Effects of Bax on Cochleae in D-galactose-Induced Aging Rats

DU Zhengde; GAO Chunsheng; YANG Qiong; GAO Jinliang; HU Jing; LIU Lin

doi:10.3969/j.issn.1672-2922.2014.03.036

Abstract：Objective To investigate the effects of Bax on the cochlea in D-galactose-induced aging rats and the mech-anism of cell apoptosis in the peripheral auditory system in presbycusis. Methods Thirty-six 1-month male Sprague-Dawley rats were randomly divided into two groups (18 in each):①rats in D-galactose group received aily subcutaneous injection of D-gal at 500 mg/kg for 8 weeks, and②rats in the control group received the same volume of the vehicle (0.9%saline) once a day for 8 weeks. After the experiment termination, cochlear tissues were harvested. The accumulation of mitochondrial DNA (mtDNA) common deletion (CD) was detected by real-time PCR. Protein levels of Bax and Cleaved caspase-3 were evaluated by western blot and immunohistochemical analysis. Apoptotic cells were determined by terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP) nick-end-labelling (TUNEL) assay. All experimental data was analyzed using two-sample t-test. Results In comparison with the control group, the accumulation of mtDNA CD in the cochlea in rats of the D-galactose group was significantly increased (t=6.631, P<0.01). Protein expressions of Bax and Cleaved caspase-3 in the cochlea were also significantly increased (t=20.914 and 20.043, respectively, P<0.01). TUNEL-positive cells were found only in the cochlea of D-gal-induced aging rats, with a small number of these cells limited to the stria vascularis of the basal turn. Conclusions Bax-dependent cell apoptosis may contribute to D-galactose-induced aging process in the cochlea and may be an important reason for the occurrence of cell apoptosis in the peripheral auditory system in presbycusis.