Abstract
Purpose :
Usher syndrome (USH) is the most common cause of deaf and blindness and has four clinical types (USH1-4) based on the severity and age of onset. USH1 is the most severe form and accounts for 25–44% of all USH cases. Of these, type 1C (USH1C) is caused by mutations in the USH1C gene, which expresses three Harmonin protein isoforms (a, b, c) via alternative splicing of multiple Ush1c transcripts. The USH1C c.216G>A (216A) 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 mice treated with 216A-targeted 2′ O-methoxyethyl (MOE) antisense oligonucleotides (ASOs). To improve upon these results, here we tested 216A-targeted MOE, Morpholino (MO), or a combination of both ASO chemistries (Combo-ASO) for the treatment of visual dysfunction in a mouse model of USH1C.
Methods :
Juvenile USH1C mice were treated by intravitreal injection (IVI) one time with 216A-targeted MOE-, MO-, or Combo-ASOs, or untreated. Visual function was assessed at 3, 6, and 12 months of age by electroretinogram (ERG) analysis. Retinal tissues were harvested at 1, 3, 6, and 12 months of age for analyses of gene and protein expression via Next Generation Sequencing (NGS) and immunohistochemistry (IHC) analyses, respectively.
Results :
USH1C mice treated with the Combo-ASO therapy had significantly improved ERGs at all ages tested compared with untreated USH1C mice. Whereas treatment with MOE-ASOs showed significantly improved ERGs at 3-months-of-age; and treatment with MO-ASOs showed significantly improved ERGs at 3- and 6 months-of-age. Splicing analysis in USH1C retinas two weeks post-IVI at 1-month-of age showed significantly increased WT transcripts with the Combo-ASO, compared with MOE, MO, or untreated USH mice (Combo: 39%, MOE: 26%, MO: 17%, untreated USH, 3%). Analyses in aged mice, including IHC, are ongoing.
Conclusions :
These data demonstrate that a single intravitreal dose of a combination of ASO chemistries targeting the 216A mutation significantly improved retinal gene expression and extended the duration of improved visual function in USH mice.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.