Functionally different α-synuclein inclusions yield insight into Parkinson’s disease pathology (original) (raw)

The formation of α-synuclein (α-S) amyloid aggregates, called Lewy bodies (LBs), is a hallmark of Parkinson's disease (PD). The function of LBs in the disease process is however still unclear; they have been associated with both neuroprotection and toxicity. To obtain insight into this contradiction, we induced the formation of α-S inclusions, using three different induction methods in SH-SY5Y cells and rat-derived primary neuronal cells. Using confocal and STED microscopy we observed inductiondependent differences in α-S inclusion morphology, location and function. The aggregation of α-S in functionally different compartments correlates with the toxicity of the induction method measured in viability assays. The most cytotoxic treatment largely correlates with the formation of proteasomeassociated, juxta-nuclear inclusions. With less toxic methods cytosolic deposits that are not associated with the proteasome are more prevalent. The distribution of α-S over at least two different types of inclusions is not limited to cell models, but is also observed in primary neuronal cells and in human mesencephalon. The existence of functionally different LBs, in vivo and in vitro, gives important insights in the impact of Lewy Body formation on neuronal functioning and may thereby provide a platform for discovering therapeutics. The aggregation of soluble proteins into insoluble, β-sheet-rich amyloid fibrils is characteristic for many neurodegenerative diseases. Intraneuronal aggregates of α-synuclein (α-S) are for example found in Parkinson's disease (PD), Lewy body dementia and multiple system atrophy 1-3. Whereas extracellular β-amyloid deposits and intracellular accumulations of phosphorylated tau protein occur in Alzheimer's disease 4,5. In Huntington's disease, polyglutamine-expanded huntingtin (htt) protein accumulates within intranuclear inclusion bodies or neurites 6 and in amyotrophic lateral sclerosis, motor neurons develop protein-rich inclusions containing superoxide dismutase 1, TAR DNA-binding protein 43 or the RNA-binding protein fused-in-sarcoma in their cell bodies and axons 7-10. In PD, α-S amyloid inclusions such as Lewy neurites (LN) and Lewy bodies (LB) can be found in neurons and glia cells 2,3,11. The topographical progression of neuronal death, and the development of α-S immunoreactive Lewy body related structures 12,13 , here abbreviated to Lewy body like inclusions (LBLI), throughout the brain is used to stage PD pathology 14. The pathologically determined stages are in many cases related to clinical features observed in patients 15. Nevertheless, the role of LBLI during the progression of PD is unclear. LBLI may be indicative of cellular dysfunction and death 16,17 but have also been described as harmless, inert or neuroprotective protein aggregates 18. PD symptoms have been shown to directly correlate with the density of neurons in the substantia nigra pars compacta 19 , but no correlation could be established between the number of LBLI and the severity of disease symptoms 16. Assuming LBLI are indeed inert, one would expect the affected cells to have a normal life span. With the loss of other cells in the tissue 19 , the proportion of cells with LBLI should therefore