Administration of LPS-stimulated autologous macrophages induces α-synuclein aggregation in dopaminergic neurons of rat brain

Review: The Role of Intestinal Dysbiosis in Parkinson's Disease

Several studies have highlighted the roles played by the gut microbiome in central nervous system diseases. Clinical symptoms and neuropathology have suggested that Parkinson’s disease may originate in the gut, which is home to approximately 100 trillion microbes. Alterations in the gastrointestinal microbiota populations may promote the development and progression of Parkinson’s disease. Here, we reviewed existing studies that have explored the role of intestinal dysbiosis in Parkinson’s disease, focusing on the roles of microbiota, their metabolites, and components in inflammation, barrier failure, microglial activation, and α-synuclein pathology. We conclude that there are intestinal dysbiosis in Parkinson’s disease. Intestinal dysbiosis is likely involved in the pathogenesis of Parkinson’s disease through mechanisms that include barrier destruction, inflammation and oxidative stress, decreased dopamine production, and molecular mimicry. Additional studies remain necessary to explore and verify the mechanisms through which dysbiosis may cause or promote Parkinson’s disease. Preclinical studies have shown that gastrointestinal microbial therapy may represent an effective and novel treatment for Parkinson’s disease; however, more studies, especially clinical studies, are necessary to explore the curative effects of microbial therapy in Parkinson’s disease.

Trans-synaptic and retrograde axonal spread of Lewy pathology following pre-formed fibril injection in an in vivo A53T alpha-synuclein mouse model of synucleinopathy

It is necessary to develop an understanding of the specific mechanisms involved in alpha-synuclein aggregation and propagation to develop disease modifying therapies for age-related synucleinopathies, including Parkinson's disease and Dementia with Lewy Bodies. To adequately address this question, we developed a new transgenic mouse model of synucleinopathy that expresses human A53T SynGFP under control of the mouse prion protein promoter. Our characterization of this mouse line demonstrates that it exhibits several distinct advantages over other, currently available, mouse models. This new model allows rigorous study of the initial location of Lewy pathology formation and propagation in the living brain, and strongly suggests that aggregation begins in axonal structures with retrograde propagation to the cell body. This model also shows expeditious development of alpha-synuclein pathology following induction with small, in vitro-generated alpha-synuclein pre-formed fibrils (PFFs), as well as accelerated cell death of inclusion-bearing cells. Using this model, we found that aggregated alpha-synuclein somatic inclusions developed first in neurons, but later showed a second wave of inclusion formation in astrocytes. Interestingly, astrocytes appear to survive much longer after inclusion formation than their neuronal counterparts. This model also allowed careful study of peripheral-to-central spread of Lewy pathology after PFF injection into the hind limb musculature. Our results clearly show evidence of progressive, retrograde trans-synaptic spread of Lewy pathology through known neuroanatomically connected pathways in the motor system. As such, we have developed a promising tool to understand the biology of neurodegeneration associated with alpha-synuclein aggregation and to discover new treatments capable of altering the neurodegenerative disease course of synucleinopathies.

Gut, oral and nasal microbiota and Parkinson's disease

Parkinson’s disease (PD) is the second most prevalent neurodegenerative disease, and in an effort to identify novel therapeutic target for this disease in recent years, human microbiota has attracted much interest. This paper briefly summarizes the main findings concerning the differences of human microbiome across several important mucosal interfaces, including nose, mouth, and gut between PD patients and controls as obtained from a total of 13 studies published since 2015, which covered a total of 943 PD patients and 831 matched controls from 6 countries. Overall, these studies supported the differences of gut microbiota between PD patients and matched controls, while significantly altered bacterial taxa among studies were not identical. Due to relatively limited number of available studies and covered patients, the associations between oral and nasal microbiota and PD remain inconclusive. The therapeutic and diagnostic potentials of gut microbiota for PD are discussed. More well-designed clinical studies recruiting large-scale PD patients are encouraged in future.

Neuroimmunological processes in Parkinson's disease and their relation to α-synuclein: microglia as the referee between neuronal processes and peripheral immunity

The role of neuroinflammation and the adaptive immune system in PD (Parkinson's disease) has been the subject of intense investigation in recent years, both in animal models of parkinsonism and in post-mortem PD brains. However, how these processes relate to and modulate α-syn (α-synuclein) pathology and microglia activation is still poorly understood. Specifically, how the peripheral immune system interacts, regulates and/or is induced by neuroinflammatory processes taking place during PD is still undetermined. We present herein a comprehensive review of the features and impact that neuroinflamation has on neurodegeneration in different animal models of nigral cell death, how this neuroinflammation relates to microglia activation and the way microglia respond to α-syn in vivo. We also discuss a possible role for the peripheral immune system in animal models of parkinsonism, how these findings relate to the state of microglia activation observed in these animal models and how these findings compare with what has been observed in humans with PD. Together, the available data points to the need for development of dual therapeutic strategies that modulate microglia activation to change not only the way microglia interact with the peripheral immune system, but also to modulate the manner in which microglia respond to encounters with α-syn. Lastly, we discuss the immune-modulatory strategies currently under investigation in animal models of parkinsonism and the degree to which one might expect their outcomes to translate faithfully to a clinical setting.