Parkinson's disease (PD) is a common, disabling, and incurable neurodegenerative disorder with evidence for substantial heritability. Approximately 30 distinct PD risk loci have been identified based on genome-wide association studies (GWAS). However, most of the implicated genomic regions contain multiple genes that are equally likely to be affected by associated polymorphisms, and potential functions for the majority of these gene candidates are completely unknown. Therefore, the critical next steps for translational research in PD genomics are (1) to determine the responsible gene(s) at each susceptibility locus, and (2) to define their impact on disease mechanisms. Answering these questions will be essential for turning insights from human genetics into clinical breakthroughs in PD therapeutics. Based on overwhelming evidence, alpha-synuclein (alphaSyn) neurotoxicity is a central mechanism in PD susceptibility and pathogenesis, and we hypothesize that many risk loci may modulate the relevant biological pathways. We have developed an improved model of synucleinopathy in the fruit fly, Drosophila melanogaster, that dynamically and robustly recapitulates alphaSyn toxicity in the adult nervous system, including early dysfunction in synaptic transmission and progressive neurodegenerative cell loss. Importantly, this system is amenable to high-throughput genetic screening.
In Aim 1, we will leverage the rapid capabilities of fly genetics and the availability of near-saturation reagents for the Drosophila genome to comprehensively evaluate candidate genes at ~30 PD susceptibility loci from human GWAS. For ~100 genes, we will identify Drosophila orthologs, obtain lines predicted to disrupt or activate gene function, and screen for genetic interactions with alphaSyn neurotoxicity in vivo. A versatile and high-throughput screen in the fly retina will allow parallel assessments of ?Syn-mediated structural and functional neurodegeneration.
In Aim 2, the most promising modifier genes will be validated in the adult Drosophila brain examining age-dependent, alphaSyn-induced dopaminergic neuronal loss and resulting locomotor impairment. In order to define the key mechanisms, the top modifier genes demonstrating consistent and robust interactions will be profiled in vivo for their impact on alphaSyn dynamics, including protein levels, phosphorylation, misfolding/aggregation, and inclusion formation. The proposed strategy will enable us to move efficiently from lists of associated polymorphisms to in vivo confirmation of the causal genes and validation of roles in ?Syn-mediated neurodegeneration. The definitive identification and functional elucidation of PD susceptibility genes holds great promise for the discovery of new treatment strategies for this devastating disorder.
Parkinson's disease is a disabling and incurable neurodegenerative disorder affecting as many as one million individuals in the US. Integrating recent advances in human genetics with innovative model organism studies, we will systematically define the genes responsible for Parkinson's disease susceptibility and begin to establish their mechanisms. Functional validation of Parkinson's disease genetic risk factors holds enormous potential for therapeutic breakthroughs.
|Rousseaux, Maxime W C; Vázquez-Vélez, Gabriel E; Al-Ramahi, Ismael et al. (2018) A Druggable Genome Screen Identifies Modifiers of ?-Synuclein Levels via a Tiered Cross-Species Validation Approach. J Neurosci 38:9286-9301|
|Wangler, Michael F; Hu, Yanhui; Shulman, Joshua M (2017) Drosophila and genome-wide association studies: a review and resource for the functional dissection of human complex traits. Dis Model Mech 10:77-88|
|Robak, Laurie A; Jansen, Iris E; van Rooij, Jeroen et al. (2017) Excessive burden of lysosomal storage disorder gene variants in Parkinson's disease. Brain 140:3191-3203|
|Jansen, Iris E; Ye, Hui; Heetveld, Sasja et al. (2017) Discovery and functional prioritization of Parkinson's disease candidate genes from large-scale whole exome sequencing. Genome Biol 18:22|
|Farlow, Janice L; Robak, Laurie A; Hetrick, Kurt et al. (2016) Whole-Exome Sequencing in Familial Parkinson Disease. JAMA Neurol 73:68-75|
|Chouhan, Amit K; Guo, Caiwei; Hsieh, Yi-Chen et al. (2016) Uncoupling neuronal death and dysfunction in Drosophila models of neurodegenerative disease. Acta Neuropathol Commun 4:62|
|Shulman, Joshua M (2015) Drosophila and experimental neurology in the post-genomic era. Exp Neurol 274:4-13|