RNA interference to reduceexpression in rods delays retinal degeneration in a model of retinitis pigmentosa.

Abstract

PURPOSE: Retinitis pigmentosa (RP) is a heterogeneous group of inherited retinal diseases characterized by progressive photoreceptor degeneration. The early growth response-1 gene () is an immediate-early gene implicated in neurodegenerative and stress responses in the retina, among many other tissues. While its expression is induced in the retina across various RP models, its functional role in the degenerative process remains unclear. This study aimed to investigate the contribution ofto photoreceptor degeneration in vivo. METHODS: We used adeno-associated virus (AAV)-mediated RNA interference and transgenic overexpression to modifylevels in rod and cone photoreceptors of wild-type andmice. Rod- and cone-specific promoters enabled cell-specific expression. Exposure to high levels of white light was used to induce retinal degeneration in wild-type mice. We assessed retinal structure and transgene expression through funduscopy, optical coherence tomography (OCT), immunofluorescence, and histological analysis. We measuredmRNA expression levels via real-time PCR and assessed the effects ofmodulation on the retina by determining the thickness of the outer nuclear layer (ONL) and the number of surviving cones. RESULTS: Similar to other models of retinal degeneration,was induced in the retina after light exposure and in themouse during degeneration. AAV-mediated down- or upregulation ofin rods or cones did not affect retinal morphology in wild-type mice. Inmice,knockdown in rods modestly preserved ONL thickness up to 12 weeks after AAV injection. Overexpression did not accelerate degeneration beyond controls.modulation in cones of wild-type ormice did not affect cone survival. CONCLUSIONS: upregulation is a consistent early marker of photoreceptor stress, independent of the nature of the underlying stimulus. Since moderate support for cell survival and preservation of retinal morphology was achieved through the downregulation ofexpression in rods, but not in cones of themouse, the function of EGR1 in degenerative processes may be cell type specific. Althoughmay contribute to disease progression, it is unlikely to be a causative factor for degeneration. Our findings underscore the complexity of the transcriptional response in retinal degeneration and suggest thatis a secondary effector of degenerative processes in rods.