Antiapoptotic effects of erythropoietin in differentiated neuroblastoma SH-SY5Y cells require activation of both the STAT5 and AKT signaling pathways

Asialo-rhuEPO as a Potential Neuroprotectant for Ischemic Stroke Treatment

Neuroprotective drugs to protect the brain against cerebral ischemia and reperfusion (I/R) injury are urgently needed. Mammalian cell-produced recombinant human erythropoietin (rhuEPOM) has been demonstrated to have excellent neuroprotective functions in preclinical studies, but its neuroprotective properties could not be consistently translated in clinical trials. The clinical failure of rhuEPOM was thought to be mainly due to its erythropoietic activity-associated side effects. To exploit its tissue-protective property, various EPO derivatives with tissue-protective function only have been developed. Among them, asialo-rhuEPO, lacking terminal sialic acid residues, was shown to be neuroprotective but non-erythropoietic. Asialo-rhuEPO can be prepared by enzymatic removal of sialic acid residues from rhuEPOM (asialo-rhuEPOE) or by expressing human EPO gene in glycoengineered transgenic plants (asialo-rhuEPOP). Both types of asialo-rhuEPO, like rhuEPOM, displayed excellent neuroprotective effects by regulating multiple cellular pathways in cerebral I/R animal models. In this review, we describe the structure and properties of EPO and asialo-rhuEPO, summarize the progress on neuroprotective studies of asialo-rhuEPO and rhuEPOM, discuss potential reasons for the clinical failure of rhuEPOM with acute ischemic stroke patients, and advocate future studies needed to develop asialo-rhuEPO as a multimodal neuroprotectant for ischemic stroke treatment.

Streamlining Culture Conditions for the Neuroblastoma Cell Line SH-SY5Y: A Prerequisite for Functional Studies

The neuroblastoma cell line SH-SY5Y has been a well-established and very popular in vitro model in neuroscience for decades, especially focusing on neurodevelopmental disorders, such as Parkinson’s disease. The ability of this cell type to differentiate compared with other models in neurobiology makes it one of the few suitable models without having to rely on a primary culture of neuronal cells. Over the years, various, partly contradictory, methods of cultivation have been reported. This study is intended to provide a comprehensive guide to the in vitro cultivation of undifferentiated SH-SY5Y cells. For this purpose, the morphology of the cell line and the differentiation of the individual subtypes are described, and instructions for cell culture practice and long-term cryoconservation are provided. We describe the key growth characteristics of this cell line, including proliferation and confluency data, optimal initial seeding cell numbers, and a comparison of different culture media and cell viability during cultivation. Furthermore, applying an optimized protocol in a long-term cultivation over 60 days, we show that cumulative population doubling (CPD) is constant over time and does not decrease with incremental passage, enabling stable cultivation, for example, for recurrent differentiation to achieve the highest possible reproducibility in subsequent analyses. Therefore, we provide a solid guidance for future research that employs the neuroblastoma cell line SH-SY5Y.

Recombinant human erythropoietin protects long-term cultured ageing primary nerve cells by upregulating the PI3K/Akt pathway

OBJECTIVE

Previous studies have found that recombinant human erythropoietin (rhEPO) protects long-term cultured ageing primary nerve cells by enhancing the endogenous antioxidant capacity of cells; however, its signalling pathways are not clear. This study aimed to explore the relationship between the rhEPO and PI3K/Akt pathways in the protection of senescent nerve cells at the cellular level.

METHODS

Primary nerve cells were cultured for 22 days to mimic the natural ageing process of nerve cells. rhEPO and LY294002 were administered as an intervention on the 11th day of culture. Western blot, immunochemistry, 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyltetrazolium bromide, immunofluorescence double-labelling staining, Annexin V-FITC/PI double-labelling flow cytometry, and SA-β-gal staining experiments were used to observe the expression levels of erythropoietin receptor (EPOR) and phosphorylated Akt (p-Akt) protein and the related indices of nerve cell senescence.

RESULTS

Western blot experiments showed that in ageing long-term cultured primary neurons, the EPOR and p-Akt decreased and rhEPO upregulated the expression levels of EPOR and p-Akt protein. The rest showed that the PI3K/Akt pathway blockade reduced the antioxidation capacity, cell viability, cell morphology, and ratio of apoptotic cells and senescent cells of rhEPO on ageing long-term cultured primary nerve cells.

CONCLUSIONS

This study explored the relationship between the rhEPO and PI3K/Akt pathways in the protection of ageing nerve cells at the cellular level and found that rhEPO protects long-term cultured ageing primary nerve cells by upregulating the PI3K/Akt pathway. These findings provide a theoretical basis and experimental evidence for the antiaeging mechanism of EPO in the nervous system.

Photobiomodulation Improves the Inflammatory Response and Intracellular Signaling Proteins Linked to Vascular Function and Cell Survival in the Brain of Aged Rats

Photobiomodulation is a non-pharmacological tool widely used to reduce inflammation in many tissues. However, little is known about its effects on the inflammatory response in the aged brain. We conducted the study to examine anti-inflammatory effects of photobiomodulation in aging brains. We used aged rats (20 months old) with control (handled, laser off) or transcranial laser (660 nm wavelength, 100 mW power) treatments for 10 consecutive days and evaluated the level of inflammatory cytokines and chemokines, and the expression and activation of intracellular signaling proteins in the cerebral cortex and the hippocampus. Inflammatory analysis showed that aged rats submitted to transcranial laser treatment had increased levels of IL-1alpha and decreased levels of IL-5 in the cerebral cortex. In the hippocampus, the laser treatment increased the levels of IL-1alpha and decreased levels of IL-5, IL-18, and fractalkine. Regarding the intracellular signaling proteins, a reduction in the ERK and p38 expression and an increase in the STAT3 and ERK activation were observed in the cerebral cortex of aged rats from the laser group. In addition, the laser treatment increased the hippocampal expression of p70S6K, STAT3, and p38 of aged rats. Taken together, our data indicate that transcranial photobiomodulation can improve the inflammatory response and the activation of intracellular signaling proteins linked to vascular function and cell survival in the aged brain.

The Role of PI3K/AKT and MAPK Signaling Pathways in Erythropoietin Signalization

Erythropoietin (EPO) is a glycoprotein cytokine known for its pleiotropic effects on various types of cells and tissues. EPO and its receptor EPOR trigger signaling cascades JAK2/STAT5, MAPK, and PI3K/AKT that are interconnected and irreplaceable for cell survival. In this article, we describe the role of the MAPK and PI3K/AKT signaling pathways during red blood cell formation as well as in non-hematopoietic tissues and tumor cells. Although the central framework of these pathways is similar for most of cell types, there are some stage-specific, tissue, and cell-lineage differences. We summarize the current state of research in this field, highlight the novel members of EPO-induced PI3K and MAPK signaling, and in this respect also the differences between erythroid and non-erythroid cells.

Cytoprotective effects of erythropoietin: What about the lung?

Erythropoietin (Epo) is a pleiotropic cytokine, essential for erythropoiesis. Epo and its receptor (Epo-R) are produced by several tissues and it is now admitted that Epo displays other physiological functions than red blood cell synthesis. Indeed, Epo provides cytoprotective effects, which consist in prevention or fight against pathological processes. This perspective article reviews the various protective effects of Epo in several organs and tries to give a proof of concept about its effects in the lung. The tissue-protective effects of Epo could be a promising approach to limit the symptoms of acute and chronic lung diseases.

Carbamylated form of human erythropoietin normalizes cardiorespiratory disorders triggered by intermittent hypoxia mimicking sleep apnea syndrome

BACKGROUND AND OBJECTIVE

Chronic intermittent hypoxia (CIH), one of the main features of obstructive sleep apnea (OSA), enhances carotid body-mediated chemoreflex and induces hypertension and breathing disorders. The carbamylated form of erythropoietin (cEpo) may have beneficial effects as it retains its antioxidant/anti-inflammatory and neuroprotective profile without increasing red blood cells number. However, no studies have evaluated the potential therapeutic effect of cEpo on CIH-related cardiorespiratory disorders. We aimed to determine whether cEpo normalized the CIH-enhanced carotid body ventilatory chemoreflex, the hypertension and ventilatory disorders in rats.

METHODS

Male Sprague-Dawley rats (250 g) were exposed to CIH (5% O2, 12/h, 8 h/day) for 28 days. cEPO (20 μg/kg, i.p) was administrated from day 21 every other day for one more week. Cardiovascular and respiratory function were assessed in freely moving animals.

RESULTS

Twenty-one days of CIH increased carotid body-mediated chemoreflex responses as evidenced by a significant increase in the hypoxic ventilatory response (FiO2 10%) and triggered irregular eupneic breathing, active expiration, and produced hypertension. cEpo treatment significantly reduced the carotid body--chemoreflex responses, normalizes breathing patterns and the hypertension in CIH. In addition, cEpo treatment effectively normalized carotid body chemosensory responses evoked by acute hypoxic stimulation in CIH rats.

CONCLUSION

Present results strongly support beneficial cardiorespiratory therapeutic effects of cEpo during CIH exposure.

A novel regulatory role of RGS4 in STAT5B activation, neurite outgrowth and neuronal differentiation

The Regulator of G protein Signalling 4 (RGS4) is a multitask protein that interacts with and negatively modulates opioid receptor signalling. Previously, we showed that the δ-opioid receptor (δ-OR) forms a multiprotein signalling complex consisting of Gi/Go proteins and the Signal Transducer and Activator of Transcription 5B (STAT5B) that leads to neuronal differentiation and neurite outgrowth upon δ-ΟR activation. Here, we investigated whether RGS4 could participate in signalling pathways to regulate neurotropic events. We demonstrate that RGS4 interacts directly with STAT5B independently of δ-ΟR presence both in vitro and in living cells. This interaction involves the N-terminal portion of RGS4 and the DNA-binding SH3 domain of STAT5B. Expression of RGS4 in HEK293 cells expressing δ-OR and/or erythropoietin receptor results in inhibition of [D-Ser², Leu⁵, Thr⁶]-enkephalin (DSLET)-and erythropoietin-dependent STAT5B phosphorylation and subsequent transcriptional activation. DSLET-dependent neurite outgrowth of neuroblastoma cells is also blocked by RGS4 expression, whereas primary cortical cultures of RGS4 knockout mice (RGS4^-/-) exhibit enhanced neuronal sprouting after δ-OR activation. Additional studies in adult brain extracts from RGS4^-/- mice revealed increased levels of p-STAT5B. Finally, neuronal progenitor cultures from RGS4^-/- mice exhibit enhanced proliferation with concomitant increases in the mRNA levels of the anti-apoptotic STAT5B target genes bcl2 and bcl-xl. These observations suggest that RGS4 is implicated in opioid dependent neuronal differentiation and neurite outgrowth via a "non-canonical" signaling pathway regulating STAT5B-directed responses.

Argon mediates protection by interleukin-8 suppression via a TLR2/TLR4/STAT3/NF-κB pathway in a model of apoptosis in neuroblastoma cells in vitro and following ischemia-reperfusion injury in rat retina in vivo

Argon has recently come into scientific focus as a neuroprotective agent. The underlying neuroprotective mechanism remains unknown although toll-like receptors were recently suggested to play an important role. We hypothesized that TLR-associated downstream transcription factors are responsible for argon's effects, leading to anti-apoptotic and anti-inflammatory properties. Apoptosis was induced in human neuroblastoma cells. Immediately afterwards, argon treatment (75 Vol% for 2 h) was initiated. Cells were analyzed, measuring mitochondrial membrane potential, reactive-oxygen-species, annexin-V/propidium iodide staining, transcription factor phosphorylation and binding activity as well as protein and mRNA expression of interleukins. Argon's in vivo effects were analyzed by quantification of retinal ganglion cell density, mRNA expression, serum cytokine analysis and immunohistochemistry after retinal ischemia reperfusion injury (IRI) in rats. Argon diminished rotenone-induced kappa-light-chain-enhancer' of activated B-cells (NF-κB) and signal transducer and activator of transcription 3 (STAT3) but not STAT5 or cAMP-response element-binding protein (CREB) phosphorylation and DNA-binding activity. Argon treatment attenuated apoptosis by preservation of mitochondrial membrane potential and decline in reactive oxygen species (ROS) generation. NF-κB and STAT3 inhibition, as well as TLR2 and TLR4 inhibition reversed argon's effects on IL-8 mRNA expression. Argon attenuated rotenone-induced IL-8 protein and mRNA expression in vitro. Inhibition of TLR2 and 4 attenuated argon's protective effect in vivo reducing IRI driven retinal IL-8 expression. IL-8 expression was found in the retina in co-localization with Müller cells and retinal ganglion cells. Argon mediates its neuroprotective effects by TLR-mediated regulation of transcription factors NF-κB and STAT3, thus decreasing interleukin-8 expression in vitro and in vivo. These findings may open up new opportunities to effectively treat cerebral ischemia and reperfusion injury through the inhalation of argon. Argon exerts its protective effects in vitro and in vivo via toll-like receptors TLR2 and TLR4 signaling, followed by alteration of downstream enzymes. In conclusion, argon mediates its beneficial effects by suppression of STAT3 and NF-κB phosphorylation and subsequent suppression of interleukin IL-8 protein expression. These novel findings may open up opportunities for argon as a therapeutic agent, particularly in the treatment of neuronal injury. Cover image for this issue: doi: 10.1111/jnc.13334.

Erythropoietin Pathway: A Potential Target for the Treatment of Depression

During the past decade, accumulating evidence from both clinical and experimental studies has indicated that erythropoietin may have antidepressant effects. In addition to the kidney and liver, many organs have been identified as secretory tissues for erythropoietin, including the brain. Its receptor is expressed in cerebral and spinal cord neurons, the hypothalamus, hippocampus, neocortex, dorsal root ganglia, nerve axons, and Schwann cells. These findings may highlight new functions for erythropoietin, which was originally considered to play a crucial role in the progress of erythroid differentiation. Erythropoietin and its receptor signaling through JAK2 activate multiple downstream signaling pathways including STAT5, PI3K/Akt, NF-κB, and MAPK. These factors may play an important role in inflammation and neuroprogression in the nervous system. This is particularly true for the hippocampus, which is possibly related to learning, memory, neurocognitive deficits and mood alterations. Thus, the influence of erythropoietin on the downstream pathways known to be involved in the treatment of depression makes the erythropoietin-related pathway an attractive target for the development of new therapeutic approaches. Focusing on erythropoietin may help us understand the pathogenic mechanisms of depression and the molecular basis of its treatment.

Oxygen-dependent Regulation of Erythropoietin Receptor Turnover and Signaling

von Hippel-Lindau (VHL) disease is a rare familial cancer predisposition syndrome caused by a loss or mutation in a single gene,VHL, but it exhibits a wide phenotypic variability that can be categorized into distinct subtypes. The phenotypic variability has been largely argued to be attributable to the extent of deregulation of the α subunit of hypoxia-inducible factor α, a well established target of VHL E3 ubiquitin ligase, ECV (Elongins/Cul2/VHL). Here, we show that erythropoietin receptor (EPOR) is hydroxylated on proline 419 and 426 via prolyl hydroxylase 3. EPOR hydroxylation is required for binding to the β domain of VHL and polyubiquitylation via ECV, leading to increased EPOR turnover. In addition, several type-specific VHL disease-causing mutants, including those that have retained proper binding and regulation of hypoxia-inducible factor α, showed a severe defect in binding prolyl hydroxylated EPOR peptides. These results identify EPOR as the secondbona fidehydroxylation-dependent substrate of VHL that potentially influences oxygen homeostasis and contributes to the complex genotype-phenotype correlation in VHL disease.

Effects of erythropoietin preconditioning on rat cerebral ischemia-reperfusion injury and the GLT-1/GLAST pathway

The aim of the present study was to investigate whether erythropoietin (EPO) preconditioning affects the expression of glutamate transporter 1 (GLT-1) and glutamate aspartate transporter (GLAST) and protects against rat cerebral ischemia-reperfusion injury. A total of 140 Sprague Dawley rats were randomly assigned to one of the following four groups: Sham, EPO-sham, middle cerebral artery occlusion (MCAO) and EPO-MCAO. Neurological function scores were obtained 24, 36 and 72 h after reperfusion. Seventy-two hours after the induction of cerebral ischemia-reperfusion, the number of apoptotic neural cells and the cerebral infarct volume of each group were measured. The mRNA levels of GLT-1 and GLAST were determined using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis, while the GLT-1 and GLAST protein levels were assessed using western blotting. The cerebral infarct volume was significantly increased in the MCAO group compared with that in the sham group (P<0.01); however, the infarct volume of the EPO-MCAO group was significantly lower than that of the MCAO group (P<0.01). In addition, the number of apoptotic cells found in the MCAO group was higher than that in the sham group (P<0.01), but the number of apoptotic cells in the EPO-MCAO group was significantly lower than that in the MCAO group (P<0.01). The GLT-1 and GLAST mRNA and protein levels were significantly decreased 72 h after the cerebral ischemia-reperfusion (P<0.01) compared with those in the sham group, whereas the same levels were increased significantly in the EPO-MCAO group relative to those in the MCAO group (P<0.01). In conclusion, EPO preconditioning protected against cerebral ischemia-reperfusion injury and upregulated the GLT-1 and GLAST expression.

DNA methylation is necessary for erythropoietin to improve spatial learning and memory in SAMP8 mice

OBJECTIVE

To reveal the role of Dnmts in the improvement of spatial learning and memory induced by erythropoietin (EPO) in SAMP8 mice.

METHODS

The Morris water maze (MWM) was used to assess spatial learning and memory. Mice were administered by intraperitoneal (i.p.) injection of recombinant human EPO and hippocamppi infusion (IH) of 5-aza-2'-deoxycytidine (5-AZA). The expression of genes Dnmt1, Dnmt3a and Dnmt3b in the hippocampus was detected by real-time qPCR. The level of proteins DNMT1, DNMT3A and DNMT3B was measured by Western blotting.

RESULTS

Spatial learning and memory in SAMP8 were promoted after i.p. injection of EPO (5000IU/kg/day) and expression of Dnmt3b mRNA and DNMT3B proteins in the hippocampus increased. The improved memory by EPO was blocked after IH 5-AZA.

CONCLUSION

DNA methylation is necessary for EPO to enhance spatial learning and memory in SAMP8 mice.

Erythropoietin protects neuroblastoma cells against etoposide and vincristine by activating ERK and AKT pathways but has no effect in kidney cells

AIMS

Chemotherapy induces anaemia in neuroblastoma patients. Cancer-associated anaemia may be treated with recombinant erythropoietin. However, the potential effects of erythropoietin on neuroblastoma and kidney cells have not been extensively evaluated. The present study was designed to investigate the effect of erythropoietin on the proliferation, and protection against vincristine- and etoposide-induced cell death in neuroblastoma (MSN), and embryonic kidney (HEK 293) cells.

MAIN METHODS

The expression of erythropoietin and its receptor in MSN and HEK 293 was analysed by RT-PCR, immunocytochemistry, and Western blotting. The effect of erythropoietin on cell viability and proliferation was evaluated by the MTT assay, and by the Click-iT EdU Alexa Fluor 647 kit, respectively. For the cyto-protective assays, cells were incubated with erythropoietin before etoposide and vincristine treatment. Activation of signalling pathways was studied by Western blotting.

KEY FINDINGS

MSN and HEK 293 cells expressed the erythropoietin receptor, but not erythropoietin. Erythropoietin induced proliferation and protection against vincristine and etoposide in MSN cells. HEK 293 cells were not affected by erythropoietin. Erythropoietin showed an anti-apoptotic effect which was dependent on the activation of ERK1/2 and AKT. HEK 293 cells presented constitutively phosphorylated AKT, and showed no activation of ERK1/2 upon erythropoietin stimulation.

SIGNIFICANCE

These results indicate that erythropoietin induces proliferation of MSN cells, and that it can ameliorate vincristine- and etoposide-induced apoptosis of these cells. Erythropoietin-mediated neuroprotection was regulated by the combined effect of the ERK1/2 and AKT signalling pathways. Our findings provide further insights into the potential effect of erythropoietin on neuroblastoma cells.

Discovery and Characterization of Nonpeptidyl Agonists of the Tissue-Protective Erythropoietin Receptor

Erythropoietin (EPO) and its receptor are expressed in a wide variety of tissues, including the central nervous system. Local expression of both EPO and its receptor is upregulated upon injury or stress and plays a role in tissue homeostasis and cytoprotection. High-dose systemic administration or local injection of recombinant human EPO has demonstrated encouraging results in several models of tissue protection and organ injury, while poor tissue availability of the protein limits its efficacy. Here, we describe the discovery and characterization of the nonpeptidyl compound STS-E412 (2-[2-(4-chlorophenoxy)ethoxy]-5,7-dimethyl-[1,2,4]triazolo[1,5-a]pyrimidine), which selectively activates the tissue-protective EPO receptor, comprising an EPO receptor subunit (EPOR) and the common β-chain (CD131). STS-E412 triggered EPO receptor phosphorylation in human neuronal cells. STS-E412 also increased phosphorylation of EPOR, CD131, and the EPO-associated signaling molecules JAK2 and AKT in HEK293 transfectants expressing EPOR and CD131. At low nanomolar concentrations, STS-E412 provided EPO-like cytoprotective effects in primary neuronal cells and renal proximal tubular epithelial cells. The receptor selectivity of STS-E412 was confirmed by a lack of phosphorylation of the EPOR/EPOR homodimer, lack of activity in off-target selectivity screening, and lack of functional effects in erythroleukemia cell line TF-1 and CD34(+) progenitor cells. Permeability through artificial membranes and Caco-2 cell monolayers in vitro and penetrance across the blood-brain barrier in vivo suggest potential for central nervous system availability of the compound. To our knowledge, STS-E412 is the first nonpeptidyl, selective activator of the tissue-protective EPOR/CD131 receptor. Further evaluation of the potential of STS-E412 in central nervous system diseases and organ protection is warranted.

The lack of CD131 and the inhibition of Neuro-2a growth by carbamylated erythropoietin

Recombinant human erythropoietin (EPO), a glycohormone, is one of the leading biopharmaceutical products, while carbamylated erythropoietin (CEPO), an EPO derivative, is attracting widespread interest due to its neuroprotective effects without erythropoiesis in several cells and animal models. However, exogenous EPO promotes an angiogenic response from tumor cells and is associated with tumor growth, but knowledge of CEPO on tumor growth is lacking. Here we show that CEPO, but not EPO, inhibited Neuro-2a growth and viability. As expected, CEPO--unlike EPO--did not activate JAK-2 either in primary neurons or in Neuro-2a cells. Interestingly, CEPO did not induce GDNF expression and subsequent AKT activation in Neuro-2a cells. Before CEPO/EPO treatment, glial cell line-derived neurotrophic factor (GDNF) neutralization and GFR receptor blocking decreased the viability of EPO-treated Neuro-2a cells but did not influence CEPO-treated Neuro-2a cells. As compared to primary neurons, the expression of CD131, as a receptor complex binding to CEPO, is almost lacking in Neuro-2a cells. In BABL/C-nu mice, CEPO did not promote the growth of Neuro-2a cells nor extended the survival time compared to mice treated with EPO. The results indicate that CEPO did not promote tumor growth because of lower expression of CD131 and subsequent dysfunction of CD131/GDNF/AKT pathway in Neuro-2a cells, revealing its therapeutic potential in future clinical application.

JAK2/STAT5/Bcl-xL signalling is essential for erythropoietin-mediated protection against apoptosis induced in PC12 cells by the amyloid β-peptide Aβ25-35

BACKGROUND AND PURPOSE

Erythropoietin (EPO) exerts neuroprotective actions in the CNS, including protection against apoptosis induced by the amyloid β-peptide Aβ25-35 . However, it remains unclear which signalling pathway activated by EPO is involved in this neuroprotection. Here, we have investigated whether JAK2/STAT5/Bcl-xL and ERK1/2 signalling pathways are essential for EPO-mediated protection against apoptosis induced by Aβ25-35 .

EXPERIMENTAL APPROACH

EPO was added to cultures of PC12 cells, 1 h before Aβ25-35 . For kinase inhibitor studies, AG490 and PD98059 were added to PC12 cells, 0.5 h before the addition of EPO. Transfection with siRNA was used to knockdown STAT5. Activation of JAK2/STAT5/Bcl-xL and ERK1/2 signalling pathways were investigated by Western blotting. Cell viability was measured by 3-(4,5-dimethylthiazol-2-yl) 2,5-diphenyl-tetrazolium bromide assay and apoptosis was detected by TUNEL and acridine orange-ethidium bromide double staining.

KEY RESULTS

EPO increased phosphorylation of JAK2 and STAT5 in PC12 cells treated with Aβ25-35 . Furthermore, EPO modulated the nuclear translocation of phospho-STAT5, which increased expression of Bcl-xL and decreased levels of caspase-3. These beneficial effects were blocked by the JAK2 inhibitor, AG490 or STAT5 knockdown. However, the ERK1/2 pathway did not play a crucial role in our model.

CONCLUSIONS AND IMPLICATIONS

EPO protected PC12 cells against Aβ25-35 -induced neurotoxicity. Activation of JAK2/STAT5/Bcl-xL pathway was important in EPO-mediated neuroprotection. EPO may serve as a novel protective agent against Aβ25-35 -induced cytotoxicity in, for instance, Alzheimer's disease.

Erythropoietin improves neurobehavior by reducing dopaminergic neuron loss in a 6‑hydroxydopamine‑induced rat model

The purpose of this study was to determine the effectiveness of the systemic administration of high dose erythropoietin (EPO) in a 6-hydroxydopamine (6-OHDA)- induced rat model. Rats were divided into 7 groups. Groups 1–4 were administered daily EPO doses of 0; 2,500; 5,000 and 10,000 U/kg via intraperitoneal injection (i.p.) for 5 days. The EPO concentration in cerebrospinal fluid (CSF) was determined by enzyme-linked immunosorbent assay (ELISA) and western blot analysis. The dose of 10,000 U/kg was then selected for subsequent experiments. In group 5, rats received saline via medial forebrain bundle (MFB). In group 6, rats received 6-OHDA via MFB. In group 7, an EPO concentration of 10,000 U/kg was constantly administered i.p. for 5 days to rats prior to 6-OHDA injection via MFB. Behavioral analysis was performed for groups 5–7 by rat rotation tests. The number of tyrosine hydroxylase (TH)-immunopositive cells in the substantia nigra (SN) was measured by immunocytochemistry. The activation of c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinases (MAPKs) and caspase-3 signaling in rats were analyzed using western blotting. The results showed that there was a significant increase in EPO levels in the CSF in 10,000 U/kg group compared with the 2,500 and 5,000 U/kg groups (P<0.01). Significantly fewer rotational counts were obtained in rats that were pretreated with EPO compared with saline-pretreated 6-OHDA-lesioned rats (P<0.001). The dopaminergic neurons in the 6-OHDA-lesioned SN were also increased in the EPO-pretreated rats when compared with control rats (P<0.01). Western blot analysis revealed that EPO inhibited the 6-OHDA-induced activation of JNK, ERK, p38 MAPK and caspase-3 signaling in the rat model. In conclusion, systemic administration of a high dose of EPO exerted neuroprotective effects in reversing behavioral deficits associated with Parkinson’s disease and prevented loss of the dopaminergic neurons through the MAPK pathway.

Erythropoietin-mediated protection of insect brain neurons involves JAK and STAT but not PI3K transduction pathways

The cytokine erythropoietin (Epo) initiates adaptive cellular responses to both moderate environmental challenges and tissue damaging insults in various non-hematopoietic mammalian tissues including the nervous system. Neuroprotective and neuroregenerative functions of Epo in mammals are mediated through receptor-associated Janus kinase 2 and intracellular signaling cascades that modify the transcription of Epo-regulated genes. Signal transducers and activators of transcription (STAT) and phosphoinositol-3-kinase (PI3K) represent key components of two important Epo-induced transduction pathways. Our previous study on insects revealed neuroprotective and regenerative functions of recombinant human Epo (rhEpo) similar to those in mammalian nervous tissues. Here we demonstrate that rhEpo effectively rescues primary cultured locust brain neurons from apoptotic cell death induced by hypoxia or the chemical compound H-7. The Janus kinase inhibitor AG-490 and the STAT inhibitor sc-355797 abolished protective effects of rhEpo on locust brain neurons. In contrast, inhibition of PI3K with LY294002 had no effect on rhEpo-mediated neuroprotection. The results indicate that rhEpo mediates the protection of locust brain neurons through interference with apoptotic pathways by the activation of a Janus kinase-associated receptor and STAT transcription factor(s). The involvement of similar transduction pathways in mammals and insects for the mediation of neuroprotection and support of neural regeneration by Epo indicates that an Epo/Epo receptor-like signaling system with high structural and functional similarity exists in both groups of animals. Epo-like signaling involved in tissue protection appears to be an ancient beneficial function shared by vertebrates and invertebrates.

Erythropoietin in cancer: a dilemma in risk therapy

Erythropoietin (EPO) is a frequently prescribed drug for treatment of cancer-related and chemotherapy-induced anemia in cancer patients. Paradoxically, recent preclinical and clinical studies indicate that EPO could potentially accelerate tumor growth and jeopardize survival in cancer patients. In this review I critically discuss the current knowledge and broad biological functions of EPO in association with tumor growth, invasion, and angiogenesis. The emphasis is focused on discussing the complex interplay between EPO and other tumor-derived factors in angiogenesis, tumor growth, invasion, and metastasis. Understanding the multifarious functions of EPO and its reciprocal relation with other signaling pathways is crucial for developing more effective agents for cancer therapy and for minimizing risks for cancer patients.

Oxidant stress and signal transduction in the nervous system with the PI 3-K, Akt, and mTOR cascade

Oxidative stress impacts multiple systems of the body and can lead to some of the most devastating consequences in the nervous system especially during aging. Both acute and chronic neurodegenerative disorders such as diabetes mellitus, cerebral ischemia, trauma, Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, and tuberous sclerosis through programmed cell death pathways of apoptosis and autophagy can be the result of oxidant stress. Novel therapeutic avenues that focus upon the phosphoinositide 3-kinase (PI 3-K), Akt (protein kinase B), and the mammalian target of rapamycin (mTOR) cascade and related pathways offer exciting prospects to address the onset and potential reversal of neurodegenerative disorders. Effective clinical translation of these pathways into robust therapeutic strategies requires intimate knowledge of the complexity of these pathways and the ability of this cascade to influence biological outcome that can vary among disorders of the nervous system.

The erythropoietin/erythropoietin receptor signaling pathway promotes growth and invasion abilities in human renal carcinoma cells

Co-expression of erythropoietin (Epo) and erythropoietin receptor (EpoR) has been found in various non-hematopoietic cancers including hereditary and sporadic renal cell carcinomas (RCC), but the Epo/EpoR autocrine and paracrine mechanisms in tumor progression have not yet been identified. In this study, we used RNA interference method to down-regulate EpoR to investigate the function of Epo/EpoR pathway in human RCC cells. Epo and EpoR co-expressed in primary renal cancer cells and 6 human RCC cell lines. EpoR signaling was constitutionally phosphorylated in primary renal cancer cells, 786-0 and Caki-1 cells, and recombinant human Epo (rhEpo) stimulation had no significant effects on further phosphorylation of EpoR pathway, proliferation, and invasiveness of the cells. Down-regulation of EpoR expression in 786-0 cells by lentivirus-introduced siRNA resulted in inhibition of growth and invasiveness in vitro and in vivo, and promotion of cell apoptosis. In addition, rhEpo stimulation slightly antagonized the anti-tumor effect of Sunitinib on 786-0 cells. Sunitinib could induce more apoptotic cells in 786-0 cells with knockdown EpoR expression. Our results suggested that Epo/EpoR pathway was involved in cell growth, invasion, survival, and sensitivity to the multi-kinases inhibitor Sunitinib in RCC cells.

Erythropoietin: new directions for the nervous system

New treatment strategies with erythropoietin (EPO) offer exciting opportunities to prevent the onset and progression of neurodegenerative disorders that currently lack effective therapy and can progress to devastating disability in patients. EPO and its receptor are present in multiple systems of the body and can impact disease progression in the nervous, vascular, and immune systems that ultimately affect disorders such as Alzheimer's disease, Parkinson's disease, retinal injury, stroke, and demyelinating disease. EPO relies upon wingless signaling with Wnt1 and an intimate relationship with the pathways of phosphoinositide 3-kinase (PI 3-K), protein kinase B (Akt), and mammalian target of rapamycin (mTOR). Modulation of these pathways by EPO can govern the apoptotic cascade to control β-catenin, glycogen synthase kinase-3β, mitochondrial permeability, cytochrome c release, and caspase activation. Yet, EPO and each of these downstream pathways require precise biological modulation to avert complications associated with the vascular system, tumorigenesis, and progression of nervous system disorders. Further understanding of the intimate and complex relationship of EPO and the signaling pathways of Wnt, PI 3-K, Akt, and mTOR are critical for the effective clinical translation of these cell pathways into robust treatments for neurodegenerative disorders.

The effect of erythropoietin on normal and neoplastic cells

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

Signal transducer and activator of transcription-5 mediates neuronal apoptosis induced by inhibition of Rac GTPase activity

In several neuronal cell types, the small GTPase Rac is essential for survival. We have shown previously that the Rho family GTPase inhibitor Clostridium difficile toxin B (ToxB) induces apoptosis in primary rat cerebellar granule neurons (CGNs) principally via inhibition of Rac GTPase function. In the present study, incubation with ToxB activated a proapoptotic Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway, and a pan-JAK inhibitor protected CGNs from Rac inhibition. STAT1 expression was induced by ToxB; however, CGNs from STAT1 knock-out mice succumbed to ToxB-induced apoptosis as readily as wild-type CGNs. STAT3 displayed enhanced tyrosine phosphorylation following treatment with ToxB, and a reputed inhibitor of STAT3, cucurbitacin (JSI-124), reduced CGN apoptosis. Unexpectedly, JSI-124 failed to block STAT3 phosphorylation, and CGNs were not protected from ToxB by other known STAT3 inhibitors. In contrast, STAT5A tyrosine phosphorylation induced by ToxB was suppressed by JSI-124. In addition, roscovitine similarly inhibited STAT5A phosphorylation and protected CGNs from ToxB-induced apoptosis. Consistent with these results, adenoviral infection with a dominant negative STAT5 mutant, but not wild-type STAT5, significantly decreased ToxB-induced apoptosis of CGNs. Finally, chromatin immunoprecipitation with a STAT5 antibody revealed increased STAT5 binding to the promoter region of prosurvival Bcl-xL. STAT5 was recruited to the Bcl-xL promoter region in a ToxB-dependent manner, and this DNA binding preceded Bcl-xL down-regulation, suggesting transcriptional repression. These data indicate that a novel JAK/STAT5 proapoptotic pathway significantly contributes to neuronal apoptosis induced by the inhibition of Rac GTPase.

Recombinant human erythropoietin promotes the acquisition of a malignant phenotype in head and neck squamous cell carcinoma cell lines in vitro

Background

Recent studies indicate an increase in tumor progression and recurrence in head and neck squamous cell carcinomas (HNSCC) of cancer patients taking recombinant human erythropoietin (rhEpo) for anemia. This study was undertaken to investigate the potential role of rhEpo in invasion, proliferation, and cisplatin-induced cell death in HNSCC cell lines.

Methods

The following experiments were performed with two HNSCC cell lines, UMSCC-10B and UMSCC-22B. Presence of EpoR in both cell lines was determined by western blot and quantitative PCR. Colorimetric MTS assays and clonogenic assays were used to study the effect of rhEpo at pharmacologically relevant doses on cell proliferation. Matrigel invasion assays were performed in order to determine effects of exogenous rhEpo on invasive abilities. Clonogenic assays were also used to study potential cytoprotective effects of rhEpo against cisplatin. Immunoblotting was done to analyze the effect of rhEpo on Akt phosphorylation. Finally, MTS and TUNEL assays were performed to test our hypothesis that Akt activation by PI3K was involved in rhEpo-mediated cisplatin resistance.

Results

HNSCC cell lines were shown to express Epo receptor (EpoR). RhEpo increased invasion 1.8-fold in UMSCC-10B and 2.6-fold in UMSCC-22B compared to control. RhEpo at 10 U/ml increased cell proliferation by 41% and 53% in UMSCC-10B and UMSCC-22B, respectively, and colony formation by 1.5-fold and 1.8-fold. UMSCC-10B treated with cisplatin and exposed to rhEpo at 1 and 10 U/ml resulted in a 1.7-fold and 3.0-fold increase in colony number compared to control, respectively. UMSCC-22B treated with cisplatin and rhEpo at 1 or 10 U/ml resulted in ~2.5-fold increase in colony number. A TUNEL assay demonstrated a 30.5% and 76.5% increase in survival in UMSCC-10B and UMSCC-22B cells, respectively, in cisplatin and rhEpo-treated cells compared to cisplatin alone. MTS assay showed similar cytoprotective effects. Western blot revealed increased phosphorylation of Akt upon exposure of HNSCC cell lines to rhEpo. MTS assay and TUNEL analyses implicate Akt as a likely contributor to regulation of rhEpo-mediated cytoprotection.

Conclusions

The results demonstrate that, in HNSCC cells expressing functional EpoR, rhEpo promotes invasion, cell proliferation, and induces resistance to cisplatin, which may contribute to tumor progression.

Neuroprotective cytokines repress PUMA induction in the 1-methyl-4-phenylpyridinium (MPP(+)) model of Parkinson's disease

The hematopoietic cytokines erythropoietin (Epo) and granulocyte-colony stimulating factor (G-CSF) provide neuroprotection in several in vitro and in vivo models of Parkinson's disease (PD). The molecular mechanism by which Epo and G-CSF signals reduce the neuronal death in PD is not clear. Here, we show that in rat pheochromocytoma PC12 cells, Epo and G-CSF efficiently repressed the 1-methyl-4-phenylpyridinium (MPP(+))-induced expression of the proapoptotic protein PUMA (p53 up-regulated modulator of apoptosis). Accordingly, Epo and G-CSF treatment reduced the PC12 cell fraction that underwent apoptosis by MPP(+) treatment and thus improved cell viability. Downregulation of PUMA expression by Epo and G-CSF in MPP(+)-treated PC12 cells seems to be mediated by repression of p53, as the expression of p53 was increased by MPP(+)-treatment and reduced by Epo and G-CSF. Together, these results suggest that the neuroprotective activities of Epo and G-CSF in an experimental model of PD involve the repression of the apoptosis-inducing action of PUMA.

Therapeutic promise and principles: metabotropic glutamate receptors

For a number of disease entities, oxidative stress becomes a significant factor in the etiology and progression of cell dysfunction and injury. Therapeutic strategies that can identify novel signal transduction pathways to ameliorate the toxic effects of oxidative stress may lead to new avenues of treatment for a spectrum of disorders that include diabetes, Alzheimer's disease, Parkinson's disease and immune system dysfunction. In this respect, metabotropic glutamate receptors (mGluRs) may offer exciting prospects for several disorders since these receptors can limit or prevent apoptotic cell injury as well as impact upon cellular development and function. Yet the role of mGluRs is complex in nature and may require specific mGluR modulation for a particular disease entity to maximize clinical efficacy and limit potential disability. Here we discuss the potential clinical translation of mGluRs and highlight the role of novel signal transduction pathways in the metabotropic glutamate system that may be vital for the clinical utility of mGluRs.

Erythropoietin protects pancreatic β-cell line NIT-1 cells against cytokine-induced apoptosis via phosphatidylinositol 3-kinase/Akt signaling

OBJECTIVE

Erythropoietin (EPO) is a cytokine that regulates the proliferation, differentiation, and survival of erythroid progenitor cells. EPO has recently been demonstrated to have a tissue-protective role by mediating anti-apoptotic signals through the erythropoietin receptor (EPOR) in various tissues, including brain, liver, and heart. We have previously examined pancreatic β-cell line NIT-1 cells for the expression of EPOR by real-time PCR and determined that these cells were protected by EPO against cytokine-induced apoptosis. The precise underlying anti-apoptotic mechanisms in pancreatic β-cells are poorly understood. The purpose of this study is to examine erythropoietin receptor expression in the NIT-1 pancreatic beta-cell line and the intracellular pathway related with its anti-apoptosis effect in NIT-1 cells.

METHODS

we examined the expression of EPOR by western blot. We investigate the role of erythropoietin in the survival of these cells, and whether the PI3K/AKT pathway is involved in this protective process.

RESULTS

NIT-1 cells expressed EPOR and, in the presence of certain cytokines, exposure of NIT-1 cells to recombinant human erythropoietin (rhEPO) significantly improved the impaired insulin secretion and inhibited cytokine-induced apoptosis. RhEPO caused a rapid activation of Akt and increased expression of Bcl-2. The protective anti-apoptotic effect of rhEPO was significantly abolished by a specific phosphatidylinositol 3-kiniase (PI3K) inhibitor, LY294002.

CONCLUSIONS

Our findings indicate that EPOR is expressed in pancreatic β-cell line NIT-1 cells and suggest that EPO may act as a survival factor requiring the PI3K/Akt pathway.

Protective effects of TRH and its analogues against various cytotoxic agents in retinoic acid (RA)-differentiated human neuroblastoma SH-SY5Y cells

TRH (thyroliberin) and its analogues were reported to possess neuroprotective effects in cellular and animal experimental models of acute and chronic neurodegenerative diseases. In the present study we evaluated effects of TRH and its three stable analogues, montirelin (CG-3703), RGH-2202 and Z-TRH (N-(carbobenzyloxy)-pGlutamyl-Histydyl-Proline) on the neuronally differentiated human neuroblastoma SH-SY5Y cell line, which is widely accepted for studying potential neuroprotectants. We found that TRH and all the tested analogues at concentrations 0.1-50 μM attenuated cell damage induced by MPP(+) (2 mM), 3-nitropropionate (10 mM), hydrogen peroxide (0.5 mM), homocysteine (250 μM) and beta-amyloid (20μM) in retinoic acid differentiated SH-SY5Y cells. Furthermore, we demonstrated that TRH and its analogues decreased the staurosporine (0.5 μM)-induced LDH release, caspase-3 activity and DNA fragmentation, which indicate the anti-apoptotic proprieties of these peptides. The neuroprotective effects of TRH (10 μM) and RGH-2202 (10 μM) on St-induced cell death was attenuated by inhibitors of PI3-K pathway (wortmannin and LY294002), but not MAPK/ERK1/2 (PD98059 and U0126). Moreover, TRH and its analogues at neuroprotective concentrations (1 and 10 μM) increased expression of Bcl-2 protein, as confirmed by Western blot analysis. All in all, these results extend data on neuroprotective properties of TRH and its analogues and provide evidence that mechanism of anti-apoptotic effects of these peptides in SH-SY5Y cell line involves induction of PI3K/Akt pathway and Bcl-2. Furthermore, the data obtained on human cell line with a dopaminergic phenotype suggest potential utility of TRH and its analogues in the treatment of some neurodegenerative diseases including Parkinson's disease.

Cellular basis of uraemic cardiomyopathy: a role for erythropoietin?

The use of erythropoietin (EPO) has revolutionized the treatment of anaemia associated with many conditions including chronic kidney disease (CKD). However, little is known of the cellular impact of EPO on the uraemic heart. The discovery that the EPO receptor (EPOR) is also expressed on non-haematopoietic cells including cardiomyocytes highlights a role of EPO beyond haematopoiesis. Animal models of heart failure have shown EPO can potentially reverse cardiac remodelling and improve myocardial function. Damage to the kidney, during uraemia, results in a decreased EPO production, which may render the uraemic heart more susceptible to damage and heart failure. Here we review current data on the cellular actions of EPO in models of left ventricular hypertrophy and heart failure and highlight parallels with the uraemic heart.

Darbepoetin-α treatment enhances glomerular regenerative process in the Thy-1 glomerulonephritis model

Recent studies have demonstrated that erythropoietin (EPO) and its analogs induce cytoprotective effects on many nonerythroid cells. In this study, we examined whether darbepoetin-α might prevent glomerular lesions in the Thy-1.1 model of glomerulonephritis (Thy-1-GN). GN was induced in Wistar rats by a single injection of monoclonal anti-Thy-1.1 antibody. Rats were killed at 24 h, 72 h, 7 days, 10 days, or 15 days after antibody injection. Kidneys were removed for histological analysis, and proteinuria was measured. Because at day 7 the maximal degree of renal damage and proteinuria was found, the effect of darbepoetin-α was tested at day 7 and two different protocols of administration were used; After anti-Thy-1.1 injection, rats received two doses of darbepoetin-α or vehicle at days 0 and 4 or at days 4 and 6. At day 7, proteinuria, plasma creatinine concentration, and renal morphology analysis were performed. Also, α-actin, desmin, caspase-3, and Ki67 protein expression were evaluated by immunohistochemistry. Our results showed that in both protocols of administration, darbepoetin-α treatment decreased proteinuria in Thy-1-GN rats and this effect correlated with the improvement in renal morphology. Glomerular lesions, α-actin, and caspase-3 protein expression, observed in most glomeruli of Thy-1-GN rats, were significantly reduced in darbepoetin-α-treated rats, while cell proliferation was significantly enhanced. The results indicate that darbepoetin-α treatment promotes glomerular recovery.

Differential antiapoptotic effect of erythropoietin on undifferentiated and retinoic acid-differentiated SH-SY5Y cells

Erythropoietin (Epo) is known to have a significant role in tissues outside the hematopoietic system. In this work, we investigated the function of Epo in cells of neuronal origin subjected to differentiation. Treatment of SH-SY5Y cells with all-trans-retinoic acid (atRA) generated differentiated neuron-like cells, observed by increased expression of neuronal markers and morphological changes. Exposure of undifferentiated cells to proapoptotic stimuli such as staurosporine, TNF-alpha, or hypoxia, significantly increased programmed cell death, which was prevented by previous treatment with Epo. In contrast, atRA-differentiated cultures showed cell resistance to apoptosis. No additional effect of Epo was detected in previously differentiated cells. The inhibition of the PI3K/Akt pathway by Ly294002 abrogated the protective effects induced by either Epo or atRA. The effect of atRA was mediated by an increased expression of Bcl-2 whereas the Epo treatment upregulated not only Bcl-2 but also Bcl-xL. This upregulation by Epo was not detected in atRA-differentiated cells, thus confirming the lack of the protective effect of Epo. As expected, assays with AG490, an inhibitor of Jak2, blocked the Epo action only in undifferentiated cells. This reduced neuroprotective function of Epo on SH-SY5Y differentiated cells could be explained at least in part by downregulation of the Epo receptor expression, which was observed in atRA-differentiated cells. This study shows differential cellular protection induced by Epo at two stages of SH-SY5Y differentiation. The results allow us to suggest that this differential cell behavior can be ascribed to the interaction between atRA and the signaling pathways mediated by Epo.

Diabetes mellitus: channeling care through cellular discovery

Diabetes mellitus (DM) impacts a significant portion of the world's population and care for this disorder places an economic burden on the gross domestic product for any particular country. Furthermore, both Type 1 and Type 2 DM are becoming increasingly prevalent and there is increased incidence of impaired glucose tolerance in the young. The complications of DM are protean and can involve multiple systems throughout the body that are susceptible to the detrimental effects of oxidative stress and apoptotic cell injury. For these reasons, innovative strategies are necessary for the implementation of new treatments for DM that are generated through the further understanding of cellular pathways that govern the pathological consequences of DM. In particular, both the precursor for the coenzyme beta-nicotinamide adenine dinucleotide (NAD(+)), nicotinamide, and the growth factor erythropoietin offer novel platforms for drug discovery that involve cellular metabolic homeostasis and inflammatory cell control. Interestingly, these agents and their tightly associated pathways that consist of cell cycle regulation, protein kinase B, forkhead transcription factors, and Wnt signaling also function in a broader sense as biomarkers for disease onset and progression.

Effective targeting of STAT5-mediated survival in myeloproliferative neoplasms using ABT-737 combined with rapamycin

Signal transducer and activator of transcription-5 (STAT5) is a critical transcription factor for normal hematopoiesis and its sustained activation is associated with hematologic malignancy. A persistently active mutant of STAT5 (STAT5a^S711F) associates with Grb2 associated binding protein 2 (Gab2) in myeloid leukemias and promotes growth in vitro through AKT activation. Here we have retrovirally transduced wild-type or Gab2^−/− mouse bone marrow cells expressing STAT5a^S711F and transplanted into irradiated recipient mice to test an in vivo myeloproliferative disease (MPD) model. To target Gab2-independent AKT/mTOR activation, wild-type mice were treated separately with rapamycin. In either case, mice lacking Gab2 or treated with rapamycin displayed attenuated myeloid hyperplasia and modestly improved survival, but the effects were not cytotoxic and were reversible. To improve upon this approach, in vitro targeting of STAT5-mediated AKT/mTOR using rapamycin was combined with inhibition of the STAT5 direct target genes bcl-2 and bcl-X_L using ABT-737. Striking synergy with both drugs was observed in mouse BaF3 cells expressing STAT5a^S711F, TEL-JAK2, or BCR-ABL and in the relatively single agent-resistant human BCR-ABL positive K562 cell line. Therefore, targeting distinct STAT5 mediated survival signals, e.g. bcl-2/bcl-X_L and AKT/mTOR may be an effective therapeutic approach for human myeloproliferative neoplasms.

Insertion of an NPVY sequence into the cytosolic domain of the erythropoietin receptor selectively affects erythropoietin-mediated signalling and function

EPO (erythropoietin), the major hormone regulating erythropoiesis, functions via activation of its cell-surface receptor (EPO-R) present on erythroid progenitor cells. One of the most striking properties of EPO-R is its low expression on the cell surface, as opposed to its high intracellular levels. The low cell-surface expression of EPO-R may thus limit the efficacy of EPO that is routinely used to treat primary and secondary anaemia. In a recent study [Nahari, Barzilay, Hirschberg and Neumann (2008) Biochem. J. 410, 409–416] we have shown that insertion of an NPVY sequence into the intracellular domain of EPO-R increases its cell-surface expression. In the present study we demonstrate that this NPVY EPO-R insert has a selective effect on EPO-mediated downstream signalling in Ba/F3 cells expressing this receptor (NPVY-EPO-R). This is monitored by increased phosphorylation of the NPVY-EPO-R (on Tyr479), Akt, JAK2 (Janus kinase 2) and ERK1/2 (extracellular-signal-regulated kinase 1/2), but not STAT5 (signal transducer and activator of transcription 5), as compared with cells expressing wild-type EPO-R. This enhanced signalling is reflected in augmented proliferation at low EPO levels (0.05 units/ml) and protection against etoposide-induced apoptosis. Increased cell-surface levels of NPVY-EPO-R are most probably not sufficient to mediate these effects as the A234E-EPO-R mutant that is expressed at high cell-surface levels does not confer an augmented response to EPO. Taken together, we demonstrate that insertion of an NPVY sequence into the cytosolic domain of the EPO-R confers not only improved maturation, but also selectively affects EPO-mediated signalling resulting in an improved responsiveness to EPO reflected in cell proliferation and protection against apoptosis.

Gab2 promotes hematopoietic stem cell maintenance and self-renewal synergistically with STAT5

Background

Grb2-associated binding (Gab) adapter proteins play major roles in coordinating signaling downstream of hematopoietic cytokine receptors. In hematopoietic cells, Gab2 can modulate phosphatidylinositol–3 kinase and mitogen associated protein kinase activities and regulate the long-term multilineage competitive repopulating activity of hematopoietic stem cells (HSCs). Gab2 may also act in a linear pathway upstream or downstream of signal transducer and activator of transcription-5 (STAT5), a major positive regulator of HSC function. Therefore, we aimed to determine whether Gab2 and STAT5 function in hematopoiesis in a redundant or non-redundant manner.

Methodology/Principal Findings

To do this we generated Gab2 mutant mice with heterozygous and homozygous deletions of STAT5. In heterozygous STAT5 mutant mice, deficiencies in HSC/multipotent progenitors were reflected by decreased long-term repopulating activity. This reduction in repopulation function was mirrored in the reduced growth response to early-acting cytokines from sorted double mutant c-Kit⁺Lin⁻Sca-1⁺ (KLS) cells. Importantly, in non-ablated newborn mice, the host steady-state engraftment ability was impaired by loss of Gab2 in heterozygous STAT5 mutant background. Fetal liver cells isolated from homozygous STAT5 mutant mice lacking Gab2 showed significant reduction in HSC number (KLS CD150⁺CD48⁻), reduced HSC survival, and dramatic loss of self-renewal potential as measured by serial transplantation.

Conclusions/Significance

These data demonstrate new functions for Gab2 in hematopoiesis in a manner that is non-redundant with STAT5. Furthermore, important synergy between STAT5 and Gab2 was observed in HSC self-renewal, which might be exploited to optimize stem cell-based therapeutics.

Erythropoietin Receptor Signaling Through STAT3 Is Required For Glioma Stem Cell Maintenance

Recombinant erythropoietin (EPO) is a growth factor used in the treatment of chemotherapy-induced anemia, but recent studies suggest that EPO may accelerate cancer growth. Although several cancers express EPO receptors (EPORs), the mechanism by which EPOR promotes tumor growth remains poorly understood. Glioblastomas display a cellular hierarchy of self-renewal and tumor propagation restricted to glioma stem cells (GSCs). We find that GSCs express higher levels of EPOR than matched non-stem glioma cells. Prospective enrichment for EPOR on GSCs increased neurosphere formation, suggesting that EPOR can select for a subset of GSCs with increased self-renewal capacity. Targeting EPOR expression with lentiviral mediated short hairpin RNA (shRNA) reduced GSC growth, survival, and neurosphere formation capacity, defining a crucial role for EPOR in GSC maintenance. We further find that STAT3 is an important mediator of EPOR signals in GSCs. EPOR knockdown attenuated the basal activation of STAT3 present in GSCs, and a small molecule inhibitor of STAT3 reduced GSC growth and survival. EPOR signaling was critical for survival in vivo, as targeting EPOR expression decreased GSC tumorigenic potential. Elevated EPOR expression also associated with poor patient outcome. Thus, EPOR on GSCs promotes tumor growth and may explain the poor survival of cancer patients treated with EPO.

STAT5 activation is critical for the transformation mediated by myeloproliferative disorder-associated JAK2 V617F mutant

It has been well established that disruption of JAK2 signaling regulation is involved in various hematopoietic disorders; however, the detailed mechanism by which abnormal activation of JAK2 exhibits transforming activity remains to be elucidated. Here, to clarify the functional role of the erythropoietin receptor (EpoR) and its downstream transcription factor STAT5 in the abnormal activation of JAK2-induced hematopoietic diseases, we generated a stable transfectant of Ba/F3 cells expressing EpoR and analyzed the molecular mechanism of how JAK2 mutation induces cell growth disorder. JAK2 V617F mutant exhibited transforming activity when EpoR was coexpressed. According to a study utilizing several truncated mutants of EpoR, the ability of EpoR to facilitate the transforming activity of JAK2 V617F mutant required the intracellular domain to interact with STAT5. Strikingly, once the truncated EpoR (EpoR-H) was mutated on Tyr-343, the phosphorylation of which is known to be important for interaction with STAT5, JAK2 V617F mutant failed to exhibit transforming activity, suggesting that STAT5 is critical for JAK2 mutant-induced hematopoietic disorder. Furthermore, the expression of the constitutively active STAT5 mutant exhibited transforming activity in Ba/F3 cells, and short hairpin RNA-mediated knockdown of STAT5 significantly inhibited the transforming activity of JAK2 V617F mutant. Taking these observations together, STAT5 plays an essential role in EpoR-JAK2 V617F mutant-induced hematopoietic disorder. Although it remains unclear why the presence of EpoR is required to activate oncogenic signaling via the JAK2 mutant and STAT5, its interacting ability is a target for the treatment of these hematopoietic diseases.

Erythropoietin: a multimodal neuroprotective agent

The tissue protective functions of the hematopoietic growth factor erythropoietin (EPO) are independent of its action on erythropoiesis. EPO and its receptors (EPOR) are expressed in multiple brain cells during brain development and upregulated in the adult brain after injury. Peripherally administered EPO crosses the blood-brain barrier and activates in the brain anti-apoptotic, anti-oxidant and anti-inflammatory signaling in neurons, glial and cerebrovascular endothelial cells and stimulates angiogenesis and neurogenesis. These mechanisms underlie its potent tissue protective effects in experimental models of stroke, cerebral hemorrhage, traumatic brain injury, neuroinflammatory and neurodegenerative disease. The preclinical data in support of the use of EPO in brain disease have already been translated to first clinical pilot studies with encouraging results with the use of EPO as a neuroprotective agent.

Experimental Models of Acute Renal Failure and Erythropoietin: What Evidence of a Direct Effect?

The kidney can achieve a structural and functional recovery after the damage induced by ischemia and reperfusion. This is due to the regeneration of epithelial tubular cells, the intervention of immature cells mainly localized in the medulla, and a small number of bone marrow-derived stem cells. In many instances, however, recovery is delayed or does not occur at all. The mechanisms allowing the renal cells to de-differentiate still need to be clarified in order to find a therapeutic approach that can amplify this ability and then stop the fibroid involution and the progression toward renal failure. Several authors have hypothesized a protective effect of EPO against ischemic and cytotoxic renal damage and observed that patients precociously treated with EPO showed a slower progression of renal failure. EPO has been demonstrated to have proliferative and anti-apoptotic effects in ischemia-reperfusion models in the brain and cell cultures. Moreover, EPO can mobilize stem cells and increase the plasmatic levels and the renal expression of VEGF. These effects seem to be dose-dependent and could be due to the activation of signal transduction systems, like Jak and STAT. In the presence of high doses of exogenous EPO or during the treatment with long-acting EPO-like molecules, non-specific receptors may be activated through a low-affinity link. Further investigations are needed to determine new therapeutic applications for EPO and other analogous hormones. Very long-acting molecules or molecules with cyto-protective but no erythropoietic effect may represent useful tools in the study of the molecular mechanisms underlying EPO's action and may have a rapid and safe therapeutic application.

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

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