The Role of Connexin and Pannexin Large-Pore Channels in Hearing
Abstract
Connexin and pannexin large-pore channels allow the regulated passage of small molecules at sites of cell-cell contacts, and from the cytosol to the extracellular milieu, respectively. Since it has been known for many years that Cx26 and Cx30 gap junction proteins are crucial in hearing we propose that Cx43 might also be important in hearing. Here we used two different genetically modified mouse lines that contain systemic Cx43 gene mutations that reduces gap junctional intercellular communication (GJIC) to examine whether Cx43 is also important for proper hearing function. Furthermore, since pannexins have also been postulated to be involved in auditory function we used three different Panx global knock-out mice to evaluate their hearing profiles. We showed that Cx43 mutant mice that had severe loss of Cx43 channel function had hearing loss, while mutant mice with a modest loss of Cx43 function exhibited normal hearing. Surprisingly, Panx1-/-, Panx3-/-, and double knock-out (dKO) mice did not have hearing loss, suggesting that pannexins do not play an important role in hearing. To evaluate whether large-pore channels played a role in noise-induced hearing loss (NIHL), we challenged Cx43 mutant and pannexin knock-out mice with a loud noise-exposure and examined their permanent hearing loss. Interestingly, only Panx3-/- and Panx dKO mice were slightly protected against permanent hearing damage. Finally, organotypic cochlear cultures from Cx43 mutant mice and a CRISPR Cas9 Cx43 ablated cochlear-derived cell line, revealed that GJIC does not exacerbate drug-induced hearing loss but does cause supporting cell reorganization. Collectively, our results highlight the importance of Cx43 GJIC in hearing function, but not noise- or drug-induced ototoxicity. Furthermore, our studies support the notion that Panxs are not involved in baseline hearing, but loss of Panx3 may lead to slight protection against permanent NIHL.