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

Brain exposure to SARS-CoV-2 virions perturbs synaptic homeostasis

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is associated with short- and long-term neurological complications. The variety of symptoms makes it difficult to unravel molecular mechanisms underlying neurological sequalae after coronavirus disease 2019 (COVID-19). Here we show that SARS-CoV-2 triggers the up-regulation of synaptic components and perturbs local electrical field potential. Using cerebral organoids, organotypic culture of human brain explants from individuals without COVID-19 and post-mortem brain samples from individuals with COVID-19, we find that neural cells are permissive to SARS-CoV-2 to a low extent. SARS-CoV-2 induces aberrant presynaptic morphology and increases expression of the synaptic components Bassoon, latrophilin-3 (LPHN3) and fibronectin leucine-rich transmembrane protein-3 (FLRT3). Furthermore, we find that LPHN3-agonist treatment with Stachel partially restored organoid electrical activity and reverted SARS-CoV-2-induced aberrant presynaptic morphology. Finally, we observe accumulation of relatively static virions at LPHN3-FLRT3 synapses, suggesting that local hindrance can contribute to synaptic perturbations. Together, our study provides molecular insights into SARS-CoV-2-brain interactions, which may contribute to COVID-19-related neurological disorders.

A Comprehensive Review of Membrane Transporters and MicroRNA Regulation in Alzheimer's Disease

Alzheimer's disease (AD) is a distressing neurodegenerative condition characterized by the accumulation of amyloid-beta (Aβ) plaques and tau tangles within the brain. The interconnectedness between membrane transporters (SLCs) and microRNAs (miRNAs) in AD pathogenesis has gained increasing attention. This review explores the localization, substrates, and functions of SLC transporters in the brain, emphasizing the roles of transporters for glutamate, glucose, nucleosides, and other essential compounds. The examination delves into the significance of SLCs in AD, their potential for drug development, and the intricate realm of miRNAs, encompassing their transcription, processing, functions, and regulation. MiRNAs have emerged as significant players in AD, including those associated with mitochondria and synapses. Furthermore, this review discusses the intriguing nexus of miRNAs targeting SLC transporters and their potential as therapeutic targets in AD. Finally, the review underscores the interaction between SLC transporters and miRNA regulation within the context of Alzheimer's disease, underscoring the need for further research in this area. This comprehensive review aims to shed light on the complex mechanisms underlying the causation of AD and provides insights into potential therapeutic approaches.

Unveiling the regulatory role of miRNAs in stroke pathophysiology and diagnosis

Stroke, a major global cause of mortality, leads to a range of problems for those who survive. Besides its brutal events, stroke also tends to have a characteristic of recurrence, making it a complex disease involving intricate regulatory networks. One of the major cellular regulators is the non-coding RNAs (ncRNA), specifically microRNAs (miRNAs), thus the possible functions of miRNAs in the pathogenesis of stroke are discussed as well as the possibility of using miRNA-based therapeutic approaches. Firstly, the molecular mechanisms by which miRNAs regulate vital physiological processes, including synaptic plasticity, oxidative stress, apoptosis, and the integrity of the blood-brain barrier (BBB) are reviewed. The miRNA indirectly impacts stroke outcomes by regulating BBB function and angiogenesis through the targeting of transcription factors and angiogenic factors. In addition, the tendency for some miRNAs to be upregulated in response to hypoxia, which is a prevalent phenomenon in stroke and various neurological disorders, highlights the possibility that it controls hypoxia-inducible factor (HIF) signaling and angiogenesis, thereby influencing the integrity of the BBB as examples of the discussed mechanisms. Furthermore, this review explores the potential therapeutic targets that miRNAs may offer for stroke recovery and highlights their promising capacity to alleviate post-stroke complications. This review provides researchers and clinicians with valuable resources since it attempts to decipher the complex network of miRNA-mediated mechanisms in stroke. Additionally, the review addresses the interplay between miRNAs and stroke risk factors as well as clinical applications of miRNAs as diagnostic and prognostic markers.

Loss of Depalmitoylation Disrupts Homeostatic Plasticity of AMPARs in a Mouse Model of Infantile Neuronal Ceroid Lipofuscinosis

Protein palmitoylation is the only reversible post-translational lipid modification. Palmitoylation is held in delicate balance by depalmitoylation to precisely regulate protein turnover. While over 20 palmitoylation enzymes are known, depalmitoylation is conducted by fewer enzymes. Of particular interest is the lack of the depalmitoylating enzyme palmitoyl-protein thioesterase 1 (PPT1) that causes the devastating pediatric neurodegenerative condition infantile neuronal ceroid lipofuscinosis (CLN1). While most of the research on Ppt1 function has centered on its role in the lysosome, recent findings demonstrated that many Ppt1 substrates are synaptic proteins, including the AMPA receptor (AMPAR) subunit GluA1. Still, the impact of Ppt1-mediated depalmitoylation on synaptic transmission and plasticity remains elusive. Thus, the goal of the present study was to use the Ppt1 -/- mouse model (both sexes) to determine whether Ppt1 regulates AMPAR-mediated synaptic transmission and plasticity, which are crucial for the maintenance of homeostatic adaptations in cortical circuits. Here, we found that basal excitatory transmission in the Ppt1 -/- visual cortex is developmentally regulated and that chemogenetic silencing of the Ppt1 -/- visual cortex excessively enhanced the synaptic expression of GluA1. Furthermore, triggering homeostatic plasticity in Ppt1 -/- primary neurons caused an exaggerated incorporation of GluA1-containing, calcium-permeable AMPARs, which correlated with increased GluA1 palmitoylation. Finally, Ca2+ imaging in awake Ppt1 -/- mice showed visual cortical neurons favor a state of synchronous firing. Collectively, our results elucidate a crucial role for Ppt1 in AMPAR trafficking and show that impeded proteostasis of palmitoylated synaptic proteins drives maladaptive homeostatic plasticity and abnormal recruitment of cortical activity in CLN1.SIGNIFICANCE STATEMENT Neuronal communication is orchestrated by the movement of receptors to and from the synaptic membrane. Protein palmitoylation is the only reversible post-translational lipid modification, a process that must be balanced precisely by depalmitoylation. The significance of depalmitoylation is evidenced by the discovery that mutation of the depalmitoylating enzyme palmitoyl-protein thioesterase 1 (Ppt1) causes severe pediatric neurodegeneration. In this study, we found that the equilibrium provided by Ppt1-mediated depalmitoylation is critical for AMPA receptor (AMPAR)-mediated plasticity and associated homeostatic adaptations of synaptic transmission in cortical circuits. This finding complements the recent explosion of palmitoylation research by emphasizing the necessity of balanced depalmitoylation.

Specific downregulation of microRNA-186 induces neural stem cell self-renewal by upregulating Bmi-1/FoxG1 expression

Self-renewal and differentiation in neural stem cells (NSCs) are modulated by microRNAs (miRNAs). However, the recent evidence available is not enough to elucidate the role of miRNA in the self-renewal and differentiation of NSCs from developing brain. In this study, we isolated primary NSCs from the forebrain of fetal rat for in vitro analysis. Downregulation of miRNA-186 in response to a specific miRNA inhibitor resulted in upregulation of Bmi-1 and FoxG1, while maintaining NCS self-renewal. Bmi-1 overexpression restored the maintenance of NSCs in vitro. FoxG1 was found to promote the methylation of Foxo3 promoter and inhibited Foxo3 expression. miR-186 upregulation increased the expression of Foxo3 and inhibited NSC self-renewal in the absence of Foxo3. Therefore, we propose that downregulation of miR-186 maintained NSC self-renewal in the postnatal brain by upregulating the Bmi1/FoxG1 expression via FoxO3 elevation.

Ethanol-induced AMPA alterations are mediated by mGLU5 receptors through miRNA upregulation in hippocampal slices

Prenatal alcohol exposure (PAE) affects neuronal networks and brain development causing a range of physical, cognitive and behavioural disorders in newborns that persist into adulthood. The array of consequences associated with PAE can be grouped under the umbrella-term 'fetal alcohol spectrum disorders' (FASD). Unfortunately, there is no cure for FASD as the molecular mechanisms underlying this pathology are still unknown. We have recently demonstrated that chronic EtOH exposure, followed by withdrawal, induces a significant decrease in AMPA receptor (AMPAR) expression and function in developing hippocampus in vitro. Here, we explored the EtOH-dependent pathways leading to hippocampal AMPAR suppression. Organotypic hippocampal slices (2 days in cultures) were exposed to EtOH (150 mM) for 7 days followed by 24 h EtOH withdrawal. Then, the slices were analysed by means of RT-PCR for miRNA content, western blotting for AMPA and NMDA related-synaptic proteins expression in postsynaptic compartment and electrophysiology to record electrical properties from CA1 pyramidal neurons. We observed that EtOH induces a significant downregulation of postsynaptic AMPA and NMDA subunits and relative scaffolding protein expression and, accordingly, a decrease of AMPA-mediated neurotransmission. Simultaneously, we found that chronic EtOH induced-upregulation of miRNA 137 and 501-3p and decreased AMPA-mediated neurotransmission are prevented by application of the selective mGlu5 antagonist MPEP during EtOH withdrawal. Our data indicate mGlu5 via miRNA137 and 501-3p expression as key factors in the regulation of AMPAergic neurotransmission that may contribute, at least in part, to the pathogenesis of FASD.

GluA1-Shank3 interaction decreases in response to chronic neuronal depolarization

Interactions between AMPA receptors and synaptic scaffolding proteins are key regulators of synaptic receptor density and, thereby, synapse strength. Shank3 is one such scaffolding protein with high clinical relevance, as genetic variants and deletions of this protein have been linked to autism spectrum disorder. Shank3 acts as a master regulator of the postsynaptic density of glutamatergic synapses, interacting with ionotropic and metabotropic glutamate receptors and cytoskeletal elements to modulate synaptic structure. Notably, Shank3 has been shown to interact directly with the AMPAR subunit GluA1, and Shank3 knockout animals show deficits in AMPAR-mediated synaptic transmission. In this study, we sought to characterize the stability of GluA1-Shank3 interaction in response to chronic stimuli using a highly sensitive and specific proximity ligation assay. We found that GluA1-Shank3 interactions decrease in response to prolonged neuronal depolarization induced by elevated extracellular potassium, and that this reduced interaction is blocked by NMDA receptor antagonism. These results firmly establish the close interaction of GluA1 and Shank3 in cortical neurons in vitro, and that this select interaction is subject to modulation by depolarization.

Non-coding RNA in the wiring and remodeling of neural circuits

The brain constantly adapts to changes in the environment, a capability that underlies memory and behavior. Long-term adaptations require the remodeling of neural circuits that are mediated by activity-dependent alterations in gene expression. Over the last two decades, it has been shown that the expression of protein-coding genes is significantly regulated by a complex layer of non-coding RNA (ncRNA) interactions. The aim of this review is to summarize recent discoveries regarding the functional involvement of ncRNAs during different stages of neural circuit development, activity-dependent circuit remodeling, and circuit maladapations underlying neurological and neuropsychiatric disorders. In addition to the intensively studied microRNA (miRNA) family, we focus on more recently added ncRNA classes, such as long ncRNAs (lncRNAs) and circular RNAs (circRNAs), and discuss the complex regulatory interactions between these different RNAs. We conclude by discussing the potential relevance of ncRNAs for cell-type and -state-specific regulation in the context of memory formation, the evolution of human cognitive abilities, and the development of new diagnostic and therapeutic tools in brain disorders.

Transcriptome Sequencing of CeRNA Network Constructing in Status Epilepticus Mice Treated by Low-Frequency Repetitive Transcranial Magnetic Stimulation

It is shown that great progress was recently made in the treatment of repetitive transcranial magnetic stimulation (rTMS) for neurological and psychiatric diseases. This study aimed to address how rTMS exerted it therapeutic effects by regulating competitive endogenous RNAs (ceRNAs) of lncRNA-miRNA-mRNA. The distinction of lncRNA, miRNA and mRNA expression in male status epilepticus (SE) mice treated by two different ways, low-frequency rTMS (LF-rTMS) vs. sham rTMS, was analyzed by high-throughput sequencing. The Gene Ontology (GO) functional enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses were carried out. Gene-Gene Cross Linkage Network was established; pivotal genes were screened out. qRT-PCR was used to verify gene-gene interactions. Our results showed that there were 1615 lncRNAs, 510 mRNAs, and 17 miRNAs differentially which were expressed between the LF-rTMS group and the sham rTMS group. The expression difference of these lncRNAs, mRNAs, and miRNAs by microarray detection were consistent with the results by qPCR. GO functional enrichment showed that immune-associated molecular mechanisms, biological processes, and GABA-A receptor activity played a role in SE mice treated with LF-rTMS. KEGG pathway enrichment analysis revealed that differentially expressed genes were correlated to T cell receptor signaling pathway, primary immune deficiency and Th17 cell differentiation signaling pathway. Gene-gene cross linkage network was established on the basis of Pearson's correlation coefficient and miRNA. In conclusion, LF-rTMS alleviates SE through regulating the GABA-A receptor activity transmission, improving immune functions, and biological processes, suggesting the underlying ceRNA molecular mechanisms of LF-rTMS treatment for epilepsy.

Age-dependent NMDA receptor function is regulated by the amyloid precursor protein

N-methyl-D-aspartate receptors (NMDARs) are critical for the maturation and plasticity of glutamatergic synapses. In the hippocampus, NMDARs mainly contain GluN2A and/or GluN2B regulatory subunits. The amyloid precursor protein (APP) has emerged as a putative regulator of NMDARs, but the impact of this interaction to their function is largely unknown. By combining patch-clamp electrophysiology and molecular approaches, we unravel a dual mechanism by which APP controls GluN2B-NMDARs, depending on the life stage. We show that APP is highly abundant specifically at the postnatal postsynapse. It interacts with GluN2B-NMDARs, controlling its synaptic content and mediated currents, both in infant mice and primary neuronal cultures. Upon aging, the APP amyloidogenic-derived C-terminal fragments, rather than APP full-length, contribute to aberrant GluN2B-NMDAR currents. Accordingly, we found that the APP processing is increased upon aging, both in mice and human brain. Interfering with stability or production of the APP intracellular domain normalized the GluN2B-NMDARs currents. While the first mechanism might be essential for synaptic maturation during development, the latter could contribute to age-related synaptic impairments.

Regulation of LncRNAs and microRNAs in neuronal development and disease

Non-coding RNAs (ncRNAs) are RNAs that do not encode proteins but play important roles in regulating cellular processes. Multiple studies over the past decade have demonstrated the role of microRNAs (miRNAs) in cancer, in which some miRNAs can act as biomarkers or provide therapy target. Accumulating evidence also points to the importance of long non-coding RNAs (lncRNAs) in regulating miRNA-mRNA networks. An increasing number of ncRNAs have been shown to be involved in the regulation of cellular processes, and dysregulation of ncRNAs often heralds disease. As the population ages, the incidence of neurodegenerative diseases is increasing, placing enormous pressure on global health systems. Given the excellent performance of ncRNAs in early cancer screening and treatment, here we attempted to aggregate and analyze the regulatory functions of ncRNAs in neuronal development and disease. In this review, we summarize current knowledge on ncRNA taxonomy, biogenesis, and function, and discuss current research progress on ncRNAs in relation to neuronal development, differentiation, and neurodegenerative diseases.

Event-triggered STED imaging

Monitoring the proteins and lipids that mediate all cellular processes requires imaging methods with increased spatial and temporal resolution. STED (stimulated emission depletion) nanoscopy enables fast imaging of nanoscale structures in living cells but is limited by photobleaching. Here, we present event-triggered STED, an automated multiscale method capable of rapidly initiating two-dimensional (2D) and 3D STED imaging after detecting cellular events such as protein recruitment, vesicle trafficking and second messengers activity using biosensors. STED is applied in the vicinity of detected events to maximize the temporal resolution. We imaged synaptic vesicle dynamics at up to 24 Hz, 40 ms after local calcium activity; endocytosis and exocytosis events at up to 11 Hz, 40 ms after local protein recruitment or pH changes; and the interaction between endosomal vesicles at up to 3 Hz, 70 ms after approaching one another. Event-triggered STED extends the capabilities of live nanoscale imaging, enabling novel biological observations in real time.

miR ‐124‐dependent tagging of synapses by synaptopodin enables input‐specific homeostatic plasticity

Homeostatic synaptic plasticity is a process by which neurons adjust their synaptic strength to compensate for perturbations in neuronal activity. Whether the highly diverse synapses on a neuron respond uniformly to the same perturbation remains unclear. Moreover, the molecular determinants that underlie synapse‐specific homeostatic synaptic plasticity are unknown. Here, we report a synaptic tagging mechanism in which the ability of individual synapses to increase their strength in response to activity deprivation depends on the local expression of the spine‐apparatus protein synaptopodin under the regulation of miR‐124. Using genetic manipulations to alter synaptopodin expression or regulation by miR‐124, we show that synaptopodin behaves as a “postsynaptic tag” whose translation is derepressed in a subpopulation of synapses and allows for nonuniform homeostatic strengthening and synaptic AMPA receptor stabilization. By genetically silencing individual connections in pairs of neurons, we demonstrate that this process operates in an input‐specific manner. Overall, our study shifts the current view that homeostatic synaptic plasticity affects all synapses uniformly to a more complex paradigm where the ability of individual synapses to undergo homeostatic changes depends on their own functional and biochemical state.

MDGAs are fast-diffusing molecules that delay excitatory synapse development by altering neuroligin behavior

MDGA molecules can bind neuroligins and interfere with trans-synaptic interactions to neurexins, thereby impairing synapse development. However, the subcellular localization and dynamics of MDGAs, or their specific action mode in neurons remain unclear. Here, surface immunostaining of endogenous MDGAs and single molecule tracking of recombinant MDGAs in dissociated hippocampal neurons reveal that MDGAs are homogeneously distributed and exhibit fast membrane diffusion, with a small reduction in mobility across neuronal maturation. Knocking-down/out MDGAs using shRNAs and CRISPR/Cas9 strategies increases the density of excitatory synapses, the membrane confinement of neuroligin-1, and the phosphotyrosine level of neuroligins associated with excitatory post-synaptic differentiation. Finally, MDGA silencing reduces the mobility of AMPA receptors, increases the frequency of miniature EPSCs (but not IPSCs), and selectively enhances evoked AMPA-receptor-mediated EPSCs in CA1 pyramidal neurons. Overall, our results support a mechanism by which interactions between MDGAs and neuroligin-1 delays the assembly of functional excitatory synapses containing AMPA receptors.

MicroRNA Alteration, Application as Biomarkers, and Therapeutic Approaches in Neurodegenerative Diseases

MicroRNAs (miRNAs) are essential post-transcriptional gene regulators involved in various neuronal and non-neuronal cell functions and play a key role in pathological conditions. Numerous studies have demonstrated that miRNAs are dysregulated in major neurodegenerative diseases, such as Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, amyotrophic lateral sclerosis, or Huntington’s disease. Hence, in the present work, we constructed a comprehensive overview of individual microRNA alterations in various models of the above neurodegenerative diseases. We also provided evidence of miRNAs as promising biomarkers for prognostic and diagnostic approaches. In addition, we summarized data from the literature about miRNA-based therapeutic applications via inhibiting or promoting miRNA expression. We finally identified the overlapping miRNA signature across the diseases, including miR-128, miR-140-5p, miR-206, miR-326, and miR-155, associated with multiple etiological cellular mechanisms. However, it remains to be established whether and to what extent miRNA-based therapies could be safely exploited in the future as effective symptomatic or disease-modifying approaches in the different human neurodegenerative disorders.

MDGA1 negatively regulates amyloid precursor protein-mediated synapse inhibition in the hippocampus

Balanced synaptic inhibition, controlled by multiple synaptic adhesion proteins, is critical for proper brain function. MDGA1 (meprin, A-5 protein, and receptor protein-tyrosine phosphatase mu [MAM] domain-containing glycosylphosphatidylinositol anchor protein 1) suppresses synaptic inhibition in mammalian neurons, yet the molecular mechanisms underlying MDGA1-mediated negative regulation of GABAergic synapses remain unresolved. Here, we show that the MDGA1 MAM domain directly interacts with the extension domain of amyloid precursor protein (APP). Strikingly, MDGA1-mediated synaptic disinhibition requires the MDGA1 MAM domain and is prominent at distal dendrites of hippocampal CA1 pyramidal neurons. Down-regulation of APP in presynaptic GABAergic interneurons specifically suppressed GABAergic, but not glutamatergic, synaptic transmission strength and inputs onto both the somatic and dendritic compartments of hippocampal CA1 pyramidal neurons. Moreover, APP deletion manifested differential effects in somatostatin- and parvalbumin-positive interneurons in the hippocampal CA1, resulting in distinct alterations in inhibitory synapse numbers, transmission, and excitability. The infusion of MDGA1 MAM protein mimicked postsynaptic MDGA1 gain-of-function phenotypes that involve the presence of presynaptic APP. The overexpression of MDGA1 wild type or MAM, but not MAM-deleted MDGA1, in the hippocampal CA1 impaired novel object-recognition memory in mice. Thus, our results establish unique roles of APP-MDGA1 complexes in hippocampal neural circuits, providing unprecedented insight into trans-synaptic mechanisms underlying differential tuning of neuronal compartment-specific synaptic inhibition.

MDGA1 negatively regulates amyloid precursor protein-mediated synapse inhibition in the hippocampus

Balanced synaptic inhibition, controlled by multiple synaptic adhesion proteins, is critical for proper brain function. MDGA1 (meprin, A-5 protein, and receptor protein-tyrosine phosphatase mu [MAM] domain-containing glycosylphosphatidylinositol anchor protein 1) suppresses synaptic inhibition in mammalian neurons, yet the molecular mechanisms underlying MDGA1-mediated negative regulation of GABAergic synapses remain unresolved. Here, we show that the MDGA1 MAM domain directly interacts with the extension domain of amyloid precursor protein (APP). Strikingly, MDGA1-mediated synaptic disinhibition requires the MDGA1 MAM domain and is prominent at distal dendrites of hippocampal CA1 pyramidal neurons. Down-regulation of APP in presynaptic GABAergic interneurons specifically suppressed GABAergic, but not glutamatergic, synaptic transmission strength and inputs onto both the somatic and dendritic compartments of hippocampal CA1 pyramidal neurons. Moreover, APP deletion manifested differential effects in somatostatin- and parvalbumin-positive interneurons in the hippocampal CA1, resulting in distinct alterations in inhibitory synapse numbers, transmission, and excitability. The infusion of MDGA1 MAM protein mimicked postsynaptic MDGA1 gain-of-function phenotypes that involve the presence of presynaptic APP. The overexpression of MDGA1 wild type or MAM, but not MAM-deleted MDGA1, in the hippocampal CA1 impaired novel object-recognition memory in mice. Thus, our results establish unique roles of APP-MDGA1 complexes in hippocampal neural circuits, providing unprecedented insight into trans-synaptic mechanisms underlying differential tuning of neuronal compartment-specific synaptic inhibition.

The many faces of the AMPA-type ionotropic glutamate receptor

Knowledge of the biology of ionotropic glutamate receptors (iGluRs) is a prerequisite for any student of the neurosciences. But yet, half a century ago, the situation was quite different. There was fierce debate on whether simple amino acids, such as l-glutamic acid (L-Glu), should even be considered as putative neurotransmitter candidates that drive excitatory synaptic signaling in the vertebrate brain. Organic chemist, Jeff Watkins, and physiologist, Dick Evans, were amongst the pioneering scientists who shed light on these tribulations. By combining their technical expertise, they performed foundational work that explained that the actions of L-Glu were, in fact, mediated by a family of ion-channels that they named NMDA-, AMPA- and kainate-selective iGluRs. To celebrate and reflect upon their seminal work, Neuropharmacology has commissioned a series of issues that are dedicated to each member of the Glutamate receptor superfamily that includes both ionotropic and metabotropic classes. This issue brings together nine timely reviews from researchers whose work has brought renewed focus on AMPA receptors (AMPARs), the predominant neurotransmitter receptor at central synapses. Together with the larger collection of papers on other GluR family members, these issues highlight that the excitement, passion, and clarity that Watkins and Evans brought to the study of iGluRs is unlikely to fade as we move into a new era on this most interesting of ion-channel families.

Altered White Matter and microRNA Expression in a Murine Model Related to Williams Syndrome Suggests That miR-34b/c Affects Brain Development via Ptpru and Dcx Modulation

Williams syndrome (WS) is a multisystem neurodevelopmental disorder caused by a de novo hemizygous deletion of ~26 genes from chromosome 7q11.23, among them the general transcription factor II-I (GTF2I). By studying a novel murine model for the hypersociability phenotype associated with WS, we previously revealed surprising aberrations in myelination and cell differentiation properties in the cortices of mutant mice compared to controls. These mutant mice had selective deletion of Gtf2i in the excitatory neurons of the forebrain. Here, we applied diffusion magnetic resonance imaging and fiber tracking, which showed a reduction in the number of streamlines in limbic outputs such as the fimbria/fornix fibers and the stria terminalis, as well as the corpus callosum of these mutant mice compared to controls. Furthermore, we utilized next-generation sequencing (NGS) analysis of cortical small RNAs' expression (RNA-Seq) levels to identify altered expression of microRNAs (miRNAs), including two from the miR-34 cluster, known to be involved in prominent processes in the developing nervous system. Luciferase reporter assay confirmed the direct binding of miR-34c-5p to the 3'UTR of PTPRU-a gene involved in neural development that was elevated in the cortices of mutant mice relative to controls. Moreover, we found an age-dependent variation in the expression levels of doublecortin (Dcx)-a verified miR-34 target. Thus, we demonstrate the substantial effect a single gene deletion can exert on miRNA regulation and brain structure, and advance our understanding and, hopefully, treatment of WS.

Homeostatic scaling is driven by a translation-dependent degradation axis that recruits miRISC remodeling

Homeostatic scaling in neurons has been attributed to the individual contribution of either translation or degradation; however, there remains limited insight toward understanding how the interplay between the two processes effectuates synaptic homeostasis. Here, we report that a codependence between protein synthesis and degradation mechanisms drives synaptic homeostasis, whereas abrogation of either prevents it. Coordination between the two processes is achieved through the formation of a tripartite complex between translation regulators, the 26S proteasome, and the miRNA-induced silencing complex (miRISC) components such as Argonaute, MOV10, and Trim32 on actively translating transcripts or polysomes. The components of this ternary complex directly interact with each other in an RNA-dependent manner. Disruption of polysomes abolishes this ternary interaction, suggesting that translating RNAs facilitate the combinatorial action of the proteasome and the translational apparatus. We identify that synaptic downscaling involves miRISC remodeling, which entails the mTORC1-dependent translation of Trim32, an E3 ligase, and the subsequent degradation of its target, MOV10 via the phosphorylation of p70 S6 kinase. We find that the E3 ligase Trim32 specifically polyubiquitinates MOV10 for its degradation during synaptic downscaling. MOV10 degradation alone is sufficient to invoke downscaling by enhancing Arc translation through its 3' UTR and causing the subsequent removal of postsynaptic AMPA receptors. Synaptic scaling was occluded when we depleted Trim32 and overexpressed MOV10 in neurons, suggesting that the Trim32-MOV10 axis is necessary for synaptic downscaling. We propose a mechanism that exploits a translation-driven protein degradation paradigm to invoke miRISC remodeling and induce homeostatic scaling during chronic network activity.

Regulation of AMPAR expression by microRNAs

AMPA receptors (AMPARs) are the major excitatory neurotransmitter receptor in the brain, and their expression at synapses is a critical determinant of synaptic transmission and therefore brain function. Synaptic plasticity involves increases or decreases in synaptic strength, caused by changes in the number or subunit-specific subtype of AMPARs expressed at synapses, and resulting in modifications of functional connectivity of neuronal circuits, a process which is thought to underpin learning and the formation or loss of memories. Furthermore, numerous neurological disorders involve dysregulation of excitatory synaptic transmission or aberrant recruitment of plasticity processes. MicroRNAs (miRNAs) repress the translation of target genes by partial complementary base pairing with mRNAs, and are the core component of a mechanism widely used in a range of cell processes for regulating protein translation. MiRNA-dependent translational repression can occur locally in neuronal dendrites, close to synapses, and can also result in relatively rapid changes in protein expression. MiRNAs are therefore well-placed to regulate synaptic plasticity via the local control of AMPAR subunit synthesis, and can also result in synaptic dysfunction in the event of dysregulation in disease. Here, I will review the miRNAs that have been identified as playing a role in physiological or pathological changes in AMPAR subunit expression at synapses, focussing on miRNAs that target mRNAs encoding AMPAR subunits, and on miRNAs that target AMPAR accessory proteins involved in AMPAR trafficking and hence the regulation of AMPAR synaptic localisation.

GluA4 facilitates cerebellar expansion coding and enables associative memory formation

AMPA receptors (AMPARs) mediate excitatory neurotransmission in the central nervous system (CNS) and their subunit composition determines synaptic efficacy. Whereas AMPAR subunits GluA1–GluA3 have been linked to particular forms of synaptic plasticity and learning, the functional role of GluA4 remains elusive. Here, we demonstrate a crucial function of GluA4 for synaptic excitation and associative memory formation in the cerebellum. Notably, GluA4-knockout mice had ~80% reduced mossy fiber to granule cell synaptic transmission. The fidelity of granule cell spike output was markedly decreased despite attenuated tonic inhibition and increased NMDA receptor-mediated transmission. Computational network modeling incorporating these changes revealed that deletion of GluA4 impairs granule cell expansion coding, which is important for pattern separation and associative learning. On a behavioral level, while locomotor coordination was generally spared, GluA4-knockout mice failed to form associative memories during delay eyeblink conditioning. These results demonstrate an essential role for GluA4-containing AMPARs in cerebellar information processing and associative learning.

Emerging role of microRNAs in major depressive disorder and its implication on diagnosis and therapeutic response

BACKGROUND

Major depressive disorder (MDD) is a serious and common psychiatric disorder with a high prevalence in the population. Although great advances have been made, its pathogenesis is still unclear and a validated biomarker for diagnosis or therapeutic response remains unidentified. This review aims at summarizing the functional role of miRNAs in MDD pathogenesis and their potential as biomarkers for MDD diagnosis and antidepressant response.

METHODS

We performed a bibliographic research on the main databases (PubMed, Google Scholar and Web of Science) using the terms "microRNAs", "major depressive disorder", "synaptic plasticity", "biomarker", "antidepressant treatment", in order to find studies that propose the role of microRNAs in MDD pathogenesis and their potential as biomarkers for MDD diagnosis and antidepressant response.

RESULTS

microRNAs (miRNAs), a class of small noncoding RNAs, act as key regulators of synaptic plasticity in MDD pathogenesis. Growing researches provide the evidence for peripheral miRNAs as potential biomarkers for MDD diagnosis and antidepressant response. These results suggest that targeting miRNAs directly could be therapeutically beneficial for MDD and miRNAs are potential biomarkers of MDD and its treatment.

LIMITATIONS

The role of miRNAs in MDD pathogenesis needs further investigation. Whether miRNAs in peripheral tissues truly represent brain-derived miRNAs is still unclear at the present time. Moreover, only a few blood miRNAs alterations are consistent across studies.

CONCLUSIONS

Overall, miRNAs act key regulators of synaptic plasticity in MDD pathogenesis and hold significant promise as biomarkers or therapeutic targets for MDD, but further research is still needed.

microRNA-186 alleviates oxygen-glucose deprivation/reoxygenation-induced injury by directly targeting hypoxia-inducible factor-1α

Previous studies have suggested that microRNA-186 (miR-186) can be induced under hypoxic conditions, and is associated with apoptosis. This study was undertaken to explore the exact role of this microRNA (miRNA) in the apoptotic death of neurons during cerebral ischemic/reperfusion (I/R) injury. To model cerebral ischemia/reperfusion (I/R) injuries, we utilized a transient middle cerebral artery occlusion approach in rats, as well as a model of oxygen-glucose deprivation/reoxygenation (OGD/R) in Neuro2a cells. We found that in both in vitro and in vivo models of cerebral I/R injuries, levels of miR-186 were markedly decreased. When we overexpressed miR-186, this was associated with a reduction in the apoptotic death of neuroblastoma cells in the OGD/R model system, whereas the opposite was true when this miRNA was instead inhibited. We further found miR-186 to directly target hypoxia-inducible factor 1α (HIF-1α) by interacting with the 3'-untranslated region of this mRNA. When we knocked down HIF-1α, this partially overcame the apoptotic death of cells in response to OGD/R injury and associated miR-186 downregulation. Our findings indicate that miR-186 is able to reduce ischemic injury to neurons at least in part through downregulating HIF-1α, suggesting that the miR-186/HIF-1α axis is a potential therapeutic target for the treatment of ischemic stroke.

microRNAs as Early Biomarkers of Alzheimer's Disease: A Synaptic Perspective

Pathogenic processes underlying Alzheimer's disease (AD) affect synaptic function from initial asymptomatic stages, long time before the onset of cognitive decline and neurodegeneration. Therefore, reliable biomarkers enabling early AD diagnosis and prognosis are needed to maximize the time window for therapeutic interventions. MicroRNAs (miRNAs) have recently emerged as promising cost-effective and non-invasive biomarkers for AD, since they can be readily detected in different biofluids, including cerebrospinal fluid (CSF) and blood. Moreover, a growing body of evidence indicates that miRNAs regulate synaptic homeostasis and plasticity processes, suggesting that they may be involved in early synaptic dysfunction during AD. Here, we review the current literature supporting a role of miRNAs during early synaptic deficits in AD, including recent studies evaluating their potential as AD biomarkers. Besides targeting genes related to Aβ and tau metabolism, several miRNAs also regulate synaptic-related proteins and transcription factors implicated in early synaptic deficits during AD. Furthermore, individual miRNAs and molecular signatures have been found to distinguish between prodromal AD and healthy controls. Overall, these studies highlight the relevance of considering synaptic-related miRNAs as potential biomarkers of early AD stages. However, further validation studies in large cohorts, including longitudinal studies, as well as implementation of standardized protocols, are needed to establish miRNA-based biomarkers as reliable diagnostic and prognostic tools.

microRNAs Mediated Regulation of the Ribosomal Proteins and its Consequences on the Global Translation of Proteins

Ribosomal proteins (RPs) are mostly derived from the energy-consuming enzyme families such as ATP-dependent RNA helicases, AAA-ATPases, GTPases and kinases, and are important structural components of the ribosome, which is a supramolecular ribonucleoprotein complex, composed of Ribosomal RNA (rRNA) and RPs, coordinates the translation and synthesis of proteins with the help of transfer RNA (tRNA) and other factors. Not all RPs are indispensable; in other words, the ribosome could be functional and could continue the translation of proteins instead of lacking in some of the RPs. However, the lack of many RPs could result in severe defects in the biogenesis of ribosomes, which could directly influence the overall translation processes and global expression of the proteins leading to the emergence of different diseases including cancer. While microRNAs (miRNAs) are small non-coding RNAs and one of the potent regulators of the post-transcriptional gene expression, miRNAs regulate gene expression by targeting the 3' untranslated region and/or coding region of the messenger RNAs (mRNAs), and by interacting with the 5' untranslated region, and eventually finetune the expression of approximately one-third of all mammalian genes. Herein, we highlighted the significance of miRNAs mediated regulation of RPs coding mRNAs in the global protein translation.

The role of synaptic microRNAs in Alzheimer's disease

Structurally and functionally active synapses are essential for neurotransmission and for maintaining normal synaptic and cognitive functions. Researchers have found that synaptic dysfunction is associated with the onset and progression of neurodegenerative diseases, such as Alzheimer's disease (AD), and synaptic dysfunction is even one of the main physiological hallmarks of AD. MiRNAs are present in small, subcellular compartments of the neuron such as neural dendrites, synaptic vesicles, and synaptosomes are known as synaptic miRNAs. Synaptic miRNAs involved in governing multiple synaptic functions that lead to healthy brain functioning and synaptic activity. However, the precise role of synaptic miRNAs has not been determined in AD progression. This review emphasizes the presence of miRNAs at the synapse, synaptic compartments and roles of miRNAs in multiple synaptic functions. We focused on synaptic miRNAs alteration in AD, and how the modulation of miRNAs effect the synaptic functions in AD. We also discussed the impact of synaptic miRNAs in AD progression concerning the synaptic ATP production, mitochondrial function, and synaptic activity.

AVPR1A main effect and OXTR-by-environment interplay in individual differences in depression level

Background

Multiple studies of depression indicated a significant role of gene-by-environment interactions; however, they are mainly limited to the examination of modulating effect of recent stressful life events. Other environmental factors occurring at different stages of ante- and postnatal development may affect the association between multiple genes and depression. The study aimed to analyze the main and haplotype-based effect of serotonergic system and HPA-axis gene polymorphisms on depression and to detect gene-by-environment interaction models explaining individual variance in depression in mentally healthy young adults from Russia.

Methods

Depression score was assessed using Beck Depression Inventory (BDI) in 623 healthy individuals (81% women; 17-25 years) of Caucasian origin (Russians, Tatars, Udmurts) from Russia. The main- and gene-based effects of 12 SNPs in SLC6A4 (5-HTTLPR, rs1042173), HTR2A (rs7322347), OXTR (rs7632287, rs2254298, rs13316193, rs53576, rs2228485, rs237911), AVPR1A (rs3803107, rs1042615), and AVPR1B (rs33911258) genes, and gene-by-environment interactions were tested with linear regression models (PLINK v.1.9) adjusted for multiple comparisons.

Results

We observed ethnicity-specific main effect of the AVPR1A rs3803107 (P = 0.003; P_FDR = 0.047) and gene-based effect of the OXTR gene (Р = 0.005; P_perm = 0.034) on BDI-measured depression, and modifying effect of paternal care on OXTR rs53576 (P = 0.004; P_FDR = 0.012) and birth order on OXTR rs237911 (P = 0.006; P_FDR = 0.018) association with depression level.

Limitations

A hypothesis driven candidate gene approach, which examined a limited number of genetic variants in a moderately large sample, was used.

Conclusions

Our preliminary findings indicate that familial environment may play a permissive role modulating the manifestation of OXTR-based depression variance in mentally healthy subjects.

Deletion of Kv10.2 Causes Abnormal Dendritic Arborization and Epilepsy Susceptibility

The abnormal function of the voltage-gated potassium channel Kv10.2 can induce epilepsy. However, the physiological function of Kv10.2 in the central nervous system remains unclear. In this study, we found that Kv10.2 knockout (KO) increased the complexity of neurons in the CA3 subarea of hippocampus. Kv10.2 KO led to enlarged somata, elongated dendritic length, and increased the number of dendritic tips in cultured rat hippocampus neurons. Kv10.2 KO also increased Synapsin I and PSD95 protein density in cultured rat hippocampal neurons. Whole cell patch-clamp recordings of brain slices in the CA3 subarea of hippocampus revealed that Kv10.2 KO increased the amplitude of spontaneous excitatory postsynaptic currents (sEPSC) and miniature excitatory postsynaptic currents (mEPSC), depolarized the resting membrane potential and increased the action potential firing, reduced the rheobase and increased the input resistance, which results in enhanced neuronal excitability. Furthermore, we made electroencephalogram (EEG) recordings of brain activity in freely moving rats before and after inducing seizures by pentylenetetrazole (PTZ) injection. Kv10.2 KO rats dramatically increased the EEG amplitude during epilepsy. Behavioral observation after seizure induction revealed that Kv10.2 KO rats demonstrated shortened onset latency, prolonged duration, and increased seizure severity when compared with wild type rats. Therefore, this study provides a new link between Kv10.2 and neuronal morphology and higher intrinsic excitability.

Anodal and cathodal tDCS modulate neural activity and selectively affect GABA and glutamate syntheses in the visual cortex of cats

KEY POINTS

The present study showed that anodal and cathodal transcranial direct current stimulation (tDCS) can respectively increase and decrease the amplitude of visually evoked field potentials in the stimulated visual cortex of cats, with the effect lasting for ∼60-70 min. We directly measured tDCS-induced changes in the concentration of inhibitory and excitatory neurotransmitters in the visual cortex using the enzyme-linked immunosorbent assay method and showed that anodal and cathodal tDCS can selectively decrease the concentration of GABA and glutamate in the stimulated cortical area. Anodal and cathodal tDCS can selectively inhibit the synthesis of GABA and glutamate by suppressing the expression of GABA- and glutamate-synthesizing enzymes, respectively.

ABSTRACT

Transcranial direct current stimulation (tDCS) evokes long-lasting neuronal excitability in the target brain region. The underlying neural mechanisms remain poorly understood. The present study examined tDCS-induced alterations in neuronal activities, as well as the concentration and synthesis of GABA and glutamate (GLU), in area 21a (A21a) of cat visual cortex. Our analysis showed that anodal and cathodal tDCS respectively enhanced and suppressed neuronal activities in A21a, as indicated by a significantly increased and decreased amplitude of visually evoked field potentials (VEPs). The tDCS-induced effect lasted for ∼60-70 min. By contrast, sham tDCS had no significant impact on the VEPs in A21a. On the other hand, the concentration of GABA, but not that of GLU, in A21a significantly decreased after anodal tDCS relative to sham tDCS, whereas the concentration of GLU, but not that of GABA, in A21a significantly decreased after cathodal tDCS relative to sham tDCS. Furthermore, the expression of GABA-synthesizing enzymes GAD65 and GAD67 in A21a significantly decreased in terms of both mRNA and protein concentrations after anodal tDCS relative to sham tDCS, whereas that of GLU-synthesizing enzyme glutaminase (GLS) did not change significantly after anodal tDCS. By contrast, both mRNA and protein concentrations of GLS in A21a significantly decreased after cathodal tDCS relative to sham tDCS, whereas those of GAD65/GAD67 showed no significant change after cathodal tDCS. Taken together, these results indicate that anodal and cathodal tDCS may selectively reduce GABA and GLU syntheses and thus respectively enhance and suppress neuronal excitability in the stimulated brain area.

miRNA-Dependent Control of Homeostatic Plasticity in Neurons

Homeostatic plasticity is a form of plasticity in which neurons compensate for changes in neuronal activity through the control of key physiological parameters such as the number and the strength of their synaptic inputs and intrinsic excitability. Recent studies revealed that miRNAs, which are small non-coding RNAs repressing mRNA translation, participate in this process by controlling the translation of multiple effectors such as glutamate transporters, receptors, signaling molecules and voltage-gated ion channels. In this review, we present and discuss the role of miRNAs in both cell-wide and compartmentalized forms of homeostatic plasticity as well as their implication in pathological processes associated with homeostatic failure.