Enhanced IRE1α Phosphorylation/Oligomerization-Triggered XBP1 Splicing Contributes to Parkin-Mediated Prevention of SH-SY5Y Cell Death under Nitrosative Stress

Mutations in parkin, a neuroprotective protein, are the predominant cause of autosomal recessive juvenile Parkinson's disease. Neuroinflammation-derived nitrosative stress has been implicated in the etiology of the chronic neurodegeneration. However, the interactions between genetic predisposition and nitrosative stress contributing to the degeneration of dopaminergic (DA) neurons remain incompletely understood. Here, we used the SH-SY5Y neuroblastoma cells to investigate the function of parkin and its pathogenic mutants in relation to cell survival under nitric oxide (NO) exposure. The results showed that overexpression of wild-type parkin protected SH-SY5Y cells from NO-induced apoptosis in a reactive oxygen species-dependent manner. Under nitrosative stress conditions, parkin selectively upregulated the inositol-requiring enzyme 1oc/X-box binding protein 1 (IRE1oc/XBP1) signaling axis, an unfolded protein response signal through the sensor IRE1oc, which controls the splicing of XBP1 mRNA. Inhibition of XBP1 mRNA splicing either by pharmacologically inhibiting IRE1oc endoribonuclease activity or by genetically knocking down XBP1 interfered with the protective activity of parkin. Furthermore, pathogenic parkin mutants with a defective protective capacity showed a lower ability to activate the IRE1oc/XBP1 signaling. Finally, we demonstrated that IRE1oc activity augmented by parkin was possibly mediated through interacting with IRE1oc to regulate its phosphorylation/oligomerization processes, whereas mutant parkin diminished its binding to and activation of IRE1oc. Thus, these results support a direct link between the protective activity of parkin and the IRE1oc/XBP1 pathway in response to nitrosative stress, and mutant parkin disrupts this function.

Automated summary

This study reveals that mutations in the parkin gene contribute to the degeneration of dopaminergic neurons under nitrosative stress, while the normal parkin gene can protect the neurons from cell apoptosis induced by nitric oxide exposure. Furthermore, parkin enhances the protective function through the IRE1oc/XBP1 signaling pathway, while mutant parkin disrupts this function.