Dissociation of locomotor and cerebellar deficits in a murine Angelman syndrome model

Three-Dimensional Gait Analysis of School-Age Children With Angelman Syndrome: A Case-Control Study

Gait disturbance is a common motor symptom in Angelman syndrome (AS), but its characteristics have been poorly studied quantitatively. This study aimed to analyze gait characteristics in school-age children with AS using three-dimensional gait analysis (3DGA). Patients with clinically and genetically confirmed AS and healthy children aged 6-15 years were included. For gait assessments, 3DGA was performed using an eight-camera motion analysis system and eight force plates. Gait metrics, including gait speed, step length, step width, gait variability, gait deviation index, and kinematic and kinetic data of lower extremity joints were compared between the groups. Eight children with AS and 24 healthy controls were evaluated. Seven children with AS had flat feet. While step length and gait speed were similar between groups, children with AS showed greater variability in these parameters and larger step widths. Their average gait deviation index was 74.5, indicating significant gait disturbance, and characteristic features included anterior pelvic tilt, insufficient hip extension, excessive knee flexion during early stance, and reduced ankle joint power. School-age children with AS exhibit unstable, prancing gait characterized by knee flexion in the early stance phase, quantifiable using 3DGA. These findings provide foundation for evaluating therapeutic interventions.

Peptidomimetic inhibitors targeting TrkB/PSD-95 signaling improves cognition and seizure outcomes in an Angelman Syndrome mouse model

Angelman syndrome (AS) is a rare genetic neurodevelopmental disorder with profoundly debilitating symptoms with no FDA-approved cure or therapeutic. Brain-derived neurotrophic factor (BDNF), and its receptor tropomyosin receptor kinase B (TrkB), have a well-established role as regulators of synaptic plasticity, dendritic outgrowth and spine formation. Previously, we reported that the association of postsynaptic density protein 95 (PSD-95) with TrkB is critical for intact BDNF signaling in the AS mouse model, as illustrated by attenuated PLCγ and PI3K signaling and intact MAPK pathway signaling. These data suggest that drugs tailored to enhance the TrkB-PSD-95 interaction may provide a novel approach for the treatment of AS and a variety of neurodevelopmental disorders (NDDs). To evaluate this critical interaction, we synthesized a class of high-affinity PSD-95 ligands that bind specifically to the PDZ3 domain of PSD-95, denoted as Syn3 peptidomimetic ligands. We evaluated Syn3 and its analog D-Syn3 (engineered using dextrorotary (D)-amino acids) in vivo using the Ube3a exon 2 deletion mouse model of AS. Following systemic administration of Syn3 and D-Syn3, we demonstrate improvement in the seizure domain of AS. Learning and memory using the novel object recognition assay also illustrated improved cognition following Syn3 and D-Syn3, along with restored long-term potentiation. A pharmacokinetic analysis of D-Syn3 demonstrates that it crosses the blood-brain barrier (BBB), and the brain influx rate is in the range of CNS therapeutics. Finally, D-Syn3 treated mice showed a partial rescue in motor learning. Neither Syn3 nor D-Syn3 improved gross exploratory locomotion deficits, nor gait impairments that have been well documented in the AS rodent models. These findings highlight the need for further investigation of this compound class as a potential therapeutic for AS and other genetic NDDs.

PIEZO ion channels: force sensors of the interoceptive nervous system

Many organs are designed to move: the heart pumps each second, the gastrointestinal tract squeezes and churns to digest food, and we contract and relax skeletal muscles to move our bodies. Sensory neurons of the peripheral nervous system detect signals from bodily tissues, including the forces generated by these movements, to control physiology. The processing of these internal signals is called interoception, but this is a broad term that includes a wide variety of both chemical and mechanical sensory processes. Mechanical senses are understudied, but rapid progress has been made in the last decade, thanks in part to the discovery of the mechanosensory PIEZO ion channels (Coste et al., 2010). The role of these mechanosensors within the interoceptive nervous system is the focus of this review. In defining the transduction molecules that govern mechanical interoception, we will have a better grasp of how these signals drive physiology.

Peptidomimetic inhibitors targeting TrkB/PSD-95 signaling improves cognition and seizure outcomes in an Angelman Syndrome mouse model

Angelman syndrome (AS) is a rare genetic neurodevelopmental disorder with profoundly debilitating symptoms with no FDA-approved cure or therapeutic. Brain-derived neurotrophic factor (BDNF), and its receptor TrkB, have a well-established role as regulators of synaptic plasticity, dendritic outgrowth, dendritic spine formation and maintenance. Previously, we reported that the association of PSD-95 with TrkB is critical for intact BDNF signaling in the AS mouse model, as illustrated by attenuated PLCγ and PI3K signaling and intact MAPK pathway signaling. These data suggest that drugs tailored to enhance the TrkB-PSD-95 interaction may provide a novel approach for the treatment of AS and a variety of NDDs. To evaluate this critical interaction, we synthesized a class of high-affinity PSD-95 ligands that bind specifically to the PDZ3 domain of PSD-95, denoted as Syn3 peptidomimetic ligands. We evaluated Syn3 and its analog D-Syn3 (engineered using dextrorotary (D)-amino acids) in vivo using the Ube3a exon 2 deletion mouse model of AS. Following systemic administration of Syn3 and D-Syn3, we demonstrated improvement in the seizure domain of AS. Learning and memory using the novel object recognition assay also illustrated improved cognition following Syn3 and D-Syn3, along with restored long-term potentiation. Finally, D-Syn3 treated mice showed a partial rescue in motor learning. Neither Syn3 nor D-Syn3 improved gross exploratory locomotion deficits, nor gait impairments that have been well documented in the AS rodent models. These findings highlight the need for further investigation of this compound class as a potential therapeutic for AS and other genetic NDDs.

Prenatal delivery of a therapeutic antisense oligonucleotide achieves broad biodistribution in the brain and ameliorates Angelman syndrome phenotype in mice

Angelman syndrome (AS), an early-onset neurodevelopmental disorder characterized by abnormal gait, intellectual disabilities, and seizures, occurs when the maternal allele of the UBE3A gene is disrupted, since the paternal allele is silenced in neurons by the UBE3A antisense (UBE3A-AS) transcript. Given the importance of early treatment, we hypothesized that prenatal delivery of an antisense oligonucleotide (ASO) would downregulate the murine Ube3a-AS, resulting in increased UBE3A protein and functional rescue. Using a mouse model with a Ube3a-YFP allele that reports on-target ASO activity, we found that in utero, intracranial (IC) injection of the ASO resulted in dose-dependent activation of paternal Ube3a, with broad biodistribution. Accordingly, in utero injection of the ASO in a mouse model of AS also resulted in successful restoration of UBE3A and phenotypic improvements in treated mice on the accelerating rotarod and fear conditioning. Strikingly, even intra-amniotic (IA) injection resulted in systemic biodistribution and high levels of UBE3A reactivation throughout the brain. These findings offer a novel strategy for early treatment of AS using an ASO, with two potential routes of administration in the prenatal window. Beyond AS, successful delivery of a therapeutic ASO into neurons has implications for a clinically feasible prenatal treatment for numerous neurodevelopmental disorders.

Gut microbes in central nervous system development and related disorders

The association between gut microbiota and central nervous system (CNS) development has garnered significant research attention in recent years. Evidence suggests bidirectional communication between the CNS and gut microbiota through the brain-gut axis. As a long and complex process, CNS development is highly susceptible to both endogenous and exogenous factors. The gut microbiota impacts the CNS by regulating neurogenesis, myelination, glial cell function, synaptic pruning, and blood-brain barrier permeability, with implication in various CNS disorders. This review outlines the relationship between gut microbiota and stages of CNS development (prenatal and postnatal), emphasizing the integral role of gut microbes. Furthermore, the review explores the implications of gut microbiota in neurodevelopmental disorders, such as autism spectrum disorder, Rett syndrome, and Angelman syndrome, offering insights into early detection, prompt intervention, and innovative treatments.

A PSD-95 peptidomimetic mitigates neurological deficits in a mouse model of Angelman syndrome

Angelman Syndrome (AS) is a severe cognitive disorder caused by loss of neuronal expression of the E3 ubiquitin ligase UBE3A. In an AS mouse model, we previously reported a deficit in brain-derived neurotrophic factor (BDNF) signaling, and set out to develop a therapeutic that would restore normal signaling. We demonstrate that CN2097, a peptidomimetic compound that binds postsynaptic density protein-95 (PSD-95), a TrkB associated scaffolding protein, mitigates deficits in PLC-CaMKII and PI3K/mTOR pathways to restore synaptic plasticity and learning. Administration of CN2097 facilitated long-term potentiation (LTP) and corrected paired-pulse ratio. As the BDNF-mTORC1 pathway is critical for inhibition of autophagy, we investigated whether autophagy was disrupted in AS mice. We found aberrantly high autophagic activity attributable to a concomitant decrease in mTORC1 signaling, resulting in decreased levels of synaptic proteins, including Synapsin-1 and Shank3. CN2097 increased mTORC1 activity to normalize autophagy and restore hippocampal synaptic protein levels. Importantly, treatment mitigated cognitive and motor dysfunction. These findings support the use of neurotrophic therapeutics as a valuable approach for treating AS pathology.

Stem cell models of Angelman syndrome

Angelman syndrome (AS) is an imprinted neurodevelopmental disorder that lacks a cure, characterized by developmental delay, intellectual impairment, seizures, ataxia, and paroxysmal laughter. The condition arises due to the loss of the maternally inherited copy of the UBE3A gene in neurons. The paternally inherited UBE3A allele is unable to compensate because it is silenced by the expression of an antisense transcript (UBE3A-ATS) on the paternal chromosome. UBE3A, encoding enigmatic E3 ubiquitin ligase variants, regulates target proteins by either modifying their properties/functions or leading them to degradation through the proteasome. Over time, animal models, particularly the Ube3a mat-/pat+ Knock-Out (KO) mice, have significantly contributed to our understanding of the molecular mechanisms underlying AS. However, a shift toward human pluripotent stem cell models (PSCs), such as human embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs), has gained momentum. These stem cell models accurately capture human genetic and cellular characteristics, offering an alternative or a complement to animal experimentation. Human stem cells possess the remarkable ability to recapitulate neurogenesis and generate "brain-in-a-dish" models, making them valuable tools for studying neurodevelopmental disorders like AS. In this review, we provide an overview of the current state-of-the-art human stem cell models of AS and explore their potential to become the preclinical models of choice for drug screening and development, thus propelling AS therapeutic advancements and improving the lives of affected individuals.

Imbalanced expression of cation-chloride cotransporters as a potential therapeutic target in an Angelman syndrome mouse model

Angelman syndrome is a neurodevelopmental disorder caused by loss of function of the maternally expressed UBE3A gene. Treatments for the main manifestations, including cognitive dysfunction or epilepsy, are still under development. Recently, the Cl^- importer Na⁺-K⁺-Cl^- cotransporter 1 (NKCC1) and the Cl^- exporter K⁺-Cl^- cotransporter 2 (KCC2) have garnered attention as therapeutic targets for many neurological disorders. Dysregulation of neuronal intracellular Cl^- concentration ([Cl^-]_i) is generally regarded as one of the mechanisms underlying neuronal dysfunction caused by imbalanced expression of these cation-chloride cotransporters (CCCs). Here, we analyzed the regulation of [Cl^-]_i and the effects of bumetanide, an NKCC1 inhibitor, in Angelman syndrome models (Ube3a^m-/p+ mice). We observed increased NKCC1 expression and decreased KCC2 expression in the hippocampi of Ube3a^m-/p+ mice. The average [Cl^-]_i of CA1 pyramidal neurons was not significantly different but demonstrated greater variance in Ube3a^m-/p+ mice. Tonic GABA_A receptor-mediated Cl^- conductance was reduced, which may have contributed to maintaining the normal average [Cl^-]_i. Bumetanide administration restores cognitive dysfunction in Ube3a^m-/p+ mice. Seizure susceptibility was also reduced regardless of the genotype. These results suggest that an imbalanced expression of CCCs is involved in the pathophysiological mechanism of Ube3a^m-/p+ mice, although the average [Cl^-]_i is not altered. The blockage of NKCC1 may be a potential therapeutic strategy for patients with Angelman syndrome.

Linoleic acid improves PIEZO2 dysfunction in a mouse model of Angelman Syndrome

Angelman syndrome (AS) is a neurogenetic disorder characterized by intellectual disability and atypical behaviors. AS results from loss of expression of the E3 ubiquitin-protein ligase UBE3A from the maternal allele in neurons. Individuals with AS display impaired coordination, poor balance, and gait ataxia. PIEZO2 is a mechanosensitive ion channel essential for coordination and balance. Here, we report that PIEZO2 activity is reduced in Ube3a deficient male and female mouse sensory neurons, a human Merkel cell carcinoma cell line and female human iPSC-derived sensory neurons with UBE3A knock-down, and de-identified stem cell-derived neurons from individuals with AS. We find that loss of UBE3A decreases actin filaments and reduces PIEZO2 expression and function. A linoleic acid (LA)-enriched diet increases PIEZO2 activity, mechano-excitability, and improves gait in male AS mice. Finally, LA supplementation increases PIEZO2 function in stem cell-derived neurons from individuals with AS. We propose a mechanism whereby loss of UBE3A expression reduces PIEZO2 function and identified a fatty acid that enhances channel activity and ameliorates AS-associated mechano-sensory deficits.

UBE3A expression during early postnatal brain development is required for proper dorsomedial striatal maturation

Angelman syndrome (AS) is a severe neurodevelopmental disorder (NDD) caused by loss of functional ubiquitin protein ligase E3A (UBE3A). Previous studies showed that UBE3A plays an important role in the first postnatal weeks of mouse brain development, but its precise role is unknown. Since impaired striatal maturation has been implicated in several mouse models for NDDs, we studied the importance of UBE3A in striatal maturation. We used inducible Ube3a mouse models to investigate the maturation of medium spiny neurons (MSNs) from dorsomedial striatum. MSNs of mutant mice matured properly till postnatal day 15 (P15) but remained hyperexcitable with fewer excitatory synaptic events at later ages, indicative of stalled striatal maturation in Ube3a mice. Reinstatement of UBE3A expression at P21 fully restored MSN excitability but only partially restored synaptic transmission and the operant conditioning behavioral phenotype. Gene reinstatement at P70 failed to rescue both electrophysiological and behavioral phenotypes. In contrast, deletion of Ube3a after normal brain development did not result in these electrophysiological and behavioral phenotypes. This study emphasizes the role of UBE3A in striatal maturation and the importance of early postnatal reinstatement of UBE3A expression to obtain a full rescue of behavioral phenotypes associated with striatal function in AS.

Epilepsy and Molecular Phenotype Affect the Neurodevelopment of Pediatric Angelman Syndrome Patients in China

OBJECTIVE

This study investigated the mental development of children with Angelman syndrome (AS) in China and evaluated the relationship between neurodevelopment and molecular subtype, age, epilepsy, and sex using the Chinese version of the Griffith Mental Development Scale (GMDS-C) to provide detailed baseline data regarding neurodevelopment with AS in China.

METHODS

Participants were recruited from the AS Natural History Study. The GMDS-C was used to evaluate all participants' mental age and developmental quotients. The general quotient (GQ) and quotients of five subscales (sports, personal-social, auditory language, eye-hand coordination, and comprehensive performance) were calculated.

RESULTS

A total of 119 children (average age: 42.12 months; range, 7.5-95.5 months) with a genetic diagnosis of AS were enrolled. The median GQ score of the GMDS was 29.6 points (95% confidence interval, 28.6-33.25). The children had relatively good locomotor and personal-social skills but poor language skills. Overall, 89% (106/119) had mental ages younger than 24 months for all five subscales. The non-deletion group (i.e., without deletion in chromosome 15q11-13) had higher GQs and locomotor, personal-social, and performance subscale quotients. The GQ was significantly different among the three age subgroups and significantly correlated with age. Compared with the non-epilepsy group, the epilepsy group had lower GQs and lower quotients for the locomotor, personal-social, speech, language, and eye-hand coordination subscales.

CONCLUSION

Children with AS in China experience severe neurodevelopmental deterioration. In addition to age, molecular subtypes and the onset of seizures may also correlate with these patients' intellectual development. The GMDS-C is an accurate tool that can assess the clinical characteristics of AS. The data of this study can be used as baseline data for clinical trials performed to evaluate drug development or other AS treatment development.

A cross-species spatiotemporal proteomic analysis identifies UBE3A-dependent signaling pathways and targets

Angelman syndrome (AS) is a severe neurodevelopmental disorder caused by the loss of neuronal E3 ligase UBE3A. Restoring UBE3A levels is a potential disease-modifying therapy for AS and has recently entered clinical trials. There is paucity of data regarding the molecular changes downstream of UBE3A hampering elucidation of disease therapeutics and biomarkers. Notably, UBE3A plays an important role in the nucleus but its targets have yet to be elucidated. Using proteomics, we assessed changes during postnatal cortical development in an AS mouse model. Pathway analysis revealed dysregulation of proteasomal and tRNA synthetase pathways at all postnatal brain developmental stages, while synaptic proteins were altered in adults. We confirmed pathway alterations in an adult AS rat model across multiple brain regions and highlighted region-specific differences. UBE3A reinstatement in AS model mice resulted in near complete and partial rescue of the proteome alterations in adolescence and adults, respectively, supporting the notion that restoration of UBE3A expression provides a promising therapeutic option. We show that the nuclear enriched transketolase (TKT), one of the most abundantly altered proteins, is a novel direct UBE3A substrate and is elevated in the neuronal nucleus of rat brains and human iPSC-derived neurons. Taken together, our study provides a comprehensive map of UBE3A-driven proteome remodeling in AS across development and species, and corroborates an early UBE3A reinstatement as a viable therapeutic option. To support future disease and biomarker research, we present an accessible large-scale multi-species proteomic resource for the AS community ( https://www.angelman-proteome-project.org/ ).

Dual-isoform hUBE3A gene transfer improves behavioral and seizure outcomes in Angelman syndrome model mice

Loss of the maternal UBE3A allele causes Angelman syndrome (AS), a debilitating neurodevelopmental disorder. Here, we devised an AS treatment strategy based on reinstating dual-isoform expression of human UBE3A (hUBE3A) in the developing brain. Kozak sequence engineering of our codon-optimized vector (hUBE3Aopt) enabled translation of both short and long hUBE3A protein isoforms at a near-endogenous 3:1 (short/long) ratio, a feature that could help to support optimal therapeutic outcomes. To model widespread brain delivery and early postnatal onset of hUBE3A expression, we packaged the hUBE3Aopt vector into PHP.B capsids and performed intracerebroventricular injections in neonates. This treatment significantly improved motor learning and innate behaviors in AS mice, and it rendered them resilient to epileptogenesis and associated hippocampal neuropathologies induced by seizure kindling. hUBE3A overexpression occurred frequently in the hippocampus but was uncommon in the neocortex and other major brain structures; furthermore, it did not correlate with behavioral performance. Our results demonstrate the feasibility, tolerability, and therapeutic potential for dual-isoform hUBE3A gene transfer in the treatment of AS.

Deleting a UBE3A substrate rescues impaired hippocampal physiology and learning in Angelman syndrome mice

In humans, loss-of-function mutations in the UBE3A gene lead to the neurodevelopmental disorder Angelman syndrome (AS). AS patients have severe impairments in speech, learning and memory, and motor coordination, for which there is currently no treatment. In addition, UBE3A is duplicated in > 1-2% of patients with autism spectrum disorders-a further indication of the significant role it plays in brain development. Altered expression of UBE3A, an E3 ubiquitin ligase, is hypothesized to lead to impaired levels of its target proteins, but identifying the contribution of individual UBE3A targets to UBE3A-dependent deficits remains of critical importance. Ephexin5 is a putative UBE3A substrate that has restricted expression early in development, regulates synapse formation during hippocampal development, and is abnormally elevated in AS mice, modeled by maternally-derived Ube3a gene deletion. Here, we report that Ephexin5 can be directly ubiquitylated by UBE3A. Furthermore, removing Ephexin5 from AS mice specifically rescued hippocampus-dependent behaviors, CA1 physiology, and deficits in dendritic spine number. Our findings identify Ephexin5 as a key driver of hippocampal dysfunction and related behavioral deficits in AS mouse models. These results demonstrate the exciting potential of targeting Ephexin5, and possibly other UBE3A substrates, to improve symptoms of AS and other UBE3A-related developmental disorders.

Electrophysiological Characterization of Regular and Burst Firing Pyramidal Neurons of the Dorsal Subiculum in an Angelman Syndrome Mouse Model

Angelman syndrome (AS) is a debilitating neurogenetic disorder characterized by severe developmental delay, speech impairment, gait ataxia, sleep disturbances, epilepsy, and a unique behavioral phenotype. AS is caused by a microdeletion or mutation in the maternal 15q11-q13 chromosome region containing UBE3A gene. The hippocampus is one of the important brain regions affected in AS mice leading to substantial hippocampal-dependent cognitive and behavioral deficits. Recent studies have suggested an abnormal increase in the α1-Na/K-ATPase (α1-NaKA) in AS mice as the precipitating factor leading to the hippocampal deficits. A subsequent study showed that the hippocampal-dependent behavioral deficits occur as a result of altered calcium (Ca⁺²) dynamics in the CA1 pyramidal neurons (PNs) caused by the elevated α1-NaKA expression levels in the AS mice. Nonetheless, a causal link between hippocampal deficits and major behavioral phenotypes in AS is still obscure. Subiculum, a region adjacent to the hippocampal CA1 is the major output source of the hippocampus and plays an important role in the transfer of information from the CA1 region to the cortical areas. However, in spite of the robust hippocampal deficits and several known electrophysiological alterations in multiple brain regions in AS mice, the neuronal properties of the subicular neurons were never investigated in these mice. Additionally, subicular function is also implied in many neuropsychiatric disorders such as autism, schizophrenia, Alzheimer’s disease, and epilepsy that share some common features with AS. Therefore, given the importance of the subiculum in these neuropsychiatric disorders and the altered electrophysiological properties of the hippocampal CA1 PNs projecting to the subiculum, we sought to examine the subicular PNs. We performed whole-cell recordings from dorsal subiculum of both WT and AS mice and found three distinct populations of PNs based on their ability to fire bursts or single action potentials following somatic current injection: strong bursting, weak bursting, and regular firing neurons. We found no overall differences in the distribution of these different subicular PN populations among AS and WT controls. However, the different cell types showed distinct alterations in their intrinsic membrane properties. Further, none of these populations were altered in their excitatory synaptic properties. Altogether, our study characterized the different subtypes of PNs in the subicular region of an AS mouse model.

Emerging Gene and Small Molecule Therapies for the Neurodevelopmental Disorder Angelman Syndrome

Angelman syndrome (AS) is a rare (~1:15,000) neurodevelopmental disorder characterized by severe developmental delay and intellectual disability, impaired communication skills, and a high prevalence of seizures, sleep disturbances, ataxia, motor deficits, and microcephaly. AS is caused by loss-of-function of the maternally inherited UBE3A gene. UBE3A is located on chromosome 15q11-13 and is biallelically expressed throughout the body but only maternally expressed in the brain due to an RNA antisense transcript that silences the paternal copy. There is currently no cure for AS, but advancements in small molecule drugs and gene therapies offer a promising approach for the treatment of the disorder. Here, we review AS and how loss-of-function of the maternal UBE3A contributes to the disorder. We also discuss the strengths and limitations of current animal models of AS. Furthermore, we examine potential small molecule drug and gene therapies for the treatment of AS and associated challenges faced by the therapeutic design. Finally, gene therapy offers the opportunity for precision medicine in AS and advancements in the treatment of this disorder can serve as a foundation for other single-gene neurodevelopmental disorders.

Motor Deficits Coupled to Cerebellar and Striatal Alterations in Ube3am-/p+ Mice Modelling Angelman Syndrome Are Attenuated by Adenosine A2A Receptor Blockade

Angelman syndrome (AS) is a neurogenetic disorder involving ataxia and motor dysfunction, resulting from the absence of the maternally inherited functional Ube3a protein in neurons. Since adenosine A2A receptor (A2AR) blockade relieves synaptic and motor impairments in Parkinson's or Machado-Joseph's diseases, we now tested if A2AR blockade was also effective in attenuating motor deficits in an AS (Ube3am-/p+) mouse model and if this involved correction of synaptic alterations in striatum and cerebellum. Chronic administration of the A2AR antagonist SCH58261 (0.1 mg/kg/day, ip) promoted motor learning of AS mice in the accelerating-rotarod task and rescued the grip strength impairment of AS animals. These motor impairments were accompanied by synaptic alterations in cerebellum and striatum typified by upregulation of synaptophysin and vesicular GABA transporters (vGAT) in the cerebellum of AS mice along with a downregulation of vGAT, vesicular glutamate transporter 1 (vGLUT1) and the dopamine active transporter in AS striatum. Notably, A2AR blockade prevented the synaptic alterations found in AS mice cerebellum as well as the downregulation of striatal vGAT and vGLUT1. This provides the first indications that A2AR blockade may counteract the characteristic motor impairments and synaptic changes of AS, although more studies are needed to unravel the underlying mechanisms.

Cerebellum-Specific Deletion of the GABAA Receptor δ Subunit Leads to Sex-Specific Disruption of Behavior

Granule cells (GCs) of the cerebellar input layer express high-affinity δ GABA_A subunit-containing GABA_A receptors (δGABA_ARs) that respond to ambient GABA levels and context-dependent neuromodulators like steroids. We find that GC-specific deletion of δGABA_A (cerebellar [cb] δ knockout [KO]) decreases tonic inhibition, makes GCs hyperexcitable, and in turn, leads to differential activation of cb output regions as well as many cortical and subcortical brain areas involved in cognition, anxiety-like behaviors, and the stress response. Cb δ KO mice display deficits in many behaviors, but motor function is normal. Strikingly, δGABA_A deletion alters maternal behavior as well as spontaneous, stress-related, and social behaviors specifically in females. Our findings establish that δGABA_ARs enable the cerebellum to control diverse behaviors not previously associated with the cerebellum in a sex-dependent manner. These insights may contribute to a better understanding of the mechanisms that underlie behavioral abnormalities in psychiatric and neurodevelopmental disorders that display a gender bias.

Rudolph et al. show that deletion of the neuromodulator and hormone-sensitive δGABA_A receptor subunit from cerebellar granule cells results in anxiety-like behaviors and female-specific deficits in social behavior and maternal care. δGABA_A deletion is associated with hyperexcitability of the cerebellar input layer and altered activation of many stress-related brain regions.

Region-specific preservation of Purkinje cell morphology and motor behavior in the ATXN1[82Q] mouse model of spinocerebellar ataxia 1

Purkinje cells are the primary processing units of the cerebellar cortex and display molecular heterogeneity that aligns with differences in physiological properties, projection patterns, and susceptibility to disease. In particular, multiple mouse models that feature Purkinje cell degeneration are characterized by incomplete and patterned Purkinje cell degeneration, suggestive of relative sparing of Purkinje cell subpopulations, such as those expressing Aldolase C/zebrinII (AldoC) or residing in the vestibulo‐cerebellum. Here, we investigated a well‐characterized Purkinje cell‐specific mouse model for spinocerebellar ataxia type 1 (SCA1) that expresses human ATXN1 with a polyQ expansion (82Q). Our pathological analysis confirms previous findings that Purkinje cells of the vestibulo‐cerebellum, i.e., the flocculonodular lobes, and crus I are relatively spared from key pathological hallmarks: somatodendritic atrophy, and the appearance of p62/SQSTM1‐positive inclusions. However, immunohistological analysis of transgene expression revealed that spared Purkinje cells do not express mutant ATXN1 protein, indicating the sparing of Purkinje cells can be explained by an absence of transgene expression. Additionally, we found that Purkinje cells in other cerebellar lobules that typically express AldoC, not only display severe pathology but also show loss of AldoC expression. The relatively preserved flocculonodular lobes and crus I showed a substantial fraction of Purkinje cells that expressed the mutant protein and displayed pathology as well as loss of AldoC expression. Despite considerable pathology in these lobules, behavioral analyses demonstrated a relative sparing of related functions, suggestive of sufficient functional cerebellar reserve. Together, the data indicate that mutant ATXN1 affects both AldoC‐positive and AldoC‐negative Purkinje cells and disrupts normal parasagittal AldoC expression in Purkinje cells. Our results show that, in a mouse model otherwise characterized by widespread Purkinje cell degeneration, sparing of specific subpopulations is sufficient to maintain normal performance of specific behaviors within the context of the functional, modular map of the cerebellum.

Communication-related assessments in an Angelman syndrome mouse model

INTRODUCTION

Angelman syndrome (AS) is a neurodevelopmental disorder characterized by motor deficits, seizures, some autistic-like behaviors, and severe impairment of speech. A dysfunction of the maternally imprinted UBE3A gene, coupled with a functional yet silenced paternal copy, results in AS. Although studies of transgenic mouse models have revealed a great deal about neural populations and rescue timeframes for specific features of AS, these studies have largely failed to examine intermediate phenotypes that contribute to the profound communicative disabilities associated with AS.

METHODS

Here, we use a variety of tasks, including assessments of rapid auditory processing and social communication. Expressive vocalizations were directly assessed and correlated against other core behavioral measures (motor, social, acoustic perception) to model putative influences on communication.

RESULTS

AS mice displayed the characteristic phenotypes associated with Angelman syndrome (i.e., social and motor deficits), as well as marginal enhancements in rapid auditory processing ability. Our characterization of adult ultrasonic vocalizations further showed that AS mice produce fewer vocalizations and vocalized for a shorter amount of time when compared to controls. Additionally, a strong correlation between motor indices and ultrasonic vocalization output was shown, suggesting that the motor impairments in AS may contribute heavily to communication impairments.

CONCLUSION

In summary, the combination of motor deficits, social impairment, marginal rapid auditory enhancements, and altered ultrasonic vocalizations reported in a mouse model of AS clearly parallel the human symptoms of the disorder. This mouse model offers a novel route to interrogate the underlying genetic, physiologic, and behavioral influences on the under-studied topic of impaired communication in AS.

The STARS Phase 2 Study: A Randomized Controlled Trial of Gaboxadol in Angelman Syndrome

OBJECTIVE

To evaluate safety and tolerability and exploratory efficacy end points for gaboxadol (OV101) compared with placebo in individuals with Angelman syndrome (AS).

METHODS

Gaboxadol is a highly selective orthosteric agonist that activates δ-subunit-containing extrasynaptic γ-aminobutyric acid type A (GABA_A) receptors. In a multicenter, double-blind, placebo-controlled, parallel-group trial, adolescent and adult individuals with a molecular diagnosis of AS were randomized (1:1:1) to 1 of 3 dosing regimens for a duration of 12 weeks: placebo morning dose and gaboxadol 15 mg evening dose (qd), gaboxadol 10 mg morning dose and 15 mg evening dose (bid), or placebo morning and evening dose. Safety and tolerability were monitored throughout the study. Prespecified exploratory efficacy end points included adapted Clinical Global Impression-Severity and Clinical Global Impression-Improvement (CGI-I) scales, which documented the clinical severity at baseline and change after treatment, respectively.

RESULTS

Eighty-eight individuals were randomized. Of 87 individuals (aged 13-45 years) who received at least 1 dose of study drug, 78 (90%) completed the study. Most adverse events (AEs) were mild to moderate, and no life-threatening AEs were reported. Efficacy of gaboxadol, as measured by CGI-I improvement in an exploratory analysis, was observed in gaboxadol qd vs placebo (p = 0.0006).

CONCLUSION

After 12 weeks of treatment, gaboxadol was found to be generally well-tolerated with a favorable safety profile. The efficacy as measured by the AS-adapted CGI-I scale warrants further studies.

CLINICALTRIALSGOV IDENTIFIER

NCT02996305.

CLASSIFICATION OF EVIDENCE

This study provides Class I evidence that, for individuals with AS, gaboxadol is generally safe and well-tolerated.

Assessing the requirements of prenatal UBE3A expression for rescue of behavioral phenotypes in a mouse model for Angelman syndrome

Background

Angelman syndrome (AS) is a rare neurodevelopmental disorder caused by the loss of functional ubiquitin protein ligase E3A (UBE3A). In neurons, UBE3A expression is tightly regulated by a mechanism of imprinting which suppresses the expression of the paternal UBE3A allele. Promising treatment strategies for AS are directed at activating paternal UBE3A gene expression. However, for such strategies to be successful, it is important to know when such a treatment should start, and how much UBE3A expression is needed for normal embryonic brain development.

Methods

Using a conditional mouse model of AS, we further delineated the critical period for UBE3A expression during early brain development. Ube3a gene expression was induced around the second week of gestation and mouse phenotypes were assessed using a behavioral test battery. To investigate the requirements of embryonic UBE3A expression, we made use of mice in which the paternal Ube3a allele was deleted.

Results

We observed a full behavioral rescue of the AS mouse model phenotypes when Ube3a gene reactivation was induced around the start of the last week of mouse embryonic development. We found that full silencing of the paternal Ube3a allele was not completed till the first week after birth but that deletion of the paternal Ube3a allele had no significant effect on the assessed phenotypes.

Limitations

Direct translation to human is limited, as we do not precisely know how human and mouse brain development aligns over gestational time. Moreover, many of the assessed phenotypes have limited translational value, as the underlying brain regions involved in these tasks are largely unknown.

Conclusions

Our findings provide further important insights in the requirement of UBE3A expression during brain development. We found that loss of up to 50% of UBE3A protein during prenatal mouse brain development does not significantly impact the assessed mouse behavioral phenotypes. Together with previous findings, our results indicate that the most critical function for mouse UBE3A lies in the early postnatal period between birth and P21.

Disrupted Functional and Structural Connectivity in Angelman Syndrome

BACKGROUND AND PURPOSE

This work investigated alterations in functional connectivity (FC) and associated structures in patients with Angelman syndrome (AS) by using integrated quantitative imaging analysis and connectivity measures.

MATERIALS AND METHODS

We obtained 3T brain MR imaging, including resting-state functional MR imaging, diffusion tensor imaging, and 3D T1-weighted imaging from children with AS (n = 14) and age- and sex-matched controls (n = 28). The brains of patients with AS were analyzed by measuring FC, white matter microstructural analysis, cortical thickness, and brain volumes; these were compared with brains of controls.

RESULTS

Interregional FC analysis revealed significantly reduced intra- and interhemispheric FC, especially in the basal ganglia and thalamus, in patients with AS. Significant reductions in fractional anisotropy were found in the corpus callosum, cingulum, posterior limb of the internal capsules, and arcuate fasciculus in patients with AS. Quantitative structural analysis also showed gray matter volume loss of the basal ganglia and diffuse WM volume reduction in AS compared with the control group.

CONCLUSIONS

This integrated quantitative MR imaging analysis demonstrated poor functional and structural connectivity, as well as brain volume reduction, in children with AS, which may explain the motor and language dysfunction observed in this well-characterized neurobehavioral phenotype.

Angelman syndrome: a journey through the brain

Angelman syndrome (AS) is an incurable neurodevelopmental disease caused by loss of function of the maternally inherited UBE3A gene. AS is characterized by a defined set of symptoms, namely severe developmental delay, speech impairment, uncontrolled laughter, and ataxia. Current understanding of the pathophysiology of AS relies mostly on studies using the murine model of the disease, although alternative models based on patient-derived stem cells are now emerging. Here, we summarize the literature of the last decade concerning the three major brain areas that have been the subject of study in the context of AS: hippocampus, cortex, and the cerebellum. Our comprehensive analysis highlights the major phenotypes ascribed to the different brain areas. Moreover, we also discuss the major drawbacks of current models and point out future directions for research in the context of AS, which will hopefully lead us to an effective treatment of this condition in humans.

Angelman Syndrome: From Mouse Models to Therapy

The UBE3A gene is part of the chromosome 15q11-q13 region that is frequently deleted or duplicated, leading to several neurodevelopmental disorders (NDD). Angelman syndrome (AS) is caused by the absence of functional maternally derived UBE3A protein, while the paternal UBE3A gene is present but silenced specifically in neurons. Patients with AS present with severe neurodevelopmental delay, with pronounced motor deficits, absence of speech, intellectual disability, epilepsy, and sleep problems. The pathophysiology of AS is still unclear and a treatment is lacking. Animal models of AS recapitulate the genotypic and phenotypic features observed in AS patients, and have been invaluable for understanding the disease process as well as identifying apropriate drug targets. Using these AS mouse models we have learned that loss of UBE3A probably affects many areas of the brain, leading to increased neuronal excitability and a loss of synaptic spines, along with changes in a number of distinct behaviours. Inducible AS mouse models have helped to identify the critical treatment windows for the behavioral and physiological phenotypes. Additionally, AS mouse models indicate an important role for the predominantly nuclear UBE3A isoform in generating the characteristic AS pathology. Last, but not least, the AS mice have been crucial in guiding Ube3a gene reactivation treatments, which present a very promising therapy to treat AS.

Sex-Dependent Sensory Phenotypes and Related Transcriptomic Expression Profiles Are Differentially Affected by Angelman Syndrome

Angelman syndrome (AS) is a genetic disorder which entails autism, intellectual disability, lack of speech, motor deficits, and seizure susceptibility. It is caused by the lack of UBE3A protein expression, which is an E3-ubiquitin ligase. Despite AS equal prevalence in males and females, not much data on how sex affects the syndrome was reported. In the herein study, we thoroughly characterized many behavioral phenotypes of AS mice. The behavioral data acquired was analyzed with respect to sex. In addition, we generated a new mRNA sequencing dataset. We analyzed the coding transcriptome expression profiles with respect to the effects of genotype and sex observed in the behavioral phenotypes. We identified several neurobehavioral aspects, especially sensory perception, where AS mice either lack the male-to-female differences observed in wild-type littermates or even show opposed differences. However, motor phenotypes did not show male-to-female variation between wild-type (WT) and AS mice. In addition, by utilizing the mRNA sequencing, we identified genes and isoforms with expression profiles that mirror the sensory perception results. These genes are differentially regulated in the two sexes with inverse expression profiles in AS mice compared to WT littermates. Some of these are known pain-related and estrogen-dependent genes. The observed differences in sex-dependent neurobehavioral phenotypes and the differential transcriptome expression profiles in AS mice strengthen the evidence for molecular cross talk between Ube3a protein and sex hormone receptors or their elicited pathways. These interactions are essential for understanding Ube3a deletion effects, beyond its E3-ligase activity.

Adult Ube3a Gene Reinstatement Restores the Electrophysiological Deficits of Prefrontal Cortex Layer 5 Neurons in a Mouse Model of Angelman Syndrome

E3 ubiquitin ligase (UBE3A) levels in the brain need to be tightly regulated, as loss of functional UBE3A protein is responsible for the severe neurodevelopmental disorder Angelman syndrome (AS), whereas increased activity of UBE3A is associated with nonsyndromic autism. Given the role of mPFC in neurodevelopmental disorders including autism, we aimed to identify the functional changes resulting from loss of UBE3A in infralimbic and prelimbic mPFC areas in a mouse model of AS. Whole-cell recordings from layer 5 mPFC pyramidal neurons obtained in brain slices from adult mice of both sexes revealed that loss of UBE3A results in a strong decrease of spontaneous inhibitory transmission and increase of spontaneous excitatory transmission potentially leading to a marked excitation/inhibition imbalance. Additionally, we found that loss of UBE3A led to decreased excitability and increased threshold for action potential of layer 5 fast spiking interneurons without significantly affecting the excitability of pyramidal neurons. Because we previously showed that AS mouse behavioral phenotypes are reversible upon Ube3a gene reactivation during a restricted period of early postnatal development, we investigated whether Ube3a gene reactivation in a fully mature brain could reverse any of the identified physiological deficits. In contrast to our previously reported behavioral findings, restoring UBE3A levels in adult animals fully rescued all the identified physiological deficits of mPFC neurons. Moreover, the kinetics of reversing these synaptic deficits closely followed the reinstatement of UBE3A protein level. Together, these findings show a striking dissociation between the rescue of behavioral and physiological deficits.SIGNIFICANCE STATEMENT Here we describe significant physiological deficits in the mPFC of an Angelman syndrome mouse model. We found a marked change in excitatory/inhibitory balance, as well as decreased excitability of fast spiking interneurons. A promising treatment strategy for Angelman syndrome is aimed at restoring UBE3A expression by activating the paternal UBE3A gene. Here we find that the physiological changes in the mPFC are fully reversible upon gene reactivation, even when the brain is fully mature. This indicates that there is no critical developmental window for reversing the identified physiological deficits in mPFC.

Touchscreen learning deficits in Ube3a, Ts65Dn and Mecp2 mouse models of neurodevelopmental disorders with intellectual disabilities

Mutant mouse models of neurodevelopmental disorders with intellectual disabilities provide useful translational research tools, especially in cases where robust cognitive deficits are reproducibly detected. However, motor, sensory and/or health issues consequent to the mutation may introduce artifacts that preclude testing in some standard cognitive assays. Touchscreen learning and memory tasks in small operant chambers have the potential to circumvent these confounds. Here we use touchscreen visual discrimination learning to evaluate performance in the maternally derived Ube3a mouse model of Angelman syndrome, the Ts65Dn trisomy mouse model of Down syndrome, and the Mecp2Bird mouse model of Rett syndrome. Significant deficits in acquisition of a 2-choice visual discrimination task were detected in both Ube3a and Ts65Dn mice. Procedural control measures showed no genotype differences during pretraining phases or during acquisition. Mecp2 males did not survive long enough for touchscreen training, consistent with previous reports. Most Mecp2 females failed on pretraining criteria. Significant impairments on Morris water maze spatial learning were detected in both Ube3a and Ts65Dn, replicating previous findings. Abnormalities on rotarod in Ube3a, and on open field in Ts65Dn, replicating previous findings, may have contributed to the observed acquisition deficits and swim speed abnormalities during water maze performance. In contrast, these motor phenotypes do not appear to have affected touchscreen procedural abilities during pretraining or visual discrimination training. Our findings of slower touchscreen learning in 2 mouse models of neurodevelopmental disorders with intellectual disabilities indicate that operant tasks offer promising outcome measures for the preclinical discovery of effective pharmacological therapeutics.

Enhanced Operant Extinction and Prefrontal Excitability in a Mouse Model of Angelman Syndrome

Angelman syndrome (AS), a neurodevelopmental disorder associated with intellectual disability, is caused by loss of maternal allele expression of UBE3A in neurons. Mouse models of AS faithfully recapitulate disease phenotypes across multiple domains, including behavior. Yet in AS, there has been only limited study of behaviors encoded by the prefrontal cortex, a region broadly involved in executive function and cognition. Because cognitive impairment is a core feature of AS, it is critical to develop behavioral readouts of prefrontal circuit function in AS mouse models. One such readout is behavioral extinction, which has been well described mechanistically and relies upon prefrontal circuits in rodents. Here we report exaggerated operant extinction in male AS model mice, concomitant with enhanced excitability in medial prefrontal neurons from male and female AS model mice. Abnormal behavior was specific to operant extinction, as two other prefrontally dependent tasks (cued fear extinction and visuospatial discrimination) were largely normal in AS model mice. Inducible deletion of Ube3a during adulthood was not sufficient to drive abnormal extinction, supporting the hypothesis that there is an early critical period for development of cognitive phenotypes in AS. This work represents the first formal experimental analysis of prefrontal circuit function in AS, and identifies operant extinction as a useful experimental paradigm for modeling cognitive aspects of AS in mice.SIGNIFICANCE STATEMENT Prefrontal cortex encodes "high-level" cognitive processes. Thus, understanding prefrontal function is critical in neurodevelopmental disorders where cognitive impairment is highly penetrant. Angelman syndrome is a neurodevelopmental disorder associated with speech and motor impairments, an outwardly happy demeanor, and intellectual disability. We describe a behavioral phenotype in a mouse model of Angelman syndrome and related abnormalities in prefrontal cortex function. We hypothesize that robust and reliable prefrontally encoded behavior may be used to model cognitive impairments in Angelman syndrome.

Enhanced Transmission at the Calyx of Held Synapse in a Mouse Model for Angelman Syndrome

The neurodevelopmental disorder Angelman syndrome (AS) is characterized by intellectual disability, motor dysfunction, distinct behavioral aspects, and epilepsy. AS is caused by a loss of the maternally expressed UBE3A gene, and many of the symptoms are recapitulated in a Ube3a mouse model of this syndrome. At the cellular level, changes in the axon initial segment (AIS) have been reported, and changes in vesicle cycling have indicated the presence of presynaptic deficits. Here we studied the role of UBE3A in the auditory system by recording synaptic transmission at the calyx of Held synapse in the medial nucleus of the trapezoid body (MNTB) through in vivo whole cell and juxtacellular recordings. We show that MNTB principal neurons in Ube3a mice exhibit a hyperpolarized resting membrane potential, an increased action potential (AP) amplitude and a decreased AP half width. Moreover, both the pre- and postsynaptic AP in the calyx of Held synapse of Ube3a mice showed significantly faster recovery from spike depression. An increase in AIS length was observed in the principal MNTB neurons of Ube3a mice, providing a possible substrate for these gain-of-function changes. Apart from the effect on APs, we also observed that EPSPs showed decreased short-term synaptic depression (STD) during long sound stimulations in AS mice, and faster recovery from STD following these tones, which is suggestive of a presynaptic gain-of-function. Our findings thus provide in vivo evidence that UBE3A plays a critical role in controlling synaptic transmission and excitability at excitatory synapses.

RNF8/UBC13 ubiquitin signaling suppresses synapse formation in the mammalian brain

Although ubiquitin ligases have been implicated in autism, their roles and mechanisms in brain development remain incompletely understood. Here, we report that in vivo knockdown or conditional knockout of the autism-linked ubiquitin ligase RNF8 or associated ubiquitin-conjugating enzyme UBC13 in rodent cerebellar granule neurons robustly increases the number of parallel fiber presynaptic boutons and functional parallel fiber/Purkinje cell synapses. In contrast to the role of nuclear RNF8 in proliferating cells, RNF8 operates in the cytoplasm in neurons to suppress synapse differentiation in vivo. Proteomics analyses reveal that neuronal RNF8 interacts with the HECT domain protein HERC2 and scaffold protein NEURL4, and knockdown of HERC2 or NEURL4 phenocopies the inhibition of RNF8/UBC13 signaling on synapse differentiation. In behavior analyses, granule neuron-specific knockout of RNF8 or UBC13 impairs cerebellar-dependent learning. Our study defines RNF8 and UBC13 as components of a novel cytoplasmic ubiquitin-signaling network that suppresses synapse formation in the brain.

Enhanced Nociception in Angelman Syndrome Model Mice

Angelman syndrome (AS) is a severe neurodevelopmental disorder caused by mutation or deletion of the maternal UBE3A allele. The maternal UBE3A allele is expressed in nearly all neurons of the brain and spinal cord, whereas the paternal UBE3A allele is repressed by an extremely long antisense transcript (UBE3A-ATS). Little is known about expression of UBE3A in the peripheral nervous system, where loss of maternal UBE3A might contribute to AS phenotypes. Here we sought to examine maternal and paternal Ube3a expression in DRGs neurons and to evaluate whether nociceptive responses were affected in AS model mice (global deletion of maternal Ube3a allele; Ube3a^m-/p+). We found that most large-diameter proprioceptive and mechanosensitive DRG neurons expressed maternal Ube3a and paternal Ube3a-ATS In contrast, most small-diameter neurons expressed Ube3a biallelically and had low to undetectable levels of Ube3a-ATS Analysis of single-cell DRG transcriptomes further suggested that Ube3a is expressed monoallelically in myelinated large-diameter neurons and biallelically in unmyelinated small-diameter neurons. Behavioral responses to some noxious thermal and mechanical stimuli were enhanced in male and female AS model mice; however, nociceptive responses were not altered by the conditional deletion of maternal Ube3a in the DRG. These data suggest that the enhanced nociceptive responses in AS model mice are due to loss of maternal Ube3a in the central, but not peripheral, nervous system. Our study provides new insights into sensory processing deficits associated with AS.SIGNIFICANCE STATEMENT Angelman syndrome (AS) is a neurodevelopmental disorder caused by loss or mutation of the maternal UBE3A allele. While sensory processing deficits are frequently associated with AS, it is currently unknown whether Ube3a is expressed in peripheral sensory neurons or whether maternal deletion of Ube3a affects somatosensory responses. Here, we found that Ube3a is primarily expressed from the maternally inherited allele in myelinated large-diameter sensory neurons and biallelically expressed in unmyelinated small-diameter neurons. Nociceptive responses to select noxious thermal and mechanical stimuli were enhanced following global, but not sensory neuron-specific, deletion of maternal Ube3a in mice. These data suggest that maternal loss of Ube3a affects nociception via a central, but not peripheral mechanism, with implications for AS.

Cerebellar and Striatal Pathologies in Mouse Models of Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a complex neurodevelopmental condition with a strong genetic component. To date, several hundred different genetic mutations have been identified to play a role in its aetiology. The heterogeneity of genetic abnormalities combined with the different brain regions where aberrations are found makes the search for causative mechanisms a daunting task. Even within a limited number of brain regions, a myriad of different neural circuit dysfunctions may lead to ASD. Here, we review mouse models that incorporate mutations of ASD risk genes causing pathologies in the cerebellum and striatum and highlight the vulnerability of related circuit dysfunctions within these brain regions in ASD pathophysiology.

Angelman syndrome: Current and emerging therapies in 2016

Angelman syndrome (AS) is a severe neurodevelopmental disorder caused by a loss of the maternally-inherited UBE3A; the paternal UBE3A is silenced in neurons by a mechanism involving an antisense transcript (UBE3A-AS) at the unmethylated paternal locus. We reviewed all published information on the clinical trials that have been completed as well as the publicly available information on ongoing trials of therapies in AS. To date, all clinical trials that strove to improve neurodevelopment in AS have been unsuccessful. Attempts at hypermethylating the maternal locus through dietary compounds were ineffective. The results of an 8-week open-label trial using minocycline as a matrix metalloproteinase-9 inhibitor were inconclusive, while a subsequent randomized placebo-controlled trial suggested that treatment with minocycline for 8 weeks did not result in any neurodevelopmental gains. A 1-year randomized placebo-controlled trial using levodopa to alter the phosphorylation of calcium/calmodulin-dependent kinase II did not lead to any improvement in neurodevelopment. Topoisomerase inhibitors and antisense oligonucleotides are being developed to directly inhibit UBE3A-AS. Artificial transcription factors are being developed to "super activate" UBE3A or inhibit UBE3A-AS. Other strategies targeting specific pathways are briefly discussed. We also reviewed the medications that are currently used to treat seizures and sleep disturbances, which are two of the more common complications of AS. © 2016 Wiley Periodicals, Inc.

LTD-like molecular pathways in developmental synaptic pruning

In long-term depression (LTD) at synapses in the adult brain, synaptic strength is reduced in an experience-dependent manner. LTD thus provides a cellular mechanism for information storage in some forms of learning. A similar activity-dependent reduction in synaptic strength also occurs in the developing brain and there provides an essential step in synaptic pruning and the postnatal development of neural circuits. Here we review evidence suggesting that LTD and synaptic pruning share components of their underlying molecular machinery and may thus represent two developmental stages of the same type of synaptic modulation that serve different, but related, functions in neural circuit plasticity. We also assess the relationship between LTD and synaptic pruning in the context of recent findings of LTD dysregulation in several mouse models of autism spectrum disorder (ASD) and discuss whether LTD deficits can indicate impaired pruning processes that are required for proper brain development.

From Cortical and Subcortical Grey Matter Abnormalities to Neurobehavioral Phenotype of Angelman Syndrome: A Voxel-Based Morphometry Study

Angelman syndrome (AS) is a rare neurogenetic disorder due to loss of expression of maternal ubiquitin-protein ligase E3A (UBE3A) gene. It is characterized by severe developmental delay, speech impairment, movement or balance disorder and typical behavioral uniqueness. Affected individuals show normal magnetic resonance imaging (MRI) findings, although mild dysmyelination may be observed. In this study, we adopted a quantitative MRI analysis with voxel-based morphometry (FSL-VBM) method to investigate disease-related changes in the cortical/subcortical grey matter (GM) structures. Since 2006 to 2013 twenty-six AS patients were assessed by our multidisciplinary team. From those, sixteen AS children with confirmed maternal 15q11-q13 deletions (mean age 7.7 ± 3.6 years) and twenty-one age-matched controls were recruited. The developmental delay and motor dysfunction were assessed using Bayley III and Gross Motor Function Measure (GMFM). Principal component analysis (PCA) was applied to the clinical and neuropsychological datasets. High-resolution T1-weighted images were acquired and FSL-VBM approach was applied to investigate differences in the local GM volume and to correlate clinical and neuropsychological changes in the regional distribution of GM. We found bilateral GM volume loss in AS compared to control children in the striatum, limbic structures, insular and orbitofrontal cortices. Voxel-wise correlation analysis with the principal components of the PCA output revealed a strong relationship with GM volume in the superior parietal lobule and precuneus on the left hemisphere. The anatomical distribution of cortical/subcortical GM changes plausibly related to several clinical features of the disease and may provide an important morphological underpinning for clinical and neurobehavioral symptoms in children with AS.

GABAergic Neuron-Specific Loss of Ube3a Causes Angelman Syndrome-Like EEG Abnormalities and Enhances Seizure Susceptibility

Loss of maternal UBE3A causes Angelman syndrome (AS), a neurodevelopmental disorder associated with severe epilepsy. We previously implicated GABAergic deficits onto layer (L) 2/3 pyramidal neurons in the pathogenesis of neocortical hyperexcitability, and perhaps epilepsy, in AS model mice. Here we investigate consequences of selective Ube3a loss from either GABAergic or glutamatergic neurons, focusing on the development of hyperexcitability within L2/3 neocortex and in broader circuit and behavioral contexts. We find that GABAergic Ube3a loss causes AS-like increases in neocortical EEG delta power, enhances seizure susceptibility, and leads to presynaptic accumulation of clathrin-coated vesicles (CCVs)-all without decreasing GABAergic inhibition onto L2/3 pyramidal neurons. Conversely, glutamatergic Ube3a loss fails to yield EEG abnormalities, seizures, or associated CCV phenotypes, despite impairing tonic inhibition onto L2/3 pyramidal neurons. These results substantiate GABAergic Ube3a loss as the principal cause of circuit hyperexcitability in AS mice, lending insight into ictogenic mechanisms in AS.