Study On The Role Of Murine Cytomegalovirus Infection In Progressive Hearing Loss

ObjectiveTo investigate the changes in hearing and cochlear structure of Balb/c mice infected with murine cytomegalovirus within 24 hours after birth,and to explore its role in progressive hearing loss.MethodsBalb/c mice within 24 hours after birth were randomly divided into infection group(MCMV group)and control group,and intraperitoneal injections of murine cytomegalovirus(MCMV)or the same amount of DMEM were injected respectively.The auditory brainstem response(ABR)was used to measure the auditory function of two groups of mice at the age of 4 weeks and 24 weeks,frozen sections of the cochlea and basement membrane spreading technology were conducted respectively to observe the quantity and distribution of spiral ganglion neurons,hair cells’ ribbon synapses by immunofluorescence.Total protein of auditory cortex and cochlear of four-week mice were separately extracted,and then Western Blot technology was performed to evaluate the expression level of protein PARP、caspase-3、cleaved caspase-3.PC12 cells were cultured and infected with MCMV to simulate the spiral ganglion neurons’ infection in vitro.24 hours after infection,the cells were gathered,and PCR was conducted to assess the expression level of NLRP3、IFN-γ and IL-6 in MCMV-infected PC12 cells.ResultsAt 4 weeks of age,11 out of 50(22%)Balb/c mice in the MCMV group had a significantly higher ABR threshold and a reduced I wave amplitude,with 3 bilateral hearing loss and 8 unilateral hearing loss;the rest of MCMV group and all of the control group mice were normal.At 24 weeks of age,9 out of 15(60%)MCMV group mice had a significantly higher ABR response threshold and a reduced I wave amplitude,with 1bilateral hearing loss and 8 unilateral hearing loss.Immunofluorescence showed that the number of spiral ganglion neurons decreased in the cochlea of MCMV group mice with increased ABR threshold compared to the control group,and the number of ribbon synapses decreased;at 4 weeks of age,3 out of 39 MCMV group mice with normal ABR threshold showed that the spiral ganglion neuron cells got lost and the number of ribbon synapses decreased;at 24 weeks of age,3 out 6 MCMV group mice with normal ABR threshold revealed significantly loss of spiral ganglion neuron cells.The expression level of protein caspase-3 in the auditory cortex of MCMV group mice was significantly higher than that of control group.While little difference was observed in two group as to protein PARP、caspase 3 and cleaved caspase-3 in the cochlear.After infected with MCMV for24 h,the m RNA expression level of NLRP3 、IFN-γ and IL-6 got higher than the control group.ConclusionsCytomegalovirus infection within 24 hours after birth can significantly increase the ABR threshold and decrease the amplitude of wave I,and lead to a decrease in the number of spiral ganglion neuron cells and ribbon synapses.The conditions mentioned above will develop with age.Besides,apoptosis may accumulated in the auditory cortex of infected mice.The above-mentioned changes in the structure of the cochlea may partly explain the progressive hearing loss caused by cytomegalovirus infection within postnatal 24 hours.