Discovery of a nitric oxide-dependent response and a functional analysis of genes regulating the response in a Drosophila model of Parkinson's disease

The processes of neuroinflammation and oxidative stress are thought to be among the primary mechanisms playing roles in the etiology and pathophysiology of Parkinson's disease (PD). Recently, it has been proposed that microglia, the innate immune cells of the mammalian brain, become hyperactivated and deregulated in response to neuronal dysfunction in PD and thereby, accelerate dopaminergic neuronal loss. The mechanisms for neuroinflammatory responses that exaggerate neurotoxicity are poorly understood. Moreover, the studies to date that investigate neuroinflammatory mechanisms have utilized primarily in vitro approaches. We have established a DrosophilaPD model based on ingestion of the herbicide paraquat, which recapitulates most behavioral and patho-physiological features of PD, including loss of dopaminergic neurons. Using this model, we have discovered that paraquat ingestion induces nitric oxide synthase (NOS) and a corresponding elevation of NO production in the adult Drosophila brain. Mammalian microglia have been shown to be a source of NOS, recognized as a major component/marker in neuron death, in mammalian PD models. Therefore, the observation of NOS induction during Drosophilaneurodegeneration parallels the mammalian process. The paraquat-induced stimulation of NOS was further confirmed using pharmacological approaches, which demonstrated that inhibition of NOS partially rescued adult Drosophila from the deleterious effects of paraquat. Minocycline, a tetracycline derivative, has been reported to act primarily on microglia, ameliorating excessive activation of NOS, in mammalian neurodegenerative disease models including PD. Similarly, ingestion of minocycline by adult Drosophilaameliorates the effects of paraquat, including reduction of NOS activity and protection of dopaminergic neurons. The paraquat-induced PD model was also employed to identify the mechanisms of action that confer the neuroprotective properties of minocycline. Components of signaling pathways that potentially could mediate DA toxicity in this PD model were tested for their ability to modify the action of minocycline. The discovery of a NOS-dependent paraquat response in flies provides the foundation for future work to explore cellular and molecular mechanisms directing NOS induction and action in Drosophila, which exhibits features resembling neuroinflammation. This research also takes advantage of the ease of genetic and pharmacological methods in the Drosophila model to identify important genetic components of this process. (Published By University of Alabama Libraries