This is a Discovery Research Grant awarded to Dr Nicolas Michalski at the Institut Pasteur, France, in 2020. We are co-funding this grant in partnership with Alzheimer’s Research UK.
Dementia is a highly disabling condition that’s on the increase and expected to affect 100 million people by 2050.
Several risk factors for dementia have been identified. For some, such as age, the risk can’t be mitigated, but for others, such as social isolation and hearing loss, it might be possible to reduce the risk through changes in people’s behaviour.
People with mild, moderate or severe hearing loss in mid-life have risks of developing dementia later in life that are 2, 3 and 5 times higher, respectively, than people without hearing loss. This makes hearing loss the most significant potentially reversible risk factor for dementia.
However, we know very little about the biological processes that link hearing loss and dementia. A better understanding of these processes could help us to determine whether managing hearing loss (e.g. with hearing aids) could prevent or delay the onset and progression of dementia, and could help us to identify new targets for treatment.
Nerve cells, such as those nerve cells within the brain which process sound information, require a continuous supply of oxygen and nutrients to remain healthy. The blood circulatory system is therefore a crucial factor in diseases which affect nerve cell survival in the brain, including dementia. However, whether the circulatory system is involved in the link between hearing loss and dementia is unknown.
The researchers will test the idea that hearing loss makes dementia worse by its effects on blood circulation in the brain.
They’ll study mouse models of different types of hearing loss and use new brain imaging methods to investigate the patterns of blood vessels in the brains of these mice.
They’ll look at:
- The impact of different types of hearing loss on the circulatory system in the brain
- Whether any changes in the circulatory system in the brain as a result of hearing loss lead to abnormal increases in the levels of typical biological markers of dementia
- And whether restoring hearing to deaf mice can prevent these changes to the circulatory system in the long term, and, as a result, prevent damage to nerve cells.
If hearing loss impacts the blood circulatory system in the brain, then it might be possible to use existing drugs that are known to boost or protect blood circulation in the brain to reverse these changes, or to develop appropriate new drugs.
This work could also provide a scientific basis to measure the potential benefits of hearing rehabilitation, through the use of hearing aids in particular, in decreasing the risk of dementia in people with hearing loss. Such a finding could have major clinical impact, promoting the importance of addressing hearing loss at an early stage. This could lead to changes in health policies to favour systematic screening for hearing loss in the general population and the wider use of hearing aids.