Dysregulation of Serpinb6a-Gch1 axis contributes to DFNB91 deafness that is amendable to gene therapies

Hereditary deafness accounts for 60% of congenital hearing loss, and more than 300 deafness genes have been identified. SERPINB6, a gene associated with recessive deafness, also named DFNB91, is linked to non-syndromic progressive hearing loss based on studies of humans and its mouse ortholog Serpinb6a knockout mice. However, the mechanism and biological therapy for SERPINB6 mutation-induced deafness remain unknown. Here, we demonstrate that Gch1 is aberrantly overexpressed in Serpinb6a-deficient hair cells. Upregulation of Gch1 in wild-type mice cochlea via adeno-associated virus (AAV) resulted in hearing loss and hair cell death, while downregulation of GCH1 by its inhibitor DAHP effectively protected hair cells and auditory function in Serpinb6a knockout mice. Dysregulation of the Serpinb6a/Gch1 axis resulted in elevated expression of BH4 and then iNOS, leading to increased ROS production and eventually causing hair cell damage. These findings revealed that Gch1 overexpression is the mechanism underlying deafness induced by Serpinb6a mutation. Critically, Myo15 promoter-driven AAV delivery of exogenous Serpinb6a effectively rescues auditory function and hair cell survival in Serpinb6a-deficient mice. These findings suggested that AAV-based gene therapy offers a potential treatment for Serpinb6a knockout mice, which may serve as a promising strategy for treating DFNB91 patients in clinical settings.