Altered brain microRNA biogenesis contributes to phenotypic deficits in a 22q11-deletion mouse model

MicroRNA-338 modulates cortical neuronal placement and polarity

The precise spatial and temporal regulation of gene expression orchestrates the many intricate processes during brain development. In the present study we examined the role of the brain-enriched microRNA-338 (miR-338) during mouse cortical development. Reduction of miR-338 levels in the developing mouse cortex, using a sequence-specific miR-sponge, resulted in a loss of neuronal polarity in the cortical plate and significantly reduced the number of neurons within this cortical layer. Conversely, miR-338 overexpression in developing mouse cortex increased the number of neurons, which exhibited a multipolar morphology. All together, our results raise the possibility for a direct role for this non-coding RNA, which was recently associated with schizophrenia, in the regulation of cortical neuronal polarity and layer placement.

Deletion Extents Are Not the Cause of Clinical Variability in 22q11.2 Deletion Syndrome: Does the Interaction between DGCR8 and miRNA-CNVs Play a Major Role?

In humans, the most common genomic disorder is the hemizygous deletion of the chromosome 22q11.2 region, that results in the “22q11.2 deletion syndrome” (22q11.2DS). A peculiarity of 22q11.2DS is its great phenotypic variability that makes this pathology a classic example of a syndrome with variable expressivity and incomplete penetrance. The reasons for this variability have not been elucidated yet, and the molecular substrates underlying the different clinical features of 22q11.2DS are still debated. A cohort of 21 patients has been analyzed by array CGH in order to detect some of the genetic differences that may influence this variability. Two aspects have been investigated: (1) the precise localization of the deletion breakpoints within the low copy repeats (LCRs), (2) the additional Copy Number Variations (CNVs) elsewhere in the genome, by analyzing their gene content. Both protein-coding genes and miRNAs were considered, in order to discover possible epistatic interactions between genes of the 22q11.2 region and the rest of the genome. Eighteen out of twenty-one patients had a deletion of ~3 Mb mediated by LCR22-A and D, whereas 3/21 had a smaller deletion. The breakpoints within the LCR22-A and D do not have a major role in the phenotypic variability since they are rather clustered and the small differences concern genes that are not directly related to clinical signs of 22q11.2DS. A detailed analysis of the gene content of 22q11.2 deleted region indicates that this syndrome could be a bioenergetic disorder or consequence of an altered post-transcriptional gene regulation, due to the presence of DGCR8, a major player of the microRNA (miRNA) biogenesis. Only four genes with mitochondrial function are harbored in the additional CNVs, whereas 11 miRNA, all related to biological pathways present in the 22q11.2DS, have been detected in 19/21 patients. CNVs and miRNAs are new entities that have changed the order of complexity at the level of gene expression and regulation, thus CNV-miRNAs (miRNA harbored in the CNVs) are potential functional variants that should be considered high priority candidate variants in genotype-phenotype association studies. Deletion of DGCR8, the main actor in miRNA biogenesis, amplifies this variability. To our knowledge, this is the first report that focus on the miRNA-CNVs in 22q11.2DS, with the aim of trying to better understand their role in the variable expressivity and incomplete penetrance.

Associations between neurodevelopmental genes, neuroanatomy, and ultra high risk symptoms of psychosis in 22q11.2 deletion syndrome

22q11.2 deletion syndrome is a neurogenetic disorder resulting in the deletion of over 40 genes. Up to 40% of individuals with 22q11.2DS develop schizophrenia, though little is known about the underlying mechanisms. We hypothesized that allelic variation in functional polymorphisms in seven genes unique to the deleted region would affect lobar brain volumes, which would predict risk for psychosis in youth with 22q11.2DS. Participants included 56 individuals (30 males) with 22q11.2DS. Anatomic MR images were collected and processed using Freesurfer. Participants were genotyped for 10 SNPs in the COMT, DGCR8, GNB1L, PIK4CA, PRODH, RTN4R, and ZDHHC8 genes. All subjects were assessed for ultra high risk symptoms of psychosis. Allelic variation of the rs701428 SNP of RTN4R was significantly associated with volumetric differences in gray matter of the lingual gyrus and cuneus of the occipital lobe. Moreover, occipital gray matter volumes were robustly associated with ultra high risk symptoms of psychosis in the presence of the G allele of rs701428. Our results suggest that RTN4R, a relatively under-studied gene at the 22q11 locus, constitutes a susceptibility gene for psychosis in individuals with this syndrome through its alteration of the architecture of the brain. © 2017 Wiley Periodicals, Inc.

Optimized CLARITY technique detects reduced parvalbumin density in a genetic model of schizophrenia

BACKGROUND

Novel tissue clearing technologies have, for the first time, made it possible to study intact tissue samples. This approach provides a tool for further clarifying findings from animal models of schizophrenia by studying parvalbumin-positive (PV+) interneuron density from a 3D perspective.

NEW METHOD

This study has developed an optimised CLARITY protocol, including an improved electrophoretic tissue clearing (ETC) chamber, an evaluation of antibody diffusion into cleared tissue slices, and a computational method for detecting PV+ interneurons in 3D.

RESULTS

A reduced PV+ interneuron density was found in both prelimbic and motor cortex regions of the Df(h15q13)/+ mice, while no changes were observed in the Df(h22q11)/+ mice.

COMPARISON WITH EXISTING METHOD

The developed ETC chamber enables tissue clearing of variable tissue sizes while minimizing the resistance. It was found that a high concentration of primary and secondary antibodies were necessary for sufficient antibody staining of PV+ interneurons. Additionally, the developed computational method showed improved detection rates of interneurons compared to non-processed image stacks.

CONCLUSION

Our optimization of the CLARITY technology and automated 3D counting of cells were found to be useful for quantification of PV+ interneuron density. The results may provide insight into understanding the pathophysiology underlying the phenotype observed in Df(h15q13)/+ mice.

System-based proteomic and metabonomic analysis of the Df(16)A+/- mouse identifies potential miR-185 targets and molecular pathway alterations

Deletions on chromosome 22q11.2 are a strong genetic risk factor for development of schizophrenia and cognitive dysfunction. We employed shotgun liquid chromatography-mass spectrometry (LC-MS) proteomic and metabonomic profiling approaches on prefrontal cortex (PFC) and hippocampal (HPC) tissue from Df(16)A^+/- mice, a model of the 22q11.2 deletion syndrome. Proteomic results were compared with previous transcriptomic profiling studies of the same brain regions. The aim was to investigate how the combined effect of the 22q11.2 deletion and the corresponding miRNA dysregulation affects the cell biology at the systems level. The proteomic brain profiling analysis revealed PFC and HPC changes in various molecular pathways associated with chromatin remodelling and RNA transcription, indicative of an epigenetic component of the 22q11.2DS. Further, alterations in glycolysis/gluconeogenesis, mitochondrial function and lipid biosynthesis were identified. Metabonomic profiling substantiated the proteomic findings by identifying changes in 22q11.2 deletion syndrome (22q11.2DS)-related pathways, such as changes in ceramide phosphoethanolamines, sphingomyelin, carnitines, tyrosine derivates and panthothenic acid. The proteomic findings were confirmed using selected reaction monitoring mass spectrometry, validating decreased levels of several proteins encoded on 22q11.2, increased levels of the computationally predicted putative miR-185 targets UDP-N-acetylglucosamine-peptide N-acetylglucosaminyltransferase 110 kDa subunit (OGT1) and kinesin heavy chain isoform 5A and alterations in the non-miR-185 targets serine/threonine-protein phosphatase 2B catalytic subunit gamma isoform, neurofilament light chain and vesicular glutamate transporter 1. Furthermore, alterations in the proteins associated with mammalian target of rapamycin signalling were detected in the PFC and with glutamatergic signalling in the hippocampus. Based on the proteomic and metabonomic findings, we were able to develop a schematic model summarizing the most prominent molecular network findings in the Df(16)A^+/- mouse. Interestingly, the implicated pathways can be linked to one of the most consistent and strongest proteomic candidates, (OGT1), which is a predicted miR-185 target. Our results provide novel insights into system-biological mechanisms associated with the 22q11DS, which may be linked to cognitive dysfunction and an increased risk to develop schizophrenia. Further investigation of these pathways could help to identify novel drug targets for the treatment of schizophrenia.

Using hiPSCs to model neuropsychiatric copy number variations (CNVs) has potential to reveal underlying disease mechanisms

Schizophrenia is a neuropsychological disorder with a strong heritable component; genetic risk for schizophrenia is conferred by both common variants of relatively small effect and rare variants with high penetrance. Genetically engineered mouse models can recapitulate rare variants, displaying some behavioral defects associated with schizophrenia; however, these mouse models cannot recapitulate the full genetic architecture underlying the disorder. Patient-derived human induced pluripotent stem cells (hiPSCs) present an alternative approach for studying rare variants, in the context of all other risk alleles. Genome editing technologies, such as CRISPR-Cas9, enable the generation of isogenic hiPSC lines with which to examine the functional contribution of single variants within any genetic background. Studies of these rare variants using hiPSCs have the potential to identify commonly disrupted pathways in schizophrenia and allow for the identification of new therapeutic targets. This article is part of a Special Issue entitled SI:StemsCellsinPsychiatry.

Mitochondria in complex psychiatric disorders: Lessons from mouse models of 22q11.2 deletion syndrome: Hemizygous deletion of several mitochondrial genes in the 22q11.2 genomic region can lead to symptoms associated with neuropsychiatric disease

Mitochondrial ATP synthesis, calcium buffering, and trafficking affect neuronal function and survival. Several genes implicated in mitochondrial functions map within the genomic region associated with 22q11.2 deletion syndrome (22q11DS), which is a key genetic cause of neuropsychiatric diseases. Although neuropsychiatric diseases impose a serious health and economic burden, their etiology and pathogenesis remain largely unknown because of the dearth of valid animal models and the challenges in investigating the pathophysiology in neuronal circuits. Mouse models of 22q11DS are becoming valid tools for studying human psychiatric diseases, because they have hemizygous deletions of the genes that are deleted in patients and exhibit neuronal and behavioral abnormalities consistent with neuropsychiatric disease. The deletion of some 22q11DS genes implicated in mitochondrial function leads to abnormal neuronal and synaptic function. Herein, we summarize recent findings on mitochondrial dysfunction in 22q11DS and extend those findings to the larger context of schizophrenia and other neuropsychiatric diseases.

Persistent gating deficit and increased sensitivity to NMDA receptor antagonism after puberty in a new mouse model of the human 22q11.2 microdeletion syndrome: a study in male mice

BACKGROUND

The hemizygous 22q11.2 microdeletion is a common copy number variant in humans. The deletion confers high risk for neurodevelopmental disorders, including autism and schizophrenia. Up to 41% of deletion carriers experience psychotic symptoms.

METHODS

We present a new mouse model (Df(h22q11)/+) of the deletion syndrome (22q11.2DS) and report on, to our knowledge, the most comprehensive study undertaken to date in 22q11.2DS models. The study was conducted in male mice.

RESULTS

We found elevated postpubertal N-methyl-D-aspartate (NMDA) receptor antagonist-induced hyperlocomotion, age-independent prepulse inhibition (PPI) deficits and increased acoustic startle response (ASR). The PPI deficit and increased ASR were resistant to antipsychotic treatment. The PPI deficit was not a consequence of impaired hearing measured by auditory brain stem responses. The Df(h22q11)/+ mice also displayed increased amplitude of loudness-dependent auditory evoked potentials. Prefrontal cortex and dorsal striatal elevations of the dopamine metabolite DOPAC and increased dorsal striatal expression of the AMPA receptor subunit GluR1 was found. The Df(h22q11)/+ mice did not deviate from wild-type mice in a wide range of other behavioural and biochemical assays.

LIMITATIONS

The 22q11.2 microdeletion has incomplete penetrance in humans, and the severity of disease depends on the complete genetic makeup in concert with environmental factors. In order to obtain more marked phenotypes reflecting the severe conditions related to 22q11.2DS it is suggested to expose the Df(h22q11)/+ mice to environmental stressors that may unmask latent psychopathology.

CONCLUSION

The Df(h22q11)/+ model will be a valuable tool for increasing our understanding of the etiology of schizophrenia and other psychiatric disorders associated with the 22q11DS.

Replication analyses of four chromosomal deletions with schizophrenia via independent large-scale meta-analyses

Recent studies suggest that copy number variations (CNVs) are also involved in the genetic risk of schizophrenia. Using a Cochran-Mantel-Haenszel (CMH) adjusted meta-analysis in 18,497 schizophrenia patients and 25,522 healthy controls from 14 independent samples, we conducted replication analyses of four chromosomal deletions at 1q21.1, 15q11.2, 15q13.3, and 22q11.2 Loci for their associations with schizophrenia. Only CNVs larger than 100 kb that had >50% reciprocal overlap with the canonical deletion chromosomal regions were considered. We successfully replicate the significant associations at 1q21.1 (P value = 3.101 × 10^-7 , odds ratio (OR) = 6.91), 15q13.3 (P value = 4.771 × 10^-4 , OR = 7.83), and 22q11.2 (P value = 1.725 × 10^-5 , OR = 9.21) deletions, although the effect sizes are relatively smaller than the original studies, which is not unexpected and adds further support for the involvement of these genetic lesions in the risk of schizophrenia. The 15q11.2 deletion, which shows higher frequency in healthy populations than the other three CNV loci, though is not significant in the present meta-analysis (P value = 0.1545, OR = 1.42), it shows the same direction of effects with previous studies. These results further confirm the genetic connections between rare CNVs and schizophrenia, and suggest the importance of adequate sample size in replication analyses for such risk loci with low frequency in general populations. © 2016 Wiley Periodicals, Inc.

Thalamic miR-338-3p mediates auditory thalamocortical disruption and its late onset in models of 22q11.2 microdeletion

Although 22q11.2 deletion syndrome (22q11DS) is associated with early-life behavioral abnormalities, affected individuals are also at high risk for the development of schizophrenia symptoms, including psychosis, later in life. Auditory thalamocortical (TC) projections recently emerged as a neural circuit that is specifically disrupted in mouse models of 22q11DS (hereafter referred to as 22q11DS mice), in which haploinsufficiency of the microRNA (miRNA)-processing-factor-encoding gene Dgcr8 results in the elevation of the dopamine receptor Drd2 in the auditory thalamus, an abnormal sensitivity of thalamocortical projections to antipsychotics, and an abnormal acoustic-startle response. Here we show that these auditory TC phenotypes have a delayed onset in 22q11DS mice and are associated with an age-dependent reduction of miR-338-3p, a miRNA that targets Drd2 and is enriched in the thalamus of both humans and mice. Replenishing depleted miR-338-3p in mature 22q11DS mice rescued the TC abnormalities, and deletion of Mir338 (which encodes miR-338-3p) or reduction of miR-338-3p expression mimicked the TC and behavioral deficits and eliminated the age dependence of these deficits. Therefore, miR-338-3p depletion is necessary and sufficient to disrupt auditory TC signaling in 22q11DS mice, and it may mediate the pathogenic mechanism of 22q11DS-related psychosis and control its late onset.

Integrative transcriptome network analysis of iPSC-derived neurons from schizophrenia and schizoaffective disorder patients with 22q11.2 deletion

BACKGROUND

Individuals with 22q11.2 Deletion Syndrome (22q11.2 DS) are a specific high-risk group for developing schizophrenia (SZ), schizoaffective disorder (SAD) and autism spectrum disorders (ASD). Several genes in the deleted region have been implicated in the development of SZ, e.g., PRODH and DGCR8. However, the mechanistic connection between these genes and the neuropsychiatric phenotype remains unclear. To elucidate the molecular consequences of 22q11.2 deletion in early neural development, we carried out RNA-seq analysis to investigate gene expression in early differentiating human neurons derived from induced pluripotent stem cells (iPSCs) of 22q11.2 DS SZ and SAD patients.

METHODS

Eight cases (ten iPSC-neuron samples in total including duplicate clones) and seven controls (nine in total including duplicate clones) were subjected to RNA sequencing. Using a systems level analysis, differentially expressed genes/gene-modules and pathway of interests were identified. Lastly, we related our findings from in vitro neuronal cultures to brain development by mapping differentially expressed genes to BrainSpan transcriptomes.

RESULTS

We observed ~2-fold reduction in expression of almost all genes in the 22q11.2 region in SZ (37 genes reached p-value < 0.05, 36 of which reached a false discovery rate < 0.05). Outside of the deleted region, 745 genes showed significant differences in expression between SZ and control neurons (p < 0.05). Function enrichment and network analysis of the differentially expressed genes uncovered converging evidence on abnormal expression in key functional pathways, such as apoptosis, cell cycle and survival, and MAPK signaling in the SZ and SAD samples. By leveraging transcriptome profiles of normal human brain tissues across human development into adulthood, we showed that the differentially expressed genes converge on a sub-network mediated by CDC45 and the cell cycle, which would be disrupted by the 22q11.2 deletion during embryonic brain development, and another sub-network modulated by PRODH, which could contribute to disruption of brain function during adolescence.

CONCLUSIONS

This study has provided evidence for disruption of potential molecular events in SZ patient with 22q11.2 deletion and related our findings from in vitro neuronal cultures to functional perturbations that can occur during brain development in SZ.

Analysis of induced pluripotent stem cells carrying 22q11.2 deletion

Given the complexity and heterogeneity of the genomic architecture underlying schizophrenia, molecular analyses of these patients with defined and large effect-size genomic defects could provide valuable clues. We established human-induced pluripotent stem cells from two schizophrenia patients with the 22q11.2 deletion (two cell lines from each subject, total of four cell lines) and three controls (total of four cell lines). Neurosphere size, neural differentiation efficiency, neurite outgrowth, cellular migration and the neurogenic-to-gliogenic competence ratio were significantly reduced in patient-derived cells. As an underlying mechanism, we focused on the role of DGCR8, a key gene for microRNA (miRNA) processing and mapped in the deleted region. In mice, Dgcr8 hetero-knockout is known to show a similar phenotype of reduced neurosphere size (Ouchi et al., 2013). The miRNA profiling detected reduced expression levels of miRNAs belonging to miR-17/92 cluster and miR-106a/b in the patient-derived neurospheres. Those miRNAs are reported to target p38α, and conformingly the levels of p38α were upregulated in the patient-derived cells. p38α is known to drive gliogenic differentiation. The inhibition of p38 activity by SB203580 in patient-derived neurospheres partially restored neurogenic competence. Furthermore, we detected elevated expression of GFAP, a gliogenic (astrocyte) marker, in postmortem brains from schizophrenia patients without the 22q11.2 deletion, whereas inflammation markers (IL1B and IL6) remained unchanged. In contrast, a neuronal marker, MAP2 expressions were decreased in schizophrenia brains. These results suggest that a dysregulated balance of neurogenic-to-gliogenic competence may underlie neurodevelopmental disorders such as schizophrenia.

Using model systems to understand errant plasticity mechanisms in psychiatric disorders

In vivo model systems are a critical tool for gaining insight into the pathology underlying psychiatric disorders. Although modern functional imaging tools allow study of brain correlates of behavior in clinical groups and genome-wide association studies are beginning to uncover the complex genetic architecture of psychiatric disorders, there is less understanding of pathology at intervening levels of organization. Several psychiatric disorders derive from pathological neural plasticity, and studying the mechanisms that underlie these processes, including reinforcement learning and spike-timing-dependent plasticity, requires the use of animals. It will be particularly important to understand how individual differences in plasticity mechanisms at a cellular level confer resilience on some but lead to disease in others.

Multimarker analysis suggests the involvement of BDNF signaling and microRNA biosynthesis in suicidal behavior

Despite moderate heritability estimates the genetics of suicidal behavior remains unclear, genome-wide association and candidate gene studies focusing on single nucleotide associations reported inconsistent findings. Our study explored biologically informed, multimarker candidate gene associations with suicidal behavior in mood disorders. We analyzed the GAIN Whole Genome Association Study of Bipolar Disorder version 3 (n = 999, suicidal n = 358) and the GAIN Major Depression: Stage 1 Genomewide Association in Population-Based Samples (n = 1,753, suicidal n = 245) datasets. Suicidal behavior was defined as severe suicidal ideation or attempt. Candidate genes were selected based on literature search (Geneset1, n = 35), gene expression data of microRNA genes, (Geneset2, n = 68) and their target genes (Geneset3, n = 11,259). Quality control, dosage analyses were carried out with PLINK. Gene-based associations of Geneset1 were analyzed with KGG. Polygenic profile scores of suicidal behavior were computed in the major depression dataset both with PRSice and LDpred and validated in the bipolar disorder data. Several nominally significant gene-based associations were detected, but only DICER1 associated with suicidal behavior in both samples, while only the associations of NTRK2 in the depression sample reached family wise and experiment wise significance. Polygenic profile scores negatively predicted suicidal behavior in the bipolar sample for only Geneset2, with the strongest prediction by PRSice at Pt  < 0.03 (Nagelkerke R(2)  = 0.01, P < 0.007). Gene-based association results confirmed the potential involvement of the BDNF-NTRK2-CREB pathway in the pathogenesis of suicide and the cross-disorder association of DICER1. Polygenic risk prediction of the selected miRNA genes indicates that the miRNA system may play a mediating role, but with considerable pleiotropy. © 2016 Wiley Periodicals, Inc.

Adult Neurogenesis and Psychiatric Disorders

Psychiatric disorders continue to be among the most challenging disorders to diagnose and treat because there is no single genetic or anatomical locus that is causative for the disease. Current treatments are often blunt tools used to ameliorate the most severe symptoms, at the risk of disrupting functional neural systems. There is a critical need to develop new therapeutic strategies that can target circumscribed functional or anatomical domains of pathology. Adult hippocampal neurogenesis may be one such domain. Here, we review the evidence suggesting that adult hippocampal neurogenesis plays a role in emotional regulation and forms of learning and memory that include temporal and spatial memory encoding and context discrimination, and that its dysregulation is associated with psychiatric disorders, such as affective disorders, schizophrenia, and drug addiction. Further, adult neurogenesis has proven to be an effective model to investigate basic processes of neuronal development and converging evidence suggests that aberrant neural development may be an etiological factor, even in late-onset diseases. Constitutive neurogenesis in the hippocampus of the mature brain reflects large-scale plasticity unique to this region and could be a potential hub for modulation of a subset of cognitive and affective behaviors that are affected by multiple psychiatric disorders.

Assessing the Cognitive Translational Potential of a Mouse Model of the 22q11.2 Microdeletion Syndrome

A chromosomal microdeletion at the 22q11.2 locus is associated with extensive cognitive impairments, schizophrenia and other psychopathology in humans. Previous reports indicate that mouse models of the 22q11.2 microdeletion syndrome (22q11.2DS) may model the genetic basis of cognitive deficits relevant for neuropsychiatric disorders such as schizophrenia. To assess the models usefulness for drug discovery, a novel mouse (Df(h22q11)/+) was assessed in an extensive battery of cognitive assays by partners within the NEWMEDS collaboration (Innovative Medicines Initiative Grant Agreement No. 115008). This battery included classic and touchscreen-based paradigms with recognized sensitivity and multiple attempts at reproducing previously published findings in 22q11.2DS mouse models. This work represents one of the most comprehensive reports of cognitive functioning in a transgenic animal model. In accordance with previous reports, there were non-significant trends or marginal impairment in some tasks. However, the Df(h22q11)/+ mouse did not show comprehensive deficits; no robust impairment was observed following more than 17 experiments and 14 behavioral paradigms. Thus - within the current protocols - the 22q11.2DS mouse model fails to mimic the cognitive alterations observed in human 22q11.2 deletion carriers. We suggest that the 22q11.2DS model may induce liability for cognitive dysfunction with additional "hits" being required for phenotypic expression.

miRNAs in NMDA receptor-dependent synaptic plasticity and psychiatric disorders

The identification and functional delineation of miRNAs (a class of small non-coding RNAs) have added a new layer of complexity to our understanding of the molecular mechanisms underlying synaptic plasticity. Genome-wide association studies in conjunction with investigations in cellular and animal models, moreover, provide evidence that miRNAs are involved in psychiatric disorders. In the present review, we examine the current knowledge about the roles played by miRNAs in NMDA (N-methyl-D-aspartate) receptor-dependent synaptic plasticity and psychiatric disorders.

MicroRNAs: Key Regulators in the Central Nervous System and Their Implication in Neurological Diseases

MicroRNAs (miRNAs) are a class of small, well-conserved noncoding RNAs that regulate gene expression post-transcriptionally. They have been demonstrated to regulate a lot of biological pathways and cellular functions. Many miRNAs are dynamically regulated during central nervous system (CNS) development and are spatially expressed in adult brain indicating their essential roles in neural development and function. In addition, accumulating evidence strongly suggests that dysfunction of miRNAs contributes to neurological diseases. These observations, together with their gene regulation property, implicated miRNAs to be the key regulators in the complex genetic network of the CNS. In this review, we first focus on the ways through which miRNAs exert the regulatory function and how miRNAs are regulated in the CNS. We then summarize recent findings that highlight the versatile roles of miRNAs in normal CNS physiology and their association with several types of neurological diseases. Subsequently we discuss the limitations of miRNAs research based on current studies as well as the potential therapeutic applications and challenges of miRNAs in neurological disorders. We endeavor to provide an updated description of the regulatory roles of miRNAs in normal CNS functions and pathogenesis of neurological diseases.

Age-Dependent Specific Changes in Area CA2 of the Hippocampus and Social Memory Deficit in a Mouse Model of the 22q11.2 Deletion Syndrome

Several neuropsychiatric disorders are associated with cognitive and social dysfunction. Postmortem studies of patients with schizophrenia have revealed specific changes in area CA2, a long-overlooked region of the hippocampus recently found to be critical for social memory formation. To examine how area CA2 is altered in psychiatric illness, we used the Df(16)A(+/-) mouse model of the 22q11.2 microdeletion, a genetic risk factor for developing several neuropsychiatric disorders, including schizophrenia. We report several age-dependent CA2 alterations: a decrease in the density of parvalbumin-expressing interneurons, a reduction in the amount of feedforward inhibition, and a change in CA2 pyramidal-neuron intrinsic properties. Furthermore, we found that area CA2 is less plastic in Df(16)A(+/-) mice, making it nearly impossible to evoke action potential firing in CA2 pyramidal neurons. Finally, we show that Df(16)A(+/-) mice display impaired social cognition, providing a potential mechanism and a neural substrate for this impairment in psychiatric disorders.

The Drosophila Dicer-1 Partner Loquacious Enhances miRNA Processing from Hairpins with Unstable Structures at the Dicing Site

In Drosophila, Dicer-1 binds Loquacious-PB (Loqs-PB) as its major co-factor. Previous analyses indicated that loqs mutants only partially impede miRNA processing, but the activity of minor isoforms or maternally deposited Loqs was not eliminated in these studies. We addressed this by generating a cell line from loqs-null embryos and found that only ∼40% of miRNAs showed clear Loqs dependence. Genome-wide comparison of the hairpin structure and Loqs dependence suggested that Loqs substrates are influenced by base-pairing status at the dicing site. Artificial alteration of base-pairing stability at this position in model miRNA hairpins resulted in predicted changes in Loqs dependence, providing evidence for this hypothesis. Finally, we found that evolutionarily young miRNA genes tended to be Loqs dependent. We propose that Loqs may have roles in assisting the de novo emergence of miRNA genes by facilitating dicing of suboptimal hairpin substrates.

Impairments in dendrite morphogenesis as etiology for neurodevelopmental disorders and implications for therapeutic treatments

Dendrite morphology is pivotal for neural circuitry functioning. While the causative relationship between small-scale dendrite morphological abnormalities (shape, density of dendritic spines) and neurodevelopmental disorders is well established, such relationship remains elusive for larger-scale dendrite morphological impairments (size, shape, branching pattern of dendritic trees). Here, we summarize published data on dendrite morphological irregularities in human patients and animal models for neurodevelopmental disorders, with focus on autism and schizophrenia. We next discuss high-risk genes for these disorders and their role in dendrite morphogenesis. We finally overview recent developments in therapeutic attempts and we discuss how they relate to dendrite morphology. We find that both autism and schizophrenia are accompanied by dendritic arbor morphological irregularities, and that majority of their high-risk genes regulate dendrite morphogenesis. Thus, we present a compelling argument that, along with smaller-scale morphological impairments in dendrites (spines and synapse), irregularities in larger-scale dendrite morphology (arbor shape, size) may be an important part of neurodevelopmental disorders' etiology. We suggest that this should not be ignored when developing future therapeutic treatments.

Molecular genetic models related to schizophrenia and psychotic illness: heuristics and challenges

Schizophrenia is a heritable disorder that may involve several common genes of small effect and/or rare copy number variation, with phenotypic heterogeneity across patients. Furthermore, any boundaries vis-à-vis other psychotic disorders are far from clear. Consequently, identification of informative animal models for this disorder, which typically relate to pharmacological and putative pathophysiological processes of uncertain validity, faces considerable challenges. In juxtaposition, the majority of mutant models for schizophrenia relate to the functional roles of a diverse set of genes associated with risk for the disorder or with such putative pathophysiological processes. This chapter seeks to outline the evidence from phenotypic studies in mutant models related to schizophrenia. These have commonly assessed the degree to which mutation of a schizophrenia-related gene is associated with the expression of several aspects of the schizophrenia phenotype or more circumscribed, schizophrenia-related endophenotypes; typically, they place specific emphasis on positive and negative symptoms and cognitive deficits, and extend to structural and other pathological features. We first consider the primary technological approaches to the generation of such mutants, to include their relative merits and demerits, and then highlight the diverse phenotypic approaches that have been developed for their assessment. The chapter then considers the application of mutant phenotypes to study pathobiological and pharmacological mechanisms thought to be relevant for schizophrenia, particularly in terms of dopaminergic and glutamatergic dysfunction, and to an increasing range of candidate susceptibility genes and copy number variants. Finally, we discuss several pertinent issues and challenges within the field which relate to both phenotypic evaluation and a growing appreciation of the functional genomics of schizophrenia and the involvement of gene × environment interactions.

Epigenetic Mechanisms in Developmental Alcohol-Induced Neurobehavioral Deficits

Alcohol consumption during pregnancy and its damaging consequences on the developing infant brain are significant public health, social, and economic issues. The major distinctive features of prenatal alcohol exposure in humans are cognitive and behavioral dysfunction due to damage to the central nervous system (CNS), which results in a continuum of disarray that is collectively called fetal alcohol spectrum disorder (FASD). Many rodent models have been developed to understand the mechanisms of and to reproduce the human FASD phenotypes. These animal FASD studies have provided several molecular pathways that are likely responsible for the neurobehavioral abnormalities that are associated with prenatal alcohol exposure of the developing CNS. Recently, many laboratories have identified several immediate, as well as long-lasting, epigenetic modifications of DNA methylation, DNA-associated histone proteins and microRNA (miRNA) biogenesis by using a variety of epigenetic approaches in rodent FASD models. Because DNA methylation patterns, DNA-associated histone protein modifications and miRNA-regulated gene expression are crucial for synaptic plasticity and learning and memory, they can therefore offer an answer to many of the neurobehavioral abnormalities that are found in FASD. In this review, we briefly discuss the current literature of DNA methylation, DNA-associated histone proteins modification and miRNA and review recent developments concerning epigenetic changes in FASD.

Cobalt(III) Protoporphyrin Activates the DGCR8 Protein and Can Compensate microRNA Processing Deficiency

Processing of microRNA primary transcripts (pri-miRNAs) is highly regulated and defects in the processing machinery play a key role in many human diseases. In 22q11.2 deletion syndrome (22q11.2DS), heterozygous deletion of DiGeorge critical region gene 8 (DGCR8) causes a processing deficiency, which contributes to abnormal brain development. The DGCR8 protein is the RNA-binding partner of Drosha RNase, both essential for processing canonical pri-miRNAs. To identify an agent that can compensate reduced DGCR8 expression, we screened for metalloporphyrins that can mimic the natural DGCR8 heme cofactor. We found that Co(III) protoporphyrin IX (PPIX) stably binds DGCR8 and activates it for pri-miRNA processing in vitro and in HeLa cells. Importantly, treating cultured Dgcr8(+/-) mouse neurons with Co(III)PPIX can compensate the pri-miRNA processing defects. Co(III)PPIX is effective at concentrations as low as 0.2 μM and is not degraded by heme degradation enzymes, making it useful as a research tool and a potential therapeutic.

Viral vector-based tools advance knowledge of basal ganglia anatomy and physiology

Viral vectors were originally developed to deliver genes into host cells for therapeutic potential. However, viral vector use in neuroscience research has increased because they enhance interpretation of the anatomy and physiology of brain circuits compared with conventional tract tracing or electrical stimulation techniques. Viral vectors enable neuronal or glial subpopulations to be labeled or stimulated, which can be spatially restricted to a single target nucleus or pathway. Here we review the use of viral vectors to examine the structure and function of motor and limbic basal ganglia (BG) networks in normal and pathological states. We outline the use of viral vectors, particularly lentivirus and adeno-associated virus, in circuit tracing, optogenetic stimulation, and designer drug stimulation experiments. Key studies that have used viral vectors to trace and image pathways and connectivity at gross or ultrastructural levels are reviewed. We explain how optogenetic stimulation and designer drugs used to modulate a distinct pathway and neuronal subpopulation have enhanced our mechanistic understanding of BG function in health and pathophysiology in disease. Finally, we outline how viral vector technology may be applied to neurological and psychiatric conditions to offer new treatments with enhanced outcomes for patients.

MicroRNA-181 promotes synaptogenesis and attenuates axonal outgrowth in cortical neurons

MicroRNAs (miRs) are non-coding gene transcripts abundantly expressed in both the developing and adult mammalian brain. They act as important modulators of complex gene regulatory networks during neuronal development and plasticity. miR-181c is highly abundant in cerebellar cortex and its expression is increased in autism patients as well as in an animal model of autism. To systematically identify putative targets of miR-181c, we repressed this miR in growing cortical neurons and found over 70 differentially expressed target genes using transcriptome profiling. Pathway analysis showed that the miR-181c-modulated genes converge on signaling cascades relevant to neurite and synapse developmental processes. To experimentally examine the significance of these data, we inhibited miR-181c during rat cortical neuronal maturation in vitro; this loss-of miR-181c function resulted in enhanced neurite sprouting and reduced synaptogenesis. Collectively, our findings suggest that miR-181c is a modulator of gene networks associated with cortical neuronal maturation.

Involvement of FMRP in Primary MicroRNA Processing via Enhancing Drosha Translation

Fragile X mental retardation protein (FMRP), associated with fragile X syndrome, is known as an RNA-binding protein to regulate gene expression at post-transcriptional level in the brain. FMRP is also involved in microRNA (miRNA) biogenesis during the process of precursor miRNA (pre-miRNA) into mature miRNA. However, there is no description of the effect of FMRP on primary miRNA (pri-miRNA) processing. Here, we uncover a novel role of FMRP in pri-miRNA processing via controlling Drosha translation. We show that the expression of DROSHA protein, instead of its messenger RNA (mRNA) transcripts, is downregulated in both the hippocampus of Fmr1-knockout mice and the FMRP-knockdown Neuro-2a cells. Overexpression or knockdown FMRP does not alter Drosha mRNA stability. Immunoprecipitation and polysome analyses demonstrate that FMRP binds to the Drosha mRNA and enhances its translation. Additionally, we show that loss of FMRP in Fmr1-deficient mice results in the accumulation of three in six analyzed pri-miRNAs and the reduction of the corresponding pre-miRNAs and mature miRNAs. Thus, our data suggest that FMRP is involved in pri-miRNA processing via enhancing DROSHA expression that may play an important role in fragile X syndrome.

Developmental Inhibition of Gsk3 Rescues Behavioral and Neurophysiological Deficits in a Mouse Model of Schizophrenia Predisposition

While the genetic basis of schizophrenia is increasingly well characterized, novel treatments will require establishing mechanistic relationships between specific risk genes and core phenotypes. Rare, highly penetrant risk genes such as the 22q11.2 microdeletion are promising in this regard. Df(16)A(+/-) mice, which carry a homologous microdeletion, have deficits in hippocampal-prefrontal connectivity that correlate with deficits in spatial working memory. These mice also have deficits in axonal development that are accompanied by dysregulated Gsk3β signaling and can be rescued by Gsk3 antagonists. Here we show that developmental inhibition of Gsk3 rescues deficits in hippocampal-prefrontal connectivity, task-related neural activity, and spatial working memory behavior in Df(16)A(+/-) mice. Taken together, these results provide mechanistic insight into how the microdeletion results in cognitive deficits, and they suggest possible targets for novel therapies.

Hippocampal-Prefrontal Interactions in Cognition, Behavior and Psychiatric Disease

The hippocampus and prefrontal cortex (PFC) have long been known to play a central role in various behavioral and cognitive functions. More recently, electrophysiological and functional imaging studies have begun to examine how interactions between the two structures contribute to behavior during various tasks. At the same time, it has become clear that hippocampal-prefrontal interactions are disrupted in psychiatric disease and may contribute to their pathophysiology. These impairments have most frequently been observed in schizophrenia, a disease that has long been associated with hippocampal and prefrontal dysfunction. Studies in animal models of the illness have also begun to relate disruptions in hippocampal-prefrontal interactions to the various risk factors and pathophysiological mechanisms of the illness. The goal of this review is to summarize what is known about the role of hippocampal-prefrontal interactions in normal brain function and compare how these interactions are disrupted in schizophrenia patients and animal models of the disease. Outstanding questions for future research on the role of hippocampal-prefrontal interactions in both healthy brain function and disease states are also discussed.

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.

Microendophenotypes of psychiatric disorders: phenotypes of psychiatric disorders at the level of molecular dynamics, synapses, neurons, and neural circuits

Psychiatric disorders are caused not only by genetic factors but also by complicated factors such as environmental ones. Moreover, environmental factors are rarely quantitated as biological and biochemical indicators, making it extremely difficult to understand the pathological conditions of psychiatric disorders as well as their underlying pathogenic mechanisms. Additionally, we have actually no other option but to perform biological studies on postmortem human brains that display features of psychiatric disorders, thereby resulting in a lack of experimental materials to characterize the basic biology of these disorders. From these backgrounds, animal, tissue, or cell models that can be used in basic research are indispensable to understand biologically the pathogenic mechanisms of psychiatric disorders. In this review, we discuss the importance of microendophenotypes of psychiatric disorders, i.e., phenotypes at the level of molecular dynamics, neurons, synapses, and neural circuits, as targets of basic research on these disorders.

Common mechanisms of excitatory and inhibitory imbalance in schizophrenia and autism spectrum disorders

Autism Spectrum Disorders (ASD) and Schizophrenia (SCZ) are cognitive disorders with complex genetic architectures but overlapping behavioral phenotypes, which suggests common pathway perturbations. Multiple lines of evidence implicate imbalances in excitatory and inhibitory activity (E/I imbalance) as a shared pathophysiological mechanism. Thus, understanding the molecular underpinnings of E/I imbalance may provide essential insight into the etiology of these disorders and may uncover novel targets for future drug discovery. Here, we review key genetic, physiological, neuropathological, functional, and pathway studies that suggest alterations to excitatory/inhibitory circuits are keys to ASD and SCZ pathogenesis.

Micro-RNAs in cognition and cognitive disorders: Potential for novel biomarkers and therapeutics

Micro-RNAs (miRNAs) are small regulatory non-coding RNAs involved in the regulation of many biological functions. In the brain, they have distinct expression patterns depending on region, cell-type and developmental stage. Their expression profile is altered by neuronal activation in response to behavioral training or chemical/electrical stimulation. The dynamic changes in miRNA level regulate the expression of genes required for cognitive processes such as learning and memory. In addition, in cognitive dysfunctions such as dementias, expression levels of many miRNAs are perturbed, not only in brain areas affected by the pathology, but also in peripheral body fluids such as serum and cerebrospinal fluid. This presents an opportunity to utilize miRNAs as biomarkers for early detection and assessment of cognitive dysfunctions. Further, since miRNAs target many genes and pathways, they may represent key molecular signatures that can help understand the mechanisms of cognitive disorders and the development of potential therapeutic agents.

22q11.2 deletion syndrome

22q11.2 deletion syndrome (22q11.2DS) is the most common chromosomal microdeletion disorder, estimated to result mainly from de novo non-homologous meiotic recombination events occurring in approximately 1 in every 1,000 fetuses. The first description in the English language of the constellation of findings now known to be due to this chromosomal difference was made in the 1960s in children with DiGeorge syndrome, who presented with the clinical triad of immunodeficiency, hypoparathyroidism and congenital heart disease. The syndrome is now known to have a heterogeneous presentation that includes multiple additional congenital anomalies and later-onset conditions, such as palatal, gastrointestinal and renal abnormalities, autoimmune disease, variable cognitive delays, behavioural phenotypes and psychiatric illness - all far extending the original description of DiGeorge syndrome. Management requires a multidisciplinary approach involving paediatrics, general medicine, surgery, psychiatry, psychology, interventional therapies (physical, occupational, speech, language and behavioural) and genetic counselling. Although common, lack of recognition of the condition and/or lack of familiarity with genetic testing methods, together with the wide variability of clinical presentation, delays diagnosis. Early diagnosis, preferably prenatally or neonatally, could improve outcomes, thus stressing the importance of universal screening. Equally important, 22q11.2DS has become a model for understanding rare and frequent congenital anomalies, medical conditions, psychiatric and developmental disorders, and may provide a platform to better understand these disorders while affording opportunities for translational strategies across the lifespan for both patients with 22q11.2DS and those with these associated features in the general population.

Distinctive transcriptome alterations of prefrontal pyramidal neurons in schizophrenia and schizoaffective disorder

Schizophrenia is associated with alterations in working memory that reflect dysfunction of dorsolateral prefrontal cortex (DLPFC) circuitry. Working memory depends on the activity of excitatory pyramidal cells in DLPFC layer 3 and, to a lesser extent, in layer 5. Although many studies have profiled gene expression in DLPFC gray matter in schizophrenia, little is known about cell-type-specific transcript expression in these two populations of pyramidal cells. We hypothesized that interrogating gene expression, specifically in DLPFC layer 3 or 5 pyramidal cells, would reveal new and/or more robust schizophrenia-associated differences that would provide new insights into the nature of pyramidal cell dysfunction in the illness. We also sought to determine the impact of other variables, such as a diagnosis of schizoaffective disorder or medication use at the time of death, on the patterns of gene expression in pyramidal neurons. Individual pyramidal cells in DLPFC layers 3 or 5 were captured by laser microdissection from 36 subjects with schizophrenia or schizoaffective disorder and matched normal comparison subjects. The mRNA from cell collections was subjected to transcriptome profiling by microarray followed by quantitative PCR validation. Expression of genes involved in mitochondrial (MT) or ubiquitin-proteasome system (UPS) functions were markedly downregulated in the patient group (P-values for MT-related and UPS-related pathways were <10(-7) and <10(-5), respectively). MT-related gene alterations were more prominent in layer 3 pyramidal cells, whereas UPS-related gene alterations were more prominent in layer 5 pyramidal cells. Many of these alterations were not present, or found to a lesser degree, in samples of DLPFC gray matter from the same subjects, suggesting that they are pyramidal cell specific. Furthermore, these findings principally reflected alterations in the schizophrenia subjects were not present or present to a lesser degree in the schizoaffective disorder subjects (diagnosis of schizoaffective disorder was the most significant covariate, P<10(-6)) and were not attributable to factors frequently comorbid with schizophrenia. In summary, our findings reveal expression deficits in MT- and UPS-related genes specific to layer 3 and/or layer 5 pyramidal cells in the DLPFC of schizophrenia subjects. These cell type-specific transcriptome signatures are not characteristic of schizoaffective disorder, providing a potential molecular-cellular basis of differences in clinical phenotypes.

MicroRNA-derived network analysis of differentially methylated genes in schizophrenia, implicating GABA receptor B1 [GABBR1] and protein kinase B [AKT1]

BACKGROUND

While hundreds of genes have been implicated already in the etiology of schizophrenia, the exact cause is not known or the disease is considered multigenic in origin. Recent discoveries of new types of RNAs and the gradual elimination of the "junk DNA" hypothesis refocused the attention on the noncoding part of the human genome. Here we re-analyzed a recent dataset of differentially methylated genes from schizophrenic patients and cross-tabulated them with cis regulatory and repetitive elements and microRNAs known to be involved in schizophrenia.

RESULTS

We found that the number of schizophrenia-related (SZ) microRNA targets follows a scale-free distribution with several microRNA hubs and that schizophrenia-related microRNAs with shared targets form a small-world network. The top ten microRNAs with the highest number of SZ gene targets regulate approximately 80 % of all microRNA-regulated genes whereas the top two microRNAs regulate 40-52 % of all such genes. We also found that genes that are regulated by the same microRNAs tend to have more protein-protein interactions than randomly selected schizophrenia genes. This highlights the role microRNAs possibly play in coordinating the abundance of interacting proteins, an important function that has not been sufficiently explored before. The analysis revealed that GABBR1 is regulated by both of the top two microRNAs and acts as a hub by interacting with many schizophrenia-related genes and sharing several types of transcription-binding sites with its interactors. We also found that differentially methylated repetitive elements are significantly more methylated in schizophrenia, pointing out their potential role in the disease.

CONCLUSIONS

We find that GABBR1 has a central importance in schizophrenia, even if no direct cause and effect have been shown for it for the time. In addition to being a hub in microRNA-derived regulatory pathways and protein-protein interactions, its centrality is also supported by the high number of cis regulatory elements and transcription factor-binding sites that regulate its transcription. These findings are in line with several genome-wide association studies that repeatedly find the major histocompatibility region (where GABBR1 is located) to have the highest number of single nucleotide polymorphisms in schizophrenics. Our model also offers an explanation for the downregulation of protein kinase B, another consistent finding in schizophrenic patients. Our observations support the notion that microRNAs fine-tune the amount of proteins acting in the same biological pathways in schizophrenia, giving further support to the emerging theory of competing endogenous RNAs.

Whole-Genome Sequencing Suggests Schizophrenia Risk Mechanisms in Humans with 22q11.2 Deletion Syndrome

Chromosome 22q11.2 microdeletions impart a high but incomplete risk for schizophrenia. Possible mechanisms include genome-wide effects of DGCR8 haploinsufficiency. In a proof-of-principle study to assess the power of this model, we used high-quality, whole-genome sequencing of nine individuals with 22q11.2 deletions and extreme phenotypes (schizophrenia, or no psychotic disorder at age >50 years). The schizophrenia group had a greater burden of rare, damaging variants impacting protein-coding neurofunctional genes, including genes involved in neuron projection (nominal P = 0.02, joint burden of three variant types). Variants in the intact 22q11.2 region were not major contributors. Restricting to genes affected by a DGCR8 mechanism tended to amplify between-group differences. Damaging variants in highly conserved long intergenic noncoding RNA genes also were enriched in the schizophrenia group (nominal P = 0.04). The findings support the 22q11.2 deletion model as a threshold-lowering first hit for schizophrenia risk. If applied to a larger and thus better-powered cohort, this appears to be a promising approach to identify genome-wide rare variants in coding and noncoding sequence that perturb gene networks relevant to idiopathic schizophrenia. Similarly designed studies exploiting genetic models may prove useful to help delineate the genetic architecture of other complex phenotypes.

Prolonged Period of Cortical Plasticity upon Redox Dysregulation in Fast-Spiking Interneurons

BACKGROUND

Oxidative stress and the specific impairment of perisomatic gamma-aminobutyric acid circuits are hallmarks of the schizophrenic brain and its animal models. Proper maturation of these fast-spiking inhibitory interneurons normally defines critical periods of experience-dependent cortical plasticity.

METHODS

Here, we linked these processes by genetically inducing a redox dysregulation restricted to such parvalbumin-positive cells and examined the impact on critical period plasticity using the visual system as a model (3-6 mice/group).

RESULTS

Oxidative stress was accompanied by a significant loss of perineuronal nets, which normally enwrap mature fast-spiking cells to limit adult plasticity. Accordingly, the neocortex remained plastic even beyond the peak of its natural critical period. These effects were not seen when redox dysregulation was targeted in excitatory principal cells.

CONCLUSIONS

A cell-specific regulation of redox state thus balances plasticity and stability of cortical networks. Mistimed developmental trajectories of brain plasticity may underlie, in part, the pathophysiology of mental illness. Such prolonged developmental plasticity may, in turn, offer a therapeutic opportunity for cognitive interventions targeting brain plasticity in schizophrenia.