Neuronally Derived Extracellular Vesicles' Oligomeric and p129-α-Synuclein Levels for Differentiation of Parkinson's Disease from Essential Tremor

Abstract

Clinical differentiation between Parkinson's disease (PD) and essential tremor (ET) may be challenging, highlighting the need for easily assessable diagnostic biomarkers. Neuronally derived extracellular vesicles (NDEVs) have been proposed as a peripheral matrix that can well recapitulate the cellular composition of neurons. We investigated the clinical usefulness of NDEV oligomeric and p129-α-synuclein levels in discriminating between patients with PD and those with ET. NDEV oligomeric and p129-α-synuclein species were assessed using an ELISA in 43 patients with PD, 21 patients with ET, and 45 healthy controls (HCs). NDEV oligomeric α-synuclein levels were significantly higher in PD in comparison with ET and HCs, while p129-α-synuclein values were significantly lower in HCs compared to other groups. By using a receiver operator characteristic (ROC) analysis, oligomeric-α-synuclein achieved an excellent classification performance in distinguishing PD from both ET and HCs (AUC: 0.976 and 0.997, respectively), while lower performance was obtained in differentiating ET from HCs (AUC: 0.85). On the other hand, p129-α-synuclein accurately discriminated both PD and ET from HCs (AUC: 0.997 and 0.952, respectively) but had very low performance in differentiating PD from ET (AUC: 0.47). Our study suggests that NDEV oligomeric α-synuclein is an accurate blood-derived biomarker to differentiate PD from ET, while p129-α-synuclein may be useful in distinguishing ET from HCs.

Keywords: Parkinson’s disease; essential tremor; neuronally derived extracellular vesicles; oligomeric α-synuclein; p129-α-synuclein.

Figure 1

Physical characterization of EVs. EV size distribution was analyzed using tunable resistive pulse sensing (tRPS) technology (A) and transmission electron microscopy (B) (scale bar = 100 nm; insert shows higher-magnification image). Both approaches confirmed that isolated vesicles could be referred to as “small EVs”.

Figure 2

NDEV concentrations of o-α-synuclein (A) and p129-α-synuclein (B) in PD (n = 43), ET (n = 21), and HC (n = 45). Data are summarized as box plots, where upper, middle, and lower lines represent 75th percentile, median, and 25th percentile, respectively. Limits of vertical lines represent ranges, while dots represent moderate outliers. Statistical analysis was performed using ANCOVA, with sex, age (HC vs. PD vs. ET), and disease duration (PD vs. ET) as covariates, followed by Tukey’s HSD test (****: p-value < 0.0001; **: p-value < 0.01). o-α-syn = oligomeric α-synuclein; p129-α-syn = 129Ser-phosphorylated α-synuclein; PD = Parkinson’s disease; ET = essential tremor; HC = healthy control.

Figure 3

Receiver operating characteristic curves for o-α-synuclein (A,C,E) in differentiating PD from ET (A), PD from HC (C), and ET from HC (E) and for p129-α-synuclein (B,D,F) in differentiating PD from ET (B), PD from HC (D), and ET from HC (F). o-α-syn = oligomeric α-synuclein; p129-α-syn = 129Ser-phosphorylated α-synuclein; PD = Parkinson’s disease; ET = essential tremor; HC = healthy control; AUC = area under the curve.