Functional and immunochemical characterisation of different antibodies against the erythropoietin receptor

Retinopathy of prematurity protection conferred by uteroplacental insufficiency through erythropoietin signaling in an experimental Murine Model

BACKGROUND

Recent clinical studies suggest that preeclampsia, characterized by uteroplacental insufficiency (UPI) and infant intrauterine growth restriction (IUGR), may be protective against retinopathy of prematurity (ROP) in preterm infants. Experimental models of UPI/IUGR have found an association of erythropoietin (EPO) with less severe oxygen-induced retinopathy (OIR); however, it is unclear if EPO/EPO receptor (EPOR) signaling was involved. We hypothesized that maternal UPI and resultant infant IUGR would protect against features of ROP through EPO/EPOR signaling.

METHODS

We compared transgenic mice with hypoactive EPOR signaling (hWtEPOR) to littermate wild-type mice (mWtEpoR) in a novel combined model of IUGR and ROP. Thromboxane A2 (TXA2) was infused into pregnant C57Bl/6J dams to produce UPI/IUGR; postnatal pups and their foster dams were subjected to a murine OIR model.

RESULTS

Following hyperoxia, hematocrits were similar between littermate wild-type (mWtEpoR) TXA2/OIR and vehicle/OIR pups. mWtEpoR TXA2/OIR had increased serum EPO, retinal EPO and VEGF, and decreased avascular retinal area (AVA) compared to vehicle/OIR pups. In comparison to the mWtEpoR TXA2/OIR pups, AVA was not reduced in hWtEPOR TXA2/OIR pups.

CONCLUSION

Our findings provide biologic evidence that UPI/OIR-induced endogenous EPOR signaling confers protection against hyperoxia-induced vascular damage that may be related to pathophysiology in ROP.

IMPACT

Maternal preeclampsia and infant growth restriction confer retinovascular protection against high oxygen-induced damage through endogenous erythropoietin signaling.

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.

Obligatory role of Schwann cell-specific erythropoietin receptors in erythropoietin-induced functional recovery and neurogenic muscle atrophy after nerve injury

BACKGROUND

Erythropoietin (EPO) promotes myelination and functional recovery in rodent peripheral nerve injury (PNI). While EPO receptors (EpoR) are present in Schwann cells, the role of EpoR in PNI recovery is unknown because of the lack of EpoR antagonists or Schwann cell-specific EpoR knockout animals.

METHODS

Using the Cre-loxP system, we developed a myelin protein zero (Mpz) promoter-driven knockout mouse model of Schwann cell EpoR (MpzCre-EpoR^flox/flox , Mpz-EpoR-KO). Mpz-EpoR-KO and control mice were assigned to sciatic nerve crush injury followed by EPO treatment.

RESULTS

EPO treatment significantly accelerated functional recovery in control mice in contrast to significantly reduced functional recovery in Mpz-EpoR-KO mice. Significant muscle atrophy was found in the injured hindlimb of EPO-treated Mpz-EpoR-KO mice but not in EPO-treated control mice.

CONCLUSIONS

These preliminary findings provide direct evidence for an obligatory role of Schwann-cell specific EpoR for EPO-induced functional recovery and muscle atrophy following PNI.

Dual Switch Mechanism of Erythropoietin as an Antiapoptotic and Pro-Angiogenic Determinant in the Retina

Constant or intense light degenerates the retina and retinal pigment epithelial cells. Light generates reactive oxygen species and nitric oxide leading to initial reactions of retinal degeneration. Apoptosis is the primary mechanism of abnormal death of photoreceptors, retinal ganglion cells, or retinal pigment epithelium (RPE) in degenerative retinal diseases, including diabetic retinopathy and age-related macular degeneration. The current study evaluated the function of erythropoietin (EPO) on angiogenesis and apoptosis in the retina and RPE under oxidative stress. We determined the pro-angiogenic and antiapoptotic mechanism of EPO under stress conditions using a conditional EPO knockdown model using siRNA, EPO addition, proteomics, immunocytochemistry, and bioinformatic analysis. Our studies verified that EPO protected retinal cells from light-, hypoxia-, hyperoxia-, and hydrogen peroxide-induced apoptosis through caspase inhibition, whereas up-regulated angiogenic reactions through vascular endothelial growth factor (VEGF) and angiotensin pathway. We demonstrated that the EPO expression in the retina and subsequent serine/threonine/tyrosine kinase phosphorylations might be linked to oxidative stress response tightly to determining angiogenesis and apoptosis. Neuroprotective roles of EPO may involve the balance between antiapoptotic and pro-angiogenic signaling molecules, including BCL-xL, c-FOS, caspase-3, nitric oxide, angiotensin, and VEGF receptor. Our data indicate a new therapeutic application of EPO toward retinal degeneration based on the dual roles in apoptosis and angiogenesis at the molecular level under oxidative stress.

Erythropoietin induces miRNA-210 by JAK2/STAT5 signaling in PBMCs of End-stage Renal Disease patients

Anemia of chronic kidney disease is associated with blunted response/resistance to erythropoietin-stimulating agents (ESAs) in hemodialysis (HD) patients. Several molecules have been successfully associated with ESA responsiveness; however, none of them is now considered a valid therapeutic biomarker of erythropoietin resistance in these patients. We performed an evaluation of the level of specific plasma circulating miRNAs in blood samples of HD patients, in relation to ESA treatment, with a follow-up of 1 year (T0-T3). We found significantly lower circulating levels of all miRNAs analyzed at baseline (T0) in HD patients vs. healthy control (HC). The plasmatic levels of miRNA-210 resulted significantly and negatively associated with Erythropoietin Resistance Index (ERI), and the variance of ΔmiRNA-210 (miRNA-210_T3 minus miRNA-210_T0 ) explained significant percentage of ΔERI (ERI_T3 minus ERI_T0 ) variance. The receiver operating characteristic analysis at T0 showed that the plasmatic level of miRNA-210 could distinguish HD patients with positive or negative trend in ERI at T3. In vitro, recombinant human erythropoietin (EPO) induced significant release of miRNA-210 from cultured peripheral blood mononuclear cells, through the activation of Janus kinase 2 (JAK2)/ signal transducer and activator of transcription 5 (STAT5) signaling, but not by the activation of the MAPK protein 38α and extracellular signal-regulated kinase ½. Accordingly, HD patients with negative ΔERI showed higher level of phosphor-Janus kinase 2 and nuclear translocation of phosphor-signal transducer and activator of transcription 5. vs. patients with positive ΔERI or HC. Our data highlighted that chronic HD significantly reduces the circulating level of the miRNAs evaluated; within the targets analyzed, the miRNA-210 could be considered as a prognostic indicator of ESA responsiveness and index for anemia management.

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.

Treatment of Neonatal Hypoxic-Ischemic Encephalopathy with Erythropoietin Alone, and Erythropoietin Combined with Hypothermia: History, Current Status, and Future Research

Perinatal hypoxic-ischemic encephalopathy (HIE) remains a major cause of morbidity and mortality. Moderate hypothermia (33.5 °C) is currently the sole established standard treatment. However, there are a large number of infants for whom this therapy is ineffective. This inspired global research to find neuroprotectants to potentiate the effect of moderate hypothermia. Here we examine erythropoietin (EPO) as a prominent candidate. Neonatal animal studies show that immediate, as well as delayed, treatment with EPO post-injury, can be neuroprotective and/or neurorestorative. The observed improvements of EPO therapy were generally not to the level of control uninjured animals, however. This suggested that combining EPO treatment with an adjunct therapeutic strategy should be researched. Treatment with EPO plus hypothermia led to less cerebral palsy in a non-human primate model of perinatal asphyxia, leading to clinical trials. A recent Phase II clinical trial on neonatal infants with HIE reported better 12-month motor outcomes for treatment with EPO plus hypothermia compared to hypothermia alone. Hence, the effectiveness of combined treatment with moderate hypothermia and EPO for neonatal HIE currently looks promising. The outcomes of two current clinical trials on neurological outcomes at 18-24 months-of-age, and at older ages, are now required. Further research on the optimal dose, onset, and duration of treatment with EPO, and critical consideration of the effect of injury severity and of gender, are also required.

The endogenous erythropoietin in correlation with other erythrocytic parameters in patients with head and neck squamous cell carcinoma treated with platinum-based induction chemotherapy

Between January 2017 and July 2018 103 patients were included in a prospective study of erythropoietin (EPO) monitoring. The group consisted of 33% patients with oropharynx, 29% with oral cavity, 13% with nasopharynx, 6% with larynx, 6% with hypopharynx, 8% with unknown primary cancer, 4% with nasal cavity, and 1% with salivary gland cancer. Clinic stage: T4 - 50, T3 - 21, T2 - 14, T1 - 10, T0 - 8, and N3 - 19, N2 - 61, N1 - 10, N0 - 13. All patients received from one to four cycles of induction chemotherapy. EPO was measured in blood serum by enzyme-labelled chemiluminescent immunometric assay, using an Immulite 2000XPi analyser before the administration and on day 11 of each chemotherapy cycle. During induction chemotherapy the EPO level was elevated in all patients, which is expressed by means of medians: 10.7 (p = 0.000001) in the middle of cycle 1; 10.9 (p = 0.66) before cycle 2; 14.35 (p = 0.000177) in the middle of cycle 2; 14.95 (p = 0.39) before cycle 3, 17.00 (p = 0.00078) in the middle of cycle 3, and 20.9 after cycle 3 (p = 0.41). The correlation analysis conducted indicates that the administration of one chemotherapy dose results in higher EPO release (two-fold increase in EPO concentration) which intensifies reticulocytes (REC) production but without haemoglobin concentration in reticulocytes (HGB-REC) growth. In consequence, it leads to a decrease in RBC and HGB concentration (29-32 cases). The administration of two and three chemotherapy doses results in the subsequent higher release of EPO, which does not intensify REC production. In consequence, anaemia increases (35 cases).

Impact of Inadequate Methods and Data Analysis on Reproducibility

Failure to reproduce results of articles is recognized, but the causes, and therefore solutions, are not. One possibility is that deficits in quality of the work result in varying or inconclusive results. Erythropoiesis-stimulating agents have been used to treat anemia in patients with cancer, but there are concerns that erythropoiesis-stimulating agents might stimulate Epo receptors on tumor cells (Epo receptor-cancer hypothesis). Articles have been published on the topic, but the data and conclusions conflict, making them suitable for examination of a relationship between quality and reproducibility. Comprehensive literature searches were performed, and 280 relevant articles were identified. Numerous conflicts between and within these articles were apparent. The incidence of faults in quality parameters was high, including absence of adequate controls (90% of articles), inadequate validation of reagents and methods (87% of articles), and inadequate or improper statistical methods (84% of articles) with questionable interpretation of the data (81% of articles). This resulted in false-positive/negative data that varied with the reagents and methods used. The low quality of evidence may explain the poor reproducibility of Epo receptor-cancer articles.

Developmental expression patterns of erythropoietin and its receptor in mouse brainstem respiratory regions

Erythropoietin (EPO) is a hypoxia-inducible hormone, classically known to enhance red blood cell production upon binding its receptor (EPOR) present on the surface of the erythroid progenitor cells. EPO and its receptor are also expressed in the central nervous system (CNS), exerting several non-hematopoietic actions. EPO also plays an important role in the control of breathing. In this review, we summarize the known physiological actions of EPO in the neural control of ventilation during postnatal development and at adulthood in rodents under normoxic and hypoxic conditions. Furthermore, we present the developmental expression patterns of EPO and EPORs in the brainstem, and with the use of in situ hybridization (ISH) and immunofluorescence techniques we provide original data showing that EPOR is abundantly present in specific brainstem nuclei associated with central chemosensitivity and control of ventilation in the ventrolateral medulla, mainly on somatostatin negative cells. Thus, we conclude that EPO signaling may act through glutamatergic neuron populations that are the primary source of rhythmic inspiratory excitatory drive. This work underlies the importance of EPO signaling in the central control of ventilation across development and adulthood and provides new insights on the expression of EPOR at the cellular level.

Alternative Erythropoietin Receptors in the Nervous System

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

Erythropoietin Signaling Increases Choroidal Macrophages and Cytokine Expression, and Exacerbates Choroidal Neovascularization

Erythropoietin (EPO) is recognized for neuroprotective and angiogenic effects and has been associated with aging and neovascular age-related macular degeneration (AMD). We hypothesized that systemic EPO facilitates the development of choroidal neovascularization (CNV). Wild type mice expressed murine EPOR (mWtEPOR) in RPE/choroids at baseline and had significantly increased serum EPO after laser treatment. To test the role of EPO signaling, we used human EPOR knock-in mice with the mWtEPOR gene replaced by either the human EPOR gene (hWtEPOR) or a mutated human EPOR gene (hMtEPOR) in a laser-induced choroidal neovascularization (LCNV) model. Loss-of-function hWtEPOR mice have reduced downstream activation, whereas gain-of-function hMtEPOR mice have increased EPOR signaling. Compared to littermate controls (mWtEPOR), hMtEPOR with increased EPOR signaling developed larger CNV lesions. At baseline, hMtEPOR mice had increased numbers of macrophages, greater expression of macrophage markers F4/80 and CD206, and following laser injury, had greater expression of cytokines CCL2, CXCL10, CCL22, IL-6, and IL-10 than mWtEPOR controls. These data support a hypothesis that injury from age- and AMD-related changes in the RPE/choroid leads to choroidal neovascularization through EPOR-mediated cytokine production.

Carbamylated erythropoietin enhances mice ventilatory responses to changes in O2 but not CO2 levels

Erythropoietin (EPO) has beneficial tissue-protective effects in several diseases but erythrocytosis may cause deleterious effects in EPO-treated patients. Thus carbamylated-EPO (C-EPO) and other derivatives retaining tissue-protective but lacking bone marrow-stimulating actions have been developed. Although EPO modulates ventilatory responses, the effects of C-EPO on ventilation have not been investigated. Here, basal breathing and respiratory chemoreflexes were measured by plethysmography after acute and chronic treatments with recombinant human C-EPO (rhC-EPO; 15,000 IU/kg during 5days) or saline (control group). Hematocrit, plasma and brainstem rhC-EPO levels were also quantified. Chronic rhC-EPO significantly elevated tissue rhC-EPO levels but not hematocrit. None of the drug regimen altered basal ventilation (normoxia). Chronic but not acute rhC-EPO enhanced hyperoxic ventilatory depression, and sustained the hypoxic ventilatory response mainly via a reduction of the roll-off phase. By contrast, rhC-EPO did not blunt the ventilatory response to hypercapnia. Thus, chronic C-EPO may be a promising therapy to improve breathing during hypoxia while minimizing adverse effects on cardiovascular function.

Bad Science: Cause and Consequence

Scientific progress is dependent on accumulation of quality data with appropriate data analysis. Unfortunately, there are a troubling number of accounts describing an inability to replicate published work. Some explanations are lack of access to proprietary reagents and equipment, or lack of expertise and know how. However, it is clear that there are many publications that are fatally flawed, and it is difficult to ascertain which ones they are, but there are clues. Many articles are improperly controlled, resulting in false-positive or -negative results. Reagents and procedures are used without verifying their specificity. There is also confirmation bias, a tendency to seek and find conclusions that we like, which is exacerbated by faithful acceptance by readers of the publication record without assessment of merit. These and other issues have slowed progress, resulted in waste of scarce funds, and even put patients at risk when clinical decisions are made according to flawed data. Solving these and related problems requires recognition of the problem and better training. We also need to take personal responsibility for not only our own work, but also for the accuracy of information in the scientific domain.

Widespread Expression of Erythropoietin Receptor in Brain and Its Induction by Injury

Erythropoietin (EPO) exerts potent neuroprotective, neuroregenerative and procognitive functions. However, unequivocal demonstration of erythropoietin receptor (EPOR) expression in brain cells has remained difficult since previously available anti-EPOR antibodies (EPOR-AB) were unspecific. We report here a new, highly specific, polyclonal rabbit EPOR-AB directed against different epitopes in the cytoplasmic tail of human and murine EPOR and its characterization by mass spectrometric analysis of immuno-precipitated endogenous EPOR, Western blotting, immunostaining and flow cytometry. Among others, we applied genetic strategies including overexpression, Lentivirus-mediated conditional knockout of EpoR and tagged proteins, both on cultured cells and tissue sections, as well as intracortical implantation of EPOR-transduced cells to verify specificity. We show examples of EPOR expression in neurons, oligodendroglia, astrocytes and microglia. Employing this new EPOR-AB with double-labeling strategies, we demonstrate membrane expression of EPOR as well as its localization in intracellular compartments such as the Golgi apparatus. Moreover, we show injury-induced expression of EPOR. In mice, a stereotactically applied stab wound to the motor cortex leads to distinct EpoR expression by reactive GFAP-expressing cells in the lesion vicinity. In a patient suffering from epilepsy, neurons and oligodendrocytes of the hippocampus strongly express EPOR. To conclude, this new analytical tool will allow neuroscientists to pinpoint EPOR expression in cells of the nervous system and to better understand its role in healthy conditions, including brain development, as well as under pathological circumstances, such as upregulation upon distress and injury.

Functional EpoR pathway utilization is not detected in primary tumor cells isolated from human breast, non-small cell lung, colorectal, and ovarian tumor tissues

Several clinical trials in oncology have reported increased mortality or disease progression associated with erythropoiesis-stimulating agents. One hypothesis proposes that erythropoiesis-stimulating agents directly stimulate tumor proliferation and/or survival through cell-surface receptors. To test this hypothesis and examine if human tumors utilize the erythropoietin receptor pathway, the response of tumor cells to human recombinant erythropoietin was investigated in disaggregated tumor cells obtained from 186 patients with colorectal, breast, lung, ovarian, head and neck, and other tumors. A cocktail of well characterized tumor growth factors (EGF, HGF, and IGF-1) were analyzed in parallel as a positive control to determine whether freshly-isolated tumor cells were able to respond to growth factor activation ex vivo. Exposing tumor cells to the growth factor cocktail resulted in stimulation of survival and proliferation pathways as measured by an increase in phosphorylation of the downstream signaling proteins AKT and ERK. In contrast, no activation by human recombinant erythropoietin was observed in isolated tumor cells. Though tumor samples exhibited a broad range of cell-surface expression of EGFR, c-Met, and IGF-1R, no cell-surface erythropoietin receptor was detected in tumor cells from the 186 tumors examined (by flow cytometry or Western blot). Erythropoiesis-stimulating agents did not act directly upon isolated tumor cells to stimulate pathways known to promote proliferation or survival of human tumor cells isolated from primary and metastatic tumor tissues.

Prolonged erythropoietin treatment does not impact gene expression in human skeletal muscle

INTRODUCTION

We tested for the presence of erythropoietin receptor (Epo-R) in human skeletal muscle and alterations in gene expression after prolonged use of an erythropoiesis-stimulating agent (ESA).

METHODS

Nine healthy men were treated with ESA for 10 weeks (darbepoietin alfa). Muscle biopsies were collected before and after treatment. Alterations in gene expression were evaluated by gene array. Western blot and PCR analysis were used to test for Epo-R presence in human skeletal muscle.

RESULTS

Very low Epo-R mRNA levels were found, but a new and sensitive antibody did not identify Epo-R protein in human skeletal muscle. The between-subject variation in skeletal muscle gene expression was greater than that observed in response to prolonged ESA treatment.

CONCLUSIONS

Erythropoietin is unlikely to exert direct effects in human skeletal muscle due to a lack of Epo-R protein. Furthermore, prolonged ESA treatment does not seem to exert either direct or indirect effects on skeletal muscle gene expression.

Effect of erythropoietin on primed leucocyte expression profile

Resistance to erythropoietin (EPO) affects a significant number of anaemic patients with end-stage renal disease. Previous reports suggest that inflammation is one of the major independent predictors of EPO resistance, and the effects of EPO treatment on inflammatory mediators are not well established. The aim of this study was to investigate EPO-induced modification to gene expression in primary cultured leucocytes. Microarray experiments were performed on primed ex vivo peripheral blood mononuclear cells (PBMCs) and treated with human EPO-α. Data suggested that EPO-α modulated genes involved in cell movement and interaction in primed PBMCs. Of note, EPO-α exerts anti-inflammatory effects inhibiting the expression of pro-inflammatory cytokine IL-8 and its receptor CXCR2; by contrast, EPO-α increases expression of genes relating to promotion of inflammation encoding for IL-1β and CCL8, and induces de novo synthesis of IL-1α, CXCL1 and CXCL5 in primed cells. The reduction in MAPK p38-α activity is involved in modulating both IL-1β and IL-8 expression. Unlike the induction of MAPK, Erk1/2 activity leads to upregulation of IL-1β, but does not affect IL-8 expression and release. Furthermore, EPO-α treatment of primed cells induces the activation of caspase-1 upstream higher secretion of IL-1β, and this process is not dependent on caspase-8 activation. In conclusion, our findings highlight new potential molecules involved in EPO resistance and confirm the anti-inflammatory role for EPO, but also suggest a plausible in vivo scenario in which the positive correlation found between EPO resistance and elevated levels of some pro-inflammatory mediators is due to treatment with EPO itself.

Catalyzing role of erythropoietin on the nitric oxide central pathway during the ventilatory responses to hypoxia

The N‐Methyl‐d‐Aspartate (NMDA) receptors – neuronal nitric oxide synthase (nNOS) pathway is involved in the ventilatory response to hypoxia. The objective was to assess the possible effect of erythropoietin deficiency and chronic exposure to hypoxia on this pathway during ventilatory response to acute hypoxia. Wild‐type (WT) and erythropoietin‐deficient (Epo‐TAg^h) male mice were exposed (14 days) either to hypobaric hypoxia (Pb = 435 mmHg) or to normoxia. The ventilation was measured at 21% or 8% O₂ after injection of vehicle (NaCl), nNOS inhibitor (SMTC) or NMDA receptor antagonist (MK‐801). Nitric oxide production and the expression of NMDA receptor and nNOS were assessed by real‐time RT‐PCR and Western blot analyses in the medulla. At rest, Epo‐TAg^h mice displayed normal ventilatory parameters at 21% O₂ but did not respond to acute hypoxia despite a larger expression of NMDA receptors and nNOS in the medulla. Ventilatory acclimatization to hypoxia was observed in WT but was absent in Epo‐TAg^h mice. nNOS inhibition blunted the hypoxic ventilatory acclimatization of WT mice without any effect in Epo‐TAg^h mice. Acute hypoxic ventilatory response (HVR) was increased after chronic hypoxia in WT but remained unchanged in Epo‐TAg^h mice. Ventilatory response to acute hypoxia was modified by MK‐801 injection in WT and Epo‐TAg^h mice. The results confirm that adequate erythropoietin level is necessary to obtain an appropriate HVR and a significant ventilatory acclimatization to hypoxia. Furthermore, erythropoietin plays a potential catalyzing role in the NMDA‐NO central pathway during the ventilatory response and acclimatization to hypoxia.

e00223

Adequate erythropoietin level is necessary to obtain an appropriate hypoxic ventilatory response and a significant ventilatory acclimatization to hypoxia. Erythropoietin plays a potential catalyzing role on the N‐Methyl‐d‐Aspartate (NMDA)‐nNOS central pathway during the ventilatory response and acclimatization to hypoxia.

Progress in detecting cell-surface protein receptors: the erythropoietin receptor example

Testing for the presence of specific cell-surface receptors (such as EGFR or HER2) on tumor cells is an integral part of cancer care in terms of treatment decisions and prognosis. Understanding the strengths and limitations of these tests is important because inaccurate results may occur if procedures designed to prevent false-negative or false-positive outcomes are not employed. This review discusses tests commonly used to identify and characterize cell-surface receptors, such as the erythropoietin receptor (EpoR). First, a summary is provided on the biology of the Epo/EpoR system, describing how EpoR is expressed on erythrocytic progenitors and precursors in the bone marrow where it mediates red blood cell production in response to Epo. Second, studies are described that investigated whether erythropoiesis-stimulating agents could stimulate tumor progression in cancer patients and whether EpoR is expressed and functional on tumor cells or on endothelial cells. The methods used in these studies included immunohistochemistry, Northern blotting, Western blotting, and binding assays. This review summarizes the strengths and limitations of these methods. Critically analyzing data from tests for cell-surface receptors such as EpoR requires understanding the techniques utilized and demonstrating that results are consistent with current knowledge about receptor biology.

Erythropoietin and the vascular wall: the controversy continues

BACKGROUND AND AIMS

Erythropoietin (EPO) stimulates erythropoiesis through its specific receptor (EPO-R). Preclinical work has assigned a role for the EPO/EPO-R system in the heart and blood vessels. The potential use of erythropoiesis-stimulating agents (ESAs) for nonhematopoietic indications is a focus of current research. This article considers proven actions of EPO in the cardiovascular system, with emphasis on the human responses.

DATA SYNTHESIS

By use of specific anti-EPO-R antibody no EPO-R protein was detected by Western blotting in normal non-erythroid tissues. Clinical trials failed to demonstrate clear beneficial effects of high-dosed ESAs in patients with coronary syndrome or myocardial infarct. While ESA therapy may lead to an elevation in arterial blood pressure in previously anemic patients, several studies have reported no effects on vessels/blood pressure with ESAs. EPO has been reported to stimulate angiogenesis. EPO-R mRNA is detectable in human vascular endothelium. However, in most vitro studies very high concentrations of EPO were applied and well-designed studies have failed to show direct effects of ESAs on endothelial cells. Whether EPO promotes the mobilization of myeloid progenitor cells into the blood stream still needs to be studied in more detail, as this effect may prove useful for augmenting the neovascularization of ischemic tissues. With respect to the administration of ESAs to tumor patients, a deeper insight into the role of EPO for tumor angiogenesis is desirable.

CONCLUSIONS

The enthusiastic reports of the nonhematopoietic cytoprotective potential of EPO and its derivatives in the cardiovascular system have not yet been confirmed in placebo-controlled clinical trials.

The role and regulation of erythropoietin (EPO) and its receptor in skeletal muscle: how much do we really know?

Erythropoietin (EPO) primarily activates erythroid cell proliferation and growth and is active in several types of non-hematopoietic cells via its interaction with the EPO-receptor (EPO-R). This review focuses on the role of EPO in skeletal muscle. The EPO-R is expressed in skeletal muscle cells and EPO may promote myoblast differentiation and survival via the activation of the same signaling cascades as in hematopoietic cells, such as STAT5, MAPK and Akt. Inconsistent results exist with respect to the detection of the EPO-R mRNA and protein in muscle cells, tissue and across species and the use of non-specific EPO-R antibodies contributes to this problem. Additionally, the inability to reproducibly detect an activation of the known EPO-induced signaling pathways in skeletal muscle questions the functionality of the EPO-R in muscle in vivo. These equivocal findings make it difficult to distinguish between a direct effect of EPO on skeletal muscle, via the activation of its receptor, and an indirect effect resulting from a better oxygen supply to the muscle. Consequently, the precise role of EPO in skeletal muscle and its regulatory mechanism/s remain to be elucidated. Further studies are required to comprehensively establish the importance of EPO and its function in skeletal muscle health.

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.

The effect of erythropoietin on normal and neoplastic cells

Erythropoietin (Epo) is an essential hormone that binds and activates the Epo receptor (EpoR) resident on the surface of erythroid progenitor cells, thereby promoting erythropoiesis. Recombinant human erythropoietin has been used successfully for over 20 years to treat anemia in millions of patients. In addition to erythropoiesis, Epo has also been reported to have other effects, such as tissue protection and promotion of tumor cell growth or survival. This became of significant concern in 2003, when some clinical trials in cancer patients reported increased tumor progression and worse survival outcomes in patients treated with erythropoiesis-stimulating agents (ESAs). One of the potential mechanisms proffered to explain the observed safety issues was that functional EpoR was expressed in tumors and/or endothelial cells, and that ESAs directly stimulated tumor growth and/or antagonized tumor ablative therapies. Since then, numerous groups have performed further research evaluating this potential mechanism with conflicting data and conclusions. Here, we review the biology of endogenous Epo and EpoR expression and function in erythropoiesis, and evaluate the evidence pertaining to the expression of EpoR on normal nonhematopoietic and tumor cells.

Evaluation of functional erythropoietin receptor status in skeletal muscle in vivo: acute and prolonged studies in healthy human subjects

BACKGROUND

Erythropoietin receptors have been identified in human skeletal muscle tissue, but downstream signal transduction has not been investigated. We therefore studied in vivo effects of systemic erythropoietin exposure in human skeletal muscle.

METHODOLOGY/PRINCIPAL FINDINGS

The protocols involved 1) acute effects of a single bolus injection of erythropoietin followed by consecutive muscle biopsies for 1-10 hours, and 2) a separate study with prolonged administration for 16 days with biopsies obtained before and after. The presence of erythropoietin receptors in muscle tissue as well as activation of Epo signalling pathways (STAT5, MAPK, Akt, IKK) were analysed by western blotting. Changes in muscle protein profiles after prolonged erythropoietin treatment were evaluated by 2D gel-electrophoresis and mass spectrometry. The presence of the erythropoietin receptor in skeletal muscle was confirmed, by the M20 but not the C20 antibody. However, no significant changes in phosphorylation of the Epo-R, STAT5, MAPK, Akt, Lyn, IKK, and p70S6K after erythropoietin administration were detected. The level of 8 protein spots were significantly altered after 16 days of rHuEpo treatment; one isoform of myosin light chain 3 and one of desmin/actin were decreased, while three isoforms of creatine kinase and two of glyceraldehyd-3-phosphate dehydrogenase were increased.

CONCLUSIONS/SIGNIFICANCE

Acute exposure to recombinant human erythropoietin is not associated by detectable activation of the Epo-R or downstream signalling targets in human skeletal muscle in the resting situation, whereas more prolonged exposure induces significant changes in the skeletal muscle proteome. The absence of functional Epo receptor activity in human skeletal muscle indicates that the long-term effects are indirect and probably related to an increased oxidative capacity in this tissue.

Gata4 and Sp1 regulate expression of the erythropoietin receptor in cardiomyocytes

Experimental studies indicate significant cardioprotective effects of recombinant erythropoietin (Epo) by binding to the Epo receptor (EpoR) and by inducing various molecular mechanisms, including activation of Gata4, a transcription factor that induces anti-apoptotic genes. However, specific molecular mechanisms of EpoR regulation in cardiomyocytes are unknown. We identified a 774 bp regulatory domain in the EpoR 5' flanking region by reporter gene assays in murine HL-1 cardiomyocytes. The binding sites for Gata and Sp transcription factors both significantly contributed to EpoR promoter activity. DNA-binding studies (EMSA and ChIP assays) identified Gata4 and Sp1 as EpoR promoter-binding proteins in HL1 cardiomyocytes. Although Sp1 alone stimulates EpoR only slightly, forced expression of Gata4 significantly induced EpoR mRNA expression. In addition, knockdown of Gata4 (but also of Sp1) resulted in a significant decrease of EpoR transcript levels in HL-1 cardiomyocytes. Cumulative in vitro data suggest that function of the Sp1 site is essential for the Gata4-mediated transcription. In vivo, analysis of transgenic mice expressing an inducible small-hairpin RNA against Gata4 confirmed suppression of EpoR expression in the heart. Treating mice with high-dose doxorubicin not only resulted in Gata4 protein depletion, but also down-regulated EpoR, followed by up-regulation of EpoR transcripts when Gata4 levels recovered. In conclusion, we identified Gata4 as novel regulator of EpoR transcription in cardiomyocytes. In models of cardiac injury, down-regulation of Gata4 or Sp1 may limit the accessibility of the EpoR for binding of erythropoiesis-stimulating agents (ESA). Thereby our data underline the essential role of Gata4 in mediating cardioprotective effects.

From oxygen to erythropoietin: relevance of hypoxia for retinal development, health and disease

Photoreceptors and other cells of the retina consume large quantities of energy to efficiently convert light information into a neuronal signal understandable by the brain. The necessary energy is mainly provided by the oxygen-dependent generation of ATP in the numerous mitochondria of retinal cells. To secure the availability of sufficient oxygen for this process, the retina requires constant blood flow through the vasculature of the retina and the choroid. Inefficient supply of oxygen and nutrients, as it may occur in conditions of disturbed hemodynamics or vascular defects, results in tissue ischemia or hypoxia. This has profound consequences on retinal function and cell survival, requiring an adaptational response by cells to cope with the reduced oxygen tension. Central to this response are hypoxia inducible factors, transcription factors that accumulate under hypoxic conditions and drive the expression of a large variety of target genes involved in angiogenesis, cell survival and metabolism. Prominent among these factors are vascular endothelial growth factor and erythropoietin, which may contribute to normal angiogenesis during development, but may also cause neovascularization and vascular leakage under pathologically reduced oxygen levels. Since ischemia and hypoxia may have a role in various retinal diseases such as diabetic retinopathy and retinopathy of prematurity, studying the cellular and molecular response to reduced tissue oxygenation is of high relevance. In addition, the concept of preconditioning with ischemia or hypoxia demonstrates the capacity of the retina to activate endogenous survival mechanisms, which may protect cells against a following noxious insult. Part of these mechanisms is the local production of protective factors such as erythropoietin. Due to its plethora of effects in the retina including neuro- and vaso-protective activities, erythropoietin has gained strong interest as potential therapeutic factor for retinal degenerative diseases.

Erythropoietin improves memory function with reducing endothelial dysfunction and amyloid-beta burden in Alzheimer's disease models

Neurovascular degeneration contributes to the pathogenesis of Alzheimer's disease (AD). Because erythropoietin (EPO) promotes endothelial regeneration, we investigated the therapeutic effects of EPO in animal models of AD. In aged Tg2576 mice, EPO receptors (EPORs) were expressed in the cortex and hippocampus. Tg2576 mice were treated with daily injection of EPO (5000 IU/kg/day) for 5 days. At 14 days, EPO improved contextual memory as measured by fear-conditioning test. EPO enhanced endothelial proliferation and the level of synaptophysin expression in the brain. EPO also increased capillary density, and decreased the level of the receptor for advanced glycation endproducts (RAGE) in the brain, while decreasing in the amount of amyloid plaque and amyloid-β (Aβ). In cultured human endothelial cells, EPO enhanced angiogenesis and suppressed the expression of the RAGE. These results show that EPO improves memory and ameliorates endothelial degeneration induced by Aβ in AD models. This pre-clinical evidence suggests that EPO may be useful for the treatment of AD.

Disrupted erythropoietin signalling promotes obesity and alters hypothalamus proopiomelanocortin production

While erythropoietin is the cytokine known that regulates erythropoiesis, erythropoietin receptor (EpoR) expression and associated activity beyond hematopoietic tissue remain uncertain. Here we show that mice with EpoR expression restricted to hematopoietic tissues (Tg) develop obesity and insulin resistance. Tg-mice exhibit a decrease in energy expenditure and an increase in white fat mass and adipocyte number. Conversely, erythropoietin treatment of wild-type mice increases energy expenditure and reduces food intake and fat mass accumulation but showed no effect in body weight of Tg-mice. EpoR is expressed at a high level in white adipose tissue and in the proopiomelanocortin neurons of the hypothalamus. While Epo treatment in wild-type mice induces the expression of the polypeptide hormone precursor gene, proopiomelanocortin, mice lacking EpoR show reduced levels of proopiomelanocortin in the hypothalamus. This study provides the first evidence that mice lacking EpoR in nonhematopoietic tissue become obese and insulin resistant with loss of erythropoietin regulation of energy homeostasis.

Co-expression of erythropoietin receptor with human epidermal growth factor 2 may counteract trastuzumab inhibition in gastric cancer

Gastric cancer has high prevalence and high modality worldwide. For many years, few improvements in the efficacy of treatments were reported for advanced gastric cancer settings. Although a novel molecular target agent trastuzumab, in combination with chemotherapy, prolongs overall survival time in advanced gastric cancer, resistance to this drug still exists among human epidermal growth factor receptor-2 (HER2) positive patients. HER2 and erythropoietin receptor (EPOR) downstream signaling pathway have some common factors like Akt, Erk and STATs. Also there exist evidences that EPOR may express on some solid tumors and probably promote tumor progression. So it is reasonable for us to hypothesis that HER2 and EPOR may be co-expressed in the same gastric cancer cell and if so, EPOR signaling pathway may overlaps that with HER2 and promotes HER2 induced signal transduction to cell proliferation. In clinical settings, a stimulation of EPOR will play antagonistic effects on trastuzumab-induced anti-tumor activity to HER2-positive gastric cancer patients. Co-expression of EPOR and HER2 is a predictive factor for resistance of trastuzumab in gastric cancer.

Erythropoiesis-stimulating agents

Erythropoiesis is the process whereby erythroid progenitor cells differentiate and divide, resulting in increased numbers of red blood cells (RBCs). RBCs contain hemoglobin, the main oxygen carrying component in blood. The large number of RBCs found in blood is required to support the prodigious consumption of oxygen by tissues as they undergo oxygen-dependent processes. Erythropoietin is a hormone that when it binds and activates Epo receptors resident on the surface of cells results in stimulation of erythropoiesis. Successful cloning of the EPO gene allowed for the first time production of recombinant human erythropoietin and other erythropoiesis stimulating agents (ESAs), which are used to treat anemia in patients. In this chapter, the control of Epo levels and erythropoiesis, the various forms of ESAs used commercially, and their physical and biological properties are discussed.

Biosimilar epoetins and other "follow-on" biologics: update on the European experiences

After the patents of biopharmaceuticals have expired, based on specific regulatory approval pathways copied products ("biosimilars" or "follow-on biologics") have been launched in the EU. This article summarizes experiences with hematopoietic medicines, namely the epoetins (two biosimilars traded under five different brand names) and the filgrastims (two biosimilars, six brand names). Physicians and pharmacists should be familiar with the legal and pharmacological specialities of biosimilars: The production process can differ from that of the original, clinical indications can be extrapolated, glycoproteins contain varying isoforms, the formulation may differ from the original, and biopharmaceuticals are potentially immunogenic. Only on proof of quality, efficacy and safety, biosimilars are a viable option because of their lower costs.

Erythropoietin in stroke: quo vadis

IMPORTANCE OF THE FIELD

Recombinant erythropoietin (rEPO) failed in a recent clinical study to protect from damages induced by ischemic stroke. The lack of acute treatments in ischemic stroke and the promising outcome in numerous preclinical studies in vivo demands a more critical evaluation of the future use of EPO as an acute treatment.

AREAS COVERED IN THIS REVIEW

The current use and administration of rhEPO and its analogs in animal models and the future use of this cytokine in the treatment of ischemic stroke.

WHAT THE READER WILL GAIN

In this review the potential reasons for the failure of EPO in the clinical trial are analysed and whether the preclinical trials sufficiently evaluated the true potential of recombinant EPO and its analogs is assessed. Alternative methods for administration of EPO to enhance its potential as a neuroprotective drug in ischemic stroke are discussed.

TAKE HOME MESSAGE

Failure in clinical trial does not necessarily indicate the lack of therapeutic potential of EPO. This review encourages further investigation of the true potential of EPO as a candidate drug for the treatment of ischemic stroke by improved preclinical experimental design and utilization of alternative administration methods.

Epoetin delta reduces oxidative stress in primary human renal tubular cells

Erythropoietin (EPO) exerts (renal) tissue protective effects. Since it is unclear whether this is a direct effect of EPO on the kidney or not, we investigated whether EPO is able to protect human renal tubular epithelial cells (hTECs) from oxidative stress and if so which pathways are involved. EPO (epoetin delta) could protect hTECs against oxidative stress by a dose-dependent inhibition of reactive oxygen species formation. This protective effect is possibly related to the membranous expression of the EPO receptor (EPOR) since our data point to the membranous EPOR expression as a prerequisite for this protective effect. Oxidative stress reduction went along with the upregulation of renoprotective genes. Whilst three of these, heme oxygenase-1 (HO-1), aquaporin-1 (AQP-1), and B-cell CLL/lymphoma 2 (Bcl-2) have already been associated with EPO-induced renoprotection, this study for the first time suggests carboxypeptidase M (CPM), dipeptidyl peptidase IV (DPPIV), and cytoglobin (Cygb) to play a role in this process.

Absence of functional EpoR expression in human tumor cell lines

Certain oncology trials showed worse clinical outcomes in the erythropoiesis-stimulating agent (ESA) arm. A potential explanation was that ESA-activated erythropoietin (Epo) receptors (EpoRs) promoted tumor cell growth. Although there were supportive data from preclinical studies, those findings often used invalidated reagents and methodologies and were in conflict with other studies. Here, we further investigate the expression and function of EpoR in tumor cell lines. EpoR mRNA levels in 209 human cell lines representing 16 tumor types were low compared with ESA-responsive positive controls. EpoR protein production was evaluated in a subset of 66 cell lines using a novel anti-EpoR antibody. EpoR(+) control cells had an estimated 10 000 to 100 000 EpoR dimers/cell. In contrast, 54 of 61 lines had EpoR protein levels lower than 100 dimers/cell. Cell lines with the highest EpoR protein levels (400-3200 dimers/cell) were studied further, and, although one line, NCI-H661, bound detectable levels of [(125)I]-recombinant human Epo (rHuEpo), none showed evidence of ESA-induced EpoR activation. There was no increased phosphorylation of STAT5, AKT, ERK, or S6RP with rHuEpo. In addition, EpoR knockdown with siRNAs did not affect viability in 2 cell lines previously reported to express functional EpoR (A2780 and SK-OV-3). These results conflict with the hypothesis that EpoR is functionally expressed in tumors.

Identification of a sensitive anti-erythropoietin receptor monoclonal antibody allows detection of low levels of EpoR in cells

Erythropoietin (Epo) binds and activates the Epo receptor (EpoR) on the surface of erythroid progenitor cells resulting in formation of erythrocytes. Recently, EpoR was reported to be expressed on non-erythroid cells suggesting a role for Epo outside of erythropoiesis. However those studies employed antibodies with questionable specificity and the significance of the observations are controversial. In order to accurately determine the expression of EpoR proteins in cells, we have generated a panel of novel anti-human EpoR monoclonal antibodies. One of these antibodies (A82) was particularly sensitive and it detected the EpoR protein on intact cells by flow cytometry and by western blot analysis with cell lysates. Both methods were optimized and using them, EpoR protein was detected by western immunoblotting with lysates from fewer than 200 EpoR positive control cells and the positive signals were proportional to EpoR protein expression level with a minimal signal in EpoR negative cells. The proteins detected by western blot analysis using A82 included full-length EpoR ( approximately 59kDa) as well as smaller EpoR fragments derived from the EPOR gene. These results indicate that A82 can be used to examine low level EpoR expression in cells by western and flow cytometry allowing an improved understanding of EpoR expression and metabolism.

An erythropoietin autocrine/paracrine axis modulates the growth and survival of human prostate cancer cells

Erythropoietin receptors have been identified on a variety of cancer-derived cell lines and primary cancer cells, including those of prostate cancer. The functional status of these extrahematopoietic erythropoietin receptors remains a matter of some dispute. The publication of several important clinical trials suggesting a direct effect of erythropoietin on the growth and survival of primary tumors adds further importance to the question of whether erythropoietin receptors on cancer cells are functional. We have reported previously that human prostate cancer cell lines and primary prostate cancer cells express functional erythropoietin receptors that respond to exogenous erythropoietin by increased cell proliferation and STAT5 phosphorylation. We now show that prostate cancer cell lines express both the EPO gene and the biologically active erythropoietin. The coexpression of functional receptor and biologically active ligand in the cells has led us to hypothesize an autocrine/paracrine mechanism, driven by endogenous erythropoietin, which may modulate the growth and progression of prostate cancer. To test our hypothesis, we have knocked down, independently, erythropoietin receptor and erythropoietin on prostate cancer cells by transfection with short hairpin RNAs. Erythropoietin receptor knockdown cells grow significantly more slowly than their erythropoietin receptor-bearing counterparts in monolayer culture, produce fewer, smaller colonies in soft agar, and do not exhibit erythropoietin-induced signaling. Erythropoietin knockdown cells exhibit dramatically slower rates of growth, which could be restored by transfecting the cells with a murine erythropoietin gene. Taken together, our data suggest that the coordinated regulation of a functional erythropoietin/erythropoietin receptor axis in prostate cancer cells may be integral to the growth and progression of prostate cancer.

Erythropoietin-receptor gene regulation in neuronal cells

Because erythropoietin (Epo) is intensively studied as neuroprotective agent, Epo receptor (EpoR) regulation in neurons is of particular interest. Herein, we investigated molecular mechanisms of EpoR regulation in neuronal cells including the role of GATA transcription factors. First, developmental downregulation of EpoR expression in murine brain was observed. A differential expression pattern of the Gata factors was found in these specimens as well as in murine adult neural stem cells (NSC) and primary rat neurons, astrocytes, and microglia. Human SH-SY5Y cells served as a model to analyze EpoR regulation. In vitro binding of GATA-2, -3, and -4 to the 5'-flanking region was demonstrated. In reporter gene assays, the activity of a region containing two GATA binding sites was significantly induced when these GATA factors were overexpressed. However, GATA factors alone did not affect endogenous EpoR expression. Importantly, EpoR transcripts have doubled under hypoxia. Furthermore, we analyzed the methylation pattern close to the GATA motifs. Indeed, demethylation with 5-Aza-2'-deoxycytidine (Aza) resulted in upregulation of EpoR mRNA. Additionally, several CpGs were mostly nonmethylated in SH-SY5Y cells, but methylated in specific regions of the human adult brain. Thus, methylation may be involved in developmental EpoR downregulation.

Erythropoietin receptor expression is concordant with erythropoietin but not with common beta chain expression in the rat brain throughout the life span

Brain effects of erythropoietin (Epo) are proposed to involve a heteromeric receptor comprising the classical Epo receptor (Epo-R) and the common beta chain (betac). However, data documenting the pattern of betac gene expression in the healthy brain, in comparison with that of the Epo-R gene, are still lacking. The present study is the first to investigate at the same time betac, Epo-R, and Epo gene expression within different rat brain areas throughout the life span, from neonatal to elderly stages, using quantitative RT-PCR for transcripts. Corresponding proteins were localized by using immunohistochemistry. We demonstrate that the betac transcript level does not correlate with that of Epo-R or Epo, whereas the Epo-R transcript level strongly correlates with that of Epo throughout the life span in all brain structures analyzed. Both Epo and Epo-R were detected primarily in neurons. In the hippocampus, the greatest Epo-R mRNA levels were measured during the early postnatal period and in middle-aged rats, associated with an intense neuronal immunolabeling. Conversely, betac protein was barely detectable in the brain at all ages, even in neurons expressing high levels of Epo-R. Finally, betac transcript could not be detected in PC12 cells, even after nerve growth factor-induced neuritogenesis, which is a condition that dramatically enhances Epo-R transcript level. Altogether, our data suggest that most neurons are likely to express high levels of Epo-R but low, if not null, levels of betac. Given that Epo protects extended populations of neurons after injury, a yet-to-be-identified receptor heterocomplex including Epo-R may exist in the large population of brain neurons that does not express betac.

Involvement of erythropoietin in retinal ischemic preconditioning

BACKGROUND

The purpose of this study was to examine the role of erythropoietin in retinal ischemic preconditioning (IPC).

METHODS

Rats were subjected to retinal ischemia after IPC. Electroretinography assessed functional recovery after ischemia; retinal sections were examined to determine loss of retinal ganglion cells, and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling was used to assess apoptosis. Levels of downstream mediators were measured in retinal homogenates by Western blotting. To assess the involvement of erythropoietin in IPC, Western blotting was used to measure levels of erythropoietin and its receptor (EPO-R) in retinal homogenates after IPC. To examine erythropoietin's role in IPC, the impact of blocking erythropoietin via intravitreal injection of soluble EPO-R (sEPO-R) before IPC was studied.

RESULTS

Erythropoietin levels did not change after IPC, but EPO-R increased. Intravitreal injection of sEPO-R significantly attenuated both the functional and histologic neuroprotection produced by IPC in comparison to control injection of denatured sEPO-R. Apoptotic damage after ischemia was enhanced in the sEPO-R-treated retinas as indicated by fluorescent terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling. Phosphorylated extracellular-signal-regulated kinase and heat shock protein 27, but not protein kinase B, upregulated in denatured sEPO-R-treated retinae, were attenuated in eyes injected with sEPO-R.

CONCLUSIONS

These results indicate that EPO-R upregulation is a critical component of the functional, histologic, and antiapoptotic protective effect of IPC on ischemia in the retina and that several downstream effectors may be involved in the neuroprotective actions of erythropoietin.

Neuroprotective effects of erythropoietin posttreatment against kainate-induced excitotoxicity in mixed spinal cultures

Although the neuroprotective effects of erythropoietin (EPO) preconditioning are well known, the potential of postapplied EPO to protect neurons against excitotoxic injury has not been clearly established. Here we show that kainate (KA)-induced excitotoxicity, which plays a key role in secondary spinal cord injury, decreased neuron survival, inhibited neurite extension, and significantly reduced the expression of erythropoietin receptors (EpoR) in cultured spinal neurons. Posttreatment with EPO for 48 hr protected neurons against KA-induced injury, opposing KA-induced apoptosis and promoting regrowth of motoneuron neurites. These neuroprotective effects were paralleled by a restoration of EpoR expression. The importance of the EpoR signaling pathway was demonstrated using an EpoR blocking antibody, which neutralized the neuroprotective action of EPO posttreatment and prevented EPO-induced increases in EpoR expression. We also found that up-regulated EpoR stimulated the Janus kinase 2 (JAK2) pathway, which is known to facilitate neuronal growth and neurite regeneration. Although EPO posttreatment modestly attenuated KA-induced reactive gliosis in mixed neuron-glial cultures, blocking EpoR activity did not alter glial fibrillary acidic protein expression or astrocyte proliferation. In conclusion, 48 hr treatment with EPO following KA exposure induced EpoR-dependent protection against excitotoxic injury, demonstrating that preconditioning is not a prerequisite for neuroprotection by EPO. The neuroprotective effects of EPO posttreatment were mediated by an EpoR-dependent signaling pathway that possibly involves JAK2. The neuroprotective effect of EPO posttreatment against KA excitotoxicity appears to reflect direct effects on neurons and not indirect effects mediated by astrocytes.

Erythropoietin enhancement of rat pancreatic tumor cell proliferation requires the activation of ERK and JNK signals

Erythropoietin (EPO) regulates the proliferation and differentiation of erythroid cells by binding to its specific transmembrane receptor EPOR. Recent studies, however, have shown that the EPOR is additionally present in various cancer cells and EPO induces the proliferation of these cells, suggesting a different function for EPO other than erythropoiesis. Therefore, the purpose of the present study was to examine EPOR expression and the role of EPO in the proliferation and signaling cascades involved in this process, using the rat pancreatic tumor cell line AR42J. Our results showed that AR42J cells expressed EPOR, and EPO significantly enhanced their proliferation. Cell cycle analysis of EPO-treated cells indicated an increased percentage of cells in the S phase, whereas cell numbers in G0/G1 phase were significantly reduced. Phosphorylation of extracellular regulatory kinase 1/2 (ERK1/2) and c-Jun NH2terminal kinase 1/2 (JNK1/2) was rapidly stimulated and sustained after EPO addition. Treatment of cells with mitogen-activated protein/ERK kinase (MEK) inhibitor PD98059 or JNK inhibitor SP600125 significantly inhibited EPO-enhanced proliferation and also increased the fraction of cells in G0/G1 phase. Furthermore, the inhibition of JNK using small interference RNA (siRNA) suppressed EPO-enhanced proliferation of AR42J cells. Taken together, our results indicate that AR42J cells express EPOR and that the activation of both ERK1/2 and JNK1/2 by EPO is essential in regulating proliferation and the cell cycle. Thus both appear to play a key role in EPO-enhanced proliferation and suggest that the presence of both is required for EPO-mediated proliferation of AR42J cells.

Erythropoietin and cancer, a double-edged sword

This editorial is focused on the double controversial action of erythropoietin, acting as anticancer agent and as a promoting cancer agent.

The erythropoietin receptor in normal and cancer tissues

The hormone erythropoietin (EPO) is essential for the survival, proliferation and differentiation of the erythrocytic progenitors. The EPO receptor (EPO-R) of erythrocytic cells belongs to the cytokine class I receptor family and signals through various protein kinases and STAT transcription factors. The EPO-R is also expressed in many organs outside the bone marrow, suggesting that EPO is a pleiotropic anti-apoptotic factor. The controversial issue as to whether the EPO-R is functional in tumor tissue is critically reviewed. Importantly, most studies of EPO-R detection in tumor tissue have provided falsely positive results because of the lack of EPO-R specific antibodies. However, endogenous EPO appears to be necessary to maintain the viability of endothelial cells and to promote tumor angiogenesis. Although there is no clinical proof that the administration of erythropoiesis stimulating agents (ESAs) promotes tumor growth and mortality, present recommendations are that (i) ESAs should be administered at the lowest dose sufficient to avoid the need for red blood cell transfusions, (ii) ESAs should not be used in patients with active malignant disease not receiving chemotherapy or radiotherapy, (iii) ESAs should be discontinued following the completion of a chemotherapy course, (iv) the target Hb should be 12 g/dL and not higher and (v) the risks of shortened survival and tumor progression have not been excluded when ESAs are dosed to target Hb <12 g/dL.