Functional studies reveal new mechanisms for deafness caused by connexin mutations.
OBJECTIVE
Connexin26 (Cx26) and Cx30 are the major protein subunits forming gap junction (GJ) intercellular channels in the cochlea. Mutations in these 2 Cxs are the major cause of nonsyndromic early childhood deafness in humans. The underlying mechanism for cochlear abnormality is unclear. Here, we used targeted Cx30 gene deletion (Cx30-/-) mice to investigate molecular mechanisms responsible for Cx mutation-linked deafness. Our hypothesis is that specific loss of GJ-mediated biochemical coupling in the cochlea is sufficient to cause deafness.


METHODS
We compared: (1) expression of major cochlear GJ protein subunits, Cx26 and Cx30; and (2) biochemical coupling among cochlear supporting cells in the cochleae of wild type and Cx30-/- mice.


METHODS
Immunolabeling was used to examine the expression of the remaining Cx protein expression in the cochlea of Cx30-/- mice. We also used a fluorescent dye diffusion assay performed on a novel flattened cochlear preparation to examine GJ-mediated metabolite transfer among cochlear supporting cells.


RESULTS
Estimation of the residual ionic conductance indicated that considerable intercellular ionic coupling remained in the cochlea of Cx30-/- mice. Direct measurement of GJ-mediated biochemical coupling showed that the transfer of metabolites among cochlear supporting cells in Cx30-/- mice was severely reduced.


CONCLUSIONS
Our data support that deficiency in GJ-mediated biochemical coupling is sufficient to cause Cx mutation-linked deafness.
Chang
Qing
Q
Department of Otolaryngology, Emory University School of Medicine, Atlanta, Georgia 30322, USA.
Tang
Wenxue
W
Ahmad
Shoeb
S
Stong
Benjamin
B
Leu
Grace
G
Lin
Xi
X
D000818:Animals; D003051:Cochlea / Q000033:anatomy & histology / Q000502:physiology; D000072259:Connexin 26; D000075302:Connexin 30; D017630:Connexins / Q000235:genetics*; D003638:Deafness / Q000235:genetics* / Q000473:pathology*; D004058:Diffusion; D004848:Epithelium / Q000473:pathology; D005456:Fluorescent Dyes; D017629:Gap Junctions / Q000235:genetics; D005947:Glucose / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009154:Mutation / Q000235:genetics* / Q000502:physiology*
D000075302:Connexin 30; D017630:Connexins; D005456:Fluorescent Dyes; C000607042:GJB2 protein, human; C100629:Gjb6 protein, mouse; D000072259:Connexin 26; D005947:Glucose