Journal of Shanghai Jiao Tong University (Medical Science) >

2022 , Vol. 42 >Issue 8: 980 - 986

DOI: https://doi.org/10.3969/j.issn.1674-8115.2022.08.002

Innovative research team achievement column

Comparison of mitochondria and NAD+ level in the murine cochleae of C57BL/6J mice at different ages

  • Baoyi FENG ,
  • Tingting DONG ,
  • Xiaofei ZHENG ,
  • Yong TAO ,
  • Hao WU
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  • 1.Department of Otolaryngology-Head and Neck Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200011, China
    2.Ear Institute, Shanghai Jiao Tong University School of Medicine, Shanghai 200092, China
    3.Shanghai Key Laboratory of Translation Medicine on Ear and Nose Disease, Shanghai 200092, China
    4.Biobank of Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai 200092, China
WU Hao, E-mail: wuhao@shsmu.edu.cn.

Received date: 2022-01-27

  Accepted date: 2022-06-05

  Online published: 2022-08-12

Supported by

National Natural Science Foundation of China(81730028);Shanghai Municipal Education Commission—Gaofeng Clinical Medicine Grant Support(2019821);Innovative Research Team of High-level Local Universities in Shanghai(SSMU-ZLCX20180601);Fundamental Research Program Funding of Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine(JYZZ096)

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Abstract

Objective ·To investigate the changes of mitochondria and nicotinamide adenine dinucleotide (NAD+) levels in the cochleae of C57BL/6J mice at different ages, and explore potential mechanism of age-related hearing loss. Methods ·Forty C57BL/6J male mice aged 1, 4, 8, 12 months, respectively, were chosen and classified into 4 groups in terms of age (n=10). Auditory brain response (ABR) and distortion product otoacoustic emission (DPOAE) were conducted to detect the auditory function of mice at different ages; real-time quantitative PCR (RT-qPCR) was applied to compare the mRNA expression levels of the genes associated with mitochondrial energy metabolism in the cochleae of mice at different ages, including Ndufb5 (NADH: ubiquinone oxidoreductase subunit B5), Sdha (succinate dehydrogenase complex flavoprotein subunit A), Sdhc (succinate dehydrogenase complex subunit C), and Atp5b (ATP synthase, H+ transporting mitochondrial F1 complex, beta subunit); the changes of mitochondrial quantity in the cochlear hair cells from the mice aged 1 month and 12 months were observed by whole-mount immunofluorescence; the mitochondrial ultrastructure in the cochlear sensory epithelia including outer and inner hair cells, myelinate nerve fibers and spiral ganglion neurons of 1- and 12-month-old mice was observed by transmission electron microscope (TEM); NAD+ levels in the cochleae of mice at different ages were detected by quantitative colorimetry. Results ·The ABR thresholds of the 12-month-old mice were significantly elevated in comparison with those of the 1-month-old mice at the frequency range of 5.66?45.00 kHz (P<0.01); and the DPOAE thresholds of the 12-month-old mice were significantly elevated in comparison with those of the 1-month-old mice at the frequency range of 11.32?32.00 kHz (P<0.01). The expression levels of the genes related to mitochondrial functions including Ndufb5, Sdha, Sdhc, and Atp5b showed a downward trend with the age, which in the 8-month-old and 12-month-old mice were significantly different from those in the 1-month-old mice (P<0.05). Immunostaining showed that the number of mitochondria in cochlear inner hair cells of the 12-month-old mice was significantly lower than that of 1-month-old mice. It was observed by TEM that vacuolar degenerated mitochondria and larger lipofuscin existed in the inner hair cells, myelinate nerve fibers and spiral ganglion neurons of the 12-month-old mice. The NAD+ level showed a decreasing trend with age, declining significantly from 8 months of age, compared with the 1-month-old mice (P<0.01). Conclusion ·Mitochondrial dysfunction with abnormal structure and descending NAD+ levels in the cochleae is consistent with hearing function deterioration in C57BL/6J aging mice.

Key words： aged-related hearing loss; hearing loss; mitochondria; aging; nicotinamide adenine dinucleotide (NAD+)

Cite this article

Baoyi FENG , Tingting DONG , Xiaofei ZHENG , Yong TAO , Hao WU . Comparison of mitochondria and NAD+ level in the murine cochleae of C57BL/6J mice at different ages[J]. Journal of Shanghai Jiao Tong University (Medical Science), 2022 , 42(8) : 980 -986 . DOI: 10.3969/j.issn.1674-8115.2022.08.002

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