A suppressor screen in Mecp2 mutant mice implicates cholesterol metabolism in Rett syndrome

Self-regulating gene therapy ameliorates phenotypes and overcomes gene dosage sensitivity in a mouse model of Rett syndrome

Conventional methods of gene transfer lead to inconsistent transgene expression within cells. This variability can be problematic, particularly in conditions like Rett syndrome (RTT), a neurological disorder caused by mutations in the MECP2 (methyl-CpG binding protein 2) gene, because overexpression of MECP2 can also cause adverse effects. To address these challenges, we devised a gene regulation system called Expression Attenuation via Construct Tuning (EXACT), which uses a self-contained, microRNA-based feed-forward loop that not only ensures more consistent transgene expression but also protects against excessive expression. Through cell-based screening assays, we demonstrated the ability of the EXACT circuit to modulate the expression of full-length human MeCP2. Compared with a conventional construct, an EXACT-MECP2 construct exhibited a narrower range of cellular protein abundance. Furthermore, the degree of regulation by the EXACT circuit increased with higher transgene doses in vitro and in wild-type mice and mice modeling RTT. On the basis of cellular and in vivo testing, we identified an optimal configuration for the adeno-associated virus serotype 9 (AAV9) construct for self-regulated MECP2 gene therapy, designated NGN-401. Delivery of NGN-401 to neonatal male Mecp2-/y hemizygous mice via intracerebroventricular injection resulted in prolonged survival and amelioration of RTT-like phenotypes compared with vehicle-treated animals. NGN-401 was also well tolerated by female Mecp2+/- mice and healthy juvenile nonhuman primates, in contrast with a conventional construct, which caused toxicity. The results from these studies underpin a first-in-human pediatric trial of NGN-401 in RTT (ClinicalTrials.gov, NCT05898620).

Effects of combined exposure to 17α-methyltestosterone and polystyrene microplastics on lipid metabolism and the nervous system in Danio rerio

Polystyrene (PS) microplastics are pervasive environmental pollutants that are harmful to aquatic organisms upon degradation. The synthetic androgen 17α-methyltestosterone (MT) is an environmental endocrine-disrupting chemical. This study aimed to systematically evaluate the combined histological and molecular effects of MT and PS exposure on the liver and brain tissues of Danio rerio with focus on lipid metabolism and neural function disruption. Female D. rerio were exposed to 50 ng/L MT and 0.5 mg/L PS (5 μm in diameter) for 21 d. Histological observations, real-time quantitative PCR (qPCR), and RNA-sequencing (RNA-seq) analysis were employed to assess the effects of PS and MT. These results indicated that MT and PS co-exposure caused fatty degeneration of liver cells and a significant upregulation of lipid synthesis-related genes (ACSS1, CEL, FASN, and GK5). In brain tissue, the observed effects included reduced marginal layer neuron counts, cytoplasmic loosening of central layer neurons, disordered gray matter layer cells, and vascular congestion. RNA-seq analysis further revealed significant enrichment of differentially expressed genes in the "glycine, serine, and threonine metabolism" and "neuroactive ligand-receptor interaction" signaling pathways. Thus, MT and PS co-exposure induced lipid metabolism disorders in D. rerio and influence neural signaling by altering the "neuroactive ligand-receptor interaction" pathway. These findings highlight the complex risks posed by environmental pollutants to aquatic life and provide critical insights for environmental protection and aquatic health research.

NEAT1-mediated regulation of proteostasis and mRNA localization impacts autophagy dysregulation in Rett syndrome

Rett syndrome (RTT) is a severe neurodevelopmental disorder primarily caused by loss-of-function mutations in the MECP2 gene, resulting in diverse cellular dysfunctions. Here, we investigated the role of the long noncoding RNA (lncRNA) NEAT1 in the context of MeCP2 deficiency using human neural cells and RTT patient samples. Through single-cell RNA sequencing and molecular analyses, we found that NEAT1 is markedly downregulated in MECP2 knockout (KO) cells at various stages of neural differentiation. NEAT1 downregulation correlated with aberrant activation of the mTOR pathway, abnormal protein metabolism, and dysregulated autophagy, contributing to the accumulation of protein aggregates and impaired mitochondrial function. Reactivation of NEAT1 in MECP2-KO cells rescued these phenotypes, indicating its critical role downstream of MECP2. Furthermore, direct RNA-RNA interaction was revealed as the key process for NEAT1 influence on autophagy genes, leading to altered subcellular localization of specific autophagy-related messenger RNAs and impaired biogenesis of autophagic complexes. Importantly, NEAT1 restoration rescued the morphological defects observed in MECP2-KO neurons, highlighting its crucial role in neuronal maturation. Overall, our findings elucidate lncRNA NEAT1 as a key mediator of MeCP2 function, regulating essential pathways involved in protein metabolism, autophagy, and neuronal morphology.

Steatotic liver disease diagnosed in a 24-year-old woman with Rett syndrome: a case report

Rett syndrome (RTT) is a neurodevelopmental disorder caused by mutations in the MECP2 gene, potentially disrupting lipid metabolism and leading to dyslipidemia (DLD) and steatotic liver disease (SLD). Although SLD has been described in RTT mouse models, it remains undocumented in humans. We herein describe a 24-year-old woman with RTT who was evaluated for abnormal liver enzymes. Imaging revealed hepatic steatosis, and transient elastography showed a controlled attenuation parameter of 342 dB/m and stiffness of 7.1 kPa. Laboratory investigations excluded secondary causes, including insulin resistance, metabolic syndrome, alcohol use, and new medications. Her Homeostatic Model Assessment for Insulin Resistance score was 1.8, her hemoglobin A1c concentration was 4.8%, and her lipid profile showed elevated triglycerides and low-density lipoprotein, consistent with DLD. Liver biopsy confirmed SLD. This case supports the hypothesis that MECP2 mutations in RTT disrupt lipid metabolism through a unique pathophysiologic mechanism, increasing the risk of DLD and SLD independently of traditional metabolic syndrome factors. It highlights the importance of early screening for liver disease in patients with RTT, despite their young age, to prevent complications. Additionally, it validates MECP2-null mouse models as reliable tools for investigating future therapeutic strategies in RTT.

Rett syndrome

Rett syndrome (RTT) is a severe, progressive, neurodevelopmental disorder, which affects predominantly females. In most cases, RTT is associated with pathogenic variants in MECP2. MeCP2, the protein product of MECP2, is known to regulate gene expression and is highly expressed in the brain. RTT is characterized by developmental regression of spoken language and hand use that, with hand stereotypies and impaired ambulation, constitute the four core diagnostic features. Affected individuals may present multiple other neurological impairments and comorbidities, such as seizures, breathing irregularities, anxiety and constipation. Studies employing neuroimaging, neuropathology, neurochemistry and animal models show reductions in brain size and global decreases in neuronal size, as well as alterations in multiple neurotransmitter systems. Management of RTT is mainly focused on preventing the progression of symptoms, currently improved by guidelines based on natural history studies. Animal and cellular models of MeCP2 deficiency have helped in understanding the pathophysiology of RTT and guided the development of trofinetide, an IGF1-related compound, which is an approved drug for RTT, as well as of other drugs and gene therapies currently under investigation.

Unraveling autophagic imbalances and therapeutic insights in Mecp2-deficient models

Loss-of-function mutations in MECP2 are associated to Rett syndrome (RTT), a severe neurodevelopmental disease. Mainly working as a transcriptional regulator, MeCP2 absence leads to gene expression perturbations resulting in deficits of synaptic function and neuronal activity. In addition, RTT patients and mouse models suffer from a complex metabolic syndrome, suggesting that related cellular pathways might contribute to neuropathogenesis. Along this line, autophagy is critical in sustaining developing neuron homeostasis by breaking down dysfunctional proteins, lipids, and organelles.Here, we investigated the autophagic pathway in RTT and found reduced content of autophagic vacuoles in Mecp2 knock-out neurons. This correlates with defective lipidation of LC3B, probably caused by a deficiency of the autophagic membrane lipid phosphatidylethanolamine. The administration of the autophagy inducer trehalose recovers LC3B lipidation, autophagosomes content in knock-out neurons, and ameliorates their morphology, neuronal activity and synaptic ultrastructure. Moreover, we provide evidence for attenuation of motor and exploratory impairment in Mecp2 knock-out mice upon trehalose administration. Overall, our findings open new perspectives for neurodevelopmental disorders therapies based on the concept of autophagy modulation.

Rett Syndrome: The Emerging Landscape of Treatment Strategies

Rett syndrome (RTT) has enjoyed remarkable progress in achieving specific therapies. RTT, a unique neurodevelopmental disorder first described in 1966, progressed slowly until the landmark paper of Hagberg and colleagues in 1983. Thereafter, rapid advances were achieved including the development of specific diagnostic criteria and the active search for a genetic etiology, resulting 16 years later in identification of variants in the methyl-CpG-binding protein (MECP2) gene located at Xq28. Shortly thereafter, the NIH Office of Rare Diseases funded the RTT Natural History Study (NHS) in 2003, initiating the acquisition of natural history data on clinical features from a large population of individuals with RTT. This information was essential for advancement of clinical trials to provide specific therapies for this disorder. In the process, the International Rett Syndrome Association (IRSA) was formed (now the International Rett Syndrome Foundation-IRSF), which participated directly in encouraging and expanding enrollment in the NHS and, subsequently, in developing the SCOUT program to facilitate testing of potential therapeutic agents in a mouse model of RTT. The overall objective was to review clinical characteristics developed from the NHS and to discuss the status of specific therapies for this progressive neurodevelopmental disorder. The NHS study provided critical information on RTT: growth, anthropometrics, longevity, key comorbidities including epilepsy, breath abnormalities, gastroesophageal dysfunction, scoliosis and other orthopedic issues, puberty, behavior and anxiety, and progressive motor deterioration including the appearance of parkinsonian features. Phenotype-genotype correlations were noted including the role of X chromosome inactivation. Development of clinical severity and quality of life measures also proved critical for subsequent clinical trials. Further, development of biochemical and neurophysiologic biomarkers offered further endpoints for clinical trials. Initial clinical trials prior to the NHS were ineffective, but advances resulting from the NHS and other studies worldwide promoted significant interest from pharmaceutical firms resulting in several clinical trials. While some of these have been unrewarding such as sarizotan, others have been quite promising including the approval of trofinetide by the FDA in 2023 as the first agent available for specific treatment of RTT. Blarcamesine has been trialed in phase 3 trials, 14 agents have been studied in phase 2 trials, and 7 agents are being evaluated in preclinical/translational studies. A landmark study in 2007 by Guy et al. demonstrated that activation of a normal MECP2 gene in a null mouse model resulted in significant improvement. Gene replacement therapy has advanced through translational studies to two current phase 1/2 clinical trials (Taysha102 and Neurogene-401). Additional genetic therapies are also under study including gene editing, RNA editing, and X-chromosome reactivation. Taken together, progress in understanding and treating RTT over the past 40 years has been remarkable. This suggests that further advances can be expected.

Behavioral and transcriptomic analyses of mecp2 function in zebrafish

Rett syndrome (RTT), a human neurodevelopmental disorder characterized by severe cognitive and motor impairments, is caused by dysfunction of the conserved transcriptional regulator Methyl-CpG-binding protein 2 (MECP2). Genetic analyses in mouse Mecp2 mutants, which exhibit key features of human RTT, have been essential for deciphering the mechanisms of MeCP2 function; nonetheless, our understanding of these complex mechanisms is incomplete. Zebrafish mecp2 mutants exhibit mild behavioral deficits but have not been analyzed in depth. Here, we combine transcriptomic and behavioral assays to assess baseline and stimulus-evoked motor responses and sensory filtering in zebrafish mecp2 mutants from 5 to 7 days post-fertilization (dpf). We show that zebrafish mecp2 function is required for normal thigmotaxis but is dispensable for gross movement, acoustic startle response, and sensory filtering (habituation and sensorimotor gating), and reveal a previously unknown role for mecp2 in behavioral responses to visual stimuli. RNA-seq analysis identified a large gene set that requires mecp2 function for correct transcription at 4 dpf, and pathway analysis revealed several pathways that require MeCP2 function in both zebrafish and mammals. These findings show that MeCP2's function as a transcriptional regulator is conserved across vertebrates and supports using zebrafish to complement mouse modeling in elucidating these conserved mechanisms.

Ex vivo disease modelling of Rett syndrome: the transcriptomic and metabolomic implications of direct neuronal conversion

BACKGROUND

Rett syndrome (RTT) is a rare neurodevelopmental disorder that primarily affects females and is characterized by a period of normal development followed by severe cognitive, motor, and communication impairment. The syndrome is predominantly caused by mutations in the MECP2. This study aimed to use comprehensive multi-omic analysis to identify the molecular and metabolic alterations associated with Rett syndrome.

METHODS AND RESULTS

Transcriptomic and metabolomic profiling was performed using neuron-like cells derived from the fibroblasts of 3 Rett syndrome patients with different MECP2 mutations (R168X, P152R, and R133C) and 1 healthy control. Differential gene expression, alternative splicing events, and metabolite changes were analyzed to identify the key pathways and processes affected in patients with Rett syndrome. Transcriptomic analysis showed there was significant down-regulation of genes associated with the extracellular matrix (ECM) and cytoskeletal components, which was particularly notable in patient P3 (R133C mutation), who had non-random X chromosome inactivation. Additionally, significant changes in microtubule-related gene expression and alternative splicing events were observed, especially in patient P2 (P152R mutation). Metabolomic profiling showed that there were alterations in metabolic pathways, particularly up-regulation of ketone body synthesis and degradation pathways, in addition to an increase in free fatty acid levels. Integrated analysis highlighted the interplay between structural gene down-regulation and metabolic shifts, underscoring the adaptive responses to cellular stress in Rett neurons.

CONCLUSION

The present findings provide valuable insights into the molecular and metabolic landscape of Rett syndrome, emphasizing the importance of combining omic data to enlighten the molecular pathophysiology of this syndrome.

Drug repurposing in Rett and Rett-like syndromes: a promising yet underrated opportunity?

Rett syndrome (RTT) and Rett-like syndromes [i.e., CDKL5 deficiency disorder (CDD) and FOXG1-syndrome] represent rare yet profoundly impactful neurodevelopmental disorders (NDDs). The severity and complexity of symptoms associated with these disorders, including cognitive impairment, motor dysfunction, seizures and other neurological features significantly affect the quality of life of patients and families. Despite ongoing research efforts to identify potential therapeutic targets and develop novel treatments, current therapeutic options remain limited. Here the potential of drug repurposing (DR) as a promising avenue for addressing the unmet medical needs of individuals with RTT and related disorders is explored. Leveraging existing drugs for new therapeutic purposes, DR presents an attractive strategy, particularly suited for neurological disorders given the complexities of the central nervous system (CNS) and the challenges in blood-brain barrier penetration. The current landscape of DR efforts in these syndromes is thoroughly examined, with partiuclar focus on shared molecular pathways and potential common drug targets across these conditions.

Biochemical and molecular determinants of the subclinical inflammatory mechanisms in Rett syndrome

To date, Rett syndrome (RTT), a genetic disorder mainly caused by mutations in the X-linked MECP2 gene, is increasingly considered a broad-spectrum pathology, instead of just a neurodevelopmental disease, due to the multitude of peripheral co-morbidities and the compromised metabolic pathways, affecting the patients. The altered molecular processes include an impaired mitochondrial function, a perturbed redox homeostasis, a chronic subclinical inflammation and an improper cholesterol metabolism. The persistent subclinical inflammatory condition was first defined ten years ago, as a previously unrecognized feature of RTT, playing a role in the pathology progress and modulation of phenotypical severity. In light of this, the present work aims at reviewing the current knowledge on the chronic inflammatory status and the altered immune/inflammatory functions in RTT, as well as investigating the emerging mechanisms underlying this condition with a special focus on the latest findings about inflammasome system, autoimmunity responses and intestinal micro- and mycobiota. On these bases, although further research is needed, future therapeutic strategies able to re-establish an adequate immune/inflammatory response could represent potential approaches for RTT patients.

Genetic Instability and Disease Progression of Indian Rett Syndrome Patients

Rett syndrome (RTT) is the rare neurodevelopmental disorder caused by mutations in methyl CpG binding protein 2 (MECP2) gene with a prevalence of 1:10,000 worldwide. The hallmark clinical features of RTT are developmental delay, microcephaly, repetitive behaviours, gait abnormalities, respiratory abnormalities and seizures. Still, the understanding on the diagnosis of RTT among clinicians are less. The aim of our work was to study various clinical manifestations and a spectrum of MECP2 genetic heterogeneity in RTT patients from South Indian population. We screened 208 autistic patients and diagnosed 20 RTT patients, who were further divided into classical RTT (group I; N = 11) and variant RTT (group II; N = 9). The clinical severity of RTT was measured using RSSS, RSBQ, SSI, SSS and RTT gross motor scale. The biochemical analysis showed that thyroid-stimulating hormone (TSH), plasma dopamine and cholesterol levels were higher in group I when compared to group II, whereas the level of blood pressure, calcium, ferritin and high-density lipoprotein levels were significantly decreased in both RTT groups, when compared to the control group. The genetic mutational spectrum of MECP2 mutations were found in 12/20 of RTT patients, which revealed the occurrence of 60% pathogenic mutation and 20% unknown mutation and it was correlated with the clinical finding of respiratory dysfunction, scoliosis and sleeping problems. The significant results of this study provided clinical and genetic aspects of RTT diagnosis and proposed the clinicians to screen abnormal cholesterol, calcium and TSH levels tailed with MECP2 gene mutations for early prognosis of disease severity.

Modulation of Brain Cholesterol Metabolism through CYP46A1 Overexpression for Rett Syndrome

Rett syndrome (RTT) is a rare neurodevelopmental disorder caused by mutation in the X-linked gene methyl-CpG-binding protein 2 (Mecp2), a ubiquitously expressed transcriptional regulator. RTT results in mental retardation and developmental regression that affects approximately 1 in 10,000 females. Currently, there is no curative treatment for RTT. Thus, it is crucial to develop new therapeutic approaches for children suffering from RTT. Several studies suggested that RTT is linked with defects in cholesterol homeostasis, but for the first time, therapeutic evaluation is carried out by modulating this pathway. Moreover, AAV-based CYP46A1 overexpression, the enzyme involved in cholesterol pathway, has been demonstrated to be efficient in several neurodegenerative diseases. Based on these data, we strongly believe that CYP46A1 could be a relevant therapeutic target for RTT. Herein, we evaluated the effects of intravenous AAVPHP.eB-hCYP46A1-HA delivery in male and female Mecp2-deficient mice. The applied AAVPHP.eB-hCYP46A1 transduced essential neurons of the central nervous system (CNS). CYP46A1 overexpression alleviates behavioral alterations in both male and female Mecp2 knockout mice and extends the lifespan in Mecp2-deficient males. Several parameters related to cholesterol pathway are improved and correction of mitochondrial activity is demonstrated in treated mice, which highlighted the clear therapeutic benefit of CYP46A1 through the neuroprotection effect. IV delivery of AAVPHP.eB-CYP46A1 is perfectly well tolerated with no inflammation observed in the CNS of the treated mice. Altogether, our results strongly suggest that CYP46A1 is a relevant target and overexpression could alleviate the phenotype of Rett patients.

Gut microbes in central nervous system development and related disorders

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

Rett Syndrome and the Role of MECP2: Signaling to Clinical Trials

Rett syndrome (RTT) is a neurological disorder that mostly affects females, with a frequency of 1 in 10,000 to 20,000 live birth cases. Symptoms include stereotyped hand movements; impaired learning, language, and communication skills; sudden loss of speech; reduced lifespan; retarded growth; disturbance of sleep and breathing; seizures; autism; and gait apraxia. Pneumonia is the most common cause of death for patients with Rett syndrome, with a survival rate of 77.8% at 25 years of age. Survival into the fifth decade is typical in Rett syndrome, and the leading cause of death is cardiorespiratory compromise. Rett syndrome progression has multiple stages; however, most phenotypes are associated with the nervous system and brain. In total, 95% of Rett syndrome cases are due to mutations in the MECP2 gene, an X-linked gene that encodes for the methyl CpG binding protein, a regulator of gene expression. In this review, we summarize the recent developments in the field of Rett syndrome and therapeutics targeting MECP2.

Statins-Beyond Their Use in Hypercholesterolemia: Focus on the Pediatric Population

Statins are a class of medications primarily used in adults to lower cholesterol levels and reduce the risk of cardiovascular events. However, the use of statins in children is generally limited and carefully considered despite the well-documented anti-inflammatory, anti-angiogenic, and pro-apoptotic effects, as well as their effect on cell signaling pathways. These multifaceted effects, known as pleiotropic effects, encompass enhancements in endothelial function, a significant reduction in oxidative stress, the stabilization of atherosclerotic plaques, immunomodulation, the inhibition of vascular smooth muscle proliferation, an influence on bone metabolism, anti-inflammatory properties, antithrombotic effects, and a diminished risk of dementia. In children, recent research revealed promising perspectives on the use of statins in various conditions including neurological, cardiovascular, and oncologic diseases, as well as special situations, such as transplanted children. The long-term safety and efficacy of statins in children are still subjects of ongoing research, and healthcare providers carefully assess the individual risk factors and benefits before prescribing these medications to pediatric patients. The use of statins in children is generally less common than in adults, and it requires close monitoring and supervision by healthcare professionals. Further research is needed to fully assess the pleiotropic effects of statins in the pediatric population.

Systemic proteome phenotypes reveal defective metabolic flexibility in Mecp2 mutants

Genes mutated in monogenic neurodevelopmental disorders are broadly expressed. This observation supports the concept that monogenic neurodevelopmental disorders are systemic diseases that profoundly impact neurodevelopment. We tested the systemic disease model focusing on Rett syndrome, which is caused by mutations in MECP2. Transcriptomes and proteomes of organs and brain regions from Mecp2-null mice as well as diverse MECP2-null male and female human cells were assessed. Widespread changes in the steady-state transcriptome and proteome were identified in brain regions and organs of presymptomatic Mecp2-null male mice as well as mutant human cell lines. The extent of these transcriptome and proteome modifications was similar in cortex, liver, kidney, and skeletal muscle and more pronounced than in the hippocampus and striatum. In particular, Mecp2- and MECP2-sensitive proteomes were enriched in synaptic and metabolic annotated gene products, the latter encompassing lipid metabolism and mitochondrial pathways. MECP2 mutations altered pyruvate-dependent mitochondrial respiration while maintaining the capacity to use glutamine as a mitochondrial carbon source. We conclude that mutations in Mecp2/MECP2 perturb lipid and mitochondrial metabolism systemically limiting cellular flexibility to utilize mitochondrial fuels.

Model Organism Modifier (MOM): a user-friendly Galaxy workflow to detect modifiers from genome sequencing data using Caenorhabditis elegans

Genetic modifiers are variants modulating phenotypic outcomes of a primary detrimental variant. They contribute to rare diseases phenotypic variability, but their identification is challenging. Genetic screening with model organisms is a widely used method for demystifying genetic modifiers. Forward genetics screening followed by whole genome sequencing allows the detection of variants throughout the genome but typically produces thousands of candidate variants making the interpretation and prioritization process very time-consuming and tedious. Despite whole genome sequencing is more time and cost-efficient, usage of computational pipelines specific to modifier identification remains a challenge for biological-experiment-focused laboratories doing research with model organisms. To facilitate a broader implementation of whole genome sequencing in genetic screens, we have developed Model Organism Modifier or MOM, a pipeline as a user-friendly Galaxy workflow. Model Organism Modifier analyses raw short-read whole genome sequencing data and implements tailored filtering to provide a Candidate Variant List short enough to be further manually curated. We provide a detailed tutorial to run the Galaxy workflow Model Organism Modifier and guidelines to manually curate the Candidate Variant Lists. We have tested Model Organism Modifier on published and validated Caenorhabditis elegans modifiers screening datasets. As whole genome sequencing facilitates high-throughput identification of genetic modifiers in model organisms, Model Organism Modifier provides a user-friendly solution to implement the bioinformatics analysis of the short-read datasets in laboratories without expertise or support in Bioinformatics.

Cholesterol alterations in fragile X syndrome, autism spectrum disorders and other neurodevelopmental disorders

Neurodevelopmental disorders (NDDs) are a group of etiologically diverse diseases primarily associated with abnormal brain development, impaired cognition, and various behavioral problems. The majority of NDDs present a wide range of clinical phenotypes while sharing distinct cellular and biochemical alterations. Low plasma cholesterol levels have been reported in a subset of NNDs including, autism spectrum disorder (ASD) and fragile X syndrome (FXS). The present review focuses on cholesterol metabolism and discusses the current evidence of lipid disruption in ASD, FXS, and other genetically related NDDs. The characterization of these common deficits might provide valuable insights into their underlying physiopathology and help identify potential therapeutic targets.

Novel MECP2 gene therapy is effective in a multicenter study using two mouse models of Rett syndrome and is safe in non-human primates

The AAV9 gene therapy vector presented in this study is safe in mice and non-human primates and highly efficacious without causing overexpression toxicity, a major challenge for clinical translation of Rett syndrome gene therapy vectors to date. Our team designed a new truncated methyl-CpG-binding protein 2 (MECP2) promoter allowing widespread expression of MECP2 in mice and non-human primates after a single injection into the cerebrospinal fluid without causing overexpression symptoms up to 18 months after injection. Additionally, this new vector is highly efficacious at lower doses compared with previous constructs as demonstrated in extensive efficacy studies performed by two independent laboratories in two different Rett syndrome mouse models carrying either a knockout or one of the most frequent human mutations of Mecp2. Overall, data from this multicenter study highlight the efficacy and safety of this gene therapy construct, making it a promising candidate for first-in-human studies to treat Rett syndrome.

Systemic Proteome Phenotypes Reveal Defective Metabolic Flexibility in Mecp2 Mutants

Genes mutated in monogenic neurodevelopmental disorders are broadly expressed. This observation supports the concept that monogenic neurodevelopmental disorders are systemic diseases that profoundly impact neurodevelopment. We tested the systemic disease model focusing on Rett syndrome, which is caused by mutations in MECP2. Transcriptomes and proteomes of organs and brain regions from Mecp2-null mice as well as diverse MECP2-null male and female human cells were assessed. Widespread changes in the steady-state transcriptome and proteome were identified in brain regions and organs of presymptomatic Mecp2-null male mice as well as mutant human cell lines. The extent of these transcriptome and proteome modifications was similar in cortex, liver, kidney, and skeletal muscle and more pronounced than in the hippocampus and striatum. In particular, Mecp2- and MECP2-sensitive proteomes were enriched in synaptic and metabolic annotated gene products, the latter encompassing lipid metabolism and mitochondrial pathways. MECP2 mutations altered pyruvate-dependent mitochondrial respiration while maintaining the capacity to use glutamine as a mitochondrial carbon source. We conclude that mutations in Mecp2/MECP2 perturb lipid and mitochondrial metabolism systemically limiting cellular flexibility to utilize mitochondrial fuels.

Luteolin in the Qi Bi Anshen decoction improves propionic acid-induced autism-like behavior in rats by inhibiting LRP1/MMP9

BACKGROUND

A neurodevelopmental illness with a high frequency and unidentified pathophysiology is known as autism spectrum disorder (ASD). A research hotspot in this field is the identification of disease-specific biomarkers and drug intervention targets. Traditional Chinese medicine (TCM) can eliminate the symptoms of autism by precisely regulating human physiology. The Qi Bi Anshen decoction (QAT) is a commonly used TCM clinical drug commonly-used to treat for treating ASD. However, the primary active ingredients and underlying mechanisms of action of this decoction remain unknown.

PURPOSE

This study aimed to investigate the active ingredients and pharmacodynamics of QAT in the treatment of ASD using a Sprague-Dawley rat model that resembled autism.

METHODS

Autism-like rat models were established through intracerebroventricular injections of propionic acid (PPA). Subsequently, the rats were treated with QAT, and their efficacy was evaluated using the three-chamber method to analyze social interactions and grooming behavior. Additionally, open-field tests, elevated cross-maze tests, hematoxylin and eosin staining, Nissl staining, and enzyme-linked immunosorbent assays were performed; Western blot analysis was employed to determine the expression of synaptic plasticity-related proteins. Utilizing ultra-high-performance liquid chromatography-mass spectrometry (UPLC-MS), the effectiveness of active QAT components was assessed, and potential QAT targets were screened through molecular docking, surface plasmon resonance, and thermal migration experiments. To better understand the precise processes involved in treating ASD with active QAT components, in vivo and in vitro knockdown tests were also performed.

RESULTS

QATexhibited a significant improvement in autism-like behavior and a notable increase in the production of proteins associated with synaptic plasticity. Furthermore, luteolin (LUT), identified as a potentially important active ingredient in QAT for treating ASD, reduced matrix metallopeptidase-9 (MMP9) expression. However, this effect was attenuated by the knockdown of low-density lipoprotein receptor-associated protein 1 (LRP1), which is the target binding site for LUT.

CONCLUSIONS

LUT emerges as a potentially crucial active component of QAT in the treatment of ASD, with the ability to antagonize LRP1 and subsequently reduce MMP9 expression.

Differentiated Approach to Pharmacotherapy of Autism Spectrum Disorders: Biochemical Aspects

Autism Spectrum Disorders (ASD) are highly heterogeneous neurodevelopmental disorders caused by a complex interaction of numerous genetic and environmental factors and leading to deviations in the nervous system formation at the very early developmental stages. Currently, there are no accepted pharmacological treatments for the so-called core symptoms of ASD, such as social communication disorders and restricted and repetitive behavior patterns. Lack of knowledge about biological basis of ASD, absence of the clinically significant biochemical parameters reflecting abnormalities in the signaling cascades controlling the nervous system development and functioning, and lack of methods for selection of clinically and biologically homogeneous subgroups are considered as causes for the failure of clinical trials of ASD pharmacotherapy. This review considers the possibilities of applying differentiated clinical and biological approaches to the targeted search for ASD pharmacotherapy with emphasis on biochemical markers associated with ASD and attempts to stratify patients by biochemical parameters. The use of such approach as "the target-oriented therapy and assessment of the target status before and during the treatment to identify patients with a positive response to treatment" is discussed using the published results of clinical trials as examples. It is concluded that identification of biochemical parameters for selection of the distinct subgroups among the ASD patients requires research on large samples reflecting clinical and biological diversity of the patients with ASD, and use of unified approaches for such studies. An integrated approach, including clinical observation, clinical-psychological assessment of the patient behavior, study of medical history and description of individual molecular profiles should become a new strategy for stratifying patients with ASD for clinical pharmacotherapeutic trials, as well as for evaluating their efficiency.

MeCP2 Is an Epigenetic Factor That Links DNA Methylation with Brain Metabolism

DNA methylation, one of the most well-studied epigenetic modifications, is involved in a wide spectrum of biological processes. Epigenetic mechanisms control cellular morphology and function. Such regulatory mechanisms involve histone modifications, chromatin remodeling, DNA methylation, non-coding regulatory RNA molecules, and RNA modifications. One of the most well-studied epigenetic modifications is DNA methylation that plays key roles in development, health, and disease. Our brain is probably the most complex part of our body, with a high level of DNA methylation. A key protein that binds to different types of methylated DNA in the brain is the methyl-CpG binding protein 2 (MeCP2). MeCP2 acts in a dose-dependent manner and its abnormally high or low expression level, deregulation, and/or genetic mutations lead to neurodevelopmental disorders and aberrant brain function. Recently, some of MeCP2-associated neurodevelopmental disorders have emerged as neurometabolic disorders, suggesting a role for MeCP2 in brain metabolism. Of note, MECP2 loss-of-function mutation in Rett Syndrome is reported to cause impairment of glucose and cholesterol metabolism in human patients and/or mouse models of disease. The purpose of this review is to outline the metabolic abnormalities in MeCP2-associated neurodevelopmental disorders that currently have no available cure. We aim to provide an updated overview into the role of metabolic defects associated with MeCP2-mediated cellular function for consideration of future therapeutic strategies.

Cholesterol metabolism pathway in autism spectrum disorder: From animal models to clinical observations

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterized by a persistent impairment of social skills, including aspects of perception, interpretation, and response, combined with restricted and repetitive behavior. ASD is a complex and multifactorial condition, and its etiology could be attributed to genetic and environmental factors. Despite numerous clinical and experimental studies, no etiological factor, biomarker, and specific model of transmission have been consistently associated with ASD. However, an imbalance in cholesterol levels has been observed in many patients, more specifically, a condition of hypocholesterolemia, which seems to be shared between ASD and ASD-related genetic syndromes such as fragile X syndrome (FXS), Rett syndrome (RS), and Smith- Lemli-Opitz (SLO). Furthermore, it is known that alterations in cholesterol levels lead to neuroinflammation, oxidative stress, impaired myelination and synaptogenesis. Thus, the aim of this review is to discuss the cholesterol metabolic pathways in the ASD context, as well as in genetic syndromes related to ASD, through clinical observations and animal models. In fact, SLO, FXS, and RS patients display early behavioral markers of ASD followed by cholesterol disturbances. Several studies have demonstrated the role of cholesterol in psychiatric conditions and how its levels modulate brain neurodevelopment. This review suggests an important relationship between ASD pathology and cholesterol metabolism impairment; thus, some strategies could be raised - at clinical and pre-clinical levels - to explore whether cholesterol metabolism disturbance has a generally adverse effect in exacerbating the symptoms of ASD patients.

State-of-the-art therapies for Rett syndrome

Rett syndrome (RTT) is an X-linked neurogenetic disorder caused by mutations of the MECP2 (methyl-CpG-binding protein 2) gene. Over two decades of work established MeCP2 as a protein with pivotal roles in the regulation of the epigenome, neuronal physiology, synaptic maintenance, and behaviour. Given the genetic aetiology of RTT and the proof of concept of its reversal in a mouse model, considerable efforts have been made to design therapeutic approaches to re-express MeCP2. By being at the forefront of the development of innovative gene therapies, research on RTT is of paramount importance for the treatment of monogenic neurological diseases. Here we discuss the recent advances and challenges of promising genetic strategies for the treatment of RTT including gene replacement therapies, gene/RNA editing strategies, and reactivation of the silenced X chromosome. WHAT THIS PAPER ADDS: Recent advances shed light on the promises of gene replacement therapy with new vectors designed to control the levels of MeCP2 expression. New developments in DNA/RNA editing approaches or reactivation of the silenced X chromosome open the possibility to re-express the native MeCP2 locus at endogenous levels. Current strategies still face limitations in transduction efficiency and future work is needed to improve brain delivery.

Neuroprotective Properties of Cardoon Leaves Extracts against Neurodevelopmental Deficits in an In Vitro Model of Rett Syndrome Depend on the Extraction Method and Harvest Time

This study investigates the bioactive properties of different extracts of cardoon leaves in rescuing neuronal development arrest in an in vitro model of Rett syndrome (RTT). Samples were obtained from plants harvested at different maturity stages and extracted with two different methodologies, namely Naviglio^® and supercritical carbon dioxide (scCO₂). While scCO₂ extracts more hydrophobic fractions, the Naviglio^® method extracts phenolic compounds and less hydrophobic components. Only the scCO₂ cardoon leaves extract obtained from plants harvested in spring induced a significant rescue of neuronal atrophy in RTT neurons, while the scCO₂ extract from the autumn harvest stimulated dendrite outgrowth in Wild-Type (WT) neurons. The scCO₂ extracts were the richest in squalene, 3ß-taraxerol and lupeol, with concentrations in autumn harvest doubling those in spring harvest. The Naviglio^® extract was rich in cynaropicrin and exerted a toxic effect at 20 µM on both WT and RTT neurons. When cynaropicrin, squalene, lupeol and 3ß-taraxerol were tested individually, no positive effect was observed, whereas a significant neurotoxicity of cynaropicrin and lupeol was evident. In conclusion, cardoon leaves extracts with high content of hydrophobic bioactive molecules and low cynaropicrin and lupeol concentrations have pharmacological potential to stimulate neuronal development in RTT and WT neurons in vitro.

Reversibility and therapeutic development for neurodevelopmental disorders, insights from genetic animal models

Neurodevelopmental Disorders (NDDs) encompass a broad spectrum of conditions resulting from atypical brain development. Over the past decades, we have had the fortune to witness enormous progress in diagnosis, etiology discovery, modeling, and mechanistic understanding of NDDs from both fundamental and clinical research. Here, we review recent neurobiological advances from experimental models of NDDs. We introduce several examples and highlight breakthroughs in reversal studies of phenotypes using genetically engineered models of NDDs. The in-depth understanding of brain pathophysiology underlying NDDs and evaluations of reversibility in animal models paves the foundation for discovering novel treatment options. We discuss how the expanding property of cutting-edge technologies, such as gene editing and AAV-mediated gene delivery, are leveraged in animal models for the therapeutic development of NDDs. We envision opportunities and challenges toward faithful modeling and fruitful clinical translation.

Retinoic acid-induced 1 gene haploinsufficiency alters lipid metabolism and causes autophagy defects in Smith-Magenis syndrome

Smith-Magenis syndrome (SMS) is a neurodevelopmental disorder characterized by cognitive and behavioral symptoms, obesity, and sleep disturbance, and no therapy has been developed to alleviate its symptoms or delay disease onset. SMS occurs due to haploinsufficiency of the retinoic acid-induced-1 (RAI1) gene caused by either chromosomal deletion (SMS-del) or RAI1 missense/nonsense mutation. The molecular mechanisms underlying SMS are unknown. Here, we generated and characterized primary cells derived from four SMS patients (two with SMS-del and two carrying RAI1 point mutations) and four control subjects to investigate the pathogenetic processes underlying SMS. By combining transcriptomic and lipidomic analyses, we found altered expression of lipid and lysosomal genes, deregulation of lipid metabolism, accumulation of lipid droplets, and blocked autophagic flux. We also found that SMS cells exhibited increased cell death associated with the mitochondrial pathology and the production of reactive oxygen species. Treatment with N-acetylcysteine reduced cell death and lipid accumulation, which suggests a causative link between metabolic dyshomeostasis and cell viability. Our results highlight the pathological processes in human SMS cells involving lipid metabolism, autophagy defects and mitochondrial dysfunction and suggest new potential therapeutic targets for patient treatment.

Wide spectrum of neuronal and network phenotypes in human stem cell-derived excitatory neurons with Rett syndrome-associated MECP2 mutations

Rett syndrome (RTT) is a severe neurodevelopmental disorder primarily caused by heterozygous loss-of-function mutations in the X-linked gene MECP2 that is a global transcriptional regulator. Mutations in the methyl-CpG binding domain (MBD) of MECP2 disrupt its interaction with methylated DNA. Here, we investigate the effect of a novel MECP2 L124W missense mutation in the MBD of an atypical RTT patient with preserved speech in comparison to severe MECP2 null mutations. L124W protein had a limited ability to disrupt heterochromatic chromocenters due to decreased binding dynamics. We isolated two pairs of isogenic WT and L124W induced pluripotent stem cells. L124W induced excitatory neurons expressed stable protein, exhibited increased input resistance and decreased voltage-gated Na+ and K+ currents, and their neuronal dysmorphology was limited to decreased dendritic complexity. Three isogenic pairs of MECP2 null neurons had the expected more extreme morphological and electrophysiological phenotypes. We examined development and maturation of L124W and MECP2 null excitatory neural network activity using micro-electrode arrays. Relative to isogenic controls, L124W neurons had an increase in synchronous network burst frequency, in contrast to MECP2 null neurons that suffered a significant decrease in synchronous network burst frequency and a transient extension of network burst duration. A biologically motivated computational neural network model shows the observed changes in network dynamics are explained by changes in intrinsic Na+ and K+ currents in individual neurons. Our multilevel results demonstrate that RTT excitatory neurons show a wide spectrum of morphological, electrophysiological and circuitry phenotypes that are dependent on the severity of the MECP2 mutation.

Convergent cerebrospinal fluid proteomes and metabolic ontologies in humans and animal models of Rett syndrome

MECP2 loss-of-function mutations cause Rett syndrome, a neurodevelopmental disorder resulting from a disrupted brain transcriptome. How these transcriptional defects are decoded into a disease proteome remains unknown. We studied the proteome of Rett cerebrospinal fluid (CSF) to identify consensus Rett proteome and ontologies shared across three species. Rett CSF proteomes enriched proteins annotated to HDL lipoproteins, complement, mitochondria, citrate/pyruvate metabolism, synapse compartments, and the neurosecretory protein VGF. We used shared Rett ontologies to select analytes for orthogonal quantification and functional validation. VGF and ontologically selected CSF proteins had genotypic discriminatory capacity as determined by receiver operating characteristic analysis in Mecp2 -/y and Mecp2 -/+ . Differentially expressed CSF proteins distinguished Rett from a related neurodevelopmental disorder, CDKL5 deficiency disorder. We propose that Mecp2 mutant CSF proteomes and ontologies inform putative mechanisms and biomarkers of disease. We suggest that Rett syndrome results from synapse and metabolism dysfunction.

Cholesterol in Brain Development and Perinatal Brain Injury: More than a Building Block

The central nervous system (CNS) is enriched with important classes of lipids, in which cholesterol is known to make up a major portion of myelin sheaths, besides being a structural and functional unit of CNS cell membranes. Unlike in the adult brain, where the cholesterol pool is relatively stable, cholesterol is synthesized and accumulated at the highest rate in the developing brain to meet the needs of rapid brain growth at this stage, which is also a critical period for neuroplasticity. In addition to its biophysical role in membrane organization, cholesterol is crucial for brain development due to its involvement in brain patterning, myelination, neuronal differentiation, and synaptogenesis. Thus any injuries to the immature brain that affect cholesterol homeostasis may have long-term adverse neurological consequences. In this review, we describe the unique features of brain cholesterol biosynthesis and metabolism, cholesterol trafficking between different cell types, and highlight cholesterol-dependent biological processes during brain maturation. We also discuss the association of impaired cholesterol homeostasis with several forms of perinatal brain disorders in term and preterm newborns, including hypoxic-ischemic encephalopathy. Strategies targeting the cholesterol pathways may open new avenues for the diagnosis and treatment of developmental brain injury.

Outcome measurement instruments in Rett syndrome: A systematic review

OBJECTIVE

The aim of the study was to identify and characterize outcome measures for objective and subjective assessment in persons with Rett syndrome (RS).

METHODS

A systematic review was conducted consulting the EBSCO, Cochrane, Web of Science, Scielo, MEDLINE and PsycINFO databases for published studies describing the use of patient-reported outcome measures (PROMs) and other outcome measures in persons with RS. Validation studies and observational studies were included. The PROMs were first described, and then the measurement properties were evaluated using predefined criteria according to the COnsensus-based Standards for the selection of health Measurement Instruments (COSMIN). The outcome measures were then grouped according to the International Classification of Functioning, Disability and Health (ICF) to establish a relationship between outcome measures and ICF domains.

RESULTS

Twenty out of 2327 articles were appraised, and seventeen different outcome measures were identified and described. Ten outcome measures corresponded to evaluation questionnaires, while the remaining seven assessed functional outcomes: walking distance, physical activity level and ability to interact visually. A relation between these outcome measures that assess RS and the ICF allows understanding that most of the instruments (fifteen) include the assessment of activity limitations.

CONCLUSIONS

The findings of this study seem to be promising for their use by clinicians and researchers, although they have methodological limitations. The accuracy and quality of these individual outcome measures should continue to be assessed in an attempt to gather a consensus on the best tools used in RS.

Identification of Arhgef12 and Prkci as genetic modifiers of retinal dysplasia in the Crb1rd8 mouse model

Mutations in the apicobasal polarity gene CRB1 lead to diverse retinal diseases, such as Leber congenital amaurosis, cone-rod dystrophy, retinitis pigmentosa (with and without Coats-like vasculopathy), foveal retinoschisis, macular dystrophy, and pigmented paravenous chorioretinal atrophy. Limited correlation between disease phenotypes and CRB1 alleles, and evidence that patients sharing the same alleles often present with different disease features, suggest that genetic modifiers contribute to clinical variation. Similarly, the retinal phenotype of mice bearing the Crb1 retinal degeneration 8 (rd8) allele varies with genetic background. Here, we initiated a sensitized chemical mutagenesis screen in B6.Cg-Crb1rd8/Pjn, a strain with a mild clinical presentation, to identify genetic modifiers that cause a more severe disease phenotype. Two models from this screen, Tvrm266 and Tvrm323, exhibited increased retinal dysplasia. Genetic mapping with high-throughput exome and candidate-gene sequencing identified causative mutations in Arhgef12 and Prkci, respectively. Epistasis analysis of both strains indicated that the increased dysplastic phenotype required homozygosity of the Crb1rd8 allele. Retinal dysplastic lesions in Tvrm266 mice were smaller and caused less photoreceptor degeneration than those in Tvrm323 mice, which developed an early, large diffuse lesion phenotype. At one month of age, Müller glia and microglia mislocalization at dysplastic lesions in both modifier strains was similar to that in B6.Cg-Crb1rd8/Pjn mice but photoreceptor cell mislocalization was more extensive. External limiting membrane disruption was comparable in Tvrm266 and B6.Cg-Crb1rd8/Pjn mice but milder in Tvrm323 mice. Immunohistological analysis of mice at postnatal day 0 indicated a normal distribution of mitotic cells in Tvrm266 and Tvrm323 mice, suggesting normal early development. Aberrant electroretinography responses were observed in both models but functional decline was significant only in Tvrm323 mice. These results identify Arhgef12 and Prkci as modifier genes that differentially shape Crb1-associated retinal disease, which may be relevant to understanding clinical variability and underlying disease mechanisms in humans.

Changes in the Cerebrospinal Fluid and Plasma Lipidome in Patients with Rett Syndrome

Rett syndrome (RTT) is defined as a rare disease caused by mutations of the methyl-CpG binding protein 2 (MECP2). It is one of the most common causes of genetic mental retardation in girls, characterized by normal early psychomotor development, followed by severe neurologic regression. Hitherto, RTT lacks a specific biomarker, but altered lipid homeostasis has been found in RTT model mice as well as in RTT patients. We performed LC-MS/MS lipidomics analysis to investigate the cerebrospinal fluid (CSF) and plasma composition of patients with RTT for biochemical variations compared to healthy controls. In all seven RTT patients, we found decreased CSF cholesterol levels compared to age-matched controls (n = 13), whereas plasma cholesterol levels were within the normal range in all 13 RTT patients compared to 18 controls. Levels of phospholipid (PL) and sphingomyelin (SM) species were decreased in CSF of RTT patients, whereas the lipidomics profile of plasma samples was unaltered in RTT patients compared to healthy controls. This study shows that the CSF lipidomics profile is altered in RTT, which is the basis for future (functional) studies to validate selected lipid species as CSF biomarkers for RTT.

Association of 3-hydroxy-3-methylglutaryl-coenzyme A reductase gene polymorphism with obesity and lipid metabolism in children and adolescents with autism spectrum disorder

The prevalence of obesity among children and adolescents with autism spectrum disorder (ASD) is higher than that among typically developing children and adolescents. However, very few studies have explored the genetic factors associated with obesity in children and adolescents with ASD. Thus, the aim of this study was to examine the associations between 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) gene polymorphisms and obesity among children and adolescents with ASD. The study participants consisted of 33 children and adolescents with ASD and 271 age- and sex-matched typically developing controls. We compared the metabolic traits (body mass index, blood pressure, triglyceride, high-density lipoprotein, and fasting glucose levels) between the ASD and control group. Furthermore, we assessed the genotypes of rs12654264 in the HMGCR gene within the participants with ASD, and compared metabolic traits among the different allele subgroups. The mean body mass index (BMI) and triglyceride level of the ASD group were significantly higher than those of the control group. Within the ASD group, the triglyceride level of participants with rs12654264-T alleles was significantly higher than that of participants with A-alleles. A pattern of increasing values in the BMI and fasting glucose was also observed in participants with T allele. This is the first study to show that obesity in children and adolescents with ASD is associated with the cholesterol synthesis pathway. Future studies are needed to further clarify the molecular mechanisms by which the HMGCR gene influences metabolic traits.

Sex disparate gut microbiome and metabolome perturbations precede disease progression in a mouse model of Rett syndrome

Rett syndrome (RTT) is a regressive neurodevelopmental disorder in girls, characterized by multisystem complications including gut dysbiosis and altered metabolism. While RTT is known to be caused by mutations in the X-linked gene MECP2, the intermediate molecular pathways of progressive disease phenotypes are unknown. Mecp2 deficient rodents used to model RTT pathophysiology in most prior studies have been male. Thus, we utilized a patient-relevant mouse model of RTT to longitudinally profile the gut microbiome and metabolome across disease progression in both sexes. Fecal metabolites were altered in Mecp2e1 mutant females before onset of neuromotor phenotypes and correlated with lipid deficiencies in brain, results not observed in males. Females also displayed altered gut microbial communities and an inflammatory profile that were more consistent with RTT patients than males. These findings identify new molecular pathways of RTT disease progression and demonstrate the relevance of further study in female Mecp2 animal models.

Moving forward with forward genetics: A summary of the INFRAFRONTIER Forward Genetics Panel Discussion

In the last few decades, forward genetics approaches have been extensively used to identify gene function. Essentially, forward genetics is the elucidation of the genetic basis of a specific phenotype by screening a population containing random genomic modifications that alter gene function. These approaches have shed light on some essential gene functions in development and disease and have expanded the realm of understanding for genetic disorders. Due to the availability of efficient mutagenesis methods, phenotyping techniques, reliable validation, comprehensive sequence information and translational potential, mouse models are favored for forward genetics approaches. However, in this post-genomic CRISPR-Cas9 era, the relevance and future of forward genetics was brought into question. With more than 7300 mouse strains archived and close interactions with several leading mouse researchers around the world, INFRAFRONTIER - the European Research Infrastructure for mouse models organised a panel discussion on forward genetics at the International Mammalian Genome Conference 2018 to discuss the future of forward genetics as well as challenges faced by researchers using this approach in the current research environment. The commentary presents an overview of this discussion.

Dysregulation of Neuronal Nicotinic Acetylcholine Receptor-Cholesterol Crosstalk in Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a set of complex neurodevelopmental diseases that include impaired social interaction, delayed and disordered language, repetitive or stereotypic behavior, restricted range of interests, and altered sensory processing. The underlying causes of the core symptoms remain unclear, as are the factors that trigger their onset. Given the complexity and heterogeneity of the clinical phenotypes, a constellation of genetic, epigenetic, environmental, and immunological factors may be involved. The lack of appropriate biomarkers for the evaluation of neurodevelopmental disorders makes it difficult to assess the contribution of early alterations in neurochemical processes and neuroanatomical and neurodevelopmental factors to ASD. Abnormalities in the cholinergic system in various regions of the brain and cerebellum are observed in ASD, and recently altered cholesterol metabolism has been implicated at the initial stages of the disease. Given the multiple effects of the neutral lipid cholesterol on the paradigm rapid ligand-gated ion channel, the nicotinic acetylcholine receptor, we explore in this review the possibility that the dysregulation of nicotinic receptor-cholesterol crosstalk plays a role in some of the neurological alterations observed in ASD.

Metabolomic Fingerprint of Mecp2-Deficient Mouse Cortex: Evidence for a Pronounced Multi-Facetted Metabolic Component in Rett Syndrome

Using unsupervised metabolomics, we defined the complex metabolic conditions in the cortex of a mouse model of Rett syndrome (RTT). RTT, which represents a cause of mental and cognitive disabilities in females, results in profound cognitive impairment with autistic features, motor disabilities, seizures, gastrointestinal problems, and cardiorespiratory irregularities. Typical RTT originates from mutations in the X-chromosomal methyl-CpG-binding-protein-2 (Mecp2) gene, which encodes a transcriptional modulator. It then causes a deregulation of several target genes and metabolic alterations in the nervous system and peripheral organs. We identified 101 significantly deregulated metabolites in the Mecp2-deficient cortex of adult male mice; 68 were increased and 33 were decreased compared to wildtypes. Pathway analysis identified 31 mostly upregulated metabolic pathways, in particular carbohydrate and amino acid metabolism, key metabolic mitochondrial/extramitochondrial pathways, and lipid metabolism. In contrast, neurotransmitter-signaling is dampened. This metabolic fingerprint of the Mecp2-deficient cortex of severely symptomatic mice provides further mechanistic insights into the complex RTT pathogenesis. The deregulated pathways that were identified—in particular the markedly affected amino acid and carbohydrate metabolism—confirm a complex and multifaceted metabolic component in RTT, which in turn signifies putative therapeutic targets. Furthermore, the deregulated key metabolites provide a choice of potential biomarkers for a more detailed rating of disease severity and disease progression.

Proteomic and transcriptional changes associated with MeCP2 dysfunction reveal nodes for therapeutic intervention in Rett syndrome

Mutations in the methyl-CpG binding protein 2 (MECP2) gene cause Rett syndrome (RTT), an X-linked neurodevelopmental disorder predominantly impacting females. MECP2 is an epigenetic transcriptional regulator acting mainly to repress gene expression, though it plays multiple gene regulatory roles and has distinct molecular targets across different cell types and specific developmental stages. In this review, we summarize MECP2 loss-of-function associated transcriptome and proteome disruptions, delving deeper into the latter which have been comparatively severely understudied. These disruptions converge on multiple biochemical and cellular pathways, including those involved in synaptic function and neurodevelopment, NF-κB signaling and inflammation, and the vitamin D pathway. RTT is a complex neurological disorder characterized by myriad physiological disruptions, in both the central nervous system and peripheral systems. Thus, treating RTT will likely require a combinatorial approach, targeting multiple nodes within the interactomes of these cellular pathways. To this end, we discuss the use of dietary supplements and factors, namely, vitamin D and polyunsaturated fatty acids (PUFAs), as possible partial therapeutic agents given their demonstrated benefit in RTT and their ability to restore homeostasis to multiple disrupted cellular pathways simultaneously. Further unravelling the complex molecular alterations induced by MECP2 loss-of-function, and contextualizing them at the level of proteome homeostasis, will identify new therapeutic avenues for this complex disorder.

Transcriptional Regulation of MECP2E1-E2 Isoforms and BDNF by Metformin and Simvastatin through Analyzing Nascent RNA Synthesis in a Human Brain Cell Line

Methyl CpG binding protein 2 (MeCP2) is the main DNA methyl-binding protein in the brain that binds to 5-methylcytosine and 5-hydroxymethyl cytosine. MECP2 gene mutations are the main origin of Rett Syndrome (RTT), a neurodevelopmental disorder in young females. The disease has no existing cure, however, metabolic drugs such as metformin and statins have recently emerged as potential therapeutic candidates. In addition, induced MECP2-BDNF homeostasis regulation has been suggested as a therapy avenue. Here, we analyzed nascent RNA synthesis versus steady state total cellular RNA to study the transcriptional effects of metformin (an anti-diabetic drug) on MECP2 isoforms (E1 and E2) and BNDF in a human brain cell line. Additionally, we investigated the impact of simvastatin (a cholesterol lowering drug) on transcriptional regulation of MECP2E1/E2-BDNF. Metformin was capable of post-transcriptionally inducing BDNF and/or MECP2E1, while transcriptionally inhibiting MECP2E2. In contrast simvastatin significantly inhibited BDNF transcription without significantly impacting MECP2E2 transcripts. Further analysis of ribosomal RNA transcripts confirmed that the drug neither individually nor in combination affected these fundamentally important transcripts. Experimental analysis was completed in conditions of the presence or absence of serum starvation that showed minimal impact for serum deprival, although significant inhibition of steady state MECP2E1 by simvastatin was only detected in non-serum starved cells. Taken together, our results suggest that metformin controls MECP2E1/E2-BDNF transcriptionally and/or post-transcriptionally, and that simvastatin is a potent transcriptional inhibitor of BDNF. The transcriptional effect of these drugs on MECP2E1/E2-BDNF were not additive under these tested conditions, however, either drug may have potential application for related disorders.

DNA methylome profiling reveals epigenetic regulation of lipoprotein-associated phospholipase A2 in human vulnerable atherosclerotic plaque

BACKGROUND

Atherosclerotic plaque vulnerability is a key feature of atheroprogression and precipitating acute cardiovascular events. Although the pivotal role of epigenetic regulation in atherosclerotic plaque destabilization is being recognized, the DNA methylation profile and its potential role in driving the progression and destabilization of atherosclerotic cardiovascular disease remains largely unknown. We conducted a genome-wide analysis to identify differentially methylated genes in vulnerable and non-vulnerable atherosclerotic lesions to understand more about pathogenesis.

RESULTS

We compared genome-wide DNA methylation profiling between carotid artery plaques of patients with clinically symptomatic (recent stroke or transient ischemic attack) and asymptomatic disease (no recent stroke) using Infinium Methylation BeadChip arrays, which revealed 90,368 differentially methylated sites (FDR < 0.05, |delta beta|> 0.03) corresponding to 14,657 annotated genes. Among these genomic sites, 30% were located at the promoter regions and 14% in the CpG islands, according to genomic loci and genomic proximity to the CpG islands, respectively. Moreover, 67% displayed hypomethylation in symptomatic plaques, and the differentially hypomethylated genes were found to be involved in various aspects of inflammation. Subsequently, we focus on CpG islands and revealed 14,596 differentially methylated sites (|delta beta|> 0.1) located at the promoter regions of 7048 genes. Integrated analysis of methylation and gene expression profiles identified that 107 genes were hypomethylated in symptomatic plaques and showed elevated expression levels in both advanced plaques and ruptured plaques. The imprinted gene PLA2G7, which encodes lipoprotein-associated phospholipase A₂ (Lp-PLA₂), was one of the top hypomethylated genes with an increased expression upon inflammation. Further, the hypomethylated CpG site at the promoter region of PLA2G7 was identified as cg11874627, demethylation of which led to increased binding of Sp3 and expression of Lp-PLA₂ through bisulfate sequencing, chromatin immunoprecipitation assay and enzyme-linked immunosorbent assay. These effects were further enhanced by deacetylase.

CONCLUSION

Extensive DNA methylation modifications serve as a new and critical layer of biological regulation that contributes to atheroprogression and destabilization via inflammatory processes. Revelation of this hitherto unknown epigenetic regulatory mechanism could rejuvenate the prospects of Lp-PLA₂ as a therapeutic target to stabilize the atherosclerotic plaque and reduce clinical sequelae.

What Genetics Has Told Us and How It Can Inform Future Experiments for Spinal Muscular Atrophy, a Perspective

Proximal spinal muscular atrophy (SMA) is an autosomal recessive neurodegenerative disorder characterized by motor neuron loss and subsequent atrophy of skeletal muscle. SMA is caused by deficiency of the essential survival motor neuron (SMN) protein, canonically responsible for the assembly of the spliceosomal small nuclear ribonucleoproteins (snRNPs). Therapeutics aimed at increasing SMN protein levels are efficacious in treating SMA. However, it remains unknown how deficiency of SMN results in motor neuron loss, resulting in many reported cellular functions of SMN and pathways affected in SMA. Herein is a perspective detailing what genetics and biochemistry have told us about SMA and SMN, from identifying the SMA determinant region of the genome, to the development of therapeutics. Furthermore, we will discuss how genetics and biochemistry have been used to understand SMN function and how we can determine which of these are critical to SMA moving forward.

Rett syndrome: think outside the (skull) box

Rett syndrome (RTT) is a severe X-linked neurodevelopmental disorder characterized by neurodevelopmental regression between 6 and 18 months of life and associated with multi-system comorbidities. Caused mainly by pathogenic variants in the MECP2 (methyl CpG binding protein 2) gene, it is the second leading genetic cause of intellectual disability in girls after Down syndrome. RTT affects not only neurological function but also a wide array of non-neurological organs. RTT-related disorders involve abnormalities of the respiratory, cardiovascular, digestive, metabolic, skeletal, endocrine, muscular, and urinary systems and immune response. Here, we review the different aspects of RTT affecting the main peripheral groups of organs and sometimes occurring independently of nervous system defects.

Aberrant lung lipids cause respiratory impairment in a Mecp2-deficient mouse model of Rett syndrome

Severe respiratory impairment is a prominent feature of Rett syndrome (RTT), an X-linked disorder caused by mutations in methyl CpG-binding protein 2 (MECP2). Despite MECP2's ubiquitous expression, respiratory anomalies are attributed to neuronal dysfunction. Here, we show that neutral lipids accumulate in mouse Mecp2-mutant lungs, while surfactant phospholipids decrease. Conditional deletion of Mecp2 from lipid-producing alveolar epithelial 2 (AE2) cells causes aberrant lung lipids and respiratory symptoms, while deletion of Mecp2 from hindbrain neurons results in distinct respiratory abnormalities. Single-cell RNA sequencing of AE2 cells suggests lipid production and storage increase at the expense of phospholipid synthesis. Lipid production enzymes are confirmed as direct targets of MECP2-directed nuclear receptor corepressor 1/2 (NCOR1/2) transcriptional repression. Remarkably, lipid-lowering fluvastatin improves respiratory anomalies in Mecp2-mutant mice. These data implicate autonomous pulmonary loss of MECP2 in respiratory symptoms for the first time and have immediate impacts on patient care.

Transcriptomic and Epigenomic Landscape in Rett Syndrome

Rett syndrome (RTT) is an extremely invalidating, cureless, developmental disorder, and it is considered one of the leading causes of intellectual disability in female individuals. The vast majority of RTT cases are caused by de novo mutations in the X-linked Methyl-CpG binding protein 2 (MECP2) gene, which encodes a multifunctional reader of methylated DNA. MeCP2 is a master epigenetic modulator of gene expression, with a role in the organization of global chromatin architecture. Based on its interaction with multiple molecular partners and the diverse epigenetic scenario, MeCP2 triggers several downstream mechanisms, also influencing the epigenetic context, and thus leading to transcriptional activation or repression. In this frame, it is conceivable that defects in such a multifaceted factor as MeCP2 lead to large-scale alterations of the epigenome, ranging from an unbalanced deposition of epigenetic modifications to a transcriptional alteration of both protein-coding and non-coding genes, with critical consequences on multiple downstream biological processes. In this review, we provide an overview of the current knowledge concerning the transcriptomic and epigenomic alterations found in RTT patients and animal models.

The Role of Lipids, Lipid Metabolism and Ectopic Lipid Accumulation in Axon Growth, Regeneration and Repair after CNS Injury and Disease

Axons in the adult mammalian nervous system can extend over formidable distances, up to one meter or more in humans. During development, axonal and dendritic growth requires continuous addition of new membrane. Of the three major kinds of membrane lipids, phospholipids are the most abundant in all cell membranes, including neurons. Not only immature axons, but also severed axons in the adult require large amounts of lipids for axon regeneration to occur. Lipids also serve as energy storage, signaling molecules and they contribute to tissue physiology, as demonstrated by a variety of metabolic disorders in which harmful amounts of lipids accumulate in various tissues through the body. Detrimental changes in lipid metabolism and excess accumulation of lipids contribute to a lack of axon regeneration, poor neurological outcome and complications after a variety of central nervous system (CNS) trauma including brain and spinal cord injury. Recent evidence indicates that rewiring lipid metabolism can be manipulated for therapeutic gain, as it favors conditions for axon regeneration and CNS repair. Here, we review the role of lipids, lipid metabolism and ectopic lipid accumulation in axon growth, regeneration and CNS repair. In addition, we outline molecular and pharmacological strategies to fine-tune lipid composition and energy metabolism in neurons and non-neuronal cells that can be exploited to improve neurological recovery after CNS trauma and disease.

The Molecular Functions of MeCP2 in Rett Syndrome Pathology

MeCP2 protein, encoded by the MECP2 gene, binds to DNA and affects transcription. Outside of this activity the true range of MeCP2 function is still not entirely clear. As MECP2 gene mutations cause the neurodevelopmental disorder Rett syndrome in 1 in 10,000 female births, much of what is known about the biologic function of MeCP2 comes from studying human cell culture models and rodent models with Mecp2 gene mutations. In this review, the full scope of MeCP2 research available in the NIH Pubmed (https://pubmed.ncbi.nlm.nih.gov/) data base to date is considered. While not all original research can be mentioned due to space limitations, the main aspects of MeCP2 and Rett syndrome research are discussed while highlighting the work of individual researchers and research groups. First, the primary functions of MeCP2 relevant to Rett syndrome are summarized and explored. Second, the conflicting evidence and controversies surrounding emerging aspects of MeCP2 biology are examined. Next, the most obvious gaps in MeCP2 research studies are noted. Finally, the most recent discoveries in MeCP2 and Rett syndrome research are explored with a focus on the potential and pitfalls of novel treatments and therapies.