Aberrant extracellular signal-regulated kinase (ERK)1/2 signalling in suicide brain: role of ERK kinase 1 (MEK1)

New Advances in the Pharmacology and Toxicology of Lithium: A Neurobiologically Oriented Overview

Over the last six decades, lithium has been considered the gold standard treatment for the long-term management of bipolar disorder due to its efficacy in preventing both manic and depressive episodes as well as suicidal behaviors. Nevertheless, despite numerous observed effects on various cellular pathways and biologic systems, the precise mechanism through which lithium stabilizes mood remains elusive. Furthermore, there is recent support for the therapeutic potential of lithium in other brain diseases. This review offers a comprehensive examination of contemporary understanding and predominant theories concerning the diverse mechanisms underlying lithium's effects. These findings are based on investigations utilizing cellular and animal models of neurodegenerative and psychiatric disorders. Recent studies have provided additional support for the significance of glycogen synthase kinase-3 (GSK3) inhibition as a crucial mechanism. Furthermore, research has shed more light on the interconnections between GSK3-mediated neuroprotective, antioxidant, and neuroplasticity processes. Moreover, recent advancements in animal and human models have provided valuable insights into how lithium-induced modifications at the homeostatic synaptic plasticity level may play a pivotal role in its clinical effectiveness. We focused on findings from translational studies suggesting that lithium may interface with microRNA expression. Finally, we are exploring the repurposing potential of lithium beyond bipolar disorder. These recent findings on the therapeutic mechanisms of lithium have provided important clues toward developing predictive models of response to lithium treatment and identifying new biologic targets. SIGNIFICANCE STATEMENT: Lithium is the drug of choice for the treatment of bipolar disorder, but its mechanism of action in stabilizing mood remains elusive. This review presents the latest evidence on lithium's various mechanisms of action. Recent evidence has strengthened glycogen synthase kinase-3 (GSK3) inhibition, changes at the level of homeostatic synaptic plasticity, and regulation of microRNA expression as key mechanisms, providing an intriguing perspective that may help bridge the mechanistic gap between molecular functions and its clinical efficacy as a mood stabilizer.

Exploring the role of esketamine in alleviating depressive symptoms in mice via the PGC-1α/irisin/ERK1/2 signaling pathway

Esketamine provides an immediate and noticeable antidepressant effect, although the underlying molecular processes are yet unclear. Irisin induced by aerobic exercise has been implicated in the alleviation of depressive symptoms, whether irisin expression responds to the administration of esketamine remains unknown. In this study, we found that irisin was reduced in the hippocampus and peripheral blood of chronic unpredictable mild stress (CUMS) mice, whereas the irisin level was rescued by esketamine treatment. The reduction of PGC-1α expression (transcriptional regulator of irisin gene expression) in the CUMS mice was rescued by esketamine treatment, PGC-1α knockdown significantly reduced the irisin level induced by esketamine. Additionally, FNDC5/irisin-knockout mice developed more severe depressant-like behaviors than wild-type mice under CUMS stimulation, with an attenuated the antidepressant effect of esketamine. Further research indicated that irisin-mediated modulation of esketamine on depressive-like behaviors in CUMS mice involved the ERK1/2 pathway. Overall, the PGC-1α/irisin/ERK1/2 signaling activation may be a new mechanism underlying the antidepressant activity of esketamine, denoting that irisin may be a promising therapeutic target for the treatment of depression.

Cognitive dysfunction and increased phosphorylated tau are associated with reduced O-GlcNAc signaling in an aging mouse model of metabolic syndrome

Metabolic syndrome (MetS), characterized by hyperglycemia, obesity, and hyperlipidemia, can increase the risk of developing late-onset dementia. Recent studies in patients and mouse models suggest a putative link between hyperphosphorylated tau, a component of Alzheimer's disease-related dementia (ADRD) pathology, and cerebral glucose hypometabolism. Impaired glucose metabolism reduces glucose flux through the hexosamine metabolic pathway triggering attenuated O-linked N-acetylglucosamine (O-GlcNAc) protein modification. The goal of the current study was to investigate the link between cognitive function, tau pathology, and O-GlcNAc signaling in an aging mouse model of MetS, agouti KKAy+/- . Male and female C57BL/6, non-agouti KKAy-/- , and agouti KKAy+/- mice were aged 12-18 months on standard chow diet. Body weight, blood glucose, total cholesterol, and triglyceride were measured to confirm the MetS phenotype. Cognition, sensorimotor function, and emotional reactivity were assessed for each genotype followed by plasma and brain tissue collection for biochemical and molecular analyses. Body weight, blood glucose, total cholesterol, and triglyceride levels were significantly elevated in agouti KKAy+/- mice versus C57BL/6 controls and non-agouti KKAy-/- . Behaviorally, agouti KKAy+/- revealed impairments in sensorimotor and cognitive function versus age-matched C57BL/6 and non-agouti KKAy-/- mice. Immunoblotting demonstrated increased phosphorylated tau accompanied with reduced O-GlcNAc protein expression in hippocampal-associated dorsal midbrain of female agouti KKAy+/- versus C57BL/6 control mice. Together, these data demonstrate that impaired cognitive function and AD-related pathology are associated with reduced O-GlcNAc signaling in aging MetS KKAy+/- mice. Overall, our study suggests that interaction of tau pathology with O-GlcNAc signaling may contribute to MetS-induced cognitive dysfunction in aging.

The Impact of BDNF, NTRK2, NGFR, CREB1, GSK3B, AKT, MAPK1, MTOR, PTEN, ARC, and SYN1 Genetic Polymorphisms in Antidepressant Treatment Response Phenotypes

This study aimed to investigate the influence of genetic variants in neuroplasticity-related genes on antidepressant treatment phenotypes. The BDNF-TrkB signaling pathway, as well as the downstream kinases Akt and ERK and the mTOR pathway, have been implicated in depression and neuroplasticity. However, clinicians still struggle with the unpredictability of antidepressant responses in depressed patients. We genotyped 26 polymorphisms in BDNF, NTRK2, NGFR, CREB1, GSK3B, AKT, MAPK1, MTOR, PTEN, ARC, and SYN1 in 80 patients with major depressive disorder treated according to the Texas Medical Algorithm for 27 months at Hospital Magalhães Lemos, Porto, Portugal. Our results showed that BDNF rs6265, PTEN rs12569998, and SYN1 rs1142636 SNP were associated with treatment-resistant depression (TRD). Additionally, MAPK1 rs6928 and GSK3B rs6438552 gene polymorphisms were associated with relapse. Moreover, we found a link between the rs6928 MAPK1 polymorphism and time to relapse. These findings suggest that the BDNF, PTEN, and SYN1 genes may play a role in the development of TRD, while MAPK1 and GSK3B may be associated with relapse. GO analysis revealed enrichment in synaptic and trans-synaptic transmission pathways and glutamate receptor activity with TRD-associated genes. Genetic variants in these genes could potentially be incorporated into predictive models of antidepressant response.

The 5-HT1A receptor biased agonist, NLX-204, shows rapid-acting antidepressant-like properties and neurochemical changes in two mouse models of depression

Activation of cortical serotonin 5-HT_1A receptors may be a promising strategy to achieve rapid-acting antidepressant (RAAD) activity. NLX-204 is a selective 5-HT_1A receptor biased agonist that, in naïve mice, robustly decreases immobility in the forced swim test (FST), and preferentially phosphorylates extracellular signal-regulated kinase (ERK1/2), involved in antidepressant activity. Here, we evaluated the properties of NLX-204 in two mouse models of depression. Male CD-1 mice were subjected to unpredictable chronic mild stress (UCMS) for 4-weeks or to repeated corticosterone (CORT, 20 mg/kg s.c./day) for 3-weeks before receiving acute administration of NLX-204 (2 mg/kg, p.o.). Depressive-like behavior was assessed in the FST, anhedonia-like behavior in the sucrose preference test (SPT) and locomotor activity was also recorded. Phosphorylation of ERK1/2 (pERK1/2) and cAMP response binding element (pCREB) were measured ex vivo in hippocampus and prefrontal cortex (PFC). UCMS or CORT treatment increased immobility in the FST, elicited a sucrose preference deficit, and decreased pERK1/2 and pCREB levels in PFC and hippocampus. NLX-204 reduced depressive-like behavior in the FST in CORT and UCMS mice, and normalized sucrose preference in CORT mice, suggesting anti-anhedonic activity. NLX-204 increased pERK1/2 levels in PFC of UCMS mice. NLX-204 also increased pCREB levels in PFC of CORT mice. These data suggest that NLX-204 has RAAD-like properties not only in naïve mice, but also in mice in a "depressive-like" state, and that these involve changes in PFC and hippocampal pERK1/2 and pCREB levels. These data provide additional evidence that activation of 5-HT_1A receptors by selective biased agonists, such as NLX-204, may constitute a promising RAAD strategy.

Fermented Perilla frutescens Ameliorates Depression-like Behavior in Sleep-Deprivation-Induced Stress Model

Excessive stress plays a critical role in the pathogenesis of mood disorders such as depression. Fermented natural products have recently attracted attention because of their health benefits. We evaluated the antidepressant-like efficacy of fermented Perilla frutescens (FPF), and its underlying mechanisms, in sleep deprivation (SD)-induced stress mice. SD-stressed mice revealed a remarkable increase in the immobility time in both forced swimming test and tail suspension test; this increase was ameliorated by treatment with FPF at doses of 100 and 150 mg/kg. FPF treatment also reduced the level of stress hormones such as corticosterone and adrenocorticotropic hormone. Additionally, FPF increased the levels of serotonin and dopamine which were significantly decreased in the brain tissues of SD-stressed mice. The increased expression of proinflammatory cytokines, such as TNF-α and IL1β, and the decreased expression of brain-derived neurotrophic factor (BDNF) in the stressed mice were significantly reversed by FPF treatment. Furthermore, FPF also increased phosphorylation of tropomyosin receptor kinase B (TrkB), extracellular regulated protein kinase (ERK), and cAMP response element binding protein (CREB). Among the six components isolated from FPF, protocatechuic acid and luteolin-7-O-glucuronide exhibited significant antidepressant-like effects, suggesting that they are major active components. These findings suggest that FPF has therapeutic potential for SD-induced stress, by correcting dysfunction of hypothalamic-pituitary-adrenal axis and modulating the BDNF/TrkB/ERK/CREB signaling pathway.

Evaluation the Therapeutic Effect of Adipose-Derived Mesenchymal Stem Cells on Chronic Mild Stress by Activating PEBP1-GPX4 Axis in Ferroptosis Using qRT-PCR, Fluorescence Microscope and Iron Determination Analysis

About 50% of depressive patients failed to respond to the treatment, mainly because of insufficient knowledge about the pathogenesis of depression. The current study’s objectives were to look into the potential role of ferroptosis in the etiology of depression in the mice model of chronic mild stress (CMS) and investigate the effects of adipose-derived mesenchymal stem cells (ADSCs) on PEBP1-GPX4 axis controlled ferroptosis in mice. We grouped the male C57BL/6 mice randomly as follows: normal control (NC), CMS, and CMS+ADSCs. The second two groups’ animals were exposed to CMS for a total of six weeks. From the fourth week of modeling to the sixth week, cell therapy was given once a week. SPT, TST, FST, and NSFT behavior assessments were used to evaluate the depression-like behavior brought on by CMS. We selected the ferroptosis-related parameters, including the expression of GPX4, FTH1, ACSL4, and COX2. The amount of iron was determined in the hippocampus of the model organism by using the iron assay kit. By measuring the PEBP1 and ERK1/2 levels, as well as evaluating the expression of GFAP and IBA1, we assessed the biological function of astrocytes and microglia in mice hippocampus. It was found that six weeks after modeling in the CMS+ADSCs group, the mice’s depression-like behavior induced by CMS had significantly improved. We found a significantly changed level of genes, including GPX4, ACSL4, FTH1, COX2, ERK1/2, GFAP, PEBP1 and IBA1. Also, we found the differentiated level of total and ferric iron in our model mice. All these findings demonstrated that ADSCs had a therapeutic effect on CMS-induced depression-like behavior, probably by activating the PEBP1-GPX4 axis in ferroptosis. This anti-depression role of ADSCs may be associated with the activation of the PEBP1-GPX4 axis in ferroptosis, implying that regulation of ferroptosis is a crucial therapeutic target for depression.

SUMOylation and Major Depressive Disorder

Since the discovery of the small ubiquitin-like modifier (SUMO) protein in 1995, SUMOylation has been considered a crucial post-translational modification in diverse cellular functions. In neurons, SUMOylation has various roles ranging from managing synaptic transmitter release to maintaining mitochondrial integrity and determining neuronal health. It has been discovered that neuronal dysfunction is a key factor in the development of major depressive disorder (MDD). PubMed and Google Scholar databases were searched with keywords such as ‘SUMO’, ‘neuronal plasticity’, and ‘depression’ to obtain relevant scientific literature. Here, we provide an overview of recent studies demonstrating the role of SUMOylation in maintaining neuronal function in participants suffering from MDD.

Sulfuretin exerts anti-depressive effects in the lipopolysaccharide-induced depressive mouse models

BACKGROUND

Herb-derived therapeutics is an attractive strategy to treat depression. Here we report the ameliorating effects of Sulfuretin, an anti-inflammatory compound in a depressive mouse model.

METHODS

Immobility times were obtained in the tail suspension test and forced swim test performed from day 14 to day 16. Quantitative real-time PCR (qRT-PCR) and Western blot were used to measure brain-derived neurotrophic factor (BDNF) and the extracellular signal-regulated kinase (ERK) pathway of the hippocampus tissue on day 17. SL327 was used to block the ERK pathway in mice to evaluate the interaction between Sulfuretin and the ERK pathway. Mice were treated with Sulfuretin for 14 days before lipopolysaccharide (LPS) injection (0.83 mg/kg/day, i.p.) for two days.

RESULTS

Behavior tests showed that Sulfuretin dose-dependently decreased immobility times correlated with depression symptoms. BDNF levels and ERK signaling were significantly restored in the Sulfuretin-treated mice, showing the improvement of brain function. Blocking the p-ERK signaling abrogated the effects of Sulfuretin in improving behaviors and levels of BDNF.

CONCLUSION

Our study suggests that Sulfuretin exhibits anti-depressive function in LPS-induced depressive mice, in which the ERK signaling plays an essential role.

Molecular Signaling Mechanisms for the Antidepressant Effects of NLX-101, a Selective Cortical 5-HT1A Receptor Biased Agonist

Depression is the most prevalent of the mental illnesses and serotonin (5-hydroxytryptamine, 5-HT) is considered to be the major neurotransmitter involved in its etiology and treatment. In this context, 5-HT_1A receptors have attracted interest as targets for therapeutic intervention. Notably the activation of presynaptic 5-HT_1A autoreceptors delays antidepressant effects whereas the stimulation of postsynaptic 5-HT_1A heteroreceptors is needed for an antidepressant action. NLX-101 (also known as F15599) is a selective biased agonist which exhibits preferred activation of cortical over brain stem 5-HT_1A receptors. Here, we used behavioral, neurochemical and molecular methods to examine the antidepressant-like effects in rats of a single dose of NLX-101 (0.16 mg/kg, i.p.). NLX-101 reduced immobility in the forced swim test when measured 30 min but not 24 h after drug administration. NLX-101 increased extracellular concentrations of glutamate and dopamine in the medial prefrontal cortex, but no changes were detected in the efflux of noradrenaline or 5-HT. NLX-101 also produced an increase in the activation of pmTOR, pERK1/2 and pAkt, and the expression of PSD95 and GluA1, which may contribute to its rapid antidepressant action.

High-frequency repetitive transcranial magnetic stimulation mitigates depression-like behaviors in CUMS-induced rats via FGF2/FGFR1/p-ERK signaling pathway

High-frequency repetitive transcranial magnetic stimulation (rTMS) is a widely used and effective biological treatment for depression. Although previous studies have shown that astrocyte function may be modified by rTMS, the specific neurobiological mechanisms underlying its antidepressant action are not clear. Substantial evidence has accumulated indicating that neurotrophin dysfunction and neuronal apoptosis play a role in the development of depression. To evaluate this hypothesis, we applied a chronical unpredictable mild stress (CUMS) protocol to induce depression-like behaviors in rats, followed by the delivery of 10-Hz rTMS for 3 weeks. Behavioral outcome measures consisted of a sucrose preference test, forced swimming test, and open field test. Histological analysis focused on apoptosis, expression of GFAP and FGF2, and FGF2 pathway-related proteins. The results showed that after rTMS treatment, the rats' sucrose preference increased, open field performance improved while the immobility time of forced swimming decreased. The behavioral changes seen in rTMS treated rats were accompanied by marked reductions in the number of TUNEL-positive neural cells and the level of expression of BAX and by an increase in Bcl2. Furthermore, the expression of GFAP and FGF2 was increased, along with activation of FGF2 downstream pathway. These results suggest that rTMS treatment can improve depression-like behavior, attenuate neural apoptosis, and reverse reduction of astrocytes in a rat model of depression. We hypothesize that the therapeutic action of rTMS in CUMS-induced rats is linked to the activation of the FGF2/FGFR1/p-ERK signaling pathway.

Translational Informatics for Natural Products as Antidepressant Agents

Depression, a neurological disorder, is a universally common and debilitating illness where social and economic issues could also become one of its etiologic factors. From a global perspective, it is the fourth leading cause of long-term disability in human beings. For centuries, natural products have proven their true potential to combat various diseases and disorders, including depression and its associated ailments. Translational informatics applies informatics models at molecular, imaging, individual, and population levels to promote the translation of basic research to clinical applications. The present review summarizes natural-antidepressant-based translational informatics studies and addresses challenges and opportunities for future research in the field.

Intersections between Copper, β-Arrestin-1, Calcium, FBXW7, CD17, Insulin Resistance and Atherogenicity Mediate Depression and Anxiety Due to Type 2 Diabetes Mellitus: A Nomothetic Network Approach

Type 2 diabetes mellitus (T2DM) is frequently accompanied by affective disorders with a prevalence of comorbid depression of around 25%. Nevertheless, the biomarkers of affective symptoms including depression and anxiety due to T2DM are not well established. The present study delineated the effects of serum levels of copper, zinc, β-arrestin-1, FBXW7, lactosylceramide (LacCer), serotonin, calcium, magnesium on severity of depression and anxiety in 58 men with T2DM and 30 healthy male controls beyond the effects of insulin resistance (IR) and atherogenicity. Severity of affective symptoms was assessed using the Hamilton Depression and Anxiety rating scales. We found that 61.7% of the variance in affective symptoms was explained by the multivariate regression on copper, β-arrestin-1, calcium, and IR coupled with atherogenicity. Copper and LacCer (positive) and calcium and BXW7 (inverse) had significant specific indirect effects on affective symptoms, which were mediated by IR and atherogenicity. Copper, β-arrestin-1, and calcium were associated with affective symptoms above and beyond the effects of IR and atherogenicity. T2DM and affective symptoms share common pathways, namely increased atherogenicity, IR, copper, and β-arrestin-1, and lowered calcium, whereas copper, β-arrestin-1, calcium, LacCer, and FBXW7 may modulate depression and anxiety symptoms by affecting T2DM.

Hippocampal neuropathology in suicide: Gaps in our knowledge and opportunities for a breakthrough

Suicide is a major global hazard. There is a need for increasing suicide awareness and effective and evidence-based interventions, targeting both suicidal ideation and conduct. However, anti-suicide pharmacological effects are unsatisfactory. The human hippocampus is vulnerable to neuropsychiatric damages and subsequently releases psychobiological signals. Human hippocampal studies of suicide completers have shown mechanistic changes in neurobiology, which, however, could not reflect the neuropathological 'fingerprints' of fatal suicide ideations and suicide attempts. In this review, we provide several leading theories of suicide, including the serotoninergic system, Wnt pathway and brain-derived neurotrophic factor/tropomyosin receptor kinase B signalling, and discuss the evidence for their roles in suicide and treatment. Moreover, the cognitive dysfunctions associated with suicide risk are discussed, as well as the novel evidence on cognitive therapies that decrease suicidal ideation. We highlight the need to apply multi-omics techniques (including single-nucleus RNA sequencing and mass spectrometry histochemistry) on hippocampal samples from donors who died by suicide or legal euthanasia, to clarify the aetiology of suicide and propose novel therapeutic strategies.

MiR-129-5p prevents depressive-like behaviors by targeting MAPK1 to suppress inflammation

Depression is a complex etiological disease with limited effective treatments. Previous studies have indicated the involvement of miRNAs in the pathophysiology of mood disorders. In this study, we focused on the role and mechanisms of miR-129-5p in depression by successfully constructing mice models of depressive-like behavior via chronic unpredictable mild stress (CUMS) exposure. Herein, miR-129-5p expression was decreased in the hippocampus of CUMS mice model. Upregulation of miR-129-5p reduced depressive-like behaviors of CUMS mice, as revealed in sucrose preference test, novelty suppressed feeding test, forced swim test, tail suspension test, social interaction test. MiR-129-5p upregulation decreased the concentrations and protein levels of proinflammatory cytokines (IL-6, IL-1β and TNF-α), indicating the inhibitory role of miR-129-5p in inflammation. Furthermore, miR-129-5p was identified to target MAPK1. MAPK1 was negatively regulated by miR-129-5p, and silencing of MAPK1 attenuated depressive-like behaviors in CUMS mice. Moreover, MAPK1 downregulation decreased inflammation in the hippocampus of CUMS mice. Upregulation of MAPK1 reversed the suppressive effects of miR-129-5p upregulation on depressive-like behaviors and inflammation in CUMS mice. In conclusion, the current study identified that miR-129-5p reduces depressive-like behaviors and suppresses inflammation by targeting MAPK1 in CUMS mice, offering a novel molecular interpretation for depression prevention.

Baicalin ameliorates chronic unpredictable mild stress-induced depression through the BDNF/ERK/CREB signaling pathway

Brain-derived neurotrophic factor (BDNF) can activate the extracellular regulated protein kinase (ERK)/cAMP response element binding protein (CREB) cascade revealing an important role in antidepressant effects. Here, we studied the neuroprotective effect of baicalin (BA) in mice with chronic unpredictable mild stress (CUMS)-induced via a BDNF/ERK/CREB signaling pathway. Depression was induced via six weeks of CUMS in male ICR mice, and drug therapy was given simultaneously for the last three weeks. Cognitive dysfunctions were then evaluated via sucrose preference test (SPT), open field test (OFT), Morris water maze test (MWM), tail suspension test (TST), and novelty suppressed feeding test (NSF). Western blot and real-time PCR were then used to detect the relative expression of ERK, CREB, p-ERK, and p-CREB. Integrated optical density (IOD) tests of p-ERK and p-CREB were then evaluated via immunofluorescence. The behavior results showed that the cognitive dysfunctions increased in the CUMS group versus the control (CON) group (p < 0.01). There were decreases in fluoxetine (FLU) and BA groups (p < 0.05, p < 0.01). The protein ratios of p-ERK/ERK, p-CREB/CREB and ERK mRNA, and CREB mRNA expression decreased in the CUMS group (p < 0.01) and markedly increased in the FLU and BA groups (p < 0.05, p < 0.01). The IOD value of the p-ERK and p-CREB in the CUMS group was decreased versus the CON group (p < 0.01), and these changes were improved via BA and FLU treatment (p < 0.05, p < 0.01). This study indicated that BA can improve cognitive functions and has antidepressant effects in mice, which may be associated with activation of the BDNF/ERK/CREB signaling pathway in the hippocampus.

Potential Correlation Between Depression-like Behavior and the Mitogen-Activated Protein Kinase Pathway in the Rat Hippocampus Following Spinal Cord Injury

BACKGROUND

Depression induced by spinal cord injury (SCI) has been demonstrated in clinical and experimental studies; it significantly impacts patients' lives and may be associated with changes in the hippocampus. However, the biological mechanisms underlying depression after SCI are unknown. The mitogen-activated protein kinase (MAPK) signaling pathway participates in potential mechanisms of depression; it is unknown whether this pathway plays a role in SCI-induced depression.

METHODS

We applied an animal model of depression induced by SCI, established using an aneurysm clip, to determine whether MAPK activation in the hippocampus is associated with depression-like behavior.

RESULTS

SCI led to depression-like behavior, such as anhedonia in the sucrose preference test, decreased number of crossings in the open field test, decreased body weight, and decreased immobility time in the forced swim test. Western blot analysis further showed that SCI significantly increased the levels of phosphorylated p38 MAPK and cleaved caspase-3 in the hippocampus and inhibited the phosphorylation of extracellular signal-related kinase 1/2 and c-Jun N-terminal kinase 1/2. In addition, there were significant negative correlations between depression-like behavior and phosphorylated extracellular signal-related kinase 1/2 and positive correlations between depression-like behavior and phosphorylated p38 MAPK and cleaved caspase-3.

CONCLUSIONS

These findings suggest that the MAPK pathway in the rat hippocampus may be involved in the pathophysiology of depression induced by SCI.

Translating biased agonists from molecules to medications: Serotonin 5-HT1A receptor functional selectivity for CNS disorders

Biased agonism (or "functional selectivity") at G-protein-coupled receptors has attracted rapidly increasing interest as a means to improve discovery of more efficacious and safer pharmacotherapeutics. However, most studies are limited to in vitro tests of cellular signaling and few biased agonists have progressed to in vivo testing. As concerns 5-HT_1A receptors, which exert a major control of serotonergic signaling in diverse CNS regions, study of biased agonism has previously been limited by the poor target selectivity and/or partial agonism of classically available ligands. However, a new generation of highly selective, efficacious and druggable agonists has advanced the study of biased agonism at this receptor and created new therapeutic opportunities. These novel agonists show differential properties for G-protein signaling, cellular signaling (particularly pERK), electrophysiological effects, neurotransmitter release, neuroimaging by PET and pharmacoMRI, and behavioral tests of mood, motor activity and side effects. Overall, NLX-101 (a.k.a. F15599) exhibits preferential activation of cortical and brain stem 5-HT_1A receptors, whereas NLX-112 (a.k.a. befiradol or F13640) shows prominent activation of 5-HT_1A autoreceptors in Raphe nuclei and in regions associated with motor control. Accordingly, NLX-101 is potently active in rodent models of depression and respiratory control, whereas NLX-112 shows promising activity in models of Parkinson's disease across several species - rat, marmoset and macaque. Moreover, NLX-112 has also been labeled with ¹⁸F to produce the first agonist PET radiopharmaceutical (known as [¹⁸F]-F13640) for investigation of the active state of 5-HT_1A receptors in rodent, primate and human. The structure-functional activity relationships of biased agonists have been investigated by receptor modeling and novel compounds have been identified which exhibit increased affinity at 5-HT_1A receptors and new profiles of cellular signaling bias, notably for β-arrestin recruitment versus pERK. Taken together, the data suggest that 5-HT_1A receptor biased agonists constitute potentially superior pharmacological agents for treatment of CNS disorders involving serotonergic mechanisms.

Perspectives for therapy of treatment-resistant depression

A high proportion of depressed patients fail to respond to antidepressant drug treatment. Treatment-resistant depression (TRD) is a major challenge for the psychopharmacology of mood disorders. Only in the past decade have novel treatments, including deep brain stimulation (DBS) and ketamine, been discovered that provide rapid and sometimes prolonged relief to a high proportion of TRD sufferers. In this review, we consider the current status of TRD from four perspectives: the challenge of developing an appropriate regulatory framework for novel rapidly acting antidepressants; the efficacy of non-pharmacological somatic therapies; the development of an animal model of TRD and its use to understand the neural basis of antidepressant non-response; and the potential for rapid antidepressant action from targets (such as 5-HT_1A receptors) beyond the glutamate receptor.

Biased agonism in drug discovery: Is there a future for biased 5-HT1A receptor agonists in the treatment of neuropsychiatric diseases?

Serotonin (5-HT) is one of the fundamental neurotransmitters that contribute to the information essential for an organism's normal, physiological function. Serotonin acts centrally and systemically. The 5-HT_1A receptor is the most widespread serotonin receptor, and participates in many brain-related disorders, including anxiety, depression, and cognitive impairments. The 5-HT_1A receptor can activate several different biochemical pathways and signals through both G protein-dependent and G protein-independent pathways. Preclinical experiments indicate that distinct signaling pathways in specific brain regions may be crucial for antidepressant-like, anxiolytic-like, and procognitive responses. Therefore, the development of new ligands that selectively target a particular signaling pathway(s) could open new possibilities for more effective and safer pharmacotherapy. This review discusses the current state of preclinical studies focusing on the concept of functional selectivity (biased agonism) regarding the 5-HT_1A receptor and its role in antidepressant-like, anxiolytic-like, and procognitive regulation. Such work highlights not only the differential effects of targeted autoreceptors, vs. heteroreceptors, but also the importance of targeting specific downstream intracellular signaling processes, thereby enhancing favorable over unfavorable signaling activation.

Effect of fluoxetine on the MAPK-ERK1/2 signaling pathway and expression of associated factors in human conjunctival epithelial cells in culture

The aim of the present study was to evaluate the effect of fluoxetine on activation of the mitogen-activated protein kinase (MAPK) signaling pathway and the expression of apoptosis-associated factors in human conjunctival epithelial cells (HConEpiCs) in culture. HConEpiCs were isolated, cultured and characterized by immunostaining. HConEpiC cells at passage 3-4 were cultured with fluoxetine at different dosages (0, 1, 2.5, 5, 10, 20 and 40 µM) and proliferation rates were determined using a Cell Counting Kit-8 assay. Subsequently, Transwell assays were performed to evaluate the effect of fluoxetine (5 µM) on the invasion and migration capacities of HConEpiCs. ERK1/2 and phosphorylated (p-)ERK1/2 levels were also evaluated in control and fluoxetine-treated groups of HConEpiCs via immunostaining. Finally, western blot assays were performed to evaluate the intracellular protein levels of ERK, p-ERK, Bcl-2, Bax and matrix metalloproteinases (MMPs) in HConEpiCs. It was identified that, as the fluoxetine concentration increased, proliferation rates of HConEpiCs gradually decreased and 5 µΜ fluoxetine was selected for further evaluation. The results of Transwell assays indicated that fluoxetine treatment significantly repressed cell migration and invasion. Immunostaining suggested that there was no significant difference in fluorescence intensity of ERK1/2 between the control and fluoxetine-treated groups, while p-ERK1/2 was significantly enhanced in the fluoxetine-treated group. This result indicated that fluoxetine promoted ERK1/2 activation without affecting its expression. Similarly, western blot analysis revealed no significant difference in ERK1/2 and MMP levels between fluoxetine-treated and control groups, but p-ERK1/2 and Bax were upregulated and Bcl-2 was decreased in the fluoxetine-treated group. In conclusion, fluoxetine induces apoptosis of HConEpiCs in culture via activating the MAPK-ERK1/2 signaling pathway.

Cortical 5-hydroxytryptamine 1A receptor biased agonist, NLX-101, displays rapid-acting antidepressant-like properties in the rat chronic mild stress model

BACKGROUND

NLX-101 (also known as F15599) is a highly selective and efficacious 'biased' agonist at cortical 5-hydroxytryptamine 1A (5-HT_1A) heteroreceptors. In rodents, it possesses marked antidepressant-like activity, potently and completely abolishing immobility in the forced swim test (FST) with extended duration of action.

METHODS

We investigated the antidepressant-like activity of NLX-101 using the rat chronic mild stress (CMS) model of depression, considered to have a higher translational potential than the FST, as it possesses construct, face and predictive validity. The effects of CMS and repeated NLX-101 treatment were tested using sucrose consumption (a measure of anhedonia), novel object recognition (NOR; a measure of working memory) and elevated plus maze (EPM; a measure of anxiety) tests.

RESULTS

NLX-101 reversed the CMS-induced decrease of sucrose intake on day 1 of testing, with full reversal observed at the dose of 0.16 mg/kg and a less pronounced but still significant effect at 0.04 mg/kg, both given twice a day intraperitoneally. The effects of NLX-101 were maintained over the 2 week treatment period and persisted for four weeks following cessation of treatment. In the NOR test, both doses of NLX-101 rescued the deficit in discrimination index caused by CMS, without any effect on locomotor activity. However, NLX-101 had no effect on the reduction of open-arms entries produced by CMS in the EPM model. In control, non-stressed rats, NLX-101 produced non-significant effects in all three models.

CONCLUSIONS

NLX-101 displayed efficacious activity in the CMS test, with more rapid (1 day) antidepressant-like effects than pharmacological compounds tested previously under the same experimental conditions. These observations suggest that biased agonist targeting of cortical 5-HT_1A receptors constitutes a promising strategy to achieve rapid-acting and sustained antidepressant effects.

MicroRNAs expressed in depression and their associated pathways: A systematic review and a bioinformatics analysis

Depression is a debilitating mental illness, one of the most prevalent worldwide. MicroRNAs have been studied to better understand the biological mechanisms that regulate this disease. This study review systematically the literature to identify which microRNAs are currently being associated with depression and their related pathways. The electronic search was conducted in PubMed, Scopus, Scielo, ISI Web of Knowledge, and PsycINFO databases, using the search terms "Depressive Disorder" or "Depression" and "MicroRNAs". After, microRNAs that were up and down-regulated in depression were analyzed by bioinformatics. We observed that among the 77 microRNAs cited by included studies, 54 had their levels altered in depressed individuals compared to controls, 30 being up-regulated and 24 down-regulated. The bioinformatics analysis revealed that among the up-regulated microRNAs there were 81 total and 43 union pathways, with 15 presenting a significant difference. Among the down-regulated microRNAs, 67 total and 45 union pathways were found, with 14 presenting a significant difference. The miR-17-5p and let-7a-5p were the most frequently found microRNAs in the statistically significant pathways. In this study a panel of altered microRNAs in depression was created with their related pathways, which is a step towards understanding the complex network of microRNAs in depression.

Identification of gene ontology and pathways implicated in suicide behavior: Systematic review and enrichment analysis of GWAS studies

Multiple large-scale studies such as genome-wide association studies (GWAS) have been performed to identify genetic contributors to suicidal behaviors (SB). We aimed to summarize and analyze the information obtained in SB GWAS, to explore the biological process gene ontology (GO) of genes associated with SB from GWAS, and to determine the possible implications of the genes associated with SB in Kyoto encyclopedias of genes and genomes (KEGG) biological pathways. The articles included in the analysis were obtained from PubMed and Scopus databases. Enrichment analyses were performed in Enrichr to evaluate the KEGG pathways and GO of the genes associated with SB of GWAS. The findings of biological process GO analysis showed 924 GO involved in genes related with SB; of those, the regulation of glucose import in response to insulin stimulus, regulation of protein localization to plasma membrane, positive regulation of endopeptidase activity, heterotypic cell-cell adhesion, regulation of cardiac muscle cell contraction, positive regulation of protein localization to plasma membrane, and positive regulation of protein localization to cell periphery biological process GO showed significant statistical association. Furthermore, we obtained 130 KEGG pathways involved in genes related with SB, which Aldosterone synthesis and secretion, Rap1 signaling pathway and arrhythmogenic right ventricular cardiomyopathy pathways showed a significant statistical association. These findings give a better perspective of the biological participation of genes associated with SB, which will be important to perform adequate strategies to prevent and treat SB.

Novel Aryloxyethyl Derivatives of 1-(1-Benzoylpiperidin-4-yl)methanamine as the Extracellular Regulated Kinases 1/2 (ERK1/2) Phosphorylation-Preferring Serotonin 5-HT1A Receptor-Biased Agonists with Robust Antidepressant-like Activity

Novel 1-(1-benzoylpiperidin-4-yl)methanamine derivatives were designed as "biased agonists" of serotonin 5-HT_1A receptors. The compounds were tested in signal transduction assays (ERK1/2 phosphorylation, cAMP inhibition, Ca²⁺ mobilization, and β-arrestin recruitment) which identified ERK1/2 phosphorylation-preferring aryloxyethyl derivatives. The novel series showed high 5-HT_1A receptor affinity, >1000-fold selectivity versus noradrenergic α₁, dopamine D₂, serotonin 5-HT_2A, histamine H₁, and muscarinic M₁ receptors, and favorable druglike properties (CNS-MPO, Fsp³, LELP). The lead structure, (3-chloro-4-fluorophenyl)(4-fluoro-4-(((2-(pyridin-2-yloxy)ethyl)amino)methyl)piperidin-1-yl)methanone (17, NLX-204), displayed high selectivity in the SafetyScreen44 panel (including hERG channel), high solubility, metabolic stability, and Caco-2 penetration and did not block CYP3A4, CYP2D6 isoenzymes, or P-glycoprotein. Preliminary in vivo studies confirmed its promising pharmacokinetic profile. 17 also robustly stimulated ERK1/2 phosphorylation in rat cortex and showed highly potent (MED = 0.16 mg/kg) and efficacious antidepressant-like activity, totally eliminating immobility in the rat Porsolt test. These data suggest that the present 5-HT_1A receptor-biased agonists could constitute promising antidepressant drug candidates.

The ERK Pathway: Molecular Mechanisms and Treatment of Depression

Major depressive disorder is a chronic debilitating mental illness. Its pathophysiology at cellular and molecular levels is incompletely understood. Increasing evidence supports a pivotal role of the mitogen-activated protein kinase (MAPK), in particular the extracellular signal-regulated kinase (ERK) subclass of MAPKs, in the pathogenesis, symptomatology, and treatment of depression. In humans and various chronic animal models of depression, the ERK signaling was significantly downregulated in the prefrontal cortex and hippocampus, two core areas implicated in depression. Inhibiting the ERK pathway in these areas caused depression-like behavior. A variety of antidepressants produced their behavioral effects in part via normalizing the downregulated ERK activity. In addition to ERK, the brain-derived neurotrophic factor (BDNF), an immediate upstream regulator of ERK, the cAMP response element-binding protein (CREB), a transcription factor downstream to ERK, and the MAPK phosphatase (MKP) are equally vulnerable to depression. While BDNF and CREB were reduced in their activity in the prefrontal cortex and hippocampus of depressed animals, MKP activity was enhanced in parallel. Chronic antidepressant treatment readily reversed these neurochemical changes. Thus, ERK signaling in the depression-implicated brain regions was disrupted during the development of depression, which contributes to the long-lasting and transcription-dependent neuroadaptations critical for enduring depression-like behavior and the therapeutic effect of antidepressants.

Withdrawal from chronic treatment with methamphetamine induces anxiety and depression-like behavior in mice

Methamphetamine (METH) is an illicit psychostimulant that is widely abused. After producing extreme pleasure, METH abuse leads to negative emotional states during withdrawal in clinical survey. However, the mood behavioral consequences of withdrawal from chronic METH exposure in animal experiments and related mechanisms have not been clarified yet. The aim of this study was to investigate the anxiety and depression-like phenotype in mice induced by withdrawal from chronic METH treatment and the potential molecular mechanism. We found that withdrawal from chronic METH treatment increased the immobility time during the forced swimming test and decreased central activities in open field test, indicating increased anxiety and depression-like behavior. Additional experiments showed that expression of brain-derived neurotrophic factor (BDNF), phosphorylated tropomyosin receptor kinase B (p-TrkB), phosphorylated extracellular signal-related kinase 1/2 (p-ERK1/2) and phosphorylated cAMP-response element binding protein (p-CREB) were decreased in the hippocampus and prefrontal cortex of mice in METH group and the level of mitogen activated protein kinase phosphatase-1 (MKP-1) was increased. Combined, our data show that withdrawal from chronic METH exposure induces anxiety and depression-like behavior associated with aberrant changes of proteins in BDNF-ERK-CREB pathway, providing new evidence for the involvement of BDNF pathway in the negative emotional states induced by withdrawal from METH.

Association between completed suicide and bipolar disorder: A systematic review of the literature

BACKGROUND

Completed suicide is a major cause of death in bipolar disorder (BD) patients.

OBJECTIVE

The aim of this paper is to provide an overall review of the existing literature of completed suicide in BD patients, including clinical and genetic data DATA SOURCES: We performed a systematic review of English and non-English articles published on MEDLINE/PubMed, PsycInfo and Cochrane database (1970-2017). Additional studies were identified by contacting clinical experts, searching bibliographies, major textbooks and website of World Health Organization. Initially we did a broad search for the association of bipolar disorder and suicide and we were narrowing the search in terms included "bipolar disorder" and "completed suicide".

STUDY SELECTION

Inclusion criteria were articles about completed suicide in patients with BD. Articles exclusively focusing on suicide attempts and suicidal behaviour have been excluded. We used PRISMA (Preferred Reporting Items for Systematic reviews and Meta-Analyses) consensus for drafting this systematic review.

RESULTS

The initial search generated 2806 articles and a total of 61 meeting our inclusion criteria. We reviewed epidemiological data, genetic factors, risk factors and treatment of completed suicide in BD. Suicide rates in BD vary between studies but our analyses show that they are approximately 20-30-fold greater than in general population. The highest risk of successful suicide was observed in BD-II subjects. The heritability of completed suicide is about 40% and some genes related to major neurotransmitter systems have been associated with suicide. Lithium is the only treatment that has shown anti-suicide potential.

LIMITATIONS

The most important limitation of the present review is the limited existing literature on completed suicide in BD.

CONCLUSIONS

BD patients are at high risk for suicide. It is possible to identify some factors related to completed suicide, such as early onset, family history of suicide among first-degree relatives, previous attempted suicides, comorbidities and treatment. However it is necessary to promote research on this serious health problem.

Prefrontal cortical trkB, glucocorticoids, and their interactions in stress and developmental contexts

The tropomyosin/tyrosine receptor kinase B (trkB) and glucocorticoid receptor (GR) regulate neuron structure and function and the hormonal stress response. Meanwhile, disruption of trkB and GR activity (e.g., by chronic stress) can perturb neuronal morphology in cortico-limbic regions implicated in stressor-related illnesses like depression. Further, several of the short- and long-term neurobehavioral consequences of stress depend on the developmental timing and context of stressor exposure. We review how the levels and activities of trkB and GR in the prefrontal cortex (PFC) change during development, interact, are modulated by stress, and are implicated in depression. We review evidence that trkB- and GR-mediated signaling events impact the density and morphology of dendritic spines, the primary sites of excitatory synapses in the brain, highlighting effects in adolescents when possible. Finally, we review the role of neurotrophin and glucocorticoid systems in stress-related metaplasticity. We argue that better understanding the long-term effects of developmental stressors on PFC trkB, GR, and related factors may yield insights into risk for chronic, remitting depression and related neuropsychiatric illnesses.

Adolescent Nicotine Exposure Induces Dysregulation of Mesocorticolimbic Activity States and Depressive and Anxiety-like Prefrontal Cortical Molecular Phenotypes Persisting into Adulthood

Considerable evidence demonstrates strong comorbidity between nicotine dependence and mood and anxiety disorders. Nevertheless, the neurobiological mechanisms linking adolescent nicotine exposure to mood and anxiety disorders are not known. Disturbances in the mesocorticolimbic dopamine (DA) system, comprising the prefrontal cortex (PFC), ventral tegmental area (VTA), and nucleus accumbens (NAc), are correlates of mood and anxiety-related symptoms and this circuitry is strongly influenced by acute or chronic nicotine exposure. Using a combination of behavioral pharmacology, in vivo neuronal electrophysiology and molecular analyses, we examined and compared the effects of chronic nicotine exposure in rats during adolescence versus adulthood to characterize the mechanisms by which adolescent nicotine may selectively confer increased risk of developing mood and anxiety-related symptoms in later life. We report that exposure to nicotine, selectively during adolescence, induces profound and long-lasting neuronal, molecular and behavioral disturbances involving PFC DA D1R and downstream extracellular-signal-related kinase 1-2 (ERK 1-2) signaling. Remarkably, adolescent nicotine induced a persistent state of hyperactive DA activity in the ventral tegmental area (VTA) concomitant with hyperactive neuronal activity states in the PFC. Our findings identify several unique neuronal and molecular biomarkers that may serve as functional risk mechanisms for the long-lasting neuropsychiatric effects of adolescent smoking behaviors.

Unfolded protein response and associated alterations in toll-like receptor expression and interaction in the hippocampus of restraint rats

Recent evidence suggests that the cellular response to stress often elicits the unfolded protein response (UPR), which has an active role in major depression in emotionally relevant regions of the brain, such as the hippocampus. Much of the UPR activity has been found to be coalesced with the pro-inflammatory environment of the depressed brain. Specifically, downstream transcriptions of pro-inflammatory cytokines and increased regulation of candidate inflammatory mediators, such as toll-like receptors (TLRs), are promoted by the UPR. The present study examined the hippocampus associated expression profile of Tlr genes and their interaction with the UPR chaperone GRP94 in stress-induced rodent model of depression (restraint stress model). Also, the expression status of UPR related genes was evaluated in hippocampus using the same model. mRNA and protein levels of Tlr and UPR associated genes were examined by qRT-PCR and Western blot, respectively. Co-immunoprecipitation (Co-IP) method was used to determine the direct interaction between TLRs with GRP94 in depressed rat brain. The results showed that both UPR (Xbp-1, its spliced variant sXbp-1, Atf-6, Chop, and Grp94) and Tlr (2, 3, 4, 7 and 9) genes were significantly upregulated in the hippocampi of rats who were exposed to restraint stress. Similar upregulation was observed in the protein levels of the above-mentioned TLRs and the UPR chaperone protein GRP94 as well as total and phosphorylated forms of sensor proteins IRE1α and PERK. Further, a significantly increased interaction was observed between GRP94 and the activated TLR proteins. Since, increased inflammatory activity in vulnerable areas like hippocampus is coherently associated with depressed brain; our present data suggest that the UPR may be an integral part of increased activity of inflammatory regulations in depression.

Vicarious Social Defeat Stress Induces Depression-Related Outcomes in Female Mice

BACKGROUND

Stress is a prevailing risk factor for mood-related illnesses, wherein women represent the majority of those affected by major depression. Despite the growing literature suggesting that affective disorders can arise after a traumatic event is vicariously experienced, this relationship remains understudied in female subjects at the preclinical level. Thus, the objective of the current investigation was to examine whether exposure to emotional and/or psychological stress (ES) mediates depression-related outcomes in female mice.

METHODS

Female C57BL/6 mice (8 weeks old, null parity) vicariously experienced the defeat bout of a male conspecific, by a male CD1 aggressor, for 10 consecutive days. Twenty-four hours after the last stress exposure, female mice were tested in the social interaction, sucrose preference, tail suspension, or elevated plus maze tests. Furthermore, we examined whether ketamine and chlordiazepoxide, pharmacological agents used to treat mood-related disorders in the clinical population, would reverse the ES-induced social dysfunction.

RESULTS

When compared with control mice, female mice exposed to ES displayed decreased social behavior and preference for sucrose, along with increased immobility in the tail suspension test. Also, they displayed higher levels of blood serum corticosterone, as well as decreased body weight. Lastly, the ES-induced avoidance-like phenotype was ameliorated by both ketamine and chlordiazepoxide.

CONCLUSIONS

Our data indicate that female mice exposed to ES display a behavioral and physiologic profile that mimics symptoms of depression in the clinical population. As such, this experimental model may be adopted to examine vicarious stress-induced mood-related disorders, as well as pharmacological antidepressant response, in a sex-specific manner.

Association analysis between mitogen-activated protein/extracellular signal-regulated kinase (MEK) gene polymorphisms and depressive disorder in the Han Chinese population

BACKGROUND

Recent research findings suggest that BDNF and BDNF signaling pathways participate in the development of major depressive disorder. Mitogen-activated extracellular signal-regulated kinase (MEK) is the most important kinase in the extracellular signal-regulated kinase pathway, and the extracellular signal-regulated kinase pathway is the key signaling pathway of BDNF, so it may play a role in development of depressive disorder. The aim of this study is to investigate the association between polymorphisms of the MAP2K1 (also known as MEK) gene and depressive disorder.

RESULTS

Three single nucleotide polymorphisms (SNPs), were significantly associated with depressive disorder: rs1549854 (p = 0.006), rs1432441 (p = 0.025), and rs7182853 (p = 0.039). When subdividing the sample by gender, two of the SNPs remained statistically associated with depressive disorder in females: rs1549854 (p = 0.013) and rs1432441 (p = 0.04).

CONCLUSION

The rs1549854 and rs1432441 polymorphisms of the MAP2K1 gene may be associated with major depressive disorder, especially in females. This study is the first to report that the MAP2K1 gene may be a genetic marker for depressive disorder.

Sex-specific transcriptional signatures in human depression

Major depressive disorder (MDD) is a leading cause of disease burden worldwide. While the incidence, symptoms and treatment of MDD all point toward major sex differences, the molecular mechanisms underlying this sexual dimorphism remain largely unknown. Here, combining differential expression and gene coexpression network analyses, we provide a comprehensive characterization of male and female transcriptional profiles associated with MDD across six brain regions. We overlap our human profiles with those from a mouse model, chronic variable stress, and capitalize on converging pathways to define molecular and physiological mechanisms underlying the expression of stress susceptibility in males and females. Our results show a major rearrangement of transcriptional patterns in MDD, with limited overlap between males and females, an effect seen in both depressed humans and stressed mice. We identify key regulators of sex-specific gene networks underlying MDD and confirm their sex-specific impact as mediators of stress susceptibility. For example, downregulation of the female-specific hub gene Dusp6 in mouse prefrontal cortex mimicked stress susceptibility in females, but not males, by increasing ERK signaling and pyramidal neuron excitability. Such Dusp6 downregulation also recapitulated the transcriptional remodeling that occurs in prefrontal cortex of depressed females. Together our findings reveal marked sexual dimorphism at the transcriptional level in MDD and highlight the importance of studying sex-specific treatments for this disorder.

Brain-Derived Neurotrophic Factor, Depression, and Physical Activity: Making the Neuroplastic Connection

Brain-derived neurotrophic factor (BDNF) is a neurotrophin that is vital to the survival, growth, and maintenance of neurons in key brain circuits involved in emotional and cognitive function. Convergent evidence indicates that neuroplastic mechanisms involving BDNF are deleteriously altered in major depressive disorder (MDD) and animal models of stress. Herein, clinical and preclinical evidence provided that stress-induced depressive pathology contributes to altered BDNF level and function in persons with MDD and, thereby, disruptions in neuroplasticity at the regional and circuit level. Conversely, effective therapeutics that mitigate depressive-related symptoms (e.g., antidepressants and physical activity) optimize BDNF in key brain regions, promote neuronal health and recovery of function in MDD-related circuits, and enhance pharmacotherapeutic response. A greater knowledge of the interrelationship between BDNF, depression, therapeutic mechanisms of action, and neuroplasticity is important as it necessarily precedes the derivation and deployment of more efficacious treatments.

Nine differentially expressed genes from a post mortem study and their association with suicidal status in a sample of suicide completers, attempters and controls

Several lines of evidence indicate that suicidal behaviour is partly heritable, with multiple genes implicated in its aetiology. We focused on nine genes (S100A13, EFEMP1, PCDHB5, PDGFRB, CDCA7L, SCN2B, PTPRR, MLC1 and ZFP36) which we previously detected as differentially expressed in the cortex of suicide victims compared to controls. We investigated 84 variants within these genes in 495 suicidal subjects (299 completers and 196 attempters) and 1513 controls (109 post-mortem and 1404 healthy). We evaluated associations with: 1) suicidal phenotype; 2) possible endophenotypes for suicidal behaviour. Overall positive results did not survive the correction threshold. However, we found a nominally different distribution of EFEMP1 genotypes, alleles and haplotypes between suicidal subjects and controls, results that were partially replicated when we separately considered the subgroup of suicide completers and post-mortem controls. A weaker association emerged also for PTPRR. Both EFEMP1 and PTPRR genes were also related to possible endophenotypes for suicidal behaviour such as anger, depression-anxiety and fatigue. Because of the large number of analyses performed and the low significance values further replication are mandatory. Nevertheless, neurotrophic gene variants, in particular EFEMP1 and PTPRR, may have a role in the pathogenesis of suicidal behaviour.

Altered miRNA expression network in locus coeruleus of depressed suicide subjects

Norepinephrine (NE) is produced primarily by neurons in the locus coeruleus (LC). Retrograde and ultrastructural examinations reveal that the core of the LC and its surrounding region receives afferent projections from several brain areas which provide multiple neurochemical inputs to the LC with changes in LC neuronal firing, making it a highly coordinated event. Although NE and mediated signaling systems have been studied in relation to suicide and psychiatric disorders that increase the risk of suicide including depression, less is known about the corresponding changes in molecular network within LC. In this study, we examined miRNA networks in the LC of depressed suicide completers and healthy controls. Expression array revealed differential regulation of 13 miRNAs. Interaction between altered miRNAs and target genes showed dense interconnected molecular network. Functional clustering of predicated target genes yielded stress induced disorders that collectively showed the complex nature of suicidal behavior. In addition, 25 miRNAs were pairwise correlated specifically in the depressed suicide group, but not in the control group. Altogether, our study revealed for the first time the involvement of LC based dysregulated miRNA network in disrupting cellular pathways associated with suicidal behavior.

Effects of electroacupuncture on the cortical extracellular signal regulated kinase pathway in rats with cerebral ischaemia/reperfusion

OBJECTIVE

To explore the effects of electroacupuncture (EA) on the phosphorylated extracellular signal regulated kinase (p-ERK) pathway of the cerebral cortex in a rat model of focal cerebral ischaemia/reperfusion (I/R).

METHODS

160 adult Sprague-Dawley rats underwent middle carotid artery occlusion (MCAO) to establish I/R injury and were randomly divided into four groups (n=40 each) that remained untreated (I/R group) or received EA at LU5, LI4, ST36 and SP6 (I/R+EA group), the ERK inhibitor PD98059 (I/R+PD group), or both interventions (I/R+PD+EA groups). An additional 40 rats undergoing sham surgery formed a healthy control group. Eight rats from each group were sacrificed at the following time points: 2 hours, 6 hours, 1 day, 3 days and 1 week. Neurological function was assessed using neurological deficit scores, morphological examination was performed following haematoxylin-eosin staining of cortical tissues, and apoptotic indices were calculated after terminal deoxyribonucleotidyl transferase (TdT)-mediated biotin-16-dUTP nick-end labelling. Cortical protein and mRNA expression of p-ERK and ERK were measured by immunohistochemistry and real-time quantitative PCR, respectively.

RESULTS

Compared with the I/R group, neurological deficit scores and apoptotic indices were lower in the I/R+EA group at 1 and 3 days, whereas mRNA/protein expression of ERK/p-ERK was higher in the EA group at all time points studied.

CONCLUSION

Our results suggest that EA can alleviate neurological deficits and reduce cortical apoptosis in rats with I/R injury. These anti-apoptotic effects may be due to upregulation of p-ERK. Moreover, apoptosis appeared to peak at 1 day after I/R injury, which might therefore represent the optimal time point for targeting of EA.

Disinhibition of the extracellular-signal-regulated kinase restores the amplification of circadian rhythms by lithium in cells from bipolar disorder patients

Bipolar disorder (BD) is characterized by depression, mania, and circadian rhythm abnormalities. Lithium, a treatment for BD stabilizes mood and increases circadian rhythm amplitude. However, in fibroblasts grown from BD patients, lithium has weak effects on rhythm amplitude compared to healthy controls. To understand the mechanism by which lithium differentially affects rhythm amplitude in BD cells, we investigated the extracellular-signal-regulated kinase (ERK) and related signaling molecules linked to BD and circadian rhythms. In fibroblasts from BD patients, controls and mice, we assessed the contribution of the ERK pathway to lithium-induced circadian rhythm amplification. Protein analyses revealed low phospho-ERK1/2 (p-ERK) content in fibroblasts from BD patients vs.

CONTROLS

Pharmacological inhibition of ERK1/2 by PD98059 attenuated the rhythm amplification effect of lithium, while inhibition of two related kinases, c-Jun N-terminal kinase (JNK), and P38 did not. Knockdown of the transcription factors CREB and EGR-1, downstream effectors of ERK1/2, reduced baseline rhythm amplitude, but did not alter rhythm amplification by lithium. In contrast, ELK-1 knockdown amplified rhythms, an effect that was not increased further by the addition of lithium, suggesting this transcription factor may regulate the effect of lithium on amplitude. Augmentation of ERK1/2 signaling through DUSP6 knockdown sensitized NIH3T3 cells to rhythm amplification by lithium. In BD fibroblasts, DUSP6 knockdown reversed the BD rhythm phenotype, restoring the ability of lithium to increase amplitude in these cells. We conclude that the inability of lithium to regulate circadian rhythms in BD may reflect reduced ERK activity, and signaling through ELK-1.

Expression of p21-activated kinases 1 and 3 is altered in the brain of subjects with depression

The p21-activated kinases (PAKs) of group I are the main effectors for the small Rho GTPases, critically involved in neurodevelopment, plasticity and maturation of the nervous system. Moreover, the neuronal complexity controlled by PAK1/PAK3 signaling determines the postnatal brain size and synaptic properties. Stress induces alterations at the level of structural and functional synaptic plasticity accompanied by reductions in size and activity of the hippocampus and the prefrontal cortex (PFC). These abnormalities are likely to contribute to the pathology of depression and, in part, reflect impaired cytoskeleton remodeling pointing to the role of Rho GTPase signaling. Thus, the present study assessed the expression of the group I PAKs and their activators in the brain of depressed subjects. Using quantitative polymerase chain reaction (qPCR), mRNA levels and coexpression of the group I PAKs: PAK1, PAK2, and PAK3 as well as of their activators: RAC1, CDC42 and ARHGEF7 were examined in postmortem samples from the PFC (n=25) and the hippocampus (n=23) of subjects with depression and compared to control subjects (PFC n=24; hippocampus n=21). Results demonstrated that mRNA levels of PAK1 and PAK3, are significantly reduced in the brain of depressed subjects, with PAK1 being reduced in the PFC and PAK3 in the hippocampus. No differences were observed for the ubiquitously expressed PAK2. Following analysis of gene coexpression demonstrated disruption of coordinated gene expression in the brain of subjects with depression. Abnormalities in mRNA expression of PAK1 and PAK3 as well as their altered coexpression patterns were detected in the brain of subjects with depression.

Clinical and genetic factors associated with suicide in mood disorder patients

Suicidality is a continuum ranging from ideation to attempted and completed suicide, with a complex etiology involving both genetic heritability and environmental factors. The majority of suicide events occur in the context of psychiatric conditions, preeminently major depression and bipolar disorder. The present study investigates clinical factors associated with suicide in a sample of 553 mood disorder patients, recruited within the 'Psy Pluriel' center, Centre Européen de Psychologie Médicale, and the Department of Psychiatry of Erasme Hospital (Brussels). Furthermore, genetic association analyses examining polymorphisms within COMT, BDNF, MAPK1 and CREB1 genes were performed in a subsample of 259 bipolar patients. The presence or absence of a previous suicide attempt and of current suicide risk were assessed. A positive association with suicide attempt was reported for younger patients, females, lower educated, smokers, those with higher scores on depressive symptoms and higher functional disability and those with anxiety comorbidity and familial history of suicidality in first- and second-degree relatives. Anxiety disorder comorbidity was the stronger predictor of current suicide risk. No associations were found with polymorphisms within COMT and BDNF genes, whereas significant associations were found with variations in rs13515 (MAPK1) and rs6740584 (CREB1) polymorphisms. From a clinical perspective, our study proposes several clinical characteristics, such as increased depressive symptomatology, anxiety comorbidity, functional disability and family history of suicidality, as correlates associated with suicide. Genetic risk variants in MAPK1 and CREB1 genes might be involved in a dysregulation of inflammatory and neuroplasticity pathways and are worthy of future investigation.

Chronic Fluoxetine Treatment Upregulates the Activity of the ERK1/2-NF-κB Signaling Pathway in the Hippocampus and Prefrontal Cortex of Rats Exposed to Forced-Swimming Stress

OBJECTIVES

The aim of this study was to explore whether or not the antidepressant actions of fluoxetine (FLX) are correlated with extracellular signal-regulated kinase 1 and 2 (ERK1/2) and nuclear factor κ-light chain enhancer of activated B cells (NF-κB) in the hippocampus (HC) and prefrontal cortex (PFC) of rats.

MATERIALS AND METHODS

A total of 108 male Sprague-Dawley rats were randomly divided into 6 groups of 18 rats each. Group 1 was the control group, while group 2 comprised the depressed model in which rats were subjected to 28 days of forced-swimming stress (FST); groups 3-6 were also subjected to 28 days of FST and treated with FLX once a day for 1 day (group 3; F1d), 1 week (group 4; F1w), 2 weeks (group 5; F2w), or 4 weeks (group 6; F4w). The control group was not subjected to FST or treated with FLX. Behavior tests that included the Morris water maze (MWM) and saccharin preference were performed, and ERK1/2 and NF-κB proteins were assayed using Western blot.

RESULTS

The rats in the control group and in groups 5 and 6 (F2w and F4w, respectively) had a significantly shorter average escape latency, needed more attempts in order to successfully cross the platform, and had a greater saccharin preference than those in the depressed group (p < 0.05). In the depressed group, the phosphorylated ERK1/2 (p-ERK1/2) and phosphorylated NF-κB (p-NF-κB) expression in the HC and PFC were lower than in the control group (p < 0.05). Treatment with FLX reversed the changes in the expression of p-ERK1/2 and p-NF-κB in rats in the F2w and F4w groups.

CONCLUSIONS

In this study, FLX treatment for 2 weeks or longer reversed the impaired spatial learning, memory, and anhedonia observed in the depressed model rats and upregulated the activities of the ERK1/2-NF-κB signaling pathway.

[Biological basis of suicidal behavior]

Based on current clinical and classification concepts of suicidality, the biological parameters characteristic of suicidal behavior, completed and uncompleted suicides reported in the last few decades are discussed. The results obtained in the studies of neurotransmitter and other brain systems, immune system, lipid and other types of metabolism as well as data of neuroimaging brain studies and post-mortem investigation of brain structures are presented.

Altered ERK1/2 Signaling in the Brain of Learned Helpless Rats: Relevance in Vulnerability to Developing Stress-Induced Depression

Extracellular signal-regulated kinase 1/2- (ERK1/2-) mediated cellular signaling plays a major role in synaptic and structural plasticity. Although ERK1/2 signaling has been shown to be involved in stress and depression, whether vulnerability to develop depression is associated with abnormalities in ERK1/2 signaling is not clearly known. The present study examined ERK1/2 signaling in frontal cortex and hippocampus of rats that showed vulnerability (learned helplessness, (LH)) or resiliency (non-learned helplessness, (non-LH)) to developing stress-induced depression. In frontal cortex and hippocampus of LH rats, we found that mRNA and protein expressions of ERK1 and ERK2 were significantly reduced, which was associated with their reduced activation and phosphorylation in cytosolic and nuclear fractions, where ERK1 and ERK2 target their substrates. In addition, ERK1/2-mediated catalytic activities and phosphorylation of downstream substrates RSK1 (cytosolic and nuclear) and MSK1 (nuclear) were also lower in the frontal cortex and hippocampus of LH rats without any change in their mRNA or protein expression. None of these changes were evident in non-LH rats. Our study indicates that ERK1/2 signaling is differentially regulated in LH and non-LH rats and suggests that abnormalities in ERK1/2 signaling may be crucial in the vulnerability to developing depression.

Chronic corticosterone-mediated dysregulation of microRNA network in prefrontal cortex of rats: relevance to depression pathophysiology

Stress plays a major role in inducing depression, which may arise from interplay between complex cascades of molecular and cellular events that influence gene expression leading to altered connectivity and neural plasticity. In recent years, microRNAs (miRNAs) have carved their own niche owing to their innate ability to induce disease phenotype by regulating expression of a large number of genes in a cohesive and coordinated manner. In this study, we examined whether miRNAs and associated gene networks have a role in chronic corticosterone (CORT; 50 mg  kg(-1) × 21 days)-mediated depression in rats. Rats given chronic CORT showed key behavioral features that resembled depression phenotype. Expression analysis revealed differential regulation of 26 miRNAs (19 upregulated, 7 downregulated) in prefrontal cortex of CORT-treated rats. Interaction between altered miRNAs and target genes showed dense interconnected molecular network, in which multiple genes were predicated to be targeted by the same miRNA. A majority of altered miRNAs showed binding sites for glucocorticoid receptor element, suggesting that there may be a common regulatory mechanism of miRNA regulation by CORT. Functional clustering of predicated target genes yielded disorders such as developmental, inflammatory and psychological that could be relevant to depression. Prediction analysis of the two most prominently affected miRNAs miR-124 and miR-218 resulted into target genes that have been shown to be associated with depression and stress-related disorders. Altogether, our study suggests miRNA-mediated novel mechanism by which chronic CORT may be involved in depression pathophysiology.