Complexities of Rett syndrome and MeCP2

MeCP2 gene therapy ameliorates disease phenotype in mouse model for Pitt Hopkins syndrome

The neurodevelopmental disorder Pitt Hopkins syndrome (PTHS) causes clinical symptoms similar to Rett syndrome (RTT) patients. However, RTT is caused by MECP2 mutations whereas mutations in the TCF4 gene lead to PTHS. The mechanistic commonalities underling these two disorders are unknown, but their shared symptomology suggest that convergent pathway-level disruption likely exists. We reprogrammed patient skin derived fibroblasts into induced neuronal progenitor cells. Interestingly, we discovered that MeCP2 levels were decreased in PTHS patient iNPCs relative to healthy controls and that both iNPCs and iAstrocytes displayed defects in function and differentiation in a mutation-specific manner. When Tcf4+/- mice were genetically crossed with mice overexpressing MeCP2, molecular and phenotypic defects were significantly ameliorated, underlining and important role of MeCP2 in PTHS pathology. Importantly, post-natal intracerebroventricular gene replacement therapy with adeno-associated viral vector serotype 9 (AAV9)-expressing MeCP2 (AAV9.P546.MeCP2) significantly improved iNPC and iAstrocyte function and effectively ameliorated histological and behavioral defects in Tcf4+/- mice. Combined, our data suggest a previously unknown role of MeCP2 in PTHS pathology and common pathways that might be affected in multiple neurodevelopmental disorders. Our work highlights potential novel therapeutic targets for PTHS, including upregulation of MeCP2 expression or its downstream targets or, potentially, MeCP2-based gene therapy.

A small-molecule TrkB ligand improves dendritic spine phenotypes and atypical behaviors in female Rett syndrome mice

Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in MECP2, which encodes methyl-CpG-binding protein 2, a transcriptional regulator of many genes, including brain-derived neurotrophic factor (BDNF). BDNF levels are lower in multiple brain regions of Mecp2-deficient mice, and experimentally increasing BDNF levels improve atypical phenotypes in Mecp2 mutant mice. Due to the low blood-brain barrier permeability of BDNF itself, we tested the effects of LM22A-4, a brain-penetrant, small-molecule ligand of the BDNF receptor TrkB (encoded by Ntrk2), on dendritic spine density and form in hippocampal pyramidal neurons and on behavioral phenotypes in female Mecp2 heterozygous (HET) mice. A 4-week systemic treatment of Mecp2 HET mice with LM22A-4 restored spine volume in MeCP2-expressing neurons to wild-type (WT) levels, whereas spine volume in MeCP2-lacking neurons remained comparable to that in neurons from female WT mice. Female Mecp2 HET mice engaged in aggressive behaviors more than WT mice, the levels of which were reduced to WT levels by the 4-week LM22A-4 treatment. These data provide additional support to the potential usefulness of novel therapies not only for RTT but also to other BDNF-related disorders.

Random allelic expression in the adult human body

Genes are typically assumed to express both parental alleles similarly, yet cell lines show random allelic expression (RAE) for many autosomal genes that could shape genetic effects. Thus, understanding RAE in human tissues could improve our understanding of phenotypic variation. Here, we develop a methodology to perform genome-wide profiling of RAE and biallelic expression in GTEx datasets for 832 people and 54 tissues. We report 2,762 autosomal genes with some RAE properties similar to randomly inactivated X-linked genes. We found that RAE is associated with rapidly evolving regions in the human genome, adaptive signaling processes, and genes linked to age-related diseases such as neurodegeneration and cancer. We define putative mechanistic subtypes of RAE distinguished by gene overlaps on sense and antisense DNA strands, aggregation in clusters near telomeres, and increased regulatory complexity and inputs compared with biallelic genes. We provide foundations to study RAE in human phenotypes, evolution, and disease.

Protein tyrosine phosphatase 1B (PTP1B) as a potential therapeutic target for neurological disorders

Protein tyrosine phosphatase 1B (PTP1B) is a typical member of the PTP family, considered a direct negative regulator of several receptor and receptor-associated tyrosine kinases. This widely localized enzyme has been involved in the pathophysiology of several diseases. More recently, PTP1B has attracted attention in the field of neuroscience, since its activation in brain cells can lead to schizophrenia-like behaviour deficits, anxiety-like effects, neurodegeneration, neuroinflammation and depression. Conversely, PTP1B inhibition has been shown to prevent microglial activation, thus exerting a potent anti-inflammatory effect and has also shown potential to increase the cognitive process through the stimulation of hippocampal insulin, leptin and BDNF/TrkB receptors. Notwithstanding, most research on the clinical efficacy of targeting PTP1B has been developed in the field of obesity and type 2 diabetes mellitus (TD2M). However, despite the link existing between these metabolic alterations and neurodegeneration, no clinical trials assessing the neurological advantages of PTP1B inhibition have been performed yet. Preclinical studies, though, have provided strong evidence that targeting PTP1B could allow to reach different pathophysiological mechanisms at once. herefore, specific interventions or trials should be designed to modulate PTP1B activity in brain, since it is a promising strategy to decelerate or prevent neurodegeneration in aged individuals, among other neurological diseases. The present paper fails to include all neurological conditions in which PTP1B could have a role; instead, it focuses on those which have been related to metabolic alterations and neurodegenerative processes. Moreover, only preclinical data is discussed, since clinical studies on the potential of PTP1B inhibition for treating neurological diseases are still required.

Development and Psychometric Properties of the Multi-System Profile of Symptoms Scale in Patients with Rett Syndrome

Background: Rett Syndrome (RTT) is a rare, neurodevelopmental disorder characterised by a range of problematic symptoms. There is yet to be a robust instrument to adequately capture the range of disease severity across the lifespan. In this study, we aimed to develop and assess the validity of an RTT-specific electronic Observer Reported Outcome (eObsRO), the Multi-System Profile of Symptoms Scale (MPSS). Methods: The study was conducted in two phases. Phase 1 consisted of a systematic literature review, focus groups, expert feedback, and a pilot test of the new scale. Modifications were made based on preliminary analysis and feedback collected in the pilot phase. Phase 2 consisted of the validation of the questionnaire based on two samples (Sample 1, n = 18; Sample 2, n = 106). Participants were all parents or caregivers of individuals with RTT. Results: The MPSS consists of 12 validated sub-scales (mental health problems, autonomic problems, cardiac problems, communication problems, problems in social behaviour, problems in engagement, gastrointestinal problems, problems in motor skills, neurological problems, orofacial problems, respiratory problems, and sleep problems), which explore symptom frequency in the past month and a supplement to the scale consisting of five sub-scales (sensory problems, immune dysfunction and infection, endocrine problems, skeletal problems, and dermatological problems), which is designed to capture symptom changes over a longer time period. The frequency of symptoms was rated on a 10-point slider scale, which then was automatically transformed into a 0 to 5 Likert score. All 12 sub-scales showed strong internal consistency (α ≥ 0.700) and good stability, ranging from 0.707 to 0.913. Pearson’s correlation showed a statistically significant (r = 0.649) correlation between the MPSS and the Rett Syndrome Behaviour Questionnaire (RSBQ) total score and significant correlations between sub-scales with items that were presented in both the MPSS and RSBQ. Conclusions: The MPSS is a psychometrically validated eObsRO using the HealthTrackerTM platform and has the potential to be used in clinical trials.

Anti-Semaphorin 4D Rescues Motor, Cognitive, and Respiratory Phenotypes in a Rett Syndrome Mouse Model

Rett syndrome is a neurodevelopmental disorder caused by mutations of the methyl-CpG binding protein 2 gene. Abnormal physiological functions of glial cells contribute to pathogenesis of Rett syndrome. Semaphorin 4D (SEMA4D) regulates processes central to neuroinflammation and neurodegeneration including cytoskeletal structures required for process extension, communication, and migration of glial cells. Blocking SEMA4D-induced gliosis may preserve normal glial and neuronal function and rescue neurological dysfunction in Rett syndrome. We evaluated the pre-clinical therapeutic efficacy of an anti-SEMA4D monoclonal antibody in the Rett syndrome Mecp2T158A transgenic mouse model and investigated the contribution of glial cells as a proposed mechanism of action in treated mice and in primary glial cultures isolated from Mecp2T158A/y mutant mice. SEMA4D is upregulated in neurons while glial fibrillary acidic protein and ionized calcium binding adaptor molecule 1-positive cells are upregulated in Mecp2T158A/y mice. Anti-SEMA4D treatment ameliorates Rett syndrome-specific symptoms and improves behavioural functions in both pre-symptomatic and symptomatic cohorts of hemizygous Mecp2T158A/y male mice. Anti-SEMA4D also reduces astrocyte and microglia activation in vivo. In vitro experiments demonstrate an abnormal cytoskeletal structure in mutant astrocytes in the presence of SEMA4D, while anti-SEMA4D antibody treatment blocks SEMA4D–Plexin B1 signaling and mitigates these abnormalities. These results suggest that anti-SEMA4D immunotherapy may be an effective treatment option to alleviate symptoms and improve cognitive and motor function in Rett syndrome.

Circulating 4-F4t-Neuroprostane and 10-F4t-Neuroprostane Are Related to MECP2 Gene Mutation and Natural History in Rett Syndrome

Neuroprostanes, a family of non-enzymatic metabolites of the docosahexaenoic acid, have been suggested as potential biomarkers for neurological diseases. Objective biological markers are strongly needed in Rett syndrome (RTT), which is a progressive X-linked neurodevelopmental disorder that is mainly caused by mutations in the methyl-CpG binding protein 2 (MECP2) gene with a predominant multisystemic phenotype. The aim of the study is to assess a possible association between MECP2 mutations or RTT disease progression and plasma levels of 4(RS)-4-F_4t-neuroprostane (4-F_4t-NeuroP) and 10(RS)-10-F_4t-neuroprostane (10-F_4t-NeuroP) in typical RTT patients with proven MECP2 gene mutation. Clinical severity and disease progression were assessed using the Rett clinical severity scale (RCSS) in n = 77 RTT patients. The 4-F_4t-NeuroP and 10-F_4t-NeuroP molecules were totally synthesized and used to identify the contents of the plasma of the patients. Neuroprostane levels were related to MECP2 mutation category (i.e., early truncating, gene deletion, late truncating, and missense), specific hotspot mutations (i.e., R106W, R133C, R168X, R255X, R270X, R294X, R306C, and T158M), and disease stage (II through IV). Circulating 4-F_4t-NeuroP and 10-F_4t-NeuroP were significantly related to (i) the type of MECP2 mutations where higher levels were associated to gene deletions (p ≤ 0.001); (ii) severity of common hotspot MECP2 mutation (large deletions, R168X, R255X, and R270X); (iii) disease stage, where higher concentrations were observed at stage II (p ≤ 0.002); and (iv) deficiency in walking (p ≤ 0.0003). This study indicates the biological significance of 4-F_4t-NeuroP and 10-F_4t-NeuroP as promising molecules to mark the disease progression and potentially gauge genotype-phenotype associations in RTT.

miR-132 downregulation alleviates behavioral impairment of rats exposed to single prolonged stress, reduces the level of apoptosis in PFC, and upregulates the expression of MeCP2 and BDNF

Post-traumatic stress disorder (PTSD) is usually accompanied by anxiety symptoms and decreased expression of brain-derived neurotrophic factor (BDNF), which played an important role in promoting neuronal proliferation and survival. Methyl CpG-binding protein 2 (MeCP2) is a positive mediator of BDNF and is regulated by miR-132-3p. In the present study, we explored the possible molecular mechanism of miR-132, focusing on the involvement of MeCP2 and BDNF in the formation of anxiety-like symptoms of PTSD. Single prolonged stress (SPS) was used to establish a model of PTSD in adult rats and the anxiety-like behavior was tested by the elevated plus-maze (EPM). The level of miR-132 in the prefrontal cortex (PFC) was increased and intraventricular injection of anti-miR-132 could significantly improve the anxiety-like behavior of rats exposed to SPS through MeCP2 and the subsequent upregulation of BDNF levels. Then tropomyosin-related kinase B (TrkB) and downstream signals, including MAP kinase ERK1/2 and phosphoinositol 3-kinase (PI3K)/Akt pathways, were activated by BDNF upregulation, and might participate in regulating dendritic complexity and the expression of postsynaptic density-95 (PSD95) and synapsin I in the PFC of SPS rats. Furthermore, we found that the apoptosis of cells in PFC induced by SPS procedure could be alleviated by miR-132 inhibition. Our results suggest that miR-132 might be involved in the formation of anxiety-like symptoms of adult rat PTSD models by targeting MeCP2, and this effect is related to BDNF/TrkB and its downstream ERK and Akt signaling pathways.

Severe offtarget effects following intravenous delivery of AAV9-MECP2 in a female mouse model of Rett syndrome

Rett syndrome (RTT) is a severe X-linked neurodevelopmental disorder that is primarily caused by mutations in the methyl CpG binding protein 2 gene (MECP2). RTT is the second most prevalent genetic cause of intellectual disability in girls, and there is currently no cure for the disease. We have previously shown that gene therapy using a self-complementary AAV9 viral vector expressing a codon-optimized Mecp2 version (AAV9-MCO) significantly improved symptoms and increased survival in male Mecp2-deficient mice. Here, we pursued our studies and investigated the safety and efficacy of long-term gene therapy in the genetically relevant RTT mouse model: the heterozygous (HET) Mecp2 deficient female mouse. These mice were injected with the AAV9-MCO vector through the tail vein and an array of behavioral tests was performed. At 16- and 30-weeks post-injection, this treatment was able to rescue apneas and improved the spontaneous locomotor deficits and circadian locomotor activity in Mecp2 HET mice treated with AAV9-MCO at a dose of 5 × 10¹¹ vg/mouse. To examine whether a higher dose of vector could result in increased improvements, we injected Mecp2 HET mice with a higher MCO vector dose (10¹² vg/mouse), which resulted in some severe, sometimes lethal, side effects. In order to confirm these effects, a new cohort of Mecp2 HET mice were administered increasing doses of MCO vector (10¹¹, 5 × 10¹¹ and 10¹² vg/mouse). Again, two weeks after vector administration, some Mecp2 HET mice were found dead while others displayed severe side effects and had to be euthanized. These deleterious effects were not observed in Mecp2 HET mice injected with a high dose of AAV9-GFP and were directly proportionate to vector dosage (0, 23 or 54% mortality at an AAV9-MCO dose of 10¹¹, 5 × 10¹¹, 10¹² vg/mouse, respectively), and no such lethality was observed in wild-type (WT) mice. In the Mecp2 HET mice treated with the high and medium AAV9-MCO doses, blood chemistry analysis and post-mortem histology showed liver damage with drastically elevated levels of liver transaminases and disorganized liver architecture. Apoptosis was confirmed by the presence of TUNEL- and cleaved-caspase 3-positive cells in the Mecp2 HET mice treated with the higher doses of AAV9-MCO. We then studied the involvement of the unfolded protein response (UPR) in triggering apoptosis since it can be activated by AAV vectors. Increased expression of the C/EBP homologous protein (CHOP), one of UPR downstream effectors, was confirmed in Mecp2 HET mice after vector administration. The toxic reaction seen in some treated mice indicates that, although gene therapy for RTT improved breathing deficits observed in Mecp2 HET mice, further studies are needed to better understand the underlying mechanisms and caution must be exercised before similar attempts are undertaken in female Rett patients.

Graded and pan-neural disease phenotypes of Rett Syndrome linked with dosage of functional MeCP2

Rett syndrome (RTT) is a progressive neurodevelopmental disorder, mainly caused by mutations in MeCP2 and currently with no cure. We report here that neurons from R106W MeCP2 RTT human iPSCs as well as human embryonic stem cells after MeCP2 knockdown exhibit consistent and long-lasting impairment in maturation as indicated by impaired action potentials and passive membrane properties as well as reduced soma size and spine density. Moreover, RTT-inherent defects in neuronal maturation could be pan-neuronal and occurred in neurons with both dorsal and ventral forebrain features. Knockdown of MeCP2 led to more severe neuronal deficits as compared to RTT iPSC-derived neurons, which appeared to retain partial function. Strikingly, consistent deficits in nuclear size, dendritic complexity and circuitry-dependent spontaneous postsynaptic currents could only be observed in MeCP2 knockdown neurons but not RTT iPSC-derived neurons. Both neuron-intrinsic and circuitry-dependent deficits of MeCP2-deficient neurons could be fully or partially rescued by re-expression of wild type or T158M MeCP2, strengthening the dosage dependency of MeCP2 on disease phenotypes and also the partial function of the mutant. Our findings thus reveal stable neuronal maturation deficits and unexpectedly, graded sensitivities of neuron-inherent and neural transmission phenotypes towards the extent of MeCP2 deficiency, which is informative for future therapeutic development.

Brain protein changes in Mecp2 mouse mutant models: Effects on disease progression of Mecp2 brain specific gene reactivation

Rett syndrome (RTT) is a leading cause of severe intellectual disability in females, caused by de novo loss-of function mutations in the X-linked methyl-CpG binding protein 2 (MECP2). To better investigate RTT disease progression/pathogenesis animal models of Mecp2 deficiency have been developed. Here, Mecp2 mouse models are employed to investigate the role of protein patterns in RTT. A proteome analysis was carried out in brain tissue from i) Mecp2 deficient mice at the pre-symptomatic and symptomatic stages and, ii) mice in which the disease phenotype was reversed by Mecp2 reactivation. Several proteins were shown to be differentially expressed in the pre-symptomatic (n = 18) and symptomatic (n = 20) mice. Mecp2 brain reactivated mice showed wild-type comparable levels of expression for twelve proteins, mainly related to proteostasis (n = 4) and energy metabolic pathways (n = 4). The remaining ones were found to be involved in redox homeostasis (n = 2), nitric oxide regulation (n = 1), neurodevelopment (n = 1). Ten out of twelve proteins were newly linked to Mecp2 deficiency. Our study sheds light on the relevance of the protein-regulation of main physiological process in the complex mechanisms leading from Mecp2 mutation to the RTT clinical phenotype. SIGNIFICANCE: We performed a proteomic study of a Mecp2^stop/y mouse model for Rett syndrome (RTT) at the pre-symptomatic and symptomatic Mecp2 deficient mice stage and for the brain specific reactivated Mecp2 model. Our results reveal major protein expression changes pointing out to defects in proteostasis or energy metabolic pathways other than, to a lesser extent, in redox homeostasis, nitric oxide regulation or neurodevelopment. The Mecp2 mouse rescued model provides the possibility to select target proteins more susceptible to the Mecp2 gene mutation, potential and promising therapeutical targets.

Genomic insights into MeCP2 function: A role for the maintenance of chromatin architecture

Methyl-CpG binding protein 2 (MeCP2) plays fundamental roles in the nervous system, as both gain-of-function and loss-of-function of MECP2 are associated with severe neurological conditions. Understanding the molecular function of MeCP2 will not only provide insights into the pathogenesis of MeCP2-related disorders, but will also shed light on the epigenetic regulation of neuronal function. In the past few years, a number of studies have provided mechanistic evidence that MeCP2 recruits co-repressor complexes to particular sequences of methylated DNA. Additionally, innovative design and high-throughput sequencing technologies have provided opportunities to study the effects of MeCP2 on the neuronal transcriptome at an unprecedented level of detail, demonstrating that MeCP2 modulates gene expression in a context-specific manner. These findings have raised new questions and challenged current models of MeCP2 function. In this review, we describe several recent developments, highlight future challenges, and articulate a model by which MeCP2 functions as an organizer of chromatin architecture to modulate global gene expression in the nervous system.

Glial Dysfunction in MeCP2 Deficiency Models: Implications for Rett Syndrome

Rett syndrome (RTT) is a rare, X-linked neurodevelopmental disorder typically affecting females, resulting in a range of symptoms including autistic features, intellectual impairment, motor deterioration, and autonomic abnormalities. RTT is primarily caused by the genetic mutation of the Mecp2 gene. Initially considered a neuronal disease, recent research shows that glial dysfunction contributes to the RTT disease phenotype. In the following manuscript, we review the evidence regarding glial dysfunction and its effects on disease etiology.

Disturbed redox homeostasis and oxidative stress: Potential players in the developmental regression in Rett syndrome

Rett syndrome (RTT) is a neurodevelopmental disorder affecting mostly girls. A seemingly normal initial development is followed by developmental stagnation and regression, leading to severe mental impairment with autistic features, motor dysfunction, irregular breathing and epilepsy. Currently, a cure does not exist. Due to the close association of RTT with mitochondrial alterations, cellular redox-impairment and oxidative stress, compounds stabilizing mitochondrial function, cellular redox-homeostasis, and oxidant detoxification are increasingly considered as treatment concepts. Indeed, antioxidants and free-radical scavengers ameliorate certain aspects of the complex and severe clinical presentation of RTT. To further evaluate these strategies, reliable biosensors are needed to quantify redox-conditions in brain and peripheral organs of mouse models or in patient-derived cells. Genetically-encoded redox-sensors meet these requirements. Expressed in transgenic mouse-models such as our unique Rett-redox indicator mice, they will report for any cell type desired the severity of oxidant stress throughout the various disease stages of RTT. Furthermore, these sensors will be crucial to evaluate in vitro and in vivo the outcome of mitochondria- and redox-balance targeted treatments.

Measuring Preweaning Sensorial and Motor Development in the Mouse

The immaturity at birth and the slowness of ontogenic processes in mice provide the opportunity to measure rates of development. We describe here 18 measures covering the sensorial and motor onset from birth to weaning. The measures are non-invasive, making a follow-up strategy possible. The first basic protocol indicates how to produce mice with known conceptional or chronological age, as the control of the age is a prerequisite to compare rates of development in groups of mice. The second basic protocol describes a set of methods for identifying the pups during a follow-up study. A third basic protocol describes testing newborn mice for the appearance of sensorial and motor abilities in a follow-up design. Taken together, the three protocols make possible the validation of potential murine models of interest for understanding human developmental disorders. © 2018 by John Wiley & Sons, Inc.

Neural stem cells from a mouse model of Rett syndrome are prone to senescence, show reduced capacity to cope with genotoxic stress, and are impaired in the differentiation process

Several aspects of stem cell life are governed by epigenetic variations, such as DNA methylation, histone modifications, and chromatin remodeling. Epigenetic events are also connected with the impairment of stem cell functions. For example, during senescence, there are significant changes in chromatin organization that alter transcription. The MECP2 protein can bind methylated cytosines and contribute to regulating gene expression at one of the highest hierarchical levels. Researchers are particularly interested in this protein, as up to 90% of Rett syndrome patients have an MECP2 gene mutation. Nevertheless, the role of MECP2 in this disease remains poorly understood. We used a mouse model of Rett syndrome to evaluate whether residual MECP2 activity in neural stem cells (NSCs) induced the senescence phenomena that could affect stem cell function. Our study clearly demonstrated that the reduced expression of MECP2 is connected with an increase in senescence, an impairment in proliferation capacity, and an accumulation of unrepaired DNA foci. Mecp2^+/− NSCs did not cope with genotoxic stress in the same way as the control cells did. Indeed, after treatment with different DNA-damaging agents, the NSCs from mice with mutated Mecp2 accumulated more DNA damage foci (γ-H2AX+) and were more prone to cell death than the controls. Senescence in Mecp2^+/− NSCs decreased the number of stem cells and progenitors and gave rise to a high percentage of cells that expressed neither stem/progenitor nor differentiation markers. These cells could be senescent and dysfunctional.

In Rett syndrome, neural stem cells lose some of their “stem cell like” properties, impairing brain functions. Patients with this rare neurological condition, almost exclusively girls, show impaired movement and speech beginning at 6–18 months of age. Mutations in the MECP2 gene are known to be involved, but the specifics are poorly understood. Umberto Galderisi at Temple University in Philadelphia and co-workers in Italy used a mouse model to trace how MECP2 mutations affect neural stem cells. They found that the mutated cells lost key stem cell abilities, including the capacity to renew themselves by dividing, and the ability to differentiate, or turn into other cell types. The cells were also highly susceptible to DNA damage and unable to repair it. These results improve our understanding of Rett syndrome and may help develop new treatments.

CREB Signaling Is Involved in Rett Syndrome Pathogenesis

Rett syndrome (RTT) is a debilitating neurodevelopmental disorder caused by mutations in the MECP2 gene. To facilitate the study of cellular mechanisms in human cells, we established several human stem cell lines: human embryonic stem cell (hESC) line carrying the common T158M mutation (MECP2^T158M/T158M ), hESC line expressing no MECP2 (MECP2-KO), congenic pair of wild-type and mutant RTT patient-specific induced pluripotent stem cell (iPSC) line carrying the V247fs mutation (V247fs-WT and V247fs-MT), and iPSC line in which the V247fs mutation was corrected by CRISPR/Cas9-based genome editing (V247fs-MT-correction). Detailed analyses of forebrain neurons differentiated from these human stem cell lines revealed genotype-dependent quantitative phenotypes in neurite growth, dendritic complexity, and mitochondrial function. At the molecular level, we found a significant reduction in the level of CREB and phosphorylated CREB in forebrain neurons differentiated from MECP2^T158M/T158M , MECP2-KO, and V247fs-MT stem cell lines. Importantly, overexpression of CREB or pharmacological activation of CREB signaling in those forebrain neurons rescued the phenotypes in neurite growth, dendritic complexity, and mitochondrial function. Finally, pharmacological activation of CREB in the female Mecp2 heterozygous mice rescued several behavioral defects. Together, our study establishes a robust in vitro platform for consistent quantitative evaluation of genotype-dependent RTT phenotypes, reveals a previously unappreciated role of CREB signaling in RTT pathogenesis, and identifies a potential therapeutic target for RTT.SIGNIFICANCE STATEMENT Our study establishes a robust human stem cell-based platform for consistent quantitative evaluation of genotype-dependent Rett syndrome (RTT) phenotypes at the cellular level. By providing the first evidence that enhancing cAMP response element binding protein signaling can alleviate RTT phenotypes both in vitro and in vivo, we reveal a previously unappreciated role of cAMP response element binding protein signaling in RTT pathogenesis, and identify a potential therapeutic target for RTT.

A codon-optimized Mecp2 transgene corrects breathing deficits and improves survival in a mouse model of Rett syndrome

Rett syndrome (RTT) is a severe X-linked neurodevelopmental disorder that is primarily caused by mutations in the methyl CpG binding protein 2 gene (MECP2). RTT is the second most prevalent cause of intellectual disability in girls and there is currently no cure for the disease. The finding that the deficits caused by the loss of Mecp2 are reversible in the mouse has bolstered interest in gene therapy as a cure for RTT. In order to assess the feasibility of gene therapy in a RTT mouse model, and in keeping with translational goals, we investigated the efficacy of a self-complementary AAV9 vector expressing a codon-optimized version of Mecp2 (AAV9-MCO) delivered via a systemic approach in early symptomatic Mecp2-deficient (KO) mice. Our results show that AAV9-MCO administered at a dose of 2×10¹¹ viral genome (vg)/mouse was able to significantly increase survival and weight gain, and delay the occurrence of behavioral deficits. Apneas, which are one of the core RTT breathing deficits, were significantly decreased to WT levels in Mecp2 KO mice after AAV9-MCO administration. Semi-quantitative analysis showed that AAV9-MCO administration in Mecp2 KO mice resulted in 10 to 20% Mecp2 immunopositive cells compared to WT animals, with the highest Mecp2 expression found in midbrain regions known to regulate cardio-respiratory functions. In addition, we also found a cell autonomous increase in tyrosine hydroxylase levels in the A1C1 and A2C2 catecholaminergic Mecp2+ neurons in treated Mecp2 KO mice, which may partly explain the beneficial effect of AAV9-MCO administration on apneas occurrence.

Pathogenesis of Börjeson-Forssman-Lehmann syndrome: Insights from PHF6 function

Intellectual disability encompasses a large set of neurodevelopmental disorders of cognition that are more common in males than females. Although mutations in over 100 X-linked genes associated to intellectual disability have been identified, only a few X-linked intellectual disability proteins have been intensively studied. Hence, the molecular mechanisms underlying the majority of X-linked intellectual disability disorders remain poorly understood. A substantial fraction of X-linked intellectual disability genes encode nuclear proteins, suggesting that elucidating their functions in the regulation of transcription may provide novel insights into the pathogenesis of intellectual disability. Recent studies have uncovered mechanisms by which mutations of the gene encoding plant homeodomain (PHD)-like finger protein 6 (PHF6) contribute to the pathogenesis of the X-linked intellectual disability disorder Börjeson-Forssman-Lehmann syndrome (BFLS). PHF6 plays a critical role in the migration of neurons in the mouse cerebral cortex in vivo, and patient-specific mutations disrupt the ability of PHF6 to promote neuronal migration. Interestingly, PHF6 physically associates with the PAF1 transcriptional elongation complex and thereby drives neuronal migration in the cerebral cortex. PHF6 also interacts with the NuRD chromatin remodeling complex and with the nucleolar transcriptional regulator UBF, though the biological role of these interactions remains to be characterized. In other studies, PHF6 mRNA has been identified as the target of the microRNA miR-128 in the cerebral cortex, providing new insights into regulation of PHF6 function in neuronal migration. Importantly, deregulation of PHF6 function in neuronal migration triggers the formation of white matter heterotopias that harbor neuronal hyperexcitability, which may be relevant to the pathogenesis of intellectual disability and seizures in BFLS. Collectively, these studies are beginning to provide key insights into the molecular pathogenesis of BFLS.

Functional conservation of MBD proteins: MeCP2 and Drosophila MBD proteins alter sleep

Proteins containing a methyl-CpG-binding domain (MBD) bind 5mC and convert the methylation pattern information into appropriate functional cellular states. The correct readout of epigenetic marks is of particular importance in the nervous system where abnormal expression or compromised MBD protein function, can lead to disease and developmental disorders. Recent evidence indicates that the genome of Drosophila melanogaster is methylated and two MBD proteins, dMBD2/3 and dMBD-R2, are present. Are Drosophila MBD proteins required for neuronal function, and as MBD-containing proteins have diverged and evolved, does the MBD domain retain the molecular properties required for conserved cellular function across species? To address these questions, we expressed the human MBD-containing protein, hMeCP2, in distinct amine neurons and quantified functional changes in sleep circuitry output using a high throughput assay in Drosophila. hMeCP2 expression resulted in phase-specific sleep loss and sleep fragmentation with the hMeCP2-mediated sleep deficits requiring an intact MBD domain. Reducing endogenous dMBD2/3 and dMBD-R2 levels also generated sleep fragmentation, with an increase in sleep occurring upon dMBD-R2 reduction. To examine if hMeCP2 and dMBD-R2 are targeting common neuronal functions, we reduced dMBD-R2 levels in combination with hMeCP2 expression and observed a complete rescue of sleep deficits. Furthermore, chromosomal binding experiments indicate MBD-R2 and MeCP2 associate on shared genomic loci. Our results provide the first demonstration that Drosophila MBD-containing family members are required for neuronal function and suggest that the MBD domain retains considerable functional conservation at the whole organism level across species.

Essential Roles for ARID1B in Dendritic Arborization and Spine Morphology of Developing Pyramidal Neurons

De novo truncating mutations in ARID1B, a chromatin-remodeling gene, cause Coffin-Siris syndrome, a developmental disorder characterized by intellectual disability and speech impairment; however, how the genetic elimination leads to cognitive dysfunction remains unknown. Thus, we investigated the neural functions of ARID1B during brain development. Here, we show that ARID1B regulates dendritic differentiation in the developing mouse brain. We knocked down ARID1B expression in mouse pyramidal neurons using in utero gene delivery methodologies. ARID1B knockdown suppressed dendritic arborization of cortical and hippocampal pyramidal neurons in mice. The abnormal development of dendrites accompanied a decrease in dendritic outgrowth into layer I. Furthermore, knockdown of ARID1B resulted in aberrant dendritic spines and synaptic transmission. Finally, ARID1B deficiency led to altered expression of c-Fos and Arc, and overexpression of these factors rescued abnormal differentiation induced by ARID1B knockdown. Our results demonstrate a novel role for ARID1B in neuronal differentiation and provide new insights into the origin of cognitive dysfunction associated with developmental intellectual disability.

SIGNIFICANCE STATEMENT

Haploinsufficiency of ARID1B, a component of chromatin remodeling complex, causes intellectual disability. However, the role of ARID1B in brain development is unknown. Here, we demonstrate that ARID1B is required for neuronal differentiation in the developing brain, such as in dendritic arborization and synapse formation. Our findings suggest that ARID1B plays a critical role in the establishment of cognitive circuitry by regulating dendritic complexity. Thus, ARID1B deficiency may cause intellectual disability via abnormal brain wiring induced by the defective differentiation of cortical neurons.

Quantitative and qualitative insights into the experiences of children with Rett syndrome and their families

Rett syndrome is a rare neurodevelopmental disorder caused by a mutation in the MECP2 gene. It is associated with severe functional impairments and medical comorbidities such as scoliosis and poor growth. The population-based and longitudinal Australian Rett Syndrome Database was established in 1993 and has supported investigations of the natural history of Rett syndrome and effectiveness of treatments, as well as a suite of qualitative studies to identify deeper meanings. This paper describes the early presentation of Rett syndrome, including regression and challenges for families seeking a diagnosis. We discuss the importance of implementing strategies to enhance daily communication and movement, describe difficulties interpreting the presence of pain and discomfort, and argue for a stronger evidence base in relation to management. Finally, we outline a framework for understanding quality of life in Rett syndrome and suggest areas of life to which we can direct efforts in order to improve quality of life. Each of these descriptions is illustrated with vignettes of child and family experiences. Clinicians and researchers must continue to build this framework of knowledge and understanding with efforts committed to providing more effective treatments and supporting the best quality of life for those affected.

Loss of MeCP2 in the rat models regression, impaired sociability and transcriptional deficits of Rett syndrome

Mouse models of the transcriptional modulator Methyl-CpG-Binding Protein 2 (MeCP2) have advanced our understanding of Rett syndrome (RTT). RTT is a 'prototypical' neurodevelopmental disorder with many clinical features overlapping with other intellectual and developmental disabilities (IDD). Therapeutic interventions for RTT may therefore have broader applications. However, the reliance on the laboratory mouse to identify viable therapies for the human condition may present challenges in translating findings from the bench to the clinic. In addition, the need to identify outcome measures in well-chosen animal models is critical for preclinical trials. Here, we report that a novel Mecp2 rat model displays high face validity for modelling psychomotor regression of a learned skill, a deficit that has not been shown in Mecp2 mice. Juvenile play, a behavioural feature that is uniquely present in rats and not mice, is also impaired in female Mecp2 rats. Finally, we demonstrate that evaluating the molecular consequences of the loss of MeCP2 in both mouse and rat may result in higher predictive validity with respect to transcriptional changes in the human RTT brain. These data underscore the similarities and differences caused by the loss of MeCP2 among divergent rodent species which may have important implications for the treatment of individuals with disease-causing MECP2 mutations. Taken together, these findings demonstrate that the Mecp2 rat model is a complementary tool with unique features for the study of RTT and highlight the potential benefit of cross-species analyses in identifying potential disease-relevant preclinical outcome measures.

How can clinical ethics guide the management of comorbidities in the child with Rett syndrome?

Rett syndrome is a rare disorder caused by a mutation in the MECP2 gene. Those affected generally have severe functional impairments, and medical comorbidities such as scoliosis and poor growth are common. There is a paucity of information on the natural history of many rare disorders and an even greater deficit of evidence to guide best practice. The population-based and longitudinal Australian Rett Syndrome Database established in 1993 has supported investigations of the natural history of Rett syndrome and effectiveness of treatments. This paper reviews the disorder Rett syndrome and evidence for the management of scoliosis and poor growth within a clinical ethics framework. Compared with conservative management, we have shown that spinal fusion is associated with reduced mortality and better respiratory health. We have also shown that gastrostomy insertion is associated with subsequent weight gain. Family counselling for both procedures necessarily must include family perspectives and careful clinical attention to their needs and wishes. Vignettes describing family decision-making and experiences are presented to illustrate the principals of beneficence and autonomy in determining the best interests of the child and family. A blend of evidence-based practice with a strong clinical ethics framework has capacity to build existing strengths in families and reduce the negative impacts of disability and in so doing, optimise the health and wellbeing of those with Rett syndrome.

Where Environment Meets Cognition: A Focus on Two Developmental Intellectual Disability Disorders

One of the most challenging questions in neuroscience is to dissect how learning and memory, the foundational pillars of cognition, are grounded in stable, yet plastic, gene expression states. All known epigenetic mechanisms such as DNA methylation and hydroxymethylation, histone modifications, chromatin remodelling, and noncoding RNAs regulate brain gene expression, both during neurodevelopment and in the adult brain in processes related to cognition. On the other hand, alterations in the various components of the epigenetic machinery have been linked to well-known causes of intellectual disability disorders (IDDs). Two examples are Down Syndrome (DS) and Fragile X Syndrome (FXS), where global and local epigenetic alterations lead to impairments in synaptic plasticity, memory, and learning. Since epigenetic modifications are reversible, it is theoretically possible to use epigenetic drugs as cognitive enhancers for the treatment of IDDs. Epigenetic treatments act in a context specific manner, targeting different regions based on cell and state specific chromatin accessibility, facilitating the establishment of the lost balance. Here, we discuss epigenetic studies of IDDs, focusing on DS and FXS, and the use of epidrugs in combinatorial therapies for IDDs.

Characterization of Rett Syndrome-like phenotypes in Mecp2-knockout rats

Background

Rett Syndrome (RTT) is a neurodevelopmental disease caused by the disruption of the MECP2 gene. Several mouse models of RTT have been developed with Mecp2 disruptions. Although the mouse models are widely used in RTT research, results obtained need to be validated in other species. Therefore, we performed these studies to characterize phenotypes of a novel Mecp2^−/Y rat model and compared them with the Mecp2^tm1.1Bird mouse model of RTT.

Methods

RTT-like phenotypes were systematically studied and compared between Mecp2^−/Y rats and Mecp2^−/Y mice. In-cage conditions of the rats were monitored. Grip strength and spontaneous locomotion were used to evaluate the motor function. Three-chamber test was performed to show autism-type behaviors. Breathing activity was recorded with the plethysmograph. Individual neurons in the locus coeruleus (LC) were studied in the whole-cell current clamp. The lifespan of the rats was determined with their survival time.

Results

Mecp2^−/Y rats displayed growth retardation, malocclusion, and lack of movements, while hindlimb clasping was not seen. They had weaker forelimb grip strength and a lower rate of locomotion than the WT littermates. Defects in social interaction with other rats were obvious. Breathing frequency variation and apnea in the null rats were significantly higher than in the WT. LC neurons in the null rats showed excessive firing activity. A half of the null rats died in 2 months. Most of the RTT-like symptoms were comparable to those seen in Mecp2^−/Y mice, while some appeared more or less severe. The findings that most RTT-like symptoms exist in the rat model with moderate variations and differences from the mouse models support the usefulness of both Mecp2^−/Y rodent models.

Conclusions

The novel Mecp2^−/Y rat model recapitulated numerous RTT-like symptoms as Mecp2^−/Y mouse models did, which makes it a valuable alternative model in the RTT studies when the body size matters.

Transcriptome analysis of human brain tissue identifies reduced expression of complement complex C1Q Genes in Rett syndrome

Background

MECP2, the gene mutated in the majority of Rett syndrome cases, is a transcriptional regulator that can activate or repress transcription. Although the transcription regulatory function of MECP2 has been known for over a decade, it remains unclear how transcriptional dysregulation leads to the neurodevelopmental disorder. Notably, little convergence was previously observed between the genes abnormally expressed in the brain of Rett syndrome mouse models and those identified in human studies.

Methods

Here we carried out a comprehensive transcriptome analysis of human brain tissue from Rett syndrome brain using both RNA-seq and microarrays.

Results

We identified over two hundred differentially expressed genes, and identified the complement C1Q complex genes (C1QA, C1QB and C1QC) as a point of convergence between gene expression changes in human and mouse Rett syndrome brain.

Conclusions

The results of our study support a role for alterations in the expression level of C1Q complex genes in RTT pathogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2746-7) contains supplementary material, which is available to authorized users.

MECP2 Duplication Syndrome: Evidence of Enhanced Oxidative Stress. A Comparison with Rett Syndrome

Rett syndrome (RTT) and MECP2 duplication syndrome (MDS) are neurodevelopmental disorders caused by alterations in the methyl-CpG binding protein 2 (MECP2) gene expression. A relationship between MECP2 loss-of-function mutations and oxidative stress has been previously documented in RTT patients and murine models. To date, no data on oxidative stress have been reported for the MECP2 gain-of-function mutations in patients with MDS. In the present work, the pro-oxidant status and oxidative fatty acid damage in MDS was investigated (subjects n = 6) and compared to RTT (subjects n = 24) and healthy condition (subjects n = 12). Patients with MECP2 gain-of-function mutations showed increased oxidative stress marker levels (plasma non-protein bound iron, intraerythrocyte non-protein bound iron, F₂-isoprostanes, and F₄-neuroprostanes), as compared to healthy controls (P ≤ 0.05). Such increases were similar to those observed in RTT patients except for higher plasma F₂-isoprostanes levels (P < 0.0196). Moreover, plasma levels of F₂-isoprostanes were significantly correlated (P = 0.0098) with the size of the amplified region. The present work shows unique data in patients affected by MDS. For the first time MECP2 gain-of-function mutations are indicated to be linked to an oxidative damage and related clinical symptoms overlapping with those of MECP2 loss-of-function mutations. A finely tuned balance of MECP2 expression appears to be critical to oxidative stress homeostasis, thus shedding light on the relevance of the redox balance in the central nervous system integrity.

Excitatory/Inhibitory Balance and Circuit Homeostasis in Autism Spectrum Disorders

Autism spectrum disorders (ASDs) and related neurological disorders are associated with mutations in many genes affecting the ratio between neuronal excitation and inhibition. However, understanding the impact of these mutations on network activity is complicated by the plasticity of these networks, making it difficult in many cases to separate initial deficits from homeostatic compensation. Here we explore the contrasting evidence for primary defects in inhibition or excitation in ASDs and attempt to integrate the findings in terms of the brain's ability to maintain functional homeostasis.

Blood transcriptomics of drug-naïve sporadic Parkinson's disease patients

BACKGROUND

Parkinson's disease (PD) is a chronic progressive neurodegenerative disorder that is clinically defined in terms of motor symptoms. These are preceded by prodromal non-motor manifestations that prove the systemic nature of the disease. Identifying genes and pathways altered in living patients provide new information on the diagnosis and pathogenesis of sporadic PD.

METHODS

Changes in gene expression in the blood of 40 sporadic PD patients and 20 healthy controls ("Discovery set") were analyzed by taking advantage of the Affymetrix platform. Patients were at the onset of motor symptoms and before initiating any pharmacological treatment. Data analysis was performed by applying Ranking-Principal Component Analysis, PUMA and Significance Analysis of Microarrays. Functional annotations were assigned using GO, DAVID, GSEA to unveil significant enriched biological processes in the differentially expressed genes. The expressions of selected genes were validated using RT-qPCR and samples from an independent cohort of 12 patients and controls ("Validation set").

RESULTS

Gene expression profiling of blood samples discriminates PD patients from healthy controls and identifies differentially expressed genes in blood. The majority of these are also present in dopaminergic neurons of the Substantia Nigra, the key site of neurodegeneration. Together with neuronal apoptosis, lymphocyte activation and mitochondrial dysfunction, already found in previous analysis of PD blood and post-mortem brains, we unveiled transcriptome changes enriched in biological terms related to epigenetic modifications including chromatin remodeling and methylation. Candidate transcripts as CBX5, TCF3, MAN1C1 and DOCK10 were validated by RT-qPCR.

CONCLUSIONS

Our data support the use of blood transcriptomics to study neurodegenerative diseases. It identifies changes in crucial components of chromatin remodeling and methylation machineries as early events in sporadic PD suggesting epigenetics as target for therapeutic intervention.

Heightened Delta Power during Slow-Wave-Sleep in Patients with Rett Syndrome Associated with Poor Sleep Efficiency

Sleep problems are commonly reported in Rett syndrome (RTT); however the electroencephalographic (EEG) biomarkers underlying sleep dysfunction are poorly understood. The aim of this study was to analyze the temporal evolution of quantitative EEG (qEEG) biomarkers in overnight EEGs recorded from girls (2–9 yrs. old) diagnosed with RTT using a non-traditional automated protocol. In this study, EEG spectral analysis identified high delta power cycles representing slow wave sleep (SWS) in 8–9h overnight sleep EEGs from the frontal, central and occipital leads (AP axis), comparing age-matched girls with and without RTT. Automated algorithms quantitated the area under the curve (AUC) within identified SWS cycles for each spectral frequency wave form. Both age-matched RTT and control EEGs showed similar increasing trends for recorded delta wave power in the EEG leads along the antero-posterior (AP). RTT EEGs had significantly fewer numbers of SWS sleep cycles; therefore, the overall time spent in SWS was also significantly lower in RTT. In contrast, the AUC for delta power within each SWS cycle was significantly heightened in RTT and remained heightened over consecutive cycles unlike control EEGs that showed an overnight decrement of delta power in consecutive cycles. Gamma wave power associated with these SWS cycles was similar to controls. However, the negative correlation of gamma power with age (r = -.59; p<0.01) detected in controls (2–5 yrs. vs. 6–9 yrs.) was lost in RTT. Poor % SWS (i.e., time spent in SWS overnight) in RTT was also driven by the younger age-group. Incidence of seizures in RTT was associated with significantly lower number of SWS cycles. Therefore, qEEG biomarkers of SWS in RTT evolved temporally and correlated significantly with clinical severity.

MicroRNAs downregulated in neuropathic pain regulate MeCP2 and BDNF related to pain sensitivity

Nerve injury induces chronic pain and dysregulation of microRNAs in dorsal root ganglia (DRG). Several downregulated microRNAs are predicted to target Mecp2. MECP2 mutations cause Rett syndrome and these patients report decreased pain perception. We confirmed MeCP2 upregulation in DRG following nerve injury and repression of MeCP2 by miRNAs in vitro. MeCP2 regulates brain-derived neurotrophic factor (BDNF) and downregulation of MeCP2 by microRNAs decreased Bdnf in vitro. MeCP2 T158A mice exhibited reduced mechanical sensitivity and Mecp2-null and MeCP2 T158A mice have decreased Bdnf in DRG. MeCP2-mediated regulation of Bdnf in the DRG could contribute to altered pain sensitivity.

Functional alterations of astrocytes in mental disorders: pharmacological significance as a drug target

Astrocytes play an essential role in supporting brain functions in physiological and pathological states. Modulation of their pathophysiological responses have beneficial actions on nerve tissue injured by brain insults and neurodegenerative diseases, therefore astrocytes are recognized as promising targets for neuroprotective drugs. Recent investigations have identified several astrocytic mechanisms for modulating synaptic transmission and neural plasticity. These include altered expression of transporters for neurotransmitters, release of gliotransmitters and neurotrophic factors, and intercellular communication through gap junctions. Investigation of patients with mental disorders shows morphological and functional alterations in astrocytes. According to these observations, manipulation of astrocytic function by gene mutation and pharmacological tools reproduce mental disorder-like behavior in experimental animals. Some drugs clinically used for mental disorders affect astrocyte function. As experimental evidence shows their role in the pathogenesis of mental disorders, astrocytes have gained much attention as drug targets for mental disorders. In this paper, I review functional alterations of astrocytes in several mental disorders including schizophrenia, mood disorder, drug dependence, and neurodevelopmental disorders. The pharmacological significance of astrocytes in mental disorders is also discussed.

Molecular underpinnings of prefrontal cortex development in rodents provide insights into the etiology of neurodevelopmental disorders

The prefrontal cortex (PFC), seat of the highest-order cognitive functions, constitutes a conglomerate of highly specialized brain areas and has been implicated to have a role in the onset and installation of various neurodevelopmental disorders. The development of a properly functioning PFC is directed by transcription factors, guidance cues and other regulatory molecules and requires the intricate and temporal orchestration of a number of developmental processes. Disturbance or failure of any of these processes causing neurodevelopmental abnormalities within the PFC may contribute to several of the cognitive deficits seen in patients with neurodevelopmental disorders. In this review, we elaborate on the specific processes underlying prefrontal development, such as induction and patterning of the prefrontal area, proliferation, migration and axonal guidance of medial prefrontal progenitors, and their eventual efferent and afferent connections. We furthermore integrate for the first time the available knowledge from genome-wide studies that have revealed genes linked to neurodevelopmental disorders with experimental molecular evidence in rodents. The integrated data suggest that the pathogenic variants in the neurodevelopmental disorder-associated genes induce prefrontal cytoarchitectonical impairments. This enhances our understanding of the molecular mechanisms of prefrontal (mis)development underlying the four major neurodevelopmental disorders in humans, that is, intellectual disability, autism spectrum disorders, attention deficit hyperactivity disorder and schizophrenia, and may thus provide clues for the development of novel therapies.

Valproate-induced neurodevelopmental deficits in Xenopus laevis tadpoles

Autism spectrum disorder (ASD) is increasingly thought to result from low-level deficits in synaptic development and neural circuit formation that cascade into more complex cognitive symptoms. However, the link between synaptic dysfunction and behavior is not well understood. By comparing the effects of abnormal circuit formation and behavioral outcomes across different species, it should be possible to pinpoint the conserved fundamental processes that result in disease. Here we use a novel model for neurodevelopmental disorders in which we expose Xenopus laevis tadpoles to valproic acid (VPA) during a critical time point in brain development at which neurogenesis and neural circuit formation required for sensory processing are occurring. VPA is a commonly prescribed antiepileptic drug with known teratogenic effects. In utero exposure to VPA in humans or rodents results in a higher incidence of ASD or ASD-like behavior later in life. We find that tadpoles exposed to VPA have abnormal sensorimotor and schooling behavior that is accompanied by hyperconnected neural networks in the optic tectum, increased excitatory and inhibitory synaptic drive, elevated levels of spontaneous synaptic activity, and decreased neuronal intrinsic excitability. Consistent with these findings, VPA-treated tadpoles also have increased seizure susceptibility and decreased acoustic startle habituation. These findings indicate that the effects of VPA are remarkably conserved across vertebrate species and that changes in neural circuitry resulting from abnormal developmental pruning can cascade into higher-level behavioral deficits.

MeCP2 plays an analgesic role in pain transmission through regulating CREB / miR-132 pathway

Background

The Methyl CpG binding protein 2 gene (MeCP2 gene) encodes a critical transcriptional repressor and is widely expressed in mammalian neurons. MeCP2 plays a critical role in neuronal differentiation, neural development, and synaptic plasticity. Mutations and duplications of the human MECP2 gene lead to severe neurodevelopmental disorders, such as Rett syndrome and autism. In this study we investigate the role of MeCP2 in the spinal cord and found that MeCP2 plays an important role as an analgesic mediator in pain circuitry.

Findings

Experiments using MeCP2 transgenic mice showed that overexpression of MeCP2 weakens both acute mechanical pain and thermal pain, suggesting an analgesic role of MeCP2 in acute pain transduction. We found that through p-CREB/miR-132 signaling cascade is involved in MeCP2-mediated pain transduction. We also examined the role of MeCP2 in chronic pain formation using spared nerve injury (SNI) model. Strikingly, we found that development of neuropathic pain attenuates in MeCP2 transgenic mice comparing to wild type (WT) mice.

Conclusions

Our study shows that MeCP2 plays an analgesic role in both acute pain transduction and chronic pain formation through regulating CREB-miR-132 pathway. This work provides a potential therapeutic target for neural pathologic pain, and also sheds new lights on the abnormal sensory mechanisms associated with autism spectrum orders.

Targeted pharmacological treatment of autism spectrum disorders: fragile X and Rett syndromes

Autism spectrum disorders (ASDs) are genetically and clinically heterogeneous and lack effective medications to treat their core symptoms. Studies of syndromic ASDs caused by single gene mutations have provided insights into the pathophysiology of autism. Fragile X and Rett syndromes belong to the syndromic ASDs in which preclinical studies have identified rational targets for drug therapies focused on correcting underlying neural dysfunction. These preclinical discoveries are increasingly translating into exciting human clinical trials. Since there are significant molecular and neurobiological overlaps among ASDs, targeted treatments developed for fragile X and Rett syndromes may be helpful for autism of different etiologies. Here, we review the targeted pharmacological treatment of fragile X and Rett syndromes and discuss related issues in both preclinical studies and clinical trials of potential therapies for the diseases.

Deletion of protein tyrosine phosphatase, non-receptor type 4 (PTPN4) in twins with a Rett syndrome-like phenotype

Rett syndrome (RTT), a neurodevelopmental disorder that predominantly affects females, is primarily caused by variants in MECP2. Variants in other genes such as CDKL5 and FOXG1 are usually associated with individuals who manifest distinct phenotypes that may overlap with RTT. Individuals with phenotypes suggestive of RTT are typically screened for variants in MECP2 and then subsequently the other genes dependent on the specific phenotype. Even with this screening strategy, there are individuals in whom no causative variant can be identified, suggesting that there are other novel genes that contribute to the RTT phenotype. Here we report a de novo deletion of protein tyrosine phosphatase, non-receptor type 4 (PTPN4) in identical twins with a RTT-like phenotype. We also demonstrate the reduced expression of Ptpn4 in a Mecp2 null mouse model of RTT, as well as the activation of the PTPN4 promoter by MeCP2. Our findings suggest that PTPN4 should be considered for addition to the growing list of genes that warrant screening in individuals with a RTT-like phenotype.

Astrocyte-specific regulation of hMeCP2 expression in Drosophila

Alterations in the expression of Methyl-CpG-binding protein 2 (MeCP2) either by mutations or gene duplication leads to a wide spectrum of neurodevelopmental disorders including Rett Syndrome and MeCP2 duplication disorder. Common features of Rett Syndrome (RTT), MeCP2 duplication disorder, and neuropsychiatric disorders indicate that even moderate changes in MeCP2 protein levels result in functional and structural cell abnormalities. In this study, we investigated two areas of MeCP2 pathophysiology using Drosophila as a model system: the effects of MeCP2 glial gain-of-function activity on circuits controlling sleep behavior, and the cell-type specific regulation of MeCP2 expression. In this study, we first examined the effects of elevated MeCP2 levels on microcircuits by expressing human MeCP2 (hMeCP2) in astrocytes and distinct subsets of amine neurons including dopamine and octopamine (OA) neurons. Depending on the cell-type, hMeCP2 expression reduced sleep levels, altered daytime/nighttime sleep patterns, and generated sleep maintenance deficits. Second, we identified a 498 base pair region of the MeCP2e2 isoform that is targeted for regulation in distinct subsets of astrocytes. Levels of the full-length hMeCP2e2 and mutant RTT R106W protein decreased in astrocytes in a temporally and spatially regulated manner. In contrast, expression of the deletion Δ166 hMeCP2 protein was not altered in the entire astrocyte population. qPCR experiments revealed a reduction in full-length hMeCP2e2 transcript levels suggesting transgenic hMeCP2 expression is regulated at the transcriptional level. Given the phenotypic complexities that are caused by alterations in MeCP2 levels, our results provide insight into distinct cellular mechanisms that control MeCP2 expression and link microcircuit abnormalities with defined behavioral deficits.

MicroRNA-132, -134, and -138: a microRNA troika rules in neuronal dendrites

Dendritic mRNA transport and local translation in the postsynaptic compartment play an important role in synaptic plasticity, learning and memory. Local protein synthesis at the synapse has to be precisely orchestrated by a plethora of factors including RNA binding proteins as well as microRNAs, an extensive class of small non-coding RNAs. By binding to complementary sequences in target mRNAs, microRNAs fine-tune protein synthesis and thereby represent critical regulators of gene expression at the post-transcriptional level. Research over the last years identified an entire network of dendritic microRNAs that fulfills an essential role in synapse development and physiology. Recent studies provide evidence that these small regulatory molecules are highly regulated themselves, at the level of expression as well as function. The importance of microRNAs for correct function of the nervous system is reflected by an increasing number of studies linking dysregulation of microRNA pathways to neurological disorders. By focusing on three extensively studied examples (miR-132, miR-134, miR-138), this review will attempt to illustrate the complex regulatory roles of dendritic microRNAs at the synapse and their implications for pathological conditions.

Evaluation of current pharmacological treatment options in the management of Rett syndrome: from the present to future therapeutic alternatives

Neurodevelopmental disorders are a large family of conditions of genetic or environmental origin that are characterized by deficiencies in cognitive and behavioral functions. The therapeutic management of individuals with these disorders is typically complex and is limited to the treatment of specific symptoms that characterize each disorder. The neurodevelopmental disorder Rett syndrome (RTT) is the leading cause of severe intellectual disability in females. Mutations in the gene encoding the transcriptional regulator methyl-CpG-binding protein 2 (MECP2), located on the X chromosome, have been confirmed in more than 95% of individuals meeting diagnostic criteria for classical RTT. RTT is characterized by an uneventful early infancy followed by stagnation and regression of growth, motor, language, and social skills later in development. This review will discuss the genetics, pathology, and symptoms that distinguish RTT from other neurodevelopmental disorders associated with intellectual disability. Because great progress has been made in the basic and clinical science of RTT, the goal of this review is to provide a thorough assessment of current pharmacotherapeutic options to treat the symptoms associated with this disorder. Furthermore, we will highlight recent discoveries made with novel pharmacological interventions in experimental preclinical phases, and which have reversed pathological phenotypes in mouse and cell culture models of RTT and may result in clinical trials.

MeCP2 repression of G9a in regulation of pain and morphine reward

Opioids are commonly used for pain relief, but their strong rewarding effects drive opioid misuse and abuse. How pain affects the liability of opioid abuse is unknown at present. In this study, we identified an epigenetic regulating cascade activated by both pain and the opioid morphine. Both persistent pain and repeated morphine upregulated the transcriptional regulator MeCP2 in mouse central nucleus of the amygdala (CeA). Chromatin immunoprecipitation analysis revealed that MeCP2 bound to and repressed the transcriptional repressor histone dimethyltransferase G9a, reducing G9a-catalyzed repressive mark H3K9me2 in CeA. Repression of G9a activity increased expression of brain-derived neurotrophic factor (BDNF). Behaviorally, persistent inflammatory pain increased the sensitivity to acquiring morphine-induced, reward-related behavior of conditioned place preference in mice. Local viral vector-mediated MeCP2 overexpression, Cre-induced G9a knockdown, and CeA application of BDNF mimicked, whereas MeCP2 knockdown inhibited, the pain effect. These results suggest that MeCP2 directly represses G9a as a shared mechanism in central amygdala for regulation of emotional responses to pain and opioid reward, and for their behavioral interaction.