Gap junction-mediated intercellular biochemical coupling in cochlear supporting cells is required for normal cochlear functions

Abstract

Dysfunction of gap junctions (GJs) caused by mutations in connexin26 (Cx26) and Cx30 accounts for nearly half of all cases of hereditary nonsyndromic deafness cases. Although it is widely held that GJs connecting supporting cells in the organ of Corti mainly provide ionic pathways for rapid removal of K ؉ around the base of hair cells, the function of GJs in the cochlea remains unknown. Here we show that GJs were not assembled in the supporting cells of the organ of Corti until 3 days after birth in mice and then gradually matured to connect supporting cells before the onset of hearing. In organotypic cochlear cultures that were confirmed to express GJs, GJs mediated the propagation of intracellular Ca 2؉ concentration waves in supporting cells by allowing intercellular diffusion of inositol 1,4,5-trisphosphate. We found that a subset of structurally mild Cx26 mutations located at the second transmembrane region (V84L, V95M, and A88S) and a Cx30 mutation located at the first cytoplasmic segment (T5M) specifically affect the intercellular exchange of larger molecules but leave the ionic permeability intact. Our results indicated that Cx26 and Cx30 mutations that are linked to sensorineural deafness retained ionic coupling but were deficient in biochemical permeability. Therefore, GJ-mediated intercellular exchange of biochemically important molecules is required for normal cochlear functions.connexin ͉ deafness ͉ mutation

Noise-Induced Loss of Hair Cells and Cochlear Synaptopathy Are Mediated by the Activation of AMPK

“…***p Ͻ 0.001, **p Ͻ 0.01, *p Ͻ 0.05. against metabolic stress, as supporting cells are resistant to inner ear insults, while sensory hair cells are vulnerable (Tiede et al, 2009;Jensen-Smith et al, 2012;May et al, 2013). It is possible that the maintenance of homeostasis and the correction of ion imbalances in supporting cells is more effective and efficient due to the presence of gap junctions between supporting cells that allow for the diffusion and flux of ions and second messengers providing enhanced resilience compared with sensory hair cells (Denoyelle et al, 1998;Xia et al, 1998;Zhang et al, 2005;Anselmi et al, 2008;Lahne and Gale, 2010). Moreover, the antioxidant abilities of supporting cells may be stronger than those of sensory hair cells, as supporting cells secrete HSP70 (May et al, 2013), which increases the aptitude of supporting cells to recover from a metabolic disruption and prevents proapoptotic signaling pathways.…”

A Mouse Model for Degeneration of the Spiral Ligament

“…Degeneration of SL fibrocytes by 3-NP results in the destruction of connective tissue gap junction networks of the fibrocytes in the lateral wall. Gap junctions are responsible not only for anionic molecule permeability but also for metabolic communications (Zhang et al 2005;Zhao 2005). Therefore, destruction of gap junctions may cause metabolic disorders in OHCs leading to OHC death.…”

Connexin channel permeability to cytoplasmic molecules

“…Also in Cx26, in another study, V84L, V95M and A88S (all in M2), and a T5M mutation of Cx30 (in the N-terminal domain), affected the ability to support intercellular Ca signaling without effects on junctional conductance (Zhang et al, 2005). For these mutants, the junctional permeability to propidium iodide was affected, however, but single channel measurements were not made.…”

“…43j > 32j(0.12) (Goldberg et al, 2002) 1b 6 43j ≫ 32j(0.03) (Goldberg et al, 1999) (Goldberg et al, 2002) 1b 6 43j ≫ 32j(0.03) (Goldberg et al, 1999) 1a 6 IP3 26h (Locke et al, 2004;Ayad et al, 2006) 3f 26j 2 26j (Paemeleire et al, 2000) 1b 2 26j (Beltramello et al, 2005) 1a 1b 2 26j (Hernandez et al, 2007) 1a 1b 26j or 26/30j (Zhang et al, 2005) 1a 1b 2 (Ca injection used to rule out Ca flux) 26/32h (Locke et al, 2004) 3f (not permeable through all heteromeric channels) 26/32h (Ayad et al, 2006) 3f (not permeable through all the heteromeric channels; differential permeability among inositol triphosphate isoforms) 26/32j or 32j 2 26/32j or 32j (Clair et al, 2001) 1a 2 (Ca flux ruled out as causing Ca signaling) 32h (Locke et al, 2004;Ayad et al, 2006) 3f 32j (Brehm et al, 1989) 2 5 32j (Paemeleire et al, 2000) 1b 2…”

“…IP3 (Zhang et al, 2005) 1a 1b 2 (Ca injection used to rule out Ca flux) 26/32j siRNA 22mer (Valiunas et al, 2005) 1a φ RNA 12mer (Valiunas et al, 2005) 1a 26/32j or 32j IP3 2 IP3 (Clair et al, 2001) 1a 2 (Ca flux ruled out as causing Ca signaling) 32h ATP (Cotrina et al, 1998) 3a 3b 3c (connexin block had only partial effect)…”