Reciprocal actions of REST and a microRNA promote neuronal identity

MicroRNAs in glaucoma and neurodegenerative diseases

MicroRNAs (miRNAs) constitute a class of short, non-coding RNAs, which have important role in post-transcriptional regulation of genes expression by base-pairing with their target messenger RNA (mRNA). In recent years, miRNAs biogenesis, gene silencing mechanism and implication in various diseases have been thoroughly investigated. Many scientific findings indicate the altered expression of specific miRNA in the brains of patients affected by neurodegenerative diseases (NDs) such as Alzheimer's disease, Parkinson's disease and Huntington disease. The progressive optic nerve neuropathy associated with changed miRNA profile was also observed during glaucoma development. This suggests that the miRNAs may have a crucial role in these disorders, contributing to the neuronal cell death. A better understanding of molecular mechanism of these disorders will open a new potential way of ND treatment. In this review, the miRNAs role in particular neurodegenerative disorders and their possible application in medicine was discussed.

miRNAs: Key Players in Neurodegenerative Disorders and Epilepsy

MicroRNAs (miRNAs) are endogenous, ∼22 nucleotide, non-coding RNA molecules that function as post-transcriptional regulators of gene expression. miRNA dysregulation has been observed in cancer and in neurodegenerative disorders such as Alzheimer's, Parkinson's, and Huntington's diseases, amyotrophic lateral sclerosis, and the neurological disorder, epilepsy. Neuronal degradation and death are important hallmarks of neurodegenerative disorders. Additionally, abnormalities in metabolism, synapsis and axonal transport have been associated with Alzheimer's disease, Parkinson's disease, and frontotemporal dementia. A number of recently published studies have demonstrated the importance of miRNAs in the nervous system and have contributed to the growing body of evidence on miRNA dysregulation in neurological disorders. Knowledge of the expressions and activities of such miRNAs may aid in the development of novel therapeutics. In this review, we discuss the significance of miRNA dysregulation in the development of neurodegenerative disorders and the use of miRNAs as targets for therapeutic intervention.

Transgenic Mouse Expressing Optical MicroRNA Reporter for Monitoring MicroRNA-124 Action during Development

MicroRNAs (miRNAs) fine-tune target protein synthesis by suppressing gene expression, temporally changing along development and possibly in pathological conditions. A method to monitor the action of miRNAs in vivo shall help understand their dynamic behavior during development. In this study, we established a transgenic mouse harboring miR-124 responsive element in their luciferase-eGFP reporter transgenes which enabled monitoring the action of miR-124 in the brain and other organs in vivo by the bioluminescence imaging. The mouse model was produced and verified by imaging ex vivo so that luminescence by luciferase shone and then reduced during development with miR-124 expression. Bioluminescence dramatically decreased in the brain between embryonic day 13 and 16 as endogenous miR-124 expression increased, which sustained into adulthood. The inverse relationship of miR-124 expression was observed with luciferase bioluminescence and activity ex vivo as well as in vivo. Taken together, one can use this microRNA-transgenic mouse to investigate the temporal changes of microRNA action in vivo in the brain as well as in other organs.

μ Opioid Receptor Expression after Morphine Administration Is Regulated by miR-212/132 Cluster

Since their discovery, miRNAs have emerged as a promising therapeutical approach in the treatment of several diseases, as demonstrated by miR-212 and its relation to addiction. Here we prove that the miR-212/132 cluster can be regulated by morphine, through the activation of mu opioid receptor (Oprm1). The molecular pathways triggered after morphine administration also induce changes in the levels of expression of oprm1. In addition, miR-212/132 cluster is actively repressing the expression of mu opioid receptor by targeting a sequence in the 3’ UTR of its mRNA. These findings suggest that this cluster is closely related to opioid signaling, and function as a post-transcriptional regulator, modulating morphine response in a dose dependent manner. The regulation of miR-212/132 cluster expression is mediated by MAP kinase pathway, CaMKII-CaMKIV and PKA, through the phosphorylation of CREB. Moreover, the regulation of both oprm1 and of the cluster promoter is mediated by MeCP2, acting as a transcriptional repressor on methylated DNA after prolonged morphine administration. This mechanism explains the molecular signaling triggered by morphine as well as the regulation of the expression of the mu opioid receptor mediated by morphine and the implication of miR-212/132 in these processes.

The interplay of microRNAs and post-ischemic glutamate excitotoxicity: an emergent research field in stroke medicine

Stroke is the second leading cause of death and the most common cause of adult disabilities among elderlies. It involves a complex series of mechanisms among which, excitotoxicity is of great importance. Also, miRNAs appear to play role in post-stroke excitotoxicity, and changes in their transcriptome occur right after cerebral ischemia. Recent data indicate that specific miRNAs such as miRNA-223, miRNA-181, miRNA-125a, miRNA-125b, miRNA-1000, miRNA-132 and miRNA-124a regulate glutamate neurotransmission and excitotoxicity during stroke. However, limitations such as poor in vivo stability, side effects and inappropriate biodistribution in miRNA-based therapies still exist and should be overcome before clinical application. Thence, investigation of the effect of application of these miRNAs after the onset of ischemia is a pivotal step for manipulating these miRNAs in clinical use. Given this, present review concentrates on miRNAs roles in post-ischemic stroke excitotoxicity.

MicroRNA: Small RNA mediators of the brains genomic response to environmental stress

The developmental processes that establish the synaptic architecture of the brain while retaining capacity for activity-dependent remodeling, are complex and involve a combination of genetic and epigenetic influences. Dysregulation of these processes can lead to problems with neural circuitry which manifest in humans as a range of neurodevelopmental syndromes, such as schizophrenia, bipolar disorder and fragile X mental retardation. Recent studies suggest that prenatal, postnatal and intergenerational environmental factors play an important role in the aetiology of stress-related psychopathology. A number of these disorders have been shown to display epigenetic changes in the postmortem brain that reflect early life experience. These changes affect the regulation of gene expression though chromatin remodeling (transcriptional) and post-transcriptional influences, especially small noncoding microRNA (miRNA). These dynamic and influential molecules appear to play an important function in both brain development and its adaption to stress. In this review, we examine the role of miRNA in mediating the brain's response to both prenatal and postnatal environmental perturbations and explore how stress- induced alterations in miRNA expression can regulate the stress response via modulation of the immune system. Given the close relationship between environmental stress, miRNA, and brain development/function, we assert that miRNA hold a significant position at the molecular crossroads between neural development and adaptations to environmental stress. A greater understanding of the dynamics that mediate an individual's predisposition to stress-induced neuropathology has major human health benefits and is an important area of research.

Genetics and Epigenetics in Adult Neurogenesis

The cellular basis of adult neurogenesis is neural stem cells residing in restricted areas of the adult brain. These cells self-renew and are multipotent. The maintenance of "stemness" and commitment to differentiation are tightly controlled by intricate molecular networks. Epigenetic mechanisms, including chromatin remodeling, DNA methylation, and noncoding RNAs (ncRNAs), have profound regulatory roles in mammalian gene expression. Significant advances have been made regarding the dynamic roles of epigenetic modulation and function. It has become evident that epigenetic regulators are key players in neural-stem-cell self-renewal, fate specification, and final maturation of new neurons, therefore, adult neurogenesis. Altered epigenetic regulation can result in a number of neurological and neurodevelopmental disorders. Here, we review recent discoveries that advance our knowledge in epigenetic regulation of mammalian neural stem cells and neurogenesis. Insights from studies of epigenetic gene regulation in neurogenesis may lead to new therapies for the treatment of neurodevelopmental 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.

Altered microRNA expression profiles in a rat model of spina bifida

MicroRNAs (miRNAs) are dynamically regulated during neurodevelopment, yet few reports have examined their role in spina bifida. In this study, we used an established fetal rat model of spina bifida induced by intragastrically administering olive oil-containing all-trans retinoic acid to dams on day 10 of pregnancy. Dams that received intragastric administration of all-trans retinoic acid-free olive oil served as controls. The miRNA expression profile in the amniotic fluid of rats at 20 days of pregnancy was analyzed using an miRNA microarray assay. Compared with that in control fetuses, the expression of miRNA-9, miRNA-124a, and miRNA-138 was significantly decreased (> 2-fold), whereas the expression of miRNA-134 was significantly increased (> 4-fold) in the amniotic fluid of rats with fetuses modeling spina bifida. These results were validated using real-time quantitative reverse-transcription polymerase chain reaction. Hierarchical clustering analysis of the microarray data showed that these differentially expressed miRNAs could distinguish fetuses modeling spina bifida from control fetuses. Our bioinformatics analysis suggested that these differentially expressed miRNAs were associated with many cytological pathways, including a nervous system development signaling pathway. These findings indicate that further studies are warranted examining the role of miRNAs through their regulation of a variety of cell functional pathways in the pathogenesis of spina bifida. Such studies may provide novel targets for the early diagnosis and treatment of spina bifida.

Fluorescence imaging of in vivo miR-124a-induced neurogenesis of neuronal progenitor cells using neuron-specific reporters

Background

Facilitation of the differentiation of the stem cells toward neuronal lineage is crucial for enhancing the differentiation efficacy of grafted stem cells for the possible treatment of neurodegenerative disorders. MicroRNA124a (miR-124a) has been considered as a neuronal lineage regulator, possessing the capability to activate neuronal differentiation. In this study, using a neuronal promoter-based reporter and live-cell fluorescence imaging, we visualized in vitro and in vivo the enhanced neuronal differentiation of neuronal progenitor cells with miR-124a overproduction.

Methods

The neuron specific alpha1 tubulin promoter-driven RFP reporter (pTa1-RFP) was used to trace the miR-124a-induced neuronal differentiation in live cell condition. MiR-124a or miR-scramble in 10 % glucose buffer was mixed with in vivo-jetPEITM and in vivo fluorescence images were obtained daily using Maestro spectral fluorescent imager.

Results

Neurite outgrowth was clearly seen in F11 cells after miR-124a transfection, and immunofluorescence staining showed increase of Tuj1 and NF at 48 hours. When pTa1-RFP-transfected F11 cells were implanted simultaneously with miR-124a into the nude mice, gradually increasing reporter signals and morphological changes indicated neuronal differentiation for 48 hours in live cells in vitro. The miR-124a-treated F11 cells showed higher reporter signals on in vivo fluorescence imaging than miR-scramble-treated cells, which were verified by ex vivo confirmation of Tuj1 and NF expression.

Conclusions

These results indicated that neuronal reporter-based neurogenesis imaging can be used for monitoring miR-124a acting as neuronal activator when miRNA was injected in in vivo PEI-coated form for miRNA-mediated regenerative therapy.

The role of epigenetics and long noncoding RNA MIAT in neuroendocrine prostate cancer

Neuroendocrine prostate cancer (NEPC) is the most lethal prostatic neoplasm. NEPC is thought to originate from the transdifferentiation of AR-positive adenocarcinoma cells. We have previously shown that an epigenetic/noncoding interactome (ENI) orchestrates cancer cells' plasticity, thereby allowing the emergence of metastatic, drug-resistant neoplasms. The primary objective of this manuscript is to discuss evidence indicating that some components of the ENI (Polycomb genes, miRNAs) play a key role in NEPC initiation and progression. Long noncoding RNAs represent vast and largely unexplored component of the ENI. Their role in NEPC has not been investigated. We show preliminary evidence indicating that a lncRNA (MIAT) is selectively upregulated in NEPCs and might interact with Polycomb genes. Our results indicate that long noncoding RNAs can be exploited as new biomarkers and therapeutic targets for NEPC.

Prolonged Induction of miR-212/132 and REST Expression in Rat Striatum Following Cocaine Self-Administration

Chronic exposure to cocaine in vivo induces long-term synaptic plasticity associated with the brain’s circuitry that underlies development of repetitive and automatic behaviors called habits. In fact, prolonged drug consumption results in aberrant expression of protein-coding genes and small regulatory RNAs, including miRNAs that are involved in synaptic plasticity and neuroadaptations. However, the mechanisms mediating cocaine use disorder are still not fully understood. The present study is designed to examine the expression of miR-124, miR-132, miR-134, and miR-212, as well as the levels of the Ago2, Pum2, and REST mRNAs and proteins implicated in their regulation. We applied rat cocaine self-administration (SA) and extinction training procedures with a yoked triad to assess the changes in the levels of four miRNAs and three protein-coding genes and corresponding proteins in the dorsal striatum. We demonstrated that elevated expression of mature miR-212 and miR-132 is long-lasting and persists in the drug-free period (till 10-day abstinence). Moreover, mRNA and protein of REST, a regulator of neuronal transcription, was raised selectively in cocaine self-administering rats and Ago2 transcript decreased after cocaine treatment. Unexpectedly, the expression level of Ago2 and Pum2 proteins changed only in the active cocaine-receiving animals. These results point out the important aspects of long-lasting alterations in microRNAs, genes, and protein expressions involved in the control of synaptic plasticity associated with reward and motivation learning related to cocaine addiction.

Dual and Opposing Roles of MicroRNA-124 in Epilepsy Are Mediated through Inflammatory and NRSF-Dependent Gene Networks

Insult-provoked transformation of neuronal networks into epileptic ones involves multiple mechanisms. Intervention studies have identified both dysregulated inflammatory pathways and NRSF-mediated repression of crucial neuronal genes as contributors to epileptogenesis. However, it remains unclear how epilepsy-provoking insults (e.g., prolonged seizures) induce both inflammation and NRSF and whether common mechanisms exist. We examined miR-124 as a candidate dual regulator of NRSF and inflammatory pathways. Status epilepticus (SE) led to reduced miR-124 expression via SIRT1--and, in turn, miR-124 repression--via C/EBPα upregulated NRSF. We tested whether augmenting miR-124 after SE would abort epileptogenesis by preventing inflammation and NRSF upregulation. SE-sustaining animals developed epilepsy, but supplementing miR-124 did not modify epileptogenesis. Examining this result further, we found that synthetic miR-124 not only effectively blocked NRSF upregulation and rescued NRSF target genes, but also augmented microglia activation and inflammatory cytokines. Thus, miR-124 attenuates epileptogenesis via NRSF while promoting epilepsy via inflammation.

microRNAs as neuroregulators, biomarkers and therapeutic agents in neurodegenerative diseases

The last decade has experienced the emergence of microRNAs as a key molecular tool for the diagnosis and prognosis of human diseases. Although the focus has mostly been on cancer, neurodegenerative diseases present an exciting, yet less explored, platform for microRNA research. Several studies have highlighted the significance of microRNAs in neurogenesis and neurodegeneration, and pre-clinical studies have shown the potential of microRNAs as biomarkers. Despite this, no bona fide microRNAs have been identified as true diagnostic or prognostic biomarkers for neurodegenerative disease. This is mainly due to the lack of precisely defined patient cohorts and the variability within and between individual cohorts. However, the discovery that microRNAs exist as stable molecules at detectable levels in body fluids has opened up new avenues for microRNAs as potential biomarker candidates. Furthermore, technological developments in microRNA biology have contributed to the possible design of microRNA-mediated disease intervention strategies. The combination of these advancements, with the availability of well-defined longitudinal patient cohort, promises to not only assist in developing invaluable diagnostic tools for clinicians, but also to increase our overall understanding of the underlying heterogeneity of neurodegenerative diseases. In this review, we present a comprehensive overview of the existing knowledge of microRNAs in neurodegeneration and provide a perspective of the applicability of microRNAs as a basis for future therapeutic intervention strategies.

MicroRNA-124 regulates neuronal differentiation of mesenchymal stem cells by targeting Sp1 mRNA

MicroRNAs play an important role in neuronal development and function. miR-124 is the most abundantly expressed miRNA in the nervous system. Several different mRNA targets have been proposed for miR-124, but the precise function of endogenous miR-124 and its mRNA targets remain to be further elucidated. Specificity protein 1 (Sp1) is a transcription factor that plays key roles in many cell processes including cell cycle. However, this transcription factor is nearly absent in differentiated neurons and a remarkable suppression of Sp1 expression was shown after neurogenesis. Since miR-124 is expressed abundantly in neurons and because Sp1 levels decrease during neurogenesis, it is possible that miR-124 could regulate the expression of Sp1 during neuronal development. Therefore, the aim of the present study was to evaluate the putative targeting of Sp1 by miR-124. Overexpression of miR-124 using a plasmid coding for pri-miR-124 in HEK293 cells decreased the expression of Sp1 mRNA. The results of dual-luciferase reporter assay demonstrated that miR-124 directly targeted the 3'-untranslated regions of Sp1 mRNA. To evaluate whether Sp1 expression was regulated by miR-124 during the process of neuronal differentiation, Adipose-derived mesenchymal stem cells (A-MSCs) were differentiated into neuron-like cells. The results of qPCR analysis showed that with the gradual increase of miR-124 expression during neurogenesis, the expression of Sp1 mRNA decreased accordingly. In summary, this study demonstrated for the first time that miR-124 is able to suppress Sp1 expression, which in turn affected the neuronal differentiation of mesenchymal stem cells.

Dephosphorylating eukaryotic RNA polymerase II

The phosphorylation state of the C-terminal domain of RNA polymerase II is required for the temporal and spatial recruitment of various factors that mediate transcription and RNA processing throughout the transcriptional cycle. Therefore, changes in CTD phosphorylation by site-specific kinases/phosphatases are critical for the accurate transmission of information during transcription. Unlike kinases, CTD phosphatases have been traditionally neglected as they are thought to act as passive negative regulators that remove all phosphate marks at the conclusion of transcription. This over-simplified view has been disputed in recent years and new data assert the active and regulatory role phosphatases play in transcription. We now know that CTD phosphatases ensure the proper transition between different stages of transcription, balance the distribution of phosphorylation for accurate termination and re-initiation, and prevent inappropriate expression of certain genes. In this review, we focus on the specific roles of CTD phosphatases in regulating transcription. In particular, we emphasize how specificity and timing of dephosphorylation are achieved for these phosphatases and consider the various regulatory factors that affect these dynamics.

The REST remodeling complex protects genomic integrity during embryonic neurogenesis

The timely transition from neural progenitor to post-mitotic neuron requires down-regulation and loss of the neuronal transcriptional repressor, REST. Here, we have used mice containing a gene trap in the Rest gene, eliminating transcription from all coding exons, to remove REST prematurely from neural progenitors. We find that catastrophic DNA damage occurs during S-phase of the cell cycle, with long-term consequences including abnormal chromosome separation, apoptosis, and smaller brains. Persistent effects are evident by latent appearance of proneural glioblastoma in adult mice deleted additionally for the tumor suppressor p53 protein (p53). A previous line of mice deleted for REST in progenitors by conventional gene targeting does not exhibit these phenotypes, likely due to a remaining C-terminal peptide that still binds chromatin and recruits co-repressors. Our results suggest that REST-mediated chromatin remodeling is required in neural progenitors for proper S-phase dynamics, as part of its well-established role in repressing neuronal genes until terminal differentiation.

DOI:http://dx.doi.org/10.7554/eLife.09584.001

In the brain, cells called neurons connect to each other to form complex networks through which information is rapidly processed. These cells start to form in the developing brains of animal embryos when “neural” stem cells divide in a process called neurogenesis. For this process to proceed normally, particular genes in the stem cells have to be switched on or off at different times. This ensures that the protein products of the genes are only made when they are needed.

Proteins called transcription factors can bind to DNA to activate or inactivate particular genes; for example, a transcription factor called REST inactivates thousands of genes that are needed by neurons. During neurogenesis, the production of REST normally declines, and some studies have shown that if the production of this protein is artificially increased, the formation of neurons is delayed. However, other studies suggest that REST may not play a major role in neurogenesis.

Here, Nechiporuk et al. re-examine the role of REST in mice. The experiments used genetically modified mice in which the gene that encodes REST was prematurely switched off in neural stem cells. Compared with normal mice, these mutant mice had much smaller brains that contained fewer neurons because the stem cells stopped dividing earlier than normal. Unexpectedly, many genes that are normally switched off by REST, were not significantly changed, while genes that are not normally regulated by REST – such as the gene that encodes a protein called p53 – were active.

It is known from previous work that p53 is expressed when cells are exposed to harmful conditions that can damage DNA. This helps to prevent cells from becoming cancerous. Nechiporuk et al. found that cells that lacked REST had higher levels of DNA damage than normal cells due to errors during the process of copying DNA before a cell divides. Furthermore, when both REST and p53 were absent, the neural stem cells became cancerous and formed tumors in the mice.

Nechiporuk et al.’s findings suggest that REST protects the DNA of genes that are needed for neurons to form and work properly. The new challenge is to understand where in the genome the damage is occurring.

DOI:http://dx.doi.org/10.7554/eLife.09584.002

miR-124-9-9* potentiates Ascl1-induced reprogramming of cultured Müller glia

The Müller glia of fish provide a source for neuronal regeneration after injury, but they do not do so in mammals. We previously showed that lentiviral gene transfer of the transcription factor Achaete-scute homolog 1 (Ascl1/Mash1) in murine Müller glia cultures resulted in partial reprogramming of the cells to retinal progenitors. The microRNAs (miRNAs) miR-124-9-9* facilitate neuronal reprogramming of fibroblasts, but their role in glia reprogramming has not been reported. The aim of this study was to test whether (1) lentiviral gene transfer of miR-124-9-9* can reprogram Müller glia into retinal neurons and (2) miR-124-9-9* can improve Ascl1-induced reprogramming. Primary Müller glia cultures were generated from postnatal day (P) 11/12 mice, transduced with lentiviral particles, i.e., miR-124-9-9*-RFP, nonsense-RFP, Ascl1-GFP, or GFP-control. Gene expression and immunofluorescence analyses were performed within 3 weeks after infection. 1. Overexpression of miR-124-9-9* induced the expression of the proneural factor Ascl1 and additional markers of neurons, including TUJ1 and MAP2. 2. When Ascl1 and miR-124-9-9* were combined, 50 to 60% of Müller glia underwent neuronal reprogramming, whereas Ascl1 alone results in a 30 to 35% reprogramming rate. 3. Analysis of the miR-124-9-9* treated glial cells showed a reduction in the level of Ctdsp1 and Ptbp1, indicating a critical role for the REST pathway in the repression of neuronal genes in Müller glia. Our data further suggest that miR-124-9-9* and the REST complex may play a role in regulating the reprogramming of Müller glia to progenitors that underlies retinal regeneration in zebrafish.

Transcriptional regulation of microRNA-100, -146a, and -150 genes by p53 and NFκB p65/RelA in mouse striatal STHdh(Q7)/ Hdh(Q7) cells and human cervical carcinoma HeLa cells

MicroRNA (miRNA) genes generally share many features common to those of protein coding genes. Various transcription factors (TFs) and co-regulators are also known to regulate miRNA genes. Here we identify novel p53 and NFκB p65/RelA responsive miRNAs and demonstrate that these 2 TFs bind to the regulatory sequences of miR-100, -146a and -150 in both mouse striatal and human cervical carcinoma cells and regulate their expression. p53 represses the miRNAs while NFκB p65/RelA induces them. Further, we provide evidence that exogenous p53 inhibits NFκB p65/RelA activity by reducing its nuclear content and competing with it for CBP binding. This suggests for the existence of a functional cross-talk between the 2 TFs in regulating miRNA expression. Moreover, promoter occupancy assay reveals that exogenous p53 excludes NFκB p65/RelA from its binding site in the upstream sequence of miR-100 gene thereby causing its repression. Thus, our work identifies novel p53 and NFκB p65/RelA responsive miRNAs in human and mouse and uncovers possible mechanisms of co-regulation of miR-100. It is to be mentioned here that cross-talks between p53 and NFκB p65/RelA have been observed to define the outcome of several biological processes and that the pro-apoptotic effect of p53 and the pro-survival functions of NFκB can be largely mediated via the biological roles of the miRNAs these TFs regulate. Our observation with cell lines thus provides an important platform upon which further work is to be done to establish the biological significance of such co-regulation of miRNAs by p53 and NFκB p65/RelA.

The role of miR-9 during neuron differentiation of mouse retinal stem cells

Retinal stem cells (RSCs) have been defined as neural cells with the potential to self-renew and to generate all the different cell types of the nervous system following differentiation, which are an ideal engraft in retinal regeneration. In this research, mouse RSCs were isolated from retina, induced differentiation into neuron cells in vitro after over-expression of miR-9. The results showed that the RSCs could induce differentiation into neuron cells under the special medium, but when the miR-9 was over-expressed, the differentiated efficiency of neuron cells from RSCs could be promoted. This reason was demonstrated that polypyrimidine tract-binding protein 1 (PTBP1) was a repressor for polypyrimidine tract-binding protein 2 (PTBP2), during neuronal differentiation, miR-9 reduced PTBP1 levels, leading to the accumulation of correctly spliced PTBP2 mRNA and a dramatic increase in PTBP2 protein. And then miR-9 promoted neuron cells from RSCs were successful colonized into injured spinal cord for participation in tissue-repair. In conclusion, our research showed that the miR-9 promoted the differentiation of neuronal cells from RSCs, and this mechanism was miR-9 reduced the expression of PTBP1, increased the expression of PTBP2.

MicroRNAs: Not "Fine-Tuners" but Key Regulators of Neuronal Development and Function

MicroRNAs (miRNAs) are a class of short non-coding RNAs that operate as prominent post-transcriptional regulators of eukaryotic gene expression. miRNAs are abundantly expressed in the brain of most animals and exert diverse roles. The anatomical and functional complexity of the brain requires the precise coordination of multilayered gene regulatory networks. The flexibility, speed, and reversibility of miRNA function provide precise temporal and spatial gene regulatory capabilities that are crucial for the correct functioning of the brain. Studies have shown that the underlying molecular mechanisms controlled by miRNAs in the nervous systems of invertebrate and vertebrate models are remarkably conserved in humans. We endeavor to provide insight into the roles of miRNAs in the nervous systems of these model organisms and discuss how such information may be used to inform regarding diseases of the human brain.

REST-Governed Gene Expression Profiling in a Neuronal Cell Model Reveals Novel Direct and Indirect Processes of Repression and Up-Regulation

The role of REST changes in neurons, including the rapid decrease of its level during differentiation and its fluctuations during many mature functions and diseases, is well established. However, identification of many thousand possible REST-target genes, mostly based on indirect criteria, and demonstration of their operative dependence on the repressor have been established for only a relatively small fraction. In the present study, starting from our recently published work, we have expanded the identification of REST-dependent genes, investigated in two clones of the PC12 line, a recognized neuronal cell model, spontaneously expressing different levels of REST: very low as in neurons and much higher as in most non-neural cells. The molecular, structural and functional differences of the two PC12 clones were shown to depend largely on their different REST level and the ensuing variable expression of some dependent genes. Comprehensive RNA-Seq analyses of the 13,700 genes expressed, validated by parallel RT-PCR and western analyses of mRNAs and encoded proteins, identified in the high-REST clone two groups of almost 900 repressed and up-regulated genes. Repression is often due to direct binding of REST to target genes; up-regulation to indirect mechanism(s) mostly mediated by REST repression of repressive transcription factors. Most, but not all, genes governing neurosecretion, excitability, and receptor channel signaling were repressed in the high REST clone. The genes governing expression of non-channel receptors (G protein-coupled and others), although variably affected, were often up-regulated together with the genes of intracellular kinases, small G proteins, cytoskeleton, cell adhesion, and extracellular matrix proteins. Expression of REST-dependent genes governing functions other than those mentioned so far were also identified. The results obtained by the parallel investigation of the two PC12 clones revealed the complexity of the REST molecular and functional role, deciphering new aspects of its participation in neuronal functions. The new findings could be relevant for further investigation and interpretation of physiological processes typical of neurons. Moreover, they could be employed as tools in the study of neuronal diseases recently shown to depend on REST for their development.

Repressor element-1 silencing transcription factor (REST) is present in human control and Huntington's disease neurones

AIMS

The repressor element-1 silencing transcription factor/neurone-restrictive silencer factor (REST/NRSF) is a master regulator of neuronal gene expression. REST/NRSF functions by recruiting other cofactors to genomic loci that contain the repressor element 1/neurone restrictive silencer element (RE1/NRSE) binding motif. In brain, demonstration of REST protein presence in neurones has remained controversial. However, RE1/NRSE containing neuronal genes are actively modulated and REST dysregulation is implicated in Huntington's disease (HD). We aimed to investigate REST distribution in autopsy brain from control and HD patients.

METHODS

Brain tissues from six controls and six HD cases (Vonsattel grade 3 and 4) were investigated using immunohistochemical analysis.

RESULTS

REST was present in neurones and glial cells of the cortex, caudate nucleus, hippocampus and cerebellum. REST labelling was mainly cytoplasmic in neurones while preferential nuclear staining of REST was found in glial cells. We also found that REST and huntingtin (HTT) colocalize in human neurones. Low levels of cytoplasmic REST were detected in neurones of the HD cortex and caudate but no direct relationship between decreased neuronal REST expression and disease grade was observed.

CONCLUSIONS

These data support the notion of REST presence in human brain neurones and glial cells and indicate the importance of developing compounds able to restore REST-regulated transcription of neuronal genes in HD.

Sexually dimorphic effects of gestational endocrine-disrupting chemicals on microRNA expression in the developing rat hypothalamus

This study examined developmental changes and sexual dimorphisms in hypothalamic microRNAs, and whether gestational exposures to environmental endocrine-disrupting chemicals (EDCs) altered their expression patterns. Pregnant rat dams were treated on gestational days 16 and 18 with vehicle, estradiol benzoate, or a mixture of polychlorinated biphenyls. Male and female offspring were euthanized on postnatal days (P) 15, 30, 45, or 90, and microRNA and mRNA targets were quantified in the medial preoptic nucleus (MPN) and ventromedial nucleus (VMN) of the hypothalamus. MicroRNAs showed robust developmental changes in both regions, and were sexually dimorphic in the MPN, but not VMN. Importantly, microRNAs in females were up-regulated by EDCs at P30, and down-regulated in males at P90. Few changes in mRNAs were found. Thus, hypothalamic microRNAs are sensitive to prenatal EDC treatment in a sex-, developmental age-, and brain region-specific manner.

Fragile X Syndrome FMRP Co-localizes with Regulatory Targets PSD-95, GABA Receptors, CaMKIIα, and mGluR5 at Fiber Cell Membranes in the Eye Lens

Fmr1 and FMRP underlie Fragile X Syndrome (FXS) and are linked with related autism spectrum disorders (ASD). Fmr1 also has an essential role in eye and lens development. Lenses express FMRP along with γ-aminobutyric acid (GABA) receptors (GABARs), post-synaptic density protein 95 (PSD-95), Tyr-phosphatase STEP, CaMKIIα and Alzheimer's disease Aβ precursor protein, which are verified targets of FMRP regulation in neurons and outline major topics in FXS/ASD research. PSD-95 as well as CaMKIIα transcripts undergo polypryimidine tract binding protein dependent alternative splicing in lens, consistent with PSD-95 translation in lens. At least 13 GABAR subunits and GAD25/65/67 GABA metabolism enzymes are expressed in lenses beginning in embryonic development, matching neural development. Interestingly, GABAergic drugs (e.g. baclofen) studied as FXS/ASD therapeutics are shown to resolve developmental vision defects in experimental myopia. Here, we demonstrated that FMRP co-localizes at fiber cell membranes with PSD-95, GABAAδ, GABAAβ3, GABBR1, STEP, CaMKIIα, and mGluR5 in young adult lenses. GAD65 and GABA detection was greatest at the peri-nuclear lens region where fiber cell terminal differentiation occurs. These findings add to an extensive list of detailed parallels between fiber cell and neuron morphology and their lateral membrane spine/protrusions, also reflected in the shared expression of genes involved in the morphogenesis and function of these membrane structures, and shared use of associated regulatory mechanisms first described as distinguishing the neuronal phenotype. Future studies can determine if GABA levels currently studied as a FXS/ASD biomarker in the brain, and generated by GAD25/65/67 in a comparable cell environment in the lens, may be similarly responsive to Fmr1 mutation in lens. The present demonstration of FMRP and key regulatory targets in the lens identifies a potential for the lens to provide a new research venue, in the same individual, to inform about Fmr1/FMRP pathobiology in brain as well as lens.

Bioimaging of microRNA124a-independent neuronal differentiation of human G2 neural stem cells

•

A bioinformatics approach was used to analyze neuron-specific miRNA expression.

•

A noninvasive luciferase imaging tool was used to confirm the miRNA expression profile.

•

An integrated research strategy provided complementary information of better reliability.

•

This strategy will be useful for study of miRNAs associated with differentiation and diseases.

Evaluation of the function of microRNAs (miRNAs or miRs) through miRNA expression profiles during neuronal differentiation plays a critical role not only in identifying unique miRNAs relevant to cellular development but also in understanding regulatory functions of the cell-specific miRNAs in living organisms. Here, we examined the microarray-based miRNA expression profiles of G2 cells (recently developed human neural stem cells) and monitored the expression pattern of known neuron-specific miR-9 and miR-124a during neuronal differentiation of G2 cells in vitro and in vivo. Of 500 miRNAs analyzed by microarray of G2 cells, the expression of 90 miRNAs was significantly increased during doxycycline-dependent neuronal differentiation of G2 cells and about 60 miRNAs showed a gradual enhancement of gene expression as neuronal differentiation progressed. Real-time PCR showed that expression of endogenous mature miR-9 was continuously and gradually increased in a pattern dependent on the period of neuronal differentiation of G2 cells while the increased expression of neuron-specific mature miR-124a was barely observed during neurogenesis. Our recently developed miRNA reporter imaging vectors (CMV/Gluc/3×PT_miR-9 and CMV/Gluc/3×PT_miR-124a) containing Gaussia luciferase, CMV promoter and three copies of complementary nucleotides of each corresponding miRNA showed that luciferase activity from CMV/Gluc/3×PT_miR-9 was gradually decreased both in vitro and in vivo in G2 cells induced to differentiate into neurons. However, in vitro and in vivo bioluminescence signals for CMV/Gluc/3×PT_miR-124a were not significantly different between undifferentiated and differentiated G2 cells. Our results demonstrate that biogenesis of neuron-specific miR-124a is not necessary for doxycycline-dependent neurogenesis of G2 cells.

The Transcription Repressor REST in Adult Neurons: Physiology, Pathology, and Diseases

REST [RE1-silencing transcription factor (also called neuron-restrictive silencer factor)] is known to repress thousands of possible target genes, many of which are neuron specific. To date, REST repression has been investigated mostly in stem cells and differentiating neurons. Current evidence demonstrates its importance in adult neurons as well. Low levels of REST, which are acquired during differentiation, govern the expression of specific neuronal phenotypes. REST-dependent genes encode important targets, including transcription factors, transmitter release proteins, voltage-dependent and receptor channels, and signaling proteins. Additional neuronal properties depend on miRNAs expressed reciprocally to REST and on specific splicing factors. In adult neurons, REST levels are not always low. Increases occur during aging in healthy humans. Moreover, extensive evidence demonstrates that prolonged stimulation with various agents induces REST increases, which are associated with the repression of neuron-specific genes with appropriate, intermediate REST binding affinity. Whether neuronal increases in REST are protective or detrimental remains a subject of debate. Examples of CA1 hippocampal neuron protection upon depolarization, and of neurodegeneration upon glutamate treatment and hypoxia have been reported. REST participation in psychiatric and neurological diseases has been shown, especially in Alzheimer’s disease and Huntington’s disease, as well as epilepsy. Distinct, complex roles of the repressor in these different diseases have emerged. In conclusion, REST is certainly very important in a large number of conditions. We suggest that the conflicting results reported for the role of REST in physiology, pathology, and disease depend on its complex, direct, and indirect actions on many gene targets and on the diverse approaches used during the investigations.

Neural fate decisions mediated by combinatorial regulation of Hes1 and miR-9

In the nervous system, Hes1 shows an oscillatory manner in neural progenitors but a persistent one in neurons. Many models involving Hes1 have been provided for the study of neural differentiation but few of them take the role of microRNA into account. It is known that a microRNA, miR-9, plays crucial roles in modulating Hes1 oscillations. However, the roles of miR-9 in controlling Hes1 oscillations and inducing transition between different cell fates still need to be further explored. Here we provide a mathematical model to show the interaction between miR-9 and Hes1, with the aim of understanding how the Hes1 oscillations are produced, how they are controlled, and further, how they are terminated. Based on the experimental findings, the model demonstrates the essential roles of Hes1 and miR-9 in regulating the dynamics of the system. In particular, the model suggests that the balance between miR-9 and Hes1 plays important roles in the choice between progenitor maintenance and neural differentiation. In addition, the synergistic (or antagonistic) effects of several important regulations are investigated so as to elucidate the effects of combinatorial regulation in neural decision-making. Our model provides a qualitative mechanism for understanding the process in neural fate decisions regulated by Hes1 and miR-9.

MicroRNA-mediated regulation of differentiation and trans-differentiation in stem cells

MicroRNAs (miRNAs) are key components of a broadly conserved post-transcriptional mechanism that controls gene expression by targeting mRNAs. miRNAs regulate diverse biological processes, including the growth and differentiation of stem cells as well as the regulation of both endogenous tissue repair that has critical implications in the development of regenerative medicine approaches. In this review, we first describe key features of miRNA biogenesis and their role in regulating self-renewal, and then discuss the involvement of miRNAs in the determination of cell fate decisions. We highlight the role of miRNAs in the emergent field of reprogramming and trans-differentiation of somatic cells that could further our understanding of miRNA biology and regenerative medicine applications. Finally, we describe potential techniques for proper delivery of miRNAs in target cells.

Loss of microRNA-124 expression in neurons in the peri-lesion area in mice with spinal cord injury

MicroRNA-124 (miR-124) is abundantly expressed in neurons in the mammalian central nervous system, and plays critical roles in the regulation of gene expression during embryonic neurogenesis and postnatal neural differentiation. However, the expression profile of miR-124 after spinal cord injury and the underlying regulatory mechanisms are not well understood. In the present study, we examined the expression of miR-124 in mouse brain and spinal cord after spinal cord injury using in situ hybridization. Furthermore, the expression of miR-124 was examined with quantitative RT-PCR at 1, 3 and 7 days after spinal cord injury. The miR-124 expression in neurons at the site of injury was evaluated by in situ hybridization combined with NeuN immunohistochemical staining. The miR-124 was mainly expressed in neurons throughout the brain and spinal cord. The expression of miR-124 in neurons significantly decreased within 7 days after spinal cord injury. Some of the neurons in the peri-lesion area were NeuN(+)/miR-124(-). Moreover, the neurons distal to the peri-lesion site were NeuN(+)/miR-124(+). These findings indicate that miR-124 expression in neurons is reduced after spinal cord injury, and may reflect the severity of spinal cord injury.

Transcriptome dynamics of the microRNA inhibition response

We report a high-resolution time series study of transcriptome dynamics following antimiR-mediated inhibition of miR-9 in a Hodgkin lymphoma cell-line—the first such dynamic study of the microRNA inhibition response—revealing both general and specific aspects of the physiological response. We show miR-9 inhibition inducing a multiphasic transcriptome response, with a direct target perturbation before 4 h, earlier than previously reported, amplified by a downstream peak at ∼32 h consistent with an indirect response due to secondary coherent regulation. Predictive modelling indicates a major role for miR-9 in post-transcriptional control of RNA processing and RNA binding protein regulation. Cluster analysis identifies multiple co-regulated gene regulatory modules. Functionally, we observe a shift over time from mRNA processing at early time points to translation at later time points. We validate the key observations with independent time series qPCR and we experimentally validate key predicted miR-9 targets. Methodologically, we developed sensitive functional data analytic predictive methods to analyse the weak response inherent in microRNA inhibition experiments. The methods of this study will be applicable to similar high-resolution time series transcriptome analyses and provides the context for more accurate experimental design and interpretation of future microRNA inhibition studies.

The effects of microRNA on the absorption, distribution, metabolism and excretion of drugs

The importance of genetic factors (e.g. sequence variation) in the absorption, distribution, metabolism, excretion (ADME) and overall efficacy of therapeutic agents is well established. Our ability to identify, interpret and utilize these factors is the subject of much clinical investigation and therapeutic development. However, drug ADME and efficacy are also heavily influenced by epigenetic factors such as DNA/histone methylation and non-coding RNAs [especially microRNAs (miRNAs)]. Results from studies using tools, such as in silico miRNA target prediction, in vitro functional assays, nucleic acid profiling/sequencing and high-throughput proteomics, are rapidly expanding our knowledge of these factors and their effects on drug metabolism. Although these studies reveal a complex regulation of drug ADME, an increased understanding of the molecular interplay between the genome, epigenome and transcriptome has the potential to provide practically useful strategies to facilitate drug development, optimize therapeutic efficacy, circumvent adverse effects, yield novel diagnostics and ultimately become an integral component of personalized medicine.

An updated role of microRNA-124 in central nervous system disorders: a review

MicroRNA-124 (miR-124) is the most abundant miRNA in the brain. Biogenesis of miR-124 displays specific temporal and spatial profiles in various cell and tissue types and affects a broad spectrum of biological functions in the central nervous system (CNS). Recently, the link between dysregulation of miR-124 and CNS disorders, such as neurodegeneration, CNS stress, neuroimmune disorders, stroke, and brain tumors, has become evident. Here, we provide an overview of the specific molecular function of miR-124 in the CNS and a revealing insight for the therapeutic potential of miR-124 in the treatment of human CNS diseases.

The aryl hydrocarbon receptor/microRNA-212/132 axis in T cells regulates IL-10 production to maintain intestinal homeostasis

Aryl hydrocarbon receptor (Ahr), a transcription factor, plays a critical role in autoimmune inflammation of the intestine. In addition, microRNAs (miRNAs), small non-coding oligonucleotides, mediate pathogenesis of inflammatory bowel diseases (IBD). However, the precise mechanism and interactions of these molecules in IBD pathogenesis have not yet been investigated. We analyzed the role of Ahr and Ahr-regulated miRNAs in colonic inflammation. Our results show that deficiency of Ahr in intestinal epithelial cells in mice exacerbated inflammation in dextran sodium sulfate-induced colitis. Deletion of Ahr in T cells attenuated colitis, which was manifested by suppressed Th17 cell infiltration into the lamina propria. Candidate miRNA analysis showed that induction of colitis elevated expression of the miR-212/132 cluster in the colon of wild-type mice, whereas in Ahr (-/-) mice, expression was clearly lower. Furthermore, miR-212/132(-/-) mice were highly resistant to colitis and had reduced levels of Th17 cells and elevated levels of IL-10-producing CD4(+) cells. In vitro analyses revealed that induction of type 1 regulatory T (Tr1) cells was significantly elevated in miR-212/132(-/-) T cells with increased c-Maf expression. Our findings emphasize the vital role of Ahr in intestinal homeostasis and suggest that inhibition of miR-212/132 represents a viable therapeutic strategy for treating colitis.

Lens GABA receptors are a target of GABA-related agonists that mitigate experimental myopia

Coordinated growth of eye tissues is required to achieve visual acuity. However, visual experience also guides this process. Experimental myopia can be produced by altering light entering the eye, but also by changing light/dark regimens. Drug discovery studies demonstrated that γ-aminobutyric acid (GABA)-related agonists (e.g., baclofen) will mitigate experimental myopia, and are also drugs studied for their capacity to affect neurodevelopmental disorders that include Fragile X Syndrome and related autism spectrum disorders. GABA receptors thought to mediate these responses in the eye have been studied in the neural retina as well as the cornea and sclera which are both innervated tissues. In addition to neurons, lenses express GAD25/65/67 GABA metabolic enzymes and at least 13 GABA receptor subunits with developmental expression profiles that match neural development. Evidence that lens GABA receptors are expressed in a cell environment comparable to neurons is seen in the lens expression of AMPA and NMDA glutamate receptors together with an unexpectedly comprehensive array of associated signaling proteins that include post-synaptic-density 95 (PSD95), calcium calmodulin kinase IIα (CaMKIIα), Fragile X Syndrome mental retardation protein (FMRP), ephrin receptors, Ca(V)1.2, 1.3 channels, cyclin-dependent kinase 5 (Cdk5), and neuronal C-src among others. Moreover, lens cells share fundamental molecular regulatory mechanisms that integrate the regulation and function of these genes at the DNA, RNA, and protein levels in neurons. GABA has trophic, growth promoting effects early in neuron development and later assumes its classic inhibitory role in the adult neural system. We hypothesize that the extensive parallels between GABA and glutamate receptor biology in lens and brain identifies the lens as a site of GABA agonist drug action affecting experimental myopia, acting through lens GABA receptors to similarly affect growth in both elongated cell types.

Non-Coding RNAs in Stroke and Neuroprotection

This review will focus on the current state of knowledge regarding non-coding RNAs (ncRNA) in stroke and neuroprotection. There will be a brief introduction to microRNAs (miRNA), long ncRNAs (lncRNA), and piwi-interacting RNAs (piRNA), followed by evidence for the regulation of ncRNAs in ischemia. This review will also discuss the effect of neuroprotection induced by a sublethal duration of ischemia or other stimuli given before a stroke (preconditioning) on miRNA expression and the role of miRNAs in preconditioning-induced neuroprotection. Experimental manipulation of miRNAs and/or their targets to induce pre- or post-stroke protection will also be presented, as well as discussion on miRNA responses to current post-stroke therapies. This review will conclude with a brief discussion of future directions for ncRNAs studies in stroke, such as new approaches to model complex ncRNA datasets, challenges in ncRNA studies, and the impact of extracellular RNAs on human diseases such as stroke.

RE1 silencing transcription factor/neuron-restrictive silencing factor regulates expansion of adult mouse subventricular zone-derived neural stem/progenitor cells in vitro

Adult neural stem cell (aNSC) activity is tuned by external stimuli through the recruitment of transcription factors. This study examines the RE1 silencing transcription factor (REST) in neural stem/progenitor cells isolated from the subventricular zone of adult mouse brain and provides the first extensive characterization of REST-mediated control of the cellular and molecular properties. This study shows that REST knockdown affects the capacity of progenitor cells to generate neurospheres, reduces cell proliferation, and triggers cell differentiation despite the presence of growth factors. Genome- and transcriptome-wide analyses show that REST binding sites are significantly enriched in genes associated with synaptic transmission and nervous system development and function. Seeking candidate regulators of aNSC function, this study identifies a member of the bone morphogenetic protein (BMP) family, BMP6, the mRNA and protein of which increased after REST knockdown. The results of this study extend previous findings, demonstrating a reciprocal control of REST expression by BMPs. Administration of exogenous BMP6 inhibits aNSC proliferation and induces the expression of the astrocytic marker glial fibrillary acidic protein, highlighting its antimitogenic and prodifferentiative effects. This study suggests that BMP6 produced in a REST-regulated manner together with other signals can contribute to regulation of NSC maintenance and fate.

MicroRNA miR-124 controls the choice between neuronal and astrocyte differentiation by fine-tuning Ezh2 expression

Polycomb group protein Ezh2 is a histone H3 Lys-27 histone methyltransferase orchestrating an extensive epigenetic regulatory program. Several nervous system-specific genes are known to be repressed by Ezh2 in stem cells and derepressed during neuronal differentiation. However, the molecular mechanisms underlying this regulation remain poorly understood. Here we show that Ezh2 levels are dampened during neuronal differentiation by brain-enriched microRNA miR-124. Expression of miR-124 in a neuroblastoma cells line was sufficient to up-regulate a significant fraction of nervous system-specific Ezh2 target genes. On the other hand, naturally elevated expression of miR-124 in embryonic carcinoma cells undergoing neuronal differentiation correlated with down-regulation of Ezh2 levels. Importantly, overexpression of Ezh2 mRNA with a 3′-untranslated region (3′-UTR) lacking a functional miR-124 binding site, but not with the wild-type Ezh2 3′-UTR, hampered neuronal and promoted astrocyte-specific differentiation in P19 and embryonic mouse neural stem cells. Overall, our results uncover a molecular mechanism that allows miR-124 to balance the choice between alternative differentiation possibilities through fine-tuning the expression of a critical epigenetic regulator.

Detrusor induction of miR-132/212 following bladder outlet obstruction: association with MeCP2 repression and cell viability

The microRNAs (miRNAs) miR-132 and miR-212 have been found to regulate synaptic plasticity and cholinergic signaling and recent work has demonstrated roles outside of the CNS, including in smooth muscle. Here, we examined if miR-132 and miR-212 are induced in the urinary bladder following outlet obstruction and whether this correlates with effects on gene expression and cell growth. Three to seven-fold induction of miR-132/212 was found at 10 days of obstruction and this was selective for the detrusor layer. We cross-referenced putative binding sites in the miR-132/212 promoter with transcription factors that were predicted to be active in the obstruction model. This suggested involvement of Creb and Ahr in miR-132/212 induction. Creb phosphorylation (S-133) was not increased, but the number of Ahr positive nuclei increased. Moreover, we found that serum stimulation and protein kinase C activation induced miR-132/212 in human detrusor cells. To identify miR-132/212 targets, we correlated the mRNA levels of validated targets with the miRNA levels. Significant correlations between miR-132/212 and MeCP2, Ep300, Pnkd and Jarid1a were observed, and the protein levels of MeCP2, Pnkd and Ache were reduced after obstruction. Reduction of Ache however closely matched a 90% reduction of synapse density arguing that its repression was unrelated to miR-132/212 induction. Importantly, transfection of antimirs and mimics in cultured detrusor cells increased and decreased, respectively, the number of cells and led to changes in MeCP2 expression. In all, these findings show that obstruction of the urethra increases miR-132 and miR-212 in the detrusor and suggests that this influences gene expression and limits cell growth.

MicroRNA-124 inhibits the progression of adjuvant-induced arthritis in rats

Objective

MicroRNAs (miRNAs) are small endogenous, non-coding RNAs that act as post-transcriptional regulators. We analysed the in vivo effect of miRNA-124 (miR-124, the rat analogue of human miR-124a) on adjuvant-induced arthritis (AIA) in rats.

Methods

AIA was induced in Lewis rats by injecting incomplete Freund's adjuvant with heat-killed Mycobacterium tuberculosis. Precursor (pre)-miR-124 was injected into the right hind ankle on day 9. Morphological changes in the ankle joint were assessed by micro-CT and histopathology. Cytokine expression was examined by western blotting and real-time RT-PCR. The effect of miR-124 on predicted target messenger RNAs (mRNAs) was examined by luciferase reporter assays. The effect of pre-miR-124 or pre-miR-124a on the differentiation of human osteoclasts was examined by tartrate-resistant acid phosphatase staining.

Results

We found that miR-124 suppressed AIA in rats, as demonstrated by decreased synoviocyte proliferation, leucocyte infiltration and cartilage or bone destruction. Osteoclast counts and expression level of receptor activator of the nuclear factor κB ligand (RANKL), integrin β1 (ITGB1) and nuclear factor of activated T cells cytoplasmic 1 (NFATc1) were reduced in AIA rats treated with pre-miR-124. Luciferase analysis showed that miR-124 directly targeted the 3′UTR of the rat NFATc1, ITGB1, specificity protein 1 and CCAAT/enhancer-binding protein α mRNAs. Pre-miR-124 also suppressed NFATc1 expression in RAW264.7 cells. Both miR-124 and miR-124a directly targeted the 3′-UTR of human NFATc1 mRNA, and both pre-miR-124 and pre-miR-124a suppressed the differentiation of human osteoclasts.

Conclusions

We found that miR-124 ameliorated AIA by suppressing critical prerequisites for arthritis development, such as RANKL and NFATc1. Thus, miR-124a is a candidate for therapeutic use for human rheumatoid arthritis.

microRNA and Autism

Autism is a complex neurodevelopmental disorder characterized by deficiencies in social interaction and communication, and by repetitive and stereotyped behaviors. According to a recent report, the prevalence of this pervasive developmental disorder has risen to 1 in 88. This will have enormous public health implications in the future, and has necessitated the need to discover predictive biomarkers that could index for autism before the onset of symptoms. microRNAs (miRNAs) are small, noncoding RNAs that regulate gene expression at the posttranscriptional level. They have recently emerged as prominent epigenetic regulators of various cellular processes including neurodevelopment. They are abundantly present in the brain, and their dysfunction has been implicated in an array of neuropathological conditions including autism. miRNAs, previously known to be expressed only in cells and tissues, have also been detected in extracellular body fluids such as serum, plasma, saliva, and urine. Altered expression of cellular and circulating miRNAs have been observed in autistic individuals compared to healthy controls. miRNAs are now being considered as potential targets for the development of novel therapeutic strategies for autism.

MicroRNA-dependent genetic networks during neural development

The development of the structurally and functionally diverse mammalian nervous system requires the integration of numerous levels of gene regulation. Accumulating evidence suggests that microRNAs are key mediators of genetic networks during neural development. Importantly, microRNAs are found to regulate both feedback and feedforward loops during neural development leading to large changes in gene expression. These repressive interactions provide an additional mechanism that facilitates the establishment of complexity within the nervous system. Here, we review studies that have enabled the identification of microRNAs enriched in the brain and discuss the way that genetic networks in neural development depend on microRNAs.

The role of microRNAs in human neural stem cells, neuronal differentiation and subtype specification

The impressive neuronal diversity found within the nervous system emerges from a limited pool of neural progenitor cells that proceed through different gene expression programs to acquire distinct cell fates. Here, we review recent evidence indicating that microRNAs (miRNAs) are critically involved in conferring neural cell identities during neural induction, neuronal differentiation and subtype specification. Several studies have shown that miRNAs act in concert with other gene regulatory factors and genetic switches to regulate the spatial and temporal expression profiles of important cell fate determinants. So far, most studies addressing the role of miRNAs during neurogenesis were conducted using animal models. With the advent of human pluripotent stem cells and the possibility to differentiate these into neural stem cells, we now have the opportunity to study miRNAs in a human context. More insight into the impact of miRNA-based regulation during neural fate choice could in the end be exploited to develop new strategies for the generation of distinct human neuronal cell types.

Introduction to microRNAs: Biogenesis, Action, Relevance of Tissue microRNAs in Disease Pathogenesis, Diagnosis and Therapy-The Concept of Circulating microRNAs

MicroRNAs as the endogenous mediators of RNA interference have principal roles in gene expression regulation. Since their discovery in the early 1990s, their number has steadily grown to approximately 2500 known microRNAs at present in humans. MicroRNAs encoded by distinct genes regulate the expression of about 30-60 % of human protein coding genes by targeting their messenger RNAs (mRNAs) and induce mostly posttranscriptional inhibition, or in some cases enhancement. MicroRNAs, as fine regulators of the gene expression, have important roles in development, the physiological functioning of the organism, e.g. organogenesis, immune functioning, vascular system, etc. The deregulation of microRNA expression has been observed in many disorders, such as in carcinogenesis. Given their tissue specificity and stability, and specific disease-related alterations, tissue microRNAs can be exploited as excellent biomarkers in the diagnosis. Moreover, microRNAs might also be envisaged as novel therapeutic targets. Beside tissue microRNAs, novel data show that microRNAs are also present in body fluids that could further extend their diagnostic utility as minimally invasive biomarkers of various diseases, but also raises intriguing questions regarding their biological relevance. In this introductory chapter, we summarise the most relevant features of microRNAs including their biogenesis, action, the biological, pathological, diagnostic and potential therapeutical relevance of tissue microRNAs.

PTBP-dependent PSD-95 and CamKIIα alternative splicing in the lens

PURPOSE

Parallels described between neurons and lens fiber cells include detailed similarities in sub-cellular structures that increasingly show shared expression of genes involved in the construction and function of these structures in neurons. Intriguingly, associated modes of molecular regulation of these genes that had been thought to distinguish neurons have been identified in the lens as well. Both elongated cell types form membrane protrusions with similar size, shape, and spacing that exclude microtubules, contain F-actin, and are coated with the clathrin/AP-2 adaptor. Lenses express glutamate and gamma-aminobutyric acid (GABA) receptors with signaling and channel proteins shown to act together at neuronal membranes. Postsynaptic density protein 95 (PSD-95) and Ca(2+)/calmodulin-dependent protein kinase (CaMKIIα) expression and functions illustrate the integration of aspects of neuronal molecular and cell biology and were investigated here in the lens.

METHODS

Immunofluorescence, immunoblot, and RT-PCR methods were used to assess protein expression and alternative transcript splicing.

RESULTS

We showed the essential dendritic spine scaffold protein PSD-95 is expressed in lenses and demonstrated lens PSD-95 transcripts undergo polypyrimidine tract binding protein (PTBP)-dependent alternative splicing of its pivotal exon 18 required to avoid nonsense-mediated decay, and showed PTBP-dependent alternative splicing of CaMKIIα transcripts in the lens. The PSD-95 protein was observed at fiber cell membranes overlapping with N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate and GABA receptor proteins, tyrosine phosphatase STEP, CaMKIIα, the Ca(V)1.3 calcium channel, and clathrin, which were previously identified at lens fiber cell membranes. During neurogenesis, miR-124 is expressed that suppresses PTBP1 and promotes these splicing events. miR-124 is also expressed in mammalian lenses and upregulated during lens regeneration in amphibians, consistent with previous demonstrations of PTBP1,2 and PTBP-dependent PTBP2 exon 10 splicing in rodent lenses.

CONCLUSIONS

Findings of this dendritic spine scaffold protein and conservation of its key mode of molecular regulation in the lens provides further evidence that key aspects of the neuron morphogenetic program are shared with the lens.

Emerging role of microRNAs in major depressive disorder: diagnosis and therapeutic implications

Major depressive disorder (MDD) is a major public health concern. Despite tremendous advances, the pathogenic mechanisms associated with MDD are still unclear. Moreover, a significant number of MDD subjects do not respond to the currently available medication. MicroRNAs (miRNAs) are a class of small noncoding RNAs that control gene expression by modulating translation, messenger RNA (mRNA) degradation, or stability of mRNA targets. The role of miRNAs in disease pathophysiology is emerging rapidly. Recent studies demonstrating the involvement of miRNAs in several aspects of neural plasticity, neurogenesis, and stress response, and more direct studies in human postmortem brain provide strong evidence that miRNAs can not only play a critical role in MDD pathogenesis, but can also open up new avenues for the development of therapeutic targets. Circulating miRNAs are now being considered as possible biomarkers in disease pathogenesis and in monitoring therapeutic responses because of the presence and/or release of miRNAs in blood cells as well as in other peripheral tissues. In this review, these aspects are discussed in a comprehensive and critical manner.