Transmission of Synucleinopathies in the Enteric Nervous System of A53T Alpha-Synuclein Transgenic Mice

Abstract

Parkinson's disease (PD) and dementia with Lewy bodies (DLB) are characterized by abnormal deposition of α-synuclein aggregates in many regions of the central and peripheral nervous systems. Accumulating evidence suggests that the α-synuclein pathology initiates in a few discrete regions and spreads to larger areas in the nervous system. Recent pathological studies of PD patients have raised the possibility that the enteric nervous system is one of the initial sites of α-synuclein aggregation and propagation. Here, we evaluated the induction and propagation of α-synuclein aggregates in the enteric nervous system of the A53T α-synuclein transgenic mice after injection of human brain tissue extracts into the gastric walls of the mice. Western analysis of the brain extracts showed that the DLB extract contained detergent-stable α-synuclein aggregates, but the normal brain extract did not. Injection of the DLB extract resulted in an increased deposition of α-synuclein in the myenteric neurons, in which α-synuclein formed punctate aggregates over time up to 4 months. In these mice, inflammatory responses were increased transiently at early time points. None of these changes were observed in the A53T mice injected with saline or the normal brain extract, nor were these found in the wild type mice injected with the DLB extract. These results demonstrate that pathological α-synuclein aggregates present in the brain of DLB patient can induce the aggregation of endogenous α-synuclein in the myenteric neurons in A53T mice, suggesting the transmission of synucleinopathy lesions in the enteric nervous system.

Keywords: Lewy body; Parkinson's disease; dementia with Lewy bodies; enteric nervous system; inflammation; protein aggregation.

Fig. 1

α-Synuclein proteins in the brain extracts of a DLB patient and a control subject. Total brain extracts (10 µg) from a normal control and a DLB patient were immunoblotted for α-synuclein. The arrow indicates α-synuclein monomers and a bracket shows high MW α-synuclein aggregates.

Fig. 2

Accumulation of α-synuclein aggregates in the myenteric plexus of injected A53T mice. Normal and DLB brain extracts or saline were injected to the stomach walls of the A53T tg mice. The whole-mount staining of stomach tissue was performed at (A) 1 month, (B) 2 months, (C) 3 months, and (D) 4 months. Antibodies for β3-tubulin as a neuronal marker and human α-synuclein (274) were used. Arrows in the enlarged images indicate α-synuclein aggregates (Scale bar: 20 µm).

Fig. 3

Quantification of α-synuclein deposition in the myenteric neurons. The graph represents the degree of α-synuclein aggregation shown in Fig. 2. The abundance and size of α-synuclein aggregates are represented in a scale of 0 to 3, with 0 being no aggregates.

Fig. 4

Inflammatory responses precedes the accumulation of α-synuclein in the DLB extract-injected A53T mice. Normal and DLB Brain extracts or saline were injected to the stomach walls of the A53T tg mice. The whole-mount staining of stomach tissue was performed at (A) 1 month, (B) 2 months, (C) 3 months, and (D) 4 months with antibodies for astrocyte marker GFAP and a marker for activated macrophage MHCII. Note that the MHCII staining was increased 1 month after injection, and more so at 2 months in the DLB extract-injected mice, but decreased afterwards (Scale bar: 20 µm).

Fig. 5

Lack of α-synuclein accumulation and inflammation in the myenteric plexus of the DLB extract-injected wild type mice. Wild type C57BL6 mice injected with the DLB extract, and 4 months after injection, the wholemount staining of stomach tissue was performed as in Figs. 2 and 4 (Scale bar: 20 µm).