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Investigation of erythrocytes from spontaneous or engineered germ-line mutant mice has been instrumental in characterizing the physiological functions of components of the red cell cytoskeleton and membrane. However, the red blood cell expresses some proteins whose germline loss-of-function is embryonic-lethal, perinatal-lethal, or confers reduced post-weaning viability. Promoter regions of erythroid-specific genes have been used to engineer erythroid-specific expression of Cre recombinase. Through breeding with mice carrying appropriately spaced insertions of loxP sequences, generation of erythroid-specific knockouts has been carried out for signaling enzymes, transcription factors, peptide hormones, and single transmembrane span signaling receptors. We report here the use of Cre recombinase expression driven by the erythropoietin receptor (EpoR) promoter to generate EpoR-Cre;Kcc3 f / f mice, designed to express erythroid-specific knockout of the KCC3 K-Cl cotransporter encoded by Kcc3/Slc12A6. We confirm KCC3 as the predominant K-Cl cotransporter of adult mouse red cells in mice with better viability than previously exhibited by Kcc3 -/- germline knockouts. We demonstrate roughly proportionate preservation of K-Cl stimulation by hypotonicity, staurosporine, and urea in the context of reduced, but not abrogated, K-Cl function in EpoR-Cre;Kcc3 f / f mice. We also report functional evidence suggesting incomplete recombinase-mediated excision of the Kcc3 gene in adult erythroid tissues., (© 2022 The Authors. Physiological Reports published by Wiley Periodicals LLC on behalf of The Physiological Society and the American Physiological Society.)

Context: An imbalance of proangiogenic and antiangiogenic factors is thought to induce the widespread vascular dysfunction characteristic of preeclampsia (PreE). Erythropoietin (Epo), a pleiotropic cytokine, has important angiogenic and vasoactive properties; however, its contribution to maternal vascular dysfunction in PreE is unknown., Objectives: Because high altitude (HA) raises the incidence of PreE, we asked whether HA increased maternal Epo and soluble Epo receptor (sEpoR) levels and whether such effects differed between PreE and normotensive controls at HA., Design, Setting, and Participants: Longitudinal studies were conducted in pregnant Andean residents at HA (n = 28; 3600 m) or sea level (SL; n = 16; 300 m). Cross-sectional studies included 34 gestational age‒matched Andean PreE cases (n = 17) and controls (n = 17) in La Paz-El Alto, Bolivia (3600 to 4100 m)., Results: HA augmented the pregnancy-associated rise in Epo relative to SL (P = 0.002), despite similar reductions in hemoglobin (Hb) across pregnancy at each altitude (7% to 9%, P < 0.001 for both). HA PreE cases had circulating Epo levels equivalent to those of controls but greater sEpoR (P < 0.05) and reduced Hb (P = 0.06, trend)., Conclusion(s): Our findings suggest that an augmented pregnancy-associated rise in Epo may be important for successful vascular adaptation to pregnancy at HA. We further speculate that the elevated sEpoR observed in PreE vs controls at HA impedes the effect of Epo to maintain endothelial function and may, in turn, be of pathological relevance for PreE at HA., (Copyright © 2017 by the Endocrine Society)

Excessive erythrocytosis (EE) is the main sign of Chronic Mountain Sickness (CMS), a highly prevalent syndrome in Andean highlanders. Low pulse O2 saturation (SpO2) during sleep and serum androgens have been suggested to contribute to EE in CMS patients. However, whether these factors have a significant impact on the erythropoietin (Epo) system leading to EE is still unclear. We have recently shown that morning soluble Epo receptor (sEpoR), an endogenous Epo antagonist, is decreased in CMS patients suggesting increased Epo availability (increased Epo/sEpoR). The present study aimed to characterize the nocturnal concentration profile of sEpoR and Epo and their relationship with SpO2, Hct, and serum testosterone in healthy highlanders (HH) and CMS patients. Epo and sEpoR concentrations were evaluated every 4 h (6 PM to 6 AM) and nighttime SpO2 was continuously monitored (10 PM to 6 AM) in 39 male participants (CMS, n = 23; HH, n = 16) aged 21-65 yr from Cerro de Pasco, Peru (4,340 m). CMS patients showed higher serum Epo concentrations throughout the night and lower sEpoR from 10 PM to 6 AM. Consequently, Epo/sEpoR was significantly higher in the CMS group at every time point. Mean sleep-time SpO2 was lower in CMS patients compared with HH, while the percentage of sleep time spent with SpO2 < 80% was higher. Multiple-regression analysis showed mean sleep-time SpO2 and Epo/sEpoR as significant predictors of hematocrit corrected for potential confounders (age, body mass index, and testosterone). Testosterone levels were associated neither with Hct nor with erythropoietic factors. In conclusion, our results show sustained erythropoietic stimulus driven by the Epo system in CMS patients, further enhanced by a continuous exposure to accentuated nocturnal hypoxemia., (Copyright © 2016 the American Physiological Society.)

Recombinant human erythropoietin receptor (rhEPOR) has applicability as an affinity ligand for purification of recombinant human erythropoietin (rHuEPO) because of its specific binding to rHuEPO. For application of rhEPOR as a ligand for purification of rHuEPO, soluble rhEPOR was expressed in the periplasm of Escherichia coli and engineered by directed evolution through random mutagenesis and integration of mutations. From the screening of random mutagenesis, we identified an amino acid mutation (H114Y) contributing to rHuEPO binding and four amino acid mutations (R76S, A132D, A162D, and C181Y) contributing to expression of soluble rhEPOR. However, the rHuEPO that binds to engineered rhEPOR having H114Y mutation is difficult to dissociate from the engineered rhEPOR. Therefore, H114Y mutation was not suitable for the construction of the rhEPOR ligand. As a rhEPOR ligand, engineered rhEPOR containing four amino acid mutations (EPORm4L) was constructed by integration of mutations except for H114Y. The expression of EPORm4L (127mgl(-1) of culture medium) was markedly increased in comparison with wild-type rhEPOR (2mgl(-1) of culture medium). Small-scale affinity chromatography demonstrated that EPORm4L worked as an affinity ligand for purification of rHuEPO., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Background: Correction of low hemoglobin (Hb) levels is associated with improved survival and greater quality of life in dialysis patients, but frequent administration of erythropoiesis stimulating agent (ESA) therapy is unsatisfactory for peritoneal dialysis patients., Objective: The objective of this study was to assess Hb stability in an unselected population of maintenance peritoneal dialysis patients receiving once-monthly treatment with C.E.R.A., a continuous erythropoietin receptor activator., Methods: In a prospective, non-interventional, single-arm study at 33 Germany dialysis centers, peritoneal dialysis patients with or without ESA treatment prior to study entry received once-monthly treatment with C.E.R.A. Hb stability was assessed by the proportion of patients for whom all measured Hb values during months 6-8 (the evaluation phase) were within the range 11-12, 11-13, 10-12 or 11-12.5 g/dL., Results: 220 patients received at least one dose of C.E.R.A. During the evaluation phase, 185 patients provided ≥1 Hb measurement (efficacy population) and 162 patients provided ≥2 Hb measurements (the modified efficacy population). The mean (SD) time between C.E.R.A. doses was 28.2 (7.2) days and mean (SD) C.E.R.A. dose was 109 (57) μg per application. Mean (SD) Hb level was 11.1 (1.4) g/dL at baseline and 11.5 (1.3) g/dL at the end of the study (modified efficacy population). The primary efficacy variable, all measured Hb values in the range 11-12 g/dL, was 18.4 % (34/185) and 14.8 % (24/162) in the efficacy and modified efficacy populations, respectively. The mean (SD) maximum intra-individual fluctuation in Hb level was 0.56 (0.50) g/dL in the efficacy population and 0.58 (0.49) g/dL in the modified efficacy population, with maximum intra-individual fluctuation ≤1 g/dL in 85.4 % (158/185) and 83.3 % (135/162) of patients, respectively. No adverse drug reactions were reported during the study., Conclusion: In this large population of maintenance peritoneal dialysis patients, once-monthly administration of C.E.R.A. achieved a high degree of Hb stability and was well-tolerated.

This study was purposed to investigate the role of cytokines in pathogenesis of lymphoma-associated anemia. The levels of IFN-γ, IL-1β, IL-6, TNF-α and EPO in serum from 45 lymphoma patients and 12 normal controls were detected by using ELISA, the EPOR level on bone marrow cells were detected by flow cytometry, the CFU-E of bone marrow cultured in vitro was counted under inverted microscope. The results showed that 25 (55.6%) out of 45 newly diagnosed lymphoma patients had anemia before diagnosis, 13 (28.9%) had anemia during therapy, 7 (15.5%)never had anemia. The IFN-γ and TNF-α levels in serum of patients with moderate and severe anemia were significantly higher than those in patients with mild anemia and without anemia as well as normal controls. The EPO, IL-6 and IFN-γ levels correlated negatively with Hb concentration in patients, the EPOR level in patients without anemia significantly higher than that in patients with anemia and normal controls. The bone marrow CFU-E amount in patients showed positive correlation with Hb and EPOR levels. It is concluded that the increased IFN-γ, TNF-α and IL-6 may contribute to the anemia in lymphoma, and yet the EPO and EPOR levels are elevated to balance negative regulatory effects on hematopoiesis and maintain normal hematopoiesis.

Objective: To study the expression of erythropoietin (EPO) and its receptor (EPOR) in the brain of newborn rats suffering fetal distress., Methods: A model of fetal distress was prepared by ligating bilateral uterine arteries of the rats with full-term pregnancy for 10 minutes before cesarean sections. The expression levels of EPO and EPOR in the brain of newborn rats were detected by reverse transcription polymerase chain reaction (RT-PCR) and Western blot at 0, 2, 6, 12, 24, 48, 72 hrs and 7 days after birth. Serum EPO levels were measured using ELISA simultaneously. The newborn rats born by cesarean sections which were not subjected to uterine artery ligation were used as the control group., Results: The expression of EPO protein and mRNA in brain tissues in the fetal distress group increased significantly compared with the control group 2, 6 and 12 hrs after birth (P<0.05). The expression of EPOR protein and mRNA in brain tissues in the fetal distress group increased significantly compared with the control group 2, 6, 12, 24 and 48 hrs, and 3 days after birth (P<0.05). Serum EPO levels in the fetal distress group were significantly higher than in the control group 2 hrs after birth., Conclusions: The EPO and EPOR levels in the brain increase quickly after birth in newborn rats suffering from fetal distress. The EPOR is high expressed for a longer time than EPO. This can provide a basis for the treatment of neonatal brain damage induced by fetal distress by exogenous EPO.

Erythropoietin (EPO) is a cytokine hormone with cytoprotective effects in many tissues including the brain. Although the benefits of administration of recombinant human EPO (rhEPO) for neonatal hypoxic brain injury have been demonstrated in neuronal tissue, the effect on non-neuronal cell populations is unclear. We tested the hypothesis that rhEPO would not only protect neuronal cells but also glial cells at a stage of brain development where their maturation was particularly sensitive, and also protect the vasculature. This was evaluated in a rat model of hypoxic injury. 1000 IU/kg rhEPO was delivered intraperitoneally at the start of 4 h hypoxia or normoxia. Treatment groups of neonatal rats (day of birth, at least N = 10 per group) were as follows: normoxia; normoxia plus rhEPO; hypoxia (8% FiO(2) delivered in temperature-controlled chambers); and hypoxia plus rhEPO. Day of birth in rats is equivalent to human gestation of 28-32 weeks. The effects of rhEPO administration, especially to non-neuronal cell populations, and the associated molecular pathways, were investigated. Apoptosis was increased with hypoxia and this was significantly reduced with rhEPO (p < 0.05). The neuronal marker, microtubule-associated protein-2, increased in expression (p < 0.05) when apoptosis was significantly reduced by rhEPO. In addition, compared with hypoxia alone, rhEPO-treated hypoxia had the following significant protein expression increases (p < 0.05): the intermediate filament structural protein nestin; myelin basic protein (oligodendrocytes); and glial fibrillary acidic protein (astrocytes). In conclusion, rhEPO protects the developing brain via anti-apoptotic mechanisms and promotes the health of non-neuronal as well as neuronal cell populations at a time when loss of these cells would have long-lasting effects on brain function., (Copyright © 2011 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.)

Background: Mortality and morbidity after acute myocardial infarction (AMI) remain high even when myocardial reperfusion is successful. Erythropoietin (EPO) protects against experimental MI., Methods: The aim of this single-centre study was to investigate the effects of short-term high-dose erythropoietin on peripheral blood cells (PBCs) and infarct size in 30 patients with a first uncomplicated AMI undergoing percutaneous coronary intervention (PCI) who were randomly assigned to treatment with EPO (33 × 10(3)IU before PCI, and 24 and 48 h after admission), or placebo. We considered short-term CD34+ cell mobilisation, quantitative PBC gene expression in the apoptotic, angiogenic and inflammatory pathways, and enzymatically estimated infarct size. Echocardiographic and cardiac magnetic resonance studies were performed in the acute phase and six months later., Results: CD34+ cell mobilisation 72 h after admission was greater in the EPO-treated patient group (93 cells/μl [36-217] vs 22 cells/μl [6-51]; p = 0.002), who also showed higher expression of the anti-apoptotic AKT and NFkB, the pro-angiogenic VEGFR-2, and the EPO-R genes, and lower expression of the pro-apoptotic CASP3 and TP53 and pro-inflammatory IL12a genes. Moreover, they showed smaller infarct size (30% reduction in CK-MB release; p = 0.025), and a favourable pattern of left ventricular remodelling., Conclusions: Short-term high-dose EPO administration in patients with AMI treated by PCI and standard anti-platelet therapy increases the levels of circulating CD34+ cells, shifts PBC gene expression towards anti-apoptotic, pro-angiogenic and anti-inflammatory pathways, and decreases infarct size. The clinical relevance of these results needs to be confirmed in specifically tailored trials., (Copyright © 2009 Elsevier Ireland Ltd. All rights reserved.)

Recent studies have shown that anemia is commonly observed after exposure to pathogens or pathogen-derived products, which are recognized via Toll-like receptor 9 (TLR9). In the current study, we demonstrate that CpG oligodeoxynucleotide-2006, a TLR9 ligand with phosphodiester (PO; 2006-PO) but not with the phosphorothioate backbone, selectively inhibits the erythroid growth derived from human CD34(+) cells. The 2006-PO was internalized by the erythroid progenitors within 30 minutes; however, expression of TLR9 mRNA was not detected in these cells. The 2006-PO directly inhibited burst-forming unit-erythroid growth, resulted in the accumulation of cells in S and G(2)/M phases, and increased cell size and frequency of apoptotic cells. These features were similar to those observed in erythroid progenitors infected with human parvovirus B19 that causes pure red cell aplasia. The consensus sequence of 2006-PO was defined as 5'-GTTTTGT-3', which was located in the P6-promoter region of B19 and inhibited erythroid growth in a sequence-specific manner and down-regulated expression of erythropoietin receptor (EPOR) mRNA and EPOR. B19 genome extracted from serum also inhibited erythroid growth and down-regulated expression of EPOR on glycophorin A(+) cells. These results provide a possible insight into our understanding of the mechanisms of human parvovirus B19-mediated inhibition of erythropoiesis.

Background: Erythropoietin is a growth factor commonly used to manage anemia in patients with chronic kidney disease. A significant clinical challenge is relative resistance to erythropoietin, which leads to use of successively higher erythropoietin doses, failure to achieve target hemoglobin levels, and increased risk of adverse outcomes. Erythropoietin acts through the erythropoietin receptor (EpoR) present in erythroblasts. Alternative mRNA splicing produces a soluble form of EpoR (sEpoR) found in human blood, however its role in anemia is not known., Methods and Findings: Using archived serum samples obtained from subjects with end stage kidney disease we show that sEpoR is detectable as a 27kDa protein in the serum of dialysis patients, and that higher serum sEpoR levels correlate with increased erythropoietin requirements. Soluble EpoR inhibits erythropoietin mediated signal transducer and activator of transcription 5 (Stat5) phosphorylation in cell lines expressing EpoR. Importantly, we demonstrate that serum from patients with elevated sEpoR levels blocks this phosphorylation in ex vivo studies. Finally, we show that sEpoR is increased in the supernatant of a human erythroleukaemia cell line when stimulated by inflammatory mediators such as interleukin-6 and tumor necrosis factor alpha implying a link between inflammation and erythropoietin resistance., Conclusions: These observations suggest that sEpoR levels may contribute to erythropoietin resistance in end stage renal disease, and that sEpoR production may be mediated by pro-inflammatory cytokines.

Erythropoietin-stimulating agents (ESAs) were originally designed to replace endogenous erythropoietin in patients with anemia secondary to renal failure. Their use has subsequently been expanded to include patients with anemia of other causes, including cancer patients, in whom deficiency of erythropoietin, per se, is not the primary cause of anemia. Although early studies showed promise of ESA administration in reducing the need for transfusions and improving the quality of life in cancer patients, several large randomized clinical trials have recently shown a potential detrimental effect of ESA administration on tumor progression and survival in these patients. These studies have called into question the safety of ESAs as supportive therapy in patients being treated for oncologic conditions. However, numerous questions remain to be addressed regarding the design of these studies, the effect of various targeted hemoglobin levels, and the potential biologic mechanisms proposed to explain promotion of tumor progression and reduced survival.

To purify human erythropoietin-binding protein (Epo-bp), the recombinant vector JYL26 was constructed by inserting human Epo-receptor cDNA by PCR into a pGEX-2T plasmid vector with a thrombin cleavage site. EpoRex-th fusion protein, containing glutathione-S-transferase (GST) and Epo-bp, was purified by glutathione-affinity chromatography. Biologically active pure human Epo-bp (MW=29 kDa) was then purified by Epo-agarose chromatography after cleaving off the GST by thrombin. Purified Epo-bp has a strong binding affinity to 125I-Epo, and unlabeled Epo eliminates the binding (p<0.0001). Trypsin digested Epo-bp to approximately 20 kDa and completely eliminated the binding. Thus, Epo-bp ligand binding is specific and it may require an intact Epo-bp. Ligand-binding sites were detected using fluorescein-labeling in our new products, Epo-bp and anti-Epo-bp antibody (alpha Epo-bp), in various blood cell progenitors, including megakaryocytes, erythroblasts, normoblasts, and myeloblasts, while fluorescein-labeled pre-immune Fab-treated cells did not show any binding. Epo, Epo-bp, and their antibodies were measured in serum and plasma specimens by enzyme immunoassay methods developed in our laboratory; Epo in serum and plasma: 25.4+/-2.17 and 24.2+/-2.35; Epo-bp in serum and plasma: 24.2+/-1.84 and 25.0+/-1.26 mU/ml, respectively. These assays are simple, sensitive, and precise, compared to the conventional Epo radioimmunoassay, and are more environmentally friendly than assays that use radioactive reagents.

Recent discoveries in the molecular pathogenesis of both polycythemia vera (PV) and congenital polycythemia (CP) underline the prospect of a genetic diagnosis in these disorders. At the forefront are the mutually exclusive exon 14 (JAK2V617F) and exon 12 JAK2 mutations that are almost always present in PV but not in polycythemias of other causes. Similarly, the molecular basis of CP is being unraveled, and several cases are now associated with germline mutations involving the von Hippel-Lindau (VHL) or erythropoietin receptor (EPOR) genes. Therefore, current diagnostic work-up for acquired polycythemia should start with peripheral blood JAK2 mutation screening, whereas VHL and/or EPOR mutations should be considered when CP is suspected. In all instances, serum erythropoietin measurement provides complementary information; the serum erythropoietin level is expected to be decreased in PV regardless of JAK2 mutation status, increased in VHL mutation-associated CP, and decreased or normal in the presence of an EPOR mutation.

Purpose: Polycythemia vera (PV) and essential thrombocythemia (ET) can present in pediatric age as sporadic or familial diseases. To define the biologic profile of childhood PV and ET, we evaluated specific markers in a cohort of pediatric patients affected by PV and ET, including cases with familial occurrence., Patients and Methods: Thirty-eight children with PV and ET were investigated. The control group included 58 adults with PV and ET. Endogenous erythroid colonies, qualitative reverse transcriptase polymerase chain reaction for polycythemia rubra vera-1 (PRV-1) RNA expression, human androgen receptor assay and allele specific polymerase chain reaction for JAK2 V617F mutation were undertaken in all patients. Thrombopoietin, thrombopoietin receptor (c-mpl), and erythropoietin receptor mutation analysis was performed by direct sequencing in familial cases., Results: The JAK2 V617F mutation in children with PV was significantly less frequent than in adult PV. The most common myeloproliferative marker found in these patients was PRV-1 RNA overexpression. Children and adults with sporadic ET showed a similar proportion of patients with PRV-1 RNA overexpression, JAK2 V617F mutation, and clonality, while none of the familial ET showed JAK2 V617F mutation and clonality. Also, PRV-1 RNA overexpression was significantly less common. Furthermore, most patients with familial ET exhibited the dominant-positive activating mutation of c-mpl. Finally, children with PV and ET had a significant lower incidence of thrombosis than adults., Conclusion: This study demonstrates that familial and sporadic ET recognize different pathogenetic mechanisms. Myeloproliferative markers are specific tests for the diagnosis of ET in children with sporadic forms, while a significant proportion of children with PV can prove negative.

Rationale: The intimate mechanisms of early onset anemia observed in critically ill patients with septic shock remain unclear., Objectives: We investigated erythropoiesis abnormalities in this setting by studying morphologic, functional, and biochemical patterns of erythroid lineage., Methods: Erythroid lineage in the bone marrow from patients with septic shock who developed early-onset anemia was compared with that of healthy control subjects. Survival and proliferation capacities were quantified in both groups. Biochemical and flow cytometry patterns of apoptosis were dissected by exploring antiapoptotic (erythropoietin [Epo] receptor-dependent) and proapoptotic (death receptor-dependent) pathways., Measurements and Main Results: Erythroid lineage was morphologically similar in both groups. Apoptosis of glycophorin-A-positive erythroid precursors was increased in patients versus control subjects as assessed by labeling with annexin V (26.1 +/- 8.8 vs. 3.1 +/- 2.9%, p < 0.05) or 3-3'-dihexyloxacarbocyanine iodide (55.9 +/- 10.5 vs. 19.1 +/- 5.4%, p < 0.05), respectively. This was associated with significant overexpression of Fas on erythroid precursors and higher tumor necrosis factor-alpha plasma levels in patients with septic shock vs. control subjects. Moreover, growth capacities of late erythroid progenitors of burst-forming unit erythroids (BFU-Es) at Day 10 were impaired in the presence of serum from patients with septic shock as compared with the effect of serum from control subjects (27 +/- 12 vs. 109 +/- 27 per 10(5) seeded cells, respectively; p < 0.001). Saturating concentrations of recombinant human Epo (rHuEpo) restored growth capacity of patients' BFU-Es (72 +/- 14 per 10(5) seeded cells) in autologous conditions of serum., Conclusions: Early-onset anemia that may be observed in patients with septic shock is associated with defective erythropoiesis related to an excess of apoptosis that can be counterbalanced in vitro by rHuEpo.

Recombinant human erythropoietin(rHuEpo) is effective for the treatment of renal anemia associated with chronic renal failure(CRF). However, we have encountered some patients with CRF who have sometimes developed a resistance to rHuEpo. This resistance can be due to iron or folate deficiency, aluminum toxicity, hyperparathyroidism, or auto-antibodies for rHuEpo. In this study, we focused on the soluble erythropoietin receptor(sEpoR), which can bind to rHuEpo. To demonstrate the possibility that the sweeping of rHuEpo by sEpoR results in resistance to rHuEpo, we performed a bioassay using the rHuEpo-dependent cell line, UT7/EPO. The results showed that recombinant mouse sEpoR(rmsEpoR) can reduce the proliferation of UT7/EPO induced by rHuEpo in a dose-dependent manner. We consider that this cell line could be a useful tool in a bioassay to detect the inhibitory factor(s) against Epo. We selected sera from three groups of patients with renal anemia associated with CRF who were receiving hemodialysis three times a week: the first was a patient group that needed a high dose of rHuEpo(7,500-9,000 unit/dialysis), the second was a patient group that needed an intermediate dose of rHuEpo (4,500 unit/dialysis), the third was a patient group that needed a low dose of rHuEpo(below 1,500 unit/dialysis). Interestingly, the proliferation of UT7/EPO determined with [3H]-thymidine incorporation was reduced by the addition of sera from the first group, but not by the addition of sera from the third group. These results suggested that serum sEpoR may play an important role in signal transduction via EpoR on erythroid progenitor in CRF patients.

Background: The pathogenesis of posttransplant erythrocytosis (PTE) has been elusive. Angiotensin converting enzyme inhibitors (ACEI) are efficacious in lowering the hematocrit of patients with PTE and angiotensin II (AII) type I receptors (AT1R) were recently detected on red blood cell precursors, burst-forming unit-erythroid- (BFU-E) derived cells. The purpose of this study was to determine whether there is increased expression of the AT1R on BFU-E-derived cells of patients with PTE, which might contribute to the pathogenesis of PTE., Methods: Twelve healthy volunteers and 25 transplant recipients (13 patients with and 12 without PTE) were studied. BFU-E from peripheral blood were cultured in methylcellulose and BFU-E-derived colonies were harvested on day 10. Western blotting was used to detect AT1R and erythropoietin receptor (EpoR) expression. Intracellular free calcium in response to AII and erythropoietin (Epo) was measured with digital video imaging., Results: There were no differences between transplant patients, with and without PTE, with respect to weight, age, sex, blood pressure, serum creatinine, circulating renin, angiotensin II, and Epo levels. Hematocrit, red blood cell number, BFU-E-derived colony number,and size were significantly increased in PTE compared with other two groups. AT1R expression was increased by 44% on the erythroid progenitors of PTE versus non posttransplant erythrocytosis patients and by 32% in PTE patients versus normal volunteers. AT1R expression correlated significantly with the hematocrit in PTE (Spearman r=0.68, P=0.01). In contrast, EpoR expression was equivalent in all groups. The AT1R was functional since a significant increase in [Ca(i)] was observed in Fura-2 loaded day 10 cells when stimulated with AII (182%, P<0.0001)., Conclusion: An increase in AT1R density was observed in erythroid precursors of transplant patients with PTE compared to those without PTE and normal volunteers, and the level of AT1R expression in PTE correlated significantly with the hematocrit. In contrast, EpoR expression was not different in PTE compared with non posttransplant erythrocytosis or normal controls. This study supports a role for the AT1 receptor signaling pathway in the pathogenesis of PTE.

In order to improve prediction of hematopoietic recovery, we conducted a pilot study, analyzing the significance of growth factor receptor expression in autografts as well as endogenous growth factor levels in blood before, during and after stem cell transplantation. Three early acting (stem cell factor (SCF), Flt3 ligand (Flt3) and fetal antigen 1 (FA1)) and three lineage-specific growth factors (EPO, G-CSF and thrombopoietin (Tpo)) were analyzed by ELISA in 16 patients with multiple myeloma (MM) and 16 patients with non-Hodgkin's lymphoma (NHL). The relative number of SCF, Flt3, Tpo and G-CSF receptor positive, CD34+ progenitor cells were measured by flow cytometry in the leukapheresis product used for transplantation in a subgroup of 15 patients (NHL, n = 8, MM, n = 7). Three factors were identified as having a significant impact on platelet recovery. First, the level of Tpo in blood at the time of the nadir (day +7). Second, the percentage of re-infused thrombopoietin receptor positive progenitors and finally, the percentage of Flt3 receptor positive progenitors. On the other hand, none of the analyzed factors significantly predicted myeloid or erythroid recovery. These findings need to be confirmed in prospectively designed studies.

The ability of circulating progenitor cells from 22 patients with sickle cell disease (SCD) to develop erythroid colonies was studied in vitro in the presence or absence of growth factors (5637-CM and erythropoietin). In both conditions, SCD patients presented significantly higher numbers of circulating burst-forming unit-erythroid (BFU-E/5x10[5]MNC) when compared to control subjects. The study of the expression of erythropoietin receptors revealed an increased level in SCD patients. Moreover, there was a correlation between both stimulated and autocrine (without stimulus) BFU-E and the expression of erythropoietin receptors. These results are of particular interest since they indicate that the phenomenon of spontaneous BFU-E-derived colonies observed in SCD patients may be due to an increased expression of erythropoietin receptors.

The detection of functional growth factor (GF) receptors on subpopulations of hemopoietic cells may provide a further dissection of immature cell subsets. Since little information is available about coexpression of different GF receptors at the level of single hemopoietic cells, we studied the feasibility of simultaneous cell staining with a combination of biotin- and digoxigenin-labeled GFs for flow cytometric detection of functional receptors. Using this methodology, coexpression of Kit and receptors for erythropoietin (EPO), interleukin 6 (IL-6), and GM-CSF on hemopoietic cells was studied by triple-staining of rhesus monkey bone marrow (BM) cells with labeled GFs and antibodies against other cell surface markers. Most of the immature, CD34+2 cells were Kit+ but did not display detectable levels of EPO-receptors (EPO-Rs) or GM-CSF-R. Approximately 60% of these CD34+2/Kit+ cells coexpressed the IL-6-R, demonstrating that immature cells are heterogeneous with respect to IL-6-R expression. Maturation of monomyeloid progenitors, as demonstrated by decreasing CD34 and increasing CD11b expression, is accompanied by a decline of Kit and an increase in GM-CSF-R expression in such a way that Kit+/GM-CSF-R+ cells are hardly detectable. IL-6-R expression is maintained or even increased during monomyeloid differentiation. IL-6-R and GM-CSF-R were not identified on most CD71+2 cells, which indicated that these receptors are probably not expressed during erythroid differentiation. Together with previous results, our data show that both Kit and CD71 are upregulated with erythroid commitment of immature progenitors. Upon further differentiation, Kit+/EPO-R-cells lose CD34 and acquire EPO-R. Maturing erythroid cells eventually lose CD71 and Kit expression but retain the EPO-R. In conclusion, this approach enables further characterization of the specificity of GFs for different bone marrow subpopulations. Apart from insight into the differentiation stages on which individual GFs may act, information about receptor coexpression may be used to identify individual cells that can respond to multiple GFs, and allows for further characterization of the regulation of lineage-specific differentiation.