Alternative splicing of nucleoredoxin-like 1 (Nxnl1) results in 2 isoforms of the rod-derived cone viability factor. The truncated form (RdCVF) is a thioredoxin-like protein secreted by rods that promotes cone survival, while the full-length isoform (RdCVFL), which contains a thioredoxin fold, is involved in oxidative signaling and protection against hyperoxia. Here, we evaluated the effects of these different isoforms in 2 murine models of rod-cone dystrophy. We used adeno-associated virus (AAV) to express these isoforms in mice and found that both systemic and intravitreal injection of engineered AAV vectors resulted in RdCVF and RdCVFL expression in the eye. Systemic delivery of AAV92YF vectors in neonates resulted in earlier onset of RdCVF and RdCVFL expression compared with that observed with intraocular injection using the same vectors at P14. We also evaluated the efficacy of intravitreal injection using a recently developed photoreceptor-transducing AAV variant (7m8) at P14. Systemic administration of AAV92YF-RdCVF improved cone function and delayed cone loss, while AAV92YF-RdCVFL increased rhodopsin mRNA and reduced oxidative stress by-products. Intravitreal 7m8-RdCVF slowed the rate of cone cell death and increased the amplitude of the photopic electroretinogram. Together, these results indicate different functions for Nxnl1 isoforms in the retina and suggest that RdCVF gene therapy has potential for treating retinal degenerative disease.
Authors
Leah C. Byrne, Deniz Dalkara, Gabriel Luna, Steven K. Fisher, Emmanuelle Clérin, Jose-Alain Sahel, Thierry Léveillard, John G. Flannery
(A) Injections of 7m8-scCAG-RdCVF in homozygous P23H/P23H mice, a model of dominant RP, resulted in sustained amplitudes of the photopic ERG 1 month after injection (n = 6). (B) Time course of ERGs recorded from P23H/+ mice injected with 7m8-scCAG-RdCVF (n = 5) or 7m8-scCAG-RdCVFL (n = 6). In mice injected with RdCVF, ERG amplitudes were higher in treated eyes compared with those in control, PBS-injected, and contralateral eyes at 1 and 4 months, but not 6 months, after injection. In mice treated with 7m8-scCAG-RdCVFL, ERG amplitudes were not significantly different from those in sham-injected eyes at any of the time points measured.