The Hearing Loss Of EphA2 KO Mice And Its Mechanism

Objective Hearing loss,which makes a serious influence to the life qualities of the patients,is one of common human diseases.The means for the clinical prevention or treatments such as installing auxiliary device,stem cell transplantation and gene therapy technology have been developing in recent years.Screening out hearing disorder genes and the studies about their mechanisms are the foundation of gene therapy technology.The purpose of this experiment is to validate that EphA2 gene may be associated with presbycusis and study the mechanism of the hearing loss induced by the absence of EphA2 gene in mice.Methods(1)For gaining a stable source of experimental animals,three EphA2 KO C57 BL/6J adult male mice(bought from the Jackson Laboratory Company)and the same genetic background adult female mice(obtained from the Southern Medical University Laboratory Animal Center)were cohabitating in ovulatory period and we confirmed the genotype of the offspring by the gel-based PCR assay.(2)The ABR(stimulated by Click or Tone burst sounds)of the three genotype mice with different sheared index marks were detected at about 2-4 months and 6-8 months age.(3)We confirmed the expression of EphA2 in cochlea by WB.(4)The endocochlear potential of the three genotype mice were detected in two months to confirm whether the function of stria vascularis is normal or not.(5)Whole-mount SV,whole-mount cochleae and cochleae sections were used for histopathology or immunohistochemistry to find out the anomalies of the capillaries in SV and ribbon synapses in inner hair cells at 2-4 months and 6-8 months ages.Results The heterozygous and homozygous mice somehow have the same phenotype who could be called the experimental group or mice.(1)The experimental mice have a age-related hearing loss which begins in high frequency and then tends to the middle and low frequency gradually.(2)EphA2 were expressed in cochlea.(3)The lesions of capillaries in SV are not obvious at 2-4 months but show a severe change at 6-8 months age.(4)The basal EP of experimental mice already is abnormal at 2-4 months age.(5)The numbers of hair cells in experimental mice have no difference with control mice at 2-4 months age while a great loss of basal out hair cells and inner hair cells happened in experimental mice at 6-8 months age.(6)Numbers of ribbon synapses in middle and basal inner hair cells on the experimental mice are lower than those on control mice at 2-4 months age.The ribbon synapses in apical inner hair cells on the experimental mice decreased at the age of 6-8 months.(7)At two ages,both the thickness of SV and density of SGNs on the experimental mice have no difference with those on control mice.Conclusion The absence of EphA2 gene in C57BL/6 J mice leads to a age-related hearing loss by affecting the SV capillary network,EP,the survival of cochlear hair cells and cochlear auditory nerve projection.The hearing loss in the earlier stage may be brought by abnormal middle and basal cochlear auditory nerve projection and a lower EP in the base.The further SV lesion and loss of hair cells may have a relatively dominant position in the hearing loss at the old-aged period.