The effects of pdr1, djr1.1 and pink1 loss in manganese-induced toxicity and the role of α-synuclein in C-elegans

Parkinson's disease (PD) is a neurodegenerative brain disorder characterized by selective dopaminergic (DAergic) cell loss that results in overt motor and cognitive deficits. Current treatment options exist to combat PD symptomatology, but are unable to directly target its pathogenesis due to a lack of knowledge concerning its etiology. Several genes have been linked to PD, including three genes associated with an early-onset familial form: parkin, pink1 and dj1. All three genes are implicated in regulating oxidative stress pathways. Another hallmark of PD pathophysiology is Lewy body deposition, associated with the gain-of-function genetic risk factor a-synuclein. The function of a-synuclein is poorly understood, as it shows both neurotoxic and neuroprotective activities in PD. Using the genetically tractable invertebrate Caenorhabditis elegans (C. elegans) model system, the neurotoxic or neuroprotective role of a-synuclein upon acute Mn exposure in the background of mutated pdr1, pink1 or djr1.1 was examined. The pdr1 and djr1.1 mutants showed enhanced Mn accumulation and oxidative stress that was reduced by a-synuclein. Moreover, DAergic neurodegeneration, while unchanged with Mn exposure, returned to wild-type (WT) levels for pdr1, but not djr1.1 mutants expressing a-synuclein. Taken together, this study uncovers a novel, neuroprotective role for WT human a-synuclein in attenuating Mn-induced toxicity in the background of PD-associated genes, and further supports the role of extracellular dopamine in exacerbating Mn neurotoxicity.