Mutations in the rhodopsin gene may cause photoreceptor degeneration in autosomal dominant retinitis pigmentosa (ADRP) by dominant negative or toxic gain of function mechanisms. Controversy exists as to the mechanism by which the widely studied P23H mutation induces rod cell dysfunction and death. Inherited disease caused by dominant negative mutations may be amenable to treatment using wild type gene augmentation. Indeed, prior studies in the <i>RHO<sup>P23H</sup>, Rho<sup>+/-</sup></i> transgenic mouse model of ADRP have suggested that a therapeutic benefit may be achieved when wild type rhodopsin is overexpressed following subretinal delivery of a recombinant adeno-associated viral (AAV) vector. In this study, we investigated the effect of wild type rhodopsin supplementation on the rate of retinal degeneration in the more clinically relevant <i>Rho<sup>P23H/+</sup></i> knock-in mouse model of ADRP. Four AAVs carrying the human rhodopsin coding sequence were first designed and compared for efficacy in the rhodopsin knockout mouse. All four vectors were capable of driving expression of the human transgene in the knockout retina with the protein being appropriately trafficked to de novo rod outer segments. The most efficient of these vectors was injected at one of two doses into the subretinal space of <i>Rho<sup>P23H/+</sup></i> mice and the effect on retinal structure and function determined longitudinally by spectral-domain optical coherence tomography and electroretinography respectively over a three-month period. Although significant overexpression of rhodopsin protein was achieved in this model, no beneficial effect on retinal structure or function was observed at either dose. Lack of therapeutic efficacy in this model may be attributable to the relative rapidity of degeneration in the <i>Rho<sup>P23H/+</sup></i> mouse relative to the human disease, over- or under dosing at the level of individual photoreceptors, late timing of the intervention, or a possible predominant toxic gain of function mechanism of degeneration.
Hum Gene Ther