Human patient-specific FOXG1 syndrome mouse model revealed FOXG1-MYCN-mediated regulation of protein homeostasis in neurodevelopmental disorder.

The postnatal injection of AAV9-FOXG1 rescues corpus callosum agenesis and other brain deficits in the mouse model of FOXG1 syndrome

FOXG1 Syndrome (FS) is a devastating neurodevelopmental disorder that is caused by a heterozygous loss-of-function (LOF) mutation of the FOXG1 gene, which encodes a transcriptional regulator important for telencephalic brain development. People with FS have marked developmental delays, impaired ambulation, movement disorders, seizures, and behavior abnormalities including autistic features. Current therapeutic approaches are entirely symptomatic, however the ability to rescue phenotypes in mouse models of other genetic neurodevelopmental disorders such as Rett syndrome, Angelman syndrome, and Phelan-McDermid syndrome by postnatal expression of gene products has led to hope that similar approaches could help modify the disease course in other neurodevelopmental disorders such as FS. While FoxG1 protein function plays a critical role in embryonic brain development, the ongoing adult expression of FoxG1 and behavioral phenotypes that present when FoxG1 function is removed postnatally provides support for opportunity for improvement with postnatal treatment. Here we generated a new mouse allele of Foxg1 that disrupts protein expression and characterized the behavioral and structural brain phenotypes in heterozygous mutant animals. These mutant animals display changes in locomotor behavior, gait, anxiety, social interaction, aggression, and learning and memory compared to littermate controls. Additionally, they have structural brain abnormalities reminiscent of people with FS. This information provides a framework for future studies to evaluate the potential for post-natal expression of FoxG1 to modify the disease course in this severe neurodevelopmental disorder.

Single allelic mutations in the gene encoding the forebrain-specific transcription factor FOXG1 lead to FOXG1 syndrome (FS). Patient-specific animal models are needed to understand the etiology of FS, as FS patients show a wide spectrum of symptoms correlated with location and mutation type in the FOXG1 gene. Here we report the first patient-specific FS mouse model, Q84Pfs heterozygous (Q84Pfs-Het) mice, mimicking one of the most predominant single nucleotide variants in FS. Intriguingly, we found that Q84Pfs-Het mice faithfully recapitulate human FS phenotypes at the cellular, brain structural, and behavioral levels. Importantly, Q84Pfs-Het mice exhibited myelination deficits like FS patients. Further, our transcriptome analysis of Q84Pfs-Het cortex revealed a new role for FOXG1 in synapse and oligodendrocyte development. The dysregulated genes in Q84Pfs-Het brains also predicted motor dysfunction and autism-like phenotypes. Correspondingly, Q84Pfs-Het mice showed movement deficits, repetitive behaviors, increased anxiety, and prolonged behavior arrest. Together, our study revealed the crucial postnatal role of FOXG1 in neuronal maturation and myelination and elucidated the essential pathophysiology mechanisms of FS.

Perspectives on disrupted-inschizophrenia 1 signaling in neurogenesis

Single allelic mutations in the forebrain-specific transcription factor gene FOXG1 lead to FOXG1 syndrome (FS). To decipher the disease mechanisms of FS, which vary depending on FOXG1 mutation types, patient-specific animal models are critical. Here, we report the first patient-specific FS mouse model, Q84Pfs heterozygous (Q84Pfs-Het) mice, which emulates one of the most predominant FS variants. Remarkably, Q84Pfs-Het mice recapitulate various human FS phenotypes across cellular, brain structural, and behavioral levels, such as microcephaly, corpus callosum agenesis, movement disorders, repetitive behaviors, and anxiety. Q84Pfs-Het cortex showed dysregulations of genes controlling cell proliferation, neuronal projection and migration, synaptic assembly, and synaptic vesicle transport. Interestingly, the FS-causing Q84Pfs allele produced the N-terminal fragment of FOXG1, denoted as Q84Pfs protein, in Q84Pfs-Het mouse brains. Q84Pfs fragment forms intracellular speckles, interacts with FOXG1 full-length protein, and triggers the sequestration of FOXG1 to distinct subcellular domains. Q84Pfs protein also promotes the radial glial cell identity and suppresses neuronal migration in the cortex. Together, our study uncovered the role of the FOXG1 fragment derived from FS-causing FOXG1 variants and identified the genes involved in FS-like cellular and behavioral phenotypes, providing essential insights into the pathophysiology of FS.

Background: GABAergic signaling plays a crucial role in modulating neuronal proliferation, migration, and the formation of neural network connections. The termination of GABA transmission primarily occurs through the action of GABA transporter 1 (GAT1), encoded by the SLC6A1 gene. Multiple SLC6A1 mutations have been implicated in neurodevelopmental disorders, but their effects on the nervous system are unclear. Methods: We estimated the expression pattern of the GAT1 (S295L) protein using the Slc6a1S295L/S295L mouse model via RT-PCR, Western blotting, and confocal immunofluorescence. The effect of GAT1 (S295L) on hippocampal neurogenesis was investigated by neuronal marker staining (Sox2, Tbr2, NeuroD1, DCX, NeuN) and BrdU label experiments. The dendritic complexity was mapped through Sholl analysis. RNA-Seq was utilized to explore the signaling pathways and molecules associated with neurodevelopmental disorders. Results: We detected a remarkable decline in the quantity of type-2b intermediate progenitor cells, neuroblasts, and immature neurons in the dentate gyrus (DG) of Slc6a1S295L/S295L mice at 4 weeks. These abnormalities were exacerbated in adulthood, as evidenced by compromised dendritic length and height as well as the complexity of immature neurons. Immunofluorescence staining showed the abnormal aggregation of GAT1 (S295L) protein in neurons. RNA-seq analysis identified pathways associated with neurodevelopment, neurological disorders, protein homeostasis, and neuronutrition. The neurotrophin Bdnf decreased at all ages in the Slc6a1S295L/S295L mice. Conclusions: Our data provide new evidence that GAT1 (S295L) causes impaired neurogenesis in the DG. GAT1 mutation not only disrupts GABA homeostasis but also impairs the neurotrophic support necessary for normal hippocampal development, which may be one of the factors contributing to impaired neurogenesis.

FOXG1 syndrome is a neurodevelopmental disorder caused by mutations in the FOXG1 gene. Here, an induced pluripotent stem cell (iPSC) line was generated from human dermal fibroblasts of an individual with the c.490dupG (p.Glu154fs) mutation in the FOXG1 gene. Fibroblasts were reprogrammed using non-integrating episomal plasmids and pluripotency marker expression was confirmed by both immunocytochemistry and quantitative PCR in the resultant iPSC line. There were no karyotypic abnormalities and the cell line successfully differentiated into all three germ layers. This cell line may prove useful in the study of the pathogenic mechanisms that underpin FOXG1 syndrome.

Rett syndrome (RS) is a neurodevelopmental disorder that affects girls almost exclusively. The identification of mutations in the MECP2 and CDKL5 genes offers genetic confirmation of the clinical diagnosis. The FOXG1 gene appears to be a novel cause of the congenital variant of RS. We describe the first Spanish patient with the atypical (congenital) variant of RS with mutation of the FOXG1 gene and the case is compared with 12 patients previously reported in the literature; clinical criteria that suggest alterations in FOXG1 are proposed. The patient was referred at the age of 6 months due to overall retardation, axial hypotonia, microcephaly and a peculiar phenotype. Magnetic resonance imaging of the brain revealed hypoplasia of the corpus callosum, frontal atrophy and ventriculomegaly. The appearance of hand-to-mouth stereotypic movements at 12 months pointed the clinical diagnosis towards an atypical variant of RS, the congenital form; there was progressive improvement of visual contact and interest in her surroundings. Frequent respiratory infections and obstructive sleep apnoea syndrome. At the age of 5 years there was partial control over the axial tone, grasping with the hands, good contact and babbling, without epilepsy or behavioural disorders. The MECP2 and subtelomeric deletion study did not reveal any alterations; two polymorphisms were identified in the CDKL5 gene and a pathogenic mutation was found in FOXG1 (c.624C>G p.Tyr203X). It has been shown that 92% of patients with mutations in the FOXG1 gene present the congenital form of RS with severe generalised hypotonia, early acquired microcephaly (-3 to -6 standard deviations) and peculiar phenotype. When faced with a diagnosis of RS with no alterations in the MECP2 and CDKL5 genes, especially in the case of the congenital variant, the FOXG1 gene must be investigated. The molecular diagnosis confirms the clinical diagnosis and provides the family with genetic counselling.

Neurodevelopmental disorders (NDDs) are often linked to disruption in brain development and present challenges for affected individuals in achieving their cognitive, emotional, and motor developmental milestones. NDDs encompass a spectrum of conditions, including autism spectrum disorder (ASD), schizophrenia (SCZ), attention-deficit hyperactivity disorder (ADHD), and epilepsy. The unequivocal diagnosis of an NDD is often challenging due to overlapping signs and symptoms across different conditions. Synaptic plasticity, the activity-driven modification of synaptic strength and efficacy, plays a crucial role in brain network formation and organization and is frequently altered in NDDs. Here, we explore the multifaceted roles of postsynaptic density-95 kDa (PSD-95) in NDDs. Psd-95 is a scaffolding protein belonging to the membrane-associated guanylate kinases (MAGUKs) family, located at the core of synapses, and is central to synaptic plasticity. Dysregulation of PSD-95 is linked to various neuropsychiatric disorders. In SCZ, decreased PSD-95 expression affects synaptic plasticity, thereby impacting learning and memory. Genes associated with ASD interact with PSD-95, and its removal in mice leads to ASD-like behavioral abnormalities. Furthermore, PSD-95 is implicated in ADHD, where its modulation influences neurotransmission. Medications used in NDD treatment, such as antipsychotic drugs and selective serotonin reuptake inhibitors (SSRIs), can alter PSD-95 levels, potentially influencing synapse formation. Alpha-2 adrenergic agonists might enhance synaptic integrity by impacting PSD-95. Alternative pharmacotherapies such as memantine, allopurinol, and ketamine, all influencing PSD-95 to a certain extent, hold promise in managing NDDs. Understanding the role of PSD-95 in these disorders can deepen our biological comprehension and pave the way for targeted therapies. Specifically, exploring how PSD-95 affects synaptic plasticity and dendritic spine development could uncover opportunities for repurposing drugs to treat NDDs associated with mutations in the DLG4 gene encoding PSD-95.

FOXG1 syndrome is a rare neurodevelopmental disorder associated with severe cognitive dysfunction, autistic behavior, and early-onset hyperkinetic movement disorders. Patients have also been reported to experience sleep disturbances. However, these findings are mainly based on subjective caregivers' reports, and limited by small case numbers. Moreover, no studies using objective evaluation tools, such as actigraphy, have been reported. We analyzed the clinical and sleep manifestations of children with FOXG1 syndrome registered in the FOXG1 Research Foundation Patient Registry database. A total of 258 individuals with FOXG1 syndrome were included in this research. 132 (51.16%) had sleep disturbances. The more impaired of language acquisitions (absence of speech, OR: 3.99, 95%CI = 1.69-9.42, p = 0.002), hyperkinetic movement disorders (OR: 2.64, 95%CI = 1.34-5.20 p =0.005) and feeding difficulties (OR: 2.81, 95% CI = 1.52-5.19, p = 0.001) were significantly associated with an increase in odds of sleep disturbance after adjusting for age, sex, and antiepileptic drugs. We also performed sleep studies on six individuals with FOXG1 syndrome using The Children's Sleep Habits Questionnaire (CSHQ), the Sleep Disturbance Scale for Children (SDSC), and 7-day data from Actiwatch. The Pittsburgh Sleep Quality Index (PSQI) and 7-day data from Actiwatch were also used to evaluate the sleep condition of their parents. The CSHQ scores revealed bedtime resistance, sleep onset delay, sleep duration, sleep anxiety, night-waking, and parasomnia. Sleep-wake transition disorders and disorders of initiating and maintaining sleep were also suggested by the SDSC scores. The children's actigraphy revealed short sleep durations, impaired sleep efficiency, longer wake after sleep onset, and frequent night-waking. All caregivers reported significantly higher PSQI scores, mildly declined sleep efficiency, and shorter total sleep duration. Sleep disturbances, especially in initiating and maintaining sleep, are common in individuals with FOXG1 syndrome and their caregivers. Sleep disorders in patients with FOXG1 syndrome and their caregivers should be investigated.

New neurons are generated throughout life. This discovery has challenged firmly held concepts about the structural plasticity and regenerative capacity of the mammalian brain. In this special issue of the EJN, leaders in the field summarize and review recent advances aiming to understand the molecular mechanisms underlying adult neurogenesis and the impact of new neurons on brain function in health and disease. Below we discuss pivotal yet unsolved aspects of adult neurogenesis as well as potential future directions in the field.

Disruption of mitochondrial function and protein homeostasis plays a central role in aging. However, how these processes interact and what governs their failure in aging remain poorly understood. Here, we showed that ceramide biosynthesis controls the decline in mitochondrial and protein homeostasis during muscle aging. Analysis of transcriptome datasets derived from muscle biopsies obtained from both aged individuals and patients with a diverse range of muscle disorders revealed that changes in ceramide biosynthesis, as well as disturbances in mitochondrial and protein homeostasis pathways, are prevalent features in these conditions. By performing targeted lipidomics analyses, we found that ceramides accumulated in skeletal muscle with increasing age across Caenorhabditis elegans, mice, and humans. Inhibition of serine palmitoyltransferase (SPT), the rate-limiting enzyme of the ceramide de novo synthesis, by gene silencing or by treatment with myriocin restored proteostasis and mitochondrial function in human myoblasts, in C. elegans, and in the skeletal muscles of mice during aging. Restoration of these age-related processes improved health and life span in the nematode and muscle health and fitness in mice. Collectively, our data implicate pharmacological and genetic suppression of ceramide biosynthesis as potential therapeutic approaches to delay muscle aging and to manage related proteinopathies via mitochondrial and proteostasis remodeling.

mTOR Inhibition Ameliorates Cognitive and Affective Deficits Caused by Disc1 Knockdown in Adult-Born Dentate Granule Neurons

BackgroundDeveloping biomarkers is a priority for drug development for all conditions, but vital in the rare neurodevelopmental disorders where sensitive outcome measures are lacking. We have previously demonstrated the feasibility and tracking of evoked potentials to disease severity in Rett syndrome and CDKL5 deficiency disorder. The aim of the current study is to characterize evoked potentials in two related developmental encephalopathies, MECP2 duplication syndrome and FOXG1 syndrome, and compare across all four groups to better understand the potential of these measures to serve as biomarkers of clinical severity for the developmental encephalopathies.MethodsVisual and auditory evoked potentials were acquired from participants with MECP2 duplication syndrome and FOXG1 syndrome across five sites of the Rett Syndrome and Rett-Related Disorders Natural History Study. A group of age-matched individuals (mean = 7.8 years; range = 1–17) with Rett syndrome, CDKL5 deficiency disorder, and typically-developing participants served as a comparison group. The analysis focused on group-level differences as well as associations between the evoked potentials and measures of clinical severity from the Natural History Study.ResultsAs reported previously, group-level comparisons revealed attenuated visual evoked potentials (VEPs) in participants with Rett syndrome (n = 43) and CDKL5 deficiency disorder (n = 16) compared to typically-developing participants. VEP amplitude was also attenuated in participants with MECP2 duplication syndrome (n = 15) compared to the typically-developing group. VEP amplitude correlated with clinical severity for Rett syndrome and FOXG1 syndrome (n = 5). Auditory evoked potential (AEP) amplitude did not differ between groups, but AEP latency was prolonged in individuals with MECP2 duplication syndrome (n = 14) and FOXG1 syndrome (n = 6) compared to individuals with Rett syndrome (n = 51) and CDKL5 deficiency disorder (n = 14). AEP amplitude correlated with severity in Rett syndrome and CDKL5 deficiency disorder. AEP latency correlated with severity in CDKL5 deficiency disorder, MECP2 duplication syndrome, and FOXG1 syndrome.ConclusionsThere are consistent abnormalities in the evoked potentials in four developmental encephalopathies some of which correlate with clinical severity. While there are consistent changes amongst these four disorders, there are also condition specific findings that need to be further refined and validated. Overall, these results provide a foundation for further refinement of these measures for use in future clinical trials for these conditions.

Chapter 22 - Translational Medicine Strategies in Drug Development for Neurodevelopmental Disorders