Collaborative Centers for Parkinson's Disease Environmental Research

Emory University

Emory University Collaborative Centers for Parkinson's Disease Environmental Research
Mahlon Delong, M.D.
medmrd@emory.edu
http://www.neurology.emory.edu/CND/index.htm

Project Description

The purpose of the Emory CCPDER is to perform cutting-edge collaborative research on Parkinson's disease (PD) pathogenesis, with a focus on gene-environment interactions. Although uncommon, Parkinson's disease can be caused by environmental exposure alone (e.g., MPTP) or by single gene mutations alone (e.g., α-synuclein or parkin). However, we believe that most Parkinson's Disease is caused by an interaction between genetically determined susceptibilities and environmental exposures. Furthermore, we believe that environmental and genetic causes of Parkinson's Disease are converging on common biochemical pathways of pathogenesis involving pesticides, oxidative stress, abnormal dopamine compartmentalization and the ubiquitin/proteasome system of protein degradation.

The projects of the Emory CCPDER focus on these themes of pesticides, oxidative damage, dopamine compartmentalization, the ubiquitin/proteasome system, gene-environment interactions and identifying potential new genes. The multidisciplinary group of Emory investigators brings a wide range of skills, expertise and techniques to bear on the roles of genes and environment in Parkinson's Disease . The projects underway take advantage of recent advances in human genetics by using animals that express mutant human genes associated with Parkinson's Disease . To study gene-environment interactions we make use of available epidemiological information to help determine which environmental contaminants to test in these models. Finally, our collaboration with deCODE Genetics combines clinical research and human genetics to help pinpoint other genes that may confer a susceptibility to Parkinson's Disease . Our overall goal is to use cellular and molecular neuroscience in combination with genetic, epidemiological and clinical approaches to uncover the causes and mechanisms that underlie the development and progression of Parkinson's Disease .

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Project 1:  New Models of Parkinson's Disease : Pathogenesis and Neuroprotection

Principal Investigator: J. Timothy Greenamyre, M.D., Ph.D.
jgreena@pitt.edu

We recently developed a novel model of Parkinson's Disease (PD) in the rat, which is based on long-term exposure to the pesticide, rotenone. This model reproduces many of the features of Parkinson's Disease including the motor impairment and damage to dopamine neurons in the brain. We will use this model to study the interaction of environmental exposures and genetic factors that may determine the susceptibility or resistance of the brain to Parkinson's Disease .

Due to the availability of genetically altered mice strains, we will adapt the previously developed rat rotenone model for use in mice. Mice with different genetic alterations will be exposed to rotenone at levels known to cause brain damage characteristic to Parkinson's Disease . Mice that express human α-synuclein, a gene associated with the occurrence of Parkinson's Disease in humans, will be used to determine if the presence of this gene increases the susceptibility to the damaging effects of rotenone. In separate studies, mice that do not have "Parkin," a gene which when mutated has also been associated with human Parkinson's Disease , will be studied to establish if the absence of this gene increases the damaging effects of rotenone. Other genetic variables that may be involved in rotenone-induced damage will also be studied, such as genes that regulate antioxidants and genes that affect the normal clearance of the neurotransmitter dopamine in the brain. Finally, other commonly used pesticides will be tested in this animal model to screen for potentially dangerous environmental agents that may increase the susceptibility of the brain to Parkinson's Disease .

In addition to the mouse model, we will use cultured brain slices ("organotypic" slices) to further examine rotenone-induced damage to brain cells. In this technique, brain regions that are most affected in Parkinson's Disease will be removed from the mouse brain and kept alive in a dish, where they will be studied closely during rotenone exposure. This approach will allow us to directly manipulate specific cellular functions to determine their importance in mediating or protecting against rotenone-induced cellular damage. The dopamine neurons that die in Parkinson's Disease may be vulnerable because of their dopamine content. This is because dopamine and its metabolism can produce free radicals and oxidative damage. Because dopamine is easily altered in this organotypic slice system, we will be able to study the role of dopamine in rotenone-induced cell

death. In addition, brain slices taken from the genetically altered mice used in the whole-animal studies will be used to examine the affects of these genes on rotenone-induced damage. Finally, compounds that may protect cells from rotenone-induced damage will be screened to determine their potential usefulness in the whole animal mouse model.

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Project 2: Vesicular Monoamine Transporter as a Target of Environmental Toxicants

Principal Investigator: Gary W. Miller, Ph.D.
gwmille@emory.edu

Genetic and environmental factors are thought to contribute to Parkinson's Disease (PD). One gene that has been associated with the occurrence of Parkinson's Disease in humans is alpha-synuclein. The mutated form of alpha-synuclein can cause familial Parkinson's Disease and normal alpha-synuclein has been found accumulated in areas of the brain that have been damaged in Parkinson's Disease patients. Recent studies indicate that certain pesticides can increase the presence of this deleterious protein and thus may worsen the progression of Parkinson's Disease .

In addition to the interaction between pesticides and alpha-synuclein, both appear to interact with the vesicular monoamine transporter (VMAT2). VMAT2 is a key regulator of the levels of the dopamine neurotransmitter in the brain. VMAT2 is located within dopamine neurons and may inhibit cellular damage typical of Parkinson's Disease by storing dopamine within compartments inside the neuron thus protecting cells from the harmful byproducts of dopamine breakdown. In contrast, reduced VMAT2 function allows dopamine to persist in areas where it is susceptible to oxidative stress thereby increasing the potential for cellular damage. Since damage to dopamine neurons is one of the basic hallmarks of Parkinson's Disease , VMAT2 function could have direct consequences on disease progression.

To determine if alpha-synuclein and pesticides decrease VMAT2 function, cultured cell lines expressing both alpha-synuclein and VMAT2 will be tested for VMAT2-mediated dopamine uptake in the presence and absence of pesticide exposure. It is hypothesized that alpha-synuclein alone will decrease VMAT2-mediated function and that pesticide exposure will also negatively impact VMAT2 function. In parallel studies, tissue from mice that express human alpha-synuclein or have been exposed to chronic pesticides will be isolated and also tested for VMAT2 function. It is hypothesized that tissue from alpha-synuclein mice and the mice exposed to pesticides will both have decreased VMAT2 function as compared to control mice.

In addition to the effects of alpha-synuclein and pesticides on VMAT2, pesticides and VMAT2 may also impact alpha-synuclein levels. To assess the interaction between pesticides and alpha-synuclein, dopamine cells collected from the brains of mice exposed to pesticides will be collected and analyzed for the presence of alpha-synuclein. It is predicted that alpha-synuclein will be increased in the dopamine cells of mice that were exposed previously to pesticides. To investigate the impact of VMAT2 on alpha-synuclein, mice that have less VMAT2 gene expression will be used. It is hypothesized that mice with reduced VMAT2 expression will have higher levels of alpha-synuclein in the brain regions and cell types most affected in Parkinson's Disease .

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Project 3: Genetic and Pathological Study of Sporadic Parkinson's Disease in Iceland and Atlanta

Principal Investigator: Allan I. Levey, M.D.
alevey@emory.edu

Parkinson's Disease (PD) is a disabling and common neurodegenerative disease involving complex environmental and genetic interactions. Mutations in a few genes have been associated with rare inherited cases of Parkinson's Disease with early onset, but new studies indicate that genetics also play a role in late onset sporadic Parkinson's Disease . Our exciting preliminary findings describe a novel chromosomal location called the PARK10 locus, which has been found in late onset Parkinson's Disease patients from Iceland. The proposed research project between deCODE genetics and Emory University investigators now capitalizes on this finding to expand the search for the responsible gene in Icelanders and in Americans in the Atlanta, Georgia area.

Our collaborators at deCODE will study blood samples from Parkinson's Disease patients in the Atlanta area to determine if the PARK10 locus contributes to an increased risk of late-onset Parkinson's Disease as has been shown in Parkinson's Disease patients from Iceland. This will allow us to determine if the PARK10/PD association is widespread in the late-onset Parkinson's Disease population. Genes found at this chromosome location that are potential contributors to Parkinson's Disease will be studied further for the purpose of specific identification. Genes that cause diseases often make proteins that can show altered levels and/or localizations in tissue affected by the disease pathology. Thus, it is possible that a PARK10 gene found to be specifically associated with Parkinson's Disease will make a protein that is different in Parkinson's Disease patient brains than in brains from people without Parkinson's Disease . Thus, postmortem brains from Parkinson's Disease patients as well as brain tissue from the pesticide animal models of Parkinson's Disease will be tested using techniques that can show the presence and absence of proteins in specific brain areas. It is hypothesized that the protein products of the isolated genes will be found at higher levels in brain regions most damaged in Parkinson's Disease . These studies will not only show a link for genes responsible for late-onset Parkinson's Disease , but will also provide evidence that environmental factors may contribute to the disease process in a similar way.

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