Modeling human mitochondrial diseases related to MPV17 and APOPT1 in Drosophila melanogaster

Mitochondrial diseases are a clinically heterogeneous group of inherited disorders associated with defects in the oxidative phosphorylation system, with an estimated incidence in between 1:5,000 and 1:10,000 live births. Mitochondrial respiratory chain function depends on the coordinated expression of both mitochondrial and nuclear genomes. Thus, also mutations affecting nuclear-encoded mitochondrial proteins are responsible for mitochondrial disease onset. During the last decades, an increasing number of novel nuclear disease genes have been identified. Among those genes, human MPV17 and APOPT1 have already been linked to mitochondrial diseases but their role in mitochondrial physiology and disease remains still puzzling. Mutations in the human MPV17 nuclear gene, encoding a small hydrophobic mitochondrial inner membrane protein, are a prominent cause of a pediatric hepatocerebral form of mitochondrial DNA depletion syndrome. APOPT1 mutations are responsible for an infantile or childhood mitochondrial encephalopathy hallmarked by profound deficiencies in both COX activity and amount. In order to dissect out the role of these two genes, in this PhD project we focused our attention on the functional and molecular characterization of Drosophila melanogaster orthologs of MPV17 and APOPT1. We found that dMpv17 down-regulation in flies causes a profound mitochondrial DNA depletion in the fat bodies (a Drosophila organ analogous to human liver). Depletion is also detected, albeit moderate, in dMpv17 KD cells. Our results reveal that dMpv17 can form a channel when inserted in an artificial planar lipid bilayer. Moreover, we also show that the Drosophila protein could interact with dMic19, a component of the MICOS complex, as well as dMrp4, that could play a role in dMpv17 gating regulation. The analysis of mitochondrial morphology in dMpv17 down-regulated cells together with the interaction with Mic19 suggest a possible role for dMpv17 in the maintenance of the structural and functional stability of the inner mitochondrial membrane. Further, we confirmed that Drosophila is a reliable model for studying human mitochondrial disease also in the case of APOPT1. Indeed, our preliminary data show that dApopt1 down-regulation in flies causes motor impairment and COX deficiency, characteristic features of the human disease. Not only COX activity but also coxI transcript is decreased in dApopt1 down-regulated flies. Finally, we show that H2O2 treatment and, in turn, oxidative stress induce an increase in dApopt1 transcript. Finally, our data shed new light on the possible role of dMpv17 and dApopt1 in physiological and pathological conditions