Analysis of mitochondrial quality control using a Drosophila model of Parkinson’s disease

Parkinson’s disease (PD) is the most common neurodegenerative movement disorder. Despite recent advances, the cause for most PD cases remains unclear. The discovery of mutations in PINK1 (PTEN-induced putative kinase 1) reinforced the importance of mitochondrial impairment in PD. Mitochondria are essential organelles for energy generation in eukaryotic cells, whose compromise can eventually cause cell death. Multicellular organisms have evolved quality control mechanisms to ensure the viability of mitochondria and ultimately the cell. Molecular quality control through the mitochondrial chaperones and proteases acts to promote the proper folding of polypeptides and the degradation of misfolded or damaged proteins. When molecular quality control is overwhelmed, organellar quality control ensures mitochondrial recycling through a selective form of autophagy called mitophagy. PINK1 has been proposed to act in both molecular and organellar quality control, by modulating the activity of chaperones, namely HtrA2 and TRAP1, and acting on mitophagy through Parkin recruitment to damaged mitochondria. The work in this thesis provides evidence of a genetic interaction between Trap1, Pink1 and parkin in Drosophila melanogaster. Trap1 is essential to maintain mitochondrial and dopaminergic neuronal functions and is associated with resistance to stress. Importantly, neuronal expression of Trap1 is sufficient to rescue the Pink1 mutants. Moreover, the expression of Trap1 ameliorates parkin-mutant phenotypes and parkin expression suppresses Trap1-mutant phenotypes, suggesting that molecular and organellar quality control pathways act in parallel downstream from Pink1. p62 is an autophagy adaptor that acts in the PINK1/Parkin pathway, facilitating the aggregation and elimination of depolarised mitochondria through mitophagy. In this work it is shown that loss-of-function mutations in the Drosophila orthologue of p62, ref(2)P, result in a reduction in lifespan and age-dependent neurodegeneration. ref(2)P expression rescues the Pink1-mutant phenotypes and its presence is essential for the parkin-mediated rescue of Pink1 mutant flies.