Study On The APE1 In The Cochlear Nucleus Of The Mimetic Aging Rat Model

Objective: Preliminarily investigate the expression of APE1 and Nrf-2 in the cochlear nucleus of d-galactose induced mimetic aging rats so as to reveal the pathogenesis of presbycusis, providing novel theoretical foundation for the treatment and precaution of age-related hearing loss.Methods: One hundred and sixty two 2 month-old Sprague-Dawley were randomly 2and the control group. Each of which contains eighty one rats. The experimental group received daily subcutaneous injection of Dgalactose with a dose of 500 mg / kg dissolved by saline for eight weeks as well as the control group were given pure saline in the same way. Three subgroup was divided in both the experimental group and the control group, that is the 4-month group( killed right after the complete of the model), the 10-month group( killed 6 month after the complete of the model) and the 16-month group( killed 12 month of the complete of the model).Before sacrifice all the model animals were given auditory brainstem response(ABR) test to detect their auditory threshold and during the sacrifice the cochlear nucleus of all the model animals were obtained. Using TUNEL staining to determine the apoptosis level of the cochlear nucleus tissue. Nissl's staining method was used to observe the neuron density in the cochlear nucleus tissue. Western blot analysis and Immunohistochemistry staining were employed to detect the expression and protein level of APE1 and Nrf-2 in the cochlear nucleus tissue in both the experimental and control groups.Results: The auditory brainstem response(ABR) test results showed that for subgroups of the same month of age and same frequency( 4k Hz?8k Hz?16k Hz?24k Hz?32k Hz), the difference auditory threshold level between the experimental group and the control group has no statistically significance. The TUNEL staining results showed that in the 4-month group, the difference between the experimental group and the control group didn't has statistically significance while for the 10-month and 16-month groups, the apoptosis level of the experimental groups are higher than that of the control groups(p<0.05). According to the Nissl's staining results, for the 4-month and 10-month groups, the neuron density of cochlear nucleus in the experimental groups showed no statistically significance when compared with that of the control groups while for the 16-month groups, the neuron density of the experimental groups is lower when compared with that of the control groups(p<0.05). The western blot results shows that for APE1, the protein level between the 4-month groups show no difference of statistically significance while in 10-month and 16-month groups, the protein level of APE1 in the experimental groups are lower than that of the control groups(p<0.01). As for the protein level of Nrf-2, the experimental groups is lower than that of the control group(p<0.01) in every time points. Based on the results of the Immunohistochemistry staining, APE1 protein level didn't show difference of statistically significance between the 4-month groups, however in the 10-month and 16-month groups the protein expression of APE1 of the experimental groups is lower than that of the control groups. The protein level of Nrf-2 in the experimental groups is lower than that of the control group in every time points.Conclusion: High dose of d-galactose leads to the increase of apoptosis and decrease of neuron density of cochlear nucleus tissue thus contributes to the acceleration of aging in the mimetic aging model of Sprague-Dawley rats. The protein expression level of APE1 and Nrf-2 vary between mimetic aging groups and control groups in different time points in the cochlear nucleus tissue, they may take part in the process of apoptosis of the neurons and contribute to accelerate the aging of cochlear nucleus.