Loss of MeCP2 in cholinergic neurons causes part of RTT-like phenotypes via α7 receptor in hippocampus

Physiological and cellular mechanisms of ischemic preconditioning microRNAs-mediated in underlying of ischemia/reperfusion injury in different organs

Ischemia-reperfusion (I/R) injury, as a pathological phenomenon, takes place when blood supply to an organ is disrupted and then aggravated during restoration of blood flow. Ischemic preconditioning (IPC) is a potent method for attenuating subsequent events of IR damage in numerous organs. IPC protocol is determined by a brief and sequential time periods of I/R before the main ischemia. MicroRNAs are endogenous non-coding RNAs that regulate post-transcriptionally target mRNA translation via degrading it and/or suppressing protein synthesis. This review introduces the physiological and cellular mechanisms of ischemic preconditioning microRNAs-mediated after I/R insult in different organs such as the liver, kidney, heart, brain, and intestine. Data of this review have been collected from the scientific articles published in databases such as Science Direct, Scopus, PubMed, Web of Science, and Scientific Information Database from 2000 to 2023. Based on these literature studies, IPC/IR intervention can affect cellular mechanisms including oxidative stress, apoptosis, angiogenesis, and inflammation through up-regulation or down-regulation of multiple microRNAs and their target genes.

Melatonin attenuates scopolamine-induced cognitive dysfunction through SIRT1/IRE1α/XBP1 pathway

BACKGROUND

The prevalence of dementia around the world is increasing, and these patients are more likely to have cognitive impairments, mood and anxiety disorders (depression, anxiety, and panic disorder), and attention deficit disorders over their lifetime. Previous studies have proven that melatonin could improve memory loss, but its specific mechanism is still confused.

METHODS

In this study, we used in vivo and in vitro models to examine the neuroprotective effect of melatonin on scopolamine (SCOP)-induced cognitive dysfunction. The behavioral tests were performed. 18F-FDG PET imaging was used to assess the metabolism of the brain. Protein expressions were determined through kit detection, Western blot, and immunofluorescence. Nissl staining was conducted to reflect neurodegeneration. MTT assay and RNAi transfection were applied to perform the in vitro experiments.

RESULTS

We found that melatonin could ameliorate SCOP-induced cognitive dysfunction and relieve anxious-like behaviors or HT22 cell damage. 18F-FDG PET-CT results showed that melatonin could improve cerebral glucose uptake in SCOP-treated mice. Melatonin restored the cholinergic function, increased the expressions of neurotrophic factors, and ameliorated oxidative stress in the brain of SCOP-treated mice. In addition, melatonin upregulated the expression of silent information regulator 1 (SIRT1), which further relieved endoplasmic reticulum (ER) stress by decreasing the expression of phosphorylate inositol-requiring enzyme (p-IRE1α) and its downstream, X-box binding protein 1 (XBP1).

CONCLUSIONS

These results indicated that melatonin could ameliorate SCOP-induced cognitive dysfunction through the SIRT1/IRE1α/XBP1 pathway. SIRT1 might be the critical target of melatonin in the treatment of dementia.

Effect and Potential Mechanism of Immunotherapy on Cognitive Deficits in Animal Models of Alzheimer's Disease: A Systematic Review and Meta-Analysis

OBJECTIVE

Immunotherapy has been reported to ameliorate Alzheimer's disease (AD) in the animal model; however, the immunologic approaches and mechanisms have not been specifically described. Thus, the systematic review and meta-analysis were conducted to explore the effect and potential mechanism of immunotherapy on AD animal experiments based on behavioral indicators.

METHODS

According to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses and the Cochrane Collaboration guidelines and the inclusion/exclusion criteria of immunotherapy in animal studies, 15 studies were systematically reviewed after extraction from a collected database of 3,742 publications. Finally, the effect and mechanism of immunotherapy on AD models were described by performing multiple subgroup analyses.

RESULTS

After immunotherapy, the escape latency was reduced by 18.15 seconds and the number of crossings over the platform location was increased by 1.60 times in the Morris Water Maze. Furthermore, compared to the control group, active and passive immunization could markedly ameliorate learning and memory impairment in 3 × Tg AD animal models, and active immunization could ameliorate the learning and memory ability of the APPswe/PS1ΔE9 AD animal model. Meanwhile, it could be speculated that cognitive dysfunction was improved by immunotherapy, perhaps mainly via reducing Aβ40, Aβ42, and Tau levels, as well as increasing IL-4 levels.

CONCLUSION

Immunotherapy significantly ameliorated the cognitive dysfunction of AD animal models by assessing behavioral indicators.

Reversal of neurological deficits by painless nerve growth factor in a mouse model of Rett syndrome

Rett syndrome is a rare genetic neurodevelopmental disease, affecting 1 in over 10 000 females born worldwide, caused by de novo mutations in the X-chromosome-located methyl-CpG-binding protein 2 (MeCP2) gene. Despite the great effort put forth by the scientific community, a therapy for this devastating disease is still needed. Here, we tested the therapeutic effects of a painless mutein of the nerve growth factor (NGF), called human NGF painless (hNGFp), via a non-invasive intranasal delivery in female MeCP2+/- mice. Of note, previous work had demonstrated a broad biodistribution of hNGFp in the mouse brain by the nasal delivery route. We report that (i) the long-term lifelong treatment of MeCP2+/- mice with hNGFp, starting at 2 months of age, increased the chance of survival while also greatly improving behavioural parameters. Furthermore, when we assessed the phenotypic changes brought forth by (ii) a short-term 1-month-long hNGFp-treatment, starting at 3 months of age (right after the initial presentation of symptoms), we observed the rescue of a well known neuronal target population of NGF, cholinergic neurons in the medial septum. Moreover, we reveal a deficit in microglial morphology in MeCP2+/- mice, completely reversed in treated animals. This effect on microglia is in line with reports showing microglia to be a TrkA-dependent non-neuronal target cell population of NGF in the brain. To understand the immunomodulatory activity of hNGFp, we analysed the cytokine profile after hNGFp treatment in MeCP2+/- mice, to discover that the treatment recovered the altered expression of key neuroimmune-communication molecules, such as fractalkine. The overall conclusion is that hNGFp delivered intranasally can ameliorate symptoms in the MeCP2+/- model of Rett syndrome, by exerting strong neuroprotection with a dual mechanism of action: directly on target neurons and indirectly via microglia.

Effect and Mechanism of Rapamycin on Cognitive Deficits in Animal Models of Alzheimer's Disease: A Systematic Review and Meta-analysis of Preclinical Studies

Background

Alzheimer's disease (AD), the most common form of dementia, remains long-term and challenging to diagnose. Furthermore, there is currently no medication to completely cure AD patients. Rapamycin has been clinically demonstrated to postpone the aging process in mice and improve learning and memory abilities in animal models of AD. Therefore, rapamycin has the potential to be significant in the discovery and development of drugs for AD patients.

Objective

The main objective of this systematic review and meta-analysis was to investigate the effects and mechanisms of rapamycin on animal models of AD by examining behavioral indicators and pathological features.

Methods

Six databases were searched and 4,277 articles were retrieved. In conclusion, 13 studies were included according to predefined criteria. Three authors independently judged the selected literature and methodological quality. Use of subgroup analyses to explore potential mechanistic effects of rapamycin interventions: animal models of AD, specific types of transgenic animal models, dosage, and periodicity of administration.

Results

The results of Morris Water Maze (MWM) behavioral test showed that escape latency was shortened by 15.60 seconds with rapamycin therapy, indicating that learning ability was enhanced in AD mice; and the number of traversed platforms was increased by 1.53 times, indicating that the improved memory ability significantly corrected the memory deficits.

CONCLUSIONS

Rapamycin therapy reduced age-related plaque deposition by decreasing AβPP production and down-regulating β-secretase and γ-secretase activities, furthermore increased amyloid-β clearance by promoting autophagy, as well as reduced tau hyperphosphorylation by up-regulating insulin-degrading enzyme levels.

Advances in the study of cholinergic circuits in the central nervous system

OBJECTIVE

Further understanding of the function and regulatory mechanism of cholinergic neural circuits and related neurodegenerative diseases.

METHODS

This review summarized the research progress of the central cholinergic nervous system, especially for the cholinergic circuit of the medial septal nucleus-hippocampus, vertical branch of diagonal band-hippocampus, basal nucleus of Meynert-cerebral cortex cholinergic loop, amygdala, pedunculopontine nucleus, and striatum-related cholinergic loops.

RESULTS

The extensive and complex fiber projection of cholinergic neurons form the cholinergic neural circuits, which regulate several nuclei in the brain through neurotransmission and participate in learning and memory, attention, emotion, movement, etc. The loss of cholinergic neurotransmitters, the reduction, loss, and degeneration of cholinergic neurons or abnormal theta oscillations and cholinergic neural circuits can induce cognitive disorders such as AD, PD, PDD, and DLB.

INTERPRETATION

The projection and function of cholinergic fibers in some nuclei and the precise regulatory mechanisms of cholinergic neural circuits in the brain remain unclear. Further investigation of cholinergic fiber projections in various brain regions and the underlying mechanisms of the neural circuits are expected to open up new avenues for the prevention and treatment of senile neurodegenerative diseases.

Hyperconnectivity of Two Separate Long-Range Cholinergic Systems Contributes to the Reorganization of the Brain Functional Connectivity during Nicotine Withdrawal in Male Mice

Chronic nicotine results in dependence with withdrawal symptoms on discontinuation of use, through desensitization of nicotinic acetylcholine receptors and altered cholinergic neurotransmission. Nicotine withdrawal is associated with increased whole-brain functional connectivity and decreased network modularity; however, the role of cholinergic neurons in those changes is unknown. To identify the contribution of nicotinic receptors and cholinergic regions to changes in the functional network, we analyzed the contribution of the main cholinergic regions to brain-wide activation of the immediate early-gene Fos during withdrawal in male mice and correlated these changes with the expression of nicotinic receptor mRNA throughout the brain. We show that the main functional connectivity modules included the main long-range cholinergic regions, which were highly synchronized with the rest of the brain. However, despite this hyperconnectivity, they were organized into two anticorrelated networks that were separated into basal forebrain-projecting and brainstem-thalamic-projecting cholinergic regions, validating a long-standing hypothesis of the organization of the brain cholinergic systems. Moreover, baseline (without nicotine) expression of Chrna2, Chrna3, Chrna10, and Chrnd mRNA of each brain region correlated with withdrawal-induced changes in Fos expression. Finally, by mining the Allen Brain mRNA expression database, we were able to identify 1755 gene candidates and three pathways (Sox2-Oct4-Nanog, JAK-STAT, and MeCP2-GABA) that may contribute to nicotine withdrawal-induced Fos expression. These results identify the dual contribution of the basal forebrain and brainstem-thalamic cholinergic systems to whole-brain functional connectivity during withdrawal; and identify nicotinic receptors and novel cellular pathways that may be critical for the transition to nicotine dependence.

Hyperconnectivity of two separate long-range cholinergic systems contributes to the reorganization of the brain functional connectivity during nicotine withdrawal in male mice

Chronic nicotine results in dependence with withdrawal symptoms upon discontinuation of use, through desensitization of nicotinic acetylcholine receptors and altered cholinergic neurotransmission. Nicotine withdrawal is associated with increased whole-brain functional connectivity and decreased network modularity, however, the role of cholinergic neurons in those changes is unknown. To identify the contribution of nicotinic receptors and cholinergic regions to changes in the functional network, we analyzed the contribution of the main cholinergic regions to brain-wide activation of the immediate early-gene FOS during withdrawal in male mice and correlated these changes with the expression of nicotinic receptor mRNA throughout the brain. We show that the main functional connectivity modules included the main long-range cholinergic regions, which were highly synchronized with the rest of the brain. However, despite this hyperconnectivity they were organized into two anticorrelated networks that were separated into basal forebrain projecting and brainstem-thalamic projecting cholinergic regions, validating a long-standing hypothesis of the organization of the brain cholinergic systems. Moreover, baseline (without nicotine) expression of Chrna2 , Chrna3 , Chrna10 , and Chrnd mRNA of each brain region correlated with withdrawal-induced changes in FOS expression. Finally, by mining the Allen Brain mRNA expression database, we were able to identify 1755 gene candidates and three pathways (Sox2-Oct4-Nanog, JAK-STAT, and MeCP2-GABA) that may contribute to nicotine withdrawal-induced FOS expression. These results identify the dual contribution of the basal forebrain and brainstem-thalamic cholinergic systems to whole-brain functional connectivity during withdrawal; and identify nicotinic receptors and novel cellular pathways that may be critical for the transition to nicotine dependence.

Significance Statement

Discontinuation of nicotine use in dependent users is associated with increased whole-brain activation and functional connectivity and leads to withdrawal symptoms. Here we investigated the contribution of the nicotinic cholinergic receptors and main cholinergic projecting brain areas in the whole-brain changes associated with withdrawal. This not only allowed us to visualize and confirm the previously described duality of the cholinergic brain system using this novel methodology, but also identify nicotinic receptors together with 1751 other genes that contribute, and could thus be targets for treatments against, nicotine withdrawal and dependence.

The Effects of Positive Allosteric Modulators of α7–nAChR on Social Play Behavior in Adolescent Rats Prenatally Exposed to Valproic Acid

There is still no effective treatment that addresses the core symptoms of autism spectrum disorders (ASD), including social and communication deficits. A comprehensive body of evidence points to the cholinergic system, including alpha7–nicotinic acetylcholine receptors (α7–nAChRs), as a potential target of pharmacotherapy. A promising approach is based on positive allosteric modulators (PAMs) of these receptors due to their advantages over direct agonists. Nevertheless, α7 n–AChR ligands have not been widely studied in the context of autism. Therefore, using one of the most widely used rodent models of ASD, that is, prenatal exposure to valproic acid (VPA), we examined the impact of α7–nAChR PAMs (PNU–120596 and CCMI) on socio-communicative behavior during social play in adolescent male and female rats. The current study demonstrated that PAM treatment affected certain aspects of socio-communicative behavior in adolescent rats. Accordingly, PNU–120596 ameliorated deficient play abilities in VPA-exposed males, as revealed by increased play time during a social encounter. In addition, this compound enhanced the emission of ultrasonic vocalizations that accompanied playful interactions. Moreover, we observed the overall effect of PNU–120596 on non-playful forms of social behavior (i.e., social exploration) and acoustic parameters (i.e., the duration) of emitted calls. The present results suggest the ability of α7–nAChR PAMs to facilitate socio-communicative behavior in adolescent rats.

Effect and Mechanism of Exogenous Melatonin on Cognitive Deficits in Animal Models of Alzheimer's Disease: A Systematic review and Meta-analysis

Melatonin (MT) has been reported to control and prevent Alzheimer's disease (AD) in the clinic; however, the effect and mechanism of MT on AD have not been specifically described. Therefore, the main purpose of this meta-analysis was to explore the effect and mechanism of MT on AD models by studying behavioural indicators and pathological features. Seven databases were searched and 583 articles were retrieved. Finally, nine studies (13 analyses, 294 animals) were included according to pre-set criteria. Three authors independently judged the selected literature and the methodological quality. Meta-analysis showed that MT markedly ameliorated the learning ability by reducing the escape latency (EL), and the memory deficit was significantly corrected by increasing the dwell time in the target quadrant and crossings over the platform location in the Morris Water Maze (MWM). Among the pathological features, subgroup analysis found that MT may ease the symptoms of AD mainly by reducing the deposition of Aβ40 and Aβ42 in the cortex. In addition, MT exerted a superior effect on ameliorating the learning ability of senescence-related and metabolic AD models, and corrected the memory deficit of the toxin-induced AD model. The study was registered at PROSPERO (CRD42021226594).

Medial septum: relevance for social memory

Animal species are named social when they develop the capability of complex behaviors based on interactions with conspecifics that include communication, aggression, mating and parental behavior, crucial for well-being and survival. The underpinning of such complex behaviors is social memory, namely the capacity to discriminate between familiar and novel individuals. The Medial Septum (MS), a region localized in the basal forebrain, is part of the brain network involved in social memory formation. MS receives several cortical and subcortical synaptic and neuromodulatory inputs that make it an important hub in processing social information relevant for social memory. Particular attention is paid to synaptic inputs that control both the MS and the CA2 region of the hippocampus, one of the major MS output, that has been causally linked to social memory. In this review article, we will provide an overview of local and long range connectivity that allows MS to integrate and process social information. Furthermore, we will summarize previous strategies used to determine how MS controls social memory in different animal species. Finally, we will discuss the impact of an altered MS signaling on social memory in animal models and patients affected by neurodevelopmental and neurodegenerative disorders, including autism and Alzheimer’s Disease.

Integrating network pharmacology analysis and pharmacodynamic evaluation for exploring the active components and molecular mechanism of moutan seed coat extract to improve cognitive impairment

Paeonia suffruticosa (Moutan) is a traditional medicinal plant in China. Its seed coat is rich in resveratrol oligomer, especially suffruticosol B (SB). Previous studies had shown that the seed coat extracts of Paeonia suffruticosa (PSCE) had good cholinesterase inhibitory activity and neuroprotective effect, but the effective dose range was unknown, and the pharmacodynamic components and molecular mechanism of PSCE had not been discussed. The current study aimed to screen the pharmacodynamic components in PSCE and investigate the improvement effect of PSCE and the selected SB on scopolamine-induced cognitive dysfunction in mice and its mechanism. The results of high-throughput sequencing and bioinformatics analysis showed that suffruticosol B (SB) and trans-gnetin H (GH) might be the main active components of PSCE; PSCE might improve cognitive dysfunction through p53, HIF-1, MAPK, and PI3K-Akt signaling pathways, while SB and GH might improve cognitive dysfunction through HIF-1 signaling pathway. SB and GH had good molecular docking activity with the target of HIF-1 signaling pathway. The pharmacodynamic activities of PSCE and SB were further verified by behavioral experiments. PSCE and SB could improve the recognition ability of familiar and new objects and shorten the escape latency in the Morris Water Maze test (PSCE 120 mg∙kg-1, p < 0.05; SB 60 mg∙kg-1, p < 0.01); PSCE and SB could increase Ach and GSH levels, enhance the activities of ChAT, SOD and CAT, decrease the levels of IL-1β, IL-6, and TNF-α, and decrease the activity of AChE. In conclusion, the results indicated that PSCE might exert pharmacodynamic activity through multiple components, targets, and pathways, and SB and GH might be the main active components of PSCE. PSCE and SB might improve cognitive dysfunction by regulating cholinergic, antioxidant, and anti-inflammatory effects. These results indicated that PSCE and SB might be potential anti-AD drug candidates, providing a scientific basis for the development and utilization of Moutan bark.

Prefrontal Circuits guiding Social Preference: Implications in Autism Spectrum Disorder

Although Autism Spectrum Disorder (ASD) is increasing in diagnostic prevalence, treatment options are inadequate largely due to limited understanding of ASD's underlying neural mechanisms. Contributing to difficulties in treatment development is the vast heterogeneity of ASD, from physiological causes to clinical presentations. Recent studies suggest that distinct genetic and neurological alterations may converge onto similar underlying neural circuits. Therefore, an improved understanding of neural circuit-level dysfunction in ASD may be a more productive path to developing broader treatments that are effective across a greater spectrum of ASD. Given the social preference behavioral deficits commonly seen in ASD, dysfunction in circuits mediating social preference may contribute to the atypical development of social cognition. We discuss some of the animal models used to study ASD and examine the function and effects of dysregulation of the social preference circuits, notably the medial prefrontal cortex-amygdala and the medial prefrontal cortex-nucleus accumbens circuits, in these animal models. Using the common circuits underlying similar behavioral disruptions of social preference behaviors as an example, we highlight the importance of identifying disruption in convergent circuits to improve the translational success of animal model research for ASD treatment development.

Epigenetic genes and epilepsy - emerging mechanisms and clinical applications

An increasing number of epilepsies are being attributed to variants in genes with epigenetic functions. The products of these genes include factors that regulate the structure and function of chromatin and the placing, reading and removal of epigenetic marks, as well as other epigenetic processes. In this Review, we provide an overview of the various epigenetic processes, structuring our discussion around five function-based categories: DNA methylation, histone modifications, histone-DNA crosstalk, non-coding RNAs and chromatin remodelling. We provide background information on each category, describing the general mechanism by which each process leads to altered gene expression. We also highlight key clinical and mechanistic aspects, providing examples of genes that strongly associate with epilepsy within each class. We consider the practical applications of these findings, including tissue-based and biofluid-based diagnostics and precision medicine-based treatments. We conclude that variants in epigenetic genes are increasingly found to be causally involved in the epilepsies, with implications for disease mechanisms, treatments and diagnostics.

Advances in the pathogenesis of Rett syndrome using cell models

Rett syndrome (RTT) is a progressive neurodevelopmental disorder that occurs mainly in girls with a range of typical symptoms of autism spectrum disorders. MeCP2 protein loss-of-function in neural lineage cells is the main cause of RTT pathogenicity. As it is still hard to understand the mechanism of RTT on the basis of only clinical patients or animal models, cell models cultured in vitro play indispensable roles. Here we reviewed the research progress in the pathogenesis of RTT at the cellular level, summarized the preclinical-research-related applications, and prospected potential future development.

Optimized Administration of the M4 PAM VU0467154 Demonstrates Broad Efficacy, but Limited Effective Concentrations in Mecp2+/- Mice

Hypofunction of cholinergic circuits and diminished cholinergic tone have been associated with the neurodevelopmental disorder Rett syndrome (RTT). Specifically, deletion of Mecp2 in cholinergic neurons evokes the same social and cognitive phenotypes in mice seen with global Mecp2 knockout, and decreased choline acetyltransferase activity and vesamicol binding have been reported in RTT autopsy samples. Further, we recently identified significant decreases in muscarinic acetylcholine receptor subtype 4 (M₄) expression in both the motor cortex and cerebellum of RTT patient autopsies and established proof of concept that an acute dose of the positive allosteric modulator (PAM) VU0467154 (VU154) rescued phenotypes in Mecp2^+/- mice. Here, we expand the assessment of M₄ PAMs in RTT to address clinically relevant questions of tolerance, scope of benefit, dose response, chronic treatment, and mechanism. We show that VU154 has efficacy on anxiety, social preference, cognitive, and respiratory phenotypes in Mecp2^+/- mice; however, the therapeutic range is narrow, with benefits seen at 3 mg/kg concentrations, but not 1 or 10 mg/kg. Further, sociability was diminished in VU154-treated Mecp2^+/- mice, suggestive of a potential adverse effect. Compound efficacy on social, cognitive, and respiratory phenotypes was conserved with a 44-day treatment paradigm, with the caveat that breath rate was moderately decreased with chronic treatment in Mecp2^+/+ and Mecp2^+/- mice. VU154 effects on respiratory function correlated with an increase in Gsk3β inhibition in the brainstem. These results identify the core symptom domains where efficacy and adverse effects may present with M₄ administration in RTT model mice and advocate for the continued evaluation as potential RTT therapeutics.

Loss of neurodevelopmental-associated miR-592 impairs neurogenesis and causes social interaction deficits

microRNA-592 (miR-592) has been linked to neurogenesis, but the influence of miR-592 knockout in vivo remains unknown. Here, we report that miR-592 knockout represses IPC-to-mature neuron transition, impairs motor coordination and reduces social interaction. Combining the RNA-seq and tandem mass tagging-based quantitative proteomics analysis (TMT protein quantification) and luciferase reporter assays, we identified MeCP2 as the direct targetgene of miR-592 in the mouse cortex. In Tg(MECP2) mice, lipofection of miR-592 efficiently reduced MECP2 expression in the brains of Tg(MECP2) mice at E14.5. Furthermore, treatment with miR-592 partially ameliorated the autism-like phenotypes observed in adult Tg(MECP2) mice. The findings demonstrate that miR-592 might play a novel role in treating the neurodevelopmental-associated disorder.

Excitation and Inhibition Imbalance in Rett Syndrome

A loss of the excitation/inhibition (E/I) balance in the neural circuit has emerged as a common neuropathological feature in many neurodevelopmental disorders. Rett syndrome (RTT), a prevalent neurodevelopmental disorder that affects 1:10,000-15,000 women globally, is caused by loss-of-function mutations in the Methyl-CpG-binding Protein-2 (Mecp2) gene. E/I imbalance is recognized as the leading cellular and synaptic hallmark that is fundamental to diverse RTT neurological symptoms, including stereotypic hand movements, impaired motor coordination, breathing irregularities, seizures, and learning/memory dysfunctions. E/I balance in RTT is not homogeneously altered but demonstrates brain region and cell type specificity instead. In this review, I elaborate on the current understanding of the loss of E/I balance in a range of brain areas at molecular and cellular levels. I further describe how the underlying cellular mechanisms contribute to the disturbance of the proper E/I ratio. Last, I discuss current pharmacologic innervations for RTT and their role in modifying the E/I balance.

Role of the Cholinergic Anti-Inflammatory Reflex in Central Nervous System Diseases

In several central nervous system diseases, it has been reported that inflammation may be related to the etiologic process, therefore, therapeutic strategies are being implemented to control inflammation. As the nervous system and the immune system maintain close bidirectional communication in physiological and pathological conditions, the modulation of inflammation through the cholinergic anti-inflammatory reflex has been proposed. In this review, we summarized the evidence supporting chemical stimulation with cholinergic agonists and vagus nerve stimulation as therapeutic strategies in the treatment of various central nervous system pathologies, and their effect on inflammation.

In vivo evidence for the cellular basis of central hypoventilation of Rett syndrome and pharmacological correction in the rat model

Rett syndrome (RTT) is a neurodevelopmental disorder caused mostly by mutations in the MECP2 gene. RTT patients show periodical hypoventilation attacks. The breathing disorder contributing to the high incidence of sudden death is thought to be due to depressed central inspiratory (I) activity via unknown cellular processes. Demonstration of such processes may lead to targets for pharmacological control of the RTT-type hypoventilation. We performed in vivo recordings from medullary respiratory neurons on the RTT rat model. To our surprise, both I and expiratory (E) neurons in the ventral respiratory column (VRC) increased their firing activity in Mecp2-null rats with severe hypoventilation. These I neurons including E-I phase-spanning and other I neurons remained active during apneas. Consistent with enhanced central I drive, ectopic phrenic discharges during expiration as well as apnea were observed in the Mecp2-null rats. Considering the increased I neuronal firing and ectopic phrenic activity, the RTT-type hypoventilation does not seem to be caused by depression in central I activity, neither reduced medullary I premotor output. This as well as excessive E neuronal firing as shown in our previous studies suggests inadequate synaptic inhibition for phase transition. We found that the abnormal respiratory neuronal firing, ectopic phrenic discharge as well as RTT-type hypoventilation all can be corrected by enhancing GABAergic inhibition. More strikingly, Mecp2-null rats reaching humane endpoints with severe hypoventilation can be rescued by GABAergic augmentation. Thus, defective GABAergic inhibition among respiratory neurons is likely to play a role in the RTT-type hypoventilation, which can be effectively controlled with pharmacological agents.

Differential signalling induced by α7 nicotinic acetylcholine receptors in hippocampal dentate gyrus in vitro and in vivo

The activation of α7 nicotinic acetylcholine receptors (nAChRs) has been shown to improve hippocampus-dependent learning and memory. α7 nAChRs are densely expressed among several different cell types in the hippocampus, with high Ca²⁺  permeability, although it is unclear if α7 nAChRs mobilize differential signalling mechanisms among distinct neuronal populations. To address this question, we compared α7 nAChR agonist-induced responses (i.e. calcium and cAMP changes) between granule cells and GABAergic neurons in the hippocampal dentate gyrus both in vitro and in vivo. In cultured organotypic hippocampal slices, we observed robust intracellular calcium and cAMP increases in dentate granule cells upon activation of α7 nAChRs. In contrast, GABAergic interneurons displayed little change in either calcium or cAMP concentration after α7 nAChR activation, even though they displayed much larger α7 nAChR current responses than those of dentate granule cells. We found that this was due to smaller α7 nAChR-induced Ca²⁺ rises in GABAergic interneurons. Thus, the regulation of the Ca²⁺ transients in different cell types resulted in differential subsequent intracellular signalling cascades and likely the ultimate outcome of α7 nAChR activation. Furthermore, we monitored neuronal activities of dentate granule cells and GABAergic interneurons in vivo via optic fibre photometry. We observed enhancement of neuronal activities after nicotine administration in dentate granule cells, but not in GABAergic neurons, which was absent in α7 nAChR-deficient granule cells. In summary, we reveal a mechanism for α7 nAChR-mediated increase of neuronal activity via cell type-specific intracellular signalling pathways. KEY POINTS: α7 nicotinic acetylcholine receptors (nAChRs) are widely distributed throughout the central nervous system and regulate a variety of brain functions including learning and memory. Understanding the cellular signalling mechanisms of their activations among different neuronal populations is important for delineating their actions in cognitive function, and developing effective treatment strategies for cognitive deficits. We report that α7 nAChR activation leads to Ca²⁺ and cAMP increases in granule cells (but not in GABAergic interneurons) in hippocampal dentate gyrus in vitro, a key region for pattern separation during learning. We also found that nicotine enhanced granule cell (but not in GABAergic interneurons) activity in an α7 nAChR-dependent manner via in vivo fibre photometry recording. Based on our findings, we propose that differential responses to α7 nAChR activation between granule cells and GABAergic interneurons is responsible for the increase of excitation by α7 nAChR agonists in hippocampal circuits synergistically.

Reviewing Evidence for the Relationship of EEG Abnormalities and RTT Phenotype Paralleled by Insights from Animal Studies

Rett syndrome (RTT) is a rare neurodevelopmental disorder that is usually caused by mutations of the MECP2 gene. Patients with RTT suffer from severe deficits in motor, perceptual and cognitive domains. Electroencephalogram (EEG) has provided useful information to clinicians and scientists, from the very first descriptions of RTT, and yet no reliable neurophysiological biomarkers related to the pathophysiology of the disorder or symptom severity have been identified to date. To identify consistently observed and potentially informative EEG characteristics of RTT pathophysiology, and ascertain areas most worthy of further systematic investigation, here we review the literature for EEG abnormalities reported in patients with RTT and in its disease models. While pointing to some promising potential EEG biomarkers of RTT, our review identify areas of need to realize the potential of EEG including (1) quantitative investigation of promising clinical-EEG observations in RTT, e.g., shift of mu rhythm frequency and EEG during sleep; (2) closer alignment of approaches between patients with RTT and its animal models to strengthen the translational significance of the work (e.g., EEG measurements and behavioral states); (3) establishment of large-scale consortium research, to provide adequate Ns to investigate age and genotype effects.

Cholinergic Signaling, Neural Excitability, and Epilepsy

Epilepsy is a common brain disorder characterized by recurrent epileptic seizures with neuronal hyperexcitability. Apart from the classical imbalance between excitatory glutamatergic transmission and inhibitory γ-aminobutyric acidergic transmission, cumulative evidence suggest that cholinergic signaling is crucially involved in the modulation of neural excitability and epilepsy. In this review, we briefly describe the distribution of cholinergic neurons, muscarinic, and nicotinic receptors in the central nervous system and their relationship with neural excitability. Then, we summarize the findings from experimental and clinical research on the role of cholinergic signaling in epilepsy. Furthermore, we provide some perspectives on future investigation to reveal the precise role of the cholinergic system in epilepsy.

Nicotinic Acetylcholine Receptor α7 Subunit Is an Essential Regulator of Seizure Susceptibility

A large body of data has confirmed that α7 nicotinic acetylcholine receptors (nAChRs) play a pivotal role in cognition, memory, and other neuropsychiatric diseases, but their effect on seizure susceptibility in C57BL/6 wild-type mice is not fully understood. Here, we showed that decreased activity of α7 nAChRs could increase the excitability of CA1 pyramidal neurons and shorten the onset time of epilepsy in pilocarpine-induced mouse models. However, compared with the control group, there was no apparent effect of increasing the activity of α7 nAChRs. Moreover, the expression of α7 nAChRs is downregulated in human epileptogenic tissues. Taken together, our findings indicate that α7 nAChR is an essential regulator of seizure susceptibility.

Pharmacological reversal of synaptic and network pathology in human MECP2-KO neurons and cortical organoids

Duplication or deficiency of the X-linked MECP2 gene reliably produces profound neurodevelopmental impairment. MECP2 mutations are almost universally responsible for Rett syndrome (RTT), and particular mutations and cellular mosaicism of MECP2 may underlie the spectrum of RTT symptomatic severity. No clinically approved treatments for RTT are currently available, but human pluripotent stem cell technology offers a platform to identify neuropathology and test candidate therapeutics. Using a strategic series of increasingly complex human stem cell-derived technologies, including human neurons, MECP2-mosaic neurospheres to model RTT female brain mosaicism, and cortical organoids, we identified synaptic dysregulation downstream from knockout of MECP2 and screened select pharmacological compounds for their ability to treat this dysfunction. Two lead compounds, Nefiracetam and PHA 543613, specifically reversed MECP2-knockout cytologic neuropathology. The capacity of these compounds to reverse neuropathologic phenotypes and networks in human models supports clinical studies for neurodevelopmental disorders in which MeCP2 deficiency is the predominant etiology.

Role of miR-132/methyl-CpG-binding protein 2 in the regulation of neural stem cell differentiation

Methyl-CpG-binding protein 2 (MeCP2) is a well-known transcription repressor, and mutations in MECP2 cause serious neurological disorders. Many studies have suggested that MeCP2 is involved in neural maturation only, and have not reported its role in neural stem cell differentiation. In the present study, we investigated this possible role of MeCP2 in neural stem cells. We used two different differentiation methods to explore how MeCP2 influences neural stem cell differentiation. When we transfected MeCP2-overexpressing lentivirus into neural stem cells, astrocytic differentiation was impaired. This impaired astrocytic differentiation occurred even in conditions of 20% fetal bovine serum, which favored astrocytic differentiation. In addition, miR-132 had the largest expression change after differentiation among several central nervous system related miRNAs. A luciferase assay confirmed that miR-132 directly targeted MeCP2, and that miR-132 was able to reduce MeCP2 expression at both the RNA and protein levels. The upregulation of miR-132 by miRNA mimics promoted astrocytic differentiation, which was fully recovered by MeCP2 overexpression. These results indicate that miR-132 regulates cell lineage differentiation by reducing MeCP2. The study was approved by the Ethics Committee of Shanghai Tenth People's Hospital of TongJi University, China (approval No. SHDSYY-2018-4748) on March 10, 2018.

The Role of Nicotinic Receptors in the Attenuation of Autism-Related Behaviors in a Murine BTBR T + tf/J Autistic Model

Nicotinic receptors are distributed throughout the central and peripheral nervous system. Postmortem studies have reported that some nicotinic receptor subtypes are altered in the brains of autistic people. Recent studies have demonstrated the importance of nicotinic acetylcholine receptors (nAChRs) in the autistic behavior of BTBR T + tf/J mouse model of autism. This study was undertaken to examine the behavioral effects of targeted nAChRs using pharmacological ligands, including nicotine and mecamylamine in BTBR T + tf/J and C57BL/6J mice in a panel of behavioral tests relating to autism. These behavioral tests included the three-chamber social interaction, self-grooming, marble burying, locomotor activity, and rotarod test. We examined the effect of various oral doses of nicotine (50, 100, and 400 mcg/mL; po) over a period of 2 weeks in BTBR T + tf/J mouse model. The results indicated that the chronic administration of nicotine modulated sociability and repetitive behavior in BTBR T + tf/J mice while no effects observed in C57BL/6J mice. Furthermore, the nonselective nAChR antagonist, mecamylamine, reversed nicotine effects on sociability and increased repetitive behaviors in BTBR T + tf/J mice. Overall, the findings indicate that the pharmacological modulation of nicotinic receptors is involved in modulating core behavioral phenotypes in the BTBR T + tf/J mouse model. LAY SUMMARY: The involvement of brain nicotinic neurotransmission system plays a crucial role in regulating autism-related behavioral features. In addition, the brain of the autistic-like mouse model has a low acetylcholine level. Here, we report that nicotine, at certain doses, improved sociability and reduced repetitive behaviors in a mouse model of autism, implicating the potential therapeutic values of a pharmacological intervention targeting nicotinic receptors for autism therapy. Autism Res 2020, 13: 1311-1334. © 2020 International Society for Autism Research, Wiley Periodicals, Inc.

Dysregulation of BRD4 Function Underlies the Functional Abnormalities of MeCP2 Mutant Neurons

Rett syndrome (RTT), mainly caused by mutations in methyl-CpG binding protein 2 (MeCP2), is one of the most prevalent intellectual disorders without effective therapies. Here, we used 2D and 3D human brain cultures to investigate MeCP2 function. We found that MeCP2 mutations cause severe abnormalities in human interneurons (INs). Surprisingly, treatment with a BET inhibitor, JQ1, rescued the molecular and functional phenotypes of MeCP2 mutant INs. We uncovered that abnormal increases in chromatin binding of BRD4 and enhancer-promoter interactions underlie the abnormal transcription in MeCP2 mutant INs, which were recovered to normal levels by JQ1. We revealed cell-type-specific transcriptome impairment in MeCP2 mutant region-specific human brain organoids that were rescued by JQ1. Finally, JQ1 ameliorated RTT-like phenotypes in mice. These data demonstrate that BRD4 dysregulation is a critical driver for RTT etiology and suggest that targeting BRD4 could be a potential therapeutic opportunity for RTT.

A Whole-Brain Cell-Type-Specific Sparse Neuron Labeling Method and Its Application in a Shank3 Autistic Mouse Model

Single neurons, as the basic unit of the brain, consist of a cell body and processes, including dendrites and axons. Even neurons of the same type show various subtle process characteristics to fit into the diverse neural circuits. Different cell types of neurons form complicated circuits in the brain. Therefore, detailed neuronal morphology is required to understand normal neuronal function and pathological mechanisms, such as those that occur in autism. Here, we developed a strategy to sparsely label the same type of neurons throughout the whole brain and tested its application in an autistic animal model—Shank3 knockout (KO) mice. To achieve this, we designed an adeno-associated virus (AAV) that expresses Cre recombinase-dependent regular and membrane-targeted enhanced green fluorescent protein (EGFP) under a human synapsin 1 promoter and verified it in several Cre transgenic mice. We could sparsely label the projection neurons in multiple brain areas by retro-ocular injection of the virus into CaMKIIα-Cre mice. Then, we analyzed the morphology of the projection neurons in Shank3 KO mice with this method. We found differential dendritic complexity and dendritic spine changes in projection neurons in Shank3 KO mice crossed with CaMKIIα-Cre mice compared with littermate control mice in the striatum, cortex, and hippocampus. By combining this method with various Cre mouse lines crossed with mouse models of disease, we can screen the morphological traits of distinct types of neurons throughout the whole brain that will help us to understand the exact role of the specific cell types of neurons not only in autism spectrum disorder (ASD) mouse models but also in other psychiatric disorder mouse models.

MeCP2 in cholinergic interneurons of nucleus accumbens regulates fear learning

Methyl-CpG-binding protein 2 (MeCP2) encoded by the MECP2 gene is a transcriptional regulator whose mutations cause Rett syndrome (RTT). Mecp2-deficient mice show fear regulation impairment; however, the cellular and molecular mechanisms underlying this abnormal behavior are largely uncharacterized. Here, we showed that Mecp2 gene deficiency in cholinergic interneurons of the nucleus accumbens (NAc) dramatically impaired fear learning. We further found that spontaneous activity of cholinergic interneurons in Mecp2-deficient mice decreased, mediated by enhanced inhibitory transmission via α2-containing GABA_A receptors. With MeCP2 restoration, opto- and chemo-genetic activation, and RNA interference in ChAT-expressing interneurons of the NAc, impaired fear retrieval was rescued. Taken together, these results reveal a previously unknown role of MeCP2 in NAc cholinergic interneurons in fear regulation, suggesting that modulation of neurons in the NAc may ameliorate fear-related disorders.

Locus-specific DNA methylation of Mecp2 promoter leads to autism-like phenotypes in mice

Autism spectrum disorder (ASD) is a neurodevelopmental disease with a strong heritability, but recent evidence suggests that epigenetic dysregulation may also contribute to the pathogenesis of ASD. Especially, increased methylation at the MECP2 promoter and decreased MECP2 expression were observed in the brains of ASD patients. However, the causative relationship of MECP2 promoter methylation and ASD has not been established. In this study, we achieved locus-specific methylation at the transcription start site (TSS) of Mecp2 in Neuro-2a cells and in mice, using nuclease-deactivated Cas9 (dCas9) fused with DNA methyltransferase catalytic domains, together with five locus-targeting sgRNAs. This locus-specific epigenetic modification led to a reduced Mecp2 expression and a series of behavioral alterations in mice, including reduced social interaction, increased grooming, enhanced anxiety/depression, and poor performance in memory tasks. We further found that specifically increasing the Mecp2 promoter methylation in the hippocampus was sufficient to induce most of the behavioral changes. Our finding therefore demonstrated for the first time the casual relationship between locus-specific DNA methylation and diseases symptoms in vivo, warranting potential therapeutic application of epigenetic editing.

An Evolving Therapeutic Rationale for Targeting the α7 Nicotinic Acetylcholine Receptor in Autism Spectrum Disorder

Abnormalities of cholinergic nuclei, cholinergic projections, and cholinergic receptors, as well as abnormalities of growth factors involved in the maturation and maintenance of cholinergic neurons, have been described in postmortem brains of persons with autism spectrum disorder (ASD). Further, microdeletions of the 15q13.3 locus that encompasses CHRNA7, the gene coding the α₇ nicotinic acetylcholine receptor (α₇ nAChR), are associated with a spectrum of neurodevelopmental disorders, including ASD. The heterozygous 15q13.3 microdeletion syndrome suggests that diminished or impaired transduction of the acetylcholine (ACh) signal by the α₇ nAChR can be a pathogenic mechanism of ASD. The α₇ nAChR has a role in regulating the firing and function of parvalbumin (PV)-expressing GABAergic projections, which synchronize the oscillatory output of assemblies of pyramidal neurons onto which they project. Synchronous oscillatory output is an electrophysiological substrate for higher executive functions, such as working memory, and functional connectivity between discrete anatomic areas of the brain. The α₇ nAChR regulates PV expression and works cooperatively with the co-expressed NMDA receptor in subpopulations of GABAergic interneurons in mouse models of ASD. An evolving literature supports therapeutic exploration of selectively targeted cholinergic interventions for the treatment of ASD, especially compounds that target the α₇ nAChR subtype. Importantly, development and availability of high-affinity, brain-penetrable, α₇ nAChR-selective agonists, partial agonists, allosteric agonists, and positive allosteric modulators (PAMs) should facilitate "proof-of-principle/concept" clinical trials. nAChRs are pentameric allosteric proteins that function as ligand-gated ion channel receptors constructed from five constituent polypeptide subunits, all of which share a common structural motif. Importantly, in addition to α₇ nAChR-gated Ca²⁺ conductance causing membrane depolarization, there are emerging data consistent with possible metabotropic functions of this ionotropic receptor. The ability of α₇-selective type II PAMs to "destabilize" the desensitized state and promote ion channel opening may afford them therapeutic advantages over orthosteric agonists. The current chapter reviews historic and recent literature supporting selective therapeutic targeting of the α₇ nAChR in persons affected with ASD.

Sensory evoked potentials in patients with Rett syndrome through the lens of animal studies: Systematic review

OBJECTIVE

Systematically review the abnormalities in event related potential (ERP) recorded in Rett Syndrome (RTT) patients and animals in search of translational biomarkers of deficits related to the particular neurophysiological processes of known genetic origin (MECP2 mutations).

METHODS

Pubmed, ISI Web of Knowledge and BIORXIV were searched for the relevant articles according to PRISMA standards.

RESULTS

ERP components are generally delayed across all sensory modalities both in RTT patients and its animal model, while findings on ERPs amplitude strongly depend on stimulus properties and presentation rate. Studies on RTT animal models uncovered the abnormalities in the excitatory and inhibitory transmission as critical mechanisms underlying the ERPs changes, but showed that even similar ERP alterations in auditory and visual domains have a diverse neural basis. A range of novel approaches has been developed in animal studies bringing along the meaningful neurophysiological interpretation of ERP measures in RTT patients.

CONCLUSIONS

While there is a clear evidence for sensory ERPs abnormalities in RTT, to further advance the field there is a need in a large-scale ERP studies with the functionally-relevant experimental paradigms.

SIGNIFICANCE

The review provides insights into domain-specific neural basis of the ERP abnormalities and promotes clinical application of the ERP measures as the non-invasive functional biomarkers of RTT pathophysiology.

Mecp2 Deletion from Cholinergic Neurons Selectively Impairs Recognition Memory and Disrupts Cholinergic Modulation of the Perirhinal Cortex

Rett Syndrome is a neurological disorder caused by mutations in the gene encoding methyl CpG binding protein 2 (MeCP2) and characterized by severe intellectual disability. The cholinergic system is a critical modulator of cognitive ability and is affected in patients with Rett Syndrome. To better understand the importance of MeCP2 function in cholinergic neurons, we studied the effect of selective Mecp2 deletion from cholinergic neurons in mice. Mice with Mecp2 deletion from cholinergic neurons were selectively impaired in assays of recognition memory, a cognitive task largely mediated by the perirhinal cortex (PRH). Deletion of Mecp2 from cholinergic neurons resulted in profound alterations in baseline firing of L5/6 neurons and eliminated the responses of these neurons to optogenetic stimulation of cholinergic input to PRH. Both the behavioral and the electrophysiological deficits of cholinergic Mecp2 deletion were rescued by inhibiting ACh breakdown with donepezil treatment.

Deep learning of spontaneous arousal fluctuations detects early cholinergic defects across neurodevelopmental mouse models and patients

Neurodevelopmental spectrum disorders like autism (ASD) are diagnosed, on average, beyond age 4 y, after multiple critical periods of brain development close and behavioral intervention becomes less effective. This raises the urgent need for quantitative, noninvasive, and translational biomarkers for their early detection and tracking. We found that both idiopathic (BTBR) and genetic (CDKL5- and MeCP2-deficient) mouse models of ASD display an early, impaired cholinergic neuromodulation as reflected in altered spontaneous pupil fluctuations. Abnormalities were already present before the onset of symptoms and were rescued by the selective expression of MeCP2 in cholinergic circuits. Hence, we trained a neural network (ConvNetACh) to recognize, with 97% accuracy, patterns of these arousal fluctuations in mice with enhanced cholinergic sensitivity (LYNX1-deficient). ConvNetACh then successfully detected impairments in all ASD mouse models tested except in MeCP2-rescued mice. By retraining only the last layers of ConvNetACh with heart rate variation data (a similar proxy of arousal) directly from Rett syndrome patients, we generated ConvNetPatients, a neural network capable of distinguishing them from typically developing subjects. Even with small cohorts of rare patients, our approach exhibited significant accuracy before (80% in the first and second year of life) and into regression (88% in stage III patients). Thus, transfer learning across species and modalities establishes spontaneous arousal fluctuations combined with deep learning as a robust noninvasive, quantitative, and sensitive translational biomarker for the rapid and early detection of neurodevelopmental disorders before major symptom onset.

Cell-Genotype Specific Effects of Mecp2 Mutation on Spontaneous and Nicotinic Acetylcholine Receptor-Evoked Currents in Medial Prefrontal Cortical Pyramidal Neurons in Female Rett Model Mice

Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutation in the X-linked MECP2 gene. Random X-inactivation produces a mosaic of mutant (MT) and wild-type (WT) neurons in female Mecp2+/- (het) mice. Many RTT symptoms are alleviated by increasing activity in medial prefrontal cortex (mPFC) in RTT model mice (Howell et al., 2017). Using a GFP-MeCP2 fusion protein to distinguish WT from MT pyramidal neurons in mPFC we found cell autonomous (cell genotype specific) and non-autonomous effects of MeCP2 deficiency on spontaneous excitatory/inhibitory balance, nicotinic acetylcholine receptor (nAChR) currents and evoked activity. MT Layer 5 and 6 (L5, L6) neurons of male nulls, and MT L6 of het mice had reduced spontaneous excitatory synaptic input compared to WT in wild-type male (WTm), female (WTf) and het mice. Inhibitory synaptic charge in MT L6 equaled WT in 2-4-month hets. At 6-7 months inhibitory charge in WT in het slices was increased compared to both MT in het and WT in WTf; however, in hets the excitatory/inhibitory charge ratio was still greater in WT compared to MT. nAChR currents were reduced in L6 of nulls and MT L6 in het slices compared to WT neurons of het, WTm and WTf. At 2-4 months, ACh perfusion increased frequency of inhibitory currents to L6 neurons equally in all genotypes but increased excitatory inputs to MT and WT in hets less than WT in WTfs. Unexpectedly ACh perfusion evoked greater sustained IPSC and EPSC input to L5 neurons of nulls compared to WTm.

Suppression of Akt-mTOR pathway rescued the social behavior in Cntnap2-deficient mice

Autism spectrum disorders (ASD) form a heterogeneous, neurodevelopmental syndrome characterized by deficits in social interactions and repetitive behavior/restricted interests. Dysregulation of mTOR signaling has been implicated in the pathogenesis of certain types of ASD, and inhibition of mTOR by rapamycin has been demonstrated to be an effective therapeutics for impaired social interaction in Tsc1+/−, Tsc2+/−, Pten−/− mice and valproic acid-induced ASD animal models. However, it is still unknown if dysregulation of mTOR signaling is responsible for the ASD-related deficit caused by other genes mutations. Contactin associated protein-like 2 (CNTNAP2) is the first widely replicated autism-predisposition gene. Mice deficient in Cntnap2 (Cntnap2−/− mice) show core ASD-like phenotypes, and have been demonstrated as a validated model for ASD-relevant drug discovery. In this study, we found hyperactive Akt-mTOR signaling in the hippocampus of Cntnap2−/− mice with RNA sequencing followed with biochemical analysis. Treatment with Akt inhibitor LY294002 or mTOR inhibitor rapamycin rescued the social deficit, but had no effect on hyperactivity and repetitive behavior/restricted behavior in Cntnap2−/− mice. We further showed that the effect of LY294002 and rapamycin on social behaviors is reversible. Our results thus identified hyperactive Akt-mTOR signaling pathway as a therapeutic target for abnormal social behavior in patients with dysfunction of CNTNAP2.

Specific Basal Forebrain-Cortical Cholinergic Circuits Coordinate Cognitive Operations

Based on recent molecular genetics, as well as functional and quantitative anatomical studies, the basal forebrain (BF) cholinergic projections, once viewed as a diffuse system, are emerging as being remarkably specific in connectivity. Acetylcholine (ACh) can rapidly and selectively modulate activity of specific circuits and ACh release can be coordinated in multiple areas that are related to particular aspects of cognitive processing. This review discusses how a combination of multiple new approaches with more established techniques are being used to finally reveal how cholinergic neurons, together with other BF neurons, provide temporal structure for behavior, contribute to local cortical state regulation, and coordinate activity between different functionally related cortical circuits. ACh selectively modulates dynamics for encoding and attention within individual cortical circuits, allows for important transitions during sleep, and shapes the fidelity of sensory processing by changing the correlation structure of neural firing. The importance of this system for integrated and fluid behavioral function is underscored by its disease-modifying role; the demise of BF cholinergic neurons has long been established in Alzheimer's disease and recent studies have revealed the involvement of the cholinergic system in modulation of anxiety-related circuits. Therefore, the BF cholinergic system plays a pivotal role in modulating the dynamics of the brain during sleep and behavior, as foretold by the intricacies of its anatomical map.

Total RNA Sequencing of Rett Syndrome Autopsy Samples Identifies the M4 Muscarinic Receptor as a Novel Therapeutic Target

Mutations in the MeCP2 gene are responsible for the neurodevelopmental disorder Rett syndrome (RTT). MeCP2 is a DNA-binding protein whose abundance and ability to complex with histone deacetylase 3 is linked to the regulation of chromatin structure. Consequently, loss-of-function mutations in MeCP2 are predicted to have broad effects on gene expression. However, to date, studies in mouse models of RTT have identified a limited number of gene or pathway-level disruptions, and even fewer genes have been identified that could be considered amenable to classic drug discovery approaches. Here, we performed RNA sequencing (RNA-seq) on nine motor cortex and six cerebellar autopsy samples from RTT patients and controls. This approach identified 1887 significantly affected genes in the motor cortex and 2110 genes in the cerebellum, with a global trend toward increased expression. Pathway-level analysis identified enrichment in genes associated with mitogen-activated protein kinase signaling, long-term potentiation, and axon guidance. A survey of our RNA-seq results also identified a significant decrease in expression of the CHRM4 gene, which encodes a receptor [muscarinic acetylcholine receptor 4 (M4)] that is the subject of multiple large drug discovery efforts for schizophrenia and Alzheimer's disease. We confirmed that CHRM4 expression was decreased in RTT patients, and, excitingly, we demonstrated that M4 potentiation normalizes social and cognitive phenotypes in Mecp2+/- mice. This work provides an experimental paradigm in which translationally relevant targets can be identified using transcriptomics in RTT autopsy samples, back-modeled in Mecp2+/- mice, and assessed for preclinical efficacy using existing pharmacological tool compounds.

mGlu7 potentiation rescues cognitive, social, and respiratory phenotypes in a mouse model of Rett syndrome

Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in the methyl-CpG binding protein 2 (MECP2) gene. The cognitive impairments seen in mouse models of RTT correlate with deficits in long-term potentiation (LTP) at Schaffer collateral (SC)-CA1 synapses in the hippocampus. Metabotropic glutamate receptor 7 (mGlu₇) is the predominant mGlu receptor expressed presynaptically at SC-CA1 synapses in adult mice, and its activation on GABAergic interneurons is necessary for induction of LTP. We demonstrate that pathogenic mutations in MECP2 reduce mGlu₇ protein expression in brain tissue from RTT patients and in MECP2-deficient mouse models. In rodents, this reduction impairs mGlu₇-mediated control of synaptic transmission. We show that positive allosteric modulation of mGlu₇ activity restores LTP and improves contextual fear learning, novel object recognition, and social memory. Furthermore, mGlu₇ positive allosteric modulation decreases apneas in Mecp2^+/- mice, suggesting that mGlu₇ may be a potential therapeutic target for multiple aspects of the RTT phenotype.

Disruption of AT-hook 1 domain in MeCP2 protein caused behavioral abnormality in mice

MECP2 is the causative gene for autism spectrum disorders, including Rett syndrome, a regressive neurodevelopmental rare disease mainly occurring in girls. Except for the distinct methyl-CpG binding domain and the transcriptional repression domain in MeCP2, three AT-hook-like domains have recently been identified. Several mutations in AT-hook 1 domain have been reported in autism cases or Rett database. However, the role of AT-hook 1 domain is still unclear. In this study, we generated a mouse line carrying deletion of eight conserved amino acids in AT-hook 1 domain by clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 technology. Mecp2^ΔAT-hook1/y mutant male mice exhibited low locomotor activity, motor incoordination and cognitive deficit. In addition, these mutant mice exhibited increased anxiety. Moreover, pain insensitivity was noted in the mutant males. However, the social interactions were unaffected in AT-hook 1 mutant mice. Thinner CA1 region of the hippocampus was observed in the mutant mice. On the molecular basis, Western blot analysis showed increased expression of mutant MeCP2 protein in the cortex. Additionally, several genes expressed specifically in inhibitory neurons were markedly changed in the cerebrum. Taken together, these data demonstrate that disruption of AT-hook 1 domain in MeCP2 caused behavioral abnormality in mice, which suggests that AT-hook 1 is a critical region for the function of MeCP2 protein.

Ablation of TFR1 in Purkinje Cells Inhibits mGlu1 Trafficking and Impairs Motor Coordination, But Not Autistic-Like Behaviors

Group 1 metabotropic glutamate receptors (mGlu1/5s) are critical to synapse formation and participate in synaptic LTP and LTD in the brain. mGlu1/5 signaling alterations have been documented in cognitive impairment, neurodegenerative disorders, and psychiatric diseases, but underlying mechanisms for its modulation are not clear. Here, we report that transferrin receptor 1 (TFR1), a transmembrane protein of the clathrin complex, modulates the trafficking of mGlu1 in cerebellar Purkinje cells (PCs) from male mice. We show that conditional knock-out of TFR1 in PCs does not affect the cytoarchitecture of PCs, but reduces mGlu1 expression at synapses. This regulation by TFR1 acts in concert with that by Rab8 and Rab11, which modulate the internalization and recycling of mGlu1, respectively. TFR1 can bind to Rab proteins and facilitate their expression at synapses. PC ablation of TFR1 inhibits parallel fiber-PC LTD, whereas parallel fiber-LTP and PC intrinsic excitability are not affected. Finally, we demonstrate that PC ablation of TFR1 impairs motor coordination, but does not affect social behaviors in mice. Together, these findings underscore the importance of TFR1 in regulating mGlu1 trafficking and suggest that mGlu1- and mGlu1-dependent parallel fiber-LTD are associated with regulation of motor coordination, but not autistic behaviors.SIGNIFICANCE STATEMENT Group 1 metabotropic glutamate receptor (mGlu1/5) signaling alterations have been documented in cognitive impairment, neurodegenerative disorders, and psychiatric diseases. Recent work suggests that altered mGlu1 signaling in Purkinje cells (PCs) may be involved in not only motor learning, but also autistic-like behaviors. We find that conditional knock-out of transferrin receptor 1 (TFR1) in PCs reduces synaptic mGlu1 by tethering Rab8 and Rab11 in the cytosol. PC ablation of TFR1 inhibits parallel fiber-PC LTD, whereas parallel fiber-PC LTP and PC intrinsic excitability are intact. Motor coordination is impaired, but social behaviors are normal in TFR1^flox/flox;pCP2-cre mice. Our data reveal a new regulator for trafficking and synaptic expression of mGlu1 and suggest that mGlu1-dependent LTD is associated with motor coordination, but not autistic-like behaviors.

Deciphering MECP2-associated disorders: disrupted circuits and the hope for repair

MECP2 is a critical gene for neural development, mutations or duplication of which led to severe neurodevelopmental disorders, such as Rett syndrome (RTT) and autism spectrum disorders (ASD). Extensive works during the past decade yield ample insights into the molecular and cellular functions of MeCP2 in neural development. Furthermore, genetic manipulations in Mecp2 mouse models strongly suggested that deficiency in synaptic plasticity and various behaviors of Mecp2 null or transgenic mice could be rescued in adulthood. Further studies elucidating neural circuits responsible for symptoms in MECP2-associated disorders in rodent and non-human primate models will shed light on the development of potential therapeutic interventions.

Dynamic changes in murine forebrain miR-211 expression associate with cholinergic imbalances and epileptiform activity

Epilepsy is a common neurological disease, manifested in unprovoked recurrent seizures. Epileptogenesis may develop due to genetic or pharmacological origins or following injury, but it remains unclear how the unaffected brain escapes this susceptibility to seizures. Here, we report that dynamic changes in forebrain microRNA (miR)-211 in the mouse brain shift the threshold for spontaneous and pharmacologically induced seizures alongside changes in the cholinergic pathway genes, implicating this miR in the avoidance of seizures. We identified miR-211 as a putative attenuator of cholinergic-mediated seizures by intersecting forebrain miR profiles that were Argonaute precipitated, synaptic vesicle target enriched, or differentially expressed under pilocarpine-induced seizures, and validated TGFBR2 and the nicotinic antiinflammatory acetylcholine receptor nAChRa7 as murine and human miR-211 targets, respectively. To explore the link between miR-211 and epilepsy, we engineered dTg-211 mice with doxycycline-suppressible forebrain overexpression of miR-211. These mice reacted to doxycycline exposure by spontaneous electrocorticography-documented nonconvulsive seizures, accompanied by forebrain accumulation of the convulsive seizures mediating miR-134. RNA sequencing demonstrated in doxycycline-treated dTg-211 cortices overrepresentation of synaptic activity, Ca²⁺ transmembrane transport, TGFBR2 signaling, and cholinergic synapse pathways. Additionally, a cholinergic dysregulated mouse model overexpressing a miR refractory acetylcholinesterase-R splice variant showed a parallel propensity for convulsions, miR-211 decreases, and miR-134 elevation. Our findings demonstrate that in mice, dynamic miR-211 decreases induce hypersynchronization and nonconvulsive and convulsive seizures, accompanied by expression changes in cholinergic and TGFBR2 pathways as well as in miR-134. Realizing the importance of miR-211 dynamics opens new venues for translational diagnosis of and interference with epilepsy.

Cellular and Circuitry Bases of Autism: Lessons Learned from the Temporospatial Manipulation of Autism Genes in the Brain

Transgenic mice carrying mutations that cause Autism Spectrum Disorders (ASDs) continue to be valuable for determining the molecular underpinnings of the disorders. Recently, researchers have taken advantage of such models combined with Cre-loxP and similar systems to manipulate gene expression over space and time. Thus, a clearer picture is starting to emerge of the cell types, circuits, brain regions, and developmental time periods underlying ASDs. ASD-causing mutations have been restricted to or rescued specifically in excitatory or inhibitory neurons, different neurotransmitter systems, and cells specific to the forebrain or cerebellum. In addition, mutations have been induced or corrected in adult mice, providing some evidence for the plasticity and reversibility of core ASD symptoms. The limited availability of Cre lines that are highly specific to certain cell types or time periods provides a challenge to determining the cellular and circuitry bases of autism, but other technological advances may eventually overcome this obstacle.

Selective preservation of cholinergic MeCP2 rescues specific Rett-syndrome-like phenotypes in MeCP2stop mice

RTT is a neurodevelopmental disorder characterized by growth regression, motor dysfunction, stereotypic hand movements, and autism features. Typical Rett syndrome (RTT) is predominantly caused by mutations in X-linked MeCP2 gene which encodes methyl-CpG-binding protein 2 (MeCP2). The brain-abundant MeCP2 protein mainly functions as a transcriptional regulator for neurodevelopment-associated genes. Specific functions of MeCP2 in certain neuron types remain to be known. Although cholinergic system is an important modulating system in brain, how MeCP2 in cholinergic neurons contribute to RTT has not been clearly understood. Here we use a mouse model with selectively activated endogenous MeCP2 in cholinergic neurons in otherwise MeCP2^stop mice to determine the cholinergic MeCP2 effects on rescuing the RTT-like phenotypes. We found cholinergic MeCP2 preservation could reverse some aspects of the RTT-like phenotypes in mice including hypolocomotion and increased anxiety level, and delay the onset of underweight, instead of improving the hypersocial abnormality and the poor general conditions such as short lifespan, low brain weight, and increasing severity score. Our findings suggest that selective activation of cholinergic MeCP2 is sufficient to reverse the locomotor impairment and increased anxiety-like behaviors at least in early symptomatic stage, supporting future development of RTT therapies associated with cholinergic system.

Restoration of Mecp2 expression in GABAergic neurons is sufficient to rescue multiple disease features in a mouse model of Rett syndrome

The postnatal neurodevelopmental disorder Rett syndrome, caused by mutations in MECP2, produces a diverse array of symptoms, including loss of language, motor, and social skills and the development of hand stereotypies, anxiety, tremor, ataxia, respiratory dysrhythmias, and seizures. Surprisingly, despite the diversity of these features, we have found that deleting Mecp2 only from GABAergic inhibitory neurons in mice replicates most of this phenotype. Here we show that genetically restoring Mecp2 expression only in GABAergic neurons of male Mecp2 null mice enhanced inhibitory signaling, extended lifespan, and rescued ataxia, apraxia, and social abnormalities but did not rescue tremor or anxiety. Female Mecp2^+/- mice showed a less dramatic but still substantial rescue. These findings highlight the critical regulatory role of GABAergic neurons in certain behaviors and suggest that modulating the excitatory/inhibitory balance through GABAergic neurons could prove a viable therapeutic option in Rett syndrome.

DOI:http://dx.doi.org/10.7554/eLife.14198.001

Rett syndrome is a childhood brain disorder that mainly affects girls and causes symptoms including anxiety, tremors, uncoordinated movements and breathing difficulties. Rett syndrome is caused by mutations in a gene called MECP2, which is found on the X chromosome. Males with MECP2 mutations are rare but have more severe symptoms and die young. Many researchers who study Rett syndrome use mice as a model of the disorder. In particular, male mice with the mouse equivalent of the human MECP2 gene switched off in every cell in the body (also known as Mecp2-null mice) show many of the features of Rett syndrome and die at a young age.

The MECP2 gene is important for healthy brain activity. The brain contains two major types of neurons: excitatory neurons, which encourage other neurons to be active; and inhibitory neurons, which stop or dampen the activity of other neurons. In 2010, researchers reported that mice lacking Mecp2 in only their inhibitory neurons develop most of the same problems as those mice with no Mecp2 at all. This discovery led Ure et al. – including a researcher involved in the 2010 study – to ask if activating Mecp2 in the same neurons in otherwise Mecp2-null mice was enough to prevent some of their Rett syndrome-like symptoms.

The experiments showed that male mice that only have Mecp2 activated in their inhibitory neurons lived several months longer than male Mecp2-null mice. These male “rescue mice” also moved normally and had a normal body weight, though they still experienced anxiety, tremors and breathing difficulties. Female mice represent a better model of human Rett syndrome patients, and Ure et al. found that female rescue mice showed smaller improvements than the males.

These data suggest that when a brain is missing Mecp2 everywhere, as in male Mecp2-null mice, turning on Mecp2 in inhibitory neurons can make the brain network nearly normal and prevent most Rett-syndrome-like symptoms. However, the brains of female rescue mice contain both normal cells and cells with mutated Mecp2. This mixture of normal and abnormal cells appears to cause abnormalities that cannot be overcome by rescuing just the activity of the inhibitory neurons. These findings also highlight the importance of doing future studies in female mice to better understand the development of Rett syndrome.

The next challenge is to test different ways of activating the inhibitory neurons in the female mouse brain, for example by using drugs that target these neurons. It is hoped these methods will help researchers to refine a path toward potential new treatments for Rett syndrome patients. Finally, in a related study, Meng et al. asked how deleting or activating Mecp2 only in the excitatory neurons of mice affected Rett-syndrome-like symptoms.

DOI:http://dx.doi.org/10.7554/eLife.14198.002