Novel Nasal Epithelial Cell Markers of Parkinson's Disease Identified Using Cells Treated with α-Synuclein Preformed Fibrils

Parkinson's disease (PD) is the most common neurodegenerative movement disorder, characterized by olfactory dysfunction in the early stages. α-Synuclein pathologies in the olfactory organs are shown to spread to the brain through the nose-brain axis. We first developed a nasal epithelial PD cellular model by treating RPMI-2650 cells with α-synuclein preformed fibrils (PFF). Upon uptake of PFF, RPMI-2650 cells showed mitochondrial proteome alteration and downregulation of parkin, which has previously been identified as a nasal biomarker of PD. Functional cluster analysis of differentially expressed genes in RPMI-2650 cells revealed various pathways affected by α-synuclein pathology, including the detection of chemical stimulus involved in sensory perception, olfactory receptor activity, and sensory perception of smell. Among genes that were most affected, we validated, by real-time quantitative PCR, the downregulation of MAP3K8, OR10A4, GRM2, OR51B6, and OR9A2, as well as upregulation of IFIT1B, EPN1, OR1D5, LCN, and OTOL1 in PFF-treated RPMI-2650 cells. Subsequent analyses of clinical samples showed a downregulation of OR10A4 and OR9A2 transcripts and an upregulation of IFIT1B in cells isolated from the nasal fluid of PD patients, as compared to those from the controls (cutoff value = 0.5689 for OR9A2, with 72.4% sensitivity and 75% specificity, and 1.4658 for IFIT1B, with 81.8% sensitivity and 77.8% specificity). Expression levels of these nasal PD markers were not altered in nasal fluid cells from SWEDD (scans without evidence of dopaminergic deficits) patients with PD-like motor symptoms. These nasal markers were significantly altered in patients of PD with hyposmia compared to the control hyposmic subjects. Our results validated the α-synuclein-treated nasal epithelial cell model to identify novel biomarkers for PD and suggest the utility of olfactory transcripts, along with olfactory dysfunction, in the diagnosis of PD.