Low oxygen concentration as a general physiologic regulator of erythropoiesis beyond the EPO-related downstream tuning and a tool for the optimization of red blood cell production ex vivo

SARS-CoV-2 Impact on Red Blood Cell Morphology

Severe COVID-19 alters the biochemical and morphological characteristics of blood cells in a wide variety of ways. To date, however, the vast majority of research has been devoted to the study of leukocytes, while erythrocyte morphological changes have received significantly less attention. The aim of this research was to identify erythrocyte morphology abnormalities that occur in COVID-19, compare the number of different poikilocyte types, and measure erythrocyte sizes to provide data on size dispersion. Red blood cells obtained from 6 control donors (800-2200 cells per donor) and 5 COVID-19 patients (800-1900 cells per patient) were examined using low-voltage scanning electron microscopy. We did not discover any forms of erythrocyte morphology abnormalities that would be specific to COVID-19. Among COVID-19 patients, we observed an increase in the number of acanthocytes (p = 0.01) and a decrease in the number of spherocytes (p = 0.03). In addition, our research demonstrates that COVID-19 causes an increase in the median (p = 0.004) and interquartile range (p = 0.009) when assessing erythrocyte size. The limitation of our study is a small number of participants.

Expansion and differentiation of ex vivo cultured erythroblasts in scalable stirred bioreactors

Transfusion of donor-derived red blood cells (RBCs) is the most common form of cell therapy. Production of transfusion-ready cultured RBCs (cRBCs) is a promising replacement for the current, fully donor-dependent therapy. A single transfusion unit, however, contains 2 × 10¹² RBC, which requires large scale production. Here, we report on the scale-up of cRBC production from static cultures of erythroblasts to 3 L stirred tank bioreactors, and identify the effect of operating conditions on the efficiency of the process. Oxygen requirement of proliferating erythroblasts (0.55-2.01 pg/cell/h) required sparging of air to maintain the dissolved oxygen concentration at the tested setpoint (2.88 mg O₂ /L). Erythroblasts could be cultured at dissolved oxygen concentrations as low as 0.7 O₂ mg/ml without negative impact on proliferation, viability or differentiation dynamics. Stirring speeds of up to 600 rpm supported erythroblast proliferation, while 1800 rpm led to a transient halt in growth and accelerated differentiation followed by a recovery after 5 days of culture. Erythroblasts differentiated in bioreactors, with final enucleation levels and hemoglobin content similar to parallel cultures under static conditions.

Regulatory Crosstalk between Physiological Low O2 Concentration and Notch Pathway in Early Erythropoiesis

Physiological low oxygen (O2) concentration (<5%) favors erythroid development ex vivo. It is known that low O2 concentration, via the stabilization of hypoxia-induced transcription factors (HIFs), intervenes with Notch signaling in the control of cell fate. In addition, Notch activation is implicated in the regulation of erythroid differentiation. We test here if the favorable effects of a physiological O2 concentration (3%) on the amplification of erythroid progenitors implies a cooperation between HIFs and the Notch pathway. To this end, we utilized a model of early erythropoiesis ex vivo generated from cord blood CD34+ cells transduced with shHIF1α and shHIF2α at 3% O2 and 20% O2 in the presence or absence of the Notch pathway inhibitor. We observed that Notch signalization was activated by Notch2R−Jagged1 ligand interaction among progenitors. The inhibition of the Notch pathway provoked a modest reduction in erythroid cell expansion and promoted erythroid differentiation. ShHIF1α and particularly shHIF2α strongly impaired erythroid progenitors’ amplification and differentiation. Additionally, HIF/NOTCH signaling intersects at the level of multipotent progenitor erythroid commitment and amplification of BFU-E. In that, both HIFs contribute to the expression of Notch2R and Notch target gene HES1. Our study shows that HIF, particularly HIF2, has a determining role in the early erythroid development program, which includes Notch signaling.

Effects of miR‑210‑3p on the erythroid differentiation of K562 cells under hypoxia

GATA binding protein 1 (GATA-1) is one of the most important hematopoietic transcription factors in the production of blood cells, such as platelets, eosinophils, mast cells and erythrocytes. GATA-1 regulates the participation of microRNA (miRNAs/miRs) in erythroid differentiation under normoxia. However, GATA-1 expression and the regulation of miR-210-3p in the context of erythroid differentiation under hypoxia remain unknown. The present study examined the expression levels of GATA-1 and miR-210-3p in the model of erythroid differentiation in K562 cells under hypoxia, and determined the effects of GATA-1, miR-210-3p and SMAD2 on erythroid differentiation through lentivirus transfection experiments. The present study detected increased GATA-1 expression under hypoxia. Moreover, miR-210-3p was identified as a positive regulator of erythroid differentiation, which was upregulated both during erythroid differentiation and in GATA-1 overexpression experiments under hypoxia. Importantly, in the K562 cell model of erythroid differentiation under hypoxia, miR-210-3p was upregulated in a GATA-1-dependent manner. Using a double luciferase reporter assay, miR-210-3p was identified as a downstream target of GATA-1-mediated regulation of erythropoiesis. Gain- or loss-of-function analysis of miR-210-3p identified its importance in erythroid differentiation. Furthermore, it was found that SMAD2 may be a downstream target gene for miR-210-3p. Bioinformatics predictions suggested that SMAD2 mediated miR-210-3p-induced regulation of erythroid differentiation. Collectively, the present study provides novel insights into the miRNA regulation of erythroid differentiation.

Whole Blood miR-210, miR-122, miR-223 Expression Levels and Their Relationship With Iron Status Parameters and Hypercoagulability Indices in Children With Iron Deficiency Anemia

MicroRNAs have the potential to regulate systemic and cellular iron homeostasis at multiple points. In iron deficiency anemia (IDA), hypoxia, platelet reactivity, and potentially microRNAs play a role in the development of hypercoagulability. A total of 57 children diagnosed with IDA between October 2016 and October 2017 and 48 healthy children were included in this cross-sectional study. Blood count parameters, serum iron, transferrin saturation, ferritin level, maximum clot firmness (MCF), and clot formation time index, which are indicators of hypercoagulability in rotational thromboelastometry test, of the IDA and control groups obtained in our previous study were recorded. miR-210, miR-122, and miR-223 levels were analyzed. There was no difference in the miR-210, miR-122, and miR-223 levels between the IDA and control groups. Patients with hemoglobin (Hb) <8 g/dL had higher miR-210 levels than patients with Hb>8 g/dL (P<0.05). There was a negative correlation between miR-210 and Hb and ferritin levels, a positive correlation between miR-122 and ferritin levels, and a negative correlation between miR-223 and MCF index. In IDA, there is a close relationship between the severity of anemia and miR-210, and miR-210 expression is slightly increased in those with severe anemia. miR-210 and miR-122 collectively play a role in maintaining the iron balance. The correlation between miR-223, a platelet function regulator, and the MCF index, suggested that miR-223 has a role in the development of hypercoagulability in IDA.

Hypoxia promotes erythroid differentiation through the development of progenitors and proerythroblasts

Oxygen is a critical noncellular component of the bone marrow microenvironment that plays an important role in the development of hematopoietic cell lineages. In this study, we investigated the impact of low oxygen (hypoxia) on ex vivo myeloerythroid differentiation of human cord blood-derived CD34⁺ hematopoietic stem and progenitor cells. We characterized the culture conditions to demonstrate that low oxygen inhibits cell proliferation and causes a metabolic shift in the stem and progenitor populations. We found that hypoxia promotes erythroid differentiation by supporting the development of progenitor populations. Hypoxia also increases the megakaryoerythroid potential of the common myeloid progenitors and the erythroid potential of megakaryoerythroid progenitors and significantly accelerates maturation of erythroid cells. Specifically, we determined that hypoxia promotes the loss of CD71 and the appearance of the erythroid markers CD235a and CD239. Further, evaluation of erythroid populations revealed a hypoxia-induced increase in proerythroblasts and in enucleation of CD235a⁺ cells. These results reveal the extensive role of hypoxia at multiple steps during erythroid development. Overall, our work establishes a valuable model for further investigations into the relationship between erythroid progenitors and/or erythroblast populations and their hypoxic microenvironment.

Discarded plasma obtained after cord blood volume reduction as an alternative for fetal calf serum in mesenchymal stromal cells cultures

BACKGROUND

Utilization of the fetal calf serum (FCS) carries a potential health risk and raises growing economic and ethical problems. Umbilical cord blood volume reduction, required for banking, provides clinical-grade umbilical cord blood plasma (UCBP) discarded as a waste. The aim of this study was to test whether serum derived from UCBP could replace FCS for the amplification of mesenchymal stromal cells (MSCs).

STUDY DESIGN AND METHODS

To this end, the amplification of the MSCs and mesenchymal progenitors was estimated in the presence of serum derived from UCBP and its cytokine content was determined by cytometric bead array and enzyme-linked immunosorbent assay techniques. As a comparison, other sources of clinical-grade human serum were tested in parallel: serum derived from solvent/detergent-treated fresh-frozen plasma (S/D-FFP) and from platelet (PLT)-rich and PLT-poor umbilical plasma.

RESULTS

Serum derived from UCBP-supplemented culture sustains identical amplification of MSCs and their progenitors as in the case of FCS addition. Furthermore, the assays reveal the presence in the serum derived from UCBP of cytokines influencing the properties of MSCs (basic fibroblast growth factor, transforming growth factor-β, vascular endothelial growth factor, and interleukin-8) or involved in the development of the myeloid lineage (thrombopoietin, erythropoietin, granulocyte-colony-stimulating factor, and granulocyte-macrophage-colony-stimulating factor). Also, our study indicates important differences between neonatal and adult-derived serum. Poor cytokine content in the S/D-FFP makes a less efficient replacement of FCS comparing to other human blood-derived supplements.

CONCLUSION

Our work shows that the discarded human cord blood plasma from volume reduction is an easily obtainable and greatly available, xeno-free source of serum that is a highly efficient replacement of FCS in sustaining MSC growth.

The effect of hypoxia on the proliferation capacity of dermal papilla cell by regulating lactate dehydrogenase

Hypoxia is of great significance for stem cells to maintain the proliferation and differentiation capacity. As a specialized mesenchymal component of the hair follicle (HF), the dermal papilla cell (DPC) not only regulates HF cycle, but also plays a pivotal role in differentiating hair follicle stem cell(HFSC) into HF. However, whether hypoxia could affect DPCs on proliferation or metabolism remains unclear. In our study, DPCs were cultured in normoxia (20%O₂) or hypoxia (5%O₂). Cell viability assays were performed, and lactate dehydrogenase (LDH) activity and lactate level in DPCs were detected. After that, LDH was overexpressed or knocked down in DPCs; then, the expression of protein markers (ALP, Ki‐67) was assessed by Western blotting, and cell proliferation was also detected after overexpression or knockdown of LDH. Hypoxia did show positive effect on proliferation of DPCs. The LDH activity of DPCs cultured under hypoxic condition was significantly higher than that of cultured under normoxic condition. Overexpression of LDH significantly up‐regulates the expression of ALP and Ki‐67 compared with knockdown and negative control. Cell proliferation was also promoted in DPCs with elevated LDH. Our findings showed that the proliferation activity of DPCs could be stimulated under hypoxia. Meanwhile, LDH plays an important role in maintaining the activity of DPCs in hypoxic condition.

Humanized Culture Medium for Clinical-Grade Generation of Erythroid Cells from Umbilical Cord Blood CD34+ Cells

Purpose: Transfusion of red blood cells (RBCs) is a supportive and common treatment in surgical care, trauma, and anemia. However, in vivo production of RBC seems to be a suitable alternative for blood transfusions due to the limitation of blood resources, the possibility of disease transmission, immune reactions, and the presence of rare blood groups. Cell cultures require serum-free or culture media supplemented with highly expensive animal serum, which can transmit xenoviruses. Platelet lysate (PL) can be considered as a suitable alternative containing a high level of growth factors and a low production cost.

Methods: Three-step culture media supplemented with PL or fetal bovine serum (FBS) were used for proliferation and differentiation of CD34⁺ umbilical cord blood stem cells to erythrocytes in co-culture with bone marrow mesenchymal stem cells (BM-MSCs). The cells were cultivated for 15 days and cell proliferation and expansion were assessed using cell counts at different days. Erythroid differentiation genes, CD71 and glycophorin A expression levels were evaluated.

Results: Maximum hematopoietic stem cells (HSCs) proliferation was observed on day 15 in PL-containing medium (99±17×10³-fold). Gene expression and surface markers showed higher differentiation of cells in PL-containing medium.

Conclusion: The results of this study indicate that PL can enhance erythroid proliferation and differentiation of CD34⁺ HSCs. PL can also be used as a proper alternative for FBS in the culture medium and HSCs differentiation.

PSC-RED and MNC-RED: Albumin-free and low-transferrin robust erythroid differentiation protocols to produce human enucleated red blood cells

Many methods have been developed to produce cultured red blood cells (cRBCs) in vitro but translational applications have been hampered by high costs of production and by low rates of enucleation. We have developed R6 and IMIT, two chemically defined culture media and combined them into robust erythroid differentiation (RED) protocols to differentiate induced-pluripotent stem cells (iPSCs) and peripheral blood mononuclear cells (MNCs) into enucleated erythroid cells. The RED protocols do not require any albumin or animal components and require ten- to twentyfold less transferrin (Tf) than previously, because iron is provided to the differentiating erythroblasts by small amounts of recombinant Tf supplemented with FeIII-EDTA, an iron chelator that allows Tf recycling to take place in cell culture. Importantly, cRBCs produced by iPSC differentiation using the long PSC-RED protocol enucleate at much higher rates than with previous protocols, eliminating one of the impediments to the use of these cells to produce clinically useful cRBCs. The absence of albumin, the reduced amounts of Tf, the improved reproducibility associated with the elimination of all animal components, and the high yield on the RED protocols decrease the cost of production of cultured red blood cells. RED protocols should therefore help to make translational applications of cultured RBCs more economically realistic.

ATP produced by anaerobic glycolysis is essential for enucleation of human erythroblasts

More than 2million human erythroblasts extrude their nuclei every second in bone marrow under hypoxic conditions (<7% O₂). Enucleation requires specific signal transduction pathways and the local assembly of contractile actomyosin rings. However, the energy source driving these events has not yet been identified. We examined whether different O₂ environments (hypoxic [5% O₂] and normoxic [21% O₂] conditions) affected human CD34⁺ cell erythroblast differentiation. We also investigated the regulatory mechanisms underlying energy production in erythroblasts during terminal differentiation under 5% or 21% O₂ conditions. The results obtained revealed that the enucleation ratio and intracellular levels of adenosine triphosphate (ATP), lactate dehydrogenase (LDH) M₃H, and hypoxia-inducible factor 1α in erythroblasts during terminal differentiation were higher under the 5% O₂ condition than under the 21% O₂ condition. We also found that the enzymatic inhibition of glyceraldehyde 3-phosphate dehydrogenase and LDH, key enzymes in anaerobic glycolysis, blocked the proliferation of colony-forming units-erythroid and enucleation of erythroblasts, and also reduced ATP levels in erythroblasts under both hypoxic and normoxic conditions. Under both conditions, phosphorylation of the Ser232, Ser293, and Ser300 residues in pyruvate dehydrogenase (inactive state of the enzyme) in erythroblasts was involved in regulating the pathway governing energy metabolism during erythroid terminal differentiation. This reaction may be mediated by pyruvate dehydrogenase kinase (PDK) 4, the major PDK isozyme expressed in erythroblasts undergoing enucleation. Collectively, these results suggest that ATP produced by anaerobic glycolysis is the main source of energy for human erythroblast enucleation in the hypoxic bone marrow environment.

Generation of clinical-grade red blood cells from human umbilical cord blood mononuclear cells

A xeno-free method for ex vivo generation of red blood cells (RBCs) is attempted in order to replicate for large-scale production and clinical applications. An efficient milieu was formulated using injectable drugs substituting the animal-derived components in the culture medium. Unfractionated mononuclear cells isolated from human umbilical cord blood were used hypothesizing that the heterogeneous cell population could effectively contribute to erythroid cell generation. The strategy adopted includes a combination of erythropoietin and other injectable drugs under low oxygen levels, which resulted in an increase in the number of mature RBCs produced in vitro. The novelty in this study is the addition of supplements to the medium in a stage-specific manner for the differentiation of unfractionated umbilical cord blood mononuclear cells (MNCs) into erythropoietic lineage. The erythropoietic lineage was well established by day 21, wherein the mean cell count of RBCs was found to be 21.36 ± 0.9 × 10⁸ and further confirmed by an upregulated expression of CD235a⁺ specific to RBCs. The rationale was to have a simple method to produce erythroid cells from umbilical cord blood isolates in vitro by mitigating the effects of multiple erythroid-activating agents and batch to batch variability.

Surface-enhanced Raman scattering for rapid hematopoietic stem cell differentiation analysis

Raman-spectroscopy-based methods, such as surface-enhanced Raman spectroscopy, are a well-evolved method to molecular fingerprint cell types. Here we demonstrate that surface-enhanced Raman spectroscopy can enable us to distinguish cell development stages of bone marrow hematopoietic stem cells towards red blood cells through the identification of specific surface-enhanced Raman spectroscopy biomarkers. The approach taken here is to allow cells to take in gold nanoparticles as Raman enhancement platforms for kinetic structural observations presented here through the view of the multidimensional parameter contribution, thereby enabling profiling of bone marrow hematopoietic stem cells acquired from proliferation (stage one), differentiation (stage two), and mature red blood cells (stage three).

3D models of the hematopoietic stem cell niche under steady-state and active conditions

Hematopoietic stem cells (HSCs) in the bone marrow are able to differentiate into all types of blood cells and supply the organism each day with billions of fresh cells. They are applied to cure hematological diseases such as leukemia. The clinical need for HSCs is high and there is a demand for being able to control and multiply HSCs in vitro. The hematopoietic system is highly proliferative and thus sensitive to anti-proliferative drugs such as chemotherapeutics. For many of these drugs suppression of the hematopoietic system is the dose-limiting toxicity. Therefore, biomimetic 3D models of the HSC niche that allow to control HSC behavior in vitro and to test drugs in a human setting are relevant for the clinics and pharmacology. Here, we describe a perfused 3D bone marrow analog that allows mimicking the HSC niche under steady-state and activated conditions that favor either HSC maintenance or differentiation, respectively, and allows for drug testing.

Large-Scale Ex Vivo Generation of Human Red Blood Cells from Cord Blood CD34+ Cells

The ex vivo generation of human red blood cells on a large scale from hematopoietic stem and progenitor cells has been considered as a potential method to overcome blood supply shortages. Here, we report that functional human erythrocytes can be efficiently produced from cord blood (CB) CD34⁺ cells using a bottle turning device culture system. Safety and efficiency studies were performed in murine and nonhuman primate (NHP) models. With the selected optimized culture conditions, one human CB CD34⁺ cell could be induced ex vivo to produce up to 200 million erythrocytes with a purity of 90.1% ± 6.2% and 50% ± 5.7% (mean ± SD) for CD235a⁺ cells and enucleated cells, respectively. The yield of erythrocytes from one CB unit (5 million CD34⁺ cells) could be, in theory, equivalent to 500 blood transfusion units in clinical application. Moreover, induced human erythrocytes had normal hemoglobin content and could continue to undergo terminal maturation in the murine xenotransplantation model. In NHP model, xenotransplantation of induced human erythrocytes enhanced hematological recovery and ameliorated the hypoxia situation in the primates with hemorrhagic anemia. These findings suggested that the ex vivo-generated erythrocytes could be an alternative blood source for traditional transfusion products in the clinic. Stem Cells Translational Medicine 2017;6:1698-1709.

Stem cell evolutionary paradigm and cell engineering

Studying hematopoietic and mesenchymal stem cells for almost three decades revealed some similarities between the stem cell entity and the single-celled eukaryotes exhibiting the anaerobic/facultative aerobic metabolic features. A careful analysis of nowadays knowledge concerning the early eukaryotic evolution allowed us to reveal some analogies between stem cells in the metazoan tissues and the single-celled eukaryotes which existed during the first phase of eukaryotes evolution in mid-Proterozoic era. In fact, it is possible to trace the principle of the self-renewal back to the first eukaryotic common ancestor, the first undifferentiated nucleated cell possessing the primitive, mostly anaerobically-respiring mitochondria and a capacity to reproduction by a simple cell division "à l'identique". Similarly, the diversification of these single-cell eukaryotes and acquiring of complex life cycle allowed/conditioned by the increase of O₂ in atmosphere (and consequently in the water environment) represents a prototype for the phenomenon of commitment/differentiation. This point of view allowed to predict the ex-vivo behavior of stem cells with respect to the O₂ availability and metabolic profile which enabled to conceive the successful protocols of stem cell expansion and ex vivo conditioning based on "respecting" this relationship between the anaerobiosis and stemness. In this review, the basic elements of this paradigm and a possible application in cell engineering were discussed.

Diverse of Erythropoiesis Responding to Hypoxia and Low Environmental Temperature in Vertebrates

Erythrocytes are responsible for transporting oxygen to tissue and are essential for the survival of almost all vertebrate animals. Circulating erythrocyte counts are tightly regulated and respond to erythrocyte mass and oxygen tension. Since the discovery of erythropoietin, the erythropoietic responses to environment and tissue oxygen tension have been investigated in mice and human. Moreover, it has recently become increasingly clear that various environmental stresses could induce the erythropoiesis via various modulating systems, while all vertebrates live in various environments and habitually adapt to environmental stress. Therefore, it is considered that investigations of erythropoiesis in vertebrates provide a lead to the various erythropoietic responses to environmental stress. This paper comparatively introduces the present understanding of erythropoiesis in vertebrates. Indeed, there is a wide range of variations in vertebrates' erythropoiesis. This paper also focused on erythropoietic responses to environmental stress, hypoxia, and lowered temperature in vertebrates.

Measuring dissolved oxygen to track erythroid differentiation of hematopoietic progenitor cells in culture

As stem cell technologies move from the developmental to the commercial stage strategies must be developed to monitor culture operations. These will ensure consistency of differentiation programs and maintenance of optimum cell viability during production runs. Due to the sensitivity of stem cells to their environment, and their variability in response to external stimuli, accurate monitoring of in vitro conditions will be crucial for effective large-scale culturing of therapeutic stem cells. Here we describe a simple method to monitor the expansion and maturation of adult human haematopoietic stem/progenitor cells into red blood cells in vitro by measuring the oxygen consumption rate of cultures. Cell cultures followed a characteristic pattern of oxygen consumption that is reflective of in vivo erythroid maturation. This method could be easily developed as an online system to map erythroid differentiation and maturation of cultured cells as effectively as the more time consuming process of flow cytometric analysis of surface marker expression patterns.

MerTK-mediated engulfment of pyrenocytes by central macrophages in erythroblastic islands

An in vitro system for the engulfment of pyrenocytes was established using erythroblastic islands. MerTK, a receptor kinase, was essential for the engulfment of pyrenocytes by the central macrophages at erythroblastic islands.

Erythropoietic potential of CD34+ hematopoietic stem cells from human cord blood and G-CSF-mobilized peripheral blood

Red blood cell (RBC) supply for transfusion has been severely constrained by the limited availability of donor blood and the emergence of infection and contamination issues. Alternatively, hematopoietic stem cells (HSCs) from human organs have been increasingly considered as safe and effective blood source. Several methods have been studied to obtain mature RBCs from CD34+ hematopoietic stem cells via in vitro culture. Among them, human cord blood (CB) and granulocyte colony-stimulating factor-mobilized adult peripheral blood (mPB) are common adult stem cells used for allogeneic transplantation. Our present study focuses on comparing CB- and mPB-derived stem cells in differentiation from CD34+ cells into mature RBCs. By using CD34+ cells from cord blood and G-CSF mobilized peripheral blood, we showed in vitro RBC generation of artificial red blood cells. Our results demonstrate that CB- and mPB-derived CD34+ hematopoietic stem cells have similar characteristics when cultured under the same conditions, but differ considerably with respect to expression levels of various genes and hemoglobin development. This study is the first to compare the characteristics of CB- and mPB-derived erythrocytes. The results support the idea that CB and mPB, despite some similarities, possess different erythropoietic potentials in in vitro culture systems.

Low oxygen atmosphere facilitates proliferation and maintains undifferentiated state of umbilical cord mesenchymal stem cells in an hypoxia inducible factor-dependent manner

BACKGROUND AIMS

As we approach the era of mesenchymal stem cell (MSC) application in the medical clinic, the standarization of their culture conditions are of the particular importance. We re-evaluated the influences of oxygens concentration on proliferation, stemness and differentiation of human umbilical cord Wharton Jelly-derived MSCs (WJ-MSCs).

METHODS

Primary cultures growing in 21% oxygen were either transferred into 5% O2 or continued to grow under standard 21% oxygen conditions. Cell expansion was estimated by WST1/enzyme-linked immunosorbent assay or cell counting. After 2 or 4 weeks of culture, cell phenotypes were evaluated using microscopic, immunocytochemical, fluorescence-activated cell-sorting and molecular methods. Genes and proteins typical of mesenchymal cells, committed neural cells or more primitive stem/progenitors (Oct4A, Nanog, Rex1, Sox2) and hypoxia inducible factor (HIF)-1α-3α were evaluated.

RESULTS

Lowering O2 concentration from 21% to the physiologically relevant 5% level substantially affected cell characteristics, with induction of stemness-related-transcription-factor and stimulation of cell proliferative capacity, with increased colony-forming unit fibroblasts (CFU-F) centers exerting OCT4A, NANOG and HIF-1α and HIF-2α immunoreactivity. Moreover, the spontaneous and time-dependent ability of WJ-MSCs to differentiate into neural lineage under 21% O2 culture was blocked in the reduced oxygen condition. Importantly, treatment with trichostatin A (TSA, a histone deacetylase inhibitor) suppressed HIF-1α and HIF-2α expression, in addition to blockading the cellular effects of reduced oxygen concentration.

CONCLUSIONS

A physiologically relevant microenvironment of 5% O2 rejuvenates WJ-MSC culture toward less-differentiated, more primitive and faster-growing phenotypes with involvement of HIF-1α and HIF-2α-mediated and TSA-sensitive chromatin modification mechanisms. These observations add to the understanding of MSC responses to defined culture conditions, which is the most critical issue for adult stem cells translational applications.

The effect of hypoxia on the stemness and differentiation capacity of PDLC and DPC

Introduction. Stem cells are regularly cultured under normoxic conditions. However, the physiological oxygen tension in the stem cell niche is known to be as low as 1-2% oxygen, suggesting that hypoxia has a distinct impact on stem cell maintenance. Periodontal ligament cells (PDLCs) and dental pulp cells (DPCs) are attractive candidates in dental tissue regeneration. It is of great interest to know whether hypoxia plays a role in maintaining the stemness and differentiation capacity of PDLCs and DPCs. Methods. PDLCs and DPCs were cultured either in normoxia (20% O₂) or hypoxia (2% O₂). Cell viability assays were performed and the expressions of pluripotency markers (Oct-4, Sox2, and c-Myc) were detected by qRT-PCR and western blotting. Mineralization, glycosaminoglycan (GAG) deposition, and lipid droplets formation were assessed by Alizarin red S, Safranin O, and Oil red O staining, respectively. Results. Hypoxia did not show negative effects on the proliferation of PDLCs and DPCs. The pluripotency markers and differentiation potentials of PDLCs and DPCs significantly increased in response to hypoxic environment. Conclusions. Our findings suggest that hypoxia plays an important role in maintaining the stemness and differentiation capacity of PDLCs and DPCs.

Large-scale production of red blood cells from stem cells: what are the technical challenges ahead?

Blood-transfusion centers regularly face the challenge of donor blood shortages, especially for rare blood groups. The possibility of producing universal red blood cells from stem cells industrially has become a possible alternative since the successful injection of blood generated in vitro into a human being in 2011. Although there remains many biological and regulatory issues concerning the efficacy and safety of this new product, the major challenge today for future clinical applications is switching from the current limited 2-dimensional production techniques to large-scale 3-dimensional bioreactors. In addition to requiring technological breakthroughs, the whole process also has to become at least five-fold more cost-efficient to match the current prices of high-quality blood products. The current review sums up the main biological advances of the past decade, outlines the key biotechnological challenges for the large-scale cost-effective production of red blood cells, proposes solutions based on strategies used in the bioindustry and presents the state-of-the-art of large-scale blood production.

Enhanced erythroid cell differentiation in hypoxic condition is in part contributed by miR-210

Erythropoiesis, a process of erythroid production, is controlled by several factors including oxygen level. In this study, the effect of oxygen tension on erythropoiesis was investigated in K562 erythroleukemic cell line and erythroid progenitor cells derived from normal and β-thalassemia/hemoglobin (Hb) E individuals. The enhanced erythroid differentiation specific markers including increased levels of α-, β- and γ-globin gene expressions, numbers of HbF positive cells and the presence of glycophorin A surface marker were observed during cell culture under hypoxic atmosphere. The result also showed that miR-210, one of the hypoxia-induced miRNAs, was up-regulated in K562 and β-thalassemia/HbE progenitor cells cultured under hypoxic condition. Inhibition of miR-210 expression leads to reduction of the globin gene expression and delayed maturation in K562 and erythroid progenitor cells. This indicated that miR-210 contributes to hypoxia-induced erythroid differentiation in both K562 cells and β-thalassemia/HbE erythroid progenitor cells.

Ex vivo expansion of cord blood haematopoietic stem/progenitor cells under physiological oxygen tensions: clear-cut effects on cell proliferation, differentiation and metabolism

Physiologically low O(2) tensions are believed to regulate haematopoietic stem cell (HSC) functions in the bone marrow (BM; 0-5%). In turn, placenta and umbilical cord are characterized by slightly higher physiological O(2) tensions (3-10%). We hypothesized that O(2) concentrations within this range may be exploited to augment the ex vivo expansion/maintenance of HSCs from umbilical cord (placental) blood (UCB). The expansion of UCB CD34(+) -enriched cells was studied in co-culture with BM mesenchymal stem/stromal cells (MSCs) under 2%, 5%, 10% and 21% O(2). 2% O(2) resulted in a significantly lower CD34(+) cell expansion (25-fold vs 60-, 64- and 92-fold at day 10 for 5%, 21%, 10% O(2), respectively). In turn, 10% O(2) promoted the highest CD34(+) CD90(+) cell expansion, reaching 22 ± 5.4- vs 5.6 ± 2.4- and 5.7 ± 2.0-fold for 2%, 5% and 21% O(2), respectively, after 14 days. Similar differentiation patterns were observed under different O(2) tensions, being primarily shifted towards the neutrophil lineage. Cell division kinetics revealed a higher proliferative status of cells cultured under 10% and 21% vs 2% O(2). Expectedly, higher specific glucose consumption and lactate production rates were determined at 2% O(2) when compared to higher O(2) concentrations (5-21%). Overall, these results suggest that physiological oxygen tensions, in particular 10% O(2), can maximize the ex vivo expansion of UCB stem/progenitor cells in co-culture with BM MSCs. Importantly, these studies highlight the importance of exploiting knowledge of the intricate microenvironment of the haematopoietic niche towards the definition of efficient and controlled ex vivo culture systems capable of generating large HSCs numbers for clinical applications.

Biological validation of bio-engineered red blood cell productions

The generation in vitro of cultured red blood cells (cRBC) could become an alternative to classical transfusion products. However, even when derived from healthy donors, the cRBC generated in vitro from hematopoietic stem cells may display alterations resulting from a poor controlled production process. In this context, we attempted to monitor the quality of the transfusion products arising from new biotechnologies. For that purpose, we developed an in vitro erythrophagocytosis (EP) test with the murine fibroblast cell line MS-5 and human macrophages (reference method). We evaluated 38 batches of cRBC, at the stage of reticulocyte, generated from CD34(+) cells isolated from placental blood or by leukapheresis. We showed that (i) the EP test performed with the MS-5 cell line was sensitive and can replace human macrophages for the evaluation of cultured cells. (ii) The EP tests revealed disparities among the batches of cRBC. (iii) The viability of the cells (determined by calcein-AM test), the expression of CD47 (antiphagocytosis receptor) and the externalization of phosphatidylserine (PS, marker of phagocytosis) were not critical parameters for the validation of the cRBC. (iv) Conversely, the cell deformability determined by ektacytometry was inversely correlated with the intensity of the phagocytic index. Assuming that the culture conditions directly influence the quality of the cell products generated, optimization of the production mode could benefit from the erythrophagocytosis test.

Combination of low O(2) concentration and mesenchymal stromal cells during culture of cord blood CD34(+) cells improves the maintenance and proliferative capacity of hematopoietic stem cells

The physiological approach suggests that an environment associating the mesenchymal stromal cells (MSC) and low O(2) concentration would be most favorable for the maintenance of hematopoietic stem cells (HSCs) in course of ex vivo expansion of hematopoietic grafts. To test this hypothesis, we performed a co-culture of cord blood CD34(+) cells with or without MSC in presence of cytokines for 10 days at 20%, 5%, and 1.5% O(2) and assessed the impact on total cells, CD34(+) cells, committed progenitors (colony-forming cells-CFC) and stem cells activity (pre-CFC and Scid repopulating cells-SRC). Not surprisingly, the expansion of total cells, CD34(+) cells, and CFC was higher in co-culture and at 20% O(2) compared to simple culture and low O(2) concentrations, respectively. However, co-culture at low O(2) concentrations provided CD34(+) cell and CFC amplification similar to classical culture at 20% O(2) . Interestingly, low O(2) concentrations ensured a better pre-CFC and SRC preservation/expansion in co-culture. Indeed, SRC activity in co-culture at 1.5% O(2) was higher than in freshly isolated CD34(+) cells. Interleukin-6 production by MSC at physiologically low O(2) concentrations might be one of the factors mediating this effect. Our data demonstrate that association of co-culture and low O(2) concentration not only induces sufficient expansion of committed progenitors (with respect to the classical culture), but also ensures a better maintenance/expansion of hematopoietic stem cells (HSCs), pointing to the oxygenation as a physiological regulatory factor but also as a cell engineering tool.

Ex-vivo expansion of red blood cells: how real for transfusion in humans?

Blood transfusion is indispensable for modern medicine. In developed countries, the blood supply is adequate and safe but blood for alloimmunized patients is often unavailable. Concerns are increasing that donations may become inadequate in the future as the population ages prompting a search for alternative transfusion products. Improvements in culture conditions and proof-of-principle studies in animal models have suggested that ex-vivo expanded red cells may represent such a product. Compared to other cell therapies transfusion poses the unique challenge of requiring great cell doses (2.5×10(12) cells vs 10(7) cells). Although production of such cell numbers is theoretically possible, current technologies generate red cells in numbers sufficient only for safety studies. It is conceived that by the time these studies will be completed, technical barriers to mass cell production will have been eliminated making transfusion with ex-vivo generated red cells a reality.

Regulation of bone marrow hematopoietic stem cell is involved in high-altitude erythrocytosis

OBJECTIVE

Hypoxia at high altitudes can lead to increased production of red blood cells through the hormone erythropoietin (EPO). In this study, we observed how the EPO-unresponsive hematopoietic stem cell (HSC) compartment responds to high-altitude hypoxic environments and contributes to erythropoiesis.

MATERIALS AND METHODS

Using a mouse model at simulated high altitude, the bone marrow (BM) and spleen lineage marker(-)Sca-1(+)c-Kit(+) (LSK) HSC compartment were observed in detail. Normal LSK cells were then cultured under different conditions (varying EPO levels, oxygen concentrations, and BM supernatants) to investigate the causes of the HSC responses.

RESULTS

Hypoxic mice exhibited a marked expansion in BM and spleen LSK compartments, which were associated with enhanced proliferation. BM HSCs seemed to play a more important role in erythropoiesis at high altitude than spleen HSCs. There was also a lineage fate change of BM HSCs in hypoxic mice that was manifested in increased megakaryocyte-erythrocyte progenitors and periodically reduced granulocyte-macrophage progenitors in the BM. The LSK cells in hypoxic mice displayed upregulated erythroid-specific GATA-1 and downregulated granulocyte-macrophage-specific PU.1 messenger RNA expression, as well as the capacity to differentiate into more erythroid precursors after culture. BM culture supernatant from hypoxic mice (but not elevated EPO or varying O(2) tension) could induce expansion and erythroid-priority differentiation of the HSC population, a phenomenon partially caused by increasing interleukin-3 and interleukin-6 secretion in the BM.

CONCLUSIONS

The present study suggests a new EPO-independent HSC mechanism of high-altitude erythrocytosis.

Very low oxygen concentration (0.1%) reveals two FDCP-Mix cell subpopulations that differ by their cell cycling, differentiation and p27KIP1 expression

Oxygen (O(2)) concentrations in bone marrow vary from 4% in capillaries to <0.1% in subendosteum, in which hematopoietic stem cells reside in specific niches. Culture at low O(2) concentrations (3, 1 and 0.1%) influences hematopoietic stem and progenitor cells survival, proliferation and differentiation, depending on their level of differentiation. Culture of human CD34(+) cells at low O(2) concentrations (O(2) ≤3%) maintains stem cell engraftment potential better than at 20% O(2) (NOD/Scid xenograft model). In contrast, progenitors disappear from cultures at/or <1% O(2) concentrations. A very low O(2) concentration (0.1%) induces CD34(+) quiescence in G(0). The exploration of molecules and mechanisms involved in hematopoietic stem and progenitor cells' quiescence and differentiation related to low O(2) concentrations is unfeasible with primary CD34(+) cells. Therefore, we performed it using murine hematopoietic nonleukemic factor-dependent cell Paterson (FDCP)-Mix progenitor cell line. The culture of the FDCP-Mix line at 0.1% O(2) induced in parallel G(0) quiescence and granulo-monocytic differentiation of most cells, whereas a minority of undifferentiated self-renewing cells remained in active cell cycle. Hypoxia also induced hypophosphorylation of pRb and increased the expression of p27(KIP1), the two proteins that have a major role in the control of G(0) and G(1) to S-phase transition.

Cancer stem cells and angiogenesis

Most cancers contain tumor cells that display stem cell-like characteristics. How and when such cells appear in tumors are not clear, but may involve both stochastic as well as hierarchical events. Most likely, tumor cells that display stem cell-like characteristics can undergo asymmetric cell division giving rise to tumor cells that trigger angiogenic programs. As normal stem cells the cancer stem-like cells seem to adapt to hypoxic environments and will use metabolic pathways that involve increased conversion of glucose to pyruvate and lactate, and a concomitant decrease in mitochondrial metabolism and mitochondrial mass. The molecular pathways responsible for inducing glycolysis are now being explored. These pathways seem to mediate multiple metabolic functions in cancer stem-like cells, leading to a highly migratory and angiogenesis-independent phenotype. Future challenges will be to identify and validate molecular targets involved in anaerobic metabolic pathways active in cancer stem-like cells and to determine how these pathways differ from regulatory pathways involved in normal stem cell function.

The potential of human peripheral blood derived CD34+ cells for ex vivo red blood cell production

The potential of peripheral blood derived CD34+ cells for ex vivo erythropoiesis was investigated in a stroma-free culture system using a novel strategy of daily passaging. By expanding PB-derived CD34+ cells up to 1.5 x 10(6)-fold this method achieved expansion factors previously only reported for CD34+ cells derived from more potent stem cell sources such as cord blood, bone marrow and mobilized peripheral blood. Analysis of cell surface markers showed differentiation of immature CD34+ cells to populations with 80% CD71-/GpA+ cells and up to 45% enucleated cells, indicating a significant amount of terminal maturation. Cell crowdedness was found to have decisive effects on in vitro erythropoiesis. Cell density per surface area rather than cell concentration per media volume determined cell expansion during exponential growth where more crowded cells showed reduced overall expansion. In late stage erythropoiesis, however, when cells no longer proliferating, increased cell density was seen to enhance cell viability. These results indicate that peripheral blood derived haematopoietic stem cells can be an alternative to cells sourced from bone marrow, cord blood or leukapheresis in terms of expansion potential. This provides distinct advantages in terms of availability for studies of conditions for scale-up and maturation, and may have particular clinical applications in the future.