Polycythemia as the first manifestation of Cushing's disease

Impact of etiology, sex, diabetes mellitus and remission status on erythrocytic profile in patients with cushing's syndrome: a large population database study

PURPOSE

The study aimed to characterize the erythrocytic profile in patients with cushing's syndrome (CS) versus controls from the normal population according to etiology, sex, presence of diabetes mellitus (DM) and hypercortisolemia remission status.

METHODS

This retrospective cohort analysis compared erythrocytic parameters between patients with CS of pituitary (CD) and adrenal (aCS) etiology and age, sex, body mass index (BMI) and socioeconomic status-matched controls in a 1:5 ratio. Laboratory values at baseline were calculated as mean values during the year preceding CS diagnosis, and over one year thereafter.

RESULTS

The cohort included 397 CS patients (68.26% female; mean age 51.11 ± 16.85 years) and 1970 controls. Patients with CS had significantly higher baseline median levels of hemoglobin (Hgb) (13.70 g/dL vs. 13.12 g/dL [p < 0.0001]) and hematocrit (Hct) (41.64% vs. 39.80% [p < 0.0001]) compared to controls. These differences were observed for both CD and aCS and for both sexes. Patients who attained remission had Hgb and Hct levels comparable to controls (13.20 g/dL and 40.08% in patients with CD and aCS vs. 13.20 g/dL and 39.98% in controls). Meanwhile, those with persistent/recurrent disease maintained elevated levels. Patients with comorbid DM had similar Hgb but higher Hct (p = 0.0419), while patients without DM showed elevated erythrocytic values compared to controls (p < 0.0001).

CONCLUSION

Our data illustrates that erythrocytic parameters are directly influenced by glucocorticoid excess as Hgb and Hct are higher in patients with CS, and normalize after remission. We have identified the influence of DM on erythrocytic parameters in patients with CS for the first time.

Erythropoiesis in Cushing syndrome: sex-related and subtype-specific differences. Results from a monocentric study

CONTEXT

Cushing syndrome (CS) is associated with different hematological abnormalities. Nevertheless, conflicting data about erythropoiesis in CS have been reported. Furthermore, it is unclear whether CS sex and subtype-specific alterations in red blood cells (RBC) parameters are present.

OBJECTIVE

To investigate sex and subtype-specific changes in RBC in patients with CS at initial diagnosis and after remission.

DESIGN

Retrospective, monocentric study including 210 patients with CS (women, n = 162) matched 1:1 for sex and age to patients with pituitary microadenomas or adrenal incidentalomas (both hormonally inactive). RBC parameters were evaluated at initial diagnosis and after remission.

RESULTS

Women with CS had higher hematocrit (median 42.2 vs 39.7%), hemoglobin (14.1 vs 13.4 g/dl) and mean corpuscular volume (MCV) (91.2 vs 87.9 fl) compared to the controls (all p < 0.0001). Women with Cushing disease (CD) showed higher hematocrit, RBC and hemoglobin levels than those with ectopic Cushing (ECS) (all p < 0.005). Men with CS had lower hematocrit (42.9 vs 44.7%), RBC count (4.8 vs 5.1n*106/µl) and hemoglobin (14.2 vs 15.4 g/dl), but higher MCV (90.8 vs 87.5 fl) than controls (all p < 0.05). In men with CS, no subtype-specific differences were identified. Three months after remission hemoglobin decreased in both sexes.

CONCLUSION

CS is characterized by sexual and subtype-specific differences in RBC parameters. Compared to controls, women with CS showed higher hematocrit/hemoglobin levels, whereas men had lower hematocrit/hemoglobin, which further decreased directly after remission. Therefore, anemia should be considered as complication of CS in men. In women, differences in RBC parameters may help to differentiate CD from ECS.

Patients with hypercortisolemic Cushing disease possess a distinct class of hematopoietic progenitor cells leading to erythrocytosis

Although human cell cultures stimulated with dexamethasone suggest that the glucocorticoid receptor (GR) activates stress erythropoiesis, the effects of GR activation on erythropoiesis in vivo remain poorly understood. We characterized the phenotype of a large cohort of patients with Cushing disease, a rare condition associated with elevated cortisol levels. Results from hypercortisolemic patients with active Cushing disease were compared with those obtained from eucortisolemic patients after remission and from volunteers without the disease. Patients with active Cushing disease exhibited erythrocytosis associated with normal hemoglobin F levels. In addition, their blood contained elevated numbers of GR-induced CD163+ monocytes and a unique class of CD34+ cells expressing CD110, CD36, CD133 and the GR-target gene CXCR4. When cultured, these CD34+ cells generated similarly large numbers of immature erythroid cells in the presence and absence of dexamethasone, with raised expression of the GR-target gene GILZ. Of interest, blood from patients with Cushing disease in remission maintained high numbers of CD163+ monocytes and, although their CD34+ cells had a normal phenotype, these cells were unresponsive to added dexamethasone. Collectively, these results indicate that chronic exposure to excess glucocorticoids in vivo leads to erythrocytosis by generating erythroid progenitor cells with a constitutively active GR. Although remission rescues the erythrocytosis and the phenotype of the circulating CD34+ cells, a memory of other prior changes is maintained in remission.

Toward a Diagnostic Score in Cushing's Syndrome

Cushing's syndrome (CS) is a classical rare disease: it is often suspected in patients who do not have the disease; at the same time, it takes a mean of 3 years to diagnose CS in affected individuals. The main reason is the extreme rarity (1-3/million/year) in combination with the lack of a single lead symptom. CS has to be suspected when a combination of signs and symptoms is present, which together make up the characteristic phenotype of cortisol excess. Unusual fat distribution affecting the face, neck, and trunk; skin changes including plethora, acne, hirsutism, livid striae, and easy bruising; and signs of protein catabolism such as thinned and vulnerable skin, osteoporotic fractures, and proximal myopathy indicate the need for biochemical screening for CS. In contrast, common symptoms like hypertension, weight gain, or diabetes also occur quite frequently in the general population and per se do not justify biochemical testing. First-line screening tests include urinary free cortisol excretion, dexamethasone suppression testing, and late-night salivary cortisol measurements. All three tests have overall reasonable sensitivity and specificity, and first-line testing should be selected on the basis of the physiologic conditions of the patient, drug intake, and available laboratory quality control measures. Two normal test results usually exclude the presence of CS. Other tests and laboratory parameters like the high-dose dexamethasone suppression test, plasma ACTH, the CRH test, and the bilateral inferior petrosal sinus sampling are not part of the initial biochemical screening. As a general rule, biochemical screening should only be performed if the pre-test probability for CS is reasonably high. This article provides an overview about the current standard in the diagnosis of CS starting with clinical scores and screenings, the clinical signs, relevant differential diagnoses, the first-line biochemical screening, and ending with a few exceptional cases.

GATA1 insufficiencies in primary myelofibrosis and other hematopoietic disorders: consequences for therapy

INTRODUCTION

GATA1, the founding member of a family of transcription factors, plays important roles in the development of hematopoietic cells of several lineages. Although loss of GATA1 has been known to impair hematopoiesis in animal models for nearly 25 years, the link between GATA1 defects and human blood diseases has only recently been realized. Areas covered: Here the current understanding of the functions of GATA1 in normal hematopoiesis and how it is altered in disease is reviewed. GATA1 is indispensable mainly for erythroid and megakaryocyte differentiation. In erythroid cells, GATA1 regulates early stages of differentiation, and its deficiency results in apoptosis. In megakaryocytes, GATA1 controls terminal maturation and its deficiency induces proliferation. GATA1 alterations are often found in diseases involving these two lineages, such as congenital erythroid and/or megakaryocyte deficiencies, including Diamond Blackfan Anemia (DBA), and acquired neoplasms, such as acute megakaryocytic leukemia (AMKL) and the myeloproliferative neoplasms (MPNs). Expert commentary: Since the first discovery of GATA1 mutations in AMKL, the number of diseases that are associated with impaired GATA1 function has increased to include DBA and MPNs. With respect to the latter, we are only just now appreciating the link between enhanced JAK/STAT signaling, GATA1 deficiency and disease pathogenesis.

Concise Review: Advanced Cell Culture Models for Diamond Blackfan Anemia and Other Erythroid Disorders

In vitro surrogate models of human erythropoiesis made many contributions to our understanding of the extrinsic and intrinsic regulation of this process in vivo and how they are altered in erythroid disorders. In the past, variability among the levels of hemoglobin F produced by adult erythroblasts generated in vitro by different laboratories identified stage of maturation, fetal bovine serum, and accessory cells as "confounding factors," that is, parameters intrinsically wired in the experimental approach that bias the results observed. The discovery of these factors facilitated the identification of drugs that accelerate terminal maturation or activate specific signaling pathways for the treatment of hemoglobinopathies. It also inspired studies to understand how erythropoiesis is regulated by macrophages present in the erythroid islands. Recent cell culture advances have greatly increased the number of human erythroid cells that can be generated in vitro and are used as experimental models to study diseases, such as Diamond Blackfan Anemia, which were previously poorly amenable to investigation. However, in addition to the confounding factors already identified, improvement in the culture models has introduced novel confounding factors, such as possible interactions between signaling from cKIT, the receptor for stem cell factor, and from the glucocorticoid receptor, the cell proliferation potential and the clinical state of the patients. This review will illustrate these new confounding factors and discuss their clinical translation potential to improve our understanding of Diamond Blackfan Anemia and other erythroid disorders. Stem Cells 2018;36:172-179.

Androgens correlate with increased erythropoiesis in women with congenital adrenal hyperplasia

OBJECTIVE

Hyperandrogenism in congenital adrenal hyperplasia (CAH) provides an in vivo model for exploring the effect of androgens on erythropoiesis in women. We investigated the association of androgens with haemoglobin (Hb) and haematocrit (Hct) in women with CAH.

DESIGN

Cross-validation study.

PATIENTS

Women with CAH from Sheffield Teaching Hospitals, UK (cohort 1, the training set: n = 23) and National Institutes of Health, USA (cohort 2, the validation set: n = 53).

MEASUREMENTS

Androgens, full blood count and basic biochemistry, all measured on the same day. Demographic and anthropometric data.

RESULTS

Significant age-adjusted correlations (P < 0·001) were observed for Ln testosterone with Hb and Hct in cohorts 1 and 2 (Hb r = 0·712 & 0·524 and Hct r = 0·705 & 0·466), which remained significant after adjustments for CAH status, glucocorticoid treatment dose and serum creatinine. In the combined cohorts, Hb correlated with androstenedione (P = 0·002) and 17-hydroxyprogesterone (P = 0·008). Hb and Hct were significantly higher in cohort 1 than those in cohort 2, while there were no group differences in androgen levels, glucocorticoid treatment dose or body mass index. In both cohorts, women with Hb and Hct in the highest tertile had significantly higher testosterone levels than women with Hb and Hct in the lowest tertile.

CONCLUSIONS

In women with CAH, erythropoiesis may be driven by androgens and could be considered a biomarker for disease control.

The Central Nervous System Regulates Embryonic HSPC Production via Stress-Responsive Glucocorticoid Receptor Signaling

Hematopoietic stem and progenitor cell (HSPC) specification is regulated by numerous defined factors acting locally within the hemogenic niche; however, it is unclear whether production can adapt to fluctuating systemic needs. Here we show that the CNS controls embryonic HSPC numbers via the hypothalamic-pituitary-adrenal/interrenal (HPA/I) stress response axis. Exposure to serotonin or the reuptake inhibitor fluoxetine increased runx1 expression and Flk1(+)/cMyb(+) HSPCs independent of peripheral innervation. Inhibition of neuronal, but not peripheral, tryptophan hydroxlyase (Tph) persistently reduced HSPC number. Consistent with central HPA/I axis induction and glucocorticoid receptor (GR) activation, GR agonists enhanced, whereas GR loss diminished, HSPC formation. Significantly, developmental hypoxia, as indicated by Hif1α function, induced the HPA/I axis and cortisol production. Furthermore, Hif1α-stimulated HSPC enhancement was attenuated by neuronal tph or GR loss. Our data establish that embryonic HSC production responds to physiologic stress via CNS-derived serotonin synthesis and central feedback regulation to control HSC numbers.

Dexamethasone targeted directly to macrophages induces macrophage niches that promote erythroid expansion

Cultures of human CD34(pos) cells stimulated with erythroid growth factors plus dexamethasone, a model for stress erythropoiesis, generate numerous erythroid cells plus a few macrophages (approx. 3%; 3:1 positive and negative for CD169). Interactions occurring between erythroblasts and macrophages in these cultures and the biological effects associated with these interactions were documented by live phase-contrast videomicroscopy. Macrophages expressed high motility interacting with hundreds/thousands of erythroblasts per hour. CD169(pos) macrophages established multiple rapid 'loose' interactions with proerythroblasts leading to formation of transient erythroblastic island-like structures. By contrast, CD169(neg) macrophages established 'tight' interactions with mature erythroblasts and phagocytosed these cells. 'Loose' interactions of CD169(pos) macrophages were associated with proerythroblast cytokinesis (the M phase of the cell cycle) suggesting that these interactions may promote proerythroblast duplication. This hypothesis was tested by experiments that showed that as few as 103 macrophages significantly increased levels of 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide incorporation frequency in S/G2/M and cytokinesis expressed by proerythroblasts over 24 h of culture. These effects were observed also when macrophages were co-cultured with dexamethasone directly conjugated to a macrophage-specific CD163 antibody. In conclusion, in addition to promoting proerythroblast proliferation directly, dexamethasone stimulates expansion of these cells indirectly by stimulating maturation and cytokinesis supporting activity of macrophages.

Gender-dependent changes in haematological parameters in patients with Cushing's disease before and after remission

OBJECTIVE

Glucocorticoids stimulate several steps in red blood cell (RBC) development; however, little is known on changes in erythroid parameters in patients with Cushing's disease. The aim of this study was to assess both RBC and white blood cell (WBC) parameters in a large cohort of patients with Cushing's disease and report on alterations in the active phase and after surgical remission.

DESIGN AND METHODS

A total of 80 patients with Cushing's disease (63 women and 17 men) were studied before and for up to 254 months' follow-up (mean follow-up 65.8 ± 6.71 months) after pituitary/adrenal surgery. Details of blood counts were reviewed and compared with data obtained from a database of healthy subjects.

RESULTS

The RBC counts and haemoglobin levels were low in men with active Cushing's disease (over 80% of values in the lowest quartile) and four patients were overtly anaemic, whereas erythrocyte counts and haemoglobin levels were evenly distributed across the normal range in women with active Cushing's disease. Low erythroid parameters were linked to hypogonadism in men with Cushing's disease. Recovery in erythroid parameters occurred slowly after remission of hypercortisolism in men, in parallel with improvements in testosterone levels. Over 50% of patients with active disease presented increased WBC counts, irrespective of gender, and prompt normalisation within 1 month after surgery.

CONCLUSIONS

Male patients with Cushing's disease present reduced RBC counts and haemoglobin levels, associated with low testosterone concentrations, which resolve over time after remission of hypercortisolism. Anaemia should therefore be regarded as another unfavourable feature in men with Cushing's disease.

Chronic psychological stress activates BMP4-dependent extramedullary erythropoiesis

Psychological stress affects different physiological processes including haematopoiesis. However, erythropoietic effects of chronic psychological stress remain largely unknown. The adult spleen contains a distinct microenvironment favourable for rapid expansion of erythroid progenitors in response to stressful stimuli, and emerging evidence suggests that inappropriate activation of stress erythropoiesis may predispose to leukaemic transformation. We used a mouse model to study the influence of chronic psychological stress on erythropoiesis in the spleen and to investigate potential mediators of observed effects. Adult mice were subjected to 2 hrs daily restraint stress for 7 or 14 consecutive days. Our results showed that chronic exposure to restraint stress decreased the concentration of haemoglobin in the blood, elevated circulating levels of erythropoietin and corticosterone, and resulted in markedly increased number of erythroid progenitors and precursors in the spleen. Western blot analysis revealed significantly decreased expression of both erythropoietin receptor and glucocorticoid receptor in the spleen of restrained mice. Furthermore, chronic stress enhanced the expression of stem cell factor receptor in the red pulp. Moreover, chronically stressed animals exhibited significantly increased expression of bone morphogenetic protein 4 (BMP4) in the red pulp as well as substantially enhanced mRNA expression levels of its receptors in the spleen. These findings demonstrate for the first time that chronic psychological stress activates BMP4-dependent extramedullary erythropoiesis and leads to the prolonged activation of stress erythropoiesis pathways. Prolonged activation of these pathways along with an excessive production of immature erythroid cells may predispose chronically stressed subjects to a higher risk of leukaemic transformation.

The expression of the glucocorticoid receptor in human erythroblasts is uniquely regulated by KIT ligand: implications for stress erythropoiesis

Studies in mice indicated that activation of the erythroid stress pathway requires the presence of both soluble KIT ligand (KITL) and the glucocorticoid receptor (GR). To clarify the relative role of KITL and GR in stress erythropoiesis in humans, the biological activities of soluble full length- (fl-, 26-190 aa), carboxy-terminus truncated (tr-, 26-162 aa) human (hKITL) and murine (mKITL) KITL in cultures of cord blood (CB) mononuclear cells (MNCs) and CD34(pos) cells that mimic either steady state (growth factors alone) or stress (growth factors plus dexamethasone [DXM]) erythropoeisis were investigated. In steady state cultures, the KITLs investigated were equally potent in sustaining growth of hematopoietic colonies and expansion of megakaryocytes (MK) and erythroid precursors (EBs). By contrast, under stress erythropoiesis conditions, fl-hKITL generated greater numbers of EBs (fold increase [FI]=140) than tr-hKITL or mKITL (FI=20-40). Flow cytometric analyses indicated that only EBs generated with fl-hKITL remained immature (>70% CD36(pos)/CD235a(neg/low)), and therefore capable to proliferate, until day 8-12 in response to DXM. Signaling studies indicated that all KITLs investigated induced EBs to phosphorylate signal transducer and activator of transcription 5 (STAT5) but that extracellular-signaling-regulated-kinases (ERK) activation was observed mainly in the presence of fl-hKITL. EBs exposed to fl-hKITL also expressed higher levels of GRα than those exposed to mKITL (and tr-hKITL) which were reduced upon exposure to the ERK inhibitor U0126. These data reveal a unique requirement for fl-hKITL in the upregulation of GRα and optimal EB expansion in cultures that mimic stress erythropoiesis.

Ex-vivo expansion of red blood cells: how real for transfusion in humans?

Blood transfusion is indispensable for modern medicine. In developed countries, the blood supply is adequate and safe but blood for alloimmunized patients is often unavailable. Concerns are increasing that donations may become inadequate in the future as the population ages prompting a search for alternative transfusion products. Improvements in culture conditions and proof-of-principle studies in animal models have suggested that ex-vivo expanded red cells may represent such a product. Compared to other cell therapies transfusion poses the unique challenge of requiring great cell doses (2.5×10(12) cells vs 10(7) cells). Although production of such cell numbers is theoretically possible, current technologies generate red cells in numbers sufficient only for safety studies. It is conceived that by the time these studies will be completed, technical barriers to mass cell production will have been eliminated making transfusion with ex-vivo generated red cells a reality.

The dominant negative β isoform of the glucocorticoid receptor is uniquely expressed in erythroid cells expanded from polycythemia vera patients

Glucocorticoid receptor (GR) agonists increase erythropoiesis in vivo and in vitro. To clarify the effect of the dominant negative GRβ isoform (unable to bind STAT-5) on erythropoiesis, erythroblast (EB) expansion cultures of mononuclear cells from 18 healthy (nondiseased) donors (NDs) and 16 patients with polycythemia vera (PV) were studied. GRβ was expressed in all PV EBs but only in EBs from 1 ND. The A3669G polymorphism, which stabilizes GRβ mRNA, had greater frequency in PV (55%; n = 22; P = .0028) and myelofibrosis (35%; n = 20) patients than in NDs (9%; n = 22) or patients with essential thrombocythemia (6%; n = 15). Dexamethasone stimulation of ND cultures increased the number of immature EBs characterized by low GATA1 and β-globin expression, but PV cultures generated great numbers of immature EBs with low levels of GATA1 and β-globin irrespective of dexamethasone stimulation. In ND EBs, STAT-5 was not phosphorylated after dexamethasone and erythropoietin treatment and did not form transcriptionally active complexes with GRα, whereas in PV EBs, STAT-5 was constitutively phosphorylated, but the formation of GR/STAT-5 complexes was prevented by expression of GRβ. These data indicate that GRβ expression and the presence of A3669G likely contribute to development of erythrocytosis in PV and provide a potential target for identification of novel therapeutic agents.

Humanized culture medium for clinical expansion of human erythroblasts

Ex vivo-generated erythroblasts represent alternative transfusion products. However, inclusion of bovine components in media used for their growth precludes clinical use, highlighting the importance of developing culture media based on pharmaceutical grade reagents. In addition, because adult blood generates ex vivo lower numbers of erythroblasts than cord blood, cord blood has been proposed as the source of choice for ex vivo erythroblast production. To clarify the potential of adult blood to generate erythroblasts ex vivo, experiments were designed to identify growth factors [stem cell factor (SCF), interleukin-3 (IL-3), erythropoietin (EPO), and/or thrombopoietin (TPO)] and the optimal concentration and addition schedule of hormones (dexamethasone and estradiol) sustaining maximal erythroid amplification from adult blood mononuclear cells (MNC) using media with serum previously defined as human erythroid massive amplification culture (HEMA(ser)). Adult MNC stimulated with SCF and IL-3 in combination with EPO generated a 6-12-fold increase in erythroid cells while TPO was ineffective. Dexamethasone and estradiol (both at 10(-6) M) exerted partially overlapping but nonredundant functions. Dexamethasone was indispensable in the first 10 days of culture while estradiol was required from day 10 on. The growth factor and hormone combinations identified in HEMA(ser) were then used to formulate a media composed of dialyzed pharmaceutical grade human albumin, human albumin-lipid liposomes, and iron-saturated recombinant human tranferrin (HEMA(def)). HEMA(def) sustained erythroid amplification as efficiently as HEMA(ser) for cord blood MNC and 10-fold higher than HEMA(ser) for adult blood MNC. In fact, the numbers of erythroblasts generated in HEMA(def) by adult MNC were similar to those generated by cord blood MNC. In conclusion, this study identifies growth factors, hormone combinations, and human protein-based media that allow similar levels of ex vivo erythroid expansion from adult and cord blood MNC, paving the way to evaluate adult blood as a source of ex vivo-expanded erythroblasts for transfusion.

Erythroid cells in vitro: from developmental biology to blood transfusion products

PURPOSE OF REVIEW

Red blood cells (RBCs) transfusion plays a critical role in numerous therapies. Disruption of blood collection by political unrest, natural disasters and emerging infections and implementation of restrictions on the use of erythropoiesis-stimulating agents in cancer may impact blood availability in the near future. These considerations highlight the importance of developing alternative blood products.

RECENT FINDINGS

Knowledge about the processes that control RBC production has been applied to the establishment of culture conditions allowing ex-vivo generation of RBCs in numbers close to those (2.5 x 10 cells/ml) present in a transfusion, from cord blood, donated blood units or embryonic stem cells. In addition, experimental studies demonstrate that such cells protect mice from lethal bleeding. Therefore, erythroid cells generated ex vivo may be suitable for transfusion provided they can be produced safely in adequate numbers. However, much remains to be done to translate a theoretical production of approximately 2.5 x 10 RBCs in the laboratory into a 'clinical grade production process'.

SUMMARY

This review summarizes the state-of-the-art in establishing ex-vivo culture conditions for erythroid cells and discusses the most compelling issues to be addressed to translate this progress into a clinical grade transfusion product.

Interaction between the glucocorticoid and erythropoietin receptors in human erythroid cells

OBJECTIVE

The aim of this study was to identify whether the rapid membrane-associated pathway of the glucocorticoid receptor (GR) is active in erythroid cells and plays any role in determining the reversible inhibition on erythroid maturation exerted by GR.

MATERIALS AND METHODS

First we determined the biological effects (inhibition of apoptosis and induction of beta-globin expression) induced in primary erythroblasts by erythropoietin (EPO) and the GR agonist dexamethasone (DXM), alone and in combination. Next, by biochemical analysis, we determined the association between GR and EPO receptor in proerythroblasts generated in vitro from 10 normal adult donors. These studies also analyzed the levels of signal transducers and activators of transcription-5 (STAT-5) phosphorylation induced when the cells were stimulated with DXM alone or in combination with EPO.

RESULTS

DXM antagonized the beta-globin messenger RNA increases, but not the inhibition of apoptosis induced by EPO in primary cells. DXM also antagonized the ability of EPO to induce STAT-5 phosphorylation in these cells. In fact, EPO and DXM alone, but not in combination, induced phosphorylation and nuclear translocation of STAT-5. The inhibition likely occurred through an interaction between the two receptors because GR became associated with the EPO receptor and STAT-5 in cells stimulated with EPO and DXM.

CONCLUSION

These data suggest that glucocorticoids inhibit erythroid maturation not only through a transcriptional mechanism, but also through a rapid membrane-associated pathway that interferes with EPO receptor signaling.