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A novel two-step model for neurodegeneration in Parkinson’s disease

Final Report Summary - 2STEPPARKIN (A novel two-step model for neurodegeneration in Parkinson’s disease)

Parkinson’s disease (PD) is the most frequent cause of the movement disorder, which affects more than 1% of people after 60 years of age worldwide. The cardinal feature of PD is a progressive loss of dopaminergic (DA) neurons in the substantia nigra. These neurons project to the brain area controlling locomotion, and thus their loss and resulting deficiency in DA signaling causes various motor symptoms, including tremor, rigidity, postural instability and bradykinesia. Despite many years of research, the cause of PD is unknown and the treatment for PD is limited to the symptomatic relief. In aging society, better understanding of the pathogenesis of PD, leading to the development of new treatment strategy, is of growing importance.
This ERC project was aimed at understanding the mechanisms of DA neuron degeneration using a combination of invertebrate model organisms and mouse models. To this end, we have set out to establish new models of PD in invertebrates -fruit fly Drosophila and the nematode worm, c. elegans. Using both fly and worms, we first showed that mutation in the Fer2 gene lead to a progressive loss of DA neurons and associated locomotor deficits, reminiscent of PD motor symptoms. Furthermore, loss of DA neurons due to Fer2 mutation is linked to abnormality in mitochondria and elevation of oxidative stress levels throughout the brain. These cellular characteristics are common in PD patients, and thus suggest that Fer2 mutation also recapitulate molecular pathogenic processes in the PD. Altogether, these results established the Fer2 mutant flies and worms as a new model to study PD (Bou Dib et al. 2014).
We also established a second model of PD in flies: dFOXO mutants. dFOXO is the unique Drosophila homolog of FOXO family of transcription factors, which play diverse roles in cellular homeostasis. Importantly, genetic variations in the human FOXO factors are implicated in non-familial form of Parkinson’s disease. We showed that the dFOXO mutant display a progressive loss of specific DA neurons in the brain and locomotor abnormality -the phenotypes very similar to those of Fer2 mutants .Intrigued by this similarity, we conducted a series of genetic interaction assays and molecular analysis and found that dFOXO and Fer2 have partially overlapping roles in dopamine neuron protections and different environmental stressors activate one or the other transcription factor. Nevertheless, their downstream pathways converge on the regulation of mitochondrial homeostasis and autophagy, which are known to play central roles in the pathogenesis of Parkinson’s disease. Altogether, our new results highlighted the complex interaction between genetic and environmental factors underlying the pathogenesis and progression of PD (Tas et al. 2018).
Moreover, we have completed the identification of Fer2 direct downstream target genes and indirect targets using Chromatin –IP and cell-type specific transcriptome analysis. In parallel, we have made a significant progress in understanding the role of the Fer2 homolog in mice and its potential contribution to dopaminergic neuroprotection. We are at the final stage of characterising the molecular and behavioral phenotypes of Fer2 homolog conditional knockout mice. The manuscript including the results of the ChIP-transcriptome analysis and findings from the mouse model is under preparation. Overall, the results of our ERC research yielded knowledge that contributes to better understanding the pathogenesis of sporadic PD.