α-Synuclein Promotes the Recruitment of Tau to Protein Inclusions in Oligodendroglial Cells: Effects of Oxidative and Proteolytic Stress
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- Riedel, M., Goldbaum, O. & Richter-Landsberg, C. J Mol Neurosci (2009) 39: 226. doi:10.1007/s12031-009-9190-y
α-Synuclein is the major building block of cytoplasmic inclusions in neurodegenerative disorders named synucleinopathies. These inclusion bodies often contain the small heat shock protein αB-crystallin and the microtubule-associated protein tau. Oxidative modification of α-synuclein has been linked to fibril formation, and α-synuclein aggregation may induce the fibrillization of tau. To study α-synuclein aggregate formation, we have engineered oligodendroglial cells (OLN-93 cells) to stably express the longest human isoform of tau and wild-type α-synuclein or the A53T α-synuclein mutation. Under normal growth conditions, small punctuated α-synuclein aggregates were formed, which were more abundant in cells expressing the A53T mutation. After exposure to oxidative stress, protein inclusions were enlarged and were positive for thioflavin S, but the solubility of α-synuclein was not altered. Oxidative stress followed by proteasomal inhibition caused the occurrence of larger thioflavin S-positive inclusions, immunoreactive for tau and αB-crystallin, thus resembling glial cell inclusion bodies. Furthermore, this double stress situation led to a decrease in α-synuclein solubility, and αB-crystallin and HSP90 were present in the insoluble fraction. The formation and recruitment of tau to thioflavin S-positive protein aggregates in OLN-93 cells only expressing tau in the absence of α-synuclein, either after oxidative or proteasomal stress or both, was not observable. The data indicate that oxidatively modified α-synuclein is degraded by the proteasome and that it plays a pro-aggregatory role for tau in this cell culture model system.