Pathophysiology of Connexin 26-associated hearing loss

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Investigator: Dylan K. Chan, MD, PhD
Sponsor: NIH National Institute of Deafness and Communication Disorders

Location(s): United States

Description

Hearing loss is the most common sensory impairment in children. In this project, we aim to learn how mutations in Connexin 26, which account for about 20% of all childhood hearing loss, cause the ear to malfunction, and how this might be related to noise- induced hearing loss. We hope this will help us identify new targets for treating hearing loss in all children.

Hearing loss is the most common congenital sensory impairment. Mutations in Connexin 26 (Cx26) comprise the most common genetic causes of hearing loss. Cx26 forms gap junctions in supporting cells of the cochlea, but the pathophysiology of Cx26- associated hearing impairment is unclear. Mouse studies have suggested major roles in cochlear development and mature function:
1) in the neonatal period, gap-junction- mediated intercellular Ca2+ signaling (ICS) waves are necessary for functional maturation, and Cx26 knockout results in major structural abnormalities;
2) in hearing- mature animals, gap junctions may be involved in K+ recycling, cochlear amplification, and an ICS and MAPK-dependent response to acoustic trauma that recapitulates their developmental role.
The hearing-loss phenotype of Cx26 dysfunction in humans is highly variable and mutation-dependent, suggesting that differential effects on the developmental and functional roles of Cx26 may be meaningful. In order to develop targeted therapy for different kinds of Cx26-associated hearing loss, a thorough understanding of its pathophysiologic mechanisms is required. In this study, we address a major limitation in the literature surrounding the pathophysiology of Cx26-associated hearing loss. The vast majority of studies have been conducted in neonatal mice with early, complete cochlea-specific knockout of Cx26 and subsequent cochlear developmental abnormalities. We aim to
1) evaluate the role of ICS and gap junctions in an ex vivo model of the hearing gerbil cochlea; and
2) investigate the consequences of functional derangements in Cx26 (through an inducible conditional knockout, gene dosage model, and specific functional point mutations) in the otherwise normally developed mouse cochlea.
Phenotype will be assessed both at the organ level, by assessing gap-junction function, ICS behavior, and expression profiles of gap-junction constituents, downstream MAPK effectors, and synaptic labeling, and at the whole-animal physiologic level, by evaluating auditory brainstem responses and noise- induced hearing loss. By determining how Cx26 dysfunction affects cochlear and auditory function, we will be able to develop targeted therapies for a wide range of individuals with Cx26-associated hearing loss.