Targeting EPO and EPO receptor pathways in anemia and dysregulated erythropoiesis.
ABSTRACT: Recombinant human erythropoietin (rhEPO) is a first-line therapeutic for the anemia of chronic kidney disease, cancer chemotherapy, AIDS (Zidovudine therapy), and lower-risk myelodysplastic syndrome. However, rhEPO frequently elevates hypertension, is costly, and may affect cancer progression. Potentially high merit therefore exists for defining new targets for anti-anemia agents within erythropoietin (EPO) and EPO receptor (EPOR) regulatory circuits.EPO production by renal interstitial fibroblasts is subject to modulation by several regulators of hypoxia-inducible factor 2a (HIF2a) including Iron Response Protein-1, prolyl hydroxylases, and HIF2a acetylases, each of which holds potential as anti-anemia drug targets. The cell surface receptor for EPO (EPOR) preassembles as a homodimer, together with Janus Kinase 2 (JAK2), and therefore it remains attractive to develop novel agents that trigger EPOR complex activation (activating antibodies, mimetics, small-molecule agonists). Additionally, certain downstream transducers of EPOR/JAK2 signaling may be druggable, including Erythroferrone (a hepcidin regulator), a cytoprotective Spi2a serpin, and select EPOR-associated protein tyrosine phosphatases.While rhEPO (and biosimilars) are presently important mainstay erythropoiesis-stimulating agents (ESAs), impetus exists for studies of novel ESAs that fortify HIF2a's effects, act as EPOR agonists, and/or bolster select downstream EPOR pathways to erythroid cell formation. Such agents could lessen rhEPO dosing, side effects, and/or costs.
Project description:Anemia is a known driver for hypoxia inducible factor (HIF) which leads to increased renal erythropoietin (EPO) synthesis. Bone marrow (BM) EPO receptor (EPOR) signals are transduced through a JAK2-STAT5 pathway. The origins of anemia of chronic kidney disease (CKD) are multifactorial, including impairment of both renal EPO synthesis as well as intestinal iron absorption. We investigated the HIF- EPO- EPOR axis in kidney, BM and proximal tibia in anemic juvenile CKD rats.CKD was induced by 5/6 nephrectomy in young (20 days old) male Sprague-Dawley rats while C group was sham operated. Rats were sacrificed 4 weeks after CKD induction and 5 minutes after a single bolus of IV recombinant human EPO. An additional control anemic (C-A) group was daily bled for 7 days.Hemoglobin levels were similarly reduced in CKD and C-A (11.4 ± 0.3 and 10.8±0.2 Vs 13.5±0.3 g/dL in C, p<0.0001). Liver hepcidin mRNA was decreased in CA but increased in CKD. Serum iron was unchanged while transferrin levels were mildly decreased in CKD. Kidney HIF2? protein was elevated in C-A but unchanged in CKD. Kidney EPO protein and mRNA levels were unchanged between groups. However, BM EPO protein (which reflects circulating EPO) was increased in C-A but remained unchanged in CKD. BM and proximal tibia EPOR were unchanged in C-A but decreased in CKD. Proximal tibial phospho-STAT5 increased after the EPO bolus in C but not in CKD.Compared to blood loss, anemia in young CKD rats is associated with inappropriate responses in the HIF-EPO-EPO-R axis: kidney HIF2? and renal EPO are not increased, BM and bone EPOR levels, as well as bone pSTAT5 response to EPO are reduced. Thus, anemia of CKD may be treated with additional therapeutic avenues beyond iron and EPO supplementation.
Project description:While recombinant human erythropoietin (rhEpo) has been widely used to treat anemia in cancer patients, concerns about its adverse effects on patient survival have emerged. A lack of correlation between expression of the canonical EpoR and rhEpo's effects on cancer cells prompted us to consider the existence of an alternative Epo receptor. Here, we identified EphB4 as an Epo receptor that triggers downstream signaling via STAT3 and promotes rhEpo-induced tumor growth and progression. In human ovarian and breast cancer samples, expression of EphB4 rather than the canonical EpoR correlated with decreased disease-specific survival in rhEpo-treated patients. These results identify EphB4 as a critical mediator of erythropoietin-induced tumor progression and further provide clinically significant dimension to the biology of erythropoietin.
Project description:Multiple myeloma is an incurable complex disease characterized by clonal proliferation of malignant plasma cells in a hypoxic bone marrow environment. Hypoxia-dependent erythropoietin (EPO)-receptor (EPOR) signaling is central in various cancers, but the relevance of EPOR signaling in multiple myeloma cells has not yet been thoroughly investigated.Myeloma cell lines and malignant plasma cells isolated from bone marrow of myeloma patients were used in this study. Transcript levels were analysed by quantitative PCR and cell surface levels of EPOR in primary cells by flow cytometry. Knockdown of EPOR by short interfering RNA was used to show specific EPOR signaling in the myeloma cell line INA-6. Flow cytometry was used to assess viability in primary cells treated with EPO in the presence and absence of neutralizing anti-EPOR antibodies. Gene expression data for total therapy 2 (TT2), total therapy 3A (TT3A) trials and APEX 039 and 040 were retrieved from NIH GEO omnibus and EBI ArrayExpress.We show that the EPOR is expressed in myeloma cell lines and in primary myeloma cells both at the mRNA and protein level. Exposure to recombinant human EPO (rhEPO) reduced viability of INA-6 myeloma cell line and of primary myeloma cells. This effect could be partially reversed by neutralizing antibodies against EPOR. In INA-6 cells and primary myeloma cells, janus kinase 2 (JAK-2) and extracellular signal regulated kinase 1 and 2 (ERK-1/2) were phosphorylated by rhEPO treatment. Knockdown of EPOR expression in INA-6 cells reduced rhEPO-induced phospo-JAK-2 and phospho-ERK-1/2. Co-cultures of primary myeloma cells with bone marrow-derived stroma cells did not protect the myeloma cells from rhEPO-induced cell death. In four different clinical trials, survival data linked to gene expression analysis indicated that high levels of EPOR mRNA were associated with better survival.Our results demonstrate for the first time active EPOR signaling in malignant plasma cells. EPO-mediated EPOR signaling reduced the viability of myeloma cell lines and of malignant primary plasma cells in vitro. Our results encourage further studies to investigate the importance of EPO/EPOR in multiple myeloma progression and treatment.[Trial registration number for Total Therapy (TT) 2: NCT00083551 and TT3: NCT00081939 ].
Project description:Given the limited efficacy and potential disadvantages of erythropoiesis-stimulating agents (ESAs) in treating anemia of chronic kidney disease (CKD), the development of better alternative therapies has become a priority. The primary purpose of this study is to investigate the effects of <i>Angelica sinensis</i> polysaccharide (ASP) and its underlying mechanism in the treatment of renal anemia. In the present study, we found that ASP could enhance hypoxic induction of EPO in Hep3B cells, with a mechanism that involved the stabilization of HIF-2? protein. In parallel, ASP rescued the inhibition of EPO, induced by proinflammatory factor TNF-? through blocking GATA2 and NF-?B activation. In a rat model of adenine-induced anemia of CKD, oral administration of ASP corrected anemia and alleviated renal damage and inflammation. By increasing the accumulation of HIF-2? protein and reducing the expression of NF-?B and GATA2 as well as pro-inflammatory cytokines, ASP stimulated both renal and hepatic EPO production, and resulted in an elevation of serum EPO. The restoration of EPO production and EPOR mRNA expression with ASP treatment activated EPOR downstream JAK2/STAT5 and PI3K/Akt signaling, induced their target genes, such as Bcl-xL, Fam132b and Tfrc, and increased Bcl-2/Bax ratio in bone marrow-derived mononuclear cells of CKD rats. Furthermore, we found that ASP suppressed hepatic hepcidin expression, mobilized iron from spleen and liver and increased serum iron. These findings demonstrate that ASP elicits anti-anemic action by restoring EPO production and improving iron availability in the setting of CKD in rats.
Project description:Erythropoietin (Epo), along with its receptor EpoR, is the principal regulator of red cell development. Upon Epo addition, the EpoR signaling through the Janus kinase 2 (JAK2) activates multiple pathways including Stat5, phosphoinositide-3 kinase (PI-3K)/Akt, and p42/44 mitogen-activated protein kinase (MAPK). The adaptor protein Lnk is implicated in cytokine receptor signaling. Here, we showed that Lnk-deficient mice have elevated numbers of erythroid progenitors, and that splenic erythroid colony-forming unit (CFU-e) progenitors are hypersensitive to Epo. Lnk(-/-) mice also exhibit superior recovery after erythropoietic stress. In addition, Lnk deficiency resulted in enhanced Epo-induced signaling pathways in splenic erythroid progenitors. Conversely, Lnk overexpression inhibits Epo-induced cell growth in 32D/EpoR cells. In primary culture of fetal liver cells, Lnk overexpression inhibits Epo-dependent erythroblast differentiation and induces apoptosis. Lnk blocks 3 major signaling pathways, Stat5, Akt, and MAPK, induced by Epo in primary erythroblasts. In addition, the Lnk Src homology 2 (SH2) domain is essential for its inhibitory function, whereas the conserved tyrosine near the C-terminus and the pleckstrin homology (PH) domain of Lnk are not critical. Furthermore, wild-type Lnk, but not the Lnk SH2 mutant, becomes tyrosine-phosphorylated following Epo administration and inhibits EpoR phosphorylation and JAK2 activation. Hence, Lnk, through its SH2 domain, negatively modulates EpoR signaling by attenuating JAK2 activation, and regulates Epo-mediated erythropoiesis.
Project description:Sprouty proteins are established modifiers of receptor tyrosine kinase (RTK) signaling and play important roles in vasculogenesis, bone morphogenesis, and renal uteric branching. Little is understood, however, concerning possible roles for these molecular adaptors during hematopoiesis. Within erythroid lineage, Spry1 was observed to be selectively and highly expressed at CFU-e to erythroblast stages. In analyses of possible functional roles, an Mx1-Cre approach was applied to conditionally delete Spry1. At steady state, Spry1 deletion selectively perturbed erythroid development and led to reticulocytosis plus heightened splenic erythropoiesis. When challenged by hemolysis, Spry1-null mice exhibited worsened anemia and delayed recovery. During short-term marrow transplantation, Spry1-null donor marrow also failed to efficiently rescue the erythron. In each anemia model, however, hyperexpansion of erythroid progenitors was observed. Spry function depends on phosphorylation of a conserved N-terminal PY motif. Through an LC-MS/MS approach, Spry1 was discovered to be regulated via the erythropoietin receptor (EPOR), with marked EPO-induced Spry1-PY53 phosphorylation observed. When EPOR signaling pathways were analyzed within Spry1-deficient erythroid progenitors, hyperactivation of not only Erk1,2 but also Jak2 was observed. Studies implicate Spry1 as a novel regulator of erythropoiesis during anemia, transducer of EPOR signals, and candidate suppressor of Jak2 activity.
Project description:BACKGROUND: Erythropoietin (EPO) provides an alternative to transfusion for increasing red blood cell mass and treating anemia in cancer patients. However, recent studies have reported increased adverse events and/or reduced survival in patients receiving both EPO and chemotherapy, potentially related to EPO-induced cancer progression. Additional preclinical studies that elucidate the possible mechanism underlying EPO cellular growth stimulation are needed. METHODS: Using commercial tissue microarray (TMA) of a variety of cancers and benign tissues, EPO and EPO receptor immunohistochemical staining was performed. Furthermore using a panel of human renal cells (Caki-1, 786-O, 769-P, RPTEC), in vitro and in vivo experiments were performed with the addition of EPO in normoxic and hypoxic states to note phenotypic and genotypic changes. RESULTS: EPO expression score was significantly elevated in lung cancer and lymphoma (compared to benign tissues), while EPOR expression score was significantly elevated in lymphoma, thyroid, uterine, lung and prostate cancers (compared to benign tissues). EPO and EPOR expression scores in RCC and benign renal tissue were not significantly different. Experimentally, we show that exposure of human renal cells to recombinant EPO (rhEPO) induces cellular proliferation, which we report for the first time, is further enhanced in a hypoxic state. Mechanistic investigations revealed that EPO stimulates the expression of cyclin D1 while inhibiting the expression of p21cip1 and p27kip1 through the phosphorylation of JAK2 and ERK1/2, leading to a more rapid progression through the cell cycle. We also demonstrate an increase in the growth of renal cell carcinoma xenograft tumors when systemic rhEPO is administered. CONCLUSIONS: In summary, we elucidated a previously unidentified mechanism by which EPO administration regulates progression through the cell cycle, and show that EPO effects are significantly enhanced under hypoxic conditions.
Project description:Identification of the underlying defects in congenital erythrocytosis has provided mechanistic insights into the regulation of erythropoiesis and oxygen homeostasis. The Hypoxia Inducible Factor (HIF) pathway plays a key role in this regard. In this pathway, an enzyme, Prolyl Hydroxylase Domain protein 2 (PHD2), constitutively prolyl hydroxylates HIF-2?, thereby targeting HIF-2? for degradation by the von Hippel Lindau (VHL) tumor suppressor protein. Under hypoxia, this modification is attenuated, resulting in the stabilization of HIF-2? and transcriptional activation of the erythropoietin (EPO) gene. Circulating EPO then binds to the EPO receptor (EPOR) on red cell progenitors in the bone marrow, leading to expansion of red cell mass. Loss of function mutations in PHD2 and VHL, as well as gain of function mutations in HIF-2? and EPOR, are well established causes of erythrocytosis. Here, we highlight recent developments that show that the study of this condition is still evolving. Specifically, novel mutations have been identified that either change amino acids in the zinc finger domain of PHD2 or alter splicing of the VHL gene. In addition, continued study of HIF-2? mutations has revealed a distinctive genotype-phenotype correlation. Finally, novel mutations have recently been identified in the EPO gene itself. Thus, the cascade of genes that at a molecular level leads to EPO action, namely PHD2 -?>?HIF2A -?>?VHL -?>?EPO -?>?EPOR, are all mutational targets in congenital erythrocytosis.
Project description:Human erythropoietin is mainly recognized for its hematopoietic function; however, by binding to its receptor (EpoR), it can activate different signaling pathways as STAT, PI3K, MAPK and RAS to increase cellular differentiation or provide neuroprotective effects, among others. A recombinant human erythropoietin variant with low glycosylation and without hematopoietic effect (EpoL) was purified from skimmed goat milk. Recombinant human erythropoietin (Epo) was obtained from CHO cell line and used as control to compare EpoL effects. Neuroprotection studies were performed in PC12 cells and rat hippocampal slices. Cells were pretreated during 1h with EpoL or Epo and exposed to oxidative agents (H2O2 or FCCP); cell viability was assayed at the end of the experiment by the MTT method. Hippocampal slices were exposed to 15min of oxygen and glucose deprivation (OGD) and the neuroprotective drugs EpoL or Epo were incubated for 2h post-OGD in re-oxygenated medium. Cell cultures stressed with oxidative agents, and pretreated with EpoL, showed neuroprotective effects of 30% at a concentration 10 times lower than that of Epo. Moreover, similar differences were observed in OGD ex vivo assays. Neuroprotection elicited by EpoL was lost when an antibody against EpoR was present, indicating that its effect is EpoR-dependent. In conclusion, our results suggest that EpoL has a more potent neuroprotective profile than Epo against oxidative stress, mediated by activation of EpoR, thus EpoL represents an important target to develop a potential biopharmaceutical to treat different central nervous system pathologies related to oxidative stress such as stroke or neurodegenerative diseases.
Project description:OBJECTIVES:Erythrocytosis is characterized by the expansion of erythrocyte compartment including elevated red blood cell number, hematocrit, and hemoglobin content. Familial erythrocytosis (FE) is a congenital disorder with different genetic background. Type 1 FE is primary FE caused by mutation in erythropoietin receptor gene (EPOR). Type 2-5 FE are secondary FEs caused by mutations of genes involved in oxygen sensing pathway important for erythropoietin (EPO) regulation. In the present study, we summarized associations between EPOR and EPO gene variations with development of FE and searched for genetic variants located within regulatory regions. METHODS:Publications reporting EPOR and EPO sequence variants associated with FE or clinical features of erythrocytosis were retrieved from PubMed and WoS. In silico, sequence reanalysis was performed using Ensembl genomic browser, release 89 to screen for variants located within regulatory regions. RESULTS:To date, 28 variants of the EPOR and seven variants of the EPO gene have been associated with erythrocytosis or upper hematocrit. Sequence variants were also found to be present within regulatory regions. CONCLUSIONS:Role of variants in regulatory regions of the EPO gene should be further investigated.