How Does Hearing Loss Trigger Alzheimer's?

A New Molecular Mechanism Discovered in Mice!

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For years, scientific studies have revealed a connection between age-related hearing loss and the risk of Alzheimer's. However, the underlying mechanisms of this link are still being investigated. Possibilities include people socializing less due to hearing loss, and the increased burden on auditory regions of the brain affecting processing in other brain areas, thereby weakening cognitive performance.

Researchers from Wuhan University in China have uncovered a molecular mechanism behind this connection. In a study published in the journal Nature Aging, a protein called GDF1 was discovered to play a critical role in the progression of Alzheimer's disease.

New Findings on the GDF1 Signaling Pathway

Researchers worked with genetically modified mice to model Alzheimer's disease. In these mice, in which hearing loss was induced, an accumulation of Alzheimer's-specific amyloid-β plaques was observed in their brains, particularly in the hippocampus, auditory cortex, and temporal association cortex regions. Furthermore, the mice performed worse in behavioral experiments, and synaptic density in the hippocampus decreased.

When these effects of hearing loss were examined, researchers detected a significant reduction in the expression of the gdf1 gene. This led to a decrease in GDF1 protein levels. Interestingly, when GDF1 was supplemented to the mice, cognitive impairments, amyloid-β plaque load, and synaptic dysfunction were reduced. These findings suggest that hearing loss may support pathological changes caused by Alzheimer's by suppressing the GDF1 signaling pathway.

How Can We Prevent Cognitive Decline?

Hong-Bo Zhao, an ENT specialist from Yale University, emphasizes that hearing loss does not directly cause Alzheimer's. Nevertheless, according to Zhao, this study provides strong evidence that hearing loss can exacerbate the progression of Alzheimer's.

Moreover, the relationship between hearing loss and Alzheimer's is not one-way. In 2020, Zhao's laboratory showed that changes in hearing can be observed in the early stages of Alzheimer's, and these changes could be used for dementia diagnosis and monitoring (Liu et al., 2020).

According to Zhao, proven solutions such as hearing aids or cochlear implants can prevent cognitive decline in Alzheimer's patients. Zhang's team, on the other hand, continues their studies to understand in more detail the mechanisms underlying GDF1's neuroprotective effects and how hearing loss leads to changes in the central nervous system.

References:

• https://www.pnas.org/post/journal-club/mouse-study-shows-hearing-loss-drives-alzheimer-s-disease 

• Pan, L., Li, C., Meng, L., Zhang, G., Zou, L., Tian, Y., ... & Zhang, Z. (2024). GDF1 ameliorates cognitive impairment induced by hearing loss. Nature Aging, 4(4), 568-583.

• Liu, Y., Fang, S., Liu, L. M., Zhu, Y., Li, C. R., Chen, K., & Zhao, H. B. (2020). Hearing loss is an early biomarker in APP/PS1 Alzheimer’s disease mice. Neuroscience letters, 717, 134705.