Widespread Distribution of α-Synuclein Oligomers in LRRK2-related Parkinson's Disease

Abstract

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial and sporadic Parkinson's disease (PD). While the clinical features of LRRK2-PD patients resemble those of typical PD, there are significant differences in the pathological findings. The pathological hallmark of definite PD is the presence of α-synuclein (αSYN)-positive Lewy-related pathology; however, approximately half of LRRK2-PD cases do not have Lewy-related pathology. Lewy-related pathology is a late-stage αSYN aggregation that can be visualized with hematoxylin and eosin stains or conventional immunohistochemistry (IHC). Increasing evidence has indicated that αSYN oligomers, which represent the early-stage of αSYN aggregation, may have neurotoxicity. Visualization of αSYN oligomers requires specialized staining techniques, such as αSYN-proximity ligation assay (PLA). The distribution and severity of αSYN oligomers in the human brain of LRRK2-PD patients remain unknown. In this study, we performed phosphorylated αSYN-IHC and αSYN-PLA staining on postmortem brain sections of patients with three pathogenic LRRK2 mutants: p.G2019S (n=5), p.I2020T (n=5), and p.R1441C (n=4). The severity of Lewy-related pathology and αSYN oligomers were assessed semi-quantitatively in the brainstem, limbic lobe, basal ganglia, and cerebral cortex. αSYN oligomers were detected in LRRK2-PD cases even in cases without Lewy-related pathology; a negative correlation was observed between Lewy-related pathology and αSYN oligomers (r=-0.26 [-0.39, -0.12]; P<0.0001). Our findings suggest that αSYN oligomers may represent a common pathological feature of LRRK2-PD. Notably, patients harboring p.G2019S and p.I2020T had significantly higher levels of αSYN oligomers in those without Lewy-related pathology compared to those with Lewy-related pathology. These cases also had a trend toward shorter disease duration. These results imply that in LRRK2-PD, αSYN oligomers may initially accumulate in the brain but do not progress to form Lewy-related pathology. The present study suggests that targeting αSYN oligomers may be a therapeutic strategy for LRRK2-PD even if there is no Lewy-related pathology.

Keywords: Alpha-synuclein; LRRK2; Lewy bodies; Oligomers; Parkinson disease; Pathogenesis.

Figure 1

Representative images of αSYN-PLA staining. Left images are from patients without Lewy-related pathology and right images are from patients with Lewy-related pathology. The red-brown signals indicate αSYN oligomers. These αSYN oligomers accumulate in neurons and neuropil. Cases without Lewy-related pathology exhibit more abundant αSYN oligomers compared to those with Lewy-related pathology. Scale bar: 50 μm.

Figure 2

Neuronal staining patterns (A) and the severity in neuropil (B) of αSYN-PLA staining for each brain region. The staining pattern of αSYN oligomers in neurons shows a clustered appearance in one patient with p.G2019S and two patients with p.I2020T mutations. Regarding αSYN oligomers in the neuropil, two patients of each mutation exhibit severity scores of 4 or 5. αSYN, α-synuclein; PLA, proximity ligation assay; dmX, dorsal motor nucleus of the vagal nerve; N, nucleus; LC, locus coeruleus; SN, substantia nigra; CA, cornu ammonis.

Figure 3

Comparison of α-synuclein oligomer burden (A) and Lewy-related pathology (B). LRRK2-PD patients without Lewy-related pathology demonstrate more prominent αSYN oligomer accumulation compared to those with Lewy-related pathology. αSYN, α-synuclein; PLA, proximity ligation assay; dmX, dorsal motor nucleus of the vagal nerve; N, nucleus; LC, locus coeruleus; SN, substantia nigra; CA, cornu ammonis.

Figure 4

Severity of α-synuclein oligomer burden in each brain region of patients with LRRK2 mutations and control subjects. SN, substantia nigra; N, nucleus; dmX, dorsal motor nucleus of the vagal nerve; CA, cornu ammonis.