The Role Of Endoplasmic Reticulum Stress In Mouse Models Of Age-related And Noise-induced Hearing Loss

Part I The role of endoplasmic reticulum stress in a murine age-related hearing loss modelObjective:To study the relationship between the degeneration of cochlea cells andendoplasmic reticulum stress in a mouse model of age-related hearing loss.Methods:The animals(C57BL/6 mice)were divided into two groups:the young group(1?2 months old)and the aged group(12?14 months old).The levels of unfolded protein response-related protein and apoptosis-related factors in the cochlea were detected by western blot.The expression level and position of the protein in the cochlea was detected by immunohistochemistry.In addition,the apoptosis of the cochlea was detected by TUNEL and the morphological changes of the cochlea were observed by HE staining.Results:1.ABR(n = 8?10)The results showed that the hearing threshold of the aged group was significantly higher than that of the young group at low frequency to high frequency.2.The results of western blot and immunofluorescence showed that the expression of GRP78,CHOP,caspase-12 and ubiquitinated proteins in the cochlea ofthe aged group were significantly higher than those in the young group.Among them,the expression of GRP78,the key factor of unfolded protein reaction,was weaker than that of the young group in the organ of Corti and spiral ganglion neuron cells of the aged group.The expression of ubiquitinated protein was significantly increased in the aged group and mainly in the outer hair cells and spiral ganglion neuron,whereas a few ubiquitin-positive cells existed only in the SGCs in the young group.The expression of CHOP and caspase-12 in the aged group was significantly higher than that in the young group.The results of western blot show that the expression of cleaved caspase-3,cleaved caspase-3 and cleaved PARP-1 in the aged group were increased and the expression level of cleaved caspase-8 was unchanged.3.The results of TUNEL staining showed that there was apoptosis in the SV,OHC and Reissner's membrane in the cochlea of the aged group,and no apoptosis was detected in the cochlea of the young group.HE staining showed that there was a significant degeneration in the cochleae of the aged mice.A loss of OHCs was observed in the middle and basal turn in the aged group,and a slight loss in the apex turn was also found.Conclusion:In summary,an impaired UPR was found in the cochleae of aged C57BL/6 mice.The apoptosis of cells in the aged cochleae was dependent on a mitochondrial pathway that may cross-talk with ER stress via CHOP.Part ? The role of endoplasmic reticulum stress in a murine noise-induced hearing loss modelObjective:To explore the role of endoplasmic reticulum stress in a murine noise-induced hearing loss model.Methods:The animals(C57BL/6 mice)were divided into two groups:the noise exposure group and the control group.The mice in the noise exposure group were exposed to the white noise at 110 dB SPL(sound pressure level)in a soundproof chamber.Auditory brainstem response(ABR)was performed before noise exposure and 14 days post noise exposure.The levels of eIF-2?-CHOP-ERO-1? pathway proteins in the cochlea at each time point were detected by western blot,respectively.The expression level and position of the protein in the cochlea was detected by immunohistochemistry.Results:1.The ABR results showed that the hearing threshold of the noise exposure group was significantly higher than that of the control group at low frequency to high frequency at 14 days post noise exposure.2.The results of western blot showed that the phosphorylation level of eIF-2? was increased at 2 hours post noise trauma and the expression of GRP78 was mildly increased.The increased GRP78 mainly located at marginal cells of stria vascularis,whereas the expression of CHOP and ERO-1? did not altered.At 6 hours post noise trauma,significantly increased CHOP and ERO-1? were found in the cochlea and mainly located at the outer hair cells and support cells.The oxdative stress marker 4HNE was increased as well.The expression of CHOP and ERO-1? were decreased at 1 day after noise stimulation.Conclusion:In summary,eIF-2?-CHOP-ERO-1? pathway was activated in a murine noise-induced hearing loss model.The apoptosis of cells in the cochleae might be dependent on ER stress via CHOP.