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.

Erythropoietin receptor signal is crucial for periodontal ligament stem cell-based tissue reconstruction in periodontal disease

Alveolar bone loss caused by periodontal disease eventually leads to tooth loss. Periodontal ligament stem cells (PDLSCs) are the tissue-specific cells for maintaining and repairing the periodontal ligament, cementum, and alveolar bone. Here, we investigated the role of erythropoietin receptor (EPOR), which regulates the microenvironment-modulating function of mesenchymal stem cells, in PDLSC-based periodontal therapy. We isolated PDLSCs from patients with chronic periodontal disease and healthy donors, referred to as PD-PDLSCs and Cont-PDLSCs, respectively. PD-PDLSCs exhibited reduced potency of periodontal tissue regeneration and lower expression of EPOR compared to Cont-PDLSCs. EPOR-silencing suppressed the potency of Cont-PDLSCs mimicking PD-PDLSCs, whereas EPO-mediated EPOR activation rejuvenated the reduced potency of PD-PDLSCs. Furthermore, we locally transplanted EPOR-silenced and EPOR-activated PDLSCs into the gingiva around the teeth of ligament-induced periodontitis model mice and demonstrated that EPOR in PDLSCs participated in the regeneration of the periodontal ligament, cementum, and alveolar bone in the ligated teeth. The EPOR-mediated paracrine function of PDLSCs maintains periodontal immune suppression and bone metabolic balance via osteoclasts and osteoblasts in the periodontitis model mice. Taken together, these results suggest that EPOR signaling is crucial for PDLSC-based periodontal regeneration and paves the way for the development of novel options for periodontal therapy.

Hemolysis-driven IFNα production impairs erythropoiesis by negatively regulating EPO signaling in sickle cell disease

ABSTRACT

Disordered erythropoiesis is a feature of many hematologic diseases, including sickle cell disease (SCD). However, very little is known about erythropoiesis in SCD. Here, we show that although bone marrow (BM) erythroid progenitors and erythroblasts in Hbbth3/+ thalassemia mice were increased more than twofold, they were expanded by only ∼40% in Townes sickle mice (SS). We further show that the colony-forming ability of SS erythroid progenitors was decreased and erythropoietin (EPO)/EPO receptor (EPOR) signaling was impaired in SS erythroid cells. Furthermore, SS mice exhibited reduced responses to EPO. Injection of mice with red cell lysates or hemin, mimicking hemolysis in SCD, led to suppression of erythropoiesis and reduced EPO/EPOR signaling, indicating hemolysis, a hallmark of SCD, and could contribute to the impaired erythropoiesis in SCD. In vitro hemin treatment did not affect Stat5 phosphorylation, suggesting that hemin-induced erythropoiesis suppression in vivo is via an indirect mechanism. Treatment with interferon α (IFNα), which is upregulated by hemolysis and elevated in SCD, led to suppression of mouse BM erythropoiesis in vivo and human erythropoiesis in vitro, along with inhibition of Stat5 phosphorylation. Notably, in sickle erythroid cells, IFN-1 signaling was activated and the expression of cytokine inducible SH2-containing protein (CISH), a negative regulator of EPO/EPOR signaling, was increased. CISH deletion in human erythroblasts partially rescued IFNα-mediated impairment of cell growth and EPOR signaling. Knocking out Ifnar1 in SS mice rescued the defective BM erythropoiesis and improved EPO/EPOR signaling. Our findings identify an unexpected role of hemolysis on the impaired erythropoiesis in SCD through inhibition of EPO/EPOR signaling via a heme-IFNα-CISH axis.

Molecular basis of JAK2 activation in erythropoietin receptor and pathogenic JAK2 signaling

Janus kinase 2 (JAK2) mediates type I/II cytokine receptor signaling, but JAK2 is also activated by somatic mutations that cause hematological malignancies by mechanisms that are still incompletely understood. Quantitative superresolution microscopy (qSMLM) showed that erythropoietin receptor (EpoR) exists as monomers and dimerizes upon Epo stimulation or through the predominant JAK2 pseudokinase domain mutations (V617F, K539L, and R683S). Crystallographic analysis complemented by kinase activity analysis and atomic-level simulations revealed distinct pseudokinase dimer interfaces and activation mechanisms for the mutants: JAK V617F activity is driven by dimerization, K539L involves both increased receptor dimerization and kinase activity, and R683S prevents autoinhibition and increases catalytic activity and drives JAK2 equilibrium toward activation state through a wild-type dimer interface. Artificial intelligence-guided modeling and simulations revealed that the pseudokinase mutations cause differences in the pathogenic full-length JAK2 dimers, particularly in the FERM-SH2 domains. A detailed molecular understanding of mutation-driven JAK2 hyperactivation may enable novel therapeutic approaches to selectively target pathogenic JAK2 signaling.

Erythropoietin receptor is a risk factor for prognosis: A potential biomarker in lung adenocarcinoma

Lung cancer has the highest mortality rate of all cancers, and LUAD's survival rate is particularly poor. Erythropoietin receptor (EPOR) can be detected in lung adenocarcinoma (LUAD), however, the expression levels and prognostic value of EPOR in LUAD are still unclear. In our study, clinicopathological data of 92 LUAD patients between January 2008 and June 2016, multiple bioinformatics databases and immunohistochemistry were used to explore the EPOR expression, the mutant genes affecting EPOR expression, and the correlation of EPOR expression with oxidative stress - related genes, prognosis, immune microenvironment. All statistical analyses were performed in the R version 4.1.1. The study found that EPOR expression might be down-regulated at the mRNA levels and significantly up-regulated at the protein levels in LUAD, which indicates that the mRNA and protein levels of EPOR are inconsistent. The muTarget showed that the expression of EPOR was significantly different between the mutant group and the wild group of 15 genes, including DDX60L and C1orf168. Importantly, we found that EPOR was associated with VEGF and HIF family members, and had significant positive correlation with oxidative stress - related genes such as CCS, EPX and TXNRD2. This suggests that EPOR may be involved in the regulation of oxidative stress. The Kaplan-Meier Plotter and PrognoScan databases consistently concluded that EPOR was associated with prognosis in LUAD patients. Our clinicopathological data showed that high EPOR expression was associated with poorer overall survival (29.5 vs 46 months) and had a good predictive ability for 4-year and 5-year survival probability. EPOR is expected to be a potential new prognostic marker for LUAD.

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.

Liver kinase B1 (LKB1) in murine erythroid progenitors modulates erythropoietin setpoint in association with maturation control

Erythropoiesis is a tightly regulated process. It is stimulated by decreased oxygen in circulation, which leads to the secretion of the hormone erythropoietin (Epo) by the kidneys. An additional layer of control involves the coordinated sensing and use of nutrients. Much cellular machinery contributes to sensing and responding to nutrient status in cells, and one key participant is the kinase LKB1. The current study examines the role of LKB1 in erythropoiesis using a murine in vivo and ex vivo conditional knockout system. In vivo analysis showed erythroid loss of LKB1 to be associated with a robust increase in serum Epo and mild reticulocytosis. Despite these abnormalities, no evidence of anemia or hemolysis was found. Further characterization using an ex vivo progenitor culture assay demonstrated accelerated erythroid maturation in the LKB1-deficient cells. Based on pharmacologic evidence, this phenotype appeared to result from impaired AMP-activated protein kinase (AMPK) signaling downstream of LKB1. These findings reveal a role for LKB1 in fine-tuning Epo-driven erythropoiesis in association with maturational control.

Erythropoietin Receptor (EPOR) Signaling in the Osteoclast Lineage Contributes to EPO-Induced Bone Loss in Mice

Erythropoietin (EPO) is a pleiotropic cytokine that classically drives erythropoiesis but can also induce bone loss by decreasing bone formation and increasing resorption. Deletion of the EPO receptor (EPOR) on osteoblasts or B cells partially mitigates the skeletal effects of EPO, thereby implicating a contribution by EPOR on other cell lineages. This study was designed to define the role of monocyte EPOR in EPO-mediated bone loss, by using two mouse lines with conditional deletion of EPOR in the monocytic lineage. Low-dose EPO attenuated the reduction in bone volume (BV/TV) in Cx3cr1^Cre EPOR^f/f female mice (27.05%) compared to controls (39.26%), but the difference was not statistically significant. To validate these findings, we increased the EPO dose in LysM^Cre model mice, a model more commonly used to target preosteoclasts. There was a significant reduction in both the increase in the proportion of bone marrow preosteoclasts (CD115⁺) observed following high-dose EPO administration and the resulting bone loss in LysM^Cre EPOR^f/f female mice (44.46% reduction in BV/TV) as compared to controls (77.28%), without interference with the erythropoietic activity. Our data suggest that EPOR in the monocytic lineage is at least partially responsible for driving the effect of EPO on bone mass.

EpoR-tdTomato-Cre mice enable identification of EpoR expression in subsets of tissue macrophages and hematopoietic cells

The erythropoietin receptor (EpoR) has traditionally been thought of as an erythroid-specific gene. Notably, accumulating evidence suggests that EpoR is expressed well beyond erythroid cells. However, the expression of EpoR in non-erythroid cells has been controversial. In this study, we generated EpoR-tdTomato-Cre mice and used them to examine the expression of EpoR in tissue macrophages and hematopoietic cells. We show that in marked contrast to the previously available EpoR-eGFPcre mice, in which a very weak eGFP signal was detected in erythroid cells, tdTomato was readily detectable in both fetal liver (FL) and bone marrow (BM) erythroid cells at all developmental stages and exhibited dynamic changes during erythropoiesis. Consistent with our recent finding that erythroblastic island (EBI) macrophages are characterized by the expression of EpoR, tdTomato was readily detected in both FL and BM EBI macrophages. Moreover, tdTomato was also detected in subsets of hematopoietic stem cells, progenitors, megakaryocytes, and B cells in BM as well as in spleen red pulp macrophages and liver Kupffer cells. The expression of EpoR was further shown by the EpoR-tdTomato-Cre-mediated excision of the floxed STOP sequence. Importantly, EPO injection selectively promoted proliferation of the EpoR-expressing cells and induced erythroid lineage bias during hematopoiesis. Our findings imply broad roles for EPO/EpoR in hematopoiesis that warrant further investigation. The EpoR-tdTomato-Cre mouse line provides a powerful tool to facilitate future studies on EpoR expression and regulation in various non-hematopoietic cells and to conditionally manipulate gene expression in EpoR-expressing cells for functional studies.

Granulocytes Negatively Regulate Secretion of Transforming Growth Factor β1 by Bone Marrow Mononuclear Cells via Secretion of Erythropoietin Receptors in the Milieu

In my previous study, I demonstrated that bone marrow-derived mononuclear cells (BM MNCs) secrete copious amounts of Transforming Growth Factor β1 (TGFβ1) in response to erythropoietin (EPO). In this study, I investigated the principal cell type involved in the process. I found that a large percentage of various marrow cells, but not their mature counterparts present in the peripheral blood, express EPO-receptors (EPO-R). Cell depletion experiments showed that depletion of Glycophorin positive erythroblasts and CD41⁺ megakaryocytes - the prime suspects - did not affect the EPO-mediated TGFβ1 secretion by the BM MNCs. However, individual depletion of CD2⁺ T lymphocytes, CD14⁺ monocyte/macrophages, and CD19⁺ B cells affected the TGFβ1 secretion by EPO-primed MNCs: depletion of CD2⁺ cells had the most striking effect. Unexpectedly, and most interestingly, depletion of CD15⁺ granulocytes led to a significant increase in the TGFβ1 secretion by both naïve and EPO-primed BM MNCs, suggesting that these cells negatively regulate the process. Mechanistically, I show that the CD15⁺ cells exert this regulatory effect via secretion of both full-length and soluble EPO-R in the milieu. Overall my results, for the first time, unravel an in-built regulatory mechanism prevailing in the BM microenvironment that regulates the secretion of TGFβ1 by controlling EPO-EPO-R interaction.My data could be relevant in understanding the pathophysiology of several conditions associated with deregulated production of TGFβ1 in the marrow compartment.

Synthetic Receptors for Sensing Soluble Molecules with Mammalian Cells

Synthetic receptors control cell behavior in response to environmental stimuli for applications in basic research and cell therapy. However, the integration of synthetic receptors in unexplored contexts is cumbersome, especially for nonspecialist laboratories. Here, I provide a detailed protocol on how to use receptors of the generalized extracellular molecule sensor (GEMS) platform. GEMS is a modular receptor system that can be adapted to sense molecules of choice by using affinity domains that dimerize in response to the target. GEMS consist of an erythropoietin receptor scaffold that has been mutated to no longer bind to erythropoietin. N-terminal fusions with affinity domains, such as single chain variable fragments (scFvs), that bind to two epitopes on the same target activate the receptor. The intracellular receptor domain can be chosen from several signal transduction domains of single-pass transmembrane receptors to activate endogenous signaling pathways. As of now, GEMS have been used for sensing prostate specific antigen (PSA), the synthetic azo dye RR120, caffeine, nicotine, rapamycin, the SunTag peptide, and a de novo designed protein displaying two viral epitopes. The tested intracellular domains were derived from FGFR1, IL-6RB, and VEGFR2, and were used to drive transgene expression from reporter plasmids responsive to the endogenous transcription factors STAT3, NFAT, NF-κB, and a synthetic transcription factor activated by the MAPK pathway. In this protocol, I focus on transient transfections of HEK293T cells and include several general notes about cell handling. While the described methods are optimized for experiments with GEMS, most of the described techniques are general procedures to set up synthetic biology experiments in mammalian cell culture. I outline how to generate stable cell lines and share tips on how to adapt GEMS for new ligands. The main objective of this protocol is to make the GEMS technology accessible also to nonspecialist laboratories to facilitate the use of synthetic receptors in new research contexts.

ΗΙF1α, EGR1 and SP1 co-regulate the erythropoietin receptor expression under hypoxia: an essential role in the growth of non-small cell lung cancer cells

BACKGROUND

Overexpression of erythropoietin (EPO) and EPO receptor (EPO-R) is associated with poor prognosis in non-small-cell lung carcinoma (NSCLC). Hypoxia, a potent EPO inducer, is a major stimulating factor in the growth of solid tumors. However, how EPO-R expression is regulated under hypoxia is largely unknown.

METHODS

The role of EPO-R in NSCLC cell proliferation was assessed by RNA interference in vitro. Luciferase reporter assays were performed to map the promoter elements involved in the EPO-R mRNA transcription. Nuclear co-immunoprecipitation and chromatin immunoprecipitation were performed to assess the interaction among transcription factors HIF1α, SP1, and EGR1 in the regulation of EPO-R under hypoxia. The expression of key EPO-R transcription factors in clinical specimens were determined by immunohistochemistry.

RESULTS

Hypoxia induced a dosage and time dependent EPO-R mRNA expression in NSCLC cells. Knockdown of EPO-R reduced NSCLC cell growth under hypoxia (P < 0.05). Mechanistically, a SP1-EGR1 overlapped DNA binding sequence was essential to the hypoxia induced EPO-R transcription. In the early phase of hypoxia, HIF1α interacted with EGR1 that negatively regulated EPO-R. With the exit of EGR1 in late phase, HIF1α positively regulated EPO-R expression through additive interaction with SP1. In clinical NSCLC specimen, SP1 was positively while EGR1 was negatively associated with active EPO-R expression (P < 0.05).

CONCLUSIONS

HIF1α, SP1 and EGR1 mediated EPO-R expression played an essential role in hypoxia-induced NSCLC cell proliferation. Our study presents a novel mechanism of EPO-R regulation in the tumor cells, which may provide information support for NSCLC diagnosis and treatment.

Fetal chronic hypoxia and oxidative stress in diabetic pregnancy. Could fetal erythropoietin improve offspring outcomes?

Oxidative stress is responsible for microvascular complications (hypertension, nephropathy, retinopathy, peripheral neuropathy) of diabetes, which during pregnancy increase both maternal and fetal complications. Chronic hypoxia and hyperglycemia result in increased oxidative stress and decreased antioxidant enzyme activity. However, oxidative stress induces also anti-oxidative reactions both in pregnant diabetes patients and in their fetuses. Not all type 1 diabetes patients with long-lasting disease develop microvascular complications, which suggests that some of these patients have protective mechanisms against these complications. Fetal erythropoietin (EPO) is the main regulator of red cell production in the mother and in the fetus, but it has also protective effects in various maternal and fetal tissues. This dual effect of EPO is based on EPO receptor (EPO-R) isoforms, which differ structurally and functionally from the hematopoietic EPO-R isoform. The tissue protective effects of EPO are based on its anti-apoptotic, anti-oxidative, anti-inflammatory, cell proliferative and angiogenic properties. Recent experimental and clinical studies have shown that EPO has also positive metabolic effects on hyperglycemia and diabetes, although these have not yet been fully delineated. Whether the tissue protective and metabolic effects of EPO could have clinical benefits, are important topics for future research in diabetic pregnancies.

Enhanced anti-mammary gland cancer activities of tamoxifen-loaded erythropoietin-coated drug delivery system

Nanomedicine is an emerging area in the medical field, particularly in the treatment of cancers. Nanostructured lipid carrier (NLC) was shown to be a good nanoparticulated carrier for the delivery of tamoxifen (TAM). In this study, the tamoxifen-loaded erythropoietin-coated nanostructured lipid carriers (EPO-TAMNLC) were developed to enhance the anti-cancer properties and targetability of TAM, using EPO as the homing ligand for EPO receptors (EpoRs) on breast cancer tissue cells. Tamoxifen-loaded NLC (TAMNLC) was used for comparison. The LA7 cells and LA7 cell-induced rat mammary gland tumor were used as models in the study. Immunocytochemistry staining showed that LA7 cells express estrogen receptors (ERs) and EpoRs. EPO-TAMNLC and TAMNLC significantly (p<0.05) inhibited proliferation of LA7 in dose- and time-dependent manner. EPO-TAMNLC induced apoptosis and G₀/G₁ cell cycle arrest of LA7 cells. Both drug delivery systems showed anti-mammary gland tumor properties. At an intravenous dose of 5 mg kg^-1 body weight, EPO-TAMNLC and TAMNLC were not toxic to rats, suggesting that both are safe therapeutic compounds. In conclusion, EPO-TAMNLC is not only a unique drug delivery system because of the dual drug-loading feature, but also potentially highly specific in the targeting of breast cancer tissues positive for ERs and EpoRs. The incorporation of TAM into NLC with and without EPO coat had significantly (p<0.05) improved specificity and safety of the drug carriers in the treatment of mammary gland tumors.

Topological control of cytokine receptor signaling induces differential effects in hematopoiesis

Although tunable signaling by G protein-coupled receptors can be exploited through medicinal chemistry, a comparable pharmacological approach has been lacking for the modulation of signaling through dimeric receptors, such as those for cytokines. We present a strategy to modulate cytokine receptor signaling output by use of a series of designed C2-symmetric cytokine mimetics, based on the designed ankyrin repeat protein (DARPin) scaffold, that can systematically control erythropoietin receptor (EpoR) dimerization orientation and distance between monomers. We sampled a range of EpoR geometries by varying intermonomer angle and distance, corroborated by several ligand-EpoR complex crystal structures. Across the range, we observed full, partial, and biased agonism as well as stage-selective effects on hematopoiesis. This surrogate ligand strategy opens access to pharmacological modulation of therapeutically important cytokine and growth factor receptor systems.

Rhu-Epo down-regulates pro-tumorigenic activity of cancer-associated fibroblasts in multiple myeloma

We have previously demonstrated that recombinant human erythropoietin (rHuEpo) is involved in the regulation of the angiogenic response in multiple myeloma (MM) through a direct effect on macrophages and endothelial cells isolated from the bone marrow of patients with MM. The aim of the present study was designed to determine the effects of rHuEpo on cancer-associated fibroblasts (CAFs) from monoclonal gammopathy of undetermined significance (MGUS) and MM patients by means of in vitro and in vivo assays. rHuEpo treatment reduces the expression of mRNA levels of fibroblast activation markers, namely alpha smooth actin (αSMA) and fibroblast activation protein (FAP) in MGUS and MM CAFs, and of pro-inflammatory and pro-angiogenic cytokines, including interleukin (IL)-6 and IL-8, vascular endothelial growth factor-A (VEGF-A), fibroblast growth factor-2 (FGF-2), and hepatocyte growth factor (HGF) in MM CAFs. Moreover, rHuEpo inhibits the proliferative activity of MM CAFs and increased the apoptosis of MGUS and MM CAFs. Overall, these data suggest that rHu-Epo down-regulates CAFs pro-tumorigenic activity. Moreover, these results are not suggestive for a pro-angiogenic activity of rHuEpo on CAFs. In fact, rHuEpo pre-treatment induces a low angiogenic response in vivo in the chorioallantoic membrane (CAM) assay of MGUS and MM CAFs conditioned medium, not comparable to that of a well-known angiogenic cytokine, VEGF-A, tested in the same assay.

Investigation of the pronounced erythropoietin-induced reduction in hyperglycemia in type 1-like diabetic rats

Erythropoietin (EPO) is known to stimulate erythropoiesis after binding with its specific receptor. In clinics, EPO is widely used in hemodialyzed patients with diabetes. However, changes in the expression of the erythropoietin receptor (EPOR) under diabetic conditions are still unclear. Therefore, we investigated EPOR expression both in vivo and in vitro. Streptozotocin-induced type 1-like diabetic rats (STZ rats) were used to evaluate the blood glucose-lowering effects of EPO. The expression and activity of the transducer and activator of transcription 3 (STAT3), the potential signaling molecule, was investigated in cultured rat skeletal myoblast (L6) cells incubated in high-glucose (HG) medium to mimic the in vivo changes. The EPO-induced reduction in hyperglycemia was more pronounced in diabetic rats. The increased EPOR expression in the soleus muscle of diabetic rats was reversed by the reduction in hyperglycemia. Glucose uptake was also increased in high-glucose (HG)-treated L6 cells. Western blotting results indicated that the EPO-induced hyperglycemic activity was enhanced mainly through an increase in EPOR expression. Increased EPOR expression was associated with the enhanced nuclear expression of STAT3 in HG-exposed L6 cells. In addition, treatment with siRNA specific to STAT3 reversed the increased expression of EPOR observed in these cells. Treatment with Stattic at a dose sufficient to inhibit STAT3 reduced the expression level of EPOR in STZ rats. In conclusion, the increased expression of EPOR by hyperglycemia is mainly associated with an augmented expression of nuclear STAT3, which was identified both in vivo and in vitro in the present study.

Investigation and Management of Erythrocytosis

An absolute erythrocytosis is present when the red cell mass is greater than 125 % of the predicted value for sex and body mass. It can have a primary or secondary and congenital or acquired cause. New causes particularly congenital continue to be discovered and investigated. Investigation for the cause starts with repeat and confirmation of the raised hemoglobin and measurement of an erythropoietin level to indicate whether to pursue primary or secondary causes and then further investigations as appropriate. Management options include low dose aspirin and venesection. Specific management advice is available for certain specific clinical situations.

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.

Identification of Cell Type-Specific Differences in Erythropoietin Receptor Signaling in Primary Erythroid and Lung Cancer Cells

Lung cancer, with its most prevalent form non-small-cell lung carcinoma (NSCLC), is one of the leading causes of cancer-related deaths worldwide, and is commonly treated with chemotherapeutic drugs such as cisplatin. Lung cancer patients frequently suffer from chemotherapy-induced anemia, which can be treated with erythropoietin (EPO). However, studies have indicated that EPO not only promotes erythropoiesis in hematopoietic cells, but may also enhance survival of NSCLC cells. Here, we verified that the NSCLC cell line H838 expresses functional erythropoietin receptors (EPOR) and that treatment with EPO reduces cisplatin-induced apoptosis. To pinpoint differences in EPO-induced survival signaling in erythroid progenitor cells (CFU-E, colony forming unit-erythroid) and H838 cells, we combined mathematical modeling with a method for feature selection, the L₁ regularization. Utilizing an example model and simulated data, we demonstrated that this approach enables the accurate identification and quantification of cell type-specific parameters. We applied our strategy to quantitative time-resolved data of EPO-induced JAK/STAT signaling generated by quantitative immunoblotting, mass spectrometry and quantitative real-time PCR (qRT-PCR) in CFU-E and H838 cells as well as H838 cells overexpressing human EPOR (H838-HA-hEPOR). The established parsimonious mathematical model was able to simultaneously describe the data sets of CFU-E, H838 and H838-HA-hEPOR cells. Seven cell type-specific parameters were identified that included for example parameters for nuclear translocation of STAT5 and target gene induction. Cell type-specific differences in target gene induction were experimentally validated by qRT-PCR experiments. The systematic identification of pathway differences and sensitivities of EPOR signaling in CFU-E and H838 cells revealed potential targets for intervention to selectively inhibit EPO-induced signaling in the tumor cells but leave the responses in erythroid progenitor cells unaffected. Thus, the proposed modeling strategy can be employed as a general procedure to identify cell type-specific parameters and to recommend treatment strategies for the selective targeting of specific cell types.

A major challenge in the development of therapeutic interventions is the selective inhibition of a signal transduction pathway in one cell type such as a cancer cell leaving the other cell type such as a healthy cell as unaffected as possible. Here, we propose a new approach that combines mathematical modeling based on quantitative experimental data with statistical methods. We demonstrate based on simulated data that our approach can determine which parameters are the same and which parameters differ in two exemplary cell types. We compare a lung cancer cell line to the precursor cells of red blood cells. We show that the same signal transduction network induced by erythropoietin (EPO), a hormone that is frequently employed to treat anemia in cancer patients, regulates survival of both cell types. Based on our experimental data in combination with our computational approach, we identify seven cell type-specific differences in this signaling pathway. Our strategy allows predicting therapeutic targets that could be inhibited to interfere with survival of lung cancer cells while leaving production of red blood cells unaffected.

JAK2 V617F stimulates proliferation of erythropoietin-dependent erythroid progenitors and delays their differentiation by activating Stat1 and other nonerythroid signaling pathways

JAK2 V617F is a mutant-activated JAK2 kinase found in most polycythemia vera (PV) patients; it skews normal proliferation and differentiation of hematopoietic stem and progenitor cells and simulates aberrant expansion of erythroid progenitors. JAK2 V617F is known to activate some signaling pathways not normally activated in mature erythroblasts, but there has been no systematic study of signal transduction pathways or gene expression in erythroid cells expressing JAK2 V617F undergoing erythropoietin (Epo)-dependent terminal differentiation. Here we report that expression of JAK2 V617F in murine fetal liver Epo-dependent progenitors allows them to divide approximately six rather than the normal approximately four times in the presence of Epo, delaying their exit from the cell cycle. Over time, the number of red cells formed from each Epo-dependent progenitor increases fourfold, and these cells eventually differentiate into normal enucleated reticulocytes. We report that purified fetal liver Epo-dependent progenitors express many cytokine receptors additional to the EpoR. Expression of JAK2 V617F triggers activation of Stat5, the only STAT normally activated by Epo, as well as activation of Stat1 and Stat3. Expression of JAK2 V617F also leads to transient induction of many genes not normally activated in terminally differentiating erythroid cells and that are characteristic of other hematopoietic lineages. Inhibition of Stat1 activation blocks JAK2 V617F hyperproliferation of erythroid progenitors, and we conclude that Stat1-mediated activation of nonerythroid signaling pathways delays terminal erythroid differentiation and permits extended cell divisions.

Erythropoeitin Signaling in Macrophages Promotes Dying Cell Clearance and Immune Tolerance

The failure of apoptotic cell clearance is linked to autoimmune diseases, nonresolving inflammation, and developmental abnormalities; however, pathways that regulate phagocytes for efficient apoptotic cell clearance remain poorly known. Apoptotic cells release find-me signals to recruit phagocytes to initiate their clearance. Here we found that find-me signal sphingosine 1-phosphate (S1P) activated macrophage erythropoietin (EPO) signaling promoted apoptotic cell clearance and immune tolerance. Dying cell-released S1P activated macrophage EPO signaling. Erythropoietin receptor (EPOR)-deficient macrophages exhibited impaired apoptotic cell phagocytosis. EPO enhanced apoptotic cell clearance through peroxisome proliferator activated receptor-γ (PPARγ). Moreover, macrophage-specific Epor(-/-) mice developed lupus-like symptoms, and interference in EPO signaling ameliorated the disease progression in lupus-like mice. Thus, we have identified a pathway that regulates macrophages to clear dying cells, uncovered the priming function of find-me signal S1P, and found a role of the erythropoiesis regulator EPO in apoptotic cell disposal, with implications for harnessing dying cell clearance.

Truncating Erythropoietin Receptor Rearrangements in Acute Lymphoblastic Leukemia

Chromosomal rearrangements are a hallmark of acute lymphoblastic leukemia (ALL) and are important ALL initiating events. We describe four different rearrangements of the erythropoietin receptor gene EPOR in Philadelphia chromosome-like (Ph-like) ALL. All of these rearrangements result in truncation of the cytoplasmic tail of EPOR at residues similar to those mutated in primary familial congenital polycythemia, with preservation of the proximal tyrosine essential for receptor activation and loss of distal regulatory residues. This resulted in deregulated EPOR expression, hypersensitivity to erythropoietin stimulation, and heightened JAK-STAT activation. Expression of truncated EPOR in mouse B cell progenitors induced ALL in vivo. Human leukemic cells with EPOR rearrangements were sensitive to JAK-STAT inhibition, suggesting a therapeutic option in high-risk ALL.

Erythropoietin regulates POMC expression via STAT3 and potentiates leptin response

The arcuate nucleus of the hypothalamus is essential for metabolic homeostasis and responds to leptin by producing several neuropeptides including proopiomelanocortin (POMC). We previously reported that high-dose erythropoietin (Epo) treatment in mice while increasing hematocrit reduced body weight, fat mass, and food intake and increased energy expenditure. Moreover, we showed that mice with Epo receptor (EpoR) restricted to erythroid cells (ΔEpoRE) became obese and exhibited decreased energy expenditure. Epo/EpoR signaling was found to promote hypothalamus POMC expression independently from leptin. Herein we used WT and ΔEpoRE mice and hypothalamus-derived neural culture system to study the signaling pathways activated by Epo in POMC neurons. We show that Epo stimulation activated STAT3 signaling and upregulated POMC expression in WT neural cultures. ΔEpoRE mice hypothalamus showed reduced POMC levels and lower STAT3 phosphorylation, with and without leptin treatment, compared to in vivo and ex vivo WT controls. Collectively, these data show that Epo regulates hypothalamus POMC expression via STAT3 activation, and provide a previously unrecognized link between Epo and leptin response.

Analysis of the erythropoietin of a Tibetan Plateau schizothoracine fish (Gymnocypris dobula) reveals enhanced cytoprotection function in hypoxic environments

BACKGROUND

Erythropoietin (EPO) is a glycoprotein hormone that plays a principal regulatory role in erythropoiesis and initiates cell homeostatic responses to environmental challenges. The Qinghai-Tibet Plateau is a natural laboratory for hypoxia adaptation. Gymnocypris dobula is a highly specialized plateau schizothoracine fish that is restricted to > 4500 m high-altitude freshwater rivers and ponds in the Qinghai-Tibet Plateau. The role of EPO in the adaptation of schizothoracine fish to hypoxia is unknown.

RESULTS

The EPO and EPO receptor genes from G. dobula and four other schizothoracine fish from various altitudinal habitats were characterized. Schizothoracine EPOs are predicted to possess 2-3 N-glycosylation (NGS) sites, 4-5 casein kinase II phosphorylation (CK2) sites, 1-2 protein kinase C (PKC) phosphorylation sites, and four conserved cysteine residues within four helical domains, with variations in the numbers of NGS and CK2 sites in G. dobula. PAML analysis indicated a d N/d S value (ω) = 1.112 in the G. dobula lineage, and a few amino acids potentially under lineage-specific positive selection were detected within the G. dobula EPO. Similarly, EPO receptors of the two high-altitude schizothoracines (G. dobula and Ptychobarbus kaznakovi), were found to be statistically on the border of positive selection using the branch-site model (P-value = 0.096), and some amino acids located in the ligand-binding domain and the fibronectin type III domain were identified as potentially positive selection sites. Tissue EPO expression profiling based on transcriptome sequencing of three schizothoracines (G. dobula, Schizothorax nukiangensis Tsao, and Schizothorax prenanti) showed significant upregulation of EPO expression in the brain and less significantly in the gill of G. dobula. The elevated expression together with the rapid evolution of the EPO gene in G. dobula suggested a possible role for EPO in adaptation to hypoxia. To test this hypothesis, Gd-EPO and Sp-EPO were cloned into an expression vector and transfected into the cultured cell line 293 T. Significantly higher cell viability was observed in cells transfected with Gd-EPO than cells harboring Sp-EPO when challenged by hypoxia.

CONCLUSION

The deduced EPO proteins of the schizothoracine fish contain characteristic structures and important domains similar to EPOs from other taxa. The presence of potentially positive selection sites in both EPO and EPOR in G. dobula suggest possible adaptive evolution in the ligand-receptor binding activity of the EPO signaling cascade in G. dobula. Functional study indicated that the EPO from high-altitude schizothoracine species demonstrated features of hypoxic adaptation by reducing toxic effects or improving cell survival when expressed in cultured cells, providing evidence of molecular adaptation to hypoxic conditions in the Qinghai-Tibet Plateau.

Delayed hemoglobin switching and perinatal neocytolysis in mice with gain-of-function erythropoietin receptor

Mutations of the truncated cytoplasmic domain of human erythropoietin receptor (EPOR) result in gain-of-function of erythropoietin (EPO) signaling and a dominantly inherited polycythemia, primary familial and congenital polycythemia (PFCP). We interrogated the unexplained transient absence of perinatal polycythemia observed in PFCP patients using an animal model of PFCP to examine its erythropoiesis during embryonic, perinatal, and early postnatal periods. In this model, we replaced the murine EpoR gene (mEpoR) with the wild-type human EPOR (wtHEPOR) or mutant human EPOR gene (mtHEPOR) and previously reported that the gain-of-function mtHEPOR mice become polycythemic at 3~6 weeks of age, but not at birth, similar to the phenotype of PFCP patients. In contrast, wtHEPOR mice had sustained anemia. We report that the mtHEPOR fetuses are polycythemic, but their polycythemia is abrogated in the perinatal period and reappears again at 3 weeks after birth. mtHEPOR fetuses have a delayed switch from primitive to definitive erythropoiesis, augmented erythropoietin signaling, and prolonged Stat5 phosphorylation while the wtHEPOR fetuses are anemic. Our study demonstrates the in vivo effect of excessive EPO/EPOR signaling on developmental erythropoiesis switch and describes that fetal polycythemia in this PFCP model is followed by transient correction of polycythemia in perinatal life associated with low Epo levels and increased exposure of erythrocytes' phosphatidylserine. We suggest that neocytolysis contributes to the observed perinatal correction of polycythemia in mtHEPOR newborns as embryos leaving the hypoxic uterus are exposed to normoxia at birth.

KEY MESSAGE

Human gain-of-function EPOR (mtHEPOR) causes fetal polycythemia in knock-in mice. Wild-type human EPOR causes fetal anemia in knock-in mouse model. mtHEPOR mice have delayed switch from primitive to definitive erythropoiesis. Polycythemia of mtHEPOR mice is transiently corrected in perinatal life. mtHEPOR newborns have low Epo and increased exposure of erythrocytes' phosphatidylserine.

Erythropoietin Stimulates Tumor Growth via EphB4

While recombinant human erythropoietin (rhEpo) has been widely used to treat anemia in cancer patients, concerns about its adverse effects on patient survival have emerged. A lack of correlation between expression of the canonical EpoR and rhEpo's effects on cancer cells prompted us to consider the existence of an alternative Epo receptor. Here, we identified EphB4 as an Epo receptor that triggers downstream signaling via STAT3 and promotes rhEpo-induced tumor growth and progression. In human ovarian and breast cancer samples, expression of EphB4 rather than the canonical EpoR correlated with decreased disease-specific survival in rhEpo-treated patients. These results identify EphB4 as a critical mediator of erythropoietin-induced tumor progression and further provide clinically significant dimension to the biology of erythropoietin.

Expression of platelet-derived growth factor BB, erythropoietin and erythropoietin receptor in canine and feline osteosarcoma

The discovery of expression of the erythropoietin receptor (EPO-R) on neoplastic cells has led to concerns about the safety of treating anaemic cancer patients with EPO. In addition to its endocrine function, the receptor may play a role in tumour progression through an autocrine mechanism. In this study, the expression of EPO, EPO-R and platelet-derived growth factor BB (PDGF-BB) was analysed in five feline and 13 canine osteosarcomas using immunohistochemistry (IHC) and reverse transcription polymerase chain reaction (RT-PCR).

EPO expression was positive in all tumours by IHC, but EPO mRNA was only detected in 38% of the canine and 40% of the feline samples. EPO-R was expressed in all samples by quantitative RT-PCR (RT-qPCR) and IHC. EPO-R mRNA was expressed at higher levels in all feline tumours, tumour cell lines, and kidney when compared to canine tissues. PDGF-BB expression was variable by IHC, but mRNA was detected in all samples. To assess the functionality of the EPO-R on tumour cells, the proliferation of canine and feline osteosarcoma cell lines was evaluated after EPO administration using an alamarBlue assay and Ki67 immunostaining. All primary cell lines responded to EPO treatment in at least one of the performed assays, but the effect on proliferation was very low indicating only a weak responsiveness of EPO-R. In conclusion, since EPO and its receptor are expressed by canine and feline osteosarcomas, an autocrine or paracrine tumour progression mechanism cannot be excluded, although in vitro data suggest a minimal role of EPO-R in osteosarcoma cell proliferation.

Chronic erythropoietin treatment improves diet-induced glucose intolerance in rats

Erythropoietin (EPO) ameliorates glucose metabolism through mechanisms not fully understood. In this study, we investigated the effect of EPO on glucose metabolism and insulin signaling in skeletal muscle. A 2-week EPO treatment of rats fed with a high-fat diet (HFD) improved fasting glucose levels and glucose tolerance, without altering total body weight or retroperitoneal fat mass. Concomitantly, EPO partially rescued insulin-stimulated AKT activation, reduced markers of oxidative stress, and restored heat-shock protein 72 expression in soleus muscles from HFD-fed rats. Incubation of skeletal muscle cell cultures with EPO failed to induce AKT phosphorylation and had no effect on glucose uptake or glycogen synthesis. We found that the EPO receptor gene was expressed in myotubes, but was undetectable in soleus. Together, our results indicate that EPO treatment improves glucose tolerance but does not directly activate the phosphorylation of AKT in muscle cells. We propose that the reduced systemic inflammation or oxidative stress that we observed after treatment with EPO could contribute to the improvement of whole-body glucose metabolism.

The influence of artificially introduced N-glycosylation sites on the in vitro activity of Xenopus laevis erythropoietin

Erythropoietin (EPO), the primary regulator of erythropoiesis, is a heavily glycosylated protein found in humans and several other mammals. Intriguingly, we have previously found that EPO in Xenopus laevis (xlEPO) has no N-glycosylation sites, and cross-reacts with the human EPO (huEPO) receptor despite low homology with huEPO. In this study, we introduced N-glycosylation sites into wild-type xlEPO at the positions homologous to those in huEPO, and tested whether the glycosylated mutein retained its biological activity. Seven xlEPO muteins, containing 1–3 additional N-linked carbohydrates at positions 24, 38, and/or 83, were expressed in COS-1 cells. The muteins exhibited lower secretion efficiency, higher hydrophilicity, and stronger acidic properties than the wild type. All muteins stimulated the proliferation of both cell lines, xlEPO receptor-expressing xlEPOR-FDC/P2 cells and huEPO receptor-expressing UT-7/EPO cells, in a dose-dependent manner. Thus, the muteins retained their in vitro biological activities. The maximum effect on xlEPOR-FDC/P2 proliferation was decreased by the addition of N-linked carbohydrates, but that on UT-7/EPO proliferation was not changed, indicating that the muteins act as partial agonists to the xlEPO receptor, and near-full agonists to the huEPO receptor. Hence, the EPO-EPOR binding site in X. laevis locates the distal region of artificially introduced three N-glycosylation sites, demonstrating that the vital conformation to exert biological activity is conserved between humans and X. laevis, despite the low similarity in primary structures of EPO and EPOR.

Erythropoietin Receptor Antagonist Suppressed Ectopic Hemoglobin Synthesis in Xenografts of HeLa Cells to Promote Their Destruction

The aim of this study is to explore a cause-oriented therapy for patients with uterine cervical cancer that expresses erythropoietin (Epo) and its receptor (EpoR). Epo, by binding to EpoR, stimulates the proliferation and differentiation of erythroid progenitor cells into hemoglobin-containing red blood cells. In this study, we report that the HeLa cells in the xenografts expressed ε, γ, and α globins as well as myoglobin (Mb) to produce tetrameric α2ε2 and α2γ2 and monomeric Mb, most of which were significantly suppressed with an EpoR antagonist EMP9. Western blotting revealed that the EMP9 treatment inhibited the AKT-pAKT, MAPKs-pMAPKs, and STAT5-pSTAT5 signaling pathways. Moreover, the treatment induced apoptosis and suppression of the growth and inhibited the survival through disruption of the harmonized hemoprotein syntheses in the tumor cells concomitant with destruction of vascular nets in the xenografts. Furthermore, macrophages and natural killer (NK) cells with intense HIF-1α expression recruited significantly more in the degenerating foci of the xenografts. These findings were associated with the enhanced expressions of nNOS in the tumor cells and iNOS in macrophages and NK cells in the tumor sites. The treated tumor cells exhibited a substantial number of perforations on the cell surface, which indicates that the tumors were damaged by both the nNOS-induced nitric oxide (NO) production in the tumor cells as well as the iNOS-induced NO production in the innate immune cells. Taken together, these data suggest that HeLa cells constitutively acquire ε, γ and Mb synthetic capacity for their survival. Therefore, EMP9 treatment might be a cause-oriented and effective therapy for patients with squamous cell carcinoma of the uterine cervix.

In vivo regulation of erythropoiesis by chemically inducible dimerization of the erythropoietin receptor intracellular domain

Erythropoietin (Epo) and its receptor (EpoR) are required for the regulation of erythropoiesis. Epo binds to the EpoR homodimer on the surface of erythroid progenitors and erythroblasts, and positions the intracellular domains of the homodimer to be in close proximity with each other. This conformational change is sufficient for the initiation of Epo-EpoR signal transduction. Here, we established a system of chemically regulated erythropoiesis in transgenic mice expressing a modified EpoR intracellular domain (amino acids 247-406) in which dimerization is induced using a specific compound (chemical inducer of dimerization, CID). Erythropoiesis is reversibly induced by oral administration of the CID to the transgenic mice. Because transgene expression is limited to hematopoietic cells by the Gata1 gene regulatory region, the effect of the CID is limited to erythropoiesis without adverse effects. Additionally, we show that the 160 amino acid sequence is the minimal essential domain of EpoR for intracellular signaling of chemically inducible erythropoiesis in vivo. We propose that the CID-dependent dimerization system combined with the EpoR intracellular domain and the Gata1 gene regulatory region generates a novel peroral strategy for the treatment of anemia.

Signals mediating Klotho-induced neuroprotection in hippocampal neuronal cells

The erythropoietin (Epo) receptor (EpoR) is expressed in the brain and was shown to have neuroprotective effects against brain damage in animal models. A recent study indicated that EpoR and its activity are the downstream effectors of Klotho for cytoprotection in the kidney. Thus, we propose that Klotho can stimulate the expression of EpoR in neuronal cells to enhance Epo-mediated protection. H19-7 hippocampal neuronal cells were treated with recombinant Klotho. In H19-7 cells, Klotho increased the expression of both the EpoR protein and mRNA. Klotho also enhanced the transcription activity of the EpoR promoter in H19-7 cells. Moreover, Klotho augmented the Epo-triggered phosphorylation of Jak2 and Stat5 and protected H19-7 cells from hydrogen peroxide cytotoxicity. The silencing of EpoR abolished the protective effect of Klotho against peroxide-induced cytotoxicity. Finally, the silencing of GATA1 diminished the Klotho-induced increase in EpoR protein and mRNA expression as well as its promoter activity. In conclusion, Klotho increased EpoR expression in neuronal cells through GATA1, thereby enabling EpoR to function as a cytoprotective protein against oxidative injury.

Complex pattern of interaction between in utero hypoxia-ischemia and intra-amniotic inflammation disrupts brain development and motor function

BACKGROUND

Infants born preterm commonly suffer from a combination of hypoxia-ischemia (HI) and infectious perinatal inflammatory insults that lead to cerebral palsy, cognitive delay, behavioral issues and epilepsy. Using a novel rat model of combined late gestation HI and lipopolysaccharide (LPS)-induced inflammation, we tested our hypothesis that inflammation from HI and LPS differentially affects gliosis, white matter development and motor impairment during the first postnatal month.

METHODS

Pregnant rats underwent laparotomy on embryonic day 18 and transient systemic HI (TSHI) and/or intra-amniotic LPS injection. Shams received laparotomy and anesthesia only. Pups were born at term. Immunohistochemistry with stereological estimates was performed to assess regional glial loads, and western blots were performed for protein expression. Erythropoietin ligand and receptor levels were quantified using quantitative PCR. Digigait analysis detected gait deficits. Statistical analysis was performed with one-way analysis of variance and post-hoc Bonferonni correction.

RESULTS

Microglial and astroglial immunolabeling are elevated in TSHI + LPS fimbria at postnatal day 2 compared to sham (both P < 0.03). At postnatal day 15, myelin basic protein expression is reduced by 31% in TSHI + LPS pups compared to shams (P < 0.05). By postnatal day 28, white matter injury shifts from the acute injury pattern to a chronic injury pattern in TSHI pups only. Both myelin basic protein expression (P < 0.01) and the phosphoneurofilament/neurofilament ratio, a marker of axonal dysfunction, are reduced in postnatal day 28 TSHI pups (P < 0.001). Erythropoietin ligand to receptor ratios differ between brains exposed to TSHI and LPS. Gait analyses reveal that all groups (TSHI, LPS and TSHI + LPS) are ataxic with deficits in stride, paw placement, gait consistency and coordination (all P < 0.001).

CONCLUSIONS

Prenatal TSHI and TSHI + LPS lead to different patterns of injury with respect to myelination, axon integrity and gait deficits. Dual injury leads to acute alterations in glial response and cellular inflammation, while TSHI alone causes more prominent chronic white matter and axonal injury. Both injuries cause significant gait deficits. Further study will contribute to stratification of injury mechanisms in preterm infants, and guide the use of promising therapeutic interventions.

Molecular and functional characterization of erythropoietin receptor of the goldfish (Carassius auratus L.)

Erythropoietin receptor (EPOR) is a member of the class I cytokine receptor superfamily and signaling through this receptor is important for the proliferation, differentiation and survival of erythrocyte progenitor cells. This study reports on the molecular and functional characterization of goldfish EPOR. The identified goldfish EPOR sequence possesses the conserved EPOR ligand binding domain, the fibronectin domain, the class I cytokine receptor superfamily motif (WSXWS) as well as several intracellular signaling motifs characteristic of other vertebrate EPORs. The expression of epor mRNA in goldfish tissues, cell populations and cells treated with recombinant goldfish EPO (rgEPO) were evaluated by quantitative PCR revealing that goldfish epor mRNA is transcribed in both erythropoietic tissues (blood, kidney and spleen) and non-hematopoietic tissues (brain, heart and gill), as well as in immature erythrocytes. Recombinant goldfish EPOR (rgEPOR), consisting of its extracellular domain, dose-dependently inhibited proliferation of progenitor cells induced by rgEPO. In vitro binding studies indicated that rgEPO exists as monomer, dimer and/or trimmer and that rgEPOR exists as monomer and/or homodimer, and when incubated together, formed a ligand-receptor complex. Our results demonstrate that goldfish EPO/EPOR signaling has been highly conserved throughout vertebrate evolution as a required mechanism for erythrocyte development.

Erythropoietin signaling: a novel regulator of white adipose tissue inflammation during diet-induced obesity

Obesity-induced white adipose tissue (WAT) inflammation and insulin resistance are associated with macrophage (Mф) infiltration and phenotypic shift from "anti-inflammatory" M2-like to predominantly "proinflammatory" M1-like cells. Erythropoietin (EPO), a glycoprotein hormone indispensable for erythropoiesis, has biological activities that extend to nonerythroid tissues, including antiapoptotic and anti-inflammatory effects. Using comprehensive in vivo and in vitro analyses in mice, EPO treatment inhibited WAT inflammation, normalized insulin sensitivity, and reduced glucose intolerance. We investigated EPO receptor (EPO-R) expression in WAT and characterized the role of its signaling during obesity-induced inflammation. Remarkably, and prior to any detectable changes in body weight or composition, EPO treatment reduced M1-like Mф and increased M2-like Mф in WAT, while decreasing inflammatory monocytes. These anti-inflammatory effects were found to be driven, at least in part, by direct EPO-R response in Mф via Stat3 activation, where EPO effects on M2 but not M1 Mф required interleukin-4 receptor/Stat6. Using obese ∆EpoR mice with EPO-R restricted to erythroid cells, we demonstrated an anti-inflammatory role for endogenous EPO. Collectively, our findings identify EPO-R signaling as a novel regulator of WAT inflammation, extending its nonerythroid activity to encompass effects on both Mф infiltration and subset composition in WAT.

Identification of erythropoietin receptor-derived peptides having the potential to induce cancer-reactive cytotoxic T lymphocytes from HLA-A24(+) patients with renal cell carcinoma

Molecular targeting therapy with anti-angiogenic agents, including sunitinib and sorafenib, has been proven to be the first- and second-line standard treatments for metastatic renal cell carcinoma (mRCC) worldwide. Despite their significant antitumor effects, most of the patients with mRCC have not been cured. Under such circumstances, anti-cancer immunotherapy has been considered as a promising treatment modality for mRCC, and cytotoxic T lymphocytes (CTLs) are the most powerful effectors among several immune cells and molecules. Therefore, we previously conducted anti-cancer vaccine therapy with peptides derived from carbonic anhydrase-9 and vascular endothelial growth factor receptor-1 as phase-I/II trials for mRCC patients and reported their clinical benefits. Alternatively, up-regulated expression of erythropoietin (Epo) and its receptor (EpoR) in RCC has been reported, and their co-expression is involved in tumorigenesis. In order to increase options for peptide-based vaccination therapy, we searched for novel EpoR-peptides for HLA-A24(+) RCC patients. Among 5 peptides derived from EpoR, which were prepared based on the binding motif to the HLA-A24 allele, EpoR52-60 peptide had the potential to induce peptide-specific CTLs from peripheral blood mononuclear cells of HLA-A24(+) RCC patients. Cytotoxicity toward HLA-A24(+) and EpoR-expressing RCC cells was ascribed to peptide-specific CD8(+) T cells. These results indicate that the EpoR52-60 peptide could be a promising candidate for a peptide-based anti-cancer vaccine for HLA-A24(+) mRCC patients.

Phenotyping of human melanoma cells reveals a unique composition of receptor targets and a subpopulation co-expressing ErbB4, EPO-R and NGF-R

Malignant melanoma is a life-threatening skin cancer increasingly diagnosed in the western world. In advanced disease the prognosis is grave. Growth and metastasis formation in melanomas are regulated by a network of cytokines, cytokine-receptors, and adhesion molecules. However, little is known about surface antigens and target expression profiles in human melanomas. We examined the cell surface antigen profile of human skin melanoma cells by multicolor flow cytometry, and compared their phenotype with 4 melanoma cell lines (A375, 607B, Mel-Juso, SK-Mel28). Melanoma cells were defined as CD45-/CD31- cells co-expressing one or more melanoma-related antigens (CD63, CD146, CD166). In most patients, melanoma cells exhibited ErbB3/Her3, CD44/Pgp-1, ICAM-1/CD54 and IGF-1-R/CD221, but did not express CD20, ErbB2/Her2, KIT/CD117, AC133/CD133 or MDR-1/CD243. Melanoma cell lines were found to display a similar phenotype. In most patients, a distinct subpopulation of melanoma cells (4-40%) expressed the erythropoietin receptor (EPO-R) and ErbB4 together with PD-1 and NGF-R/CD271. Both the EPO-R+ and EPO-R- subpopulations produced melanoma lesions in NOD/SCID IL-2Rgamma(null) (NSG) mice in first and secondary recipients. Normal skin melanocytes did not express ErbB4 or EPO-R, but expressed a functional KIT receptor (CD117) as well as NGF-R, ErbB3/Her3, IGF-1-R and CD44. In conclusion, melanoma cells display a unique composition of surface target antigens and cytokine receptors. Malignant transformation of melanomas is accompanied by loss of KIT and acquisition of EPO-R and ErbB4, both of which are co-expressed with NGF-R and PD-1 in distinct subfractions of melanoma cells. However, expression of EPO-R/ErbB4/PD-1 is not indicative of a selective melanoma-initiating potential.

Erythroid-extrinsic regulation of normal erythropoiesis by retinoic acid receptors

Vitamin A and its derivatives (retinoids) are important regulators of haematopoiesis, acting via retinoic acid receptors (RARs). Epidemiological studies indicated an association of vitamin A deficiency with anaemia in humans. To define the requirements of RARs in erythropoiesis, we evaluated erythroid parameters in RAR germ-line deficient and conditional knock out mice with erythroid specific deletion of RARs. Adult RARγ(-/-) mice were anaemic, however, Epor-Cre Rara(fl/fl) , Epor-Cre Rarg(fl/fl) and Epor-Cre Rara(fl/fl) g(fl/fl) mice were normal, indicating a lack of an erythroid intrinsic RAR function. Therefore, erythroid-specific RAR function is dispensable for erythropoiesis and RARγ plays an erythroid extrinsic role in erythropoiesis.

PPARα and Sirt1 mediate erythropoietin action in increasing metabolic activity and browning of white adipocytes to protect against obesity and metabolic disorders

Erythropoietin (EPO) has shown beneficial effects in the regulation of obesity and metabolic syndrome; however, the detailed mechanism is still largely unknown. Here, we created mice with adipocyte-specific deletion of EPO receptor. These mice exhibited obesity and decreased glucose tolerance and insulin sensitivity, especially when fed a high-fat diet. Moreover, EPO increased oxidative metabolism, fatty acid oxidation, and key metabolic genes in adipocytes and in white adipose tissue from diet-induced obese wild-type mice. Increased metabolic activity by EPO is associated with induction of brown fat-like features in white adipocytes, as demonstrated by increases in brown fat gene expression, mitochondrial content, and uncoupled respiration. Peroxisome proliferator-activated receptor (PPAR)α was found to mediate EPO activity because a PPARα antagonist impaired EPO-mediated induction of brown fat-like gene expression and uncoupled respiration. PPARα also cooperates with Sirt1 activated by EPO through modulating the NAD+ level to regulate metabolic activity. PPARα targets, including PPARγ coactivator 1α, uncoupling protein 1, and carnitine palmitoyltransferase 1α, were increased by EPO but impaired by Sirt1 knockdown. Sirt1 knockdown also attenuated adipose response to EPO. Collectively, EPO, as a novel regulator of adipose energy homeostasis via these metabolism coregulators, provides a potential therapeutic strategy to protect against obesity and metabolic disorders.

Erythropoietin receptor expression is a potential prognostic factor in human lung adenocarcinoma

Recombinant human erythropoietins (rHuEPOs) are used to treat cancer-related anemia. Recent preclinical studies and clinical trials, however, have raised concerns about the potential tumor-promoting effects of these drugs. Because the clinical significance of erythropoietin receptor (EPOR) signaling in human non-small cell lung cancer (NSCLC) also remains controversial, our aim was to study whether EPO treatment modifies tumor growth and if EPOR expression has an impact on the clinical behavior of this malignancy. A total of 43 patients with stage III–IV adenocarcinoma (ADC) and complete clinicopathological data were included. EPOR expression in human ADC samples and cell lines was measured by quantitative real-time polymerase chain reaction. Effects of exogenous rHuEPOα were studied on human lung ADC cell lines in vitro. In vivo growth of human ADC xenografts treated with rHuEPOα with or without chemotherapy was also assessed. In vivo tumor and endothelial cell (EC) proliferation was determined by 5-bromo-2’-deoxy-uridine (BrdU) incorporation and immunofluorescent labeling. Although EPOR mRNA was expressed in all of the three investigated ADC cell lines, rHuEPOα treatment (either alone or in combination with gemcitabine) did not alter ADC cell proliferation in vitro. However, rHuEPOα significantly decreased tumor cell proliferation and growth of human H1975 lung ADC xenografts. At the same time, rHuEPOα treatment of H1975 tumors resulted in accelerated tumor endothelial cell proliferation. Moreover, in patients with advanced stage lung ADC, high intratumoral EPOR mRNA levels were associated with significantly increased overall survival. This study reveals high EPOR level as a potential novel positive prognostic marker in human lung ADC.

Age-dependent astroglial vulnerability to hypoxia and glutamate: the role for erythropoietin

Extracellular accumulation of toxic concentrations of glutamate (Glu) is a hallmark of many neurodegenerative diseases, often accompanied by hypoxia and impaired metabolism of this neuromediator. To address the question whether the multifunctional neuroprotective action of erythropoietin (EPO) extends to the regulation of extracellular Glu-level and is age-related, young and culture-aged rat astroglial primary cells (APC) were simultaneously treated with 1mM Glu and/or human recombinant EPO under normoxic and hypoxic conditions (NC and HC). EPO increased the Glu uptake by astrocytes under both NC and especially upon HC in culture-aged APC (by 60%). Moreover, treatment with EPO up-regulated the activity of glutamine synthetase (GS), the expression of glutamate-aspartate transporter (GLAST) and the level of EPO mRNA. EPO alleviated the Glu- and hypoxia-induced LDH release from astrocytes. These protective EPO effects were concentration-dependent and they were strongly intensified with age in culture. More than a 4-fold increase in apoptosis and a 2-fold decrease in GS enzyme activity was observed in APC transfected with EPO receptor (EPOR)-siRNA. Our in vivo data show decreased expression of EPO and a strong increase of EPOR in brain homogenates of APP/PS1 mice and their wild type controls during aging. Comparison of APP/PS1 and age-matched WT control mice revealed a stronger expression of EPOR but a weaker one of EPO in the Alzheimer's disease (AD) model mice. Here we show for the first time the direct correlation between the extent of differentiation (age) of astrocytes and the efficacy of EPO in balancing extracellular glutamate clearance and metabolism in an in-vitro model of hypoxia and Glu-induced astroglial injury. The clinical relevance of EPO and EPOR as markers of brain cells vulnerability during aging and neurodegeneration is evidenced by remarkable changes in their expression levels in a transgenic model of AD and their WT controls.

In vivo knockdown of adipocyte erythropoietin receptor does not alter glucose or energy homeostasis

The growing prevalence of obesity and diabetes necessitate a better understanding of the role of adipocyte biology in metabolism. Increasingly, erythropoietin (EPO) has been shown to have extraerythropoietic and cytoprotective roles. Exogenous administration has recently been shown to have beneficial effects on obesity and diabetes in mouse models and EPO can modulate adipogenesis and insulin signaling in 3T3-L1 adipocytes. However, its physiological role in adipocytes has not been identified. Using male and female mice with adipose tissue-specific knockdown of the EPO receptor, we determine that adipocyte EPO signaling is not essential for the maintenance of energy homeostasis or glucose metabolism. Adipose tissue-specific disruption of EPO receptor did not alter adipose tissue expansion, adipocyte morphology, insulin resistance, inflammation, or angiogenesis in vivo. In contrast to the pharmacological effects of EPO, we demonstrate that EPO signaling at physiological levels is not essential for adipose tissue regulation of metabolism.

Genetically heterogeneous origins of idiopathic erythrocytosis

The idiopathic erythrocytosis (IE) group of disorders is defined by an absolute increase in red cell mass and hematocrit without elevation of the megakaryocytic or granulocytic lineages. It is associated with a wide range of serum erythropoietin (Epo) levels and broadly falls into groups of raised/inappropriately normal or low/undetectable Epo levels. A spectrum of molecular defects has been described in association with IE, which reflects the heterogeneity of this disorder. To date the most common identified cause of IE has been mutations in the von Hippel Landau (VHL) protein, which results in aberrant oxygen sensing and dysregulated Epo production. Studying the molecular basis of IE will provide insights into the control of Epo synthesis and Epo-induced signaling pathways.

Epo receptors are not detectable in primary human tumor tissue samples

Erythropoietin (Epo) is a cytokine that binds and activates an Epo receptor (EpoR) expressed on the surface of erythroid progenitor cells to promote erythropoiesis. While early studies suggested EpoR transcripts were expressed exclusively in the erythroid compartment, low-level EpoR transcripts were detected in nonhematopoietic tissues and tumor cell lines using sensitive RT-PCR methods. However due to the widespread use of nonspecific anti-EpoR antibodies there are conflicting data on EpoR protein expression. In tumor cell lines and normal human tissues examined with a specific and sensitive monoclonal antibody to human EpoR (A82), little/no EpoR protein was detected and it was not functional. In contrast, EpoR protein was reportedly detectable in a breast tumor cell line (MCF-7) and breast cancer tissues with an anti-EpoR polyclonal antibody (M-20), and functional responses to rHuEpo were reported with MCF-7 cells. In another study, a functional response was reported with the lung tumor cell line (NCI-H838) at physiological levels of rHuEpo. However, the specificity of M-20 is in question and the absence of appropriate negative controls raise questions about possible false-positive effects. Here we show that with A82, no EpoR protein was detectable in normal human and matching cancer tissues from breast, lung, colon, ovary and skin with little/no EpoR in MCF-7 and most other breast and lung tumor cell lines. We show further that M-20 provides false positive staining with tissues and it binds to a non-EpoR protein that migrates at the same size as EpoR with MCF-7 lysates. EpoR protein was detectable with NCI-H838 cells, but no rHuEpo-induced phosphorylation of AKT, STAT3, pS6RP or STAT5 was observed suggesting the EpoR was not functional. Taken together these results raise questions about the hypothesis that most tumors express high levels of functional EpoR protein.

Exploratory bioinformatics study of lncRNAs in Alzheimer's disease mRNA sequences with application to drug development

Long noncoding RNA (lncRNA) within mRNA sequences of Alzheimer's disease genes, namely, APP, APOE, PSEN1, and PSEN2, has been analyzed using fractal dimension (FD) computation and correlation analysis. We examined lncRNA by comparing mRNA FD to corresponding coding DNA sequences (CDSs) FD. APP, APOE, and PSEN1 CDSs select slightly higher FDs compared to the mRNA, while PSEN2 CDSs FDs are lower. The correlation coefficient for these sequences is 0.969. A comparative study of differentially expressed MAPK signaling pathway lncRNAs in pancreatic cancer cells shows a correlation of 0.771. Selection of higher FD CDSs could indicate interaction of Alzheimer's gene products APP, APOE, and PSEN1. Including hypocretin sequences (where all CDSs have higher fractal dimensions than mRNA) in the APP, APOE, and PSEN1 sequence analyses improves correlation, but the inclusion of erythropoietin (where all CDSs have higher FD than mRNA) would suppress correlation, suggesting that HCRT, a hypothalamus neurotransmitter related to the wake/sleep cycle, might be better when compared to EPO, a glycoprotein hormone, for targeting Alzheimer's disease drug development. Fractal dimension and entropy correlation have provided supporting evidence, consistent with evolutionary studies, for using a zebrafish model together with a mouse model, in HCRT drug development.

Changes in the Expression of Transcription Factors Involved in Modulating the Expression of EPO-R in Activated Human CD4-Positive Lymphocytes

We have recently described the presence of the erythropoietin receptor (EPO-R) on CD4⁺ lymphocytes and demonstrated that its expression increases during their activation, reaching a level reported to be typical for erythroid progenitors. This observation suggests that EPO-R expression is modulated during lymphocyte activation, which may be important for the cells’ function. Here we investigated whether the expression of GATA1, GATA3 and Sp1 transcription factors is correlated with the expression of EPO-R in human CD4⁺ lymphocytes stimulated with monoclonal anti-CD3 antibody. The expression of GATA1, GATA3 and Sp1 transcription factors in CD4⁺ cells was estimated before and after stimulation with anti-CD3 antibody by Western Blot and flow cytometry. The expression of EPO-R was measured using real-time PCR and flow cytometry. There was no change in the expression of GATA1 and GATA3 in CD4⁺ lymphocytes after stimulation with anti-CD3 antibody. However, stimulation resulted in the significantly increased expression of the Sp1 factor. CD4⁺ lymphocytes stimulated with anti-CD3 antibody exhibited an increase in both the expression level of EPOR gene and the number of EPO-R molecules on the cells’ surface, the latter being significantly correlated with the increased expression of Sp1. Sp1 is noted to be the single transcription factor among the ones studied whose level changes as a result of CD4⁺ lymphocyte stimulation. It seems that Sp1 may significantly affect the number of EPO-R molecules present on the surface of activated CD4⁺ lymphocytes.

Erythropoietin improves insulin resistance via the regulation of its receptor-mediated signaling pathways in 3T3L1 adipocytes

Recombinant human erythropoietin (rHuEPO) reduces serum insulin levels, increases insulin sensitivity, and reduces insulin resistance (IR). However, the mechanisms behind these effects are unclear. This study aimed to investigate the mechanism by which rHuEPO effects IR in 3T3L1 adipocytes. After treatment with different concentrations of rHuEPO, glucose consumption, and tumor necrosis factor (TNF-α), adiponectin, and leptin levels were assayed with a commercial enzyme-linked immunosorbent assays. Endogenous erythropoietin receptor (EPOR) expression was inhibited using small interfering RNA (siRNA). EPOR protein and mRNA expression was detected via immunofluorescence and real-time PCR analyses, respectively. The expression of pAKT/AKT and p-STAT5/STAT5 was determined via Western blot analysis. rHuEPO treatment improved glucose uptake, increased adiponectin levels, and reduced TNF-α and leptin levels in 3T3L1 adipocytes with dexamethasone-induced IR. Whereas EPOR protein and gene expression was absent in preadipocytes, it was observed in mature 3T3L1 adipocytes. However, the expression of EPOR in insulin resistant 3T3L1 adipocytes was significantly decreased (p<0.05). rHuEPO increased the expression of EPOR, and upregulated the expression of pAKT/AKT and pSTAT5/STAT5 in 3T3L1 adipocytes (p<0.05), which was blocked by siEPOR, the phosphatidylinositol-3-kinase (PI3K) inhibitor, LY294002, and a STAT5 inhibitor, respectively. In summary, rHuEPO reduced IR in adipocytes by increasing glucose uptake and improving the adipokine profile. rHuEPO-induced EPOR protein expression and subsequent induction of pAKT and pSTAT5 suggest that the EPO-EPOR system may play a role in glucose metabolism within adipocytes.