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

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.