Abstract
Purpose :
Usher syndrome (USH) is the most common cause of deaf-blindness and there are four clinical USH types. USH1 is the most severe form and accounts for 25–44% in all USH cases. Of these, type 1C (USH1C) is caused by mutations in the USH1C gene, which expresses three Harmonin protein isoforms via alternative splicing. The USH1C c.216G>A is a founder mutation in Acadian populations of Louisiana and Canada that causes aberrant splicing which results in truncated Ush1c transcripts and harmonin proteins. Transgenic mice with the 216AA splicing mutation have retinal dysfunction, as well as profound hearing and vestibular deficits, similar to patients. Previously, we showed short-term rescue of hearing, balance, and vision in the Ush1c-216AA mice treated with 216A-targeted 2′ O-methoxyethyl (MOE) antisense oligonucleotides (ASOs). To improve upon these results, we tested various ASO chemistries with a similar sequence in a mouse model of Ush1c-216AA
Methods :
Juvenile Ush1c-216AA mice were treated with intravitreal injection (IVI) one time with 216A-targeted MOE-, morpholino (MO)-, or Vivo-MO-ASOs, or untreated. Visual function was assessed with electroretinogram (ERG) analysis at 3-12 months of age. Retinal tissues were also harvested for analyses of Ush1c transcript splicing/expression via Next Generation Sequencing (NGS)
Results :
Two weeks post-IVI, the relative abundance of WT Ush1c transcripts was significantly increased in the retinas of Ush1c-216AA mice treated with the MOE or MO, but not Vivo-MO, compared with untreated Ush1c-216AA control mice (MOE: 26%, MO: 17%, Vivo-MO: 4%, untreated, 3%, respectively). Interestingly, Vivo-MO treated retinas showed a significant increase in the relative abundance of exon 3-skipped Ush1c transcripts compared with MOE, MO and untreated retinas (Vivo-MO: 90%, MOE: 10%, MO: 8%, untreated, 0%). Analyses in aged mice are ongoing. Retinal function of Ush1c-216AA mice treated one time with MOE showed significantly improved ERGs at 3-months-of-age; whereas treatment with MO showed significantly improved ERGs at 3- and 6 months-of-age, however, Vivo-MO did not improve retina function at any age as compared to untreated mice
Conclusions :
These data demonstrate that the chemistry of an ASO sequence targeting the 216A mutation in the Ush1c gene significantly alters its ability to effect splicing of retinal Ush1c transcripts and visual function in Ush1c-216AA mice
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.