Moreover, 5-HT regulates Tau phosphorylation through various signaling pathways, such as the mTOR/GSK-3β, CDK5/GSK-3β, Fyn/GSK-3β, Fyn-PKA/ERK1/2, and MARK4 pathways, offering crucial insights into potential therapeutic targets for AD. This evidence concerns the gene FYN and Alzheimer disease.