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

Repeated diagnostic ultrasound exposure modifies the structural properties of CA1 dendrites and alters the hippocampal transcriptome

The development of neurons is regulated by several spatiotemporally changing factors, which are crucial to give the ability of neurons to form functional networks. While external physical stimuli may impact the early developmental stages of neurons, the medium and long-term consequences of these influences have yet to be thoroughly examined. Using an animal model, this study focuses on the morphological and transcriptome changes of the hippocampus that may occur as a consequence of fetal ultrasound examination. We selectively labeled CA1 neurons of the hippocampus with in-utero electroporation to analyze their morphological features. Furthermore, certain samples also went through RNA sequencing after repetitive ultrasound exposure. US exposure significantly changed several morphological properties of the basal dendritic tree. A notable increase was also observed in the density of spines on the basal dendrites, accompanied by various alterations in individual spine morphology. Transcriptome analysis revealed several up or downregulated genes, which may explain the molecular background of these alterations. Our results suggest that US-derived changes in the dendritic trees of CA1 pyramidal cells might be connected to modification of the transcriptome of the hippocampus and may lead to an increased dendritic input.

MiR-93 alleviates DEHP plasticizer-induced neurotoxicity by negatively regulating TNFAIP1 and inhibiting ubiquitin-mediated degradation of CK2β

Di-(2-ethylhexyl) phthalate (DEHP) is a plasticizer that is widely used in various products, such as plastic packaging in food industries. As an environmental endocrine disruptor, it induces adverse effects on brain development and function. However, the molecular mechanisms by which DEHP induces learning and memory impairment remain poorly understood. Herein, we found that DEHP impaired learning and memory in pubertal C57BL/6 mice, decreased the number of neurons, downregulated miR-93 and the β subunit of casein kinase 2 (CK2β), upregulated tumor necrosis factor-induced protein 1 (TNFAIP1), and inhibited Akt/CREB pathway in mouse hippocampi. Coimmunoprecipitation and western blotting assays revealed that TNFAIP1 interacted with CK2β and promoted its degradation by ubiquitination. Bioinformatics analysis showed a miR-93 binding site in the 3'-untranslated region of Tnfaip1. A dual-luciferase reporter assay revealed that miR-93 targeted TNFAIP1 and negatively regulated its expression. MiR-93 overexpression prevented DEHP-induced neurotoxicity by downregulating TNFAIP1 and then activating CK2/Akt/CREB pathway. These data indicate that DEHP upregulates TNFAIP1 expression by downregulating miR-93, thus promoting ubiquitin-mediated degradation of CK2β, subsequently inhibiting Akt/CREB pathway, and finally inducing learning and memory impairment. Therefore, miR-93 can relieve DEHP-induced neurotoxicity and may be used as a potential molecular target for prevention and treatment of related neurological disorders.

On the origin and nature of nongenetic information in eumetazoans

Nongenetic information implies all the forms of biological information not related to genes and DNA in general. Despite the deep scientific relevance of the concept, we currently lack reliable knowledge about its carriers and origins; hence, we still do not understand its true nature. Given that genes are the targets of nongenetic information, it appears that a parsimonious approach to find the ultimate source of that information is to trace back the sequential steps of the causal chain upstream of the target genes up to the ultimate link as the source of the nongenetic information. From this perspective, I examine seven nongenetically determined phenomena: placement of locus-specific epigenetic marks on DNA and histones, changes in snRNA expression patterns, neural induction of gene expression, site-specific alternative gene splicing, predator-induced morphological changes, and cultural inheritance. Based on the available evidence, I propose a general model of the common neural origin of all these forms of nongenetic information in eumetazoans.

Technical approaches and challenges to study AMPA receptors in oligodendrocyte lineage cells: Past, present, and future

Receptors for α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPARs) are ligand-gated ionotropic receptors for glutamate that is a major excitatory neurotransmitter in the central nervous system. AMPARs are located at postsynaptic sites of neuronal synapses where they mediate fast synaptic signaling and synaptic plasticity. Remarkably, AMPARs are also expressed by glial cells. Their expression by the oligodendrocyte (OL) lineage cells is of special interest because AMPARs mediate fast synaptic communication between neurons and oligodendrocyte progenitor cells (OPCs), modulate proliferation and differentiation of OPCs, and may also be involved in regulation of myelination. On the other hand, during pathological conditions, AMPARs may mediate damage of the OL lineage cells. In the present review, we focus on the technical approaches that have been used to study AMPARs in the OL lineage cells, and discuss future perspectives of AMPAR research in these glial cells.

RNA epitranscriptomics dysregulation: A major determinant for significantly increased risk of ASD pathogenesis

Autism spectrum disorders (ASDs) are perhaps the most severe, intractable and challenging child psychiatric disorders. They are complex, pervasive and highly heterogeneous and depend on multifactorial neurodevelopmental conditions. Although the pathogenesis of autism remains unclear, it revolves around altered neurodevelopmental patterns and their implications for brain function, although these cannot be specifically linked to symptoms. While these affect neuronal migration and connectivity, little is known about the processes that lead to the disruption of specific laminar excitatory and inhibitory cortical circuits, a key feature of ASD. It is evident that ASD has multiple underlying causes and this multigenic condition has been considered to also dependent on epigenetic effects, although the exact nature of the factors that could be involved remains unclear. However, besides the possibility for differential epigenetic markings directly affecting the relative expression levels of individual genes or groups of genes, there are at least three mRNA epitranscriptomic mechanisms, which function cooperatively and could, in association with both genotypes and environmental conditions, alter spatiotemporal proteins expression patterns during brain development, at both quantitative and qualitative levels, in a tissue-specific, and context-dependent manner. As we have already postulated, sudden changes in environmental conditions, such as those conferred by maternal inflammation/immune activation, influence RNA epitranscriptomic mechanisms, with the combination of these processes altering fetal brain development. Herein, we explore the postulate whereby, in ASD pathogenesis, RNA epitranscriptomics might take precedence over epigenetic modifications. RNA epitranscriptomics affects real-time differential expression of receptor and channel proteins isoforms, playing a prominent role in central nervous system (CNS) development and functions, but also RNAi which, in turn, impact the spatiotemporal expression of receptors, channels and regulatory proteins irrespective of isoforms. Slight dysregulations in few early components of brain development, could, depending upon their extent, snowball into a huge variety of pathological cerebral alterations a few years after birth. This may very well explain the enormous genetic, neuropathological and symptomatic heterogeneities that are systematically associated with ASD and psychiatric disorders at large.

microRNA-dependent regulation of gene expression in GABAergic interneurons

Information processing within neuronal circuits relies on their proper development and a balanced interplay between principal and local inhibitory interneurons within those circuits. Gamma-aminobutyric acid (GABA)ergic inhibitory interneurons are a remarkably heterogeneous population, comprising subclasses based on their morphological, electrophysiological, and molecular features, with differential connectivity and activity patterns. microRNA (miRNA)-dependent post-transcriptional control of gene expression represents an important regulatory mechanism for neuronal development and plasticity. miRNAs are a large group of small non-coding RNAs (21-24 nucleotides) acting as negative regulators of mRNA translation and stability. However, while miRNA-dependent gene regulation in principal neurons has been described heretofore in several studies, an understanding of the role of miRNAs in inhibitory interneurons is only beginning to emerge. Recent research demonstrated that miRNAs are differentially expressed in interneuron subclasses, are vitally important for migration, maturation, and survival of interneurons during embryonic development and are crucial for cognitive function and memory formation. In this review, we discuss recent progress in understanding miRNA-dependent regulation of gene expression in interneuron development and function. We aim to shed light onto mechanisms by which miRNAs in GABAergic interneurons contribute to sculpting neuronal circuits, and how their dysregulation may underlie the emergence of numerous neurodevelopmental and neuropsychiatric disorders.

Small Extracellular Vesicles in Milk Cross the Blood-Brain Barrier in Murine Cerebral Cortex Endothelial Cells and Promote Dendritic Complexity in the Hippocampus and Brain Function in C57BL/6J Mice

Human milk contains large amounts of small extracellular vesicles (sEVs) and their microRNA cargos, whereas infant formulas contain only trace amounts of sEVs and microRNAs. We assessed the transport of sEVs across the blood-brain barrier (BBB) and sEV accumulation in distinct regions of the brain in brain endothelial cells and suckling mice. We further assessed sEV-dependent gene expression profiles and effects on the dendritic complexity of hippocampal granule cells and phenotypes of EV depletion in neonate, juvenile and adult mice. The transfer of sEVs across the BBB was assessed by using fluorophore-labeled bovine sEVs in brain endothelial bEnd.3 monolayers and dual chamber systems, and in wild-type newborn pups fostered to sEV and cargo tracking (ECT) dams that express sEVs labeled with a CD63-eGFP fusion protein for subsequent analysis by serial two-photon tomography and staining with anti-eGFP antibodies. Effects of EVs on gene expression and dendritic architecture of granule cells was analyzed in hippocampi from juvenile mice fed sEV and RNA-depleted (ERD) and sEV and RNA-sufficient (ERS) diets by using RNA-sequencing analysis and Golgi-Cox staining followed by integrated neuronal tracing and morphological analysis of neuronal dendrites, respectively. Spatial learning and severity of kainic acid-induced seizures were assessed in mice fed ERD and ERS diets. bEnd.3 cells internalized sEVs by using a saturable transport mechanism and secreted miR-34a across the basal membrane. sEVs penetrated the entire brain in fostering experiments; major regions of accumulation included the hippocampus, cortex and cerebellum. Two hundred ninety-five genes were differentially expressed in hippocampi from mice fed ERD and ERS diets; high-confidence gene networks included pathways implicated in axon guidance and calcium signaling. Juvenile pups fed the ERD diet had reduced dendritic complexity of dentate granule cells in the hippocampus, scored nine-fold lower in the Barnes maze test of spatial learning and memory, and the severity of seizures was 5-fold higher following kainic acid administration in adult mice fed the ERD diet compared to mice fed the ERS diet. We conclude that sEVs cross the BBB and contribute toward optimal neuronal development, spatial learning and memory, and resistance to kainic acid-induced seizures in mice.

Perspectives on Mechanisms Supporting Neuronal Polarity From Small Animals to Humans

Axon-dendrite formation is a crucial milestone in the life history of neurons. During this process, historically referred as “the establishment of polarity,” newborn neurons undergo biochemical, morphological and functional transformations to generate the axonal and dendritic domains, which are the basis of neuronal wiring and connectivity. Since the implementation of primary cultures of rat hippocampal neurons by Gary Banker and Max Cowan in 1977, the community of neurobiologists has made significant achievements in decoding signals that trigger axo-dendritic specification. External and internal cues able to switch on/off signaling pathways controlling gene expression, protein stability, the assembly of the polarity complex (i.e., PAR3-PAR6-aPKC), cytoskeleton remodeling and vesicle trafficking contribute to shape the morphology of neurons. Currently, the culture of hippocampal neurons coexists with alternative model systems to study neuronal polarization in several species, from single-cell to whole-organisms. For instance, in vivo approaches using C. elegans and D. melanogaster, as well as in situ imaging in rodents, have refined our knowledge by incorporating new variables in the polarity equation, such as the influence of the tissue, glia-neuron interactions and three-dimensional development. Nowadays, we have the unique opportunity of studying neurons differentiated from human induced pluripotent stem cells (hiPSCs), and test hypotheses previously originated in small animals and propose new ones perhaps specific for humans. Thus, this article will attempt to review critical mechanisms controlling polarization compiled over decades, highlighting points to be considered in new experimental systems, such as hiPSC neurons and human brain organoids.

Identification of microRNAs associated with human fragile X syndrome using next-generation sequencing

Fragile X syndrome (FXS) is caused by a mutation in the FMR1 gene which can lead to a loss or shortage of the FMR1 protein. This protein interacts with specific miRNAs and can cause a range of neurological disorders. Therefore, miRNAs could act as a novel class of biomarkers for common CNS diseases. This study aimed to test this theory by exploring the expression profiles of various miRNAs in Iranian using deep sequencing-based technologies and validating the miRNAs affecting the expression of the FMR1 gene. Blood samples were taken from 15 patients with FXS (9 males, 6 females) and 12 controls. 25 miRNAs were differentially expressed in individuals with FXS compared to controls. Levels of 9 miRNAs were found to be significantly changed (3 upregulated and 6 downregulated). In Patients, the levels of hsa-miR-532-5p, hsa-miR-652-3p and hsa-miR-4797-3p were significantly upregulated while levels of hsa-miR-191-5p, hsa-miR-181-5p, hsa-miR-26a-5p, hsa-miR-30e-5p, hsa-miR-186-5p, and hsa-miR-4797-5p exhibited significant downregulation; and these dysregulations were confirmed by RT-qPCR. This study presents among the first evidence of altered miRNA expression in blood samples from patients with FXS, which could be used for diagnostic, prognostic, and treatment purposes. Larger studies are required to confirm these preliminary results.

MiR-191-5p alleviates microglial cell injury by targeting Map3k12 (mitogen-activated protein kinase kinase kinase 12) to inhibit the MAPK (mitogen-activated protein kinase) signaling pathway in Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease. Multiple reports have elucidated that microRNAs are promising biomarkers for AD diagnosis and treatment. Herein, the effect of miR-191-5p on microglial cell injury and the underlying mechanism were explored. APP/PS1 transgenic mice were utilized to establish mouse model of AD. Amyloid-β protein 1-42 (Aβ1-42)-treated microglia were applied to establish in vitro cell model of AD. MiR-191-5p expression in hippocampus and microglia was measured by reverse transcription quantitative polymerase chain reaction. The viability and apoptosis of microglia were evaluated by Cell Counting Kit-8 assays and flow cytometry analyses, respectively. The binding relationship between miR-191-5p and its downstream target mitogen-activated protein kinase kinase kinase 12 (Map3k12) was determined by luciferase reporter assays. Pathological degeneration of hippocampus was tested using hematoxylin-eosin staining and Nissl staining. Aβ expression in hippocampus was examined via immunohistochemistry. In this study, miR-191-5p was downregulated in Aβ1-42-stimulated microglia and hippocampal tissues of APP/PS1 mice. MiR-191-5p overexpression facilitated cell viability and inhibited apoptosis rate of Aβ1-42-treated microglia. Mechanically, miR-191-5p targeted Map3k12 3'-untranslated region to downregulate Map3k12 expression. MiR-191-5p inhibited Aβ1-42-induced microglial cell injury and inactivated the MAPK signaling by downregulating Map3k12. Overall, miR-191-5p alleviated Aβ1-42-induced microglia cell injury by targeting Map3k12 to inhibit the MAPK signaling pathway in microglia.

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

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

Exosomes derived from miR-26a-modified MSCs promote axonal regeneration via the PTEN/AKT/mTOR pathway following spinal cord injury

Background

Exosomes derived from the bone marrow mesenchymal stem cell (MSC) have shown great potential in spinal cord injury (SCI) treatment. This research was designed to investigate the therapeutic effects of miR-26a-modified MSC-derived exosomes (Exos-26a) following SCI.

Methods

Bioinformatics and data mining were performed to explore the role of miR-26a in SCI. Exosomes were isolated from miR-26a-modified MSC culture medium by ultracentrifugation. A series of experiments, including assessment of Basso, Beattie and Bresnahan scale, histological evaluation, motor-evoked potential recording, diffusion tensor imaging, and western blotting, were performed to determine the therapeutic influence and the underlying molecular mechanisms of Exos-26a in SCI rats.

Results

Exos-26a was shown to promote axonal regeneration. Furthermore, we found that exosomes derived from miR-26a-modified MSC could improve neurogenesis and attenuate glial scarring through PTEN/AKT/mTOR signaling cascades.

Conclusions

Exosomes derived from miR-26a-modified MSC could activate the PTEN-AKT-mTOR pathway to promote axonal regeneration and neurogenesis and attenuate glia scarring in SCI and thus present great potential for SCI treatment.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02282-0.

RETRACTED: microRNA-139-5p alleviates neurological deficit in hypoxic-ischemic brain damage via HDAC4 depletion and BCL-2 activation

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief as there are concerns about the reliability of the results. Concerns have been raised about the western blot bands in Figs. 5A, 6D having the same eyebrow shaped phenotype as found in many other publications as tabulated here (https://docs.google.com/spreadsheets/d/149EjFXVxpwkBXYJOnOHb6RhAqT4a2llhj9LM60MBffM/edit#gid=0). The journal requested the corresponding author to comment on these concerns and send the raw data, however the author was not able to provide uncropped images of the original gels. The Editor-in-Chief therefore no longer has confidence in the data and conclusions of this study.

New insights on epigenetic mechanisms supporting axonal development: histone marks and miRNAs

Mechanisms supporting axon growth and the establishment of neuronal polarity have remained largely disconnected from their genetic and epigenetic fundamentals. Recently, post-transcriptional modifications of histones involved in chromatin folding and transcription, and microRNAs controlling translation have emerged as regulators of axonal specification, growth, and guidance. In this article, we review novel evidence supporting the concept that epigenetic mechanisms work at both transcriptional and post-transcriptional levels to shape axons. We also discuss the role of splicing on axonal growth, as one of the most (if not the most) powerful post-transcriptional mechanism to diversify genetic information. Overall, we think exploring the gap between epigenetics and axonal growth raises new questions and perspectives to the development of axons in physiological and pathological contexts.

Plasma Exosomal MiRNAs Expression Profile in Mesial Temporal Lobe Epilepsy With Hippocampal Sclerosis: Case-Control Study and Analysis of Potential Functions

Background

To explore an expression profile in plasma exosomal miRNAs of mesial temporal lobe epilepsy with hippocampal sclerosis (mTLE + HS) patients and investigate the associated clinical significance and putative pathways involved.

Methods

Plasma exosomal miRNAs were measured in six mTLE + HS patients who were confirmed with pre-surgical stereo-electroencephalography and six without hippocampal sclerosis (mTLE−HS) using Illumina HiSeq 2500. Then six dysregulated miRNAs were chosen for validation in an independent sample of 18 mTLE + HS patients and 18 mTLE−HS controls using RT-qPCR. Receiver operating characteristic curve was conducted to evaluate the diagnostic value of miRNAs in HS. Bioinformatic analyses were conducted to reveal in which pathways these miRNAs were involved.

Results

We revealed that a total of 42 exosomal miRNAs were differentially expressed in mTLE + HS. Among them, 25 were increased and 17 decreased. After validation, hsa-miR-129-5p, -214-3p, -219a-5p, and -34c-5p were confirmed as being upregulated, while hsa-miR-421 and -184 were significantly downregulated in mTLE + HS. Moreover, hsa-miR-184 had the best diagnostic value for discriminating mTLE + HS with 88.9% sensitivity and 83.3% specificity. These six miRNAs regulated several genes from neurotrophin-, hippo-, p53-, TGF- beta-, HIF- 1-, mTOR-related pathways.

Conclusion

Six miRNAs were dysregulated in mTLE + HS patients and targeted several genes. This result might facilitate pathological mechanistic studies of miRNAs in HS and represent potential diagnostic biomarkers. These provided the rationale for further confirmation studies in larger cohorts of prospective patients.

Surfaceome dynamics reveal proteostasis-independent reorganization of neuronal surface proteins during development and synaptic plasticity

Neurons are highly compartmentalized cells with tightly controlled subcellular protein organization. While brain transcriptome, connectome and global proteome maps are being generated, system-wide analysis of temporal protein dynamics at the subcellular level are currently lacking. Here, we perform a temporally-resolved surfaceome analysis of primary neuron cultures and reveal dynamic surface protein clusters that reflect the functional requirements during distinct stages of neuronal development. Direct comparison of surface and total protein pools during development and homeostatic synaptic scaling demonstrates system-wide proteostasis-independent remodeling of the neuronal surface, illustrating widespread regulation on the level of surface trafficking. Finally, quantitative analysis of the neuronal surface during chemical long-term potentiation (cLTP) reveals fast externalization of diverse classes of surface proteins beyond the AMPA receptor, providing avenues to investigate the requirement of exocytosis for LTP. Our resource (neurosurfaceome.ethz.ch) highlights the importance of subcellular resolution for systems-level understanding of cellular processes.

Cell surface proteins contribute to neuronal development and activity-dependent synaptic plasticity. Here, the authors perform a time-resolved surfaceome analysis of developing primary neurons and in response to homeostatic synaptic scaling and chemical long-term potentiation (cLTP), revealing surface proteome remodeling largely independent of global proteostasis.

Hexachloronaphthalene Induces Mitochondrial-Dependent Neurotoxicity via a Mechanism of Enhanced Production of Reactive Oxygen Species

Hexachloronaphthalene (PCN67) is one of the most toxic among polychlorinated naphthalenes. Despite the known high bioaccumulation and persistence of PCN67 in the environment, it is still unclear to what extent exposure to these substances may interfere with normal neuronal physiology and lead to neurotoxicity. Therefore, the primary goal of this study was to assess the effect of PCN67 in neuronal in vitro models. Neuronal death was assessed upon PCN67 treatment using differentiated PC12 cells and primary hippocampal neurons. At 72 h postexposure, cell viability assays showed an IC₅₀ value of 0.35 μg/ml and dose-dependent damage of neurites and concomitant downregulation of neurofilaments L and M. Moreover, we found that younger primary neurons (DIV4) were much more sensitive to PCN67 toxicity than mature cultures (DIV14). Our comprehensive analysis indicated that the application of PCN67 at the IC₅₀ concentration caused necrosis, which was reflected by an increase in LDH release, HMGB1 protein export to the cytosol, nuclear swelling, and loss of homeostatic control of energy balance. The blockage of mitochondrial calcium uniporter partially rescued the cell viability, loss of mitochondrial membrane potential (ΔΨ_m), and the overproduction of reactive oxygen species, suggesting that the underlying mechanism of neurotoxicity involved mitochondrial calcium accumulation. Increased lipid peroxidation as a consequence of oxidative stress was additionally seen for 0.1 μg/ml of PCN67, while this concentration did not affect ΔΨ_m and plasma membrane permeability. Our results show for the first time that neuronal mitochondria act as a target for PCN67 and indicate that exposure to this drug may result in neuron loss via mitochondrial-dependent mechanisms.

Astrocyte-Derived Small Extracellular Vesicles Regulate Dendritic Complexity through miR-26a-5p Activity

In the last few decades, it has been established that astrocytes play key roles in the regulation of neuronal morphology. However, the contribution of astrocyte-derived small extracellular vesicles (sEVs) to morphological differentiation of neurons has only recently been addressed. Here, we showed that cultured astrocytes expressing a GFP-tagged version of the stress-regulated astrocytic enzyme Aldolase C (Aldo C-GFP) release small extracellular vesicles (sEVs) that are transferred into cultured hippocampal neurons. Surprisingly, Aldo C-GFP-containing sEVs (Aldo C-GFP sEVs) displayed an exacerbated capacity to reduce the dendritic complexity in developing hippocampal neurons compared to sEVs derived from control (i.e., GFP-expressing) astrocytes. Using bioinformatics and biochemical tools, we found that the total content of overexpressed Aldo C-GFP correlates with an increased content of endogenous miRNA-26a-5p in both total astrocyte homogenates and sEVs. Notably, neurons magnetofected with a nucleotide sequence that mimics endogenous miRNA-26a-5p (mimic 26a-5p) not only decreased the levels of neuronal proteins associated to morphogenesis regulation, but also reproduced morphological changes induced by Aldo-C-GFP sEVs. Furthermore, neurons magnetofected with a sequence targeting miRNA-26a-5p (antago 26a-5p) were largely resistant to Aldo C-GFP sEVs. Our results support a novel and complex level of astrocyte-to-neuron communication mediated by astrocyte-derived sEVs and the activity of their miRNA content.

The conserved microRNA miR-34 regulates synaptogenesis via coordination of distinct mechanisms in presynaptic and postsynaptic cells

Micro(mi)RNA-based post-transcriptional regulatory mechanisms have been broadly implicated in the assembly and modulation of synaptic connections required to shape neural circuits, however, relatively few specific miRNAs have been identified that control synapse formation. Using a conditional transgenic toolkit for competitive inhibition of miRNA function in Drosophila, we performed an unbiased screen for novel regulators of synapse morphogenesis at the larval neuromuscular junction (NMJ). From a set of ten new validated regulators of NMJ growth, we discovered that miR-34 mutants display synaptic phenotypes and cell type-specific functions suggesting distinct downstream mechanisms in the presynaptic and postsynaptic compartments. A search for conserved downstream targets for miR-34 identified the junctional receptor CNTNAP4/Neurexin-IV (Nrx-IV) and the membrane cytoskeletal effector Adducin/Hu-li tai shao (Hts) as proteins whose synaptic expression is restricted by miR-34. Manipulation of miR-34, Nrx-IV or Hts-M function in motor neurons or muscle supports a model where presynaptic miR-34 inhibits Nrx-IV to influence active zone formation, whereas, postsynaptic miR-34 inhibits Hts to regulate the initiation of bouton formation from presynaptic terminals.

Although micro(mi)RNA-based post-transcriptional regulatory mechanisms have been implicated in the assembly and modulation of synaptic connections, few miRNAs have been identified that control synapse formation. Here, authors performed an unbiased screen for novel regulators of synapse morphogenesis at the Drosophila larval neuromuscular junction and discovered that miR-34 inhibits Nrx-IV to influence active zone formation, whereas, postsynaptic miR-34 inhibits Hts to regulate the initiation of bouton formation from presynaptic terminals.

MicroRNAs are Necessary for BMP-7-induced Dendritic Growth in Cultured Rat Sympathetic Neurons

Neuronal connectivity is dependent on size and shape of the dendritic arbor. However, mechanisms controlling dendritic arborization, especially in the peripheral nervous system, are not completely understood. Previous studies have shown that bone morphogenetic proteins (BMPs) are important initiators of dendritic growth in peripheral neurons. In this study, we examined the hypothesis that post-transcriptional regulation mediated by microRNAs (miRNAs) is necessary for BMP-7-induced dendritic growth in these neurons. To examine the role of miRNAs in BMP-7-induced dendritic growth, microarray analyses was used to profile miRNA expression in cultured sympathetic neurons from the superior cervical ganglia of embryonic day 21 rat pups at 6 and 24 h after treatment with BMP-7 (50 ng/mL). Our data showed that BMP-7 significantly regulated the expression of 43 of the 762 miRNAs. Of the 43 miRNAs, 22 showed robust gene expression; 14 were upregulated by BMP-7 and 8 were downregulated by BMP-7. The expression profile for miR-335, miR-664-1*, miR-21, and miR-23b was confirmed using qPCR analyses. Functional studies using morphometric analyses of dendritic growth in cultured sympathetic neurons transfected with miRNA mimics and inhibitors indicated that miR-664-1*, miR-23b, and miR-21 regulated early stages of BMP-7-induced dendritic growth. In summary, our data provide evidence for miRNA-mediated post-transcriptional regulation as important downstream component of BMP-7 signaling during early stages of dendritic growth in sympathetic neurons.

Identification of Abundant and Evolutionarily Conserved Opioid Receptor Circular RNAs in the Nervous System Modulated by Morphine

Circular RNAs (circRNAs) are a distinct category of single-stranded, covalently closed RNAs formed by backsplicing. The functions of circRNAs are incompletely known and are under active investigation. Here, we report that in addition to traditional linear mRNAs (linRNA), mouse, rat, and human opioid receptor genes generate exonic circRNA isoforms. Using standard molecular biologic methods, Oprm1 circRNAs (circOprm1) were detected in RNAs of rodent and human brains and spinal cords, as well as human neuroblastoma cells, suggesting evolutionary conservation. Sequencing confirmed backsplicing using canonical splice sites. Oprm1 circRNAs were sense-stranded circRNAs resistant to RNase R digestion. The relative abundance of Oprm1 circRNA to linRNA determined by quantitative reverse transcription polymerase chain reaction varied among mouse brain regions, with circRNA isoforms predominating in rostral structures and less abundant in brain stem. Chronic morphine exposure in mice increased brain circOprm1e2.3 and circOprm1.e2.e3.e4(302) levels by 1.5- to 1.6-fold relative to linRNA. Sequence analysis predicted numerous microRNA binding sites within Oprm1 circRNA sequences, suggesting a potential role in microRNA sequestration through sponging. In addition, we observed that other opioid receptor genes including δ, κ, and nociceptin receptor genes produced similar circRNAs. In conclusion, all members of the opioid receptor gene family express circRNAs, with Oprm1 circRNA levels exceeding those of linear forms in some regions. SIGNIFICANCE STATEMENT: The modulation of Oprm1 circular RNA (circRNA) expression by morphine, coupled with the high abundance and existence of potential miRNA binding sites with circRNA sequences suggests the potential role of Oprm1 circRNAs in chronic opioid effects such as tolerance.

miR-146a and miR-181a are involved in the progression of mild cognitive impairment to Alzheimer's disease

The identification of mechanisms associated with Alzheimer's disease (AD) development in mild cognitive impairment (MCI) would be of great usefulness to clarify AD pathogenesis and to develop preventive and therapeutic strategies. In this study, blood levels of the candidate microRNAs (small noncoding RNAs that play a pivotal role in gene expression) miR-146a, miR-181a, miR-181b, miR-24-3p, miR-186a, miR-101, miR-339, miR-590, and miR-22 have been investigated for association to AD conversion within 2 years in a group of 45 patients with MCI. Baseline miR-146a (p = 0.036) and miR-181a (p = 0.026) showed a significant upregulation in patients with MCI who later converted to AD. These alterations were related to AD hallmarks: a significant negative correlation was found with amyloid beta cerebrospinal fluid concentration for miR-146a (p = 0.006) and miR-181a (p = 0.001). Moreover, higher levels of miR-146a were associated to apolipoprotein E ε4 allele presence, smaller volume of the hippocampus (p = 0.045) and of the CA1 (p = 0.013) and the subiculum (p = 0.027) subfields. Increased levels of miR-146a (p = 0.031) and miR-181a (p = 0.002) were also linked with diffusivity alterations in the cingulum. These data support a role for miR-146a and miR-181a in the mechanisms of AD progression.

The mir-465 family is upregulated with age and attenuates growth hormone signaling in mouse liver

We analyzed the small RNA transcriptome from 5‐month‐old, 24‐month‐old, and 36‐month‐old mouse liver and found 56 miRNAs that changed their expression profile with age. Among these is a cluster of 18 miRNAs that are upregulated between 50‐ and 1,000‐fold at 24 and 36 months of age. This cluster is located in a 60‐kb region of the X‐chromosome that is devoid of other coding sequences and is part of a lamin‐associated domain. Potential targets of the miRNAs in the cluster suggest they may regulate several pathways altered in aging, including the PI3K‐Akt pathway. Total transcriptome analyses indicate that expression of several potential genes in the PI3K‐Akt pathway that may be targeted by the mir‐465 family (mmu‐mir‐465a, mmu‐mir‐465b, and mmu‐mir‐465c) is downregulated with age. Transfection of the liver cell line AML12 with mir‐465 family members leads to a reduction of three of these potential targets at the mRNA level: a 40% reduction of the growth hormone receptor (GHR), and a 25% reduction in Kitl and PPP2R3C. Further investigation of the GHR 3′UTR revealed that the mir‐465 family directly targets the GHR mRNA. Cells transfected with mir‐465 showed a reduction of JAK2 and STAT5 phosphorylation upon growth hormone (GH) stimulation, resulting in a reduction in insulin‐like growth factor 1 (IGF‐1) and IGF‐1‐binding protein 3 expression. With age, GH signaling falls and there is a reduction in circulating IGF‐1. Our data suggest that an increase in expression of the mir‐465 family with age may contribute to the reduction in the GH signaling.

MicroRNA-186-5p controls GluA2 surface expression and synaptic scaling in hippocampal neurons

Homeostatic synaptic scaling is a negative feedback response to fluctuations in synaptic strength induced by developmental or learning-related processes, which maintains neuronal activity stable. Although several components of the synaptic scaling apparatus have been characterized, the intrinsic regulatory mechanisms promoting scaling remain largely unknown. MicroRNAs may contribute to posttranscriptional control of mRNAs implicated in different stages of synaptic scaling, but their role in these mechanisms is still undervalued. Here, we report that chronic blockade of glutamate receptors of the AMPA and NMDA types in hippocampal neurons in culture induces changes in the neuronal mRNA and miRNA transcriptomes, leading to synaptic upscaling. Specifically, we show that synaptic activity blockade persistently down-regulates miR-186-5p. Moreover, we describe a conserved miR-186-5p-binding site within the 3'UTR of the mRNA encoding the AMPA receptor GluA2 subunit, and demonstrate that GluA2 is a direct target of miR-186-5p. Overexpression of miR-186 decreased GluA2 surface levels, increased synaptic expression of GluA2-lacking AMPA receptors, and blocked synaptic scaling, whereas inhibition of miR-186-5p increased GluA2 surface levels and the amplitude and frequency of AMPA receptor-mediated currents, and mimicked excitatory synaptic scaling induced by synaptic inactivity. Our findings elucidate an activity-dependent miRNA-mediated mechanism for regulation of AMPA receptor expression.

MicroRNA-132 provides neuroprotection for tauopathies via multiple signaling pathways

MicroRNAs (miRNA) regulate fundamental biological processes, including neuronal plasticity, stress response, and survival. Here, we describe a neuroprotective function of miR-132, the miRNA most significantly downregulated in neurons in Alzheimer’s disease. We demonstrate that miR-132 protects primary mouse and human wild-type neurons and more vulnerable Tau-mutant neurons against amyloid β-peptide (Aβ) and glutamate excitotoxicity. It lowers the levels of total, phosphorylated, acetylated, and cleaved forms of Tau implicated in tauopathies, promotes neurite elongation and branching, and reduces neuronal death. Similarly, miR-132 attenuates PHF-Tau pathology and neurodegeneration, and enhances long-term potentiation in the P301S Tau transgenic mice. The neuroprotective effects are mediated by direct regulation of the Tau modifiers acetyltransferase EP300, kinase GSK3β, RNA-binding protein Rbfox1, and proteases Calpain 2 and Caspases 3/7. These data suggest miR-132 as a master regulator of neuronal health and indicate that miR-132 supplementation could be of therapeutic benefit for the treatment of Tau-associated neurodegenerative disorders.

SA4503, A Potent Sigma-1 Receptor Ligand, Ameliorates Synaptic Abnormalities and Cognitive Dysfunction in a Mouse Model of ATR-X Syndrome

α-thalassemia X-linked intellectual disability (ATR-X) syndrome is caused by mutations in ATRX. An ATR-X model mouse lacking Atrx exon 2 displays phenotypes that resemble symptoms in the human intellectual disability: cognitive defects and abnormal dendritic spine formation. We herein target activation of sigma-1 receptor (Sig-1R) that can induce potent neuroprotective and neuroregenerative effects by promoting the activity of neurotrophic factors, such as brain-derived neurotrophic factor (BDNF). We demonstrated that treatment with SA4503, a potent activator of Sig-1R, reverses axonal development and dendritic spine abnormalities in cultured cortical neurons from ATR-X model mice. Moreover, the SA4503 treatment rescued cognitive deficits exhibited by the ATR-X model mice. We further found that significant decreases in the BDNF-protein level in the medial prefrontal cortex of ATR-X model mice were recovered with treatment of SA4503. These results indicate that the rescue of dendritic spine abnormalities through the activation of Sig-1R has a potential for post-diagnostic therapy in ATR-X syndrome.

Potential Role of miRNAs as Theranostic Biomarkers of Epilepsy

Epilepsy includes a group of disorders of the brain characterized by an enduring predisposition to generate epileptic seizures. Although familial epilepsy has a genetic component and heritability, the etiology of the majority of non-familial epilepsies has no known associated genetic mutations. In epilepsy, recent epigenetic profiles have highlighted a possible role of microRNAs in its pathophysiology. In particular, molecular profiling identifies a significant number of microRNAs (miRNAs) altered in epileptic hippocampus of both animal models and human tissues. In this review, analyzing molecular profiles of different animal models of epilepsy, we identified a group of 20 miRNAs commonly altered in different epilepsy-animal models. As emerging evidences highlighted the poor overlap between signatures of animal model tissues and human samples, we focused our analysis on miRNAs, circulating in human biofluids, with a principal role in epilepsy hallmarks, and we identified a group of 8 diagnostic circulating miRNAs. We discussed the functional role of these 8 miRNAs in the epilepsy hallmarks. A few of them have also been proposed as therapeutic molecules for epilepsy treatment, revealing a great potential for miRNAs as theranostic molecules in epilepsy.

MIR137 schizophrenia-associated locus controls synaptic function by regulating synaptogenesis, synapse maturation and synaptic transmission

The MIR137 locus is a replicated genetic risk factor for schizophrenia. The risk-associated allele is reported to increase miR-137 expression and miR-137 overexpression alters synaptic transmission in mouse hippocampus. We investigated the cellular mechanisms underlying these observed effects in mouse hippocampal neurons in culture. First, we correlated the risk allele to expression of the genes in the MIR137 locus in human postmortem brain. Some evidence for increased MIR137HG expression was observed, especially in hippocampus of the disease-associated genotype. Second, in mouse hippocampal neurons, we confirmed previously observed changes in synaptic transmission upon miR-137 overexpression. Evoked synaptic transmission and spontaneous release were 50% reduced. We identified defects in release probability as the underlying cause. In contrast to previous observations, no evidence was obtained for selective synaptic vesicle docking defects. Instead, ultrastructural morphometry revealed multiple effects of miR-137 overexpression on docking, active zone length and total vesicle number. Moreover, proteomic analyses of neuronal protein showed that expression of Syt1 and Cplx1, previously reported as downregulated upon miR-137 overexpression, was unaltered. Immunocytochemistry of synapses overexpressing miR-137 showed normal Synaptotagmin1 and Complexin1 protein levels. Instead, our proteomic analyses revealed altered expression of genes involved in synaptogenesis. Concomitantly, synaptogenesis assays revealed 31% reduction in synapse formation. Taken together, these data show that miR-137 regulates synaptic function by regulating synaptogenesis, synaptic ultrastructure and synapse function. These effects are plausible contributors to the increased schizophrenia risk associated with miR-137 overexpression.

A Combination of Resveratrol and Curcumin is Effective Against Aluminum Chloride-Induced Neuroinflammation in Rats

BACKGROUND

Experimental studies have demonstrated that aluminum is an environmental toxin that induces neuroinflammation and the development of Alzheimer's disease.

OBJECTIVE

In this report, we investigated the beneficial effect of a combination of resveratrol and curcumin to reduce aluminum-induced neuroinflammation.

METHOD

We employed both an in vivo model of aluminum-induced neuroinflammation and an in vitro aluminum stimulated cultured PC-12 cells. Neuroinflammation in rats was assessed by measuring the expression of β-secretase, amyloid-β protein precursor, and γ-subunits (PS-1 and PS-2), along with the inflammatory COX-2, Il-1β, Il-1α, and TNF-α. Furthermore, we measured the expression profiles of neuro-protective Apurinic/apyrimidinic endonuclease 1 (APE1) protein and let-7c microRNA. In parallel, PC-12 cells were treated with 0.5 mM aluminum to induce a neuroinflammation-like state. In addition, curcumin effect, as a selective COX-2 expression inhibitor, was detected in a time course manner.

RESULTS

An overall significant attenuation of the inflammatory markers, as well as a decrease in the amyloidogenic mediators, was observed in resveratrol-curcumin treated rats. The therapeutic effect was also confirmed by transmission electron microscopic analysis of the brain cortexes. APE1 was significantly induced by resveratrol-curcumin combination. Both in vivo and in vitro studies indicated that Let-7c expression is significantly reduced after aluminum stimulation, an effect that was partially suppressed by co-addition of either resveratrol or curcumin and totally restored to the normal level by their combination.

CONCLUSIONS

The present study clearly indicates the synergistic and therapeutic effect of a  resveratrol-curcumin combination. We also show that both compounds exert beneficial effect either cooperatively or through differential molecular mechanisms in counteracting aluminum-induced neuroinflammation.

Quantitative Map of Proteome Dynamics during Neuronal Differentiation

Neuronal differentiation is a multistep process that shapes and re-shapes neurons by progressing through several typical stages, including axon outgrowth, dendritogenesis, and synapse formation. To systematically profile proteome dynamics throughout neuronal differentiation, we took cultured rat hippocampal neurons at different developmental stages and monitored changes in protein abundance using a combination of stable isotope labeling and high-resolution liquid chromatography-tandem mass spectrometry (LC-MS/MS). Almost one third of all 4,500 proteins quantified underwent a more than 2-fold expression change during neuronal differentiation, indicating extensive remodeling of the neuron proteome. To highlight the strength of our resource, we studied the neural-cell-adhesion molecule 1 (NCAM1) and found that it stimulates dendritic arbor development by promoting actin filament growth at the dendritic growth cone. We anticipate that our quantitative map of neuronal proteome dynamics is a rich resource for further analyses of the many identified proteins in various neurodevelopmental processes.

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Systematic profile of proteome dynamics throughout neuronal development in vitro

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Approximately 1,800 proteins show significant expression changes during differentiation

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Six expression profile clusters describe stage-specific patterns of protein dynamics

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This protein database may help to identify neurodevelopment mechanisms

Activity-dependent spatially localized miRNA maturation in neuronal dendrites

MicroRNAs (miRNAs) regulate gene expression by binding to target messenger RNAs (mRNAs) and preventing their translation. In general, the number of potential mRNA targets in a cell is much greater than the miRNA copy number, complicating high-fidelity miRNA-target interactions. We developed an inducible fluorescent probe to explore whether the maturation of a miRNA could be regulated in space and time in neurons. A precursor miRNA (pre-miRNA) probe exhibited an activity-dependent increase in fluorescence, suggesting the stimulation of miRNA maturation. Single-synapse stimulation resulted in a local maturation of miRNA that was associated with a spatially restricted reduction in the protein synthesis of a target mRNA. Thus, the spatially and temporally regulated maturation of pre-miRNAs can be used to increase the precision and robustness of miRNA-mediated translational repression.

Application of induced pluripotent stem cells to understand neurobiological basis of bipolar disorder and schizophrenia

The etiology of neuropsychiatric disorders, such as schizophrenia and bipolar disorder, usually involves complex combinations of genetic defects/variations and environmental impacts, which hindered, for a long time, research efforts based on animal models and patients' non-neuronal cells or post-mortem tissues. However, the development of human induced pluripotent stem cell (iPSC) technology by the Yamanaka group was immediately applied to establish cell research models for neuronal disorders. Since then, techniques to achieve highly efficient differentiation of different types of neural cells following iPSC modeling have made much progress. The fast-growing iPSC and neural differentiation techniques have brought valuable insights into the pathology and neurobiology of neuropsychiatric disorders. In this article, we first review the application of iPSC technology in modeling neuronal disorders and discuss the progress in the accompanying neural differentiation. Then, we summarize the progress in iPSC-based research that has been accomplished so far regarding schizophrenia and bipolar disorder.

miR-135a Regulates Synaptic Transmission and Anxiety-Like Behavior in Amygdala

MicroRNAs are a class of non-coding RNAs with a growing relevance in the regulation of gene expression related to brain function and plasticity. They have the potential to orchestrate complex phenomena, such as the neuronal response to homeostatic challenges. We previously demonstrated the involvement of miR-135a in the regulation of early stress response. In the present study, we examine the role of miR-135a in stress-related behavior. We show that the knockdown (KD) of miR-135a in the mouse amygdala induces an increase in anxiety-like behavior. Consistently with behavioral studies, electrophysiological experiments in acute brain slices indicate an increase of amygdala spontaneous excitatory postsynaptic currents, as a result of miR-135a KD. Furthermore, we presented direct evidences, by in vitro assays and in vivo miRNA overexpression in the amygdala, that two key regulators of synaptic vesicle fusion, complexin-1 and complexin-2, are direct targets of miR-135a. In vitro analysis of miniature excitatory postsynaptic currents on miR-135a KD primary neurons indicates unpaired quantal excitatory neurotransmission. Finally, increased levels of complexin-1 and complexin-2 proteins were detected in the mouse amygdala after acute stress, accordingly to the previously observed stress-induced miR-135a downregulation. Overall, our results unravel a previously unknown miRNA-dependent mechanism in the amygdala for regulating anxiety-like behavior, providing evidences of a physiological role of miR-135a in the modulation of presynaptic mechanisms of glutamatergic neurotransmission.

Dynamic regulation of small RNAome during the early stage of cardiac differentiation from pluripotent embryonic stem cells

Embryonic stem cells (mESCs), having potential to differentiate into three germ-layer cells including cardiomyocytes, shall be a perfect model to help understanding heart development. Here, using small RNA deep sequencing, we studied the small RNAome in the early stage of mouse cardiac differentiation. We found that the expression pattern of most microRNA (miRNA) were highly enriched at the beginning and declined thereafter, some were still insufficiently expressed on day 6, and most miRNAs recovered in the following days. When pluripotent embryonic stem cells are differentiating to cardiomyocytes, targeted genes are concentrated on TGF, WNT and cytoskeletal remodeling pathway. The pathway and network of dynamically changed target genes of the miRNAs at different time points were also investigated. Furthermore, we demonstrated that small rDNA-derived RNAs (srRNAs) were significantly up-regulated during differentiation, especially in stem cells. The pathways of srRNAs targeted genes were also presented. We described the existence and the differential expression of transfer RNA (tRNA), Piwi-interacting RNA (piRNA) and Endogenous siRNAs (endo-siRNAs) in this process. This study reports the genome-wide small RNAome profile, and provides a uniquely comprehensive view of the small RNA regulatory network that governs embryonic stem cell differentiation and cardiac development.

Synaptic Dysfunction in Alzheimer's Disease: Aβ, Tau, and Epigenetic Alterations

Alzheimer's disease (AD) is a complex neurodegenerative disorder characterized in the early stages by loss of learning and memory. However, the mechanism underlying these symptoms remains unclear. The best correlation between cognitive decline and pathological changes is in synaptic dysfunction. Histopathological hallmarks of AD are the abnormal aggregation of Aβ and Tau. Evidence suggests that Aβ and Tau oligomers contribute to synaptic loss in AD. Recently, direct links between epigenetic alterations, such as dysfunction in non-coding RNAs (ncRNAs), and synaptic pathologies have emerged, raising interest in exploring the potential roles of ncRNAs in the synaptic deficits in AD. In this paper, we summarize the potential roles of Aβ, Tau, and epigenetic alterations (especially by ncRNAs) in the synaptic dysfunction of AD and discuss the novel findings in this area.

The Mechanism of Long Non-coding RNA MEG3 for Neurons Apoptosis Caused by Hypoxia: Mediated by miR-181b-12/15-LOX Signaling Pathway

Objective: lncRNAs are recently thought to play a significant role in cellular homeostasis during pathological process of diseases by competing inhibiting miRNA function. The aim of present study was to assess the function of long non-coding RNA (lncRNA) MEG3 and its functional interaction with microRNA-181b in cerebral ischemic infarct of mice and hypoxia-induced neurons apoptosis.

Methods: To address this question, we performed the experiments with in vivo middle cerebral artery occlusion (MCAO) mice model and in vitro oxygen-glucose deprivation (OGD)-cultured neuronal HT22 cell line. Relative expression of MEG3, miR-181b, and 12/15-LOX (lipoxygenase) mRNA was determined using quantitative RT-PCR. Western blot was used to evaluate 12/15-LOX protein expression. TUNEL assay was performed to assess cell apoptosis.

Results: In both MCAO mice and OGD-cultured HT22 cell, ischemia, or hypoxia treatment results in a time-dependent increase in MEG3 and 12/15-LOX expression and decrease in miR-181b expression. Knockdown of MEG3 contributes to attenuation of hypoxia-induced apoptosis of HT22 cell. Also, expression level of MEG3 negatively correlated with miR-181b expression and positively correlated with 12/15-LOX expression. In contrary to MEG3, miR-181b overexpression attenuated hypoxia-induced HT22 cell apoptosis, as well as suppressed hypoxia-induced increase in 12/15-LOX expression. By luciferase reporter assay, we concluded that miR-181b directly binds to 12/15-LOX 3′-UTR, thereby negatively regulates 12/15-LOX expression.

Conclusion: Our data suggested that long non-coding RNA MEG3 functions as a competing endogenous RNA for miR-181b to regulate 12/15-LOX expression in middle cerebral artery occlusion-induced ischemic infarct of brain nerve cells.

MiRNAs in Astrocyte-Derived Exosomes as Possible Mediators of Neuronal Plasticity

Astrocytes use gliotransmitters to modulate neuronal function and plasticity. However, the role of small extracellular vesicles, called exosomes, in astrocyte-to-neuron signaling is mostly unknown. Exosomes originate in multivesicular bodies of parent cells and are secreted by fusion of the multivesicular body limiting membrane with the plasma membrane. Their molecular cargo, consisting of RNA species, proteins, and lipids, is in part cell type and cell state specific. Among the RNA species transported by exosomes, microRNAs (miRNAs) are able to modify gene expression in recipient cells. Several miRNAs present in astrocytes are regulated under pathological conditions, and this may have far-reaching consequences if they are loaded in exosomes. We propose that astrocyte-derived miRNA-loaded exosomes, such as miR-26a, are dysregulated in several central nervous system diseases; thus potentially controlling neuronal morphology and synaptic transmission through validated and predicted targets. Unraveling the contribution of this new signaling mechanism to the maintenance and plasticity of neuronal networks will impact our understanding on the physiology and pathophysiology of the central nervous system.

miRNAs in NMDA receptor-dependent synaptic plasticity and psychiatric disorders

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

Associations of rs3740677 within GAB2 Gene with LOAD in Chinese Han Population

GRB2-associated binding protein 2 (GAB2) has been identified as a crucial factor in Alzheimer's disease (AD), and ten common variants within GAB2 have been detected to be associated with AD onset risk in genome-wide association studies (GWAS). Here, we first screened a common locus (rs3740677) in 3' UTR of GAB2 sequence which is targeted by the miRNA-185 and initiatively explored the probable associations of rs3740677 with risk for late-onset AD (LOAD) in a large scale case-control study from Chinese Han populations (992 LOAD patients and 1358 healthy subjects). Eventually, the genotype (P = 0.024) and allele (P = 0.008) distribution of rs3740677 showed significant difference between LOAD and control group, and we observed a significant association of T allele in rs3740677 with LOAD risk in multivariate analysis and it decreased the risk for LOAD (dominant: OR = 0.831, 95 % CI = 0.702-0.983, P = 0.031; additive: OR = 0.855, 95 % CI = 0.745-0.983, P = 0.027) adjusted for age, gender, and APOE ε4 status. Our study further confirmed the association of GAB2 and AD. However, the absolute and correct association of rs3740677 with AD still required more investigations in diverse regions and ethnics.

Identification of miRNomes associated with adult neurogenesis after stroke using Argonaute 2-based RNA sequencing

Neurogenesis is associated with functional recovery after stroke. However, the underlying molecular mechanisms have not been fully investigated. Using an Ago2-based RNA immunoprecipitation to immunoprecipated Ago2-RNA complexes followed by RNA sequencing (Ago2 RIP-seq) approach, we profiled the miRNomes in neural progenitor cells (NPCs) harvested from the subventricular zone (SVZ) of the lateral ventricles of young adult rats. We identified more than 7 and 15 million reads in normal and ischemic NPC libraries, respectively. We found that stroke substantially changed Ago2-associated miRNA profiles in NPCs compared to those in non-ischemic NPCs. We also discovered a new complex repertoire of isomiRs and multiple miRNA-miRNA* pairs and numerous novel miRNAs in the non-ischemic and ischemic NPCs. Among them, pc-3p-17172 significantly regulated NPC proliferation and neuronal differentiation. Collectively, the present study reveals profiles of Ago2-associated miRNomes in non-ischemic and ischemic NPCs, which provide a molecular basis to further investigate the role of miRNAs in mediating adult neurogenesis under physiological and ischemic conditions.

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.

miR-204 downregulates EphB2 in aging mouse hippocampal neurons

Hippocampal synaptic function and plasticity deteriorate with age, often resulting in learning and memory deficits. As MicroRNAs (miRNAs) are important regulators of neuronal protein expression, we examined whether miRNAs may contribute to this age‐associated decline in hippocampal function. We first compared the small RNA transcriptome of hippocampal tissues from young and old mice. Among 269 hippocampal miRNAs, 80 were differentially expressed (≥ twofold) among the age groups. We focused on 36 miRNAs upregulated in the old mice compared with those in the young mice. The potential targets of these 36 miRNAs included 11 critical Eph/Ephrin synaptic signaling components. The expression levels of several genes in the Eph/Ephrin pathway, including EphB2, were significantly downregulated in the aged hippocampus. EphB2 is a known regulator of synaptic plasticity in hippocampal neurons, in part by regulating the surface expression of the NMDA receptor NR1 subunit. We found that EphB2 is a direct target of miR‐204 among miRNAs that were upregulated with age. The transfection of primary hippocampal neurons with a miR‐204 mimic suppressed both EphB2 mRNA and protein expression and reduced the surface expression of NR1. Transfection of miR‐204 also decreased the total expression of NR1. miR‐204 induces senescence‐like phenotype in fully matured neurons as evidenced by an increase in p16‐positive cells. We suggest that aging is accompanied by the upregulation of miR‐204 in the hippocampus, which downregulates EphB2 and results in reduced surface and total NR1 expression. This mechanism may contribute to age‐associated decline in hippocampal synaptic plasticity and the related cognitive functions.

Targeted deletion of miR-132/-212 impairs memory and alters the hippocampal transcriptome

miR-132 and miR-212 are structurally related microRNAs that have been found to exert powerful modulatory effects within the central nervous system (CNS). Notably, these microRNAs are tandomly processed from the same noncoding transcript, and share a common seed sequence: thus it has been difficult to assess the distinct contribution of each microRNA to gene expression within the CNS. Here, we employed a combination of conditional knockout and transgenic mouse models to examine the contribution of the miR-132/-212 gene locus to learning and memory, and then to assess the distinct effects that each microRNA has on hippocampal gene expression. Using a conditional deletion approach, we show that miR-132/-212 double-knockout mice exhibit significant cognitive deficits in spatial memory, recognition memory, and in tests of novel object recognition. Next, we utilized transgenic miR-132 and miR-212 overexpression mouse lines and the miR-132/-212 double-knockout line to explore the distinct effects of these two miRNAs on the transcriptional profile of the hippocampus. Illumina sequencing revealed that miR-132/-212 deletion increased the expression of 1138 genes; Venn analysis showed that 96 of these genes were also downregulated in mice overexpressing miR-132. Of the 58 genes that were decreased in animals overexpressing miR-212, only four of them were also increased in the knockout line. Functional gene ontology analysis of downregulated genes revealed significant enrichment of genes related to synaptic transmission, neuronal proliferation, and morphogenesis, processes known for their roles in learning, and memory formation. These data, coupled with previous studies, firmly establish a role for the miR-132/-212 gene locus as a key regulator of cognitive capacity. Further, although miR-132 and miR-212 share a seed sequence, these data indicate that these miRNAs do not exhibit strongly overlapping mRNA targeting profiles, thus indicating that these two genes may function in a complex, nonredundant manner to shape the transcriptional profile of the CNS. The dysregulation of miR-132/-212 expression could contribute to signaling mechanisms that are involved in an array of cognitive disorders.

Microtubule-binding protein doublecortin-like kinase 1 (DCLK1) guides kinesin-3-mediated cargo transport to dendrites

In neurons, the polarized distribution of vesicles and other cellular materials is established through molecular motors that steer selective transport between axons and dendrites. It is currently unclear whether interactions between kinesin motors and microtubule-binding proteins can steer polarized transport. By screening all 45 kinesin family members, we systematically addressed which kinesin motors can translocate cargo in living cells and drive polarized transport in hippocampal neurons. While the majority of kinesin motors transport cargo selectively into axons, we identified five members of the kinesin-3 (KIF1) and kinesin-4 (KIF21) subfamily that can also target dendrites. We found that microtubule-binding protein doublecortin-like kinase 1 (DCLK1) labels a subset of dendritic microtubules and is required for KIF1-dependent dense-core vesicles (DCVs) trafficking into dendrites and dendrite development. Our study demonstrates that microtubule-binding proteins can provide local signals for specific kinesin motors to drive polarized cargo transport.

Upregulation of miR-181 decreases c-Fos and SIRT-1 in the hippocampus of 3xTg-AD mice

MicroRNAs are a group of small RNAs that regulate diverse cellular processes including neuronal function. Recent studies have shown that dysregulation of specific microRNAs is critically involved in the development of Alzheimer's disease (AD). Most of these reports have focused on microRNAs implicated in alterations of amyloid-β and tau. However, studies exploring the relation between microRNAs dysregulation in AD and synaptic plasticity are scarce despite the well-known involvement of microRNAs in synaptic plasticity. Since impairments in synaptic plasticity and neuronal loss are two important features displayed in AD patients, it is feasible to hypothesize that alterations in plasticity-related microRNAs underlie AD progression. Here, levels of a small number of microRNAs implicated in normal neuronal function and/or plasticity were examined in an AD model. Twelve-month old 3xTg-AD mice with plaques and tangles presented a significant upregulation of miR-181 in the hippocampus compared to age-matched wild type mice. Increased miR-181 was not detected in pre-pathological 3xTg-AD mice. Analysis of predicted targets of miR-181 identified c-Fos and SIRT-1, proteins critically involved in memory formation. Both c-Fos and SIRT-1 levels were significantly decreased in the ventral hippocampus of twelve-month old 3xTg-AD mice. Overexpression of miR-181 in SH-SY5Y cells significantly decreased c-Fos and SIRT-1, strongly suggesting that miR-181 directly regulates the expression of these two proteins. These findings indicate a connection between miR-181 and proteins involve in synaptic plasticity and memory processing in a transgenic mouse model of AD. Our results suggest that microRNAs involved in synaptic plasticity might be an important factor that contributes to AD neuropathology.

MicroRNA Profiling of Neurons Generated Using Induced Pluripotent Stem Cells Derived from Patients with Schizophrenia and Schizoaffective Disorder, and 22q11.2 Del

We are using induced pluripotent stem cell (iPSC) technology to study neuropsychiatric disorders associated with 22q11.2 microdeletions (del), the most common known schizophrenia (SZ)-associated genetic factor. Several genes in the region have been implicated; a promising candidate is DGCR8, which codes for a protein involved in microRNA (miRNA) biogenesis. We carried out miRNA expression profiling (miRNA-seq) on neurons generated from iPSCs derived from controls and SZ patients with 22q11.2 del. Using thresholds of p<0.01 for nominal significance and 1.5-fold differences in expression, 45 differentially expressed miRNAs were detected (13 lower in SZ and 32 higher). Of these, 6 were significantly down-regulated in patients after correcting for genome wide significance (FDR<0.05), including 4 miRNAs that map to the 22q11.2 del region. In addition, a nominally significant increase in the expression of several miRNAs was found in the 22q11.2 neurons that were previously found to be differentially expressed in autopsy samples and peripheral blood in SZ and autism spectrum disorders (e.g., miR-34, miR-4449, miR-146b-3p, and miR-23a-5p). Pathway and function analysis of predicted mRNA targets of the differentially expressed miRNAs showed enrichment for genes involved in neurological disease and psychological disorders for both up and down regulated miRNAs. Our findings suggest that: i. neurons with 22q11.2 del recapitulate the miRNA expression patterns expected of 22q11.2 haploinsufficiency, ii. differentially expressed miRNAs previously identified using autopsy samples and peripheral cells, both of which have significant methodological problems, are indeed disrupted in neuropsychiatric disorders and likely have an underlying genetic basis.