Mutations and activation of glucocerebrosidase (GBA) play a prominent role in the pathogenesis of the alpha- synucleinopathies, PD and LBD. GBA plays a pivotal role in the lysosomal degradation pathway by functioning as a lysosomal enzyme. Most disease causing mutations of GBA are thought to be loss of function mutations that ultimately lead to the GBA deficiency, compromised glucosylceremide (GlcCer) metabolism and the subsequent failure of lysosomal mediated degradation of GBA substrates including alpha-synuclein. Depletion of GBA results in ?-synuclein accumulation and neurodegeneration suggesting compromised GBA cascade contributes to the pathogenesis of ?-synucleinopathies. We and others have found that brains of PD patients with or without mutations in GBA, as well as brains of A53T alpha-synuclein transgenic (Tg) mice, exhibit reduced GBA activity suggesting a role of the enzyme in the pathogenesis of the disease. Interestingly, the loss of catalytic activity of GBA correlated with its quantitative protein reduction, suggesting that unidentified key modulators might play an important role in GBA protein levels and activity though posttranslational modifications (PTMs). Accordingly, we investigated the mechanisms underlying the loss of GBA activity and protein levels by identifying key GBA modulators using tandem affinity purification (TAP) analysis. In preliminary data, we discovered GIP1 (GBA interacting protein 1) and show that GIP1 belongs to a new class of E3 ligases. In this project, we propose to explore the regulation of the GBA by GIP1 and their roles in regulating the pathogenesis of ?-synuclein in PD and LBD.
In specific aim 1 we will determine whether GIP1 interacts with and ubiquitinates GBA in vitro and in vivo.
In specific aim 2 we will examine whether GIP1 targets GBA for degradation, thus regulating GBA activity and its substrates, GlcCer. Since GBA is a lysosomal enzyme that potentially regulates the expression of alpha synuclein, we will also explore whether GIP1 mediated GBA degradation ultimately regulates alpha-synuclein expression and aggregation. To accomplish these specific aims we will utilize lenti-GIP1 shRNA virus to knockdown GIP1 and a herpes simplex-GIP1 virus to overexpress GIP1. In preliminary studies we discovered that GIP1 accumulates in A53T alpha-synuclein Tg mice, PD brains and neurons treated with alpha-synuclein preformed fibrils (PFFs). Thus, in specific aim 3 we will further evaluate whether alpha-synuclein pathology is associated with accumulation of GIP1 and if its accumulation correlates with GBA deficiency and the severity of the alpha-synuclein pathology in A53T alpha-synuclein Tg mice and PD patients, as well as ?-synuclein PFFs treated neurons. Moreover, preliminary data indicates that depletion of GIP1 significant reduces alpha-synuclein PFFs induced neuronal death. Thus, in specific aim 3, we will also evaluate the role of GIP1 in alpha-synuclein PFFs induced neuronal death. Ultimately this project will determine the full implications of the GIP1-GBA-alpha-synulcein neurodegenerative pathway and will identify new targets for therapeutic intervention in PD and LBD.

Public Health Relevance

Mutations in GBA are the most prevalent risk factor of PD, yet little is known about how this protein functions in the pathogenesis of PD and alpha-synucleinopathies. The goals for this project are to understand the function and dysfunction of GBA and identify the potential therapeutic targets to treat PD and alpha-synucleinopathies.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
1R01NS082205-01A1
Application #
8590323
Study Section
Cellular and Molecular Biology of Neurodegeneration Study Section (CMND)
Program Officer
Sutherland, Margaret L
Project Start
2013-07-01
Project End
2018-06-30
Budget Start
2013-07-01
Budget End
2014-06-30
Support Year
1
Fiscal Year
2013
Total Cost
$354,375
Indirect Cost
$135,625
Name
Johns Hopkins University
Department
Neurology
Type
Schools of Medicine
DUNS #
001910777
City
Baltimore
State
MD
Country
United States
Zip Code
21218
Kam, Tae-In; Mao, Xiaobo; Park, Hyejin et al. (2018) Poly(ADP-ribose) drives pathologic ?-synuclein neurodegeneration in Parkinson's disease. Science 362:
Kim, Donghoon; Hwang, Heehong; Choi, Seulah et al. (2018) D409H GBA1 mutation accelerates the progression of pathology in A53T ?-synuclein transgenic mouse model. Acta Neuropathol Commun 6:32
Kim, Sangjune; Yun, Seung Pil; Lee, Saebom et al. (2018) GBA1 deficiency negatively affects physiological ?-synuclein tetramers and related multimers. Proc Natl Acad Sci U S A 115:798-803
Kim, Donghoon; Yoo, Je Min; Hwang, Heehong et al. (2018) Graphene quantum dots prevent ?-synucleinopathy in Parkinson's disease. Nat Nanotechnol :
Yun, Seung Pil; Kim, Donghoon; Kim, Sangjune et al. (2018) ?-Synuclein accumulation and GBA deficiency due to L444P GBA mutation contributes to MPTP-induced parkinsonism. Mol Neurodegener 13:1
Dawson, Ted M; Golde, Todd E; Lagier-Tourenne, Clotilde (2018) Animal models of neurodegenerative diseases. Nat Neurosci 21:1370-1379
Lee, Saebom; Kim, Sangjune; Park, Yong Joo et al. (2018) The c-Abl inhibitor, Radotinib HCl, is neuroprotective in a preclinical Parkinson's disease mouse model. Hum Mol Genet 27:2344-2356
Xiong, Yulan; Neifert, Stewart; Karuppagounder, Senthilkumar S et al. (2018) Robust kinase- and age-dependent dopaminergic and norepinephrine neurodegeneration in LRRK2 G2019S transgenic mice. Proc Natl Acad Sci U S A 115:1635-1640
Yun, Seung Pil; Kam, Tae-In; Panicker, Nikhil et al. (2018) Block of A1 astrocyte conversion by microglia is neuroprotective in models of Parkinson's disease. Nat Med 24:931-938
Yun, Seung Pil; Kim, Hyojung; Ham, Sangwoo et al. (2017) VPS35 regulates parkin substrate AIMP2 toxicity by facilitating lysosomal clearance of AIMP2. Cell Death Dis 8:e2741

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