Detection of prion-like proteins in human olfactory samples collected by nasal swabs

Prion-like proteins are proteins with the capacity to self-propagate via templated misfolding and intercellular dissemination, like prions. These proteins are involved in several neurodegenerative diseases causing neuronal death. To date, detecting these proteins in affected patients is still challenging. Therefore, the need to be able to provide evidence of these causative proteins is urgent. The olfactory neuroepithelium shows the expression pattern of prion-like proteins in patients affected by different neurodegenerative disorders and healthy controls, and it can be harvested using a non-invasive procedure such as a nasal swab. The cell populations composing the human olfactory epithelium, consisting primarily of olfactory sensory neurons, supporting cells and basal cells, are not completely characterized. Thus, the first objective was to describe the samples collected with the nasal swab by immunofluorescence using commercially available antibodies. The second objective was the detection of disease-associated prion-like proteins, such as TDP-43, α-synuclein, huntingtin and the prion protein. For the first time, the expression of pathological forms of these proteins was shown in nasal swab samples of patients with neurodegenerative disorders compared to controls. In parallel, Real-Time Quaking-Induced Conversion (RT-QuIC) assay, an in vitro technique originally developed for prion seeding activity detection, was set up for TDP-43 in olfactory samples, allowing 86% sensitivity in identifying genetic cases of frontotemporal dementia and 70% sensitivity in non-genetic patients. RT-QuIC assay for α-synuclein in the olfactory samples of patients with Parkinson’s disease showed a sensitivity of ~46% in previous studies. Thus, we investigated whether olfactory mucosa sampling from different areas, within the nasal vault, could influence the result. Nasal swabs performed at the agger nasi and the middle turbinate provided a sensitivity of ~80% and ~45%, respectively. A higher representation of neuronal-shaped cells at the agger nasi was also shown. In conclusion, the nasal swab is a versatile tool that allows in vivo detection of multiple prion-like proteins involved in neurodegeneration.