Optimizing oligotherapeutics for visual loss in Usher syndrome mice

Purpose : Usher syndrome (Usher) is a syndromic form of inherited retinal dystrophy (IRD) characterized by hearing impairment in combination with retinitis pigmentosa. Although considered rare, it is the most common genetic cause of deaf-blindness. To study mechanisms and develop therapies, we engineered a mouse model to contain the founder mutation (216A) in exon 3 of the USH1C gene responsible for Acadian Usher syndrome (USH1C) and developed a treatment targeting this mutation using antisense oligonucleotides (ASO). USH1C mice treated with 216A-targeted ASOs shows appreciable short-term rescue of visual function. The purpose of this study was to optimize ASO targeting for a longer duration of improved visual function in USH1C mice. Methods : USH1C mice were treated at post-natal day 21 by intravitreal injection (IVI) with ASOs designed to target different sequences in exon 3 of the Ush1c gene and with various chemical modifications. Ush1c gene expression was measured by RT-PCR and next-generation sequencing. Visual function was measured by electroretinogram (ERG) analysis at 3 and 6 months of age. Results : USH1C mice treated with ASOs of various sequences containing 2’-O-Methoxyethyl (2’MOE), 2’-O-Methyl (2’ME), morpholino (MO), or vivo-morpholino modifications showed dose dependent improvements in Ush1c expression in the retina 2 weeks post-IVI. Visual function testing showed significantly improved ERGs 14 weeks post-treatment with a single dose of 2’MOE-, MO-modified, or a combination of the two ASOs in USH1C mice compared with untreated or control-treated USH1C mice. Conclusions : Our results show that ASOs with various chemical modifications and targets in exon 3 of the Ush1c gene delivered locally to the eye can effectively target Ush1c mutations in the retina and improve visual function in USH1C mice. These results suggest the therapeutic potential of ASO intervention to improve gene expression and visual function in Usher syndrome, and IRDs in general. Future studies will include an analysis of aged USH1C mice treated with optimized ASOs to determine the duration of the visual benefits. This is a 2020 ARVO Annual Meeting abstract.