Connexin30 deficiency causes instrastrial fluid-blood barrier disruption within the cochlear stria vascularis.
The endocochlear potential (EP) is essential to hearing, because it provides approximately half of the driving force for the mechanoelectrical transduction current in auditory hair cells. The EP is produced by the stria vascularis (SV), a vascularized bilayer epithelium of the cochlea lateral wall. The absence of the gap junction protein connexin30 (Cx30) in Cx30(-/-) mice results in the SV failure to produce an EP, which mainly accounts for the severe congenital hearing impairment of these mice. Here, we show that the SV components of the EP electrogenic machinery and the epithelial barriers limiting the intrastrial fluid space, which are both necessary for the EP production, were preserved in Cx30(-/-) mice. In contrast, the endothelial barrier of the capillaries supplying the SV was disrupted before EP onset. This disruption is expected to result in an intrastrial electric shunt that is sufficient to account for the absence of the EP production. Immunofluorescence analysis of wild-type mice detected Cx30 in the basal and intermediate cells of the SV but not in the endothelial cells of the SV capillaries. Moreover, dye-coupling experiments showed that endothelial cells were not coupled to the SV basal, intermediate, and marginal cells. SV transcriptome analysis revealed a significant down-regulation of betaine homocysteine S-methyltransferase (Bhmt) in the Cx30(-/-) mice, which was restricted to the SV and resulted in a local increase in homocysteine, a known factor of endothelial dysfunction. Disruption of the SV endothelial barrier is a previously undescribed pathogenic process underlying hearing impairment.
Cohen-Salmon
Martine
M
Unité de Génétique des Déficits Sensoriels, Unité Mixte de Recherche S 587, Institut National de la Santé et de la Recherche Médicale, 75724 Paris Cedex 15, France. martin.cohen-salmon@college-de-france.fr
Regnault
Béatrice
B
Cayet
Nadège
N
Caille
Dorothée
D
Demuth
Karine
K
Hardelin
Jean-Pierre
JP
Janel
Nathalie
N
Meda
Paolo
P
Petit
Christine
C
D000818:Animals; D050940:Betaine-Homocysteine S-Methyltransferase / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D003055:Cochlear Microphonic Potentials / Q000235:genetics; D000075302:Connexin 30; D017630:Connexins / Q000172:deficiency* / Q000235:genetics; D003545:Cysteine / Q000097:blood; D017931:DNA Primers; D004730:Endothelium, Vascular / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D005614:Freeze Fracturing; D020869:Gene Expression Profiling; D034381:Hearing Loss / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D046228:Microarray Analysis; D046529:Microscopy, Electron, Transmission; D013316:Stria Vascularis / Q000378:metabolism* / Q000648:ultrastructure
D000075302:Connexin 30; D017630:Connexins; D017931:DNA Primers; C100629:Gjb6 protein, mouse; D050940:Betaine-Homocysteine S-Methyltransferase; C494549:Bhmt protein, mouse; D003545:Cysteine