Neurotrophic effect of hematopoietic cytokines on cholinergic and other neurons in vitro

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.

Erythropoietin produced by genetic-modified NIH/3T3 fibroblasts enhances the survival of degenerating neurons

BACKGROUND

Erythropoietin (EPO) has potent neuroprotective effects. The short-term delivery of high-dose EPO seemed to improve patients' neuromuscular functions; however, excessive EPO resulted in systematically high hematocrit and thrombotic risk. In our study, we established a cellular material for future in vivo studies of neurodegenerative diseases based on EPO provided regionally at a nontoxic level.

METHODS

A mouse EPO cDNA was subcloned into the pCMS-EGFP vector and transfected into NIH/3T3 fibroblasts to design a biological provider that can regionally release EPO for the treatment of neurological diseases. After G418 selection, a stable EPO-overexpressing cell line, EPO-3T3-EGFP, was established. To further confirm the neuroprotective abilities of secreted EPO from EPO-3T3-EGFP cells, a cell model of neurodegeneration, PC12-INT-EGFP, was applied.

RESULTS

The expression level of EPO was highly elevated in EPO-3T3-EGFP cells, and an abundant amount of EPO secreted from EPO-3T3-EGFP cells was detected in the extracellular milieu. After supplementation with conditioned medium prepared from EPO-3T3-EGFP cells, the survival rate of PC12-INT-EGFP cells was significantly enhanced. Surprisingly, a fraction of aggregated cytoskeletal EGFP-tagged α-internexin in PC12-INT-EGFP cells was disaggregated and transported into neurites dynamically. The immunocytochemical distribution of IF proteins, including NF-M, phosphorylated-NF-M, and the α-INT-EGFP fusion protein, were less aggregated in the perikaryal region and transported into neurites after the EPO treatment.

CONCLUSION

The established EPO-overexpressing NIH/3T3 cell line, EPO-3T3-EGFP, may provide a material for future studies of cell-based therapies for neurodegenerative diseases via the secretion of EPO on a short-term, high-dose, regional basis.

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.

Long-term moderate dose exogenous erythropoietin treatment protects from intermittent hypoxia-induced spatial learning deficits and hippocampal oxidative stress in young rats

Exposure to intermittent hypoxia (IH) is associated with cognitive impairments and oxidative stress in brain regions involved in learning and memory. In earlier studies, erythropoietin (EPO) showed a neuroprotective effect in large doses. The aim of the present study was to explore the effect of smaller doses of EPO, such as those used in the treatment of anemia, on IH-induced cognitive deficits and hippocampal oxidative stress in young rats. The effect of concurrent EPO treatment (500 and 1,000 IU/kg/day ip) on spatial learning and memory deficits induced by long-term exposure to IH for 6 weeks was tested using the Morris water maze (MWM) test and the elevated plus maze (EPM) test. Moreover, the effect on hippocampal glutamate and oxidative stress were assessed. Exposure to IH induced a significant impairment of spatial learning and cognition of animals in both MWM and EPM performance parameters. Moreover, hippocampal glutamate and thiobarbituric acid reactive substances (TBARS) increased while antioxidant defenses (GSH and GSH-Px) decreased. EPO in the tested doses significantly reduced the IH-induced spatial learning deficits in both MWM and EPM tests and dose-dependently antagonized the effects of IH on hippocampal glutamate, TBARS, GSH levels, and GSH-Px activity. Treatment with EPO in moderate doses that used for anemia, concurrently with IH exposure can antagonize IH-induced spatial learning deficits and protect hippocampal neurons from IH-induced lipid peroxidation and oxidative stress-induced damage in young rats, possibly through multiple mechanisms involving a potential antioxidative effect.

Tissue-protective cytokines: structure and evolution

Cytokines are important mediators of host defense and immunity, and were first identified for their role in immunity to infections. It was then found that some of them are pathogenic mediators in inflammatory diseases and much of the emphasis is now on pro-inflammatory cytokines, also in consideration of the fact that TNF inhibitors became effective drugs in chronic inflammatory diseases. The recent studies on the tissue-protective activities of erythropoietin (EPO) led to the term "tissue-protective cytokine." We discuss here how tissue-protective actions might be common to other cytokines, particularly those of the 4-alpha helical structural superfamily.

Carbamylated erythropoietin ameliorates hypoxia-induced cognitive and behavioral defects with the generation of choline acetyltransferase-positive neurons

Carbamylated erythropoietin (CEPO) is attracting widespread interest because of its neuroprotective effects without influencing erythropoiesis. Here we show that CEPO, unlike EPO, does not stimulate erythropoiesis. Both CEPO and EPO inhibit the death/apoptosis of neurons in the hypoxic model of primary neurons and induce neuron proliferation and differentiation in hypoxic mice. Hypoxic mice show apparent memory deficits at 3 and 30 days after hypoxia. The administration of CEPO/EPO significantly improves cognitive and behavioral defects after hypoxic insults. Further investigation shows that CEPO/EPO induces neuron proliferation and differentiation and promotes the generation of choline acetyltransferase (ChAT)(+) neurons in hypoxic mice. Phosphorylated AKT was colabeled with ChAT(+) neurons and coexpressed in bromodeoxyuridine-positive cells, suggesting that the PI3K/AKT pathway may play a pivotal role in CEPO/EPO-cholinergic neuron generation. These results reveal that CEPO/EPO ameliorates hypoxia-induced cognitive and behavioral defects possibly through the generation of ChAT-positive neurons.

Effects of erythropoietin on memory deficits and brain oxidative stress in the mouse models of dementia

The present study was undertaken to explore the potential of erythropoietin in memory deficits of mice. Memory impairment was produced by scopolamine (0.5 mg/kg, i.p.) and intracerebroventricular streptozotocin (i.c.v STZ, 3 mg/kg, 10 µl, 1(st) and 3(rd) day) in separate groups of animals. Morris water-maze test was employed to assess learning and memory. The levels of brain thio-barbituric acid reactive species (TBARS) and reduced glutathione (GSH) were estimated to assess degree of oxidative stress. Brain acetylcholinesterase enzyme (AChE) activity was also measured. Scopolamine/streptozotocin administration induced significant impairment of learning and memory in mice as indicated by marked decrease in Morris water-maze performance. Scopolamine/streptozotocin administration also produced a significant enhancement of brain AChE activity and brain oxidative stress (an increase in TBARS and a decrease in GSH) levels. Treatment of erythropoietin (500 and 1,000 IU/Kg i.p.) significantly reversed scopolamine- as well as streptozotocin-induced learning and memory deficits along with attenuation of those-induced rise in brain AChE activity and brain oxidative stress levels. It may be concluded that erythropoietin exerts a beneficial effect in memory deficits of mice possibly through its multiple actions including potential anti-oxidative effect.

Fasudil, a Rho kinase inhibitor, drives mobilization of adult neural stem cells after hypoxia/reoxygenation injury in mice

Rho kinase (ROCK) is important in fundamental processes of cell proliferation and survival. Blockade of ROCK promotes stem cell survival in vitro and axonal regeneration in vivo, exhibiting therapeutic potential such as spinal cord injuries and stroke. Here, we used the model of hypoxia/reoxygenation (H/R) injury to explore the possibility whether Fasudil, a ROCK inhibitor in clinical application for subarachnoid hemorrhage and stroke, mobilizes adult neural stem cells in vivo. Most interestingly, Fasudil triggers neurogenesis especially in the subventricular zone after H/R. The increase of Brdu+ cholinergic neurons was observed in striatum and forebrain cortex of Fasudil-treated mice after 30 days. Further observation demonstrates that both levels of granulocyte colony-stimulating factor (G-CSF) and astrocytes expressing G-CSF were elevated in mice treated with Fasudil, as compared to mice injected with saline. In vitro H/R model of cultured astrocytes, Fasudil promoted astrocytes to produce G-CSF in a dose-dependent manner. In addition, antibody neutralization and receptor blocking of the G-CSF pathway clearly demonstrate that Fasudil-induced neurogenesis was mediated partially through astrocyte-derived G-CSF. Our results indicate that Fasudil might represent a promising therapeutic perspective by mobilizating endogenous adult neural stem cells in the CNS.

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.

The signal transduction mediated by erythropoietin and proinflammatory cytokines in the JAK/STAT pathway in the children with cerebral palsy

It is well established that erythropoietin (EPO) is a pleiotropic cytokine, which has a brain-derived neuroprotective effect in the central nervous system (CNS). Immune abnormality has a close relationship with cerebral palsy (CP), and may be even involved in the development of CP. There is evidence that the amount of EPO in CP children is lower than in normal children, but the levels of proinflammatory cytokines, such as interleukin (IL)-6 and tumor necrosis factor (TNF)-alpha, are higher in the CP children. The signal transduction mediated by EPO that has a neuroprotective effect and mediated by proinflammatory cytokines that lead to brain damage shares the common JAK/STAT pathway. Under acute stress, the JAK/STAT pathway is occupied by massive proinflammatory cytokines, and the negative feedback inhibition factors like suppressor of cytokine signaling (SOCS) proteins are simultaneously activated, which exist in reciprocal inhibition to EPO in the JAK/STAT pathway. As a result, the signal transduction mediated by EPO is prevented or reduced, and the neuroprotective effect of EPO is eventually weakened. In this review, a novel approach to CP treatment through neurodevelopmental treatment (NDT) is put forward by analysis of the interrelationship of signal transduction mediated by EPO and proinflammatory cytokines in the JAK/STAT pathway and their roles in the development of CP, and some reasonable ideas for CP treatment are provided.

Promotion of neurite outgrowth and protective effect of erythropoietin on the retinal neurons of rats

OBJECTIVE

To clarify the effect of erythropoietin (EPO) on neurite outgrowth of the cultured retinal neurocytes, and investigate whether EPO might potentially be beneficial in protecting cultured retinal neurocytes suffering from glutamate-induced cytotoxity.

METHODS

After the retinal neurocytes were cultured for 48 hours, the culture media was replaced with serum-free media, and the cultured retinal cells were exposed to 1.0 U/ml, 3.0 U/ml and 6.0 U/ml EPO for another 48 hours; then the cells were stained with Sudan Black B, and the neurite outgrowth of those cells were evaluated by an image-analysis system. After the retinal neurocytes were cultured for 48 hours, the cells were cultured in serum-free media containing 5 mM or 10 mM glutamate, and the cells were incubated in the presence or absence of Epo (1.0 U/ml, 3.0 U/ml, 6.0 U/ml respectively) for another 48 hours. The survival and apoptosis rates of those cells were estimated by MTT assay and fluorescein isothiocyanate (FITC)-annexin V/propidium Iodide (PI) flow cytometry respectively.

RESULTS

EPO induced a stable improvement of neurite outgrowth of retinal neurocytes in a dose-dependent manner. Compared with the control group, the neurite outgrowth length increased to 162.8% at 6.0 U/ml EPO exposure. EPO had no any significant effect on the survival and apoptosis rates of the retinal neurocytes cultured in serum-free media, but it was beneficial in promoting the survival and decreasing the early and total apoptosis rates of the cultured retinal neurocytes suffering from glutamate-induced cytotoxicity.

CONCLUSION

EPO had a significant biological effect on neurite outgrowth of the dissociated retinal neurocytes in vitro. EPO was beneficial in promoting the survival and decreasing the apoptosis rates of the cultured retinal neurocytes suffering from glutamate-induced cytotoxicity.

Epo and other hematopoietic factors

The growth factors erythropoietin and granulocyte-colony stimulating factor have hematopoietic and non-hematopoietic functions. Both are used clinically in their recombinant forms. Both also have interesting tissue-protective effects in other organs, which are unrelated to their hematopoietic functions. They have clinical hematopoietic uses in neonatal populations and in experimental non-hematopoietic research, and clinical potential as neuroprotective or tissue-protective agents.

Converging evidence for a pseudoautosomal cytokine receptor gene locus in schizophrenia

Schizophrenia is a strongly heritable disorder, and identification of potential candidate genes has accelerated in recent years. Genomewide scans have identified multiple large linkage regions across the genome, with fine-mapping studies and other investigations of biologically plausible targets demonstrating several promising candidate genes of modest effect. The recent introduction of technological platforms for whole-genome association (WGA) studies can provide an opportunity to rapidly identify novel targets, although no WGA studies have been reported in the psychiatric literature to date. We report results of a case-control WGA study in schizophrenia, examining approximately 500 000 markers, which revealed a strong effect (P=3.7 x 10(-7)) of a novel locus (rs4129148) near the CSF2RA (colony stimulating factor, receptor 2 alpha) gene in the pseudoautosomal region. Sequencing of CSF2RA and its neighbor, IL3RA (interleukin 3 receptor alpha) in an independent case-control cohort revealed both common intronic haplotypes and several novel, rare missense variants associated with schizophrenia. The presence of cytokine receptor abnormalities in schizophrenia may help explain prior epidemiologic data relating the risk for this illness to altered rates of autoimmune disorders, prenatal infection and familial leukemia.

Erythropoietin and GDNF enhance ventral mesencephalic fiber outgrowth and capillary proliferation following neural transplantation in a rodent model of Parkinson's disease

Low dopaminergic cell survival and suboptimal fiber reinnervation are likely major contributing factors for the limited benefits of neural transplantation in Parkinson's disease (PD) patients. Glial cell lined-derived neurotrophic factor (GDNF) has been shown to enhance dopaminergic cell survival and fiber outgrowth of the graft site as well as promote behavioral recovery in rodent models of PD, while erythropoietin (EPO) can produce dopaminergic neuroprotective effects against 6-hydroxydopamine (6-OHDA) exposure on cultured neurons and 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice. The aim of this study was to determine if fetal ventral mesencephalic (FVM) tissue exposed to hibernation media containing a combination of GDNF and EPO could enhance dopaminergic graft survival, striatal reinnervation and functional recovery in a 6-OHDA rodent model of PD. FVM tissue was dissected from 14-day-old rat fetuses and placed for 6 days in hibernation media alone, and in hibernation media that received either a daily administration of GDNF, EPO or a combination of GDNF and EPO. Following hibernation, FVM cells were transplanted as a single cell suspension into the striatum of unilateral 6-OHDA-lesioned rats. Rotational behavioral assessment revealed animals that received FVM tissue exposed to GDNF, EPO or the combination of both drugs had accelerated functional recovery. Immunohistochemical and stereological assessment revealed a significant increase in graft fiber density and angiogenesis into the graft when compared with control. These findings suggest that the hibernation of FVM tissue in a combination of GDNF and EPO can enhance graft efficacy and may have important implications for tissue preparation protocols for clinical neural transplantation in PD.

Ischaemic preconditioning: therapeutic implications for stroke?

Ischaemic preconditioning (IPC), also known as ischaemic tolerance (IT), is a phenomenon whereby tissue is exposed to a brief, sublethal period of ischaemia, which activates endogenous protective mechanisms, thereby reducing cellular injury that may be caused by subsequent lethal ischaemic events. The first description of this phenomenon was in the heart, which was reported by Murry and co-workers in 1986. Subsequent studies demonstrated IPC in lung, kidney and liver tissue, whereas more recent studies have concentrated on the brain. The cellular mechanisms underlying the beneficial effects of IPC remain largely unknown. This phenomenon, which has been demonstrated by using various injury paradigms in both cultured neurons and animal brain tissue, may be utilised to identify and characterise therapeutic targets for small-molecule, antibody, or protein intervention. This review will examine the experimental evidence demonstrating the phenomenon termed IPC in models of cerebral ischaemia, the cellular mechanisms that may be involved and the therapeutic implications of these findings.

Erythropoietin enhances neurogenesis and restores spatial memory in rats after traumatic brain injury

Erythropoietin (EPO) is neuroprotective in models of stroke and traumatic brain injury (TBI) when administered prior to or within the first few hours after injury. We seek to demonstrate that EPO also has neurorestorative effects when administered late (i.e., 1 day) after TBI in the rat. Twelve rats were subjected to TBI. Six rats were treated with EPO daily for 14 days starting 1 day after injury, and an additional six rats were treated with saline. Bromodeoxyuridine (BrdU) was administered daily for 14 days. Memory tests using a Morris Water Maze were performed prior to and after injury and treatment. Animals were sacrificed at 15 days after TBI, and their brains were prepared for histological analysis of damage to the dentate gyrus (DG) and for evaluation of newly formed neurons using double labeling of BrdU and MAP-2. The data revealed a significant improvement in spatial memory and significant increase in the number of newly formed neurons with EPO treatment compared with control animals. These data suggest that EPO treatment initiated 1 day after TBI is neurorestorative by enhancing neurogenesis, as well as neuroprotective.

Protective effects of erythropoietin against ethanol-induced apoptotic neurodegenaration and oxidative stress in the developing C57BL/6 mouse brain

The developing central nervous system is extremely sensitive to ethanol, with well-defined temporal periods of vulnerability. Recent studies have shown that administration of ethanol to infant rats during the synaptogenesis period triggers extensive apoptotic neurodegeneration throughout many regions of the developing brain. Furthermore, acute ethanol administration produces lipid peroxidation in the brain as an indicator of oxidative stress. In recent years, it has been shown that erythropoietin (EPO) has a critical role in the development, maintenance, protection, and repair of the nervous system. In the present study, we investigated the effect of EPO against ethanol-induced neurodegeneration and oxidative stress in the developing C57BL/6 mouse brain. Seven-day-old C57BL/6 mice were divided into three groups: control group, saline-treated group, EPO-treated group. Ethanol was administered to mice at a dosage of 2.5 g/kg for two times with a 2-h interval. Recombinant human EPO (rhEPO) was given 1000 U/kg. Twenty-four hours after the first dose of ethanol, all the animals were killed. Neuronal cell death, apoptosis, thiobarbituric acid substance (TBARS) levels, superoxide dismutase (SOD), and glutathione peroxidase (Gpx) enzymes activities were evaluated. Histopathological evaluation demonstrated that EPO significantly diminished apoptosis in the cerebellum, prefrontal cortex, and hippocampus and also spared hippocampal CA1, CA2, and CA3 neurons. Simultaneous administration of EPO along with ethanol attenuated the lipid peroxidation process and restored the levels of antioxidants. Regarding the wide use of erythropoietin in premature newborns, this agent may be potentially beneficial in treating ethanol-induced brain injury in the perinatal period.

Neuroprotective effects of erythropoietin on glutamate and nitric oxide toxicity in primary cultured retinal ganglion cells

Erythropoietin receptor (EpoR) is expressed in the central nervous system (CNS), however, no clear consensus has been obtained whether Epo acts as a prosurvival factor in neurons. Because retinal ganglion cell (RGC) death is a common cause of reduced visual function in several ocular diseases, we explored whether Epo might potentially be beneficial in protecting RGCs from glutamate and nitric oxide (NO)-induced cytotoxicity, using isolated RGCs by a two-step panning method. Brain-derived neurotrophic factor (BDNF) was used as a positive control. EpoR mRNA was expressed in isolated RGCs, and EpoR protein was expressed on the RGCs in the normal and ischemic retinas. Epo had less potential to improve the survival of primary RGCs in serum-free medium than BDNF. In these cells, BDNF, but not Epo, downregulated the expression of Bim, a proapoptotic Bcl-2 family member that plays a key role in cytokine-mediated cell survival, suggesting a possible mechanism for this difference. When RGCs were cultured with glutamate or an NO-generating reagent, the survival of RGCs was compromised, and Bcl-2 expression was decreased in these cells. Both Epo and BDNF significantly reduced RGC death induced by glutamate and NO. In agreement with this, these factors reversed the Bcl-2 expression. These findings suggest that Epo may be a potent neuroprotective therapeutic agent for the treatment of ocular diseases that are characterized by RGC death.

Erythropoietin prevents long-term sensorimotor deficits and brain injury following neonatal hypoxia-ischemia in rats

Perinatal asphyxia accounts for behavioral dysfunctions that often manifest as sensorimotor, learning or memory disabilities throughout development and into maturity. Erythropoietin (Epo) has been shown to exert neuroprotective effects in different models of brain injury including experimental models of perinatal asphyxia. However, the effect of Epo on functional abilities following cerebral hypoxia-ischemia (HI) in neonatal rats is not known. The aim of the present study is to investigate the effect of Epo on sensorimotor deficits and brain injury induced by hypoxia-ischemia. Seven-day-old rats underwent unilateral, permanent carotid artery ligation followed by 1 h of hypoxia. Epo was administered as a single dose immediately after the hypoxic insult (2000 U/kg). The neuroprotective effect of Epo was evaluated at postnatal day 42 by using a battery of behavioral tests and histological analysis. The results of the present study suggest that Epo treatment immediately after HI insult significantly facilitated recovery of sensorimotor function. Consistently, histopathological evaluation demonstrated that Epo significantly attenuated brain injury and preserved the integrity of cerebral cortex. These findings indicate that long-term neuroprotective effect of Epo on neonatal HI-induced brain injury might be associated with the preservation of sensorimotor functions.

Brain and cancer: the protective role of erythropoietin

Erythropoietin (Epo) is a pleiotropic agent, that is to say, it can act on several cell types in different ways. An independent system Epo/Epo receptor (EpoR) was detected in brain, leading to the hypothesis that this hormone could be involved in cerebral functions. Epo/EpoR expression changes during ontogenesis, thus indicating the importance of this system in neurodevelopment. Moreover, the hypoxia-induced production of Epo in the adult brain suggests that it could exert a neurotrophic and neuroprotective effect in case of brain injury. Epo could also influence neurotransmission, inducing neurotransmitters (NT) release. Epo therapy in anemic cancer patients is still a controversial issue, because of its possible action as a growth and an angiogenic factor. In our speculative hypothesis Epo could be involved in a "two steps process" that, after a neovascularization phase, leads to its down regulation. Moreover, Epo-activated signaling pathways could be modulated as possible targets to interfere in neoplastic cells cycle. In conclusion, treatment with rHuEpo could change therapeutical perspectives in different pathological conditions, such as central nervous system (CNS) diseases, but further studies are needed to clarify its physiopathological activities in different clinical fields.

Erythropoietin on a tightrope: balancing neuronal and vascular protection between intrinsic and extrinsic pathways

Enthusiasm for erythropoietin (EPO) as a broad cytoprotective agent continues to increase at an almost exponential rate. The premise that EPO was required only for erythropoiesis was eventually shed by recent work demonstrating the existence of EPO and its receptor in other organs and tissues outside of the liver and the kidney, such as the brain and heart. As a result, EPO has been identified as a possible candidate in the formulation of therapeutic strategies for both cardiac and nervous system diseases. EPO has been shown to mediate an array of vital cellular functions that involve progenitor stem cell development, cellular protection, angiogenesis, DNA repair, and cellular longevity. An important requirement to achieve the goal of preventing or even reducing cellular injury by any cytoprotective agent is the ability to uncover the cellular pathways that ultimately drive a cell to its demise. We present for consideration several critical cellular pathways modulated by EPO that involve Janus kinase 2 (Jak2), the serine-threonine kinase Akt, forkhead transcription factors, glycogen synthase kinase-3beta (GSK-3beta), cellular calcium, protein kinase C, caspases, as well as the control of inflammatory microglial activation. As we continue to gain new insight into these pathways, EPO should emerge as a critical agent for the development, maturation, and survival of cells throughout the body.

Role of granulocyte—macrophage colony—stimulating factor in preventing apoptosis and improving functional outcome in experimental spinal cord contusion injury

Object. Granulocyte—macrophage colony—stimulating factor (GM-CSF) is a potent hemopoietic cytokine that stimulates stem cell proliferation in the bone marrow and inhibits apoptotic cell death in leukocytes. Its effects in the central nervous system, however, are still unclear. The present study was undertaken to determine if GM-CSF can rescue neuronal cells from apoptosis and improve neurological function in a spinal cord injury (SCI) model.

Methods. To study the effect of GM-CSF on apoptotic neuronal death, the authors used a staurosporine-induced neuronal death model in an N2A cell line (in vitro) and in a rat SCI model (in vivo). The N2A cells were preincubated with GM-CSF for 60 minutes before being exposed to staurosporine for 24 hours. To inhibit GM-CSF, N2A cells were pretreated with antibodies against the GM-CSF receptor for 60 minutes. Clip compression was used to induce SCI. Animals were treated with daily doses of GM-CSF (20 µg/day) for 5 days. The number of apoptotic cells in the spinal cord and neurological improvements were assessed.

Pretreatment with GM-CSF was found to protect N2A cells significantly from apoptosis, and neutralizing antibodies for the GM-CSF receptors inhibited the rescuing effect of GM-CSF on apoptosis. In the rat SCI model, neurological function improved significantly in the GM-CSF—treated group compared with controls treated with phosphate-buffered saline. Terminal deoxynucleotidyl transferase—mediated deoxyuridine triphosphate nick-end labeling staining showed that GM-CSF administration reduced apoptosis in the injured spinal cord.

Conclusions. Treatment of SCI with GM-CSF showed beneficial effects. Neuronal protection against apoptosis is viewed as a likely mechanism underlying the therapeutic effect of GM-CSF in SCI.

A novel role for an established player: anemia drug erythropoietin for the treatment of cerebral hypoxia/ischemia

Erythropoietin, a hematopoietic growth-factor possessing manifold, potent neuroprotective properties, after multiple testing in cell culture and animal studies now gradually finds its way into clinical neuroscience. The first time this took place was in 1998 with a pilot study in stroke patients, the "Göttingen EPO-Stroke-Trial". This study was able to demonstrate that EPO is perfectly well tolerated and safe with this indication. Furthermore, the EPO-treated patients showed a significantly better outcome regarding their clinical progress as well as regarding the infarct size as observed by MRI, when compared to the placebo treated patients. At the moment a multicenter study is being carried out in Germany.

Erythropoietin improves long-term spatial memory deficits and brain injury following neonatal hypoxia-ischemia in rats

It is well known that neonatal hypoxic-ischemic brain injury leads to mental retardation and deficits in cognitive abilities such as learning and memory in human beings. The ameliorative effect of erythropoietin (Epo) on experimental hypoxic-ischemic brain injury in neonatal rats has been recently reported. However, the effect of Epo on cognitive abilities in the hypoxic-ischemic brain injury model is unknown. The aim of this study is to investigate the effects of Epo on learning-memory, behavior and neurodegeneration induced by hypoxia-ischemia. Seven days old Wistar Albino rat pups have been used in the study (n = 28). Experimental groups in the study were: (1) saline-treated hypoxia-ischemia group, (2) Epo-treated (i.p., 1000 U/kg) hypoxia-ischemia group, (3) sham-operated group, (4) control group. In hypoxia-ischemia groups, left common carotid artery was ligated permanently on the seventh postnatal day. Two hours after the procedure, hypoxia (92% nitrogen and 8% oxygen) was induced for 2.5 h. Epo was administered as a single dose immediately after the hypoxia period. When pups were 22 days old, learning experiments were performed using Morris water maze. On the 20th week, when brain development is accepted to be complete, learning experiments were repeated. Rats were then perfused and brains removed for macroscopic and microscopic evaluation. Epo treatment immediately after hypoxic-ischemic insult significantly improved long-term neurobehavioral achievements when tested during the subsequent phase of brain maturation and even into adulthood. Histopathological evaluation demonstrated that Epo also significantly diminished brain injury and spared hippocampal CA1 neurons. In conclusion, Epo administrated as a single dose immediately after neonatal hypoxic-ischemic insult provides benefit over a prolonged period in the still developing rat brain. Since the wide use of Epo in premature newborns, this agent may be potentially beneficial in treating asphyxial brain damage in the perinatal period.

Erythropoietin and the nervous system

Erythropoietin (Epo) is a hematopoietic growth factor and cytokine which stimulates erythropoiesis. In recent years, Epo has been shown to have important nonhematopoietic functions in the nervous system. Nonerythropoietic actions of Epo include a critical role in the development, maintenance, protection and repair of the nervous system. A wide variety of experimental studies have shown that Epo and its receptor are expressed in the nervous system and Epo exerts remarkable neuroprotection in cell culture and animal models of nervous system disorders. In this review, we summarize the current knowledge on the neurotrophic and neuroprotective properties of Epo, the mechanisms by which Epo produces neuroprotection and the signal transduction systems regulated by Epo in the nervous system.

Recombinant erythropoietin as a neuroprotective treatment: in vitro and in vivo models

The biologic effects of erythropoietin in the central and peripheral nervous system involve the activation of its specific cell surface receptor and corresponding signal transduction pathways. This article reviews the neuroprotective effects of erythropoietin in brain, emphasizing the progress made using in vitro and in vivo research models.

Granulocyte macrophage colony-stimulating factor regulates activity of the nervous system

OBJECTIVES

The peripheral administration of granulocyte macrophage colony-stimulating factor (GM-CSF), widely used for the treatment of cytopenias, is often associated with neurological effects [Lieschke et al., N Engl J Med 1992;327:28-34]. This cytokine has recently been reported to affect neurotransmitter metabolism in the nervous system [Bianchi, Neuroreport 1997;8:3587-3590]. To further investigate the neuromodulatory effect of GM-CSF we studied the influence of GM-CSF on the efferent electric activity in the splenic nerve and the integral neuronal activity in medullary gigantocellular reticular formation (MGRF) in rats.

METHODS

Anaesthetized (sodium thiopental 70 mg/kg, i.p.) Wistar rats were injected subcutaneously with 1 microg/kg of hr GM-CSF. Efferent electric activity in the splenic nerve and integral electric activity in MGRF were analyzed. The effectiveness of the applied dose of GM-CSF was verified by determining the elevation of the white blood cell count in peripheral blood 60 min after injection.

RESULTS

We found that GM-CSF increases efferent electric activity in the splenic nerve and decreases that of MGRF as is evident by the frequency of electric discharges. The latency of both effects was 5-15 min.

CONCLUSIONS

This data support the view that GM-CSF exerts a neuromodulatory effect and may provide a new link of neuroimmune communication.

Erythropoietin in the central nervous system, and its use to prevent hypoxic-ischemic brain damage

A new field of clinical and scientific interest has recently developed based on the discovery that the hematopoietic cytokine erythropoietin (Epo) has important non-hematopoietic functions in the brain and other organs, particularly during development. The biological effects of Epo in the central nervous system (CNS) involve activation of its specific receptor and corresponding signal transduction pathways. Epo receptor expression is abundant in the developing mammalian brain, and decreases as term approaches. Epo has been identified as a neurotrophic and neuroprotective agent in a wide variety of experimental paradigms, from neuronal cell culture to in vivo models of brain injury. Several mechanisms by which Epo produces neuroprotection are recognized. Epo (i) decreases glutamate toxicity, (ii) induces the generation of neuronal anti-apoptotic factors, (iii) reduces inflammation, (iv) decreases nitric oxide-mediated injury, and (v) has direct antioxidant effects.

CONCLUSION

Collectively, the evidence suggests that Epo may provide a new approach to the treatment of a variety of CNS disorders in adults and children, especially as a possible therapy for perinatal asphyxia. This review summarizes the current knowledge on the neurotrophic and neuroprotective functions of Epo in the developing and injured brain.

The pleiotropic effects of erythropoietin in the central nervous system

Erythropoietin (Epo) is a hydrophobic sialoglycoproteic hormone produced by the kidney and responsible for the proliferation, maturation, and differentiation of the precursors of the erythroid cell line. Human recombinant erythropoietin (rHuEpo) is used to treat different types of anemia, not only in uremic patients but also in newborns with anemia of prematurity, in patients with cancer-related anemia or myeloproliferative disease, thalassemias, bone marrow transplants, or those with chronic infectious diseases. The pleiotropic functions of Epo are well known. It has been shown that this hormone can modulate the inflammatory and immune response, has direct hemodynamic and vasoactive effects, could be considered a proangiogenic factor because of its interaction with vascular endothelial growth factor, and its ability to stimulate mitosis and motility of endothelial cells. The multifunctional role of Epo has further been confirmed by the discovery in the central nervous system of a specific Epo/Epo receptor (EpoR) system. Both Epo and EpoR are expressed by astrocytes and neurons and Epo is present in the cerebrospinal fluid (CSF). Therefore, novel functions of Epo, tissue-specific regulation, and the mechanisms of action have been investigated. In this review we have tried to summarize the current data on the role of Epo on brain function. We discuss the different sites of cerebral expression and mechanisms of regulation of Epo and its receptor and its role in the development and maturation of the brain. Second, we discuss the neurotrophic and neuroprotective function of Epo in different conditions of neuronal damage, such as hypoxia, cerebral ischemia, and subarachnoid hemorrhage, and the consequent possibility that rHuEpo therapy could soon be used in clinical practice to limit neuronal damage induced by these diseases.

Cytokines and chemokines as mediators of protection and injury in the central nervous system assessed in transgenic mice

Cytokines and chemokines are potent biologic response molecules that play a key role in cellular communication in physiologic and pathophysiologic states. An understanding of the actions and roles of these molecules in CNS biology has been greatly facilitated by molecular genetic approaches that permit the targeted manipulation of gene expression in an intact organism. Studies in promoter-driven transgenic mice with CNS production of a number of cytokines or chemokines have demonstrated that these factors can directly induce a spectrum of cellular alterations often resulting in pronounced neurological disease (Table 1). Thus, these factors, in addition to initiating and maintaining immunoinflammatory responses, can be direct mediators of CNS injury. The neuropathological outcomes in the transgenic mice often recapitulate those reported in human neurological disorders such as MS, neurological diseases associated with AIDS and Alzheimer's disease, pointing to the importance of these animal models to our understanding of the role of cytokines and chemokines in these human disorders. Despite problems of timing and tissue specificity as well as some inconsistencies in the findings from different groups, knockout mice have begun to provide insights that are altering our view of the contribution made by individual cytokines to immunoinflammatory responses in the brain. For example, IL-6 and TNF were originally viewed as having minor and major proinflammatory contributions, respectively, in EAE, but now, based on findings from knockout mice, the opposite seems true. Studies in transgenic and knockout mice now offer strong evidence that, in addition to being mediators of damage, cytokines can have beneficial functions, e.g. the antiviral functions of the IFNs or the trophic and/or neuroprotective actions of some cytokines such as IL-6 and TNF. Clearly, studies in mutant mice, as summarized here, will continue to provide important insights into the nature of cytokine and chemokine actions in the CNS and will offer the possibility that we may identify new targets for effective therapeutic intervention in neuroinflammatory disorders.

The biology of erythropoietin in the central nervous system and its neurotrophic and neuroprotective potential

This review summarizes published as well as preliminary data on the biology of erythropoietin (Epo) in the developing and mature human central nervous system (CNS). Both Epo receptor (Epo-R) and Epo gene expression underlie developmental changes and a brain-specific regulation. These features suggest a different role of Epo in normal brain development than in neuroprotection and neuronal tissue repair after brain injury. Epo concentrations in the cerebrospinal fluid may have primary paracrine effects. While the transport of Epo across the intact blood brain barrier (BBB) is generally limited in humans, systemically produced or administrated Epo may cross during BBB dysfunction. Summarized data of the in vivo and in vitro effects of Epo in the CNS show significant neuroprotective and neurotrophic effects of this molecule. These effects are mediated by several mechanisms, including the activation of a variety of genes and their consecutive protein production. Therapeutic strategies involving activation of the CNS Epo-R are discussed, including the potential use of Epo mimetic peptides.

Beyond erythropoiesis: novel applications for recombinant human erythropoietin

Erythropoietin (EPO) primarily is produced in the kidney and acts as a principal mediator of the physiologic response to hypoxia by increasing red blood cell production. Astrocytes and neurons in the central nervous system (CNS) also are known to produce EPO in response to hypoxia/ischemia. EPO appears to play a neuroprotective role based on preclinical data demonstrating the ability of recombinant human erythropoietin (r-HuEPO) to shield neurons from hypoxic/ischemic stress when administered intracerebraventricularly. In CNS models, systemically administered r-HuEPO has not been intensely investigated because large glycosylated molecules generally were deemed incapable of crossing the blood-brain barrier (BBB). A collaborative research effort identified expression of EPO receptors on human brain capillaries and a specific receptor-mediated transport of r-HuEPO across the BBB after a single intraperitoneal (IP) injection in rodents, with subsequent protection against various types of neuronal damage. For example, administration of r-HuEPO 24 hours before or up to 6 hours after focal ischemic stroke significantly reduced the extent of infarction. r-HuEPO also attenuated concussive brain injury, kainate-induced seizure activity, and autoimmune encephalomyelitis. These preclinical findings suggest that r-HuEPO may have therapeutic potential for stroke, head trauma, and epilepsy; additional studies are needed to confirm and extend these encouraging observations in animal models.

Erythropoietin prevents neuronal apoptosis after cerebral ischemia and metabolic stress

Erythropoietin (EPO) promotes neuronal survival after hypoxia and other metabolic insults by largely unknown mechanisms. Apoptosis and necrosis have been proposed as mechanisms of cellular demise, and either could be the target of actions of EPO. This study evaluates whether antiapoptotic mechanisms can account for the neuroprotective actions of EPO. Systemic administration of EPO (5,000 units/kg of body weight, i.p.) after middle-cerebral artery occlusion in rats dramatically reduces the volume of infarction 24 h later, in concert with an almost complete reduction in the number of terminal deoxynucleotidyltransferase-mediated dUTP nick-end labeling of neurons within the ischemic penumbra. In both pure and mixed neuronal cultures, EPO (0.1--10 units/ml) also inhibits apoptosis induced by serum deprivation or kainic acid exposure. Protection requires pretreatment, consistent with the induction of a gene expression program, and is sustained for 3 days without the continued presence of EPO. EPO (0.3 units/ml) also protects hippocampal neurons against hypoxia-induced neuronal death through activation of extracellular signal-regulated kinases and protein kinase Akt-1/protein kinase B. The action of EPO is not limited to directly promoting cell survival, as EPO is trophic but not mitogenic in cultured neuronal cells. These data suggest that inhibition of neuronal apoptosis underlies short latency protective effects of EPO after cerebral ischemia and other brain injuries. The neurotrophic actions suggest there may be longer-latency effects as well. Evaluation of EPO, a compound established as clinically safe, as neuroprotective therapy in acute brain injury is further supported.

Production and processing of erythropoietin receptor transcripts in brain

The expression of erythropoietin receptor (EpoR) in brain and neuronal cells, and hypoxia-responsive production of erythropoietin (Epo) in the brain suggests that the function of Epo as a survival or viability factor may extend beyond hematopoietic tissue and erythroid progenitor cells. Epo, produced by astrocytes and neurons, can be induced by hypoxia by severalfold, and in animal models Epo administration is neuroprotective to ischemic challenge. We characterized the human EpoR transcript in brain and neuronal cells to determine its contribution in regulating the Epo response in brain. Screening of a human brain cDNA library and quantitative analysis of EpoR transcripts indicate that the EpoR gene locus is transcriptionally active in brain. In addition to the proximal promoter that is active in hematopoietic cells, a significant proportion of transcripts originates far upstream from the EpoR coding region. Unlike erythroid cells with efficient splicing of EpoR transcripts to its mature form, brain EpoR transcripts are inefficiently or alternately processed with a bias towards the 3' coding region. In human EpoR transgenic mice, anemic stress induces expression of the transgene and endogenous EpoR gene in hematopoietic tissue and brain. In culture of neuronal cells, hypoxia induces EpoR expression and increases sensitivity to Epo. Induction of EpoR expression appears to be a consequence of increased transcription from the upstream region and proximal promoter, and a shift towards increased processing efficiency. These data suggest that in contrast to erythropoiesis where erythroid progenitor cells express high levels of EpoR and are directly responsive to Epo stimulation, the neuroprotective effect of Epo and its receptor may require two molecular events: the induction of Epo production by hypoxia and an increase in EpoR expression in neuronal cells resulting in increased sensitivity to Epo.

Erythropoietin crosses the blood-brain barrier to protect against experimental brain injury

Erythropoietin (EPO), recognized for its central role in erythropoiesis, also mediates neuroprotection when the recombinant form (r-Hu-EPO) is directly injected into ischemic rodent brain. We observed abundant expression of the EPO receptor at brain capillaries, which could provide a route for circulating EPO to enter the brain. In confirmation of this hypothesis, systemic administration of r-Hu-EPO before or up to 6 h after focal brain ischemia reduced injury by approximately 50-75%. R-Hu-EPO also ameliorates the extent of concussive brain injury, the immune damage in experimental autoimmune encephalomyelitis, and the toxicity of kainate. Given r-Hu-EPO's excellent safety profile, clinical trials evaluating systemically administered r-Hu-EPO as a general neuroprotective treatment are warranted.

Nonerythropoietic roles of erythropoietin in the fetus and neonate

Epo was once regarded as a cytokine with only hematopoietic effects. It is now clear that the distributions of Epo and Epo-R are more widespread in the developing human. Epo-R is widely distributed during early fetal development, leading to speculation that Epo acts in concert with other growth factors to optimize growth and development. Areas in which Epo has important recognized effects are on endothelial cells, and in the developing heart, gastrointestinal tract, and brain. It may also be important in the regulation of vascular growth during the menstrual cycle, and in the stimulation of testosterone production in men. Epo and Epo-R are prominent in the brain during fetal development, leading to speculation that they play an important role in neurodevelopment. There are also promising data regarding rEpo as a possible neuroprotective agent in such conditions as hypoxia, because it decreases programmed cell death induced during such adverse conditions. It is unlikely, however, that rEpo crosses the blood-brain barrier in normal premature infants, and it is not clear whether the CNS effects of rEpo, should it cross the blood-brain barrier, are harmful or beneficial in the setting of a developing brain.

Erythropoietin protects cultured cortical neurons, but not astroglia, from hypoxia and AMPA toxicity

In addition to its better-known hemopoietic action, erythropoietin (Epo) has neurotrophic properties and neuroprotective effects in some models of hypoxic-ischemic injury. To define further the cellular mechanisms underlying neuroprotection by Epo, we studied the effects of Epo on hypoxia with glucose deprivation in cultured rat cortical neurons and astroglia and on exposure to excitotoxins in cultured rat cortical neurons. Epo (30 pM) reduced neuronal, but not astroglial, cell death from hypoxia with glucose deprivation, and also attenuated the neurotoxic effect of (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA), but not other excitotoxins. Epo appears to protect against cerebral ischemia through a direct effect on neurons that may be mediated in part by AMPA receptors.

The distribution of granulocyte-macrophage colony-stimulating factor and its receptor in the developing human fetus

The purpose of the present study was to determine the distribution of granulocyte-macrophage colony-stimulating factor (GM-CSF) and its receptor (GM-CSF-R) in the human fetus. We used reverse transcription PCR to detect GM-CSF and GM-CSF-R mRNA in human fetal organs at 8 and 16 wk postconception, and cell-specific protein expression was localized in tissues by immunohistochemistry. GM-CSF was also measured by ELISA in paired samples of spinal fluid and plasma. GM-CSF mRNA and/or protein were detected in lung macrophages, spleen, adrenal cortex, placenta, and CNS including neurons and astrocytes. GM-CSF was detected by ELISA in 10 of the 39 cerebrospinal fluid samples tested. GM-CSF-R mRNA expression was present in all organs tested. Immunoreactivity for GM-CSF-R in most organs was limited to macrophages, but, brain, neurons and glial cells showed immunoreactivity. We conclude that GM-CSF is produced in lung, spleen, adrenal, placenta, and neural tissues during human fetal development and that GM-CSF-responsive cells include macrophages, neurons, and glial cells.

Immunohistochemical localization of erythropoietin and its receptor in the developing human brain

We have previously shown erythropoietin (Epo) and its receptor (Epo-R) to be present in the fetal human central nervous system (CNS), and Epo to be present in the spinal fluid of normal preterm and term infants. To investigate the cellular specificities and developmental patterns of expression of these polypeptides in the human brain-areas that have not been well researched-we designed the following study. Human brains ranging in maturity from 5 weeks post-conception to adult were preserved at the time of elective abortion, surgical removal (tubal pregnancy, or removal for temporal lobe epilepsy), or autopsy. Immunohistochemistry was used to localize Epo and Epo-R reactivity in brains of different stages of development. Astrocytes, neurons, and microglia were identified in sequential tissue sections by specific antibodies. At 5 to 6 weeks post-conception, both Epo and Epo-R localized to cells in the periventricular germinal zone. At 10 weeks post-conception, Epo immunoreactivity was present throughout the cortical wall, with the most intense immunoreactivity present in the ventricular and subventricular zones. Epo-R, in contrast, was localized primarily to the subventricular zone, with little staining evident in the ventricular zone. In late fetal brains, Epo-R reactivity was most prominent in astrocytic cells, although modest reactivity was observed in certain neuron populations. In contrast, Epo staining localized primarily to neurons in fetal brains, although a subpopulation of astrocytes was also immunoreactive. In postnatal brains, both astrocyte and neuron populations were immunoreactive with antibodies to Epo-R and Epo. From these results it is clear that Epo and its receptor are present in the developing human brain as early as 5 weeks post-conception, and each protein shows a specific distribution that changes with development. We speculate that Epo is important in neurodevelopment, and that it also plays a role in brain homeostasis later in life, functioning in an autocrine or paracrine manner.

Members of the JAK/STAT proteins are expressed and regulated during development in the mammalian forebrain

The presence and activation of members of the Janus Kinases/Signal Transducers and Activator of Transcription proteins in response to specific cytokines is currently the focus of intense investigation in the hematopoietic system. Although some evidence suggests that cytokines might play an important role in brain development and brain pathologies, very limited information is available on the presence of the JAK/STAT proteins in the Central Nervous System. Here we provide Western blot and immunohistochemistry data on the presence of Jak2 in vivo in the immature brain, its expression being greater in early stages of the embryonic life and gradually diminishing towards adulthood. Conversely, Jak1 was found expressed at a lower level compared to Jak2 and not modulated during brain maturation. Western blot data also show that specific members of the STAT family, the cytoplasmic substrates of the Janus Kinases, are present in vivo and that the extent of their expression is modulated differently at various stages. In particular, Stat6 protein levels were markedly attenuated at advanced stages of differentiation, as well as in the adult brain, with respect to early embryonic life. On the contrary, Stat3 levels did not vary. Analysis of Statl and Stat5 proteins showed a more complex expression pattern. These data indicate that members of the JAK/STAT proteins are present and modulated in vivo in the embryonic and postnatal brain, therefore supporting their role in the modulation of gene expression during the different stages of brain maturation.

Tissue distribution of erythropoietin and erythropoietin receptor in the developing human fetus

OBJECTIVE

Erythropoietin receptors (Epo-R) have been demonstrated on several nonhematopoietic cell types in animal models and in cell culture. Our objective was to determine the tissue distribution and cellular specificity of erythropoietin (Epo) and its receptor in the developing human fetus.

STUDY DESIGN

The expression of Epo and Epo-R mRNA was ascertained by RT-PCR for organs ranging in maturity from 5 to 24 weeks postconception. The cellular location of protein immunoreactivity was then determined using specific antiEpo and antiEpo-R antibodies. Antibody specificity was established by Western analysis.

RESULTS

mRNA for Epo and Epo-R was found in all organs in the first two trimesters. Immunolocalization of Epo was limited to the liver parenchymal cells, kidney interstitial cells and proximal tubules, neural retina of the eye, and adrenal cortex. As development progressed, immunoreactivity in the kidney became more prominent. In contrast, immunoreactivity for Epo-R was widespread throughout the body, in cell types including endothelial cells, myocardiocytes, macrophages, retinal cells, cells of the adrenal cortex and medulla, as well as in small bowel, spleen, liver, kidney, and lung.

CONCLUSIONS

The distribution of Epo and its receptor is more widespread in the developing human than was initially postulated. Epo-R is expressed on many cell types during early fetal development, leading us to speculate that Epo acts in concert with somatic growth and development factors during this period. Further investigation is required to understand the nonhematopoietic role of Epo during human development.

Interleukin-1beta and its type 1 receptor are expressed in developing neural circuits in the frog, Xenopus laevis

The cytokine interleukin-1 beta (IL-1beta) is an evolutionarily conserved molecule that was originally identified in the immune system. In addition to regulating peripheral immune responses, IL-1beta plays an important role in mediating neural-immune interactions and regulating glial activities during healing and repair in the damaged nervous system. Active IL-1beta is produced by interleukin-converting enzyme (ICE), a caspase thought to be involved in the induction of apoptosis. We report that, in the developing frog, Xenopus laevis, IL-1beta and the IL-1 type 1 receptor proteins are coexpressed in specific neurons that comprise early sensory-motor circuits. IL-1beta and IL-1 type 1 receptor proteins are colocalized in specific midbrain and hindbrain reticular cells, including Mauthner's neuron; specific cells in the trigeminal (fifth), lateral line (seventh), and vestibular (eighth) cranial ganglia; oculomotor neurons; and the primordial Purkinje cells of the lateral cerebellar auricle. In the spinal cord, Rohon-Beard sensory neurons, dorsal root ganglion cells, and primary motoneurons are immunopositive. Anteriorly, the olfactory pits, olfactory nerves, and olfactory bulbs are labeled, as are retinal cells, especially photoreceptor inner segments. With regard to the function of IL-1beta during neural development, IL-1beta and its type 1 receptor are present throughout the course of neural development in identifiable, long-lived neurons, such as Mauthner's neuron. These and other data suggest that IL-1beta and its type 1 receptor may be involved in the maintenance of cell survival rather than induction of neuronal death.

Interleukin-3 and interleukin-3 receptors in the brain

We have previously demonstrated that interleukin 3 (IL-3) has a neurotrophic effect on central cholinergic neurons and have demonstrated the presence of IL-3 receptor (IL-3R)beta subunits in septal cholinergic neurons by reverse-transcribed polymerase chain reaction (RT-PCR) and immunohistochemistry. In order to confirm that the expressed IL-3R is functional, we conducted experiments to show an alpha subunit of IL-3R. The alpha subunit was clearly demonstrated by RT-PCR in the central cholinergic neuronal hybrid cell line SN6, but not in its mother cell line N18TG2, and the expression was slightly upregulated after IL-3 treatment. Choline acetyltransferase and vesicular acetylcholine transporter mRNAs were significantly increased in SN6 after treatment with IL-3. Immunohistochemically, IL-3R alpha-positive cells were mainly present in the medial septal and basal forebrain region, and the stained cells were similar to choline acetyltransferase-positive cells in shape and distribution. The IL-3R alpha-positive cells slightly increased two days after fimbria-fornix transection and decreased seven days after. These findings suggest that functional IL-3 receptors are expressed in the central cholinergic neurons and contribute to some physiological roles such as the differentiation and maintenance of these neurons.

Erythropoietin and erythropoietin receptor in the developing human central nervous system

We have previously shown the presence of erythropoietin (Epo) within the spinal fluid of normal preterm and term infants, and the presence of Epo receptor (Epo-R) in the spinal cords of human fetuses. It is not known, however: 1) whether cells within the fetal central nervous system (CNS) express Epo; 2) if so, whether this expression changes with development; 3) which cells within the CNS express Epo-R; 4) whether Epo-R expression within the CNS changes with development; and 5) whether Epo-R within the fetal CNS are functional. Expression of mRNA for Epo and Epo-R was sought by reverse transcription-PCR in mixed primary cultures of fetal spinal cords as well as NT2 and hNT cells, human cell lines of neuronal precursors and mature neurons, respectively. Epo was measured by ELISA in spent media from primary cell culture, and immunohistochemistry was used to identify Epo-R on neurons and glia in cell culture, and in brain sections. Developmental changes in Epo and Epo-R expression were sought in spinal cords and brains from fetuses of 7-24 wk postconception by semiquantitative PCR. To assess Epo-R function, NT2 cells were exposed to conditions which stimulate programmed cell death, and rescue from apoptosis by the addition of recombinant Epo was evaluated by nuclear matrix protein ELISA, cell counts, and by Klenow labeling of DNA fragments. Epo and Epo-R mRNA were expressed in mixed primary cultures of neural tissues and NT2 and hNT cells. Epo was detected by ELISA in media removed from mixed cell cultures, and immunohistochemical staining confirmed the presence of Epo-R on neurons and their supporting cells. Semiquantitative PCR revealed no significant change in expression of either Epo or Epo-R in spinal cords between 7 and 16 wk of gestation, with increased expression of Epo and Epo-R in brains from 8 to 24 wk of gestation. Epo mRNA expression from neurons doubled under conditions of hypoxia. Recombinant Epo decreased apoptotic cell death of neurons under conditions of hypoxia. Protein and mRNA for Epo and its receptor are expressed by human neurons and glial cells in spinal cord and brain during fetal development. These receptors appear to have a neuroprotective effect in conditions of hypoxia.

Regulated human erythropoietin receptor expression in mouse brain

Erythropoietin (Epo) is known for its role in erythropoiesis and acts by binding to its receptor (EpoR) on the surface of erythroid progenitors. EpoR activity follows the site of hematopoiesis from the embryonic yolk sac to the fetal liver and then the adult spleen and bone marrow. Expression of EpoR has also been observed in selected cells of non-hematopoietic origin, such as the embryonic mouse brain during mid-gestation, at levels comparable to adult bone marrow. EpoR transcripts in brain decrease during development falling by birth to less than 1-3% of the level in hematopoietic tissue. We have now recapitulated this pattern of expression using a human EpoR transgene consisting of an 80-kb human EpoR genomic fragment. The highest level of expression was observed in the embryonic yolk sac and fetal liver, analogous to the endogenous gene, in addition to expression in adult spleen and bone marrow. Although activity of this transgene in brain is initially lower than the endogenous gene, it does exhibit the down-regulation observed for the endogenous gene in adult brain. The expression pattern of hybrid transgenes of an hEpoR promoter fused to beta-galactosidase in 9. 5-day embryos suggested that the hEpoR promoter region between -1778 and -150 bp 5' of the transcription start site is necessary to direct EpoR expression in the neural tube. EpoR expression in the neural tube may be the origin of the EpoR transcripts detected in brain during development. These data demonstrate that both the mouse and human EpoR genes contain regulatory elements to direct significant levels of expression in a developmentally controlled manner in brain and suggest that in addition to its function during erythropoiesis, EpoR may play a role in the development of selected non-hematopoietic tissue.