Research ArticleGENE EDITING

In vivo base editing restores sensory transduction and transiently improves auditory function in a mouse model of recessive deafness

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Science Translational Medicine  03 Jun 2020:
Vol. 12, Issue 546, eaay9101
DOI: 10.1126/scitranslmed.aay9101

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At the base of deafness

Mutations in the transmembrane channel-like 1 (TMC1) gene can cause hereditary hearing loss. Current treatments do not target the cause of the disease, focusing mainly on sound amplification. Here, Yeh et al. used base editing methods to treat a mouse model of genetic deafness caused by a point mutation in Tmc1. The authors included a cytosine base editor into a dual–adeno-associated virus (AAV) system and injected it into the inner ear of the animals with hearing loss. The treatment reversed the mutation, improved sensory transduction, and partially restored hearing in mice. These results suggest that base editing might be effective for rescuing recessive genetic hearing loss.

Abstract

Most genetic diseases arise from recessive point mutations that require correction, rather than disruption, of the pathogenic allele to benefit patients. Base editing has the potential to directly repair point mutations and provide therapeutic restoration of gene function. Mutations of transmembrane channel-like 1 gene (TMC1) can cause dominant or recessive deafness. We developed a base editing strategy to treat Baringo mice, which carry a recessive, loss-of-function point mutation (c.A545G; resulting in the substitution p.Y182C) in Tmc1 that causes deafness. Tmc1 encodes a protein that forms mechanosensitive ion channels in sensory hair cells of the inner ear and is required for normal auditory function. We found that sensory hair cells of Baringo mice have a complete loss of auditory sensory transduction. To repair the mutation, we tested several optimized cytosine base editors (CBEmax variants) and guide RNAs in Baringo mouse embryonic fibroblasts. We packaged the most promising CBE, derived from an activation-induced cytidine deaminase (AID), into dual adeno-associated viruses (AAVs) using a split-intein delivery system. The dual AID-CBEmax AAVs were injected into the inner ears of Baringo mice at postnatal day 1. Injected mice showed up to 51% reversion of the Tmc1 c.A545G point mutation to wild-type sequence (c.A545A) in Tmc1 transcripts. Repair of Tmc1 in vivo restored inner hair cell sensory transduction and hair cell morphology and transiently rescued low-frequency hearing 4 weeks after injection. These findings provide a foundation for a potential one-time treatment for recessive hearing loss and support further development of base editing to correct pathogenic point mutations.

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