Parkinson's and Prokaryotes: roles of bacteria, gut permeability, innate immunity, and genetics in C. elegans dopaminergic neurodegeneration

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Abstract Parkinson’s disease (PD), characterized by the degeneration of dopaminergic (DA) neurons via 𝛼-Synuclein (𝛼S) aggregation, costs $51.9 billion annually in the US and is predicted to affect 1.2 million Americans by 2030. Current treatments only provide limited and symptomatic relief, with no functional cure, largely due to the mysterious nature in which PD is initiated. Thus, a deeper, mechanistic understanding of PD pathogenesis is vital for effective treatment. An emerging hypothesis is that PD begins in the gut, where 𝛼S aggregates spread from the gut to the brain via routes like the vagus nerve. Interestingly, these 𝛼S aggregates are detected in the gut years before PD diagnosis. In addition, gut permeability and dysfunction are common in PD patients. Although these intestinal pathologies likely lead to in the translocation of gut bacteria and microbe-associated molecular patterns (MAMPs) into host tissues and subsequent induction of inflammation via innate immune receptor activation, this has not been directly investigated. Thus, the role of gut bacteria and innate immune receptors in 𝛼S aggregation and PD progression is unclear. Furthermore, mammalian models for PD like mice are biologically complex, harbor a diverse gut microbiota, and cannot undergo unbiased mutagenesis screens to identify novel PD factors. Thus, a minimalist model which is genetically tractable and permits mutagenesis screens for both the host and individual microbes would empower identification of novel host and bacterial factors crucial to PD pathogenesis. To this end, I propose to use the nematode Caenorhabditis elegans, a model organism widely used in disease study and PD research, to investigate how gut bacteria may trigger inflammatory responses that exacerbate DA neurodegeneration. The particular model that I will use co-expresses human 𝛼S and GFP in DA neurons, causing a progressive loss of DA neurons as indicated by GFP signal loss. My proposed studies will use the CRISPR-Cas9 genome editing technique to inactivate genes crucial for gut barrier integrity and innate immune receptors and then investigate the spatial role of these genes in PD pathogenesis by monitoring fluorescently- labeled 𝛼S and GFP-labeled DA neurons. Furthermore, bacterial species or specific MAMPs will be individually given to C. elegans as bacterial food sources or treatments, respectively, to identify what bacterial characteristics may enhance or suppress PD. Lastly, I will conduct mutagenesis screens on C. elegans and individual bacterial lawns to identify novel host and bacterial factors, respectively, which either promote or inhibit PD progression. My proposed study will help identify novel therapeutic targets and treatments to block or potentially reverse PD, using C. elegans as a cost-efficient screening tool. This project is highly interdisciplinary, combining immunology, neurobiology, microbiology, enteric biology, and genetics. This strategy improves the possibility of identifying novel factors and treatments which affect PD pathogenesis.