Cui Yh

Simultaneously reduced NKCC1 and Na,K-ATPase expression in murine cochlear lateral wall contribute to conservation of endocochlear potential following a sensorineural hearing loss

The mechanisms of the response in the murine cochlear lateral wall following sensorineural hearing loss (SNHL) are poorly understood. We focused on comparing the endocochlear potential (EP) with morphological changes in the lateral wall and expression of four important potassium (K(+)) transporters in a mouse model of SNHL induced by co-administration of aminoglycoside and loop diuretic. The expression of the α1 and α2 isoforms of Na,K-ATPase, Na-K-2Cl-Cotransporter-1 (NKCC1) and potassium channel KCNQ1 was assessed. The EP showed a significant decline at 12h post-treatment followed by complete recovery by 2 days post-treatment. The EP was maintained at near normal levels in animals deafened for periods up to 112 days. Despite this recovery, there was a significant and progressive decrease in the thickness of the stria vascularis, which was predominantly due to atrophy of marginal cells. Both protein and mRNA expression of α1 and α2 isoforms of Na,K-ATPase and NKCC1 in the lateral wall were dramatically reduced following a long-term deafening. KCNQ1 expression remained unchanged. These observations provide insight into the detailed mechanisms of EP modulation following SNHL and may have crucial implications in the future treatment of aminoglycoside-induced hearing loss.

Conservation of endocochlear potential in mice with profound hearing loss induced by co-administration of kanamycin and furosemide

Research in mammalian hair cell regeneration is hampered by a lack of in vivo model of adult mouse inner ear injury. In the present study we investigated the effects of a combination of a single dose of aminoglycoside followed by a loop diuretic in adult mice. The auditory brainstem response threshold shift, extent and defining characteristics of the cochlear lesion were assessed and verified at different time points post-treatment. Our data indicated that this drug combination caused the rapid and extensive death of outer hair cells (OHCs). OHC death presented throughout the cochlea that commenced in the basal turn by 24 h and progressed apically. In contrast, inner hair cell (IHC) loss was delayed and mild. Terminal deoxynucleotidyl transferase dUTP nick end labelling-positive nuclei demonstrated that the majority of OHCs died via an apoptotic pathway. Auditory threshold shifts of up to 90 dB SPL indicated a profound hearing loss. In addition, the endocochlear potential (EP) in the drug-treated animals displayed a significant decline at 12 h post-treatment followed by recovery by 48 h post-treatment. Despite this recovery, there was a significant and progressive decrease in strial vascularis thickness, which was predominantly due to atrophy of marginal cells. The present study reproduced an adult mouse model of aminoglycoside-induced hearing loss. The mechanism underlying the recovered EP in the model with extensive hair cell death is discussed.

The expression of plasma membrane Ca2+-ATPase isoform 2 and its splice variants at sites A and C in the neonatal rat cochlea

OBJECTIVE To study the expression of plasma membrane Ca(2+)-ATPase isoform 2 (PMCA2) and its alternative splicing at sites A (the first intracellular loop) and C (the C-terminal region) in the neonatal rat cochlea. METHODS The cochleae from rats postnatal day 3 to postnatal day 4 (P3-P4) were dissected, fixed, embedded, and sectioned. Meanwhile, the cochlear coils from neonatal rats were isolated and fixed. Using immunofluorescence staining, the expression of PMCA2 was respectively examined in the cochlear sections and cochlear coils. In addition, the total RNAs of basilar membrane (BM, including the organ of corti, the same below), spiral ganglion (SG), spiral ligament (SL, including SV, the same below), and the whole cochlea from neonatal rats were respectively extracted and reverse transcribed to cDNAs, then subjected to primers flanking site A or C in the PMCA2 gene using reverse transcription polymerase chain reaction (RT-PCR). Western blot was also applied to detect the expression of PMCA2 isoforms in the cochlear tissues. RESULTS We found that PMCA2 is strongly expressed in outer hair cell (OHC) bundles, SG, and stria vascularis (SV), weakly expressed in Reissners membrane (RM), and occasionally expressed in inner hair cell (IHC) bundles. Moreover, w/a is the major splice form of PMCA2 present in hair cell bundles, z/b and z/c are the major splice forms of PMCA2 present in SG, and w/a and w/c are the major splice forms of PMCA2 present in SV. In the whole cochlea, variants w, y, and z were detected at site A, and variants a, b, and c were detected at site C. Using Western blot, variant a or b was also detectable in the same cochlear tissues mentioned above. CONCLUSIONS PMCA2 and its splice variants at sites A and C are differentially expressed in cochlear tissues of neonatal rat.