Role of manganese toxicity on endosomal trafficking, exosomal proteins and potential biomarkers identification for Parkinson\u27s disease

Parkinson\u27s disease (PD) is an enduring multifaceted neurological condition affecting 1% of the populace more than 60 years old, and its prevalence increases with increasing age. Approximately 1 million people in the United States and about 10 million worldwide live with PD (Foundation). Years of research and resulting constructive outcomes suggest that complicated interplay between environmental and genetic factors plays a crucial role in disease onset and progression. Considering -Synuclein (-Syn) aggregation in Lewy bodies and progressive loss of dopaminergic neurons in substantia nigra as the key aspects of the disease pathogenesis, while the physiological role of -Syn and factors affecting its aggregation and propagation remains debatable. With progression of the disease, Lewy body propagation and pathology can exist in neocortical and cortical areas of the brain. Manganese (Mn) is very well-known environmental and occupational metal toxicant that can affect central nervous system CNS leading to adverse neurological conditions, including PD. Multiple epidemiological studies involving humans exposed to excessive Mn through activities such as mining, dry-battery manufacturing, or welding have described links with PD like pathogenesis. Following the novel findings of our previous Mn- toxicity study that demonstrated -Syn aggregation and cell-to-cell transmission through exosomes, we carried out a comprehensive analysis of various molecular pathways involved in exosomal -Syn secretion. We also analyzed similar molecular pathways in astrocytes, key glial cell populations in adult CNS. Following findings about Mn toxicity and the role of exosomes in PD, we identified a potential serum exosomal biomarker useful for diagnostic purposes. Utilizing a dopaminergic cell αSyn-expressing model, we demonstrated that Mn exposure compromises the endosomal trafficking pathway by affecting key Rab proteins and also impairs -Syn degradation mechanisms. Chronic and persistent neuroinflammation has been associated with neurodegenerative diseases and many other pathological conditions, and Mn exposure induces neuroinflammation, ultimately leading to neurotoxicity. Astrocytes accumulate greater amounts of Mn than other cell types in adult CNS, so astrocytes are crucial targets for Mn-induced toxicity. Following our findings of Mn\u27s role in endosomal trafficking and Rab proteins that increases release of exosomal -Syn from neuronal cells, we analyzed Rab proteins and exosome release in U373 astrocytes. We observed that Mn exposure induces release of a significantly high number of exosomes through regulating Rab11a and Rab27a proteins, and results from this study also demonstrated that Mn affects metal transporters such as ATP13a2 and SLC30A10 in U373 astrocytes. Exosomes released from Mn-exposed U373 astrocytes contain increased amounts of key proteins involved in PD pathogenesis. Clinical symptoms of PD occur late in the disease progression, and by that time the major amount of neuronal damage has already occurred, making treatment of PD at late stages impossible. Finding reliable biomarkers for the diagnostic purpose would therefore provide a crucial tool for use in the field. We for the first time demonstrate that serum exosomes from pesticide-exposed farmers as well as PD patients have significantly higher acetylated APOA1, so acetylated APOA1 could be a possible reliable and less invasive biomarker. Together these exciting results provide significant insight into the role of Mn, exosomes, and exosomal proteins in neurodegenerative diseases such as Parkinson\u27s disease