Molecular and Genetic Analysis of Parkin in the Pathogenesis of Parkinson's Disease

The ultimate goal of this proposal is to create new, more effective means of preventing, diagnosing and treating neural degeneration associated with Parkinson's disease (PD). PD is a chronic progressive disorder with a lifetime prevalence of 1-2% and is thought to be caused by degeneration of dopaminergic neurons in the substantia nigra. Based on familial inheritance studies, autosomal recessive mutations in parkin have been associated with juvenile onset parkinsonism. In addition, mutations in the alpha-synuclein gene have been associated with an autosomal dominant inheritance pattern for the early onset Parkinson's phenotype. However, the exact roles of neither parkin nor alpha-synuclein in the pathogenesis of PD have yet to be clearly established. Fortunately, the fruit fly Drosophila melanogaster offers an unparalleled combination of powerful molecular and genetic tools and has proven to be an excellent in vivo animal model system for developmental and degenerative processes directly relevant to human biology. Drosophila has been successfully used to study neurological disorders such as Huntington's Disease, Spinocerebellar Ataxia 3 and PD. Specifically, misexpression of alpha-synuclein in the Drosophila central nervous system causes neurodegeneration and progressive age-dependent locomotor dysfunction that is similar to pathologic and clinical manifestations of PD. As mutations in alpha-synuclein are responsible for only a small subset of the PD patient population, understanding the role of other genes involved in this disease, such as parkin, is of great importance. Furthermore, a study of potential interactions between parkin and alpha-synuclein may help elucidate molecular mechanisms of PD pathogenesis. While the best approach for identifying reagents for treatment is to have a complete understanding of the molecular and genetic mechanisms that lead to the disease state, methods for genetic analysis in mammals are time-consuming and expensive. Fortunately, we have identified a Drosophila homolog of human parkin, dparkin, which will generate powerful tools for deciphering the mechanisms of parkin function. We propose to exploit the power of Drosophila genetics to determine the loss- and gain-of-function phenotypes of dparkin mutants. Moreover, we will conduct genome-wide genetic screens to identify new, conserved genes that interact with parkin to cause neural degeneration. In addition, we will determine if parkin and alpha-synuclein interact in vivo to cause neural pathology. These experiments outline a strategy for the rapid elucidation of a pathway critical to the pathogenesis of Parkinson's disease that cannot be matched by any mammalian system. As new genes are identified and characterized, we will then study vertebrate homologs of such genes both in humans and in mice.