“Losing the ability to smell is one of the first symptoms of Alzheimer’s diseases.” I hear this a lot, but people usually can’t comment more than this. So I looked into it:
The cells involved in first helping you smell (the olfactory sensory neurons) have a really high turnover rate with a lifespan averaging about a month [1]. I assumed that the correlation between losing the ability to smell and having degrading memory is linked by the region’s dependency to high levels of neurogenesis (development of new cells). And this is where it really interesting! There is growing evidence of molecules associated with Alzheimer’s diseases (like presenilin-1/2, amyloid precursor protein, and its metabolites) being involved with neurogenesis. (A helpful schematic with many cross-talk of signaling molecules are found in a review by Lazarov and Marr [2].) Apparently, young mouse models of Alzheimer’s diseases show impairments of cell proliferation and differentiation in regions with high neurogenesis and is believed to contribute to neuronal dysfunction (reviewed in [2]). In other words, alterations of cell signaling in developing cells are evident early and might be involved in the development of Alzheimer’s disease.
[1] PMID: 1699323
[2] PMID: 19699201
Originally posted on Instagram February 9, 2019
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