Human Hematopoietic Progenitors Express Erythropoietin

Effect of Zinc Supplementation on Renal Anemia in 5/6-Nephrectomized Rats and a Comparison with Treatment with Recombinant Human Erythropoietin

Anemia is a severe complication in patients with chronic kidney disease (CKD). Treatment with exogenous erythropoietin (EPO) can correct anemia in many with CKD. We produced 5/6-nephrectomized rats that became uremic and anemic at 25 days post surgery. Injection of the anemic 5/6-nephrectomized rats with 2.8 mg zinc/kg body weight raised their red blood cell (RBC) levels from approximately 85% of the control to 95% in one day and continued for 4 days. We compared the effect of ZnSO4 and recombinant human erythropoietin (rHuEPO) injections on relieving anemia in 5/6-nephrectomized rats. After three consecutive injections, both the ZnSO4 and rHuEPO groups had significantly higher RBC levels (98 ± 6% and 102 ± 6% of the control) than the saline group (90 ± 3% of the control). In vivo, zinc relieved anemia in 5/6-nephrectomized rats similar to rHuEPO. In vitro, we cultured rat bone marrow cells supplemented with ZnCl2, rHuEPO, or saline. In a 4-day suspension culture, we found that zinc induced erythropoiesis similar to rHuEPO. When rat bone marrow cells were supplement-cultured with zinc, we found that zinc stimulated the production of EPO in the culture medium and that the level of EPO produced was dependent on the concentration of zinc supplemented. The production of EPO via zinc supplementation was involved in the process of erythropoiesis.

Pleiotropic effects of Erythropoietin. Influence of Erythropoietin on processes of mesenchymal stem cells differentiation

Structure and synthesis of Erythropoietin: Erythropoietin (EPO) is a glycoprotein hormone.

Recombinant Erythropoietin (Epoetin): Human recombinant erythropoietin is characterised as a factor which stimulates differentiation and proliferation of erythroid precursor cells, and as a tissue protective factor.

Anti-ischemic effects of recombinant Erythropoietin: Erythropoietin is one of the most perspective humoral agents which are involved in the preconditioning phenomenon.

Erythropoietin receptors and signal transduction pathways: Erythropoietin effects on cells through their interconnection with erythropoietin receptors, which triggers complex intracellular signal cascades, such as JAK2/STAT signaling pathway, phosphatidylinositol 3-kinase (PI3K), protein kinase C, mitogen-activated protein kinase (MAPK), and nuclear factor (NF)-κB signaling pathways.

Mechanisms of the effect of Erythropoietin on hematopoietic and non-hematopoietic cells and tissues: In addition to regulation of haemopoiesis, erythropoietin mediates bone formation as it has an effect on hematopoietic stem cells and osteoblastic niche, and this illustrates connection between the processes of haematopoiesis and osteopoiesis which take place in the red bone marrow.

The effect of Erythropoietin on mesenchymal stem cells and process of bone tissue formation: Erythropoietin promotes mesenchymal stem cells proliferation, migration and differentiation in osteogenic direction. The evidence of which is expression of bone phenotype by cells under the influence of EPO, including activation of bone specific transcription factors Runx2, osteocalcin and bone sialoprotein.

Conclusion: Erythropoietin has a pleiotropic effect on various types of cells and tissues. But the mechanisms which are involved in the process of bone tissue restoration via erythropoietin are still poorly understood.

Zinc Supplementation Stimulates Red Blood Cell Formation in Rats

In rats, mice, and humans, it is known that zinc deficiency may be related to anemia, and zinc supplementation influences hemoglobin production. Our previous studies indicate that in fish, zinc supplementation stimulates red blood cell (RBC) formation (erythropoiesis). However, it is not clear whether the mechanism of zinc-induced erythropoiesis stimulation in fish also occurs in rats. We induced anemia in rats using phenylhydrazine (PHZ) and injected either saline or ZnSO₄ solution. We found that an appropriate amount of zinc stimulated erythropoiesis in the PHZ-induced anemic rats. The effects of ZnSO₄ injection were dose-dependent. When the concentration of ZnSO₄ was higher than 2.8 mg zinc/kg body weight, the RBC level of the anemic rats increased from 60 ± 7% to 88 ± 10% that of the normal rats in two days. Rat bone marrow cells with or without ZnCl₂ supplementation were cultured in suspension in vitro. In the cell culture when the zinc concentration was at 0.3 mM, a 1.6-fold proliferation of nascent immature reticulocytes (new RBCs) was observed after one day. In the rat blood, zinc was combined with serum transferrin to induce erythropoiesis. The stimulation of RBC formation by zinc appears to be common among different animals.

Erythropoietin and G-csf Receptors in Human Tumor Cells: Expression and Aspects regarding Functionality

Aims and Background

Recombinant human erythropoietin (Epo) and granulocyte-colony-stimulating factor (G-CSF) are used to stimulate hematopoiesis in patients with malignant diseases. These cytokines transduce their biological signal via the Epo receptor (EpoR) and G-CSF receptor (G-CSF-R) into the cell. We therefore investigated in human tumor cell lines the expression of these receptors in tumor cells as well as their response to Epo and G-CSF.

Methods and Study Design

The expression of EpoR and G-CSF-R mRNA was analyzed with reverse transcription-polymerase chain reaction (RT-PCR). EpoR protein expression was further monitored with Western blot and immunocytochemistry analysis. The cellular response to various concentrations of Epo was evaluated using 3[H]-thymidine uptake, Northern blot of c-fos expression and tyrosine kinase activity assay. The proliferation after G-CSF incubation was analyzed with the MTS assay.

Results

In this study EpoR mRNA and protein were detected in various human tumor cell lines. Treatment with Epo did not influence the proliferation rate of examined EpoR-positive tumor cell lines. Epo did not stimulate the tyrosine kinase activity nor did it affect the c-fos mRNA in these cell lines. G-CSF-R mRNA was only detected in two myeloid cell lines. Treatment with G-CSF did not increase the proliferation of these cells.

Conclusions

These results demonstrate that Epo and G-CSF did not modulate the growth rate of examined receptor-positive tumor cell lines; the presence of the Epo receptor seems not essential for cell growth of these tumor cells in cell culture.

A Gain-of-Function Mutation in EPO in Familial Erythrocytosis

Familial erythrocytosis with elevated erythropoietin levels is frequently caused by mutations in genes that regulate oxygen-dependent transcription of the gene encoding erythropoietin ( EPO). We identified a mutation in EPO that cosegregated with disease with a logarithm of the odds (LOD) score of 3.3 in a family with autosomal dominant erythrocytosis. This mutation, a single-nucleotide deletion (c.32delG), introduces a frameshift in exon 2 that interrupts translation of the main EPO messenger RNA (mRNA) transcript but initiates excess production of erythropoietin from what is normally a noncoding EPO mRNA transcribed from an alternative promoter located in intron 1. (Funded by the Gebert Rüf Foundation and others.).

Polyurethane scaffolds seeded with CD34(+) cells maintain early stem cells whilst also facilitating prolonged egress of haematopoietic progenitors

We describe a 3D erythroid culture system that utilises a porous polyurethane (PU) scaffold to mimic the compartmentalisation found in the bone marrow. PU scaffolds seeded with peripheral blood CD34⁺ cells exhibit a remarkable reproducibility of egress, with an increased output when directly compared to human bone scaffolds over 28 days. Immunofluorescence demonstrated the persistence of CD34⁺ cells within the scaffolds for the entirety of the culture. To characterise scaffold outputs, we designed a flow cytometry panel that utilises surface marker expression observed in standard 2D erythroid and megakaryocyte cultures. This showed that the egress population is comprised of haematopoietic progenitor cells (CD36⁺GPA^−/low). Control cultures conducted in parallel but in the absence of a scaffold were also generally maintained for the longevity of the culture albeit with a higher level of cell death. The harvested scaffold egress can also be expanded and differentiated to the reticulocyte stage. In summary, PU scaffolds can behave as a subtractive compartmentalised culture system retaining and allowing maintenance of the seeded “CD34⁺ cell” population despite this population decreasing in amount as the culture progresses, whilst also facilitating egress of increasingly differentiated cells.

Whole-Genome Sequencing of Native Sheep Provides Insights into Rapid Adaptations to Extreme Environments

Global climate change has a significant effect on extreme environments and a profound influence on species survival. However, little is known of the genome-wide pattern of livestock adaptations to extreme environments over a short time frame following domestication. Sheep (Ovis aries) have become well adapted to a diverse range of agroecological zones, including certain extreme environments (e.g., plateaus and deserts), during their post-domestication (approximately 8–9 kya) migration and differentiation. Here, we generated whole-genome sequences from 77 native sheep, with an average effective sequencing depth of ∼5× for 75 samples and ∼42× for 2 samples. Comparative genomic analyses among sheep in contrasting environments, that is, plateau (>4,000 m above sea level) versus lowland (<100 m), high-altitude region (>1500 m) versus low-altitude region (<1300 m), desert (<10 mm average annual precipitation) versus highly humid region (>600 mm), and arid zone (<400 mm) versus humid zone (>400 mm), detected a novel set of candidate genes as well as pathways and GO categories that are putatively associated with hypoxia responses at high altitudes and water reabsorption in arid environments. In addition, candidate genes and GO terms functionally related to energy metabolism and body size variations were identified. This study offers novel insights into rapid genomic adaptations to extreme environments in sheep and other animals, and provides a valuable resource for future research on livestock breeding in response to climate change.

The Local HIF-2α/EPO Pathway in the Bone Marrow is Associated with Excessive Erythrocytosis and the Increase in Bone Marrow Microvessel Density in Chronic Mountain Sickness

AIM

Chronic mountain sickness (CMS) is characterized by excessive erythrocytosis, and angiogenesis may be involved in the pathogenesis of this disease. The bone marrow niche is the primary site of erythropoiesis and angiogenesis. This study was aimed at investigating the associations of the levels of hypoxia-inducible factors (HIFs), erythropoietin (EPO), and erythropoietin receptor (EPOR), as well as microvessel density (MVD) in the bone marrow with CMS.

RESULTS

A total of 34 patients with CMS and 30 control subjects residing in areas at altitudes of 3000-4500 m were recruited for this study. The mRNA and protein expression of HIF-2α and EPO in the bone marrow cells was significantly higher in the CMS patients than in the controls. Moreover, changes in HIF-2α expression in CMS patients were significantly correlated with EPO and hemoglobin levels. In contrast, the expression of mRNA and protein expression of HIF-1α and EPOR did not differ significantly between the CMS and control patients. Increased MVD was observed in the bone marrow of the patients with CMS and it was significantly correlated with hemoglobin.

CONCLUSIONS

Bone marrow cells of CMS patients may show enhanced activity of the HIF-2α/EPO pathway, and EPO may regulate the erythropoiesis and vasculogenesis through autocrine or/and paracrine mechanisms in the bone marrow niche. The increased MVD in the bone marrow of CMS patients appears to be involved in the pathogenesis of this disease.

Activation of mitochondrial function and Hb expression in non-haematopoietic cells by an EPO inducer ameliorates ischaemic diseases in mice

BACKGROUND AND PURPOSE

Many organs suffer from ischaemic injuries that reduce their ability to generate sufficient energy, which is required for functional maintenance and repair. Erythropoietin (EPO) ameliorates ischaemic injuries by pleiotropic effects. The aim of this study was to investigate the effect and mechanism of a small molecule EH-201, and found it as a potent EPO inducer and its effect in non-haematopoietic cells for therapeutic potential in ischemic disorders.

EXPERIMENTAL APPROACH

Mice kidney slices, primary hepatocytes, primary cardiomyocytes and C2C12 myoblasts were treated with EH-201. The effects of this treatment on EPO, Hb expression and mitochondrial biogenesis were analysed. In vivo, doxorubicin-induced cardiomyopathic mice were treated with EH-201. The mice were subjected to an endurance test, electrocardiography and echocardiography, and a histological examination of the isolated hearts was performed. EH-201 was also administered to cisplatin-induced nephropathic mice.

KEY RESULTS

In non-haematopoietic cells, EH-201 was potent at inducing EPO. EH-201 also stimulated mitochondrial biogenesis and enhanced the expression of Hb by a mechanism dependent on EPO-mediated signalling. In mechanistic studies, using EPO and EPO receptor-neutralizing antibodies, we confirmed that EH-201 enhances EPO-EPOR autocrine activity. EH-201 robustly increased the endurance performance activity of healthy and cardiomyopathic mice during hypoxic stress, enhanced myocardial mitochondrial biogenesis and Hb expression, and also improved cardiac function. EH-201 ameliorated anaemia and renal dysfunction in nephropathic mice.

CONCLUSIONS AND IMPLICATIONS

The enhancement and recovery of cellular functions through the stimulation of mitochondrial activity and Hb production in non-haematopoietic cells by an inducer of endogenous EPO has potential as a therapeutic strategy for ischaemic diseases.

Flow cytometric analysis of STAT5 phosphorylation and CD95 expression in CD4+ T lymphocytes treated with recombinant human erythropoietin

Erythropoietin receptor (EPO-R) appears on the cell surface in the early stages of erythropoiesis. It also has been found on human T and B lymphocytes and monocytes suggesting that EPO could directly influence these cells. Moreover, earlier reports have shown that treatment with recombinant human (rh) EPO in chronic renal failure (CRF) patients improves interleukin-2 production and restores CD4+ T lymphocyte functions. We decided to investigate possibility of direct action of rhEPO on these cells in vitro by phosphorylated signal transducer and activator of transcription 5 (pSTAT5) detection and changes in CD95 antigen expression observation. Flow cytometry was used for detection of pSTAT5 and CD95 expression in CD4+ T lymphocytes treated with rhEPO. Our results show that presence of rhEPO in cell culture of lymphocytes stimulated with anti-CD3 antibody increases percentage of CD4+ T lymphocytes expressing pSTAT5. Stimulating effect of rhEPO was dose dependent. RhEPO presence also increases CD95 expression on these cells but still activated T lymphocytes are resistant to CD95-mediated apoptosis. These observations show that EPO is able to directly influence CD4+ T lymphocytes' signaling pathways.

Hypoxia. 5. Hypoxia and hematopoiesis

Our understanding of organismal responses to hypoxia has stemmed from studies of erythropoietin regulation by hypoxia that led to the discovery of the master regulator of the hypoxic response, i.e., hypoxia-inducible factor (HIF). This is a transcription factor that is now known to induce the expression of a battery of genes in response to hypoxia. HIF-1 and HIF-2 regulate many genes that are involved in erythropoiesis and iron metabolism, which are essential for tissue oxygen delivery.

Erythropoietin receptor is expressed on human peripheral blood T and B lymphocytes and monocytes and is modulated by recombinant human erythropoietin treatment

Erythropoietin receptor (EPO-R) appears on the cell surface in the early stages of erythropoiesis. It has also been found on endothelial cells and polymorphonuclear leukocytes, suggesting erythropoietin (EPO) role beyond erythropoiesis itself. Earlier reports have shown that treatment with recombinant human erythropoietin (rhEPO) in chronic renal failure (CRF) patients improves interleukin-2 production and restores the T lymphocyte function. We decided to investigate possible expression of EPO-R on circulating peripheral blood lymphocytes and monocytes of CRF patients in order to assess the possibility of rhEPO direct action on these cells. Flow cytometry was used for detection and quantification of EPO-R, and reverse transcription polymerase chain reaction for detection of the EPO receptor mRNA. Our results show for the first time the existence of EPO-R on cell surface of human T and B lymphocytes and monocytes as well as at the transcriptional activity of the EPO-R gene in these cells, both in healthy and CRF individuals. We have also found significant differences between the numbers of EPO-R molecules on T and B lymphocytes of CRF patients not treated and treated with rhEPO and healthy control. Discovery of EPO-R expression on human lymphocytes suggests that EPO is probably able to directly modulate some signaling pathways important for these cells.

Erythropoietin and renoprotection

In the haematopoietic system, the principal function of erythropoietin (EPO) is the regulation of RBC production. Consequently, following the cloning of the EPO gene, recombinant human EPO (rHuEPO) forms have been widely used for treatment of anaemia in chronic kidney disease and chemotherapy-induced anaemia in cancer patients. However, a steadily growing body of evidence indicates that the therapeutic benefits of rHuEPO could be far beyond the correction of anaemia. Several articles have been recently published on the tissue-protective, nonhaematological effects of rHuEPO that prevent ischaemia-induced tissue damage in several organs including the kidney.In this review, we focus on nonhaematological effects of rHuEPO in various experimental settings of acute and chronic kidney injury. Because this tissue-protective action of rHuEPO is not the result of correction of anaemia-related tissue hypoxia, we will also discuss potential molecular pathways involved. Finally, we will review the current literature on clinical studies with rHuEPO or analogous substances and progression of chronic kidney disease, and propose possible clinical renoprotective strategies.

The non-haematopoietic biological effects of erythropoietin

In the haematopoietic system, the principal function of erythropoietin (Epo) is the regulation of red blood cell production, mediated by its specific cell surface receptor (EpoR). Following the cloning of the Epo gene (EPO) and characterization of the selective haematopoietic action of Epo in erythroid lineage cells, recombinant Epo forms (epoetin-alfa, epoetin-beta and the long-acting analogue darbepoetin-alfa) have been widely used for treatment of anaemia in chronic kidney disease and chemotherapy-induced anaemia in cancer patients. Ubiquitous EpoR expression in non-erythroid cells has been associated with the discovery of diverse biological functions for Epo in non-haematopoietic tissues. During development, Epo-EpoR signalling is required not only for fetal liver erythropoiesis, but also for embryonic angiogenesis and brain development. A series of recent studies suggest that endogenous Epo-EpoR signalling contributes to wound healing responses, physiological and pathological angiogenesis, and the body's innate response to injury in the brain and heart. Epo and its novel derivatives have emerged as major tissue-protective cytokines that are being investigated in the first human studies involving neurological and cardiovascular diseases. This review focuses on the scientific evidence documenting the biological effects of Epo in non-haematopoietic tissues and discusses potential future applications of Epo and its derivatives in the clinic.

Activation and inhibition of the erythropoietin receptor by a membrane-anchored erythropoietin

OBJECTIVE

To investigate whether expression of a membrane-anchored form of erythropoietin (MbEpo) results in self-controlled, autocrine proliferation, and differentiation of erythroid cells. This would provide a possible approach to the selective expansion of genetically corrected erythroid cells in gene-therapy protocols.

MATERIALS AND METHODS

We designed retroviral vectors encoding MbEpo or secreted erythropoietin (Epo) and enhanced green fluorescent protein. Several Epo-dependent cell lines were transduced and their proliferative capacity evaluated. This approach was also assessed in human bone marrow CD34(+) cells and mouse bone marrow transplants.

RESULTS

Retroviral vector-mediated MbEpo expression induced autocrine proliferation of the Epo-dependent cell lines DAE7 and UT7/Epo. However, it blocked the Epo receptor (EpoR)-induced activation of granulocyte macrophage colony-stimulating factor-dependent UT7/GM cells and the erythroid differentiation of both human hematopoietic cells in vitro and of mouse bone marrow cells in transplant experiments. MbEpo was present at the surface of UT7/GM cells. It did not affect the membrane localization of the EpoR, but prevented its normal Epo-dependent phosphorylation and internalization. By contrast to these inhibitory effects, a higher rate of EpoR replenishment in UT7/GM cells before MbEpo production rendered cell proliferation independent of exogenous growth factor.

CONCLUSIONS

Activation of EpoR gene expression before MbEpo-induced EpoR activation is essential for activation or inhibition of growth and differentiation of Epo-dependent cell lines. It will be necessary to delay MbEpo expression in late erythroid progenitors until after EpoR gene activation, for erythroid cell expansion to be achieved in vivo.

Insulin-like growth factor-II: a novel autocrine growth factor modulating the apoptosis and maturation of umbilical cord blood erythroid progenitors

OBJECTIVE

To search a novel function of erythroid progenitor cells circulating as the major nucleated cell population in umbilical cord blood (CB) cells.

MATERIALS AND METHODS

Human CB-derived CD36(+) erythroid progenitors were subjected to cDNA microarray. Gene expression and biological property of CB-erythroid progenitors and adult peripheral blood (PB)-erythroid progenitors were compared by using real-time polymerase chain reaction (PCR) and serum-free culture system with erythropoietin (EPO).

RESULTS

The microarray revealed 124-fold higher levels of insulin-like growth factor-II (IGF-II) gene expression in CB-CD36(+) erythroid progenitors than in stimulated lymphocytes of adult PB. Real-time PCR verified that IGF-II mRNA levels were highest in CB-CD36(+) erythroid progenitors compared to other CB- or adult PB-fractionated cells. When CB-CD36(+) erythroid progenitors were cultured with EPO in serum-free medium, anti-IGF-II-antibody (Ab) reduced the number of erythroid colonies. When CB- and adult PB-derived erythroid colony-forming cells (ECFCs) were cultured with interleukin-3, stem cell factor, and EPO, mRNA levels per cells of IGF-II peaked on day 12, but those of type 1 and type 2 receptors did not increase with ECFCs maturation. The maturation rate by IGF-II was higher in CB-ECFCs than in adult PB-ECFCs. The majority of CB-ECFCs expressed IGF-II protein. Anti-IGF-II-Ab, but not anti-IGF-I-Ab, reduced the number of CB-ECFCs in liquid culture with EPO. Anti-IGF-II-Ab accelerated apoptosis of ECFCs, assessed by dimethylthiazole tetrazolium bromide, bromodeoxyuridine, and flow cytometric analyses. ECFCs failed to attain full maturity in the presence of anti-IGF-II-Ab.

CONCLUSIONS

These results suggest that IGF-II is produced by erythroid progenitors themselves, and has a crucial role in fetal erythropoiesis by modulating apoptosis and maturation in an autocrine fashion.

Detection and quantification of functionally defined hematopoietic progenitor cells and tissue specific mRNA within the peripheral blood of myeloma patients after administration of granulocyte colony-stimulating factor and erythropoietin

OBJECTIVE

Hematopoietic progenitor cells (HPC) as well as tissue committed stem cells expressing mRNA specific to various somatic tissues are thought to be part of the CD34+ bone marrow compartment. In this study, we explore and quantify their mobilization in patients with multiple myeloma undergoing chemotherapy upon administration of granulocyte colony-stimulating factor (G-CSF) plus/minus erythropoietin (EPO).

PATIENTS AND METHODS

HPC were quantified by flow cytometry and functional assays within the blood of healthy donors and myeloma patients before and after chemotherapy followed by G-CSF or G-CSF + EPO given subcutaneously. The mRNA expression was studied by quantitative polymerase chain reaction (PCR). Cytokines and peripheral blood protease levels were measured by an enzyme-linked immunosorbent assay.

RESULTS

EPO did not significantly alter the number of HPC mobilized by G-CSF alone, and mRNA specific for liver, brain, muscle and kidney was detected in both treatment groups. Quantitative PCR analysis revealed a 2.7-fold increased expression of glial fibrillary acidic protein after G-CSF + EPO administration compared to G-CSF alone (P = 0.003). The concentration of G-CSF rose from 62 +/- 22 pg/mL and 48 +/- 10 pg/mL to 28 +/- 9 ng/mL and 85 +/- 10 ng/mL after 10 d of treatment with G-CSF and G-CSF + EPO, respectively. The concentration of neutrophil elastase (NE) rose only in the G-CSF group by a factor 1.5.

CONCLUSION

The alteration of G-CSF and NE levels as well as the expression of tissue committed RNA after the administration of EPO in addition to G-CSF indicate that different growth factors mobilize different stem cells that might potentially be used for the support of tissue repair in future treatment protocols.

Pathophysiology of anemia and erythrocytosis

An increasing understanding of the process of erythropoiesis raises some interesting questions about the pathophysiology, diagnosis and treatment of anemia and erythrocytosis. The mechanisms underlying the development of many of the erythrocytoses, previously characterised as idiopathic, have been elucidated leading to an increased understanding of oxygen homeostasis. Characterisation of anemia and erythrocytosis in relation to serum erythropoietin levels can be a useful addition to clinical diagnostic criteria and provide a rationale for treatment with erythropoiesis stimulating agents (ESAs). Recombinant human erythropoietin as well as other ESAs are now widely used to treat anemias associated with a range of conditions, including chronic kidney disease, chronic inflammatory disorders and cancer. There is also heightened awareness of the potential abuse of ESAs to boost athletic performance in competitive sport. The discovery of erythropoietin receptors outside of the erythropoietic compartment may herald future applications for ESAs in the management of neurological and cardiac diseases. The current controversy concerning optimal hemoglobin levels in chronic kidney disease patients treated with ESAs and the potential negative clinical outcomes of ESA treatment in cancer reinforces the need for cautious evaluation of the pleiotropic effects of ESAs in non-erythroid tissues.

Cytokine-producing activity of bone marrow erythrokaryocytes and its regulation under normal conditions

We showed that inhibition of cytokine production by bone marrow adherent cells and their soluble products is a mechanism of regulation of cytokine-producing activity of bone marrow erythrokaryocytes under normal conditions.

Microcytosis in ank/ank mice and the role of ANKH in promoting erythroid differentiation

Progressive ankylosis (Ank and the human homolog, ANKH) is a transmembrane protein which regulates transport of inorganic pyrophosphate (PPi). ank/ank mice with a mutated ank gene, have calcification and bone ankylosis of the affected joints. In the course of studying these mutant mice, we found that they have microcytosis. These mutant mice have lower mean red blood cell volume (MCV) and lower hemoglobin content in red cells (mean corpuscular hemoglobin, MCH) than normal mice. Using quantitative real-time PCR analysis, we showed that Ank was expressed in the E/Meg bipotent precursor, BFU-E, CFU-E, but there was no Ank expression in the hemoglobinizing erythroblasts. Stable ANKH transfectants in K562 cells highly expressed two immature erythroid cell markers, E-cadherin and endoglin. Enhanced Erythropoietin (Epo) expression and downregulation of SHP-1 were detected in these transfectants. Consequently, the autocrine Epo-EpoR signaling pathway was activated, as evidenced by higher p-Tyr JAK2, p-Tyr EpoR and p-Tyr STAT5B in the ANKH transfectants. Our results revealed a novel function of ANKH in the promotion of early erythroid differentiation in K562 cells. We also showed that ank/ank mice have lower serum levels of Epo than the normal littermates, and this is the likely cause of microcytosis in these mutant mice.

Polycythemia vera is not initiated by JAK2V617F mutation

OBJECTIVE

The somatic JAK2(V617F) mutation is seen in most polycythemia vera (PV) patients; however, it is not clear if JAK2(V617F) is the PV-initiating mutation.

METHODS

In order to examine this issue, we developed a novel real-time quantitative allele-specific PCR, in which allelic discrimination is enhanced by the synergistic effect of a mismatch in the -1 position, and a locked nucleic acid (LNA) nucleoside at the -2 position.

RESULTS

Determination of allelic frequencies was reproducible (SD = 1.5%) and sensitive--0.1% mutant allele detected in 40 ng of DNA. The JAK2(V617F) frequency in clonal granulocytes from 3 PV females was less than 50% (27.5 +/- 11) and in 7 females greater than 50% (75 +/- 10.5). We also found that wild-type JAK2 BFU-E colonies from PV patients can grow without erythropoietin. The identification of the primary genetic lesion resulting in PV is essential for the development of novel therapeutic strategies.

CONCLUSION

Our studies correlating the frequency of JAK2(V617F) mutant allele and clonality, as well as the presence of homozygous wild-type JAK2 erythropoietin-independent erythroid colonies, provide compelling evidence that the JAK2(V617F) is not the PV-initiating mutation. This supports a model wherein the JAK2(V617F) mutation arises as a secondary genetic event. Furthermore, our results indicate that an undefined molecular lesion, preceding JAK2(V617F), is responsible for clonal hematopoiesis in PV. We conclude that development of therapeutic strategies that target the JAK2(V617F) clonal cells may not be sufficient for eradication of PV.

Analysis of ARD1 Function in Hypoxia Response Using Retroviral RNA Interference

Cellular hypoxia response is regulated at the level of hypoxia-inducible factor (HIF) activity. A number of recently identified oxygen sensors are HIF-modifying enzymes that respond to low oxygen by altering HIF modification and thus lead to its activation. In addition to the HIF proline hydroxylases and asparagine hydroxylases, ARD1 is recently described as a HIF-1alpha acetylase that regulates its stability. We found that ARD1 is down-regulated in a number of cell lines in response to hypoxia and hypoxia mimic compounds. After surveying these lines for erythropoietin production and retroviral transfection efficiency, we chose to use HepG2 cells to study the function of ARD1. ARD1 short hairpin RNA delivered by a retroviral vector caused >80% reduction in ARD1 message. We observed decreases in erythropoietin and vascular endothelial growth factor protein production, whereas there was no change in the HIF-1alpha protein level. A gene chip analysis of HepG2 cells transduced with virus expressing ARD1 short hairpin RNA under normoxia and hypoxia conditions or with virus overexpressing recombinant ARD1 confirmed that inhibition of ARD1 does not cause activation of HIF and downstream target genes. However, this analysis revealed that ARD1 is involved in cell proliferation and in regulating a series of cellular metabolic pathways that are regulated during hypoxia response. The role of ARD1 in cell proliferation is confirmed using fluorescence labeling analysis of cell division. From these studies we conclude that ARD1 is not required to suppress HIF but is required to maintain cell proliferation in mammalian cells.

HIF-2α regulates murine hematopoietic development in an erythropoietin-dependent manner

Erythropoiesis in the adult mammal depends critically on erythropoietin, an inducible cytokine with pluripotent effects. Erythropoietin gene expression increases under conditions associated with lowered oxygen content such as anemia and hypoxia. HIF-1α, the founding member of the hypoxia-inducible factor (HIF) alpha class, was identified by its ability to bind and activate the hypoxia-responsive enhancer in the erythropoietin regulatory region in vitro. The existence of multiple HIF alpha members raises the question of which HIF alpha member or members regulates erythropoietin expression in vivo. We previously reported that mice lacking wild-type HIF-2α, encoded by the EPAS1 gene, exhibit pancytopenia. In this study, we have characterized the etiology of this hematopoietic phenotype. Molecular studies of EPAS1-null kidneys reveal dramatically decreased erythropoietin gene expression. EPAS1-null as well as heterozygous mice have impaired renal erythropoietin induction in response to hypoxia. Treatment of EPAS1-null mice with exogenous erythropoietin reverses the hematopoietic and other defects. We propose that HIF-2α is an essential regulator of murine erythropoietin production. Impairments in HIF signaling, involving either HIF-1α or HIF-2α, may play a prominent role in conditions involving altered hematopoietic or erythropoietin homeostasis.

Erythroid cells in immunoregulation: characterization of a novel suppressor factor

Nucleated erythroid cells (EC) have been previously reported to possess a potent natural suppressor (NS) activity for B-cell responses. In this study, we demonstrate that murine EC are able to reduce not only lipopolysaccharide (LPS)-driven B-cell proliferation, but also proliferative and cytotoxic T-cell responses generated in a primary allogeneic mixed lymphocyte culture (MLC); and that a soluble low molecular weight factor may be involved in such EC-derived immunoregulation. In addition, the erythroid cell-derived suppressor factor (ESF) was found to be capable of effectively reducing the allergen-driven proliferation of peripheral blood mononuclear cells (PBMC) isolated from allergic patients. From the data presented herein, it appears that ESF is heat-stable (80 degrees C for 20 min) and has molecular weight (MW) lower or close to 0.5 kDa. ESF activity is resistant to both enzyme (trypsin plus chymotrypsin) proteolysis and action of the enzymes such as lipase and phospholipase C. On the other hand, ESF is effectively inactivated by neuraminidase treatment, suggesting the presence in its structure of sialic residue(s). The neuraminidase-sensitive, ESF-like activity is readily detected in the medium conditioned with normal mouse bone marrow (BM) cells. On fractionation of low MW erythroid products on a reversed-phase C16 column in a linear acetonitrile gradient (5-95%), ESF activity is detected in the first peak alone with the shortest time of its retention by the column. The results suggest that (1) by producing ESF, EC may regulate both B- and T-cell-mediated immune processes and (2) based on its physicochemical and biological characteristics, ESF can be distinguished from each of earlier characterised suppressor mediators of bone marrow origin.

Early Fetal Liver Readily Repopulates B Lymphopoiesis in Adult Bone Marrow

Fetal liver (FL) becomes a major organ of hematopoiesis at mouse embryonic day (E) 11 and E12, when definitive hematopoietic stem cells, originating from the aorta-gonads-mesonephros region, colonize the hepatic tissue. Unipotent B-cell progenitors are very rare in FL by day 12, whereas erythropoiesis prevails. We have studied hematopoiesis in FL from different gestational ages, with special emphasis on B lymphopoiesis. The mRNA levels of selected liver-specific genes, hematopoietic lineage-specific genes, and genes for selected cytokines/hormones as well as for their receptors were evaluated by real-time polymerase chain reaction in FL from E12.5, E14.5, and E17.5, adult liver and adult bone marrow (BM). The level of B lineage-related gene expression in FL was very low at E12.5. There was also a significantly lower fraction of B220+ and CD19+ B cells in E12.5 FL compared with E17.5 FL. To analyze whether these differences reflect different stem cell potentials occurring during FL development, 10(6) or 5 x 10(6) of FL cells collected from embryos at E12.5 or E17.5 and those from adult BM were transplanted into sublethally irradiated (3- or 6-Gy) congenic mice. Short-term and long-term repopulation of B and T cells and granulocyte/macrophage lineages from donor FL or adult BM cells were evaluated in competition to adult hematopoiesis of sublethally irradiated recipients. In short-term repopulation, the transplantation of E12.5 FL cells resulted in a lower blood chimerism compared with that of E17.5 FL cells. However, the proportion of B lymphopoiesis exerted by E12.5 FL cells was not different from that of E17.5 FL or adult BM. This study demonstrates that E12.5 FL contains hematopoietic stem cells with fully developed B-cell repopulating capacity and that the developmental period of fetal hematopoiesis between E12.5 and E17.5 is not an obligatory phase for the adult B lymphopoiesis.

Autocrine erythropoietin signaling inhibits hypoxia-induced apoptosis in human breast carcinoma cells

Disordered perfusion and the resulting hypoxia are important features conferring tumor heterogeneity, which may contribute to relapse. Hypoxic tumor cells have been associated with resistance both to radiation and to cytotoxic drugs. Hypoxia may also serve as a selection pressure in tumors by promoting apoptosis of some cells and expanding variants with decreased apoptotic potential, and thus play a role in the development of a more aggressive phenotype. Erythropoietin (Epo), induced by hypoxia, controls erythropoiesis and plays a role in protection of neurons from hypoxic damage. We have recently demonstrated hypoxia-stimulated expression of Epo and Epo receptor (EpoR) in human breast and cervix cancers, suggesting a role for autocrine Epo signaling in the hypoxic adaptations of carcinomas. In the current study we provide evidence that increased autocrine Epo signaling induced by moderate levels of hypoxia inhibits hypoxia-induced apoptosis and promotes survival in MCF-7 human breast cancer cells. The anti-apoptotic effect of Epo correlates with upregulation of bcl-2 and bcl-XL, suggesting a mechanism similar to those described in hematopoietic cells. The resulting decreased apoptotic potential of hypoxic tumor cells may contribute to increased aggressiveness and therapy resistance of breast cancers.

Identification of a human mutation of DMT1 in a patient with microcytic anemia and iron overload

Divalent metal transporter 1 (DMT1) is a transmembrane protein crucial for duodenal iron absorption and erythroid iron transport. DMT1 function has been elucidated largely in studies of the mk mouse and the Belgrade rat, which have an identical single nucleotide mutation of this gene that affects protein processing, stability, and function. These animals exhibit hypochromic microcytic anemia due to impaired intestinal iron absorption, and defective iron utilization in red cell precursors. We report here the first human mutation of DMT1 identified in a female with severe hypochromic microcytic anemia and iron overload. This homozygous mutation in the ultimate nucleotide of exon 12 codes for a conservative E399D amino acid substitution; however, its pre-dominant effect is preferential skipping of exon 12 during processing of pre-messenger RNA (mRNA). The lack of full-length mRNA would predict deficient iron absorption in the intestine and deficient iron utilization in erythroid precursors; however, unlike the animal models of DMT1 mutation, the patient is iron overloaded. This does not appear to be due to up-regulation of total DMT1 mRNA. DMT1 protein is easily detectable by immunoblotting in the patient's duodenum, but it is unclear whether the protein is properly processed or targeted.

Growth autonomy and lineage switching in BCR-ABL-transduced human cord blood cells depend on different functional domains of BCR-ABL

The tyrosine kinase activity of p210BCR-ABL is essential to its leukemogenic potential, but the role of other functional domains in primary human hematopoietic cells has not been previously investigated. Here we show that infection of normal human CD34+ cord blood (CB) cells with a retroviral vector encoding p210BCR-ABL rapidly activates a factor-independent phenotype and autocrine interleukin-3/granulocyte colony-stimulating factor/erythropoietin production in the transduced cells. These changes are characteristic of primitive chronic myeloid leukemic (CML) cells and are important to the leukemogenicity of BCR-ABL-transduced murine hematopoietic stem cells. When BCR-ABL-transduced human CB cells were incubated with imatinib mesylate, an inhibitor of the p210BCR-ABL kinase, or when human CB cells were transduced with a BCR-ABL cDNA lacking the SH2 domain (p210DeltaSH2), factor independence was significantly reduced. In contrast, deletion of the SH2 domain had little impact on the p210BCR-ABL kinase-dependent promotion of erythropoietic differentiation also seen immediately following the BCR-ABL transduction of primitive human CB cells, but not in naturally occurring CML. Thus, p210BCR-ABL has distinct biological effects in primary human hematopoietic cells, which variably mimic features of human CML, and activation of these changes can show different dependencies on the integrity of the SH1 and SH2 domains of p210BCR-ABL.

Detection of erythropoietin in human seminal plasma

OBJECTIVE

To examine the presence of erythropoietin (EPO) in ejaculates and the association between EPO levels in seminal plasma and semen parameters.

DESIGN

Retrospective analysis.

SETTING

University hospital in Japan.

PATIENT(S)

Eighty-three infertile males and 16 volunteers with proven fertility.

INTERVENTION(S)

Semen was obtained by masturbation after 5 days of abstinence. Blood sample and split ejaculates of 16 volunteers with proven fertility were collected.

MAIN OUTCOME MEASURE(S)

Western blot analysis and enzyme-linked immunoassay in the seminal plasma and sperm parameters.

RESULT(S)

Western blot analysis showed that EPO protein was present in the seminal plasma. The EPO titers in the seminal plasma ranged from 1.5 mIU/mL to 45.0 mIU/mL by enzyme-linked immunoassay. There was no significant association between EPO levels and semen parameters. The first fraction of samples obtained by split ejaculation contained almost the same amount of EPO as the second fraction.

CONCLUSION(S)

Erythropoietin protein was constitutively present in seminal plasma. The seminal EPO originated from the prostate and seminal vesicle. No association between EPO levels in seminal plasma and sperm parameters was found in the present study.

Neutralization of autocrine transforming growth factor-beta in human cord blood CD34(+)CD38(-)Lin(-) cells promotes stem-cell-factor-mediated erythropoietin-independent early erythroid progenitor development and reduces terminal differentiation

Transforming growth factor (TGF)-beta1 exerts autocrine and paracrine effects on hematopoiesis. Here, we have attempted to evaluate the effect of endogenous TGF-beta1 on early erythroid development from primitive human hematopoietic stem cells (HSCs) and to assess the effects of TGF-beta1 on different phases of erythropoiesis. Cord blood CD34(+)CD38(-) lineage-marker-negative (Lin(-)) cells were cultured in serum-free conditions using various combinations of stem cell factor (SCF), erythropoietin (Epo), and TGF-beta-neutralizing antibody. Generation of erythroid progenitors was assessed using colony assay and flow cytometry. Terminal erythroid differentiation was examined when SCF/Epo-stimulated cells were recultured in the presence of Epo with and without TGF-beta1. Anti-TGF-beta augmented the proliferation of CD34(+)CD38(-)Lin(-) cells (day 21) in SCF-stimulated (6.4-fold +/- 1.5-fold) and SCF/Epo-stimulated (2.9-fold +/- 1.2-fold) cultures. Cells stimulated by SCF/Epo underwent similar levels of erythroid differentiation with and without anti-TGF-beta. While SCF alone stimulated the production of tryptase-positive mast cells, cells stimulated by SCF/anti-TGF-beta were predominantly erythroid (CD36(+)CD14(-) and glycophorin A positive). A distinct expansion of erythroid progenitors (CD34(+)CD36(+)CD14(-)) with the potential to form erythroid colonies was seen, revealing early Epo-independent erythroid development. In contrast, the kinetics of erythroid progenitor generation from primitive HSCs indicate that TGF-beta1 is not inhibitory in late erythropoiesis, but it accelerated the conversion of large BFU-E into colony-forming units-erythroid. Finally, TGF-beta1 accelerated Epo-induced terminal erythroid differentiation and resulted in a greater level of enucleation (22% +/- 6% versus 7% +/- 3%) in serum-free conditions. Serum addition stimulated enucleation (54% +/- 18%), which was lower (26% +/- 14%) with anti-TGF-beta, suggesting that optimal erythroid enucleation is Epo dependent, requiring serum factors including TGF-beta1.

Angiotensin II receptor type 1 expression in erythroid progenitors: implications for the pathogenesis of postrenal transplant erythrocytosis

Under normal physiological conditions red blood cell production is controlled primarily by erythropoietin, although multiple additional stimulatory factors are likely to be involved. One of these factors, angiotensin II, can modulate erythropoiesis directly via its type 1 receptor, as well as indirectly through multiple secondary mediators. We propose that angiotensin II exerts its stimulatory effect during the early stages of erythropoiesis, and that this effect serves as an important compensatory mechanism if erythropoietin production is chronically inadequate. We speculate that if this compensatory stimulation continues to be abnormally high after restoration of erythropoietin production following renal transplantation, erythrocytosis ensues.

A Cross-Talk Between Hypoxia and TGF-β Orchestrates Erythropoietin Gene Regulation Through SP1 and Smads

Erythropoietin (Epo) is the humoral regulator of red blood-cell production. Low oxygen tension increases the Epo levels by enhancing transcription, through the hypoxia-inducible factor (HIF)-1, a transcriptional modulator in oxygen-regulated gene expression. In the present work, a cooperative interaction between hypoxia, mediated by the HIF-1 complex, and transforming growth factor-beta (TGF-beta), mediated by Smad3/4, was revealed in the Epo gene. This cooperation is due to physical interaction between Smad3/4 and HIF-1alpha. The Smad3/4 binding site is located within the 3' Epo enhancer, downstream from the HRE consensus, and immediately adjacent to the orphan hepatic nuclear factor receptor (HNF-4). HNF-4 is interacting also with Smad3 and the HIF-1 complex, to potentiate further the cooperative effect between both factors. Moreover, Sp1 has been identified as the factor binding the promoter necessary for the full hypoxia inducibility of the EPO gene. However, this full induction is achieved only if the TGF-beta pathway is mediating a cross-talk between promoter (Sp1) and enhancer (HIF-1alpha) regions through Smad3. We show that Sp1 binding to the proximal promoter is relevant for Epo transcription, and contributes to the Epo induction by hypoxia. A functional cooperation among the transcription factors mediating hypoxia (HIF-1, Sp1), the TGF-beta pathway (Smad3/4), and tissue-specific HNF-4 is proposed for the regulation of the Epo gene. In this model, the physical contact between the upstream promoter and the 3' downstream enhancer is mediated by Sp1 and Smad3 factors, and would occur upon bending of the DNA intervening sequences. Thus, Sp1 would reinforce the promoter/enhancer contact, while Smad3 would stabilize the multifactorial complex by interacting with HIF-1/Sp1/HNF-4 and the coactivator CBP/p300. This model may be extended to other genes where collaboration between TGF-beta and hypoxia takes place.

Differential STAT3, STAT5, and NF-kappaB activation in human hematopoietic progenitors by endogenous interleukin-15: implications in the expression of functional molecules

Different forms of interleukin-15 (IL-15) have been identified and shown to elicit different transduction pathways whose impact on hematopoiesis is poorly understood. We demonstrated herein that hematopoietic CD34+ cells constitutively produced endogenous secreted IL-15 (ES-IL-15) that activated different transcription factors and controlled the expression of several functional proteins, depending on the progenitor source. Thus, nuclear factor-kappa B (NF-kappa B) was activated in bone marrow (BM) and cord blood (CB) progenitors, whereas signal transducer and activator of transcription 3 (STAT3) and STAT5 activation was restricted to peripheral granulocyte-colony-stimulating factor (G-CSF)-mobilized and BM progenitors, respectively. ES-IL-15 acts through autocrine/paracrine loops controlled by high-affinity receptors involving IL-15 receptor alpha (IL-15Ralpha). Furthermore, ES-IL-15 was found to differentially control the expression of several functional molecules important for hematopoietic differentiation. Indeed, in BM precursors, neutralizing anti-IL-15 monoclonal antibody (mAb) inhibits the expression of the gamma c chain and of the chemokine stromal derived factor-1 (SDF-1) but had no effect on vascular cell adhesion molecule 1 (VCAM-1) and beta1 integrin adhesion molecule expression. Conversely, in CB progenitors, anti-IL-15 mAb inhibited VCAM-1 and beta1 integrin expression without affecting gammac chain expression and, most important, up-regulated SDF-1 expression. In conclusion, unprimed human hematopoietic CD34+ cells secrete cell-unbound IL-15, which activates through autocrine/paracrine loop distinct signaling pathways, depending on the progenitor source, thereby influencing the expression of several molecules important in the control of hematopoiesis.

Hypoxia-inducible erythropoietin signaling in squamous dysplasia and squamous cell carcinoma of the uterine cervix and its potential role in cervical carcinogenesis and tumor progression

Tissue hypoxia is a characteristic property of cervical cancers that makes tumors resistant to chemo- and radiation therapy. Erythropoietin (Epo) is a hypoxia-inducible stimulator of erythropoiesis. Acting via its receptor (EpoR), Epo up-regulates bcl-2 and inhibits apoptosis of erythroid cells and rescues neurons from hypoxic damage. In addition to human papillomavirus infection, increased bcl-2 expression and decreased apoptosis are thought to play a role in the progression of cervical neoplasia. Using reverse transcriptase-polymerase chain reaction and Western blotting we showed that HeLa and SiHa cervical carcinoma cells and human cervical carcinomas express EpoR, and that hypoxia enhances EpoR expression. Exogenous Epo stimulated tyrosine phosphorylation and inhibited the cytotoxic effect of cisplatin in HeLa cervical carcinoma cells. Using immunohistochemistry, we examined the expression of Epo, EpoR, p16, hypoxia-inducible factor (HIF)-1alpha, and bcl-2 in benign and dysplastic cervical squamous epithelia and invasive squamous cell carcinomas (ISCCs). EpoR expression in benign epithelia was confined to the basal cell layers, whereas in dysplasias it increasingly appeared in more superficial cell layers and showed a significant correlation with severity of dysplasia. Diffuse EpoR expression was found in all ISCCs. Expression of Epo and HIF-1alpha was increased in dysplasias compared to benign epithelia. Focal Epo and HIF-1alpha expression was seen near necrotic areas in ISCCs, and showed correlation in their spatial distribution. Significant correlation was found between expression of EpoR, and p16 and bcl-2 in benign and dysplastic squamous epithelia. Our results suggest that increased expression of Epo and EpoR may play a significant role in cervical carcinogenesis and tumor progression. Hypoxia-inducible Epo signaling may play a significant role in the aggressive behavior and treatment resistance of hypoxic cervical cancers.

Biological significance of the different erythropoietic factors secreted by normal human early erythroid cells

Evidence is accumulating that autocrine/paracrine regulatory mechanisms play an important role in regulating normal hematopoiesis. To support this, various growth factors, cytokines and chemokines are expressed and secreted by normal early and differentiated hematopoietic cells. In this review, we summarize recent advances in the identification and understanding of the role of autocrine/paracrine axes in normal human erythropoiesis. We will also address a biological significance of the secretion of (i) metalloproteinases which in addition to growth factors and cytokines are secreted by normal erythroid cells and (ii) membrane-derived microvesicles (MV), that are shed from the surface of maturating erythroblasts/reticulocytes, and as we postulate may also play a role in intercellular communication. We hypothesize that all these factors together play an important role in a crosstalk between erythroid cells and their environment. A better understanding of intercellular crosstalk operating in normal erythropoiesis and of the mechanisms regulating synthesis of these endogenously produced factors may allow us to develop more efficient therapeutic strategies to treat various erythropoietic disorders.

Contribution of quinolinic acid in the development of anemia in renal insufficiency

Quinolinic acid (QA) is a potent endogenous excitotoxin; elevation of its concentration in an organism has been implicated in the pathogenesis of various disorders. The purpose of this study was the assessment of QA impact on the process of erythropoiesis. Marked increase of QA concentration was observed in plasma and peripheral tissues of uremic rats. These changes were proportional to the amount of the removed renal tissue and positively correlated with the concentration of creatinine but negatively correlated with hematological parameters, i.e., hematocrit and Hb red blood cells count. The changes were accompanied by a slight decrease in the concentration of endogenic erythropoietin (EPO) in the plasma of animals with uremia. Chronic treatment with QA diminished the increase in EPO concentration after introduction of cobalt in rats. These changes were associated with the decrease in all hematological parameters after QA administration. The in vitro study in the conditions of hypoxia showed that QA inhibited the EPO release from HepG2 cells to the culture base. Additionally, in HepG2 cells QA had a dose-dependent inhibitory effect on hypoxia- and cobalt-induced EPO gene expression without any cell toxicity. In conclusion, the erythropoiesis in chronic renal failure could be attributed to the influence of QA on EPO synthesis. Thus we propose that QA can be a uremic toxin responsible for anemia in animals or patients with renal failure.

Perturbation of autocrine/paracrine loops of burst-forming units of erythroid-derived cells in rHuEPO-hyporesponsive hemodialysis patients

BACKGROUND

Quantitative or qualitative abnormalities of erythroid progenitors in patients with chronic renal failure (CRF) could be the major factor for recombinant human erythropoietin (rHuEPO) hyporesponsiveness and severe anemia in hemodialysis (HD) patients receiving rHuEPO therapy.

METHODS

Purified 1 x 10(4) circulating CD34+ cells isolated from rHuEPO-hyporesponsive HD patients (EPO-H; n = 10), rHuEPO-responsive non-HD patients with CRF (EPO-R; n = 8), nonanemic HD patients without rHuEPO therapy (EPO-W/O; n = 10), and healthy volunteer controls (CON; n = 10) were subjected to a methylcellulose culture system supplemented with rHuEPO, recombinant human interleukin-3 (IL-3), recombinant human stem cell factor (SCF), and recombinant human granulocyte-macrophage colony-stimulating factor (GM-CSF) for 14 days.

RESULTS

The average number of burst-forming units of erythroids (BFU-Es) was significantly less in the EPO-H group compared with the CON and EPO-W/O groups. Furthermore, colony size also was significantly smaller in the EPO-H group. Total RNAs were extracted from approximately 100 colonies/patient and subjected to complementary DNA expression array studies of 268 growth factors, cytokines, chemokines, and their receptors. A characteristic cluster upregulated in the EPO-R and EPO-W/O groups and downregulated in the EPO-H group was identified that contained various cytokines and growth factors, including IL-6, GM-CSF, vascular endothelial growth factor B, IL-9, IL-3, leukemia inhibitory factor, and interferon alpha-2, and such receptors as thrombopoietin receptor, IL-9 receptor, and colony-stimulating factor 1 receptor.

CONCLUSION

These data suggest that the cross-talk network or autocrine/paracrine regulatory loop is critically impaired in BFU-E-derived cells in EPO-H patients, and investigation of these cluster genes would facilitate the development of novel therapeutic strategies for such patients.

Mutations in the VHL gene in sporadic apparently congenital polycythemia

The congenital polycythemic disorders with elevated erythropoietin (Epo) have been until recently an enigma, and abnormality in the hypoxia-sensing pathway has been hypothesized as a possible mechanism. The tumor suppressor von Hippel-Lindau (VHL) participates in the hypoxia-sensing pathway, as it binds to the proline-hydroxylated form of the hypoxia-inducible factor 1alpha (HIF-1alpha) and mediates its ubiquitination and proteosomal degradation. The loss of VHL function may result in the accumulation of HIF-1alpha and overproduction of HIF-1 downstream target genes including Epo. VHL syndrome is an autosomal dominant disorder predisposing to the development of tumors, due to inherited mutations in the VHL gene. Some rare patients with VHL syndrome have polycythemia, which has been attributed to Epo production by a tumor. It was recently found that homozygosity for the VHL Arg200Trp mutation is the cause of Chuvash polycythemia, an autosomal recessive polycythemic disorder characterized by elevated serum Epo and hypersensitivity of erythroid cells to Epo. We evaluated the role of VHL in 8 children with a history of polycythemia and an elevated serum Epo level and found 3 different germline VHL mutations in 4 of them. One child was homozygous for the Arg200Trp VHL mutation, and another compound heterozygous for the Arg200Trp and the Val130Leu mutations. Two children (siblings) were heterozygous for an Asp126Tyr mutation, one of them fulfilling some criteria of VHL syndrome. We propose that mutations of the VHL gene represent an important cause of pediatric sporadic polycythemias with an inappropriately high serum Epo concentration.

Autocrine stimulation by erythropoietin in transgenic mice results in erythroid proliferation without neoplastic transformation

Erythropoietin (Epo) autocrine stimulation has been implicated in erythroleukemia. To develop a model of Epo autocrine stimulation, we made transgenic mice using a construct that linked the human Epo gene to an erythroid-specific regulatory element, designated 5'HS-2, from the human beta-globin locus control region. We hypothesized that Epo gene expression would be targeted to erythroid cells in these mice, resulting in autocrine stimulation of erythroid progenitor cell growth in culture, and that chronic autocrine Epo stimulation would result in erythroleukemia. Transgenic mice containing intact copies of the 5'HS-2Epo construction had elevated hematocrits, reticulocyte counts and serum Epo levels and marked splenic enlargement. Analysis of RNA isolated from organs of transgenic mice revealed constitutive Epo mRNA expression primarily in spleen, blood and bone marrow. RNA samples from anemic transgenic mice revealed Epo gene induction only in the liver. Marrow derived from 5'HS-2Epo mice grew BFU-E in the absence of exogenous Epo. Despite observation of up to 2 years, no mouse developed erythroleukemia, demonstrating that Epo autocrine stimulation alone is insufficient for progression to malignancy. These studies show that 5'HS-2 can be used to target Epo gene expression to erythroid tissue. These mice could provide a model system for studying autocrine growth regulation.

Disruption of oxygen homeostasis underlies congenital Chuvash polycythemia

Chuvash polycythemia is an autosomal recessive disorder that is endemic to the mid-Volga River region. We previously mapped the locus associated with Chuvash polycythemia to chromosome 3p25. The gene associated with von Hippel-Lindau syndrome, VHL, maps to this region, and homozygosity with respect to a C-->T missense mutation in VHL, causing an arginine-to-tryptophan change at amino-acid residue 200 (Arg200Trp), was identified in all individuals affected with Chuvash polycythemia. The protein VHL modulates the ubiquitination and subsequent destruction of hypoxia-inducible factor 1, subunit alpha (HIF1alpha). Our data indicate that the Arg200Trp substitution impairs the interaction of VHL with HIF1alpha, reducing the rate of degradation of HIF1alpha and resulting in increased expression of downstream target genes including EPO (encoding erythropoietin), SLC2A1 (also known as GLUT1, encoding solute carrier family 2 (facilitated glucose transporter), member 1), TF (encoding transferrin), TFRC (encoding transferrin receptor (p90, CD71)) and VEGF (encoding vascular endothelial growth factor).

Ex vivo differentiation of umbilical cord blood progenitor cells in the presence of placental conditioned medium

Hematopoetic stem cells (HSC) are the progenitors for the lympho-hematopoietic system, with long lifespan and high proliferation potential. Transplantation of HSC from bone marrow or peripheral blood represents a standard therapy in severe hematological conditions. A possible alternative source of HSC is the umbilical cord blood, prepared by various separation procedures followed by expansion in cultures supplemented with hematopoietic growth factors. In order to check the effects of placental conditioned medium (PCM) from placental cells culture upon viability of HSC, we added plasma, PCM, dimetil sulfoxyde or hemin in HSC cultures. Flow cytometry or direct scoring of solid cultures using CD45+, CD34+, CD71+ and CD14+ fluorescent-labeled monoclonal antibodies evaluated the effects upon cell proliferation and colony forming ability of HSC cultures, versus controls. PCM produced the highest proliferation, followed by plasma, DMSO and hemin. PCM improved the survival time and maintained a higher proportion of immature cells. PCM stimulates the differentiation towards myeloid lineage progenitor cells (>90% being CD45+), increasing the percentage of CD14+, granulocites /monocytes precursors. It is highly suggestive that PCM contains growth factors or cytokines, which regulate the development of HSC. Characterization of these factors is in progress.

Immunohistochemical expression of erythropoietin and erythropoietin receptor in breast carcinoma

BACKGROUND

Erythropoietin (Epo), induced by hypoxia, controls the survival, proliferation, and differentiation of Epo receptor (EpoR)-bearing erythroid progenitors and plays a role in the protection of neurons from hypoxic damage. Hypoxia in malignant disease is associated with invasion, metastasis, resistance to therapy, and selection for cells with diminished apoptotic potential. The authors recently demonstrated the basal and hypoxia-stimulated expression of Epo and EpoR in human breast carcinoma cell lines and in breast carcinomas, suggesting a role for autocrine Epo signaling in the hypoxic adaptations of mammary neoplasms.

METHODS

The authors characterized the expression of Epo and EpoR by immunohistochemistry in 184 invasive mammary carcinomas and 158 in situ mammary carcinomas and benign mammary epithelium. They analyzed the correlation of Epo and EpoR immunostaining with clinicopathologic tumor features and the patients' smoking history.

RESULTS

Benign mammary epithelial cells showed weak-to-moderate expression of Epo and EpoR. EpoR immunostaining was increased in carcinomas compared with benign epithelium both in nonsmokers and smokers, and Epo immunostaining was increased in carcinomas compared with benign epithelium in nonsmokers but not in smokers. Prominent Epo staining was seen in tumor cells adjacent to necrotic areas and at the infiltrating edge of tumors. EpoR staining, but not Epo staining, was significantly greater in tumors that showed high histologic grade, tumor necrosis, lymphovascular invasion, lymph node metastases, and loss of hormone receptor expression.

CONCLUSIONS

The current findings suggest that increased EpoR expression may play an important role in breast carcinogenesis. The induction of autocrine or paracrine Epo signaling may represent a novel mechanism by which hypoxia can promote breast carcinoma.

Apoptosis protection by the Epo target Bcl-X(L) allows factor-independent differentiation of primary erythroblasts

BACKGROUND

Erythropoietin (Epo) is required for correct execution of the erythroid differentiation program. Erythropoiesis requires Bcl-X(L), a major late target of Epo-receptor signaling. Mice lacking Bcl-X(L) die around embryonic age E12.5, forming normal erythroid progenitors but lacking functional red cells. Recently, serum-free culture conditions for expansion of murine red cell progenitors were developed, yielding cells capable of in vivo-like terminal differentiation into enucleated erythrocytes, in response to Epo/insulin. Here we address whether Epo function during terminal maturation involves a cytokine-independent "default program," requiring only apoptosis inhibition through Epo-dependent upregulation of Bcl-X(L).

RESULTS

Exogenous expression of Bcl-X(L) or Bcl-2 in primary murine erythroblasts or clonal erythroblast lines derived from p53(-/-) mice allowed these cells to undergo terminal erythroid maturation, in the complete absence of cytokines. A potential autocrine Epo loop was ruled out by respective neutralizing antibodies. Importantly, sustained proliferation of Bcl-X(L)-expressing immature erythroblasts still required respective factors (Epo, stem cell factor [SCF], and the glucocorticoid receptor ligand dexamethasone [Dex]). Epo-independent differentiation in these Bcl-X(L)- or Bcl-2-expressing, primary erythroblasts was thus triggered by removal of the renewal factors SCF and Dex. This initiated the maturation-specific expression cascade of erythroid transcription factors, followed by differentiation divisions (characterized by a short G1 phase and decrease in cell size), hemoglobin accumulation, and enucleation.

CONCLUSIONS

During erythroid maturation, Epo regulates red cell numbers via apoptosis inhibition, caused by Epo-dependent upregulation of the antiapoptotic protein Bcl-X(L). This allows "default" terminal differentiation of apoptosis-protected, committed erythroblasts, independent of any exogenous signals.

Functional significance of erythropoietin receptor expression in breast cancer

Erythropoietin (EPO) is the principal hematopoietic cytokine that regulates mammalian erythropoiesis by binding to its transmembrane receptor EpoR. Recent experimental evidence suggests that the biologic effects of EPO are not limited to the regulation of erythropoiesis. In studies focusing on nonhematopoietic effects of EpoR signaling, we found high levels of EpoR protein expression in human breast cancer cells. The purpose of the present study was to evaluate clinical breast cancer specimens for EPO and EpoR expression, characterize the relationship between EPO expression and tumor hypoxia in biopsies prelabeled with hypoxia marker pimonidazole, analyze breast cancer cell lines for EpoR expression, and study the functional significance of EpoR expression in breast cancer cells in vivo. Immunohistochemical analysis for EPO, EpoR expression, and pimonidazole adducts was performed on 26 tumor biopsies with contiguous sections from 10 patients with breast cancer. High levels of EpoR expression were found in cancer cells in 90% of tumors. EPO expression was found in 60% of tumors and EPO and EpoR colocalization in tumor cells was present in many cases. The expression pattern of EPO with respect to tumor hypoxia was variable, without consistent colocalization of EPO and hypoxia in tumor cells. Human and rat breast cancer tissue culture cells express EpoR mRNA and protein. To study the in vivo function of EpoR expression in breast cancer cells, we used rat syngeneic R3230Ac mammary adenocarcinoma cells in a tumor Z-chamber model (dual porous plexiglass chambers containing fibrin gel, cancer cells, and a putative anti-tumor compound implanted into the subcutaneous tissue of rats). Local, one-time administration of a neutralizing anti-EPO antibody, soluble EPO receptor, or an inhibitor of Jak2, a cytoplasmic tyrosine kinase essential for EPO-mediated mitogenesis, resulted in a delay in tumor growth with 45% reduction in maximal tumor depth in tumor Z-chambers in a dose-dependent manner. These studies demonstrate the expression of functional receptors for EPO in breast cancer cells.

TRAIL (Apo2L) suppresses growth of primary human leukemia and myelodysplasia progenitors

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL, APO2L) has been shown to induce apoptosis in a number of tumor cell lines as well as in some primary tumors whereas cells from most normal tissues are highly resistant to TRAIL-induced apoptosis. We have studied the susceptibility of primary malignant and normal bone marrow hematopoietic progenitors to TRAIL-induced apoptosis. Extracellular domain of human TRAIL with N-terminal His(6) tag (His-TRAIL, amino acids 95-281) was produced in E. coli and its apoptosis-inducing ability was compared with the leucine-zipper containing TRAIL, LZ-TRAIL. Both variants of TRAIL had the same apoptosis-inducing ability. Clonogenic progenitor assays showed that His-TRAIL significantly reduced the number of myeloid colonies (CFU-GM) and clusters from patients with acute myeloid leukemia (AML), chronic myeloid leukemia (CML), and myelodysplastic syndromes (MDS). His-TRAIL had no negative effect on the number of CFU-GM colonies and clusters derived from bone marrow cells of AML patients in complete remission, and lymphoma patients without bone marrow involvement, as well as those derived from normal cord blood cells. Moreover, we found that normal human stem cells treated with high doses of His-TRAIL maintain a repopulating potential when transplanted into NOD/SCID mice. To conclude, our data document that TRAIL does not affect normal human hematopoiesis but suppresses the growth of early primary leukemia and myelodysplasia progenitors.

Erythropoietin expression in primary rat Sertoli and peritubular myoid cells

Kidney and liver are the major organs of erythropoietin (Epo) synthesis. However, Epo messenger RNA (mRNA) has been detected in several organs, such as brain, lung, and testis. Furthermore, functional Epo receptors have been demonstrated on different cell types, including rat Leydig cells. The aim of the study was to identify testicular cells expressing Epo mRNA and to quantitate its levels by competitive reverse transcriptase-polymerase chain reaction (RT-PCR). Besides whole testis, Epo transcripts were found in Sertoli and peritubular myoid cells, while no signal was detected in Leydig cells. Exposure of Sertoli cells to CoCl(2) led to an increase of Epo mRNA level. Semiquantitative competitive RT-PCR presented an increase in the level of Epo mRNA in Sertoli cells stimulated by follicle-stimulating hormone, while exposure of peritubular myoid cells cultures to testosterone reduced Epo mRNA expression. Due to the blood-testis barrier, basal expression of Epo suggests a not yet defined function of this hormone in testis.

Autocrine/paracrine mechanisms in human hematopoiesis

Autocrine/paracrine regulatory mechanisms are believed to play a role in the pathophysiology of several hematologic malignancies. Evidence is accumulating that various growth factors, cytokines, and chemokines are expressed and secreted by normal early and differentiated hematopoietic cells and thus could also regulate normal hematopoiesis in an autocrine/paracrine manner. In this review we summarize recent advances in identification and understanding of the role of autocrine/paracrine axes in the growth of both malignant and normal human hematopoietic cells. Better understanding of intercellular crosstalk operating in normal and pathological states and the mechanisms regulating synthesis of these endogenously produced factors (potential targets for various pharmacological approaches) may allow us to improve antileukemia treatments, undertake more efficient ex vivo stem cell expansion, and develop other therapeutic strategies.