Miyeon Choi

Neuritin produces antidepressant actions and blocks the neuronal and behavioral deficits caused by chronic stress

Decreased neuronal dendrite branching and plasticity of the hippocampus, a limbic structure implicated in mood disorders, is thought to contribute to the symptoms of depression. However, the mechanisms underlying this effect, as well as the actions of antidepressant treatment, remain poorly characterized. Here, we show that hippocampal expression of neuritin, an activity-dependent gene that regulates neuronal plasticity, is decreased by chronic unpredictable stress (CUS) and that antidepressant treatment reverses this effect. We also show that viral-mediated expression of neuritin in the hippocampus produces antidepressant actions and prevents the atrophy of dendrites and spines, as well as depressive and anxiety behaviors caused by CUS. Conversely, neuritin knockdown produces depressive-like behaviors, similar to CUS exposure. The ability of neuritin to increase neuroplasticity is confirmed in models of learning and memory. Our results reveal a unique action of neuritin in models of stress and depression, and demonstrate a role for neuroplasticity in antidepressant treatment response and related behaviors.

Ketamine produces antidepressant-like effects through phosphorylation-dependent nuclear export of histone deacetylase 5 (HDAC5) in rats

Significance The rapid antidepressant response is produced by ketamine administration. However, the molecular mechanisms underlying the antidepressant-like action of ketamine remain incomplete. Here we show for the first time to our knowledge that ketamine stimulates the phosphorylation (Ser259/Ser498) and nuclear export of histone deacetylase 5 (HDAC5). As a consequence, myocyte enhancer factor 2 (MEF2) transcriptional activity is enhanced and results in the induction of MEF2 target gene expression. We further show that ketamine down-regulates and, at the same time, phosphorylates HDAC5 to attenuate its repressive influence on transcription in the hippocampus. These studies unveil a previously unidentified role of HDAC5 in regulating neuronal function in response to ketamine, and thus provide the foundation for new approaches for the treatment of major depression. Ketamine produces rapid antidepressant-like effects in animal assays for depression, although the molecular mechanisms underlying these behavioral actions remain incomplete. Here, we demonstrate that ketamine rapidly stimulates histone deacetylase 5 (HDAC5) phosphorylation and nuclear export in rat hippocampal neurons through calcium/calmodulin kinase II- and protein kinase D-dependent pathways. Consequently, ketamine enhanced the transcriptional activity of myocyte enhancer factor 2 (MEF2), which leads to regulation of MEF2 target genes. Transfection of a HDAC5 phosphorylation-defective mutant (Ser259/Ser498 replaced by Ala259/Ala498, HDAC5-S/A), resulted in resistance to ketamine-induced nuclear export, suppression of ketamine-mediated MEF2 transcriptional activity, and decreased expression of MEF2 target genes. Behaviorally, viral-mediated hippocampal knockdown of HDAC5 blocked or occluded the antidepressant effects of ketamine both in unstressed and stressed animals. Taken together, our results reveal a novel role of HDAC5 in the actions of ketamine and suggest that HDAC5 could be a potential mechanism contributing to the therapeutic actions of ketamine.

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.

Comparison of Neurite Outgrowth Induced by Erythropoietin (EPO) and Carbamylated Erythropoietin (CEPO) in Hippocampal Neural Progenitor Cells.

A previous animal study has shown the effects of erythropoietin (EPO) and its non-erythropoietic carbamylated derivative (CEPO) on neurogenesis in the dentate gyrus. In the present study, we sought to investigate the effect of EPO on adult hippocampal neurogenesis, and to compare the ability of EPO and CEPO promoting dendrite elongation in cultured hippocampal neural progenitor cells. Two-month-old male BALB/c mice were given daily injections of EPO (5 U/g) for seven days and were sacrificed 12 hours after the final injection. Proliferation assays demonstrated that EPO treatment increased the density of bromodeoxyuridine (BrdU)-labeled cells in the subgranular zone (SGZ) compared to that in vehicle-treated controls. Functional differentiation studies using dissociated hippocampal cultures revealed that EPO treatment also increased the number of double-labeled BrdU/microtubule-associated protein 2 (MAP2) neurons compared to those in vehicle-treated controls. Both EPO and CEPO treatment significantly increased the length of neurites and spine density in MAP2(+) cells. In summary, these results provide evidences that EPO and CEPO promote adult hippocampal neurogenesis and neuronal differentiation. These suggest that EPO and CEPO could be a good candidate for treating neuropsychiatric disorders such as depression and anxiety associated with neuronal atrophy and reduced hippocampal neurogenesis.

Changes in vascular endothelial growth factor (VEGF) induced by the Morris water maze task.

The present study was undertaken to evaluate the effects on hippocampal vascular endothelial growth factor (VEGF) levels in rats when they experience hippocampal-dependent spatial learning via the Morris water maze (MWM) task. Rats underwent one of two different versions of the MWM: weak or intensive. After one day of intensive training, a highly sensitive enzyme-linked immunosorbent assay (ELISA) was used to measure VEGF protein levels in the hippocampus, cortex, and serum, and higher levels were found in the trained group compared to a naive control group. VEGF levels also increased in rats that swam only for durations equal to the intensive training periods. In contrast, rats trained under the weaker MWM paradigm for five days showed a decrease in hippocampal VEGF protein level. Mimicking increases in neuronal VEGF in the hippocampus by direct infusion of VEGF into CA1 resulted in up-regulation of the phosphorylation of the cAMP response element-binding (CREB) protein and the Ca2+/calmodulin-dependent protein kinases II (CaMKII). These results suggest that VEGF may be a physiological parameter involved in learning procedures that include physical activity.

Effects of Serotonin on Erythropoietin Expression in Mouse Hippocampus

Serotonin (5-hydroxytryptamine, 5-HT), a monoamine neurotransmitter, regulates neurological functions such as mood, sleep, and appetite. Erythropoietin (EPO) is well known for erythropoiesis but has recently emerged as a therapeutic agent in brain diseases. However, the mechanisms that induce EPO in the brain remain unclear. The present study was undertaken to investigate whether the effects of 5-HT involve EPO in murine hippocampal neurons. 5-HT produced a significant increase in neuronal differentiation of hippocampal neural progenitor cells. Expression of erythropoietin was increased in 5-HT-treated cells as well. The actions of 5-HT and EPO appeared to be similar in neurite outgrowth and spine formation. In addition, we show that hippocampal expression of EPO was decreased by chronic unpredictable stress (CUS) and that antidepressant treatment to maintain 5-HT concentration in synaptic cleft reversed this effect. In conclusion, actions of antidepressants might involve EPO induction in the brain.

Hippocampal VEGF is necessary for antidepressant-like behaviors but not sufficient for antidepressant-like effects of ketamine in rats.

We investigated the effects of ketamine on both the temporal and spatial profiles of neural precursor cells located in the hippocampus, and on antidepressant-like behaviors in rats. A single dose of ketamine resulted in a significant increase in the number of 5-bromo-2-deoxyuridine-positive (BrdU(+)) cells in the dentate gyrus (DG) of rats at 24h, but not at 28days, after treatment completion. Ketamine caused antidepressant-like behaviors in the forced swim test (FST) and novelty suppressed feeding test (NSFT). Viral-mediated hippocampal knockdown of vascular endothelial growth factor (VEGF) produced depressive-like behaviors in the FST and NSFT, which were partially recovered by ketamine to the level observed in the control group. The behavioral effects of VEGF knock down were accompanied by a decrease in hippocampal neurogenesis, which was also partially recovered by ketamine. Our results suggest that basal hippocampal VEGF expression is necessary for ketamine-induced antidepressant-like behaviors in rats, but ketamine-induced VEGF expression only partially contributes to hippocampal neurogenesis and the antidepressant-like effects of ketamine.

Overexpression of human GATA-1 and GATA-2 interferes with spine formation and produces depressive behavior in rats.

Functional consequences to which vertebrate GATA transcription factors contribute in the adult brain remain largely an open question. The present study examines how human GATA-1 and GATA-2 (hGATA-1 and hGATA-2) are linked to neuronal differentiation and depressive behaviors in rats. We investigated the effects of adeno-associated viral expression of hGATA-1 and hGATA-2 (AAV-hGATA1 and AAV-hGATA2) in the dentate gyrus (DG) of the dorsal hippocampus on dendrite branching and spine number. We also examined the influence of AAV-hGATA1 and AAV-hGATA2 infusions into the dorsal hippocampus on rodent behavior in models of depression. Viral expression of hGATA-1 and hGATA-2 cDNA in rat hippocampal neurons impaired dendritic outgrowth and spine formation. Moreover, viral-mediated expression of hGATA-1 and hGATA-2 in the dorsal hippocampus caused depressive-like deficits in the forced swim test and learned helplessness models of depression, and decreased the expression of several synapse-related genes as well as spine number in hippocampal neurons. Conversely, shRNA knockdown of GATA-2 increased synapse-related gene expression, spine number, and dendrite branching. The results demonstrate that hGATA-1 and hGATA-2 expression in hippocampus is sufficient to cause depressive like behaviors that are associated with reduction in spine synapse density and expression of synapse-related genes.

TRPV1 Regulates Stress Responses through HDAC2

Stress causes changes in neurotransmission in the brain, thereby influencing stress-induced behaviors. However, it is unclear how neurotransmission systems orchestrate stress responses at the molecular and cellular levels. Transient receptor potential vanilloid 1 (TRPV1), a non-selective cation channel involved mainly in pain sensation, affects mood and neuroplasticity in the brain, where its role is poorly understood. Here, we show that Trpv1-deficient (Trpv1-/-) mice are more stress resilient than control mice after chronic unpredictable stress. We also found that glucocorticoid receptor (GR)-mediated histone deacetylase 2 (HDAC) 2 expression and activity are reduced in the Trpv1-/- mice and that HDAC2-regulated, cell-cycle- and neuroplasticity-related molecules are altered. Hippocampal knockdown of TRPV1 had similar effects, and its behavioral effects were blocked by HDAC2 overexpression. Collectively, our findings indicate that HDAC2 is a molecular link between TRPV1 activity and stress responses.

Ketamine induces brain-derived neurotrophic factor expression via phosphorylation of histone deacetylase 5 in rats

Ketamine shows promise as a therapeutic agent for the treatment of depression. The increased expression of brain-derived neurotrophic factor (BDNF) has been associated with the antidepressant-like effects of ketamine, but the mechanism of BDNF induction is not well understood. In the current study, we demonstrate that the treatment of rats with ketamine results in the dose-dependent rapid upregulation of Bdnf promoter IV activity and expression of Bdnf exon IV mRNAs in rat hippocampal neurons. Transfection of histone deacetylase 5 (HDAC5) into rat hippocampal neurons similarly induces Bdnf mRNA expression in response to ketamine, whereas transfection of a HDAC5 phosphorylation-defective mutant (Ser259 and Ser498 replaced by Ala259 and Ala498), results in the suppression of ketamine-mediated BDNF promoter IV transcriptional activity. Viral-mediated hippocampal knockdown of HDAC5 induces Bdnf mRNA and protein expression, and blocks the enhancing effects of ketamine on BDNF expression in both unstressed and stressed rats, and thereby providing evidence for the role of HDAC5 in the regulation of Bdnf expression. Taken together, our findings implicate HDAC5 in the ketamine-induced transcriptional regulation of Bdnf, and suggest that the phosphorylation of HDAC5 regulates the therapeutic actions of ketamine.