AAV-Mediated Rhodopsin Replacement Provides Therapeutic Benefit in Mice with a Targeted Disruption of the Rhodopsin Gene

The rhodopsin gene (RHO) encodes a highly expressed G protein-coupled receptor (GPCR) which is central to visual transduction in rod photoreceptors. A suite of recombinant 2/5 adeno-associated virus (AAV) RHO replacement vectors has been generated in an attempt to recapitulate endogenous rhodopsin levels from exogenously delivered AAV vectors in the retina of mice with a targeted disruption in the rhodopsin gene (Rho-/-mice). Approximately 40% of wild type mouse rhodopsin mRNA levels (RNA taken from whole retinas) were achieved in vivo in AAV-RHO-injected eyes, representing approximately 50-fold increases in expression comparative with the initial vector. The main focus of this study was to test whether expression of AAV-RHO replacement in Rho-/-mice provided therapeutic benefit, which to date had not been achieved. Rho-/-mice neither elaborate rod outer segments nor have rod-derived electroretinograms (ERG). Our results indicate for the first time in this model that subretinal AAV-RHO delivery leads not only to RHO immunolabelling but the generation of rod outer segments as evaluated by light and transmission electron microscopy. Improved histology was accompanied by rod photoreceptor activity as assessed by ERG for at least twelve weeks post-injection. The most efficient AAV-RHO constructs presented in this study provide sufficient levels of RHO to be of therapeutic benefit in Rho-/-mice and therefore represent important steps towards generating potent AAV-RHO replacement genes for gene therapy in RHO-linked human retinopathies.