| Parkinson's disease (PD) is a common neurodegenerative disease for which there is no known cure or lasting treatment. PD targets dopaminergic neurons in the substantia nigra, resulting in motor disturbances such as resting tremor, bradykinesia, and rigidity. Pathogenic processes likely occur over several decades, since an overwhelming percentage of neurons are already dead at the time of clinical diagnosis. For this reason, the usage of animal model systems to discover the early steps in the pathologic cascade is required. These include exposure to the neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), which selectively kills dopamine neurons in the substantia nigra, and genetic models incorporating mutations in the alpha-synuclein gene that cause disease in human patients. Through the evaluation of these models at multiple time points, we aimed to discover novel gene expression changes that may underlie disease pathogenesis. Specifically, we hypothesized that animal models of PD and human PD brains would share a gene expression profile that signifies certain aspects of pathogenesis and/or recovery-resistance. To test this hypothesis, we utilized new microarray technology that enabled us to sample thousands of genes' expression level in one assay. Because the technology is fairly new and results can vary depending on methods used, we carefully evaluated multiple array and data mining options in order to make the most accurate inferences as to differentially expressed genes in each set of samples. We developed a fusion classifier approach whereby individual data mining algorithms generate lists of significant genes. The lists are subsequently queried and only genes unanimously called significant are retained for further validation. A portion of the significant genes was validated by quantitative real time PCR and in some cases, in situ hybridization. While we identified hundreds of differentially expressed genes in each of the PD systems, only a few were common between the human and animal SN or striatum. These were by and large related to synaptic function and cytoskeletal stability, implicating the pre-synaptic terminal as a primary site of injury. Our time course studies indicate that if the synaptic changes could be prevented, it may alleviate some cell death, since these changes precede neuronal loss. |
