Glycosylphosphatidylinositol (GPI) anchors are a class of post-translational modifications observed on over 150 proteins. Pathogenic variants in the GPI biosynthesis enzyme, PIGA, in humans are associated with several brain anomalies such as hypomyelination, cerebellar hypoplasia, ataxic gait, and can lead to premature mortality. We previously genetically deleted Piga from the embryonic mouse brain which led to early postnatal death and significant structural brain malformations similar to those observed in humans with PIGA variants. The current treatment options for PIGA patients only manage symptoms and provides palliative care, demonstrating a need for new therapeutic options. We employed an AAV9-mediated PIGA gene-replacement (AAV9-hPIGA) strategy to assess the efficacy of gene therapy in the brain. We show that a single intracerebroventricular treatment on the first day of life successfully rescued survival rates, structural brain anomalies, and neurological impairments. Additionally, we used mass spectrometry to identify and quantify GPI-anchored proteins in untreated and treated mutant mice. We found that AAV9-hPIGA treatment restored GPI-anchored protein levels in mutant animals. These investigations enhance our understanding of GPI-anchored protein production during brain development and contribute to the development of a more effective intervention for PIGA-related symptoms.

Intra-cerebrospinal fluid (CSF) drug delivery bypasses the blood-brain barrier, making it a promising route of delivery to treat central nervous system (CNS) diseases. Optimizing this delivery route is challenging because of complex interactions among drug kinetics, CSF flow dynamics and anatomical variations. Non-human primate (NHP) models provide an approximation to human physiology, making a suitable surrogate for studying intra-CSF drug dispersion. We present a NHP digital model for pharmacokinetic prediction of intra-CSF solute neuraxial dispersion that incorporates craniospinal compliance and other key physiological features. A 3D subject-specific digital model of the NHP CSF system was formulated using a 3D multi-phase computational fluid dynamics (CFD) approach with flow and geometric boundary conditions using animal-specific in vivo MRI data. Initial digital model drug dispersion predictions were carried out assuming rigid dura and pial surfaces and verified by comparison to a 3D-printed NHP bench-top model replicating the in vivo measurements utilizing fluorescein as a surrogate drug tracer. Once verified, the digital model was extended to mimic craniospinal compliance by incorporating a dynamic mesh to allow dura surface motion that replicated the non-uniform CSF flow along the neuroaxis. Results were quantified over a one-hour period after a 1 mL drug injection via lumbar puncture needle in terms of spatial-temporal drug dispersion along the neuroaxis for the rigid, compliant and bench-top models. Regional percent of injected dose was assessed across the lumbar, thoracic, cervical and cranial regions, while total exposure at each 1 mm section was calculated as the area-under-the-curve (AUC) along the neuroaxis. The rigid digital model tracer dispersion predictions were verified through comparison with the NHP bench-top model, showing high spatial-temporal agreement (R² = 0.88). The introduction of dynamic mesh motion in the compliant digital model resulted in 10X reduction in peak lumbar CSF flowrate compared with the rigid model (0.065 versus 0.65 mL/min). This decrease in peak CSF flowrate contributed to a reduction in the average Reynolds number along the neuroaxis, dropping from 250 in the rigid model to under 100 in the compliant model leading to decreased tracer dispersion in the lumbar region. At 1 h following injection, tracer distribution to the lumbar, thoracic, cervical and intracranial CSF was 91.9, 8.1, 0 and 0

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

Neuroinflammation is a miscreant in accelerating progression of many neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). However, treatments targeting neuroinflammation alone have led to disappointing results in clinical trials. Both neuronal and non-neuronal cell types have been implicated in the pathogenesis of ALS, and multiple studies have shown correction of each cell type has beneficial effects on disease outcome. Previously, we shown that AAV9-mediated superoxide dismutase 1 (SOD1) suppression in motor neurons and astrocytes significantly improves motor function and extends survival in ALS mouse models. Despite neuron and astrocyte correction, ALS mice still succumb to death with microgliosis observed in endpoint tissue. Therefore, we hypothesized that the optimal therapeutic approach will target and simultaneously correct motor neurons, astrocytes, and microglia. Here, we developed a novel approach to indirectly target microglia with galectin-1 (Gal1) and combined this with our previously established AAV9.SOD1.short hairpin RNA treatment. We show Gal1 conditioning of SOD1 G93A microglia decreases inflammatory markers and rescues motor neuron death in vitro. When paired with SOD1 downregulation, we found a synergistic effect of combination treatment in vivo and show a significant extension of survival of SOD1 G93A mice over SOD1 suppression alone. These results highlight the importance of targeting inflammatory microglia as a critical component in future therapeutic development.

RNA helicases constitute a large protein family implicated in cellular RNA homeostasis and disease development. Here, we show that the RNA helicase IGHMBP2, linked to the neuromuscular disorder spinal muscular atrophy with respiratory distress type 1 (SMARD1), associates with polysomes and impacts translation of mRNAs containing short, GC-rich, and structured 5' UTRs. The absence of IGHMBP2 causes ribosome stalling at the start codon of target mRNAs, leading to reduced translation efficiency. The main mRNA targets of IGHMBP2-mediated regulation encode for components of the THO complex (THOC), linking IGHMBP2 to mRNA production and nuclear export. Accordingly, failure of IGHMBP2 regulation of THOC causes perturbations of the transcriptome and its encoded proteome, and ablation of THOC subunits phenocopies these changes. Thus, IGHMBP2 is an upstream regulator of THOC. Of note, IGHMBP2-dependent regulation of THOC is also observed in astrocytes derived from patients with SMARD1 disease, suggesting that deregulated mRNA metabolism contributes to SMARD1 etiology and may enable alternative therapeutic avenues.

Thirty genes are involved in the biosynthesis and modification of glycosylphosphatidylinositol (GPI)-anchored proteins, and defects in these genes cause inherited GPI deficiency (IGD). PIGA is X-linked and involved in the first step of GPI biosynthesis, and only males are affected by variations in this gene. The main symptoms of IGD are neurological abnormalities, such as developmental delay and seizures. There is no effective treatment at present. We crossed Nestin-Cre mice with Piga-floxed mice to generate CNS-specific Piga knockout (KO) mice. Hemizygous KO male mice died by P10 with severely defective growth. Heterozygous Piga KO female mice are mosaic for Piga expression and showed severe defects in growth and myelination and died by P25. Using these mouse models, we evaluated the effect of gene replacement therapy with adeno-associated virus (AAV). It expressed efficacy within 6 days, and the survival of male mice was extended to up to 3 weeks, whereas 40% of female mice survived for approximately 1 year and the growth defect was improved. However, liver cancer developed in all three treated female mice at 1 year of age, which was probably caused by the AAV vector bearing a strong CAG promoter.

Heterozygous mutations in the FOXG1 gene manifest as FOXG1 syndrome, a severe neurodevelopmental disorder characterized by structural brain anomalies, including agenesis of the corpus callosum, hippocampal reduction, and myelination delays. Despite the well-defined genetic basis of FOXG1 syndrome, therapeutic interventions targeting the underlying cause of the disorder are nonexistent. In this study, we explore the therapeutic potential of adeno-associated virus 9 (AAV9) mediated delivery of the FOXG1 gene. Remarkably, intracerebroventricular injection of AAV9-FOXG1 to Foxg1 heterozygous mouse model at the postnatal stage rescues a wide range of brain pathologies. This includes the amelioration of corpus callosum deficiencies, the restoration of dentate gyrus morphology in the hippocampus, the normalization of oligodendrocyte lineage cell numbers, and the rectification of myelination anomalies. Our findings highlight the efficacy of AAV9-based gene therapy as a viable treatment strategy for FOXG1 syndrome and potentially other neurodevelopmental disorders with similar brain malformations, asserting its therapeutic relevance in postnatal stages.

The blood-brain barrier (BBB) serves as a highly intricate and dynamic interface connecting the brain and the bloodstream, playing a vital role in maintaining brain homeostasis. BBB dysfunction has been associated with multiple neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS); however, the role of the BBB in neurodegeneration is understudied. We developed an ALS patient-derived model of the BBB by using cells derived from 5 patient donors carrying C9ORF72 mutations. Brain microvascular endothelial-like cells (BMEC-like cells) derived from C9ORF72-ALS patients showed altered gene expression, compromised barrier integrity, and increased P-glycoprotein transporter activity. In addition, mitochondrial metabolic tests demonstrated that C9ORF72-ALS BMECs display a significant decrease in basal glycolysis accompanied by increased basal and ATP-linked respiration. Moreover, our study reveals that C9-ALS derived astrocytes can further affect BMECs function and affect the expression of the glucose transporter Glut-1. Finally, C9ORF72 patient-derived BMECs form leaky barriers through a cell-autonomous mechanism and have neurotoxic properties towards motor neurons.

Duchenne muscular dystrophy (DMD) is a progressive muscle-wasting disease, caused by mutations in DMD gene leading to absence of dystrophin. Additionally, around one-third of patients present cognitive impairments. Several therapeutic approaches including exon-skipping have used efficient systemic delivery of adeno-associated virus (AAV). However, the high dose of vector needed to treat adult patients represents a risk, especially for the liver. We have investigated an alternative administration route using cerebrospinal fluid (CSF) delivery to avoid potential liver toxicity and improve brain transduction. Newborn C57BL/6 mice were intracerebroventricular (ICV) or face vein (FV) injected with 1E+11vg scAAV9.CBA.GFP to study virus biodistribution. After one and three months (mo) post-injection (pi), similar levels of GFP expression were observed in all muscles for CSF and systemic groups. However, a higher expression was detected in the brain after ICV injection and liver was less transduced by ICV injection compared to FV, which was confirmed by RT-PCR and WB. To conclude, CSF and systemic delivery allowed similar levels of muscle transduction by AAV9, although the brain transduction after ICV injection was superior and liver was less transduced, supporting the use of CSF delivery for the simultaneous distribution of AAV9 to muscles and CNS.

EDITORIAL article Front. Mol. Med, 04 January 2024Sec. Molecular Mechanisms of Neurodegeneration Volume 3 - 2023 | https://doi.org/10.3389/fmmed.2023.1337286

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 pro-tein 2 (MECP2) promoter allowing widespread expression of MECP2 in mice and non-human primates after a single injec-tion 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.

EDITORIAL article Front. Cell Dev. Biol., 16 November 2023Sec. Molecular and Cellular Pathology Volume 11 - 2023 | https://doi.org/10.3389/fcell.2023.1329048