 60 hours, p < 0.01). [Ca2+]i increased in Group H compared with Group C (10.91 ± 0.12 versus 2.53 ± 0.06 at 24 hours, p < 0.01;14.55 ± 0.05 versus 4.63 ± 0.08 at 60 hours, p < 0.01). ROS decreased in Group E compared with Group H (6.80 ± 0.05 at 24 hours, p < 0.01; 16.82 ± 0.06 at 60 hours, p < 0.01). [Ca2+]i decreased in Group E compared with Group H (7.63 ± 0.14 at 24 hours, p < 0.01; 10.72 ± 0.07 at 60 hours, p < 0.01). CONCLUSIONS: Our research showed eryptosis was triggered by H2O2 and paralleled by increased ROS and [Ca2+]i which was partially reversed by EPO. It indicated that EPO could protect erythrocytes against oxidative stress-induced eryptosis.

[Current insights into anemia in old age : Summary of the symposium "Anemia in old age" on the occasion of the annual congress of the German Society for Geriatrics (DGG) 2016 in Stuttgart]. / Aktuelle Einblicke in die Anämie im Alter : Zusammenfassung zum Symposium "Anämie im Alter" anlässlich der DGG-Jahrestagung 2016 in Stuttgart.

Anemia in advanced age is often a multifactorial condition requiring an interdisciplinary approach. The contributions to the opening interdisciplinary symposium on anemia in older subjects focused on physiological and histopathological as well as on nephrological and neurogeriatric aspects and on the therapeutic implications of this underdiagnosed, yet highly frequent disease. The symposium was the kick-off event for the founding of the German Geriatric Society special interest group on anemia in advanced age.

Storage of Erythrocytes Induces Suicidal Erythrocyte Death.

BACKGROUND/AIMS: Similar to apoptosis of nucleated cells, red blood cells (RBC) can undergo suicidal cell death - called eryptosis. It is characterized by cell shrinkage and phosphatidylserine translocation. Eryptosis is triggered by an increase of intracellular calcium concentration due to activation of nonselective cation channels. The cation channels and consequently eryptosis are inhibited by erythropoietin. Eryptotic RBC are engulfed by macrophages and thus rapidly cleared from circulating blood. In this study, we explored whether storage of RBC influences the rate of eryptosis. METHODS: Flow cytometry was employed to quantify phosphatidylserine exposing erythrocytes from annexin V binding and cytosolic Ca2+ activity from Fluo-3 fluorescence. Clearance of stored murine RBC was tested by injection of carboxyfluorescein succinimidyl ester (CFSE)-labelled erythrocytes. RESULTS: Storage for 42 days significantly increased the percentage of phosphatidylserine exposing and haemolytic erythrocytes, an effect blunted by removal of extracellular calcium. Phosphatidylserine exposure could be inhibited by addition of erythropoietin. Upon transfusion, the clearance of murine CFSE-labelled RBC from circulating blood was significantly higher following storage for 10 days when compared to 2 days of storage. CONCLUSION: Storage of RBC triggers eryptosis by Ca2+ and erythropoietin sensitive mechanisms.

The emerging roles of eryptosis in liver diseases.

Erythrocytes undergo programmed cell death, similar to apoptosis, known as eryptosis. This process is a result of several factors including hyperosmolarity, oxidative stress, and exposure to xenobiotics, and is characterized by the breakdown of membrane phospholipid asymmetry, the clustering of band 3, and the generation of red blood cell-derived microparticles. Under pathological conditions, the liver is the primary site of erythrocyte clearance and plays an important role in iron recycling. Phosphatidylserine exposure and band-3 clustering on eryptotic erythrocytes represent mainly pro-phagocytic signals. Further, the percentage of eryptotic erythrocytes is enhanced in the circulating blood of patients with hepatic failure, hyperbilirubinemia, and nonalcoholic steatohepatitis. In this review, we concentrate on recent progress regarding the pathophysiological roles of eryptosis in liver diseases.

Erythrocyte deformability and eryptosis during inflammation, and impaired blood rheology.

OBJECTIVE: This review focusses on the erythrocytes (RBCs) and their structural changes during inflammation and impaired blood rheology. We discuss systemic inflammation and the effects of dysregulated inflammatory molecules. These pro-inflammatory molecules directly affect the haematological system, and particularly the RBCs, platelets and plasma proteins. We focus on the three main changes; increased RBC eryptosis (programmed cell death, similar to apoptosis) and pathological deformability, platelet hyperreactivity and anomalous blood clotting, due to pathological changes to fibrin(ogen) protein structure. This pro-inflammatory haematological system directly affects blood rheology. In turn, hemorheological parameters such as RBC deformability are important parameters in hypercoagulation, which is a hallmark of inflammation. For RBC deformation to happen during blood flow, the RBC membrane needs to be elastic to elongate sufficiently to squeeze through small capillaries. However, of greater importance is that the cell must return to its original biconcave shape after exiting the small diameter capillaries. CONCLUSION: Hemorheological parameters such as RBC deformability are of great importance clinically, to both identify the presence and extent of inflammation, and to study these parameters during intervention therapies. RBC rheology and deformability may therefore be a useful cell model for pharmaceutical testing.