The genome-wide activity of transcription factors (TFs) on multiple regulatory elements precludes their use as gene-specific regulators. Here we show that ectopic expression of a TF in a cell-specific context can be used to silence the expression of a specific gene as a therapeutic approach to regulate gene expression in human disease. We selected the TF Krüppel-like factor 15 ( KLF15 ) based on its putative ability to recognize a specific DNA sequence motif present in the rhodopsin ( RHO ) promoter and its lack of expression in terminally differentiated rod photoreceptors (the RHO -expressing cells). Adeno-associated virus (AAV) vector–mediated ectopic expression of KLF15 in rod photoreceptors of pigs enables Rho silencing with limited genome-wide transcriptional perturbations. Suppression of a RHO mutant allele by KLF15 corrects the phenotype of a mouse model of retinitis pigmentosa with no observed toxicity. Cell-specific-context conditioning of TF activity may prove a novel mode for somatic gene–targeted manipulation.

Gene-expression programs modulated by transcription factors (TFs) mediate key developmental events. Here, we show that the synthetic transcriptional repressor (TR; ZF6-DB), designed to treat Rhodopsin-mediated autosomal dominant retinitis pigmentosa (RHO-adRP), does not perturb murine retinal development, while maintaining its ability to block Rho expression transcriptionally. To express ZF6-DB into the developing retina, we pursued two approaches, (i) the retinal delivery (somatic expression) of ZF6-DB by Adeno-associated virus (AAV) vector (AAV-ZF6-DB) gene transfer during retinogenesis and (ii) the generation of a transgenic mouse (germ-line transmission, TR-ZF6-DB). Somatic and transgenic expression of ZF6-DB during retinogenesis does not affect retinal function of wild-type mice. The P347S mouse model of RHO-adRP, subretinally injected with AAV-ZF6-DB, or crossed with TR-ZF6-DB or shows retinal morphological and functional recovery. We propose the use of developmental transitions as an effective mode to challenge the safety of retinal gene therapies operating at genome, transcriptional, and transcript levels.

Introduction: α-synuclein aggregates have been identified in the retina of Parkinson’s disease patients associated to vision impairment. In this study, we sought to determine the effects of α-synuclein overexpression on the survival and function of dopaminergic (DA) amacrine cells in the retina. Methods: Adult mice were intravitreally injected with an adeno-associated viral (AAV) vector to overexpress human wild-type α-synuclein in the inner retina. Following systemic injections of levodopa (L-DOPA), retinal responses and visual acuity driven behavior were measured by electroretinography (ERG) and water maze task, respectively. Amacrine cells and ganglion cells were counted at 1, 2 and 3 months post-injection. Results: α-synuclein led to an early loss of DA cells, which was associated with the decrease of light-adapted ERG responses and visual acuity. Systemic injections of L-DOPA rescued these retinal and visual abnormalities. Conclusions: The data show that α-synuclein affects dopamine neurons in the retina. The approach provides a novel accessible mode of modeling the underlying mechanisms implicated in synucleinophaties pathogenesis and for testing novel treatments.