The Parkinson disease-associated A30P mutation stabilizes alpha-synuclein against proteasomal degradation triggered by heme oxygenase-1 over-expression in human neuroblastoma cells

Manganese induces the overexpression of α-synuclein in PC12 cells via ERK activation

Manganese has been known to induce neurological disorders. In the present study, we determined the effect of manganese on the expression of α-synuclein in PC12 cells and its role in manganese-induced cytotoxicity. We also investigated the relationship between α-synuclein expression and the change of ERK1/2 MAPK activity. In our research, manganese exposure induced the overexpression of α-synuclein, while siRNA knockdown of α-synuclein reversed manganese-induced cytotoxicity. Furthermore, manganese induced the activation of ERK1/2 MAPK. The MEK1 inhibitor PD98059, which inhibits the activation of ERK MAPK, attenuated the overexpression of α-synuclein and the cytotoxicity induced by manganese. In conclusion, our studies show that manganese may induce the overexpression of α-synuclein via ERK1/2 activation, which may play a role in manganese-induced cytotoxicity.

Alpha-synuclein aggregation is involved in the toxicity induced by ferric iron to SK-N-SH neuroblastoma cells

Increased nigral iron levels and intracytoplasmic Lewy bodies (LBs) in the degenerating neurons are found in Parkinson's disease (PD). Whether LBs formation is involved in the toxicity of iron is largely unknown. In the present study, we observed that the toxicity of ferric iron was enhanced when SK-N-SH cells were overexpressed with wild-type alpha-synuclein. The mitochondrial transmembrane potential (Δψ(m)) and cell viability were decreased in these cells, while the intracellular reactive oxygen species (ROS) were increased, compared with that of control. More aggregated alpha-synuclein was observed in these cells. However, while silencing the expression of alpha-synuclein in SK-N-SH cells with siRNA, iron-induced toxicity could be partially alleviated, indicated by the returned Δψ(m) and cell viability and reduced ROS formation compared with that of control. No alpha-synuclein aggregation could be observed in these cells. The results suggest that alpha-synuclein aggregation was involved in the toxicity of iron to SK-N-SH neuroblastoma cells. Targeting the aggregation of alpha-synuclein might provide a therapeutic strategy for PD in the future.

Low-dose bafilomycin attenuates neuronal cell death associated with autophagy-lysosome pathway dysfunction

We have shown previously that the plecomacrolide antibiotics bafilomycin A1 and B1 significantly attenuate cerebellar granule neuron death resulting from agents that disrupt lysosome function. To further characterize bafilomycin-mediated cytoprotection, we examined its ability to attenuate the death of naïve and differentiated neuronal SH-SY5Y human neuroblastoma cells from agents that induce lysosome dysfunction in vitro, and from in vivo dopaminergic neuron death in C. elegans. Low-dose bafilomycin significantly attenuated SH-SY5Y cell death resulting from treatment with chloroquine, hydroxychloroquine amodiaquine and staurosporine. Bafilomycin also attenuated the chloroquine-induced reduction in processing of cathepsin D, the principal lysosomal aspartic acid protease, to its mature 'active' form. Chloroquine induced autophagic vacuole accumulation and inhibited autophagic flux, effects that were attenuated upon treatment with bafilomycin and were associated with a significant decrease in chloroquine-induced accumulation of detergent-insoluble alpha-synuclein oligomers. In addition, bafilomycin significantly and dose-dependently attenuated dopaminergic neuron death in C. elegans resulting from in vivo over-expression of human wild-type alpha-synuclein. Together, our findings suggest that low-dose bafilomycin is cytoprotective in part through its maintenance of the autophagy-lysosome pathway, and underscores its therapeutic potential for treating Parkinson's disease and other neurodegenerative diseases that exhibit disruption of protein degradation pathways and accumulation of toxic protein species.