Improved neuronal transgene expression from an AAV‐2 vector with a hybrid CMV enhancer/PDGF‐β promoter

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Abstract
Background Adeno‐associated virus type 2 (AAV‐2) vectors are highly promising tools for gene therapy of neurological disorders. After accommodating a cellular promoter, AAV‐2 vectors are able to drive sustained expression of transgene in the brain. This study aimed to develop AAV‐2 vectors that also facilitate a high level of neuronal expression by enhancing the strength of a neuron‐specific promoter, the human platelet‐derived growth factor β‐chain (PDGF) promoter. Methods and results A hybrid promoter approach was adopted to fuse the enhancer of human cytomegalovirus immediately early (CMV) promoter to the PDGF promoter. In cultured cortex neurons, AAV‐2 vectors containing the hybrid promoter augmented transgene expression up to 20‐fold over that mediated by titer‐matched AAV‐2 vectors with the PDGF promoter alone and 4‐fold over the CMV enhancer/promoter. Injection of AAV‐2 vectors with the hybrid promoter into the rat striatum resulted in neuron‐specific transgene expression, the level of which was about 10‐fold higher than those provided by the two control AAV‐2 expression cassettes at 4 weeks post‐injection and maintained for at least 12 weeks. Gene expression in the substantia nigra through possible retrograde transport of the AAV‐2 vectors injected into the striatum was not obvious. After direct injection of AAV‐2 vectors into the substantia nigra, transgene expression driven by the hybrid promoter was observed specifically in dopaminergic neurons and its level was about 3 and 17 times higher than that provided by the PDGF promoter alone and the CMV enhancer/promoter, respectively. Conclusions Enhanced transgene capacity plus neuron‐specificity of the AAV‐2 vectors developed in this study might prove valuable for gene therapy of Parkinson's disease. Copyright © 2005 John Wiley & Sons, Ltd.