Early-Onset Hearing Loss in Mouse Models of Alzheimer’s Disease correlates to DNA Damage in Cochlea

ABSTRACT: Alzheimer's disease (AD) is the most common type of dementia and is characterized by cognitive and behavioral impairment that significantly interferes with social functioning. Over the last decade, there has been an increased interest in whether sensory deficiency may be associated with the development of AD. Notably, the relationship between hearing impairment and AD is of great relevance, but still poorly understood. In this study, we found an early-onset hearing loss in 3xTgAD and 3xTgAD/Polβ+/− mouse models. The hearing assessment was measured by auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) recordings. Herein, we report that both 3xTgAD and 3xTgAD/Polβ+/− mice showed increased ABR thresholds between at 16 and 32 kHz at 4 weeks of age, much earlier than any AD behavioral changes. The ABR thresholds were significantly higher in 3xTgAD/Polβ+/− mice than in 3xTgAD mice at 16 kHz, and DPOAE signals were also reduced, indicating that DNA damage may affect hearing impairment in AD. Poly ADP-ribosylation levels and protein expression of DNA damage markers increased significantly and NAD+ levels were reduced in the cochlea of 3xTgAD and 3xTgAD/Polβ+/− mice. Remarkably, we observed the downregulation of phosphoglycerate mutase 2 (PGAM2) in cochlea and a decrease in the number of synaptic ribbons in the presynaptic zones of inner hair cells in 3xTgAD/Polβ+/− mice. We also find that the activity of sirtuin 3 (SIRT3) is downregulated in cochlea, indicative of impaired mitochondrial function. Taken together, hearing impairment may be a potential early marker of AD. In addition, these findings provide new insights into the mechanism of the relationship between hearing dysfunction and AD and suggest that DNA damage in the cochlea can contributes to the development of early hearing loss of AD. The hearing assessment was measured by auditory brainstem response (ABR) and distortion product otoacoustic emission (DPOAE) at 4 weeks of age, thereafter whole cochlea and auditory cortex tissue were collected from each mouse (WT, Polβ+/−, 3xTgAD, and 3xTgAD/Polβ+/−) and subjected to total RNA isolation to understand what metabolism-related gene expression changes in cochlea and auditory cortex.

ORGANISM(S): Mus musculus

PROVIDER: GSE232205 | GEO | 2024/03/27

REPOSITORIES: GEO