Adeno-Associated Virus Capsid-Promoter Interactions in the Brain Translate from Rat to the Nonhuman Primate

Recently, we established an adeno-associated virus (AAV9) capsid-promoter interaction that directly determined cell-specific gene expression across two synthetic promoters, Cbh and CBA, in the rat striatum. These studies not only expand this capsid-promoter interaction to include another promoter in the rat striatum but also establish AAV capsid-promoter interactions in the nonhuman primate brain. When AAV serotype 9 (AAV9) vectors were injected into the rat striatum, the minimal synthetic promoter JetI drove green fluorescent protein (GFP) gene expression predominantly in oligodendrocytes. However, similar to our previous findings, the insertion of six alanines into VP1/VP2 of the AAV9 capsid (AAV9AU) significantly shifted JetI-driven GFP gene expression to neurons. In addition, previous retrograde tracing studies in the nonhuman primate brain also revealed the existence of a capsid-promoter interaction. When rAAV2-Retro vectors were infused into the frontal eye field (FEF) of rhesus macaques, local gene expression was prominent using either the hybrid chicken beta actin (CAG) or human synapsin (hSyn) promoters. However, only the CAG promoter, not the hSyn promoter, led to gene expression in the ipsilateral claustrum and contralateral FEF. Conversely, infusion of rAAV2-retro-hSyn vectors, but not rAAV2-retro-CAG, into the macaque superior colliculus led to differential and selective retrograde gene expression in cerebellotectal afferent cells. Clearly, this differential promoter/capsid expression profile could not be attributed to promoter inactivation from retrograde transport of the rAAV2-Retro vector. In summary, we document the potential for AAV capsid/promoter interactions to impact cell-specific gene expression across species, experimental manipulations, and engineered capsids, independent of capsid permissivity.