Adeno-Associated Viruses for Modeling Neurological Diseases in Animals: Achievements and Prospects

Development of an AAV-RNAi strategy to silence the dominant variant GNAO1 c.607G>A linked to encephalopathy

Heterozygous mutations in GNAO1 cause an ultra-rare neurodevelopmental disease called GNAO1 encephalopathy, characterized by infantile epilepsy and movement disorder. Here, we provide a functional characterization of the hotspot mutation GNAO1 c.607G>A (p.G203R) and conduct early-phase development of an adeno-associated virus (AAV)-mediated gene therapy approach. The GNAO1 gene encodes the Gαo protein that is involved in neuronal signaling. We showed that the Gαo-G203R lost its ability to enhance forskolin-stimulated cAMP synthesis in HEK293T cells. In primary neuronal culture, Gαo-G203R had a dominant-negative effect on neuronal activity and GABAB-dependent synaptic release. To ablate the mutant protein, we used selective silencing of the pathogenic variant using effectors of RNA interference (RNAi). We selected the short hairpin RNA (sh1500) that suppressed the c.607G>A transcripts, resulting in a 3.8-fold increase in the ratio of wild-type to mutant GNAO1 transcripts in patient-specific neurons. We also detected off-target effects of sh1500 as well as transcriptome changes associated with AAV transduction and RNAi activation. We improved the AAV construct by using an artificial miRNA (miR1500) and the neuron-specific hSyn promoter. Systemic administration of AAV9-hSyn-miR1500 did not cause pathological changes in Gnao1-GGA mice with a "humanized" target sequence. Importantly, AAV9 transduced Gαo-positive neurons in the striatum, thalamus, substantia nigra, and cerebellum, which we defined as primary targets for gene therapy. Our findings pave the road toward the development of AAV-RNAi approaches for dominant-negative GNAO1 variants.

Efficient AAV9 Purification Using a Single-Step AAV9 Magnetic Affinity Beads Isolation

Adeno-associated viruses (AAVs) have emerged as promising tools for gene therapy due to their safety and efficacy in delivering therapeutic genes or gene editing sequences to various tissues and organs. AAV serotype 9 (AAV9), among AAV serotypes, stands out for its ability to efficiently target multiple tissues, thus holding significant potential for clinical applications. However, existing methods for purifying AAVs are cumbersome, expensive, and often yield inconsistent results. In this study, we explore a novel purification strategy utilizing Dynabeads™ CaptureSelect™ magnetic beads. The AAV9 magnetic beads capture AAV9 with high specificity and recovery between 70 and 90%, whereas the AAVX magnetic beads did not bind to the AAV9. Through continuous interaction with AAVs in solution, these beads offer enhanced clearance of genomic DNA and plasmids even in the absence of endonuclease. The beads could be regenerated at least eight times, and the used beads could be stored for up to six months and reused without a significant reduction in recovery. The potency of the AAV9-purified vectors in vivo was comparable to that of iodixanol purified vectors.

Need of orthogonal approaches in neurological disease modeling in mouse

Over the years, advancements in modeling neurological diseases have revealed innovative strategies aimed at gaining deeper insights and developing more effective treatments for these complex conditions. However, these progresses have recently been overshadowed by an increasing number of failures in clinical trials, raising doubts about the reliability and translatability of this type of disease modeling. This mini-review does not aim to provide a comprehensive overview of the current state-of-the-art in disease mouse modeling. Instead, it offers a brief excursus over some recent approaches in modeling neurological diseases to pinpoint a few intriguing strategies applied in the field that may serve as sources of inspiration for improving currently available animal models. In particular, we aim to guide the reader toward the potential success of adopting a more orthogonal approach in the study of human diseases.

Viral-based animal models in polyglutamine disorders

Polyglutamine disorders are a complex group of incurable neurodegenerative disorders caused by an abnormal expansion in the trinucleotide cytosine-adenine-guanine tract of the affected gene. To better understand these disorders, our dependence on animal models persists, primarily relying on transgenic models. In an effort to complement and deepen our knowledge, researchers have also developed animal models of polyglutamine disorders employing viral vectors. Viral vectors have been extensively used to deliver genes to the brain, not only for therapeutic purposes but also for the development of animal models, given their remarkable flexibility. In a time- and cost-effective manner, it is possible to use different transgenes, at varying doses, in diverse targeted tissues, at different ages, and in different species, to recreate polyglutamine pathology. This paper aims to showcase the utility of viral vectors in disease modelling, share essential considerations for developing animal models with viral vectors, and provide a comprehensive review of existing viral-based animal models for polyglutamine disorders.

Novel chemical tyrosine functionalization of adeno-associated virus improves gene transfer efficiency in liver and retina

Decades of biological and clinical research have led to important advances in recombinant adeno-associated viruses rAAV-based gene therapy gene therapy. However, several challenges must be overcome to fully exploit the potential of rAAV vectors. Innovative approaches to modify viral genome and capsid elements have been used to overcome issues such as unwanted immune responses and off-targeting. While often successful, genetic modification of capsids can drastically reduce vector yield and often fails to produce vectors with properties that translate across different animal species, such as rodents, non-human primates, and humans. Here, we describe a chemical bioconjugation strategy to modify tyrosine residues on AAV capsids using specific ligands, thereby circumventing the need to genetically engineer the capsid sequence. Aromatic electrophilic substitution of the phenol ring of tyrosine residues on AAV capsids improved the in vivo transduction efficiency of rAAV2 vectors in both liver and retinal targets. This tyrosine bioconjugation strategy represents an innovative technology for the engineering of rAAV vectors for human gene therapy.

AAV-GRN partially corrects motor deficits and ALS/FTLD-related pathology in Tmem106b-/-Grn-/- mice

Loss of function of progranulin (PGRN), encoded by the granulin (GRN) gene, is implicated in several neurodegenerative diseases. Several therapeutics to boost PGRN levels are currently in clinical trials. However, it is difficult to test the efficacy of PGRN-enhancing drugs in mouse models due to the mild phenotypes of Grn-/- mice. Recently, mice deficient in both PGRN and TMEM106B were shown to develop severe motor deficits and pathology. Here, we show that intracerebral ventricle injection of PGRN-expressing AAV1/9 viruses partially rescues motor deficits, neuronal loss, glial activation, and lysosomal abnormalities in Tmem106b-/-Grn-/- mice. Widespread expression of PGRN is detected in both the brain and spinal cord for both AAV subtypes. However, AAV9 but not AAV1-mediated expression of PGRN results in high levels of PGRN in the serum. Together, these data support using the Tmem106b-/-Grn-/- mouse strain as a robust mouse model to determine the efficacy of PGRN-elevating therapeutics.