Xiaowen Huang

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.

Downregulation of Cav1.3 calcium channel expression in the cochlea is associated with age-related hearing loss in C57BL/6J mice.

Age-related hearing loss (ARHL) is the most common human morbidity. However, the molecular mechanisms underlying ARHL are little known. In the present study, the expression of Cav1.3 calcium channels in the C57BL/6J ARHL mouse cochlea was investigated. The hearing threshold was assessed by auditory brainstem response and the expressions of Cav1.3 calcium channels at the protein and mRNA levels were detected by immunohistochemistry, western blot, and real-time RT-PCR. Associated with the auditory brainstem response threshold increased with age, the Cav1.3 expression was gradually decreased. In comparison with 4-week-old mice, Cav1.3 expressions in the cochlea at 14, 24, and 48 weeks of age were significantly and gradually decreased at both the protein and the mRNA levels. Immunohistochemistry showed that the expression of Cav1.3 was apparently reduced at the inner hair cells, outer hair cells, and stria vascularis in the cochlear lateral wall in the aged mice. Our findings indicate that Cav1.3 calcium channel expression in the cochlea is reduced in the ARHL mice and is associated with ARHL. The data also support a view that Cav1.3 calcium channel is a good target for prevention and therapy of ARHL.

Correlation of PDCD5 and apoptosis in hair cells and spiral ganglion neurons of different age of C57BL/6J mice

This study examined the expression pattern of programmed cell death 5 (PDCD5) in cochlear hair cells and spiral ganglion neurons (SGNs) and its association with age-related hearing loss in mice. Sixty C57BL/6J (C57) mice at different ages were divided into four groups (3, 6, 9 or 12 months). PDCD5 expression was detected by using immunohistochemistry, real-time PCR and Western blot. Morphological change of the cochleae was also evaluated by using immunoassay. The results showed that the expression of PDCD5 had a gradual increase with ageing in both protein and RNA levels in C57 mice, as well as gradually increased apoptosis of cochlear hair cells and SGNs. In addition, we also found that caspase-3 activity was enhanced and its expression was enhanced with ageing. It is implied that overexpression of PDCD5 causes the increase in caspase-3 activity and the subsequent increase of apoptosis in cochlear hair cells and SGNs, and thereby plays a role in the pathogenesis of presbycusis. Thus, PDCD5 may be a new target site for the treatment and prevention of age-related hearing loss.SummaryThis study examined the expression pattern of programmed cell death 5 (PDCD5) in cochlear hair cells and spiral ganglion neurons (SGNs) and its association with age-related hearing loss in mice. Sixty C57BL/6J (C57) mice at different ages were divided into four groups (3, 6, 9 or 12 months). PDCD5 expression was detected by using immunohistochemistry, real-time PCR and Western blot. Morphological change of the cochleae was also evaluated by using immunoassay. The results showed that the expression of PDCD5 had a gradual increase with ageing in both protein and RNA levels in C57 mice, as well as gradually increased apoptosis of cochlear hair cells and SGNs. In addition, we also found that caspase-3 activity was enhanced and its expression was enhanced with ageing. It is implied that overexpression of PDCD5 causes the increase in caspase-3 activity and the subsequent increase of apoptosis in cochlear hair cells and SGNs, and thereby plays a role in the pathogenesis of presbycusis. Thus, PDCD5 may be a new target site for the treatment and prevention of age-related 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.

Expression patterns of CaV1.3 channels in the rat cochlea

Although Ca(V)1.3 channels are known to be essential for neuronal excitation and signal transduction in the auditory system, their expression patterns in the cochlea are still not fully understood, particularly in the regions where non-sensory cells are located. We performed immunohistochemistry, western blotting and reverse transcription-polymerase chain reaction (RT-PCR) to identify the expression and distribution of Ca(V)1.3 channels in the rat cochlea. Immunohistochemistry revealed that Ca(V)1.3 channels were localized in the outer hair cells (OHCs), inner hair cells (IHCs), limbus laminae spiralis, spiral ganglion cell, spiral ligament (SL), and stria vascularis (STV). The results of RT-PCR and western blotting demonstrated Ca(V)1.3 channels had a tissue-specific expression pattern. Ca(V)1.3 mRNA and protein were intensively expressed in the basilar membrane and spiral ganglion while moderate level of Ca(V)1.3 channels was observed in SL and STV. Our study preliminarily revealed the expression patterns of Ca(V)1.3 channels in the rat cochlea, providing a theoretical basis for further research on the role of Ca(V)1.3 channels in the periphery auditory system.