A polymorphism in the microRNA-30e precursor associated with major depressive disorder risk and P300 waveform

MicroRNA signatures in neuroplasticity, neuroinflammation and neurotransmission in association with depression

Depression is a multifactorial disorder that occurs mainly on account of the dysregulation of neuroplasticity, neurotransmission and neuroinflammation in the brain. In addition to environmental /lifestyle factors, the pathogenesis of disease has been associated with genetic and epigenetic factors that affect the reprogramming of normal brain function. MicroRNA (miRNAs), a type of non-coding RNAs, are emerging as significant players that play a vital role in the regulation of gene expression and have been extensively explored in neurodegenerative disorders. Recent studies have also shown the role of gut microbiota that forms a complex bidirectional network with gut brain axis, impacting neuroinflammation in case of Parkinson's disease and depression. Translating targeted miRNA-based therapies for the treatment of neurological disorders including depression, into clinical practice remains challenging due to the ineffective delivery of the therapeutic molecules and off-target effects of the specific miRNAs. This review provides significant insights into how miRNAs are emerging as vital players in the development of depression, especially the ones involved in three important processes including neuroplasticity, neurotransmission and neuroinflammation. In this review, the current status of miRNAs as biomarkers for therapeutic interventions in the case of depression has been discussed along with an overview of future perspectives, like use of nanotechnology and gene editing, keeping in view other multifactorial disorders where such interventions by mimics and inhibitors have already reached clinical trials. The challenges for targeting the specific miRNAs for therapeutic outcomes have also been highlighted.

Role of miRNA Gene Variants (miR-22 and miR-155) as the Factors Affecting Susceptibility to Panic Disorder

Objective

Variants within genes encoding microRNAs (miRNAs) may alter the expression of both miRNAs and their target genes, thus contributing to the etiology of psychiatric disorders. The involvement of miRNAs in neuronal differentiation and synaptic plasticity supported this hypothesis. We aimed to investigate the links between miR-155 rs767649/miR-22 rs8076112 and the risk of panic disorder (PD) in a sample of Turkish population.

Methods

In this experimental study, 134 PD patients and 140 healthy controls were recruited. Genotyping was carried out using Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) method. To evaluate PD phenotypes, Panic Disorder Severity Scale (PDSS) was also administered to patients to clarify possible associations between the scale and risk variants analyzed.

Results

The genotype analysis of miR-155 rs767649 did not show an association with PD risk and it was not related to the disease severity. For miR-22 rs8076112 variant, a statistically significant association was determined; CC genotypes were lower in patients compared to controls. Logistic regression analysis proved the highly protective effect (80.4%) of CC genotype against PD (p = 0.041; OR = 0.196, 95% CI = 0.041-0.934). Though its significance in disease liability, miR-22 rs8076112 was not associated with the disease severity.

Conclusion

Our findings firstly report the combined analysis of miR-155 rs767649 and miR-22 rs8076112 in PD in terms of both disease susceptibility and severity. These findings await replication in independent cohorts with enrichment of other miRNA gene variants. Thus, certain miRNAs and their target genes involved in the etiology and phenotypes of PD could be enlightened.

Influence of antipsychotic drugs on microRNA expression in schizophrenia patients - A systematic review

Schizophrenia (SCZ) is a severe psychiatric disorder with unclear pathophysiology. Moreover, there is no specific biological marker to help clinicians to define a diagnosis, and medication is decided according to the psychiatrist's experience. In this scenario, microRNAs (miRNAs), which are small noncoding RNA molecules that regulate several genes, emerge as potential peripheral biomarkers to help not only the evaluation of the disease state but also the treatment response. Here, we systematically reviewed indexed literature and evaluated follow-up studies investigating the changes in miRNA expression due to antipsychotic treatment. We also assessed target genes and performed pathway enrichment analysis of miRNAs listed in this systematic review. A total of 11 studies were selected according to research criteria, and we observed that 28 miRNAs play a relevant role in schizophrenia pathogenesis or response to antipsychotic treatment, seven of those of extreme interest as possible biomarkers either for condition or treatment. Predicted targets of the miRNAs reviewed here were previously associated with schizophrenia in genome-wide studies, and pathway analysis showed enrichment for genes related to neural processes. With this review, we expect to highlight the importance of miRNAs in schizophrenia pathogenesis and its treatment and point out interesting miRNAs to future studies.

Epigenetic regulation in major depression and other stress-related disorders: molecular mechanisms, clinical relevance and therapeutic potential

Major depressive disorder (MDD) is a chronic, generally episodic and debilitating disease that affects an estimated 300 million people worldwide, but its pathogenesis is poorly understood. The heritability estimate of MDD is 30-40%, suggesting that genetics alone do not account for most of the risk of major depression. Another factor known to associate with MDD involves environmental stressors such as childhood adversity and recent life stress. Recent studies have emerged to show that the biological impact of environmental factors in MDD and other stress-related disorders is mediated by a variety of epigenetic modifications. These epigenetic modification alterations contribute to abnormal neuroendocrine responses, neuroplasticity impairment, neurotransmission and neuroglia dysfunction, which are involved in the pathophysiology of MDD. Furthermore, epigenetic marks have been associated with the diagnosis and treatment of MDD. The evaluation of epigenetic modifications holds promise for further understanding of the heterogeneous etiology and complex phenotypes of MDD, and may identify new therapeutic targets. Here, we review preclinical and clinical epigenetic findings, including DNA methylation, histone modification, noncoding RNA, RNA modification, and chromatin remodeling factor in MDD. In addition, we elaborate on the contribution of these epigenetic mechanisms to the pathological trait variability in depression and discuss how such mechanisms can be exploited for therapeutic purposes.

Bipolar‐associated miR ‐499‐5p controls neuroplasticity by downregulating the Cav1.2 subunit CACNB2

Bipolar disorder (BD) is a chronic mood disorder characterized by manic and depressive episodes. Dysregulation of neuroplasticity and calcium homeostasis are frequently observed in BD patients, but the underlying molecular mechanisms are largely unknown. Here, we show that miR‐499‐5p regulates dendritogenesis and cognitive function by downregulating the BD risk gene CACNB2. miR‐499‐5p expression is increased in peripheral blood of BD patients, as well as in the hippocampus of rats which underwent juvenile social isolation. In rat hippocampal neurons, miR‐499‐5p impairs dendritogenesis and reduces surface expression and activity of the L‐type calcium channel Cav1.2. We further identified CACNB2, which encodes a regulatory β‐subunit of Cav1.2, as a direct functional target of miR‐499‐5p in neurons. miR‐499‐5p overexpression in the hippocampus in vivo induces short‐term memory impairments selectively in rats haploinsufficient for the Cav1.2 pore forming subunit Cacna1c. In humans, miR‐499‐5p expression is negatively associated with gray matter volumes of the left superior temporal gyrus, a region implicated in auditory and emotional processing. We propose that stress‐induced miR‐499‐5p overexpression contributes to dendritic impairments, deregulated calcium homeostasis, and neurocognitive dysfunction in BD.

MicroRNAs as novel peripheral markers for suicidality in patients with major depressive disorder

OBJECTIVE

Major depressive disorder (MDD) constitutes a main risk factor for suicide. Suicide risk in psychiatric patients is primarily determined by often unreliable, self-reported information. We assessed serum levels of three microRNAs (miRNAs), previously demonstrated to be dysregulated in post-mortem brain samples of suicide victims, as potential peripheral biomarkers for suicidality.

METHODS

All study participants were diagnosed with MDD according to Diagnostic and Statistical Manual of Mental Disorders, 5th edition criteria. Suicidality, defined as acute suicide risk or suicide attempt within one week prior to study entry, was assessed by clinical interview. Relative serum levels of miR-30a, miR-30e, and miR-200a, normalized to U6, were measured by quantitative real-time PCR in MDD inpatients with (MDD/SI, N = 19) and without (MDD, N = 31) acute suicide risk. Median age and gender distribution were comparable in both groups.

RESULTS

Levels of miR-30a, miR-30e, and miR-200a were significantly elevated in MDD/SI compared to MDD. Subgroup analysis of the MDD/SI group showed that levels of miR-30e and miR-200a were significantly higher and miR-30a was increased by trend in patients admitted following a suicide attempt (N = 7) compared to patients with acute suicide risk but without recent suicide attempt (N = 12). Additionally, use of two databases for in silico transcription factor-miRNA interaction prediction indicated early growth response protein (EGR) 1 as potential transcriptional regulator for all three miRNAs.

CONCLUSION

This study demonstrates suicide risk in MDD patients to be associated with increased levels of miR-30a, miR-30e, and miR-200a. Thus, these miRNAs might constitute potential biomarkers to predict suicidal behavior in MDD patients.

MicroRNAs as Critical Biomarkers of Major Depressive Disorder: A Comprehensive Perspective

Major Depressive Disorder (MDD) represents a major global health concern, a body-mind malady of rising prevalence worldwide nowadays. The complex network of mechanisms involved in MDD pathophysiology is subjected to epigenetic changes modulated by microRNAs (miRNAs). Serum free or vesicles loaded miRNAs have starred numerous publications, denoting a key role in cell-cell communication, systematically and in brain structure and neuronal morphogenesis, activity and plasticity. Upregulated or downregulated expression of these signaling molecules may imply the impairment of genes implicated in pathways of MDD etiopathogenesis (neuroinflammation, brain-derived neurotrophic factor (BDNF), neurotransmitters, hypothalamic-pituitary-adrenal (HPA) axis, oxidative stress, circadian rhythms...). In addition, these miRNAs could serve as potential biomarkers with diagnostic, prognostic and predictive value, allowing to classify severity of the disease or to make decisions in clinical management. They have been considered as promising therapy targets as well and may interfere with available antidepressant treatments. As epigenetic malleable regulators, we also conclude emphasizing lifestyle interventions with physical activity, mindfulness and diet, opening the door to new clinical management considerations.

Non-coding RNAs in depression: Promising diagnostic and therapeutic biomarkers

Non-coding RNAs (ncRNAs), including microRNAs, circular RNAs, and long non-coding RNAs, are important regulators of normal biological processes and their abnormal expression may be involved in the pathogenesis of human diseases including depression. Multiple studies have demonstrated a significantly increased or reduced ncRNAs expression in depressed patients compared with healthy subjects and that antidepressant therapy can alter the aberrant expression of ncRNAs in depressed patients. Although the existing evidence is important, it is also mixed and a comprehensive review to guide an effective clinical translation is lacking. Focused on human research, this review summarizes clinical findings of ncRNAs in depression, including those in brain tissues and peripheral samples. We outlined the characteristics and functions of ncRNAs and highlighted their performance in the diagnosis and treatment of depression. Although their precise roles in depression remain uncertain, ncRNAs have shown potential value as biomarkers for diagnosis and therapy in depressed patients.

MiRNA-199a-5p targets WNT2 to regulate depression through the CREB/BDNF signaling in hippocampal neuron

INTRODUCTION

This study mainly investigated the role of miR-199a-5p in depression.

METHODS

qRT-PCR and western blotting were employed to detect the expressions of miR-199a-5p, CREB and BDNF. Sucrose preference test, forced swimming test, and tail suspension test were performed to evaluate depression-related symptoms. MTT assays and flow cytometry were used to examine the cell reproduction and apoptotic cells of hippocampal neuron.

RESULTS

The data demonstrated that the expression levels of miR-199a-5p in the cerebrospinal fluids and serums of depression patient and the hippocampus of chronic unpredictable mild stress (CUMS) mouse were significantly increased. However, the expressions of WNT2, p-CREB, and BDNF were inhibited. In addition, miR-199a-5p-inhibitor enhanced sucrose preferences of CUMS mouse and decreased immobile time in sucrose preference test and forced swimming test. Knockdown of WNT2 attenuated the effects of miR-199a-5p-inhibitor on cell reproduction and apoptotic cells of hippocampal neuron and the expression of WNT2, p-CREB, and BDNF.

CONCLUSION

MiR-199a-5p can target WNT2 to enhance the development of depression through regulation of the CREB/BDNF signaling.

TRIAL REGISTRATION

JNU-Hos-49284.

Epigenetics and depression

The risk for major depression is both genetically and environmentally determined. It has been proposed that epigenetic mechanisms could mediate the lasting increases in depression risk following exposure to adverse life events and provide a mechanistic framework within which genetic and environmental factors can be integrated. Epigenetics refers to processes affecting gene expression and translation that do not involve changes in the DNA sequence and include DNA methylation (DNAm) and microRNAs (miRNAs) as well as histone modifications. Here we review evidence for a role of epigenetics in the pathogenesis of depression from studies investigating DNAm, miRNAs, and histone modifications using different tissues and various experimental designs. From these studies, a model emerges where underlying genetic and environmental risk factors, and interactions between the two, could drive aberrant epigenetic mechanisms targeting stress response pathways, neuronal plasticity, and other behaviorally relevant pathways that have been implicated in major depression.
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Association Between hsa-miR-30e Polymorphisms and Sporadic Primary Hyperparathyroidism Risk

BACKGROUND/AIM

Almost 15% of patients with sporadic primary hyperparathyroidism (sPHPT) present with multiple gland disease (MGD). The aim of this study was to investigate the potential role of two polymorphisms of the hsa-miR-30e, in sPHPT tumorigenesis.

PATIENTS AND METHODS

One-hundred twenty sPHPT patients, 77 presenting a single adenoma and 43 with MGD, and 54 healthy controls were genotyped. The SNPs were identified using the allele-specific PCR methodology, while the hsa-miR-30e expression was analyzed by real-time quantitative reverse transcriptase PCR.

RESULTS

Hsa-miR-30e expression was found to be significantly higher in patients with MGD compared to patients with single adenomas (p=0.0019), but no differences were found regarding specific genotype carriers. The genotype frequencies for ss178077483 and rs7556088 were significantly different between patients and healthy controls.

CONCLUSION

Although the polymorphisms cannot be used as biomarkers for the differential diagnosis of MGD, hsa-miR-30e expression could potentially serve as a biomarker for this purpose.

Individual differences in inflammatory and oxidative mechanisms of stress-related mood disorders

Emotional stress leads to the development of peripheral disorders and is recognized as a modifiable risk factor for psychiatric disorders, particularly depression and anxiety. However, not all individuals develop the negative consequences of emotional stress due to different stress coping strategies and resilience to stressful stimuli. In this review, we discuss individual differences in coping styles and the potential mechanisms that contribute to individual vulnerability to stress, such as parameters of the immune system and oxidative state. Initial differences in inflammatory and oxidative processes determine resistance to stress and stress-related disorders via the alteration of neurotransmitter content in the brain and biological fluids. Differences in coping styles may serve as possible predictors of resistance to stress and stress-related disorders, even before stressful conditions. The investigation of natural variabilities in stress resilience may allow the development of new methods for preventive medicine and the personalized treatment of stress-related conditions.

Attenuated palmitoylation of serotonin receptor 5-HT1A affects receptor function and contributes to depression-like behaviors

The serotonergic system and in particular serotonin 1A receptor (5-HT1AR) are implicated in major depressive disorder (MDD). Here we demonstrated that 5-HT1AR is palmitoylated in human and rodent brains, and identified ZDHHC21 as a major palmitoyl acyltransferase, whose depletion reduced palmitoylation and consequently signaling functions of 5-HT1AR. Two rodent models for depression-like behavior show reduced brain ZDHHC21 expression and attenuated 5-HT1AR palmitoylation. Moreover, selective knock-down of ZDHHC21 in the murine forebrain induced depression-like behavior. We also identified the microRNA miR-30e as a negative regulator of Zdhhc21 expression. Through analysis of the post-mortem brain samples in individuals with MDD that died by suicide we find that miR-30e expression is increased, while ZDHHC21 expression, as well as palmitoylation of 5-HT1AR, are reduced within the prefrontal cortex. Our study suggests that downregulation of 5-HT1AR palmitoylation is a mechanism involved in depression, making the restoration of 5-HT1AR palmitoylation a promising clinical strategy for the treatment of MDD.

Palmitoylation is a post translational modification that regulates GPCR activity. Here the authors show that palmitoylation of 5-HT1AR by the palmitoyltransferase enzyme ZDHHC21 contributes to depression-like behaviour in rodents and might be implicated in major depressive disorder.

miR-30 Family miRNAs Mediate the Effect of Chronic Social Defeat Stress on Hippocampal Neurogenesis in Mouse Depression Model

Depression is a debilitating psychiatric disorder with a high rate of relapse and a low rate of response to antidepressant treatment. There is a dearth of new antidepressants due to an incomplete understanding of the molecular mechanisms involved in its etiopathology. Chronic stress appears to be one of the foremost underlying causes of depression. Studies in animal models in the past decade have implicated epigenetic mechanisms in mediating the negative effects of chronic stressful events on the progression/manifestation of depression and other co-morbid neuropsychiatric disorders. However, non-coding RNAs, another layer of epigenetic regulation is relatively less studied in depression. Here, using the chronic social defeat stress (CSDS)-induced depression model, we hypothesized dysregulation in miRNA-mRNA networks in the neurogenic dentate gyrus (DG) region of male C57BL/6 mice. Among several dysregulated miRNAs identified via miRNA arrays, the most striking finding was the downregulation of miRNAs of the miR-30 family in stressed/defeated mice. To investigate miRNAs in the DG-resident neural stem/progenitor cells (NSCs/NPCs), we used the in vitro neurosphere culture, where proliferating NSCs/NPCs were subjected to differentiation. Among several differentially expressed miRNAs, we observed an upregulation of miR-30 family miRNAs upon differentiation. To search for the gene targets of these miRNAs, we performed gene arrays followed by bioinformatics analysis, miRNA manipulations and luciferase assays. Our results suggest that miR-30 family miRNAs mediate chronic stress-induced depression-like phenotype by altering hippocampal neurogenesis and neuroplasticity via controlling the epigenetic and transcription regulators such as Mll3 and Runx1; and cell signaling regulators like Socs3, Ppp3r1, Gpr125, and Nrp1.

Altered microRNA 5692b and microRNA let-7d expression levels in children and adolescents with attention deficit hyperactivity disorder

Attention-deficit/hyperactivity disorder (ADHD) is a prevalent neurodevelopmental disorder. Its etiology is not clearly understood yet, but neurobiological, genetic and environmental factors are shown to play a role. The relationship between ADHD and miRNAs has been studied quite recently, and few studies have been conducted up to now. In this study, peripheral blood expression levels of miR-5692b, miR-let-7d, miR-124-3p, miR-4447 and miR-107 of 30 children and adolescents with combined type ADHD were compared to 30 healthy controls to understand the roles of these miRNAs in the ADHD etiopathogenesis. Compared to controls, levels of miR-5692b (p = 0.006) were found higher and levels of miR-let-7d (p = 0.017) were found lower in the ADHD group. There was no significant difference in terms of miR-124-3p, miR-4447, and miR-107 levels between the groups. In conclusion, our findings support other studies suggesting the importance of miRNAs in the pathogenesis of ADHD. Regarding the regulatory role of miRNAs in gene regulation, their contribution to etiopathogenesis and heterogeneity of ADHD should be investigated further.

Protein Translation and Psychiatric Disorders

Although historically research has focused on transcription as the central governor of protein expression, protein translation is now increasingly being recognized as a major factor for determining protein levels within cells. The central nervous system relies on efficient updating of the protein landscape. Thus, coordinated regulation of mRNA localization, initiation, or termination of translation is essential for proper brain function. In particular, dendritic protein synthesis plays a key role in synaptic plasticity underlying learning and memory as well as cognitive processes. Increasing evidence suggests that impaired mRNA translation is a common feature found in numerous psychiatric disorders. In this review, we describe how malfunction of translation contributes to development of psychiatric diseases, including schizophrenia, major depression, bipolar disorder, and addiction.

MiR-221 is involved in depression by regulating Wnt2/CREB/BDNF axis in hippocampal neurons

OBJECTIVE

The aim of this study was to investigate the mechanism of miR-221 in depression.

METHODS

The molecules expressions were measured by qRT-PCR and western blot. The sucrose preference test (SPT), forced swimming test (FST) and tail suspension test (TST) were used to detect depressive-like symptoms. MTT assay and flow cytometric was used to measure the proliferation and apoptosis of hippocampal neuronal.

RESULTS

MiR-221 expression in the cerebrospinal fluid and serum of major depressive disorder patients and the hippocampus of chronic unpredictable mild stress (CUMS) mice were increased, while the expression of Wnt2, p-CREB and BDNF were decreased. Additionally, silence of miR-221 increased sucrose preference of CUMS mice and shortened the immobility time of CUMS mice in SPT and FST. MiR-221 could targeted regulate Wnt2, and knockdown of Wnt2 reversed the effect of miR-221 inhibitor on the proliferation and apoptosis of hippocampal neurons and countered the promoting effect of miR-221 inhibitor on the expression of Wnt2, p-CREB and BDNF.

CONCLUSION

MiR-221 could promote the development of depression by regulating Wnt2/CREB/BDNF axis.

Could a blood test for PTSD and depression be on the horizon?

INTRODUCTION

Depression and posttraumatic stress disorder (PTSD) are two complex and debilitating psychiatric disorders that result in poor life and destructive behaviors against self and others. Currently, diagnosis is based on subjective rather than objective determinations leading to misdiagnose and ineffective treatments. Advances in novel neurobiological methods have allowed assessment of promising biomarkers to diagnose depression and PTSD, which offers a new means of appropriately treating patients. Areas covered: Biomarkers discovery in blood represents a fundamental tool to predict, diagnose, and monitor treatment efficacy in depression and PTSD. The potential role of altered HPA axis, epigenetics, NPY, BDNF, neurosteroid biosynthesis, the endocannabinoid system, and their function as biomarkers for mood disorders is discussed. Insofar, we propose the identification of a biomarker axis to univocally identify and discriminate disorders with large comorbidity and symptoms overlap, so as to provide a base of support for development of targeted treatments. We also weigh in on the feasibility of a future blood test for early diagnosis. Expert commentary: Potential biomarkers have already been assessed in patients' blood and need to be further validated through multisite large clinical trial stratification. Another challenge is to assess the relation among several interdependent biomarkers to form an axis that identifies a specific disorder and secures the best-individualized treatment. The future of blood-based tests for PTSD and depression is not only on the horizon but, possibly, already around the corner.

Cis-acting single nucleotide polymorphisms alter MicroRNA-mediated regulation of human brain-expressed transcripts

Substantial variability exists in the presentation of complex neurological disorders, and the study of single nucleotide polymorphisms (SNPs) has shed light on disease mechanisms and pathophysiological variability in some cases. However, the vast majority of disease-linked SNPs have unidentified pathophysiological relevance. Here, we tested the hypothesis that SNPs within the miRNA recognition element (MRE; the region of the target transcript to which the miRNA binds) can impart changes in the expression of those genes, either by enhancing or reducing transcript and protein levels. To test this, we cross-referenced 7,153 miRNA-MRE brain interactions with the SNP database (dbSNP) to identify candidates, and functionally assessed 24 SNPs located in the 3’UTR or the coding sequence (CDS) of targets. For over half of the candidates tested, SNPs either enhanced (4 genes) or disrupted (10 genes) miRNA binding and target regulation. Additionally, SNPs causing a shift from a common to rare codon within the CDS facilitated miRNA binding downstream of the SNP, dramatically repressing target gene expression. The biological activity of the SNPs on miRNA regulation was also confirmed in induced pluripotent stem cell (iPSC) lines. These studies strongly support the notion that SNPs in the 3’UTR or the coding sequence of disease-relevant genes may be important in disease pathogenesis and should be reconsidered as candidate modifiers.

Aberrant resting state in microRNA-30e rat model of cognitive impairment

Increasing evidence suggests that microRNA (miRNA)-30e is implicated in the cognitive symptoms of many neuropsychiatric diseases. Our previous studies showed that miRNA-30e is associated with cognitive impairment in schizophrenia and depression. Neuroimaging studies have suggested that cognitive impairment is best characterized as abnormal local activity or a disconnection syndrome. Therefore, we constructed a cognitively impaired overexpressing miRNA-30e rat model for study using functional MRI (fMRI). The model was developed by transfected lentiviral particles carrying the miRNA-30e into the hippocampal dentate gyrus. The Morris water maze and open-field test were used to evaluate cognitive ability. We used the regional homogeneity approach to analyze resting-state fMRI data to explore the changes in regional synchronization. We then used Granger causality analysis to explore connectivity between the hippocampus, striatum, and thalamus. The model group showed higher regional homogeneity in the right hippocampus and striatum. One-way Granger causality connections were observed from the thalamus to the hippocampus in the model group, whereas connections from the thalamus to the striatum were observed in normal rats. After fluoxetine treatment, we found indirect connections between the thalamus and the striatum; we also found connections from the hippocampus to the striatum after Shuganjieyu capsule treatment. Our results support the hypothesis that cognitive impairment is related to disrupted local functionality or aberrant brain connectivity, with antidepressant drugs partially reversing cognitive impairment. The characteristics of resting-state fMRI in miRNA-30e overexpressing rats can provide further evidence for investigating the neural mechanisms of cognitive impairment in mental disorders. Video abstract; Supplemental digital content 1, http://links.lww.com/WNR/A385.

Downregulation of microRNA‑124‑3p suppresses the mTOR signaling pathway by targeting DDIT4 in males with major depressive disorder

Recent investigations have suggested that microRNAs (miRNAs or miRs) are involved in several pathways that may contribute to the pathomechanism of major depressive disorder (MDD). Sex may not only act as a demographic factor in clinical practive, but may also play a vital role in the molecular heterogeneity of MDD. Although many molecular changes correlated with MDD are found in males, the molecular mechanisms of MDD remain poorly understood. The present study performed bioinformatics analysis to investigate the pathomechanism of MDD in males. The present study identified miR‑124‑3p as one of the most dysregulated miRNAs in MDD, with decreased expression in the post‑mortem BA44 brain area of male patients with MDD. In addition, miR‑124‑3p targets DNA damage‑inducible transcript 4 (DDIT4) and specificity protein 1 (SP1), a DDIT4 transcription factor, in the validated target module of the miRWalk 2.0 database. This is concurrent with an increase in the expression level of DDIT4, which is an inhibitor of the mammalian target of rapamycin (mTOR) signaling pathway. It was also demonstrated that miR‑124‑3p expression was positively associated with mTOR signaling and this relationship was dependent on the tuberous sclerosis proteins 1/2 complex. Taken together, these results provided a novel insight on miR‑124‑3p involvement in the biological alterations of male patients with MDD and suggested that this miRNA may also serve as a male‑specific target for antidepressant treatment.

microRNA-124 targets glucocorticoid receptor and is involved in depression-like behaviors

Dysregulation of microRNA (miRNA) has been shown to be involved in early observations of depression. MicroRNA-124-3p (miR-124) is the most abundant microRNA in the brain. Previous studies have shown that miR-124 plays a major role in depression. Here we showed that miR-124 directly targeted glucocorticoid receptor (GR) in HEK 293 cells. In addition, inhibition of miR-124 by its antagomir (2nmol/every two days) could reverse the decrease of sucrose preference and the increase of immobility time in mice exposed to chronic corticosterone (CORT, 40mg/kg) injection. Moreover, these effects on behavioral improvement were coupled to the activation of brain-derived neurotrophic factor (BDNF), TrkB, ERK, and CREB, as well as the induction of synaptogenesis and neuronal proliferation. Altogether, our study suggests that miR-124 can be served as a biomarker for depression and a novel target for drug development, and demonstrates that inhibition of miR-124 may be a strategy for treating depression by activating BDNF-TrkB signaling pathway in the hippocampus.

The interaction of miR-34b/c polymorphisms and negative life events increases susceptibility to major depressive disorder in Han Chinese population

BACKGROUND

Previous studies have shown that microRNAs(miRNAs) are involved in the pathogenesis of MDD; in particular, miR-34b/c has been implicated in MDD risk and found to exert antidepressant effects. However, the effects of miR-34b/c polymorphisms on MDD risk have not been investigated.

METHODS

In this study, we evaluated the effect of miR-34b/c gene polymorphisms and their interaction with negative life events in relation to MDD, using data from 381 Han Chinese patients with MDD and 291 healthy volunteers. Allelic, genotypic, haplotypic, and gene-environment associations were analyzed using UNPHASED and SPSS software.

RESULTS

After discarding data with extremely severe negative life events in our study population, we found an association between rs4938723, rs2187473 polymorphisms and MDD in the dominant models (TC/CC vs. TT, OR=1.45, P=0.027; TC/CC vs. TT, OR=3.32, P=0.030). In haplotype analysis, the C-G haplotype (rs4938723/rs28757623) showed the strongest association with MDD (OR=1.95, P=0.026). Additionally, we found significant gene-environment combination rs4938723 C allele, rs28757623 G allele and high level of negative life events (C-G-HN) was significantly associated with MDD (OR, 3.85; 95% CI, 1.62-9.13). In addition, the combination of (C-C-HN) is of significance (OR, 2.99; 95% CI, 1.36-6.60), indicating that the rs28757623 C allele may contribute to the risk of MDD as well.

LIMITATIONS

The sample size was small and the role of miR-34b/c polymorphisms for MDD should be assessed using independent samples from other ethnic populations.

CONCLUSIONS

Our results suggest that miR-34b/c is a susceptibility factor for MDD stratified by negative life events and that rs4938723 is a significant association locus for gene-environment interaction in relation to MDD risk.

Endophenotype best practices

This review examines the current state of electrophysiological endophenotype research and recommends best practices that are based on knowledge gleaned from the last decade of molecular genetic research with complex traits. Endophenotype research is being oversold for its potential to help discover psychopathology relevant genes using the types of small samples feasible for electrophysiological research. This is largely because the genetic architecture of endophenotypes appears to be very much like that of behavioral traits and disorders: they are complex, influenced by many variants (e.g., tens of thousands) within many genes, each contributing a very small effect. Out of over 40 electrophysiological endophenotypes covered by our review, only resting heart, a measure that has received scant advocacy as an endophenotype, emerges as an electrophysiological variable with verified associations with molecular genetic variants. To move the field forward, investigations designed to discover novel variants associated with endophenotypes will need extremely large samples best obtained by forming consortia and sharing data obtained from genome wide arrays. In addition, endophenotype research can benefit from successful molecular genetic studies of psychopathology by examining the degree to which these verified psychopathology-relevant variants are also associated with an endophenotype, and by using knowledge about the functional significance of these variants to generate new endophenotypes. Even without molecular genetic associations, endophenotypes still have value in studying the development of disorders in unaffected individuals at high genetic risk, constructing animal models, and gaining insight into neural mechanisms that are relevant to clinical disorder.

All Roads Lead to the miRNome: miRNAs Have a Central Role in the Molecular Pathophysiology of Psychiatric Disorders

Current treatment strategies for psychiatric disorders remain inadequate. Impeding development of novel therapeutics is our incomplete knowledge of the molecular pathophysiology underlying these disorders. Changes to miRNA function and expression are increasingly being associated with pathological behavioral states. Furthermore, the prospect of using of miRNA expression profiles (the miRNome) as objective psychiatric diagnosis tools is gaining traction. In this review, we focus on recent findings surrounding the link between miRNA function and psychiatric disorders, and outline some of the key challenges that will need to be overcome if the therapeutic potential of these molecular effectors is to be fully realized.

The significance of microRNAs in the course of rDD

BACKGROUND

In recent years, special attention in genetic studies dedicated to the development of various diseases, including mental disorders, has been paid to micro ribonucleic acids (miRNA, microRNA). As an object of our analysis we have selected the miRNAs which - due to the profile of their activity - may be significant in the aetiology and course of recurrent depressive disorders, i.e. miRNA-370, miRNA-411, miRNA-433, miRNA-487b and miRNA-539.

METHODS

The examined population included 138 patients suffering from depression and 95 individuals from the control group (CG). The subjects suffering from depression were divided into two sub-groups: ED-I group (46 patients), rDD group (92 patients).

RESULTS

No significant statistical differences were observed between the ED-I and rDD group for all the variables included in the analysis. No significant interrelation was noticed between the number of depression episodes, the severity of depressive disorders and the expression of miRNA selected. Results of the analysis indicate statistically significant differences between the control subjects and the patients with symptoms of depression in terms of all the variables analysed.

CONCLUSIONS

1. There is no significant difference in miRNAs expression between patients with recurrent depressive disorders and those in the first episode of depression. 2. The differences in terms of expression of the analysed variables between the subjects with symptoms of depression and healthy individuals were confirmed.

MicroRNA 101b Is Downregulated in the Prefrontal Cortex of a Genetic Model of Depression and Targets the Glutamate Transporter SLC1A1 (EAAT3) in Vitro

BACKGROUND

MicroRNAs (miRNAs) are small regulatory molecules that cause translational repression by base pairing with target mRNAs. Cumulative evidence suggests that changes in miRNA expression may in part underlie the pathophysiology and treatment of neuropsychiatric disorders, including major depressive disorder (MDD).

METHODS

A miRNA expression assay that can simultaneously detect 423 rat miRNAs (miRBase v.17) was used to profile the prefrontal cortex (PFC) of a genetic rat model of MDD (the Flinders Sensitive Line [FSL]) and the controls, the Flinders Resistant Line (FRL). Gene expression data from the PFC of FSL/FRL animals (GEO accession no. GSE20388) were used to guide mRNA target selection. Luciferase reporter assays were used to verify miRNA targets in vitro.

RESULTS

We identified 23 miRNAs that were downregulated in the PFC of the FSL model compared with controls. Interestingly, one of the identified miRNAs (miR-101b) is highly conserved between rat and human and was recently found to be downregulated in the PFC of depressed suicide subjects. Using a combination of in silico and in vitro analyses, we found that miR-101b targets the neuronal glutamate transporter SLC1A1 (also known as EAAC1 or EAAT3). Accordingly, both mRNA and protein levels of SLC1A1 were found to be upregulated in the PFC of the FSL model.

CONCLUSIONS

Besides providing a list of novel miRNAs associated with depression-like states, this preclinical study replicated the human association of miR-101 with depression. In addition, since one of the targets of miR-101b appears to be a glutamate transporter, our preclinical data support the hypothesis of a glutamatergic dysregulation being implicated in the etiology of depression.

MicroRNAs and psychiatric disorders: From aetiology to treatment

The emergence of psychiatric disorders relies on the interaction between genetic vulnerability and environmental adversities. Several studies have demonstrated a crucial role for epigenetics (e.g. DNA methylation, post-translational histone modifications and microRNA-mediated post-transcriptional regulation) in the translation of environmental cues into adult behavioural outcome, which can prove to be harmful thus increasing the risk to develop psychopathology. Within this frame, non-coding RNAs, especially microRNAs, came to light as pivotal regulators of many biological processes occurring in the Central Nervous System, both during the neuronal development as well as in the regulation of adult function, including learning, memory and neuronal plasticity. On these basis, in recent years it has been hypothesised a central role for microRNA modulation and expression regulation in many brain disorders, including neurodegenerative disorders and mental illnesses. Indeed, the aim of the present review is to present the most recent state of the art regarding microRNA involvement in psychiatric disorders. We will first describe the mechanisms that regulate microRNA biogenesis and we will report evidences of microRNA dysregulation in peripheral body fluids, in postmortem brain tissues from patients suffering from psychopathology as well as in animal models. Last, we will discuss the potential to consider microRNAs as putative target for pharmacological intervention, using common psychotropic drugs or more specific tools, with the aim to normalize functions that are disrupted in different psychiatric conditions.

Pathogenetic and therapeutic applications of microRNAs in major depressive disorder

As a class of noncoding RNAs, microRNAs (miRNAs) regulate gene expression by inhibiting translation of messenger RNAs. These miRNAs have been shown to play a critical role in higher brain functioning and actively participate in synaptic plasticity. Pre-clinical evidence demonstrates that expression of miRNAs is differentially altered during stress. On the other hand, depressed individuals show marked changes in miRNA expression in brain. MiRNAs are also target of antidepressants and electroconvulsive therapy. Moreover, these miRNAs are present in circulating blood and can be easily detected. Profiling of miRNAs in blood plasma/serum provides evidence that determination of miRNAs in blood can be used as possible diagnostic and therapeutic tool. In this review article, these aspects are critically reviewed and the role of miRNAs in possible etiopathogenesis and therapeutic implications in the context of major depressive disorder is discussed.

Cerebralcare Granule® attenuates cognitive impairment in rats continuously overexpressing microRNA-30e

Previous studies have demonstrated that dysregulation of micro (mi)RNAs is associated with the etiology of various neuropsychiatric disorders, including depression and schizophrenia. Cerebralcare Granule^® (CG) is a Chinese herbal medicine, which has been reported to have an ameliorative effect on brain injury by attenuating blood-brain barrier disruption and improving hippocampal neural function. The present study aimed to evaluate the cognitive behavior of rats continuously overexpressing miRNA-30e (lenti-miRNA-30e), prior to and following the administration of CG. In addition, the mechanisms underlying the ameliorative effects of CG were investigated. The cognitive ability of the rats was assessed using an open-field test and a Morris water maze spatial reference/working memory test. A terminal deoxynucleotidyl transferase dUTP nick end labeling assay was used to detect neuronal apoptosis in the dentate gyrus of the hippocampus. Immunohistochemical analysis and western blotting were conducted to detect the expression levels of B-cell lymphoma 2 (BCL-2) and ubiquitin-conjugating enzyme 9 (UBC9), in order to examine neuronal apoptosis. The lenti-miRNA-30e rats exhibited increased signs of anxiety, depression, hyperactivity and schizophrenia, which resulted in a severe impairment in cognitive ability. Furthermore, in the dentate gyrus of these rats, the expression levels of BCL-2 and UBC9 were reduced and apoptosis was increased. The administration of CG alleviated cognitive impairment, enhanced the expression levels of BCL-2 and UBC9, and reduced apoptosis in the dentate gyrus in the lenti-miRNA-30e rats. No significant differences were detected in behavioral indicators between the lenti-miRNA-30e rats treated with CG and the normal controls. These findings suggested that CG exerts a potent therapeutic effect, conferred by its ability to enhance the expression levels of BCL-2 and UBC9, which inhibits the apoptotic process in neuronal cells. Therefore, CG may be considered a potential therapeutic strategy for the treatment of cognitive impairment in mental disorders.

MicroRNA-30 mediates anti-inflammatory effects of shear stress and KLF2 via repression of angiopoietin 2

MicroRNAs are endogenously expressed small noncoding RNAs that regulate gene expression. Laminar blood flow induces atheroprotective gene expression in endothelial cells (ECs) in part by upregulating the transcription factor KLF2. Here, we identified KLF2- and flow-responsive miRs that affect gene expression in ECs. Bioinformatic assessment of mRNA expression patterns identified the miR-30-5p seed sequence to be highly enriched in mRNAs that are downregulated by KLF2. Indeed, KLF2 overexpression and shear stress stimulation in vitro and in vivo increased the expression of miR-30-5p family members. Furthermore, we identified angiopoietin 2 (Ang2) as a target of miR-30. MiR-30 overexpression reduces Ang2 levels, whereas miR-30 inhibition by LNA-antimiRs induces Ang2 expression. Consistently, miR-30 reduced basal and TNF-α-induced expression of the inflammatory cell–cell adhesion molecules E-selectin, ICAM1 and VCAM1, which was rescued by stimulation with exogenous Ang2. In summary, KLF2 and shear stress increase the expression of the miR-30-5p family which acts in an anti-inflammatory manner in ECs by impairing the expression of Ang2 and inflammatory cell–cell adhesion molecules. The upregulation of miR-30-5p family members may contribute to the atheroprotective effects of shear stress.

[Molecular-genetic and electroencephalographic markers of neurocognitive processes in depressive disorders]

Perspectives of molecular-genetic approaches to the establishment of mechanisms of development and causes of heterogeneity of neurocognitive impairment are discussed. The current results indicate that candidate genes for depression can contribute to the variance of memory and regulatory functions in patients. At the same time, these genes are closely related to affective information processing and .cortisol level. By that fact, it can't be excluded that affective processes moderate the association between cognition and genes. EEG parameters could be useful phenotypes in the search for and understanding of genetic mechanisms of cognitive deficit in depression. Parameters of resting EEG and its reactive changes are known to reflect the certain cognitive processes. They are influenced by genetic factors and are sensitive indicators of mechanisms that might underlie cognitive impairment in depressive patients. Accumulating data on molecular-genetic correlates of normal electric brain activity may be a source of choosing new candidate genes for cognitive impairment in depression.

MicroRNA and Posttranscriptional Dysregulation in Psychiatry

Psychiatric syndromes, including schizophrenia, mood disorders, and autism spectrum disorders, are characterized by a complex range of symptoms, including psychosis, depression, mania, and cognitive deficits. Although the mechanisms driving pathophysiology are complex and remain largely unknown, advances in the understanding of gene association and gene networks are providing significant clues to their etiology. In recent years, small noncoding RNA molecules known as microRNA (miRNA) have emerged as potential players in the pathophysiology of mental illness. These small RNAs regulate hundreds of target transcripts by modifying their stability and translation on a broad scale, influencing entire gene networks in the process. There is evidence to suggest that numerous miRNAs are dysregulated in postmortem neuropathology of neuropsychiatric disorders, and there is strong genetic support for association of miRNA genes and their targets with these conditions. This review presents the accumulated evidence linking miRNA dysregulation and dysfunction with schizophrenia, bipolar disorder, major depressive disorder, and autism spectrum disorders and the potential of miRNAs as biomarkers or therapeutics for these disorders. We further assess the functional roles of some outstanding miRNAs associated with these conditions and how they may be influencing the development of psychiatric symptoms.

MicroRNAs as biomarkers of resilience or vulnerability to stress

Identifying novel biomarkers of resilience or vulnerability to stress could provide valuable information for the prevention and treatment of stress-related psychiatric disorders. To investigate the utility of blood microRNAs as biomarkers of resilience or vulnerability to stress, microRNAs were assessed before and after 7days of chronic social defeat in rats. Additionally, microRNA profiles of two important stress-regulatory brain regions, the medial prefrontal cortex (mPFC) and basolateral amygdala (BLA), were assessed. Rats that displayed vulnerability to subsequent chronic stress exhibited reductions in circulating miR-24-2-5p, miR-27a-3p, miR-30e-5p, miR-3590-3p, miR-362-3p, and miR-532-5p levels. In contrast, rats that became resilient to stress displayed reduced levels of miR-139-5p, miR-28-3p, miR-326-3p, and miR-99b-5p compared to controls. In the mPFC, miR-126a-3p and miR-708-5p levels were higher in vulnerability compared to resilient rats. In the BLA, 77 microRNAs were significantly altered by stress but none were significantly different between resilient and vulnerable animals. These results provide proof-of-principle that assessment of circulating microRNAs is useful in identifying individuals who are vulnerable to the effects of future stress or individuals who have become resilient to the effects of stress. Furthermore, these data suggest that microRNAs in the mPFC but not in the BLA are regulators of resilience/vulnerability to stress.

CSF miR-16 is decreased in major depression patients and its neutralization in rats induces depression-like behaviors via a serotonin transmitter system

BACKGROUND

Animal and cell line studies demonstrated that miR-16 may be associated with major depressive disorder (MDD) via regulation of the expression of serotonin transporter (SERT) gene. However, human studies about miR-16 of patients with MDD are still lacking. The aim of this study was to investigate the possible involvement of miR-16 in the mechanism of MDD in humans.

METHODS

Thirty-six drug-free patients with MDD and 30 healthy controls aged between 18 and 45 years old were recruited. 24-item Hamilton depression scale test was performed for each subject. MiR-16 in cerebrospinal fluid (CSF) and blood, as well as serotonin in CSF were assayed by the qRT-PCR or ELISA method. To confirm the role of CSF miR-16 in MDD, animal study about intracerebroventricular injection of anti-miR-16 was also performed. Depression-like behaviors, CSF miR-16 and serotonin, blood miR-16, and raphe SERT protein of rats were also tested.

RESULTS

CSF miR-16 in MDD patients was significantly lower than that in controls. It was negatively correlated with Hamilton scores and positively associated with CSF serotonin. However, blood miR-16 was not significantly different between two groups and it was not statistically correlated with CSF miR-16. In animal study, anti-miR-16-treated rats were evaluated to exhibit depression-like behaviors, extremely lower CSF miR-16, significantly higher CSF serotonin, and obviously higher raphe SERT protein than control rats.

LIMITATION

We did not detect SERT protein in human brain due to the impossibility of sample collection.

CONCLUSION

Our study suggested that CSF miR-16 participated in the physiopathology of MDD via the modulation of serotonin transmitter system in brain.

Pathogenesis of depression: Insights from human and rodent studies

Major depressive disorder (MDD) will affect one out of every five people in their lifetime and is the leading cause of disability worldwide. Nevertheless, mechanisms associated with the pathogenesis of MDD have yet to be completely understood and current treatments remain ineffective in a large subset of patients. In this review, we summarize the most recent discoveries and insights for which parallel findings have been obtained in human depressed subjects and rodent models of mood disorders in order to examine the potential etiology of depression. These mechanisms range from synaptic plasticity mechanisms to epigenetics and the immune system where there is strong evidence to support a functional role in the development of specific depression symptomology. Ultimately we conclude by discussing how novel therapeutic strategies targeting central and peripheral processes might ultimately aid in the development of effective new treatments for MDD and related stress disorders.

Coordinated messenger RNA/microRNA changes in fibroblasts of patients with major depression

BACKGROUND

Peripheral biomarkers for major psychiatric disorders have been an elusive target for the last half a century. Dermal fibroblasts are a simple, relevant, and much underutilized model for studying molecular processes of patients with affective disorders, as they share considerable similarity of signal transduction with neuronal tissue.

METHODS

Cultured dermal fibroblast samples from patients with major depressive disorder (MDD) and matched control subjects (n = 16 pairs, 32 samples) were assayed for genome-wide messenger RNA (mRNA) expression using microarrays. In addition, a simultaneous quantitative polymerase chain reaction-based assessment of >1000 microRNA (miRNA) species was performed. Finally, to test the relationship between the mRNA-miRNA expression changes, the two datasets were correlated with each other.

RESULTS

Our data revealed that MDD fibroblasts, when compared with matched control subjects, showed a strong mRNA gene expression pattern change in multiple molecular pathways, including cell-to-cell communication, innate/adaptive immunity, and cell proliferation. Furthermore, the same patient fibroblasts showed altered expression of a distinct panel of 38 miRNAs, which putatively targeted many of the differentially expressed mRNAs. The miRNA-mRNA expression changes appeared to be functionally connected, as the majority of the miRNA and mRNA changes were in the opposite direction.

CONCLUSIONS

Our data suggest that combined miRNA-mRNA assessments are informative about the disease process and that analyses of dermal fibroblasts might lead to the discovery of promising peripheral biomarkers of MDD that could be potentially used to aid the diagnosis and allow mechanistic testing of disturbed molecular pathways.

Differential expression of microRNA in peripheral blood mononuclear cells as specific biomarker for major depressive disorder patients

Currently, diagnosis and treatment of major depressive disorder (MDD) are based on the patients' description of symptoms, mental status examinations, and clinical behavioral observations, which increases the chance of misdiagnosis. There is a serious need to find a practical biomarker for the proper diagnosis of MDD. This study aimed to explore the possibility of microRNA (miRNA) in peripheral blood mononuclear cells (PBMCs) as specific blood-based biomarker for MDD patients. By using an Affymetrix array that covers 723 human miRNAs, we identified 26 miRNAs with significant changes in expression in PBMCs of MDD patients. Real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis in a larger cohort of 81 MDD patients and 46 healthy controls confirmed that the expression levels of 5 miRNAs (miRNA-26b, miRNA-1972, miRNA-4485, miRNA-4498, and miRNA-4743) were up-regulated. By receiver operating characteristic (ROC) curve analysis, the combining area under the ROC curve (AUC) of these five miRNAs was 0.636 [95% confidence interval (CI): 0.58-0.90]. MiRNA target gene prediction and functional annotation analysis showed that there was a significant enrichment in several pathways associated with nervous system and brain functions, supporting the hypothesis that differentially-regulated miRNAs may be involved in mechanism underlying development of MDD. We conclude that altered expression of miRNAs in PMBCs might be involved in multiple stages of MDD pathogenesis, and thus might be able to serve as specific biomarker for diagnosis of MDD.

Heterogeneity and individuality: microRNAs in mental disorders

MicroRNAs are about 22 nucleotide long single-stranded RNA molecules, negatively regulating gene expression of a single gene or a gene network. In neural tissues, they have been implicated in developmental and neuroplasticity-related processes, such as neurogenesis, differentiation, apoptosis and long-term potentiation. Their molecular mode of action is reminiscent of findings of genome-wide association studies in mental disorders, unable to attribute the risk of disease to a specific gene, but rather to multiple genes, gene-networks and gene-environment interaction. As such, microRNAs are an attractive target for research. Here, we review clinical studies conducted in humans on microRNAs in mental disorders with a particular focus on schizophrenia, bipolar disorder, major depressive disorder and anxiety disorders. The majority of clinical studies have focused on schizophrenia. The most robust finding has been reported for rs1625579 located in MIR137HG, which was associated with schizophrenia on a genome-wide level. Concerning bipolar disorder, major depression and anxiety disorders, promising results have been published, but only a considerably smaller number of clinical studies is available and genome-wide association studies did not suggest a direct link to microRNAs so far. Expression of microRNAs as biomarkers of mental disorders and treatment response is currently emerging with preliminary results. Larger-scaled genetic and functional studies along with translational research are needed to enhance our understanding of microRNAs in mental disorders. These studies will aid in disentangling the complex genetic nature of these disorders and possibly contribute to the development of novel, individualized diagnostic and therapeutic approaches.

Faster, better, stronger: towards new antidepressant therapeutic strategies

Major depression is a highly prevalent disorder and is predicted to be the second leading cause of disease burden by 2020. Although many antidepressant drugs are currently available, they are far from optimal. Approximately 50% of patients do not respond to initial first line antidepressant treatment, while approximately one third fail to achieve remission following several pharmacological interventions. Furthermore, several weeks or months of treatment are often required before clinical improvement, if any, is reported. Moreover, most of the commonly used antidepressants have been primarily designed to increase synaptic availability of serotonin and/or noradrenaline and although they are of therapeutic benefit to many patients, it is clear that other therapeutic targets are required if we are going to improve the response and remission rates. It is clear that more effective, rapid-acting antidepressants with novel mechanisms of action are required. The purpose of this review is to outline the current strategies that are being taken in both preclinical and clinical settings for identifying superior antidepressant drugs. The realisation that ketamine has rapid antidepressant-like effects in treatment resistant patients has reenergised the field. Further, developing an understanding of the mechanisms underlying the rapid antidepressant effects in treatment-resistant patients by drugs such as ketamine may uncover novel therapeutic targets that can be exploited to meet the Olympian challenge of developing faster, better and stronger antidepressant drugs.

Identification of suitable plasma-based reference genes for miRNAome analysis of major depressive disorder

BACKGROUND

Mounting evidence has demonstrated microRNA involvement in the set of diverse pathways associated with major depressive disorder (MDD). Reverse transcription quantitative real-time PCR (RT-qPCR) has been widely used in microRNA expression studies. To achieve accurate and reproducible microRNA RT-qPCR data, reference genes are required. The goal of this study is to systematically identify suitable reference genes for normalizing RT-qPCR assays of microRNA expression in the plasma of MDD patients.

METHODS

Candidate reference genes were selected from plasma samples of both MDD and healthy controls by miRNA microarrays, in addition to a frequently used reference gene - U6 small nuclear RNA. Putative reference genes were thereafter validated by RT-qPCR in plasma samples, and analyzed by the four statistical algorithms geNorm, NormFinder, BestKeeper and the comparative delta-Ct method. Finally, the validity of the selected reference genes was assessed with two significantly decreased miRNAs identified by microarray.

RESULTS

Five miRNAs (miR-320d, miR-101-3p, miR-106a-5p, miR-423-5p, miR-93-5p) based on microarray data and U6 were identified as putative reference genes. The results of the merged data from four statistical algorithms revealed that the most adequate microRNAs tested for normalization were miR-101-3p and miR-93-5p. Assessment of the validity of the selected reference genes confirms the suitability of applying the combination of miR-101-3p and miR-93-5p as optimal references genes.

LIMITATIONS

Relatively small sample size; and lack of other disease groups.

CONCLUSIONS

The normalization methods proposed here can contribute to improve studies on MDD biomarker identification and/or pathogenesis by providing more reliable and accurate expression measurements.

MicroRNA 135 is essential for chronic stress resiliency, antidepressant efficacy, and intact serotonergic activity

The link between dysregulated serotonergic activity and depression and anxiety disorders is well established, yet the molecular mechanisms underlying these psychopathologies are not fully understood. Here, we explore the role of microRNAs in regulating serotonergic (5HT) neuron activity. To this end, we determined the specific microRNA "fingerprint" of 5HT neurons and identified a strong microRNA-target interaction between microRNA 135 (miR135), and both serotonin transporter and serotonin receptor-1a transcripts. Intriguingly, miR135a levels were upregulated after administration of antidepressants. Genetically modified mouse models, expressing higher or lower levels of miR135, demonstrated major alterations in anxiety- and depression-like behaviors, 5HT levels, and behavioral response to antidepressant treatment. Finally, miR135a levels in blood and brain of depressed human patients were significantly lower. The current results suggest a potential role for miR135 as an endogenous antidepressant and provide a venue for potential treatment and insights into the onset, susceptibility, and heterogeneity of stress-related psychopathologies.