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.
A significant body of research has demonstrated that antidepressants regulate neurotrophic factors and that neurotrophins themselves are capable of independently producing antidepressant-like ...effects. While brain derived neurotrophic factor (BDNF) remains the best studied molecule in this context, there are several structurally diverse trophic factors that have shown comparable behavioral effects, including basic fibroblast growth factor (FGF-2), insulin-like growth factor 1 (IGF-1) and vascular endothelial growth factor (VEGF). In this review we discuss the structural and biochemical signaling aspects of these neurotrophic factors with antidepressant activity. We also include a discussion on a cytokine molecule erythropoietin (EPO), widely known and prescribed as a hormone to treat anemia but has recently been shown to function as a neurotrophic factor in the central nervous system (CNS).
Cerebral hypoperfusion is associated with enhanced cognitive decline and increased risk of neuropsychiatric disorders. Erythropoietin (EPO) is a neurotrophic factor known to improve cognitive ...function in preclinical and clinical studies of neurodegenerative and psychiatric disorders. However, the clinical application of EPO is limited due to its erythropoietic activity that can adversely elevate hematocrit in non-anemic populations. Carbamoylated erythropoietin (CEPO), a chemically engineered non-erythropoietic derivative of EPO, does not alter hematocrit and maintains neurotrophic and behavioral effects comparable to EPO. Our study aimed to investigate the role of CEPO in cerebral hemodynamics. Magnetic resonance imaging (MRI) analysis indicated increased blood perfusion in the hippocampal and striatal region without altering tight junction integrity. In vitro and in vivo analyses indicated that hippocampal neurotransmission was unaltered and increased cerebral perfusion was likely due to EDRF, CGRP, and NOS-mediated vasodilation. In vitro analysis using human umbilical vein endothelial cells (HUVEC) and hippocampal vascular gene expression analysis showed CEPO to be a non-angiogenic agent which regulates the MEOX2 gene expression. The results from our study demonstrate a novel role of CEPO in modulating cerebral vasodilation and blood perfusion.
Knockdown of orexin/hypocretin 2 receptor (Orx2) in the basolateral amygdala (BLA) affects anxious and depressive behavior. We use a new behavioral paradigm, the Stress Alternatives Model (SAM), ...designed to improve translational impact. The SAM induces social stress in adult male mice by aggression from larger mice, allowing for adaptive decision-making regarding escape. In this model, mice remain (Stay) in the oval SAM arena or escape from social aggression (Escape) via routes only large enough for the smaller mouse. We hypothesized intracerebroventricular (icv) stimulation of Orx2 receptors would be anxiolytic and antidepressive in SAM-related social behavior and the Social Interaction/Preference (SIP) test. Conversely, we predicted that icv antagonism of Orx2 receptors would promote anxious and depressive behavior in these same tests. Anxious behaviors such as freezing (both cued and conflict) and startle are exhibited more often in Stay compared with Escape phenotype mice. Time spent attentive to the escape route is more frequent in Escape mice. In Stay mice, stimulation of Orx2 receptors reduces fear conditioning, conflict freezing and startle, and promotes greater attention to the escape hole. This anxiolysis was accompanied by activation of a cluster of inhibitory neurons in the amygdala. A small percentage of those Stay mice also begin escaping; whereas Escape is reversed by the Orx2 antagonist. Escape mice were also Resilient, and Stay mice Susceptible to stress (SIP), with both conditions reversed by Orx2 antagonism or stimulation respectively. Together, these results suggest that the Orx2 receptor may be a useful potential target for anxiolytic or antidepressive therapeutics.
•Stress Alternatives Model (SAM) produces resilient (Escape) and susceptible (Stay) phenotypes.•icv Orx2 agonist reduces anxious and depressive behaviors in Stay mice.•icv Orx2 antagonist increases anxious and depressive behavior plus plasma corticosterone.•Stay mice exhibit fear conditioning, reversed by an Orx2 agonist.•icv Orx2 agonist increases immediate-early gene EGR1 in BLA parvalbumin GABA interneurons.
The inbred mouse strains, C57BL/6 and BALB/c have been used widely in preclinical psychiatric research. The differences in stress susceptibility of available strains has provided a useful platform to ...test pharmacological agents and behavioral responses. Previous brain gene profiling efforts have indicated that the inflammation and immune response gene pathway is the predominant gene network in the differential stress response of BALB/c and C57BL/6 mice. The implication is that a composite stress paradigm that includes a sequence of extended, varied and unpredictable stressors induces inflammation-related genes in the hippocampus. We hypothesized that the regulation of inflammation genes in the brain could constitute a primary stress response and tested this by employing a simple stress protocol, repeated exposure to the same stressor for 10 days, 2 h of restraint per day. We examined stress-induced regulation of 13 proinflammatory cytokine genes in male BALB/c and C57BL/6 mice using quantitative PCR. Elevated cytokine genes included tumor necrosis factor alpha (TNFα), interleukin 6 (IL6), interleukin 10 (IL10), tumor necrosis factor (TNF) super family members and interleukin 1 receptor 1 (IL1R1). In addition, we examined restraint stress-induced regulation of 12 glutamate receptor genes in both strains. Our results show that restraint stress is sufficient to elevate the expression of inflammation-related genes in the hippocampus of both BABLB/c and C57BL/6 mice, but they differ in the genes that are induced and the magnitude of change. Cell types that are involved in this response include endothelial cells and astrocytes. Lay summary Repeated exposure to a simple restraint stress altered the activities of genes involved in inflammation and the functions of the excitatory neurotransmitter, glutamate. These changes in the hippocampus of the mouse brain showed differences that were dependent on the strain of mice and the length of the stress exposure. The effects of stress on activity of these genes may lead to alterations in behavior.
Trophic factors are secreted proteins that can modulate neuronal integrity, structure, and function. Previous preclinical studies have shown synergistic effects on decreasing apoptosis and improving ...behavioral performance after stroke when combining two such trophic factors, erythropoietin (EPO) and insulin-like growth factor-1 (IGF-1). However, EPO can elevate the hematocrit level, which can be life-threatening for non-anemic individuals. A chemically engineered derivative of EPO, carbamoylated EPO (CEPO), does not impact hematological parameters but retains neurotrophic effects similar to EPO. To obtain insight into CEPO and IGF-1 combination signaling, we examined immediate early gene (IEG) expression after treatment with CEPO, IGF-1, or CEPO + IGF-1 in rat pheochromocytoma (PC-12) cells and found that combining CEPO and IGF-1 produced a synergistic increase in IEG expression. An in vivo increase in the protein expression of Npas4 and Nptx2 was also observed in the rat hippocampus. We also examined which kinase signaling pathways might be mediating these effects and found that while AKT inhibition did not alter the pattern of IEG expression, both ERK and JAK2 inhibition significantly decreased IEG expression. These results begin to define the molecular effects of combining CEPO and IGF-1 and indicate the potential for these trophic factors to produce positive, synergistic effects.
In recent years, erythropoietin (EPO) has emerged as a useful neuroprotective and neurotrophic molecule that produces antidepressant and cognitive-enhancing effects in psychiatric disorders. However, ...EPO robustly induces erythropoiesis and elevates red blood cell counts. Chronic administration is therefore likely to increase blood viscosity and produce adverse effects in non-anemic populations. Carbamoylated erythropoietin (CEPO), a chemically engineered modification of EPO, is non-erythropoietic but retains the neurotrophic and neurotrophic activity of EPO. Blood profile analysis after EPO and CEPO administration showed that CEPO has no effect on red blood cell or platelet counts. We conducted an unbiased, quantitative, mass spectrometry-based proteomics study to comparatively investigate EPO and CEPO-induced protein profiles in neuronal phenotype PC12 cells. Bioinformatics enrichment analysis of the protein expression profiles revealed the upregulation of protein functions related to memory formation such as synaptic plasticity, long term potentiation (LTP), neurotransmitter transport, synaptic vesicle priming, and dendritic spine development. The regulated proteins, with roles in LTP and synaptic plasticity, include calcium/calmodulin-dependent protein kinase type 1 (Camk1), Synaptosomal-Associated Protein, 25 kDa (SNAP-25), Sectretogranin-1 (Chgb), Cortactin (Cttn), Elongation initiation factor 3a (Eif3a) and 60S acidic ribosomal protein P2 (Rplp2). We examined the expression of a subset of regulated proteins, Cortactin, Grb2 and Pleiotrophin, by immunofluorescence analysis in the rat brain. Grb2 was increased in the dentate gyrus by EPO and CEPO. Cortactin was induced by CEPO in the molecular layer, and pleiotrophin was increased in the vasculature by EPO. The results of our study shed light on potential mechanisms whereby EPO and CEPO produce cognitive-enhancing effects in clinical and preclinical studies.
Depression affects approximately 7.1% of the United States population every year and has an annual economic burden of over $210 billion dollars. Several recent studies have sought to investigate the ...pathophysiology of depression utilizing focused cerebrospinal fluid (CSF) and serum analysis. Inflammation and metabolic dysfunction have emerged as potential etiological factors from these studies. A dysregulation in the levels of inflammatory proteins such as IL-12, TNF, IL-6 and IFN-γ have been found to be significantly correlated with depression.
CSF samples were obtained from 15 patients, seven with major depressive disorder and eight age- and gender-matched non-psychiatric controls. CSF protein profiles were obtained using quantitative mass spectrometry. The data were analyzed by Progenesis QI proteomics software to identify significantly dysregulated proteins. The results were subjected to bioinformatics analysis using the Ingenuity Pathway Analysis suite to obtain unbiased mechanistic insight into biologically relevant interactions and pathways.
Several dysregulated proteins were identified. Bioinformatics analysis indicated that the potential disorder/disease pathways include inflammatory response, metabolic disease and organismal injury. Molecular and cellular functions that were affected include cellular compromise, cell-to-cell signaling & interaction, cellular movement, protein synthesis, and cellular development. The major canonical pathway that was upregulated was acute phase response signaling. Endogenous upstream regulators that may influence dysregulation of proinflammatory molecules associated with depression are interleukin-6 (IL-6), signal transducer and activator of transcription 3 (STAT3), oncostatin M, PR domain zinc finger protein 1 (PRDM1), and peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PPARGC1A).
The proteome profiling data in this report identifies several potential biological functions that may be involved in the pathophysiology of major depressive disorder. Future research into how the differential expression of these proteins is involved in the etiology and severity of depression will be important.
The two strains of inbred mice, BALB/c and C57BL/6, are widely used in pre-clinical psychiatry research due to their differences in stress susceptibility. Gene profiling studies in these strains have ...implicated the inflammation pathway as the main contributor to these differences. We focused our attention on female mice and tested their response to 5- or 10-day exposure to restraint stress. We examined the stress induced changes in the regulation of 11 inflammatory cytokine genes and 12 glutamate receptor genes in the hippocampus of female BALB/c and C57BL/6 mice using quantitative PCR. Elevated proinflammatory cytokine genes include Tumor Necrosis Factor alpha (TNFa), nuclear factor kappa-light-chain-enhancer of activated B cells (NFKB), Interleukin 1 alpha (IL1a), Interleukin 1 receptor (IL1R), Interleukin 10 receptor alpha subunit (IL10Ra), Interleukin 10 receptor beta subunit (IL10Rb), and tumor necrosis factor (TNF) super family members. Our results show that BALB/c and C57BL/6 mice differ in the genes induced in response to stress exposure and the level of gene regulation change. Our results show that the gene regulation in female BALB/c and C57BL/6 mice differs between strains in the genes regulated and the magnitude of the changes.
Background The neuroprotective and trophic actions of erythropoietin (EPO) have been tested in several animal models of insult, injury, and neurodegeneration. Recent studies in human volunteers ...demonstrated that EPO improves cognition and also elicits antidepressant effects. It is believed that the behavioral effects are mediated by EPO's trophic effect on neuronal systems. We therefore tested whether EPO is able to alter behavior and brain gene expression in rats. Methods The expression of EPO and EPO receptor (EPOR) in multiple brain regions was examined by quantitative polymerase chain reaction, in situ hybridization, and immunohistochemistry. The regulation of EPO and the transcription factor hypoxia-induced factor–alpha (HIF1α) after electroconvulsive seizure (ECS) was investigated. Behavioral effects of EPO were tested in the rodent forced swimming and novelty-induced hypophagia (NIH) models. EPO gene profiles were obtained by microarray analysis of the hippocampus after intracerebroventricular infusion. Results EPO and EPOR were widely expressed in the brain albeit at low levels. Highest level of EPO and EPOR were in the choroid plexus and striatum, respectively. Peripheral administration of EPO was sufficient to produce a robust antidepressant-like effect in the forced swim and NIH tests. Gene expression profiles revealed that EPO induces the expression of neurotrophic genes such as brain-derived neurotrophic factor, VGF (nonacronymic), and neuritin. Conclusions EPO is induced by ECS and independently exhibits antidepressant-like efficacy in the forced swim and NIH tests. EPO regulates the expression of genes implicated in antidepressant action and appears to be a candidate molecule for further testing in neuropsychiatry.
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