miRNA genes and the brain: implications for psychiatric disordersa

Impaired myelin ultrastructure is reversed by citalopram treatment in a mouse model for major depressive disorder

Major depressive disorder (MDD) is the most common and widespread mental disorder. Selective serotonin reuptake inhibitors (SSRIs) are the first-line treatment for MDD. The relation between the inhibition of serotonin reuptake in the central nervous system and remission from MDD remains controversial, as reuptake inhibition occurs rapidly, but remission from MDD takes weeks to months. Myelination-related deficits and white matter abnormalities were shown to be involved in psychiatric disorders such as MDD. This may explain the delay in remission following SSRI administration. The raphe nuclei (RN), located in the brain stem, consist of clusters of serotonergic (5-HT) neurons that project to almost all regions of the brain. Thus, the RN are an intriguing area for research of the potential effect of SSRI on myelination, and their involvement in MDD. MicroRNAs (miRNAs) regulate many biological features that might be altered by antidepressants. Two cohorts of chronic unpredictable stress (CUS) mouse model for depression underwent behavioral tests for evaluating stress, anxiety, and depression levels. Following application of the CUS protocol and treatment with the SSRI, citalopram, 48 mice of the second cohort were tested via magnetic resonance imaging and diffusion tensor imaging for differences in brain white matter tracts. RN and superior colliculus were excised from both cohorts and measured for changes in miRNAs, mRNA, and protein levels of candidate genes. Using MRI-DTI scans we found lower fractional anisotropy and axial diffusivity in brains of stressed mice. Moreover, both miR-30b-5p and miR-101a-3p were found to be downregulated in the RN following CUS, and upregulated following CUS and citalopram treatment. The direct binding of these miRNAs to Qki, and the subsequent effects on mRNA and protein levels of myelin basic protein (Mbp), indicated involvement of these miRNAs in myelination ultrastructure processes in the RN, in response to CUS followed by SSRI treatment. We suggest that SSRIs are implicated in repairing myelin deficits resulting from chronic stress that leads to depression.

The Predictive Value of Contrast-Enhanced Ultrasound Combined with Serum miR-124 Level in Acute Cerebral Infarction and Their Correlation with the Contrast Enhancement of Carotid Atherosclerotic Plaque

OBJECTIVE

To investigate the predictive value of contrast-enhanced ultrasound (CEUS) combined with serum miR-124 level in acute cerebral infarction (ACI) and their association with the contrast enhancement of carotid atherosclerotic plaque.

METHODS

Totally 60 patients diagnosed with ACI and 60 controls were included in the study. All the subjects had carotid atherosclerotic plaques, and all of them were examined by CEUS and were tested for serum miR-124 levels.

RESULTS

Time to peak (TTP) and mean transit time (MTT) in the ACI group were significantly shorter than those in the control group (P < 0.05), but the peak intensity ratio (PIR), the area under the curve (AUC), and relative expression levels of serum miR-124 were notably greater in the ACI group (P < 0.05). There were statistically significant differences in TTP, MTT, PIR, AUC, and serum miR-124 expression in patients with different cerebral infarct areas in the ACI group (P < 0.05). Besides, the sensitivity and specificity of serum miR-124 levels for the prediction of ACI were 71.67% and 90.00%, respectively, with a cut-off value of 1.52, and the sensitivity was 86.67% and specificity was 93.33% of CEUS combined with serum miR-124 in the prediction of ACI. The ACI group showed a higher proportion of grades 2 and 3 (P < 0.001). Pearson correlation analysis showed that the intraplaque contrast enhancement was negatively related to TTP and MTT but had a positive correlation with PIR, AUC, and serum miR-124 levels.

CONCLUSION

Grades 2 and 3 intraplaque contrast enhancement and serum miR-124 level of 1.52 had high sensitivity and specificity to predict ACI. Moreover, the CEUS parameters combined with serum miR-124 level could improve the performance in predicting ACI and had auxiliary value in evaluating the stability of carotid atherosclerotic plaques.

Maternal high-sugar diet results in NMDA receptors abnormalities and cognitive impairment in rat offspring

Cognitive impairment affects patients suffering from various neuropsychiatric diseases, which are often accompanied by changes in the glutamatergic system. Epidemiological studies indicate that predispositions to the development of neuropsychiatric diseases may be programmed prenatally. Mother's improper diet during pregnancy and lactation may cause fetal abnormalities and, consequently, predispose to diseases in childhood and even adulthood. Considering the prevalence of obesity in developed countries, it seems important to examine the effects of diet on the behavior and physiology of future generations. We hypothesized that exposure to sugar excess in a maternal diet during pregnancy and lactation would affect memory as the NMDA receptor-related processes. Through the manipulation of the sugar amount in the maternal diet in rats, we assessed its effect on offspring's memory. Then, we evaluated if memory alterations were paralleled by molecular changes in NMDA receptors and related modulatory pathways in the prefrontal cortex and the hippocampus of adolescent and young adult female and male offspring. Behavioral studies have shown sex-related changes like impaired recognition memory in adolescent males and spatial memory in females. Molecular results confirmed an NMDA receptor hypofunction along with subunit composition abnormalities in the medial prefrontal cortex of adolescent offspring. In young adults, GluN2A-containing receptors were dominant in the medial prefrontal cortex, while in the hippocampus the GluN2B subunit contribution was elevated. In conclusion, we demonstrated that a maternal high-sugar diet can affect the memory processes in the offspring by disrupting the NMDA receptor composition and regulation in the medial prefrontal cortex and the hippocampus.

Genetic variants in miRNAs differentially expressed during brain development and their relevance to psychiatric disorders susceptibility

OBJECTIVES

MicroRNAs (miRNAs) play an important regulatory role in the expression of genes involved in brain functions during development. Genetic variants in miRNA genes may impact their regulatory function and lead to psychiatric disorders. To evaluate the role of genetic variants in genes of miRNAs differentially expressed during neurodevelopment on autism spectrum disorder (ASD), attention deficit/hyperactivity disorder (ADHD), schizophrenia (SCZ), and major depressive disorder (MDD).

METHODS

The miRNAs were identified in the literature. Summary statistics from the most recent genome-wide association studies to date were used to evaluate the association between the selected polymorphisms and each disorder in a look-up approach. In a global analysis, we compared the standardised risk effect of variants in neurodevelopment-related miRNAs with those in the remaining miRNAs from miRBase.

RESULTS

The global analysis showed that variants in neurodevelopment-related miRNAs had higher risk effects compared to the other miRNAs for SCZ (p = 0.010) and ADHD (p = 0.001). MIR33B, MIR29B2, MIR29C, MIR137, and MIR135A1 were significantly associated with SCZ, while 55.9% of the miRNAs were at least nominally associated with one or more psychiatric disorders (p < 0.05).

CONCLUSIONS

Genetic variants in neurodevelopment-related miRNAs play an important role in the genetic susceptibility of psychiatric disorders, mainly SCZ and ADHD.

MiR-132 down-regulates high glucose-induced β-dystroglycan degradation through Matrix Metalloproteinases-9 up-regulation in primary neurons

Cognitive dysfunction is one of the complications of diabetes. Unfortunately, there is no effective methods to block its progression currently. One of the pathophysiological mechanisms is synaptic protein damage and neuronal signal disruption because of glucose metabolism disorder. Dystroglycan protein, located in the post‐synaptic membrane of neurons, links the intracellular cytoskeleton with extracellular matrix. Abnormal expression of dystroglycan protein affects neuronal biological functions and leads to cognitive impairment. However, there are no relevant studies to observe the changes of β‐dystroglycan protein in diabetes rat brain and in primary neurons under high glucose exposure. Our data demonstrated the alterations of cognitive abilities in the diabetic rats; β‐dystroglycan protein degradation occurred in hippocampal and cortical tissues in diabetic rat brain. We further explored the mechanisms underlying of this phenomenon. When neurons are exposed to high glucose environment in long‐term period, microRNA‐132 (miR‐132) would be down‐regulated in neurons. Matrix Metalloproteinases‐9 (MMP‐9) mRNA, as a target of miR‐132, could be up‐regulated; higher expression and overlay activity of MMP‐9 protein could increase β‐DG protein degradation. In this way, β‐DG degradation may affect structure and functions among the synapses, which related to cognition decline. It may provide some theoretical basis for elucidating the molecular mechanism of diabetes‐induced cognitive dysfunction.

Sex-specific effects of social defeat stress on miRNA expression in the anterior BNST

Women are more likely to suffer from stress-related affective disorders than men, but the underlying mechanisms of sex differences remain unclear. Previous works show that microRNA (miRNA) profiles are altered in stressed animals and patients with depression and anxiety disorders. In this study, we investigated how miRNA expression in the anterior bed nucleus of stria terminalis (BNST) was affected by social defeat stress in female and male California mice (Peromyscus californicus). We performed sequencing to identify miRNA transcripts in the whole brain and anterior BNST followed by qPCR analysis to compare miRNA expression between control and stressed animals. The results showed that social defeat stress induced sex-specific miRNA expression changes in the anterior BNST. Let-7a, let-7f and miR-181a-5p were upregulated in stressed female but not male mice. Our study provided evidence that social stress produces distinct molecular responses in the BNST of males and females.

MicroRNA profiling of the pig periaqueductal grey (PAG) region reveals candidates potentially related to sex-dependent differences

Background

MicroRNAs indirectly orchestrate myriads of essential biological processes. A wide diversity of miRNAs of the neurodevelopmental importance characterizes the brain tissue, which, however, exhibits region-specific miRNA profile differences. One of the most conservative regions of the brain is periaqueductal grey (PAG) playing vital roles in significant functions of this organ, also those observed to be sex-influenced. The domestic pig is an important livestock species but is also believed to be an excellent human model. This is of particular importance for neurological research because of the similarity of pig and human brains as well as difficult access to human samples. However, the pig PAG profile has not been characterized so far. Moreover, molecular bases of sex differences connected with brain functioning, including miRNA expression profiles, have not been fully deciphered yet.

Methods

Thus, in this study, we applied next-generation sequencing to characterize pig PAG expressed microRNAs. Furthermore, we performed differential expression analysis between females and males to identify changes of the miRNA profile and reveal candidates underlying sex-related differences.

Results

As a result, known brain-enriched, and new miRNAs which will expand the available profile, were identified. The downstream analysis revealed 38 miRNAs being differentially expressed (DE) between female and male samples. Subsequent pathway analysis showed that they enrich processes vital for neuron growth and functioning, such as long-term depression and axon guidance. Among the identified sex-influenced miRNAs were also those associated with the PAG physiology and diseases related to this region.

Conclusions

The obtained results broaden the knowledge on the porcine PAG miRNAome, along with its dynamism reflected in different isomiR signatures. Moreover, they indicate possible mechanisms associated with sex-influenced differences mediated via miRNAs in the PAG functioning. They also provide candidate miRNAs for further research concerning, i.e., sex-related bases of physiological and pathological processes occurring in the nervous system.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13293-020-00343-2.

A functional SNP in MIR124-1, a brain expressed miRNA gene, is associated with aggressiveness in a Colombian sample

Background:

Interpersonal violence and suicide are among the main causes of mortality and morbidity around the world. In several developing countries, such as Colombia, they are among the first five entities of public health concern. Aggressiveness is an important endophenotype for aggression and suicidal behavior, having a heritability of around 50%. Exploration of classical candidate genes, involved in serotoninergic and dopaminergic neurotransmission, has identified few consistent risk factors for aggressiveness. miRNAs are a novel class of molecules with a growing role in normal neural function and neuropsychiatric disorders; of special interest, miR-124 is a brain-specific miRNA that is key for neuronal plasticity. We evaluated the hypothesis that a functional polymorphism in MIR124-1 gene might be associated with aggressiveness in a Colombian sample.

Methods:

The Spanish adaptation of the refined version of the Aggression Questionnaire and the abbreviated Barratt Impulsiveness Scale were applied to 170 young subjects. The functional SNP in MIR124-1 (rs531564) was genotyped by a TaqMan assay.

Results:

We found a significant association between the MIR124-1 and aggressiveness in our sample, with G/G carriers having lower scores (P = 0.01). This association seemed to be specific for aggressiveness, as it was not significant for impulsiveness.

Conclusions:

We showed for the first time the association of a functional polymorphism in MIR124-1 and aggressiveness. Known targets of miR-124 (such as BDNF and DRD4 genes) could explain the effect of this miRNA on behavior. A future analysis of additional novel functional polymorphisms in other brain expressed miRNAs could be useful for a deeper understanding of aggression in humans.

A functional SNP in the synaptic SNAP25 gene is associated with impulsivity in a Colombian sample

The aim of the current study was to test the hypothesis that a functional polymorphism in the synaptosome associated protein 25 (SNAP25) gene could be associated with impulsivity scores in a sample of young Colombian subjects. Impulsivity has been postulated as an endophenotype for several psychiatric disorders of high epidemiological relevance. There is a need for the study of additional candidate genes for impulsivity. One hundred seventy-five young Colombian subjects completed the Spanish version of the short form of the Barratt Impulsiveness Scale (BIS-15S). A TaqMan assay was used to genotype a functional polymorphism (rs3746544) in the SNAP25 gene. A significant association was found between the functional polymorphism in the SNAP25 gene and impulsivity in the Colombian sample, with subjects carrying T/T and G/G genotypes showing lower mean scores in the non-planning subfactor (p = 0.02). This is the first report of an association of a functional polymorphism in the SNAP25 gene and a subfactor of the BIS-15S scale of impulsivity. In addition, this the first genetic study of impulsivity scores in a Latin American sample. Future studies should explore additional variants in brain-expressed miRNAs and in their binding sites as candidates for impulsivity in different populations.

The Role of MIR9-2 in Shared Susceptibility of Psychiatric Disorders during Childhood: A Population-Based Birth Cohort Study

BACKGROUND

It has been suggested that microRNAs (miRNAs; short non-protein-coding RNA molecules that mediate post-transcriptional regulation), including mir-9 and mir-34 families, are important for brain development. Current data suggest that mir-9 and mir-34 may have shared effects across psychiatric disorders. This study aims to explore the role of genetic polymorphisms in the MIR9-2 (rs4916723) and MIR34B/C (rs4938723) genes on the susceptibility of psychiatric disorders in children from the 2004 Pelotas Birth Cohort.

METHODS

Psychiatric disorders were assessed in 3585 individuals using Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM-IV), criteria through the application of standard semi-structured interviews (using the Development and Well-Being Assessment, DAWBA) at the six-years-of-age follow-up. The outcome was defined as the presence of any mental disorder. We also considered two broad groups of internalizing and externalizing disorders to further investigate the role of these variants in mental health.

RESULTS

We observed an association between rs4916723 (MIR9-2) and the presence of any psychiatric disorder (odds ratios (OR) = 0.820; 95% CI = 0.7130-0.944; p = 0.006) and a suggestive effect on internalizing disorders (OR = 0.830; 95% CI = 0.698-0.987; p = 0.035). rs4938723 (MIR34B/C) was not associated with any evaluated outcome.

CONCLUSION

The study suggests that MIR9-2 may have an important role on a broad susceptibility for psychiatric disorders and may be important mainly for internalization problems.

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.

Catalpol may improve axonal growth via regulating miR-124 regulated PI3K/AKT/mTOR pathway in neurons after ischemia

Background

MicroRNA-124 (miR-124) is a brain-specific miRNA molecule, the highest expression in the cortex and is associated with neuronal protection after stroke. This study aimed to investigate whether catalpol could affect miR-124 to regulate PI3K/AKT/mTOR pathway, promoting axonal growth in stroke rats.

Methods

Cells were divided into three groups: control group, miRNA124 agomir group, and miRNA124 antagomir group. To explore the mechanism, cells were divided into seven groups: control group, OGD group (OGD/R), miRNA124 agomir group, miRNA124 agomir plus catalpol group, miRNA124 antagomir group, miRNA124 antagomir plus catalpol group, and catalpol group. Before OGD/R, miRNA124 antagomir and microRNA124 agomir were transfected into neurons for 6 h by using ribo FECT nd Consumablesn/reper transfection kit. Cell survival and cell death were detected by MTT and LDH assay. Axonal growth was assessed by MAP-2 immunofluorescence staining. Western blotting and qPCR were used to detect the expression of molecules in the PI3K/AKT/mTOR pathway.

Results

Inhibition of miR-124 activated PI3K/AKT/mTOR pathway and promoted neuronal survival and axonal growth. The expression of miR-124 increased after OGD/R, and catalpol could inhibit miR-124 to activate PI3K/AKT/mTOR pathway to further promote axonal growth.

Conclusions

It is concluded that catalpol may inhibit miR-124 to activate PI3K/AKT/mTOR pathway, promoting axonal growth.

Depressive symptoms are associated with a functional polymorphism in a miR-433 binding site in the FGF20 gene

Genetic studies of major depressive disorder and its associated endophenotypes are useful for the identification of candidate genes. In recent years, variations in non-coding RNA genes, such as miRNAs, have been explored as novel candidates for psychiatric disorders and related endophenotypes. The aim of the present study was to evaluate the possible association between a functional polymorphism (rs12720208) in the FGF20 gene, which regulates its modulation by miR-433, and depressive symptoms in young adults. A sample of 270 participants from Colombia were evaluated with the Hospital Anxiety and Depression Scale - Depression Subscale (HADS-D) and genotyped for the rs12720208 polymorphism using a TaqMan assay. A lineal regression analysis was used. A statistically significant association of the functional polymorphism in the FGF20 gene (rs12720208) with depressive symptoms was found. It was observed that individuals with the G/A genotype had higher scores for the HADS-D subscale. Our results are the first description in the scientific literature about a significant association between a functional polymorphism in the FGF20 gene, which regulates its modulation by miR-433, and depressive symptoms.

Zebrafish models relevant to studying central opioid and endocannabinoid systems

The endocannabinoid and opioid systems are two interplaying neurotransmitter systems that modulate drug abuse, anxiety, pain, cognition, neurogenesis and immune activity. Although they are involved in such critical functions, our understanding of endocannabinoid and opioid physiology remains limited, necessitating further studies, novel models and new model organisms in this field. Zebrafish (Danio rerio) is rapidly emerging as one of the most effective translational models in neuroscience and biological psychiatry. Due to their high physiological and genetic homology to humans, zebrafish may be effectively used to study the endocannabinoid and opioid systems. Here, we discuss current models used to target the endocannabinoid and opioid systems in zebrafish, and their potential use in future translational research and high-throughput drug screening. Emphasizing the high degree of conservation of the endocannabinoid and opioid systems in zebrafish and mammals, we suggest zebrafish as an excellent model organism to study these systems and to search for the new drugs and therapies targeting their evolutionarily conserved mechanisms.

miRNA-regulated transcription associated with mouse strains predisposed to hypnotic effects of ethanol

INTRODUCTION

Studying innate sensitivity to ethanol can be an important first step toward understanding alcohol use disorders. In brain, we investigated transcripts, with evidence of miRNA modulation related to a predisposition to the hypnotic effect of ethanol, as measured by loss of righting reflex (LORR).

METHODS

Expression of miRNAs (12 samples) and expression of mRNAs (353 samples) in brain were independently analyzed for an association with LORR in mice from the LXS recombinant inbred panel gathered across several small studies. These results were then integrated via a meta-analysis of miRNA-mRNA target pairs identified in miRNA-target interaction databases.

RESULTS

We found 112 significant miRNA-mRNA pairs where a large majority of miRNAs and mRNAs were highly interconnected. Most pairs indicated a pattern of increased levels of miRNAs and reduced levels of mRNAs being associated with more alcohol-sensitive strains. For example, CaMKIIn1 was targeted by multiple miRNAs associated with LORR. CAMK2N1 is an inhibitor of CAMK2, which among other functions, phosphorylates, or binds to GABAA and NMDA receptors.

CONCLUSIONS

Our results suggest a novel role of miRNA-mediated regulation of an inhibitor of CAMK2 and its downstream targets including the GABAA and NMDA receptors, which have been previously implicated to have a role in ethanol-induced sedation and sensitivity.

A Functional Polymorphism in the DRD1 Gene, That Modulates Its Regulation by miR-504, Is Associated with Depressive Symptoms

OBJECTIVE

The aim of this study was to examine a possible association between depressive symptoms and a functional polymorphism (rs686) that modulates the regulation of DRD1 gene by miR-504.

METHODS

A total of 239 young Colombian subjects were evaluated with the Patient Health Questionnaire-9 (PHQ-9) scale and genotyped for the rs686 polymorphism. A linear regression model, corrected by age and gender, was used.

RESULTS

A significant association between the rs686 polymorphism and PHQ-9 scores was found, under a dominant genetic model (p=0.0094).

CONCLUSION

These results provide novel evidence about the growing role of inherited variants in binding sites for brain-expressed miRNAs on depressive symptomatology.

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.

Dysregulation of autism-associated synaptic proteins by psychoactive pharmaceuticals at environmental concentrations

Autism Spectrum Disorders (ASD) are complex neurological disorders for which the prevalence in the U.S. is currently estimated to be 1 in 50 children. A majority of cases of idiopathic autism in children likely result from unknown environmental triggers in genetically susceptible individuals. These triggers may include maternal exposure of a developing embryo to environmentally relevant minute concentrations of psychoactive pharmaceuticals through ineffectively purified drinking water. Previous studies in our lab examined the extent to which gene sets associated with neuronal development were up- and down-regulated (enriched) in the brains of fathead minnows treated with psychoactive pharmaceuticals at environmental concentrations. The aim of this study was to determine whether similar treatments would alter in vitro expression of ASD-associated synaptic proteins on differentiated human neuronal cells. Human SK-N-SH neuroblastoma cells were differentiated for two weeks with 10μM retinoic acid (RA) and treated with environmentally relevant concentrations of fluoxetine, carbamazepine or venlafaxine, and flow cytometry technique was used to analyze expression of ASD-associated synaptic proteins. Data showed that carbamazepine individually, venlafaxine individually and mixture treatment at environmental concentrations significantly altered the expression of key synaptic proteins (NMDAR1, PSD95, SV2A, HTR1B, HTR2C and OXTR). Data indicated that psychoactive pharmaceuticals at extremely low concentrations altered the in vitro expression of key synaptic proteins that may potentially contribute to neurological disorders like ASD by disrupting neuronal development.

A comprehensive regional analysis of genome-wide expression profiles for major depressive disorder

BACKGROUND

Major depressive disorder (MDD) is a global health challenge. In recent years, a large number of genome-wide expression studies (GWES) have been carried out to identify the transcriptomic profiles for MDD. The objective of this work was to carry out a comprehensive meta-analysis of available GWES for MDD.

METHODS

GWES for MDD with available raw data were searched in NCBI GEO, Array Express and Stanley databases. Raw GWES data were preprocessed and normalized and meta-analytical procedures were carried out with the Network Analyst program. 743 samples from 24 primary studies were included in our meta-analyses for blood (Blo), amygdala (Amy), cerebellum (Cer), anterior cingulate cortex (ACC) and prefrontal cortex (PFC) regions. A functional enrichment analysis was carried out.

RESULTS

We identified 35, 793, 231, 668 and 252 differentially expressed (DE) genes for Blo, Amy, Cer, ACC and PFC regions. A region-dependent significant enrichment for several functional categories, such as gene ontologies, signaling pathways and topographic parameters, was identified. There was convergence with other available genome-wide studies, such as GWAS, DNA methylation analyses and miRNA expression studies.

LIMITATIONS

Raw data were not available for several primary studies that have been published previously.

CONCLUSIONS

This is the largest meta-analysis for GWES in MDD. The examination of convergence of genome-wide evidence and of the functional enrichment analysis provides a global overview of potential neural signaling mechanisms dysregulated in MDD. Our comprehensive analysis of several brain regions identified lists of DE genes for MDD that are interesting candidates for further studies.

Prenatal exposure to valproic acid increases miR-132 levels in the mouse embryonic brain

Background

MicroRNAs, small non-coding RNAs, are highly expressed in the mammalian brain, and the dysregulation of microRNA levels may be involved in neurodevelopmental disorders such as autism spectrum disorder (ASD). In the present study, we examined whether prenatal valproic acid (VPA) exposure affects levels of microRNAs, especially the brain specific and enriched microRNAs, in the mouse embryonic brain.

Results

Prenatal exposure to VPA at E12.5 immediately increased miR-132 levels, but not miR-9 or miR-124 levels, in the male embryonic brain. Prenatal exposure to VPA at E12.5 also increased miR-132 levels in the female embryonic brain. We further found that the prenatal exposure to VPA at E12.5 increased mRNA levels of Arc, c-Fos and brain-derived neurotrophic factor in both male and female embryonic brains, prior to miR-132 expression. In contrast, prenatal exposure to VPA at E14.5 did not affect miR-132 levels in either male or female embryonic brain. The prenatal VPA exposure at E12.5 also decreased mRNA levels of methyl-CpG-binding protein 2 and Rho GTPase-activating protein p250GAP, both of which are molecular targets of miR-132. Furthermore, RNA sequence analysis revealed that prenatal VPA exposure caused changes in several microRNA levels other than miR-132 in the embryonic whole brain.

Conclusions

These findings suggest that the alterations in neuronal activity-dependent microRNAs levels, including an increased level of miR-132, in the embryonic period, at least in part, underlie the ASD-like behaviors and cortical pathology produced by prenatal VPA exposure.

Functional and Genomic Features of Human Genes Mutated in Neuropsychiatric Disorders

Background:

In recent years, a large number of studies around the world have led to the identification of causal genes for hereditary types of common and rare neurological and psychiatric disorders.

Objective:

To explore the functional and genomic features of known human genes mutated in neuropsychiatric disorders.

Methods:

A systematic search was used to develop a comprehensive catalog of genes mutated in neuropsychiatric disorders (NPD). Functional enrichment and protein-protein interaction analyses were carried out. A false discovery rate approach was used for correction for multiple testing.

Results:

We found several functional categories that are enriched among NPD genes, such as gene ontologies, protein domains, tissue expression, signaling pathways and regulation by brain-expressed miRNAs and transcription factors. Sixty six of those NPD genes are known to be druggable. Several topographic parameters of protein-protein interaction networks and the degree of conservation between orthologous genes were identified as significant among NPD genes.

Conclusion:

These results represent one of the first analyses of enrichment of functional categories of genes known to harbor mutations for NPD. These findings could be useful for a future creation of computational tools for prioritization of novel candidate genes for NPD.

MiR-124 Promotes Newborn Olfactory Bulb Neuron Dendritic Morphogenesis and Spine Density

Using microarray analysis, we detected microRNA-124 (miR-124) to be abundantly expressed in the olfactory bulb (OB). miR-124 regulates adult neurogenesis in the subventricular zone (SVZ). However, much less is known about its role in newborn OB neurons. Here, using both gain-of-function and loss-of-function approaches, we demonstrate that brain-specific miR-124 affects dendritic morphogenesis and spine density in newborn OB neurons. Functional Annotation Clustering of miR-124 targets was enriched in "cell morphogenesis involved in neuron differentiation."

MIR137 is the key gene mediator of the syndromic obesity phenotype of patients with 1p21.3 microdeletions

Background

Deletions in the long arm of chromosome 1 have been described in patients with a phenotype consisting primarily of obesity, intellectual disability and autism-spectrum disorder. The minimal region of overlap comprises two genes: DPYD and MIR137.

Case presentation

We describe a 10-year-old boy with syndromic obesity who carries a novel 1p21.3 deletion overlapping the critical region with the MIR137 gene only.

Conclusions

This study suggests that MIR137 is the mediator of the obesity phenotype of patients carrying 1p21.3 microdeletions.

Fluoxetine Increases the Expression of miR-572 and miR-663a in Human Neuroblastoma Cell Lines

Evidence suggests neuroprotective effects of fluoxetine, a selective serotonin reuptake inhibitor (SSRI), on the developed neurons in the adult brain. In contrast, the drug may be deleterious to immature or undifferentiated neural cells, although the mechanism is unclear. Recent investigations have suggested that microRNAs (miRNA) may be critical for effectiveness of psychotropic drugs including SSRI. We investigated whether fluoxetine could modulate expressions of neurologically relevant miRNAs in two neuroblastoma SK-N-SH and SH-SY5Y cell lines. Initial screening results revealed that three (miR-489, miR-572 and miR-663a) and four (miR-320a, miR-489, miR-572 and miR-663a) miRNAs were up-regulated in SK-N-SH cells and SH-SY5Y cells, respectively, after 24 hours treatment of fluoxetine (1–25 μM). Cell viability was reduced according to the dose of fluoxetine. The upregulation of miR-572 and miR-663a was consistent in both the SH-SY5Y and SK-N-SH cells, confirmed by a larger scale culture condition. Our data is the first in vitro evidence that fluoxetine could increase the expression of miRNAs in undifferentiated neural cells, and that putative target genes of those miRNAs have been shown to be involved in fundamental neurodevelopmental processes.

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.

The SNP rs1625579 in miR-137 gene and risk of schizophrenia in Chinese population: A meta-analysis

BACKGROUND

Schizophrenia is a severe psychiatric disorder with a high heritability. A single nucleotide polymorphism (SNP) rs1625579 (G/T; T is the common and presumed risk allele) within an intron of miR-137 gene has been recently suggested to contribute to the susceptibility to schizophrenia by a large-scale genome-wide association study (GWAS) in a sample of predominantly European ancestry. However, subsequent genetic association studies in Chinese population yielded inconsistent results.

METHODS

A meta-analysis reporting the association between rs1625579 and schizophrenia in Chinese population was carried out, pooling 4 eligible case-control studies involving 2847 patients and 3018 controls.

RESULTS

This meta-analysis demonstrated a significant association between rs1625579 and schizophrenia under the allele model [T versus G, odds ratio (OR):1.20, 95% confidence interval (CI): 1.06-1.36] and the recessive model (TT versus GT+GG; OR: 1.19; 95% CI: 1.04-1.37). Additionally, a marginal significant association under the additive model (TT versus GG; OR: 1.64; 95% CI: 1.00-2.69) was observed. However, no significant association was observed under the dominant model (TT+GT versus GG; OR: 1.58; 95% CI: 0.97-2.59).

CONCLUSIONS

This meta-analysis suggested that the SNP rs1625579 in miR-137 gene might be involved in schizophrenia susceptibility in Chinese Han population.

A network of synaptic genes associated with schizophrenia and bipolar disorder

Identification of novel candidate genes for schizophrenia (SZ) and bipolar disorder (BP), two psychiatric disorders with large epidemiological impacts, is a key research area in neurosciences and psychiatric genetics. Previous evidence from genome-wide studies suggests an important role for genes involved in synaptic plasticity in the risk for SZ and BP. We used a convergent genomics approach, combining different lines of biological evidence, to identify genes involved in the cAMP/PKA/CREB functional pathway that could be novel candidates for BP and SZ: CREB1, CREM, GRIN2C, NPY2R, NF1, PPP3CB and PRKAR1A. These 7 genes were analyzed in a HapMap based association study comprising 48 common SNPs in 486 SZ, 351 BP patients and 514 control individuals recruited from an isolated population in Northern Sweden. Genetic analysis showed significant allelic associations of SNPs in PRKAR1A with SZ and of PPP3CB and PRKAR1A with BP. Our results highlight the feasibility and the importance of convergent genomic data analysis for the identification of candidate genes and our data provide support for the role of common inherited variants in synaptic genes and their involvement in the etiology of BP and SZ.

Long-term exposure to black carbon, cognition and single nucleotide polymorphisms in microRNA processing genes in older men

INTRODUCTION

Air pollution exposure has been linked to impaired cognitive aging, but little is known about biomarkers modifying this association. MicroRNAs (miRNAs) control gene expression and neuronal programming. miRNA levels vary due to single nucleotide polymorphisms (SNPs) in genes processing miRNAs from precursor molecules.

OBJECTIVES

To investigate whether SNPs in miRNA-processing genes are associated with cognition and modify the relationship between black carbon (BC), marker of traffic-related pollution, and cognitive functions.

METHODS

533 Normative Aging Study men (mean±SD 72±7years) were tested ≤4 times (mean=1.7 times) using seven cognitive tests between 1995 and 2007. We tested interactions of 16 miRNA-related SNPs with 1-year average BC from a validated land-use-regression model. We used covariate-adjusted logistic regression for low (≤25) Mini-Mental tate Examination (MMSE) and mixed-effect regression for a global cognitive score combining six other tests.

RESULTS

Global cognition was negatively associated with the homozygous minor variant of rs595961 AGO1 (-0.42SD; 95%CI: (-0.71, -0.13)) relative to the major variant. BC-MMSE association was stronger in heterozygous carriers of rs11077 XPO5 (OR=1.99; 95%CI: (1.39, 2.85)) and minor variant carriers of GEMIN4 rs2740348 (OR=1.34; 95%CI: (1.05, 1.7)), compared to their major variant. The BC-global-cognition association was stronger in heterozygous carriers of GEMIN4 rs4968104 (-0.10SD; 95%CI: (-0.18, -0.02)), and GEMIN4 rs910924 (-0.09SD; 95%CI: (-0.17, -0.02)) relative to the major variant. Blood miRNA expression analyses showed associations only of XPO5 rs11077 with miR-9 and miR-96.

CONCLUSIONS

Carriers of particular miRNA-processing SNPs had higher susceptibility to BC in BC-cognition associations, possibly due to influences on miRNA expression.

A functional variant in MIR137, a candidate gene for schizophrenia, affects Stroop test performance in young adults

MIR137, a brain expressed miRNA, has been identified as a top novel susceptibility gene for schizophrenia (SZ). 230 healthy participants completed the Stroop test and were genotyped for a functional Variable Number Tandem Repeat (VNTR) in MIR137 gene. MIR137 VNTR genotypes were associated with differences in Stroop facilitation and accuracies in congruent trials and for the total number of errors. This is the first study of the functional VNTR in MIR137 gene and Stroop test performance in healthy subjects. Our results could have important implications for the identification of genetic candidates for endophenotypes for SZ.

Serum miR-132 is a risk marker of post-stroke cognitive impairment

BACKGROUND/AIMS

Recently, it has been reported that the microRNA-132(miR-132) is linked with synaptic plasticity and cognitive impairment. The present study investigates that whether miR-132 is altered in circulating blood serum samples of post-stroke cognitive impairment (PSCI) patients.

METHODS

We collected samples from 39 subjects with PSCI, 37 subjects with post-stroke cognitive normality (PSCN), and 38 age-matched controls (AMC) for which ages, gender and education level were matched. MiR-132 was detected using a quantitative real-time PCR (qRT-PCR) method. To test the predictive value of miR-132 for PSCI, prediction capabilities were compared using the receiver operating characteristic (ROC) curves and area under curve (AUC) analysis.

RESULTS

The level of miR-132 in PSCI patient serum was significantly elevated compared to that of PSCN and AMC subjects. The ROC curve showed that miR-132 achieved an AUC of 0.961 (p<0.0001). Importantly, the miR-132 level was correlated with the Montreal Cognitive Assessment (MoCA) score in PSCI patients.

CONCLUSIONS

These results indicated that there was a substantial correlation between serum miR-132 expression and post-stroke cognitive functionality, suggesting that miR-132 may be a risk marker for PSCI. Because of the limitations of this study, the results should be treated with caution.

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.

Polymorphisms in MicroRNA Genes And Genes Involving in NMDAR Signaling and Schizophrenia: A Case-Control Study in Chinese Han Population

Disturbances in glutamate signaling caused by disruption of N-methyl-D-aspartate-type glutamate receptor (NMDAR) have been implicated in schizophrenia. Findings suggested that miR-219, miR-132 and miR-107 could involve in NMDAR signaling by influencing the expression of pathway genes or the signaling transmission and single nucleotide polymorphisms (SNPs) within miRNA genes or miRNA target sites could result in their functional changes. Therefore, we hypothesized that SNPs in miRNAs and/or their target sites were associated with schizophrenia. 3 SNPs in hsa-pri-miR-219/132/107 and 6 SNPs in 3′UTRs of GRIN2A/2B/3A and CAMK2G were selected and genotyped in a case-control study of 1041 schizophrenia cases and 953 healthy controls in Chinese Han population. In the present study, GRIN2B rs890 showed significant associations with schizophrenia. Further functional analyses showed that the rs890 variant C allele led to significantly lower luciferase activity, compared with the A allele. MDR analysis showed that a 4-locus model including rs107822, rs2306327, rs890 and rs12342026 was the best model. These findings suggest that GRIN2B may be associated with schizophrenia and interaction effects of the polymorphisms in hsa-miR-219, CAKM2G, GRIN2B and GRIN3A may confer susceptibility to schizophrenia in the Chinese Han population.

Meta-analysis of six genes (BDNF, DRD1, DRD3, DRD4, GRIN2B and MAOA) involved in neuroplasticity and the risk for alcohol dependence

BACKGROUND

Alcohol-related problems have a large impact on human health, accounting for around 4% of deaths and 4.5% of disability-adjusted life-years around the world. Genetic factors could explain a significant fraction of the risk for alcohol dependence (AD). Recent meta-analyses have found significant pooled odds ratios (ORs) for variants in the ADH1B, ADH1C, DRD2 and HTR2A genes.

METHODS

In the present study, we carried out a meta-analysis of common variants in 6 candidate genes involved in neurotransmission and neuroplasticity: BDNF, DRD1, DRD3, DRD4, GRIN2B and MAOA. We carried out a systematic search for published association studies that analyzed the genes of interest. Relevant articles were retrieved and demographic and genetic data were extracted. Pooled ORs were calculated using a random-effects model using the Meta-Analyst program. Dominant, recessive and allelic models were tested and analyses were also stratified by ethnicity.

RESULTS

Forty two published studies were included in the current meta-analysis: BDNF-rs6265 (nine studies), DRD1-rs4532 (four studies), DRD3-rs6280 (eleven studies), DRD4-VNTR (seven studies), GRIN2B-rs1806201 (three studies) and MAOA-uVNTR (eight studies). We did not find significant pooled ORs for any of the six genes, under different models and stratifying for ethnicity.

CONCLUSIONS

In terms of the number of candidate genes included, this is one of the most comprehensive meta-analyses for genetics of AD. Pooled ORs did not support consistent associations with any of the six candidate genes tested. Future studies of novel genes of functional relevance and meta-analyses of quantitative endophenotypes could identify further susceptibility molecular factors for AD.

Expression quantitative trait loci (eQTLs) in microRNA genes are enriched for schizophrenia and bipolar disorder association signals

BACKGROUND

Schizophrenia (SZ) and bipolar disorder (BD) have substantial negative impact on the quality of human life. Both, microRNA (miRNA) expression profiling in SZ and BD postmortem brains [and genome-wide association studies (GWAS)] have implicated miRNAs in disease etiology. Here, we aim to determine whether significant GWAS signals observed in the Psychiatric Genetic Consortium (PGC) are enriched for miRNAs.

METHOD

A two-stage approach was used to determine whether association signals from PGC affect miRNAs: (i) statistical assessment of enrichment using a Simes test and sum of squares test (SST) and (ii) biological evidence that quantitative trait loci (eQTL) mapping to known miRNA genes affect their expression in an independent sample of 78 postmortem brains from the Stanley Medical Research Institute.

RESULTS

A total of 2567 independent single nucleotide polymorphisms (SNPs) (R2 > 0.8) were mapped locally, within 1 Mb, to all known miRNAs (miRBase v. 21). We show robust enrichment for SZ- and BD-related SNPs with miRNAs using Simes (SZ: p ≤ 0.0023, BD: p ≤ 0.038), which remained significant after adjusting for background inflation in SZ (empirical p = 0.018) and approached significance in BD (empirical p = 0.07). At a false discovery rate of 10%, we identified a total of 32 eQTLs to influence miRNA expression; 11 of these overlapped with BD.

CONCLUSIONS

Our approach of integrating PGC findings with eQTL results can be used to generate specific hypotheses regarding the role of miRNAs in SZ and BD.

Study of five novel non-synonymous polymorphisms in human brain-expressed genes in a Colombian sample

Background

Non-synonymous single nucleotide polymorphisms (nsSNPs) in brain-expressed genes represent interesting candidates for genetic research in neuropsychiatric disorders.

Purpose

To study novel nsSNPs in brain-expressed genes in a sample of Colombian subjects.

Methods

We applied an approach based on in silico mining of available genomic data to identify and select novel nsSNPs in brain-expressed genes. We developed novel genotyping assays, based in allele-specific PCR methods, for these nsSNPs and genotyped them in 171 Colombian subjects.

Results

Five common nsSNPs (rs6855837; p.Leu395Ile, rs2305160; p.Thr394Ala, rs10503929; p.Met289Thr, rs2270641; p.Thr4Pro and rs3822659; p.Ser735Ala) were studied, located in the CLOCK, NPAS2, NRG1, SLC18A1 and WWC1 genes. We reported allele and genotype frequencies in a sample of South American healthy subjects. There is previous experimental evidence, arising from genome-wide expression and association studies, for the involvement of these genes in several neuropsychiatric disorders and endophenotypes, such as schizophrenia, mood disorders or memory performance.

Conclusions

Frequencies for these nsSNPSs in the Colombian samples varied in comparison to different HapMap populations. Future study of these nsSNPs in brain-expressed genes, a synaptogenomics approach, will be important for a better understanding of neuropsychiatric diseases and endophenotypes in different populations.

Survival of motor neuron protein downregulates miR-9 expression in patients with spinal muscular atrophy

Spinal muscular atrophy (SMA) is a lethal hereditary disease caused by homozygous absence of the survival of the motor neuron (SMN) 1 gene (SMN1), and it is the leading genetic cause of infant mortality. The severity of SMA is directly correlated with SMN protein levels in affected patients; however, the cellular regulatory mechanisms for SMN protein expression are not completely understood. In this study, we investigated the regulatory effects between SMN expression and miR-9a, a downstream noncoding small RNA. Using an inducible SMN short hairpin RNA interference (shRNAi) system in NSC 34 and human skin fibroblast cells, cellular miR-9 levels and SMN protein repression were time-dependently upregulated. Conversely, cellular miR-9 levels decreased when HeLa cells were transfected with SMN protein fused with green fluorescent protein. In SMA-like mice spinal cords and human primary skin fibroblasts isolated from patients with different degrees of SMA, human SMN exhibited a disease severity-dependent decrease, whereas cellular miR-9 levels increased. These results clearly suggested that cellular SMN proteins regulated miR-9 expression and that miR-9 expression was related to SMA severity. Thus, miR-9 may be a marker for SMA prognosis.

The role of microRNAs in human diseases

About 20 years have passed since the discovery of the first microRNA (miRNA) and by now microRNAs are implicated in a variety of physiological and pathological processes. Since the discovery of the powerful effect miRNAs have on biological processes, it has been suggested that mutations affecting miRNA function may play a role in the pathogenesis of human diseases. Over the past several years microRNAs have been found to play a major role in various human diseases. In addition, many studies aim to apply miRNAs for diagnostic and therapeutic applications in human diseases. In this chapter, we summarize the role of miRNAs in pathological processes and discuss how miRNAs could be used as disease biomarkers.

Regulatory role of miRNAs in polyamine gene expression in the prefrontal cortex of depressed suicide completers

MicroRNAs (miRNAs) are small, non-coding RNA molecules that play an important role in the post-transcriptional regulation of mRNA. These molecules have been the subject of growing interest as they are believed to control the regulation of a large number of genes, including those expressed in the brain. Evidence suggests that miRNAs could be involved in the pathogenesis of neuropsychiatric disorders. Alterations in metabolic enzymes of the polyamine system have been reported to play a role in predisposition to suicidal behaviour. We have previously shown the expression of the polyamine genes SAT1 and SMOX to be down-regulated in the brains of suicide completers. In this study, we hypothesized that the dysregulation of these genes in depressed suicide completers could be influenced by miRNA post-transcriptional regulation. Using a stringent target prediction analysis, we identified several miRNAs that target the 3'UTR of SAT1 and SMOX. We profiled the expression of 10 miRNAs in the prefrontal cortex (BA44) of suicide completers (N = 15) and controls (N = 16) using qRT-PCR. We found that several miRNAs showed significant up-regulation in the prefrontal cortex of suicide completers compared to psychiatric healthy controls. Furthermore, we demonstrated a significant correlation between these miRNAs and the expression levels of both SAT1 and SMOX. Our results suggest a relationship between miRNAs and polyamine gene expression in the suicide brain, and postulate a mechanism for SAT1 and SMOX down-regulation by post-transcriptional activity of miRNAs.

MicroRNAs as the cause of schizophrenia in 22q11.2 deletion carriers, and possible implications for idiopathic disease: a mini-review

The 22q11.2 deletion is the strongest known genetic risk factor for schizophrenia. Research has implicated microRNA-mediated dysregulation in 22q11.2 deletion syndrome (22q11.2DS) schizophrenia-risk. Primary candidate genes are DGCR8 (DiGeorge syndrome critical region gene 8), which encodes a component of the microprocessor complex essential for microRNA biogenesis, and MIR185, which encodes microRNA 185. Mouse models of 22q11.2DS have demonstrated alterations in brain microRNA biogenesis, and that DGCR8 haploinsufficiency may contribute to these alterations, e.g., via down-regulation of a specific microRNA subset. miR-185 was the top-scoring down-regulated microRNA in both the prefrontal cortex and the hippocampus, brain areas which are the key foci of schizophrenia research. This reduction in miR-185 expression contributed to dendritic and spine development deficits in hippocampal neurons. In addition, miR-185 has two validated targets (RhoA, Cdc42), both of which have been associated with altered expression levels in schizophrenia. These combined data support the involvement of miR-185 and its down-stream pathways in schizophrenia. This review summarizes evidence implicating microRNA-mediated dysregulation in schizophrenia in both 22q11.2DS-related and idiopathic cases.

Developmental and activity-dependent miRNA expression profiling in primary hippocampal neuron cultures

MicroRNAs (miRNAs) are evolutionarily conserved non-coding RNAs of ∼22 nucleotides that regulate gene expression at the level of translation and play vital roles in hippocampal neuron development, function and plasticity. Here, we performed a systematic and in-depth analysis of miRNA expression profiles in cultured hippocampal neurons during development and after induction of neuronal activity. MiRNA profiling of primary hippocampal cultures was carried out using locked nucleic-acid-based miRNA arrays. The expression of 264 different miRNAs was tested in young neurons, at various developmental stages (stage 2-4) and in mature fully differentiated neurons (stage 5) following the induction of neuronal activity using chemical stimulation protocols. We identified 210 miRNAs in mature hippocampal neurons; the expression of most neuronal miRNAs is low at early stages of development and steadily increases during neuronal differentiation. We found a specific subset of 14 miRNAs with reduced expression at stage 3 and showed that sustained expression of these miRNAs stimulates axonal outgrowth. Expression profiling following induction of neuronal activity demonstrates that 51 miRNAs, including miR-134, miR-146, miR-181, miR-185, miR-191 and miR-200a show altered patterns of expression after NMDA receptor-dependent plasticity, and 31 miRNAs, including miR-107, miR-134, miR-470 and miR-546 were upregulated by homeostatic plasticity protocols. Our results indicate that specific miRNA expression profiles correlate with changes in neuronal development and neuronal activity. Identification and characterization of miRNA targets may further elucidate translational control mechanisms involved in hippocampal development, differentiation and activity-depended processes.

Blood microRNA changes in depressed patients during antidepressant treatment

MicroRNAs (miRNAs) are potent modulators of protein expression that play key roles in brain pathways regulating neurogenesis and synaptic plasticity. These small RNAs may be critical for the pathophysiology of mental disorders and may influence the effectiveness of psychotropic drugs. To investigate the possible involvement of miRNAs in the mechanism of action of antidepressants (AD), we conducted a whole-miRNome quantitative analysis with qRT-PCR of the changes in the blood of 10 depressed subjects after 12 weeks of treatment with escitalopram. Thirty miRNAs were differentially expressed after the AD treatment: 28 miRNAs were up-regulated, and 2 miRNAs were strongly down-regulated. miRNA target gene prediction and functional annotation analysis showed that there was a significant enrichment in several pathways associated with neuronal brain function (such as neuroactive ligand-receptor interaction, axon guidance, long-term potentiation and depression), supporting the hypothesis that the differentially regulated miRNAs may be involved in the AD mechanism.

MicroRNAs and intellectual disability (ID) in Down syndrome, X-linked ID, and Fragile X syndrome

Intellectual disability (ID) is one of the many features manifested in various genetic syndromes leading to deficits in cognitive function among affected individuals. ID is a feature affected by polygenes and multiple environmental factors. It leads to a broad spectrum of affected clinical and behavioral characteristics among patients. Until now, the causative mechanism of ID is unknown and the progression of the condition is poorly understood. Advancement in technology and research had identified various genetic abnormalities and defects as the potential cause of ID. However, the link between these abnormalities with ID is remained inconclusive and the roles of many newly discovered genetic components such as non-coding RNAs have not been thoroughly investigated. In this review, we aim to consolidate and assimilate the latest development and findings on a class of small non-coding RNAs known as microRNAs (miRNAs) involvement in ID development and progression with special focus on Down syndrome (DS) and X-linked ID (XLID) [including Fragile X syndrome (FXS)].

Incorporating Information of microRNAs into Pathway Analysis in a Genome-Wide Association Study of Bipolar Disorder

MicroRNAs (miRNAs) are known to be important post-transcriptional regulators that are involved in the etiology of complex psychiatric traits. The present study aimed to incorporate miRNAs information into pathway analysis using a genome-wide association dataset to identify relevant biological pathways for bipolar disorder (BPD). We selected psychiatric- and neurological-associated miRNAs (N = 157) from PhenomiR database. The miRNA target genes (miTG) predictions were obtained from microRNA.org. Canonical pathways (N = 4,051) were downloaded from the Molecule Signature Database. We employed a novel weighting scheme for miTGs in pathway analysis using methods of gene set enrichment analysis and sum-statistic. Under four statistical scenarios, 38 significantly enriched pathways (P-value < 0.01 after multiple testing correction) were identified for the risk of developing BPD, including pathways of ion channels associated (e.g., gated channel activity, ion transmembrane transporter activity, and ion channel activity) and nervous related biological processes (e.g., nervous system development, cytoskeleton, and neuroactive ligand receptor interaction). Among them, 19 were identified only when the weighting scheme was applied. Many miRNA-targeted genes were functionally related to ion channels, collagen, and axonal growth and guidance that have been suggested to be associated with BPD previously. Some of these genes are linked to the regulation of miRNA machinery in the literature. Our findings provide support for the potential involvement of miRNAs in the psychopathology of BPD. Further investigations to elucidate the functions and mechanisms of identified candidate pathways are needed.

Impact of a microRNA MIR137 susceptibility variant on brain function in people at high genetic risk of schizophrenia or bipolar disorder

A recent 'mega-analysis' combining genome-wide association study data from over 40,000 individuals identified novel genetic loci associated with schizophrenia (SCZ) at genome-wide significance level. The strongest finding was a locus within an intron of a putative primary transcript for microRNA MIR137. In the current study, we examine the impact of variation at this locus (rs1625579, G/T; where T is the common and presumed risk allele) on brain activation during a sentence completion task that differentiates individuals with SCZ, bipolar disorder (BD), and their relatives from controls. We examined three groups of individuals performing a sentence completion paradigm: (i) individuals at high genetic risk of SCZ (n=44), (ii) individuals at high genetic risk of BD (n=90), and (iii) healthy controls (n=81) in order to test the hypothesis that genotype at rs1625579 would influence brain activation. Genotype groups were assigned as 'RISK-' for GT and GG individuals, and 'RISK+' for TT homozygotes. The main effect of genotype was significantly greater activation in the RISK- individuals in the posterior right medial frontal gyrus, BA 6. There was also a significant genotype(*)group interaction in the left amygdala and left pre/postcentral gyrus. This was due to differences between the controls (where individuals with the RISK- genotype showed greater activation than RISK+ subjects) and the SCZ high-risk group, where the opposite genotype effect was seen. These results suggest that the newly identified SCZ locus may influence brain activation in a manner that is partly dependent on the presence of existing genetic susceptibility for SCZ.

MicroRNAs in learning, memory, and neurological diseases

MicroRNAs (miRNAs) represent a class of small regulatory noncoding RNAs ∼22 bp in length that mediate post-transcriptional silencing of gene expression via the recognition of specific sequences in target messenger (m)RNAs. The current body of literature suggests that miRNAs are fine-tuning regulators of gene expression profiles in a wide range of biological processes, from development to cancer. Many miRNAs are highly expressed in the adult nervous system in a spatially and temporally controlled manner in normal physiology, as well as in certain pathological conditions. These findings emphasize that gene regulation networks based on miRNA activities may be particularly important to brain function, and that perturbation of these networks may result in abnormal brain function. Indeed, miRNAs have been implicated in various aspects of dendrite remodeling and synaptic plasticity, as well as in experience-dependent adaptive changes of neural circuits in the postnatal developmental and adult brain. Recent advances in methods of next-generation sequencing, such as RNA-seq, offer the means to quantitatively evaluate the functions of miRNAs in a genome-wide manner in large cohorts of samples. These new technologies have already yielded valuable information and are expanding our understanding of miRNA-based mechanisms in higher-order brain processing, including learning and memory and cognition, as well as in neuropsychiatric disorders.