Jagger, DJ; Nickel, R; Forge, A; (2014) Gap Junctional Coupling is Essential for Epithelial Repair in the Avian Cochlea. The Journal of Neuroscience , 34 (48) pp. 15851-15860. 10.1523/JNEUROSCI.1932-14.2014.

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Abstract

The loss of auditory hair cells triggers repair responses within the population of non-sensory supporting cells. When hair cells are irreversibly lost from the mammalian cochlea, supporting cells expand to fill the resulting lesions in the sensory epithelium, an initial repair process which is dependent on gap junctional intercellular communication (GJIC). In the chicken cochlea (the “basilar papilla”, BP) dying hair cells are extruded from the epithelium and supporting cells expand to fill the lesions, and supporting cells then replace hair cells via mitotic and/or conversion mechanisms. Here we investigated the involvement of GJIC in the initial epithelial repair process in the aminoglycoside-damaged BP. Gentamicin-induced hair cell loss was associated with a decrease of chicken connexin43 (cCx43) immunofluorescence, yet cCx30-labeled gap junction plaques remained. FRAP experiments confirmed GJIC remained robust in gentamicin-damaged explants, though regionally asymmetric coupling was no longer evident. Dye injections in slice preparations from undamaged BP explants identified cell types with characteristic morphologies along the neural-abneural axis, but these were electrophysiologically indistinct. In gentamicin damaged BP, supporting cells expanded to fill space formerly occupied by hair cells and displayed more variable electrophysiological phenotypes. When GJIC was inhibited during the aminoglycoside damage paradigm the epithelial repair response halted. Dying hair cells were retained within the sensory epithelium, and supporting cells remained unexpanded. These observations suggest repair of the auditory epithelium shares common mechanisms across vertebrate species, and emphasize the importance of functional gap junctions in maintaining a homeostatic environment permissive for subsequent hair cell regeneration.

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