A multiplex model in a Drosophilaidentifies novel gene-environment interactions: A step towards personalized medicine.

Epidemiological studies strongly support a role for environmental factors, particularly pesticide exposure, in the pathogenesis of Parkinson's disease (PD). Genetic risk factors, including penetrant single-gene mutations and risk factors identified from genome-wide associated studies (GWAS), also contribute to PD risk and progression, but available model systems are limited in their ability to interrogate gene-environment crosstalk in vivo and at scale. Here we use Drosophila as a model system to understand complex gene-environment interactions in PD. We developed a multiplex model in Drosophilain which we knocked down GWAS candidate genes in neurons in a robust new α-synucleinopathy model and exposed the flies to environmental neurotoxicants. We identified an interaction between LRRK2, rotenone, and α-synuclein. Expression of the disease-causing Lrrk-G2019S mutant in the presence of rotenone and alpha-synuclein induced behavioral deficits and mitochondrial dysfunction. Further, super-resolution microscopy analysis revealed that the interaction of LRRK2, α-synuclein, and rotenone leads to hyperstabilization of the actin cytoskeleton. We have previously shown that LRRK2 has actin severing activity, and previous studies have implicated the GTPase domain in regulating actin severing. We next expressed a GTPase domain mutant, Lrrk-Q1003H, designed to mimic the human protective mutant LRRK2-R1398H. Interestingly, expression of the LRRK2 protective mutant attenuated behavioral deficits mediated by LRRK2-rotenone-synuclein interactions. Further, the expression of the protective mutant also attenuated the actin stabilization and mitochondrial deficits. Moreover, genetic analysis from a patient cohort who had previous pesticide exposure revealed that the patient's LRRK2-R1398H mutation reduces the chance of developing PD. Since global actin severing may have unwanted side effects, we used a combination of forward genetic screen and proteomics to identify potential kinases that can be druggable targets. We identified Cdc42 binding protein kinase MRCKα, an actin-binding protein, as a potential target. Genetic and pharmacological inhibition of MRCKα in Drosophila can modify the toxicity induced by the interaction among LRRK2, α-synuclein, and rotenone by inhibiting actin hyperstabilization. Using our novel multiplex model in Drosophila, we have identified an interaction between LRRK2, α-synuclein, and rotenone which is modulated by actin stabilization and mitochondrial dysfunction. We have further demonstrated that using this multiplex approach, we can study the mechanism of these interactions as well as identify novel drug targets for the interactions. Our findings have implications towards the development of a personalized approach for drug discovery and lead identification.