Advancing Gene Therapy for PDE6A Retinitis Pigmentosa

Area of Science:

• Ophthalmology
• Genetics
• Molecular Biology

Background:

• Mutations in the phosphodiesterase 6 alpha subunit (PDE6A) gene cause autosomal recessive retinitis pigmentosa (RP), a condition with no current treatment.
• PDE6A-RP accounts for 3-4% of RP cases, highlighting the need for therapeutic interventions.
• Existing research utilizes four animal models (one dog, three mice) with varying PDE6A mutations to study the disease and test potential therapies.

Purpose of the Study:

• To evaluate the efficacy of gene augmentation therapy for PDE6A-RP using adeno-associated virus (AAV) vectors.
• To assess the restoration of visual function and preservation of retinal structure in preclinical models of PDE6A-RP.

Main Methods:

• Proof-of-concept studies employed subretinal delivery of AAV serotype 8 vectors carrying species-specific PDE6A cDNAs in a dog and an Asp670Gly mouse model.
• A translatable vector, AAV8 with a human rhodopsin promoter and human PDE6A cDNA, was subsequently tested in the dog and Asp670Gly mouse models.
• Functional outcomes were assessed via electroretinography (ERG) measuring rod- and cone-mediated responses, alongside morphological analysis of retinal structure.

Main Results:

• Gene augmentation with AAV8 vectors partially restored rod-mediated function and preserved retinal structure in both dog and mouse models.
• The translatable vector demonstrated robust restoration of rod function, improved dim-light vision, and enhanced photoreceptor layer morphology in the dog model.
• In the Asp670Gly mouse model, the therapy preserved photoreceptors and maintained cone-mediated ERG responses, indicating cone survival.

Conclusions:

• Adeno-associated virus-mediated gene therapy is a viable strategy for treating PDE6A-RP.
• These preclinical findings represent a significant advancement toward developing a translatable therapy for patients with PDE6A-RP.
• The successful restoration of visual function and retinal integrity in animal models provides a strong foundation for future clinical trials.