A stress-enhanced model for discovery of disease-modifying gene: Ece1-suppresses the toxicity of α-synuclein A30P

Parkinson's disease (PD) is a progressive motor neurodegenerative disorder, characterized by a selective loss of dopaminergic neurons in the substantia nigra. The complexity of disease etiology includes both genetic and environmental factors. No effective drug that can modify disease progression and protect dopamine neurons from degeneration is presently available. Human α-Synuclein A30P (A30P) is a mutant gene identified in early onset PD and showed to result selective dopamine neuron loss in transgenic A30P flies and mice. Paraquat (PQ) is an herbicide and an oxidative stress generator, linked to sporadic PD. We hypothesized that vital PD modifier genes are conserved across species and would show unique transcriptional changes to oxidative stress in animals expressing a PD-associated gene, such as A30P. We also hypothesized that manipulation of PD modifier genes would provide neuroprotection across species. To identify disease modifier genes, we performed two independently-duplicated experiments of microarray, capturing genome-wide transcriptional changes in A30P flies, chronically fed with PQ-contaminated food. We hypothesized that the best time point of identifying a disease modifier gene is at time when flies showed maximal combined toxicity of A30P transgene and PQ treatment during an early stage of disease and that effective disease modifiers gene are those showing transcriptional changes to oxidative stress in A30P expressing and not in wild type animals. Fly Neprilysin3 (Nep3) is one identified gene that is highly conserved. Its mouse and human homolog is endothelin-converting enzyme-1 (Ece1). To investigate the neuroprotective effect of Ece1, we used NS1 cells and mouse midbrain neurons expressing A30P, treated with or without PQ. We found that ECE1 expression protected against A30P toxicity on cell viability, on neurite outgrowth and ameliorated A30P accumulation in vitro. Expression of ECE1 in vivo suppressed dopamine neuron loss and alleviated the corresponding motor deficits in mice with A30P-expression. Our study leverages a new approach to identify disease modifier genes using a stress-enhanced PD animal model.