Generation of committed erythroid BFU-E and CFU-E progenitors does not require erythropoietin or the erythropoietin receptor

Hematopoietic growth factors: the scenario in zebrafish

Humoral regulation by ligand/receptor interactions is a fundamental feature of vertebrate hematopoiesis. Zebrafish are an established vertebrate animal model of hematopoiesis, sharing with mammals conserved genetic, molecular and cell biological regulatory mechanisms. This comprehensive review considers zebrafish hematopoiesis from the perspective of the hematopoietic growth factors (HGFs), their receptors and their actions. Zebrafish possess multiple HGFs: CSF1 (M-CSF) and CSF3 (G-CSF), kit ligand (KL, SCF), erythropoietin (EPO), thrombopoietin (THPO/TPO), and the interleukins IL6, IL11, and IL34. Some ligands and/or receptor components have been duplicated by various mechanisms including the teleost whole genome duplication, adding complexity to the ligand/receptor interactions possible, but also providing examples of several different outcomes of ligand and receptor subfunctionalization or neofunctionalization. CSF2 (GM-CSF), IL3 and IL5 and their receptors are absent from zebrafish. Overall the humoral regulation of hematopoiesis in zebrafish displays considerable similarity with mammals, which can be applied in biological and disease modelling research.

TET2 deficiency leads to stem cell factor-dependent clonal expansion of dysfunctional erythroid progenitors

Myelodysplastic syndromes (MDSs) are clonal hematopoietic stem cell disorders characterized by ineffective hematopoiesis. Anemia is the defining cytopenia of MDS patients, yet the molecular mechanisms for dyserythropoiesis in MDSs remain to be fully defined. Recent studies have revealed that heterozygous loss-of-function mutation of DNA dioxygenase TET2 is 1 of the most common mutations in MDSs and that TET2 deficiency disturbs erythroid differentiation. However, mechanistic insights into the role of TET2 on disordered erythropoiesis are not fully defined. Here, we show that TET2 deficiency leads initially to stem cell factor (SCF)-dependent hyperproliferation and impaired differentiation of human colony-forming unit-erythroid (CFU-E) cells, which were reversed by a c-Kit inhibitor. We further show that this was due to increased phosphorylation of c-Kit accompanied by decreased expression of phosphatase SHP-1, a negative regulator of c-Kit. At later stages, TET2 deficiency led to an accumulation of a progenitor population, which expressed surface markers characteristic of normal CFU-E cells but were functionally different. In contrast to normal CFU-E cells that require only erythropoietin (EPO) for proliferation, these abnormal progenitors required SCF and EPO and exhibited impaired differentiation. We termed this population of progenitors "marker CFU-E" cells. We further show that AXL expression was increased in marker CFU-E cells and that the increased AXL expression led to increased activation of AKT and ERK. Moreover, the altered proliferation and differentiation of marker CFU-E cells were partially rescued by an AXL inhibitor. Our findings document an important role for TET2 in erythropoiesis and have uncovered previously unknown mechanisms by which deficiency of TET2 contributes to ineffective erythropoiesis.

Studies of the effects and mechanisms of ginsenoside Re and Rk3 on myelosuppression induced by cyclophosphamide

Background

Ginsenoside Re (Re) is one of the major components of Panax ginseng Meyer. Ginsenoside Rk₃ (Rk₃) is a secondary metabolite of Re. The aim of this study was to investigate and compare the effects and underlying mechanisms of Re and Rk₃ on cyclophosphamide-induced myelosuppression.

Methods

The mice myelosuppression model was established by intraperitoneal (i.p.) injection of cyclophosphamide. Peripheral blood cells, bone marrow nucleated cells, and colony yield of hematopoietic progenitor cells in vitro were counted. The levels of erythropoietin, thrombopoietin, and granulocyte macrophage colony-stimulating factor in plasma were measured by enzyme-linked immunosorbent assay. Bone marrow cell cycle was performed by flow cytometry. The expression of apoptotic protein bcl-2, bax, and caspase-3 was detected by Western blotting.

Results

Both Re and Rk₃ could improve peripheral blood cells, bone marrow nucleated cell counts, thymus index, and spleen index. Furthermore, they could enhance the yield of colonies cultured in vitro and make the levels of granulocyte macrophage colony-stimulating factor, erythropoietin, and thrombopoietin normal, reduce the ratio of G₀/G₁ phase cells, and increase the proliferation index. Finally, Re and Rk₃ could upregulate the expression of bcl-2, whereas they could downregulate the expression of bax and caspase-3.

Conclusion

Re and Rk₃ could improve the hematopoietic function of myelosuppressed mice. The effect of Rk₃ was superior to that of Re at any dose. Regulating the levels of cytokines, promoting cells enter the normal cell cycle, regulating the balance of bcl-2/bax, and inhibiting the expression of caspase-3 may be the effects of Re and Rk₃ on myelosuppression.

Normal and pathological erythropoiesis in adults: from gene regulation to targeted treatment concepts

Pathological erythropoiesis with consequent anemia is a leading cause of symptomatic morbidity in internal medicine. The etiologies of anemia are complex and include reactive as well as neoplastic conditions. Clonal expansion of erythroid cells in the bone marrow may result in peripheral erythrocytosis and polycythemia but can also result in anemia when clonal cells are dysplastic and have a maturation arrest that leads to apoptosis and hinders migration, a constellation typically seen in the myelodysplastic syndromes. Rarely, clonal expansion of immature erythroid blasts results in a clinical picture resembling erythroid leukemia. Although several mechanisms underlying normal and abnormal erythropoiesis and the pathogenesis of related disorders have been deciphered in recent years, little is known about specific markers and targets through which prognosis and therapy could be improved in anemic or polycythemic patients. In order to discuss new markers, targets and novel therapeutic approaches in erythroid disorders and the related pathologies, a workshop was organized in Vienna in April 2017. The outcomes of this workshop are summarized in this review, which includes a discussion of new diagnostic and prognostic markers, the updated WHO classification, and an overview of new drugs used to stimulate or to interfere with erythropoiesis in various neoplastic and reactive conditions. The use and usefulness of established and novel erythropoiesis-stimulating agents for various indications, including myelodysplastic syndromes and other neoplasms, are also discussed.

Erythropoietin response to anaemia in heart failure

Background

Despite multiple factors correlating with the high prevalence of anaemia in heart failure, the prevailing mechanisms have yet to be established. The purpose of this study is to systematically review the literature and determine whether low circulating haemoglobin is primarily underlain by erythropoietin resistance or defective production in heart failure.

Design and methods

We conducted a systematic search of MEDLINE since its inception until May 2017 for articles reporting erythropoietin and haemoglobin concentrations in heart failure patients not treated with erythropoietin-stimulating agents. The primary outcome was the mean difference in observed/predicted (O/P) erythropoietin ratio between heart failure patients and normal reference values. Meta-regression analyses assessed the influence of potential moderating factors.

Results

Forty-one studies were included after systematic review, comprising a total of 3137 stable heart failure patients with mean age and left ventricular ejection fraction ranging from 52 years to 80 years and 21% to 59%. The O/P erythropoietin ratio was below reference values in 24 of 25 studies in anaemic heart failure patients ( n = 1094, range = 0.49–1.05), whereas only one out of 16 studies in non-anaemic heart failure patients presented a low O/P erythropoietin ratio ( n = 2043, range = 0.91–1.97). In studies comparing anaemic versus non-anaemic heart failure patients ( n = 1531), the mean O/P erythropoietin ratio was consistently reduced in anaemic heart failure patients (mean difference = –0.68, 95% confidence interval = −0.78, −0.57; p < 0.001). In meta-regression, the O/P erythropoietin ratio was negatively associated with age, female sex, left ventricular ejection fraction, inflammation and disease severity.

Conclusion

Anaemia in heart failure is overwhelmingly characterized by impaired erythropoietin production, which is exacerbated with age, female sex, left ventricular ejection fraction, inflammation and disease severity.

Global loss of leucine carboxyl methyltransferase-1 causes severe defects in fetal liver hematopoiesis

Leucine carboxyl methyltransferase-1 (LCMT-1) methylates the C-terminal leucine α-carboxyl group of the catalytic subunits of the protein phosphatase 2A (PP2A) subfamily of protein phosphatases, PP2Ac, PP4c, and PP6c. LCMT-1 differentially regulates the formation and function of a subset of the heterotrimeric complexes that PP2A and PP4 form with their regulatory subunits. Global LCMT-1 knockout causes embryonic lethality in mice, but LCMT-1 function in development is unknown. In this study, we analyzed the effects of global LCMT-1 loss on embryonic development. LCMT-1 knockout causes loss of PP2Ac methylation, indicating that LCMT-1 is the sole PP2Ac methyltransferase. PP2A heterotrimers containing the Bα and Bδ B-type subunits are dramatically reduced in whole embryos, and the steady-state levels of PP2Ac and the PP2A structural A subunit are also down ∼30%. Strikingly, global loss of LCMT-1 causes severe defects in fetal hematopoiesis and usually death by embryonic day 16.5. Fetal livers of homozygous lcmt-1 knockout embryos display hypocellularity, elevated apoptosis, and greatly reduced numbers of hematopoietic stem and progenitor cell-enriched Kit+Lin-Sca1+ cells. The percent cycling cells and mitotic indices of WT and lcmt-1 knockout fetal liver cells are similar, suggesting that hypocellularity may be due to a combination of apoptosis and/or defects in specification, self-renewal, or survival of stem cells. Indicative of a possible intrinsic defect in stem cells, noncompetitive and competitive transplantation experiments reveal that lcmt-1 loss causes a severe multilineage hematopoietic repopulating defect. Therefore, this study reveals a novel role for LCMT-1 as a key player in fetal liver hematopoiesis.

Cell-extrinsic hematopoietic impact of Ezh2 inactivation in fetal liver endothelial cells

Despite the well-established cell-intrinsic role of epigenetic factors in normal and malignant hematopoiesis, their cell-extrinsic role remains largely unexplored. Herein we investigated the hematopoietic impact of inactivating Ezh2, a key component of polycomb repressive complex 2 (PRC2), in the fetal liver (FL) vascular niche. Hematopoietic specific (Vav-iCre) Ezh2 inactivation enhanced FL hematopoietic stem cell (HSC) expansion with normal FL erythropoiesis. In contrast, endothelium (Tie2-Cre) targeted Ezh2 inactivation resulted in embryonic lethality with severe anemia at embryonic day 13.5 despite normal emergence of functional HSCs. Ezh2-deficient FL endothelium overexpressed Mmp9, which cell-extrinsically depleted the membrane-bound form of Kit ligand (mKitL), an essential hematopoietic cytokine, in FL. Furthermore, Mmp9 inhibition in vitro restored mKitL expression along with the erythropoiesis supporting capacity of FL endothelial cells. These data establish that Ezh2 is intrinsically dispensable for FL HSCs and provides proof of principle that modulation of epigenetic regulators in niche components can exert a marked cell-extrinsic impact.

A truncating mutation in EPOR leads to hypo-responsiveness to erythropoietin with normal haemoglobin

The cytokine erythropoietin (EPO), signalling through the EPO receptor (EPO-R), is essential for the formation of red blood cells. We performed a genome-wide association study (GWAS) testing 32.5 million sequence variants for association with serum EPO levels in a set of 4187 individuals. We detect an association between a rare and well imputed stop-gained variant rs370865377[A] (p.Gln82Ter) in EPOR, carried by 1 in 550 Icelanders, and increased serum EPO levels (MAF = 0.09%, Effect = 1.47 SD, P = 3.3 × 10-7). We validated these findings by measuring serum EPO levels in 34 additional pairs of carriers and matched controls and found carriers to have 3.23-fold higher EPO levels than controls (P = 1.7 × 10-6; P combined = 1.6 × 10-11). In contrast to previously reported EPOR mutations, p.Gln82Ter does not associate with haemoglobin levels (Effect = -0.045 SD, P = 0.32, N = 273,160), probably due to a compensatory EPO upregulation in response to EPO-R hypo-responsiveness.

Concise Review: Bipotent Megakaryocytic-Erythroid Progenitors: Concepts and Controversies

Hematopoietic stem and progenitor cells maintain blood formation throughout our lifetime by undergoing long- and short-term self-renewal, respectively. As progenitor cells progress through the hematopoiesis process, their differentiation capabilities narrow, such that the precursors become committed to only one or two lineages. This Review focuses on recent advances in the identification and characterization of bipotent megakaryocytic-erythroid progenitors (MEP), the cells that can further produce two completely different functional outputs: platelets and red blood cells. The existence of MEP has sparked controversy as studies describing the requirement for this intermediate progenitor stage prior to commitment to the erythroid and megakaryocytic lineages have been potentially contradictory. Interpretation of these studies is complicated by the variety of species, cell sources, and analytical approaches used along with inherent challenges in the continuum of hematopoiesis, where hematopoietic progenitors do not stop at discrete steps on single paths as classically drawn in hematopoietic hierarchy models. With the goal of improving our understanding of human hematopoiesis, we discuss findings in both human and murine cells. Based on these data, MEP clearly represent a transitional stage of differentiation in at least one route to the generation of both megakaryocytes and erythroid cells. Stem Cells 2018;36:1138-1145.

Physiology and pathophysiology of renal erythropoietin-producing cells

Anemia is a common complication and contributes to increased morbidity and mortality in chronic kidney disease (CKD) patients. Whereas there has been a significant improvement of understanding the underlying mechanism of erythropoiesis, the treatment of renal anemia is still restricted to erythropoietin (EPO)-stimulating agents. The purpose of this article is to review the physiology of erythropoiesis, functional role of EPO and underlying molecular and cellular basis that regulate EPO production. Regulation of EPO production is at mRNA level. When anemia or hypoxia occurs, transcriptional factor, hypoxia-inducible factor (HIF), binds to EPO 5' hypoxic response element and EPO gene transcription increases. The renal EPO is mainly produced by pericytes. In CKD, pericytes transdifferentiate to myofibroblasts, and subsequently the ability of EPO production decreases, leading to renal anemia. Recent experimental and clinical studies show the promising efficacy of prolyl hydroxylase inhibitors in renal anemia through increasing EPO production by stabilizing HIF. Recent advances on epigenetics create a new field to study EPO gene expression at chromatin level. We will discuss the role of demethylating agent on restoring EPO expression, providing a novel approach to the treatment of renal anemia.

New pathogenic mechanisms induced by germline erythropoietin receptor mutations in primary erythrocytosis

Primary familial and congenital polycythemia is characterized by erythropoietin hypersensitivity of erythroid progenitors due to germline nonsense or frameshift mutations in the erythropoietin receptor gene. All mutations so far described lead to the truncation of the C-terminal receptor sequence that contains negative regulatory domains. Their removal is presented as sufficient to cause the erythropoietin hypersensitivity phenotype. Here we provide evidence for a new mechanism whereby the presence of novel sequences generated by frameshift mutations is required for the phenotype rather than just extensive truncation resulting from nonsense mutations. We show that the erythropoietin hypersensitivity induced by a new erythropoietin receptor mutant, p.Gln434Profs*11, could not be explained by the loss of negative signaling and of the internalization domains, but rather by the appearance of a new C-terminal tail. The latter, by increasing erythropoietin receptor dimerization, stability and cell-surface localization, causes pre-activation of erythropoietin receptor and JAK2, constitutive signaling and hypersensitivity to erythropoietin. Similar results were obtained with another mutant, p.Pro438Metfs*6, which shares the same last five amino acid residues (MDTVP) with erythropoietin receptor p.Gln434Profs*11, confirming the involvement of the new peptide sequence in the erythropoietin hypersensitivity phenotype. These results suggest a new mechanism that might be common to erythropoietin receptor frameshift mutations. In summary, we show that primary familial and congenital polycythemia is more complex than expected since distinct mechanisms are involved in the erythropoietin hypersensitivity phenotype, according to the type of erythropoietin receptor mutation.

Altered compensatory cytokine signaling underlies the discrepancy between Flt3-/- and Flt3l-/- mice

The receptor Flt3 and its ligand Flt3L are both critical for dendritic cell (DC) development, but DC deficiency is more severe in Flt3l^-/- mice than in Flt3^-/- mice. This has led to speculation that Flt3L binds to another receptor that also supports DC development. However, we found that Flt3L administration does not generate DCs in Flt3^-/- mice, arguing against a second receptor. Instead, Flt3^-/- DC progenitors matured in response to macrophage colony-stimulating factor (M-CSF) or stem cell factor, and deletion of Csf1r in Flt3^-/- mice further reduced DC development, indicating that these cytokines could compensate for Flt3. Surprisingly, Flt3^-/- DC progenitors displayed enhanced M-CSF signaling, suggesting that loss of Flt3 increased responsiveness to other cytokines. In agreement, deletion of Flt3 in Flt3l^-/- mice paradoxically rescued their severe DC deficiency. Thus, multiple cytokines can support DC development, and the discrepancy between Flt3^-/- and Flt3l^-/- mice results from the increased sensitivity of Flt3^-/- progenitors to these cytokines.

Erythropoiesis: insights into pathophysiology and treatments in 2017

Erythropoiesis is a tightly-regulated and complex process originating in the bone marrow from a multipotent stem cell and terminating in a mature, enucleated erythrocyte.Altered red cell production can result from the direct impairment of medullary erythropoiesis, as seen in the thalassemia syndromes, inherited bone marrow failure as well as in the anemia of chronic disease. Alternatively, in disorders such as sickle cell disease (SCD) as well as enzymopathies and membrane defects, medullary erythropoiesis is not, or only minimally, directly impaired. Despite these differences in pathophysiology, therapies have traditionally been non-specific, limited to symptomatic control of anemia via packed red blood cell (pRBC) transfusion, resulting in iron overload and the eventual need for iron chelation or splenectomy to reduce defective red cell destruction. Likewise, in polycythemia vera overproduction of red cells has historically been dealt with by non-specific myelosuppression or phlebotomy. With a deeper understanding of the molecular mechanisms underlying disease pathophysiology, new therapeutic targets have been identified including induction of fetal hemoglobin, interference with aberrant signaling pathways and gene therapy for definitive cure. This review, utilizing some representative disorders of erythropoiesis, will highlight novel therapeutic modalities currently in development for treatment of red cell disorders.

VHL and Hypoxia Signaling: Beyond HIF in Cancer

Von Hippel-Lindau (VHL) is an important tumor suppressor that is lost in the majority of clear cell carcinoma of renal cancer (ccRCC). Its regulatory pathway involves the activity of E3 ligase, which targets hypoxia inducible factor α (including HIF1α and HIF2α) for proteasome degradation. In recent years, emerging literature suggests that VHL also possesses other HIF-independent functions. This review will focus on VHL-mediated signaling pathways involving the latest identified substrates/binding partners, including N-Myc downstream-regulated gene 3 (NDRG3), AKT, and G9a, etc., and their physiological roles in hypoxia signaling and cancer. We will also discuss the crosstalk between VHL and NF-κB signaling. Lastly, we will review the latest findings on targeting VHL signaling in cancer.

Terminal Maturation of Orthochromatic Erythroblasts Is Impaired in Burn Patients

Mechanisms of erythropoietin (Epo)-resistant anemia in burn patients are poorly understood. We have recently found that administering a nonselective beta 1,2-adrenergic blocker propranolol (PR) was effective in reversing myelo-erythroid commitment through MafB regulation and increase megakaryocyte erythrocyte progenitors in burn patients' peripheral blood mononuclear cell (PBMC)-derived ex vivo culture system. Having known that Epo-dependent proliferation of early erythroblasts is intact after burn injury, here we inquired whether or not Epo-independent maturation stage of erythropoiesis is affected by burn injury and the relative role of PR on late-stage erythropoiesis. While majority of erythropoiesis occurs in the bone marrow, maturation into reticulocytes is crucial for their release into sinusoids to occupy the peripheral circulation for which enucleation is vital. peripheral blood mononuclear cells (PBMCs) from burn patients were extended beyond commitment and proliferation stages to late maturation stage in ex vivo culture to understand the role of PR in burn patients. Burn impedes late maturation of orthochromatic erythroblasts into reticulocytes by restricting the enucleation step. Late-stage erythropoiesis is impaired in burn patients irrespective of PR treatment. Further, substituting the microenvironment with control plasma (homologous) in place of autologous plasma rescues the conversion of orthochromatic erythroblasts to reticulocytes. Results show promise in formulating interventions to regulate late-stage erythropoiesis, which can be used in combination with PR to reduce the number of transfusions.

SF3B1 deficiency impairs human erythropoiesis via activation of p53 pathway: implications for understanding of ineffective erythropoiesis in MDS

BACKGROUND

SF3B1 is a core component of splicing machinery. Mutations in SF3B1 are frequently found in myelodysplastic syndromes (MDS), particularly in patients with refractory anemia with ringed sideroblasts (RARS), characterized by isolated anemia. SF3B1 mutations have been implicated in the pathophysiology of RARS; however, the physiological function of SF3B1 in erythropoiesis remains unknown.

METHODS

shRNA-mediated approach was used to knockdown SF3B1 in human CD34+ cells. The effects of SF3B1 knockdown on human erythroid cell differentiation, cell cycle, and apoptosis were assessed by flow cytometry. RNA-seq, qRT-PCR, and western blot analyses were used to define the mechanisms of phenotypes following knockdown of SF3B1.

RESULTS

We document that SF3B1 knockdown in human CD34+ cells leads to increased apoptosis and cell cycle arrest of early-stage erythroid cells and generation of abnormally nucleated late-stage erythroblasts. RNA-seq analysis of SF3B1-knockdown erythroid progenitor CFU-E cells revealed altered splicing of an E3 ligase Makorin Ring Finger Protein 1 (MKRN1) and subsequent activation of p53 pathway. Importantly, ectopic expression of MKRN1 rescued SF3B1-knockdown-induced alterations. Decreased expression of genes involved in mitosis/cytokinesis pathway including polo-like kinase 1 (PLK1) was noted in SF3B1-knockdown polychromatic and orthochromatic erythroblasts comparing to control cells. Pharmacologic inhibition of PLK1 also led to generation of abnormally nucleated erythroblasts.

CONCLUSIONS

These findings enabled us to identify novel roles for SF3B1 in human erythropoiesis and provided new insights into its role in regulating normal erythropoiesis. Furthermore, these findings have implications for improved understanding of ineffective erythropoiesis in MDS patients with SF3B1 mutations.

Regulatory Effects of Neuroinflammatory Responses Through Brain-Derived Neurotrophic Factor Signaling in Microglial Cells

Inhibition of microglial over-activation is an important strategy to counter balance neurodegenerative progression. We previously demonstrated that the adenosine monophosphate-activated protein kinase (AMPK) may be a therapeutic target in mediating anti-neuroinflammatory responses in microglia. Brain-derived neurotrophic factor (BDNF) is one of the major neurotrophic factors produced by astrocytes to maintain the development and survival of neurons in the brain, and have recently been shown to modulate homeostasis of neuroinflammation. Therefore, the present study focused on BDNF-mediated neuroinflammatory responses and may provide an endogenous regulation of neuroinflammation. Among the tested neuroinflammation, epigallocatechin gallate (EGCG) and minocycline exerted BDNF upregulation to inhibit COX-2 and proinflammatory mediator expressions. Furthermore, both EGCG and minocycline upregulated BDNF expression in microglia through AMPK signaling. In addition, minocycline and EGCG also increased expressions of erythropoietin (EPO) and sonic hedgehog (Shh). In the endogenous modulation of neuroinflammation, astrocyte-conditioned medium (AgCM) also decreased the expression of COX-2 and upregulated BDNF expression in microglia. The anti-inflammatory effects of BDNF were mediated through EPO/Shh in microglia. Our results indicated that the BDNF-EPO-Shh novel-signaling pathway underlies the regulation of inflammatory responses and may be regarded as a potential therapeutic target in neurodegenerative diseases. This study also reveals a better understanding of an endogenous crosstalk between astrocytes and microglia to regulate anti-inflammatory actions, which could provide a novel strategy for the treatment of neuroinflammation and neurodegenerative diseases.

Alternative Erythropoietin Receptors in the Nervous System

In addition to its regulatory function in the formation of red blood cells (erythropoiesis) in vertebrates, Erythropoietin (Epo) contributes to beneficial functions in a variety of non-hematopoietic tissues including the nervous system. Epo protects cells from apoptosis, reduces inflammatory responses and supports re-establishment of compromised functions by stimulating proliferation, migration and differentiation to compensate for lost or injured cells. Similar neuroprotective and regenerative functions of Epo have been described in the nervous systems of both vertebrates and invertebrates, indicating that tissue-protective Epo-like signaling has evolved prior to its erythropoietic function in the vertebrate lineage. Epo mediates its erythropoietic function through a homodimeric Epo receptor (EpoR) that is also widely expressed in the nervous system. However, identification of neuroprotective but non-erythropoietic Epo splice variants and Epo derivatives indicated the existence of other types of Epo receptors. In this review, we summarize evidence for potential Epo receptors that might mediate Epo's tissue-protective function in non-hematopoietic tissue, with focus on the nervous system. In particular, besides EpoR, we discuss three other potential neuroprotective Epo receptors: (1) a heteroreceptor consisting of EpoR and common beta receptor (βcR), (2) the Ephrin (Eph) B4 receptor and (3) the human orphan cytokine receptor-like factor 3 (CRLF3).

Effects of erythropoietin abuse on exercise performance

The present review provides a comprehensive overview on the erythropoietic and non-erythropoietic effects of rHuEpo on human sport performance, paying attention to quantifying numerically how rHuEpo affects exercise performance and describing physiological changes regarding the most important exercise variables. Much attention has been paid to treatment schedules, in particular, to assess the effects of microdoses of rHuEpo and the prolonged effects on sport performance following withdrawal. Moreover, the review takes into account non-erythropoietic ergogenic effects of rHuEpo, including cognitive benefits of rHuEpo. A significant increase in both Vo2max and maximal cycling power was evidenced in studies taken into account for this review. rHuEpo, administered at clinical dosage, may have significant effects on haematological values, maximal and submaximal physiological variables, whereas few reports show positive effects on exercise perfomance. However, the influence of micro-dose rHuEpo on endurance performance in athletes is still unclear and further studies are warranted.

Erythropoietin induces bone marrow and plasma fibroblast growth factor 23 during acute kidney injury

It is accepted that osteoblasts/osteocytes are the major source for circulating fibroblast growth factor 23 (FGF23). However, erythropoietic cells of bone marrow also express FGF23. The modulation of FGF23 expression in bone marrow and potential contribution to circulating FGF23 has not been well studied. Moreover, recent studies show that plasma FGF23 may increase early during acute kidney injury (AKI). Erythropoietin, a kidney-derived hormone that targets erythropoietic cells, increases in AKI. Here we tested whether an acute increase of plasma erythropoietin induces FGF23 expression in erythropoietic cells of bone marrow thereby contributing to the increase of circulating FGF23 in AKI. We found that erythroid progenitor cells of bone marrow express FGF23. Erythropoietin increased FGF23 expression in vivo and in bone marrow cell cultures via the homodimeric erythropoietin receptor. In experimental AKI secondary to hemorrhagic shock or sepsis in rodents, there was a rapid increase of plasma erythropoietin, and an induction of bone marrow FGF23 expression together with a rapid increase of circulating FGF23. Blockade of the erythropoietin receptor fully prevented the induction of bone marrow FGF23 and partially suppressed the increase of circulating FGF23. Finally, there was an early increase of both circulating FGF23 and erythropoietin in a cohort of patients with severe sepsis who developed AKI within 48 hours of admission. Thus, increases in plasma erythropoietin and erythropoietin receptor activation are mechanisms implicated in the increase of plasma FGF23 in AKI.

Mechanisms of erythrocyte development and regeneration: implications for regenerative medicine and beyond

Hemoglobin-expressing erythrocytes (red blood cells) act as fundamental metabolic regulators by providing oxygen to cells and tissues throughout the body. Whereas the vital requirement for oxygen to support metabolically active cells and tissues is well established, almost nothing is known regarding how erythrocyte development and function impact regeneration. Furthermore, many questions remain unanswered relating to how insults to hematopoietic stem/progenitor cells and erythrocytes can trigger a massive regenerative process termed 'stress erythropoiesis' to produce billions of erythrocytes. Here, we review the cellular and molecular mechanisms governing erythrocyte development and regeneration, and discuss the potential links between these events and other regenerative processes.

Dissecting Regulatory Mechanisms Using Mouse Fetal Liver-Derived Erythroid Cells

Multipotent hematopoietic stem cells differentiate into an ensemble of committed progenitor cells that produce the diverse blood cells essential for life. Physiological mechanisms governing hematopoiesis, and mechanistic aberrations underlying non-malignant and malignant hematologic disorders, are often very similar in mouse and man. Thus, mouse models provide powerful systems for unraveling mechanisms that control hematopoietic stem/progenitor cell (HSPC) function in their resident microenvironments in vivo. Ex vivo systems, involving the culture of HSPCs generated in vivo, allow one to dissociate microenvironment-based and cell intrinsic mechanisms, and therefore have considerable utility. Dissecting mechanisms controlling cellular proliferation and differentiation is facilitated by the use of primary cells, since mutations and chromosome aberrations in immortalized and cancer cell lines corrupt normal mechanisms. Primary erythroid precursor cells can be expanded or differentiated in culture to yield large numbers of progeny at discrete maturation stages. We described a robust method for isolation, culture, and analysis of primary mouse erythroid precursor cells and their progeny.

Erythropoietin induces the osteogenesis of periodontal mesenchymal stem cells from healthy and periodontitis sources via activation of the p38 MAPK pathway

Erythropoietin (Epo), a hematopoietic hormone, has multiple biological functions. Recently, the positively osteogenic effects of Epo on mesenchymal stem cells (MSCs) have attracted broad interest. However, the effects of Epo on the osteogenesis of human periodontal ligament tissue‑derived mesenchymal stem cells (hPDLSCs) and periodontitis mesenchymal stem cells (pPDLSCs) from patients with periodontitis remain unknown. In the present study, osteogenic effects of Epo on hPDLSCs and pPDLSCs were investigated, and the results suggested that the effects were mediated by promoting the expression of runt related transcription factor 2, alkaline phosphatase (ALP) and osteocalcin. Using Alizarin Red and ALP staining, it was demonstrated that Epo exerted positive osteogenic effects on hPDLSCs and pPDLSCs. Additionally, Epo upregulated the proliferation of hPDLSCs and pPDLSCs, based on flow cytometric analyses of the cell cycle. To determine the underlying mechanism, the role of the p38 mitogen‑activated protein kinase (MAPK) pathway, which is associated with the osteogenesis of hPDLSCs and pPDLSCs, was investigated further. Epo increases p38 phosphorylation (the target of the MAPK pathway) in hPDLSCs and pPDLSCs. Furthermore, when the cells were treated with SB203580, an inhibitor of the p38 MAPK pathway, the osteogenic effects of Epo on hPDLSCs and pPDLSCs were attenuated. In conclusion, Epo may upregulate the bone formation ability of hPDLSCs and pPDLSCs via the p38 MAPK pathways.

Targeting erythropoietin protects against proteinuria in type 2 diabetic patients and in zebrafish

Objective

Adult human kidneys produce erythropoietin (EPO), which regulates red blood cell formation; however, whether EPO also functions directly on kidney development and controls diabetic kidney disease remains unknown. Here we analyzed the role of EPO in kidney development and under hyperglycemic conditions in zebrafish and in humans.

Methods

Diabetic patients and respective controls were enrolled in two cohorts. Serum EPO level and urine protein change upon human EPO administration were then analyzed. Transient knockdown and permanent knockout of EPO and EPOR in renal TG(WT1B:EGFP) zebrafish were established using the morpholino technology and CRISPR/Cas9 technology. Zebrafish embryos were phenotypically analyzed using fluorescence microscopy, and functional assays were carried out with the help of TexasRed labeled 70 kDa Dextran. Apoptosis was determined using the TUNEL assay and Annexin V staining, and caspase inhibitor zVADfmk was used for rescue experiments.

Results

In type 2 diabetic patients, serum EPO level decreased with the duration of diabetes, which was linked to reduced kidney function. Human recombinant EPO supplementation ameliorated proteinuria in diabetic nephropathy patients. In zebrafish, loss-of-function studies for EPO and EPOR, showed morphological and functional alterations within the pronephros, adversely affecting pronephric structure, leading to slit diaphragm dysfunction by increasing apoptosis within the pronephros. Induction of hyperglycemia in zebrafish embryos induced pronephros alterations which were further worsened upon silencing of EPO expression.

Conclusions

EPO was identified as a direct renal protective factor, promoting renal embryonic development and protecting kidneys from hyperglycemia induced nephropathy.

•

EPO exhibited renal protective and proteinuria ameliorating function in type 2 DM patients and in hyperglycemic zebrafish embryos.

•

Enhanced co-expression of EPO and EPOR was identified in both glomeruli and tubuli of DN patients.

•

EPO and its receptor directly regulate physiological kidney development via repressing apoptosis.

Erythropoietin Signaling Regulates Key Epigenetic and Transcription Networks in Fetal Neural Progenitor Cells

Erythropoietin (EPO) and its receptor are highly expressed in the developing nervous system, and exogenous EPO therapy is potentially neuroprotective, however the epigenetic and transcriptional changes downstream of EPO signaling in neural cells are not well understood. To delineate epigenetic changes associated with EPO signaling, we compared histone H3 lysine 4 dimethylation (H3K4me2) in EPO treated and control fetal neural progenitor cells, identifying 1,150 differentially bound regions. These regions were highly enriched near protein coding genes and had significant overlap with H4Acetylation, a mark of active regulatory elements. Motif analyses and co-occupancy studies revealed a complex regulatory network underlying the differentially bound regions, including previously identified mediators of EPO signaling (STAT5, STAT3), and novel factors such as REST, an epigenetic modifier central to neural differentiation and plasticity, and NRF1, a key regulator of antioxidant response and mitochondrial biogenesis. Global transcriptome analyses on neural tubes isolated from E9.0 EpoR-null and littermate control embryos validated our in vitro findings, further suggesting a role for REST and NRF1 downstream of EPO signaling. These data support a role for EPO in regulating the survival, proliferation, and differentiation of neural progenitor cells, and suggest a basis for its function in neural development and neuroprotection.

Erythropoietin signaling increases neurogenesis and oligodendrogenesis of endogenous neural stem cells following spinal cord injury both in vivo and in vitro

Erythropoietin (Epo) promotes functional recovery following spinal cord injury (SCI); however, the exact underlying mechanisms are yet to be determined. Although endogenous neural stem cells (NSCs) in the adult spinal cord are a therapeutic target in SCI models, the effect of Epo on this NSC population remains unknown. The present study investigated the effects of Epo on endogenous NSCs in the adult spinal cord both in vitro and in vivo. For the in vivo analyses, normal rats (Normal) and SCI contusion model rats (SCI) received either recombinant human Epo or saline treatment for 7 days (5,000 U/kg), and spinal cords were subsequently analyzed at 2, 8, and 14 days. For in vitro analyses, NSCs harvested from adult rat spinal cords were exposed to Epo (10 U/ml). A significant increase in β-tubulin⁺ new neurons (P<0.01) was observed at all three time points and O4⁺ new oligodendrocytes (P<0.05) at days 8 and 14 in the SCI+Epo group compared with the SCI+Saline group. This was concomitant with a prolonged activation of Epo signaling; however, no effect on NSCs proliferation was observed. Similar results were also obtained in vitro. Motor functional recovery was also noted at days 8 and 14 only in the Epo-treated SCI rats. Although the expression of Epo and EpoR significantly increased in Normal+Epo rats compared with Normal+Saline rats (P<0.05), the cell numbers and phenotype were comparable between the two groups. To the best of the author's knowledge, this is the first study to demonstrate that Epo signaling promotes both neurogenesis and oligodendrogenesis following SCI and that these may represent the underlying mechanisms for the functional recovery and therapeutic effects of Epo following SCI.

Discrete β-adrenergic mechanisms regulate early and late erythropoiesis in erythropoietin-resistant anemia

BACKGROUND

Anemia of critical illness is resistant to exogenous erythropoietin. Packed red blood cells transfusions is the only treatment option, and despite related cost and morbidity, there is a need for alternate strategies. Erythrocyte development can be divided into erythropoietin-dependent and erythropoietin-independent stages. We have shown previously that erythropoietin-dependent development is intact in burn patients and the erythropoietin-independent early commitment stage, which is regulated by β1/β2-adrenergic mechanisms, is compromised. Utilizing the scald burn injury model, we studied erythropoietin-independent late maturation stages and the effect of β1/β2, β-2, or β-3 blockade in burn mediated erythropoietin-resistant anemia.

METHODS

Burn mice were randomized to receive daily injections of propranolol (nonselective β1/β2 antagonist), nadolol (long-acting β1/β2 antagonist), butoxamine (selective β2 antagonist), or SR59230A (selective β3 antagonist) for 6 days after burn. Total bone marrow cells were characterized as nonerythroid cells, early and late erythroblasts, nucleated orthochromatic erythroblasts and enucleated reticulocyte subsets using CD71, Ter119, and Syto-16 by flow cytometry. Multipotential progenitors were probed for MafB expressing cells.

RESULTS

Although propranolol improved early and late erythroblasts, only butoxamine and selective β3-antagonist administrations were positively reflected in the peripheral blood hemoglobin and red blood cells count. While burn impeded early commitment and late maturation stages, β1/β2 antagonism increased the early erythroblasts through commitment stages via β2 specific MafB regulation. β3 antagonism was more effective in improving overall red blood cells through late maturation stages.

CONCLUSION

The study unfolds novel β2 and β3 adrenergic mechanisms orchestrating erythropoietin resistant anemia after burn, which impedes both the early commitment stage and the late maturation stages, respectively.

Thyroid hormone receptor beta and NCOA4 regulate terminal erythrocyte differentiation

An effect of thyroid hormone (TH) on erythropoiesis has been known for more than a century but the molecular mechanism(s) by which TH affects red cell formation is still elusive. Here we demonstrate an essential role of TH during terminal human erythroid cell differentiation; specific depletion of TH from the culture medium completely blocked terminal erythroid differentiation and enucleation. Treatment with TRβ agonists stimulated premature erythroblast differentiation in vivo and alleviated anemic symptoms in a chronic anemia mouse model by regulating erythroid gene expression. To identify factors that cooperate with TRβ during human erythroid terminal differentiation, we conducted RNA-seq in human reticulocytes and identified nuclear receptor coactivator 4 (NCOA4) as a critical regulator of terminal differentiation. Furthermore, Ncoa4^-/- mice are anemic in perinatal periods and fail to respond to TH by enhanced erythropoiesis. Genome-wide analysis suggests that TH promotes NCOA4 recruitment to chromatin regions that are in proximity to Pol II and are highly associated with transcripts abundant during terminal differentiation. Collectively, our results reveal the molecular mechanism by which TH functions during red blood cell formation, results that are potentially useful to treat certain anemias.

Thermal injury of the skin induces G-CSF-dependent attenuation of EPO-mediated STAT signaling and erythroid differentiation arrest in mice

Inflammation-mediated impairment of erythropoiesis plays a central role in the development of the anemia of critical illness (ACI). ACI develops despite elevation of endogenous erythropoietin (EPO), does not respond to exogenous erythropoietin (EPO) supplementation, and contributes significantly to transfusion requirements in burned patients. We have reported previously that the reduction of red blood cell mass in the bone marrow of a burn-injured ACI mouse model is granulocyte colony-stimulating factor (G-CSF) dependent. Given that elevated G-CSF levels also have been associated with lower hemoglobin levels and increased transfusion requirements in trauma victims, we postulated that G-CSF mediates postburn EPO resistance. In ACI mice, we found that bone marrow erythroid differentiation, viability, and proliferation are impaired after thermal injury of the skin. These changes in the marrow were associated with attenuated phosphorylation of known EPO-responsive signaling nodes, signal transducer and activator of transcription 5 (STAT5) Y694 and STAT3 S727, in bone marrow erythroid cells and developed despite highly elevated levels of endogenous EPO. Severely blunted STAT5 Y694 phosphorylation in bone marrow erythroid cells after exogenous EPO supplementation confirmed that EPO signaling was impaired in ACI mice. Importantly, parenteral administration of anti-G-CSF largely rescued postburn bone marrow erythroid differentiation arrest and EPO signaling in erythroid cells. Together, these data provide strong evidence for a role for G-CSF in the development of ACI after burn injury through suppression of EPO signaling in bone marrow erythroid cells.

Direct targets of pSTAT5 signalling in erythropoiesis

Erythropoietin (EPO) acts through the dimeric erythropoietin receptor to stimulate proliferation, survival, differentiation and enucleation of erythroid progenitor cells. We undertook two complimentary approaches to find EPO-dependent pSTAT5 target genes in murine erythroid cells: RNA-seq of newly transcribed (4sU-labelled) RNA, and ChIP-seq for pSTAT5 30 minutes after EPO stimulation. We found 302 pSTAT5-occupied sites: ~15% of these reside in promoters while the rest reside within intronic enhancers or intergenic regions, some >100kb from the nearest TSS. The majority of pSTAT5 peaks contain a central palindromic GAS element, TTCYXRGAA. There was significant enrichment for GATA motifs and CACCC-box motifs within the neighbourhood of pSTAT5-bound peaks, and GATA1 and/or KLF1 co-occupancy at many sites. Using 4sU-RNA-seq we determined the EPO-induced transcriptome and validated differentially expressed genes using dynamic CAGE data and qRT-PCR. We identified known direct pSTAT5 target genes such as Bcl2l1, Pim1 and Cish, and many new targets likely to be involved in driving erythroid cell differentiation including those involved in mRNA splicing (Rbm25), epigenetic regulation (Suv420h2), and EpoR turnover (Clint1/EpsinR). Some of these new EpoR-JAK2-pSTAT5 target genes could be used as biomarkers for monitoring disease activity in polycythaemia vera, and for monitoring responses to JAK inhibitors.

Pathogenesis of Myeloproliferative Disorders

Myeloproliferative neoplasms (MPNs) are a set of chronic hematopoietic neoplasms with overlapping clinical and molecular features. Recent years have witnessed considerable advances in our understanding of their pathogenetic basis. Due to their protracted clinical course, the evolution to advanced hematological malignancies, and the accessibility of neoplastic tissue, the study of MPNs has provided a window into the earliest stages of tumorigenesis. With the discovery of mutations in CALR, the majority of MPN patients now bear an identifiable marker of clonal disease; however, the mechanism by which mutated CALR perturbs megakaryopoiesis is currently unresolved. We are beginning to understand better the role of JAK2(V617F) homozygosity, the function of comutations in epigenetic regulators and spliceosome components, and how these mutations cooperate with JAK2(V617F) to modulate MPN phenotype.

Real-World Impact of Cardiovascular Disease and Anemia on Quality of Life and Productivity in Patients with Non-Dialysis-Dependent Chronic Kidney Disease

INTRODUCTION

Patients with chronic kidney disease (CKD) have an increased risk of comorbid conditions, including cardiovascular disease (CVD). Anemia is prevalent in the CKD population and worsens as kidney function declines, resulting in a diminished quality of life and increased morbidity/mortality. The purpose of this secondary analysis was to determine the real-world prevalence of CVD among patients with non-dialysis-dependent CKD (NDD-CKD), with and without comorbid anemia, and to assess the impact of these conditions on quality of life (QoL) and work productivity.

METHODS

Data were drawn from the Adelphi CKD Disease-Specific Programme, conducted in France, Germany, Italy, Spain, and the UK (2012). Anonymized data were collected via patient record forms and patient-completed questionnaires. Patient data were stratified by anemic status and the presence of CVD comorbidity.

RESULTS

Data were collected by physicians for 1993 patients, of whom 867 completed a patient-completed questionnaire. A total of 61.4% of patients had anemia, and the prevalence of anemia increased with CKD stage. Patients with anemia had a higher mean number of cardiovascular comorbidities than non-anemic patients (1.27 vs 0.95, respectively; P < 0.001). The presence of cardiovascular conditions was associated with a significantly reduced QoL (EuroQol EQ-5D-3L visual analog scale: coefficient, -5.68 in anemic patients; P = 0.028) and work productivity and activity impairment (WPAI activity impairment: coefficient, +8.04 in anemic patients; P = 0.032), particularly among anemic patients.

CONCLUSIONS

The presence of anemia in this cohort of NDD-CKD patients was high. The presence of concomitant cardiovascular conditions was more common in NDD-CKD patients with comorbid anemia, and was associated with reduced QoL and work productivity outcomes.

Characterization of erythropoietin and hepcidin in the regulation of persistent injury-associated anemia

BACKGROUND

The cause of persistent injury-associated anemia is multifactorial and includes acute blood loss, an altered erythropoietin (EPO) response, dysregulation of iron homeostasis, and impaired erythropoiesis in the setting of chronic inflammation/stress. Hepcidin plays a key role in iron homeostasis and is regulated by anemia and inflammation. Erythropoietin is a main regulator of erythropoiesis induced by hypoxia. A unique rodent model of combined lung injury (LC)/hemorrhagic shock (HS) (LCHS)/chronic restraint stress (CS) was used to produce persistent injury-associated anemia to further investigate the roles of EPO, hepcidin, iron, ferritin, and the expression of EPO receptors (EPOr).

METHODS

Male Sprague-Dawley rats were randomly assigned into one of the four groups of rodent models: naive, CS alone, combined LCHS, or LCHS/CS. Plasma was used to evaluate levels of EPO, hepcidin, iron, and ferritin. RNA was isolated from bone marrow and lung tissue to evaluate expression of EPOr. Comparisons between models were performed by t tests followed by one-way analysis of variance.

RESULTS

After 7 days, only LCHS/CS was associated with persistent anemia despite significant elevation of plasma EPO. Combined LCHS and LCHS/CS led to a persistent decrease in EPOr expression in bone marrow on Day 7. The LCHS/CS significantly decreased plasma hepcidin levels by 75% on Day 1 and 84% on Day 7 compared to LCHS alone. Hepcidin plasma levels are inversely proportional to EPO plasma levels (Pearson R = -0.362, p < 0.05).

CONCLUSION

Tissue injury, hemorrhagic shock, and stress stimulate and maintain high levels of plasma EPO while hepcidin levels are decreased. In addition, bone marrow EPOr and plasma iron availability are significantly reduced following LCHS/CS. The combined deficit of reduced iron availability and reduced bone marrow EPOr expression may play a key role in the ineffective EPO response associated with persistent injury-associated anemia.

Characterization, regulation, and targeting of erythroid progenitors in normal and disordered human erythropoiesis

PURPOSE OF REVIEW

The erythroid progenitors burst-forming unit-erythroid and colony-forming unit-erythroid have a critical role in erythropoiesis. These cells represent a heterogeneous and poorly characterized population with modifiable self-renewal, proliferation and differentiation capabilities. This review focuses on the current state of erythroid progenitor biology with regard to immunophenotypic identification and regulatory programs. In addition, we will discuss the therapeutic implications of using these erythroid progenitors as pharmacologic targets.

RECENT FINDINGS

Erythroid progenitors are classically characterized by the appearance of morphologically defined colonies in semisolid cultures. However, these prior systems preclude a more thorough understanding of the composite nature of progenitor populations. Recent studies employing novel flow cytometric and cell-based assays have helped to redefine hematopoiesis, and suggest that erythroid progenitors may arise from different levels of the hematopoietic tree. Moreover, the identification of cell surface marker patterns in human burst-forming unit-erythroid and colony-forming unit-erythroid enhance our ability to perform downstream functional and molecular analyses at the population and single cell level. Advances in these techniques have already revealed novel subpopulations with increased self-renewing capacity, roles for erythroid progenitors in globin gene expression, and insights into pharmacologic mechanisms of glucocorticoids and pomalidomide.

SUMMARY

Immunophenotypic and molecular characterization resolves the diversity of erythroid progenitors, and may ultimately lead to the ability to target these progenitors to ameliorate diseases of dyserythropoiesis.

Hypoxia, HIF, and Associated Signaling Networks in Chronic Kidney Disease

The pathogenesis of chronic kidney disease (CKD) is complex and apparently multifactorial. Hypoxia or decrease in oxygen supply in kidney tissues has been implicated in CKD. Hypoxia inducible factors (HIF) are a small family of transcription factors that are mainly responsive to hypoxia and mediate hypoxic response. HIF plays a critical role in renal fibrosis during CKD through the modulation of gene transcription, crosstalk with multiple signaling pathways, epithelial-mesenchymal transition, and epigenetic regulation. Moreover, HIF also contributes to the development of various pathological conditions associated with CKD, such as anemia, inflammation, aberrant angiogenesis, and vascular calcification. Treatments targeting HIF and related signaling pathways for CKD therapy are being developed with promising clinical benefits, especially for anemia. This review presents an updated analysis of hypoxia response, HIF, and their associated signaling network involved in the pathogenesis of CKD.

The ISWI ATPase Smarca5 (Snf2h) Is Required for Proliferation and Differentiation of Hematopoietic Stem and Progenitor Cells

The imitation switch nuclear ATPase Smarca5 (Snf2h) is one of the most conserved chromatin remodeling factors. It exists in a variety of oligosubunit complexes that move DNA with respect to the histone octamer to generate regularly spaced nucleosomal arrays. Smarca5 interacts with different accessory proteins and represents a molecular motor for DNA replication, repair, and transcription. We deleted Smarca5 at the onset of definitive hematopoiesis (Vav1-iCre) and observed that animals die during late fetal development due to anemia. Hematopoietic stem and progenitor cells accumulated but their maturation toward erythroid and myeloid lineages was inhibited. Proerythroblasts were dysplastic while basophilic erythroblasts were blocked in G2/M and depleted. Smarca5 deficiency led to increased p53 levels, its activation at two residues, one associated with DNA damage (S15^Ph °^s ) second with CBP/p300 (K376^Ac ), and finally activation of the p53 targets. We also deleted Smarca5 in committed erythroid cells (Epor-iCre) and observed that animals were anemic postnatally. Furthermore, 4-hydroxytamoxifen-mediated deletion of Smarca5 in the ex vivo cultures confirmed its requirement for erythroid cell proliferation. Thus, Smarca5 plays indispensable roles during early hematopoiesis and erythropoiesis. Stem Cells 2017;35:1614-1623.

Erythropoietin facilitates definitive endodermal differentiation of mouse embryonic stem cells via activation of ERK signaling

Artificially generated pancreatic β-cells from pluripotent stem cells are expected for cell replacement therapy for type 1 diabetes. Several strategies are adopted to direct pluripotent stem cells toward pancreatic differentiation. However, a standard differentiation method for clinical application has not been established. It is important to develop more effective and safer methods for generating pancreatic β-cells without toxic or mutagenic chemicals. In the present study, we screened several endogenous factors involved in organ development to identify the factor, which induced the efficiency of pancreatic differentiation and found that treatment with erythropoietin (EPO) facilitated the differentiation of mouse embryonic stem cells (ESCs) into definitive endoderm. At an early stage of differentiation, EPO treatment significantly increased Sox17 gene expression, as a marker of the definitive endoderm. Contrary to the canonical function of EPO, it did not affect the levels of phosphorylated JAK2 and STAT5, but stimulated the phosphorylation of ERK1/2 and Akt. The MEK inhibitor U0126 significantly inhibited EPO-induced Sox17 expression. The differentiation of ESCs into definitive endoderm is an important step for the differentiation into pancreatic and other endodermal lineages. This study suggests a possible role of EPO in embryonic endodermal development and a new agent for directing the differentiation into endodermal lineages like pancreatic β-cells.

Neuroprotective erythropoietin attenuates microglial activation, including morphological changes, phagocytosis, and cytokine production

Erythropoietin (EPO), a hematopoietic hormonal cytokine induced in response to hypoxia, has neuroprotective effects. EPO receptor (EPOR) is expressed in microglia, resident immune cells in the brain. However, the effect of EPO on microglial activation is not clear. In the present study, we demonstrated that the EPOR is highly expressed in microglia, rather than in neurons or astrocytes, in in vitro experiments. Therefore, we investigated whether EPO could attenuate lipopolysaccharide (LPS)-mediated activation of microglia in vitro. The BV-2 microglial cell line was treated with LPS in the absence or presence of EPO. In the presence of EPO, microglial expression of LPS-induced inflammatory cytokine genes was significantly decreased. In addition, EPO suppressed the LPS-induced phagocytic activity of BV-2 cells towards fluorescent beads, as well as induction of inducible nitric oxide synthase. In in vivo experiments, EPO significantly decreased the LPS-induced expression of inflammatory cytokine genes in mouse brains. Furthermore, morphological analysis of cortical microglia in the brains of mice stimulated with LPS revealed that combined treatment with EPO alleviated LPS-induced morphological changes in the microglia. These data indicate that EPO attenuates microglial activation, including morphological changes in vivo, phagocytosis in vitro, and the production of inflammatory cytokines in vivo and in vitro. Further investigation of EPO modulation of LPS-induced microglial activation may contribute to the development of novel neuroprotective therapies.

Distinct roles for TET family proteins in regulating human erythropoiesis

The ten-eleven translocation (TET) family of proteins plays important roles in a wide range of biological processes by oxidizing 5-methylcytosine (5mC) to 5-hydroxy-methylcytosine. However, their function in erythropoiesis has remained unclear. We show here that TET2 and TET3 but not TET1 are expressed in human erythroid cells, and we explore the role of these proteins in erythropoiesis. Knockdown experiments revealed that TET2 and TET3 have different functions. Suppression of TET3 expression in human CD34⁺ cells markedly impaired terminal erythroid differentiation, as reflected by increased apoptosis, the generation of bi/multinucleated polychromatic/orthochromatic erythroblasts, and impaired enucleation, although without effect on erythroid progenitors. In marked contrast, TET2 knockdown led to hyper-proliferation and impaired differentiation of erythroid progenitors. Surprisingly, knockdown of neither TET2 nor TET3 affected global levels of 5mC. Thus, our findings have identified distinct roles for TET2 and TET3 in human erythropoiesis, and provide new insights into their role in regulating human erythroid differentiation at distinct stages of development. Moreover, because knockdown of TET2 recapitulates certain features of erythroid development defects characteristic of myelodysplastic syndromes (MDSs), and the TET2 gene mutation is one of the most common mutations in MDS, our findings may be relevant for improved understanding of dyserythropoiesis of MDS.

Renal Anemia Model Mouse Established by Transgenic Rescue with an Erythropoietin Gene Lacking Kidney-Specific Regulatory Elements

The erythropoietin (Epo) gene is under tissue-specific inducible regulation. Because the kidney is the primary EPO-producing tissue in adults, impaired EPO production in chronic kidney disorders results in serious renal anemia. The Epo gene contains a liver-specific enhancer in the 3' region, but the kidney-specific enhancer for gene expression in renal EPO-producing (REP) cells remains elusive. Here, we examined a conserved upstream element for renal Epo regulation (CURE) region that spans 17.4 kb to 3.6 kb upstream of the Epo gene and harbors several phylogenetically conserved elements. We prepared various Epo gene-reporter constructs utilizing a bacterial artificial chromosome and generated a number of transgenic-mouse lines. We observed that deletion of the CURE region (δCURE) abrogated Epo gene expression in REP cells. Although transgenic expression of the δCURE construct rescued Epo-deficient mice from embryonic lethality, the rescued mice had severe EPO-dependent anemia. These mouse lines serve as an elaborate model for the search for erythroid stimulatory activity and are referred to as AnRED (anemic model with renal EPO deficiency) mice. We also dissected the CURE region by exploiting a minigene harboring four phylogenetically conserved elements in reporter transgenic-mouse analyses. Our analyses revealed that Epo gene regulation in REP cells is a complex process that utilizes multiple regulatory influences.

Protein abundance of AKT and ERK pathway components governs cell type-specific regulation of proliferation

Signaling through the AKT and ERK pathways controls cell proliferation. However, the integrated regulation of this multistep process, involving signal processing, cell growth and cell cycle progression, is poorly understood. Here, we study different hematopoietic cell types, in which AKT and ERK signaling is triggered by erythropoietin (Epo). Although these cell types share the molecular network topology for pro‐proliferative Epo signaling, they exhibit distinct proliferative responses. Iterating quantitative experiments and mathematical modeling, we identify two molecular sources for cell type‐specific proliferation. First, cell type‐specific protein abundance patterns cause differential signal flow along the AKT and ERK pathways. Second, downstream regulators of both pathways have differential effects on proliferation, suggesting that protein synthesis is rate‐limiting for faster cycling cells while slower cell cycles are controlled at the G1‐S progression. The integrated mathematical model of Epo‐driven proliferation explains cell type‐specific effects of targeted AKT and ERK inhibitors and faithfully predicts, based on the protein abundance, anti‐proliferative effects of inhibitors in primary human erythroid progenitor cells. Our findings suggest that the effectiveness of targeted cancer therapy might become predictable from protein abundance.

Myelo-erythroid commitment after burn injury is under β-adrenergic control via MafB regulation

Severely injured burn patients receive multiple blood transfusions for anemia of critical illness despite the adverse consequences. One limiting factor to consider alternate treatment strategies is the lack of a reliable test platform to study molecular mechanisms of impaired erythropoiesis. This study illustrates how conditions resulting in a high catecholamine microenvironment such as burns can instigate myelo-erythroid reprioritization influenced by β-adrenergic stimulation leading to anemia. In a mouse model of scald burn injury, we observed, along with a threefold increase in bone marrow LSK cells (lin^neg Sca1⁺cKit⁺), that the myeloid shift is accompanied with a significant reduction in megakaryocyte erythrocyte progenitors (MEPs). β-Blocker administration (propranolol) for 6 days after burn, not only reduced the number of LSKs and MafB⁺ cells in multipotent progenitors, but also influenced myelo-erythroid bifurcation by increasing the MEPs and reducing the granulocyte monocyte progenitors in the bone marrow of burn mice. Furthermore, similar results were observed in burn patients' peripheral blood mononuclear cell-derived ex vivo culture system, demonstrating that commitment stage of erythropoiesis is impaired in burn patients and intervention with propranolol (nonselective β1,2-adrenergic blocker) increases MEPs. Also, MafB⁺ cells that were significantly increased following standard burn care could be mitigated when propranolol was administered to burn patients, establishing the mechanistic regulation of erythroid commitment by myeloid regulatory transcription factor MafB. Overall, results demonstrate that β-adrenergic blockers following burn injury can redirect the hematopoietic commitment toward erythroid lineage by lowering MafB expression in multipotent progenitors and be of potential therapeutic value to increase erythropoietin responsiveness in burn patients.

p53-/- synergizes with enhanced NrasG12D signaling to transform megakaryocyte-erythroid progenitors in acute myeloid leukemia

Somatic mutations in TP53 and NRAS are associated with transformation of human chronic myeloid diseases to acute myeloid leukemia (AML). Here, we report that concurrent RAS pathway and TP53 mutations are identified in a subset of AML patients and confer an inferior overall survival. To further investigate the genetic interaction between p53 loss and endogenous Nras^G12D/+ in AML, we generated conditional Nras^G12D/+p53^-/- mice. Consistent with the clinical data, recipient mice transplanted with Nras^G12D/+p53^-/- bone marrow cells rapidly develop a highly penetrant AML. We find that p53^-/- cooperates with Nras^G12D/+ to promote increased quiescence in megakaryocyte-erythroid progenitors (MEPs). Nras^G12D/+p53^-/- MEPs are transformed to self-renewing AML-initiating cells and are capable of inducing AML in serially transplanted recipients. RNA sequencing analysis revealed that transformed MEPs gain a partial hematopoietic stem cell signature and largely retain an MEP signature. Their distinct transcriptomes suggests a potential regulation by p53 loss. In addition, we show that during AML development, transformed MEPs acquire overexpression of oncogenic Nras, leading to hyperactivation of ERK1/2 signaling. Our results demonstrate that p53^-/- synergizes with enhanced oncogenic Nras signaling to transform MEPs and drive AML development. This model may serve as a platform to test candidate therapeutics in this aggressive subset of AML.

Hematopoietic stem cell-independent hematopoiesis: emergence of erythroid, megakaryocyte, and myeloid potential in the mammalian embryo

Steady-state production of all circulating blood cells in the adult ultimately depends on hematopoietic stem cells (HSCs), which first arise in small numbers beginning at embryonic day (E) 10.5 in large arterial vessels of the murine embryo. However, blood cell synthesis first begins in the yolk sac beginning at E7.25 and consists of two waves of hematopoietic progenitors. The first wave consists of primitive erythroid, megakaryocyte, and macrophage progenitors that rapidly give rise to maturing blood cells of all three lineages. This 'primitive' wave of progenitors is followed by a partially overlapping wave of 'erythro-myeloid progenitors', which contain definitive erythroid, megakaryocyte, macrophage, neutrophil, and mast cell progenitors that seed the fetal liver and jump-start hematopoiesis before the engraftment and expansion of HSCs. These two waves of progenitors that arise in the yolk sac are necessary and even sufficient to sustain the survival of the mouse embryo until birth in the absence of HSCs. They provide key signals to support HSC emergence. Finally, HSC-independent hematopoiesis also provides long-lived tissue-resident macrophage populations that function in multiple adult organs.

Reduction in central venous pressure enhances erythropoietin synthesis: role of volume-regulating hormones

AIMS

Erythropoiesis is a tightly controlled biological event, but its regulation under non-hypoxic conditions, however, remains unresolved. We examined whether acute changes in central venous blood pressure (CVP) elicited by whole-body tilting affect erythropoietin (EPO) concentration according to volume-regulating hormones.

METHODS

Plasma EPO, angiotensin II (ANGII), aldosterone, pro-atrial natriuretic peptide (proANP) and copeptin concentrations were measured at supine rest and up to 3 h during 30° head-up (HUT) and head-down tilt (HDT) in ten healthy male volunteers. Plasma albumin concentration was used to correct for changes in plasma volume and CVP was estimated through the internal jugular vein (IJV) aspect ratio with ultrasonography.

RESULTS

From supine rest, the IJV aspect ratio was decreased and increased throughout HUT and HDT respectively. Plasma EPO concentration increased during HUT (13%; P = 0.001, P for linear component = 0.017), independent of changes in albumin concentration. Moreover, ANGII and copeptin concentrations increased during HUT, while proANP decreased. The increase in EPO concentration during HUT disappeared when adjusted for changes in copeptin. During HDT, EPO, ANGII and copeptin concentrations remained unaffected while proANP increased. In regression analyses, EPO was positively associated with copeptin (β = 0.55; 95% CI = 0.18, 0.93; P = 0.004) irrespective of changes in other hormones and albumin concentration.

CONCLUSION

Reduction in CVP prompts an increase in plasma EPO concentration independent of hemoconcentration and hence suggests CVP per se as an acute regulator of EPO synthesis. This effect may be explained by changes in volume-regulating hormones.