α-Synuclein Over-Expression Induces Increased Iron Accumulation and Redistribution in Iron-Exposed Neurons

Parkinson's disease is the most common alpha-synucleinopathy, and increased levels of iron are found in the substantia nigra of Parkinson's disease patients, but the potential interlink between both molecular changes has not been fully understood. Metal to protein binding assays have shown that alpha-synuclein can bind iron in vitro; therefore, we hypothesized that iron content and iron distribution could be modified in cellulo, in cells over-expressing alpha-synuclein. Owing to particle-induced X-ray emission and synchrotron X-ray fluorescence chemical nano-imaging, we were able to quantify and describe the iron distribution at the subcellular level. We show that, in neurons exposed to excess iron, the mere over-expression of human alpha-synuclein results in increased levels of intracellular iron and in iron redistribution from the cytoplasm to the perinuclear region within alpha-synuclein-rich inclusions. Reproducible results were obtained in two distinct recombinant expression systems, in primary rat midbrain neurons and in a rat neuroblastic cell line (PC12), both infected with viral vectors expressing human alpha-synuclein. Our results link two characteristic molecular features found in Parkinson's disease, the accumulation of alpha-synuclein and the increased levels of iron in the substantia nigra.