Downregulating Nrl Expression and Rod Photoreceptor Protection.

Retinitis pigmentosa (RP) is a genetically heterogeneous group of inherited retinal degenerations with primary degeneration of rod photoreceptors followed by secondary cone loss. We investigated whether downregulating Nrl (neural retina leucine zipper), a key transcription factor specifying rod fate, can reprogram rods into a more resilient state. In a transgenic NrlN/N mouse in which Nrl was markedly downregulated, the rod phenotype became more like a rod precursor, particularly in the inferior retina. Crossing NrlN/N mice with two rod degeneration models, rd1 (Pde6brd1/rd1) and rhodopsin P23H knock-in (RhoP23H/P23H) mice, showed significantly improved photoreceptor survival in double-mutant mice. In addition, AAV-mediated delivery of shRNA targeting Nrl mRNA substantially enhanced photoreceptor survival in rd10 (Pde6brd10/rd10) mice. These findings demonstrate that downregulation of Nrl reprograms rods and confers broad resistance to degeneration across multiple RP models. AAV-mediated Nrl knockdown represents a promising mutation-independent therapeutic strategy for autosomal recessive and dominant forms of RP.