Nuclear α-Synuclein-Derived Cytotoxic Effect via Altered Ribosomal RNA Processing in Primary Mouse Embryonic Fibroblasts

alpha-Synuclein (alpha Syn) is an important player in Parkinson's disease (PD) pathogenesis. The aggregation of alpha Syn is mainly formed in the cytoplasm, whereas some alpha Syn accumulation has also been found in the nuclei of neurons. To assess the effect of nuclear alpha Syn, we generated alpha Syn conjugated with a nuclear export signal (NES) or a nuclear localization signal (NLS), and compared them with wild-type alpha Syn in primary mouse embryonic fibroblasts (MEF) using DNA transfection. Overexpression of NLS-alpha Syn increased cytotoxicity. The levels of apoptotic markers were increased by NLS-alpha Syn in MEF. Interestingly, an increase in the levels of 40S ribosomal protein 15 was observed in MEF expressing NLS-alpha Syn. These MEF also showed a higher 28S/18S rRNA ratio. Intriguingly, the expression of NLS-alpha Syn in MEF enhanced segmentation of nucleolin (NCL)-positive nucleolar structures. We also observed that the downregulation of NCL, using shRNA, promoted a relatively higher 28S/18S rRNA ratio. The reduction in NCL expression accelerated the accumulation of alpha Syn, and NCL transfection enhanced the degradation of alpha Syn. These results suggest that nuclear alpha Syn contributes to the alteration in ribosomal RNA processing via NCL malfunction-mediated nucleolar segmentation, and that NCL is a key factor for the degradation of alpha Syn.

Automated summary

This study found that nuclear alpha-Synuclein (alpha Syn) plays an important role in the pathogenesis of Parkinson's disease (PD). Overexpression of alpha Syn conjugated with a nuclear localization signal (NLS) increased cytotoxicity and apoptotic markers in mouse embryonic fibroblasts (MEF). The presence of NLS-alpha Syn also led to changes in nucleolar structure and abnormal ribosomal RNA processing.