Research Article: E46K mutant α-synuclein is more degradation resistant and exhibits greater toxic effects than wild-type α-synuclein in Drosophila models of Parkinson’s disease

Date Published: June 26, 2019

Publisher: Public Library of Science

Author(s): Ryusuke Sakai, Mari Suzuki, Morio Ueyama, Toshihide Takeuchi, Eiko N. Minakawa, Hideki Hayakawa, Kousuke Baba, Hideki Mochizuki, Yoshitaka Nagai, Stephan N. Witt.

http://doi.org/10.1371/journal.pone.0218261

Abstract

Parkinson’s disease (PD) is one of the most common neurodegenerative diseases, which is characterized by progressive motor dysfunction as well as non-motor symptoms. Pathological and genetic studies have demonstrated that α-synuclein (αSyn) plays key roles in the pathogenesis of PD. Although several missense mutations in the αSyn gene have been identified as causes of familial PD, the mechanisms underlying the variance in the clinical phenotypes of familial PD caused by different mutations remain elusive. Here, we established novel Drosophila models expressing either wild-type (WT) αSyn or one of five αSyn mutants (A30P, E46K, H50Q, G51D, and A53T) using site-specific transgenesis, which express transgenes at equivalent levels. Expression of either WT or mutant αSyn in the compound eyes by the GMR-GAL4 driver caused mild rough eye phenotypes with no obvious difference among the mutants. Upon pan-neuronal expression by the nSyb-GAL4 driver, these αSyn-expressing flies showed a progressive decline in locomotor function. Notably, we found that E46K, H50Q, G51D, and A53T αSyn-expressing flies showed earlier onset of locomotor dysfunction than WT αSyn-expressing flies, suggesting their enhanced toxic effects. Whereas mRNA levels of WT and mutant αSyn were almost equivalent, we found that protein expression levels of E46K αSyn were higher than those of WT αSyn. In vivo chase experiments using the drug-inducible GMR-GeneSwitch driver demonstrated that degradation of E46K αSyn protein was significantly slower than WT αSyn protein, indicating that the E46K αSyn mutant gains resistance to degradation in vivo. We therefore conclude that our novel site-specific transgenic fly models expressing either WT or mutant αSyn are useful to explore the mechanisms by which different αSyn mutants gain toxic functions in vivo.

Partial Text

Parkinson’s disease (PD) is one of the most common neurodegenerative diseases, and is characterized by progressive motor dysfunction, such as resting tremor, bradykinesia, and rigidity, as well as non-motor symptoms, including olfactory deficit, autonomic dysfunction, and sleep disturbance. The pathological hallmark of PD is the loss of dopaminergic neurons in the substantia nigra, accompanied by the deposition of intraneuronal inclusions called Lewy bodies (LBs), which is comprised mainly of α-synuclein (αSyn). Although the majority of PD cases are sporadic, about 10% of cases are familial, and both missense and multiplication mutations in the αSyn gene (SNCA) were discovered to cause familial PD [1–4]. Moreover, genome-wide association studies identified single-nucleotide polymorphisms (SNPs) in the SNCA gene to be major risk factors for sporadic PD [5,6]. Considering these pathological and genetic findings, αSyn is thought to play key roles in the pathogenesis of PD.

In this study, we established novel Drosophila models expressing WT αSyn or αSyn mutants using site-specific transgenesis, which express transgenes at equivalent levels. We showed that flies expressing either E46K, H50Q, G51D, or A53T αSyn show earlier onset of locomotor dysfunction than flies expressing WT αSyn. We found that the expression level of the E46K αSyn protein was higher than that of WT αSyn, despite equivalent mRNA expression levels. In vivo chase experiments demonstrated that degradation of the E46K αSyn protein was significantly delayed compared with WT αSyn, indicating that the E46K αSyn has higher resistance to degradation than WT αSyn in vivo.

 

Source:

http://doi.org/10.1371/journal.pone.0218261