Expression of constitutively active erythropoietin receptor in pyramidal neurons of cortex and hippocampus boosts higher cognitive functions in mice

Erythropoietin restrains the inhibitory potential of interneurons in the mouse hippocampus

Severe psychiatric illnesses, for instance schizophrenia, and affective diseases or autism spectrum disorders, have been associated with cognitive impairment and perturbed excitatory-inhibitory balance in the brain. Effects in juvenile mice can elucidate how erythropoietin (EPO) might aid in rectifying hippocampal transcriptional networks and synaptic structures of pyramidal lineages, conceivably explaining mitigation of neuropsychiatric diseases. An imminent conundrum is how EPO restores synapses by involving interneurons. By analyzing ~12,000 single-nuclei transcriptomic data, we generated a comprehensive molecular atlas of hippocampal interneurons, resolved into 15 interneuron subtypes. Next, we studied molecular alterations upon recombinant human (rh)EPO and saw that gene expression changes relate to synaptic structure, trans-synaptic signaling and intracellular catabolic pathways. Putative ligand-receptor interactions between pyramidal and inhibitory neurons, regulating synaptogenesis, are altered upon rhEPO. An array of in/ex vivo experiments confirms that specific interneuronal populations exhibit reduced dendritic complexity, synaptic connectivity, and changes in plasticity-related molecules. Metabolism and inhibitory potential of interneuron subgroups are compromised, leading to greater excitability of pyramidal neurons. To conclude, improvement by rhEPO of neuropsychiatric phenotypes may partly owe to restrictive control over interneurons, facilitating re-connectivity and synapse development.

Expression of erythropoietin receptor protein in the mouse hippocampus in response to normobaric hypoxia

Background

Over the past decades, accumulating research on erythropoietin (EPO) and its receptor (EPOR) has revealed various neuroprotective actions and upregulation in hypoxic conditions. To our knowledge, EPOR protein levels in the hippocampus and isocortex have never been measured. Therefore, the aim of this study was to measure EPOR protein in the hippocampus (HPC) and prefrontal cortex (PFC). Further objectives were to examine the effects of exposure to normobaric hypoxia of various degrees and durations on EPOR protein and to explore how long-lasting these effects were.

Method

Adult C57BL/6 mice were randomized into a control group (N = 12) or various hypoxia groups (N = 5-11). Mice were exposed to three different O2 concentrations (10 %, 12 %, or 18 %) for 8 h a day for 5 days and sacrificed immediately after the last exposure. The effect of exposure to 12 % O2 for 1 day and 4 weeks (8 h per day) at this survival time was also examined. Additionally, groups of mice were exposed to 12 % O2 for 1 or 5 days (8 h per day) and euthanized at various times (up to 3 weeks) thereafter to examine the duration of EPOR protein regulation in the HPC and the PFC. EPOR protein was detected with a sandwich-ELISA method.

Results

EPOR protein was present in the HPC and PFC, at 206.64 ± 43.98 pg/mg and 184.25 ± 48.21 pg/mg, respectively. The highest increase in EPOR protein was observed in the HPC after 5 days of 8 h exposure to 12 % O2 and was most pronounced 24 h after last exposure. The effect of hypoxia normalized within one week after the last exposure.

Conclusion

This study successfully measured hippocampal EPOR protein and showed a significant association between normobaric hypoxia and acute EPOR elevation. It is our hope that this study can provide guidance to future research on the neuroprotective effects of EPO.

Physiological and cognitive changes after treatments of cyclophosphamide, methotrexate, and fluorouracil: implications of the gut microbiome and depressive-like behavior

Introduction

Chemotherapy-induced cognitive impairment colloquially referred to as chemobrain is a poorly understood phenomenon affecting a highly variable proportion of patients with breast cancer. Here we investigate the association between anxiety and despair-like behaviors in mice treated with cyclophosphamide, methotrexate, and fluorouracil (CMF) along with host histological, proteomic, gene expression, and gut microbial responses.

Methods

Forced swim and sociability tests were used to evaluate depression and despair-like behaviors. The tandem mass tag (TMT) proteomics approach was used to assess changes in the neural protein network of the amygdala and hippocampus. The composition of gut microbiota was assessed through 16S rRNA gene sequencing. Finally, quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to evaluate changes in intestinal gap junction markers.

Results and discussion

We observed that CMF induced social and despair-like behavior in mice 96 hours following treatment. Proteomic analysis identified changes in various proteins related to progressive neurological disease, working memory deficit, primary anxiety disorder, and gene expression revealing increases in NMDA and AMPA receptors in both the hippocampus and the amygdala because of CMF treatment. These changes finally, we observed immediate changes in the microbial population after chemotherapy treatment, with a notable abundance of Muribaculaceae and Romboutsia which may contribute to changes seen in the gut.

Erythropoietin re-wires cognition-associated transcriptional networks

Recombinant human erythropoietin (rhEPO) has potent procognitive effects, likely hematopoiesis-independent, but underlying mechanisms and physiological role of brain-expressed EPO remained obscure. Here, we provide transcriptional hippocampal profiling of male mice treated with rhEPO. Based on ~108,000 single nuclei, we unmask multiple pyramidal lineages with their comprehensive molecular signatures. By temporal profiling and gene regulatory analysis, we build developmental trajectory of CA1 pyramidal neurons derived from multiple predecessor lineages and elucidate gene regulatory networks underlying their fate determination. With EPO as 'tool', we discover populations of newly differentiating pyramidal neurons, overpopulating to ~200% upon rhEPO with upregulation of genes crucial for neurodifferentiation, dendrite growth, synaptogenesis, memory formation, and cognition. Using a Cre-based approach to visually distinguish pre-existing from newly formed pyramidal neurons for patch-clamp recordings, we learn that rhEPO treatment differentially affects excitatory and inhibitory inputs. Our findings provide mechanistic insight into how EPO modulates neuronal functions and networks.

Ameliorating age-dependent effects of resveratrol on VPA-induced social impairments and anxiety-like behaviors in a rat model of Neurodevelopmental Disorder

Although anxiety disorders, as well as difficulties in social interaction, are documented in children with autism spectrum disorder (ASD) as a neurodevelopmental disorder, the effectiveness of potential therapeutic procedures considering age and sex differences is under serious discussion. The present study aimed to investigate the effect of resveratrol (RSV) on anxiety-like behaviors and social interaction in juvenile and adult rats of both sex in a valproic acid (VPA)-induced autistic-like model. Prenatal exposure to VPA was associated with increased anxiety, also causing a significant reduction in social interaction in juvenile male subjects. Further administration of RSV attenuated VPA-induced anxiety symptoms in both sexes of adult animals and significantly increased the sociability index in male and female juvenile rats. Taken together, it can be concluded that treatment with RSV can attenuate some of the harsh effects of VPA. This treatment was especially effective on anxiety-like traits in adult subjects of both sexes regarding their performance in open field and EPM. We encourage future research to consider the sex and age-specific mechanisms behind the RSV treatment in the prenatal VPA model of autism.

Erythropoietin as a Neuroprotective Drug for Newborn Infants: Ten Years after the First Use

Protective strategies against perinatal brain injury represent a major challenge for modern neonatology. Erythropoietin (Epo) enhances endogenous mechanisms of repair and angiogenesis. In order to analyse the newest evidence on the role of Epo in prematurity, hypoxic ischemic encephalopathy (HIE) and perinatal stroke, a critical review using 2020 PRISMA statement guidelines was conducted. This review uncovered 26 clinical trials examining the use of Epo for prematurity and brain injury-related outcomes. The effects of Epo on prematurity were analysed in 16 clinical trials. Erythropoietin was provided until 32–35 weeks of corrected postnatal age with a dosage between 500–3000 UI/kg/dose. Eight trials reported the Epo effects on HIE term newborn infants: Erythropoietin was administered in the first weeks of life, at different multiple doses between 250–2500 UI/kg/dose, as either an adjuvant therapy with hypothermia or a substitute for hypothermia. Two trials investigated Epo effects in perinatal stroke. Erythropoietin was administered at a dose of 1000 IU/kg for three days. No beneficial effect in improving morbidity was observed after Epo administration in perinatal stroke. A positive effect on neurodevelopmental outcome seems to occur when Epo is used as an adjuvant therapy with hypothermia in the HIE newborns. Administration of Epo in preterm infants still presents inconsistencies with regard to neurodevelopmental outcome. Clinical trials show significant differences mainly in target population and intervention scheme. The identification of specific markers and their temporal expression at different time of recovery after hypoxia-ischemia in neonates might be implemented to optimize the therapeutic scheme after hypoxic-ischemic injury in the developing brain. Additional studies on tailored regimes, accounting for the risk stratification of brain damage in newborns, are required.

Introducing the brain erythropoietin circle to explain adaptive brain hardware upgrade and improved performance

Executive functions, learning, attention, and processing speed are imperative facets of cognitive performance, affected in neuropsychiatric disorders. In clinical studies on different patient groups, recombinant human (rh) erythropoietin (EPO) lastingly improved higher cognition and reduced brain matter loss. Correspondingly, rhEPO treatment of young rodents or EPO receptor (EPOR) overexpression in pyramidal neurons caused remarkable and enduring cognitive improvement, together with enhanced hippocampal long-term potentiation. The 'brain hardware upgrade', underlying these observations, includes an EPO induced ~20% increase in pyramidal neurons and oligodendrocytes in cornu ammonis hippocampi in the absence of elevated DNA synthesis. In parallel, EPO reduces microglia numbers and dampens their activity and metabolism as prerequisites for undisturbed EPO-driven differentiation of pre-existing local neuronal precursors. These processes depend on neuronal and microglial EPOR. This novel mechanism of powerful postnatal neurogenesis, outside the classical neurogenic niches, and on-demand delivery of new cells, paralleled by dendritic spine increase, let us hypothesize a physiological procognitive role of hypoxia-induced endogenous EPO in brain, which we imitate by rhEPO treatment. Here we delineate the brain EPO circle as working model explaining adaptive 'brain hardware upgrade' and improved performance. In this fundamental regulatory circle, neuronal networks, challenged by motor-cognitive tasks, drift into transient 'functional hypoxia', thereby triggering neuronal EPO/EPOR expression.

Repeated episodes of transient reduction of oxygen exposure simulating aircraft cabin conditions enhance resilience to stress in mice

Pilots and crew of domestic flights are exposed to transient periods of mild reductions of partial pressure of inspired oxygen each day, and this might have functional consequence on their performance in the long range. Here, we exposed mice to mild reductions of oxygen exposure (ROE) four times per day for 21 days by lowering oxygen partial pressure to levels corresponding to an altitude of about 2300 m, which is the quote of pressurization of the air cabin. Four groups of mice were studied: unstressed or stressed mice exposed to ROE or normoxic conditions. Mice were exposed to chronic unpredictable stress (CUS) for 28 days, and ROE was delivered in the last 21 days of CUS. In normoxic mice, CUS caused anhedonia in the sucrose preference test, anxiety-like behaviour in the open field test, learning impairment in the Morris water maze, reduced hippocampal neurogenesis, increased serum corticosterone levels and increased expression of depression-related genes (Pclo, Mthfr and Grm5) in the hippocampus. All these changes were reversed by ROE, which had little or no effect in unstressed mice. These findings suggest that ROE simulating air cabin conditions of domestic flights may enhance resilience to stress improving mood, anxiety and learning ability.

Erythropoietin and Non-Erythropoietic Derivatives in Cognition

Cognitive deficits are widespread in psychiatric disorders, including major depression and schizophrenia. These deficits are known to contribute significantly to the accompanying functional impairment. Progress in the development of targeted treatments of cognitive deficits has been limited and there exists a major unmet need to develop more efficacious treatments. Erythropoietin (Epo) has shown promising procognitive effects in psychiatric disorders, providing support for a neurotrophic drug development approach. Several preclinical studies with non-erythropoietic derivatives have demonstrated that the modulation of behavior is independent of erythropoiesis. In this review, we examine the molecular, cellular and cognitive actions of Epo and non-erythropoietic molecular derivatives by focusing on their neurotrophic, synaptic, myelin plasticity, anti-inflammatory and neurogenic mechanisms in the brain. We also discuss the role of receptor signaling in Epo and non-erythropoietic EPO-mimetic molecules in their procognitive effects.

Erythropoietin and derivatives: Potential beneficial effects on the brain

Erythropoietin (Epo), the main erythropoiesis-stimulating factor widely prescribed to overcome anemia, is also known nowadays for its cytoprotective action on non-hematopoietic tissues. In this context, Epo showed not only its ability to cross the blood-brain barrier, but also its expression in the brain of mammals. In clinical trials, recombinant Epo treatment has been shown to stimulate neurogenesis; improve cognition; and activate antiapoptotic, antioxidant, and anti-inflammatory signaling pathways. These mechanisms, proposed to characterize a neuroprotective property, opened new perspectives on the Epo pharmacological potencies. However, many questions arise about a possible physiological role of Epo in the central nervous system (CNS) and the factors or environmental conditions that induce its expression. Although Epo may be considered a strong candidate to be used against neuronal damage, long-term treatments, particularly when high Epo doses are needed, may induce thromboembolic complications associated with increases in hematocrit and blood viscosity. To avoid these adverse effects, different Epo analogs without erythropoietic activity but maintaining neuroprotection ability are currently being investigated. Carbamylated erythropoietin, as well as alternative molecules like Epo fusion proteins and partial peptides of Epo, seems to match this profile. This review will focus on the discussion of experimental evidence reported in recent years linking erythropoietin and CNS function through investigations aimed at finding benefits in the treatment of neurodegenerative diseases. In addition, it will review the proposed mechanisms for novel derivatives which may clarify and, eventually, improve the neuroprotective action of Epo.

CaMKIIα Expressing Neurons to Report Activity-Related Endogenous Hypoxia upon Motor-Cognitive Challenge

We previously introduced the brain erythropoietin (EPO) circle as a model to explain the adaptive 'brain hardware upgrade' and enhanced performance. In this fundamental circle, brain cells, challenged by motor-cognitive tasks, experience functional hypoxia, triggering the expression of EPO among other genes. We attested hypoxic cells by a transgenic reporter approach under the ubiquitous CAG promoter, with Hif-1α oxygen-dependent degradation-domain (ODD) fused to CreERT2-recombinase. To specifically focus on the functional hypoxia of excitatory pyramidal neurons, here, we generated CaMKIIα-CreERT2-ODD::R26R-tdTomato mice. Behavioral challenges, light-sheet microscopy, immunohistochemistry, single-cell mRNA-seq, and neuronal cultures under normoxia or hypoxia served to portray these mice. Upon complex running wheel performance as the motor-cognitive task, a distinct increase in functional hypoxic neurons was assessed immunohistochemically and confirmed three-dimensionally. In contrast, fear conditioning as hippocampal stimulus was likely too short-lived to provoke neuronal hypoxia. Transcriptome data of hippocampus under normoxia versus inspiratory hypoxia revealed increases in CA1 CaMKIIα-neurons with an immature signature, characterized by the expression of Dcx, Tbr1, CaMKIIα, Tle4, and Zbtb20, and consistent with accelerated differentiation. The hypoxia reporter response was reproduced in vitro upon neuronal maturation. To conclude, task-associated activity triggers neuronal functional hypoxia as a local and brain-wide reaction mediating adaptive neuroplasticity. Hypoxia-induced genes such as EPO drive neuronal differentiation, brain maturation, and improved performance.

Erythropoietin Stimulates GABAergic Maturation in the Mouse Hippocampus

Several neurodevelopmental disabilities are strongly associated with alterations in GABAergic transmission, and therapies to stimulate its normal development are lacking. Erythropoietin (EPO) is clinically used in neonatology to mitigate acute brain injury, and to stimulate neuronal maturation. Yet it remains unclear whether EPO can stimulate maturation of the GABAergic system. Here, with the use of a transgenic mouse line that constitutively overexpresses neuronal EPO (Tg21), we show that EPO stimulates postnatal GABAergic maturation in the hippocampus. We show an increase in hippocampal GABA-immunoreactive neurons, and postnatal elevation of interneurons expressing parvalbumin (PV), somatostatin (SST), and neuropeptide Y (NPY). Analysis of perineuronal net (PNN) formation and innervation of glutamatergic terminals onto PV+ cells, shows to be enhanced early in postnatal development. Additionally, an increase in GABA_Aergic synapse density and IPSCs in CA1 pyramidal cells from Tg21 mice is observed. Detection of EPO receptor (EPOR) mRNA was observed to be restricted to glutamatergic pyramidal cells and increased in Tg21 mice at postnatal day (P)7, along with reduced apoptosis. Our findings show that EPO can stimulate postnatal GABAergic maturation in the hippocampus, by increasing neuronal survival, modulating critical plasticity periods, and increasing synaptic transmission. Our data supports EPO’s clinical use to balance GABAergic dysfunction.

Sex dependent alterations of resveratrol on social behaviors and nociceptive reactivity in VPA-induced autistic-like model in rats

INTRODUCTION

The present study was designed to clarify the effects of resveratrol (RSV) on social behavioral alterations and nociceptive reactivity in valproic acid (VPA)-induced autistic-like model in female and male rats.

METHODS

Pregnant Wistar rats were randomly divided in five groups. Animals received saline, DMSO, VPA, RSV and RSV + VPA. VPA was administered (600 mg/kg, i. p.) on embryonic day 12.5 (E12.5) and pretreatment by resveratrol (3.6 mg/kg, s. c.) was applied on E6.5 until E18.5. All offspring were weaned on postnatal day 21 and the experiments were done in male and female rats on day 60. Social interaction, hot plate and tail flick tests were set out to assess social deficits and pain threshold, respectively. Sociability index (SI), Social novelty index (SNI) and latency time were calculated as the standard indices of social behaviors and pain threshold, respectively.

RESULTS

The results indicated that systemic intraperitoneal administration of VPA (600 mg/kg) significantly decreased SI and SNI in social interaction test (SIT) especially in male rats, indicating the social impairments caused by VPA. RSV (3.6 mg/kg, s. c.) reversed VPA-induced social deficits in male rats, but not in female group. VPA administration resulted in significant increase in latency time in the hot plate and tail flick tests in male rats, whereas it had no such dramatic effect in females. RSV administration in combination with VPA had no significant effect on latency time compared to the valproic acid group in male rats. It is important to note that RSV by itself had no significant effect on SI, SNI and latency time in female and male rats.

CONCLUSION

It can be concluded that valproic acid produces autistic-like behaviors and increases pain threshold in male rats which may be ameliorated at least in part by resveratrol administration. Further studies are needed to elucidate the molecular mechanisms involved in valproic acid and resveratrol-induced effects.

Erythropoietin as a Neuroprotective Molecule: An Overview of Its Therapeutic Potential in Neurodegenerative Diseases

Erythropoietin (EPO) is a cytokine mainly induced in hypoxia conditions. Its major production site is the kidney. EPO primarily acts on the erythroid progenitor cells in the bone marrow. More and more studies are highlighting its secondary functions, with a crucial focus on its role in the central nervous system. Here, EPO may interact with up to four distinct isoforms of its receptor (erythropoietin receptor [EPOR]), activating different signaling cascades with roles in neuroprotection and neurogenesis. Indeed, the EPO/EPOR axis has been widely studied in the neurodegenerative diseases field. Its potential therapeutic effects have been evaluated in multiple disorders, such as Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, spinal cord injury, as well as brain ischemia, hypoxia, and hyperoxia. EPO is showing great promise by counteracting secondary neuroinflammatory processes, reactive oxygen species imbalance, and cell death in these diseases. Multiple studies have been performed both in vitro and in vivo, characterizing the mechanisms through which EPO exerts its neurotrophic action. In some cases, clinical trials involving EPO have been performed, highlighting its therapeutic potential. Together, all these works indicate the potential beneficial effects of EPO.

Functional hypoxia drives neuroplasticity and neurogenesis via brain erythropoietin

Erythropoietin (EPO), named after its role in hematopoiesis, is also expressed in mammalian brain. In clinical settings, recombinant EPO treatment has revealed a remarkable improvement of cognition, but underlying mechanisms have remained obscure. Here, we show with a novel line of reporter mice that cognitive challenge induces local/endogenous hypoxia in hippocampal pyramidal neurons, hence enhancing expression of EPO and EPO receptor (EPOR). High-dose EPO administration, amplifying auto/paracrine EPO/EPOR signaling, prompts the emergence of new CA1 neurons and enhanced dendritic spine densities. Single-cell sequencing reveals rapid increase in newly differentiating neurons. Importantly, improved performance on complex running wheels after EPO is imitated by exposure to mild exogenous/inspiratory hypoxia. All these effects depend on neuronal expression of the Epor gene. This suggests a model of neuroplasticity in form of a fundamental regulatory circle, in which neuronal networks—challenged by cognitive tasks—drift into transient hypoxia, thereby triggering neuronal EPO/EPOR expression.

EPO treatment improves cognition, but underlying mechanisms were unknown. Here the authors describe a regulatory loop in which brain networks challenged by cognitive tasks drift into functional hypoxia that drives—via neuronal EPO synthesis—neurodifferentiation and dendritic spine formation.

Erythropoietin and Friedreich Ataxia: Time for a Reappraisal?

Friedreich ataxia (FRDA) is a rare neurological disorder due to deficiency of the mitochondrial protein frataxin. Frataxin deficiency results in impaired mitochondrial function and iron deposition in affected tissues. Erythropoietin (EPO) is a cytokine which was mostly known as a key regulator of erythropoiesis until cumulative evidence showed additional neurotrophic and neuroprotective properties. These features offered the rationale for advancement of EPO in clinical trials in different neurological disorders in the past years, including FRDA. Several mechanisms of action of EPO may be beneficial in FRDA. First of all, EPO exposure results in frataxin upregulation in vitro and in vivo. By promoting erythropoiesis, EPO influences iron metabolism and induces shifts in iron pool which may ameliorate conditions of free iron excess and iron accumulation. Furthermore, EPO signaling is crucial for mitochondrial gene activation and mitochondrial biogenesis. Up to date nine clinical trials investigated the effects of EPO and derivatives in FRDA. The majority of these studies had a proof-of-concept design. Considering the natural history of FRDA, all of them were too short in duration and not powered for clinical changes. However, these studies addressed significant issues in the treatment with EPO, such as (1) the challenge of the dose finding, (2) stability of frataxin up-regulation, (3) continuous versus intermittent stimulation with EPO/regimen, or (4) tissue changes after EPO exposure in humans in vivo (muscle biopsy, brain imaging). Despite several clinical trials in the past, no treatment is available for the treatment of FRDA. Current lines of research focus on gene therapy, frataxin replacement strategies and on regulation of key metabolic checkpoints such as NrF2. Due to potential crosstalk with all these mechanisms, interventions on the EPO pathway still represent a valuable research field. The recent development of small EPO mimetics which maintain cytoprotective properties without erythropoietic action may open a new era in EPO research for the treatment of FRDA.

The Recombinant Human Erythropoietin Administered in Neonatal Rats After Excitotoxic Damage Induces Molecular Changes in the Hippocampus

In vitro and in vivo experimental evidence has contributed important knowledge regarding the antiapoptotic effect mediated by EPO signaling in the damaged brain, particularly through different models with a hypoxic component. However, little emphasis has been placed on the effectiveness of rhEPO administration against cellular alterations caused by in vivo excitotoxicity or on the molecular mechanism that regulates this effect. In this study, we investigated the effects of a single dose of rhEPO on hippocampal damage induced by subcutaneous application of monosodium glutamate (MSG) on postnatal days 1, 3, 5 and 7 in neonatal rats. We found that a dose of 1000 IU/kg of b.w. administered 24 h after MSG had the greatest protective effect. In addition, we analyzed changes in gene expression, particularly in 3 key molecules involved in EPO-mediated signaling (EPO, EPOR and βcR). We observed that the expression of EPO and EPOR was differentially modified at both the mRNA and protein levels under the evaluated conditions, while the expression of the βcR gene was substantially increased. Our data suggest that a low dose of rhEPO is sufficient to induce cellular protection under these experimental conditions and that the molecular changes could be a positive feedback mechanism, mediated by reactive astrocytes in association with in vivo neuroprotective mechanisms.

Neural correlates of improved recognition of happy faces after erythropoietin treatment in bipolar disorder

OBJECTIVE

Bipolar disorder is associated with impairments in social cognition including the recognition of happy faces. This is accompanied by imbalanced cortico-limbic response to emotional faces. We found that EPO improved the recognition of happy faces in patients with bipolar disorder. This randomized, controlled, longitudinal fMRI study explores the neuronal underpinnings of this effect.

METHOD

Forty-four patients with bipolar disorder in full or partial remission were randomized to eight weekly erythropoietin (EPO; 40 000 IU) or saline (NaCl 0.9%) infusions in a double-blind, parallel-group design. Participants underwent whole-brain fMRI at 3T, mood ratings and blood tests at baseline and week 14. During fMRI, participants viewed happy and fearful faces and performed a gender discrimination task.

RESULTS

Thirty-four patients had complete pre- and post-treatment fMRI data (EPO: N = 18, saline: N = 16). Erythropoietin vs. saline increased right superior frontal response to happy vs. fearful faces. This correlated with improved happiness recognition in the EPO group. Erythropoietin also enhanced gender discrimination accuracy for happy faces. These effects were not influenced by medication, mood, red blood cells or blood pressure.

CONCLUSIONS

Together with previous findings, the present observation suggests that increased dorsal prefrontal attention control is a common mechanism of EPO-associated improvements across several cognitive domains.

Contradictory effects of erythropoietin on inhibitory synaptic transmission in left and right prelimbic cortex of mice

Erythropoietin (EPO) has been shown to improve cognitive function in mammals as well as in patients of psychiatric diseases by directly acting on the brain. In addition, EPO attenuates the synaptic transmission and enhances short- and long-term synaptic plasticity in hippocampus of mice, although there are still many discrepancies between different studies. It has been suggested that the divergences of different studies take root in different in-vivo application schemata or in long-term trophic effects of EPO. In the current study, we investigated the direct effects of EPO in slices of prelimbic cortex (PrL) by acute ex-vivo application of EPO, so that the erythropoietic or other trophic effects could be entirely excluded. Our results showed that the EPO effects were contradictory between the left and the right PrL. It enhanced the inhibitory transmission in the left and depressed the inhibitory transmission in the right PrL. Strikingly, this lateralized effect of EPO could be consistently found in individual bi-lateral PrL of all tested mice. Thus, our data suggest that EPO differentially modulates the inhibitory synaptic transmission of neuronal networks in the left and the right PrL. We hypothesize that such lateralized effects of EPO contribute to the development of the lateralization of stress reaction in PFC and underlie the altered bilateral GAGAergic synaptic transmission and oscillation patterns under stress that impact the central emotional and cognitive control in physiology as well as in pathophysiology.

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EPO showed fast effects on inhibitory transmission in the prefrontal cortex of mice.

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EPO enhanced the inhibitory transmission in the left and depressed it in the right prelimbic cortex of mice.

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The expression of EPOR in GAD⁺-neurons is different between the left and right PFC.

Erythropoietin Induces Homeostatic Plasticity at Hippocampal Synapses

The cytokine erythropoietin (EPO) is the master regulator of erythropoiesis. Intriguingly, many studies have shown that the cognitive performance of patients receiving EPO for its hematopoietic effects is enhanced, which prompted the growing interest in the use of EPO-based strategies to treat neuropsychiatric disorders. EPO plays key roles in brain development and maturation, but also modulates synaptic transmission. However, the mechanisms underlying the latter have remained elusive. Here, we show that acute (40-60 min) exposure to EPO presynaptically downregulates spontaneous and afferent-evoked excitatory transmission, without affecting basal firing of action potentials. Conversely, prolonged (3 h) exposure to EPO, if followed by a recovery period (1 h), is able to elicit a homeostatic increase in excitatory spontaneous, but not in evoked, synaptic transmission. These data lend support to the emerging view that segregated pathways underlie spontaneous and evoked neurotransmitter release. Furthermore, we show that prolonged exposure to EPO facilitates a form of hippocampal long-term potentiation that requires noncanonical recruitment of calcium-permeable AMPA receptors for its maintenance. These findings provide important new insight into the mechanisms by which EPO enhances neuronal function, learning, and memory.

Erythropoietin suppresses D-galactose-induced aging of rats via the PI3K/Akt/Nrf2-ARE pathway

EPO (erythropoietin) is a hormone-like substance with a putative role in hematopoietic regulation. Current research suggests that it exerts a neuroprotective effect by enhancing the activity of antioxidant enzymes. Our previous studies in vitro have confirmed that EPO can delay senescence of cultured neurons by activation of nuclear factor-erythroid 2-related factor 2 (Nrf2) and the phosphoinositide-3-kinase (PI3K)/AKT pathway. Thus we set out to further substantiate the mechanism in vivo. A rat model of aging was induced by continuous subcutaneous injection of 5% D-galactose for 6 weeks. Starting at the 7th week, physiological saline or EPO was administered twice daily. LY294002, an inhibitor of the PI3K/AKT pathway, was also given to one of the groups. Improvement of learning and memory abilities were observed in the EPO intervention group. Raised levels of Cu-Zn SOD protein were detected by immunohistochemical staining and Western blot after using EPO, together with increased expression of PI3K/AKT pathway proteins. Concomitantly, there was an increase in expression of Nrf2 mRNA and a decrease in expression of Keap1 mRNA by qRT-PCR. All these effects were not found in the group injected with LY294002. We conclude that EPO can suppress aging by reducing oxidative stress. The proposed mechanism is an upregulation of the PI3K/Akt/Nrf2-ARE pathway and thus maintenance of expression and activation of antioxidant enzymes in aging rats.

Alternative Erythropoietin Receptors in the Nervous System

In addition to its regulatory function in the formation of red blood cells (erythropoiesis) in vertebrates, Erythropoietin (Epo) contributes to beneficial functions in a variety of non-hematopoietic tissues including the nervous system. Epo protects cells from apoptosis, reduces inflammatory responses and supports re-establishment of compromised functions by stimulating proliferation, migration and differentiation to compensate for lost or injured cells. Similar neuroprotective and regenerative functions of Epo have been described in the nervous systems of both vertebrates and invertebrates, indicating that tissue-protective Epo-like signaling has evolved prior to its erythropoietic function in the vertebrate lineage. Epo mediates its erythropoietic function through a homodimeric Epo receptor (EpoR) that is also widely expressed in the nervous system. However, identification of neuroprotective but non-erythropoietic Epo splice variants and Epo derivatives indicated the existence of other types of Epo receptors. In this review, we summarize evidence for potential Epo receptors that might mediate Epo's tissue-protective function in non-hematopoietic tissue, with focus on the nervous system. In particular, besides EpoR, we discuss three other potential neuroprotective Epo receptors: (1) a heteroreceptor consisting of EpoR and common beta receptor (βcR), (2) the Ephrin (Eph) B4 receptor and (3) the human orphan cytokine receptor-like factor 3 (CRLF3).

Neuroprotective effects of erythropoietin on neurodegenerative and ischemic brain diseases: the role of erythropoietin receptor

Erythropoietin (Epo) is a fundamental hormone in the regulation of hematopoiesis, and other secondary roles mediated by the binding of the hormone to its specific receptor (EpoR), which leads to an activation of key signaling pathways that induce an increase in cell differentiation, apoptosis control and neuroprotection. It has been suggested that their function depends on final conformation of glycosylations, related with affinity to the receptor and its half-life. The presence of EpoR has been reported in different tissues including central nervous system, where it has been demonstrated to exert a neuroprotective function against oxidative stress conditions, such as ischemic injury and neurodegenerative diseases. There is also evidence of an increase in EpoR expression in brain cell lysates of Alzheimer's patients with respect to healthy patients. These results are related with extensive in vitro experimental data of neuroprotection obtained from cell lines, primary cell cultures and hippocampal slices. Additionally, this data is correlated with in vivo experiments (water maze test) in mouse models of Alzheimer's disease where Epo treatment improved cognitive function. These studies support the idea that receptor activation induces a neuroprotective effect in neurodegenerative disorders including dementias, and especially Alzheimer's disease. Taken together, available evidence suggests that Epo appears to be a central element for EpoR activation and neuroprotective properties in the central nervous system. In this review, we will describe the mechanisms associated with neuroprotection and its relation with the activation of EpoR in order with identify new targets to develop pharmacological strategies.

The Insect Ortholog of the Human Orphan Cytokine Receptor CRLF3 Is a Neuroprotective Erythropoietin Receptor

The cytokine erythropoietin (Epo) mediates various cell homeostatic responses to environmental challenges and pathological insults. While stimulation of vertebrate erythrocyte production is mediated by homodimeric “classical” Epo receptors, alternative receptors are involved in neuroprotection. However, their identity remains enigmatic due to complex cytokine ligand and receptor interactions and conflicting experimental results. Besides the classical Epo receptor, the family of type I cytokine receptors also includes the poorly characterized orphan cytokine receptor-like factor 3 (CRLF3) present in vertebrates including human and various insect species. By making use of the more simple genetic makeup of insect model systems, we studied whether CRLF3 is a neuroprotective Epo receptor in animals. We identified a single ortholog of CRLF3 in the beetle Tribolium castaneum, and established protocols for primary neuronal cell cultures from Tribolium brains and efficient in vitro RNA interference. Recombinant human Epo as well as the non-erythropoietic Epo splice variant EV-3 increased the survival of serum-deprived brain neurons, confirming the previously described neuroprotective effect of Epo in insects. Moreover, Epo completely prevented hypoxia-induced apoptotic cell death of primary neuronal cultures. Knockdown of CRLF3 expression by RNA interference with two different double stranded RNA (dsRNA) fragments abolished the neuroprotective effect of Epo, indicating that CRLF3 is a crucial component of the insect Epo-responsive receptor. This suggests that a common urbilaterian ancestor of the orphan human and insect cytokine receptor CRLF3 served as a neuroprotective receptor for an Epo-like cytokine. Our work also suggests that vertebrate CRLF3, like its insect ortholog, might represent a tissue protection-mediating receptor.

Revisiting adult neurogenesis and the role of erythropoietin for neuronal and oligodendroglial differentiation in the hippocampus

Recombinant human erythropoietin (EPO) improves cognitive performance in neuropsychiatric diseases ranging from schizophrenia and multiple sclerosis to major depression and bipolar disease. This consistent EPO effect on cognition is independent of its role in hematopoiesis. The cellular mechanisms of action in brain, however, have remained unclear. Here we studied healthy young mice and observed that 3-week EPO administration was associated with an increased number of pyramidal neurons and oligodendrocytes in the hippocampus of ~20%. Under constant cognitive challenge, neuron numbers remained elevated until >6 months of age. Surprisingly, this increase occurred in absence of altered cell proliferation or apoptosis. After feeding a ¹⁵N-leucine diet, we used nanoscopic secondary ion mass spectrometry, and found that in EPO-treated mice, an equivalent number of neurons was defined by elevated ¹⁵N-leucine incorporation. In EPO-treated NG2-Cre-ERT2 mice, we confirmed enhanced differentiation of preexisting oligodendrocyte precursors in the absence of elevated DNA synthesis. A corresponding analysis of the neuronal lineage awaits the identification of suitable neuronal markers. In cultured neurospheres, EPO reduced Sox9 and stimulated miR124, associated with advanced neuronal differentiation. We are discussing a resulting working model in which EPO drives the differentiation of non-dividing precursors in both (NG2+) oligodendroglial and neuronal lineages. As endogenous EPO expression is induced by brain injury, such a mechanism of adult neurogenesis may be relevant for central nervous system regeneration.

Neuronal prolyl-4-hydroxylase 2 deficiency improves cognitive abilities in a murine model of cerebral hypoperfusion

Episodes of cerebral hypoxia/ischemia increase the risk of dementia, which is associated with impaired learning and memory. Previous studies in rodent models of dementia indicated a favorable effect of the hypoxia-inducible factor (HIF) targets VEGF (vascular endothelial growth factor) and erythropoietin (Epo). In the present study we thus investigated whether activation of the entire adaptive HIF pathway in neurons by cell-specific deletion of the HIF suppressor prolyl-4-hydroxylase 2 (PHD2) improves cognitive abilities in young (3months) and old (18-28months) mice suffering from chronic brain hypoperfusion. Mice underwent permanent occlusion of the left common carotid artery, and cognitive function was assessed using the Morris water navigation task. Under conditions of both normal and decreased brain perfusion, neuronal PHD2 deficiency resulted in improved and faster spatial learning in young mice, which was preserved to some extent also in old animals. The loss of PHD2 in neurons resulted in enhanced hippocampal mRNA and protein levels of Epo and VEGF, but did not alter local microvascular density, dendritic spine morphology, or expression of synaptic plasticity-related genes in the hippocampus. Instead, better cognitive function in PHD2 deficient animals was accompanied by an increased number of neuronal precursor cells along the subgranular zone of the dentate gyrus. Overall, our current pre-clinical findings indicate an important role for the endogenous oxygen sensing machinery, encompassing PHDs, HIFs and HIF target genes, for proper cognitive function. Thus, pharmacological compounds affecting the PHD-HIF axis might well be suited to treat cognitive dysfunction and neurodegenerative processes.

Erythropoietin Restores Long-Term Neurocognitive Function Involving Mechanisms of Neuronal Plasticity in a Model of Hyperoxia-Induced Preterm Brain Injury

Cerebral white and grey matter injury is the leading cause of an adverse neurodevelopmental outcome in prematurely born infants. High oxygen concentrations have been shown to contribute to the pathogenesis of neonatal brain damage. Here, we focused on motor-cognitive outcome up to the adolescent and adult age in an experimental model of preterm brain injury. In search of the putative mechanisms of action we evaluated oligodendrocyte degeneration, myelination, and modulation of synaptic plasticity-related molecules. A single dose of erythropoietin (20,000 IU/kg) at the onset of hyperoxia (24 hours, 80% oxygen) in 6-day-old Wistar rats improved long-lasting neurocognitive development up to the adolescent and adult stage. Analysis of white matter structures revealed a reduction of acute oligodendrocyte degeneration. However, erythropoietin did not influence hypomyelination occurring a few days after injury or long-term microstructural white matter abnormalities detected in adult animals. Erythropoietin administration reverted hyperoxia-induced reduction of neuronal plasticity-related mRNA expression up to four months after injury. Thus, our findings highlight the importance of erythropoietin as a neuroregenerative treatment option in neonatal brain injury, leading to improved memory function in adolescent and adult rats which may be linked to increased neuronal network connectivity.

Recombinant human erythropoietin improves neurological outcomes in very preterm infants

OBJECTIVE

To evaluate the efficacy and safety of repeated low-dose human recombinant erythropoietin (rhEPO) in the improvement of neurological outcomes in very preterm infants.

METHODS

A total of 800 infants of ≤32-week gestational age who had been in an intensive care unit within 72 hours after birth were included in the trial between January 2009 and June 2013. Preterm infants were randomly assigned to receive rhEPO (500IU/kg; n = 366) or placebo (n = 377) intravenously within 72 hours after birth and then once every other day for 2 weeks. The primary outcome was death or moderate to severe neurological disability assessed at 18 months of corrected age.

RESULTS

Death and moderate/severe neurological disability occurred in 91 of 338 very preterm infants (26.9%) in the placebo group and in 43 of 330 very preterm infants (13.0%) in the rhEPO treatment group (relative risk [RR] = 0.40, 95% confidence interval [CI] = 0.27-0.59, p < 0.001) at 18 months of corrected age. The rate of moderate/severe neurological disability in the rhEPO group (22 of 309, 7.1%) was significantly lower compared to the placebo group (57 of 304, 18.8%; RR = 0.32, 95% CI = 0.19-0.55, p < 0.001), and no excess adverse events were observed.

INTERPRETATION

Repeated low-dose rhEPO treatment reduced the risk of long-term neurological disability in very preterm infants with no obvious adverse effects. Ann Neurol 2016;80:24-34.

Erythropoietin and carbamylated erythropoietin promote histone deacetylase 5 phosphorylation and nuclear export in rat hippocampal neurons

Erythropoietin (EPO) produces neurotrophic effects in animal model of neurodegeneration. However, clinical use of EPO is limited due to thrombotic risk. Carbamylated EPO (cEPO), devoid of thrombotic risk, has been proposed as a novel neuroprotective and neurotrophic agent although the molecular mechanisms of cEPO remain incomplete. Here, we show a previously unidentified role of histone deacetylase 5 (HDAC5) in the actions of EPO and cEPO. EPO and cEPO regulate the HDAC5 phosphorylation at two critical sites, Ser259 and Ser498 through a protein kinase D (PKD) dependent pathway. In addition, EPO and cEPO rapidly stimulates nuclear export of HDAC5 in rat hippocampal neurons which expressing HDAC5-GFP. Consequently, EPO and cEPO enhanced the myocyte enhancer factor-2 (MEF2) target gene expression. Taken together, our results reveal that EPO and cEPO mediate MEF2 target gene expression via the regulation of HDAC5 phosphorylation at Ser259/498, and suggest that HDAC5 could be a potential mechanism contributing to the therapeutic actions of EPO and cEPO.

Selective expression of a constitutively active erythropoietin receptor in GABAergic neurons alters hippocampal network properties without affecting cognition

We have previously shown that treatment with erythropoietin (EPO) improves cognition in patients with neuropsychiatric disorders as well as in healthy mice, and that transgenic expression of a constitutively active form of the EPO receptor (cEPOR) in glutamatergic neurons boosts higher cognitive functions in mice. In the present work, we examined whether selective activation of EPOR signaling in GABAergic neurons would also modulate cognitive performance. We generated transgenic mice that express cEPOR under the control of the vesicular inhibitory amino acid transporter (Viaat) promoter and subjected them to comprehensive behavioral, cognitive, and electrophysiological analyses. We demonstrate that transgenic expression of cEPOR in GABAergic neurons alters hippocampal gamma-oscillations and enhances long-term potentiation but neither impairs nor improves cognition. To conclude, constitutively active EPOR in GABAergic neurons changes hippocampal network properties without affecting cognition, which suggests that the effect of EPO on cognition is dominated by its effect on the glutamatergic system. Treatment with EPO improves cognitive performance. We previously demonstrated that this effect is replicated by constitutive autoactivation of cEPOR in glutamatergic neurons. By contrast, cEPOR in GABAergic neurons changes hippocampal network properties but neither impairs nor enhances cognition. Thus, EPO modulates neuronal plasticity, and the cognitive benefits may be mainly attributable to its effect on the glutamatergic system.

Nonerythropoietic Erythropoietin-Derived Peptide Suppresses Adipogenesis, Inflammation, Obesity and Insulin Resistance

Erythropoietin (EPO) has been identified as being crucial for obesity modulation; however, its erythropoietic activity may limit its clinical application. EPO-derived Helix B-surface peptide (pHBSP) is nonerythrogenic but has been reported to retain other functions of EPO. The current study aimed to evaluate the effects and potential mechanisms of pHBSP in obesity modulation. We found that pHBSP suppressed adipogenesis, adipokine expression and peroxisome proliferator-activated receptor γ (PPARγ) levels during 3T3-L1 preadipocyte maturation through the EPO receptor (EPOR). In addition, also through EPOR, pHBSP attenuated macrophage inflammatory activation and promoted PPARγ expression. Furthermore, PPARγ deficiency partly ablated the anti-inflammatory activity of pHBSP in macrophages. Correspondingly, pHBSP administration to high-fat diet (HFD)-fed mice significantly improved obesity, insulin resistance (IR) and adipose tissue inflammation without stimulating hematopoiesis. Therefore, pHBSP can significantly protect against obesity and IR partly by inhibiting adipogenesis and inflammation. These findings have therapeutic implications for metabolic disorders, such as obesity and diabetes.

Synergistic effects of ceftriaxone and erythropoietin on neuronal and behavioral deficits in an MPTP-induced animal model of Parkinson's disease dementia

Both ceftriaxone (CEF) and erythropoietin (EPO) show neuroprotection and cognitive improvement in neurodegenerative disease. The present study was aimed at clarifying whether combined treatment with CEF and EPO (CEF+EPO) had superior neuroprotective and behavioral effects than treatment with CEF or EPO alone in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson's disease (PD) rat model. The rats were injected with CEF (5 mg/kg/day), EPO (100 IU/kg/day), or CEF+EPO after MPTP lesioning and underwent the bar-test, T-maze test, and object recognition test, then the brains were taken for histological evaluation. MPTP lesioning resulted in deficits in working memory and in object recognition, but the cognitive deficits were markedly reduced or eliminated in rats treated with CEF or CEF+EPO, with the combination having a greater effect. Lesioning also caused neurodegeneration in the nigrostriatal dopaminergic system and the hippocampal CA1 area and these changes were reduced or eliminated by treatment with CEF, EPO, or CEF+EPO, with the combination having a greater effect than single treatment in the densities of DAergic terminals in the striatum and neurons in the hippocampal CA1 area. Thus, compared to treatment with CEF or EPO alone, combined treatment with CEF+EPO had a greater inhibitory effect on the lesion-induced behavioral and neuronal deficits. To our knowledge, this is the first study showing a synergistic effect of CEF and EPO on neuroprotection and improvement in cognition in a PD rat model. Combined CEF and EPO treatment may have clinical potential for the treatment of the dementia associated with PD.

Erythropoietin Promotes Neural Plasticity and Spatial Memory Recovery in Fimbria-Fornix-Lesioned Rats

BACKGROUND

Erythropoietin (EPO) upregulates the mitogen activated protein kinase (MAPK) cascade, a central signaling pathway in cellular plastic mechanisms, and is critical for normal brain development.

OBJECTIVE

We hypothesized that EPO could modulate the plasticity mechanisms supporting spatial memory recovery in fimbria-fornix-transected animals.

METHODS

Fimbria-fornix was transected in 3 groups of rats. Seven days later, EPO was injected daily for 4 consecutive days within 10 minutes after training on a water maze task.

RESULTS

Our results show that EPO injections 10 minutes after training produced a substantial spatial memory recovery in fimbria-fornix-lesioned animals. In contrast, an EPO injection shortly after fimbria-fornix lesion surgery does not promote spatial-memory recovery. Neither does daily EPO injection 5 hours after the water maze performance. EPO, on the other hand, induced the expression of plasticity-related genes like arc and bdnf, but this effect was independent of training or lesion.

CONCLUSIONS

This finding supports our working hypothesis that EPO can modulate transient neuroplastic mechanisms triggered by training in lesioned animals. Consequently, we propose that EPO administration can be a useful trophic factor to promote neural restoration when given in combination with training.

Erythropoietin improves synaptic plasticity and memory deficits by decrease of the neurotransmitter release probability in the rat model of Alzheimer's disease

INTRODUCTION

Several studies indicate erythropoietin (Epo) to have remarkable neuroprotection in various central nervous system disorders, including Alzheimer's disease (AD). Amyloid beta (Aβ) is believed to be responsible for the synaptic dysfunction that occurs in AD. Therefore, the present study is aimed to investigate the effects of Epo on the Aβ-induced impairments in learning-memory and hippocampal synaptic plasticity.

MATERIALS AND METHODS

Male Sprague-Dawley rats (200-250 g) were used in this study. After the injection of Aβ, they were injected intra-peritoneal with Epo in the Aβ+Epo group or its vehicle in the Aβ+V group every other day for 12 days. A shuttle box apparatus was used for the passive avoidance learning and memory study. Moreover, paired-pulse ratio (PPR) was monitored before and after tetanic stimulation.

RESULTS

Bilateral injection of Aβ decreased step-through latency (STL), whereas the 12 day administration of Epo significantly improved memory performance in Aβ+Epo group. The field potential recording demonstrated that the in vivo administration of Aβ25-35 led to extreme inhibition in long-term potentiation, this inhibition was accompanied by a significant increase of the normalized PPR (PPR after HFS/PPR before HFS) as an index for release probability. However, administration of Epo recovers the magnitude of the LTP and the extent of normalized PPR.

CONCLUSION

The results of this study demonstrated that the injection of Aβ25-35 resulted in impaired LTP and the memory process, which is likely mediated through increasing the release probability of neurotransmitter vesicles. In addition, treatment with Epo improved the Aβ-induced deficits in memory and LTP induction, probably via recovering the release probability.

Effects of a Single Dose of Erythropoietin on Motor Function and Cognition after Focal Brain Ischemia in Adult Rats

We tested the influence of erythropoietin (EPO), a basic cytokine in erythropoiesis regulation, on the process of motor function and cognition after focal brain ischemia induced by a local application of endothelin. Endothelin-1 (ET-1) induced short lasting strong vasoconstriction, with described impact on the structure and on the function of neuronal cells. Neurological description of motor function and Morris water maze test (the swimming test is one of most widely used methods for studying cognitive functions in rodents) were used to study the process of learning and memory in three-month-old male albino Wistar rats (n=52). Both tests were performed one week before, and three weeks after ischemia induction (endothelin application on the cortex in the area of a. cerebri media dx.). Experimental group received i.p. injection of EPO (5,000 IU/kg body weight, 10 min before endothelin application). Control group of animals received one i.p. injection of saline at the dose of 1 ml/kg body weight at the same time. Only sham surgery was performed in the third group of animals. Rats with EPO pretreatment before the experimental lesion exhibited significantly better motor and cognitive function then those with saline injection. No significant changes in the motor and cognitive function were found in the third group of rats (sham operated controls).

Unexpected benefits of intermittent hypoxia: enhanced respiratory and nonrespiratory motor function

Intermittent hypoxia (IH) is most often thought of for its role in morbidity associated with sleep-disordered breathing, including central nervous system pathology. However, recent evidence suggests that the nervous system fights back in an attempt to minimize pathology by increasing the expression of growth/trophic factors that confer neuroprotection and neuroplasticity. For example, even modest ("low dose") IH elicits respiratory motor plasticity, increasing the strength of respiratory contractions and breathing. These low IH doses upregulate hypoxia-sensitive growth/trophic factors within respiratory motoneurons but do not elicit detectable pathologies such as hippocampal cell death, neuroinflammation, or systemic hypertension. Recent advances have been made toward understanding cellular mechanisms giving rise to IH-induced respiratory plasticity, and attempts have been made to harness the benefits of low-dose IH to treat respiratory insufficiency after cervical spinal injury. Our recent realization that IH also upregulates growth/trophic factors in nonrespiratory motoneurons and improves limb (or leg) function after incomplete chronic spinal injuries suggests that IH-induced plasticity is a general feature of motor systems. Collectively, available evidence suggests that low-dose IH may represent a safe and effective treatment to restore lost motor function in diverse clinical disorders that impair motor function.

Carbamylated erythropoietin promotes neurite outgrowth and neuronal spine formation in association with CBP/p300

Both erythropoietin (EPO) and carbamylated EPO (cEPO) have been shown to increase the length of neurites and spine density in neurons. However, the molecular mechanism underlying the EPO- and cEPO-induced neuronal differentiation has yet to be investigated. To address this issue, we investigated epigenetic modifications that regulate gene expression in neurons. Neurons treated with EPO or cEPO display an upregulation of E1A-binding protein (p300) and p300-mediated p53 acetylation, possibly increasing the transactivation activity of p53 on growth-associated protein 43 (GAP43). Treatment of cells with cEPO markedly increases spine formation and potentiates p300-mediated transactivation of PSD95, Shank2 and 3 compared to EPO. These results demonstrate that cEPO controls neuronal differentiation via acetylation of transcription factors and subsequent transactivation of target genes. These findings have important medical implications because cEPO is of interest in the development of therapeutic agents against neuropsychiatric disorders.

Intranasal Delivery of Bone Marrow-Derived Mesenchymal Stem Cells, Macrophages, and Microglia to the Brain in Mouse Models of Alzheimer's and Parkinson's Disease

In view of the rapid preclinical development of cell-based therapies for neurodegenerative disorders, traumatic brain injury, and tumors, the safe and efficient delivery and targeting of therapeutic cells to the central nervous system is critical for maintaining therapeutic efficacy and safety in the respective disease models. Our previous data demonstrated therapeutically efficacious and targeted delivery of mesenchymal stem cells (MSCs) to the brain in the rat 6-hydroxydopamine model of Parkinson's disease (PD). The present study examined delivery of bone marrow-derived MSCs, macrophages, and microglia to the brain in a transgenic model of PD [(Thy1)-h[A30P] aS] and an APP/PS1 model of Alzheimer's disease (AD) via intranasal application (INA). INA of microglia in naive BL/6 mice led to targeted and effective delivery of cells to the brain. Quantitative PCR analysis of eGFP DNA showed that the brain contained the highest amount of eGFP-microglia (up to 2.1 × 104) after INA of 1 × 106 cells, while the total amount of cells detected in peripheral organs did not exceed 3.4 × 103. Seven days after INA, MSCs expressing eGFP were detected in the olfactory bulb (OB), cortex, amygdala, striatum, hippocampus, cerebellum, and brainstem of (Thy1)-h[A30P] aS transgenic mice, showing predominant distribution within the OB and brainstem. INA of eGFP-expressing macrophages in 13-month-old APP/PS1 mice led to delivery of cells to the OB, hippocampus, cortex, and cerebellum. Both MSCs and macrophages contained Iba-1-positive population of small microglia-like cells and Iba-1-negative large rounded cells showing either intracellular amyloid β (macrophages in APP/PS1 model) or α-synuclein [MSCs in (Thy1)-h[A30P] aS model] immunoreactivity. Here, we show, for the first time, intranasal delivery of cells to the brain of transgenic PD and AD mouse models. Additional work is needed to determine the optimal dosage (single treatment regimen or repeated administrations) to achieve functional improvement in these mouse models with intranasal microglia/macrophages and MSCs. This manuscript is published as part of the International Association of Neurorestoratology (IANR) special issue of Cell Transplantation.

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

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

Dysregulation of hypoxia-inducible factor by presenilin/γ-secretase loss-of-function mutations

Presenilin (PSEN) 1 and 2 are the catalytic components of the γ-secretase complex, which cleaves a variety of proteins, including the amyloid precursor protein (APP). Proteolysis of APP leads to the formation of the APP intracellular domain (AICD) and amyloid β that is crucially involved in the pathogenesis of Alzheimer's disease. Prolyl-4-hydroxylase-domain (PHD) proteins regulate the hypoxia-inducible factors (HIFs), the master regulators of the hypoxic response. We previously identified the FK506 binding protein 38 (FKBP38) as a negative regulator of PHD2. Genetic ablation of PSEN1/2 has been shown to increase FKBP38 protein levels. Therefore, we investigated the role of PSEN1/2 in the oxygen sensing pathway using a variety of genetically modified cell and mouse lines. Increased FKBP38 protein levels and decreased PHD2 protein levels were found in PSEN1/2-deficient mouse embryonic fibroblasts and in the cortex of forebrain-specific PSEN1/2 conditional double knock-out mice. Hypoxic HIF-1α protein accumulation and transcriptional activity were decreased, despite reduced PHD2 protein levels. Proteolytic γ-secretase function of PSEN1/2 was needed for proper HIF activation. Intriguingly, PSEN1/2 mutations identified in Alzheimer patients differentially affected the hypoxic response, involving the generation of AICD. Together, our results suggest a direct role for PSEN in the regulation of the oxygen sensing pathway via the APP/AICD cleavage cascade.

Post-ischemic continuous infusion of erythropoeitin enhances recovery of lost memory function after global cerebral ischemia in the rat

Background

Erythropoietin (EPO) and its covalently modified analogs are neuroprotective in various models of brain damage and disease. We investigated the effect on brain damage and memory performance, of a continuous 3-day intravenous infusion of EPO, starting 20 min after a transient 10 minute period of global cerebral ischemia in the rat.

Results

We found no effect on selective neuronal damage in the CA1 region of the hippocampus, neocortical damage and damage to the striatum assessed at 7 days after ischemia. Also, no differences were observed in sensori-motor scores between EPO treated and saline treated ischemic animals. In contrast, memory performance was significantly improved in the EPO treated group. Saline treated injured animals (n = 7) failed in a test assessing recovery of spatial memory (6/6 and 5/6), while EPO treated animals had few and none failures (0/7 and 1/7).

Conclusion

We conclude that although post-ischemic treatment with EPO is not neuroprotective in a model of cardiac arrest brain ischemia, its markedly positive effect on brain plasticity and recovery of memory function warrants consideration as treatment of cardiac arrest patients.

Development of an autism severity score for mice using Nlgn4 null mutants as a construct-valid model of heritable monogenic autism

Autism is the short name of a complex and heterogeneous group of disorders (autism spectrum disorders, ASD) with several lead symptoms required for classification, including compromised social interaction, reduced verbal communication and stereotyped repetitive behaviors/restricted interests. The etiology of ASD is still unknown in most cases but monogenic heritable forms exist that have provided insights into ASD pathogenesis and have led to the notion of autism as a 'synapse disorder'. Among the most frequent monogenic causes of autism are loss-of-function mutations of the NLGN4X gene which encodes the synaptic cell adhesion protein neuroligin-4X (NLGN4X). We previously described autism-like behaviors in male Nlgn4 null mutant mice, including reduced social interaction and ultrasonic communication. Here, we extend the phenotypical characterization of Nlgn4 null mutant mice to both genders and add a series of additional autism-relevant behavioral readouts. We now report similar social interaction and ultrasonic communication deficits in females as in males. Furthermore, aggression, nest-building parameters, as well as self-grooming and circling as indicators of repetitive behaviors/stereotypies were explored in both genders. The construction of a gender-specific autism severity composite score for Nlgn4 mutant mice markedly diminishes population/sample heterogeneity typically obtained for single tests, resulting in p values of <0.00001 and a genotype predictability of 100% for male and of >83% for female mice. Taken together, these data underscore the similarity of phenotypical consequences of Nlgn4/NLGN4X loss-of-function in mouse and man, and emphasize the high relevance of Nlgn4 null mutant mice as an ASD model with both construct and face validity.

The hematopoietic cytokine granulocyte-macrophage colony stimulating factor is important for cognitive functions

We recently reported expression of hematopoietic growth factor GM-CSF and its receptor (GM-CSFR) in CNS neurons. Here we evaluated this system in learning and memory formation using GM-CSF deficient mice. In complementation, GM-CSF signalling was manipulated specifically in adult murine hippocampus by adeno-associated virus (AAV)-mediated GM-CSFR alpha overexpression or knock-down. GM-CSF ablation caused various hippocampus and amygdala-dependent deficits in spatial and fear memory while rendering intact basic parameters like motor function, inherent anxiety, and pain threshold levels. Corroborating these data, spatial memory of AAV-injected mice was positively correlated with GM-CSFRα expression levels. Hippocampal neurons of knock-out mice showed markedly pruned dendritic trees, reduced spine densities, and lower percentages of mature spines. Despite such morphological alterations, long-term potentiation (LTP) was unimpaired in the knock-out hippocampus. Collectively, these results suggest that GM-CSF signalling plays a major role in structural plasticity relevant to learning and memory.

Common variants of the genes encoding erythropoietin and its receptor modulate cognitive performance in schizophrenia

Erythropoietin (EPO) improves cognitive performance in clinical studies and rodent experiments. We hypothesized that an intrinsic role of EPO for cognition exists, with particular relevance in situations of cognitive decline, which is reflected by associations of EPO and EPO receptor (EPOR) genotypes with cognitive functions. To prove this hypothesis, schizophrenic patients (N > 1000) were genotyped for 5' upstream-located gene variants, EPO SNP rs1617640 (T/G) and EPORSTR(GA)(n). Associations of these variants were obtained for cognitive processing speed, fine motor skills and short-term memory readouts, with one particular combination of genotypes superior to all others (p < 0.0001). In an independent healthy control sample (N > 800), these associations were confirmed. A matching preclinical study with mice demonstrated cognitive processing speed and memory enhanced upon transgenic expression of constitutively active EPOR in pyramidal neurons of cortex and hippocampus. We thus predicted that the human genotypes associated with better cognition would reflect gain-of-function effects. Indeed, reporter gene assays and quantitative transcriptional analysis of peripheral blood mononuclear cells showed genotype-dependent EPO/EPOR expression differences. Together, these findings reveal a role of endogenous EPO/EPOR for cognition, at least in schizophrenic patients.

Erythropoietin: a candidate treatment for mood symptoms and memory dysfunction in depression

OBJECTIVE

Current pharmacological treatments for depression have a significant treatment-onset-response delay, an insufficient efficacy for many patients and fail to reverse cognitive dysfunction. Erythropoietin (EPO) has neuroprotective and neurotrophic actions and improves cognitive function in animal models of acute and chronic neurodegenerative conditions and in patients with cognitive decline.

METHODS

We systematically reviewed the published findings from animal and human studies exploring the potential of EPO to treat depression-related cognitive dysfunction and depression.

RESULTS

We identified five animal studies (two in male rats, two in male mice and one in male rats and mice) and seven human proof-of-concept studies (five in healthy volunteers and two in depressed patients) that investigated the above. All of the reviewed animal studies but one and all human studies demonstrated beneficial effects of EPO on hippocampus-dependent memory and antidepressant-like effects. These effects appear to be mediated through direct neurobiological actions of EPO rather than upregulation of red cell mass.

CONCLUSIONS

The reviewed studies demonstrate beneficial effects of EPO on hippocampus-dependent memory function and on depression-relevant behavior, thus highlighting EPO as a candidate agent for future management of cognitive dysfunction and mood symptoms in depression. Larger-scale clinical trials of EPO as a treatment for mood and neurocognitive symptoms in patients with mood disorder are therefore warranted.