Evidence revealing deregulation of the KLF11-MAO A pathway in association with chronic stress and depressive disorders

Type A monoamine oxidase; its unique role in mood, behavior and neurodegeneration

Monoamine oxidase catalyzes oxidative deamination of monoamine transmitters and plays a critical role in the pathogenesis of neuropsychiatric diseases. Monoamine oxidase is classified into type A and B (MAO-A, MAO-B) according to the substrate specificity and sensitivity to inhibitors. The isoenzymes are different proteins coded by different genes localized on the X-chromosome, but they have identical intron-exon organization, similar protein structure and enzymatic mechanism and are considered to be derived from the same ancestral gene. The isoform-specific transcription organization regulates expression and function of MAO-A in response to cellular signaling pathways and environmental factors. MAO-A shows distinct properties and functions: isoform-specified polymorphisms, localization in catecholamine neurons, expression during early embryonic stage, regulation of brain architecture development and mediation of death and survival of neuronal cells. MAO-A is more flexible to genetic and environmental changes than MAO-B. Defective MAO-A expression impairs embryonic brain development and causes adult abnormal mood and behavior, as shown by human male cases with MAO-A deletion. This paper presents the regulation of brain MAO-A expression epigenetically by interaction between genetic and environmental factors. Association of aberrant MAO-A expression and activity with aggression, asocial behaviors, depressive disorders, and neurodegenerative diseases is discussed. Novel therapeutic strategy for psychiatric diseases by intervention to the regulation of MAO-A expression and activity is proposed.

A bioinformatics approach to identifying the biomarkers and pathogenesis of major depressive disorder combined with acute myocardial infarction

This study investigated the pathogenesis of major depressive disorder (MDD) and acute myocardial infarction (AMI) using bioinformatics. We analyzed MDD and AMI (MDD-AMI) datasets provided by the Gene Expression Omnibus (GEO) database for genes common to MDD and AMI using GEO2R and weighted gene co-expression network analysis (WGCNA). We also performed Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses, and we used Disease Ontology (DO) analysis to identify a) the pathways through which genes function and b) comorbidities. We also created a protein-protein interaction (PPI) network using the STRING database to identify the hub genes and biomarkers. NetworkAnalyst 3.0 was used to construct a transcription factor (TF) gene regulatory network. We also identified relevant complications and potential drug candidates. The 27 genes common to MDD and AMI were enriched in the pathways regulating TFs and mediating immunity and inflammation. The hub genes in the PPI network included TLR2, HP, ICAM1, LCN2, LTF, VCAN, S100A9 and NFKBIA. Key TFs were KLF9, KLF11, ZNF24, and ZNF580. Cardiovascular, pancreatic, and skeletal diseases were common complications. Hydrocortisone, simvastatin, and estradiol were candidate treatment drugs. Identification of these genes and their pathways may provide new targets for further research on the pathogenesis, biomarkers, and treatment of MDD-AMI. Together our results suggested that TLR2 and VCAN might be the key genes associated with MDD complicated by AMI.

Central and cardiac stress resiliences consistently linked to integrated immuno-neuroendocrine responses across stress models in male mice

Stress resilience, and behavioural and cardiovascular impacts of chronic stress, are theorised to involve integrated neuro-endocrine/inflammatory/transmitter/trophin signalling. We tested for this integration, and whether behaviour/emotionality, together with myocardial ischaemic tolerance, are consistently linked to these pathways across diverse conditions in male C57Bl/6 mice. This included: Restraint Stress (RS), 1 hr restraint/day for 14 days; Chronic Unpredictable Mild Stress (CUMS), 7 stressors randomised over 21 days; Social Stress (SS), 35 days social isolation with brief social encounters in final 13 days; and Control conditions (CTRL; un-stressed mice). Behaviour was assessed via open field (OFT) and sucrose preference (SPT) tests, and neurobiology from frontal cortex (FC) and hippocampal transcripts. Endocrine factors, and function and ischaemic tolerance in isolated hearts, were also measured. Model characteristics ranged from no behavioural or myocardial changes with homotypic RS, to increased emotionality and cardiac ischaemic injury (with apparently distinct endocrine/neurobiological profiles) in CUMS and SS models. Highly integrated expression of HPA axis, neuro-inflammatory, BDNF, monoamine, GABA, cannabinoid and opioid signalling genes was confirmed across conditions, and consistent/potentially causal correlations identified for: i) Locomotor activity (noradrenaline, ghrelin; FC Crhr1, Tnfrsf1b, Il33, Nfkb1, Maoa, Gabra1; hippocampal Il33); ii) Thigmotaxis (adrenaline, leptin); iii) Anxiety-like behaviour (adrenaline, leptin; FC Tnfrsf1a; hippocampal Il33); iv) Depressive-like behaviour (ghrelin; FC/hippocampal s100a8); and v) Cardiac stress-resistance (noradrenaline, leptin; FC Il33, Tnfrsf1b, Htr1a, Gabra1, Gabrg2; hippocampal Il33, Tnfrsf1a, Maoa, Drd2). Data support highly integrated pathway responses to stress, and consistent adipokine, sympatho-adrenergic, inflammatory and monoamine involvement in mood and myocardial disturbances across diverse conditions.

Is there a relationship between morphological and functional platelet changes and depressive disorder?

BACKGROUND

Blood platelets, due to shared biochemical and functional properties with presynaptic serotonergic neurons, constituted, over the years, an attractive peripheral biomarker of neuronal activity. Therefore, the literature strongly focused on the investigation of eventual structural and functional platelet abnormalities in neuropsychiatric disorders, particularly in depressive disorder. Given their impact in biological psychiatry, the goal of the present paper was to review and critically analyze studies exploring platelet activity, functionality, and morpho-structure in subjects with depressive disorder.

METHODS

According to the PRISMA guidelines, we performed a systematic review through the PubMed database up to March 2020 with the search terms: (1) platelets in depression [Title/Abstract]"; (2) "(platelets[Title]) AND depressive disorder[Title/Abstract]"; (3) "(Platelet[Title]) AND major depressive disorder[Title]"; (4) (platelets[Title]) AND depressed[Title]"; (5) (platelets[Title]) AND depressive episode[Title]"; (6) (platelets[Title]) AND major depression[Title]"; (7) platelet activation in depression[All fields]"; and (8) platelet reactivity in depression[All fields]."

RESULTS

After a detailed screening analysis and the application of specific selection criteria, we included in our review a total of 106 for qualitative synthesis. The studies were classified into various subparagraphs according to platelet characteristics analyzed: serotonergic system (5-HT2A receptors, SERT activity, and 5-HT content), adrenergic system, MAO activity, biomarkers of activation, responsivity, morphological changes, and other molecular pathways.

CONCLUSIONS

Despite the large amount of the literature examined, nonunivocal and, occasionally, conflicting results emerged. However, the findings on structural and metabolic alterations, modifications in the expression of specific proteins, changes in the aggregability, or in the responsivity to different pro-activating stimuli, may be suggestive of potential platelet dysfunctions in depressed subjects, which would result in a kind of hyperreactive state. This condition could potentially lead to an increased cardiovascular risk. In line with this hypothesis, we speculated that antidepressant treatments would seem to reduce this hyperreactivity while representing a potential tool for reducing cardiovascular risk in depressed patients and, maybe, in other neuropsychiatric conditions. However, the problem of the specificity of platelet biomarkers is still at issue and would deserve to be deepened in future studies.

Development and Clinical Application of Positron Emission Tomography Imaging Agents for Monoamine Oxidase B

Monoamine oxidase B (MAO-B) is a high-density protein in the brain mainly found on outer mitochondrial membranes, primarily in astroglia, but additionally in serotonergic neurons and in the substantia nigra in the midbrain. It is an enzyme that participates in the oxidative metabolism of important monoamines including dopamine, norepinephrine, benzylamine, and phenylethylamine. Elevated MAO-B density may be associated with astrogliosis and inhibiting MAO-B may reduce astrogliosis. MAO-B density is elevated in postmortem sampling of pathology for many neuropsychiatric diseases including Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis, and alcohol use disorder. Initial development of positron emission tomography (PET) imaging agents focused on analogs of [¹¹C]L-deprenyl, with the most commonly applied being the deuterium substituted [¹¹C]L-deprenyl-D2. This latter radiotracer was modeled with an irreversible trapping compartment reflecting its irreversible binding to MAO-B. Subsequently, [¹¹C]SL25.1188, a reversible binding MAO-B radioligand with outstanding properties including high specific binding and excellent reversibility was developed. [¹¹C]SL25.1188 PET was applied to discover a substantive elevation of MAO-B binding in the prefrontal cortex in major depressive disorder (MDD) with an effect size of more than 1.5. Longer duration of MDD was associated with greater MAO-B binding throughout most gray matter regions in the brain, suggesting progressive astrogliosis. Important applications of [¹¹C]L-deprenyl-D2 PET are detecting a 40% loss in radiotracer accumulation in cigarette smokers, and substantial occupancy of novel therapeutics like EVT301 and sembragiline. Given the number of diseases with elevations of MAO-B density and astrogliosis, and the advance of [¹¹C]SL25.1188, clinical applications of MAO-B imaging are still at an early stage.

Transcription Factor Motifs Associated with Anterior Insula Gene Expression Underlying Mood Disorder Phenotypes

Mood disorders represent a major cause of morbidity and mortality worldwide but the brain-related molecular pathophysiology in mood disorders remains largely undefined. Because the anterior insula is reduced in volume in patients with mood disorders, RNA was extracted from the anterior insula postmortem anterior insula of mood disorder samples and compared with unaffected controls for RNA-sequencing identification of differentially expressed genes (DEGs) in (a) bipolar disorder (BD; n = 37) versus (vs.) controls (n = 33), and (b) major depressive disorder (MDD n = 30) vs. controls, and (c) low vs. high axis I comorbidity (a measure of cumulative psychiatric disease burden). Given the regulatory role of transcription factors (TFs) in gene expression via specific-DNA-binding domains (motifs), we used JASPAR TF binding database to identify TF-motifs. We found that DEGs in BD vs. controls, MDD vs. controls, and high vs. low axis I comorbidity were associated with TF-motifs that are known to regulate expression of toll-like receptor genes, cellular homeostatic-control genes, and genes involved in embryonic, cellular/organ, and brain development. Robust imaging-guided transcriptomics by using meta-analytic imaging results to guide independent postmortem dissection for RNA-sequencing was applied by targeting the gray matter volume reduction in the anterior insula in mood disorders, to guide independent postmortem identification of TF motifs regulating DEG. Our findings of TF-motifs that regulate the expression of immune, cellular homeostatic-control, and developmental genes provide novel information about the hierarchical relationship between gene regulatory networks, the TFs that control them, and proximate underlying neuroanatomical phenotypes in mood disorders.

The role of monoamine oxidase enzymes in the pathophysiology of neurological disorders

Monoamine oxidase enzymes are responsible for the degredation of serotonin, dopamine, and norepinephrine in the central neurvous system. Although it has been nearly 100 years since they were first described, we are still learning about their role in the healthy brain and how they are altered in various disease states. The present review provides a survey of our current understanding of monoamine oxidases, with a focus on their contributions to neuropsychiatric, neurodevelopmental, and neurodegenerative disease. Important species differences in monoamine oxidase function and development in the brain are highlighted. Sex-specific monoamine oxidase regulatory mechanisms and their implications for various neurological disorders are also discussed. While our understanding of these critical enzymes has expanded over the last century, gaps exist in our understanding of sex and species differences and the roles monoamine oxidases may play in conditions often comorbid with neurological disorders.

Mechanisms of repetitive transcranial magnetic stimulation for anti-depression: Evidence from preclinical studies

This review summarizes the anti-depressant mechanisms of repetitive transcranial magnetic stimulation in preclinical studies, including anti-inflammatory effects mediated by activation of nuclear factor-E2-related factor 2 signaling pathway, anti-oxidative stress effects, enhancement of synaptic plasticity and neurogenesis via activation of the endocannabinoid system and brain derived neurotrophic factor signaling pathway, increasing the content of monoamine neurotransmitters via inhibition of Sirtuin 1/monoamine oxidase A signaling pathway, and reducing the activity of the hypothalamic-pituitary-adrenocortical axis. We also discuss the shortcomings of transcranial magnetic stimulation in preclinical studies such as inaccurate positioning, shallow depth of stimulation, and difficulty in elucidating the neural circuit mechanism up- and down-stream of the stimulation target brain region.

Regulation of Social Stress and Neural Degeneration by Activity-Regulated Genes and Epigenetic Mechanisms in Dopaminergic Neurons

Transcriptional and epigenetic regulation of both dopaminergic neurons and their accompanying glial cells is of great interest in the search for therapies for neurodegenerative disorders such as Parkinson’s disease (PD). In this review, we collate transcriptional and epigenetic changes identified in adult Drosophila melanogaster dopaminergic neurons in response to either prolonged social deprivation or social enrichment, and compare them with changes identified in mammalian dopaminergic neurons during normal development, stress, injury, and neurodegeneration. Surprisingly, a small set of activity-regulated genes (ARG) encoding transcription factors, and a specific pattern of epigenetic marks on gene promoters, are conserved in dopaminergic neurons over the long evolutionary period between mammals and insects. In addition to their classical function as immediate early genes to mark acute neuronal activity, these ARG transcription factors are repurposed in both insects and mammals to respond to chronic perturbations such as social enrichment, social stress, nerve injury, and neurodegeneration. We suggest that these ARG transcription factors and epigenetic marks may represent important targets for future therapeutic intervention strategies in various neurodegenerative disorders including PD.

DNA hypomethylation of the Krüppel-like factor 11 (KLF11) gene promoter: a putative biomarker of depression comorbidity in panic disorder and of non-anxious depression?

Panic disorder (PD) is one of the most common anxiety disorders and often occurs comorbidly with major depressive disorder (MDD). Altered methylation of the monoamine oxidase A (MAOA) gene has been implicated in the etiology of both PD and MDD. The Krüppel-like factor 11 (KLF11; alias TIEG2), an activating transcription factor of the MAOA gene, has been found to be increased in MDD, but has not yet been investigated in PD. In an effort to further delineate the effects of the KLF11–MAOA pathway in anxiety and affective disorders, KLF11 promoter methylation was analyzed via pyrosequencing of sodium bisulfite-treated DNA isolated from human peripheral blood in two independent samples of PD patients with or without comorbid MDD in a case–control design (sample 1: N = 120) as well as MDD patients with and without anxious depression (sample 2: N = 170). Additionally, in sample 1, KLF11 methylation was correlated with Beck Depression Inventory (BDI-II) scores. No overall association of KLF11 promoter methylation with PD was detected. However, PD patients with comorbid MDD showed significant hypomethylation relative to both healthy controls (p = 0.010) and PD patients without comorbid MDD (p = 0.008). Furthermore, KLF11 methylation was negatively correlated with BDI-II scores in PD patients (p = 0.013). MDD patients without anxious features showed nominally decreased KLF11 methylation in comparison to MDD patients with anxious depression (p = 0.052). The present results suggest KLF11 promoter hypomethylation as a potential epigenetic marker of MDD comorbidity in PD or of non-anxious depression, respectively, possibly constituting a differential pathomechanism in anxiety and mood disorders.

A Systematic Analysis Revealed the Potential Gene Regulatory Processes of ATRA-Triggered Neuroblastoma Differentiation and Identified a Novel RA Response Sequence in the NTRK2 Gene

Retinoic acid- (RA-) triggered neuroblastoma cell lines are widely used cell modules of neuronal differentiation in neurodegenerative disease studies, but the gene regulatory mechanism underlying differentiation is unclear now. In this study, system biological analysis was performed on public microarray data from three neuroblastoma cell lines (SK-N-SH, SH-SY5Y-A, and SH-SY5Y-E) to explore the potential molecular processes of all-trans retinoic acid- (ATRA-) triggered differentiation. RT-qPCR, functional genomics analysis, western blotting, chromatin immunoprecipitation (ChIP), and homologous sequence analysis were further performed to validate the gene regulation processes and identify the RA response element in a specific gene. The potential disturbed biological pathways (111 functional GO terms in 14 interactive functional groups) and gene regulatory network (10 regulators and 71 regulated genes) in neuroblastoma differentiation were obtained. 15 of the 71 regulated genes are neuronal projection-related. Among them, NTRK2 is the only one that was dramatically upregulated in the RT-qPCR test that we performed on ATRA-treated SH-SY5Y-A cells. We further found that the overexpression of the NTRK2 gene can trigger differentiation-like changes in SH-SY5Y-A cells. Functional genomic analysis and western blotting assay suggested that, in neuroblastoma cells, ATRA may directly regulate the NTRK2 gene by activating the RA receptor (RAR) that binds in its promoter region. A novel RA response DNA element in the NTRK2 gene was then identified by bioinformatics analysis and chromatin immunoprecipitation (ChIP) assay. The novel element is sequence conservation and position variation among different species. Our study systematically provided the potential regulatory information of ATRA-triggered neuroblastoma differentiation, and in the NTRK2 gene, we identified a novel RA response DNA element, which may contribute to the differentiation in a human-specific manner.

Role of glucocorticoid- and monoamine-metabolizing enzymes in stress-related psychopathological processes

Glucocorticoid signaling is fundamental in healthy stress coping and in the pathophysiology of stress-related diseases, such as post-traumatic stress disorder (PTSD). Glucocorticoids are metabolized by cytochrome P450 (CYP) as well as 11-β-hydroxysteroid dehydrogenase type 1 (11βHSD1) and 2 (11βHSD2). Acute stress-induced increase in glucocorticoid concentrations stimulates the expression of several CYP sub-types. CYP is primarily responsible for glucocorticoid metabolism and its increased activity can result in decreased circulating glucocorticoids in response to repeated stress stimuli. In addition, repeated stress-induced glucocorticoid release can promote 11βHSD1 activation and 11βHSD2 inhibition, and the 11βHSD2 suppression can lead to apparent mineralocorticoid excess. The activation of CYP and 11βHSD1 and the suppression of 11βHSD2 may at least partly contribute to development of the blunted glucocorticoid response to stressors characteristic in high trait anxiety, PTSD, and other stress-related disorders. Glucocorticoids and glucocorticoid-metabolizing enzymes interact closely with other biomolecules such as inflammatory cytokines, monoamines, and some monoamine-metabolizing enzymes, namely the monoamine oxidase type A (MAO-A) and B (MAO-B). Glucocorticoids boost MAO activity and this decreases monoamine levels and induces oxidative tissue damage which then activates inflammatory cytokines. The inflammatory cytokines suppress CYP expression and activity. This dynamic cross-talk between glucocorticoids, monoamines, and their metabolizing enzymes could be a critical factor in the pathophysiology of stress-related disorders.Lay summaryGlucocorticoids, which are produced and released under the control by brain regulatory centers, are fundamental in the stress response. This review emphasizes the importance of glucocorticoid metabolism and particularly the interaction between the brain and the liver as the major metabolic organ in the body. The activity of enzymes involved in glucocorticoid metabolism is proposed to play not only an important role in positive, healthy glucocorticoid effects, but also to contribute to the development and course of stress-related diseases.

Targeting Kruppel-like Factor 9 in Excitatory Neurons Protects against Chronic Stress-Induced Impairments in Dendritic Spines and Fear Responses

Stress exposure is associated with the pathogenesis of psychiatric disorders, including post-traumatic stress disorder (PTSD) and major depressive disorder (MDD). Here, we show in rodents that chronic stress exposure rapidly and transiently elevates hippocampal expression of Kruppel-like factor 9 (Klf9). Inducible genetic silencing of Klf9 expression in excitatory forebrain neurons in adulthood prior to, but not after, onset of stressor prevented chronic restraint stress (CRS)-induced potentiation of contextual fear acquisition in female mice and chronic corticosterone (CORT) exposure-induced fear generalization in male mice. Klf9 silencing prevented chronic CORT and CRS induced enlargement of dendritic spines in the ventral hippocampus of male and female mice, respectively. KLF9 mRNA density was increased in the anterior dentate gyrus of women, but not men, with more severe recent stressful life events and increased mortality. Thus, Klf9 functions as a stress-responsive transcription factor that mediates circuit and behavioral resilience in a sex-specific manner.

Contribution of serotonergic and nitrergic pathways, as well as monoamine oxidase-a and Na+, K+-ATPase enzymes in antidepressant-like action of ((4-tert-butylcyclohexylidene) methyl) (4-methoxystyryl) sulfide (BMMS)

The present study investigated a possible antidepressant-like effect of ((4-tert-butylcyclohexylidene)methyl) (4-methoxystyryl) sulfide (BMMS) by using the forced swimming test (FST) and the tail suspension test (TST) in Swiss mice. The contribution of serotoninergic, glutamatergic and nitrergic systems in the antidepressant-like activity of BMMS was evaluated. We also examined the involvement of monoamine oxidase (MAO)-A, MAO-B and Na⁺, K⁺-ATPase activities in prefrontal cortex of mice. BMMS, (0.1-10 mg/kg, intragastrically (i.g.)) and fluoxetine (32 mg/kg, i.g.) decreased the immobility time in the FST and TST. The anti-immobility effect of BMMS (10 mg/kg, i.g.) in the TST was prevented by the pretreatment of mice with WAY100635 (0.1 mg/kg, subcutaneously (s.c.), a 5-HT_1A receptor antagonist), ketanserin (5 mg/kg, intraperitoneal (i.p.), a 5-HT_2A/2C receptor antagonist), and partially blocked by ondansetron (1 mg/kg, i.p., a 5-HT₃ receptor antagonist). The anti-immobility effect of BMMS (10 mg / kg, i.g.) was not avoided by pretreatment with MK-801 (0.01 mg/kg, s.c. a non-competitive N-methyl D-Aspartate (NMDA) receptor) in the TST. Pretreatment with L-arginine (500 mg/kg, i.p., a nitric oxide precursor) reversed partially the reduction in the immobility time elicited by BMMS (10 mg/kg, i.g.) in TST. BMMS altered Na⁺,K⁺-ATPase and MAO-A activities in prefrontal cortex of mice, but was not able to change the MAO-B activity. In conclusion, BMMS exerted an antidepressant-like effect in mice and serotonergic and nitrergic systems are involved in the antidepressant-like action of compound. BMMS modulated MAO-A and Na⁺, K⁺- ATPase activities in prefrontal cortex of mice.

Monoamine Oxidase B Total Distribution Volume in the Prefrontal Cortex of Major Depressive Disorder: An [11C]SL25.1188 Positron Emission Tomography Study

IMPORTANCE

Monoamine oxidase B (MAO-B) is an important, high-density enzyme in the brain that generates oxidative stress by hydrogen peroxide production, alters mitochondrial function, and metabolizes nonserotonergic monoamines. Recent advances in positron emission tomography radioligand development for MAO-B in humans enable highly quantitative measurement of MAO-B distribution volume (MAO-B VT), an index of MAO-B density. To date, this is the first investigation of MAO-B in the brain of major depressive disorder that evaluates regions beyond the raphe and amygdala.

OBJECTIVE

To investigate whether MAO-B VT is elevated in the prefrontal cortex in major depressive episodes (MDEs) of major depressive disorder.

DESIGN, SETTING, AND PARTICIPANTS

This case-control study was performed at a tertiary care psychiatric hospital from April 1, 2014, to August 30, 2018. Twenty patients with MDEs without current psychiatric comorbidities and 20 age-matched controls underwent carbon 11-labeled [11C]SL25.1188 positron emission tomography scanning to measure MAO-B VT. All participants were drug and medication free, nonsmoking, and otherwise healthy.

MAIN OUTCOMES AND MEASURES

The MAO-B VT in the prefrontal cortex (PFC). The second main outcome was to evaluate the association between MAO-B VT in the PFC and duration of major depressive disorder illness.

RESULTS

Twenty patients with MDEs (mean [SD] age, 34.2 [13.2] years; 11 women) and 20 healthy controls (mean [SD] age, 33.7 [13.1] years; 10 women) were recruited. Patients with MDEs had significantly greater MAO-B VT in the PFC (mean, 26%; analysis of variance, F1,38 = 19.6, P < .001). In individuals with MDEs, duration of illness covaried positively with MAO-B VT in the PFC (analysis of covariance, F1,18 = 15.2, P = .001), as well as most other cortex regions and the thalamus.

CONCLUSIONS AND RELEVANCE

Fifty percent (10 of 20) of patients with MDEs had MAO-B VT values in the PFC exceeding those of healthy controls. Greater MAO-B VT is an index of MAO-B overexpression, which may contribute to pathologies of mitochondrial dysfunction, elevated synthesis of neurotoxic products, and increased metabolism of nonserotonergic monoamines. Hence, this study identifies a common pathological marker associated with downstream consequences poorly targeted by the common selective serotonin reuptake inhibitor treatments. It is also recommended that the highly selective MAO-B inhibitor medications that are compatible for use with other antidepressants and have low risk for hypertensive crisis should be developed or repurposed as adjunctive treatment for MDEs.

Social Defeat Stress Decreases mRNA for Monoamine Oxidase A and Increases 5-HT Turnover in the Brain of Male Nile Tilapia (Oreochromis niloticus)

Stress induces various neurobiological responses and causes psychiatric disorders, including depression. Monoamine oxidase A (MAO-A) plays an important role in various functions of the brain, such as regulation of mood, anxiety and aggression, and dysregulation of MAO-A is observed in stress-related psychiatric disorders. This study addressed the question whether acute social stress induces changes to transcriptional and/or post-transcriptional regulation of MAO-A expression in the brain. Using male Nile tilapia (Oreochromis niloticus), we investigated whether acute social stress, induced by the presence of a dominant male fish, changes the expression of MAO-A. We measured gene expression of MAO-A by quantitative PCR, enzymatic activity of MAO-A by the luminescent method, and 5-HT and 5-HIAA levels by liquid chromatography–mass spectrometry in the brain of socially stressed and control fish. Socially stressed males showed decreased MAO-A mRNA levels, consistent MAO-A enzymatic activity, increased 5-HT turnover in the brain, and elevated plasma cortisol levels, compared to controls. Our results suggest that acute social stress suppresses the transcription of MAO-A gene, enhances 5-HT metabolism but does not affect the production of MAO-A protein.

ERβ agonist alters RNA splicing factor expression and has a longer window of antidepressant effectiveness than estradiol after long-term ovariectomy

BACKGROUND

Estrogen therapy (ET), an effective treatment for perimenopausal depression, often fails to ameliorate symptoms when initiated late after the onset of menopause. Our previous work has suggested that alternative splicing of RNA might mediate these differential effects of ET.

METHODS

Female Sprague–Dawley rats were treated with estradiol (E2) or vehicle 6 days (early ET) or 180 days (late ET) after ovariectomy (OVX). We investigated the differential expression of RNA splicing factors and tryptophan hydroxylase 2 (TPH2) protein using a customized RT2 Profiler PCR Array, reverse-transcription polymerase chain reaction, immunoprecipitation and behaviour changes in clinically relevant early and late ET.

RESULTS

Early ET, but not late ET, prolonged swimming time in the forced swim test and reduced anxiety-like behaviours in the elevated plus maze. It reversed OVX-increased (SFRS7 and SFRS16) or OVX-decreased (ZRSR2 and CTNNB1) mRNA levels of splicing factors and ERβ splicing changes in the brains of OVX rats. Early ET, but not late ET, also increased the expression of TPH2 and decreased monoamine oxidase A levels in the dorsal raphe in the brains of OVX rats. In late ET, only diarylpropionitrile (an ERβ-specific agonist) achieved similar results — not E2 (an ERα and ERβ agonist) or propylpyrazoletriol (an ERα-specific agonist).

LIMITATIONS

Our experimental paradigm mimicked early and late ET in the clinical setting, but the contribution of age and OVX might be difficult to distinguish.

CONCLUSION

These findings suggest that ERβ alternative splicing and altered responses in the regulatory system for serotonin may mediate the antidepressant efficacy of ET associated with the timing of therapy initiation. It is likely that ERβ-specific ligands would be effective estrogen-based antidepressants late after the onset of menopause.

Computational Studies Applied to Flavonoids against Alzheimer's and Parkinson's Diseases

Neurodegenerative diseases, such as Parkinson's and Alzheimer's, are understood as occurring through genetic, cellular, and multifactor pathophysiological mechanisms. Several natural products such as flavonoids have been reported in the literature for having the capacity to cross the blood-brain barrier and slow the progression of such diseases. The present article reports on in silico enzymatic target studies and natural products as inhibitors for the treatment of Parkinson's and Alzheimer's diseases. In this study we evaluated 39 flavonoids using prediction of molecular properties and in silico docking studies, while comparing against 7 standard reference compounds: 4 for Parkinson's and 3 for Alzheimer's. Osiris analysis revealed that most of the flavonoids presented no toxicity and good absorption parameters. The Parkinson's docking results using selected flavonoids as compared to the standards with four proteins revealed similar binding energies, indicating that the compounds 8-prenylnaringenin, europinidin, epicatechin gallate, homoeriodictyol, capensinidin, and rosinidin are potential leads with the necessary pharmacological and structural properties to be drug candidates. The Alzheimer's docking results suggested that seven of the 39 flavonoids studied, being those with the best molecular docking results, presenting no toxicity risks, and having good absorption rates (8-prenylnaringenin, europinidin, epicatechin gallate, homoeriodictyol, aspalathin, butin, and norartocarpetin) for the targets analyzed, are the flavonoids which possess the most adequate pharmacological profiles.

Targeted Ubiquitin-Proteasomal Proteolysis Pathway in Chronic Social Defeat Stress

Stressful events promote psychopathogenic changes that might contribute to the development of mental illnesses. Some individuals tend to recover from the stress response, while some do not. However, the molecular mechanisms of stress resilience during stress are not well-characterized. Here, we identify proteomic changes in the hippocampus using proteomic technique to examine mice following chronic social defeat stress. We showed that small ubiquitin-like modifier (SUMO)-1 expression was significantly decreased in susceptible mice following chronic social defeat stress. We also examined a protein inhibitor of activated signal transducer of transcription (PIAS)1 levels, an E3 SUMO-protein ligase protein inhibitor of activated STAT1, which is known to interact with SUMO-1. PIAS1 was shown to be profoundly decreased and monoamine oxidase (MAO)-A increased in the hippocampus of susceptible mice following chronic social defeat stress. Furthermore, the manipulated PIAS1 expression in the hippocampus also has an influence on glucocorticoid receptor (GR) translocation. We also found that knockdown of PIAS1 expression in the hippocampus then subject to submaximal stress increased GR to glucocorticoid response element (GRE)-binding site on the MAO-A promoter. The present study raises the possibility of different levels of PIAS1 between individuals in response to chronic social defeat stress and that such differences may contribute to the susceptibility to stress.

Potential Roles of microRNAs in the Regulation of Monoamine Oxidase A in the Brain

Monoamine oxidase A (MAO-A) is an enzyme that regulates the levels of monoamine neurotransmitters, such as serotonin, noradrenaline and dopamine and it has been used as a therapeutic target for depression. However, MAO-A inhibitors, which directly acts on MAO-A protein, have limited use due to their adverse effects. microRNAs (miRNAs) are 18-22 nucleotide long, small non-coding RNAs, which have recently emerged as regulators of protein levels that could potentially be new therapeutic targets for psychiatric disorders. This review article aims to discuss the current status of the treatment for depression with MAO-A inhibitors and the regulatory factors of MAO-A. Further, the review also proposes possible regulatory mechanisms of MAO-A by miRNAs, which leads to better understanding of the pathology of depressive disorders and their potential use as therapeutic agents.

Novel Phenotypes Detectable with PET in Mood Disorders: Elevated Monoamine Oxidase A and Translocator Protein Level

As a result of high prevalence and high rates of treatment resistance, major depressive disorder has become the leading cause of death and disability in moderate-income to high-income nations. Poor targeting of phenotypes is a plausible reason for treatment resistance and PET imaging offers a unique role to identify phenotypes. Both increased monoamine oxidase A binding and greater translocator protein 18 kDa binding occur throughout the gray matter during major depressive episodes, including affect-modulating brain regions such as the prefrontal and anterior cingulate cortex, and are detectable with advanced radioligand technology for both of these targets.

Regulatory Pathways of Monoamine Oxidase A during Social Stress

Social stress has a high impact on many biological systems in the brain, including serotonergic (5-HT) system-a major drug target in the current treatment for depression. Hyperactivity of hypothalamic-pituitary-adrenal (HPA) axis and monoamine oxidase A (MAO-A) are well-known stress responses, which are involved in the central 5-HT system. Although, many MAO-A inhibitors have been developed and used in the therapeutics of depression, effective management of depression by modulating the activity of MAO-A has not been achieved. Identifying the molecular pathways that regulate the activity of MAO-A in the brain is crucial for developing new drug targets for precise control of MAO-A activity. Over the last few decades, several regulatory pathways of MAO-A consisting of Kruppel like factor 11 (KLF11), Sirtuin1, Ring finger protein in neural stem cells (RINES), and Cell division cycle associated 7-like protein (R1) have been identified, and the influence of social stress on these regulatory factors evaluated. This review explores various aspects of these pathways to expand our understanding of the roles of the HPA axis and MAO-A regulatory pathways during social stress. The first part of this review introduces some components of the HPA axis, explains how stress affects them and how they interact with the 5-HT system in the brain. The second part summarizes the novel regulatory pathways of MAO-A, which have high potential as novel therapeutic targets for depression.

Brain monoamine oxidase B and A in human parkinsonian dopamine deficiency disorders

See Jellinger (doi:10.1093/awx190) for a scientific commentary on this article. The enzyme monoamine oxidases (B and A subtypes, encoded by MAOB and MAOA, respectively) are drug targets in the treatment of Parkinson's disease. Inhibitors of MAOB are used clinically in Parkinson's disease for symptomatic purposes whereas the potential disease-modifying effect of monoamine oxidase inhibitors is debated. As astroglial cells express high levels of MAOB, the enzyme has been proposed as a brain imaging marker of astrogliosis, a cellular process possibly involved in Parkinson's disease pathogenesis as elevation of MAOB in astrocytes might be harmful. Since brain monoamine oxidase status in Parkinson's disease is uncertain, our objective was to measure, by quantitative immunoblotting in autopsied brain homogenates, protein levels of both monoamine oxidases in three different degenerative parkinsonian disorders: Parkinson's disease (n = 11), multiple system atrophy (n = 11), and progressive supranuclear palsy (n = 16) and in matched controls (n = 16). We hypothesized that if MAOB is 'substantially' localized to astroglial cells, MAOB levels should be generally associated with standard astroglial protein measures (e.g. glial fibrillary acidic protein). MAOB levels were increased in degenerating putamen (+83%) and substantia nigra (+10%, non-significant) in multiple system atrophy; in caudate (+26%), putamen (+27%), frontal cortex (+31%) and substantia nigra (+23%) of progressive supranuclear palsy; and in frontal cortex (+33%), but not in substantia nigra of Parkinson's disease, a region we previously reported no increase in astrocyte protein markers. Although the magnitude of MAOB increase was less than those of standard astrocytic markers, significant positive correlations were observed amongst the astrocyte proteins and MAOB. Despite suggestions that MAOA (versus MAOB) is primarily responsible for metabolism of dopamine in dopamine neurons, there was no loss of the enzyme in the parkinsonian substantia nigra; instead, increased nigral levels of a MAOA fragment and 'turnover' of the enzyme were observed in the conditions. Our findings provide support that MAOB might serve as a biochemical imaging marker, albeit not entirely specific, for astrocyte activation in human brain. The observation that MAOB protein concentration is generally increased in degenerating brain areas in multiple system atrophy (especially putamen) and in progressive supranuclear palsy, but not in the nigra in Parkinson's disease, also distinguishes astrocyte behaviour in Parkinson's disease from that in the two 'Parkinson-plus' conditions. The question remains whether suppression of either MAOB in astrocytes or MAOA in dopamine neurons might influence progression of the parkinsonian disorders.

Subchronic glucocorticoids, glutathione depletion and a postpartum model elevate monoamine oxidase a activity in the prefrontal cortex of rats

Recent human brain imaging studies implicate dysregulation of monoamine oxidase-A (MAO-A), in particular in the prefrontal cortex (PFC) and anterior cingulate cortex (ACC), in the development of major depressive disorder (MDD). This study investigates the influence of four alterations underlying important pathologies of MDD, namely, chronic elevation of glucocorticoid levels, glutathione depletion, changes in female gonadal sex hormones and serotonin concentration fluctuation, on MAO-A and MAO-B activities in rats. Young adult rats exposed chronically to the synthetic glucocorticoid dexamethasone at 0, 0.05, 0.5, and 2.0mg/kg/day (osmotic minipumps) for eight days showed significant dose-dependent increases in activities of MAO-A in PFC (+17%, p<0.001) and ACC (+9%, p<0.01) and MAO-B in PFC (+14%, p<0.001) and increased serotonin turnover in the PFC (+31%, p<0.01), not accounted for by dexamethasone-induced changes in serotonin levels, since neither serotonin depletion nor supplementation affected MAO-A activity. Sub-acute depletion of the major antioxidant glutathione by diethyl maleate (5mmol/kg, i.p.) for three days, which resulted in a 36% loss of glutathione in PFC (p=0.0005), modestly, but significantly, elevated activities of MAO-A in PFC and MAO-B in PFC, ACC and hippocampus (+6-9%, p<0.05). Changes in estrogen and progesterone representing pseudopregnancy were associated with significantly elevated MAO-A activity in the ACC day 4-7 postpartum (10-18%, p<0.05 to p<0.0001) but not the PFC or hippocampus. Hence, our study provides data in support of strategies targeting glucocorticoid and glutathione systems, as well as changes in female sex hormones for normalization of MAO-A activities and thus treatment of mood disorders.

Chronic Social Stress and Ethanol Increase Expression of KLF11, a Cell Death Mediator, in Rat Brain

Major depressive disorder and alcoholism are significant health burdens that can affect executive functioning, cognitive ability, job responsibilities, and personal relationships. Studies in animal models related to depression or alcoholism reveal that the expression of Krüppel-like factor 11 (KLF11, also called TIEG2) is elevated in frontal cortex, which suggests that KLF11 may play a role in stress- or ethanol-induced psychiatric conditions. KLF11 is a transcriptional activator of monoamine oxidase A and B, but also serves other functions in cell cycle regulation and apoptotic cell death. In the present study, immunohistochemistry was used to quantify intensity of nuclear KLF11, combined with an unbiased stereological approach to assess nuclei in fronto-limbic, limbic, and other brain regions of rats exposed chronically to social defeat or ethanol. KLF11 immunoreactivity was increased significantly in the medial prefrontal cortex, frontal cortex, and hippocampus of both stressed rats and rats fed ethanol. However, expression of KLF11 protein was not significantly affected in the thalamus, hypothalamus, or amygdala in either treatment group compared to respective control rats. Triple-label immunofluorescence revealed that KLF11 protein was localized in nuclei of neurons and astrocytes. KLF11 was also co-localized with the immunoreactivity of cleaved caspase-3. In addition, Western blot analysis revealed a significant reduction in anti-apoptotic protein, Bcl-xL, but an increase of caspase-3 expression in the frontal cortex of ethanol-treated rats compared to ethanol-preferring controls. Thus, KLF11 protein is up-regulated following chronic exposure to stress or ethanol in a region-specific manner and may contribute to pro-apoptotic signaling in ethanol-treated rats. Further investigation into the KLF11 signaling cascade as a mechanism for neurotoxicity and cell death in depression and alcoholism may provide novel pharmacological targets to lessen brain damage and maximize neuroprotection in these disorders.