Olfactory Dysfunction Exacerbates Hippocampal Aβ Accumulation, Tau Phosphorylation and Memory Deficits in Mice.

Olfactory dysfunction is a frequent feature in patients with neurodegenerative disorders such as Alzheimer’s disease (AD). However, whether olfactory impairment is the cause or consequence of AD is unknown. We previously found that olfactory dysfunction impairs learning and memory in mice in multiple experimental paradigms, but whether olfactory dysfunction increases AD-related neuropathological changes such as Aβ deposition and tau protein phosphorylation is not clear. In this study, mice were treated with bilateral intranasal zinc sulfate (ZnSO4) solution infusion, which resulted in olfactory dysfunction for about 1 month in mice. 1, 3, 6, and 9 months after that, the Y-maze learning and memory, as well as hippocampal Aβ deposition, tau and p-tau expression were tested. We found that olfactory dysfunction leads to a long period and irreversible learning and memory impairment in mice. Olfactory dysfunction also increased Aβ deposition, Aβ42 level, and increased p-tau expression in hippocampus (HPC), which were accompanied by increased beta-site amyloid precursor protein cleaving enzyme 1 (BACE1) and decreased presenilin-1 (PS1) expression. Compared with one time of ZnSO4 treatment, repetitive ZnSO4 treatment (three times, a month apart) resulted in more significant increases in tau phosphorylation in mice hippocampus. These results suggest that olfactory dysfunction lead to behavioral and pathological changes associated with AD in mice, which suggest that olfactory dysfunction can contribute to the development of AD.