|M.Sc Student||Mekies Lucy Naomi|
|Subject||Role of Synphilin-1 on the Cellular Pathway of PINK1 and|
Parkin: Implications for Mitochondrial Dysfunction
in Parkinson's Disease
|Department||Department of Medicine||Supervisor||Professor Simone Engelender|
|Full Thesis text|
Parkinson's disease (PD) is one of the most common neurodegenerative disorders. It is characterized by the loss of dopaminergic neurons located in the substantia nigra pars compacta (SNpc) in the midbrain and the presence of cytoplasmic protein inclusions termed Lewy bodies (LBs) in surviving neurons. α-Synuclein was the first gene identified to be mutated in autosomal dominant PD. It is also the major component of LBs in the sporadic form of the disease, supporting its general role in PD. Synphilin-1 interacts in vivo with α-synuclein and leads to the formation of cytoplasmic inclusions resembling LBs. Ubiquitination of synphilin-1 by the E3 ubiquitin-ligase SIAH leads to its degradation by the proteasome. Furthermore, accumulation of ubiquitinated synphilin-1 leads to the formation of cellular inclusions. PTEN-induced kinase1 (PINK1) is involved in autosomal recessive and early-onset PD. It protects cells against several toxic insults and disease-mutations abrogate PINK1 ability to protect cells from toxic insults, suggesting that dysfunction of PINK1 might play a role in the pathogenesis of PD. Similar to PINK1, knockout of parkin, another gene involved in PD, was shown to promote mitochondrial impairment. Moreover, recent findings demonstrate that the translocation of parkin to damaged mitochondria is promoted by PINK1. Once recruited, parkin leads to increased mitochondrial degradation by autophagy, a process known as mitophagy. We obtained in our laboratory data showing that PINK1 interacts with synphilin-1 and decreases its steady-state levels. Therefore, we sought to investigate if this decrease is due to degradation of synphilin-1 by PINK1 or rather to co-aggregation of synphilin-1 and PINK1. Our results show that PINK1 promotes synphilin-1 degradation. We also investigated the interaction of synphilin-1 with PINK1 disease-mutants and determined the degradation rate of synphilin-1 by PINK1 WT and disease-mutants. We found that PINK1 disease-mutants interact less with synphilin-1 and decrease to a smaller extent the steady-state of synphilin-1 compared to PINK1 WT. In addition, PINK1 increased the translocation of synphilin-1 to the mitochondria, suggesting that PINK1 plays an important role in bringing synphilin-1 to the mitochondria. Understanding the relevance of PINK1/synphilin-1 interaction and its role in maintaining mitochondrial function and mitophagy may help shed light on the molecular events that underlie PD.