Genetic epidemiology and functional study of LRRK2 gene in the pathogenesis of Parkinson’s Disease by using Drosophila as a model system
Date Issued
2010
Date
2010
Author(s)
Lin, Chin-Hsien
Abstract
Background
Parkinson’s disease (PD) is one of the most common neurodegenerative disorders,
with a prevalence close to 1% after age 65. Causal genes for Mendelian-inherited PD
have been reported. The recent discovery of LRRK2 (Leucine-rich repeat kianse 2) as a causative PD gene has provided insights into the pathophysiology of the disease. Because the clinical phenotype of LRRK2 mutations resembles idiopathic PD, LRRK2 has emerged as the most relevant player in PD pathogenesis identified to date. Many LRRK2 gene mutations have been reported. The G2019S mutation is the hot spot mutation in Caucasians and the G2385R polymorphism is reported to be a genetic risk factor in Easten populations. Mutant Lrrk2 carrying human dominant mutations has enhanced kinase activity, resulting in cell toxicity and neurite shrinkage. Knock-down or ablation of LRRK2 in mammalian cultured neurons promotes neurite outgrowth through actin cytoskeletal rearrangment. However, the information regarding the LRRK2 mutation in the Asian population is rare and the functional relevance of these mutations (such as G2019S) or risk variant (G2385R) are unclear. In addition, very recently, aother gene for early onset-PD (PARK9/ATP13A2) was identified. The phenotype of affected individuals is juvenile onset of PD and may combine the phenotypes of dementia and pyramidal degeneration. The ATP13A2 protein is assumed to be the neuronal P-type ATPase and the intracellylar location is primarily in the lysosome. The mechanism by which loss of ATP13A2 causes parkinsonism and the possible function is unclear. To date there have been few studies examining the frequency of ATP13A2 mutations in parkinsonism, nor in different populations. The data in Asian populations are lack.
Purpose
We propose this research proposal with the following aims to evaluate the the frequency and functional significance of LRRK2 and ATP13A2 mutations in patients with PD in Taiwanese.
1. To determine the frequency of mutations of the ATP13A2 gene in PD patients of Taiwanese.
2. To determine the frequency of mutations of the LRRK2 gene in PD patients of Taiwanese.
3. To elucidate the functional relevance of LRRK2 genetic substitutions using lymphoblastoid cell lines derived from patients with LRRK2 substitutions.
4. Employing Drosophila da neurons as a model system, we aim to characterize the role of LRRK2 mutations in Drosophila dendrite morphogenesis by creating transgenic Drosophila models.
Materials and methods
We recruit more than 500 PD patients and control subjects to evaluate the frequency of ATP13A2 and LRRK2 mutations in Taiwanese populations using the method of direct sequencing in the first set of the study. In the second part, we use EBV transformed lymphoblastoid cell lines derived from patients carring LRRK2 mutations to elucidate the possible molecular functional changes. We also create transgenic Drosophila models carrying wild type LRRK2, G2019S, R1441C and G2385R to elucidate the molecular effects of these LRRK2 mutatuins in the in vivo model system.
Results
We identified one novel missense variant, Ala746Thr, in a single heterozygous state
in three patients (1.7% in EOPD). The variant was not observed in 589 ethnicity matched controls. The frequency of this variant was significantly higher in PD cases than controls (p=0.01, relative risk 4.3, 95%CI 1.9-4.3). The clinical phenotype and 18F-dopa PET image of ATP13A2 Ala78Thr carriers are similar to that seen in idiopathic PD. The variant is located between the highly conserved phosphorylation region and the 5th transmembrane domain of the ATP13A2 protein. We also found the frequencies of R1441H and G2385R in familial PD patients were 3.7% and 22.2%, respectively. The clinical phenotypes and [18F]-dopa PET findings for subjects with R1441H or G2385R resembled those of patients with idiopathic PD; however, their lymphoblastoid cell lines showed increased apoptosis following exposure to a proteosome inhibitor. Thus, LRRK2 mutations are rare in Taiwanese with familial PD.
By using Drosophila as a model system, we found that expression of G2019S mutant
in Drosophila dendritic arborization neurons induces mislocalization of the axonal protein tau in dendrites and causes dendrite degeneration. G2019S-induced dendrite degeneration is suppressed by reducing the level of tau protein and aggravated by tau coexpression. Further genetic analyses suggest that G2019S and Tau function synergistically to cause microtubule fragmentation, inclusion formation and dendrite degeneration. Mechanistically, hyperactivated G2019S promotes tau phosphorylation at the T212 site by the Drosophila GSK3β homolog Shaggy (Sgg). G2019S increases the recruitment of autoactivated Sgg, thus inducing hyperphosphorylation and mislocalization of tau with resultant dendrite degeneration.
Conclusions
Our study not only provides a genetic epidemiology information regarding the muattaion frequency of ATP13A2 and LRRK2 in Taiwnaese PD patients but also provide a molecular and cellular mechanism in understanding the regulation of neurite degeneration by LRRK2. Our restuls will be stretched to understand the pathomechanism of LRRK2-linked PD and the transgenic LRRK2 Drosophila model could be a plateform for further drug screening.
Subjects
Parkinson's disease
LRRK2(Leucine-rich repeat kinase)
G2019S(Glycine2019Serine)
G2385R (Glycine2385Arginine)
Drosophila melanogaster
animal model
neurons
SDGs
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-99-Q93421022-1.pdf
Size
23.32 KB
Format
Adobe PDF
Checksum
(MD5):5111115a224f40401c460b0b32c486fb