The Relationship Of RAGE-mediated Signal Pathway And Presbycusis Develepment

Presbycusis is also known as age-related hearing loss, it mainly refers to the gradualhigh-frequency sensorineural hearing loss with aging. Its etiology and pathogenesis iscomplex, mainly including aging、apoptosis、oxidative stress and mitochondrial mutationsfour hypotheses, in which free radical theory with aging is accepted by most people. Butoxygen free radicals can come from many parts, yet molecular mechanism has not unified,there is no effective treatment. RAGE activation by its ligands is known to be associatedwith reactive oxygen species generation, the interaction further increases transcriptionfactor NF-κB activation,which enhanced RAGE expression causing cell damage anddysfunction. RAGE-mediated oxidative stress is crucial in the disease of central nervoussystem damage. But there is few studies with RAGE in the aging inner ear. We speculatethat RAGE is involved in the development of presbycusis. In this study, we explore therole of RAGE-mediated signal pathways in the process of presbycusis. The study isdivided into three parts:Part one: Study of audiological function and inner ear histology in age-relatedC57BL/6J mice.Objective:To study audiological function and the inner ear histological characteristics indifferent months C57BL/6J mice.Methods: C57BL/6J mice were divided into three groups:2months of age（young）,4month（sadult）,10months old group（old）,10mice in each group.The auditory functionwere measured by auditory brainstem response (ABR) threshold with the stimulus clickat2kH z and4kH z. histological of cochlear were observed by HE stained and thebasilar membrane stretched.Results:(1) Audiological tests showed: ABR threshold in2months of age group ofC57BL/6J mice was10±1.24dBnHL;4months rose to18±1.87dBnHL, compared with2months of age group, p <0.05,the difference was statistically significant; ABRthreshold of10months was to60±2.91dBnHL, compared with4months group, p <0.01, difference was statistically significant;(2) HE staining: spiral ganglion cells graduallydecreased with aging, the numbers of10month were significantly lower than2、4months,stria vascularis atrophy increased with aging;(3) The inner and outer hair cells graduallyloss from the Low circle to top circle with the aging, the lost of outer hair cells occuredbefore inner hair cells.Conclusion: C57BL/6J mice hearing function decreases and inner ear morphologychanges with aging.Part two: Study of correlation between inner ear RAGE expression and ligandscontend change in C57BL/6J mice.Objective: To study the correlation between serum AGEs and inner ear S100B、RAGEexpression in C57BL/6J mice.Methods: C57BL/6J mice were divided into three groups:2months of age（young）,4months（adult）,10months old group（old）,10mice in each group. Serum AGEs wasdetected by ELISA, the ligand S100B expression of RAGE in the cochlea was measuredby semi-quantitative rt-PCR. RAGE expression in the cochlea was detected by Real timePCR.Results: In2months, serum AGEs was71.33±7.09ng/L,4months group was105.44±12.1ng/L,10months group was226.67±7.63ng/L,by pairwise comparison, p<0.05, thedifference was Statistically significant; RAGE relative expression in] inner ear of4months was1.61±0.07, as compared with2months group, p=0.049, the difference wasstatistically significant.10months group was3.13±0.08, compared with2months group,p=0.012, the differences was significant. RAGE expression was gradually increasedfrom2months to10months;Conclusion: Serum AGEs and S100B in the cochlea are increased with aging, RAGEexpression is also inceased with aging. It suggests RAGE expression in the cochlea isassoiated with the content of ligands AGEs and S100B.Part three: RAGE mediated signal pathway in the pathogenesis of the presbyacusisObjective: To study the RAGE, NF-kB, P21protein expression in the cochlea ofdifferent months C57BL/6J mice, and explore the relationship of RAGE–mediated signalpathway with the process of presbycusis. Methods: C57BL/6J mice were divided into three groups:2months（young）,4months（adult）,10month（sold）,10mice in each group. The location and expression of RAGE,NF-κB and P21in the cochlea was detected by Immunohistochemisty. mean opticaldensity (MOD) value of dyed organizations (spiral ganglion cells and stria vascularis)was calculated by IPP6software.Results: RAGE, NF-κB and P21proteins are mainly expressed in the Corti、spiralganglion cells and stria vascularis, and mean optical density values in10months group isgreater than that in4months group. MOD in4months group was higher than that in2months, p <0.05, the difference was statistically significant.Conclusion: RAGE, NF-κB, P21proteins express in the C57BL/6J mice cochlea andincrease with aging, RAGE, NF-κB, p21are involved in the pathogenesis of presbycusis.We speculated RAGE-mediated signal pathway is related to the pathogenesis ofpresbycusis.