The cellular hallmarks of Parkinson's disease (PD) are the loss of nigral dopaminergic neurons and the formation of ?-synuclein-enriched Lewy bodies and Lewy neurites in the remaining neurons. Based on the topographic distribution of Lewy bodies established after autopsy of brains from PD patients, Braak and coworkers hypothesized that Lewy pathology primes in the enteric nervous system and spreads to the brain, suggesting an active retrograde transport of ?-synuclein (the key protein component in Lewy bodies), via the vagal nerve. This hypothesis, however, has not been tested experimentally thus far. Here, we use a human PD brain lysate containing different forms of ?-synuclein (monomeric, oligomeric and fibrillar), and recombinant ?-synuclein in an in vivo animal model to test this hypothesis. We demonstrate that ?-synuclein present in the human PD brain lysate and distinct recombinant ?-synuclein forms are transported via the vagal nerve and reach the dorsal motor nucleus of the vagus in the brainstem in a time-dependent manner after injection into the intestinal wall. Using live cell imaging in a differentiated neuroblastoma cell line, we determine that both slow and fast components of axonal transport are involved in the transport of aggregated ?-synuclein. In conclusion, we here provide the first experimental evidence that different ?-synuclein forms can propagate from the gut to the brain, and that microtubule-associated transport is involved in the translocation of aggregated ?-synuclein in neurons.
Synucleinopathies, characterized by intracellular aggregation of ?-synuclein protein, share a number of features in pathology and disease progression. However, the vulnerable cell population differs significantly between the disorders, despite being caused by the same protein. While the vulnerability of dopamine cells in the substantia nigra to ?-synuclein over-expression, and its link to Parkinson's disease, is well studied, animal models recapitulating the cortical degeneration in dementia with Lewy-bodies (DLB) are much less mature. The aim of this study was to develop a first rat model of widespread progressive synucleinopathy throughout the forebrain using adeno-associated viral (AAV) vector mediated gene delivery. Through bilateral injection of an AAV6 vector expressing human wild-type ?-synuclein into the forebrain of neonatal rats, we were able to achieve widespread, robust ?-synuclein expression with preferential expression in the frontal cortex. These animals displayed a progressive emergence of hyper-locomotion and dysregulated response to the dopaminergic agonist apomorphine. The animals receiving the ?-synuclein vector displayed significant ?-synuclein pathology including intra-cellular inclusion bodies, axonal pathology and elevated levels of phosphorylated ?-synuclein, accompanied by significant loss of cortical neurons and a progressive reduction in both cortical and striatal ChAT positive interneurons. Furthermore, we found evidence of ?-synuclein sequestered by IBA-1 positive microglia, which was coupled with a distinct change in morphology. In areas of most prominent pathology, the total ?-synuclein levels were increased to, on average, two-fold, which is similar to the levels observed in patients with SNCA gene triplication, associated with cortical Lewy body pathology. This study provides a novel rat model of progressive cortical synucleinopathy, showing for the first time that cholinergic interneurons are vulnerable to ?-synuclein over-expression. This animal model provides a powerful new tool for studies of neuronal degeneration in conditions of widespread cortical ?-synuclein pathology, such as DLB, as well an attractive model for the exploration of novel biomarkers.
Related JoVE Video
Journal of Visualized Experiments
What is Visualize?
JoVE Visualize is a tool created to match the last 5 years of PubMed publications to methods in JoVE's video library.
How does it work?
We use abstracts found on PubMed and match them to JoVE videos to create a list of 10 to 30 related methods videos.
Video X seems to be unrelated to Abstract Y...
In developing our video relationships, we compare around 5 million PubMed articles to our library of over 4,500 methods videos. In some cases the language used in the PubMed abstracts makes matching that content to a JoVE video difficult. In other cases, there happens not to be any content in our video library that is relevant to the topic of a given abstract. In these cases, our algorithms are trying their best to display videos with relevant content, which can sometimes result in matched videos with only a slight relation.