Genome editing technology for hearing loss developed by Juntendo University and the University of Tokyo

A research group led by Associate Professor Kazusaku Kamiya and Part-time Assistant Professor Takao Ukaji from the Department of Otorhinolaryngology at Juntendo University Faculty of Medicine, and Professor Osamu Nureki from the Graduate School of Science at the University of Tokyo has announced the development of a genome editing technology that could potentially provide a radical cure for dominant hereditary hearing loss. By combining adeno-associated virus vectors with genome editing technology, they succeeded in delivering larger genes to inner ear cells than was previously possible. In mouse experiments, they confirmed that the abnormal gap junction proteins in the inner ear that cause hearing loss were normalized. Clinical trials are expected to begin in 5-6 years. These results are anticipated to lead to curative treatments. The group's findings were published in the March 10 issue of the international scientific journal JCI Insight.

There are more than 130 genes associated with hereditary hearing loss, but approximately 48% of cases are caused by mutations in the GJB2 gene. This gene codes for a protein that forms "gap junctions" in the inner ear. When normal gap junctions are established, the ion concentration in the inner ear is maintained at a constant level, allowing hearing to function properly. Hearing loss occurs when the homeostasis of the ionic environment is disrupted by mutant proteins.

The research group previously clarified the mechanism of hearing loss in which abnormal gap junctions form due to mutations in this gene. They had also succeeded in restoring hearing by supplementing the GJB2 gene in mouse models of hearing loss. However, in dominant hereditary type mutations, the abnormal proteins caused by the mutations inhibit inner ear function, so the introduction of normal genes alone does not restore function. This treatment required genome editing technology that could rewrite mutations into normal genes, and vectors capable of delivering it. Conventional adeno-associated virus vectors (AAV) could only carry genes of about 4.7 Kbp in size, which was insufficient for the gene sets needed for genome editing. There were also restrictions on which gene locations could be edited.

To address this, the team used proprietary gene delivery and genome editing technologies. Specifically, Juntendo University developed an AAV called "AAV-Sia6e" capable of delivering the gene. The University of Tokyo developed a new genome editing technology called "SaCas9-NNG-ABE," which has a smaller gene size and a wider target range. The developed tools, both of which are reportedly patent-pending, were combined to create an inner ear genome editing vector. Using this vector, genome editing therapy was performed on mouse models and cell models of dominant hereditary GJB2 gene mutation-type hearing loss.

As a result, the group was able to efficiently repair the targeted gene mutations with a single administration. Normal gap junction protein structures were observed in both model mice and model cells, confirming that normal substance transport capability had been restored. In the model cells, hearing loss occurs when the C in the sequence coding for arginine in the GJB2 gene changes to T, and the researchers confirmed that about 50% of this T had been restored to the normal C.

Kamiya commented: "By applying this technology, we can now target larger hearing loss genes and various mutation types that were previously not considered for gene therapy development, which will dramatically advance treatment technologies for hearing loss. We are currently creating iPS cells from various patients who have donated cells for treatment purposes. We would like to evaluate the therapeutic effects using these cells."

Journal Information
Publication: JCI Insight
Title: AAV-mediated base editing restores cochlear gap junction in GJB2 dominant-negative mutation-associated syndromic hearing loss model
DOI: 10.1172/jci.insight.185193