Neuroprotection of Vesicular Monoamine Transporter in the Pathogenesis of Parkinson’s Disease

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Yong-Jian Liu, M.D.

Department of Neurology
University of Pittsburgh School of Medicine

Abstract

Parkinson’s disease (PD) involves the selective degeneration of dopaminergic neurons in the substantia nigra of the brain. The cause of this degeneration is unknown. In addition to cell loss, PD is characterized by cytoplasmic inclusions known as Lewy bodies. The recent identification of mutations in alpha-synuclein (the major component of Lewy bodies) in familial PD and the detection of alpha-synuclein in Lewy bodies of patients with sporadic PD have suggested that alpha-synuclein may have an important pathogenic role in both familial and sporadic PD. In addition to its association with Lewy bodies in both familial and sporadic PD, alpha-synuclein is also implicated in the neural degeneration seen in Alzheimer’s disease.

Dr. Liu’s group will test the hypothesis that mutant alpha-synuclein augments dopamine toxicity and hence neural degeneration by interfering with the normal protective mechanism of vesicular monoamine transporter (VMAT). The characterization of interaction of alpha-synuclein with VMAT in transfected dopaminergic cells will indicate the potential mechanism by which mutant alpha-synuclein influences the pathogenesis of familial PD. This study may also provide information about the physiological function of alpha-synuclein, it association with synaptic vesicles, and its potential role in the pathogenesis of idiopathic PD. Furthermore, information about the sequences responsible for the interaction will help to identify targets for drug design.

Progress Report (as of 8/2002)

This report summarizes research progress on the project entitled “Neuroprotection of vesicular monoamine transporter (VMAT2) in the pathogenesis of Parkinson’s disease,” which has been supported by seed grant award. Three major research projects are discussed here.

First, we have made several critical findings in how VMAT2 protects dopamine (DA) neurons. Our recent work suggest that overexpression of VMAT2 can enhance the resistance of the transfected DA cells to neurotoxin MPP+, which serves as an important model for PD study. We also found that the secretory vesicle population is important in the VMAT2 protection. The overexpression of synaptophysin, which increases the vesicle number, can synergically enhance the neuroprotection of VMAT2 when it is co-overexpressed with the transporter in cells. In addition, to study the regulation of VMAT2 function, we have examined the dimerization of the transporter and how this characteristic of protein structure is determined by specific amino acid sequence or motif. These findings have provided sufficient preliminary results for submitting a proposal to NINDS recently as part of program project directed by Dr. M. Zigmond. The proposal will be resubmitted as an R01 to NINDS this October. Furthermore, the findings are included in a manuscript, which is under the preparation for publication.

Second, in order to study how oxidative stress contributes to neuronal death during the neurodegeneration in Alzheimer or Parkinson’s disease, we have been establishing an animal model. In this model, we will in activate the function of VMAT2 which would further induce the intracellular oxidative stress upon the increase of cytosolic DA. This model may provide some critical knowledge about how endogenous DA toxicity that produces oxidative stress would contribute to the formation of Lewy bodies and neuronal loss. Currently, we are in the process of characterizing one of the transgenic mouse strains in which the Cre recombinase is expressed under the control of tyrosine hydroxylase. This transgenic model will be very useful in studies related to dopamine neuron function. Based on this ongoing work, we have recently submitted a proposal (R21, June of 2002) to NINDS entitled “A transgenic model for endogenous oxidative stress.”

Third, part of the seed grant has been used to support an exploratory project on the induction of ES stem cell into DA neuron in vitro. The generation of DA neurons in test tube as an unlimited supply for gene therapy of Parkinson’s disease has been one of the exciting areas of research in both neurobiological and clinical neurological fields. Our study has suggested that the stromal cell from bone marrow may have both induction and neurotrophic effect during the differentiation of ES cells into DA neuron. We will examine the molecular mechanisms by which stromal cells execute such activities. This aspect of research will undoubtedly provide a strong promise to the treatment of neurodegenerative diseases effectively. The manuscript of this work is in preparation for publication. We are also in the process of preparing a research proposal applying for the research grant announced recently by the M.J. Fox Foundation.

In summary, the seed grant awarded has been an extremely important resource that has enabled our research work to progress this far. As an independent researcher who is at the beginning of tenure-track faculty career, I think that such support is very critical for young researchers as well as efficient and fruitful for the investment of your foundation.

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