Mature Red Blood Cells Research Articles

Single-cell transcriptomic landscape of nucleated cells in umbilical cord blood.

BackgroundFor both pediatric and adult patients, umbilical cord blood (UCB) transplant is a therapeutic option for a variety of hematologic diseases, such as blood cancers, myeloproliferative disorders, genetic diseases, and metabolic disorders. However, the level of cellular heterogeneity and diversity of nucleated cells in UCB has not yet been assessed in an unbiased and systemic fashion. In the present study, nucleated cells from UCB were subjected to single-cell RNA sequencing to simultaneously profile the gene expression signatures of thousands of cells, generating a rich resource for further functional studies. Here, we report the transcriptomes of 17,637 UCB cells, covering 12 major cell types, many of which can be further divided into distinct subpopulations.ResultsPseudotemporal ordering of nucleated red blood cells identifies wave-like activation and suppression of transcription regulators, leading to a polarized cellular state, which may reflect nucleated red blood cell maturation. Progenitor cells in UCB also comprise 2 subpopulations with activation of divergent transcription programs, leading to specific cell fate commitment. Detailed profiling of cytotoxic cell populations unveiled granzymes B and K signatures in natural killer and natural killer T-cell types in UCB.ConclusionsTaken together, our data form a comprehensive single-cell transcriptomic landscape that reveals previously unrecognized cell types, pathways, and mechanisms of gene expression regulation. These data may contribute to the efficacy and outcome of UCB transplant, broadening the scope of research and clinical innovations.

Mutations in the zebrafish hmgcs1 gene reveal a novel function for isoprenoids during red blood cell development

AbstractErythropoiesis is the process by which new red blood cells (RBCs) are formed and defects in this process can lead to anemia or thalassemia. The GATA1 transcription factor is an established mediator of RBC development. However, the upstream mechanisms that regulate the expression of GATA1 are not completely characterized. Cholesterol is 1 potential upstream mediator of GATA1 expression because previously published studies suggest that defects in cholesterol synthesis disrupt RBC differentiation. Here we characterize RBC development in a zebrafish harboring a single missense mutation in the hmgcs1 gene (Vu57 allele). hmgcs1 encodes the first enzyme in the cholesterol synthesis pathway and mutation of hmgcs1 inhibits cholesterol synthesis. We analyzed the number of RBCs in hmgcs1 mutants and their wild-type siblings. Mutation of hmgcs1 resulted in a decrease in the number of mature RBCs, which coincides with reduced gata1a expression. We combined these experiments with pharmacological inhibition and confirmed that cholesterol and isoprenoid synthesis are essential for RBC differentiation, but that gata1a expression is isoprenoid dependent. Collectively, our results reveal 2 novel upstream regulators of RBC development and suggest that appropriate cholesterol homeostasis is critical for primitive erythropoiesis.

Abnormal red blood cell morphological changes in thalassaemia associated with iron overload and oxidative stress

AimsIron overload is a major factor contributing to the overall pathology of thalassaemia, which is primarily mediated by ineffective erythropoiesis and shorter mature red blood cell (RBC) survival. Iron accumulation...

Improvement of Red Blood Cell Maturation In Vitro by Serum-Free Medium Optimization.

Despite recent studies on media additives, the low viability and dysplastic features of terminally mature erythroid cells are still major problems in enhancing erythroid cell yields in vitro. Moreover, research on enhancing terminal erythropoiesis has been focused on the immature stage of erythroid cells such as burst forming unit-erythroid and colony forming unit-erythroid. Here, we tested many commercially available serum-free culture media and developed a superior culture media formulation compared with the conventional control for higher expansion-fold, higher viability, and therefore enhanced red cell productivity. The addition of the specific medium to the previously known best media at a specific ratio, whose effects were not dose-dependent, enabled the generation of significantly higher erythrocyte products with over 1.3 million-fold proliferation of erythroid cells after maintenance for 21 days throughout the maturation stages from CD34+ cells. The cells cultured in this condition expressed maturation markers and were significantly superior in differentiation and enucleation. Comparative mRNA profiling revealed that erythroid cells in this medium showed more efficient maturation in mRNA levels. The cultured cells showed comparable erythroblast survival and also restored better red blood cell (RBC) functions of oxygen saturation profile with expression of adult globin up to 99%. However, to develop chemically defined media, the well-known supplements including hormones, cytokines, and serum-replacement reagents were not sufficient to replace the optimized media in producing mature RBCs. Taken together, our optimized medium formulation under serum-free culture conditions produced the best reproducible results on productivity and maturation in erythroid cells with economic benefits. These culture conditions may thus serve as a useful platform for further investigation of in vitro erythropoiesis and to develop defined serum-free media for clinical trials.

Red Blood Cell Metabolic Responses to Torpor and Arousal in the Hibernator Arctic Ground Squirrel.

Arctic ground squirrels provide a unique model to investigate metabolic responses to hibernation in mammals. During winter months these rodents are exposed to severe hypothermia, prolonged fasting, and hypoxemia. In the light of their role in oxygen transport/off-loading and owing to the absence of nuclei and organelles (and thus de novo protein synthesis capacity), mature red blood cells have evolved metabolic programs to counteract physiological or pathological hypoxemia. However, red blood cell metabolism in hibernation has not yet been investigated. Here we employed targeted and untargeted metabolomics approaches to investigate erythrocyte metabolism during entrance to torpor to arousal, with a high resolution of the intermediate time points. We report that torpor and arousal promote metabolism through glycolysis and pentose phosphate pathway, respectively, consistent with previous models of oxygen-dependent metabolic modulation in mature erythrocytes. Erythrocytes from hibernating squirrels showed up to 100-fold lower levels of biomarkers of reperfusion injury, such as the pro-inflammatory dicarboxylate succinate. Altered tryptophan metabolism during torpor was here correlated to the accumulation of potentially neurotoxic catabolites kynurenine, quinolinate, and picolinate. Arousal was accompanied by alterations of sulfur metabolism, including sudden spikes in a metabolite putatively identified as thiorphan (level 1 confidence)-a potent inhibitor of several metalloproteases that play a crucial role in nociception and inflammatory complication to reperfusion secondary to ischemia or hemorrhage. Preliminary studies in rats showed that intravenous injection of thiorphan prior to resuscitation mitigates metabolic and cytokine markers of reperfusion injury, etiological contributors to inflammatory complications after shock.

In Patients with Minor Beta-Thalassemia, Cognitive Performance Is Related to Length of Education, But not to Minor Beta-Thalassemia or Hemoglobin Levels

Objective: Thalassemia is one of the most frequent monogenic disorders, leading to impairment in the maturation and survival of red blood cells. The question examined here is whether, and if so, to what extent, people with beta-thalassemia might also be impaired in their cognitive functioning. Previous results in adults with beta-thalassemia showed cognitive impairment when compared to healthy controls. However, length of education was never taken into consideration as a possible confounder. Accordingly, the aim of the present study was to assess people with minor beta-thalassemia and compare them to healthy controls, while controlling for length of education. Method : A total of 25 adults (mean age: 29.36 years; 56% females) with beta-thalassemia and 25 healthy controls (mean age: 27.84 years; 72% females) took part in this cross-sectional study. They underwent cognitive testing (executive functions, attention, working memory), and their haemoglobin levels were assessed. Results: Cognitive performance did not significantly differ between patients with minor beta-thalassemia and healthy controls. Irrespective of group, higher cognitive performance was strongly associated with time spent in education. No gender differences were observed. Conclusion: Compared to healthy controls, cognitive performance was not impaired among patients with minor beta-thalassemia when length of education was introduced as a further co-variate. In both patients with minor beta-thalassemia and healthy controls, higher cognitive performance was associated with time spent for education. Health professionals should inform patients with minor beta-thalassemia that cognitive performance is related to the length of education and not to the health status of minor beta-thalassemia per se.

The Pleiotropic Effects of GATA1 and KLF1 in Physiological Erythropoiesis and in Dyserythropoietic Disorders.

In the last few years, the advent of new technological approaches has led to a better knowledge of the ontogeny of erythropoiesis during development and of the journey leading from hematopoietic stem cells (HSCs) to mature red blood cells (RBCs). Our view of a well-defined hierarchical model of hematopoiesis with a near-homogeneous HSC population residing at the apex has been progressively challenged in favor of a landscape where HSCs themselves are highly heterogeneous and lineages separate earlier than previously thought. The coordination of these events is orchestrated by transcription factors (TFs) that work in a combinatorial manner to activate and/or repress their target genes. The development of next generation sequencing (NGS) has facilitated the identification of pathological mutations involving TFs underlying hematological defects. The examples of GATA1 and KLF1 presented in this review suggest that in the next few years the number of TF mutations associated with dyserythropoietic disorders will further increase.

Single-cell analyses demonstrate that a heme–GATA1 feedback loop regulates red cell differentiation

AbstractErythropoiesis is the complex, dynamic, and tightly regulated process that generates all mature red blood cells. To understand this process, we mapped the developmental trajectories of progenitors from wild-type, erythropoietin-treated, and Flvcr1-deleted mice at single-cell resolution. Importantly, we linked the quantity of each cell's surface proteins to its total transcriptome, which is a novel method. Deletion of Flvcr1 results in high levels of intracellular heme, allowing us to identify heme-regulated circuitry. Our studies demonstrate that in early erythroid cells (CD71+Ter119neg-lo), heme increases ribosomal protein transcripts, suggesting that heme, in addition to upregulating globin transcription and translation, guarantees ample ribosomes for globin synthesis. In later erythroid cells (CD71+Ter119lo-hi), heme decreases GATA1, GATA1-target gene, and mitotic spindle gene expression. These changes occur quickly. For example, in confirmatory studies using human marrow erythroid cells, ribosomal protein transcripts and proteins increase, and GATA1 transcript and protein decrease, within 15 to 30 minutes of amplifying endogenous heme synthesis with aminolevulinic acid. Because GATA1 initiates heme synthesis, GATA1 and heme together direct red cell maturation, and heme stops GATA1 synthesis, our observations reveal a GATA1–heme autoregulatory loop and implicate GATA1 and heme as the comaster regulators of the normal erythroid differentiation program. In addition, as excessive heme could amplify ribosomal protein imbalance, prematurely lower GATA1, and impede mitosis, these data may help explain the ineffective (early termination of) erythropoiesis in Diamond Blackfan anemia and del(5q) myelodysplasia, disorders with excessive heme in colony-forming unit-erythroid/proerythroblasts, explain why these anemias are macrocytic, and show why children with GATA1 mutations have DBA-like clinical phenotypes.

Study of Genotoxic and Cytotoxic effects of Malathion in Japanese Quail

The effect of Malathion was studied orally on Japanese quail males (Cotrunix Cotrunix Japonica). The Median lethal Dose LD50 of malathion through 24 hours was found to be 163.6 mg / kg. Malathion was provided in doses of 75% 122.7 mg / kg b.wt., 50% 81.8 mg / kg b.wt., 25%40.9 mg/kg b.wt. LD50 of body weight plus cyclophosphamide 20 mg/kg b.wt as positive control and Corn oil as a negative control, The current study was carried out to detect the effects of malathion on cell cytotoxicity based on genetic cytotoxicity tests such as Micronuclei Test (MN for mature red blood cells in peripheral blood and immature blood cells in bone marrow for 18, 20 and 22 hours per treatment and Chromosomal Aberration (CA) test for immature red blood cells in bone marrow, And 24 hours for each treatment with subcutaneous injection of colchicine 0.5gm prior to 3-hour incubation. The results of the statistical analysis Suggested that a significant increase in P≤0.05of micronucleated mature red blood cells in peripheral blood and micronucleated immature blood cells in bone marrow for 18, 20 and 22 hours per treatment in the formation of micronuclei compared to negative control. The results of the study also Suggested that a significant increase in P≤ 0.05 on the induction of chromosomal Aberration of immature red blood cells in bone marrow.

Reduction of hemoglobin, not iron, inhibited maturation of red blood cells in male rats exposed to high intensity endurance exercises

The existence of sports anemia, induced by strenuous or long-term exercise and characterized by decreases of red blood cells (RBCs), hemoglobin and iron content, remains to be doubtful. To observe the effects of endurance exercise on RBCs and explain the underlying reason, we designed this study by observing RBCs parameters and iron metabolism in 8-weeks training rats and effects of iron supplement or protein supplement on RBCs. Results showed that erythrocyte counts, hematocrit, mean corpuscular volume and hemoglobin content decreased while RBC distribution width increased in exercised rats at later stage during 8 weeks training. But the contents of serum iron and ferritin decreased only at 1-week and 2-week and returned to normal at 4-week and 8-week. Same as iron content, apparent iron absorption rate was declined at early stage but restored to normal level at 8-week, as well as serum adrenaline, cortisol and insulin levels. Instead, the contents of total protein and albumin in serum were decreased at later stage during 8-weeks training. Furthermore, we observed that protein supplement ameliorated RBCs parameters in rats exposed to 8 weeks swimming exercise, but iron supplement had no effects on RBCs, though it obviously increased iron content of serum and the liver. Based on these results, we drew a conclusion that transient changes of iron metabolism, which may be induced by stress hormone changes, was not the reason for RBCs decrease in endurance exercises but hemoglobin reduction, induced by defects in protein supplement, impeded development of RBCs.

Autophagy in Mitochondrial Quality Control.

Autophagy plays an important role in the renewal of cellular components, which function in energy production, metabolism, and clearance of damaged organelles. Both macroautophagy and microautophagy are involved in these processes. Although it was thought that nonselective macroautophagy is responsible for the clearance of damaged or old organelles, recent studies show that the clearance of cellular organelles depends on selective processes. Mitophagy is a process for selective degradation of mitochondria, which is well documented. The selective autophagy for other organelles includes endoplasmic reticulum autophagy (reticulophagy) and peroxisome autophagy (pexophagy). Autophagy is a routine pathway for cells to degrade unused proteins and damaged organelles in cells. Autophagy selectively removes dysfunctional cellular components but not damages the normally functioning organelles, to maintain the homeostasis of cells. In addition to the maintenance of the homeostasis of cells, autophagy clears the damaged organelles in disease or injury conditions to achieve cellular quality control. In some differentiated cells, such as red blood cells, some organelles are removed during the maturation, including mitochondria. The autophagy system can selectively clear the mitochondria and other organelles, which lead to the maturation of red blood cells. Dysfunction of autophagy impairs the clearance of damaged organelles, which results in injury of cells. In the maturation of red blood cells, failure to clear the cellular organelles by autophagy will disturb the normal differentiation of red blood cells, leading to a series of diseases such as anemia.

Erythrocyte Senescent Markers by Flow Cytometry

Background: Mature red blood cells lack protein synthesis and are unable to restore inactivated enzymes, damaged cytoskeleton and membrane proteins. An oxidation breakdown of band 3 is probably part of the mechanism leading to the generation of a senescent cell antigen. This specific signal serves for the clearance of RBCs by inducing the binding of autologous IgG and C3, leading to phagocytosis. In addition, phosphatidilserin molecules appear in the outer membrane and the CD47 expression diminishes. Methods: Erythrocytes of different ages from whole blood were studied by flow cytometry analysing light scatter proprieties, binding of autologous IgG, C3 complement deposits, externalization of phosphatidylserine and CD47 expression. Dot-plot analysis based on forward scatter versus side scatter parameters showed two RBCs populations of different sizes and density. RBCs were further incubated with Alexa 488 IgG, APC-anti-C3, PE-annexin-V and PE-CD47. The comparison of the values obtained for the different variables studied in SeRBC and YRBC populations was carried out by the Student t-test for matched samples or by the Wilcoxon test (after verification of the normality assumption). Results: The percentage of IgG and C3 positive cells was significantly higher in senescent red blood cells population. The fraction of annexin-V positive RBCs was also larger in SeRBCs while the CD47 expression was lower in this population. Conclusions: These results indicate that flow cytometry allow differenciation of erythrocytes populations of different ages, turning this tool into an useful alternative option to study erythrocyte aging process. These findings will contribute to a better understanding of the process and mechanisms involved in erythrocyte senescence process.

Altered Red Blood Cell Membrane Fatty Acid Profile in Cancer Patients.

The fatty acid (FA) composition of red blood cell (RBC) membrane phospholipids of cancer patients can reflect tumor status, dietary intakes, and cancer type or therapy. However, the characteristic membrane profiles have so far not yet defined as a potential biomarker to monitor disease evolution. The present work provides the first evidence of cancer metabolic signatures affecting cell membranes that are independent of nutritional habits. From the Oncology Outpatient Unit of the Onkologikoa hospital, two groups of cancer patients (n = 54) and healthy controls (n = 37) were recruited, and mature RBCs membrane phospholipids were analyzed for FA profiling (GC-MS). Dietary habits were evaluated using a validated food frequency questionnaire. The adjusted Analysis of Covariance Test (ANCOVA) model revealed cancer patients to have a lower relative percentage of saturated fatty acids (SFA) (C16:0 (5.7%); C18:0 (15.9%)), and higher monounsaturated fatty acids (MUFA) (9c-C18:1 (12.9%) and 11c-C18:1 (54.5%)), compared to controls. In line with this, we observe that the desaturase enzymatic index (delta-9 desaturase (Δ9D), +28.3%) and the membrane saturation index (SI = SFA/MUFA; −27.3%) were similarly modulated. Polyunsaturated fatty acids (PUFA) families showed an increase of n-6 C18:2 and C20:3 (15.7% and 22.2% respectively), with no differences in n-6 C20:4 and n-3 PUFA (docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA)). Importantly, these changes were found independent of foods and fat intakes from the diet. The membrane lipid profile in RBC was useful to ascertain the presence of two main metabolic signatures of increased desaturation activity and omega-6 in cancer patients, statistically independent from dietary habits.

Sickle Human Umbilical Cord Derived Erythroid Progenitor Cells (S-HUDEP2): An Ideal in-Vitro System for Screening Anti-Sickling Compounds for Sickle Cell Disease

Background: Sickle Cell Disease (SCD) is a devastating inherited disease, characterized by polymerization of sickle hemoglobin under deoxygenated conditions that can lead to acute pain crises, ischemia, and chronic organ damage. Pharmacologic anti-sickling agents that decrease polymerization are currently under investigation, however there is no consistent in vitro system to study these compounds; whole patient blood, subject to clinical variability and limited supply, is most often used. Human Umbilical Cord Derived Erythroid Progenitor 2 cells (HUDEP2) are an immortalized CD34+ hematopoietic stem cell (HSC) derived erythroid precursor cell line that can differentiate into red blood cells. We have engineered S-HUDEP2 cells to express sickle hemoglobin (HbS) via CRISPR/Cas9 gene editing. We hypothesized that this cell line will sickle under hypoxic conditions, produce dense red blood cells (DRBC, red cells with a density>1.11 mg/mL that are dehydrated and prone to sickling. If these intrinsic, essential SCD RBC properties are found, we propose to use this novel cell line to screen drug compounds for anti-sickling capabilities.Methods: S-HUDEP cells were cultured as previously described (Kurita et al, 2013). %HbS and %HbA produced by parent HUDEP and S-HUDEP2 cells were measured by high performance liquid chromatography (HPLC). Hypoxia was induced by placing the cells at 2% O2 for four hours. Parent HUDEP and S-HUDEP2 cells were then fixed with glutaraldehyde and Giemsa stained. % sickling estimated at 40x magnification by a pathologist blinded to cell group counting sickle forms out of 1000 cells. The percentage of dense red blood cells (DRBCs) was quantified by an ADVIA hematology analyzer (Siemens). S-HUDEP2 cells were dosed with 0, 2.5 and 5 µM 5-hydroxymethylfurfural (5-HMF) and 75, 150, and 300 µM GBT440, two known anti-sickling agents, on day ten and day 14 of culture for one hour, subjected to hypoxic conditions and % sickling quantified as described above.Results: S-HUDEP2 cells express 98% HbS. Under hypoxia, 20% of S-HUDEPs sickle at day 10 of differentiation; 30% of S-HUDEP2 cells sickle at Day +14 of differentiation. Parent HUDEP-2 cells, which produce 98% HbA, did not sickle under hypoxic conditions at any stage of differentiation. 70% of S-HUDEP2 cells were determined to be DRBC under hypoxia at Day 10 and 14 time points; parent HUDEP-2 cells did not produce DRBC under hypoxia. Treatment of S-HUDEP2 cells with 5μM of 5-HMF and 150 μM of GBT440 reduced sickling by 40-50% under hypoxic conditions compared with untreated S-HUDEP2 cells (p<0.01), and reduced %DRBC by 30% (p<0.01).Conclusions: S-HUDEP2 cells express HbS, form DRBC, and sickle under hypoxic conditions, just like erythroid precursors and mature red blood cells from individuals with SCD. Exposure to two anti-sickling agents, one of which is currently in Phase III clinical trials, significantly decreased S-HUDEP2 sickling under hypoxic conditions, and reduced %DRBC, a marker of disease severity. Advantages of S-HUDEPs over patient samples include genetic and phenotypic uniformity, no human pathogens, and availability to groups without access to patient samples. We therefore conclude that S-HUDEP2s have utility in clinical research, may be used to screen anti-sickling and anti-dense cell compounds in vitro, and may lead to identification of new therapeutic options for SCD patients. DisclosuresNo relevant conflicts of interest to declare.

FBXO11 Activates Erythroid Gene Transcription By Degrading Heterochromatin-Associated Protein BAHD1

Mature red blood cells (RBC) contain approximately 95% cytosolic hemoglobin for the purpose of blood oxygen transport. This specialized state is achieved during erythropoiesis by regulated gene expression and protein degradation. During late-stage erythropoiesis, ubiquitin ligases eliminate unnecessary proteins and maintain quality control by degrading unstable proteins, including unpaired hemoglobin subunits. However, ubiquitin ligases are expressed at all stages of erythropoiesis and the functions of most are unknown. To study ubiquitin ligases involved in RBC formation, we performed a Cas9/single guide (sg) RNA screen for functional ubiquitin-proteasome components in HUDEP-2 cells, an immortalized human cell line that proliferates as immature erythroblasts and can be induced to undergo terminal maturation. We identified the E3 ubiquitin ligase FBXO11 as a top-ranked candidate. FBXO11 is a member of the F-box protein family that assembles into a SKP1-CUL1-F-box (SCF) E3 ubiquitin ligase complex. Depletion of FBXO11 by 2 different sgRNAs in HUDEP-2 cells inhibited erythroid maturation, as evidenced by reduced hemoglobinization, failure to induce the maturation marker Band3 and persistence of immature cell morphology. In primary human CD34+ cells, suppression of FBXO11 expression by Cas9 + two independent sgRNAs inhibited erythroid maturation, as evidenced by reduced Band3 expression (5.3% vs. 15.6% for non-targeting sgRNA, P < 0.001; n=4). RNA-seq analysis of FBXO11-depleted HUDEP-2 cells revealed 951 decreased transcripts (enriched for erythroid genes) and 339 increased transcripts (enriched for genes expressed in activated T-cells) compared to control cells expressing non-targeting gRNA (P < 0.05). Thus, FBXO11 is required for erythroid maturation and facilitates erythroid gene expression.We sought to establish how FBXO11 modulates erythropoiesis and erythroid gene expression by identifying the relevant ubiquitination substrate(s). Combined quantitative proteome analysis with RNA-seq of FBXO11-depleted HUDEP-2 cells identified several proteins that are upregulated with no change in their corresponding mRNA. We tested whether reduction of these candidate substrates could alleviate the erythroid maturation block conferred by FBXO11 depletion. In FBXO11 gene-disrupted HUDEP-2 cells, suppression of the heterochromatin-associated protein BAHD1 partially rescued hemoglobinization and Band3 expression (4.2% for Cas9 + non-targeting sgRNA vs. 21.7% for Cas9 + BAHD1 sgRNAs, P < 0.01; n=3) . Conversely, stable overexpression of V5-epitope-tagged BAHD1 in WT HUDEP-2 cells reduced Band3 expression from 25.0% to 11.4% (P < 0.001; n=3) and inhibited hemoglobinization. Transcriptome analysis demonstrated a significant inverse correlation between genes deregulated by BAHD1-V5 overexpression and FBXO11 deficiency in HUDEP-2 cells, particularly for erythroid genes that are downregulated (P < 0.0001).BAHD1, named after its bromo-adjacent homology domain that interacts with H3K27me3, is part of a transcriptional repressor complex. We showed that BAHD1 and FBXO11 co-immunoprecipitated in cells and that BAHD1 amino (N)-terminal segments of 188 or 240 amino acids were robustly modified with ubiquitin by SCFFBXO11 complex. Chromatin immunoprecipitation-sequencing analysis of BAHD1-V5-expressing WT HUDEP-2 cells showed strong enrichment for BAHD1 occupancy on erythroid gene promoters that were downregulated by FBXO11-deficiency (P < 0.0001). We next investigated whether a specific set of histone marks distinguish FBXO11-regulated genes in normal erythroblasts. We found that most FBXO11-regulated genes in both HUDEP-2 and primary CD34+ derived erythroblasts harbor histone marks H3K4me3 and H3K27me3, indicating a “bivalent” epigenetic state that supports low level transcription in stem or progenitor cells. Together, these data indicate that FBXO11 activates expression of erythroid genes by ubiquitinating and degrading bivalent promoter-bound BAHD1 repressor complexes with likely resolution to a monovalent transcriptionally active state.Overall, our findings identify FBXO11 as a ubiquitin ligase that utilizes a novel mechanism to activate erythroid genes during RBC formation. This newly identified pathway may contribute to known activities of FBXO11 as a tumor suppressor and developmental regulator in non-erythroid tissues. DisclosuresNo relevant conflicts of interest to declare.

Setd2-Mediated Epigenetic Regulation of Erythropoiesis and HSC Maintenance in Mouse Models

SET domain containing 2 (SETD2) is a methyltransferase for histone 3 lysine 36 tri-methylation (H3K36me3). Using a conditional knockout allele (Setd2Δ/Δ), we recently demonstrated that their SLAM-hematopoietic stem cells (SLAM-HSCs) have intrinsic defects in maintaining quiescence and multi-lineage differentiation potential. Setd2Δ/Δ mice show decreased lymphoid and myeloid progenitors except increased pre-colony-forming-unit-erythroid (Pre CFU-E) and erythroblasts in bone marrow (BM); they suffer from lethal macrocytic anemia. A decreasing H3K36me3, but increasing H3K36me1 and H3K36me2, were observed in Setd2Δ/Δ mice. As a consequence, RNA polymerase II elongation is enhanced at a subset of genes, including Myc which encodes a transcriptional factor essential for erythropoiesis and HSC activation (Zhou Y., Haematologica, 2018). In the current study, we aim to investigate the detailed mechanisms of Setd2 deficiency in the intrinsic and extrinsic mechanisms of erythropoiesis and in the maintenance of HSC from definitive HSCs to adult.Erythropoiesis from the BFU-E/CFU-E stage to mature erythrocytes is sequentially regulated by an erythropoietin (EPO)-dependent early stage and macrophages-dependent late stage. To understand the function of Setd2 in erythroid differentiation, we generated two Setd2 conditional knockout mice: Setd2flox/flox/Vav1-Cre+ (Setd2Δ/Δ) and Setd2flox/flox/EpoR-Cre+ (Setd2Δ/Δ/EpoR). Setd2Δ/Δmice harbor a pan-hematopoietic deletion, while Setd2Δ/Δ/EpoR mice harbor an erythroid stage specific deletion from CFU-Es, proerythroblasts and basophilic erythroblasts. In Setd2Δ/ΔBM, the absolute number of basophilic erythroblasts and polychromatic erythroblasts were significantly increased but mature red blood cells were decreased. Surprisingly, Setd2Δ/Δ/EpoR mice showed normal proportions of erythroid blasts and did not suffer from anemia, suggesting that Setd2 is not required for the proliferation and differentiation of EPO-dependent erythroblasts and thereafter mature erythrocytes. Central macrophages are known to play a crucial role in terminal erythropoiesis by supplying the iron and engulfing the protruded nuclei from erythroblasts in the terminal maturation process. We then analyzed macrophages in Setd2Δ/Δ mice. The total F4/80+ macrophages were not changed, however, the proportion of type II macrophages (CD206+CD80-F4/80+) were significantly increased in Setd2Δ/Δ BM. Myc is a well-known factor for polarizing type II immune phenotypes. Our data suggest that Setd2 deficiency causes a shift of central macrophage to type II, which possibly impedes the terminal maturation of erythrocytes and causes macrocytic anemia, even with significantly increased BFU-E, CFU-E, and erythroblasts.Next, we addressed whether Setd2 was required for HSC maintenance from definitive HSCs to adult HSCs in an autonomous manner. It has been shown that genes regulating the maintenance of HSC at different developmental stages are diverse. To clarify in which developmental stages Setd2 is critical for HSC maintenance, we examined the HSC populations in Setd2Δ/Δ embryos at E14.5, and in Setd2Δ/Δ mice BM at 3 weeks (wks), 8 wks and 34-38 wks of age. HSC populations from fetal liver (FL) at E14.5 and BM at 3 wks were not different from Setd2flox/flox control littermates. Significant reductions in the absolute number of SLAM-HSCs, CD201+SLAM-HSCs and multipotent progenitors were observed at 8 wks, eventually HSCs were completely exhausted for mice at 34-38 wks. We further evaluated the HSC function in a competitive bone marrow transplantation assay. Similar levels of multi-lineage reconstitution were observed in recipient mice with Setd2Δ/Δ donor cells from FL or BM transplanted at 3 wks. However, Setd2Δ/Δ HSCs from 8 wk and 34 wk BM failed to support a long-term reconstitution and there is a complete absence of donor derived Setd2Δ/Δ LSKs. Altogether, our data suggest that Setd2 is required for HSC maintenance at adult stage, but not at fetal or neonatal stages.In summary, our study revealed a previously unknown extrinsic function of Setd2 in terminal erythroid maturation; and also identified Setd2 as a critical intrinsic regulator for adult HSC maintenance. Our findings may provide unique insights into the defects in erythroid lineages, such as anemia or erythrocytosis, and also epigenetic mechanism of adult HSC maintenance. DisclosuresNo relevant conflicts of interest to declare.

A Dynamic Motility Mechanism for Reticulocyte Enucleation and Maturation

Terminal erythropoiesis involves differentiation of erythroblasts to enucleated reticulocytes, which further remove major organelles to become mature red blood cells. Several pieces of evidence indicate that the extrusion of the nucleus out of the orthochromatic erythroblasts is a fairly rapid process that lasts approximately 10 minutes. However, the detachment of the extruded nucleus from the nascent reticulocyte takes longer time, and possibly requires the aid of phagocyte to anchor the nucleus. The mechanism involved in this process is poorly understood.Previous studies have demonstrated that mDia2 is critical for erythroblast enucleation. Loss of mDia2 in mice lead to compromised cytokinesis in orthochromatic erythroblasts and decrease in enucleation. To further reveal the mechanism of the defect in enucleation in mDia2 deficient erythroid cells, we first monitored the enucleating erythroblasts using real-time microscopy. The wild type enucleating mouse erythroblast showed a dynamic motility to detach the nucleus, which can be facilitated by the macrophages. The mDia2 knockout erythroblasts retained the capacity to extrude the nucleus, even in the bi-nucleated cells. However, the nascent reticulocytes were rigid and lacked the dynamic movement to expel the nuclei. Since mDia2 is critical for linear actin polymerization, we next performed a Western blot assay of RBC ghost and found that actin and many other critical RBC cytoskeleton proteins were significantly decreased in mDia2 knockout mice (Fig 1A). Transmission electron microscope (TEM) analysis of RBC cytoskeleton revealed that spectrin filament connecting two junctional complexes was longer in mDia2 knockout RBCs (Fig 1B), which explains their rigidity and inefficient movement to detach the extruded nuclei. Further studies using stochastic optical reconstruction microscopy (STORM) revealed disorganized distribution of the major components of erythrocyte cytoskeleton, including actin (Fig 1C) and β-spectrin, in mDia2 knockout reticulocytes. The dynamic motility of the nascent reticulocytes is also required for the remodeling and removal of proteins to further mature into RBCs. We found an increase in proteins such as CD71 and CD44, as well as DNA/RNAs, in mDia2 knockout reticulocytes. Mechanistic studies revealed that mDia2 functions on vesicle trafficking through its interaction with Chmp5, one of the critical components of the ESCRT-III complex involved in vesicle formation and trafficking. This interaction stabilized Chmp5 since its level was dramatically reduced in mDia2 knockout erythroblasts and reticulocytes (Fig 1D-E).Our study reveals a critical role of the dynamic motility of the nascent reticulocyte in enucleation and maturation. Abnormal membrane cytoskeleton in mDia2 null mice compromises these processes. In one hand, mDia2 mediated actin polymerization ensures the flexibility of the erythrocyte cytoskeleton. On the other hand, mDia2 also involves vesicle biogenesis and discharging through the regulation of ESCRT complexes during reticulocyte maturation. Our study thus sheds lights on the understanding of reticulocyte maturation mechanisms. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Increased Methylation of Deamidated Asparagines and Aspartates in Stored Red Blood Cells from Glucose 6-Phosphate Dehydrogenase-Deficient Blood Donors

Blood transfusion is a life-saving intervention for millions of recipients worldwide every year. However, refrigerated storage of red blood cells (RBCs) for up to 42 days promotes impairments in energy and redox homeostasis, which impact RBC hemolytic propensity and post-transfusion performance of the storage-damaged RBC. Since mature RBCs are devoid of de novo protein synthesis - owing to the lack of organelles and nuclei - they evolved metabolic mechanisms to cope with oxidative stress. Two of these involve (i) activation of the pentose phosphate pathway (PPP), which generates reducing equivalents (NADPH) to preserve glutathione homeostasis and recharge NADPH-dependent antioxidant enzymes; and (ii) recycling of oxidatively damaged proteins via methylation of dehydrated and deamidated aspartate and asparagine residues, a process that consumes methionine as the main methyl group donor. Thus, we hypothesize that the latter mechanism is relevant to routine blood bank storage, especially in glucose-6-phosphate dehydrogenase (G6PD)-deficient donors. In this routinely accepted donor population (~10% of donors of African descent), mutations of G6PD, the rate-limiting enzyme of the PPP, result in instability and decreased enzymatic activity (e.g., <1% residual activity in the Mediterranean variant).Within the framework of the REDS-III RBC-Omics study, packed RBC units (n=599) were stored under blood bank conditions for 10, 23 and 42 days and profiled for oxidative hemolysis (following AAPH insult) and time-dependent metabolic dysregulation of the trans-sulfuration pathway. The rate of methionine consumption positively correlated with storage age and oxidative hemolysis. In a separate cohort, RBCs from G6PD-deficient and G6PD-normal donors were also collected and metabolically profiled during storage. The G6PD-deficient donors had higher pre-storage methionine levels as compared against G6PD-sufficient donors, although one week of storage was sufficient to significantly flip this ratio (p<0.01). To ensure that the phenomenon was driven by storage-induced oxidative insults, RBCs were also stored under normoxic, hyperoxic (SO2 >95%), or hypoxic conditions (SO2 = 20%, 10%, 5% of < 3%) for up to 42 days. Of note, hypoxia decreased methionine consumption rates and increased S-adenosylmethionine/S-adenosylhomocysteine ratios in comparison to normoxic control RBCs, while opposite trends were observed in response to oxidative stress. In parallel, RBCs were incubated under normoxic or hypoxic conditions for 16h, in presence or absence of a generic methyltransferase inhibitor, adenosine dialdehyde, or hydrogen peroxide (0.1 or 0.5%). 13C,15N-Methionine uptake and consumption rates were faster in response to pro-oxidant insults and were prevented by hypoxia or methyltransferase inhibition. Through a combination of proteomics approaches and 13C-methionine tracing, we observed oxidation-induced increases in both Asn deamidation to Asp and the formation of methyl-Asp on key structural proteins and enzymes, including band 3, hemoglobin, ankyrin, 4.1, spectrin beta, aldolase, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), biphosphoglycerate mutase, lactate dehydrogenase and catalase. Methylated regions tended to map proximal to the active site (e.g., N316 of GAPDH) and/or residues interacting with the N-terminal cytosolic domain of band 3. Hypoxic incubation with hydrogen peroxide phenocopied normoxic conditions in the presence of pro-oxidant insults, suggesting that the beneficial role of hypoxia in preventing methionine consumption and protein methylation is attributable to decreased oxidative stress. G6PD-deficient donor RBCs had significantly (p<0.0001) higher levels of methylated-deamidated Asn residues in hemoglobin, band 3, and GAPDH, as compared to stored G6PD-normal donor RBCs.Although methylation of basic amino acid residues is an epigenetic modification in nucleated cells, protein methylation at carboxylate side chains and deamidated Asn residues is a non-epigenetic post-translational sensor of oxidative stress and refrigerated storage in anucleate human RBCs. This damage repair mechanism is exacerbated in RBCs from G6PD-deficient donors, as a compensatory mechanism for the lack of normal PPP function. DisclosuresD'Alessandro:Hemanext inc: Membership on an entity's Board of Directors or advisory committees; Omix Technologies inc: Equity Ownership. Nemkov:Omix Technologies inc: Equity Ownership. Yoshida:Hemanext inc: Employment. Dunham:Hemanext inc: Employment. DuMont:Hemanext inc: Membership on an entity's Board of Directors or advisory committees. Hansen:Omix Technologies inc: Equity Ownership. Spitalnik:Hemanext inc: Membership on an entity's Board of Directors or advisory committees. Zimring:Rubius Therapeutics: Membership on an entity's Board of Directors or advisory committees.

Global Chromatin Occupancy and Epigenetic Signature Analysis Reveal New Insights into the Function of GATA1 N-Terminus in Erythropoiesis

Mutations in GATA1 are seen in rare cases of dyserythropoietic anemia and in a subset of patients with Diamond Blackfan Anemia (DBA). Of note the truncation mutations in DBA, known as GATA1s, closely resemble those that are more commonly associated with acute megakaryoblastic leukemia in children with Down syndrome (DS). Studies with a mouse model of the Gata1s mutation revealed that replacement of the full-length protein by the shortened isoform led to a marked yet transient enhancement in megakaryopoiesis, similar in some respects to transient myeloproliferative disorder in DS. Furthermore, these mutant mice displayed impaired embryonic erythropoiesis but ostensibly no defects in adult hematopoiesis. In our efforts to better understand the connection between GATA1s and DBA, we comprehensively studied erythropoiesis in the Gata1s mouse strain. We observed a striking impairment in erythropoiesis in fetuses at E10.5 though E12.5, but saw improvement as the animals progressed through E14.5 and beyond. Defects included impaired terminal maturation and reduced numbers of erythroid progenitors, likely at the expense of expanded megakaryopoiesis. RNA-sequencing revealed that both erythroid genes and megakaryocytic genes were altered by the Gata1s mutation. Epiproteomic histone modification analysis further revealed there was an accumulation of H3K27 methylation in the R3 (CD71hiTer119hi) erythroid progenitor population, which suggests that GATA1 has a link to the epigenetic machinery that is altered in Gata1s mutant cells. Despite a global increase in H3K27me3, critical Gata2 regulatory elements in Gata1s mutant erythroid progenitors were marked by substantially less H3K27me3 than in wild-type littermates. Given that overexpression of GATA2 has been reported to impair erythropoiesis, we investigated whether reducing the GATA2 levels would ameliorate the phenotype. Indeed, we observed that haploinsufficiency for Gata2 rescued the erythroid defects of Gata1s fetuses. Next, to comprehensively study the effect of absence of the GATA1 N-terminus genome-wide, we performed Cleavage Under Targets and Release Using Nuclease (CUT&RUN) with H3K27me3, GATA1 or GATA1s antibodies on wild-type versus Gata1s expressing fetal erythroid cells. Our data indicated that there is a substantial reduction in H3K27me3 along regulatory elements of the Runx1 gene at the late stage (R3) of fetal erythropoiesis in Gata1s mice. Along with an increase in Runx1 expression we observed strong downregulation of Klf1, a repressive target of RUNX1. Thus, failure of GATA1s to facilitate trimethylation of Runx1 and Gata2 regulatory elements appears to cause the defects in erythroid cell and megakaryocyte development. In parallel, we performed an in-depth analysis of the phenotype of adult Gata1s mice and discovered that they have reduced red cell counts, lower hemoglobin and hematocrit, increased extramedullary hematopoiesis and impaired stress erythropoiesis compared to control littermates. Although there were significantly more megakaryocyte erythrocyte progenitors (MEPs, Lin-c-Kit+Sca-1-CD34-FcgR-) in Gata1s mouse bone marrow, there were fewer pre-colony-forming unit erythroid cells (preCFU-E, Lin-c-Kit+Sca-1-CD41-FcgR-CD150hiCD105hi), likely at the expense of expanded megakaryocyte progenitors (MkP, Lin-c-Kit+Sca-1-CD41+CD150hi).Gata1s mice also developed an MDS-like disease with age. Together, our integrated genomic analysis of transcriptome, GATA1/GATA1s chromatin binding profile and chromatin signature reveal that, although Gata1s mice do not precisely model DBA, they provide novel insights into the role of the N-terminus of GATA1 in gene transcriptional regulation, lineage determination and red blood cell maturation. DisclosuresCrispino:Scholar Rock: Research Funding; Forma Therapeutics: Research Funding.

A High-Throughput Screening Approach to Identify Therapeutics for the Treatment of Diamond-Blackfan Anaemia

Diamond-Blackfan Anaemia (DBA) is a rare blood cell aplasia that presents clinically at approximately 2-3 months of age and its main characteristic is reduced erythroid precursors in the bone marrow, i.e. anemia. Mutations in different ribosomal protein (RP) genes have been associated with DBA, with mutations in RPS19 accounting for 20-25% of all cases. It has been proposed that RPS19 deficiency causes perturbations in ribosome biogenesis, thus activation of the p53-dependent Nucleolar Surveillance Pathway (NSP). In this context free RPs (predominantly L5 and L11) in a complex with 5S rRNA sequester the E3 ubiquitin ligase murine double minute 2 (MDM2), leading to the accumulation of p53 and subsequent activation of its transcriptional targets mediating cell cycle arrest or apoptosis. In DBA, one of the molecular mechanisms impairing the proliferation and thus reducing the number of erythroid progenitors that can progress to mature red blood cells is an elevation of p53 protein mediating activation of the NSP.In order to identify potential therapeutics that could be repurposed to prevent the activation of NSP in DBA patients, we have screened compound libraries of clinically approved therapeutics to identify pathways implicated in the p53-dependent NSP due to RPS19 deficiency. We quantitated both cell number and the level of p53 expression, identifying compounds that can result in low and high expression of p53, the latter for potential use in cancer therapy. Using an RPS19 depleted A549 cell line as a model system, the screen successfully identified different therapeutic groups. In the DBA context, we were most interested in the compounds that reduced p53 and had no negative effect on cell number. A selection of 22 molecules were re-evaluated in vitro, again using RPS19 depleted A549 cells, through the quantification of p53 protein expression and densitometry analysis. From this, 10candidates were evaluated ex vivofor their effects on proliferation using bone marrow obtained from an inducible Rps19 knockdown (DBA) mouse model.While we are currently testing a number of compounds in vivo using the Rps19 DBA mouse model (as described), one of the compounds tested thus far has demonstrated a partial rescue of the cKit+ population, no changes in erythroid precursors but interestingly a reversal of the defect in the Granulocyte-Monocyte Progenitor (GMP) population. Impairment in lineage progression in the GMP compartment has also been reported to present in bone marrow failure Shwachman-Diamond Syndrome. We are currently evaluating the mechanism by which this drug is rescuing the c-Kit+ and GMP populations in these mice.In summary, our high-throughput screening approach and follow up studies have identified a suite of novel therapies that may be beneficial for repurposing for the treatment of bone marrow failure by increasing hematopoietic progenitor cells. We plan to evaluate this, and potentially other therapies, in a clinical trial with DBA patients. DisclosuresFlygare:LU Holding: Patents & Royalties: Patent.