parkin-induced defects in neurophysiology and locomotion are generated by metabolic dysfunction and not oxidative stress

Abstract

Parkinson's disease (PD) is characterized by movement disorders, including bradykinesia. Analysis of inherited, juvenile PD, identified several genes linked via a common pathway to mitochondrial dysfunction. In this study, we demonstrate that the larva of the Drosophila parkin mutant faithfully models the locomotory and metabolic defects of PD and is an excellent system for investigating their inter-relationship. parkin larvae displayed a marked bradykinesia that was caused by a reduction in both the frequency of peristalsis and speed of muscle contractions. Rescue experiments confirmed that this phenotype was due to a defect in the nervous system and not in the muscle. Furthermore, recordings of motoneuron activity in parkin larvae revealed reduced bursting and a striking reduction in evoked and miniature excitatory junction potentials, suggesting a neuronal deficit. This was supported by our observations in parkin larvae that the resting potential was depolarized, oxygen consumption and ATP concentration were drastically reduced while lactate was increased. These findings suggest that neuronal mitochondrial respiration is severely compromised and there is a compensatory switch to glycolysis for energy production.parkin mutants also possessed overgrown neuromuscular synapses, indicative of oxidative stress, which could be rescued by overexpression of parkin or scavengers of reactive oxygen species (ROS). Surprisingly, scavengers of ROS did not rescue the resting membrane potential and locomotory phenotypes. We therefore propose that mitochondrial dysfunction in parkin mutants induces Parkinsonian bradykinesia via a neuronal energy deficit and resulting synaptic failure, rather than as a consequence of downstream oxidative stress.

Optimization of wrMTrck to monitor Drosophila larval locomotor activity

“…4). A previous report suggests that only the neuronal contribution of parkin affects larval locomotion speed (Vincent et al, 2012), while our data provide evidence that a muscle-specific decrease in Parkin alters locomotion speed and path attributes. These data support the neuronal and muscle phenotypes observed in parkin mutants (Guo, 2012).…”

“…Larvae that are mutant for Drosophila parkin , a gene mutated in patients that have sporadic Parkinson’s disease (PD), are already known to exhibit locomotion defects (Vincent et al, 2012). Trim32 is an E3 ubiquitin ligase and mutations that cluster in the NHL domains result in human limb-girdle muscular dystrophy type 2H (LGMD2H) (Shieh et al, 2011).…”

The function of the M-line protein, obscurin, in controlling the symmetry of the sarcomere inDrosophilaflight muscle

“…Larval crawling and fly jumping were tested as described (Elliott et al, 2007;Vincent et al, 2012). Three-day-old flies were flight tested (Cripps et al, 1994).…”

Neonatal C57BL/6J and parkin mice respond differently following developmental manganese exposure: Result of a high dose pilot study

“…Inheritable forms of PD are often associated with genetic mutations, among them a-synuclein, DJ-1 , and Park2 (Kitada et al, 1998, Bonifati et al, 2003). Parkin, encoded by the Park2 gene, is part of an E3 ubiquitin ligase complex which is part of the ubiquitin-proteasome system that mediates the targeting of proteins for degradation (Vincent et al, 2012). Parkin may have an indirect role in mitochondrial respiratory chain function, cellular responses to oxidative stress, and removal of damaged mitochondria (Narendra et al, 2008; Vincent et al, 2012).…”