Oral Mucosa Derived a-Synuclein as a Potential Diagnostic Biomarker for Parkinson's Disease

Background: Pathological alpha-synuclein (alpha-Syn) is not only exclusive to the central nervous system (CNS) in Parkinson's disease (PD), but also extended to biofluids and peripheral tissues including oral cavity. Both oral mucosa and nervous system are derived from ectodermal tissue, and potentially share common disease-specific characteristics. Oral mucosal exfoliative cytology is a non-invasive technique, which is an easily acceptable for patients and ordinary people. The purpose of this study was to determine the abnormal accumulation of alpha-Syn in oral mucosa of PD patients and to learn the diagnostic utility of oral mucosa alpha-Syn for PD.& nbsp;Methods: The oral mucosa samples were obtained from 57 patients with PD and 51 age-matched controls by cytological brush. Immunofluorescence analysis was used to investigate the presence and subcellular localization of alpha-Syn, phosphorylated alpha-Syn at Ser129 (pS129) and oligomeric alpha-Syn in the oral mucosa cells of PD patients and controls. Images taken as Z-stacks were analyzed for 3D reconstruction to visualize the alpha-Syn intracellular localization. Then, the concentrations of alpha-Syn, pS129, and oligomeric alpha-Syn in oral mucosa samples were measured using electrochemiluminescence assays.& nbsp;Results: Immunofluorescence images revealed the increased alpha-Syn, pS129, and oligomeric alpha-Syn levels in oral mucosa cells of PD patients than age-matched controls. The intracellular distributions of alpha-Syn species were determine by Z-stack images with 3D reconstruction, and alpha-Syn was detected in both the nucleus and cytoplasm. However, pS129 was mainly located in the cytoplasm, and oligomeric alpha-Syn was highly expressed in the nucleus and perinuclear cytoplasm. The concentrations of three alpha-Syn species were significantly increased in the oral mucosa cell samples of PD patients than controls (alpha-Syn, p = 0.001; pS129, p = 0.002; oligomeric alpha-Syn, p = 0.013). In PD patients, the oral mucosa alpha-Syn and oligomeric alpha-Syn levels were significantly correlated with Hoehn-Yahr scales (alpha-Syn, r = 0.495, p = 0.001; oligomeric alpha-Syn, r = 0.324, p = 0.03). The area under curve (AUC) of ROC analysis using an integrative model including alpha-Syn, pS129, and oligomeric alpha-Syn for PD diagnosis was 0.749, with 66.7% sensitivity and 72.5% specificity.& nbsp;Conclusion: This study for the first time demonstrated increased expressions of alpha-Syn, pS129, and oligomeric alpha-Syn in oral mucosa cells from PD patients, which serve as useful and non-invasive PD diagnostic biomarkers.