Retinal degeneration in BBS10 mice is ameliorated by subretinal gene replacement

Abstract

Purpose : Overexpression toxicity in BBS1 mice limits effectiveness of gene therapy. BBS1 is part of the BBSome, while BBS10 is part of the chaperonin complex. We treated BBS10 mice with subretinal gene replacement to assess toxicity and efficacy.

Methods : A mouse model of Bardet Biedl Syndrome type 10 (BBS10) was developed by knocking out the Bbs10 gene. ERG, OCT, and visually guided swim maze (VGSM) natural history data were collected. AAV2/5-Bbs10FLAG and AAV2/Anc80-Bbs10FLAG viral vectors were created. Subretinal injections of varying titers were performed in 41 BBS10 and 10 WT mice. Immunoblotting and immunohistochemistry were utilized to assess protein production and restoration of Bbs10 gene function.

Results : BBS10 mice initially weigh less than littermates (KO 7.2 gms vs WT 13.2 at P19) but become more obese by 3 months (KO 33.16 gms vs WT 23.68). ERG amplitude is lower than WT by P19 (p=0.006) and VGSM in the dark is worse by 3.5 months (p= <0.0001). Neither AAV2/5-Bbs10FLAG nor AAV2/Anc80-Bbs10FLAG subretinal injections were toxic in WT or BBS10. FLAG was detected in treated, but not untreated BBS10 eyes, documenting presence of BBS10 protein. BBS7, undetectable or barely detectable within photoreceptor cilia in untreated Bbs10^-/- eyes, was present in photoreceptor cilia in treated Bbs10^-/- eyes. VGSM in the dark was partially rescued via either AAV2/5 or AAV2/Anc80 vector treated at P30-P60 and tested at age 3.5 months (p= 1.36E-005). VGSM was better in both light and dark at age 7 months (p=. <0.0001 light; p= 0.0094 dark). 1.00E+09/microliter AAV2/5 and 1.00E+09 or 2.00E+09 AAV2/Anc80 were effective. ERG was not statistically significantly different at 3.5 months between treated and untreated eyes, however by 4.5 months there was a trend toward better ERG in treated eyes which persisted at 5.5 months. At age 3 months, OCT demonstrated thicker INL (p=0.007) and IPL (p=0.02) in both eyes of treated animals compared to untreated, but not thicker ONL (p=0.49); this persisted at 5 months (p= 0.05 INL, p=0.012 IPL and p= 0.14 ONL).

Conclusions : Treatment of BBS10 mice with subretinal gene replacement improves visual function. AAV2/5 and AAV2/Anc80 were both effective vectors. This may be translatable to BBS10 retinal degeneration in humans.

This is a 2020 ARVO Annual Meeting abstract.