Local protein synthesis and spine morphogenesis: Fragile X syndrome and beyond

Presynaptic perspective: Axonal transport defects in neurodevelopmental disorders

Disruption of synapse assembly and maturation leads to a broad spectrum of neurodevelopmental disorders. Presynaptic proteins are largely synthesized in the soma, where they are packaged into precursor vesicles and transported into distal axons to ensure precise assembly and maintenance of presynapses. Due to their morphological features, neurons face challenges in the delivery of presynaptic cargos to nascent boutons. Thus, targeted axonal transport is vital to build functional synapses. A growing number of mutations in genes encoding the transport machinery have been linked to neurodevelopmental disorders. Emerging lines of evidence have started to uncover presynaptic mechanisms underlying axonal transport defects, thus broadening the view of neurodevelopmental disorders beyond postsynaptic mechanisms. In this review, we discuss presynaptic perspectives of neurodevelopmental disorders by focusing on impaired axonal transport and disturbed assembly and maintenance of presynapses. We also discuss potential strategies for restoring axonal transport as an early therapeutic intervention.

Translational modulator ISRIB alleviates synaptic and behavioral phenotypes in Fragile X syndrome

Fragile X syndrome (FXS) is caused by the loss of fragile X messenger ribonucleoprotein (FMRP), a translational regulator that binds the transcripts of proteins involved in synaptic function and plasticity. Dysregulated protein synthesis is a central effect of FMRP loss, however, direct translational modulation has not been leveraged in the treatment of FXS. Thus, we examined the effect of the translational modulator integrated stress response inhibitor (ISRIB) in treating synaptic and behavioral symptoms of FXS. We show that FMRP loss dysregulates synaptic protein abundance, stabilizing dendritic spines through increased PSD-95 levels while preventing spine maturation through reduced glutamate receptor accumulation, thus leading to the formation of dense, immature dendritic spines, characteristic of FXS patients and Fmr1 knockout (KO) mice. ISRIB rescues these deficits and improves social recognition in Fmr1 KO mice. These findings highlight the therapeutic potential of targeting core translational mechanisms in FXS and neurodevelopmental disorders more broadly.

Striatal insights: a cellular and molecular perspective on repetitive behaviors in pathology

Animals often behave repetitively and predictably. These repetitive behaviors can have a component that is learned and ingrained as habits, which can be evolutionarily advantageous as they reduce cognitive load and the expenditure of attentional resources. Repetitive behaviors can also be conscious and deliberate, and may occur in the absence of habit formation, typically when they are a feature of normal development in children, or neuropsychiatric disorders. They can be considered pathological when they interfere with social relationships and daily activities. For instance, people affected by obsessive-compulsive disorder, autism spectrum disorder, Huntington's disease and Gilles de la Tourette syndrome can display a wide range of symptoms like compulsive, stereotyped and ritualistic behaviors. The striatum nucleus of the basal ganglia is proposed to act as a master regulator of these repetitive behaviors through its circuit connections with sensorimotor, associative, and limbic areas of the cortex. However, the precise mechanisms within the striatum, detailing its compartmental organization, cellular specificity, and the intricacies of its downstream connections, remain an area of active research. In this review, we summarize evidence across multiple scales, including circuit-level, cellular, and molecular dimensions, to elucidate the striatal mechanisms underpinning repetitive behaviors and offer perspectives on the implicated disorders. We consider the close relationship between behavioral output and transcriptional changes, and thereby structural and circuit alterations, including those occurring through epigenetic processes.

Glial-mediated dysregulation of neurodevelopment in Fragile X Syndrome

Astrocytes are highly involved in a multitude of developmental processes that are known to be dysregulated in Fragile X Syndrome. Here, we examine these processes individually and review the roles astrocytes play in contributing to the pathology of this syndrome. As a growing area of interest in the field, new and exciting insight is continually emerging. Understanding these glial-mediated roles is imperative for elucidating the underlying molecular mechanisms at play, not only in Fragile X Syndrome, but also other ASD-related disorders. Understanding these roles will be central to the future development of effective, clinically-relevant treatments of these disorders.

Caveolin-1-Mediated Cholesterol Accumulation Contributes to Exaggerated mGluR-Dependent Long-Term Depression and Impaired Cognition in Fmr1 Knockout Mice

Fragile X syndrome (FXS) is one of the most common inherited mental retardation diseases and is caused by the loss of fragile X mental retardation protein (FMRP) expression. The metabotropic glutamate receptor (mGluR) theory of FXS states that enhanced mGluR-dependent long-term depression (LTD) due to FMRP loss is involved in aberrant synaptic plasticity and autistic-like behaviors, but little is known about the underlying molecular mechanism. Here, we found that only hippocampal mGluR-LTD was exaggerated in adolescent Fmr1 KO mice, while N-methyl-D-aspartate receptor (NMDAR)-LTD was intact in mice of all ages. This development-dependent alteration was related to the differential expression of caveolin-1 (Cav1), which is essential for caveolae formation. Knockdown of Cav1 restored the enhanced mGluR-LTD in Fmr1 KO mice. Moreover, hippocampal Cav1 expression in Fmr1 KO mice induced excessive endocytosis of the α-amino-3-hydroxyl-5-methyl-4-isoxazolepropionate (AMPA) receptor subunit GluA2. This process relied on mGluR1/5 activation rather than NMDAR. Interference with Cav1 expression reversed these changes. Furthermore, massive cholesterol accumulation contributed to redundant caveolae formation, which provided the platform for mGluR-triggered Cav1 coupling to GluA2. Importantly, injection of the cholesterol scavenger methyl-β-cyclodextrin (Mβ-CD) recovered AMPA receptor trafficking and markedly alleviated hyperactivity, hippocampus-dependent fear memory, and spatial memory defects in Fmr1 KO mice. Together, our findings elucidate the important role of Cav1 in mediating mGluR-LTD enhancement and further inducing AMPA receptor endocytosis and suggest that cholesterol depletion by Mβ-CD during caveolae formation may be a novel and safe strategy to treat FXS.

Shared Etiology in Autism Spectrum Disorder and Epilepsy with Functional Disability

Autism spectrum disorders and epilepsies are heterogeneous human disorders that have miscellaneous etiologies and pathophysiology. There is considerable risk of frequent epilepsy in autism that facilitates amplified morbidity and mortality. Several biological pathways appear to be involved in disease progression, including gene transcription regulation, cellular growth, synaptic channel function, and maintenance of synaptic structure. Here, abnormalities in excitatory/inhibitory (E/I) balance ratio are reviewed along with part of an epileptiform activity that may drive both overconnectivity and genetic disorders where autism spectrum disorders and epilepsy frequently co-occur. The most current ideas concerning common etiological and molecular mechanisms for co-occurrence of both autism spectrum disorders and epilepsy are discussed along with the powerful pharmacological therapies that protect the cognition and behavior of patients. Better understanding is necessary to identify a biological mechanism that might lead to possible treatments for these neurological disorders.

Pten heterozygosity restores neuronal morphology in fragile X syndrome mice

Genetic studies of hippocampal granule neuron development have been used to elucidate cellular functions of Pten and Fmr1. While mutations in each gene cause neurodevelopmental disorders such as autism and fragile X syndrome, how Pten and Fmr1 function alone or together during normal development is not known. Moreover, Pten mRNA is bound by the fragile X mental retardation protein (FMRP) RNA binding protein, but how this physical interaction impinges on phosphatase and tensin homolog protein (PTEN) expression is not known. To understand the interaction of PTEN and FMRP, we investigated the dentate gyrus granule neuron development in Pten and Fmr1 knockout (KO) mice. Interestingly, heterozygosity of Pten restored Fmr1 KO cellular phenotypes, including dendritic arborization, and spine density, while PTEN protein expression was significantly increased in Fmr1 KO animals. However, complete deletion of both Pten and Fmr1 resulted in a dramatic increase in dendritic length, spine density, and spine length. In addition, overexpression of PTEN in Fmr1 KO Pten heterozygous background reduced dendritic length, arborization, spine density, and spine length including pS6 levels. Our findings suggest that PTEN levels are negatively regulated by FMRP, and some Fmr1 KO phenotypes are caused by dysregulation of PTEN protein. These observations provide evidence for the genetic interaction of PTEN and FMRP and a possible mechanistic basis for the pathogenesis of Fmr1-related fragile X neurodevelopmental disorders.

Coming full circle: In vivo Veritas, or expanding the neuroscience frontier

The 25-century long history of brain science can be divided into four distinct 'Eras': Era 1 (∼2000 years) started around 500 BC with reductionist studies of human and animal brains using invasive in vivo and ex vivo methods; Era 2 (∼200 years) started in the 17^th century and introduced the first invasive methods to study the function of living tissues; Era 3 started around 1838 and is the ongoing era of cellular neurophysiology; finally, Era 4 (in statu nascendi) is the era of non-invasive, holistic yet mechanistic, studies of the brain. Animal experimentation is becoming increasingly more holistic as multimodal imaging and recording techniques are combined in a single experiment on the brain of awake behaving animal. This newly emerged approach can be called in vigilo (from Latin 'in awake' or 'in vigilant state'), by analogy to the earlier introduced terms in vivo or in vitro. We introduce the Special Issue "In Vigilo Veritas: New Frontiers of Optical Imaging and Electrical Recording in the Brain of Awake Behaving Mice", which features original research articles and reviews that represent some of the finest examples of a truly multimodal studies, where behavioural readouts and tasks are combined in the same longitudinal experiment and on the same mouse with the two-photon imaging, optogenetics and/or electrophysiological recordings. This exciting multi-methodological approach creates a fertile ground for breakthrough discoveries in neurophysiology and neuropsychology of an awake behaving mammalian brain.

Reciprocal regulation of spontaneous synaptic vesicle fusion by Fragile X mental retardation protein and group I metabotropic glutamate receptors

Fragile X mental retardation protein (FMRP) is a neuronal protein mediating multiple functions, with its absence resulting in one of the most common monogenic causes of autism, Fragile X syndrome (FXS). Analyses of FXS pathophysiology have identified a range of aberrations in synaptic signaling pathways and plasticity associated with group I metabotropic glutamate (mGlu) receptors. These studies, however, have mostly focused on the post-synaptic functions of FMRP and mGlu receptor activation, and relatively little is known about their presynaptic effects. Neurotransmitter release is mediated via multiple forms of synaptic vesicle (SV) fusion, each of which contributes to specific neuronal functions. The impacts of mGlu receptor activation and loss of FMRP on these SV fusion events remain unexplored. Here we combined electrophysiological and fluorescence imaging analyses on primary hippocampal cultures prepared from an Fmr1 knockout (KO) rat model. Compared to wild-type (WT) hippocampal neurons, KO neurons displayed an increase in the frequency of spontaneous excitatory post-synaptic currents (sEPSCs), as well as spontaneous SV fusion events. Pharmacological activation of mGlu receptors in WT neurons caused a similar increase in spontaneous SV fusion and sEPSC frequency. Notably, this increase in SV fusion was not observed when spontaneous activity was blocked using the sodium channel antagonist tetrodotoxin. Importantly, the effect of mGlu receptor activation on spontaneous SV fusion was occluded in Fmr1 KO neurons. Together, our results reveal that FMRP represses spontaneous presynaptic SV fusion, whereas mGlu receptor activation increases this event. This reciprocal control appears to be mediated via their regulation of intrinsic neuronal excitability.

Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) in autism research: literature review

BACKGROUND

Autism spectrum disorder (ASD) remains a behaviourally defined condition. Its molecular basis is unknown; however, its prevalence has been increasing significantly. There have been several abnormalities in neurotransmitter systems reported in ASD. In our review, we described studies involving positron emission tomography (PET) and single-photon emission computed tomography (SPECT) that can provide useful and corroborative data.

METHOD

We conducted a literature review by comprehensive database searching on EMBASE, Scopus, PubMed, and PsychINFO looking for articles published since January 2009. Thirty-one studies were carefully selected - 22 PET studies and 9 SPECT studies - and reviewed by 2 independent researchers. References of the articles were also cross-checked.

RESULTS

Results of the studies, which mainly involve small groups of participants, are frequently inconclusive and often controversial due to the nature of ASD and its wide spectrum. Studies are conducted under different conditions and with poor control for confounding factors which creates difficulties in comparing the data.

CONCLUSIONS

There is ongoing need to improve methodology of the studies involving molecular imaging in ASD. Lack of consistent findings causes difficulties in evaluation, diagnosis, and treatment of the condition.

Dissociation of functional and structural plasticity of dendritic spines during NMDAR and mGluR-dependent long-term synaptic depression in wild-type and fragile X model mice

Many neurodevelopmental disorders are characterized by impaired functional synaptic plasticity and abnormal dendritic spine morphology, but little is known about how these are related. Previous work in the Fmr1^-/y mouse model of fragile X (FX) suggests that increased constitutive dendritic protein synthesis yields exaggerated mGluR5-dependent long-term synaptic depression (LTD) in area CA1 of the hippocampus, but an effect on spine structural plasticity remains to be determined. In the current study, we used simultaneous electrophysiology and time-lapse two photon imaging to examine how spines change their structure during LTD induced by activation of mGluRs or NMDA receptors (NMDARs), and how this plasticity is altered in Fmr1^-/y mice. We were surprised to find that mGluR activation causes LTD and AMPA receptor internalization, but no spine shrinkage in either wildtype or Fmr1^-/y mice. In contrast, NMDAR activation caused spine shrinkage as well as LTD in both genotypes. Spine shrinkage was initiated by non-ionotropic (metabotropic) signaling through NMDARs, and in wild-type mice this structural plasticity required activation of mTORC1 and new protein synthesis. In striking contrast, NMDA-induced spine plasticity in Fmr1^-/y mice was no longer dependent on acute activation of mTORC1 or de novo protein synthesis. These findings reveal that the structural consequences of mGluR and metabotropic NMDAR activation differ, and that a brake on spine structural plasticity, normally provided by mTORC1 regulation of protein synthesis, is absent in FX. Increased constitutive protein synthesis in FX appears to modify functional and structural plasticity induced through different glutamate receptors.

FMRP Modulates Activity-Dependent Spine Plasticity by Binding Cofilin1 mRNA and Regulating Localization and Local Translation

Multiple variants of intellectual disability, e.g., the Fragile X Syndrome are associated with alterations in dendritic spine morphology, thereby pointing to dysregulated actin dynamics during development and processes of synaptic plasticity. Surprisingly, although the necessity of spine actin remodeling was demonstrated repeatedly, the importance and precise role of actin regulators is often undervalued. Here, we provide evidence that structural and functional plasticity are severely impaired after NMDAR-dependent LTP in the hippocampus of Fmr1 KO mice. We can link these defects to an aberrant activity-dependent regulation of Cofilin 1 (cof1) as activity-dependent modulations of local cof1 mRNA availability, local cof1 translation as well as total cof1 expression are impaired in the absence of FMRP. Finally, we can rescue activity-dependent structural plasticity in KO neurons by mimicking the regulation of cof1 observed in WT cells, thereby illustrating the potential of actin modulators to provide novel treatment strategies for the Fragile X Syndrome.

Review of Autism Profiles and Response to Sertraline in Fragile X Syndrome-Associated Autism vs. Non-syndromic Autism; Next Steps for Targeted Treatment

Given significant genetic, molecular, and phenotypic overlaps, researchers have begun to investigate whether targeted treatments for Fragile X Syndrome (FXS) could also be beneficial for patients with Autism Spectrum Disorder (ASD). For example, low-dose sertraline, an SSRI, was used in two recent controlled trials in children with FXS and ASD. The first trial recruited 52 children with FXS, 32 of which were also diagnosed with ASD; the second trial recruited 58 children with non-syndromic ASD. One focus of the present study is to compare the response to sertraline between the FXS-associated ASD and non-syndromic ASD groups. Another focus is to compare baseline ASD-related characteristics between the groups and review these differences within the context of recent literature comparing these populations. Our comparison showed more severe ASD profiles in children with non-syndromic ASD vs. FXS-associated ASD. Regarding response to sertraline, the FXS-ASD group displayed significant improvements in language development, while the non-syndromic group did not show any significant improvements. One possible explanation for this differential response is the distinct anxiety profiles that are seen in these two groups. The heightened anxiety phenotype seen in those with FXS-ASD may have led to a greater relief of anxiety symptoms with sertraline compared to those with non-syndromic ASD; this, in turn, could have led to measurably greater developmental gains. Further research is required to solidify this connection between anxiety relief and developmental gains in these populations.

Nitrosative stress inhibits aminoacylation and editing activities of mitochondrial threonyl-tRNA synthetase by S-nitrosation

Structure and/or function of proteins are frequently affected by oxidative/nitrosative stress via posttranslational modifications. Aminoacyl-tRNA synthetases (aaRSs) constitute a class of ubiquitously expressed enzymes that control cellular protein homeostasis. Here, we found the activity of human mitochondrial (mt) threonyl-tRNA synthetase (hmtThrRS) is resistant to oxidative stress (H₂O₂) but profoundly sensitive to nitrosative stress (S-nitrosoglutathione, GSNO). Further study showed four Cys residues in hmtThrRS were modified by S-nitrosation upon GSNO treatment, and one residue was one of synthetic active sites. We analyzed the effect of modification at individual Cys residue on aminoacylation and editing activities of hmtThrRS in vitro and found that both activities were decreased. We further confirmed that S-nitrosation of mtThrRS could be readily detected in vivo in both human cells and various mouse tissues, and we systematically identified dozens of S-nitrosation-modified sites in most aaRSs, thus establishing both mitochondrial and cytoplasmic aaRS species with S-nitrosation ex vivo and in vivo, respectively. Interestingly, a decrease in the S-nitrosation modification level of mtThrRS was observed in a Huntington disease mouse model. Overall, our results establish, for the first time, a comprehensive S-nitrosation-modified aaRS network and a previously unknown mechanism on the basis of the inhibitory effect of S-nitrosation on hmtThrRS.

RNA-Binding Specificity of the Human Fragile X Mental Retardation Protein

Fragile X syndrome is the most common form of inherited intellectual disability and is caused by a deficiency of the fragile X mental retardation protein (FMRP) in neurons. FMRP regulates the translation of numerous mRNAs within dendritic synapses, but how FMRP recognizes these target mRNAs remains unknown. FMRP has KH0, KH1, KH2, and RGG domains, which are thought to bind to specific RNA recognition elements (RREs). Several studies used high-throughput methods to identify various RREs in mRNAs that FMRP may bind to in vivo. However, there is little overlap in the mRNA targets identified by each study, suggesting that the RNA-binding specificity of FMRP is still unknown. To determine the specificity of FMRP for the RREs, we performed quantitative in vitroRNA binding studies with various constructs of human FMRP. Unexpectedly, our studies show that the KH domains do not bind to the previously identified RREs. To further investigate the RNA-binding specificity of FMRP, we developed a new method called Motif Identification by Analysis of Simple sequences (MIDAS) to identify single-stranded RNA sequences bound by KH domains. We find that the FMRP KH0, KH1, and KH2 domains bind weakly to the single-stranded RNA sequences suggesting that they may have evolved to bind more complex RNA structures. Additionally, we find that the RGG motif of human FMRP binds with a high affinity to an RNAG-quadruplex structure that lacks single-stranded loops, double-stranded stems, or junctions.

Understanding intellectual disability and autism spectrum disorders from common mouse models: synapses to behaviour

Normal brain development is highly dependent on the timely coordinated actions of genetic and environmental processes, and an aberration can lead to neurodevelopmental disorders (NDDs). Intellectual disability (ID) and autism spectrum disorders (ASDs) are a group of co-occurring NDDs that affect between 3% and 5% of the world population, thus presenting a great challenge to society. This problem calls for the need to understand the pathobiology of these disorders and to design new therapeutic strategies. One approach towards this has been the development of multiple analogous mouse models. This review discusses studies conducted in the mouse models of five major monogenic causes of ID and ASDs: Fmr1, Syngap1, Mecp2, Shank2/3 and Neuroligins/Neurnexins. These studies reveal that, despite having a diverse molecular origin, the effects of these mutations converge onto similar or related aetiological pathways, consequently giving rise to the typical phenotype of cognitive, social and emotional deficits that are characteristic of ID and ASDs. This convergence, therefore, highlights common pathological nodes that can be targeted for therapy. Other than conventional therapeutic strategies such as non-pharmacological corrective methods and symptomatic alleviation, multiple studies in mouse models have successfully proved the possibility of pharmacological and genetic therapy enabling functional recovery.

Unraveling the Pathways to Neuronal Homeostasis and Disease: Mechanistic Insights into the Role of RNA-Binding Proteins and Associated Factors

The timing, dosage and location of gene expression are fundamental determinants of brain architectural complexity. In neurons, this is, primarily, achieved by specific sets of trans-acting RNA-binding proteins (RBPs) and their associated factors that bind to specific cis elements throughout the RNA sequence to regulate splicing, polyadenylation, stability, transport and localized translation at both axons and dendrites. Not surprisingly, misregulation of RBP expression or disruption of its function due to mutations or sequestration into nuclear or cytoplasmic inclusions have been linked to the pathogenesis of several neuropsychiatric and neurodegenerative disorders such as fragile-X syndrome, autism spectrum disorders, spinal muscular atrophy, amyotrophic lateral sclerosis and frontotemporal dementia. This review discusses the roles of Pumilio, Staufen, IGF2BP, FMRP, Sam68, CPEB, NOVA, ELAVL, SMN, TDP43, FUS, TAF15, and TIA1/TIAR in RNA metabolism by analyzing their specific molecular and cellular function, the neurological symptoms associated with their perturbation, and their axodendritic transport/localization along with their target mRNAs as part of larger macromolecular complexes termed ribonucleoprotein (RNP) granules.

Fragile X syndrome and fragile X-associated tremor ataxia syndrome

Fragile X-associated disorders encompass several conditions, which are caused by expansion mutations in the fragile X mental retardation 1 (FMR1) gene. Fragile X syndrome is the most common inherited etiology of intellectual disability and results from a full mutation or >200 CGG repeats in FMR1. It is associated with developmental delay, autism spectrum disorder, and seizures. Fragile X-associated tremor/ataxia syndrome is a progressive neurodegenerative disease that occurs in premutation carriers of 55-200 CGG repeats in FMR1 and is characterized by kinetic tremor, gait ataxia, parkinsonism, executive dysfunction, and neuropathy. Fragile X-associated primary ovarian insufficiency also occurs in premutation carrier women and manifests with infertility and early menopause. The diseases constituting fragile X-associated disorders differ mechanistically, due to the distinct molecular properties of premutation versus full mutations. Fragile X syndrome occurs when there is a lack of fragile X mental retardation protein (FMRP) due to FMR1 methylation and silencing. In fragile X-associated tremor ataxia syndrome, a toxic gain of function is postulated with the production of excess CGG repeat-containing FMR1 mRNA, abnormal translation of the repeat sequence leading to production of polyglycine, polyalanine, and other polypeptides and to outright deficits in translation leading to reduced FMRP at larger premutation sizes. The changes in underlying brain chemistry due to FMR1 mutations have led to therapeutic studies in these disorders, with some progress being made in fragile X syndrome. This paper also summarizes indications for testing, genetic counseling issues, and what the future holds for these disorders.

Donepezil Reverses Dendritic Spine Morphology Adaptations and Fmr1 Epigenetic Modifications in Hippocampus of Adult Rats After Adolescent Alcohol Exposure

BACKGROUND

Adolescent intermittent ethanol (AIE) exposure produces persistent impairments in cholinergic and epigenetic signaling and alters markers of synapses in the hippocampal formation, effects that are thought to drive hippocampal dysfunction in adult rodents. Donepezil (Aricept), a cholinesterase inhibitor, is used clinically to ameliorate memory-related cognitive deficits. Given that donepezil also prevents morphological impairment in preclinical models of neuropsychiatric disorders, we investigated the ability of donepezil to reverse morphological and epigenetic adaptations in the hippocampus of adult rats exposed to AIE. Because of the known relationship between dendritic spine density and morphology with the fragile X mental retardation 1 (Fmr1) gene, we also assessed Fmr1 expression and its epigenetic regulation in hippocampus after AIE and donepezil pretreatment.

METHODS

Adolescent rats were administered intermittent ethanol for 16 days starting on postnatal day 30. Rats were treated with donepezil (2.5 mg/kg) once a day for 4 days starting 20 days after the completion of AIE exposure. Brains were dissected out after the fourth donepezil dose, and spine analysis was completed in dentate gyrus granule neurons. A separate cohort of rats, treated identically, was used for molecular studies.

RESULTS

AIE exposure significantly reduced dendritic spine density and altered morphological characteristics of subclasses of dendritic spines. AIE exposure also increased mRNA levels and H3-K27 acetylation occupancy of the Fmr1 gene in hippocampus. Treatment of AIE-exposed adult rats with donepezil reversed both the dendritic spine adaptations and epigenetic modifications and expression of Fmr1.

CONCLUSIONS

These findings indicate that AIE produces long-lasting decreases in dendritic spine density and changes in Fmr1 gene expression in the hippocampal formation, suggesting morphological and epigenetic mechanisms underlying previously reported behavioral deficits after AIE. The reversal of these effects by subchronic, post-AIE donepezil treatment indicates that these AIE effects can be reversed by up-regulating cholinergic function.

Proteomic Profiling of Brain and Testis Reveals the Diverse Changes in Ribosomal Proteins in fmr1 Knockout Mice

Fragile X syndrome (FXS), the leading cause of inherited forms of mental retardation and autism, is caused by the transcriptional silencing of fmr1 encoding the fragile X mental retardation protein (FMRP). FMRP is an RNA-binding protein that is a widely expressed, but primarily in the brain and testis, and associated approximately 4% of transcripts. Macro-orchidism is a common symptom associated with FXS both in humans and mice. Thus, we analyze the pooled samples of cerebral cortex, hippocampus and testis from both the fmr1-KO and wild-type mice by a LC-MS/MS proteomic study. Among the identified proteins, most of those showing significant changes in expression were up- or downregulated in the absence of FMRP. Proteins (FMRP, RPS8, RPL23a and ATPIF1, RPL6, GAP43, MTCH2 and MPZ in brain, and FMRP, CAH3, AKR1B7 and C9 in testis) identified by MS/MS were also verified by Western blotting. The Gene Ontology and WikiPathways analysis revealed that the differentially expressed proteins were clustered in the polyribosome and RNA-binding protein categories in both cerebral cortex and hippocampus, but not in testis. Although this study was limited by the little number of samples, our results provide detailed insights into the ribosomal protein profiles of cerebral cortex, hippocampus and testis in the absence of FMRP. Our studies also provide a better understanding of protein profile changes and the underlying dysregulated pathways arising from fmr1 silencing in FXS.

Aberrant Rac1-cofilin signaling mediates defects in dendritic spines, synaptic function, and sensory perception in fragile X syndrome

Fragile X syndrome (FXS) is the most common inherited cause of intellectual disabilities and a leading cause of autism. FXS is caused by a trinucleotide expansion in the gene FMR1 on the X chromosome. The neuroanatomical hallmark of FXS is an overabundance of immature dendritic spines, a factor thought to underlie synaptic dysfunction and impaired cognition. We showed that aberrantly increased activity of the Rho GTPase Rac1 inhibited the actin-depolymerizing factor cofilin, a major determinant of dendritic spine structure, and caused disease-associated spine abnormalities in the somatosensory cortex of FXS model mice. Increased cofilin phosphorylation and actin polymerization coincided with abnormal dendritic spines and impaired synaptic maturation. Viral delivery of a constitutively active cofilin mutant (cofilinS3A) into the somatosensory cortex of Fmr1-deficient mice rescued the immature dendritic spine phenotype and increased spine density. Inhibition of the Rac1 effector PAK1 with a small-molecule inhibitor rescued cofilin signaling in FXS mice, indicating a causal relationship between PAK1 and cofilin signaling. PAK1 inhibition rescued synaptic signaling (specifically the synaptic ratio of NMDA/AMPA in layer V pyramidal neurons) and improved sensory processing in FXS mice. These findings suggest a causal relationship between increased Rac1-cofilin signaling, synaptic defects, and impaired sensory processing in FXS and uncover a previously unappreciated role for impaired Rac1-cofilin signaling in the aberrant spine morphology and spine density associated with FXS.

The MNK-eIF4E Signaling Axis Contributes to Injury-Induced Nociceptive Plasticity and the Development of Chronic Pain

Injury-induced sensitization of nociceptors contributes to pain states and the development of chronic pain. Inhibiting activity-dependent mRNA translation through mechanistic target of rapamycin and mitogen-activated protein kinase (MAPK) pathways blocks the development of nociceptor sensitization. These pathways convergently signal to the eukaryotic translation initiation factor (eIF) 4F complex to regulate the sensitization of nociceptors, but the details of this process are ill defined. Here we investigated the hypothesis that phosphorylation of the 5' cap-binding protein eIF4E by its specific kinase MAPK interacting kinases (MNKs) 1/2 is a key factor in nociceptor sensitization and the development of chronic pain. Phosphorylation of ser209 on eIF4E regulates the translation of a subset of mRNAs. We show that pronociceptive and inflammatory factors, such as nerve growth factor (NGF), interleukin-6 (IL-6), and carrageenan, produce decreased mechanical and thermal hypersensitivity, decreased affective pain behaviors, and strongly reduced hyperalgesic priming in mice lacking eIF4E phosphorylation (eIF4E^S209A ). Tests were done in both sexes, and no sex differences were found. Moreover, in patch-clamp electrophysiology and Ca²⁺ imaging experiments on dorsal root ganglion neurons, NGF- and IL-6-induced increases in excitability were attenuated in neurons from eIF4E^S209A mice. These effects were recapitulated in Mnk1/2^-/- mice and with the MNK1/2 inhibitor cercosporamide. We also find that cold hypersensitivity induced by peripheral nerve injury is reduced in eIF4E^S209A and Mnk1/2^-/- mice and following cercosporamide treatment. Our findings demonstrate that the MNK1/2-eIF4E signaling axis is an important contributing factor to mechanisms of nociceptor plasticity and the development of chronic pain.SIGNIFICANCE STATEMENT Chronic pain is a debilitating disease affecting approximately one in three Americans. Chronic pain is thought to be driven by changes in the excitability of peripheral nociceptive neurons, but the precise mechanisms controlling these changes are not elucidated. Emerging evidence demonstrates that mRNA translation regulation pathways are key factors in changes in nociceptor excitability. Our work demonstrates that a single phosphorylation site on the 5' cap-binding protein eIF4E is a critical mechanism for changes in nociceptor excitability that drive the development of chronic pain. We reveal a new mechanistic target for the development of a chronic pain state and propose that targeting the upstream kinase, MAPK interacting kinase 1/2, could be used as a therapeutic approach for chronic pain.

Autism spectrum disorder-associated genes and the development of dentate granule cells

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by severe clinical symptoms such as the deficiency of the social communication, repetitive and stereotyped behaviors, and restricted interests. Although complex genetic and environmental factors are thought to contribute to the development of ASD, the precise etiologies are largely unknown. Neuroanatomical observations have been made of developmental abnormalities in different brain regions, including dentate gyrus of hippocampus, which is widely accepted as the center for learning and memory. However, little is known about what roles ASD-associated genes play in the development of hippocampal dentate granule cells. In this article, we summarized functions and pathophysiological significance of 6 representative ASD-associated genes, SEMA5A, PTEN, NLGN, EN-2, FMR1, and MECP2, by focusing on the development of dentate gyrus. We then introduced a recently developed gene transfer method directed to neonatal dentate granule cells. This new method will be useful for elucidating physiological as well as pathophysiological significance of ASD-associated genes in the development of hippocampal formation.

Interference of the complex between NCS-1 and Ric8a with phenothiazines regulates synaptic function and is an approach for fragile X syndrome

The protein complex formed by the Ca2+ sensor neuronal calcium sensor 1 (NCS-1) and the guanine exchange factor protein Ric8a coregulates synapse number and probability of neurotransmitter release, emerging as a potential therapeutic target for diseases affecting synapses, such as fragile X syndrome (FXS), the most common heritable autism disorder. Using crystallographic data and the virtual screening of a chemical library, we identified a set of heterocyclic small molecules as potential inhibitors of the NCS-1/Ric8a interaction. The aminophenothiazine FD44 interferes with NCS-1/Ric8a binding, and it restores normal synapse number and associative learning in a Drosophila FXS model. The synaptic effects elicited by FD44 feeding are consistent with the genetic manipulation of NCS-1. The crystal structure of NCS-1 bound to FD44 and the structure-function studies performed with structurally close analogs explain the FD44 specificity and the mechanism of inhibition, in which the small molecule stabilizes a mobile C-terminal helix inside a hydrophobic crevice of NCS-1 to impede Ric8a interaction. Our study shows the drugability of the NCS-1/Ric8a interface and uncovers a suitable region in NCS-1 for development of additional drugs of potential use on FXS and related synaptic disorders.

Modeling Fragile X syndrome in neurogenesis: An unexpected phenotype and a novel tool for future therapies

FMRP is an RNA-binding protein involved in synaptic translation. Its absence causes a form of intellectual disability, the Fragile X syndrome (FXS). Small neuroanatomical abnormalities, present both in human and mouse FMRP-deficient brains, suggest a subtle critical role of this protein in neurogenesis. Stable depletion of FMRP has been obtained in a mouse embryonic stem cell line Fmr1 (shFmr1 ES) that does not display morphological alterations, but an abnormal expression of a subset of genes mainly involved in neuronal differentiation and maturation. Inducing the differentiation of shFmr1 ES cells into the neuronal lineage results in an accelerated generation of neural progenitors and neurons during the first steps of neurogenesis. This transient phenotype is due to an elevated level of the Amyloid Precursor Protein (APP), whose mRNA is a target of FMRP. APP is processed by the BACE-1 enzyme, producing the β-amyloid (Aβ) peptide accelerating neurogenesis by activating the expression of Ascll. Inhibition of the BACE-1 enzyme rescues the phenotype of shFmr1 ES cells. Here we discuss the importance of the shFmr1 ES line not only to understand the physiopathology of FXS but also as a tool to screen biomolecules for new FXS therapies.

Depletion of the Fragile X Mental Retardation Protein in Embryonic Stem Cells Alters the Kinetics of Neurogenesis

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability and a leading cause of autism. FXS is due to the silencing of the Fragile X Mental Retardation Protein (FMRP), an RNA binding protein mainly involved in translational control, dendritic spine morphology and synaptic plasticity. Despite extensive studies, there is currently no cure for FXS. With the purpose to decipher the initial molecular events leading to this pathology, we developed a stem-cell-based disease model by knocking-down the expression of Fmr1 in mouse embryonic stem cells (ESCs). Repressing FMRP in ESCs increased the expression of amyloid precursor protein (APP) and Ascl1. When inducing neuronal differentiation, βIII-tubulin, p27^kip1 , NeuN, and NeuroD1 were upregulated, leading to an accelerated neuronal differentiation that was partially compensated at later stages. Interestingly, we observed that neurogenesis is also accelerated in the embryonic brain of Fmr1-knockout mice, indicating that our cellular model recapitulates the molecular alterations present in vivo. Importantly, we rescued the main phenotype of the Fmr1 knockdown cell line, not only by reintroducing FMRP but also by pharmacologically targeting APP processing, showing the role of this protein in the pathophysiology of FXS during the earliest steps of neurogenesis. Our work allows to define an early therapeutic window but also to identify more effective molecules for treating this disorder. Stem Cells 2017;35:374-385.

Fragile X syndrome: Are signaling lipids the missing culprits?

Fragile X syndrome (FXS) is the most common cause of inherited intellectual disability and autism. FXS results from the absence of FMRP, an RNA binding protein associated to ribosomes that influences the translation of specific mRNAs in post-synaptic compartments of neurons. The main molecular consequence of the absence of FMRP is an excessive translation of neuronal protein in several areas of the brain. This local protein synthesis deregulation is proposed to underlie the defect in synaptic plasticity responsible for FXS. Recent findings in neurons of the fragile X mouse model (Fmr1-KO) uncovered another consequence of the lack of FMRP: a deregulation of the diacylglycerol (DAG)/phosphatidic acid (PA) homeostasis. DAG and PA are two interconvertible lipids that influence membrane architecture and that act as essential signaling molecules that activate various downstream effectors, including master regulators of local protein synthesis and actin polymerization. As a consequence, DAG and PA govern a variety of cellular processes, including cell proliferation, vesicle/membrane trafficking and cytoskeletal organization. At the synapse, the level of these lipids is proposed to influence the synaptic activation status. FMRP appears as a master regulator of this neuronal process by controlling the translation of a diacylglycerol kinase enzyme that converts DAG into PA. The deregulated levels of DAG and PA caused by the absence of FMRP could represent a novel therapeutic target for the treatment of FXS.

Rescue of Synaptic Phenotypes and Spatial Memory in Young Fragile X Mice

Fragile X syndrome (FXS) is characterized by synaptic immaturity, cognitive impairment, and behavioral changes. The disorder is caused by transcriptional shutdown in neurons of thefragile X mental retardation 1gene product, fragile X mental retardation protein. Fragile X mental retardation protein is a repressor of dendritic mRNA translation and its silencing leads to dysregulation of synaptically driven protein synthesis and impairments of intellect, cognition, and behavior, and FXS is a disorder that currently has no effective therapeutics. Here, young fragile X mice were treated with chronic bryostatin-1, a relatively selective protein kinase Cεactivator, which induces synaptogenesis and synaptic maturation/repair. Chronic treatment with bryostatin-1 rescues young fragile X mice from the disorder phenotypes, including normalization of most FXS abnormalities in 1) hippocampal brain-derived neurotrophic factor expression, 2) postsynaptic density-95 levels, 3) transformation of immature dendritic spines to mature synapses, 4) densities of the presynaptic and postsynaptic membranes, and 5) spatial learning and memory. The therapeutic effects were achieved without downregulation of metabotropic glutamate receptor (mGluR) 5 in the hippocampus and are more dramatic than those of a late-onset treatment in adult fragile X mice. mGluR5 expression was in fact lower in fragile X mice and its expression was restored with the bryostatin-1 treatment. Our results show that synaptic and cognitive function of young FXS mice can be normalized through pharmacological treatment without downregulation of mGluR5 and that bryostatin-1-like agents may represent a novel class of drugs to treat fragile X mental retardation at a young age and in adults.

Autism and the synapse: emerging mechanisms and mechanism-based therapies

PURPOSE OF REVIEW

Recent studies have implicated hundreds of genetic variants in the cause of autism spectrum disorder (ASD). Genes involved in 'monogenic' forms of syndromic ASD converge on common pathways that are involved in synaptic development, plasticity and signaling. In this review, we discuss how these 'developmental synaptopathies' inform our understanding of the molecular disease in ASD and highlight promising approaches that have bridged the gap between the bench and the clinic.

RECENT FINDINGS

Accumulating evidence suggests that synaptic deficits in syndromic and nonsyndromic ASD can be mapped to gene mutations in pathways that control synaptic protein synthesis and degradation, postsynaptic scaffold architecture and neurotransmitter receptors. This is recapitulated in models of Fragile X syndrome (FXS), Tuberous Sclerosis Complex (TSC), Angelman syndrome and Phelan-McDermid syndrome (PMS), all of which cause syndromic ASD. Important recent advances include the development of mouse models and patient-derived induced pluripotent stem cell (iPSC) lines that enable a detailed investigation of synaptic deficits and the identification of potential targets for therapy. Examples of the latter include mGluR5 antagonists in FXS, mTOR inhibitors in TSC and insulin-like growth factor 1 (IGF-1) in PMS.

SUMMARY

Identifying converging pathways in syndromic forms of ASD will uncover novel therapeutic targets for non-syndromic ASD. Insights into developmental synaptopathies will lead to rational development of mechanism-based therapies and clinical trials that may provide a blueprint for other common pathways implicated in the molecular neuropathology of ASD.

Increased CYFIP1 dosage alters cellular and dendritic morphology and dysregulates mTOR

Rare maternally inherited duplications at 15q11-13 are observed in ~1% of individuals with an autism spectrum disorder (ASD), making it among the most common causes of ASD. 15q11-13 comprises a complex region, and as this copy number variation encompasses many genes, it is important to explore individual genotype-phenotype relationships. Cytoplasmic FMR1-interacting protein 1 (CYFIP1) is of particular interest because of its interaction with Fragile X mental retardation protein (FMRP), its upregulation in transformed lymphoblastoid cell lines from patients with duplications at 15q11-13 and ASD and the presence of smaller overlapping deletions of CYFIP1 in patients with schizophrenia and intellectual disability. Here, we confirm that CYFIP1 is upregulated in transformed lymphoblastoid cell lines and demonstrate its upregulation in the post-mortem brain from 15q11-13 duplication patients for the first time. To investigate how increased CYFIP1 dosage might predispose to neurodevelopmental disease, we studied the consequence of its overexpression in multiple systems. We show that overexpression of CYFIP1 results in morphological abnormalities including cellular hypertrophy in SY5Y cells and differentiated mouse neuronal progenitors. We validate these results in vivo by generating a BAC transgenic mouse, which overexpresses Cyfip1 under the endogenous promotor, observing an increase in the proportion of mature dendritic spines and dendritic spine density. Gene expression profiling on embryonic day 15 suggested the dysregulation of mammalian target of rapamycin (mTOR) signaling, which was confirmed at the protein level. Importantly, similar evidence of mTOR-related dysregulation was seen in brains from 15q11-13 duplication patients with ASD. Finally, treatment of differentiated mouse neuronal progenitors with an mTOR inhibitor (rapamycin) rescued the morphological abnormalities resulting from CYFIP1 overexpression. Together, these data show that CYFIP1 overexpression results in specific cellular phenotypes and implicate modulation by mTOR signaling, further emphasizing its role as a potential convergent pathway in some forms of ASD.

Annual research review: Rare genotypes and childhood psychopathology--uncovering diverse developmental mechanisms of ADHD risk

BACKGROUND

Through the increased availability and sophistication of genetic testing, it is now possible to identify causal diagnoses in a growing proportion of children with neurodevelopmental disorders. In addition to developmental delay and intellectual disability, many genetic disorders are associated with high risks of psychopathology, which curtail the wellbeing of affected individuals and their families. Beyond the identification of significant clinical needs, understanding the diverse pathways from rare genetic mutations to cognitive dysfunction and emotional-behavioural disturbance has theoretical and practical utility.

METHODS

We overview (based on a strategic search of the literature) the state-of-the-art on causal mechanisms leading to one of the most common childhood behavioural diagnoses - attention deficit hyperactivity disorder (ADHD) - in the context of specific genetic disorders. We focus on new insights emerging from the mapping of causal pathways from identified genetic differences to neuronal biology, brain abnormalities, cognitive processing differences and ultimately behavioural symptoms of ADHD.

FINDINGS

First, ADHD research in the context of rare genotypes highlights the complexity of multilevel mechanisms contributing to psychopathology risk. Second, comparisons between genetic disorders associated with similar psychopathology risks can elucidate convergent or distinct mechanisms at each level of analysis, which may inform therapeutic interventions and prognosis. Third, genetic disorders provide an unparalleled opportunity to observe dynamic developmental interactions between neurocognitive risk and behavioural symptoms. Fourth, variation in expression of psychopathology risk within each genetic disorder points to putative moderating and protective factors within the genome and the environment.

CONCLUSION

A common imperative emerging within psychopathology research is the need to investigate mechanistically how developmental trajectories converge or diverge between and within genotype-defined groups. Crucially, as genetic predispositions modify interaction dynamics from the outset, longitudinal research is required to understand the multi-level developmental processes that mediate symptom evolution.

Fragile X mental retardation protein: A paradigm for translational control by RNA-binding proteins

Translational control is a common mechanism used to regulate gene expression and occur in bacteria to mammals. Typically in translational control, an RNA-binding protein binds to a unique sequence in the mRNA to regulate protein synthesis by the ribosomes. Alternatively, a protein may bind to or modify a translation factor to globally regulate protein synthesis by the cell. Here, we review translational control by the fragile X mental retardation protein (FMRP), the absence of which causes the neurological disease, fragile X syndrome (FXS).

Serotonin dysregulation in Fragile X Syndrome: implications for treatment

Fragile X Syndrome (FXS) is a trinucleotide repeat disorder that results in the silencing of the Fragile X Mental Retardation 1 gene (FMR1), leading to a lack of the FMR1 protein (FMRP). FMRP is an mRNA-binding protein that regulates the translation of hundreds of mRNAs important for synaptic plasticity. Several of these pathways have been identified and have guided the development of targeted treatments for FXS. Here we present evidence that serotonin is dysregulated in FXS and treatment with the selective serotonin reuptake inhibitor (SSRI) sertraline may be beneficial for individuals with FXS, particularly in early childhood.

Divergence of RNA localization between rat and mouse neurons reveals the potential for rapid brain evolution

Background

Neurons display a highly polarized architecture. Their ability to modify their features under intracellular and extracellular stimuli, known as synaptic plasticity, is a key component of the neurochemical basis of learning and memory. A key feature of synaptic plasticity involves the delivery of mRNAs to distinct sub-cellular domains where they are locally translated. Regulatory coordination of these spatio-temporal events is critical for synaptogenesis and synaptic plasticity as defects in these processes can lead to neurological diseases. In this work, using microdissected dendrites from primary cultures of hippocampal neurons of two mouse strains (C57BL/6 and Balb/c) and one rat strain (Sprague–Dawley), we investigate via microarrays, subcellular localization of mRNAs in dendrites of neurons to assay the evolutionary differences in subcellular dendritic transcripts localization.

Results

Our microarray analysis highlighted significantly greater evolutionary diversification of RNA localization in the dendritic transcriptomes (81% gene identity difference among the top 5% highly expressed genes) compared to the transcriptomes of 11 different central nervous system (CNS) and non-CNS tissues (average of 44% gene identity difference among the top 5% highly expressed genes). Differentially localized genes include many genes involved in CNS function.

Conclusions

Species differences in sub-cellular localization may reflect non-functional neutral drift. However, the functional categories of mRNA showing differential localization suggest that at least part of the divergence may reflect activity-dependent functional differences of neurons, mediated by species-specific RNA subcellular localization mechanisms.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-883) contains supplementary material, which is available to authorized users.

Nervous translation, do you get the message? A review of mRNPs, mRNA-protein interactions and translational control within cells of the nervous system

In neurons, translation of a message RNA can occur metres away from its transcriptional origin and in normal cells this is orchestrated with perfection. The life of an mRNA will see it pass through multiple steps of processing in the nucleus and the cytoplasm before it reaches its final destination. Processing of mRNA is determined by a myriad of RNA-binding proteins in multi-protein complexes called messenger ribonucleoproteins; however, incorrect processing and delivery of mRNA can cause several human neurological disorders. This review takes us through the life of mRNA from the nucleus to its point of translation in the cytoplasm. The review looks at the various cis and trans factors that act on the mRNA and discusses their roles in different cells of the nervous system and human disorders.

Mechanism-based treatments in neurodevelopmental disorders: fragile X syndrome

BACKGROUND

Fragile X syndrome (FXS) is the most common identifiable genetic cause of intellectual disability and autistic spectrum disorders. Recent major advances have been made in the understanding of the neurobiology and functions of fragile X mental retardation protein, the FMR1 gene product, which is absent or reduced in FXS, largely based on work in the fmr1 knockout mouse model. FXS has emerged as a disorder of synaptic plasticity associated with abnormalities of long-term depression and long-term potentiation and immature dendritic spine architecture, related to dysregulation of dendritic translation typically activated by group I mGluR and other receptors. This work has led to efforts to develop treatments for FXS with neuroactive molecules targeted to pathways dysregulated in the absence of fragile X mental retardation protein.

CONCLUSION

These agents have been shown to rescue molecular, spine, and behavioral phenotypes in the FXS mouse model, and clinical trials are underway to translate findings in animal models of FXS to humans, raising complex issues about trial design and outcome measures to assess disease-modifying changes that might be associated with treatment. Genes known to be causes of autistic spectrum disorders interact with the translational pathway defective in FXS and it is likely that there will be substantial overlap in molecular pathways and mechanisms of synaptic dysfunction. Thus targeted treatment and clinical trial strategies in FXS may serve as a model for ASD and other cognitive disorders.

From FMRP function to potential therapies for fragile X syndrome

Fragile X syndrome (FXS) is caused by mutations in the fragile X mental retardation 1 (FMR1) gene. Most FXS cases occur due to the expansion of the CGG trinucleotide repeats in the 5' un-translated region of FMR1, which leads to hypermethylation and in turn silences the expression of FMRP (fragile X mental retardation protein). Numerous studies have demonstrated that FMRP interacts with both coding and non-coding RNAs and represses protein synthesis at dendritic and synaptic locations. In the absence of FMRP, the basal protein translation is enhanced and not responsive to neuronal stimulation. The altered protein translation may contribute to functional abnormalities in certain aspects of synaptic plasticity and intracellular signaling triggered by Gq-coupled receptors. This review focuses on the current understanding of FMRP function and potential therapeutic strategies that are mainly based on the manipulation of FMRP targets and knowledge gained from FXS pathophysiology.

Dizocilpine reduces head diameter of dendritic spines in the hippocampus of adolescent rats

Cognitive deficits are the core symptoms of schizophrenia. Spine deficits have been found in hippocampus of schizophrenia patients, and were associated with cognitive impairments. N-methyl-D-asparate receptors (NMDARs) had been known to play a critical role in synaptic pruning and stabilization during adolescence. In the present study, male adolescent rats were exposed to dizocilpine (MK-801) (0.2mg/kg i.p qd) or 0.9% saline for 14 days. Then spatial memory, spine morphological changes and RhoA, Rac1, Cdc42 mRNA levels in hippocampus were measured. As a result, MK-801 impaired spatial memory in the adolescent rats, as well as reduced the proportion of mushroom spines and increased the proportion of stubby spines in hippocampus. MK-801 also reduced the expression levels of Rac1 and Cdc42 mRNA and upregulated RhoA mRNA in hippocampus. These results imply that subchronic MK-801 administration during adolescence might disturb the expression of RhoA, Rac1 and Cdc42 mRNA, and then lead to the decay of the spines in hippocampus, which could be involved in cognitive impairments in schizophrenia.

Outcome measures for clinical trials in fragile X syndrome

OBJECTIVE

Progress in basic neuroscience has led to identification of molecular targets for treatment in fragile X syndrome (FXS) and other neurodevelopmental disorders; however, there is a gap in translation to targeted therapies in humans. One major obstacle to the demonstration of efficacy in human trials has been the lack of generally accepted endpoints to assess improvement in function in individuals with FXS. To address this problem, the National Institutes of Health convened a meeting of leading scientists and clinicians with the goal of identifying and standardizing outcome measures for use as potential endpoints in clinical trials in FXS.

METHODS

Participants in the meeting included FXS experts, experts in the design and implementation of clinical trials and measure development, and representatives from advocacy groups, industry, and federal agencies.

RESULTS

The group generated recommendations for optimal outcome measures in cognitive, behavioral, and biomarker/medical domains, including additional testing and validation of existing measures and development of new measures in areas of need. Although no one endpoint or set of endpoints could be identified that met all criteria as an optimal measure, recommendations are presented in this report.

CONCLUSION

The report is expected to guide the selection of measures in clinical trials and lead to the use of a more consistent battery of measures across trials. Furthermore, this will help to direct research toward gaps in the development of validated FXS-specific outcome measures and to assist with interpretation of clinical trial data by creating templates for measurement of treatment efficacy.

Glia co-culture with neurons in microfluidic platforms promotes the formation and stabilization of synaptic contacts

Two novel microfluidic cell culture schemes, a vertically-layered set-up and a four chamber set-up, were developed for co-culturing central nervous system (CNS) neurons and glia. The cell chambers in these devices were separated by pressure-enabled valve barriers, which permitted us to control communication between the two cell types. The unique design of these devices facilitated the co-culture of glia with neurons in close proximity (∼50-100 μm), differential transfection of neuronal populations, and dynamic visualization of neuronal interactions, such as the development of synapses. With these co-culture devices, initial synaptic contact between neurons transfected with different fluorescent markers, such as green fluorescent protein (GFP) and mCherry-synaptophysin, was imaged using high-resolution fluorescence microscopy. The presence of glial cells had a profound influence on synapses by increasing the number and stability of synaptic contacts. Interestingly, as determined by liquid chromatography-ion mobility-mass spectrometry, neuron-glia co-cultures produced elevated levels of soluble factors compared to that secreted by individual neuron or glia cultures, suggesting a potential mechanism by which neuron-glia interactions could modulate synaptic function. Collectively, these results show that communication between neurons and glia is critical for the formation and stability of synapses and point to the importance of developing neuron-glia co-culture systems such as the microfluidic platforms described in this study.

Progress toward therapeutic potential for AFQ056 in Fragile X syndrome

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability and the leading single-gene cause of autism. It is caused by the lack of production of the Fragile X mental retardation protein (FMRP), resulting in cognitive deficits, hyperactivity, and autistic behaviors. Breakthrough advances in potential therapy for FXS followed the discovery that aberrant group 1 metabotropic glutamate receptor (mGluR) signaling is an important constituent of the pathophysiology of the syndrome. Research has indicated that upon neuronal stimulation, FMRP acts downstream of group 1 mGluRs (mGluRs1/5) to inhibit protein synthesis, long-term depression, and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor internalization. To offset the deficits caused by the lack of FMRP, many pharmaceutical companies have designed medicinal drugs to target the unrestrained stimulation of mGluR5 signaling in FXS. Indeed, promising results from animal and clinical studies suggest that mGluR5 antagonists such as AFQ056 can successfully correct many of the deficits in FXS. In this review, we cover the animal studies performed to date that test the role of AFQ056 as a selective mGluR5 antagonist to alleviate the phenotypes of FXS.

Autism as early neurodevelopmental disorder: evidence for an sAPPα-mediated anabolic pathway

Autism is a neurodevelopmental disorder marked by social skills and communication deficits and interfering repetitive behavior. Intellectual disability often accompanies autism. In addition to behavioral deficits, autism is characterized by neuropathology and brain overgrowth. Increased intracranial volume often accompanies this brain growth. We have found that the Alzheimer's disease (AD) associated amyloid-β precursor protein (APP), especially its neuroprotective processing product, secreted APP α, is elevated in persons with autism. This has led to the "anabolic hypothesis" of autism etiology, in which neuronal overgrowth in the brain results in interneuronal misconnections that may underlie multiple autism symptoms. We review the contribution of research in brain volume and of APP to the anabolic hypothesis, and relate APP to other proteins and pathways that have already been directly associated with autism, such as fragile X mental retardation protein, Ras small GTPase/extracellular signal-regulated kinase, and phosphoinositide 3 kinase/protein kinase B/mammalian target of rapamycin. We also present additional evidence of magnetic resonance imaging intracranial measurements in favor of the anabolic hypothesis. Finally, since it appears that APP's involvement in autism is part of a multi-partner network, we extend this concept into the inherently interactive realm of epigenetics. We speculate that the underlying molecular abnormalities that influence APP's contribution to autism are epigenetic markers overlaid onto potentially vulnerable gene sequences due to environmental influence.

Long-lasting effects of minocycline on behavior in young but not adult Fragile X mice

Fragile X Syndrome (FXS) is the most common single-gene inherited form of intellectual disability with behaviors characteristic of autism. People with FXS display childhood seizures, hyperactivity, anxiety, developmental delay, attention deficits, and visual-spatial memory impairment, as well as a propensity for obsessive-compulsive disorder. Several of these aberrant behaviors and FXS-associated synaptic irregularities also occur in "fragile X mental retardation gene" knock-out (Fmr1 KO) mice. We previously reported that minocycline promotes the maturation of dendritic spines - postsynaptic sites for excitatory synapses - in the developing hippocampus of Fmr1 KO mice, which may underlie the beneficial effects of minocycline on anxiolytic behavior in young Fmr1 KO mice. In this study, we compared the effectiveness of minocycline treatment in young and adult Fmr1 KO mice, and determined the dependence of behavioral improvements on short-term versus long-term minocycline administration. We found that 4- and 8-week-long treatments significantly reduced locomotor activity in both young and adult Fmr1 KO mice. Some behavioral improvements persisted in young mice post-treatment, but in adults the beneficial effects were lost soon after minocycline treatment was stopped. We also show, for the first time, that minocycline treatment partially attenuates the number and severity of audiogenic seizures in Fmr1 KO mice. This report provides further evidence that minocycline treatment has immediate and long-lasting benefits on FXS-associated behaviors in the Fmr1 KO mouse model.

Remodeling of axo-spinous synapses in the pathophysiology and treatment of depression

Dendritic spines provide a compartment for assembly and functional organization of synaptic machinery that plays a fundamental role in neuronal communication and neuroplasticity. Studies in humans as well as in animal models have demonstrated abnormal spine architecture in several psychiatric disorders, including depression and other stress-related illnesses. The negative impact of stress on the density and organization of spines is thought to contribute to the behavioral deficits caused by stress exposure. Moreover, there is now evidence that medication-induced recovery involves changes in synaptic plasticity and dendrite morphology, including increased expression of pre- and postsynaptic plasticity-related proteins, as well as the density and function of axo-spinous synapses. Here we review the evidence from brain imaging and postmortem studies demonstrating that depression is accompanied by structural and functional alterations of cortical and limbic brain regions, including the prefrontal cortex, hippocampus and amygdala. In addition, we present more direct evidence from basic research studies that exposure to stress alters spine morphology, function and plasticity and that antidepressants, particularly new rapid acting agents, reverse these effects. Elucidation of the signaling pathways and molecular mechanisms that control spine synapse assembly and plasticity will contribute to a better understanding of the pathophysiology of depression and development of novel, more effective therapeutic agents.

Fragmentation and unpredictability of early-life experience in mental disorders

Maternal sensory signals in early life play a crucial role in programming the structure and function of the developing brain, promoting vulnerability or resilience to emotional and cognitive disorders. In rodent models of early-life stress, fragmentation and unpredictability of maternally derived sensory signals provoke persistent cognitive and emotional dysfunction in offspring. Similar variability and inconsistency of maternal signals during both gestation and early postnatal human life may influence development of emotional and cognitive functions, including those that underlie later depression and anxiety.

Fragile X syndrome: a pilot proton magnetic resonance spectroscopy study in premutation carriers

Purpose

There is increasing evidence that neurodevelopmental differences in people with Fragile X syndrome (FraX) may be explained by differences in glutamatergic metabolism. Premutation carriers of FraX were originally considered to be unaffected although several recent reports demonstrate neuroanatomical, cognitive, and emotional differences from controls. However there are few studies on brain metabolism in premutation carriers of FraX.

Methods

We used proton magnetic resonance spectroscopy to compare neuronal integrity of a number of brain metabolites including N-Acetyl Aspartate, Creatine + Phosphocreatinine, Choline, myoInositol, and Glutamate containing substances (Glx) in 17 male premutation carriers of FraX and 16 male healthy control individuals.

Results

There was no significant between-group difference in the concentration of any measured brain metabolites. However there was a differential increase in N-acetyl aspartate with aging in premutation FraX individuals compared to controls.

Conclusions

This is the first ¹ H-MRS study to examine premutation FraX individuals. Although we demonstrated no difference in the concentration of any of the metabolites examined between the groups, this may be due to the large age ranges included in the two samples. The differential increase in NAA levels with aging may reflect an abnormal synaptic pruning process.