Multiomic Analysis Reveals Molecular Pathways Associated with Intestinal Aggregation of α‑Synuclein

Aggregates of the protein α-synuclein may initially
form
in the gut before propagating to the brain in Parkinson’s disease
(PD). Indeed, our prior work supports that enteroendocrine cells,
specialized intestinal epithelial cells, could play a key role in
the development of this disease. Enteroendocrine cells natively express
α-synuclein and form synapses with enteric neurons as well as
the vagus nerve. Severing the vagus nerve reduces the load of α-synuclein
aggregates in the brain, suggesting that this nerve is a conduit for
gut-to-brain spread. Enteroendocrine cells line the gut lumen; as
such, they are in constant contact with metabolites of the gut microbiota.
We previously found that when enteroendocrine cells are exposed to
nitritea potent oxidant produced by gut bacterial Enterobacteriaceaea biochemical pathway is initiated
that results in α-synuclein aggregation. Here, we detail the
cellular and molecular mechanisms involved. First, we holistically
profiled nitrite-exposed enteroendocrine cells through untargeted
proteomics. Next, we performed targeted analyses that specifically
probed the mechanistic role of dopamine, as our prior findings suggested
that dopamine is critical for nitrite-induced α-synuclein aggregation.
In dopamine-free HeLa cells treated with nitrite, α-synuclein
aggregation was indeed suppressed. Proteomic signatures in dopamine-free
cells treated with nitrite were distinct from those in nitrite-treated
enteroendocrine cells, highlighting pathways relevant to intestinal
development of PD. Intriguingly, we observed that enteroendocrine
cells maintain viability upon exposure to nitrite and in the presence
of α-synuclein aggregates. This cellular robustness suggests
that these cells may be a reservoir of toxic α-synuclein aggregates.
As a possible antidote, our findings show that benserazide and α-methyl
tyrosinechemical inhibitors of dopamine biosynthesislimited
aggregation. Curious about mechanisms of disease etiology outside
of α-synuclein aggregation, we also profiled the enteroendocrine
cell lipidomean emerging area of interest in PD researchto
motivate future targeted studies delineating the roles of dysregulated
lipid metabolism in disease onset. Overall, these studies lay a foundation
for mechanistically informed therapeutic targets to prevent the intestinal
formation of α-synuclein aggregates before they spread to the
brain.