EPO receptor-mediated ERK kinase and NF-kappaB activation in erythropoietin-promoted differentiation of astrocytes

Interleukin 3 Inhibits Glutamate-Cytotoxicity in Neuroblastoma Cell Line

Interleukin 3 (IL-3) is a well-known pleiotropic cytokine that regulates the proliferation and differentiation of hematopoietic progenitor cells, triggering classical signaling pathways such as JAK/STAT, Ras/MAPK, and PI3K/Akt to carry out its functions. Interestingly, the IL-3 receptor is also expressed in non-hematopoietic cells, playing a crucial role in cell survival. Our previous research demonstrated the expression of the IL-3 receptor in neuron cells and its protective role in neurodegeneration. Glutamate, a principal neurotransmitter in the central nervous system, can induce cellular stress and lead to neurotoxicity when its extracellular concentrations surpass normal levels. This excessive glutamate presence is frequently observed in various neurological diseases. In this study, we uncover the protective role of IL-3 as an inhibitor of glutamate-induced cell death, analyzing the cytokine's signaling pathways during its protective effect. Specifically, we examined the relevance of JAK/STAT, Ras/MAPK, and PI3 K signaling pathways in the molecular mechanism triggered by IL-3. Our results show that the inhibition of JAK, ERK, and PI3 K signaling pathways, using pharmacological inhibitors, effectively blocked IL-3's protective role against glutamate-induced cell death. Additionally, our findings suggest that Bcl-2 and Bax proteins may be involved in the molecular mechanism triggered by IL-3. Our investigation into IL-3's ability to protect neuronal cells from glutamate-induced damage offers a promising therapeutic avenue with potential clinical implications for several neurological diseases characterized by glutamate neurotoxicity.

EPO regulates neuronal differentiation of adult human neural-crest derived stem cells in a sex-specific manner

BACKGROUND

Sexual differences in the biology of human stem cells are increasingly recognized to influence their proliferation, differentiation and maturation. Especially in neurodegenerative diseases such as Alzheimers disease (AD), Parkinson's disease (PD) or ischemic stroke, sex is a key player for disease progression and recovery of damaged tissue. Recently, the glycoprotein hormone erythropoietin (EPO) has been implicated as a regulator of neuronal differentiation and maturation in female rats.

METHODS

In this study, we used adult human neural crest-derived stem cells (NCSCs) as a model system for exploring potential sex specific effects of EPO on human neuronal differentiation. We started with expression validation of the specific EPO receptor (EPOR) by performing PCR analysis in the NCSCs. Next, EPO mediated activation of nuclear factor-κB (NF-κB) via Immunocytochemistry (ICC) was performed, followed by investigating the sex-specific effects of EPO on neuronal differentiation by determining morphological changes in axonal growth and neurite formation accompanied by ICC.

RESULTS

Undifferentiated male and female NCSCs showed a ubiquitous expression of the EPO receptor (EPOR). EPO treatment resulted in a statistically profound (male p = 0.0022, female p = 0.0012) nuclear translocation of NF-κB RELA in undifferentiated NCSCs of both sexes. But after one week of neuronal differentiation, we could show a highly significant (p = 0,0079) increase of nuclear NF-κB RELA in females only. In contrast, we observed a strong decrease (p = 0,0022) of RELA activation in male neuronal progenitors. Extending the view on the role of sex during human neuronal differentiation, here we demonstrate a significant increase of axon lengths in female NCSCs-derived neurons upon EPO-treatment (+ EPO: 167,73 (SD = 41,66) µm, w/o EPO: 77,68 (SD = 18,31) µm) compared to their male counterparts (+ EPO: 68,37 (SD = 11,97) µm, w/o EPO: 70,23 (SD = 12,89) µm).

CONCLUSION

Our present findings therefore show for the first time an EPO-driven sexual dimorphism in neuronal differentiation of human neural-crest derived stem cells and emphasize sex-specific variability as a crucial parameter in stem cell biology and for treating neurodegenerative diseases.

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.

Erythropoietin regulates signaling pathways associated with neuroprotective events

Erythropoietin is a cytokine that binds to the Erythropoietin receptor and regulates the formation of erythroid cells during erythropoiesis in the bone marrow. However, many other organs and tissues express Erythropoietin and its receptor, such as the Nervous System, which principally regulates tissue protection. In the Central Nervous System, Erythropoietin is principally expressed by astrocytes, while neurons mainly express Erythropoietin receptors. Moreover, Erythropoietin acts as a pleiotropic molecule with neuroprotective effects, and its mechanisms of signal transduction pathways are defined, and there is a growing interest in its therapeutic potential. This review focuses on the role of Erythropoietin and its relationship with HIF1, PI3/Akt, GSK3B, JAK/STAT, and MAPKs signaling pathways that leads to cell survival after injury in the Central Nervous System. Knowledge of these signaling systems comprehensively could better guide EPO treatment to restoring different SNC alterations mediated by different insults.

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.

Differential effects of MEK inhibitors on rat neural stem cell differentiation: Repressive roles of MEK2 in neurogenesis and induction of astrocytogenesis by PD98059

Neural stem cells (NSCs) proliferate and differentiate into neurons and glia depending on the culture environment. However, the underlying mechanisms determining the fate of NSCs are not fully understood. Growth factors facilitate NSC proliferation through mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) and MAPK activation, and NSCs differentiate into neurons, astrocytes, or oligodendrocytes when mitogens are withdrawn from the culture media. Here, we aimed to identify the effects and roles of MEK signaling on the determination of NSC fate. MEK inhibitors, U0126, SL327, and PD98059, had differential effects on NSC differentiation. U0126 and SL327, which are known to inhibit MEK1 and MEK2, induced neuronal differentiation, whereas PD98059, which is reported to preferentially inhibit MEK1 at higher concentrations, increased astrocytogenesis. Knockdown of MEK2 using small interfering RNA increased neurogenesis and over-expression of wild type (WT) MEK2 inhibited neurogenesis, suggesting a repressive role of MEK2 in neuronal differentiation. The chemical structure of PD98059 appears to be important for induction of astrocytogenesis because not only PD98059 (2'-amino-3'-methoxyflavone) but also its chemical structural mimetic, 3'-methoxyflavone, enhanced astrocytogenesis. Therefore, in our study, we suggest that MEK inhibitors have distinct functions in determining NSC fate. Inhibition of MEK2 is important for induction of neurogenesis in NSCs. U0126 and SL327 increase neurogenesis through MEK2 inhibition, whereas PD98059 induced astrocytogenesis in NSCs, which is mediated by the chemical structure, particularly the 3'-methoxy group rather than its renowned MEK1 inhibition.

Neuroprotective effect of a new variant of Epo nonhematopoietic against oxidative stress

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.

Concordance of Several Subcellular Interactions Initiates Alzheimer's Dementia: Their Reversal Requires Combination Treatment

The pathogenesis of Alzheimer's disease involves multiple pathways that, at the macrolevel, include decreased proliferation plus increased loss affecting neurons, astrocytes, and capillaries and, at the subcellular level, involve several elements: amyloid/amyloid precursor protein, presenilins, the unfolded protein response, the ubiquitin/proteasome system, the Wnt/catenin system, the Notch signaling system, mitochondria, mitophagy, calcium, and tau. Data presented show the intimate, anatomical interactions between neurons, astrocytes, and capillaries; the interactions between the several subcellular factors affecting those cells; and the treatments that are currently available and that might correct dysfunctions in the subcellular factors. Available treatments include lithium, valproate, pioglitazone, erythropoietin, and prazosin. Since the subcellular pathogenesis involves multiple interacting elements, combination treatment would be more effective than administration of a single drug directed at only 1 element. The overall purpose of this presentation is to describe the pathogenesis in detail and to explain the proposed treatments.

The Indispensable Roles of Microglia and Astrocytes during Brain Development

Glia are essential for brain functioning during development and in the adult brain. Here, we discuss the various roles of both microglia and astrocytes, and their interactions during brain development. Although both cells are fundamentally different in origin and function, they often affect the same developmental processes such as neuro-/gliogenesis, angiogenesis, axonal outgrowth, synaptogenesis and synaptic pruning. Due to their important instructive roles in these processes, dysfunction of microglia or astrocytes during brain development could contribute to neurodevelopmental disorders and potentially even late-onset neuropathology. A better understanding of the origin, differentiation process and developmental functions of microglia and astrocytes will help to fully appreciate their role both in the developing as well as in the adult brain, in health and disease.

AG490 suppresses EPO-mediated activation of JAK2-STAT but enhances blood flow recovery in rats with critical limb ischemia

Background

Erythropoietin (EPO) has been demonstrated to enhance recovery in ischemic organs through enhancing angiogenesis. In this study, we used an experimental critical limb ischemia (CLI) rat model to reveal the underlying mechanisms and directly examine the benefits of the anti-apoptotic capacity of EPO in the acute phase of limb ischemia and following blood flow recovery.

Methods

To determine the role of the JAK2/STAT pathway in EPO-enhanced recovery after CLI, male Sprague-Dawley rats (n = 8 for each group) were divided into group 1 (normal control), group 2 (CLI treated with normal saline), group 3 (CLI treated with EPO), group 4 (CLI treated with AG490, a JAK2 inhibitor), and group 5 (CLI treated with EPO and AG490). Animals were sacrificed either at day 1 or day 14 and biochemical and histopathological examination of ischemic quadriceps were conducted.

Results

At day 1, EPO administration reduced expression levels of apoptotic indices and activated the JAK2/STAT pathway; this activation was inhibited by additional AG490 treatment. Furthermore, the decrease in the size of the infarcted area, as well as activation of ERK1/2 and JNK showed similar regulatory trends with EPO or AG490 treatment. Of Interest, EPO and AG490 in combination showed a synergistic effect, increasing expression levels of antioxidants (GR, GPx, NQO-1) and decreasing transcriptional levels of pro-inflammatory factors (TNF-α, NF-kB). At day 14, laser Doppler analysis showed that the blood flow recovery was enhanced by EPO, AG490, or combined treatment.

Conclusion

Although inhibition of the JAK2/STAT pathways reduces the anti-apoptotic effects of EPO in the early phase of CLI, the benefits of AG490 in anti-inflammation and anti-oxidation still play a positive role in enhancing blood flow recovery after CLI.

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.

Connective-Tissue Growth Factor (CTGF/CCN2) Induces Astrogenesis and Fibronectin Expression of Embryonic Neural Cells In Vitro

Connective-tissue growth factor (CTGF) is a modular secreted protein implicated in multiple cellular events such as chondrogenesis, skeletogenesis, angiogenesis and wound healing. CTGF contains four different structural modules. This modular organization is characteristic of members of the CCN family. The acronym was derived from the first three members discovered, cysteine-rich 61 (CYR61), CTGF and nephroblastoma overexpressed (NOV). CTGF is implicated as a mediator of important cell processes such as adhesion, migration, proliferation and differentiation. Extensive data have shown that CTGF interacts particularly with the TGFβ, WNT and MAPK signaling pathways. The capacity of CTGF to interact with different growth factors lends it an important role during early and late development, especially in the anterior region of the embryo. ctgf knockout mice have several cranio-facial defects, and the skeletal system is also greatly affected due to an impairment of the vascular-system development during chondrogenesis. This study, for the first time, indicated that CTGF is a potent inductor of gliogenesis during development. Our results showed that in vitro addition of recombinant CTGF protein to an embryonic mouse neural precursor cell culture increased the number of GFAP- and GFAP/Nestin-positive cells. Surprisingly, CTGF also increased the number of Sox2-positive cells. Moreover, this induction seemed not to involve cell proliferation. In addition, exogenous CTGF activated p44/42 but not p38 or JNK MAPK signaling, and increased the expression and deposition of the fibronectin extracellular matrix protein. Finally, CTGF was also able to induce GFAP as well as Nestin expression in a human malignant glioma stem cell line, suggesting a possible role in the differentiation process of gliomas. These results implicate ctgf as a key gene for astrogenesis during development, and suggest that its mechanism may involve activation of p44/42 MAPK signaling. Additionally, CTGF-induced differentiation of glioblastoma stem cells into a less-tumorigenic state could increase the chances of successful intervention, since differentiated cells are more vulnerable to cancer treatments.

The neuroprotective and neurorescue effects of carbamylated erythropoietin Fc fusion protein (CEPO-Fc) in a rat model of Parkinson's disease

Parkinson's disease is characterized by progressive degeneration of dopaminergic neurons. Thus the development of therapeutic neuroprotection and neurorescue strategies to mitigate disease progression is important. In this study we evaluated the neuroprotective/rescue effects of erythropoietin Fc fusion protein (EPO-Fc) and carbamylated erythropoietin Fc fusion protein (CEPO-Fc) in a rat model of Parkinson's disease. Adult female Sprague-Dawley rats received intraperitoneal injection of EPO-Fc, CEPO-Fc or PBS. Behavioral evaluations consisted of rota-rod, cylinder and amphetamine-induced rotation tests. In the neuroprotection experiment, the CEPO-Fc group demonstrated significant improvement compared with the EPO-Fc group on the amphetamine-induced rotation test throughout the four-week follow-up period. Histologically, significantly more tyrosine hydroxylase (TH)-positive neurons were recognized in the substantia nigra (SN) pars compacta in the CEPO-Fc group than in the PBS and EPO-Fc groups. In the neurorescue experiment, rats receiving CEPO-Fc showed significantly better behavioural scores than those receiving PBS. The histological data concerning striatum also showed that the CEPO-Fc group had significantly better preservation of TH-positive fibers compared to the PBS and EPO-Fc groups. Importantly, there were no increases in hematocrit or hemoglobin levels in the CEPO-Fc group in either the neuroprotection or the neurorescue experiments. In conclusion, the newly developed CEPO-Fc might confer neuroprotective and neurorescue benefits in a rat model of Parkinson's disease without the side effects associated with polycythemia. CEPO-Fc might be a therapeutic tool for patients with Parkinson's disease.

Erythropoietin-driven signalling and cell migration mediated by polyADP-ribosylation

Background:

Recombinant human erythropoietin (EPO) is the leading biotechnology engineered hormone for treatment of anaemia associated with chronic conditions including kidney failure and cancer. The finding of EPO receptors on cancer cells has raised the concern that in addition to its action in erythropoiesis, EPO may promote tumour cell growth. We questioned whether EPO-induced signalling and consequent malignant cell manifestation is mediated by polyADP-ribosylation.

Methods:

Erythropoietin-mediated PARP (polyADP-ribose polymerase-1) activation, gene expression and core histone H4 acetylation were examined in UT7 cells, using western blot analysis, RT–PCR and immunofluorescence. Erythropoietin-driven migration of the human breast epithelial cell line MDA-MB-435 was determined by the scratch assay and in migration chambers.

Results:

We have found that EPO treatment induced PARP activation. Moreover, EPO-driven c-fos and Egr-1 gene expression as well as histone H4 acetylation were mediated via polyADP-ribosylation. Erythropoietin-induced cell migration was blocked by the PARP inhibitor, ABT-888, indicating an essential role for polyADP-ribosylation in this process.

Conclusions:

We have identified a novel pathway by which EPO-induced gene expression and breast cancer cell migration are regulated by polyADP-ribosylation. This study introduces new possibilities regarding EPO treatment for cancer-associated anaemia where combining systemic EPO treatment with targeted administration of PARP inhibitors to the tumour may allow safe treatment with EPO, minimising its possible undesirable proliferative effects on the tumour.

Inhibitory effect of 4-O-methylhonokiol on lipopolysaccharide-induced neuroinflammation, amyloidogenesis and memory impairment via inhibition of nuclear factor-kappaB in vitro and in vivo models

Background

Neuroinflammation is important in the pathogenesis and progression of Alzheimer disease (AD). Previously, we demonstrated that lipopolysaccharide (LPS)-induced neuroinflammation caused memory impairments. In the present study, we investigated the possible preventive effects of 4-O-methylhonokiol, a constituent of Magnolia officinalis, on memory deficiency caused by LPS, along with the underlying mechanisms.

Methods

We investigated whether 4-O-methylhonokiol (0.5 and 1 mg/kg in 0.05% ethanol) prevents memory dysfunction and amyloidogenesis on AD model mice by intraperitoneal LPS (250 μg/kg daily 7 times) injection. In addition, LPS-treated cultured astrocytes and microglial BV-2 cells were investigated for anti-neuroinflammatory and anti-amyloidogenic effect of 4-O-methylhonkiol (0.5, 1 and 2 μM).

Results

Oral administration of 4-O-methylhonokiol ameliorated LPS-induced memory impairment in a dose-dependent manner. In addition, 4-O-methylhonokiol prevented the LPS-induced expression of inflammatory proteins; inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) as well as activation of astrocytes (expression of glial fibrillary acidic protein; GFAP) in the brain. In in vitro study, we also found that 4-O-methylhonokiol suppressed the expression of iNOS and COX-2 as well as the production of reactive oxygen species, nitric oxide, prostaglandin E₂, tumor necrosis factor-α, and interleukin-1β in the LPS-stimulated cultured astrocytes. 4-O-methylhonokiol also inhibited transcriptional and DNA binding activity of NF-κB via inhibition of IκB degradation as well as p50 and p65 translocation into nucleus of the brain and cultured astrocytes. Consistent with the inhibitory effect on neuroinflammation, 4-O-methylhonokiol inhibited LPS-induced Aβ_1-42 generation, β- and γ-secretase activities, and expression of amyloid precursor protein (APP), BACE1 and C99 as well as activation of astrocytes and neuronal cell death in the brain, in cultured astrocytes and in microglial BV-2 cells.

Conclusion

These results suggest that 4-O-methylhonokiol inhibits LPS-induced amyloidogenesis via anti-inflammatory mechanisms. Thus, 4-O-methylhonokiol can be a useful agent against neuroinflammation-associated development or the progression of AD.

Erythropoietin molecules to treat acute ischemic stroke: a translational dilemma!

IMPORTANCE OF THE FIELD

Since the realization that erythropoietin (EPO) molecules have 'neuroprotective' properties, they have been investigated as treatments for acute ischemic stroke (AIS), but not systematically. The results of the 2009 clinical trial showed that EPO was ineffective as a stroke treatment, and moreover, increased mortality when combined with tissue plasminogen activator. Currently, CEPO, an EPO analog, is entering into a safety, tolerability and pharmacokinetic clinical trial for the treatment of AIS.

AREAS COVERED IN THIS REVIEW

This review covers translational and clinical studies carried out over the period 1998 - 2010.

WHAT THE READER WILL GAIN

The primary aim of this article is to review the information available regarding the pharmacological and biological characteristics of EPO molecules. Second, based upon the translational research with EPO molecules in preclinical stroke models, a recommendation is made regarding the continued development of EPO molecules as an option to treat AIS.

TAKE HOME MESSAGE

EPO, CEPO and helix B peptide EPO analogs have significant neuroprotective activity is preclinical stroke models. However, given the detrimental effect of EPO in a recent clinical trial, preclinical safety studies of EPO molecules in embolic stroke models that parallel acute ischemic stroke in humans are warrented.

Erythropoietin protects intestinal epithelial barrier function and lowers the incidence of experimental neonatal necrotizing enterocolitis

The impermeant nature of the intestinal barrier is maintained by tight junctions (TJs) formed between adjacent intestinal epithelial cells. Disruption of TJs and loss of barrier function are associated with a number of gastrointestinal diseases, including neonatal necrotizing enterocolitis (NEC), the leading cause of death from gastrointestinal diseases in preterm infants. Human milk is protective against NEC, and the human milk factor erythropoietin (Epo) has been shown to protect endothelial cell-cell and blood-brain barriers. We hypothesized that Epo may also protect intestinal epithelial barriers, thereby lowering the incidence of NEC. Our data demonstrate that Epo protects enterocyte barrier function by supporting expression of the TJ protein ZO-1. As immaturity is a key factor in NEC, Epo regulation of ZO-1 in the human fetal immature H4 intestinal epithelial cell line was examined and demonstrated Epo-stimulated ZO-1 expression in a dose-dependent manner through the PI3K/Akt pathway. In a rat NEC model, oral administration of Epo lowered the incidence of NEC from 45 to 23% with statistical significance. In addition, Epo treatment protected intestinal barrier function and prevented loss of ZO-1 at the TJs in vivo. These effects were associated with elevated Akt phosphorylation in the intestine. This study reveals a novel role of Epo in the regulation of intestinal epithelial TJs and barrier function and suggests the possible use of enteral Epo as a therapeutic agent for gut diseases.

Effects of asialo-erythropoietin on pain-related behavior and expression of phosphorylated-p38 map kinase and tumor necrosis factor-alpha induced by application of autologous nucleus pulposus on nerve root in rat

STUDY DESIGN

this study was designed to examine the neuroprotective effects of asialo-erythropoietin (A-EPO) in a rat model of lumbar disc herniation.

OBJECTIVE

to investigate the effects of A-EPO on pain-related behavior, the expression of phosphorylated-p38 (p-p38) mitogen activated kinase, and the expression of tumor necrosis factor alpha (TNF-α) induced by nucleus pulposus (NP) application on the nerve root.

SUMMARY OF BACKGROUND DATA

erythropoietin (EPO) has neuroprotective effects in a variety of models of central and peripheral nerve injuries. However, EPO is a hematopoietic growth factor and can therefore cause significant side effects such as thicker blood and promotion of blood clotting. A-EPO is a neuroprotective derivative of EPO that is not hematopoietic.

METHODS

female Sprague-Dawley rats (n = 149) were used in this study. NP harvested from the tail was applied to the left L5 nerve root and the rats were then divided into four groups: NP + nontreatment group, no further treatment; NP + A-EPO group, 13.4 microg/kg A-EPO; NP + EPO group, 13.4 microg/kg EPO; and NP + vehicle group, received vehicle. The substances were administered subcutaneously 1 day before surgery and daily for 2 weeks. In the sham group of animals, the L5 nerve root was exposed and NP was not applied. Withdrawal thresholds were determined by the von-Frey test 28 days after surgery. The expressions of p-p38 and TNF-α were assessed by immunohistochemical and immunoblotting analysis. Data were analyzed by unpaired Student t test and Dunnett t test (significance level, P < 0.05).

RESULTS

in the NP + nontreatment and NP + vehicle groups, withdrawal thresholds were decreased significantly for 28 days compared with the sham group (P < 0.05). In the NP + A-EPO group, the thresholds were significantly increased on day 28, and in the NP + EPO group, the thresholds were significantly increased on days 21 and 28 (P < 0.05) compared with the NP + nontreatment and NP + vehicle groups. The expression of p-p38 in the NP + A-EPO group was significantly lower than that in the NP + vehicle group on day 1 (P < 0.05). The expression of TNF in the NP + A-EPO and NP + EPO groups was significantly lower than that in the NP + vehicle group on days 1 and 7 (P < 0.05).

CONCLUSIONS

A-EPO improved pain-related behavior and reduced the expression of p-p38 and TNF-α. The effect of A-EPO may be related to the inhibitory action of p-p38 and TNF-α in the dorsal root ganglion.

Embryonic stem cells inhibit expression of erythropoietin in the injured spinal cord

Recent observations have demonstrated neuroprotective role of erythropoietin (Epo) and Epo receptor in the central nervous system. Here we examined Epo function in the murine spinal cord after transplantation of pluripotent mouse embryonic stem (ES) cells pre-differentiated towards neuronal type following spinal cord injury. Expression of Epo was measured at both mRNA and protein levels in the ES cells as well as in the spinal cords after 1 and 7 days. Our data demonstrated that expression of Epo mRNA, as well as its protein content, in ES cells was significantly decreased after differentiation procedure. In the spinal cords, analysis showed that Epo mRNA level was significantly decreased after 1 day of ES cell injections in comparison to media-injected control. Epo protein level detected by Western blot was diminished as well. Examination of Epo production in the injured spinal cords after media or ES cells injections by indirect immunofluorescence showed increased Epo-immunopositive staining after media injections 1 day after injection. In contrast, ES cell transplantation did not induce Epo expression. Seven days after ES cell injections, Epo-immunopositive cells' distribution in the ipsilateral side was not changed, while the intensity of immunostaining on the contralateral side was increased, approaching levels in control media-injected tissues. Our data let us to presume that previously described immediate positive effects of ES cells injected into the injured zone of spinal cord are not based on Epo, but on other factors or hormones, which should be elucidated further.

Neurotrophic activity of obovatol on the cultured embryonic rat neuronal cells by increase of neurotrophin release through activation of ERK pathway

Previously, we found that obovatol, a lignan compound isolated from Magnolia officinalis, has anti-cancer, anti-inflammatory, and anxiolytic effects. Recent studies showed that honokiol, magnolol, and 4-O-methylhonokiol, lignin compounds isolated from the Magnolia family have neurotrophic activity. In this study, we examined whether or not obovatol also exhibits neurite-promoting effects on rat embryonic neuronal cells. Obovatol increased neurite outgrowth in a concentration-dependent manner. Consistent with the neurite outgrowth effect, the expression of neurite differentiation markers also increased in response to obovatol. We also found that obovatol increased levels of NGF and BDNF released into the culture medium. In addition, the combination of low concentrations of obovatol (1 and 2 μM) with NGF (50 ng/ml) or with BDNF (10 ng/ml) greatly enhanced neurite outgrowth. Subsequently, we found that obovatol increased phosphorylation of ERK. However, the neurite outgrowth, and NGF and BDNF release induced by obovatol were prevented by an ERK-specific inhibitor. These results suggest that obovatol promotes neurite outgrowth due to the increased release of neurotrophic factors via activation of the ERK pathway.

Immunohistochemical detection of phosphorylated JAK-2 and STAT-5 proteins and correlation with erythropoietin receptor (EpoR) expression status in human brain tumors

Phosphorylated (activated) forms of Janus Kinase 2 (pJAK-2) and STAT-5 transcription factor (pSTAT-5), which are preferentially expressed after binding of erythropoietin (Epo) to its receptor EpoR, are known to be implicated in the molecular mechanisms controlling brain development. The purpose of this study was to investigate the expression of these proteins (pJAK-2, pSTAT-5, and EpoR) in human brain tumors compared with normal brain. Using specific antibodies and immunohistochemistry on formalin-fixed, paraffin-embedded semi-serial tissue sections a total of 87 human brain tumors and samples from normal brain tissue were studied. pJAK-2/pSTAT-5 nuclear co-expression was detected in 39% of astrocytomas, 43% of oligodendrogliomas, 50% of ependymomas, and in all (100%) of the medulloblastomas examined. In contrast, most of the meningiomas showed weak or no immunoreactivity for pJAK-2/pSTAT-5 proteins. A significant percentage of tumors exhibited pSTAT-5 immunoreactivity, being pJAK-2 immunonegative. EpoR/pJAK-2/pSTAT-5 co-expression was detected in a small percentage of astrocytomas (18%) and ependymomas (33%). Oligodendrogliomas and medulloblastomas were EpoR immunonegative. Tumor vessels exhibited EpoR, pJAK-2, and pSTAT-5 immunoreactivity. In normal brain tissue, EpoR immunoreactivity was detected in neurons and vessels whereas pSTAT-5 and pJAK-2 immunoreactivity was limited to some neurons and a few glial cells, respectively. These results indicate the existence of ligand (other than Epo)-dependent or independent JAK-2 activation that leads to constitutive activation of STAT-5 in most human brain tumors. Given the oncogenic potential of the JAK/STAT pathway, detection of different pJAK-2 and pSTAT-5 expression profiles between groups of tumors may reflect differences in the biological behavior of the various human brain tumors.

Erythropoietin modulation of astrocyte water permeability as a component of neuroprotection

Disturbed brain water homeostasis with swelling of astroglial cells is a common complication in stroke, trauma, and meningitis and is considered to be a major cause of permanent brain damage. Astroglial cells possess the water channel aquaporin 4 (AQP4). Recent studies from our laboratory have shown that glutamate, acting on group I metabotropic glutamate receptors (mGluRs), increases the permeability of astrocyte AQP4, which, in situations of hypoxia-ischemia, will increase astrocyte water uptake. Here we report that erythropoietin (EPO), which in recent years has emerged as a potent neuro-protective agent, antagonizes the effect of a group I mGluR agonist on astrocyte water permeability. Activation of group I mGluRs triggers fast and highly regular intracellular calcium oscillations and we show that EPO interferes with this signaling event by altering the frequency of the oscillations. These effects of EPO are immediate, in contrast to the neuroprotective effects of EPO that are known to depend upon gene activation. Our findings indicate that EPO may directly reduce the risk of astrocyte swelling in stroke and other brain insults. In support of this conclusion we found that EPO reduced the neurological symptoms in a mouse model of primary brain edema known to depend upon AQP4 water transport.

Protective effects of erythropoietin on tau phosphorylation induced by beta-amyloid

Neuropathological studies have demonstrated that the presence of neurofibrillary tangles (NFTs) is one of the most prominent pathologic characteristics of Alzheimer's disease (AD). The microtubule-associated protein tau is the major component of NFTs, and its abnormal hyperphosphorylation leads to the destabilization of microtubules, impaired axonal transport, and eventual death of the neurons. The hematopoietic cytokine erythropoietin (Epo) is now considered as a viable agent with regard to central nervous system injury in a variety of cellular systems. Here we report that Epo prevented tau hyperphosphorylation in SH-SY5Y cells exposed to the beta-amyloid peptide and that this effect may depend on the PI3K/Akt-GSK-3beta pathway. This study provides new molecular insight into the neuroprotective effect of Epo and suggests its possible therapeutic role in the management of AD.

Neuro-inflammation induced by lipopolysaccharide causes cognitive impairment through enhancement of beta-amyloid generation

Background

Alzheimer's disease (AD) is characterized by extensive loss of neurons in the brain of AD patients. Intracellular accumulation of beta-amyloid peptide (Aβ) has also shown to occur in AD. Neuro-inflammation has been known to play a role in the pathogenesis of AD.

Methods

In this study, we investigated neuro-inflammation and amyloidogenesis and memory impairment following the systemic inflammation generated by lipopolysaccharide (LPS) using immunohistochemistry, ELISA, behavioral tests and Western blotting.

Results

Intraperitoneal injection of LPS, (250 μg/kg) induced memory impairment determined by passive avoidance and water maze tests in mice. Repeated injection of LPS (250 μg/kg, 3 or 7 times) resulted in an accumulation of Aβ_1–42 in the hippocampus and cerebralcortex of mice brains through increased β- and γ-secretase activities accompanied with the increased expression of amyloid precursor protein (APP), 99-residue carboxy-terminal fragment of APP (C99) and generation of Aβ_1–42 as well as activation of astrocytes in vivo. 3 weeks of pretreatment of sulindac sulfide (3.75 and 7.5 mg/kg, orally), an anti-inflammatory agent, suppressed the LPS-induced amyloidogenesis, memory dysfunction as well as neuronal cell death in vivo. Sulindac sulfide (12.5–50 μM) also suppressed LPS (1 μg/ml)-induced amyloidogenesis in cultured neurons and astrocytes in vitro.

Conclusion

This study suggests that neuro-inflammatory reaction could contribute to AD pathology, and anti-inflammatory agent could be useful for the prevention of AD.

Erythropoietin promotes axonal growth in a model of neuronal polarization

Erythropoietin (EPO) enhances neurogenesis, neuroprotection and regeneration. Here, we examined the effects of EPO on axonal and dendritic growth in a model of neuronal polarization. EPO did not effect survival or the polarized morphology of hippocampal neurons but its effect on neurite outgrowth depended upon the stage of polarization. When added to neurons in the process of establishing polarity (0-2 days in vitro (DIV)), it enhanced axonal and dendritic growth, while EPO added to early polarized cultures at 3-4 DIV promoted the growth of axons but not dendrites. EPO stimulated the phosphorylation of Akt at serine-473 and co-incubation of the Akt/PI-3 kinase pathway inhibitor LY294002 with EPO abolished its effects on Akt phosphorylation and axonal growth. However, while Leukemia Inhibitory Factor (LIF) similarly stimulated phosphorylation of Akt, it had no effect on axonal or dendritic growth, indicating that AKT phosphorylation is necessary but not sufficient for neurite outgrowth in hippocampal neurons.

Erythropoietin prevents PC12 cells from 1-methyl-4-phenylpyridinium ion-induced apoptosis via the Akt/GSK-3beta/caspase-3 mediated signaling pathway

Apoptosis is a contributing cause of dopaminergic neuron loss in Parkinson disease. Recent work has shown that erythropoietin (EPO) offers protection against apoptosis in a wide variety of tissues. We demonstrate that exposure of PC12 cells to 1-methyl-4-phenylpyridinium ion (MPP(+)) with recombinant human EPO, significantly decreased apoptosis as measured by TUNEL and caspase-3 activity when compared to MPP(+) treatment alone. EPO induced sustained phosphorylation of Akt and its substrate, GSK-3beta, reduced caspase-3 activities in PC12 cells. The anti-apoptotic effect of EPO was abrogated by co-treatment with LY294002, the specific blocker of phosphatidylinositol 3-kinase (PI3K). The effects of EPO on GSK-3beta and caspase-3 activities were also blocked by LY294002. LiCl, the inhibitor of GSK-3beta, downregulated the caspase-3 activity and blocked the apoptosis induced by MPP(+). Finally, we determined that EPO transiently activated the ERK signaling pathway, but PD98059, a specific inhibitor of ERK, does not alter the survival effect of EPO in this model system. Thus, these findings indicate that EPO protects against apoptosis in PC12 cells exposed to MPP(+), through the Akt/GSK-3beta/caspase-3 signaling pathway, but the ERK pathway is not involved in the EPO-dependent survival enhancing effect in this model system.

Functional and immunochemical characterisation of different antibodies against the erythropoietin receptor

Since it was discovered that the hematopoietic hormone erythropoetin (EPO) exerts neuroprotective effects in the CNS, many studies on the EPO receptor (EPOR) function and localisation in the CNS have been performed. For this purpose, commercially available anti-EPOR antibodies have often been applied. As the literature data on these antibodies show inconsistencies, we here systematically compared six frequently used, commercially available EPOR antibodies for different applications. Five of the antibodies appeared to specifically recognize recombinant rat and human EPOR in HEK293 cells by Western blotting, but the same antibodies yielded different and inconsistent results when human UT-7 cells or rat brain tissue were applied. Immunocytochemical staining of EPOR-transfected HEK cells only produced consistent results with three of the six antibodies. All antibodies stained neurons in rat brain sections, but with large differences in the staining pattern and only the C-20 EPOR antibody was found to label astrocytes. Since EPOR antibodies have been applied in several studies as EPOR antagonists, we further tested the antibodies for their capacity to functionally block the EPO-EPOR interaction in a cellular signalling system with STAT-5 phosphorylation as readout. Here, only the MAB307 antibody showed a partial effect at concentrations of 5-50 microg/ml.

De novo erythropoietin receptor (EPO-R) expression in human neoplastic glial cells decreases with grade of malignancy but is favourably associated with patient survival

The erythropoietin receptor (EPO-R) is mainly known as a regulator of erythropoiesis. However, recent studies revealed that the EPO-R is not exclusively expressed in haematopoietic tissues but also in various cancer cell types and normal tissue such as the central nervous system (CNS). EPO-R is up-regulated under hypoxia and is able to counteract the deleterious effects of hypoxia on tumour growth, metastasis and treatment resistance. Therefore, the EPO-EPO-R signalling pathway is considered as a possible target for tumour treatment. Here, we investigated brain tumour samples obtained from patients between 1993 and 2003 to study EPO-R expression in vivo. Tissue samples included 194 gliomas of different WHO grades, additionally 25 infiltration zone samples and 31 relapses of WHO grade IV glioblastomas as well as 23 normal CNS tissue specimens to address the in vivo situation. Immunohistochemistry of the tissue microarray samples revealed significantly higher levels of EPO-R expression in neoplastic glial cells compared with glial cells derived from normal brain. EPO-R expression showed a highly significant decrease from low- to high-grade gliomas. Age-stratified Kaplan-Meier analysis revealed longer survival for patients exhibiting high EPO-R status in high-grade gliomas. Our results show a grade-dependent EPO-R down-regulation and might contribute to the understanding of high-grade glioma resistance to radio- and chemotherapy as both were shown to be improved by a well functioning EPO-EPO-R pathway in previous studies. Further studies are needed to investigate to what extent the decreased mortality in age-stratified patient groups with high EPO-R levels reflects a direct beneficial role of EPO-R expression.

Mutant presenilin 2 increased oxidative stress and p53 expression in neuronal cells

The learning and memory impairment of presenilin 2 transgenic mice was mentioned previously. In this study, exposing the presenilin 2 transfected PC12 cells to the 50 microM Abeta(25-35), 30 mM l-glutamate and 50 microM H(2)O(2) resulted in significant increase 8-oxodG and p53 levels of the cells expressing the mutant gene. The increase was also found in the mutant presenilin 2 transgenic mice brains age-dependently in comparison to that in the wild-type presenilin 2-transgenic mice and non-transgenic ones. These findings indicated that mutant presenilin 2 clearly increases oxidative stress and p53 expression, which could be implicated in promoting mutant presenilin 2-induced neurodegeneration in Alzheimer's disease, and the influence of mutant presenilin 2 in Alzheimer's disease may be brain regional and age related effects.

Microglial integrity is maintained by erythropoietin through integration of Akt and its substrates of glycogen synthase kinase-3beta, beta-catenin, and nuclear factor-kappaB

Recognized as a robust cytoprotectant for multiple tissues of the hematopoietic, vascular, cardiac, and nervous systems, erythropoietin (EPO) also is considered to be an attractive therapeutic candidate to modulate inflammatory cell function and survival during neurodegenerative disorders. To this end, microglia of the central nervous system serve a complex function not only to dispense of foreign organisms and injured cells of the brain, but also to foster tissue repair and reorganization during neuronal and vascular cell insults. We therefore examined the ability of EPO to modulate microglial cell survival and the underlying signal transduction pathways that govern microglial integrity during oxygen-glucose deprivation (OGD)--induced oxidative stress. We demonstrate in the microglial cell line EOC 2 that EPO provides direct microglial protection against early and late apoptotic programs of membrane phosphatidylserine exposure and genomic DNA degradation. Furthermore, expression and activation of Akt1 is vital to the cytoprotective capacity of EPO, since pharmacological inhibition of the PI 3-K pathway or gene silencing of Akt1 expression eliminates the ability of EPO to protect microglial cells. Through Akt1 dependent mechanisms that can be abrogated through the gene silencing of Akt1, maintenance of microglial cell integrity during OGD by EPO is closely integrated with the phosphorylation and inhibition of glycogen synthase kinase-3beta activity as well as the intracellular trafficking of beta-catenin and nuclear factor-kappaB. Further work that continues to elucidate the ability of EPO to target the intricate pathways that determine inflammatory cell function and integrity may lay the ground work for new therapeutic avenues for neurodegenerative disease.

Cell type specific signalling by hematopoietic growth factors in neural cells

Correct timing and spatial location of growth factor expression is critical for undisturbed brain development and functioning. In terminally differentiated cells distinct biological responses to growth factors may depend on cell type specific activation of signalling cascades. We show that the hematopoietic growth factors thrombopoietin (TPO) and granulocyte colony-stimulating factor (GCSF) exert cell type specific effects on survival, proliferation and the degree of phosphorylation of Akt1, ERK1/2 and STAT3 in rat hippocampal neurons and cortical astrocytes. In neurons, TPO induced cell death and selectively activated ERK1/2. GCSF protected neurons from TPO- and hypoxia-induced cell death via selective activation of Akt1. In astrocytes, neither TPO nor GCSF had any effect on cell viability but inhibited proliferation. This effect was accompanied by activation of ERK1/2 and inhibition of STAT3 activity. A balance between growth factors, their receptors and signalling proteins may play an important role in regulation of neural cell survival.

NF-kappaB functions in the nervous system: from development to disease

The transcription factor nuclear factor-kappaB (NF-kappaB) is an ubiquitously expressed dimeric molecule with post-translationally regulated activity. Its role in the immune system and host defense has been well characterized over the last two decades. In contrast, our understanding of the function of this transcription factor in the nervous system (NS) is only emerging. Given their cytoplasmic retention and nuclear translocation upon stimulus, NF-kappaB members are likely to exert an important role in transduction of signals from synaptic terminals to nucleus, to initiate transcriptional responses. This report describes recent findings deciphering the diverse functions of NF-kappaB in NS development and activity, which range from the control of cell growth, survival and inflammatory response to synaptic plasticity, behavior and cognition. Particular attention is given to the specific roles of NF-kappaB in the various cells of the NS, e.g. neurons and glia. Current knowledge of the contribution of NF-kappaB to several neurodegenerative disorders, such as Alzheimer's, Parkinson's and Huntington's diseases is also summarized.

The brain erythropoietin system and its potential for therapeutic exploitation in brain disease

The discovery of the broad neuroprotective potential of erythropoietin (EPO), an endogenous hematopoietic growth factor, has opened new therapeutic avenues in the treatment of brain diseases. EPO expression in the brain is induced by hypoxia. Practically all brain cells are capable of production and release of EPO and expression of its receptor. EPO exerts multifaceted protective effects on brain cells. It protects neuronal cells from noxious stimuli such as hypoxia, excess glutamate, serum deprivation or kainic acid exposure in vitro by targeting a variety of mechanisms and involves neuronal, glial and endothelial cell functions. In rodent models of ischemic stroke, EPO reduces infarct volume and improves functional outcome, but beneficial effects have also been observed in animal models of subarachnoid hemorrhage, intracerebral hemorrhage, traumatic brain injury, and spinal cord injury. EPO has a convenient therapeutic window upon ischemic stroke and favorable pharmacokinetics. Results from first therapeutic trials in humans are promising, but will need to be validated in larger trials. The safety profile and effectiveness of EPO in a wide variety of neurologic disease models make EPO a candidate compound for a potential first-line therapeutic for neurologic emergencies.

Amelioration of spinal cord compressive injury by pharmacological preconditioning with erythropoietin and a nonerythropoietic erythropoietin derivative

OBJECT

Spinal cord injury (SCI) is a devastating clinical syndrome for which no truly efficacious therapy has yet been identified. In preclinical studies, erythropoietin (EPO) and its nonerythropoietic derivatives asialoEPO and carbamylated EPO have markedly improved functional outcome when administered after compressive SCI. However, an optimum treatment paradigm is currently unknown. Because the uninjured spinal cord expresses a high density of EPO receptor (EPOR) in the basal state, signaling through these existing receptors in advance of injury (pharmacological preconditioning) might confer neuroprotection and therefore be potentially useful in situations of anticipated damage.

METHODS

The authors compared asialoEPO, a molecule that binds to the EPOR with high affinity but with a brief serum half-life (t1/2 < 2 minutes), to EPO to determine whether a single dose (10 microg/kg of body weight) administered by intravenous injection 24 hours before 1 minute of spinal cord compression provides benefit as determined by a 6-week assessment of neurological outcome and by histopathological analysis. Rats pretreated with asialoEPO or EPO and then subjected to a compressive injury exhibited improved motor function over 42 days, compared with animals treated with saline solution. However, pretreatment efficacy was substantially poorer than efficacy of treatment initiated at the time of injury. Serum samples drawn immediately before compression confirmed that no detectable asialoEPO remained within the systemic circulation. Western blot and immunohistochemical analyses performed using uninjured spinal cord 24 hours after a dose of asialoEPO exhibited a marked increase in glial fibrillary acidic protein, suggesting a glial response to EPO administration.

CONCLUSIONS

These results demonstrate that EPO and its analog do not need to be present at the time of injury to provide tissue protection and that tissue protection is markedly effective when either agent is administered immediately after injury. Furthermore, the findings suggest that asialoEPO is a useful reagent with which to study the dynamics of EPO-mediated neuroprotection. In addition, the findings support the concept of using a nonerythropoietic EPO derivative to provide tissue protection without activating the undesirable effects of EPO.

Stimulation of cell growth by erythropoietin in RAW264.7 cells: Association with AP-1 activation

Erythropoietin (EPO), a hematopoietic factor, is required for normal erythrocyte developments, but it has been demonstrated to have many other functions, and its receptor is localized in other tissues. In the present study, we investigated whether EPO can promote other cell proliferation and possible molecular mechanisms. EPO restored the inhibition of the RAW264.7 and PC12 cell growth by fetal bovine serum (FBS) withdrawal in a dose dependent manner, but not that of other cell types tested. The restoring effect of EPO was completed when the RAW264.7 cells were cultured in the medium containing as low as 3% of FBS, and 10 U/mL EPO could replace FBS. The restoring effect of EPO in the RAW264.7 cells was associated with the increased of c-Fos and c-Jun expression as well as AP-1 activation. These data demonstrate that EPO can stimulate RAW264. 7 cell as well as PC12 cell growth even when the cells were cultured without FBS or in the presence of small amounts of FBS in the medium, and this stimulating effect is associated with the activation of AP-1 transcription factor.

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

The hematopoietic cytokine erythropoietin (Epo) prevents neuronal death during ischemic events in the brain and in neurodegenerative diseases, presumably through its antiapoptotic effects. To explore the role of different signaling pathways in Epo-mediated antiapoptotic effects in differentiated human neuroblastoma SH-SY5Y cells, we employed a prolactin receptor (PrlR)/erythropoietin receptor (EpoR) chimera system, in which binding of prolactin (Prl) to the extracellular domain activates EpoR signaling in the cytosol. On induction of apoptosis by staurosporine, Prl supports survival of the SH-SY5Y cells expressing the wild-type PrlR/EpoR chimera. In these cells Prl treatment strongly activates the STAT5, AKT, and MAPK signaling pathways and induces weak activation of the p65 NF-kappaB factor. Selective mutation of the eight tyrosine residues of the EpoR cytoplasmic domain results in impaired or absent activation of either STAT5 (mutation of Tyr(343)) or AKT (mutation of Tyr(479)) or both (mutation of all eight tyrosine residues). Most interestingly, Prl treatment does not prevent apoptosis in cells expressing mutant PrlR/EpoR chimeras in which either the STAT5 or the AKT signaling pathways are not activated. In contrast, ERK 1/2 is fully activated by all mutant PrlR/EpoR chimeras, comparable with the level seen with the wild-type PrlR/EpoR chimera, implying that activation of the MAPK signaling pathway per se is not sufficient for antiapoptotic activity. Therefore, the antiapoptotic effects of Epo in neuronal cells require the combinatorial activation of multiple signaling pathways, including STAT5, AKT, and potentially MAPK as well, in a manner similar to that observed in hematopoietic cells.

Erythropoietin protects CA1 neurons against global cerebral ischemia in rat: Potential signaling mechanisms

Erythropoietin (EPO) is a hormone that is neuroprotective in models of neurodegenerative diseases. This study examined whether EPO can protect against neuronal death in the CA1 region of the rat hippocampus following global cerebral ischemia. Recombinant human EPO was infused into the intracerebral ventricle either before or after the induction of ischemia produced by using the four-vessel-occlusion model in rat. Hippocampal CA1 neuron damage was ameliorated by infusion of 50 U EPO. Administration of EPO was neuroprotective if given 20 hr before or 20 min after ischemia, but not 1 hr following ischemia. Coinjection of the phosphoinositide 3 kinase inhibitor LY294002 with EPO inhibited the protective effects of EPO. Treatment with EPO induced phosphorylation of both AKT and its substrate, glycogen synthase kinase-3beta, in the CA1 region. EPO also enhanced the CA1 level of brain-derived neurotrophic factor. Finally, we determined that ERK activation played minor roles in EPO-mediated neuroprotection. These studies demonstrate that a single injection of EPO ICV up to 20 min after global ischemia is an effective neuroprotective agent and suggest that EPO is a viable candidate for treating global ischemic brain injury.

ERK-mediated production of neurotrophic factors by astrocytes promotes neuronal stem cell differentiation by erythropoietin

Erythropoietin (EPO), a hematopoietic factor, is also required for normal brain development, and its receptor is localized in brain. Our previous study showed that EPO promotes differentiation of neuronal stem cells into astrocytes. Since astrocytes have influence on the neuronal function, we investigated whether EPO-activated astrocytes could stimulate differentiation of neuronal stem cells into neurons. EPO did not promote neuronal differentiation of neuronal stem cells isolated from 17 day embryos, however, neuronal differentiation was promoted when the neuronal stem cells were co-cultured with astrocyte isolated from post neonatal (Day 1) rat brain. Moreover, neuronal differentiation was further promoted when the neuronal stem cells were cultured with astrocyte culture medium treated by EPO (10U/ml) showing increase of morphological differentiation, and expression of neuronal differentiation marker proteins, neurofilament, and tyrosine hydroxylase. The promoting effect of EPO-treated astrocyte medium was also found in the differentiation of PC12 cells. EPO-promoted morphological differentiation of neuronal stem cells as well as astrocytes was dose dependently reduced by treatment with anti-EPO receptor antibodies in culture with astrocyte culture medium. To clarify whether EPO itself or via production of well-known neurotropic factor could promote neuronal cell differentiation, we determined the level of neurotropic factors in the EPO-treated astrocytes. Compared to untreated astrocytes, EPO-treated astrocytes increased about 2-fold in beta-NGF and 3-4-fold in BMP2, but did not increase BNDF and NT-3 levels. Since the previous study showed that extracellular signal-regulated kinase (ERK) is involved in activation of astrocytes by EPO, we determined whether generation of neurotrophic factor may also be involved with the ERK pathway. In the presence of ERK inhibitor, PD98059, the generation of beta-NGF was diminished in a dose dependent manner consistent with the inhibiting effect on neuronal differentiation. These data demonstrate that EPO promotes neuronal cell differentiation through increased release of beta-NGF and BMP2 from astrocytes, and this effect may be associated with ERK pathway signals.

Erythropoietin requires NF-kappaB and its nuclear translocation to prevent early and late apoptotic neuronal injury during beta-amyloid toxicity

No longer considered exclusive for the function of the hematopoietic system, erythropoietin (EPO) is now considered as a viable agent to address central nervous system injury in a variety of cellular systems that involve neuronal, vascular, and inflammatory cells. Yet, it remains unclear whether the protective capacity of EPO may be effective for chronic neurodegenerative disorders such as Alzheimer's disease (AD) that involve beta-amyloid (Abeta) apoptotic injury to hippocampal neurons. We therefore investigated whether EPO could prevent both early and late apoptotic injury during Abeta exposure in primary hippocampal neurons and assessed potential cellular pathways responsible for this protection. Primary hippocampal neuronal injury was evaluated by trypan blue dye exclusion, DNA fragmentation, membrane phosphatidylserine (PS) exposure, and nuclear factor-kappaB (NF-kappaB) expression with subcellular translocation. We show that EPO, in a concentration specific manner, is able to prevent the loss of both apoptotic genomic DNA integrity and cellular membrane asymmetry during Abeta exposure. This blockade of Abeta generated neuronal apoptosis by EPO is both necessary and sufficient, since protection by EPO is completely abolished by co-treatment with an anti-EPO neutralizing antibody. Furthermore, neuroprotection by EPO is closely linked to the expression of NF-kappaB p65 by preventing the degradation of this protein by Abeta and fostering the subcellular translocation of NF-kappaB p65 from the cytoplasm to the nucleus to allow the initiation of an anti-apoptotic program. In addition, EPO intimately relies upon NF-kappaB p65 to promote neuronal survival, since gene silencing of NF-kappaB p65 by RNA interference removes the protective capacity of EPO during Abeta exposure. Our work illustrates that EPO is an effective entity at the neuronal cellular level against Abeta toxicity and requires the close modulation of the NF-kappaB p65 pathway, suggesting that either EPO or NF-kappaB may be used as future potential therapeutic strategies for the management of chronic neurodegenerative disorders, such as AD.

Emerging biological roles for erythropoietin in the nervous system

Erythropoietin mediates an evolutionarily conserved, ancient immune response that limits damage to the heart, the nervous system and other tissues following injury. New evidence indicates that erythropoietin specifically prevents the destruction of viable tissue surrounding the site of an injury by signalling through a non-haematopoietic receptor. Engineered derivatives of erythropoietin that have a high affinity for this receptor have been developed, and these show robust tissue-protective effects in diverse preclinical models without stimulating erythropoiesis. A recent successful proof-of-concept clinical trial that used erythropoietin to treat human patients who had suffered a stroke encourages the evaluation of both this cytokine and non-erythropoietic derivatives as therapeutic agents to limit tissue injury.