RESUMEN
Motor symptoms in Parkinson's disease (PD) are directly related to the reduction of a neurotransmitter dopamine. Therefore, its precursor L-DOPA became the gold standard for PD treatment. However, chronic use of L-DOPA causes uncontrollable, involuntary movements, called L-DOPA-induced dyskinesia (LID) in the majority of PD patients. LID is complicated and very difficult to manage. Current rodent and non-human primate models have been developed to study LID mainly using neurotoxins. Therefore, it is necessary to develop a LID animal model with defects in genetic factors causing PD in order to study the relation between LID and PD genes such as α-synuclein. In this study, we first showed that a low concentration of L-DOPA (100 µM) rescues locomotion defects (i.e., speed, angular velocity, pause time) in Drosophila larvae expressing human mutant α-synuclein (A53T). This A53T larval model of PD was used to further examine dyskinetic behaviors. High concentrations of L-DOPA (5 or 10 mM) causes hyperactivity such as body bending behavior (BBB) in A53T larva, which resembles axial dyskinesia in rodents. Using ImageJ plugins and other third party software, dyskinetic BBB has been accurately and efficiently quantified. Further, we showed that a dopamine agonist pramipexole (PRX) partially rescues BBB caused by high L-DOPA. Our Drosophila genetic LID model will provide an important experimental platform to examine molecular and cellular mechanisms underlying LID, to study the role of PD causing genes in the development of LID, and to identify potential targets to slow/reverse LID pathology.
RESUMEN
The fruit fly Drosophila melanogaster has long been used as a model organism for human diseases, including Parkinson׳s disease (PD). Its short lifespan, simple maintenance, and the widespread availability of genetic tools allow researchers to study disease mechanisms as well as potential drug therapies. Many different PD models have already been developed, including ones utilizing mutated α-Syn and chronic exposure to rotenone. However, few animal models have been used to study interaction between the PD causing factors. In this study, we developed a new model of PD for use in the larval stage in order to study interaction between genetic and environmental factors. First, the 3rd instar larvae (90-94 hours after egg laying) expressing a mutated form of human α-Syn (A53T) in dopaminergic (DA) neurons were video-taped and quantified for locomotion (e.g. crawling pattern and speed) using ImageJ software. A53T mutant larvae showed locomotion deficits and also loss of DA neurons in age-dependent manner. Similarly, larvae chronically exposed to rotenone (10 µM in food) showed age-dependent decline in locomotion accompanied by loss of DA neurons. We further show that combining the two models, by exposing A53T mutant larvae to rotenone, causes a much more severe PD phenotype (i.e. locomotor deficit). Our finding shows interaction between genetic and environmental factors underlying development of PD symptoms. This model can be used to further study mechanisms underlying the interaction between genes and different environmental PD factors, as well as to explore potential therapies for PD treatment.
