mTORC1-S6K1 inhibition or mTORC2 activation improves hippocampal synaptic plasticity and learning in Angelman syndrome mice

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.

The effect of AKT inhibition in α-synuclein-dependent neurodegeneration

Parkinson's disease (PD) is a progressive neurodegenerative disorder affecting millions of individuals worldwide. A hallmark of PD pathology is the accumulation of α-synuclein (α-Syn), a small protein known to support neuronal development and function. However, in PD, α-Syn cumulatively misfolds into toxic aggregates that disrupt cellular processes and contribute to neuronal damage and neurodegeneration. Previous studies implicated the AKT signaling pathway in α-Syn toxicity in cellular models of PD, suggesting AKT as a potential therapeutic target. Here, we investigated the effect of AKT inhibition in a Drosophila model of synucleinopathy. We observed that administration of the AKT inhibitor, A-443654 led to mild improvements in both survival and motor function in flies expressing human α-Syn. Genetic studies revealed that reduction of AKT levels decreased α-Syn protein levels, concomitant with improved physiological outcomes. The protective effects of AKT reduction appear to operate through the fly ortholog of NF-κB, Relish, suggesting a link between AKT and NF-κB in regulating α-Syn levels. These findings highlight the AKT cascade as a potential therapeutic target for synucleinopathies and provide insights into mechanisms that could be utilized to reduce α-Syn toxicity in PD and related disorders, such as multiple system atrophy.

Drug Treatments for Neurodevelopmental Disorders: Targeting Signaling Pathways and Homeostasis

PURPOSE OF THE REVIEW

Preclinical and clinical evidence support the notion that neurodevelopmental disorders (NDDs) are synaptic disorders, characterized by excitatory-inhibitory imbalance. Despite this, NDD drug development programs targeting glutamate or gamma-aminobutyric acid (GABA) receptors have been largely unsuccessful. Nonetheless, recent drug trials in Rett syndrome (RTT), fragile X syndrome (FXS), and other NDDs targeting other mechanisms have met their endpoints. The purpose of this review is to identify the basis of these successful studies.

RECENT FINDINGS

Despite increasing evidence of disruption in synaptic homeostasis, most genetic variants associated with NDDs implicate proteins involved in cell regulation and not in neurotransmission. Metabolic processes, in particular mitochondrial function, appear to play a role in NDD pathophysiology. NDDs are also characterized by distinctive cell signaling abnormalities, which link cellular and synaptic homeostasis. Recent successful trials in NDDs, including those of trofinetide, the first drug specifically approved for one of these disorders (i.e., RTT), implicate the targeting of downstream processes (i.e., signaling pathways) rather than neurotransmitter receptors. Recent positive drug studies in NDDs and their underlying mechanisms, in conjunction with new knowledge on the pathophysiology of these disorders, support the concept that targeting signaling and cellular and synaptic homeostasis may be a preferred approach for ameliorating synaptic abnormalities in many NDDs.

Alterations of synaptic plasticity in Angelman syndrome model mice are rescued by 5-HT7R stimulation

Angelman syndrome (AS) is a severe neurodevelopmental disorder characterized by motor disfunction, seizures, intellectual disability, speech deficits, and autism-like behavior, showing high comorbidity with Autism Spectrum Disorders (ASD). It is known that stimulation of the serotonin receptor 7 (5-HT7R) can rescue some of the behavioral and neuroplasticity dysfunctions in animal models of Fragile X and Rett syndrome, two pathologies associated with ASD. In view of these observations, we hypothesised that alterations of 5-HT7R signalling might also be involved in AS. To test this hypothesis, we stimulated 5-HT7R with the selective agonist LP-211 to investigate its possible beneficial effects on synaptic dysfunctions and altered behavior in the AS mice model. In mutant mice, we observed impairment of the synaptic machinery of protein synthesis, which was reversed by 5-HT7R activation. Moreover, stimulation of 5-HT7R was able to: i) enhance dendritic spine density in hippocampal neurons, which was reduced in AS mice; ii) restore impaired long-term potentiation (LTP) in hippocampal slices of the AS mice; iii) improve cognitive performance of the mutant animals subjected to the fear conditioning paradigm. Altogether, our results, showing beneficial effects of 5-HT7R stimulation in restoring molecular and cognitive deficits associated with AS, suggest that targeting 5-HT7R could be a promising therapeutic approach for the pathology.

Interlinked destinies: How ubiquitin-proteasome and autophagy systems underpin neurocognitive outcomes

The protein homeostasis, or proteostasis, is maintained through the coupling of two pivotal systems: the ubiquitin-proteasome and autophagy. Cumulative evidence has suggested E3 ubiquitin ligases specifically play a central role in this coupling, ensuring the regulation of synaptic and cognitive functions. Defects in these ligases have been identified as hallmarks in a range of neurodevelopmental and neurodegenerative disorders. Recent literature has spotlighted the E3 ubiquitin ligase, UBE3A, as a key player in this domain. Dysregulation or loss of UBE3A function has been linked to disrupted proteostasis, leading to synaptic and cognitive anomalies. Notably, such defects are prominently observed in conditions like Angelman syndrome, a neurodevelopmental disorder characterized by severe cognitive impairments. The emerging understanding of UBE3A's role in bridging the ubiquitin-proteasome and autophagy systems offers a promising therapeutic avenue. Targeting the defective pathways caused by UBE3A loss could pave the way for innovative treatments, potentially ameliorating the cognitive deficits observed in neurological disorders like Angelman syndrome. As the scientific community delves deeper into the molecular intricacies of E3 ubiquitin ligases, there is burgeoning hope for devising effective interventions for associated neurological conditions.

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.

Pharmacological inhibition of S6K1 rescues synaptic deficits and attenuates seizures and depression in chronic epileptic rats

BACKGROUND

Recent studies have shown that mTOR signaling plays an important role in synaptic plasticity. However, the function of S6K1, the mechanistic target of rapamycin kinase complex 1 (mTORC1) substrate, in epilepsy remains unknown.

AIMS

Our present study aimed to explore the mechanism by which S6K1 is involved in chronic epilepsy.

METHODS

First, immunostaining was used to measure neurite length and complexity in kainic acid (KA)-treated primary cultured neurons treated with PF-4708671, a highly selective S6K1 inhibitor. We obtained evidence for the role of S6K1 in protecting and promoting neuronal growth and development in vitro. Next, to explore the function and mechanism of the S6K1 inhibitor in epilepsy, a pilocarpine-induced chronic epileptic rat model was established. In vivo electrophysiology (including local field potentiation in CA1 and long-term potentiation), depression/anxiety-like behavior tests, and Golgi staining were performed to assess seizure behavior, power spectral density, depression/anxiety-like behavior, and synaptic plasticity. Furthermore, western blotting was applied to explore the potential molecular mechanisms.

RESULTS

We found that inhibition of S6K1 expression significantly decreased seizures and depression-like behavior and restored power at low frequencies (1-80 Hz), especially in the delta, theta, and alpha bands, in chronic epileptic rats. In addition, PF-4708671 reversed the LTP defect in hippocampal CA3-CA1 and corrected spine loss and dendritic pathology.

CONCLUSION

In conclusion, our data suggest that inhibition of S6K1 attenuates seizures and depression in chronic epileptic rats via the rescue of synaptic structural and functional deficits. Given the wide range of physiological functions of mTOR, inhibition of its effective but relatively simple functional downstream molecules is a promising target for the development of drugs for epilepsy.

The mTORC2 signaling network: targets and cross-talks

The mechanistic target of rapamycin, mTOR, controls cell metabolism in response to growth signals and stress stimuli. The cellular functions of mTOR are mediated by two distinct protein complexes, mTOR complex 1 (mTORC1) and mTORC2. Rapamycin and its analogs are currently used in the clinic to treat a variety of diseases and have been instrumental in delineating the functions of its direct target, mTORC1. Despite the lack of a specific mTORC2 inhibitor, genetic studies that disrupt mTORC2 expression unravel the functions of this more elusive mTOR complex. Like mTORC1 which responds to growth signals, mTORC2 is also activated by anabolic signals but is additionally triggered by stress. mTORC2 mediates signals from growth factor receptors and G-protein coupled receptors. How stress conditions such as nutrient limitation modulate mTORC2 activation to allow metabolic reprogramming and ensure cell survival remains poorly understood. A variety of downstream effectors of mTORC2 have been identified but the most well-characterized mTORC2 substrates include Akt, PKC, and SGK, which are members of the AGC protein kinase family. Here, we review how mTORC2 is regulated by cellular stimuli including how compartmentalization and modulation of complex components affect mTORC2 signaling. We elaborate on how phosphorylation of its substrates, particularly the AGC kinases, mediates its diverse functions in growth, proliferation, survival, and differentiation. We discuss other signaling and metabolic components that cross-talk with mTORC2 and the cellular output of these signals. Lastly, we consider how to more effectively target the mTORC2 pathway to treat diseases that have deregulated mTOR signaling.

Stabilizing Immature Dendritic Spines in the Auditory Cortex: A Key Mechanism for mTORC1-Mediated Enhancement of Long-Term Fear Memories

Mammalian target of rapamycin (mTOR) pathway has emerged as a key molecular mechanism underlying memory processes. Although mTOR inhibition is known to block memory processes, it remains elusive whether and how an enhancement of mTOR signaling may improve memory processes. Here we found in male mice that the administration of VO-OHpic, an inhibitor of the phosphatase and tensin homolog (PTEN) that negatively modulates AKT-mTOR pathway, enhanced auditory fear memory for days and weeks, while it left short-term memory unchanged. Memory enhancement was associated with a long-lasting increase in immature-type dendritic spines of pyramidal neurons into the auditory cortex. The persistence of spine remodeling over time arose by the interplay between PTEN inhibition and memory processes, as VO-OHpic induced only a transient immature spine growth in the somatosensory cortex, a region not involved in long-term auditory memory. Both the potentiation of fear memories and increase in immature spines were hampered by rapamycin, a selective inhibitor of mTORC1. These data revealed that memory can be potentiated over time by the administration of a selective PTEN inhibitor. In addition to disclosing new information on the cellular mechanisms underlying long-term memory maintenance, our study provides new insights on the molecular processes that aid enhancing memories over time.SIGNIFICANCE STATEMENT The neuronal mechanisms that may help improve the maintenance of long-term memories are still elusive. The inhibition of mammalian-target of rapamycin (mTOR) signaling shows that this pathway plays a crucial role in synaptic plasticity and memory formation. However, whether its activation may strengthen long-term memory storage is unclear. We assessed the consequences of positive modulation of AKT-mTOR pathway obtained by VO-OHpic administration, a phosphatase and tensin homolog inhibitor, on memory retention and underlying synaptic modifications. We found that mTOR activation greatly enhanced memory maintenance for weeks by producing a long-lasting increase of immature-type dendritic spines in pyramidal neurons of the auditory cortex. These results offer new insights on the cellular and molecular mechanisms that can aid enhancing memories over time.

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.

Quantitative proteomics and phosphoproteomics of PP2A-PPP2R5D variants reveal deregulation of RPS6 phosphorylation via converging signaling cascades

Genetic germline variants of PPP2R5D (encoding: phosphoprotein phosphatase 2 regulatory protein 5D) result in PPP2R5D-related disorder (Jordan's Syndrome), which is characterized by intellectual disability, hypotonia, seizures, macrocephaly, autism spectrum disorder, and delayed motor skill development. The disorder originates from de novo single nucleotide mutations, generating missense variants that act in a dominant manner. Pathogenic mutations altering 13 different amino acids have been identified, with the E198K variant accounting for ∼40% of reported cases. However, the generation of a heterozygous E198K variant cell line to study the molecular effects of the pathogenic mutation has been challenging. Here, we use CRISPR-PRIME genomic editing to introduce a transition (c.592G>A) in a single PPP2R5D allele in HEK293 cells, generating E198K-heterozygous lines to complement existing E420K variant lines. We generate global protein and phosphorylation profiles of WT, E198K, and E420K cell lines and find unique and shared changes between variants and WT cells in kinase- and phosphatase-controlled signaling cascades. We observed ribosomal protein S6 (RPS6) hyperphosphorylation as a shared signaling alteration, indicative of increased ribosomal protein S6-kinase activity. Treatment with rapamycin or an RPS6-kinase inhibitor (LY2584702) suppressed RPS6 phosphorylation in both, suggesting upstream activation of mTORC1/p70S6K. Intriguingly, our data suggests ERK-dependent activation of mTORC1 in both E198K and E420K variant cells, with additional AKT-mediated mTORC1 activation in the E420K variant. Thus, although upstream activation of mTORC1 differs between PPP2R5D-related disorder genotypes, inhibition of mTORC1 or RPS6 kinases warrants further investigation as potential therapeutic strategies for patients.

Dopamine D3 Receptor Modulates Akt/mTOR and ERK1/2 Pathways Differently during the Reinstatement of Cocaine-Seeking Behavior Induced by Psychological versus Physiological Stress

Stress triggers relapses in cocaine use that engage the activity of memory-related nuclei, such as the basolateral amygdala (BLA) and dentate gyrus (DG). Preclinical research suggests that D3 receptor (D3R) antagonists may be a promising means to attenuate cocaine reward and relapse. As D3R regulates the activity of the Akt/mTOR and MEK/ERK_1/2 pathways, we assessed the effects of SB-277011-A, a D3R antagonist, on the activity of these kinases during the reinstatement of cocaine-induced conditioned place preference (CPP) induced by psychological (restraint) and physiological (tail pinch) stress. Both stimuli reactivated an extinguished cocaine-CPP, but only restrained animals decreased their locomotor activity during reinstatement. Cocaine-seeking behavior reactivation was correlated with decreased p-Akt, p-mTOR, and p-ERK_1/2 activation in both nuclei of restrained animals. While a D3R blockade prevented stress-induced CPP reinstatement and plasma corticosterone enhancement, SB-277011-A distinctly modulated Akt, mTOR, and ERK_1/2 activation depending on the stressor and the dose used. Our data support the involvement of corticosterone in the SB-277011-A effects in restrained animals. Additionally, the ratios p-mTOR/mTOR and/or p-ERK_1/2 /ERK_1/2 in the BLA during stress-induced relapse seem to be related to the locomotor activity of animals receiving 48 mg/kg of the antagonist. Hence, our study indicates the D3R antagonist's efficacy to prevent stress-induced relapses in drug use through distinct modulation of Akt/mTOR and MEK/ERK_1/2 pathways in memory-processing nuclei.

Excessive Protein Accumulation and Impaired Autophagy in the Hippocampus of Angelman Syndrome Modeled in Mice

BACKGROUND

Angelman syndrome (AS), a neurodevelopmental disorder caused by abnormalities of the 15q11.2-q13.1 chromosome region, is characterized by impairment of cognitive and motor functions, sleep problems, and seizures. How the genetic defects of AS produce these neurological symptoms is unclear. Mice modeling AS (AS mice) accumulate activity-regulated cytoskeleton-associated protein (ARC/ARG3.1), a neuronal immediate early gene (IEG) critical for synaptic plasticity. This accumulation suggests an altered protein metabolism.

METHODS

Focusing on the dorsal hippocampus (dHC), a brain region critical for memory formation and cognitive functions, we assessed levels and tissue distribution of IEGs, de novo protein synthesis, and markers of protein synthesis, endosomes, autophagy, and synaptic functions in AS mice at baseline and following learning. We also tested autophagic flux and memory retention following autophagy-promoting treatment.

RESULTS

AS dHC exhibited accumulation of IEGs ARC, FOS, and EGR1; autophagy proteins MLP3B, SQSTM1, and LAMP1; and reduction of the endosomal protein RAB5A. AS dHC also had increased levels of de novo protein synthesis, impaired autophagic flux with accumulation of autophagosome, and altered synaptic protein levels. Contextual fear conditioning significantly increased levels of IEGs and autophagy proteins, de novo protein synthesis, and autophagic flux in the dHC of normal mice, but not in AS mice. Enhancing autophagy in the dHC alleviated AS-related memory and autophagic flux impairments.

CONCLUSIONS

A major biological deficit of AS brain is a defective protein metabolism, particularly that dynamically regulated by learning, resulting in stalled autophagy and accumulation of neuronal proteins. Activating autophagy ameliorates AS cognitive impairments and dHC protein accumulation.

ZeXieYin Formula alleviates TMAO-induced cognitive impairment by restoring synaptic plasticity damage

ETHNOPHARMACOLOGICAL RELEVANCE

Treating cognitive impairment is a challenging and necessary research topic. ZeXieYin Formula (ZXYF), is a traditional herbal formula documented in the book of HuangDiNeiJing. Our previous studies demonstrated the ameliorative effects of ZXYF on atherosclerosis by reducing the plasma trimethylamine oxide (TMAO) level. TMAO is a metabolite of gut microorganisms, our recent research found that the increasing level of TMAO may have adverse effects on cognitive functions.

AIM OF THE STUDY

Our study mainly focused on the therapeutic effects of ZXYF on TMAO-induced cognitive impairment in mice and explored its underlying mechanism.

MATERIALS AND METHODS

After the TMAO-induced cognitive impairment mice models were established, we applied behavioral tests to estimate the learning and memory ability of the ZXYF intervention mice. Liquid chromatography-mass spectrometry (LC-MS) was used to quantify the TMAO levels in plasma and the brain. The effects of ZXYF on the hippocampal synaptic structure and the neurons were observed by transmission electron microscopy (TEM) and Nissl staining. In addition, western-blotting (WB) and immunohistochemical (IHC) staining were used to detect the level of related proteins in the synaptic structure and further verify the changes in synaptic plasticity and the mTOR pathway after ZXYF administration.

RESULTS

Behavioral tests showed that the learning and memory ability of mice impaired after a period of TMAO intervention and ZXYF could alleviate these changes. A series of results showed that ZXYF partly restored the damage of hippocampal synapse and neurons in TMAO-induced mice, at the same time, the expression of synapse-related proteins and mTOR pathway-related proteins were significantly regulated compared with the damage caused by TMAO.

CONCLUSION

ZXYF could alleviate TMAO-induced cognitive impairment by improving synaptic function, reducing neuronal damage, regulating synapse-associated proteins, and regulating the mTOR signaling pathway.

Quantitative proteomics and phosphoproteomics of PPP2R5D variants reveal deregulation of RPS6 phosphorylation through converging signaling cascades

Variants in the phosphoprotein phosphatase-2 regulatory protein-5D gene ( PPP2R5D ) cause the clinical phenotype of Jordan's Syndrome (PPP2R5D-related disorder), which includes intellectual disability, hypotonia, seizures, macrocephaly, autism spectrum disorder and delayed motor skill development. The disorder originates from de novo single nucleotide mutations, generating missense variants that act in a dominant manner. Pathogenic mutations altering 13 different amino acids have been identified, with the E198K variant accounting for ∼40% of reported cases. Here, we use CRISPR-PRIME genomic editing to introduce a transition (c.592G>A) in the PPP2R5D allele in a heterozygous manner in HEK293 cells, generating E198K-heterozygous lines to complement existing E420K variant lines. We generate global protein and phosphorylation profiles of wild-type, E198K, and E420K cell lines and find unique and shared changes between variants and wild-type cells in kinase- and phosphatase-controlled signaling cascades. As shared signaling alterations, we observed ribosomal protein S6 (RPS6) hyperphosphorylation, indicative of increased ribosomal protein S6-kinase activity. Rapamycin treatment suppressed RPS6 phosphorylation in both, suggesting activation of mTORC1. Intriguingly, our data suggest AKT-dependent (E420K) and -independent (E198K) activation of mTORC1. Thus, although upstream activation of mTORC1 differs between PPP2R5D-related disorder genotypes, treatment with rapamycin or a p70S6K inhibitor warrants further investigation as potential therapeutic strategies for patients.

Lack of UBE3A-Mediated Regulation of Synaptic SK2 Channels Contributes to Learning and Memory Impairment in the Female Mouse Model of Angelman Syndrome

Angelman syndrome (AS) is a rare neurodevelopmental disorder characterized by severe developmental delay, motor impairment, language and cognition deficits, and often with increased seizure activity. AS is caused by deficiency of UBE3A, which is both an E3 ligase and a cofactor for transcriptional regulation. We previously showed that the small conductance potassium channel protein SK2 is a UBE3A substrate, and that increased synaptic SK2 levels contribute to impairments in synaptic plasticity and fear-conditioning memory, as inhibition of SK2 channels significantly improved both synaptic plasticity and fear memory in male AS mice. In the present study, we investigated UBE3a-mediated regulation of synaptic plasticity and fear-conditioning in female AS mice. Results from both western blot and immunofluorescence analyses showed that synaptic SK2 levels were significantly increased in hippocampus of female AS mice, as compared to wild-type (WT) littermates. Like in male AS mice, long-term potentiation (LTP) was significantly reduced while long-term depression (LTD) was enhanced at hippocampal CA3-CA1 synapses of female AS mice, as compared to female WT mice. Both alterations were significantly reduced by treatment with the SK2 inhibitor, apamin. The shunting effect of SK2 channels on NMDA receptor was significantly larger in female AS mice as compared to female WT mice. Female AS mice also showed impairment in both contextual and tone memory recall, and this impairment was significantly reduced by apamin treatment. Our results indicate that like male AS mice, female AS mice showed significant impairment in both synaptic plasticity and fear-conditioning memory due to increased levels of synaptic SK2 channels. Any therapeutic strategy to reduce SK2-mediated inhibition of NMDAR should be beneficial to both male and female patients.

The AKT modulator A-443654 reduces α-synuclein expression and normalizes ER stress and autophagy

Accumulation of α-synuclein is a main underlying pathological feature of Parkinson's disease and α-synucleinopathies, for which lowering expression of the α-synuclein gene (SNCA) is a potential therapeutic avenue. Using a cell-based luciferase reporter of SNCA expression we performed a quantitative high-throughput screen of 155,885 compounds and identified A-443654, an inhibitor of the multiple functional kinase AKT, as a potent inhibitor of SNCA. HEK-293 cells with CAG repeat expanded ATXN2 (ATXN2-Q58 cells) have increased levels of α-synuclein. We found that A-443654 normalized levels of both SNCA mRNA and α-synuclein monomers and oligomers in ATXN2-Q58 cells. A-443654 also normalized levels of α-synuclein in fibroblasts and iPSC-derived dopaminergic neurons from a patient carrying a triplication of the SNCA gene. Analysis of autophagy and endoplasmic reticulum stress markers showed that A-443654 successfully prevented α-synuclein toxicity and restored cell function in ATXN2-Q58 cells, normalizing the levels of mTOR, LC3-II, p62, STAU1, BiP, and CHOP. A-443654 also decreased the expression of DCLK1, an inhibitor of α-synuclein lysosomal degradation. Our study identifies A-443654 and AKT inhibition as a potential strategy for reducing SNCA expression and treating Parkinson's disease pathology.

Neuronal activity-induced SUMOylation of Akt1 by PIAS3 is required for long-term potentiation of synaptic transmission

Neuronal activity regulates spatial distribution of the SUMOylation system in cytosolic and dendritic sites, which has been implicated in learning, memory, and underlying synaptic structural and functional remodeling in the hippocampus. However, the functional target proteins for activated small ubiquitin-like modifiers (SUMOs) and downstream molecular consequences behind long-term potentiation (LTP) of synaptic plasticity remain to be elucidated. In this study, we showed that N-methyl-D-aspartate receptor-mediated neuronal activity induced the covalent modification of cytosolic Akt1 by small ubiquitin-like modifier 1 (SUMO1) in rat cortical and hippocampal CA1 neurons. Protein inhibitor of activated STAT3 (PIAS3) was involved in the activity-induced Akt1 SUMO1-ylation, and K64 and K276 residues were major SUMOylated sites. Importantly, Akt1 SUMOylation at K64 and K276 enhanced its enzymatic activity and facilitated T308 phosphorylation. Furthermore, the N-terminal SAP domain of PIAS3 bound Akt1 directly. The disruption of Akt1-PIAS3 interaction by Tat-SAP, a synthetic Tat-fused cell-permeable peptide containing PIAS3 SAP domain, inhibited neuronal activity-induced Akt1 SUMOylation and impaired LTP expression and late phase LTP maintenance in the hippocampus. Correlatedly, Tat-SAP not only blocked the LTP-related extracellular signal-regulated kinase (ERK)1/2-Elk-1-brain-derived neurotrophic factor (BDNF)/Arc signaling, but also disrupted mammalian target of rapamycin (mTOR)-eIF4E-binding protein 1 (4E-BP1) pathway. These findings reveal an activity-induced Akt1 SUMOylation by PIAS3 that contributes to ERK1/2-BDNF/Arc and mTOR-4E-BP1 cascades, and in turn, long-lasting excitatory synaptic responses.

Protein Phosphorylation Signaling Cascades in Autism: The Role of mTOR Pathway

The mammalian target of rapamycin (mTOR) signaling pathway is a central regulator of cell metabolism, growth, and survival in response to hormones, growth factors, nutrients, and stress-induced signals. In this review, we analyzed the studies on the molecular abnormalities of the mTOR-associated signaling cascades in autism spectrum disorders (ASDs) and outlined the prospects for the pathogenicity-targeting pharmacotherapeutic approaches to ASDs, in particular syndromic ASDs. Based on available experimental and clinical data, we suggest that very early detection of molecular abnormalities in the ASD risk groups can be facilitated by using peripheral blood platelets. Also, identification of the time window of critical dysregulations in the described pathways in the ASD risk groups might suggest further research directions leading to more efficacious pharmacotherapeutic interventions in ASDs.

UBE3A reinstatement as a disease-modifying therapy for Angelman syndrome

Half a century ago, Harry Angelman reported three patients with overlapping clinical features, now well known as Angelman syndrome. Angelman syndrome is caused by mutations affecting the maternally inherited UBE3A gene, which encodes an E3-ubiquitin ligase that is critical for typical postnatal brain development. Emerging evidence indicates that UBE3A plays a particularly important role in the nucleus. However, the critical substrates that are controlled by UBE3A remain elusive, which hinders the search for effective treatments. Moreover, given the multitude of signalling mechanisms that are derailed, it is unlikely that targeting a single pathway is going to be very effective. Therefore, expectations are very high for approaches that aim to restore UBE3A protein levels. A particular promising strategy is an antisense oligonucleotide approach, which activates the silenced paternal UBE3A gene. When successful, such treatments potentially offer a disease-modifying therapy for Angelman syndrome and several other neurodevelopmental disorders. What this paper adds Loss of UBE3A affects multiple signalling pathways in the brain. Emerging evidence suggests that UBE3A plays a critical role in the cell nucleus. Trials using antisense oligonucleotides to restore UBE3A levels are continuing.

Distinct Regulation of Dopamine D3 Receptor in the Basolateral Amygdala and Dentate Gyrus during the Reinstatement of Cocaine CPP Induced by Drug Priming and Social Stress

Relapse in the seeking and intake of cocaine is one of the main challenges when treating its addiction. Among the triggering factors for the recurrence of cocaine use are the re-exposure to the drug and stressful events. Cocaine relapse engages the activity of memory-related nuclei, such as the basolateral amygdala (BLA) and the hippocampal dentate gyrus (DG), which are responsible for emotional and episodic memories. Moreover, D3 receptor (D3R) antagonists have recently arisen as a potential treatment for preventing drug relapse. Thus, we have assessed the impact of D3R blockade in the expression of some dopaminergic markers and the activity of the mTOR pathway, which is modulated by D3R, in the BLA and DG during the reinstatement of cocaine-induced conditioned place preference (CPP) evoked by drug priming and social stress. Reinstatement of cocaine CPP paralleled an increasing trend in D3R and dopamine transporter (DAT) levels in the BLA. Social stress, but not drug-induced reactivation of cocaine memories, was prevented by systemic administration of SB-277011-A (a selective D3R antagonist), which was able, however, to impede D3R and DAT up-regulation in the BLA during CPP reinstatement evoked by both stress and cocaine. Concomitant with cocaine CPP reactivation, a diminution in mTOR phosphorylation (activation) in the BLA and DG occurred, which was inhibited by D3R blockade in both nuclei before the social stress episode and only in the BLA when CPP reinstatement was provoked by a cocaine prime. Our data, while supporting a main role for D3R signalling in the BLA in the reactivation of cocaine memories evoked by social stress, indicate that different neural circuits and signalling mechanisms might mediate in the reinstatement of cocaine-seeking behaviours depending upon the triggering stimuli.

CIM6P/IGF-2 Receptor Ligands Reverse Deficits in Angelman Syndrome Model Mice

Angelman syndrome (AS), a genetic disorder that primarily affects the nervous system, is characterized by delayed development, intellectual disability, severe speech impairment, and problems with movement and balance (ataxia). Most affected children also have recurrent seizures (epilepsy). No existing therapies are capable of comprehensively treating the deficits in AS; hence, there is an urgent need to identify new treatments. Here we show that insulin-like growth factor 2 (IGF-2) and mannose-6-phosphate (M6P), ligands of two independent binding sites of the cation-independent M6P/IGF-2 receptor (CIM6P/IGF-2R), reverse most major deficits of AS modeled in mice. Subcutaneous injection of IGF-2 or M6P in mice modeling AS restored cognitive impairments as assessed by measurements of contextual and recognition memories, motor deficits assessed by rotarod and hindlimb clasping, and working memory/flexibility measured by Y-maze. IGF-2 also corrected deficits in marble burying and significantly attenuated acoustically induced seizures. An observational battery of tests confirmed that neither ligand changed basic functions including physical characteristics, general behavioral responses, and sensory reflexes, indicating that they are relatively safe. Our data provide strong preclinical evidence that targeting CIM6P/IGF-2R is a promising approach for developing novel therapeutics for AS. LAY SUMMARY: There is no effective treatment for the neurodevelopmental disorder Angelman syndrome (AS). Using a validated AS mouse model, the Ube3am-/p+ , in this study we show that systemic administration of ligands of the cation independent mannose-6-phosphate receptor, also known as insulin-like growth factor 2 receptor (CIM6P/IGF-2R) reverses cognitive impairment, motor deficits, as well as seizures associated with AS. Thus, ligands that activate the CIM6P/IGF-2R may represent novel, potential therapeutic targets for AS.

Mammalian Target of Rapamycin-RhoA Signaling Impairments in Direct Striatal Projection Neurons Induce Altered Behaviors and Striatal Physiology in Mice

BACKGROUND

As an integrator of molecular pathways, mTOR (mammalian target of rapamycin) has been associated with diseases including neurodevelopmental, psychiatric, and neurodegenerative disorders such as autism spectrum disorder, schizophrenia, and Huntington's disease. An important brain area involved in all these diseases is the striatum. However, the mechanisms behind how mTOR is involved in striatal physiology and its relative role in distinct neuronal populations in these striatal-related diseases still remain to be clarified.

METHODS

Using Drd1-Cre mTOR-conditional knockout male mice, we combined behavioral, biochemical, electrophysiological, and morphological analysis aiming to untangle the role of mTOR in direct pathway striatal projection neurons and how this would impact on striatal physiology.

RESULTS

Our results indicate deep behavioral changes in absence of mTOR in Drd1-expressing neurons such as decreased spontaneous locomotion, impaired social interaction, and decreased marble-burying behavior. These alterations were accompanied by a Kv1.1-induced increase in the fast phase of afterhyperpolarization and coincident decreased distal spine density in striatal direct pathway striatal projection neurons. The physiological changes were mechanistically independent of protein synthesis but sensitive to pharmacological blockade of transforming protein RhoA activity.

CONCLUSIONS

These results identify mTOR signaling as an important regulator of striatal functions through an intricate mechanism involving RhoA and culminating in Kv1.1 overfunction, which could be targeted to treat striatal-related monogenic disorders associated with the mTOR signaling pathway.

Adenosine A2A receptors format long-term depression and memory strategies in a mouse model of Angelman syndrome

Angelman syndrome (AS) is a neurodevelopmental disorder caused by loss of function of the maternally inherited Ube3a neuronal protein, whose main features comprise severe intellectual disabilities and motor impairments. Previous studies with the Ube3a^m-/p+ mouse model of AS revealed deficits in synaptic plasticity and memory. Since adenosine A_2A receptors (A_2AR) are powerful modulators of aberrant synaptic plasticity and A_2AR blockade prevents memory dysfunction in various brain diseases, we tested if A_2AR could control deficits of memory and hippocampal synaptic plasticity in AS. We observed that Ube3a^m-/p+ mice were unable to resort to hippocampal-dependent search strategies when tested for learning and memory in the Morris water maze; this was associated with a decreased magnitude of long-term depression (LTD) in CA1 hippocampal circuits. There was an increased density of A_2AR in the hippocampus of Ube3a^m-/p+ mice and their chronic treatment with the selective A_2AR antagonist SCH58261 (0.1 mg/kg/day, ip) restored both hippocampal-dependent learning strategies, as well as LTD deficits. Altogether, this study provides the first evidence of a role of A_2AR as a new prospective therapeutic target to manage learning deficits in AS.

Behavioral Evaluation of Angelman Syndrome Mice at Older Ages

Angelman syndrome is a neurodevelopmental disorder presenting with severe deficits in motor, speech, and cognitive abilities. The primary genetic cause of Angelman syndrome is a maternally transmitted mutation in the Ube3a gene, which has been successfully modeled in Ube3a mutant mice. Phenotypes have been extensively reported in young adult Ube3a mice. Because symptoms continue throughout life in Angelman syndrome, we tested multiple behavioral phenotypes of male Ube3a mice and WT littermate controls at older adult ages. Social behaviors on both the 3-chambered social approach and male-female social interaction tests showed impairments in Ube3a at 12 months of age. Anxiety-related scores on both the elevated plus-maze and the light ↔ dark transitions assays indicated anxiety-like phenotypes in 12 month old Ube3a mice. Open field locomotion parameters were consistently lower at 12 months. Reduced general exploratory locomotion at this age prevented the interpretation of an anxiety-like phenotype, and likely impacted social tasks. Robust phenotypes in middle-aged Ube3a mice appear to result from continued motor decline. Motor deficits may provide the best outcome measures for preclinical testing of pharmacological targets, towards reductions of symptoms in adults with Angelman syndrome.

Evaluation of a TrkB agonist on spatial and motor learning in the Ube3a mouse model of Angelman syndrome

Angelman syndrome is a rare neurodevelopmental disorder caused by a mutation in the maternal allele of the gene Ube3a The primary symptoms of Angelman syndrome are severe cognitive deficits, impaired motor functions, and speech disabilities. Analogous phenotypes have been detected in young adult Ube3a mice. Here, we investigate cognitive phenotypes of Ube3a mice as compared to wild-type littermate controls at an older adult age. Water maze spatial learning, swim speed, and rotarod motor coordination and balance were impaired at 6 mo of age, as predicted. Based on previous findings of reduced brain-derived neurotrophic factor in Ube3a mice, a novel therapeutic target, the TrkB agonist 7,8-DHF, was interrogated. Semichronic daily treatment with 7,8-DHF, 5 mg/kg i.p., did not significantly improve the impairments in performance during the acquisition of the water maze hidden platform location in Ube3a mice, after training with either massed or spaced trials, and had no effect on the swim speed and rotarod deficits. Robust behavioral phenotypes in middle-aged Ube3a mice appear to result from continued motor decline. Our results suggest that motor deficits could offer useful outcome measures for preclinical testing of many pharmacological targets, with the goal of reducing symptoms in adults with Angelman syndrome.

PKA and Ube3a regulate SK2 channel trafficking to promote synaptic plasticity in hippocampus: Implications for Angelman Syndrome

The ubiquitin ligase, Ube3a, plays important roles in brain development and functions, since its deficiency results in Angelman Syndrome (AS) while its over-expression increases the risk for autism. We previously showed that the lack of Ube3a-mediated ubiquitination of the Ca²⁺-activated small conductance potassium channel, SK2, contributes to impairment of synaptic plasticity and learning in AS mice. Synaptic SK2 levels are also regulated by protein kinase A (PKA), which phosphorylates SK2 in its C-terminal domain, facilitating its endocytosis. Here, we report that PKA activation restores theta burst stimulation (TBS)-induced long-term potentiation (LTP) in hippocampal slices from AS mice by enhancing SK2 internalization. While TBS-induced SK2 endocytosis is facilitated by PKA activation, SK2 recycling to synaptic membranes after TBS is inhibited by Ube3a. Molecular and cellular studies confirmed that phosphorylation of SK2 in the C-terminal domain increases its ubiquitination and endocytosis. Finally, PKA activation increases SK2 phosphorylation and ubiquitination in Ube3a-overexpressing mice. Our results indicate that, although both Ube3a-mediated ubiquitination and PKA-induced phosphorylation reduce synaptic SK2 levels, phosphorylation is mainly involved in TBS-induced endocytosis, while ubiquitination predominantly inhibits SK2 recycling. Understanding the complex interactions between PKA and Ube3a in the regulation of SK2 synaptic levels might provide new platforms for developing treatments for AS and various forms of autism.

Characterizing spine issues: If offers novel therapeutics to Angelman syndrome

Angelman syndrome (AS) is a rare neurodevelopmental disorder characterized by severe mental retardation, microcephaly, speech impairment, frequent epilepsy, EEG abnormalities, ataxic movements, tongue protrusion, bursts of laughter, sleep abruptions, and hyperactivity. AS results from loss of function of the imprinted UBE3A (ubiquitin-protein ligase E3A) gene on chromosome 15q11-q13, including a mutation on the maternal allele of Ube3a, a large deletion of the maternally inherited chromosomal region 15q11-13, paternal uniparental disomy of chromosome 15q11-13, or an imprinting defect. The Ube3a maternal deleted mouse model recaptured the major phenotypes of AS patients include seizure, learning and memory impairments, sleep disturbance, and motor problems. Owing to the activity-dependent structural and functional plasticity, dendritic spines are believed as the basic subcellular compartment for learning and memory and the sites where LTP and LTD are induced. Defects of spine formation and dynamics are common among several neurodevelopmental disorders and neuropsychiatric disorders including AS and reflect the underlying synaptopathology, which drives clinically relevant behavioral deficits. This review will summarize the impaired spine density, morphology, and synaptic plasticity in AS and propose that future explorations on spine dynamics and synaptic plasticity may help develop novel interventions and therapy for neurodevelopmental disorders like AS.

From Genetic Testing to Precision Medicine in Epilepsy

Epilepsy includes a number of medical conditions with recurrent seizures as common denominator. The large number of different syndromes and seizure types as well as the highly variable inter-individual response to the therapies makes management of this condition often challenging. In the last two decades, a genetic etiology has been revealed in more than half of all epilepsies and single gene defects in ion channels or neurotransmitter receptors have been associated with most inherited forms of epilepsy, including some focal and lesional forms as well as specific epileptic developmental encephalopathies. Several genetic tests are now available, including targeted assays up to revolutionary tools that have made sequencing of all coding (whole exome) and non-coding (whole genome) regions of the human genome possible. These recent technological advances have also driven genetic discovery in epilepsy and increased our understanding of the molecular mechanisms of many epileptic disorders, eventually providing targets for precision medicine in some syndromes, such as Dravet syndrome, pyroxidine-dependent epilepsy, and glucose transporter 1 deficiency. However, these examples represent a relatively small subset of all types of epilepsy, and to date, precision medicine in epilepsy has primarily focused on seizure control, and other clinical aspects, such as neurodevelopmental and neuropsychiatric comorbidities, have yet been possible to address. We herein summarize the most recent advances in genetic testing and provide up-to-date approaches for the choice of the correct test for some epileptic disorders and tailored treatments that are already applicable in some monogenic epilepsies. In the next years, the most probably scenario is that epilepsy treatment will be very different from the currently almost empirical approach, eventually with a "precision medicine" approach applicable on a large scale.

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.

Interactions between sleep disruption, motor learning, and p70 S6 kinase 1 signaling

Offline gains in motor performance after initial motor learning likely depend on sleep, but the molecular mechanisms by which this occurs are understudied. Regulation of mRNA translation via p70 S6 kinase 1 (S6K1) signaling represents one potential mechanism, as protein synthesis is thought to be increased during sleep compared to wake and is necessary for several forms of long-term memory. Using phosphorylation of ribosomal protein S6 (RpS6) as a readout of S6K1 activity, we demonstrate that a period of 10 h of acute sleep disruption impairs both S6K1 signaling and offline gains in motor performance on the rotarod in adult wild type C57/Bl6 mice. Rotarod motor learning results in increased abundance of RpS6 in the striatum, and inhibition of S6K1 either indirectly with rapamycin or directly with PF-4708671 diminished the offline improvement in motor performance without affecting the initial acquisition of rotarod motor learning when sleep is normal. In sum, S6K1 activity is required for sleep-dependent offline gains in motor performance and is inhibited following acute sleep disruption, while motor learning increases the abundance of striatal RpS6. Thus, S6K1 signaling represents a plausible mechanism mediating the beneficial effects of sleep on motor performance.

N-terminal variant Asp14Asn of the human p70 S6 Kinase 1 enhances translational signaling causing different effects in developing and mature neuronal cells

The ribosomal p70 S6 Kinase 1 (S6K1) has been implicated in the etiology of complex neurological diseases including autism, depression and dementia. Though no major gene disruption has been reported in humans in RPS6KB1, single nucleotide variants (SNVs) causing missense mutations have been identified, which have not been assessed for their impact on protein function. These S6K1 mutations have the potential to influence disease progression and treatment response. We mined the Simon Simplex Collection (SSC) and SPARK autism database to find inherited SNVs in S6K1 and characterized the effect of two missense SNVs, Asp14Asn (allele frequency = 0.03282%) and Glu44Gln (allele frequency = 0.0008244%), on S6K1 function in HEK293, human ES cells and primary neurons. Expressing Asp14Asn in HEK293 cells resulted in increased basal phosphorylation of downstream targets of S6K1 and increased de novo translation. This variant also showed blunted response to the specific S6K1 inhibitor, FS-115. In human embryonic cell line Shef4, Asp14Asn enhanced spontaneous neural fate specification in the absence of differentiating growth factors. In addition to enhanced translation, neurons expressing Asp14Asn exhibited impaired dendritic arborization and increased levels of phosphorylated ERK 1/2. Finally, in the SSC families tracked, Asp14Asn segregated with lower IQ scores when found in the autistic individual rather than the unaffected sibling. The Glu44Gln mutation showed a milder, but opposite phenotype in HEK cells as compared to Asp14Asn. Although the Glu44Gln mutation displayed increased neuronal translation, it had no impact on neuronal morphology. Our results provide the first characterization of naturally occurring human S6K1 variants on cognitive phenotype, neuronal morphology and maturation, underscoring again the importance of translation control in neural development and plasticity.

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.

Towards an understanding of Angelman syndrome in mice studies

Angelman syndrome (AS) is a rare neurodevelopmental disorder characterized by severe mental retardation, absence of speech, abnormal motor coordination, abnormal EEG, and spontaneous seizure. AS is caused by a deficiency in the ubiquitin ligase E3A (Ube3a) gene product, known to play a dual role as both ubiquitin ligase and transcription coactivator. In AS animal models, multiple Ube3a substrates are accumulated in neurons. So far, studies in mouse models have either aimed at re-expressing Ube3a or manipulating downstream signaling pathways. Reintroducing Ube3a in AS mice showed promising results but may have two caveats. First, it may cause an overdosage in the Ube3a expression, which in turn is known to contribute to autism spectrum disorders. Second, in mutation cases, the exogenous Ube3a may have to compete with the mutated endogenous form. Such two caveats left spaces for developing therapies or interventions directed to targets downstream Ube3a. Notably, Ube3a expression is dynamically regulated by neuronal activity and plays a crucial role in synaptic plasticity. The abnormal synaptic plasticity uncovered in AS mice has been frequently rescued, but circuits symptoms like seizure are resistant to treatment. Future investigations are needed to further clarify the function (s) of Ube3a during development. Here I reviewed the recently identified major Ube3a substrates and signaling pathways involved in AS pathology, the Ube3a expression, imprinting and evolution, the AS mouse models that have been generated and inspired therapeutic potentials, and finally proposed some future explorations to better understand the AS pathology.

PERK, mTORC1 and eEF2 interplay during long term potentiation: An Editorial for 'Genetic removal of eIF2a kinase PERK in mice enables hippocampal L-LTP independent of mTORC1 activity' on page 133

This Editorial highlights a study by Zimmermann and coworkers in the current issue of Journal of Neurochemistry. The authors' link suppression of PKR-like endoplasmatic reticulum kinase (PERK) activity to eukaryotic elongation factor 2 (eEF2) dephosphorylation and mTORC1-independent high-frequency stimulation (HFS)-induced long-term potentiation (LTP) in acute hippocampal slices from PERK forebrain conditional knockout mice. The results suggest that functional interaction between the signaling pathways controlling different phases of the mRNA translation process is necessary for long-term plasticity in the hippocampus.

GPR30-mediated estrogenic regulation of actin polymerization and spatial memory involves SRC-1 and PI3K-mTORC2 in the hippocampus of female mice

AIMS

The G-protein-coupled estrogen receptor GPR30 (also referred to as GPER) has been implicated in the estrogenic regulation of hippocampal plasticity and spatial memory; however, the molecular mechanisms are largely unclear.

METHODS

In this study, we initially examined the levels of GPR30 in the hippocampus of postnatal, ovariectomy (OVX)- and letrozole (LET)-treated female mice. Under G1, G15, and/or OVX treatment, the spatial memory, spine density, levels of ERα, ERβ, and SRC-1, selected synaptic proteins, mTORC2 signals (Rictor and p-AKT Ser473), and actin polymerization dynamics were subsequently evaluated. Furthermore, G1, G15, and/or E2 combined with SRC-1 and/or PI3K inhibitors, actin cytoskeleton polymerization modulator JPK, and CytoD treatments were used to address the mechanisms that underlie GPR30 regulation in vitro. Finally, mTORC2 activator A-443654 (A4) was used to explore the role of mTORC2 in GPR30 regulation of spatial memory.

RESULTS

The results showed that high levels of GPR30 were detected in the adult hippocampus and the levels were downregulated by OVX and LET. OVX induced an impairment of spatial memory, and changes in other parameters previously described were reversed by G1 and mimicked by G15. Furthermore, the E2 effects on SRC-1 and mTORC2 signals, synaptic proteins, and actin polymerization were inhibited by G15, whereas G1 effects on these parameters were inhibited by the blockade of SRC-1 or PI3K; the levels of synaptic proteins were regulated by JPK and CytoD. Importantly, G15-induced actin depolymerization and spatial memory impairment were rescued by mTORC2 activation with A4.

CONCLUSIONS

Taking together, these results demonstrated that decreased GPR30 induces actin depolymerization through SRC-1 and PI3K/mTORC2 pathways and ultimately impairs learning and memory, indicating its potential role as a therapeutic target against hippocampus-based, E2-related memory impairments.

UBE3A: An E3 Ubiquitin Ligase With Genome-Wide Impact in Neurodevelopmental Disease

UBE3A is an E3 ubiquitin ligase encoded by an imprinted gene whose maternal deletion or duplication leads to distinct neurodevelopment disorders Angelman and Dup15q syndromes. Despite the known genetic basis of disease, how changes in copy number of a ubiquitin ligase gene can have widespread impact in early brain development is poorly understood. Previous studies have identified a wide array of UBE3A functions, interaction partners, and ubiquitin targets, but no central pathway fully explains its critical role in neurodevelopment. Here, we review recent UBE3A studies that have begun to investigate mechanistic, cellular pathways and the genome-wide impacts of alterations in UBE3A expression levels to gain broader insight into how UBE3A affects the developing brain. These studies have revealed that UBE3A is a multifunctional protein with important nuclear and cytoplasmic regulatory functions that impact proteasome function, Wnt signaling, circadian rhythms, imprinted gene networks, and chromatin. Synaptic functions of UBE3A interact with light exposures and mTOR signaling and are most critical in GABAergic neurons. Understanding the genome-wide influences of UBE3A will help uncover its role in early brain development and ultimately lead to identification of key therapeutic targets for UBE3A-related neurodevelopmental disorders.

Overview of genetic models of autism spectrum disorders

Autism spectrum disorders (ASDs) are a group of neurodevelopment disorders that are characterized by heterogenous cognitive deficits and genetic factors. As more ASD risk genes are identified, genetic animal models have been developed to parse out the underlying neurobiological mechanisms of ASD. In this review, we discuss a subset of genetic models of ASD, focusing on those that have been widely studied and strongly linked to ASD. We focus our discussion of these models in the context of the theories and potential mechanisms of ASD, including disruptions in cell growth and proliferation, spine dynamics, synaptic transmission, excitation/inhibition balance, intracellular signaling, neuroinflammation, and behavior. In addition to ASD pathophysiology, we examine the limitations and challenges that genetic models pose for the study of ASD biology. We end with a review of innovative techniques and concepts of ASD pathology that can be further applied to and studied using genetic ASD models.

Oxidative Stress, Maternal Diabetes, and Autism Spectrum Disorders

Autism spectrum disorders (ASD) are a group of early-onset neurodevelopmental conditions characterized by alterations in brain connectivity with cascading effects on neuropsychological functions. To date, in the framework of an increasing interest about environmental conditions which could interact with genetic factors in ASD pathogenesis, many authors have stressed that changes in the intrauterine environment at different stages of pregnancy, such as those linked to maternal metabolic pathologies, may lead to long-term conditions in the newborn. In particular, a growing number of epidemiological studies have highlighted the role of obesity and maternal diabetes as a risk factor for developing both somatic and psychiatric disorders in humans, including ASD. While literature still fails in identifying specific etiopathological mechanisms, a growing body of evidence is available about the presence of a relationship between maternal immune dysregulation, inflammation, oxidative stress, and the development of ASD in the offspring. In this framework, results from high-fat diet animal models about the role played by oxidative stress in shaping offspring neurodevelopment may help in clarifying the pathways through which maternal metabolic conditions are linked with ASD. The aim of this review is to provide an overview of literature about the effects of early life insults linked to oxidative stress which may be involved in ASD etiopathogenesis and how this relationship can be explained in biological terms.

A behavioral test battery for mouse models of Angelman syndrome: a powerful tool for testing drugs and novel Ube3a mutants

Background

Angelman syndrome (AS) is a neurodevelopmental disorder caused by mutations affecting UBE3A function. AS is characterized by intellectual disability, impaired motor coordination, epilepsy, and behavioral abnormalities including autism spectrum disorder features. The development of treatments for AS heavily relies on the ability to test the efficacy of drugs in mouse models that show reliable, and preferably clinically relevant, phenotypes. We previously described a number of behavioral paradigms that assess phenotypes in the domains of motor performance, repetitive behavior, anxiety, and seizure susceptibility. Here, we set out to evaluate the robustness of these phenotypes when tested in a standardized test battery. We then used this behavioral test battery to assess the efficacy of minocycline and levodopa, which were recently tested in clinical trials of AS.

Methods

We combined data of eight independent experiments involving 111 Ube3a mice and 120 wild-type littermate control mice. Using a meta-analysis, we determined the statistical power of the subtests and the effect of putative confounding factors, such as the effect of sex and of animal weight on rotarod performance. We further assessed the robustness of these phenotypes by comparing Ube3a mutants in different genetic backgrounds and by comparing the behavioral phenotypes of independently derived Ube3a-mutant lines. In addition, we investigated if the test battery allowed re-testing the same animals, which would allow a within-subject testing design.

Results

We find that the test battery is robust across different Ube3a-mutant lines, but confirm and extend earlier studies that several phenotypes are very sensitive to genetic background. We further found that the audiogenic seizure susceptibility phenotype is fully reversible upon pharmacological treatment and highly suitable for dose-finding studies. In agreement with the clinical trial results, we found that minocycline and levodopa treatment of Ube3a mice did not show any sign of improved performance in our test battery.

Conclusions

Our study provides a useful tool for preclinical drug testing to identify treatments for Angelman syndrome. Since the phenotypes are observed in several independently derived Ube3a lines, the test battery can also be employed to investigate the effect of specific Ube3a mutations on these phenotypes.

UBE3A-mediated p18/LAMTOR1 ubiquitination and degradation regulate mTORC1 activity and synaptic plasticity

Accumulating evidence indicates that the lysosomal Ragulator complex is essential for full activation of the mechanistic target of rapamycin complex 1 (mTORC1). Abnormal mTORC1 activation has been implicated in several developmental neurological disorders, including Angelman syndrome (AS), which is caused by maternal deficiency of the ubiquitin E3 ligase UBE3A. Here we report that Ube3a regulates mTORC1 signaling by targeting p18, a subunit of the Ragulator. Ube3a ubiquinates p18, resulting in its proteasomal degradation, and Ube3a deficiency in the hippocampus of AS mice induces increased lysosomal localization of p18 and other members of the Ragulator-Rag complex, and increased mTORC1 activity. p18 knockdown in hippocampal CA1 neurons of AS mice reduces elevated mTORC1 activity and improves dendritic spine maturation, long-term potentiation (LTP), as well as learning performance. Our results indicate that Ube3a-mediated regulation of p18 and subsequent mTORC1 signaling is critical for typical synaptic plasticity, dendritic spine development, and learning and memory.

Abnormal mTOR Activation in Autism

The mechanistic target of rapamycin (mTOR) is an important signaling hub that integrates environmental information regarding energy availability and stimulates anabolic molecular processes and cell growth. Abnormalities in this pathway have been identified in several syndromes in which autism spectrum disorder (ASD) is highly prevalent. Several studies have investigated mTOR signaling in developmental and neuronal processes that, when dysregulated, could contribute to the development of ASD. Although many potential mechanisms still remain to be fully understood, these associations are of great interest because of the clinical availability of mTOR inhibitors. Clinical trials evaluating the efficacy of mTOR inhibitors to improve neurodevelopmental outcomes have been initiated.

Inhibition of mTORC1 Signaling Reverts Cognitive and Affective Deficits in a Mouse Model of Parkinson's Disease

Non-motor symptoms, including cognitive deficits and affective disorders, are frequently diagnosed in Parkinson’s disease (PD) patients and are only partially alleviated by dopamine replacement therapy. Here, we used a 6-hydroxydopamine (6-OHDA) mouse model of PD to examine the effects exerted on non-motor symptoms by inhibition of the mammalian target of rapamycin complex 1 (mTORC1), which is involved in the control of protein synthesis, cell growth, and metabolism. We show that rapamycin, which acts as an allosteric inhibitor of mTORC1, counteracts the impairment of novel object recognition. A similar effect is produced by PF-4708671, an inhibitor of the downstream target of mTORC1, ribosomal protein S6 kinase (S6K). Rapamycin is also able to reduce depression-like behavior in PD mice, as indicated by decreased immobility in the forced swim test. Moreover, rapamycin exerts anxiolytic effects, thereby reducing thigmotaxis in the open field and increasing exploration of the open arm in the elevated plus maze. In contrast to rapamycin, administration of PF-4708671 to PD mice does not counteract depression- and anxiety-like behaviors. Altogether, these results identify mTORC1 as a target for the development of drugs that, in combination with standard antiparkinsonian agents, may widen the efficacy of current therapies for the cognitive and affective symptoms of PD.

Network Analysis of UBE3A/E6AP-Associated Proteins Provides Connections to Several Distinct Cellular Processes

Perturbations in activity and dosage of the UBE3A ubiquitin-ligase have been linked to Angelman syndrome and autism spectrum disorders. UBE3A was initially identified as the cellular protein hijacked by the human papillomavirus E6 protein to mediate the ubiquitylation of p53, a function critical to the oncogenic potential of these viruses. Although a number of substrates have been identified, the normal cellular functions and pathways affected by UBE3A are largely unknown. Previously, we showed that UBE3A associates with HERC2, NEURL4, and MAPK6/ERK3 in a high-molecular-weight complex of unknown function that we refer to as the HUN complex (HERC2, UBE3A, and NEURL4). In this study, the combination of two complementary proteomic approaches with a rigorous network analysis revealed cellular functions and pathways in which UBE3A and the HUN complex are involved. In addition to finding new UBE3A-associated proteins, such as MCM6, SUGT1, EIF3C, and ASPP2, network analysis revealed that UBE3A-associated proteins are connected to several fundamental cellular processes including translation, DNA replication, intracellular trafficking, and centrosome regulation. Our analysis suggests that UBE3A could be involved in the control and/or integration of these cellular processes, in some cases as a component of the HUN complex, and also provides evidence for crosstalk between the HUN complex and CAMKII interaction networks. This study contributes to a deeper understanding of the cellular functions of UBE3A and its potential role in pathways that may be affected in Angelman syndrome, UBE3A-associated autism spectrum disorders, and human papillomavirus-associated cancers.

Salinomycin, as an autophagy modulator-- a new avenue to anticancer: a review

Since Salinomycin (Sal) emerged its ability to target breast cancer stem cells in 2009, numerous experiments have been carried out to test Sal’s anticancer effects. What deserve to be mentioned is that Sal can efficiently induce proliferation inhibition, cell death and metastasis suppression against human cancers from different origins both in vivo and in vitro without causing serious side effects as the conventional chemotherapeutical drugs on the body. There may be novel cell death pathways involving the anticancer effects of Sal except the conventional pathways, such as autophagic pathway. This review is focused on how autophagy involves the effects of Sal, trying to describe clearly and systematically why autophagy plays a vital role in predominant anticancer effects of Sal, including its distinctive characteristic. Based on recent advances, we present evidence that a dual role of Sal involving in autophagy may account for its unique anticancer effects - the preference for cancer cells. Further researches are required to confirm the authenticity of this suppose in order to develop an ideal anticancer drug.