Degree Type

Dissertation

Date of Award

2016

Degree Name

Doctor of Philosophy

Department

Biomedical Sciences

Major

Toxicology

First Advisor

Anumantha G. Kanthasamy

Abstract

Parkinson's disease (PD) is a chronic multifaceted neurodegenerative condition caused by a complex interplay of genetic and environmental factors that affects about 1% of people over the age of 60. Although the progressive loss of dopaminergic neurons and accumulation of aggregated α-Synuclein (αSyn) protein in Lewy bodies are considered key pathophysiological features of the disease, the physiological function of αSyn and the molecular mechanisms leading to protein aggregation and propagation remain unknown. Manganese (Mn) is considered a key inhaled pollutant implicated in environmentally-linked PD as evidenced by epidemiological studies done on humans exposed to Mn during mining, welding metals, and dry battery manufacturing. However, the exact molecular mechanisms underlying Mn-induced protein aggregation are not well understood. Considering the role of the divalent metal Mn in PD-like neurological disorders, we conducted a comprehensive characterization of the role of αSyn in Mn-induced dopaminergic neurotoxicity, cell-to-cell spreading of αSyn protein aggregates and aberrant miRNA delivery via exosomes. Using an αSyn-expressing dopaminergic cell model, we show that wildtype αSyn significantly attenuates Mn-induced neurotoxicity during the early stages of exposure while prolonged Mn exposure promotes αSyn aggregation and dampens its neuroprotective effect. Our subsequent studies show that upon Mn exposure, misfolded αSyn-containing exosomes are released to its extracellular milieu, which may in turn induce neuroinflammatory, and neurodegenerative responses in cell culture and animal models of PD. We also found enhanced accumulation of misfolded αSyn species in serum exosomes of welders exposed to Mn indicating the possibility of using exosomes as biomarkers of Mn-neurotoxicity. To further elucidate the regulatory role of exosomes in Mn-induced miRNA dysregulation, we performed next-generation miRNA sequencing and identified multiple differentially expressed miRNAs in Mn-stimulated exosomes in contrast to control exosomes. Herein, our results suggest that Mn induces a novel mechanism of cell injury through modulating the protein and miRNA cargo in exosomes and altering gene expression. This may contribute to the cell-to-cell transmission of the aggregated αSyn protein and progression on neurodegeneration.

Copyright Owner

Dilshan Shanaka Gurunnaselage Don

Language

en

File Format

application/pdf

File Size

357 pages

Available for download on Saturday, April 21, 2018

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