| dc.description.abstracteng | Synucleinopathies comprise a group of neurodegenerative diseases, characterized by deposits of aggregated alpha-synuclein (aSyn) in neurons and glia. The special hallmark is the presence of Lewy bodies and Lewy neuritis, in which Parkinson's disease is the most prevalent representative of this disease group. It is assumed, that misfolded oligomeric aSyn converts natively-folded monomeric in a templated-induced conversion process (prion-like way) into toxic oligomers, which can advance to the formation of pathologic fibrils. The cause of the misfolding is still unknown, such as the mechanism for the cell-to-cell spreading of pathologic aSyn is not yet completely understood.
In this work, we analyzed the effect of cellular prion protein (PrPC) on the internalization of aSyn. Secondary cells (SH-SY5Y) were treated with monomeric and oligomeric aSyn. The comparison of SH-SY5Y WT cells and stable PRNP transfected SH-SY5Y PrP cells, with an approximately 5-fold overexpression of PrPC showed a significantly higher amount of internalized oligomeric aSyn compared to SH-SY5Y WT cells. Fractionization of the cells into distinct compartments revealed a colocalization of both proteins in the cytosol.
Moreover, we explored the potential binding of aSyn and PrPC by surface plasmon resonance spectroscopy. Here, a stable direct binding affinity of PrPC could be measured for monomeric and oligomeric aSyn.
In vivo studies were conducted with transgenic mice (Tgm83 and ThySyn), exhibiting an aSyn pathology. Crossbreeding the aSyn mouse models with a PrP-KO line (Zurich I) resulted in new double transgenic mouse lines (TgmPrP00 and ThySynPrP00). We observed that PrPC depletion in these mice did not change the expression of transgenic aSyn nor the phosphorylation of the crucial Serine 129. Though, the analysis of the cell compartments of brain lysates revealed a different distribution of aSyn in the subcellular fractions. Mice lacking PrPC had an increased level of aSyn in the cytosol compared to aSyn transgenic mice with intact PrPC WT. In addition to the biochemical analysis, the behavior of these mouse lines was tested, resulting in the rescue of certain deficits induced by the pathological aSyn phenotype in PrPC deficient mice. To identify further proteins involved in aSyn internalization, brain lysates were used to analyze PrPC and aSyn via co-immunoprecipitation (Co-IP). Precipitation of aSyn was successfully tested for PrPC and vice versa has the precipitation of cellular prion resulted in the presence of aSyn. Furthermore, these Co-IPs were analyzed via mass spectrometry to identify additional involved proteins, possibly influencing the interaction of PrPC and aSyn. There, clathrin was successfully detected in both Co-IPs as a possible additional protein.
Altogether, our results implicate the involvement of PrPC as a receptor for aSyn, promoting the internalization and potentially the spreading of misfolded aSyn in a prion-like mechanism that may contribute to a better understanding of the pathological mechanism in synucleinopathies which is important for future therapies or diagnostics. | de |