a-synuclein (a-SYN) aggregates in Lewy bodies and Lewy neurites are the pathological hallmarks of Parkinson's Disease (PD) and are found in both the brain and the nervous system innervating the gut. Mounting evidence supports "the gut hypothesis for PD pathogenesis," which posits that a-SYN pathology starts in the gut at the early stage of the disease before the typical motor manifestations emerge and spreads to the brain in later stages when the disease becomes clinically apparent. However, the molecular underpinnings of how a-SYN starts to aggregate in the gut remains unknown. Toxic environment exposures in the gut may cause perturbations in the intestinal homeostasis and initiate a-SYN aggregation in neurons of the gut (enteric neurons), and aggregates propagate into the brain through the nervous system that connects the gut and the brain.

Rotenone is a widely used pesticide, which according to a U.S. Agricultural Health Study increases the risk of PD by about 2.5-fold with duration positively correlating with the development of PD. Oral administration of rotenone in a mouse PD model generates a-SYN aggregates in gut neurons that spread to the brain. NADPH oxidase 1 (Nox1) is a superoxide-generating enzyme that is highly expressed in gut cells known as epithelial cells, especially in the colon. In our previous studies, we have found for the first time that reactive oxygen species (ROS) derived from Nox1 in dopamine-producing neurons in the brain that degenerate in PD play key roles in their demise. We have established a new mouse PD model by injecting low-dose rotenone in the gut that is not associated with systemic effects. These mice develop a-SYN aggregates in the gut, loss of midbrain dopaminergic neurons in the brain, and motor deficits; all these were ameliorated in mice that lacked the Nox1 gene. Our results support the notion that Nox1 is a key player in the initial a-SYN pathology in the gut induced by environmental toxins.

The proposed study will investigate how Nox1-derived ROS contributes to early-stage a-SYN aggregation in the gut using an innovative cell-to-cell a-SYN propagation assay and gut cell-specific Nox1-deleted mouse model. We will also test a potent and selective Nox1 inhibitor, ML171, in our gut - brain PD model. Successful completion of the project will elucidate the molecular mechanisms underpinning how a-SYN aggregation is initiated in the gut and to what extent Nox1 plays a role in this process. Moreover, the proposed study could identify a specific Nox1 inhibitor as a novel therapeutic intervention to prevent gut-driven PD development.