A functional screen implicates microRNA-138-dependent regulation of the depalmitoylation enzyme APT1 in dendritic spine morphogenesis

Dopamine-regulated microRNA MiR-181a controls GluA2 surface expression in hippocampal neurons

The dynamic expression of AMPA-type glutamate receptors (AMPA-R) at synapses is a key determinant of synaptic plasticity, including neuroadaptations to drugs of abuse. Recently, microRNAs (miRNAs) have emerged as important posttranscriptional regulators of synaptic plasticity, but whether they target glutamate receptors to mediate this effect is not known. Here we used microarray screening to identify miRNAs that regulate synaptic plasticity within the nucleus accumbens, a brain region critical to forming drug-seeking habits. One of the miRNAs that showed a robust enrichment at medium spiny neuron synapses was miR-181a. Using bioinformatics tools, we detected a highly conserved miR-181a binding site within the mRNA encoding the GluA2 subunit of AMPA-Rs. Overexpression and knockdown of miR-181a in primary neurons demonstrated that this miRNA is a negative posttranscriptional regulator of GluA2 expression. Additionally, miR-181a overexpression reduced GluA2 surface expression, spine formation, and miniature excitatory postsynaptic current (mEPSC) frequency in hippocampal neurons, suggesting that miR-181a could regulate synaptic function. Moreover, miR-181a expression was induced by dopamine signaling in primary neurons, as well as by cocaine and amphetamines, in a mouse model of chronic drug treatment. Taken together, our results identify miR-181a as a key regulator of mammalian AMPA-type glutamate receptors, with potential implications for the regulation of drug-induced synaptic plasticity.

MicroRNAs in addiction: adaptation's middlemen?

A central question in addiction is how drug-induced changes in synaptic signaling are converted into long-term neuroadaptations. Emerging evidence reveals that microRNAs (miRNAs) have a distinct role in this process through rapid response to cellular signals and dynamic regulation of local mRNA transcripts. Because each miRNA can target hundreds of mRNAs, relative changes in the expression of miRNAs can greatly impact cellular responsiveness, synaptic plasticity and transcriptional events. These diverse consequences of miRNA action occur through coordination with genes implicated in addictions, the most compelling of these being the neurotrophin BDNF, the transcription factor cAMP-responsive element-binding protein (CREB) and the DNA-binding methyl CpG binding protein 2 (MeCP2). In this study, we review the recent progress in the understanding of miRNAs in general mechanisms of plasticity and neuroadaptation and then focus on specific examples of miRNA regulation in the context of addiction. We conclude that miRNA-mediated gene regulation is a conserved means of converting environmental signals into neuronal response, which holds significant implications for addiction and other psychiatric illnesses.

miR-200c regulates FGFR-dependent epithelial proliferation via Vldlr during submandibular gland branching morphogenesis

The regulation of epithelial proliferation during organ morphogenesis is crucial for normal development, as dysregulation is associated with tumor formation. Non-coding microRNAs (miRNAs), such as miR-200c, are post-transcriptional regulators of genes involved in cancer. However, the role of miR-200c during normal development is unknown. We screened miRNAs expressed in the mouse developing submandibular gland (SMG) and found that miR-200c accumulates in the epithelial end buds. Using both loss- and gain-of-function, we demonstrated that miR-200c reduces epithelial proliferation during SMG morphogenesis. To identify the mechanism, we predicted miR-200c target genes and confirmed their expression during SMG development. We discovered that miR-200c targets the very low density lipoprotein receptor (Vldlr) and its ligand reelin, which unexpectedly regulate FGFR-dependent epithelial proliferation. Thus, we demonstrate that miR-200c influences FGFR-mediated epithelial proliferation during branching morphogenesis via a Vldlr-dependent mechanism. miR-200c and Vldlr may be novel targets for controlling epithelial morphogenesis during glandular repair or regeneration.

Targeting of the Arpc3 actin nucleation factor by miR-29a/b regulates dendritic spine morphology

Previous studies have demonstrated that microribonucleic acids (miRs) are key regulators of protein expression in the brain and modulate dendritic spine morphology and synaptic activity. To identify novel miRs involved in neuronal plasticity, we exposed adult mice to chronic treatments with nicotine, cocaine, or amphetamine, which are psychoactive drugs that induce well-documented neuroadaptations. We observed brain region- and drug-specific changes in miR expression levels and identified miR-29a/b as regulators of synaptic morphology. In vitro imaging experiments indicated that miR-29a/b reduce mushroom-shaped dendritic spines on hippocampal neurons with a concomitant increase in filopodial-like outgrowths, suggesting an effect on synapse formation via actin cytoskeleton remodeling. We identified Arpc3, a component of the ARP2/3 actin nucleation complex, as a bona fide target for down-regulation by miR-29a/b. This work provides evidence that targeting of Arpc3 by miR-29a/b fine tunes structural plasticity by regulating actin network branching in mature and developing spines.

Targeting microRNAs in neurons: tools and perspectives

In the past few years, the understanding of microRNA (miRNA) biogenesis, the molecular mechanisms by which miRNAs regulate gene expression, and the functional roles of miRNAs has been expanded. Interestingly, numerous miRNAs are expressed in a spatially and temporally controlled manner in the nervous system, suggesting that their post-transcriptional regulation may be particularly relevant in neural development and function. miRNA studies in neurobiology have shown their involvement in synaptic plasticity and brain diseases. Approaches for manipulating miRNA levels in neuronal cells in vitro and in vivo are described here. Recent applications of miRNA antisense oligonucleotides, miRNA gene knockout and miRNA sponges in neuronal cells are reviewed. Finally, miRNA-based therapies for neurological pathologies related to alterations in miRNA functions are discussed.

Understanding the functional significance of ghrelin processing and degradation

Post-translational modification, cleavage and processing of circulating hormones are common themes in the control of hormone activities. Full-length ghrelin is a 28 amino acid protein that exists in several modified and processed forms, including addition of an acyl moiety at the third serine of the N-terminus. When modified with octanoic acid, the first five N-terminal residues of ghrelin can modulate a signaling pathway via the ghrelin receptor GHSR1a. Although modification via a lipid moiety is essential for binding and activation of GHSR1a by ghrelin, many reports suggest that a desacyl form of ghrelin exists and has synergistic, opposing and distinct properties as compared to the acyl form. Therefore, it is important to clarify the physiological relevance of ghrelin derivatives. Based on lines of evidence from various studies, we propose that a larger proportion of secreted ghrelin is present in the deacylated form and furthermore, that circulating acyl and desacyl forms of ghrelin may be hydrolyzed to form short peptide fragments. Here, we summarize the results of studies aimed at understanding ghrelin processing and its implications for physiological function, as well as our recent findings regarding enzymes in the blood capable of generating processed forms of ghrelin.

Abnormal microRNA expression in Ts65Dn hippocampus and whole blood: contributions to Down syndrome phenotypes

Down syndrome (DS; trisomy 21) is one of the most common genetic causes of intellectual disability, which is attributed to triplication of genes located on chromosome 21. Elevated levels of several microRNAs (miRNAs) located on chromosome 21 have been reported in human DS heart and brain tissues. The Ts65Dn mouse model is the most investigated DS model with a triplicated segment of mouse chromosome 16 harboring genes orthologous to those on human chromosome 21. Using ABI TaqMan miRNA arrays, we found a set of miRNAs that were significantly up- or downregulated in the Ts65Dn hippocampus compared to euploid controls. Furthermore, miR-155 and miR-802 showed significant overexpression in the Ts65Dn hippocampus, thereby confirming results of previous studies. Interestingly, miR-155 and miR-802 were also overexpressed in the Ts65Dn whole blood but not in lung tissue. We also found overexpression of the miR-155 precursors, pri- and pre-miR-155 derived from the miR-155 host gene, known as B cell integration cluster, suggesting enhanced biogenesis of miR-155. Bioinformatic analysis revealed that neurodevelopment, differentiation of neuroglia, apoptosis, cell cycle, and signaling pathways including ERK/MAPK, protein kinase C, phosphatidylinositol 3-kinase, m-TOR and calcium signaling are likely targets of these miRNAs. We selected some of these potential gene targets and found downregulation of mRNA encoding Ship1, Mecp2 and Ezh2 in Ts65Dn hippocampus. Interestingly, the miR-155 target gene Ship1 (inositol phosphatase) was also downregulated in Ts65Dn whole blood but not in lung tissue. Our findings provide insights into miRNA-mediated gene regulation in Ts65Dn mice and their potential contribution to impaired hippocampal synaptic plasticity and neurogenesis, as well as hemopoietic abnormalities observed in DS.

Functions of noncoding RNAs in neural development and neurological diseases

The development of the central nervous system (CNS) relies on precisely orchestrated gene expression regulation. Dysregulation of both genetic and environmental factors can affect proper CNS development and results in neurological diseases. Recent studies have shown that similar to protein coding genes, noncoding RNA molecules have a significant impact on normal CNS development and on causes and progression of human neurological disorders. In this review, we have highlighted discoveries of functions of noncoding RNAs, in particular microRNAs and long noncoding RNAs, in neural development and neurological diseases. Emerging evidence has shown that microRNAs play an essential role in many aspects of neural development, such as proliferation of neural stem cells and progenitors, neuronal differentiation, maturation, and synaptogenesis. Misregulation of microRNAs is associated with some mental disorders and neurodegeneration diseases. In addition, long noncoding RNAs are found to play a role in neural development by regulating the expression of protein coding genes. Therefore, examining noncoding RNA-mediated gene regulations has revealed novel mechanisms of neural development and provided new insights into the etiology of human neurological diseases.

miRNA Expression profile after status epilepticus and hippocampal neuroprotection by targeting miR-132

When an otherwise harmful insult to the brain is preceded by a brief, noninjurious stimulus, the brain becomes tolerant, and the resulting damage is reduced. Epileptic tolerance develops when brief seizures precede an episode of prolonged seizures (status epilepticus). MicroRNAs (miRNAs) are small, noncoding RNAs that function as post-transcriptional regulators of gene expression. We investigated how prior seizure preconditioning affects the miRNA response to status epilepticus evoked by intra-amygdalar kainic acid in mice. The miRNA was extracted from the ipsilateral CA3 subfield 24 hours after focal-onset status epilepticus in animals that had previously received either seizure preconditioning (tolerance) or no preconditioning (injury), and mature miRNA levels were measured using TaqMan low-density arrays. Expression of 21 miRNAs was increased, relative to control, after status epilepticus alone, and expression of 12 miRNAs was decreased. Increased miR-132 levels were matched with increased binding to Argonaute-2, a constituent of the RNA-induced silencing complex. In tolerant animals, expression responses of >40% of the injury-group-detected miRNAs differed, being either unchanged relative to control or down-regulated, and this included miR-132. In vivo microinjection of locked nucleic acid-modified oligonucleotides (antagomirs) against miR-132 depleted hippocampal miR-132 levels and reduced seizure-induced neuronal death. Thus, our data strongly suggest that miRNAs are important regulators of seizure-induced neuronal death.

microRNA-34c is a novel target to treat dementias

MicroRNAs are key regulators of transcriptome plasticity and have been implicated with the pathogenesis of brain diseases. Here, we employed massive parallel sequencing and provide, at an unprecedented depth, the complete and quantitative miRNAome of the mouse hippocampus, the prime target of neurodegenerative diseases such as Alzheimer's disease (AD). Using integrative genetics, we identify miR-34c as a negative constraint of memory consolidation and show that miR-34c levels are elevated in the hippocampus of AD patients and corresponding mouse models. In line with this, targeting miR-34 seed rescues learning ability in these mouse models. Our data suggest that miR-34c could be a marker for the onset of cognitive disturbances linked to AD and indicate that targeting miR-34c could be a suitable therapy.

Mnemonic microRNAs help make memories

Researchers find that two microRNAs prime the brain to learn.

NMDA mediated contextual conditioning changes miRNA expression

We measured the expression of 187 miRNAs using quantitative real time PCR in the hippocampal CA1 region of contextually conditioned mice and cultured embryonic rat hippocampal neurons after neuronal stimulation with either NMDA or bicuculline. Many of the changes in miRNA expression after these three types of stimulation were similar. Surprisingly, the expression level of half of the 187 measured miRNAs was changed in response to contextual conditioning in an NMDA receptor-dependent manner. Genes that control miRNA biogenesis and components of the RISC also exhibited activity induced expression changes and are likely to contribute to the widespread changes in the miRNA profile. The widespread changes in miRNA expression are consistent with the finding that genes up-regulated by contextual conditioning have longer 3′ UTRs and more predicted binding sites for miRNAs. Among the miRNAs that changed their expression after contextual conditioning, several inhibit inhibitors of the mTOR pathway. These findings point to a role for miRNAs in learning and memory that includes mTOR-dependent modulation of protein synthesis.

Reversible inhibition of PSD-95 mRNA translation by miR-125a, FMRP phosphorylation, and mGluR signaling

The molecular mechanism for how RISC and microRNAs selectively and reversibly regulate mRNA translation in response to receptor signaling is unknown but could provide a means for temporal and spatial control of translation. Here we show that miR-125a targeting PSD-95 mRNA allows reversible inhibition of translation and regulation by gp1 mGluR signaling. Inhibition of miR-125a increased PSD-95 levels in dendrites and altered dendritic spine morphology. Bidirectional control of PSD-95 expression depends on miR-125a and FMRP phosphorylation status. miR-125a levels at synapses and its association with AGO2 are reduced in Fmr1 KO. FMRP phosphorylation promotes the formation of an AGO2-miR-125a inhibitory complex on PSD-95 mRNA, whereas mGluR signaling of translation requires FMRP dephosphorylation and release of AGO2 from the mRNA. These findings reveal a mechanism whereby FMRP phosphorylation provides a reversible switch for AGO2 and microRNA to selectively regulate mRNA translation at synapses in response to receptor activation.

miR-124a is required for hippocampal axogenesis and retinal cone survival through Lhx2 suppression

MicroRNA-124a (miR-124a) is the most abundant microRNA expressed in the vertebrate CNS. Despite past investigations into the role of miR-124a, inconsistent results have left the in vivo function of miR-124a unclear. We examined the in vivo function of miR-124a by targeted disruption of Rncr3 (retinal non-coding RNA 3), the dominant source of miR-124a. Rncr3(-/-) mice exhibited abnormalities in the CNS, including small brain size, axonal mis-sprouting of dentate gyrus granule cells and retinal cone cell death. We found that Lhx2 is an in vivo target mRNA of miR-124a. We also observed that LHX2 downregulation by miR-124a is required for the prevention of apoptosis in the developing retina and proper axonal development of hippocampal neurons. These results suggest that miR-124a is essential for the maturation and survival of dentate gyrus neurons and retinal cones, as it represses Lhx2 translation.

MicroRNA networks direct neuronal development and plasticity

MicroRNAs (miRNAs) constitute a class of small, non-coding RNAs that act as post-transcriptional regulators of gene expression. In neurons, the functions of individual miRNAs are just beginning to emerge, and recent studies have elucidated roles for neural miRNAs at various stages of neuronal development and maturation, including neurite outgrowth, dendritogenesis, and spine formation. Notably, miRNAs regulate mRNA translation locally in the axosomal and synaptodendritic compartments, and thereby contribute to the dynamic spatial organization of axonal and dendritic structures and their function. Given the critical role for miRNAs in regulating early brain development and in mediating synaptic plasticity later in life, it is tempting to speculate that the pathology of neurological disorders is affected by altered expression or functioning of miRNAs. Here we provide an overview of recently identified mechanisms of neuronal development and plasticity involving miRNAs, and the consequences of miRNA dysregulation.

Axotomy-induced miR-21 promotes axon growth in adult dorsal root ganglion neurons

Following injury, dorsal root ganglion (DRG) neurons undergo transcriptional changes so as to adopt phenotypic changes that promote cell survival and axonal regeneration. Here we used a microarray approach to profile changes in a population of small noncoding RNAs known as microRNAs (miRNAs) in the L4 and L5 DRG following sciatic nerve transection. Results showed that 20 miRNA transcripts displayed a significant change in expression levels, with 8 miRNAs transcripts being altered by more than 1.5-fold. Using quantitative reverse transcription PCR, we demonstrated that one of these miRNAs, miR-21, was upregulated by 7-fold in the DRG at 7 days post-axotomy. In dissociated adult rat DRG neurons lentiviral vector-mediated overexpression of miR-21 promoted neurite outgrowth on a reduced laminin substrate. miR-21 directly downregulated expression of Sprouty2 protein, as confirmed by Western blot analysis and 3' untranslated region (UTR) luciferase assays. Our data show that miR-21 is an axotomy-induced miRNA that enhances axon growth, and suggest that miRNAs are important players in regulating growth pathways following peripheral nerve injury.

microRNA-Seq reveals cocaine-regulated expression of striatal microRNAs

MicroRNAs (miRNAs) are small RNAs that modulate gene expression by binding target mRNAs. The hundreds of miRNAs expressed in the brain are critical for synaptic development and plasticity. Drugs of abuse cause lasting changes in the limbic regions of the brain that process reward, and addiction is viewed as a form of aberrant neuroplasticity. Using next-generation sequencing, we cataloged miRNA expression in the nucleus accumbens and at striatal synapses in control and chronically cocaine-treated mice. We identified cocaine-responsive miRNAs, synaptically enriched and depleted miRNA families, and confirmed cocaine-induced changes in protein expression for several predicted synaptic target genes. The miR-8 family, known for its roles in cancer, is highly enriched and cocaine regulated at striatal synapses, where its members may affect expression of cell adhesion molecules. Synaptically enriched cocaine-regulated miRNAs may contribute to long-lasting drug-induced plasticity through fine-tuning regulatory pathways that modulate the actin cytoskeleton, neurotransmitter metabolism, and peptide hormone processing.

Differentiation of single cell derived human mesenchymal stem cells into cells with a neuronal phenotype: RNA and microRNA expression profile

The adult bone marrow contains a subset of non-haematopoietic cells referred to as bone marrow mesenchymal stem cells (BMSCs). Mesenchymal stem cells (MSCs) have attracted immense research interest in the field of regenerative medicine due to their ability to be cultured for successive passages and multi-lineage differentiation. The molecular mechanisms governing the self-renewal and differentiation of MSCs remain largely unknown. In a previous paper we demonstrated the ability to induce human clonal MSCs to differentiate into cells with a neuronal phenotype (DMSCs). In the present study we evaluated gene expression profiles by Sequential Analysis of Gene Expression (SAGE) and microRNA expression profiles before and after the neuronal differentiation process. Various tissue-specific genes were weakly expressed in MSCs, including those of non-mesodermal origin, suggesting multiple potential tissue-specific differentiation, as well as stemness markers. Expression of OCT4, KLF4 and c-Myc cell reprogramming factors, which are modulated during the differentiation process, was also observed. Many peculiar nervous tissue genes were expressed at a high level in DMSCs, along with genes related to apoptosis. MicroRNA profiling and correlation with mRNA expression profiles allowed us to identify putative important genes and microRNAs involved in the differentiation of MSCs into neuronal-like cells. The profound difference in gene and microRNA expression patterns between MSCs and DMSCs indicates a real functional change during differentiation from MSCs to DMSCs.

The microRNA contribution to learning and memory

Learning and memory refer to an animal's ability to respond adequately to environmental signals that may be negative (aversive learning) or positive (appetitive learning) in nature. The extremely elaborate connectivity network of neurons in the brain is capable of governing animals' reactions (e.g., by enhancing or weakening single or multiple synapses). Such circuit plasticity is largely believed to be the very essence of memory formation. It has been suggested that long-term memory, in contrast to short-term memory, requires de novo protein synthesis and can be prevented by protein synthesis inhibitors. The local protein translation in dendrites allows neurons to selectively rebuild only those synapses that have been activated. However, substrates of protein synthesis (i.e., mRNA) have to be kept suppressed until they are needed. MicroRNAs--short, non-protein-coding RNA regulatory sequences that guide an RNA--induced silencing complex to target mRNAs-seem to be perfect candidates in fulfilling this function in neurons. In this article, the authors discuss the recently recognized role of microRNAs as regulators of memory formation and endurance.

Review of MicroRNA Deregulation in Oral Cancer. Part I

OBJECTIVES

Oral cancer is the sixth most common malignancy worldwide. Cancer development and progression requires inactivation of tumour suppressor genes and activation of proto-oncogenes. Expression of these genes is in part dependant on RNA and microRNA based mechanisms. MicroRNAs are essential regulators of diverse cellular processes including proliferation, differentiation, apoptosis, survival, motility, invasion and morphogenesis. Several microRNAs have been found to be aberrantly expressed in various cancers including oral cancer. The purpose of this article was to review the literature related to microRNA deregulation in the head and neck/oral cavity cancers.

MATERIAL AND METHODS

A comprehensive review of the available literature from 2000 to 2011 relevant to microRNA deregulation in oral cancer was undertaken using PubMed, Medline, Scholar Google and Scopus. Keywords for the search were: microRNA and oral cancer, microRNA and squamous cell carcinoma, microRNA deregulation. Only full length articles in the English language were included. Strengths and limitations of each study are presented in this review.

RESULTS

Several studies were identified that investigated microRNA alternations in the head and neck/oral cavity cancers. Significant progress has been made in identification of microRNA deregulation in these cancers. It has been evident that several microRNAs were found to be deregulated specifically in oral cavity cancers. Among these, several microRNAs have been functionally validated and their potential target genes have been identified.

CONCLUSIONS

These findings on microRNA deregulation in cancer further enhance our understanding of the disease progression, response to treatment and may assist with future development of targeted therapy.

A study of neural-related microRNAs in the developing amphioxus

BACKGROUND

MicroRNAs are small noncoding RNAs regulating expression of protein coding genes at post-transcriptional level and controlling several biological processes. At present microRNAs have been identified in various metazoans and seem also to be involved in brain development, neuronal differentiation and subtypes specification. An approach to better understand the role of microRNAs in animal gene expression is to determine temporal and tissue-specific expression patterns of microRNAs in different model organisms. Therefore, we have investigated the expression of six neural related microRNAs in amphioxus, an organism having an important phylogenetic position in terms of understanding the origin and evolution of chordates.

RESULTS

In amphioxus, all the microRNAs we examined are expressed in specific regions of the CNS, and some of them are correlated with specific cell types. In addition, miR-7, miR-137 and miR-184 are also expressed in endodermal and mesodermal tissues. Several potential targets expressed in the nervous system of amphioxus have been identified by computational prediction and some of them are coexpressed with one or more miRNAs.

CONCLUSION

We identified six miRNAs that are expressed in the nervous system of amphioxus in a variety of patterns. miR-124 is found in both differentiating and mature neurons, miR-9 in differentiated neurons, miR-7, miR-137 and miR-184 in restricted CNS regions, and miR-183 in cells of sensory organs. Therefore, such amphioxus miRNAs may play important roles in regional patterning and/or specification of neuronal cell types.

MicroRNAs in Development and Disease

MicroRNAs (miRNAs) are a class of posttranscriptional regulators that have recently introduced an additional level of intricacy to our understanding of gene regulation. There are currently over 10,000 miRNAs that have been identified in a range of species including metazoa, mycetozoa, viridiplantae, and viruses, of which 940, to date, are found in humans. It is estimated that more than 60% of human protein-coding genes harbor miRNA target sites in their 3′ untranslated region and, thus, are potentially regulated by these molecules in health and disease. This review will first briefly describe the discovery, structure, and mode of function of miRNAs in mammalian cells, before elaborating on their roles and significance during development and pathogenesis in the various mammalian organs, while attempting to reconcile their functions with our existing knowledge of their targets. Finally, we will summarize some of the advances made in utilizing miRNAs in therapeutics.

MicroRNA regulation of homeostatic synaptic plasticity

Homeostatic mechanisms are required to control formation and maintenance of synaptic connections to maintain the general level of neural impulse activity within normal limits. How genes controlling these processes are co-coordinately regulated during homeostatic synaptic plasticity is unknown. MicroRNAs (miRNAs) exert regulatory control over mRNA stability and translation and may contribute to local and activity-dependent posttranscriptional control of synapse-associated mRNAs. However, identifying miRNAs that function through posttranscriptional gene silencing at synapses has remained elusive. Using a bioinformatics screen to identify sequence motifs enriched in the 3'UTR of rapidly destabilized mRNAs, we identified a developmentally and activity-regulated miRNA (miR-485) that controls dendritic spine number and synapse formation in an activity-dependent homeostatic manner. We find that many plasticity-associated genes contain predicted miR-485 binding sites and further identify the presynaptic protein SV2A as a target of miR-485. miR-485 negatively regulated dendritic spine density, postsynaptic density 95 (PSD-95) clustering, and surface expression of GluR2. Furthermore, miR-485 overexpression reduced spontaneous synaptic responses and transmitter release, as measured by miniature excitatory postsynaptic current (EPSC) analysis and FM 1-43 staining. SV2A knockdown mimicked the effects of miR-485, and these effects were reversed by SV2A overexpression. Moreover, 5 d of increased synaptic activity induced homeostatic changes in synaptic specializations that were blocked by a miR-485 inhibitor. Our findings reveal a role for this previously uncharacterized miRNA and the presynaptic protein SV2A in homeostatic plasticity and nervous system development, with possible implications in neurological disorders (e.g., Huntington and Alzheimer's disease), where miR-485 has been found to be dysregulated.

MicroRNA-138 modulates DNA damage response by repressing histone H2AX expression

Precise regulation of DNA damage response is crucial for cellular survival after DNA damage, and its abrogation often results in genomic instability in cancer. Phosphorylated histone H2AX (γH2AX) forms nuclear foci at sites of DNA damage and facilitates DNA damage response and repair. MicroRNAs (miRNA) are short, nonprotein-encoding RNA molecules, which posttranscriptionally regulate gene expression by repressing translation of and/or degrading mRNA. How miRNAs modulate DNA damage response is largely unknown. In this study, we developed a cell-based screening assay using ionizing radiation (IR)-induced γH2AX foci formation in a human osteosarcoma cell line, U2OS, as the readout. By screening a library of human miRNA mimics, we identified several miRNAs that inhibited γH2AX foci formation. Among them, miR-138 directly targeted the histone H2AX 3'-untranslated region, reduced histone H2AX expression, and induced chromosomal instability after DNA damage. Overexpression of miR-138 inhibited homologous recombination and enhanced cellular sensitivity to multiple DNA-damaging agents (cisplatin, camptothecin, and IR). Reintroduction of histone H2AX in miR-138 overexpressing cells attenuated miR-138-mediated sensitization to cisplatin and camptothecin. Our study suggests that miR-138 is an important regulator of genomic stability and a potential therapeutic agent to improve the efficacy of radiotherapy and chemotherapy with DNA-damaging agents.

Structural modulation of dendritic spines during synaptic plasticity

The majority of excitatory synaptic input in the brain is received by small bulbous actin-rich protrusions residing on the dendrites of glutamatergic neurons. These dendritic spines are the major sites of information processing in the brain. This conclusion is reinforced by the observation that many higher cognitive disorders, such as mental retardation, Rett syndrome, and autism, are associated with aberrant spine morphology. Mechanisms that regulate the maturation and plasticity of dendritic spines are therefore fundamental to understanding higher brain functions including learning and memory. It is well known that activity-driven changes in synaptic efficacy modulate spine morphology due to alterations in the underlying actin cytoskeleton. Recent studies have elucidated numerous molecular regulators that directly alter actin dynamics within dendritic spines. This review will emphasize activity-dependent changes in spine morphology and highlight likely roles of these actin-binding proteins.

Up-regulation of microRNAs in brain of human alcoholics

BACKGROUND

MicroRNAs (miRNAs) are small, noncoding oligonucleotides with an important role in posttranscriptional regulation of gene expression at the level of translation and mRNA degradation. Recent studies have revealed that miRNAs play important roles in a variety of biological processes, such as cell proliferation, neuronal differentiation, developmental timing, synapse function, and neurogenesis. A single miRNA can target hundreds of mRNA transcripts for either translation repression or degradation, but the function of many human miRNAs is not known.

METHODS

miRNA array analysis was performed on the prefrontal cortex of 27 individual human cases (14 alcoholics and 13 matched controls). Target genes for differentially expressed miRNAs were predicted using multiple target prediction algorithms and a consensus approach, and predicted targets were matched against differentially expressed mRNAs from the same samples. Over- and under-representation analysis was performed using hypergeometric probability and z-score tests.

RESULTS

Approximately 35 miRNAs were significantly up-regulated in the alcoholic group compared with controls. Target prediction showed a large degree of overlap with our published cDNA microarray data. Functional classification of the predicted target genes of the regulated miRNAs includes apoptosis, cell cycle, cell adhesion, nervous system development, and cell-cell signaling.

CONCLUSIONS

These data suggest that the reduced expression of genes in human alcoholic cases may be because of the up-regulated miRNAs. Cellular processes fundamental to neuronal plasticity appear to represent major targets of the suggested miRNA regulation.

microRNAs in neurons: manifold regulatory roles at the synapse

The regulation of synapse formation and plasticity in the developing and adult brain underlies a complex interplay of intrinsic genetic programs and extrinsic factors. Recent research identified microRNAs (miRNAs), a class of small non-coding RNAs, as a new functional layer in this regulatory network. Within only a few years, a network of synaptic miRNAs and their target genes has been extensively characterized, highlighting the importance of this mechanism for synapse development and physiology. Very recent data further provide insight into activity-dependent regulation of miRNAs, thereby connecting miRNAs with adaptive processes of neural circuits. First direct links between miRNA dysfunction and synaptic pathologies are emerging, raising the interest in these molecules as potential biomarkers and therapeutic targets in neurological disorders.

Regulation of MiR-124, Let-7d, and MiR-181a in the accumbens affects the expression, extinction, and reinstatement of cocaine-induced conditioned place preference

Molecular adaptations underlying drug seeking and relapse remain largely unknown. Studies highlight post-transcriptional modifications mediated by microRNAs (miRNAs) in addiction and other neurological disorders. We have previously shown that chronic cocaine suppresses miR-124 and let-7d and induces the expression of miR-181a in mesolimbic pathway. To further address the role and target gene regulation network of these miRNAs in vivo in cocaine addiction, we developed lentiviral vector (LV)-expressing miRNAs and their corresponding silencers for stable and regulatable miRNA expression. We tested in vivo miRNA gain and loss of function on cocaine-induced conditioned place preference (CPP) by localized LV-miRNA regulation in the nucleus accumbens (NAc). LV-miR-124 and let-7d expression in the NAc attenuates cocaine CPP, whereas LV-miR-181a enhances it. Silencing miRNAs by corresponding LV-miRNA silencers expressing perfect miRNA target sequences inversed this effect on cocaine CPP. Doxycycline treatment for switching off silencer expression abolished the observed behavioral changes. Behavioral changes mediated by LV-miRNA regulation resulted in dynamic alterations in transcription factors, receptors, and other effector genes involved in cocaine-induced plasticity. Our results describe a complex regulatory pathway mediated by miRNAs in cocaine-mediated neuronal adaptations.

Making and breaking synapses through local mRNA regulation

Neurons are exquisitely polarized cells that extend intricate axonal and dendritic arbors. Developmental cues guide axons and dendrites into circuits by inducing rapid changes in local protein expression and cytoskeletal structure. Neurons can transduce these signals through local mRNA regulation. Here, we review the latest insights regarding post-transcriptional control of gene expression through mRNA transport and local protein synthesis in developing neurons. We focus on local mRNA regulation during axon growth and guidance, dendrite morphogenesis, and synapse formation and refinement. Dysregulated mRNA transport and translation in neurological disorders are also discussed. The collection of molecules and mechanisms reviewed includes sequence-specific RNA binding proteins, microtubule motors and adaptors, microRNAs, translation initiation factors, and the receptor-mediated signaling that modulates these molecules.

Evidence demonstrating role of microRNAs in the etiopathology of major depression

Major depression is a debilitating disease. Despite a tremendous amount of research, the molecular mechanisms associated with the etiopathology of major depression are not clearly understood. Several lines of evidence indicate that depression is associated with altered neuronal and structural plasticity and neurogenesis. MicroRNAs are a newly discovered prominent class of gene expression regulators that have critical roles in neural development, are needed for survival and optimal health of postmitotic neurons, and regulate synaptic functions, particularly by regulating protein synthesis in dendritic spines. In addition, microRNAs (miRNAs) regulate both embryonic and adult neurogenesis. Given that miRNAs are involved in neural plasticity and neurogenesis, the concept that miRNAs may play an important role in psychiatric illnesses, including major depression, is rapidly advancing. Emerging evidence demonstrates that the expression of miRNAs is altered during stress, in the brain of behaviorally depressed animals, and in human postmortem brain of depressed subjects. In this review article, the possibility that dysregulation of miRNAs and/or altered miRNA response may contribute to the etiology and pathophysiology of depressive disorder is discussed.

Activity-based protein profiling of organophosphorus and thiocarbamate pesticides reveals multiple serine hydrolase targets in mouse brain

Organophosphorus (OP) and thiocarbamate (TC) agrochemicals are used worldwide as insecticides, herbicides, and fungicides, but their safety assessment in terms of potential off-targets remains incomplete. In this study, a chemoproteomic platform, termed activity-based protein profiling, was used to broadly define serine hydrolase targets in mouse brain of a panel of 29 OP and TC pesticides. Among the secondary targets identified, enzymes involved in the degradation of endocannabinoid signaling lipids, monoacylglycerol lipase, and fatty acid amide hydrolase were inhibited by several OP and TC pesticides. Blockade of these two enzymes led to elevations in brain endocannabinoid levels and dysregulated brain arachidonate metabolism. Other secondary targets include enzymes thought to also play important roles in the nervous system and unannotated proteins. This study reveals a multitude of secondary targets for OP and TC pesticides and underscores the utility of chemoproteomic platforms in gaining insights into biochemical pathways that are perturbed by these toxicants.

Monoallelic deletion of the microRNA biogenesis gene Dgcr8 produces deficits in the development of excitatory synaptic transmission in the prefrontal cortex

BACKGROUND

Neuronal phenotypes associated with hemizygosity of individual genes within the 22q11.2 deletion syndrome locus hold potential towards understanding the pathogenesis of schizophrenia and autism. Included among these genes is Dgcr8, which encodes an RNA-binding protein required for microRNA biogenesis. Dgcr8 haploinsufficient mice (Dgcr8+/-) have reduced expression of microRNAs in brain and display cognitive deficits, but how microRNA deficiency affects the development and function of neurons in the cerebral cortex is not fully understood.

RESULTS

In this study, we show that Dgcr8+/- mice display reduced expression of a subset of microRNAs in the prefrontal cortex, a deficit that emerges over postnatal development. Layer V pyramidal neurons in the medial prefrontal cortex of Dgcr8+/- mice have altered electrical properties, decreased complexity of basal dendrites, and reduced excitatory synaptic transmission.

CONCLUSIONS

These findings demonstrate that precise microRNA expression is critical for the postnatal development of prefrontal cortical circuitry. Similar defects in neuronal maturation resulting from microRNA deficiency could represent endophenotypes of certain neuropsychiatric diseases of developmental onset.

MicroRNAs: Meta-controllers of gene expression in synaptic activity emerge as genetic and diagnostic markers of human disease

MicroRNAs are members of the non-protein-coding family of RNAs. They serve as regulators of gene expression by modulating the translation and/or stability of messenger RNA targets. The discovery of microRNAs has revolutionized the field of cell biology, and has permanently altered the prevailing view of a linear relationship between gene and protein expression. The increased complexity of gene regulation is both exciting and daunting, as emerging evidence supports a pervasive role for microRNAs in virtually every cellular process. This review briefly describes microRNA processing and formation of RNA-induced silencing complexes, with a focus on the role of RNA binding proteins in this process. We also discuss mechanisms for microRNA-mediated regulation of translation, particularly in dendritic spine formation and function, and the role of microRNAs in synaptic plasticity. We then discuss the evidence for altered microRNA function in cognitive brain disorders, and the effect of gene mutations revealed by single nucleotide polymorphism analysis on altered microRNA function and human disease. Further, we present evidence that altered microRNA expression in circulating fluids such as plasma/serum can correlate with, and serve as, novel diagnostic biomarkers of human disease.

Human microRNAs miR-22, miR-138-2, miR-148a, and miR-488 are associated with panic disorder and regulate several anxiety candidate genes and related pathways

BACKGROUND

The involvement of microRNAs (miRNAs) in neuronal differentiation and synaptic plasticity suggests a role for miRNAs in psychiatric disorders; association analyses and functional approaches were used to evaluate the implication of miRNAs in the susceptibility for panic disorder.

METHODS

Case-control studies for 712 single-nucleotide polymorphisms (SNPs) tagging 325 human miRNA regions were performed in 203 Spanish patients with panic disorder and 341 control subjects. A sample of 321 anxiety patients and 642 control subjects from Finland and 102 panic disorder patients and 829 control subjects from Estonia was used as a replica. Reporter-gene assays and miRNA overexpression experiments in neuroblastoma cells were used to functionally evaluate the spectrum of genes regulated by the associated miRNAs.

RESULTS

Two SNPs associated with panic disorder: rs6502892 tagging miR-22 (p < .0002), and rs11763020 tagging miR-339 (p < .00008). Other SNPs tagging miR-138-2, miR-488, miR-491, and miR-148a regions associated with different panic disorder phenotypes. Replication in the north-European sample supported several of these associations, although they did not pass correction for multiple testing. Functional studies revealed that miR-138-2, miR-148a, and miR-488 repress (30%-60%) several candidate genes for panic disorder--GABRA6, CCKBR and POMC, respectively--and that miR-22 regulates four other candidate genes: BDNF, HTR2C, MAOA, and RGS2. Transcriptome analysis of neuroblastoma cells transfected with miR-22 and miR-488 showed altered expression of a subset of predicted target genes for these miRNAs and of genes that might be affecting physiological pathways related to anxiety.

CONCLUSIONS

This work represents the first report of a possible implication of miRNAs in the etiology of panic disorder.

MicroRNA in central nervous system trauma and degenerative disorders

MicroRNAs (miRNAs) are a novel class of small noncoding RNAs that negatively regulate gene expression at the posttranscriptional level by binding to the 3'-untranslated region of target mRNAs leading to their translational inhibition or sometimes degradation. MiRNAs are predicted to control the activity of at least 20-30% of human protein-coding genes. Recent studies have demonstrated that miRNAs are highly expressed in the central nervous system (CNS) including the brain and spinal cord. Although we are currently in the initial stages of understanding how this novel class of gene regulators is involved in neurological biological functions, a growing body of exciting evidence suggests that miRNAs are important regulators of diverse biological processes such as cell differentiation, growth, proliferation, and apoptosis. Moreover, miRNAs are key modulators of both CNS development and plasticity. Some miRNAs have been implicated in several neurological disorders such as traumatic CNS injuries and neurodegenerative diseases. Recently, several studies suggested the possibility of miRNA involvement in neurodegeneration. Identifying the roles of miRNAs and their target genes and signaling pathways in neurological disorders will be critical for future research. miRNAs may represent a new layer of regulators for neurobiology and a novel class of therapeutic targets for neurological diseases.

The intracellular dynamic of protein palmitoylation

S-palmitoylation describes the reversible attachment of fatty acids (predominantly palmitate) onto cysteine residues via a labile thioester bond. This posttranslational modification impacts protein functionality by regulating membrane interactions, intracellular sorting, stability, and membrane micropatterning. Several recent findings have provided a tantalizing insight into the regulation and spatiotemporal dynamics of protein palmitoylation. In mammalian cells, the Golgi has emerged as a possible super-reaction center for the palmitoylation of peripheral membrane proteins, whereas palmitoylation reactions on post-Golgi compartments contribute to the regulation of specific substrates. In addition to palmitoylating and depalmitoylating enzymes, intracellular palmitoylation dynamics may also be controlled through interplay with distinct posttranslational modifications, such as phosphorylation and nitrosylation.

Reversible high affinity inhibition of phosphofructokinase-1 by acyl-CoA: a mechanism integrating glycolytic flux with lipid metabolism

The enzyme phosphofructokinase-1 (PFK-1) catalyzes the first committed step of glycolysis and is regulated by a complex array of allosteric effectors that integrate glycolytic flux with cellular bioenergetics. Here, we demonstrate the direct, potent, and reversible inhibition of purified rabbit muscle PFK-1 by low micromolar concentrations of long chain fatty acyl-CoAs (apparent Ki∼1 μM). In sharp contrast, short chain acyl-CoAs, palmitoylcarnitine, and palmitic acid in the presence of CoASH were without effect. Remarkably, MgAMP and MgADP but not MgATP protected PFK-1 against inhibition by palmitoyl-CoA indicating that acyl-CoAs regulate PFK-1 activity in concert with cellular high energy phosphate status. Furthermore, incubation of PFK-1 with [1-(14)C]palmitoyl-CoA resulted in robust acylation of the enzyme that was reversible by incubation with acyl-protein thioesterase-1 (APT1). Importantly, APT1 reversed palmitoyl-CoA-mediated inhibition of PFK-1 activity. Mass spectrometric analyses of palmitoylated PFK-1 revealed four sites of acylation, including Cys-114, Cys-170, Cys-351, and Cys-577. PFK-1 in both skeletal muscle extracts and in purified form was inhibited by S-hexadecyl-CoA, a nonhydrolyzable palmitoyl-CoA analog, demonstrating that covalent acylation of PFK-1 was not required for inhibition. Tryptic footprinting suggested that S-hexadecyl-CoA induced a conformational change in PFK-1. Both palmitoyl-CoA and S-hexadecyl-CoA increased the association of PFK-1 with Ca2+/calmodulin, which attenuated the binding of palmitoylated PFK-1 to membrane vesicles. Collectively, these results demonstrate that fatty acyl-CoA modulates phosphofructokinase activity through both covalent and noncovalent interactions to regulate glycolytic flux and enzyme membrane localization via the branch point metabolic node that mediates lipid flux through anabolic and catabolic pathways.

Ageing, neuronal connectivity and brain disorders: an unsolved ripple effect

Cognitive decline associated with ageing and age-related disorders emerges as one of the greatest health challenges in the next decades. To date, the molecular mechanisms underlying the onset of neuronal physiological changes in the central nervous system remain unclear. Functional MRI and PET studies have indicated the decline in working memory performance in older adults. Similarly, age-related disorders, such as Alzheimer's disease, are associated with changes in the prefontral cortex and related neural circuitry, which underlines the decline of integrative function between different brain regions. This is mainly attributed to the loss of synaptic connectivity, which is a feature commonly observed in neurodegenerative disorders. In humans, the morphological and functional changes in neurons, such as reduction of spine numbers and synaptic dysfunction, precede the first signs of cognitive decline and likely contribute to pathology progression. Thus, a new scenario emerges in which apparently unrelated diseases present common features, such as the remodelling of neuronal circuitries promoted by ageing. For many years, ageing was considered a process of slow deterioration triggered by accidental environmental factors. Conversely, it is now evident that ageing is a biological process tightly controlled by evolutionary highly conserved signalling pathways. Importantly, genetic mutations that enhance longevity significantly delay the loss of synaptic connectivity and, therefore, the onset of age-related brain disorders. Accordingly, tweaking ageing might be an attractive approach to prevent cognitive decline caused by age-related synaptic dysfunction.

Dynamic palmitoylation and the role of DHHC proteins in T cell activation and anergy

Although protein S-palmitoylation was first characterized >30 years ago, and is implicated in the function, trafficking, and localization of many proteins, little is known about the regulation and physiological implications of this posttranslational modification. Palmitoylation of various signaling proteins required for TCR-induced T cell activation is also necessary for their proper function. Linker for activation of T cells (LAT) is an essential scaffolding protein involved in T cell development and activation, and we found that its palmitoylation is selectively impaired in anergic T cells. The recent discovery of the DHHC family of palmitoyl acyl transferases and the establishment of sensitive and quantitative proteomics-based methods for global analysis of the palmitoyl proteome led to significant progress in studying the biology and underlying mechanisms of cellular protein palmitoylation. We are using these approaches to explore the palmitoyl proteome in T lymphocytes and, specifically, the mechanistic basis for the impaired palmitoylation of LAT in anergic T cells. This chapter reviews the history of protein palmitoylation and its role in T cell activation, the DHHC family and new methodologies for global analysis of the palmitoyl proteome, and summarizes our recent work in this area. The new methodologies will accelerate the pace of research and provide a greatly improved mechanistic and molecular understanding of the complex process of protein palmitoylation and its regulation, and the substrate specificity of the novel DHHC family. Reversible protein palmitoylation will likely prove to be an important posttranslational mechanism that regulates cellular responses, similar to protein phosphorylation and ubiquitination.

MicroRNA function in the nervous system

MicroRNAs (miRNAs) are an extensive class of small noncoding RNAs that control posttranscriptional gene expression. miRNAs are highly expressed in neurons where they play key roles during neuronal differentiation, synaptogenesis, and plasticity. It is also becoming increasingly evident that miRNAs have a profound impact on higher cognitive functions and are involved in the etiology of several neurological diseases and disorders. In this chapter, we summarize our current knowledge of miRNA functions during neuronal development, physiology, and dysfunction.

MicroRNA regulation of neural stem cells and neurogenesis

MicroRNAs are a class of small RNA regulators that are involved in numerous cellular processes, including development, proliferation, differentiation, and plasticity. The emerging concept is that microRNAs play a central role in controlling the balance between stem cell self-renewal and fate determination by regulating the expression of stem cell regulators. This review will highlight recent advances in the regulation of neural stem cell self-renewal and neurogenesis by microRNAs. It will cover microRNA functions during the entire process of neurogenesis, from neural stem cell self-renewal and fate determination to neuronal maturation, synaptic formation, and plasticity. The interplay between microRNAs and both cell-intrinsic and -extrinsic stem cell players, including transcription factors, epigenetic regulators, and extrinsic signaling molecules will be discussed. This is a summary of the topics covered in the mini-symposium on microRNA regulation of neural stem cells and neurogenesis in SFN 2010 and is not meant to be a comprehensive review of the subject.

MicroRNA loss enhances learning and memory in mice

Dicer-dependent noncoding RNAs, including microRNAs (miRNAs), play an important role in a modulation of translation of mRNA transcripts necessary for differentiation in many cell types. In vivo experiments using cell type-specific Dicer1 gene inactivation in neurons showed its essential role for neuronal development and survival. However, little is known about the consequences of a loss of miRNAs in adult, fully differentiated neurons. To address this question, we used an inducible variant of the Cre recombinase (tamoxifen-inducible CreERT2) under control of Camk2a gene regulatory elements. After induction of Dicer1 gene deletion in adult mouse forebrain, we observed a progressive loss of a whole set of brain-specific miRNAs. Animals were tested in a battery of both aversively and appetitively motivated cognitive tasks, such as Morris water maze, IntelliCage system, or trace fear conditioning. Compatible with rather long half-life of miRNAs in hippocampal neurons, we observed an enhancement of memory strength of mutant mice 12 weeks after the Dicer1 gene mutation, before the onset of neurodegenerative process. In acute brain slices, immediately after high-frequency stimulation of the Schaffer collaterals, the efficacy at CA3-to-CA1 synapses was higher in mutant than in control mice, whereas long-term potentiation was comparable between genotypes. This phenotype was reflected at the subcellular and molecular level by the elongated filopodia-like shaped dendritic spines and an increased translation of synaptic plasticity-related proteins, such as BDNF and MMP-9 in mutant animals. The presented work shows miRNAs as key players in the learning and memory process of mammals.

Identification and experimental validation of G protein alpha inhibiting activity polypeptide 2 (GNAI2) as a microRNA-138 target in tongue squamous cell carcinoma

MicroRNA deregulation is a critical event in tumor initiation and progression. The down-regulation of microRNA-138 has been frequently observed in various cancers, including tongue squamous cell carcinoma (TSCC). Our previous studies suggest that deregulation of miR-138 is associated with the enhanced proliferation and invasion in TSCC cells. Here, we seek to identify the targets of miR-138 in TSCC, and explore their functional relevance in tumorigenesis. Our genome-wide expression profiling experiments identified a panel of 194 unique transcripts that were significantly down-regulated in TSCC cells transfected with miR-138. A comprehensive screening using six different sequence-based microRNA target prediction algorithms revealed that 51 out of these 194 down-regulated transcripts are potential direct targets for miR-138. These targets include: chloride channel, nucleotide-sensitive, 1A (CLNS1A), G protein alpha inhibiting activity polypeptide 2 (GNAI2), solute carrier family 20, member 1 (SLC20A1), eukaryotic translation initiation factor 4E binding protein 1 (EIF4EBP1), and Rho-related GTP-binding protein C (RhoC). GNAI2 is a known proto-oncogene that is involved in the initiation and progression of several different types of tumors. Direct targeting of miR-138 to two candidate binding sequences located in the 3'-untranslated region of GNAI2 mRNA was confirmed using luciferase reporter gene assays. Knockdown of miR-138 in TSCC cells enhanced the expression of GNAI2 at both mRNA and protein levels. In contrast, ectopic transfection of miR-138 reduced the expression of GNAI2, which, in consequence, led to reduced proliferation, cell cycle arrest and apoptosis. In summary, we identified a number of high-confident miR-138 target genes, including proto-oncogene GNAI2, which may play an important role in TSCC initiation and progression.