Gene therapy to restore hearing in a novel mouse model of DFNB1 human connexin

Hearing and balance impairments are the most widespread human sensory deficits, and a major concern for Public Health, affecting approximately 70 million Europeans and 430 million people worldwide. www.who.int/pbd/deafness/en/. Deafness has a huge estimated socio-economical impact (213 billion euros per year in Europe, “McDaid et al., 2021). Such costs can be explained by the fact that hearing impairment prevents children from acquiring speech and language, causing delays and learning difficulties at school. Approximately, one in 500 child and 4% of people under 45 years are affected. As we age, hearing loss progressively increases in prevalence, so that over 50% of individuals above 80 years of age are affected. It is estimated In France, over one child out of 700 suffers from profound congenital deafness at birth, and an additional 1/1000 will be affected by hearing impairment prior to adulthood. In developed countries, about 80% of congenital hearing loss have a genetic etiology of which 30% is associated with balance defect. Mutations in more than 150 genes have been associated with inner ear defects, and it is estimated that genetic forms of deafness can arise from mutations in as many as 500 genes (Yan et al., 2013), highlighting the potential of gene therapy for the treatment of inherited inner ear defects. The function of the inner ear involves the sensory hair cells, supporting cells, and the primary auditory neurons. Gene defects in any of these cell types can result in inner ear defects. The associated impairments of hearing and balance can currently be treated only with hearing aids, cochlear implants, and balance rehabilitation therapy, but the outcomes of these therapies are variable. Some individuals with congenital deafness are able to have telephone conversations after being fitted with hearing aids or cochlear implants, whereas others obtain little or no benefit from these devices, and merely become aware of environmental sounds (Jeon et al., 2015; Vivero et al., 2010). Gene therapy based on AAV technology is rapidly emerging as a promising curative treatment for deafness. This approach involves delivering a healthy copy of the defective gene via a viral vector. Our team largely contributed to the actual progress in gene therapy for deafness by demonstrating that AAV therapy restored hearing in profoundly deaf DFNB9 mouse model. This finding has paved the way to successful phase 2 clinical trials in many countries including France.

The DFNB1 human deafness accounts for approximately 50% of profound hereditary deafness due to mutations in the gene (GJB2) coding for the Gap JunctionBeta-2 protein, connexin-26. Connexin-26 (Cx26) is a member of a large family of proteins involved in the formation of gap junctions that are essential for the local circulation of potassium ions between the fluids of the inner ear. Although the high incidence of human genetic deafness brings high motivation for a therapy to cure DFNB1 deafness, there is still no treatment available to date. Gene therapy approaches for replacing the defective GJB2 gene have mainly been administered at neonatal stages, which is not a relevant therapeutic window for clinical application in humans due to the delayed maturation of the mouse cochlea.

This Ph.D. project aims to establish a suitable therapeutic window for gene therapy targeting human DFNB1 deafness using the newly generated Gjb2-deficient mouse model, in which Cx26 deletion is restricted to the cochlear sensory epithelium while preserving structural integrity. In this model, hair cells, as well as the maturation and refinement of central auditory circuits, remain intact. This unique model provides an opportunity to explore the outcomes of virally mediated Cx26 gene therapy administered after hearing onset enabling us to pinpoint the optimal therapeutic window for potential clinical translation.

This Ph.D. project will focus on two interrelated objectives:

- Identification of an optimal AAV variant and promoter – Selecting the most efficient and specific AAV serotype and promoter to target connexin-expressing cells.

- In vivo gene therapy and functional assessment – Administering Cx26 gene therapy to the Gjb2-deficient mouse model at different stages after hearing onset and evaluating the outcomes. This includes analyzing the expression and cellular distribution of therapeutic Cx26 within the auditory sensory epithelium of the injected cochlea, as well as assessing hearing restoration through ABR and DPOAE recordings.

The team is part of the Institut de l’Audition (Institut Pasteur, Paris), and is also affiliated with the Departments of Neuroscience. Our team possesses the necessary skills and expertise to create mouse models mimicking various human inner ear disorders. This includes conditions such as auditory and vestibular synaptopathies, presbycusis, and agent-induced hearing loss. The team member are from diverse backgrounds, including undergraduates, graduate students, engineers, postdoctoral researchers, residents, and ENT specialists. Together, we collaborate on translational projects with the goal of bridging the gap between research and practical applications.

We are seeking a highly motivated PhD student to join our dynamic and collaborative research team, working in a stimulating and intellectually rigorous scientific environment.
The ideal candidate will have a strong background in neuroscience, cell or molecular biology, or a related field, and should be experienced or comfortable working with animal models.
Key qualities include  strong scientific curiosity, the ability to work independently as well as collaboratively, and strong oral and written communication skills in English.