Preclinical CRX augmentation therapies for CRX-associated autosomal dominant cone-rod dystrophies

Cone-rod dystrophies (CoRD) are inherited retinal diseases (IRDs) with variable ages of onset, characterized by the progressive loss of cones, followed by secondary degeneration of rods. Cone-rod homeobox (CRX) is a transcription factor that regulates gene expression essential for photoreceptor development and maintenance. Mutations in CRX gene, including CRX^E168d2 and CRX^E80A , are implicated in autosomal dominant CoRDs. Although these mutations show distinct pathogenic mechanisms, published studies in knock-in mouse models have suggested a common treatment strategy: increasing WT CRX expression to reduce the detrimental activities of mutant proteins. This study employs two independent strategies of CRX augmentation to evaluate their therapeutic potential in Crx^{E168d2/ +} and Crx^{E80A/ +} mouse models. The Tet-On-hCRX transgenic system, a platform of proof-of-principle gene therapy, induces consistent and pan-photoreceptor expression of CRX augmentation in diseased retinae, allowing for the faithful assessment of functional and behavioral recovery. AAV-mediated CRX augmentation confirms the biosafety, delivery efficiency and efficacy of viral transduction in diseased retinae. Both strategies have achieved significant treatment outcomes in cone photoreceptor survival and overall photoreceptor functions in young adulthood. Treated cones survive past the age point of complete cone loss in untreated controls of both models. Treated rods show functional improvement and long-term survival through later adulthood. This preclinical study establishes valuable treatment regimens and benchmarks for CRX augmentation in the treatment of CRX-associated IRDs, and offers new insights into the mechanisms for photoreceptor development and survival.