AAV capsid-promoter interactions determines CNS cell selective gene expression in vivo

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ABSTRACT Adeno-associated virus (AAV) vectors occupy a prominent role in recent CNS clinical trials particularly with respect to the use of AAV serotype 9 (AAV9) for single gene genetic disorders, such as spinal muscular atrophy and giant axon neuropathy (Mendell et al., 2018; Bailey et al., 2018). Given the need for selective cellular transduction, capsid modification, cell specific promoters and cell specific enhancers all have demonstrated success in achieving specific vector properties (Asokan et al., 2012; Dimidschstein et al., 2016; Grimm and Buning, 2017). In a recently accepted manuscript, we established a previously unknown interaction between the AAV9 capsid and different constitutive promoters, namely the ability to directly influence cell specific gene expression in the CNS. Using identical transgenes and the AAV9 capsid, CBA promoter driven gene expression exhibited a dominant neuronal gene expression in the rat striatum, but when gene expression was driven by the truncated Cbh promoter, gene expression was significantly shifted to striatal oligodendrocytes. Moreover, an AAV9 chimera containing six glutamate insertions after amino acid 139 in VP1/2 exhibited oligodendrocyte gene expression for both CBA and Cbh driven gene expression while a six alanine insertion in the same site reversed the Cbh driven gene expression back to neurons. Recently, preliminary findings revealed a similar AAV9 capsid interaction with the JetI synthetic promoter that influenced cellular gene expression in vivo. Given the highly novel nature of this capsid-promoter interaction, in vitro studies will define the mechanisms that underlie the glutamate and alanine shifts in cellular gene expression, including capsid conformation, intracellular trafficking, RNA splicing and VP1,2,3 interactions. In vivo studies will assess those promoter elements that contribute to the interactions, and specific AAV9 capsid elements that influence changes in in vivo cellular gene expression. Given the numerous applications of AAV9 vectors, the findings should significantly advance our understanding of basic capsid-promoter interactions and prove crucial to future design of AAV9 based gene therapies.