Region Specific Amyloid-β Accumulation in Olfactory Sensory Neurons Influences Ecto-Ventral Olfactory Dysfunction in 5xFAD Mice

Abstract Background: Hyposmia in Alzheimer’s disease (AD) is a typical early symptom according to numerous previous clinical studies. Although the causes of damage have been proposed in every olfactory system including olfactory epithelium, olfactory bulb and olfactory cortex, the main causes of AD- related hyposmia are largely unknown. Methods: We here focused on peripheral olfactory sensory neurons (OSNs) and delved deeper into the direct relationship between pathophysiological and behavioral results using odorants. We also histologically confirmed the pathological changes in three-month-old 5xFAD mouse models which recapitulates AD pathology. We introduced a numeric scale histologically to compare physiological phenomenon and local tissue lesions regardless of anatomical plane. Results: We observed the odorant group, which 5xFAD mouse could not detect, also neither did physiologically activate the OSNs that propagate to the ventral olfactory bulb. Interestingly, the amount of accumulated amyloid-β (Aβ) was high in the ecto-ventrally located OSNs that showed reduced responses to odorants. We also observed irreversible damage to the ecto-region of the olfactory epithelium by measuring impaired neuronal turnover ratio from the basal cells to the matured OSNs. Conclusions: Our results showed that partial and asymmetrical accumulation of Aβ coincided with physiologically and structurally damaged areas in the peripheral olfactory system, which evoked hyporeactivity to some odorants. Taken together, partial olfactory dysfunction closely-associated with peripheral OSN’s loss could be a leading cause of the AD-related hyposmia, a characteristic of early AD.