okadaic-acid and Parkinson-Disease

α-Synuclein (a-Syn) is a major component of fibrillar aggregates in Lewy bodies (LBs), a characteristic hallmark of Parkinson disease. Almost 90% of a-Syn deposited in LBs is phosphorylated at Ser-129. However, the role of Ser-129-phosphorylated a-Syn in the biogenesis of LBs remains unclear. Here, we investigated the metabolism of Ser-129-phosphorylated a-Syn. In SH-SY5Y cells, inhibition of protein phosphatase 2A/1 by okadaic acid, and inhibition of the proteasome pathway by MG132 or lactacystin accumulated Ser-129-phosphorylated a-Syn. However, these inhibitions did not alter the amounts of total a-Syn within the observation time. Inhibition of the autophagy-lysosome pathway by 3-methyladenine or chloroquine accumulated Ser-129-phosphorylated a-Syn in parallel to total a-Syn during longer incubations. Experiments using cycloheximide showed that Ser-129-phosphorylated a-Syn diminished rapidly (t(½) = 54.9 ± 6.4 min), in contrast to the stably expressed total a-Syn. The short half-life of Ser-129-phosphorylated a-Syn was blocked by MG132 to a greater extent than okadaic acid. In rat primary cortical neurons, either MG132, lactacystin, or okadaic acid accumulated Ser-129-phosphorylated a-Syn. Additionally, we did not find that phosphorylated a-Syn was ubiquitinated in the presence of proteasome inhibitors. These data show that Ser-129-phosphorylated a-Syn is targeted to the proteasome pathway in a ubiquitin-independent manner, in addition to undergoing dephosphorylation. The proteasome pathway may play a role in the biogenesis of Ser-129-phosphorylated a-Syn-rich LBs.

Topics: Acetylcysteine; alpha-Synuclein; Animals; Cell Line, Tumor; Cerebral Cortex; Cycloheximide; Cysteine Proteinase Inhibitors; Humans; Leupeptins; Lewy Bodies; Neurons; Okadaic Acid; Parkinson Disease; Phosphorylation; Proteasome Endopeptidase Complex; Proteasome Inhibitors; Protein Phosphatase 1; Protein Phosphatase 2; Protein Synthesis Inhibitors; Rabbits; Ubiquitin

1-methyl-4-phenylpyridinium ion (MPP(+)) has been shown to selectively inhibit mitochondrial function and induce a parkinsonism-like syndrome. MPP(+) stimulates the production of reactive oxygen species (ROS) and induces cell death in vitro. In this study, we investigated the protective effects of okadaic acid on MPP(+)-induced cell death in SH-SY5Y neuroblastoma cells. We found that MPP(+)-induced apoptosis and -ROS generation were blocked by okadaic acid. MPP(+)-mediated activation of AKT was also inhibited by okadaic acid. Taken together, these results demonstrate that okadaic acid protects against MPP(+)-induced apoptosis by blocking ROS stimulation and ROS-mediated signaling pathways in SH-SY5Y cells. These data indicated that okadaic acid could provide a therapeutic strategy for the treatment of neurodegenerative diseases including Parkinson's disease.

Topics: 1-Methyl-4-phenylpyridinium; Apoptosis; Cell Line, Tumor; Cytoprotection; Enzyme Inhibitors; Herbicides; Humans; Nerve Degeneration; Neuroblastoma; Neurons; Neuroprotective Agents; Okadaic Acid; Oxidative Stress; Parkinson Disease; Protein Phosphatase 2; Proto-Oncogene Proteins c-akt; Reactive Oxygen Species; Signal Transduction