Actinomyces viscosus promotes neuroprotection in C. elegans models of Parkinson's disease.

Parkinson's Disease is characterized by selective degeneration of dopaminergic neurons, primarily in the substantia nigra pars compacta, as well as accumulation of alpha-synuclein enriched protein aggregates within neurons. The pathogenesis of PD is still not completely understood, and no treatments exist that alter disease progression. Obvious genetic causes are detected in only a small number of PD patients (5-10 %), suggesting that environmental factors play a significant role the development of PD. Correlative studies suggest that the microbiota could be an important environmental modifier of neurodegeneration. We identified a microbiotal isolate, Actinomyces viscosus, that reduced neurodegeneration in C. elegans expressing a pathological mutant form (G2019S) of leucine-rich repeat kinase 2 (LRRK2) in dopaminergic neurons. A. viscosus also suppressed autophagic dysfunction in these animals and reduced alpha-synuclein aggregation in a synucleinopathy model. Global gene expression analysis revealed increased expression of aspartic cathepsins in response to A. viscosus. Consistent with the involvement of these proteins in neuroprotection, we found that reducing aspartic cathepsin function increased neurodegeneration in the LRRK2 transgenic model. Our findings contribute to the current understanding of how the gut microbiota may influence PD, elucidating one potential mechanism of microbiota-mediated neuroprotection.