Abstract
Widespread transduction of the CNS with a single, non-invasive systemic injection of adeno-associated virus is now possible due to the creation of blood-brain barrier-permeable capsids. However, as these capsids are mutants of AAV9, they do not have specific neuronal tropism. Therefore, it is necessary to use genetic tools to restrict expression of the transgene to neuronal tissues. Here we compare the strength and specificity of two neuron-specific promoters, human synapsin 1 and mouse calmodulin/calcium dependent kinase II, to the ubiquitous CAG promoter. Administration of a high titer of virus is necessary for widespread CNS transduction. We observed the neuron-specific promoters drive comparable overall expression in the brain to the CAG promoter. Furthermore, the neuron-specific promoters confer significantly less transgene expression in peripheral tissues compared with the CAG promoter. Future experiments will utilize these delivery platforms to over-express the Alzheimer-associated pathological proteins amyloid-beta and tau to create mouse models without transgenesis.
Highlights
Adeno-associated virus (AAV), a single-stranded DNA virus, is a member of the Dependovirus subfamily of the Parvoviridae family of viruses [1, 2]
We examined the transduction efficiency and strength of transgene expression driven by three different promoters in both the brain and select peripheral tissues
We evaluated the relative strength of the neuron selective human synapsin1 (hSyn1) and CaMKIIα promoters and assess their respective abilities to restrict peripheral expression, as compared to the ubiquitous CAG promoter, after intravenous administration of the PHP.eB variant of AAV
Summary
Adeno-associated virus (AAV), a single-stranded DNA virus, is a member of the Dependovirus subfamily of the Parvoviridae family of viruses [1, 2]. AAV has been used extensively in pre-clinical studies and clinical trials due to its efficient transduction of non-dividing cells, long-lasting expression, and low immunogenicity. Many factors may influence the transduction efficiency and targeting of AAV gene therapy such as route of delivery, use of a self-complementary AAV genome, and serotype [3]. Most preclinical experiments and clinical trials focusing on neurodegeneration deliver AAV gene therapy by intracranial injection into the brain [4, 5]. A major challenge is distributing gene therapy to the large and spatially dispersed volumes of brain affected. Capsid variants of AAV9 have been engineered using directed evolution that are more efficient at crossing the blood-brain barrier than other serotypes [6, 7]. Capsid variants named PHP.B or PHP.eB gain entry into the CNS of C57BL/6J mice by binding to specific isoforms of endothelial
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