Erythroid enucleation: a gateway into a "bloody" world

Progresses in overcoming the limitations of in vitro erythropoiesis using human induced pluripotent stem cells

Researchers have attempted to generate transfusable oxygen carriers to mitigate RBC supply shortages. In vitro generation of RBCs using stem cells such as hematopoietic stem and progenitor cells (HSPCs), embryonic stem cells (ESCs), and induced pluripotent stem cells (iPSCs) has shown promise. Specifically, the limited supplies of HSPCs and ethical issues with ESCs make iPSCs the most promising candidate for in vitro RBC generation. However, researchers have encountered some major challenges when using iPSCs to produce transfusable RBC products, such as enucleation and RBC maturation. In addition, it has proven difficult to manufacture these products on a large scale. In this review, we provide a brief overview of erythropoiesis and examine endeavors to recapitulate erythropoiesis in vitro using various cell sources. Furthermore, we explore the current obstacles and potential solutions aimed at enabling the large-scale production of transfusable RBCs in vitro.

Pivotal functions and impact of long con-coding RNAs on cellular processes and genome integrity

Recent advances in uncovering the mysteries of the human genome suggest that long non-coding RNAs (lncRNAs) are important regulatory components. Although lncRNAs are known to affect gene transcription, their mechanisms and biological implications are still unclear. Experimental research has shown that lncRNA synthesis, subcellular localization, and interactions with macromolecules like DNA, other RNAs, or proteins can all have an impact on gene expression in various biological processes. In this review, we highlight and discuss the major mechanisms through which lncRNAs function as master regulators of the human genome. Specifically, the objective of our review is to examine how lncRNAs regulate different processes like cell division, cell cycle, and immune responses, and unravel their roles in maintaining genomic architecture and integrity.

The miR-144/Hmgn2 regulatory axis orchestrates chromatin organization during erythropoiesis

Differentiation of stem and progenitor cells is a highly regulated process that involves the coordinated action of multiple layers of regulation. Here we show how the post-transcriptional regulatory layer instructs the level of chromatin regulation via miR-144 and its targets to orchestrate chromatin condensation during erythropoiesis. The loss of miR-144 leads to impaired chromatin condensation during erythrocyte maturation. Among the several targets of miR-144 that influence chromatin organization, the miR-144-dependent regulation of Hmgn2 is conserved from fish to humans. Our genetic probing of the miR-144/Hmgn2 regulatory axis establish that intact miR-144 target sites in the Hmgn2 3'UTR are necessary for the proper maturation of erythrocytes in both zebrafish and human iPSC-derived erythroid cells while loss of Hmgn2 rescues in part the miR-144 null phenotype. Altogether, our results uncover miR-144 and its target Hmgn2 as the backbone of the genetic regulatory circuit that controls the terminal differentiation of erythrocytes in vertebrates.

The miR-144/Hmgn2 regulatory axis orchestrates chromatin organization during erythropoiesis

Differentiation of stem and progenitor cells is a highly regulated process that involves the coordinated action of multiple layers of regulation. Here we show how the post-transcriptional regulatory layer instructs the level of chromatin regulation via miR-144 and its targets to orchestrate chromatin condensation during erythropoiesis. The loss of miR-144 leads to impaired chromatin condensation during erythrocyte maturation. Among the several targets of miR-144 that influence chromatin organization, the miR-144-dependent regulation of Hmgn2 is conserved from fish to humans. Our genetic probing of the miR-144/Hmgn2 regulatory axis established that intact miR-144 target sites in the Hmgn2 3'UTR are necessary for the proper maturation of erythrocytes in both zebrafish and human iPSC-derived erythroid cells while loss of Hmgn2 rescues in part the miR-144 null phenotype. Altogether, our results uncover miR-144 and its target Hmgn2 as the backbone of the genetic regulatory circuit that controls the terminal differentiation of erythrocytes in vertebrates.

Decoding human in vitro terminal erythropoiesis originating from umbilical cord blood mononuclear cells and pluripotent stem cells

Ex vivo red blood cell (RBC) production generates unsatisfactory erythroid cells. A deep exploration into terminally differentiated cells is required to understand the impairments for RBC generation and the underlying mechanisms. Here, we mapped an atlas of terminally differentiated cells from umbilical cord blood mononuclear cells (UCBMN) and pluripotent stem cells (PSC) and observed their dynamic regulation of erythropoiesis at single-cell resolution. Interestingly, we detected a few progenitor cells and non-erythroid cells from both origins. In PSC-derived erythropoiesis (PSCE), the expression of haemoglobin switch regulators (BCL11A and ZBTB7A) were significantly absent, which could be the restraint for its adult globin expression. We also found that PSCE were less active in stress erythropoiesis than in UCBMN-derived erythropoiesis (UCBE), and explored an agonist of stress erythropoiesis gene, TRIB3, could enhance the expression of adult globin in PSCE. Compared with UCBE, there was a lower expression of epigenetic-related proteins (e.g., CASPASE 3 and UBE2O) and transcription factors (e.g., FOXO3 and TAL1) in PSCE, which might restrict PSCE's enucleation. Moreover, we characterized a subpopulation with high proliferation capacity marked by CD99high in colony-forming unit-erythroid cells. Inhibition of CD99 reduced the proliferation of PSC-derived cells and facilitated erythroid maturation. Furthermore, CD99-CD99 mediated the interaction between macrophages and erythroid cells, illustrating a mechanism by which macrophages participate in erythropoiesis. This study provided a reference for improving ex vivo RBC generation.

Comprehensive Characterization and Global Transcriptome Analysis of Human Fetal Liver Terminal Erythropoiesis

The fetal liver (FL) is the key erythropoietic organ during fetal development, but knowledge on human FL erythropoiesis is very limited. In this study, we sorted primary erythroblasts from FL cells and performed RNA sequencing (RNA-seq) analyses. We found that temporal gene expression patterns reflected changes in function during primary human FL terminal erythropoiesis. Notably, the expression of genes enriched in proteolysis and autophagy was up-regulated in orthochromatic erythroblasts (OrthoEs), suggesting the involvement of these pathways in enucleation. We also performed RNA-seq of in vitro cultured erythroblasts derived from FL CD34+ cells. Comparison of transcriptomes between the primary and cultured erythroblasts revealed significant differences, indicating impacts of the culture system on gene expression. Notably, the expression of lipid metabolism-related genes was increased in cultured erythroblasts. We further immortalized erythroid cell lines from FL and cord blood (CB) CD34+ cells (FL-iEry and CB-iEry, respectively). FL-iEry and CB-iEry were immortalized at the proerythroblast stage and can be induced to differentiate into OrthoEs, but their enucleation ability was very low. Comparison of the transcriptomes between OrthoEs with and without enucleation capability revealed the down-regulation of pathways involved in chromatin organization and mitophagy in OrthoEs without enucleation capacity, indicating that defects in chromatin organization and mitophagy contribute to the inability of OrthoEs to enucleate. Additionally, the expression of HBE1, HBZ, and HBG2 was up-regulated in FL-iEry compared with CB-iEry, and such up-regulation was accompanied by down-regulated expression of BCL11A and up-regulated expression of LIN28B and IGF2BP1. Our study provides new insights into human FL erythropoiesis and rich resources for future studies.

Peroxiredoxins in erythrocytes: far beyond the antioxidant role

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

Post-transcriptional regulation of erythropoiesis

Erythropoiesis is a complex, precise, and lifelong process that is essential for maintaining normal body functions. Its strict regulation is necessary to prevent a variety of blood diseases. Normal erythropoiesis is precisely regulated by an intricate network that involves transcription levels, signal transduction, and various epigenetic modifications. In recent years, research on post-transcriptional levels in erythropoiesis has expanded significantly. The dynamic regulation of splicing transitions is responsible for changes in protein isoform expression that add new functions beneficial for erythropoiesis. RNA-binding proteins adapt the translation of transcripts to the protein requirements of the cell, yielding mRNA with dynamic translation efficiency. Noncoding RNAs, such as microRNAs and lncRNAs, are indispensable for changing the translational efficiency and/or stability of targeted mRNAs to maintain the normal expression of genes related to erythropoiesis. N6-methyladenosine-dependent regulation of mRNA translation plays an important role in maintaining the expression programs of erythroid-related genes and promoting erythroid lineage determination. This review aims to describe our current understanding of the role of post-transcriptional regulation in erythropoiesis and erythroid-associated diseases, and to shed light on the physiological and pathological implications of the post-transcriptional regulation machinery in erythropoiesis. These may help to further enrich our understanding of the regulatory network of erythropoiesis and provide new strategies for the diagnosis and treatment of erythroid-related diseases.

Immortalized erythroid cells as a novel frontier for in vitro blood production: current approaches and potential clinical application

BACKGROUND

Blood transfusions represent common medical procedures, which provide essential supportive therapy. However, these procedures are notoriously expensive for healthcare services and not without risk. The potential threat of transfusion-related complications, such as the development of pathogenic infections and the occurring of alloimmunization events, alongside the donor's dependence, strongly limits the availability of transfusion units and represents significant concerns in transfusion medicine. Moreover, a further increase in the demand for donated blood and blood transfusion, combined with a reduction in blood donors, is expected as a consequence of the decrease in birth rates and increase in life expectancy in industrialized countries.

MAIN BODY

An emerging and alternative strategy preferred over blood transfusion is the in vitro production of blood cells from immortalized erythroid cells. The high survival capacity alongside the stable and longest proliferation time of immortalized erythroid cells could allow the generation of a large number of cells over time, which are able to differentiate into blood cells. However, a large-scale, cost-effective production of blood cells is not yet a routine clinical procedure, as being dependent on the optimization of culture conditions of immortalized erythroid cells.

CONCLUSION

In our review, we provide an overview of the most recent erythroid cell immortalization approaches, while also describing and discussing related advancements of establishing immortalized erythroid cell lines.

Dynamics of Human Hematopoietic Stem and Progenitor Cell Differentiation to the Erythroid Lineage

Erythropoiesis, the development of erythrocytes from hematopoietic stem cells, occurs through four phases: erythroid progenitor development, early erythropoiesis, terminal erythroid differentiation (TED), and maturation. According to the classical model that is based on immunophenotypic profiles of cell populations, each of these phases comprises multiple differentiation states that arise in a hierarchical manner. After segregation of lymphoid potential, erythroid priming begins during progenitor development and progresses through progenitor cell types that have multilineage potential. Complete separation of the erythroid lineage is achieved during early erythropoiesis with the formation of unipotent erythroid progenitors: burst forming unit-erythroid and colony forming unit-erythroid. These erythroid committed progenitors undergo TED and maturation, which involves expulsion of the nucleus and remodeling to form functional biconcave, hemoglobin-filled erythrocytes. In the last decade or so, many studies employing advanced techniques such as single cell RNA-sequencing (scRNA-seq) as well as the conventional methods, including colony forming cell assays and immunophenotyping, have revealed heterogeneity within the stem, progenitor, and erythroblast stages, and uncovered alternate paths for segregation of erythroid lineage potential. In this review, we provide an in-depth account of immunophenotypic profiles of all cell types within erythropoiesis, highlight studies that demonstrate heterogeneous erythroid stages, and describe deviations to the classical model of erythropoiesis. Overall, although scRNA-seq approaches have provided new insights, flow cytometry remains relevant and is the primary method for validation of novel immunophenotypes.

Nucleated red blood cells explain most of the association between DNA methylation and gestational age

Determining if specific cell type(s) are responsible for an association between DNA methylation (DNAm) and a given phenotype is important for understanding the biological mechanisms underlying the association. Our EWAS of gestational age (GA) in 953 newborns from the Norwegian MoBa study identified 13,660 CpGs significantly associated with GA (p_Bonferroni<0.05) after adjustment for cell type composition. When the CellDMC algorithm was applied to explore cell-type specific effects, 2,330 CpGs were significantly associated with GA, mostly in nucleated red blood cells [nRBCs; n = 2,030 (87%)]. Similar patterns were found in another dataset based on a different array and when applying an alternative algorithm to CellDMC called Tensor Composition Analysis (TCA). Our findings point to nRBCs as the main cell type driving the DNAm-GA association, implicating an epigenetic signature of erythropoiesis as a likely mechanism. They also explain the poor correlation observed between epigenetic age clocks for newborns and those for adults.

The accumulation of miR-125b-5p is indispensable for efficient erythroblast enucleation

Erythroblast enucleation is a precisely regulated but not clearly understood process. Polycythemia shows pathological erythroblast enucleation, and we discovered a low miR-125b-5p level in terminal erythroblasts of patients with polycythemia vera (PV) compared to those of healthy controls. Exogenous upregulation of miR-125b-5p levels restored the enucleation rate to normal levels. Direct downregulation of miR-125b-5p in mouse erythroblasts simulated the enucleation issue found in patients with PV, and miR-125b-5p accumulation was found in enucleating erythroblasts, collectively suggesting the importance of miR-125b-5p accumulation for erythroblast enucleation. To elucidate the role of miR-125b-5p in enucleation, gain- and loss-of-function studies were performed. Overexpression of miR-125b-5p improved the enucleation of erythroleukemia cells and primary erythroblasts. Infused erythroblasts with higher levels of miR-125b-5p also exhibited accelerated enucleation. In contrast, miR-125b-5p inhibitors significantly suppressed erythrocyte enucleation. Intracellular imaging revealed that in addition to cytoskeletal assembly and nuclear condensation, miR-125b-5p overexpression resulted in mitochondrial reduction and depolarization. Real-time PCR, western blot analysis, luciferase reporter assays, small molecule inhibitor supplementation and gene rescue assays revealed that Bcl-2, as a direct target of miR-125b-5p, was one of the key mediators of miR-125b-5p during enucleation. Following suppression of Bcl-2, the activation of caspase-3 and subsequent activation of ROCK-1 resulted in cytoskeletal rearrangement and enucleation. In conclusion, this study is the first to reveal the pivotal role of miR-125b-5p in erythroblast enucleation.

The inner nuclear membrane protein NEMP1 supports nuclear envelope openings and enucleation of erythroblasts

Nuclear envelope membrane proteins (NEMPs) are a conserved family of nuclear envelope (NE) proteins that reside within the inner nuclear membrane (INM). Even though Nemp1 knockout (KO) mice are overtly normal, they display a pronounced splenomegaly. This phenotype and recent reports describing a requirement for NE openings during erythroblasts terminal maturation led us to examine a potential role for Nemp1 in erythropoiesis. Here, we report that Nemp1 KO mice show peripheral blood defects, anemia in neonates, ineffective erythropoiesis, splenomegaly, and stress erythropoiesis. The erythroid lineage of Nemp1 KO mice is overrepresented until the pronounced apoptosis of polychromatophilic erythroblasts. We show that NEMP1 localizes to the NE of erythroblasts and their progenitors. Mechanistically, we discovered that NEMP1 accumulates into aggregates that localize near or at the edge of NE openings and Nemp1 deficiency leads to a marked decrease of both NE openings and ensuing enucleation. Together, our results for the first time demonstrate that NEMP1 is essential for NE openings and erythropoietic maturation in vivo and provide the first mouse model of defective erythropoiesis directly linked to the loss of an INM protein.

Impact of Staining Methods and Human Factors on Accuracy of Manual Reticulocyte Enumeration

Although peripheral blood reticulocyte enumeration reflects bone marrow functional integrity, which is important for differential diagnosis of hematological diseases, the factors affecting its accuracy have not been adequately addressed. Using 100 consecutive venous blood samples being processed with four supravital staining techniques [i.e., brilliant cresyl blue (BCB), new methylene blue (NMB), and BCB/NMB with Liu’s stain] for reticulocyte enumeration, two technologists (senior vs. junior) conducted microscopic counting. The results were compared with those obtained with an automated system (Sysmex XE-5000) that served as the standard. The aims of this study were to identify (1) the technique that gave the most reliable outcome, and (2) possible human factors (i.e., seniority, repeated counting) that may affect the counting results. Analysis showed least bias (i.e., deviation from automated counting) associated with BCB staining, followed by NMB. In addition, the senior observer exhibited a higher bias in counting compared with their junior counterpart. Repeated counting also correlated with a higher rate of bias. Nevertheless, inter-observer consistency was high (intraclass correlation coefficient >0.95) and inter-/intra-observer variations were non-significant (both p > 0.05). Our results supported the use of BCB stain for reticulocyte enumeration and the reliability of manual counting despite the involvement of human factors, which had negligible impacts on the final outcomes.

Discovery of N-arylcinnamamides as novel erythroblast enucleation inducers

Derivation of mature red blood cells (RBCs) from stem cells in vitro is a promising solution to the current shortage of blood supply, in which terminal enucleation is the rate-limiting step. Here we discovered two cinnamamides B8 and B16 showed potential activities of enhancing the enucleation of erythroblasts through the screening of "in-house" compound library. Subsequently, twenty-four N-arylcinnamamides were rationally designed and synthesized on the basis of the structure of B8 and B16, in which N-(9H-carbazol-2-yl)cinnamamide (KS-2) significantly elevated the percentage of reticulocytes in the cultured mouse fetal liver cells in vitro (relative enucleation = 2.43). The underlying mechanism of KS-2 in promoting mouse erythroid enucleation is accelerating the process of cell cycle exit via p53 activation in late stage erythrocytes. These results strongly suggest that compound KS-2 is worthy of further study as a potential erythrocyte enucleation inducer.

Autism-associated chromatin remodeler CHD8 regulates erythroblast cytokinesis and fine-tunes the balance of Rho GTPase signaling

CHD8 is an ATP-dependent chromatin-remodeling factor whose monoallelic mutation defines a subtype of autism spectrum disorders (ASDs). Previous work found that CHD8 is required for the maintenance of hematopoiesis by integrating ATM-P53-mediated survival of hematopoietic stem/progenitor cells (HSPCs). Here, by using Chd8^F/FMx1-Cre combined with a Trp53^F/F mouse model that suppresses apoptosis of Chd8^−/− HSPCs, we identify CHD8 as an essential regulator of erythroid differentiation. Chd8^−/−P53^−/− mice exhibited severe anemia conforming to congenital dyserythropoietic anemia (CDA) phenotypes. Loss of CHD8 leads to drastically decreased numbers of orthochromatic erythroblasts and increased binucleated and multinucleated basophilic erythroblasts with a cytokinesis failure in erythroblasts. CHD8 binds directly to the gene bodies of multiple Rho GTPase signaling genes in erythroblasts, and loss of CHD8 results in their dysregulated expression, leading to decreased RhoA and increased Rac1 and Cdc42 activities. Our study shows that autism-associated CHD8 is essential for erythroblast cytokinesis.

Tu et al. report that CHD8, an autism-related chromatin remodeler, is essential for erythroid differentiation. Loss of CHD8 leads to unbalanced Rho GTPase signaling and defective erythroblast cytokinesis, mimicking that of congenital dyserythropoietic anemia.

Chicken cathepsin G-like - A highly specific serine protease with a peculiar tryptase specificity expressed by chicken thrombocytes

Serine proteases are major granule constituents of cells from several mammalian hematopoietic cell lineages. Despite the relatively extensive knowledge about these mammalian proteases, very little is known about their bird, reptile and amphibian homologs. In order to close this gap in our understanding of the evolution of these proteases, we have characterized the extended cleavage specificity and hematopoietic expression pattern of the chicken serine protease cathepsin G-like. This protease, which clusters in a separate subfamily of serine proteases among the vertebrate hematopoietic serine proteases, has been characterized using substrate phage display and further validated by using a panel of recombinant substrates. A preference for a lysine in the P1 position of a substrate, arginines in positions P2 and P3, and the aromatic amino acid tryptophane in the P4 position was observed. Based on the sequence alignment we could identify a consensus sequence for this protease as being PGGWRRK^↓ALSV. Mass spectrometry analysis of a peptide with the consensus sequence obtained by phage display showed that cleavage of this peptide occurred after the conserved Lys (K) residue. A screening of potential in vivo substrates based on the derived P5-P3' consensus sequence resulted in a relatively limited number of potential substrates, due to the high selectivity of this enzyme. The most interesting of these were PDGF-A, coagulation factor V and low-density lipoprotein receptor like-8. Immunohistochemical analysis of chicken white blood cells with antisera produced against chicken cathepsin G-like and chicken egg lysozyme, as a reference protein known to be expressed by hematopoietic cells, showed presence of chicken cathepsin G-like almost exclusively in thrombocytes whereas lysozyme was found at very high amounts in heterophils, and lower amounts in monocytes and thrombocytes.

Tpr Deficiency Disrupts Erythroid Maturation With Impaired Chromatin Condensation in Zebrafish Embryogenesis

Vertebrate erythropoiesis involves nuclear and chromatin condensation at the early stages of terminal differentiation, which is a unique process to distinguish mature erythrocytes from erythroblasts. However, the underlying mechanisms of chromatin condensation during erythrocyte maturation remain elusive. Here, we reported a novel zebrafish mutant cas7 with erythroid maturation deficiency. Positional cloning showed that a single base mutation in tprb gene, which encodes nucleoporin translocated promoter region (Tpr), is responsible for the disrupted erythroid maturation and upregulation of erythroid genes, including ae1-globin and be1-globin. Further investigation revealed that deficient erythropoiesis in tprb cas7 mutant was independent on HIF signaling pathway. The proportion of euchromatin was significantly increased, whereas the percentage of heterochromatin was markedly decreased in tprb cas7 mutant. In addition, TPR knockdown in human K562 cells also disrupted erythroid differentiation and dramatically elevated the expression of globin genes, which suggests that the functions of TPR in erythropoiesis are highly conserved in vertebrates. Taken together, this study revealed that Tpr played vital roles in chromatin condensation and gene regulation during erythroid maturation in vertebrates.

Macrophages form erythropoietic niches and regulate iron homeostasis to adapt erythropoiesis in response to infections and inflammation

It has recently emerged that tissue-resident macrophages are key regulators of several stem cell niches orchestrating tissue formation during development, as well as postnatally, when they also organize the repair and regeneration of many tissues including the hemopoietic tissue. The fact that macrophages are also master regulators and effectors of innate immunity and inflammation allows them to coordinate hematopoietic response to infections, injuries, and inflammation. After recently reviewing the roles of phagocytes and macrophages in regulating normal and pathologic hematopoietic stem cell niches, we now focus on the key roles of macrophages in regulating erythropoiesis and iron homeostasis. We review herein the recent advances in understanding how macrophages at the center of erythroblastic islands form an erythropoietic niche that controls the terminal differentiation and maturation of erythroblasts into reticulocytes; how red pulp macrophages in the spleen control iron recycling and homeostasis; how these macrophages coordinate emergency erythropoiesis in response to blood loss, infections, and inflammation; and how persistent infections or inflammation can lead to anemia of inflammation via macrophages. Finally, we discuss the technical challenges associated with the molecular characterization of erythroid island macrophages and red pulp macrophages.

Treatment strategies for glucose-6-phosphate dehydrogenase deficiency: past and future perspectives

Glucose-6-phosphate dehydrogenase (G6PD) maintains redox balance in a variety of cell types and is essential for erythrocyte resistance to oxidative stress. G6PD deficiency, caused by mutations in the G6PD gene, is present in ~400 million people worldwide, and can cause acute hemolytic anemia. Currently, there are no therapeutics for G6PD deficiency. We discuss the role of G6PD in hemolytic and nonhemolytic disorders, treatment strategies attempted over the years, and potential reasons for their failure. We also discuss potential pharmacological pathways, including glutathione (GSH) metabolism, compensatory NADPH production routes, transcriptional upregulation of the G6PD gene, highlighting potential drug targets. The needs and opportunities described here may motivate the development of a therapeutic for hematological and other chronic diseases associated with G6PD deficiency.

Blood Pharming – eine realistische Option?

Die Bluttransfusion ist ein wesentlicher und unersetzlicher Teil der modernen Medizin. Jedoch stellt vor allem bei Patienten mit sehr seltenen Blutgruppenkonstellationen der Mangel an Blutprodukten auch heute noch ein wichtiges Gesundheitsproblem weltweit dar. Um diesem Problem entgegenzutreten, versucht man seit einiger Zeit künstlich rote Blutzellen zu generieren. Diese haben potenzielle Vorteile gegenüber Spenderblut, wie z. B. ein verringertes Risiko für die Übertragung von Infektionskrankheiten. Diese Übersicht fasst die aktuellen Entwicklungen über den Prozess der Erythropoese, die Expansionsstrategien der erythrozytären Zellen, der verschiedenen Quellen für ex vivo expandierte Erythrozyten, die Hürden für die klinische Anwendung und die zukünftigen Möglichkeiten der Anwendung zusammen.

Mitochondrial localization and moderated activity are key to murine erythroid enucleation

Mammalian red blood cells (RBCs), which primarily contain hemoglobin, exemplify an elaborate maturation process, with the terminal steps of RBC generation involving extensive cellular remodeling. This encompasses alterations of cellular content through distinct stages of erythroblast maturation that result in the expulsion of the nucleus (enucleation) followed by the loss of mitochondria and all other organelles and a transition to anaerobic glycolysis. Whether there is any link between erythroid removal of the nucleus and the function of any other organelle, including mitochondria, remains unknown. Here we demonstrate that mitochondria are key to nuclear clearance. Using live and confocal microscopy and high-throughput single-cell imaging, we show that before nuclear polarization, mitochondria progressively move toward one side of maturing erythroblasts and aggregate near the nucleus as it extrudes from the cell, a prerequisite for enucleation to proceed. Although we found active mitochondrial respiration is required for nuclear expulsion, levels of mitochondrial activity identify distinct functional subpopulations, because terminally maturing erythroblasts with low relative to high mitochondrial membrane potential are at a later stage of maturation, contain greatly condensed nuclei with reduced open chromatin-associated acetylation histone marks, and exhibit higher enucleation rates. Lastly, to our surprise, we found that late-stage erythroblasts sustain mitochondrial metabolism and subsequent enucleation, primarily through pyruvate but independent of in situ glycolysis. These findings demonstrate the critical but unanticipated functions of mitochondria during the erythroblast enucleation process. They are also relevant to the in vitro production of RBCs as well as to disorders of the erythroid lineage.

Home Sweet Home: Plasmodium vivax-Infected Reticulocytes-The Younger the Better?

After a century of constant failure to produce an in vitro culture of the most widespread human malaria parasite Plasmodium vivax, recent advances have highlighted the difficulties to provide this parasite with a healthy host cell to invade, develop, and multiply under in vitro conditions. The actual level of understanding of the heterogeneous populations of cells—framed under the name ‘reticulocytes’—and, importantly, their adequate in vitro progression from very immature reticulocytes to normocytes (mature erythrocytes) is far from complete. The volatility of its individual stability may suggest the reticulocyte as a delusory cell, particularly to be used for stable culture purposes. Yet, the recent relevance gained by a specific subset of highly immature reticulocytes has brought some hope. Very immature reticulocytes are characterized by a peculiar membrane harboring a plethora of molecules potentially involved in P. vivax invasion and by an intracellular complexity dynamically changing upon its quick maturation into normocytes. We analyze the potentialities offered by this youngest reticulocyte subsets as an ideal in vitro host cell for P. vivax.

SETD2 is essential for terminal differentiation of erythroblasts during fetal erythropoiesis

SET domain-containing 2 (SETD2), the primary methyltransferase for histone 3 lysine-36 trimethylation (H3K36me3) in mammals, is associated with many hematopoietic diseases when mutated. Previous works have emphasized its role in maintaining adult hematopoietic stem cells or tumorigenesis, however, whether and how SETD2 regulates erythropoiesis during embryonic development is relatively unexplored. In this study, using a conditional SETD2 knockout (KO) mouse model, we reveal that SETD2 plays an essential role in fetal erythropoiesis. Loss of Setd2 in hematopoietic cells ablates H3K36me3, and leads to anemia with a significant decrease in erythroid cells in the peripheral blood at E18.5. This is due to impaired erythroblast differentiation in both spleen and liver. We also find increased proportions of nucleated erythrocytes in the blood of Setd2 KO embryos. Lastly, we ascribe embryonic erythropoiesis-related genes Vegfc, Vegfr3, and Prox1, as likely downstream targets of SETD2 regulation. Our study reveals a critical role of SETD2 in fetal erythropoiesis that precedes adult hematopoiesis, and provide unique insights into the defects in erythroid lineages, such as anemia.