Turning cells red: signal transduction mediated by erythropoietin

Activating mutations in JAK2 and CALR differentially affect intracellular calcium flux in store operated calcium entry

BACKGROUND

Calcium (Ca2+) signaling regulates various vital cellular functions, including integrin activation and cell migration. Store-operated calcium entry (SOCE) via calcium release-activated calcium (CRAC) channels represents a major pathway for Ca2+ influx from the extracellular space in multiple cell types. The impact of JAK2-V617F and CALR mutations which are disease initiating in myeloproliferative neoplasms (MPN) on SOCE, calcium flux from the endoplasmic reticulum (ER) to the cytosol, and related key signaling pathways in the presence or absence of erythropoietin (EPO) or thrombopoietin (TPO) is poorly understood. Thus, this study aimed to elucidate the effects of these mutations on the aforementioned calcium dynamics, in cellular models of MPN.

METHODS

Intracellular Ca2+ levels were measured over a time frame of 0-1080 s in Fura-2 AM labeled myeloid progenitor 32D cells expressing various mutations (JAK2-WT/EpoR, JAK2-V617F/EpoR; CALR-WT/MPL, CALR-ins5/MPL, and del52/MPL). Basal Ca2+ concentrations were assessed from 0-108 s. Subsequently, cells were stimulated with EPO/TPO in Ca2+-free Ringer solution, measuring Ca2+ levels from 109-594 s (store depletion). Then, 2 mM of Ca2+ buffer resembling physiological concentrations was added to induce SOCE, and Ca2+ levels were measured from 595-1080 s. Fura-2 AM emission ratios (F340/380) were used to quantify the integrated Ca2+ signal. Statistical significance was assessed by unpaired Student's t-test or Mann-Whitney-U-test, one-way or two-way ANOVA followed by Tukey's multiple comparison test.

RESULTS

Following EPO stimulation, the area under the curve (AUC) representing SOCE significantly increased in 32D-JAK2-V617F cells compared to JAK2-WT cells. In TPO-stimulated CALR cells, we observed elevated Ca2+ levels during store depletion and SOCE in CALR-WT cells compared to CALR-ins5 and del52 cells. Notably, upon stimulation, key components of the Ca2+ signaling pathways, including PLCγ-1 and IP3R, were differentially affected in these cell lines. Hyper-activated PLCγ-1 and IP3R were observed in JAK2-V617F but not in CALR mutated cells. Inhibition of calcium regulatory mechanisms suppressed cellular growth and induced apoptosis in JAK2-V617F cells.

CONCLUSIONS

This report highlights the impact of JAK2 and CALR mutations on Ca2+ flux (store depletion and SOCE) in response to stimulation with EPO and TPO. The study shows that the JAK2-V617F mutation strongly alters the regulatory mechanism of EpoR/JAK2-dependent intracellular calcium balance, affecting baseline calcium levels, EPO-induced calcium entry, and PLCγ-1 signaling pathways. Our results reveal an important role of calcium flux in the homeostasis of JAK2-V617F positive cells.

Role of Cytokine-Inducible SH2 Domain-Containing (CISH) Protein in the Regulation of Erythropoiesis

The cytokine-inducible SH2 domain-containing (CISH) protein was the first member of the suppressor of cytokine signaling (SOCS) family of negative feedback regulators discovered, being identified in vitro as an inducible inhibitor of erythropoietin (EPO) signaling. However, understanding of the physiological role played by CISH in erythropoiesis has remained limited. To directly assess the function of CISH in this context, mice deficient in CISH were characterized with respect to developmental, steady-state, and EPO-induced erythropoiesis. CISH was strongly expressed in the fetal liver, but CISH knockout (KO) mice showed only minor disruption of primitive erythropoiesis. However, adults exhibited mild macrocytic anemia coincident with subtle perturbation particularly of bone marrow erythropoiesis, with EPO-induced erythropoiesis blunted in the bone marrow of KO mice but enhanced in the spleen. Cish was expressed basally in the bone marrow with induction following EPO stimulation in bone marrow and spleen. Overall, this study indicates that CISH participates in the control of both basal and EPO-induced erythropoiesis in vivo.

Synergistic immunotherapy targeting cancer-associated anemia: prospects of a combination strategy

Cancer-associated anemia promotes tumor progression, leads to poor quality of life in patients with cancer, and even obstructs the efficacy of immune checkpoint inhibitors therapy. However, the precise mechanism for cancer-associated anemia remains unknown and the feasible strategy to target cancer-associated anemia synergizing immunotherapy needs to be clarified. Here, we review the possible mechanisms of cancer-induced anemia regarding decreased erythropoiesis and increased erythrocyte destruction, and cancer treatment-induced anemia. Moreover, we summarize the current paradigm for cancer-associated anemia treatment. Finally, we propose some prospective paradigms to slow down cancer-associated anemia and synergistic the efficacy of immunotherapy. Video Abstract.

Epo-IGF1R cross talk expands stress-specific progenitors in regenerative erythropoiesis and myeloproliferative neoplasm

We found that in regenerative erythropoiesis, the erythroid progenitor landscape is reshaped, and a previously undescribed progenitor population with colony-forming unit-erythroid (CFU-E) activity (stress CFU-E [sCFU-E]) is expanded markedly to restore the erythron. sCFU-E cells are targets of erythropoietin (Epo), and sCFU-E expansion requires signaling from the Epo receptor (EpoR) cytoplasmic tyrosines. Molecularly, Epo promotes sCFU-E expansion via JAK2- and STAT5-dependent expression of IRS2, thus engaging the progrowth signaling from the IGF1 receptor (IGF1R). Inhibition of IGF1R and IRS2 signaling impairs sCFU-E cell growth, whereas exogenous IRS2 expression rescues cell growth in sCFU-E expressing truncated EpoR-lacking cytoplasmic tyrosines. This sCFU-E pathway is the major pathway involved in erythrocytosis driven by the oncogenic JAK2 mutant JAK2(V617F) in myeloproliferative neoplasm. Inability to expand sCFU-E cells by truncated EpoR protects against JAK2(V617F)-driven erythrocytosis. In samples from patients with myeloproliferative neoplasm, the number of sCFU-E-like cells increases, and inhibition of IGR1R and IRS2 signaling blocks Epo-hypersensitive erythroid cell colony formation. In summary, we identified a new stress-specific erythroid progenitor cell population that links regenerative erythropoiesis to pathogenic erythrocytosis.

Mendelian randomization accounting for complex correlated horizontal pleiotropy while elucidating shared genetic etiology

Mendelian randomization (MR) harnesses genetic variants as instrumental variables (IVs) to study the causal effect of exposure on outcome using summary statistics from genome-wide association studies. Classic MR assumptions are violated when IVs are associated with unmeasured confounders, i.e., when correlated horizontal pleiotropy (CHP) arises. Such confounders could be a shared gene or inter-connected pathways underlying exposure and outcome. We propose MR-CUE (MR with Correlated horizontal pleiotropy Unraveling shared Etiology and confounding), for estimating causal effect while identifying IVs with CHP and accounting for estimation uncertainty. For those IVs, we map their cis-associated genes and enriched pathways to inform shared genetic etiology underlying exposure and outcome. We apply MR-CUE to study the effects of interleukin 6 on multiple traits/diseases and identify several S100 genes involved in shared genetic etiology. We assess the effects of multiple exposures on type 2 diabetes across European and East Asian populations.

Hypoxia-Inducible Factors Signaling in Osteogenesis and Skeletal Repair

Sufficient oxygen is required to maintain normal cellular and physiological function, such as a creature’s development, breeding, and homeostasis. Lately, some researchers have reported that both pathological hypoxia and environmental hypoxia might affect bone health. Adaptation to hypoxia is a pivotal cellular event in normal cell development and differentiation and in pathological settings such as ischemia. As central mediators of homeostasis, hypoxia-inducible transcription factors (HIFs) can allow cells to survive in a low-oxygen environment and are essential for the regulation of osteogenesis and skeletal repair. From this perspective, we summarized the role of HIF-1 and HIF-2 in signaling pathways implicated in bone development and skeletal repair and outlined the molecular mechanism of regulation of downstream growth factors and protein molecules such as VEGF, EPO, and so on. All of these present an opportunity for developing therapies for bone regeneration.

Antidepressant-like effects of trophic factor receptor signaling

A significant body of research has demonstrated that antidepressants regulate neurotrophic factors and that neurotrophins themselves are capable of independently producing antidepressant-like effects. While brain derived neurotrophic factor (BDNF) remains the best studied molecule in this context, there are several structurally diverse trophic factors that have shown comparable behavioral effects, including basic fibroblast growth factor (FGF-2), insulin-like growth factor 1 (IGF-1) and vascular endothelial growth factor (VEGF). In this review we discuss the structural and biochemical signaling aspects of these neurotrophic factors with antidepressant activity. We also include a discussion on a cytokine molecule erythropoietin (EPO), widely known and prescribed as a hormone to treat anemia but has recently been shown to function as a neurotrophic factor in the central nervous system (CNS).

Erythropoietin promotes the differentiation of fetal neural stem cells into glial cells via the erythropoietin receptor-β common receptor/Syne-1/H3K9me3 pathway

Aims

To investigate the effect of erythropoietin (EPO) on the differentiation of neural stem cells (NSCs)/neural progenitors (NPs) in the treatment of hypoxic–ischemic injury and its potential mechanisms.

Methods

Fetal NSCs/NPs were treated with EPO after oxygen and glucose deprivation/reoxygenation (OGD/R). Cell viability, proliferation, and differentiation of NSCs/NPs were detected by CellTiter‐Glo, Edu assay, flow cytometry, and quantitative real‐time PCR (qPCR). Immunofluorescence staining, co‐immunoprecipitation (Co‐IP), and western blotting were used to test the existence of EPO receptor/β common receptor (EPOR/βCR) heterodimer on NSCs/NPs and the possible pathway.

Results

EPO treatment at different time points increased cell viability without affecting proliferation. EPO treatment immediately after OGD/R promoted oligodendrocyte and astrocyte differentiation, while decreasing neuronal differentiation of NSCs/NPs. EPOR/βCR heterodimer existed on the cell surface of the fetal cortical NSCs/NPs, EPO treatment significantly increased the mRNA expression of βCR and elevated the correlation between EPOR and βCR levels. In addition, mass spectrometry analysis identified Syne‐1 as a downstream signaling molecule of the EPOR/βCR heterodimer. Immunofluorescence staining and western blotting indicated that the βCR/Syne‐1/H3K9me3 pathway was possibly involved in the differentiation of fetal neural stem cells into the glial cell effect of EPO.

Conclusion

EPO treatment immediately after OGD/R could not facilitate fetal NSCs/NPs neurogenesis but promoted the formation of the EPOR/βCR heterodimer on fetal NSCs/NPs, which mediates its function in glial differentiation.

Enhancing Erythropoiesis by a Phytoestrogen Diarylheptanoid from Curcuma comosa

Erythropoietin (Epo) is widely used for the treatment of anemia; however, non-hematopoietic effects and cancer risk limit its clinical applications. Therefore, alternative molecules to improve erythropoiesis in anemia patients are urgently needed. Here, we investigated the potential effects of a phytoestrogen diarylheptanoid (3R)-1,7-diphenyl-(4E,6E)-4,6-heptadien-3-ol, (ASPP 049) isolated from Curcuma comosa on promoting erythropoiesis. Treatment with C. comosa extract improved anemia symptoms demonstrated by increasing red blood cell numbers, hematocrit, and hemoglobin content in anemic mice. In addition, ASPP 049, the major compound isolated from C. comosa, enhanced the suboptimal Epo dosages to improve erythroid cell differentiation from hematopoietic stem cells, which was inhibited by the estrogen receptor (ER) antagonist, ICI 182,780. Moreover, the ASPP 049-activated Epo-Epo receptor (EpoR) complex subsequently induced phosphorylation of EpoR-mediated erythropoiesis pathways: STAT5, MAPK/ERK, and PI3K/AKT in Epo-sensitive UT-7 cells. Taken together, these results suggest that C. comosa extract and ASPP 049 increased erythropoiesis through ER- and EpoR-mediated signaling cascades. Our findings provide insight into the specific interaction between a phytoestrogen diarylheptanoid and Epo-EpoR in a hematopoietic system for the potential treatment of anemia.

Carbon Dots as a Potential Therapeutic Agent for the Treatment of Cancer-Related Anemia

Due to the adverse effects of erythropoietin (EPO) on cancer patient survival, it is necessary to develop new agents that can be used to efficiently manage and treat cancer-related anemia. In this study, novel distinctive carbon dots, J-CDs, derived from jujube are designed, synthesized, and characterized. Based on the obtained results, this material comprises sp² and sp³ carbon atoms, as well as oxygen/nitrogen-based groups, and it specifically promotes the proliferation of erythroid cells by stimulating the self-renewal of erythroid progenitor cells in vitro and in vivo. Moreover, J-CDs have no discernible effects on tumor proliferation and metastasis, unlike EPO. Transcriptome profiling suggests that J-CDs upregulate the molecules involved in hypoxia response, and they also significantly increase the phosphorylation levels of STAT5, the major transducer of signals for erythroid progenitor cell proliferation. Overall, this study demonstrates that J-CDs effectively promote erythrocyte production without affecting tumor proliferation and metastasis; thus, they may be promising agents for the treatment of cancer-related anemia.

Erythropoietin directly remodels the clonal composition of murine hematopoietic multipotent progenitor cells

The cytokine erythropoietin (EPO) is a potent inducer of erythrocyte development and one of the most prescribed biopharmaceuticals. The action of EPO on erythroid progenitor cells is well established, but its direct action on hematopoietic stem and progenitor cells (HSPCs) is still debated. Here, using cellular barcoding, we traced the differentiation of hundreds of single murine HSPCs, after ex vivo EPO-exposure and transplantation, in five different hematopoietic cell lineages, and observed the transient occurrence of high-output Myeloid-Erythroid-megaKaryocyte (MEK)-biased and Myeloid-B-cell-Dendritic cell (MBDC)-biased clones. Single-cell RNA sequencing (ScRNAseq) analysis of ex vivo EPO-exposed HSPCs revealed that EPO induced the upregulation of erythroid associated genes in a subset of HSPCs, overlapping with multipotent progenitor (MPP) 1 and MPP2. Transplantation of Barcoded EPO-exposed-MPP2 confirmed their enrichment in Myeloid-Erythroid-biased clones. Collectively, our data show that EPO does act directly on MPP independent of the niche, and modulates fate by remodeling the clonal composition of the MPP pool.

Erythropoietin and Non-Erythropoietic Derivatives in Cognition

Cognitive deficits are widespread in psychiatric disorders, including major depression and schizophrenia. These deficits are known to contribute significantly to the accompanying functional impairment. Progress in the development of targeted treatments of cognitive deficits has been limited and there exists a major unmet need to develop more efficacious treatments. Erythropoietin (Epo) has shown promising procognitive effects in psychiatric disorders, providing support for a neurotrophic drug development approach. Several preclinical studies with non-erythropoietic derivatives have demonstrated that the modulation of behavior is independent of erythropoiesis. In this review, we examine the molecular, cellular and cognitive actions of Epo and non-erythropoietic molecular derivatives by focusing on their neurotrophic, synaptic, myelin plasticity, anti-inflammatory and neurogenic mechanisms in the brain. We also discuss the role of receptor signaling in Epo and non-erythropoietic EPO-mimetic molecules in their procognitive effects.

The Role of Iron in Benign and Malignant Hematopoiesis

Significance: Iron is an essential element required for sustaining a normal healthy life. However, an excess amount of iron in the bloodstream and tissue generates toxic hydroxyl radicals through Fenton reactions. Henceforth, a balance in iron concentration is extremely important to maintain cellular homeostasis in both normal hematopoiesis and erythropoiesis. Iron deficiency or iron overload can impact hematopoiesis and is associated with many hematological diseases. Recent Advances: The mechanisms of action of key iron regulators such as erythroferrone and the discovery of new drugs, such as ACE-536/luspatercept, are of potential interest to treat hematological disorders, such as β-thalassemia. New therapies targeting inflammation-induced ineffective erythropoiesis are also in progress. Furthermore, emerging evidences support differential interactions between iron and its cellular antioxidant responses of hematopoietic and neighboring stromal cells. Both iron and its systemic regulator, such as hepcidin, play a significant role in regulating erythropoiesis. Critical Issues: Significant pre-clinical studies are on the way and new drugs targeting iron metabolism have been recently approved or are undergoing clinical trials to treat pathological conditions with impaired erythropoiesis such as myelodysplastic syndromes or β-thalassemia. Future Directions: Future studies should explore how iron regulates hematopoiesis in both benign and malignant conditions. Antioxid. Redox Signal. 35, 415-432.

Iron-loaded transferrin potentiates erythropoietin effects on erythroblast proliferation and survival: a novel role through transferrin receptors

Red blood cell production, or erythropoiesis, is a proliferative process that requires tight regulation. Erythropoietin (Epo) is a glycoprotein cytokine that plays a major role in erythropoiesis by triggering erythroid progenitors/precursors of varying sensitivity. The concentration of Epo in bone marrow is hypothesized to be suboptimal, and the survival of erythroid cells has been suggested to depend on Epo sensitivity. However, the key factors that control Epo sensitivity remain unknown. Two types of transferrin receptors (TfRs), TfR1 and TfR2, are known to play a role in iron uptake in erythroid cells. Here, we hypothesized that TfRs may additionally modulate Epo sensitivity during erythropoiesis by modulating Epo receptor (EpoR) signaling. Using an Epo-sensitive UT-7 (UT7/Epo) erythroid cell and human erythroid progenitor cell models, we report that iron-loaded transferrin, that is, holo-transferrin (holo-Tf), synergizes with suboptimal Epo levels to improve erythroid cell survival, proliferation, and differentiation. This is accomplished via the major signaling pathways of erythropoiesis, which include signal transducer and activator of transcription 5 (STAT5), mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK), and phosphoinositide-3-kinase (PI3K)/AKT. Furthermore, we found that this cooperation is improved by, but does not require, the internalization of TfR1. Interestingly, we observed that loss of TfR2 stabilizes EpoR levels and abolishes the beneficial effects of holo-Tf. Overall, these data reveal novel signaling properties of TfRs, which involve the regulation of erythropoiesis through EpoR signaling.

Receptor-mediated mitophagy regulates EPO production and protects against renal anemia

Erythropoietin (EPO) drives erythropoiesis and is secreted mainly by the kidney upon hypoxic or anemic stress. The paucity of EPO production in renal EPO-producing cells (REPs) causes renal anemia, one of the most common complications of chronic nephropathies. Although mitochondrial dysfunction is commonly observed in several renal and hematopoietic disorders, the mechanism by which mitochondrial quality control impacts renal anemia remains elusive. In this study, we showed that FUNDC1, a mitophagy receptor, plays a critical role in EPO-driven erythropoiesis induced by stresses. Mechanistically, EPO production is impaired in REPs in Fundc1^-/- mice upon stresses, and the impairment is caused by the accumulation of damaged mitochondria, which consequently leads to the elevation of the reactive oxygen species (ROS) level and triggers inflammatory responses by up-regulating proinflammatory cytokines. These inflammatory factors promote the myofibroblastic transformation of REPs, resulting in the reduction of EPO production. We therefore provide a link between aberrant mitophagy and deficient EPO generation in renal anemia. Our results also suggest that the mitochondrial quality control safeguards REPs under stresses, which may serve as a potential therapeutic strategy for the treatment of renal anemia.

Structural Insights into the Interaction of Heme with Protein Tyrosine Kinase JAK2*

Janus kinase 2 (JAK2) is the most important signal-transducing tyrosine kinase in erythropoietic precursor cells. Its malfunction drives several myeloproliferative disorders. Heme is a small metal-ion-carrying molecule that is incorporated into hemoglobin in erythroid precursor cells to transport oxygen. In addition, heme is a signaling molecule and regulator of various biochemical processes. Here, we show that heme exposure leads to hyperphosphorylation of JAK2 in a myeloid cancer cell line. Two peptides identified in JAK2 are heme-regulatory motifs and show low-micromolar affinities for heme. These peptides map to the kinase domain of JAK2, which is essential for downstream signaling. We suggest these motifs to be the interaction sites of heme with JAK2, which drive the heme-induced hyperphosphorylation. The results presented herein could facilitate the development of heme-related pharmacological tools to combat myeloproliferative disorders.

Signaling Through the Erythropoietin Receptor Affects Angiogenesis in Retinovascular Disease

Purpose

Exogenous erythropoietin (EPO) is being considered for tissue protection and angiogenesis in retinal vascular diseases. However, studies are limited by insufficient tools to address signaling effects through the EPO receptor (EPOR). We used a humanized mouse model of hypoactive EPOR signaling to test the hypothesis that EPOR signaling supports angiogenesis in retinovascular diseases.

Methods

Humanized Knockin EPOR mice (hWtEPOR) with hypoactive EPOR signaling were compared to littermate wild-type mice (WT). Postnatal day (p)7 mice of each genotype were exposed to 75% oxygen for five days, followed by 21% oxygen in the oxygen-induced retinopathy model (OIR) and compared to room-air (RA)–raised pups. At time points after OIR, pups were sacrificed, and flat-mounted, lectin-stained retinas were analyzed for central avascular area or intravitreal neovascular area (IVNV). Flash-frozen retinas were analyzed for angiogenic protein (Epo, VEGF, p-Stat3) and gene (Vegfa, Kdr, Epo, Hif1α, Hif2α) expression levels.

Results

In OIR, hWtEPOR mice had increased AVA compared with WT at p8, p12, and p17, but there was no difference in IVNV between hWtEPOR and WT mice at p17. Although VEGF and p-STAT3 proteins were increased in WT at p17 OIR, there were no differences in retinal angiogenic factor expression levels between hWtEPOR and WT OIR at p17 despite similar areas of IVNV.

Conclusions

Our data support the hypothesis that EPOR signaling was associated with regrowth of vascularization following oxygen-induced capillary dropout and played a role in intravitreal angiogenesis. Additional study of EPOR signaling regulation on other angiogenic factor pathways may be considered.

Biological basis for efficacy of activin receptor ligand traps in myelodysplastic syndromes

Signaling by the TGF-β superfamily is important in the regulation of hematopoiesis and is dysregulated in myelodysplastic syndromes (MDSs), contributing to ineffective hematopoiesis and clinical cytopenias. TGF-β, activins, and growth differentiation factors exert inhibitory effects on red cell formation by activating canonical SMAD2/3 pathway signaling. In this Review, we summarize evidence that overactivation of SMAD2/3 signaling pathways in MDSs causes anemia due to impaired erythroid maturation. We also describe the basis for biological activity of activin receptor ligand traps, novel fusion proteins such as luspatercept that are promising as erythroid maturation agents to alleviate anemia and related comorbidities in MDSs and other conditions characterized by impaired erythroid maturation.

Uremic Toxins Affect Erythropoiesis during the Course of Chronic Kidney Disease: A Review

Chronic kidney disease (CKD) is a global health problem characterized by progressive kidney failure due to uremic toxicity and the complications that arise from it. Anemia consecutive to CKD is one of its most common complications affecting nearly all patients with end-stage renal disease. Anemia is a potential cause of cardiovascular disease, faster deterioration of renal failure and mortality. Erythropoietin (produced by the kidney) and iron (provided from recycled senescent red cells) deficiencies are the main reasons that contribute to CKD-associated anemia. Indeed, accumulation of uremic toxins in blood impairs erythropoietin synthesis, compromising the growth and differentiation of red blood cells in the bone marrow, leading to a subsequent impairment of erythropoiesis. In this review, we mainly focus on the most representative uremic toxins and their effects on the molecular mechanisms underlying anemia of CKD that have been studied so far. Understanding molecular mechanisms leading to anemia due to uremic toxins could lead to the development of new treatments that will specifically target the pathophysiologic processes of anemia consecutive to CKD, such as the newly marketed erythropoiesis-stimulating agents.

Erythropoietin Mediated Bone Loss in Mice Is Dose-Dependent and Mostly Irreversible

Recent studies have demonstrated that erythropoietin (EPO) treatment in mice results in trabecular bone loss. Here, we investigated the dose-response relationship between EPO, hemoglobin (Hgb) and bone loss and examined the reversibility of EPO-induced damage. Increasing doses of EPO over two weeks led to a dose-dependent increase in Hgb in young female mice, accompanied by a disproportionate decrease in trabecular bone mass measured by micro-CT (µCT). Namely, increasing EPO from 24 to 540 IU/week produced a modest 12% rise in Hgb (20.2 ± 1.3 mg/dL vs 22.7 ± 1.3 mg/dL), while trabecular bone volume fraction (BV/TV) in the distal femur decreased dramatically (27 ± 8.5% vs 53 ± 10.2% bone loss). To explore the long-term skeletal effects of EPO, we treated mice for two weeks (540 IU/week) and monitored bone mass changes after treatment cessation. Six weeks post-treatment, there was only a partial recovery of the trabecular microarchitecture in the femur and vertebra. EPO-induced bone loss is therefore dose-dependent and mostly irreversible at doses that offer only a minor advantage in the treatment of anemia. Because patients requiring EPO therapy are often prone to osteoporosis, our data advocate for using the lowest effective EPO dose for the shortest period of time to decrease thromboembolic complications and minimize the adverse skeletal outcome.

Erythropoietin as a Neuroprotective Molecule: An Overview of Its Therapeutic Potential in Neurodegenerative Diseases

Erythropoietin (EPO) is a cytokine mainly induced in hypoxia conditions. Its major production site is the kidney. EPO primarily acts on the erythroid progenitor cells in the bone marrow. More and more studies are highlighting its secondary functions, with a crucial focus on its role in the central nervous system. Here, EPO may interact with up to four distinct isoforms of its receptor (erythropoietin receptor [EPOR]), activating different signaling cascades with roles in neuroprotection and neurogenesis. Indeed, the EPO/EPOR axis has been widely studied in the neurodegenerative diseases field. Its potential therapeutic effects have been evaluated in multiple disorders, such as Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, spinal cord injury, as well as brain ischemia, hypoxia, and hyperoxia. EPO is showing great promise by counteracting secondary neuroinflammatory processes, reactive oxygen species imbalance, and cell death in these diseases. Multiple studies have been performed both in vitro and in vivo, characterizing the mechanisms through which EPO exerts its neurotrophic action. In some cases, clinical trials involving EPO have been performed, highlighting its therapeutic potential. Together, all these works indicate the potential beneficial effects of EPO.

Erythropoietin Receptor Signaling Supports Retinal Function after Vascular Injury

The investigation of erythropoietin (EPO) has expanded to include potential nonhematopoietic roles in neural and retinal diseases, including diabetic retinopathy. However, it remains unclear how EPO functions to support the neural retina. Transgenic mice with hypoactive EPO receptor (EPOR) signaling (hWtEPOR) were compared with littermate control mice (WT) to test the role of EPOR signaling under normal conditions and after vascular injury and regrowth into the retina. Although retinal function tested with OptoMotry and electroretinography was comparable to adult (8-week-old) littermate WT mice, hWtEPOR mice had thinner inner and outer plexiform layers and a greater number of amacrine cells. Injury and repair caused by the oxygen-induced retinopathy model reduced visual acuity thresholds, reduced electroretinography amplitudes, and thinned the outer plexiform and inner nuclear layers of both WT and hWtEPOR 8-week-old mice. In hWtEPOR compared with WT mice, scotopic a-wave amplitudes were reduced by injury, despite no change in outer nuclear layer thickness; and peripheral rod, but not cone number, was reduced. Scotopic b-waves were reduced in injured hWtEPOR mice compared with WT, and rod bipolar cell ectopic neurites were increased in both genotypes after injury, suggesting a potential reparative process to preserve connectivity and the b-wave. Normal EPOR signaling appeared important because ectopic neurites and b-waves were lower in the hWtEPOR than WT injured mice.

Increased hypoxic proliferative response and gene expression in erythroid progenitor cells of Andean highlanders with chronic mountain sickness

Excessive erythrocytosis (EE) is the main sign of chronic mountain sickness (CMS), a maladaptive clinical syndrome prevalent in Andean and other high-altitude populations worldwide. The pathophysiological mechanism of EE is still controversial, as physiological variability of systemic respiratory, cardiovascular, and hormonal responses to chronic hypoxemia complicates the identification of underlying causes. Induced pluripotent stem cells derived from CMS highlanders showed increased expression of genes relevant to the regulation of erythropoiesis, angiogenesis, cardiovascular, and steroid-hormone function that appear to explain the exaggerated erythropoietic response. However, the cellular response to hypoxia in native CMS cells is yet unknown. This study had three related aims: to determine the hypoxic proliferation of native erythroid progenitor burst-forming unit-erythroid (BFU-E) cells derived from CMS and non-CMS peripheral blood mononuclear cells; to examine their sentrin-specific protease 1 (SENP1), GATA-binding factor 1 (GATA1), erythropoietin (EPO), and EPO receptor (EPOR) expression; and to investigate the functional upstream role of SENP1 in native progenitor differentiation into erythroid precursors. Native CMS BFU-E colonies showed increased proliferation under hypoxic conditions compared with non-CMS cells, together with an upregulated expression of SENP1, GATA1, EPOR; and no difference in EPO expression. Knock-down of the SENP1 gene abolished the augmented proliferative response. Thus, we demonstrate that native CMS progenitor cells produce a larger proportion of erythroid precursors under hypoxia and that SENP1 is essential for proliferation. Our findings suggest a significant intrinsic component for developing EE in CMS highlanders at the cellular and gene expression level that could be further enhanced by systemic factors such as alterations in respiratory control, or differential hormonal patterns.

Calcium-dependent methylation by PRMT1 promotes erythroid differentiation through the p38α MAPK pathway

Protein arginine methyltransferase 1 (PRMT1) stimulates erythroid differentiation, but the signaling events upstream are yet to be identified. Ca²⁺ plays crucial roles during erythroid differentiation. Here, we show that Ca²⁺ enhances methylation during induced erythroid differentiation and that Ca²⁺ directly upregulates the catalytic activity of recombinant PRMT1 by increasing V_max toward the substrate heterogeneous nuclear ribonucleoprotein A2. We demonstrate that PRMT1 is essential and responsible for the effect of Ca²⁺ on differentiation. Depletion of Ca²⁺ suppresses PRMT1-mediated activation of p38α and p38α-stimulated differentiation. Furthermore, Ca²⁺ stimulates methylation of p38α by PRMT1. This study uncovers a novel regulatory mechanism for PRMT1 by Ca²⁺ and identifies the PRMT1/p38α axis as an intracellular mediator of Ca²⁺ signaling during erythroid differentiation.

Modeling the Hematopoietic Landscape

Some time ago, we proposed a continuum-like view of the lineages open to hematopoietic stem cells (HSCs); each HSC self-renews or chooses from the spectrum of all end-cell options and can then "merely" differentiate. Having selected a cell lineage, an individual HSC may still "step sideways" to an alternative, albeit closely related, fate: HSC and their progeny therefore remain versatile. The hematopoietic cytokines erythropoietin, granulocyte colony-stimulating factor, macrophage colony-stimulating factor, granulocyte/macrophage colony-stimulating factor and ligand for the fms-like tyrosine kinase 3 instruct cell lineage. Sub-populations of HSCs express each of the cytokine receptors that are positively auto-regulated upon cytokine binding. Many years ago, Waddington proposed that the epigenetic landscape played an important role in cell lineage choice. This landscape is dynamic and unstable especially regarding DNA methylation patterns across genomic DNA. This may underlie the receptor diversity of HSC and their decision-making.

Identification and transcriptome analysis of erythroblastic island macrophages

The erythroblastic island (EBI), composed of a central macrophage and surrounding erythroid cells, was the first hematopoietic niche discovered. The identity of EBI macrophages has thus far remained elusive. Given that Epo is essential for erythropoiesis and that Epor is expressed in numerous nonerythroid cells, we hypothesized that EBI macrophages express Epor so that Epo can act on both erythroid cells and EBI macrophages simultaneously to ensure efficient erythropoiesis. To test this notion, we used Epor-eGFPcre knockin mouse model. We show that in bone marrow (BM) and fetal liver, a subset of macrophages express Epor-eGFP. Imaging flow cytometry analyses revealed that >90% of native EBIs comprised F4/80⁺Epor-eGFP⁺ macrophages. Human fetal liver EBIs also comprised EPOR⁺ macrophages. Gene expression profiles of BM F4/80⁺Epor-eGFP⁺ macrophages suggest a specialized function in supporting erythropoiesis. Molecules known to be important for EBI macrophage function such as Vcam1, CD169, Mertk, and Dnase2α were highly expressed in F4/80⁺Epor-eGFP⁺ macrophages compared with F4/80⁺Epor-eGFP^- macrophages. Key molecules involved in iron recycling were also highly expressed in BM F4/80⁺Epor-eGFP⁺ macrophages, suggesting that EBI macrophages may provide an iron source for erythropoiesis within this niche. Thus, we have characterized EBI macrophages in mouse and man. Our findings provide important resources for future studies of EBI macrophage function during normal as well as disordered erythropoiesis in hematologic diseases such as thalassemia, polycythemia vera, and myelodysplastic syndromes.

Erythropoietin inhalation enhances adult canine alveolar-capillary formation following pneumonectomy

Paracrine erythropoietin (EPO) signaling in the lung recruits endothelial progenitor cells, promotes cell maturation and angiogenesis, and is upregulated during canine postpneumonectomy (PNX) compensatory lung growth. To determine whether inhalational delivery of exogenous EPO augments endogenous post-PNX lung growth, adult canines underwent right PNX and received, via a permanent tracheal stoma, weekly nebulization of recombinant human EPO-containing nanoparticles or empty nanoparticles (control) for 16 wk. Lung function was assessed under anesthesia pre- and post-PNX. The remaining lobes were fixed for detailed morphometric analysis. Compared with control treatment, EPO delivery significantly increased serum EPO concentration without altering systemic hematocrit or hemoglobin concentration and abrogated post-PNX lipid oxidative stress damage. EPO delivery modestly increased post-PNX volume densities of the alveolar septum per unit of lung volume and type II epithelium and endothelium per unit of septal tissue volume in selected lobes. EPO delivery also augmented the post-PNX increase in alveolar double-capillary profiles, a marker of intussusceptive capillary formation, in all remaining lobes. EPO treatment did not significantly alter absolute resting lung volumes, lung and membrane diffusing capacities, alveolar-capillary blood volume, pulmonary blood flow, lung compliance, or extravascular alveolar tissue volumes or surface areas. Results established the feasibility of chronic inhalational delivery of growth-modifying biologics in a large animal model. Exogenous EPO selectively enhanced cytoprotection and alveolar angiogenesis in remaining lobes but not whole-lung extravascular tissue growth or resting function; the nonuniform response contributes to structure-function discrepancy, a major challenge for interventions aimed at amplifying the innate potential for compensatory lung growth.

Dosage time affects alkylating agents induced micronuclei in mouse peripheral blood reticulocytes through the function of erythropoietin

Previously, we reported that the frequency of micronucleated reticulocytes (MNRETs) in the peripheral blood of male C3H/He mice intraperitoneally administered ethylnitrosourea (ENU) (25 mg/kg body weight) in the dark period (zeitgeber time, ZT15) was higher than in the light period (ZT3). In this study, to clarify the mechanism underlying this phenomenon, we investigated the differences in micronucleus (MN) induction observed between ZT3 and ZT15 using five chemicals, methylnitrosourea (MNU), ethylmethane sulfonate (EMS), mitomycin C, cyclophosphamide and vincristin. MNU and EMS, monofunctional alkylating agents, showed higher frequencies of MNRETs in the ZT15 than the ZT3 treatment similar to ENU. However, no differences were observed for the other chemicals. In the comet assay, more DNA damage was induced by ENU in the ZT15 than the ZT3 treatment. Furthermore, the plasma erythropoietin (EPO) level, a known effector of MN induction with anti-apoptotic activity mediated by Bcl-xL expression, was higher in the dark than in the light period. EPO did not increase the frequency of MNRETs. However, in the ENU treatment group at ZT3 following EPO injection a significant increase of MNRETs was observed similar to the ZT15 treatment. Higher expression of apoptosis-related genes such as Bcl-xL was induced in bone marrow cells from mice treated with ENU at ZT15 compared with ZT3. From these results, it was speculated that the differences in MN induction in the peripheral blood of mice exposed to monofunctional alkylating agents such as ENU depend on apoptotic or anti-apoptotic conditions related to the circadian rhythms of EPO in bone marrow.

Simultaneous regulation of miR-451 and miR-191 led to erythroid fate decision of mouse embryonic stem cell

OBJECTIVES

Various microRNAs (miRNAs) are expressed during development of mammalian cells, when they aid in modulating gene expression by mediating mRNA transcript cleavage and/or regulation of translation rate. miR-191 and miR-451 have been shown to be critical regulators of hematopoiesis and have important roles in the induction of erythroid fate decision. So, the aim of this study is investigation of the miR-191 and miR-451 roles in the controlling mouse embryonic stem cell (mESC) differentiation toward the erythroid lineage.

MATERIALS AND METHODS

mESCs were infected with either pCDH-miR-Off-191 viruses in pCDH-miR-Off-191 group or simultaneously with pCDH-miR-Off-191 and pCDH-miR-451 lentiviruses in simultaneous group. Then, the expression profiles of erythroid specific transcription factors and globin genes were analyzed using QRT-PCR on day 14 and 21 of differentiation. Flow cytometry analysis was used to evaluate of TER119 and CD235a erythroid specific surface markers.

RESULTS

Gata-1, Klf-1, Epor and globin chains were found to be expressed in pCDH-miR-Off-191 and in simultaneous groups. The majority of globin chains showed changes in their expression levels with progression of differentiation from day 14 to day 21. Flow cytometry results showed that miR-451 up- regulation and miR-191 down-regulation is associated with the expression of TER119 and CD235a. Of these two groups analyzed, simultaneous group was most significantly potent in stimulation of erythroid fate decision of mESCs.

CONCLUSION

Together, present data demonstrate that down-regulation of miR-191 alone can enhance the differentiation of mESCs. However, the simultaneous effect of miR-451up-regulation and miR-191 down-regulation is much stronger and can have more practical use in artificial blood production.

Computational analysis of ligand-receptor interactions in wild-type and mutant erythropoietin complexes

Background

Erythropoietin (EPO), a pleiotropic cytokine, binds to its receptor (EPOR) in bone marrow, activating a signaling cascade that results in red blood cell proliferation. A recently discovered naturally occurring EPO mutation (R150Q) at active site 1 (AS1) of the protein was shown to attenuate its canonical downstream signaling, eliminating its hematopoietic effects and causing a fatal anemia. The purpose of this work was to analyze the EPO–EPOR complex computationally to provide a structural explanation for this signaling change.

Materials and methods

Computational structural biology analyses and molecular dynamics simulations were used to determine key interaction differences between the R150Q mutant and the wild-type form of EPO. Both were compared to another variant mutated at the same position, R150E, which also lacks hematopoietic activity.

Results

The ligand–receptor interactions of the R150Q and R150E mutants showed significant variations in how they interacted with EPOR at AS1 of the EPO–EPOR complex. Both lost specific reported salt bridges previously associated with full complex activation.

Conclusion

This work describes how the ligand–receptor interactions at AS1 of the EPO– EPOR complex respond to mutations at the 150th position. The interactions at AS1 were used to propose a potential mechanism by which the binding of EPO to the extracellular domain of EPOR influences its cytosolic domain and the resulting signaling cascade.

FAM210B is an erythropoietin target and regulates erythroid heme synthesis by controlling mitochondrial iron import and ferrochelatase activity

Erythropoietin (EPO) signaling is critical to many processes essential to terminal erythropoiesis. Despite the centrality of iron metabolism to erythropoiesis, the mechanisms by which EPO regulates iron status are not well-understood. To this end, here we profiled gene expression in EPO-treated 32D pro-B cells and developing fetal liver erythroid cells to identify additional iron regulatory genes. We determined that FAM210B, a mitochondrial inner-membrane protein, is essential for hemoglobinization, proliferation, and enucleation during terminal erythroid maturation. Fam210b deficiency led to defects in mitochondrial iron uptake, heme synthesis, and iron-sulfur cluster formation. These defects were corrected with a lipid-soluble, small-molecule iron transporter, hinokitiol, in Fam210b-deficient murine erythroid cells and zebrafish morphants. Genetic complementation experiments revealed that FAM210B is not a mitochondrial iron transporter but is required for adequate mitochondrial iron import to sustain heme synthesis and iron-sulfur cluster formation during erythroid differentiation. FAM210B was also required for maximal ferrochelatase activity in differentiating erythroid cells. We propose that FAM210B functions as an adaptor protein that facilitates the formation of an oligomeric mitochondrial iron transport complex, required for the increase in iron acquisition for heme synthesis during terminal erythropoiesis. Collectively, our results reveal a critical mechanism by which EPO signaling regulates terminal erythropoiesis and iron metabolism.

Insulin Substrate Receptor (IRS) proteins in normal and malignant hematopoiesis

The insulin receptor substrate (IRS) proteins are a family of cytoplasmic proteins that integrate and coordinate the transmission of signals from the extracellular to the intracellular environment via transmembrane receptors, thus regulating cell growth, metabolism, survival and proliferation. The PI3K/AKT/mTOR and MAPK signaling pathways are the best-characterized downstream signaling pathways activated by IRS signaling (canonical pathways). However, novel signaling axes involving IRS proteins (noncanonical pathways) have recently been identified in solid tumor and hematologic neoplasm models. Insulin receptor substrate-1 (IRS1) and insulin receptor substrate-2 (IRS2) are the best-characterized IRS proteins in hematologic-related processes. IRS2 binds to important cellular receptors involved in normal hematopoiesis (EPOR, MPL and IGF1R). Moreover, the identification of IRS1/ABL1 and IRS2/JAK2V617F interactions and their functional consequences has opened a new frontier for investigating the roles of the IRS protein family in malignant hematopoiesis. Insulin receptor substrate-4 (IRS4) is absent in normal hematopoietic tissues but may be expressed under abnormal conditions. Moreover, insulin receptor substrate-5 (DOK4) and insulin receptor substrate-6 (DOK5) are linked to lymphocyte regulation. An improved understanding of the signaling pathways mediated by IRS proteins in hematopoiesis-related processes, along with the increased development of agonists and antagonists of these signaling axes, may generate new therapeutic approaches for hematological diseases. The scope of this review is to recapitulate and review the evidence for the functions of IRS proteins in normal and malignant hematopoiesis.

Prolyl Hydroxylase Inhibitors: A Breakthrough in the Therapy of Anemia Associated with Chronic Diseases

Chronic kidney disease, cancer, chronic inflammatory disorders, nutritional, and genetic deficiency can cause anemia. Hypoxia causes induction of hypoxia-inducible factor (HIF), which stimulates erythropoietin (EPO) synthesis. Prolyl hydroxylase domain (PHD) enzyme inhibition can stabilize hypoxia-inducible factor (HIF). HIF stabilization also decreases hepcidin, a hormone of hepatic origin, which regulates iron homeostasis. PHD inhibitors represent a novel pharmacological treatment of anemia associated with chronic diseases. Many orally active PHD inhibitors like roxadustat, molidustat, vadadustat, and desidustat are in late phase clinical trials. This review discusses the role of PHD inhibitors in the treatment of anemia associated with chronic diseases.

The hypoxia inducible factor/erythropoietin (EPO)/EPO receptor pathway is disturbed in a rat model of chronic kidney disease related anemia

Objectives

Anemia is a known driver for hypoxia inducible factor (HIF) which leads to increased renal erythropoietin (EPO) synthesis. Bone marrow (BM) EPO receptor (EPOR) signals are transduced through a JAK2-STAT5 pathway. The origins of anemia of chronic kidney disease (CKD) are multifactorial, including impairment of both renal EPO synthesis as well as intestinal iron absorption. We investigated the HIF- EPO- EPOR axis in kidney, BM and proximal tibia in anemic juvenile CKD rats.

Methods

CKD was induced by 5/6 nephrectomy in young (20 days old) male Sprague-Dawley rats while C group was sham operated. Rats were sacrificed 4 weeks after CKD induction and 5 minutes after a single bolus of IV recombinant human EPO. An additional control anemic (C-A) group was daily bled for 7 days.

Results

Hemoglobin levels were similarly reduced in CKD and C-A (11.4 ± 0.3 and 10.8±0.2 Vs 13.5±0.3 g/dL in C, p<0.0001). Liver hepcidin mRNA was decreased in CA but increased in CKD. Serum iron was unchanged while transferrin levels were mildly decreased in CKD. Kidney HIF2α protein was elevated in C-A but unchanged in CKD. Kidney EPO protein and mRNA levels were unchanged between groups. However, BM EPO protein (which reflects circulating EPO) was increased in C-A but remained unchanged in CKD. BM and proximal tibia EPOR were unchanged in C-A but decreased in CKD. Proximal tibial phospho-STAT5 increased after the EPO bolus in C but not in CKD.

Conclusions

Compared to blood loss, anemia in young CKD rats is associated with inappropriate responses in the HIF-EPO-EPO-R axis: kidney HIF2α and renal EPO are not increased, BM and bone EPOR levels, as well as bone pSTAT5 response to EPO are reduced. Thus, anemia of CKD may be treated with additional therapeutic avenues beyond iron and EPO supplementation.

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.

Designing optimal experiments to discriminate interaction graph models

Modern methods for the inference of cellular networks from experimental data often express nondeterminism through an ensemble of candidate models. To discriminate among these candidates new experiments need to be carried out. Theoretically, the number of possible experiments is exponential in the number of possible perturbations. In praxis, experiments are expensive and there exist several limiting constraints. Limiting factors exist on the combinations of perturbations that are technically possible, which components can be measured, and on the number of affordable experiments. Further, not all experiments are equally well suited to discriminate model candidates. The goal of optimal experiment design is to determine those experiments that discriminate most of the candidates while minimizing the costs. We present an approach for experiment planning with interaction graph models and sign consistency methods. This new approach can be used in combination with methods for network inference and consistency checking. We applied our method to study the Erythropoietin signal transduction in human kidney cells HEK293. We first used simulated experiment data from an ODE model to demonstrate in silico that our experimental design results in the inference of the gold standard model. Finally, we used the approach to plan in vivo experiments that discriminate model candidates for the Erythropoietin signal transduction in this cell line.

Epigenetic mechanisms in health and disease: BCEC 2017

The Barcelona Conference on Epigenetics and Cancer (BCEC) entitled "Epigenetic Mechanisms in Health and Disease" was held in Barcelona, October 26-26, 2017. The 2017 BCEC was the fifth and last edition of a series of annual conferences organized as a joint effort of five leading Barcelona research institutes together with B-Debate. This edition was organized by Albert Jordan from the Molecular Biology Institute of Barcelona (IBMB-CSIC) and Marcus Bushbeck from the Josep Carreras Leukaemia Research Institute (IJC). Jordi Bernués, Marian Martínez-Balbás, and Ferran Azorín were also part of the scientific committee. In 22 talks and 51 posters, researchers presented their latest results in the fields of histone variants, epigenetic regulation, and chromatin 3D organization to an audience of around 250 participants from 16 countries. This year, a broad number of talks focused on the epigenetic causes and possible related treatments of complex diseases such as cancer. Participants at the 2017 BCEC elegantly closed the series, discussing progress made in the field of epigenetics and highlighting its role in human health and disease.

Acute Mountain Sickness Is Associated With a High Ratio of Endogenous Testosterone to Estradiol After High-Altitude Exposure at 3,700 m in Young Chinese Men

Background: A large proportion of populations suffer from acute mountain sickness (AMS) after exposure at high altitude. AMS is closely related with age and gender implying that the sex hormones may play critical roles in AMS. Our observational study aimed to identify the association between the endogenous testosterone (T), estradiol (E2) and AMS. Methods: A total of 113 subjects were recruited in 2012. The participants were evaluated at 500 m and after acute (1 day) and short-term (7 days) high-altitude exposure at 3,700 m. The subjects also completed a case report form questionnaire and underwent blood pressure measurements and an echocardiography examination. The red blood cell (RBC) count, Hb concentration ([Hb]), hematocrit (HCT), E2, T, and erythropoietin (EPO) were measured. Results: Upon acute high-altitude exposure, E2 and EPO were significantly lower in AMS⁺ group, and T/E2 and stroke volume were higher. On the 1st day, AMS score correlated positively with the T/E2 ratio while it negatively correlated with E2. After 7 days at 3,700 m, the AMS⁺ subjects had higher erythropoietic parameters: EPO, T, and T/E2 were significantly higher in the AMS⁺ group. [Hb], RBC count, HCT, EPO, T and T/E2 were also correlated with AMS score. EPO, HCT, and the RBC count were also correlated with T/E2. Regression analyses indicated that T/E2 significantly correlated to AMS score and T/E2 on the 1st day was an independent predictor for AMS on the 7th day. Conclusion: AMS was correlated with T/E2 ratio and EPO. After short-term exposure, higher T/E2 may contribute to AMS together with EPO via erythropoiesis. Furthermore, T/E2 level at high altitude in the early stage was an independent predictor for AMS in the latter stage.

Measuring Hematocrit in Mice Injected with In Vitro-Transcribed Erythropoietin mRNA

In vitro-transcribed (IVT) mRNA encoding therapeutic protein has the potential to treat a variety of diseases by serving as template for translation in the patient. To optimize conditions for such therapy, reporter protein-encoding mRNAs are usually used. One preferred reporter is erythropoietin (EPO), which stimulates erythropoiesis and leads to an increase in hematocrit. Measurement of hematocrit is a fast and reliable method to determine the potency of the in vitro-transcribed EPO mRNA. However, frequent blood draw from mice can increase hematocrit due to blood loss. Therefore, instead of using conventional hematocrit capillary tubes, we adapted glass microcapillaries for hematocrit measurement. Daily monitoring of mice can be accomplished by drawing less than 20 μL of blood, thus avoiding blood loss-related hematocrit increase. Due to the small volume of the withdrawn blood the hematocrit remains the same for mice injected with control mRNA, whereas significant hematocrit increase is measured between day 4 and 20 postinjection for those injected with pseudouridine-modified EPO mRNA. Following hematocrit measurement the microcapillaries are snapped easily to recover plasma for further analyses, including EPO measurement by ELISA.

The relationship between systemic iron homeostasis and erythropoiesis

Red blood cell production (erythropoiesis) is the single largest consumer of iron in the body; this need is satisfied by maintaining a sensitive regulation of iron levels. The level of erythropoietic demand regulates the expression of the iron hormone hepcidin and thus iron absorption. Erythropoiesis-mediated regulation of hepcidin is an area of increasing importance and recent studies have identified a number of potential regulatory proteins. This review summarizes our current knowledge about these candidate erythroid regulators of hepcidin and the relation between transferrin receptors and erythropoiesis.

Genome-wide DNA methylation drives human embryonic stem cell erythropoiesis by remodeling gene expression dynamics

AIM

To investigate the role of DNA methylation during erythrocyte production by human embryonic stem cells (hESCs).

METHODS

We employed an erythroid differentiation model from hESCs, and then tracked the genome-wide DNA methylation maps and gene expression patterns through an Infinium HumanMethylation450K BeadChip and an Ilumina Human HT-12 v4 Expression Beadchip, respectively.

RESULTS

A negative correlation between DNA methylation and gene expression was substantially enriched during the later differentiation stage and was present in both the promoter and the gene body. Moreover, erythropoietic genes with differentially methylated CpG sites that were primarily enriched in nonisland regions were upregulated, and demethylation of their gene bodies was associated with the presence of enhancers and DNase I hypersensitive sites. Finally, the components of JAK-STAT-NF-κB signaling were DNA hypomethylated and upregulated, which targets the key genes for erythropoiesis.

CONCLUSION

Erythroid lineage commitment by hESCs requires genome-wide DNA methylation modifications to remodel gene expression dynamics.

Correlated receptor transport processes buffer single-cell heterogeneity

Cells typically vary in their response to extracellular ligands. Receptor transport processes modulate ligand-receptor induced signal transduction and impact the variability in cellular responses. Here, we quantitatively characterized cellular variability in erythropoietin receptor (EpoR) trafficking at the single-cell level based on live-cell imaging and mathematical modeling. Using ensembles of single-cell mathematical models reduced parameter uncertainties and showed that rapid EpoR turnover, transport of internalized EpoR back to the plasma membrane, and degradation of Epo-EpoR complexes were essential for receptor trafficking. EpoR trafficking dynamics in adherent H838 lung cancer cells closely resembled the dynamics previously characterized by mathematical modeling in suspension cells, indicating that dynamic properties of the EpoR system are widely conserved. Receptor transport processes differed by one order of magnitude between individual cells. However, the concentration of activated Epo-EpoR complexes was less variable due to the correlated kinetics of opposing transport processes acting as a buffering system.

Cell surface receptors translate extracellular ligand concentrations to intracellular responses. Receptor transport between the plasma membrane and other cellular compartments regulates the number of accessible receptors at the plasma membrane that determines the strength of downstream pathway activation at a given ligand concentration. In cell populations, pathway activation strength and cellular responses vary between cells. Understanding origins of cell-to-cell variability is highly relevant for cancer research, motivated by the problem of fractional killing by chemotherapies and development of resistance in subpopulations of tumor cells. The erythropoietin receptor (EpoR) is a characteristic example of a receptor system that strongly depends on receptor transport processes. It is involved in several cellular processes, such as differentiation or proliferation, regulates the renewal of erythrocytes, and is expressed in several tumors. To investigate the involvement of receptor transport processes in cell-to-cell variability, we quantitatively characterized trafficking of EpoR in individual cells by combining live-cell imaging with mathematical modeling. Thereby, we found that EpoR dynamics was strongly dependent on rapid receptor transport and turnover. Interestingly, although transport processes largely differed between individual cells, receptor concentrations in cellular compartments were robust to variability in trafficking processes due to the correlated kinetics of opposing transport processes.

Erythropoietin enhances Kupffer cell number and activity in the challenged liver

Erythropoietin (EPO) is the main hormone driving mammalian erythropoiesis, with activity mediated via the surface receptor, EPO-R, on erythroid progenitor cells. Recombinant human EPO is currently used clinically for the treatment of anemia in patients with end-stage renal disease, and in certain cancer patients suffering from anemia induced either by the tumor itself or by chemotherapy. EPO-R expression is also detected in non-erythroid cells, including macrophages present in the peritoneum, spleen, and bone marrow (BM). Here we demonstrate that Kupffer cells (KCs) - the liver-resident macrophages - are EPO targets. We show that, in vitro, EPO initiated intracellular signalling and enhanced phagocytosis in a rat KC line (RKC-2) and in sorted KCs. Moreover, continuous EPO administration in mice, resulted in an increased number of KCs, up-regulation of liver EPO-R expression and elevated production of the monocyte chemoattractant CCL2, with corresponding egress of Ly6C^hi monocytes from the BM. In a model of acute acetaminophen-induced liver injury, EPO administration increased the recruitment of Ly6C^hi monocytes and neutrophils to the liver. Taken together, our results reveal a new role for EPO in stimulating KC proliferation and phagocytosis, and in recruiting Ly6C^hi monocytes in response to liver injury.

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.

Overexpression of the erythropoietin receptor in RAMA 37 breast cancer cells alters cell growth and sensitivity to tamoxifen

Erythropoietin (EPO) is the main regulator of erythropoiesis, and its receptor (EPOR) is expressed in various tissues, including tumors. Expression of EPOR in breast cancer tissue has been shown to correlate with expression of the estrogen receptor (ER). However, EPOR promotes proliferation in an EPO-independent manner. In patients with breast cancer, EPOR is associated with impaired tamoxifen response in ER-positive tumors, but not in ER-negative tumors. Furthermore, a positive correlation between EPOR/ER status and increased local cancer recurrence has been demonstrated, and EPOR expression is associated with G-protein coupled ER (GPER). Herein, we assessed the effects of EPOR on cell physiology and tamoxifen response in the absence of EPO stimulation using two cell lines that differ only in their EPOR expression status: RAMA 37 cells (low EPOR expression) and RAMA 37-28 cells (high EPOR expression). Alterations in cell growth, morphology, response to tamoxifen cytotoxicity, and EPOR-activated signal transduction were observed. RAMA 37 cells showed higher proliferation capacity without tamoxifen treatment, while RAMA 37-28 cells were more resistant to tamoxifen and proliferated more rapidly in the presence of tamoxifen. EPOR overexpression induced cell-morphology changes upon tamoxifen treatment, which resulted in the production of cell protrusions and subsequent cell death. Short-term treatment with tamoxifen (6 h) prompted RAMA 37 cells to acquired longer protrusions than RAMA 37-28 cells, which indicated a pre-apoptotic stage. Furthermore, prolonged treatment with tamoxifen (72 h) caused a greater reduction in RAMA 37 cell numbers, which indicated a higher rate of cell death. RAMA 37-28 cells showed prolonged activation of AKT signaling. We propose sustained AKT phosphorylation in EPOR-overexpressing cells as a mechanism that can lead to EPOR-induced tamoxifen resistance.