Mechanism Of Apoptosis-inducing Factor Mutation On Auditory Function In C57BL/6J Mice

Objective: In this study,we intend to compare the auditory function and inner ear structure damage of Aifm1 gene-specific mutant positive-type C57BL/6J mice and wild-type C57BL/6J mice after cisplatin treatment,and further to explore the pathological mechanism of auditory function after AIFM1 gene-specific mutant.Methods: Thirty-two Aifm1 gene-specific mutant positive-type C57BL/6J male mice and Thirty-six wild-type C57BL/6J male mice at 2 months of age with normal hearing(Click-evoked auditory brainstem response at25~35 dBSPL)were selected.Thirty-two Aifm1 gene-specific mutant male mice as positive-type cisplatin group,thirty-six wild-type male mice were randomly divided into wild-type cisplatin group(n = 26)and wild-type normal saline group(n = 10).The positive-type cisplatin group and the wild-type cisplatin group were given intraperitoneal injections of cisplatin 10mg/Kg for 3 consecutive days according to the body weight.The same volume of normal saline was injected intraperitoneally into the wild-type saline group by the body weight for 3 consecutive days,And before administration,on the first day after administration,on the second day after administration,on the third day after administration and on the fifth day after administration,we detected and recorded the threshold and latency(90 dBSPL)of Click-ABR and tone burst auditory brainstem response(tb-ABR),including tb-2 KHz,tb-4 KHz,tb-8 KHz,tb-16 KHz and tb-32 KHz).And the cochlea were collected immediately after the last hearing test.The cochlear were fixed and decalcified,then paraffin-embedded and HE staining to observe the injury of spiral gangliont.And the basilar membrane was dissected to observe the hairs cells and the ribbon synapse of inner hair cells by immunofluorescence staining.Results:(1)The change of ABR threshold: the threshold of Click-ABR and tb-ABR of positive-type cisplatin group and wild-type cisplatin group were significantly higher than wild-type normal saline group at different time points after administration,and the threshold shift of Click-ABR and tb-ABR in positive-type cisplatin group was also more obvious than that of wild-type cisplatin group at different time points,the difference between the groups were statistically,and with the increase in the number of cisplatin administration and time,the difference between the groups were more obvious.(2)The changes of latency of Click-ABR wave: the latency of Click-ABR wave of positive-type cisplatin group and wild-type cisplatin group were significantly longer than that of wild-type saline group at different time points after administration,and the prolongation of each wave latency after the cisplatin treatment,the latency of Click-ABR wave in the positive-type cisplatin group was basically longer than that in the wild-type cisplatin group,and between the groups the differences of wave latency was mainly III wave and V wave.(3)The changes of interval of Click-ABR wave,the interval of Click-ABR wave(I-III,III-V and I-V wave interval)of positive-type cisplatin group and wild-type cisplatin group were significantly longer than that of wild-type saline group at different time points after administration,the difference between the groups were statistically different to varying degrees,and the interval of Click-ABR wave in the positive-type cisplatin group was basically longer than that in the wild-type cisplatin group,the difference between groups was mainly the interval of III-V wave prolongation have different degrees of statistical significance.(4)The results of morphological: on the fifth day after administration,the deletion of cochlear outer hair cells,the decrease of CtBp2 protein of the ribbon synapse of inner hair cells and the loss of spiral ganglion cells in cochlear of wild-type cisplatin group and positive-type cisplatin group were significantly higher than those in wild-type saline group,and the change of basal cochlear gyrus was more obvious than that of the top and mid cochlear gyrus.The cochlear morphological changes in the positive-type cisplatin group were more obvious than those in the wild-type cisplatin group,and the missing number of different gyrus of outer hair cells between two groups have different degrees of statistical significance.Conclusion: Cisplatin has obvious ototoxicity,causing mainly irreversible damage to the outer hair cells,the ribbon synapse of inner hair cells and the spiral ganglion cells,leading to ABR severe threshold shift,the latency of Click-ABR wave and the interval of Click-ABR wave abviously prolong,and the ototoxicity of cisplatin has obvious dose-accumulation and post-effects.Click-ABR wave latency and Click-ABR wave interval changes are more sensitive to damage than ABR threshold shift,which can early response to hearing impairment;under the action of cisplatin,the inner ear structure and hearing impairment of Aifm1 gene-specific mutant positive mice were more severe than wild-type mice;AIFM1 gene-specific mutations lead to AIF protein redox function weakening or missing,which may be one of the pathogenesis of hereditary auditory neuropathy patients.