Systemic AAV6-synapsin-GFP administration results in lower liver biodistribution, compared to AAV1&2 and AAV9, with neuronal expression following ultrasound-mediated brain delivery

Danielle Weber-Adrian,Shawna Rideout,Sebastian Kügler,Alison Burgess,Rikke Hahn Kofoed,Kullervo Hynynen,Joseph Silburt,Zeinab Noroozian,Kairavi Shah,Isabelle Aubert

doi:10.1038/s41598-021-81046-5

Abstract

Non-surgical gene delivery to the brain can be achieved following intravenous injection of viral vectors coupled with transcranial MRI-guided focused ultrasound (MRIgFUS) to temporarily and locally permeabilize the blood–brain barrier. Vector and promoter selection can provide neuronal expression in the brain, while limiting biodistribution and expression in peripheral organs. To date, the biodistribution of adeno-associated viruses (AAVs) within peripheral organs had not been quantified following intravenous injection and MRIgFUS delivery to the brain. We evaluated the quantity of viral DNA from the serotypes AAV9, AAV6, and a mosaic AAV1&2, expressing green fluorescent protein (GFP) under the neuron-specific synapsin promoter (syn). AAVs were administered intravenously during MRIgFUS targeting to the striatum and hippocampus in mice. The syn promoter led to undetectable levels of GFP expression in peripheral organs. In the liver, the biodistribution of AAV9 and AAV1&2 was 12.9- and 4.4-fold higher, respectively, compared to AAV6. The percentage of GFP-positive neurons in the FUS-targeted areas of the brain was comparable for AAV6-syn-GFP and AAV1&2-syn-GFP. In summary, MRIgFUS-mediated gene delivery with AAV6-syn-GFP had lower off-target biodistribution in the liver compared to AAV9 and AAV1&2, while providing neuronal GFP expression in the striatum and hippocampus.

Highlights

Gene therapy for the treatment of neurodegenerative disorders, such as spinal muscular atrophy[1], Alzheimer’s2 and Parkinson’s3 diseases, has reached the clinical trial stage using adeno-associated virus (AAV) as a gene expression vector
Our results indicate that MRI-guided focused ultrasound (MRIgFUS) AAV6-syn-green fluorescent protein (GFP) gene delivery leads to transgene expression below the detectable limit of our assay in the liver, lower DNA biodistribution within the liver compared to AAV1&2, and provides neuronal GFP expression in the hippocampus and striatum
AAV serotype 9 (AAV9) injection resulted in 2.9-fold greater biodistribution in the liver compared to AAV1&2 (p < 0.0001), and 12.9-fold greater biodistribution compared to AAV6 (p < 0.0001)

Summary

Introduction

Gene therapy for the treatment of neurodegenerative disorders, such as spinal muscular atrophy[1], Alzheimer’s2 and Parkinson’s3 diseases, has reached the clinical trial stage using adeno-associated virus (AAV) as a gene expression vector. At a minimum of 1 × 1011 vector genomes or viral particles per mouse[4,5] Such systemic administration of AAV9 results in non-targeted central and peripheral transduction and expression. Thereby, MRIgFUS offers a promising method to mediate non-surgical gene delivery to targeted brain areas using AAV serotypes which do not overcome the BBB7, and AAV9 at dosages below the systemic minimum required to pass the BBB8–10. Our results indicate that MRIgFUS AAV6-syn-GFP gene delivery leads to transgene expression below the detectable limit of our assay in the liver, lower DNA biodistribution within the liver compared to AAV1&2, and provides neuronal GFP expression in the hippocampus and striatum. The development of AAV serotypes and promoters for MRIgFUS gene therapy could tailor treatment to specific neurological disorders and brain regions, without being limited to serotypes which innately overcome the BBB or surgical delivery

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Discussion

Conclusion