Promoter effects of adeno-associated viral vector for transgene expression in the cochlea in vivo

The aims of this study were to evaluate the expression of enhanced green fluorescent protein (EGFP) driven by 6 different promoters, including cytomegalovirus IE enhancer and chicken beta-actin promoter (CAG), cytomegalovirus promoter (CMV), neuron-specific enolase promoter (NSE), myosin 7A promoter (Myo), elongation factor la promoter (EF-1 alpha), and Rous sarcoma virus promoter (RSV), and assess the dose response of CAG promoter to transgene expression in the cochlea. Serotype 1 adeno-associated virus (AAV1) vectors with various constructs were transduced into the cochleae, and the level of EGFP expression was examined. We found the highest EGFP expression in the inner hair cells and other cochlear cells when CAG promoter was used. The CMV and NSE promoter drove the higher EGFP expression, but only a marginal activity was observed in EF-1 alpha promoter driven constructs. RSV promoter failed to drive the EGFP expression. Myo promoter driven EGFP was exclusively expressed in the inner hair cells of the cochlea. When driven by CAG promoter, reporter gene expression was detected in inner hair cells at a dose as low as 3 x 107 genome copies, and continued to increase in a dose-dependent manner. Our data showed that individual promoter has different ability to drive reporter gene expression in the cochlear cells. Our results might provide important information with regard to the role of promoters in regulating transgene expression and for the proper design of vectors for gene expression and gene therapy.