Nano-imaging trace elements at organelle levels in substantia nigra overexpressing alpha-synuclein to model Parkinson's disease

Sub-cellular trace element quantifications of nano-heterogeneities in brain tissues offer unprecedented ways to explore at elemental level the interplay between cellular compartments in neurodegenerative pathologies. We designed a quasi-correlative method for analytical nanoimaging of the substantia nigra, based on transmission electron microscopy and synchrotron X-ray fluorescence. It combines ultrastructural identifications of cellular compartments and trace element nanoimaging near detection limits, for increased signal-to-noise ratios. Elemental composition of different organelles is compared to cytoplasmic and nuclear compartments in dopaminergic neurons of rat substantia nigra. They exhibit 150-460 ppm of Fe, with P/Zn/Fe-rich nucleoli in a P/S-depleted nuclear matrix and Ca-rich rough endoplasmic reticula. Cytoplasm analysis displays sub-micron Fe/S-rich granules, including lipofuscin. Following AAV-mediated overexpression of alpha -synuclein protein associated with Parkinson's disease, these granules shift towards higher Fe concentrations. This effect advocates for metal (Fe) dyshomeostasis in discrete cytoplasmic regions, illustrating the use of this method to explore neuronal dysfunction in brain diseases. Lemelle et al. describe the use of TEM and synchrotron X-ray fluorescence for quasi-correlative nanoimaging and sub-cellular trace element quantification of rat brain tissue. They further observe elemental (iron and sulfur) dyshomeostasis in cytoplasmic granules when overexpressing alpha -synuclein protein associated with Parkinson's disease, demonstrating the usefulness of this method to further explore dysfunctions at organelle levels in brain diseases.