Mitochondrial quality control and autophagosomal process in Parkinson’s disease model (LB170)

Abstract

Parkinson’s disease (PD) is the second most common neurodegenerative disorder, and can be caused by genetic mutations of PTEN‐induced putative kinase 1 (PINK1) and the E3 ubiquitin ligase, Parkin. It has been proposed that Parkin contributes to policing mitochondrial fidelity by binding to dysfunctional mitochondria via PINK1 and targeting them for autophagic degradation. However, the actual role of PINK1/Parkin in controlling autophagy is unknown. To define more clearly the roles of Parkin in neurons, we quantified the behavior of mitochondria and autophagosomes in motor neurons of live Drosophila melanogaster larvae by time lapse microscopy. We analyzed the life cycle of mitochondria in Parkin mutant animals expressing mitochondrially‐targeted GFP by three distinct criteria: mitochondrial axonal transport, mitochondrial fission‐fusion and mitophagy. Autophagosomal processes were analyzed by studying autophagosomal movement and density via expressed RFP‐atg8. In motor axons, parkin mutants showed reduced flux of both anterograde and retrograde mitochondria and an increase in pause time compared to controls. However, these mutants did not show significant differences in mitochondrial velocities. Morphological measurements from parkin mutants showed that normal fission‐fusion balance was preserved in the axons of segmental nerves, while tubular and hyper‐fused mitochondria were found in the cell bodies. In addition, we did not observe a correlation between mitochondrial length and velocity or direction of axonal movement in parkin mutants. To understand the organization of mitophagy, we quantified mitochondrial density and found that parkin mutants displayed a significantly reduced mitochondrial density in motor axons. Analysis of autophagic vacuoles in parkin mutants showed reduced retrograde axonal flux and reduced density in the motor cell bodies. These results suggest that the differences in axonal mitochondrial flux in disease mutants result from the combined effects of altered mitochondrial motility and density in motor axons. Additionally, Parkin perturbation may disrupt autophagosomal retrograde transport in axons and affect mitochondrial morphology in motor cell bodies.Grant Funding Source: Supported by grant, 5 R01 NS027073 from National Institutes of Health/NINDS