Numerous candidate plasticity-related genes revealed by differential cDNA cloning

NRN1 interacts with Notch to increase oncogenic STAT3 signaling in melanoma

BACKGROUND

Melanoma is a highly heterogeneous cancer, in which frequent changes in activation of signaling pathways lead to a high adaptability to ever changing tumor microenvironments. The elucidation of cancer specific signaling pathways is of great importance, as demonstrated by the inhibitor of the common BrafV600E mutation PLX4032 in melanoma treatment. We therefore investigated signaling pathways that were influenced by neurotrophin NRN1, which has been shown to be upregulated in melanoma.

METHODS

Using a cell culture model system with an NRN1 overexpression, we investigated the influence of NRN1 on melanoma cells' functionality and signaling. We employed real time cell analysis and spheroid formation assays, while for investigation of molecular mechanisms we used a kinase phosphorylation kit as well as promotor activity analysis followed by mRNA and protein analysis.

RESULTS

We revealed that NRN1 interacts directly with the cleaved intracellular domain (NICD) of Notch1 and Notch3, causing a potential retention of NICD in the cytoplasm and thereby reducing the expression of its direct downstream target Hes1. This leads to decreased sequestration of JAK and STAT3 in a Hes1-driven phosphorylation complex. Consequently, our data shows less phosphorylation of STAT3 while presenting an accumulation of total protein levels of STAT3 in association with NRN1 overexpression. The potential of the STAT3 signaling pathway to act in both a tumor suppressive and oncogenic manner led us to investigate specific downstream targets - namely Vegf A, Mdr1, cMet - which were found to be upregulated under oncogenic levels of NRN1.

CONCLUSIONS

In summary, we were able to show that NRN1 links oncogenic signaling events between Notch and STAT3 in melanoma. We also suggest that in future research more attention should be payed to cellular regulation of signaling molecules outside of the classically known phosphorylation events.

Exogenous neuritin restores auditory following cochlear spiral ganglion neuron denervation of gerbils

Spiral ganglion neurons (SGNs) transmit sound signals received by hair cells to the auditory center to produce hearing. The quantity and function are important for maintaining normal hearing function. Limited by the regenerative capacity, SGNs are unable to regenerate spontaneously after injury. Various neurotrophic factors play an important role in the regeneration process. Neuritin is a neurite growth factor that plays an important role in neural plasticity and nerve injury repair. In this study, we used bioinformatics analysis to show that neuritin was negatively correlated with cochlear damage. Then, we aimed to establish a cochlear spiral ganglion-specific sensorineural deafness model in gerbils using ouabain and determine the effects of exogenous neuritin protein in protecting damaged cochlear SGNs and repairing damaged auditory nerve function. The provides a new research strategy and scientific basis for the prevention and treatment of sensorineural deafness caused by the loss of SGNs. We were discovered that neuritin is expressed throughout the development of the gerbil cochlea, primarily in the SGNs and Corti regions. The expression of neuritin was negatively correlated with the sensorineural deafness induced by ouabain. In vitro and in vivo revealed that neuritin significantly maintained the number and arrangement of SGNs and nerve fibers in the damaged cochlea and effectively protected the high-frequency listening function of gerbils.

From theory to practice: translating the concept of cognitive resilience to novel therapeutic targets that maintain cognition in aging adults

While the concept of cognitive resilience is well-established it has not been defined in a way that can be measured. This has been an impediment to studying its underlying biology and to developing instruments for its clinical assessment. This perspective highlights recent work that has quantified the expression of cortical proteins associated with cognitive resilience, thus facilitating studies of its complex underlying biology and the full range of its clinical effects in aging adults. These initial studies provide empirical support for the conceptualization of resilience as a continuum. Like other conventional risk factors, some individuals manifest higher-than-average cognitive resilience and other individuals manifest lower-than-average cognitive resilience. These novel approaches for advancing studies of cognitive resilience can be generalized to other aging phenotypes and can set the stage for the development of clinical tools that might have the potential to measure other mechanisms of resilience in aging adults. These advances also have the potential to catalyze a complementary therapeutic approach that focuses on augmenting resilience via lifestyle changes or therapies targeting its underlying molecular mechanisms to maintain cognition and brain health even in the presence of untreatable stressors like brain pathologies that accumulate in aging adults.

Transcriptomic analysis reveals distinct adaptive molecular mechanism in the hippocampal CA3 from rats susceptible or not-susceptible to hyperthermia-induced seizures

Febrile seizures during early childhood are a relevant risk factor for the development of mesial temporal lobe epilepsy. Nevertheless, the molecular mechanism induced by febrile seizures that render the brain susceptible or not-susceptible to epileptogenesis remain poorly understood. Because the temporal investigation of such mechanisms in human patients is impossible, rat models of hyperthermia-induced febrile seizures have been used for that purpose. Here we conducted a temporal analysis of the transcriptomic and microRNA changes in the ventral CA3 of rats that develop (HS group) or not-develop (HNS group) seizures after hyperthermic insult on the eleventh postnatal day. The selected time intervals corresponded to acute, latent, and chronic phases of the disease. We found that the transcriptional differences between the HS and the HNS groups are related to inflammatory pathways, immune response, neurogenesis, and dendritogenesis in the latent and chronic phases. Additionally, the HNS group expressed a greater number of miRNAs (some abundantly expressed) as compared to the HS group. These results indicate that HNS rats were able to modulate their inflammatory response after insult, thus presenting better tissue repair and re-adaptation. Potential therapeutic targets, including genes, miRNAs and signaling pathways involved in epileptogenesis were identified.

Integrated Proteomics to Understand the Role of Neuritin (NRN1) as a Mediator of Cognitive Resilience to Alzheimer's Disease

The molecular mechanisms and pathways enabling certain individuals to remain cognitively normal despite high levels of Alzheimer's disease (AD) pathology remain incompletely understood. These cognitively normal people with AD pathology are described as preclinical or asymptomatic AD (AsymAD) and appear to exhibit cognitive resilience to the clinical manifestations of AD dementia. Here we present a comprehensive network-based approach from cases clinically and pathologically defined as asymptomatic AD to map resilience-associated pathways and extend mechanistic validation. Multiplex tandem mass tag MS (TMT-MS) proteomic data (n = 7787 proteins) was generated on brain tissue from Brodmann area 6 and Brodmann area 37 (n = 109 cases, n = 218 total samples) and evaluated by consensus weighted gene correlation network analysis. Notably, neuritin (NRN1), a neurotrophic factor previously linked to cognitive resilience, was identified as a hub protein in a module associated with synaptic biology. To validate the function of NRN1 with regard to the neurobiology of AD, we conducted microscopy and physiology experiments in a cellular model of AD. NRN1 provided dendritic spine resilience against amyloid-β (Aβ) and blocked Aβ-induced neuronal hyperexcitability in cultured neurons. To better understand the molecular mechanisms of resilience to Aβ provided by NRN1, we assessed how exogenous NRN1 alters the proteome by TMT-MS (n = 8238 proteins) of cultured neurons and integrated the results with the AD brain network. This revealed overlapping synapse-related biology that linked NRN1-induced changes in cultured neurons with human pathways associated with cognitive resilience. Collectively, this highlights the utility of integrating the proteome from the human brain and model systems to advance our understanding of resilience-promoting mechanisms and prioritize therapeutic targets that mediate resilience to AD.

Placental DNA methylation profile as predicting marker for autism spectrum disorder (ASD)

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that impairs normal brain development and socio-cognitive abilities. The pathogenesis of this condition points out the involvement of genetic and environmental factors during in-utero life. Placenta, as an interface tissue between mother and fetus, provides developing fetus requirements and exposes it to maternal environment as well. Therefore, the alteration of DNA methylation as epigenetic consequence of gene-environmental interaction in the placenta could shed light on ASD pathogenesis. In this study, we reviewed the current findings on placental methylation status and its association with ASD. Differentially methylated regions (DMRs) in ASD-developing placenta were found to be mainly enriched in ASD gene loci affecting synaptogenesis, microtubule dynamics, neurogenesis and neuritogenesis. In addition, non-genic DMRs in ASD-placenta proposes an alternative contributing mechanism for ASD development. Our study highlights the importance of placental DNA methylation signature as a biomarker for ASD prediction.

Global Impairment of Immediate-Early Genes Expression in Rett Syndrome Models and Patients Linked to Myelination Defects

Rett syndrome (RTT) is a severe neurodevelopmental disease caused almost exclusively by mutations to the MeCP2 gene. This disease may be regarded as a synaptopathy, with impairments affecting synaptic plasticity, inhibitory and excitatory transmission and network excitability. The complete understanding of the mechanisms behind how the transcription factor MeCP2 so profoundly affects the mammalian brain are yet to be determined. What is known, is that MeCP2 involvement in activity-dependent expression programs is a critical link between this protein and proper neuronal activity, which allows the correct maturation of connections in the brain. By using RNA-sequencing analysis, we found several immediate-early genes (IEGs, key mediators of activity-dependent responses) directly bound by MeCP2 at the chromatin level and upregulated in the hippocampus and prefrontal cortex of the Mecp2-KO mouse. Quantification of the IEGs response to stimulus both in vivo and in vitro detected an aberrant expression pattern in MeCP2-deficient neurons. Furthermore, altered IEGs levels were found in RTT patient's peripheral blood and brain regions of post-mortem samples, correlating with impaired expression of downstream myelination-related genes. Altogether, these data indicate that proper IEGs expression is crucial for correct synaptic development and that MeCP2 has a key role in the regulation of IEGs.

Doublecortin-Like Kinase 1 Facilitates Dendritic Spine Growth of Pyramidal Neurons in Mouse Prefrontal Cortex

The L1 cell adhesion molecule NrCAM (Neuron-glia related cell adhesion molecule) functions as a co-receptor for secreted class 3 Semaphorins to prune subpopulations of dendritic spines on apical dendrites of pyramidal neurons in the developing mouse neocortex. The developing spine cytoskeleton is enriched in actin filaments, but a small number of microtubules have been shown to enter the spine apparently trafficking vesicles to the membrane. Doublecortin-like kinase 1 (DCLK1) is a member of the Doublecortin (DCX) family of microtubule-binding proteins with serine/threonine kinase activity. To determine if DCLK1 plays a role in spine remodeling, we generated a tamoxifen-inducible mouse line (Nex1Cre-ERT2: DCLK1flox/flox: RCE) to delete microtubule binding isoforms of DCLK1 from pyramidal neurons during postnatal stages of spine development. Homozygous DCLK1 conditional mutant mice exhibited decreased spine density on apical dendrites of pyramidal neurons in the prefrontal cortex (layer 2/3). Mature mushroom spines were selectively decreased upon DCLK1 deletion but dendritic arborization was unaltered. Mutagenesis and binding studies revealed that DCLK1 bound NrCAM at the conserved FIGQY1231 motif in the NrCAM cytoplasmic domain, a known interaction site for the actin-spectrin adaptor Ankyrin. These findings demonstrate in a novel mouse model that DCLK1 facilitates spine growth and maturation on cortical pyramidal neurons in the mouse prefrontal cortex.

Activity-Induced Cortical Glutamatergic Neuron Nascent Proteins

Neuronal activity initiates signaling cascades that culminate in diverse outcomes including structural and functional neuronal plasticity, and metabolic changes. While studies have revealed activity-dependent neuronal cell type-specific transcriptional changes, unbiased quantitative analysis of cell-specific activity-induced dynamics in newly synthesized proteins (NSPs) synthesis in vivo has been complicated by cellular heterogeneity and a relatively low abundance of NSPs within the proteome in the brain. Here we combined targeted expression of mutant MetRS (methionine tRNA synthetase) in genetically defined cortical glutamatergic neurons with tight temporal control of treatment with the noncanonical amino acid, azidonorleucine, to biotinylate NSPs within a short period after pharmacologically induced seizure in male and female mice. By purifying peptides tagged with heavy or light biotin-alkynes and using direct tandem mass spectrometry detection of biotinylated peptides, we quantified activity-induced changes in cortical glutamatergic neuron NSPs. Seizure triggered significant changes in ∼300 NSPs, 33% of which were decreased by seizure. Proteins mediating excitatory and inhibitory synaptic plasticity, including SynGAP1, Pak3, GEPH1, Copine-6, and collybistin, and DNA and chromatin remodeling proteins, including Rad21, Smarca2, and Ddb1, are differentially synthesized in response to activity. Proteins likely to play homeostatic roles in response to activity, such as regulators of proteastasis, intracellular ion control, and cytoskeleton remodeling proteins, are activity induced. Conversely, seizure decreased newly synthetized NCAM, among others, suggesting that seizure induced degradation. Overall, we identified quantitative changes in the activity-induced nascent proteome from genetically defined cortical glutamatergic neurons as a strategy to discover downstream mediators of neuronal plasticity and generate hypotheses regarding their function.SIGNIFICANCE STATEMENT Activity-induced neuronal and synaptic plasticity are mediated by changes in the protein landscape, including changes in the activity-induced newly synthesized proteins; however, identifying neuronal cell type-specific nascent proteome dynamics in the intact brain has been technically challenging. We conducted an unbiased proteomic screen from which we identified significant activity-induced changes in ∼300 newly synthesized proteins in genetically defined cortical glutamatergic neurons within 20 h after pharmacologically induced seizure. Bioinformatic analysis of the dynamic nascent proteome indicates that the newly synthesized proteins play diverse roles in excitatory and inhibitory synaptic plasticity, chromatin remodeling, homeostatic mechanisms, and proteasomal and metabolic functions, extending our understanding of the diversity of plasticity mechanisms.

NRN1 Gene as a Potential Marker of Early-Onset Schizophrenia: Evidence from Genetic and Neuroimaging Approaches

Included in the neurotrophins family, the Neuritin 1 gene (NRN1) has emerged as an attractive candidate gene for schizophrenia (SZ) since it has been associated with the risk for the disorder and general cognitive performance. In this work, we aimed to further investigate the association of NRN1 with SZ by exploring its role on age at onset and its brain activity correlates. First, we developed two genetic association analyses using a family-based sample (80 early-onset (EO) trios (offspring onset ≤ 18 years) and 71 adult-onset (AO) trios) and an independent case–control sample (120 healthy subjects (HS), 87 EO and 138 AO patients). Second, we explored the effect of NRN1 on brain activity during a working memory task (N-back task; 39 HS, 39 EO and 39 AO; matched by age, sex and estimated IQ). Different haplotypes encompassing the same three Single Nucleotide Polymorphisms(SNPs, rs3763180–rs10484320–rs4960155) were associated with EO in the two samples (GCT, TCC and GTT). Besides, the GTT haplotype was associated with worse N-back task performance in EO and was linked to an inefficient dorsolateral prefrontal cortex activity in subjects with EO compared to HS. Our results show convergent evidence on the NRN1 association with EO both from genetic and neuroimaging approaches, highlighting the role of neurotrophins in the pathophysiology of SZ.

ALS-related FUS mutations alter axon growth in motoneurons and affect HuD/ELAVL4 and FMRP activity

Mutations in the RNA-binding protein (RBP) FUS have been genetically associated with the motoneuron disease amyotrophic lateral sclerosis (ALS). Using both human induced pluripotent stem cells and mouse models, we found that FUS-ALS causative mutations affect the activity of two relevant RBPs with important roles in neuronal RNA metabolism: HuD/ELAVL4 and FMRP. Mechanistically, mutant FUS leads to upregulation of HuD protein levels through competition with FMRP for HuD mRNA 3'UTR binding. In turn, increased HuD levels overly stabilize the transcript levels of its targets, NRN1 and GAP43. As a consequence, mutant FUS motoneurons show increased axon branching and growth upon injury, which could be rescued by dampening NRN1 levels. Since similar phenotypes have been previously described in SOD1 and TDP-43 mutant models, increased axonal growth and branching might represent broad early events in the pathogenesis of ALS.

Extracellular Metalloproteinases in the Plasticity of Excitatory and Inhibitory Synapses

Long-term synaptic plasticity is shaped by the controlled reorganization of the synaptic proteome. A key component of this process is local proteolysis performed by the family of extracellular matrix metalloproteinases (MMPs). In recent years, considerable progress was achieved in identifying extracellular proteases involved in neuroplasticity phenomena and their protein substrates. Perisynaptic metalloproteinases regulate plastic changes at synapses through the processing of extracellular and membrane proteins. MMP9 was found to play a crucial role in excitatory synapses by controlling the NMDA-dependent LTP component. In addition, MMP3 regulates the L-type calcium channel-dependent form of LTP as well as the plasticity of neuronal excitability. Both MMP9 and MMP3 were implicated in memory and learning. Moreover, altered expression or mutations of different MMPs are associated with learning deficits and psychiatric disorders, including schizophrenia, addiction, or stress response. Contrary to excitatory drive, the investigation into the role of extracellular proteolysis in inhibitory synapses is only just beginning. Herein, we review the principal mechanisms of MMP involvement in the plasticity of excitatory transmission and the recently discovered role of proteolysis in inhibitory synapses. We discuss how different matrix metalloproteinases shape dynamics and turnover of synaptic adhesome and signal transduction pathways in neurons. Finally, we discuss future challenges in exploring synapse- and plasticity-specific functions of different metalloproteinases.

Activity-Dependent Gene Expression in Neurons

The function of the nervous system in conveying and processing information necessary to interact with the environment confers unique aspects on how the expression of genes in neurons is regulated. Three salient factors are that (1) neurons are the largest and among the most morphologically complex of all cells, with strict polarity, subcellular compartmentation, and long-distant transport of gene products, signaling molecules, and other materials; (2) information is coded in the temporal firing pattern of membrane depolarization; and (3) neurons must maintain a stable homeostatic level of activation to function so stimuli do not normally drive intracellular signaling to steady state. Each of these factors can require special methods of analysis differing from approaches used in non-neuronal cells. This review considers these three aspects of neuronal gene expression and the current approaches being used to analyze these special features of how the neuronal transcriptome is modulated by action potential firing.

Neuritin improves the neurological functional recovery after experimental intracerebral hemorrhage in mice

Stroke is one of the leading causes of death worldwide, with intracerebral hemorrhage (ICH) being the most lethal subtype. Neuritin (Nrn) is a neurotropic factor that has been reported to have neuroprotective effects in acute brain and spinal cord injury. However, whether Nrn has a protective role in ICH has not been investigated. In this study, ICH was induced in C57BL/6 J mice by injection of collagenase VII, while the overexpression of Nrn in the striatum was induced by an adeno-associated virus serotype 9 (AAV9) vector. We found that compared with GFP-ICH mice, Nrn-ICH mice showed improved performance in the corner, cylinder and forelimb tests after ICH, and showed less weight loss and more rapid weight recovery. Overexpression of Nrn reduced brain lesions, edema, neuronal death and white matter and synaptic integrity dysfunction caused by ICH. Western blot results showed that phosphorylated PERK and ATF4 were significantly inhibited, while phosphorylation of Akt/mammalian target of rapamycin was increased in the Nrn-ICH group, compared with the GFP-ICH group. Whole cell recording from motor neurons indicated that overexpression of Nrn reversed the decrease of spontaneous excitatory postsynaptic currents (sEPSCs) and action potential frequencies induced by ICH. These data show that Nrn improves neurological deficits in mice with ICH by reducing brain lesions and edema, inhibiting neuronal death, and possibly by increasing neuronal connections.

Follicular regulatory T cells produce neuritin to regulate B cells

Regulatory T cells prevent the emergence of autoantibodies and excessive IgE, but the precise mechanisms are unclear. Here, we show that BCL6-expressing Tregs, known as follicular regulatory T (Tfr) cells, produce abundant neuritin protein that targets B cells. Mice lacking Tfr cells or neuritin in Foxp3-expressing cells accumulated early plasma cells in germinal centers (GCs) and developed autoantibodies against histones and tissue-specific self-antigens. Upon immunization, these mice also produced increased plasma IgE and IgG1. We show that neuritin is taken up by B cells, causes phosphorylation of numerous proteins, and dampens IgE class switching. Neuritin reduced differentiation of mouse and human GC B cells into plasma cells, downregulated BLIMP-1, and upregulated BCL6. Administration of neuritin to Tfr-deficient mice prevented the accumulation of early plasma cells in GCs. Production of neuritin by Tfr cells emerges as a central mechanism to suppress B cell-driven autoimmunity and IgE-mediated allergies.

Activity-dependent regulome of human GABAergic neurons reveals new patterns of gene regulation and neurological disease heritability

Neuronal activity-dependent gene expression is essential for brain development. Although transcriptional and epigenetic effects of neuronal activity have been explored in mice, such an investigation is lacking in humans. Because alterations in GABAergic neuronal circuits are implicated in neurological disorders, we conducted a comprehensive activity-dependent transcriptional and epigenetic profiling of human induced pluripotent stem cell-derived GABAergic neurons similar to those of the early developing striatum. We identified genes whose expression is inducible after membrane depolarization, some of which have specifically evolved in primates and/or are associated with neurological diseases, including schizophrenia and autism spectrum disorder (ASD). We define the genome-wide profile of human neuronal activity-dependent enhancers, promoters and the transcription factors CREB and CRTC1. We found significant heritability enrichment for ASD in the inducible promoters. Our results suggest that sequence variation within activity-inducible promoters of developing human forebrain GABAergic neurons contributes to ASD risk.

Regulation of dopamine-dependent transcription and cocaine action by Gadd45b

Exposure to drugs of abuse produces robust transcriptional and epigenetic reorganization within brain reward circuits that outlives the direct effects of the drug and may contribute to addiction. DNA methylation is a covalent epigenetic modification that is altered following stimulant exposure and is critical for behavioral and physiological adaptations to drugs of abuse. Although activity-related loss of DNA methylation requires the Gadd45 (Growth arrest and DNA-damage-inducible) gene family, very little is known about how this family regulates activity within the nucleus accumbens or behavioral responses to drugs of abuse. Here, we combined genome-wide transcriptional profiling, pharmacological manipulations, electrophysiological measurements, and CRISPR tools with traditional knockout and behavioral approaches in rodent model systems to dissect the role of Gadd45b in dopamine-dependent epigenetic regulation and cocaine reward. We show that acute cocaine administration induces rapid upregulation of Gadd45b mRNA in the rat nucleus accumbens, and that knockout or site-specific CRISPR/Cas9 gene knockdown of Gadd45b blocks cocaine conditioned place preference. In vitro, dopamine treatment in primary striatal neurons increases Gadd45b mRNA expression through a dopamine receptor type 1 (DRD1)-dependent mechanism. Moreover, shRNA-induced Gadd45b knockdown decreases expression of genes involved in psychostimulant addiction, blocks induction of immediate early genes by DRD1 stimulation, and prevents DRD1-mediated changes in DNA methylation. Finally, we demonstrate that Gadd45b knockdown decreases striatal neuron action potential burst duration in vitro, without altering other electrophysiological characteristics. These results suggest that striatal Gadd45b functions as a dopamine-induced gene that is necessary for cocaine reward memory and DRD1-mediated transcriptional activity.

Critical aspects of neurodevelopment

Organisms have the unique ability to adapt to their environment by making use of external inputs. In the process, the brain is shaped by experiences that go hand-in-hand with optimisation of neural circuits. As such, there exists a time window for the development of different brain regions, each unique for a particular sensory modality, wherein the propensity of forming strong, irreversible connections are high, referred to as a critical period of development. Over the years, this domain of neurodevelopmental research has garnered considerable attention from many scientists, primarily because of the intensive activity-dependent nature of development. This review discusses the cellular, molecular, and neurophysiological bases of critical periods of different sensory modalities, and the disorders associated in cases the regulators of development are dysfunctional. Eventually, the neurobiological bases of the behavioural abnormalities related to developmental pathologies are discussed. A more in-depth insight into the development of the brain during the critical period of plasticity will eventually aid in developing potential therapeutics for several neurodevelopmental disorders that are categorised under critical period disorders.

Genetic variants in the bipolar disorder risk locus SYNE1 that affect CPG2 expression and protein function

Bipolar disorder (BD) is a common mood disorder characterized by recurrent episodes of mania and depression. Both genetic and environmental factors have been implicated in BD etiology, but the biological underpinnings remain elusive. Recently, genome-wide association studies (GWAS) of neuropsychiatric disorders have identified a risk locus for BD containing the SYNE1 gene, a large gene encoding multiple proteins. The BD association signal spans, almost exclusively, the part of SYNE1 encoding CPG2, a brain-specific protein localized to excitatory postsynaptic sites, where it regulates glutamate receptor internalization. Here we show that CPG2 protein levels are significantly decreased in postmortem brain tissue from BD patients, as compared to control subjects, as well as schizophrenia and depression patients. We identify genetic variants within the postmortem brains that map to the CPG2 promoter region, and show that they negatively affect gene expression. We also identify missense single nucleotide polymorphisms (SNPs) in CPG2 coding regions that affect CPG2 expression, localization, and synaptic function. Our findings link genetic variation in the CPG2 region of SYNE1 with a mechanism for glutamatergic synapse dysfunction that could underlie susceptibility to BD in some individuals. Few GWAS hits in human genetics for neuropsychiatric disorders to date have afforded such mechanistic clues. Further, the potential for genetic distinction of susceptibility to BD from other neuropsychiatric disorders with overlapping clinical traits holds promise for improved diagnostics and treatment of this devastating illness.

The Roles of Matrix Metalloproteinases and Their Inhibitors in Human Diseases

Matrix metalloproteinases (MMPs) are a family of zinc-dependent extracellular matrix (ECM) remodeling endopeptidases that have the capacity to degrade almost every component of the ECM. The degradation of the ECM is of great importance, since it is related to embryonic development and angiogenesis. It is also involved in cell repair and the remodeling of tissues. When the expression of MMPs is altered, it can generate the abnormal degradation of the ECM. This is the initial cause of the development of chronic degenerative diseases and vascular complications generated by diabetes. In addition, this process has an association with neurodegeneration and cancer progression. Within the ECM, the tissue inhibitors of MMPs (TIMPs) inhibit the proteolytic activity of MMPs. TIMPs are important regulators of ECM turnover, tissue remodeling, and cellular behavior. Therefore, TIMPs (similar to MMPs) modulate angiogenesis, cell proliferation, and apoptosis. An interruption in the balance between MMPs and TIMPs has been implicated in the pathophysiology and progression of several diseases. This review focuses on the participation of both MMPs (e.g., MMP-2 and MMP-9) and TIMPs (e.g., TIMP-1 and TIMP-3) in physiological processes and on how their abnormal regulation is associated with human diseases. The inclusion of current strategies and mechanisms of MMP inhibition in the development of new therapies targeting MMPs was also considered.

Neuritin-overexpressing transgenic mice demonstrate enhanced neuroregeneration capacity and improved spatial learning and memory recovery after ischemia-reperfusion injury

Acute ischemia-reperfusion (IR)-induced brain injury is further exacerbated by a series of slower secondary pathogenic events, including delayed apoptosis due to neurotrophic factor deficiency. Neuritin, a neurotrophic factor regulating nervous system development and plasticity, is a potential therapeutic target for treatment of IR injury. In this study, Neuritin-overexpressing transgenic (Tg) mice were produced by pronuclear injection and offspring with high overexpression used to generate a line with stable inheritance for testing the neuroprotective capacity of Neuritin against transient global ischemia (TGI). Compared to wild-type mice, transgenic mice demonstrated reduced degradation of the DNA repair factor poly [ADP-ribose] polymerase 1 (PARP 1) in the hippocampus, indicating decreased hippocampal apoptosis rate, and a greater number of surviving hippocampal neurons during the first week post-TGI. In addition, Tg mice showed increased expression of the regeneration markers NF-200, synaptophysin, and GAP-43, and improved recovery of spatial learning and memory. Our findings exhibited that the window of opportunity of neural recovery in Neuritin transgenic mice group had a tendency to move ahead after TGI, which indicated that Neuritin can be used as a potential new therapeutic strategy for improving the outcome of cerebral ischemia injury.

Bidirectional perisomatic inhibitory plasticity of a Fos neuronal network

Behavioral experiences activate the Fos transcription factor (TF) in sparse populations of neurons that are critical for encoding and recalling specific events^1–3. However, there is limited understanding of the mechanisms by which experience drives circuit reorganization to establish a network of Fos-activated cells. It is also unknown if Fos is required in this process beyond serving as a marker of recent neural activity and, if so, which of its many gene targets underlie circuit reorganization. Here we demonstrate that when mice engage in spatial exploration of novel environments, perisomatic inhibition of Fos-expressing hippocampal CA1 pyramidal neurons by parvalbumin (PV)-interneurons (INs) is enhanced, while perisomatic inhibition by cholecystokinin (CCK)-INs is weakened. This bidirectional modulation of inhibition is abolished when the function of the Fos TF complex is disrupted. Single-cell RNA-sequencing, ribosome-associated mRNA profiling, and chromatin analyses, combined with electrophysiology, reveal that Fos activates the transcription of Scg2 (secretogranin II), a gene that encodes multiple distinct neuropeptides, to coordinate these changes in inhibition. As PV- and CCK-INs mediate distinct features of pyramidal cell activity^4–6, the Scg2-dependent reorganization of inhibitory synaptic input might be predicted to affect network function in vivo. Consistent with this prediction, hippocampal gamma rhythms and pyramidal cell coupling to CA1 theta are significantly altered with loss of Scg2. These findings reveal an instructive role for Fos and Scg2 in establishing a network of Fos-activated neurons via the rewiring of local inhibition to form a selectively modulated state. The opposing plasticity mechanisms on distinct inhibitory pathways may support the consolidation of memories over time.

Neuronal activity regulates alternative exon usage

Neuronal activity-regulated gene transcription underlies plasticity-dependent changes in the molecular composition and structure of neurons. A large number of genes regulated by different neuronal plasticity inducing pathways have been identified, but altered gene expression levels represent only part of the complexity of the activity-regulated transcriptional program. Alternative splicing, the differential inclusion and exclusion of exonic sequence in mRNA, is an additional mechanism that is thought to define the activity-dependent transcriptome. Here, we present a genome wide microarray-based survey to identify exons with increased expression levels at 1, 4 or 8 h following neuronal activity in the murine hippocampus provoked by generalized seizures. We used two different bioinformatics approaches to identify alternative activity-induced exon usage and to predict alternative splicing, ANOSVA (ANalysis Of Splicing VAriation) which we here adjusted to accommodate data from different time points and FIRMA (Finding Isoforms using Robust Multichip Analysis). RNA sequencing, in situ hybridization and reverse transcription PCR validate selected activity-dependent splicing events of previously described and so far undescribed activity-regulated transcripts, including Homer1a, Homer1d, Ania3, Errfi1, Inhba, Dclk1, Rcan1, Cda, Tpm1 and Krt75. Taken together, our survey significantly adds to the comprehensive understanding of the complex activity-dependent neuronal transcriptomic signature. In addition, we provide data sets that will serve as rich resources for future comparative expression analyses.

miR‑199a decreases Neuritin expression involved in the development of Alzheimer's disease in APP/PS1 mice

Neuritin plays an important role in neural development and plasticity. A recent study demonstrated that increasing Neuritin levels attenuated synaptic damage in mice with Alzheimer's disease (AD), which exhibit a decreased Neuritin expression. However, it remains unclear as to whether Neuritin expression is regulated by microRNAs (miRNAs or miRs) in AD. In the present study, it was found that miR-199a decreased Neuritin expression and was therefore involved in the development of AD. Subsequently, differentially expressed miRNAs in AD from datasets and the literature were recruited, and those that could bind Neuritin were predicted using bioinformatics analysis. The present study then focused on the candidate miRNAs that were highly associated with Neuritin and were upregulated in AD. The expression patterns of the candidate miRNAs and Neuritin in the hippocampus and cortex of APP/PS1 (AD model) mice at different stages were then detected and analyzed. It was found that miR-199a expression was significantly increased in the early stages of AD and was negatively associated with Neuritin expression. Furthermore, it was revealed that the decreased Neuritin expression was due to the direct targeting of the Neuritin 3′-UTR by miR-199a. Finally, the association between the spatial memory capacity of APP/PS1 mice and the changes in miR-199a and Neuritin expression protein was investigated. On the whole, the data of the present study suggest that miR-199a is involved in the development of AD by regulating Neuritin expression.

Hippocampal stimulation promotes intracellular Tip60 dynamics with concomitant genome reorganization and synaptic gene activation

Genomic reorganizations mediating the engagement of target genes to transcription factories (TFs), characterized as specialized nuclear subcompartments enriched in hyperphosphorylated RNA polymerase II (RNAPII) and transcriptional regulators, act as an important layer of control in coordinating efficient gene transcription. However, their presence in hippocampal neurons and potential role in activity-dependent coregulation of genes within the brain remains unclear. Here, we investigate whether the well-characterized role for the histone acetyltransferase (HAT) Tip60 in mediating epigenetic control of inducible neuroplasticity genes involves TF associated chromatin reorganization in the hippocampus. We show that Tip60 shuttles into the nucleus following extracellular stimulation of rat hippocampal neurons with concomitant enhancement of Tip60 binding and activation of specific synaptic plasticity genes. Multicolor three-dimensional (3D) DNA fluorescent in situ hybridization (DNA-FISH) reveals that hippocampal stimulation mobilizes these same synaptic plasticity genes and Tip60 to RNAPII-rich TFs. Our data support a model by which external hippocampal stimulation promotes intracellular Tip60 HAT dynamics with concomitant TF associated genome reorganization to initiate Tip60mediated synaptic gene activation.

Demystifying the extracellular matrix and its proteolytic remodeling in the brain: structural and functional insights

The extracellular matrix (ECM) plays diverse roles in several physiological and pathological conditions. In the brain, the ECM is unique both in its composition and in functions. Furthermore, almost all the cells in the central nervous system contribute to different aspects of this intricate structure. Brain ECM, enriched with proteoglycans and other small proteins, aggregate into distinct structures around neurons and oligodendrocytes. These special structures have cardinal functions in the normal functioning of the brain, such as learning, memory, and synapse regulation. In this review, we have compiled the current knowledge about the structure and function of important ECM molecules in the brain and their proteolytic remodeling by matrix metalloproteinases and other enzymes, highlighting the special structures they form. In particular, the proteoglycans in brain ECM, which are essential for several vital functions, are emphasized in detail.

Matrix metalloproteinases in the CNS: interferons get nervous

Matrix metalloproteinases (MMPs) have been investigated in context of chronic inflammatory diseases and demonstrated to degrade multiple components of the extracellular matrix (ECM). However, following several disappointing MMP clinical trials, recent studies have demonstrated unexpected novel functions of MMPs in viral infections and autoimmune inflammatory diseases in unanticipated locations. Thus, MMPs play additional functions in inflammation than just ECM degradation. They can regulate the activity of chemokines and cytokines of the immune response by precise proteolytic processing resulting in activation or inactivation of signaling pathways. MMPs have been demonstrated to cleave multiple substrates of the central nervous systems (CNS) and contribute to promoting and dampening diseases of the CNS. Initially, believed to be solely promoting pathologies, more than 10 MMPs to date have been shown to have protective functions. Here, we present some of the beneficial and destructive roles of MMPs in CNS pathologies and discuss strategies for the use of MMP inhibitors.

Cellular stress mechanisms of prenatal maternal stress: Heat shock factors and oxidative stress

Development of the brain prenatally is affected by maternal experience and exposure. Prenatal maternal psychological stress changes brain development and results in increased risk for neuropsychiatric disorders. In this review, multiple levels of prenatal stress mechanisms (offspring brain, placenta, and maternal physiology) are discussed and their intersection with cellular stress mechanisms explicated. Heat shock factors and oxidative stress are closely related to each other and converge with the inflammation, hormones, and cellular development that have been more deeply explored as the basis of prenatal stress risk. Increasing evidence implicates cellular stress mechanisms in neuropsychiatric disorders associated with prenatal stress including affective disorders, schizophrenia, and child-onset psychiatric disorders. Heat shock factors and oxidative stress also have links with the mechanisms involved in other kinds of prenatal stress including external exposures such as environmental toxicants and internal disruptions such as preeclampsia. Integrative understanding of developmental neurobiology with these cellular and physiological mechanisms is necessary to reduce risks and promote healthy brain development.

AMPA receptors and their minions: auxiliary proteins in AMPA receptor trafficking

To correctly transfer information, neuronal networks need to continuously adjust their synaptic strength to extrinsic stimuli. This ability, termed synaptic plasticity, is at the heart of their function and is, thus, tightly regulated. In glutamatergic neurons, synaptic strength is controlled by the number and function of AMPA receptors at the postsynapse, which mediate most of the fast excitatory transmission in the central nervous system. Their trafficking to, at, and from the synapse, is, therefore, a key mechanism underlying synaptic plasticity. Intensive research over the last 20 years has revealed the increasing importance of interacting proteins, which accompany AMPA receptors throughout their lifetime and help to refine the temporal and spatial modulation of their trafficking and function. In this review, we discuss the current knowledge about the roles of key partners in regulating AMPA receptor trafficking and focus especially on the movement between the intracellular, extrasynaptic, and synaptic pools. We examine their involvement not only in basal synaptic function, but also in Hebbian and homeostatic plasticity. Included in our review are well-established AMPA receptor interactants such as GRIP1 and PICK1, the classical auxiliary subunits TARP and CNIH, and the newest additions to AMPA receptor native complexes.

The role of the genome in experience-dependent plasticity: Extending the analogy of the genomic action potential

Our past experiences shape our current and future behavior. These experiences must leave some enduring imprint on our brains, altering neural circuits that mediate behavior and contributing to our individual differences. As a framework for understanding how experiences might produce lasting changes in neural circuits, Clayton [D. F. Clayton, Neurobiol. Learn. Mem. 74, 185-216 (2000)] introduced the concept of the genomic action potential (gAP)-a structured genomic response in the brain to acute experience. Similar to the familiar electrophysiological action potential (eAP), the gAP also provides a means for integrating afferent patterns of activity but on a slower timescale and with longer-lasting effects. We revisit this concept in light of contemporary work on experience-dependent modification of neural circuits. We review the "Immediate Early Gene" (IEG) response, the starting point for understanding the gAP. We discuss evidence for its involvement in the encoding of experience to long-term memory across time and biological levels of organization ranging from individual cells to cell ensembles and whole organisms. We explore distinctions between memory encoding and homeostatic functions and consider the potential for perpetuation of the imprint of experience through epigenetic mechanisms. We describe a specific example of a gAP in humans linked to individual differences in the response to stress. Finally, we identify key objectives and new tools for continuing research in this area.

Environmentally enriched pigs have transcriptional profiles consistent with neuroprotective effects and reduced microglial activity

Environmental enrichment (EE) is widely used to study the effects of external factors on brain development, function and health in rodent models, but very little is known of the effects of EE on the brain in a large animal model such as the pig. Twenty-four young pigs (aged 5 weeks at start of study, 1:1 male: female ratio) were housed in environmentally enriched (EE) pens and provided with additional enrichment stimulation (a bag filled with straw) once daily. Litter, weight and sex matched controls n= (24) were housed in barren (B) conditions. Behaviour was recorded on alternate days from study day 10. After 21 days, RNA-sequencing of the frontal cortex of male piglets culled one hour after the enrichment stimulation, but not those at 4 h after stimulation, showed upregulation of genes involved in neuronal activity and synaptic plasticity in the EE compared to the B condition. This result is mirrored in the behavioural response to the stimulation which showed a peak in activity around the 1 h time-point. By contrast, EE piglets displayed a signature consistent with a relative decrease in microglial activity compared to those in the B condition. These results confirm those from rodents, suggesting that EE may also confer neuronal health benefits in large mammal models, through a potential relative reduction in neuroinflammatory process and increase in neuroprotection driven by an enrichment-induced increase in behavioural activity.

Immediate-Early Promoter-Driven Transgenic Reporter System for Neuroethological Research in a Hemimetabolous Insect

Genes expressed in response to increased neuronal activity are widely used as activity markers in recent behavioral neuroscience. In the present study, we established transgenic reporter system for whole-brain activity mapping in the two-spotted cricket Gryllus bimaculatus, a hemimetabolous insect used in neuroethology and behavioral ecology. In the cricket brain, a homolog of early growth response-1 (Gryllus egr-B) was rapidly induced as an immediate-early gene (IEG) in response to neuronal hyperexcitability. The upstream genomic fragment of Gryllus egr-B contains potential binding sites for transcription factors regulated by various intracellular signaling pathways, as well as core promoter elements conserved across insect/crustacean egr-B homologs. Using the upstream genomic fragment of Gryllus egr-B, we established an IEG promoter-driven transgenic reporter system in the cricket. In the brain of transgenic crickets, the reporter gene (a nuclear-targeted destabilized EYFP) was induced in response to neuronal hyperexcitability. Inducible expression of reporter protein was detected in almost all neurons after neuronal hyperexcitability. Using our novel reporter system, we successfully detected neuronal activation evoked by feeding in the cricket brain. Our IEG promoter-driven activity reporting system allows us to visualize behaviorally relevant neural circuits at cellular resolution in the cricket brain.

Functions and the related signaling pathways of the neurotrophic factor neuritin

Neuritin is a member of the neurotrophic factor family, which is activated by neural activity and neurotrophins, and promotes neurite growth and branching. It has shown to play an important role in neuronal plasticity and regeneration. It is also involved in other biological processes such as angiogenesis, tumorigenesis and immunomodulation. Thus far, however, the primary mechanisms of neuritin, including whether or not it acts through a receptor or which downstream signals might be activated following binding, are not fully understood. Recent evidence suggests that neuritin may be a potential therapeutic target in several neurodegenerative diseases. This review focuses on the recent advances in studies regarding the newly identified functions of neuritin and the signaling pathways related to these functions. We also discuss current hot topics and difficulties in neuritin research.

Neuritin promotes neurite and spine growth in rat cerebellar granule cells via L-type calcium channel-mediated calcium influx

Neuritin is a neurotrophic factor that is activated by neural activity and neurotrophins. Its major function is to promote neurite growth and branching; however, the underlying mechanisms are not fully understood. To address this issue, this study investigated the effects of neuritin on neurite and spine growth and intracellular Ca²⁺ concentration in rat cerebellar granule neurons (CGNs). Incubation of CGNs for 24 h with neuritin increased neurite length and spine density; this effect was mimicked by insulin and abolished by inhibiting insulin receptor (IR) or mitogen‐activated protein kinase kinase/extracellular signal‐regulated kinase (ERK) activity. Calcium imaging and western blot analysis revealed that neuritin enhanced the increase in intracellular Ca²⁺ level induced by high K⁺, and stimulated the cell surface expression of Ca_V1.2 and Ca_V1.3 α subunits of the L‐type calcium channel, which was suppressed by inhibition of IR or mitogen‐activated protein kinase kinase/ERK. Treatment with inhibitors of L‐type calcium channels, calmodulin, and calcineurin (CaN) abrogated the effects of neuritin on neurite length and spine density. A similar result was obtained by silencing nuclear factor of activated T cells c4, which is known to be activated by neuritin in CGNs. These results indicate that IR and ERK signaling as well as the Ca²⁺/CaN/nuclear factor of activated T cells c4 axis mediate the effects of neuritin on neurite and spine growth in CGNs.

Open Practices

Open Science: This manuscript was awarded with the Open Materials Badge.

For more information see: https://cos.io/our-services/open-science-badges/

Cover Image for this issue: doi: 10.1111/jnc.14195.

Identification of rare nonsynonymous variants in SYNE1/CPG2 in bipolar affective disorder

BACKGROUND

Bipolar affective disorder (BPD) is a severe mood disorder with a prevalence of ∼1.5% in the population. The pathogenesis of BPD is poorly understood; however, a strong heritable component has been identified. Previous genome-wide association studies have indicated a region on 6q25, coding for the SYNE1 gene, which increases disease susceptibility. SYNE1 encodes the synaptic nuclear envelope protein-1, nesprin-1. A brain-specific splice variant of SYNE1, CPG2 encoding candidate plasticity gene 2, has been identified. The intronic single-nucleotide polymorphism with the strongest genome-wide significant association in BPD, rs9371601, is present in both SYNE1 and CPG2.

METHODS

We screened 937 BPD samples for genetic variation in SYNE1 exons 14-33, which covers the CPG2 region, using high-resolution melt analysis. In addition, we screened two regions of increased transcriptional activity, one of them proposed to be the CPG2 promoter region.

RESULTS AND CONCLUSION

We identified six nonsynonymous and six synonymous variants. We genotyped three rare nonsynonymous variants, rs374866393, rs148346599 and rs200629713, in a total of 1099 BPD samples and 1056 controls. Burden analysis of these rare variants did not show a significant association with BPD. However, nine patients are compound heterozygotes for variants in SYNE1/CPG2, suggesting that rare coding variants may contribute significantly towards the complex genetic architecture underlying BPD. Imputation analysis in our own whole-genome sequencing sample of 99 BPD individuals identified an additional eight risk variants in the CPG2 region of SYNE1.

Role of neuritin in retinal ganglion cell death in adult mice following optic nerve injury

Neuritin is a small extracellular protein that plays important roles in the process of neural development, synaptic plasticity, and neural cell survival. Here we investigated the function of neuritin in a mouse model of optic nerve injury (ONI). ONI induced upregulation of neuritin mRNA in the retina of WT mice. The retinal structure and the number of retinal ganglion cells (RGCs) were normal in adult neuritin knockout (KO) mice. In vivo retinal imaging and histopathological analyses demonstrated that RGC death and inner retinal degeneration following ONI were more severe in neuritin KO mice. Immunoblot analyses revealed that ONI-induced phosphorylation of Akt and ERK were suppressed in neuritin KO mice. Our findings suggest that neuritin has neuroprotective effects following ONI and may be useful for treatment of posttraumatic complication.

Neuritin Attenuates Neuronal Apoptosis Mediated by Endoplasmic Reticulum Stress In Vitro

Neuritin is an extracellular glycophosphatidylinositol-linked protein that promotes neuronal survival, differentiation, function, and repair, but the exact mechanism of this neuroprotective effect remains unclear. Meanwhile, endoplasmic reticulum stress (ERS) induced apoptosis is attracting increased attention. In this work, we hypothesized that neuritin inhibited ERS to protect cortical neurons. To check this hypothesis, we exposed primary cultured cortical neurons to oxygen and glucose deprivation (OGD) for 45 min followed by reperfusion (R) to activate ERS. We then performed resuscitation for 6, 12, 24, and 48 h. ERS-related factors such as glucose-regulated protein 78 (GRP78), caspase-12 and CHOP were detected by Western blotting and quantitative real-time polymerase chain reaction assay. Apoptosis was assessed by Annexin V binding and propidium iodide staining. Ultrastructural changes of endoplasmic reticulum were observed under a transmission electron microscope. Results showed that GRP78 expression significantly increased at 12, 24, and 48 h and peaked at 24 h. Caspase-12 and CHOP expression significantly increased in a time-dependent manner at 12, 24, and 48 h. GRP78, caspase-12 and CHOP expression as well as apoptosis rate of primary cultured neurons and the ultrastructural changes of endoplasmic reticulum in the OGD/R + neuritin group significantly improved compared with the OGD/R group. In conclusion, the neuroprotection function of neuritin may be involved in ERS pathways.

Neuritin provides neuroprotection against experimental traumatic brain injury in rats

OBJECTIVES

Traumatic brain injury (TBI) is a leading cause of death and disability worldwide. Neuritin is a neurotrophic factor that regulates neural growth and development. However, the role of neuritin in alleviating TBI has not been investigated.

METHODS

In this study, Sprague Dawley rats (n = 144) weighing 300 ± 50 g were categorized into control, sham, TBI and TBI + neuritin groups. The neurological scores and the ultrastructure of cortical neurons, apoptotic cells and caspase-3 were measured by using Garcia scoring system, transmission electron microscopy, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling, Western blot analysis and real-time RT-PCR at various time points post-TBI.

CONCLUSIONS

Our findings indicated that neuritin plays a protective role in TBI by improving neurological scores, repairing injured neurons and protecting the cortical neurons against apoptosis through inhibition of caspase-3 expression. Further investigation of the molecular mechanisms underlying caspase-3 inhibition by neuritin will provide a research avenue for potential TBI therapeutics.

Expression of hNeuritin protein in a baculovirus expression system and the analysis of its activity

Neuritin plays an important role in the development and regeneration of the nervous system, and shows good prospects in the treatment and protection of the nervous system. To characterize neuritin function, we constructed a baculovirus expression system of neuritin, and identified the biological activity of the neuritin protein. The results and showed that the expression product could promote the neurite growth of dorsal root ganglion in chicken embryos. The neuritin open reading frame was amplified and cloned into the plasmid pFastBac™HTA. The pFastBac™HTA-neuritin was confirmed to be correct by PCR and DNA sequencing, and then transformed into Escherichia coli DH10Bac. The high purity recombinant Bacmid-neuritin (shuttle vectors) was obtained from DH10Bac through screening and identification. Recombinant virus, including the neuritin gene (virus-neuritin), was produced by transfection of SF9 cells using the bacmid-neuritin, and then amplified repeatedly to express the neuritin fusion protein. Finally, we identified the fusion protein with SDS-PAGE and western blotting, and optimized the best expression time of the neuritin fusion protein. We also analyzed the activity of the expressed protein by dorsal root ganglion from chicken embryos.

Cellular diversity of the somatosensory cortical map plasticity

Sensory maps are representations of the sensory epithelia in the brain. Despite the intuitive explanatory power behind sensory maps as being neuronal precursors to sensory perception, and sensory cortical plasticity as a neural correlate of perceptual learning, molecular mechanisms that regulate map plasticity are not well understood. Here we perform a meta-analysis of transcriptional and translational changes during altered whisker use to nominate the major molecular correlates of experience-dependent map plasticity in the barrel cortex. We argue that brain plasticity is a systems level response, involving all cell classes, from neuron and glia to non-neuronal cells including endothelia. Using molecular pathway analysis, we further propose a gene regulatory network that could couple activity dependent changes in neurons to adaptive changes in neurovasculature, and finally we show that transcriptional regulations observed in major brain disorders target genes that are modulated by altered sensory experience. Thus, understanding the molecular mechanisms of experience-dependent plasticity of sensory maps might help to unravel the cellular events that shape brain plasticity in health and disease.

Plasticity-Related Gene Expression During Eszopiclone-Induced Sleep

Study Objectives

Experimental evidence suggests that restorative processes depend on synaptic plasticity changes in the brain during sleep. We used the expression of plasticity-related genes to assess synaptic plasticity changes during drug-induced sleep.

Methods

We first characterized sleep induced by eszopiclone in mice during baseline conditions and during the recovery from sleep deprivation. We then compared the expression of 18 genes and two miRNAs critically involved in synaptic plasticity in these mice. Gene expression was assessed in the cerebral cortex and hippocampus by the TaqMan reverse transcription polymerase chain reaction and correlated with sleep parameters.

Results

Eszopiclone reduced the latency to nonrapid eye movement (NREM) sleep and increased NREM sleep amounts. Eszopiclone had no effect on slow wave activity (SWA) during baseline conditions but reduced the SWA increase during recovery sleep (RS) after sleep deprivation. Gene expression analyses revealed three distinct patterns: (1) four genes had higher expression either in the cortex or hippocampus in the group of mice with increased amounts of wakefulness; (2) a large proportion of plasticity-related genes (7 out of 18 genes) had higher expression during RS in the cortex but not in the hippocampus; and (3) six genes and the two miRNAs showed no significant changes across conditions. Even at a relatively high dose (20 mg/kg), eszopiclone did not reduce the expression of plasticity-related genes during RS period in the cortex.

Conclusions

These results indicate that gene expression associated with synaptic plasticity occurs in the cortex in the presence of a hypnotic medication.

Activation of the CREB/c-Fos Pathway during Long-Term Synaptic Plasticity in the Cerebellum Granular Layer

The induction of long-term potentiation and depression (LTP and LTD) is thought to trigger gene expression and protein synthesis, leading to consolidation of synaptic and neuronal changes. However, while LTP and LTD have been proposed to play important roles for sensori-motor learning in the cerebellum granular layer, their association with these mechanisms remained unclear. Here, we have investigated phosphorylation of the cAMP-responsive element binding protein (CREB) and activation of the immediate early gene c-Fos pathway following the induction of synaptic plasticity by theta-burst stimulation (TBS) in acute cerebellar slices. LTP and LTD were localized using voltage-sensitive dye imaging (VSDi). At two time points following TBS (15 min and 120 min), corresponding to the early and late phases of plasticity, slices were fixed and processed to evaluate CREB phosphorylation (P-CREB) and c-FOS protein levels, as well as Creb and c-Fos mRNA expression. High levels of P-CREB and Creb/c-Fos were detected before those of c-FOS, as expected if CREB phosphorylation triggered gene expression followed by protein synthesis. No differences between control slices and slices stimulated with TBS were observed in the presence of an N-methyl-D-aspartate receptor (NMDAR) antagonist. Interestingly, activation of the CREB/c-Fos system showed a relevant degree of colocalization with long-term synaptic plasticity. These results show that NMDAR-dependent plasticity at the cerebellum input stage bears about transcriptional and post-transcriptional processes potentially contributing to cerebellar learning and memory consolidation.

Neuritin Inhibits Notch Signaling through Interacted with Neuralized to Promote the Neurite Growth

Neuritin plays a key role in neural development and regeneration by promoting neurite outgrowth and synapse maturation. However, the mechanism of neuritin in modulating neurite growth has not been elucidated. Here, using yeast two-hybrid we screened and discovered the interaction of neuritin and neuralized (NEURL1), which is an important regulator that can activate Notch signaling through promoting endocytosis of Notch ligand. And then we identified the interaction of neuritin and neuralized by co-immunoprecipitation (IP) assays, and clarified that neuritin and NEURL1 were co-localized on the cell membrane of SH-SY5Y cells. Moreover, neuritin significantly suppressed Notch ligand Jagged1 (JAG1) endocytosis promoted by NEURL1, and then inhibited the activation of Notch receptor Notch intracellular domain (NICD) and decreased the expression of downstream gene hairy and enhancer of split-1 (HES1). Importantly, the effect of neuritin on inhibiting Notch signaling was rescued by NEURL1, which indicated that neuritin is an upstream and negative regulator of NEURL1 to inhibit Notch signaling through interaction with NEURL1. Notably, recombinant neuritin restored the retraction of neurites caused by activation of Notch, and neurite growth stimulated by neuritin was partially blocked by NEURL1. These findings establish neuritin as an upstream and negative regulator of NEURL1 that inhibits Notch signaling to promote neurite growth. This mechanism connects neuritin with Notch signaling, and provides a valuable foundation for further investigation of neuritin's role in neurodevelopment and neural plasticity.

Neuronal activity-regulated alternative mRNA splicing

Activity-regulated gene transcription underlies plasticity-dependent changes in the molecular composition and structure of neurons. Numerous genes whose expression is induced by different neuronal plasticity inducing pathways have been identified, but the alteration of gene expression levels represents only part of the complexity of the activity-regulated transcriptional program. Alternative splicing of precursor mRNA is an additional mechanism that modulates the activity-dependent transcriptional signature. Recently developed splicing sensitive transcriptome wide analyses improve our understanding of the underlying mechanisms and demonstrate to what extend the activity regulated transcriptome is alternatively spliced. So far, only for a small group of differentially spliced mRNAs of synaptic proteins, the functional implications have been studied in detail. These include examples in which differential exon usage can result in the expression of alternative proteins which interfere with or alter the function of preexisting proteins and cause a dominant negative functional block of constitutively expressed variants. Such altered proteins contribute to the structural and functional reorganization of pre- and postsynaptic terminals and to the maintenance and formation of synapses. In addition, activity-induced alternative splicing can affect the untranslated regions (UTRs) and generates mRNAs harboring different cis-regulatory elements. Such differential UTRs can influence mRNA stability, translation, and can change the targeting of mRNAs to subcellular compartments. Here, we summarize different categories of alternative splicing which are thought to contribute to synaptic remodeling, give an overview of activity-regulated alternatively spliced mRNAs of synaptic proteins that impact synaptic functions, and discuss splicing factors and epigenetic modifications as regulatory determinants.

Mapping Gene Expression in Excitatory Neurons during Hippocampal Late-Phase Long-Term Potentiation

The persistence of long-lasting changes in synaptic connectivity that underlie long-term memory require new RNA and protein synthesis. To elucidate the temporal pattern of gene expression that gives rise to long-lasting neuronal plasticity, we analyzed differentially-expressed (DE) RNAs in mouse hippocampal slices following induction of late phase long-term potentiation (L-LTP) specifically within pyramidal excitatory neurons using Translating Ribosome Affinity Purification RNA sequencing (TRAP-seq). We detected time-dependent changes in up- and down-regulated ribosome-associated mRNAs over 2 h following L-LTP induction, with minimal overlap of DE transcripts between time points. TRAP-seq revealed greater numbers of DE transcripts and magnitudes of LTP-induced changes than RNA-seq of all cell types in the hippocampus. Neuron-enriched transcripts had greater changes at the ribosome-loading level than the total RNA level, while RNA-seq identified many non-neuronal DE mRNAs. Our results highlight the importance of considering both time course and cell-type specificity in activity-dependent gene expression during memory formation.

Neuronal activity modifies the chromatin accessibility landscape in the adult brain

Neuronal activity-induced gene expression modulates the function and plasticity of the nervous system. It is unknown whether and to what extent neuronal activity may trigger changes in chromatin accessibility, a major mode of epigenetic regulation of gene expression. Here we compared chromatin accessibility landscapes of adult mouse dentate granule neurons in vivo before and after synchronous neuronal activation using ATAC-seq. We found widespread, genome-wide changes one hour after activation, with enrichment of gained-open sites at active enhancer regions and at binding sites for AP1 complex components, including cFos. Some changes remain stable for at least twenty-four hours. Functional analysis further implicates a critical role of cFos in initiating, but not maintaining, neuronal activity-induced chromatin opening. Our results reveal dynamic changes of chromatin accessibility in the adult mammalian brain and suggest an epigenetic mechanism by which transient neuronal activation leads to dynamic changes in gene expression via modifying chromatin accessibility.