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

Vincent A, Briggs L, Chatwin GF, Emery E, Tomlins R, Oswald M, Middleton CA, Evans GJ, Sweeney ST, Elliott CJ - Hum. Mol. Genet. (2012)

Bottom Line: 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.Surprisingly, scavengers of ROS did not rescue the resting membrane potential and locomotory phenotypes.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of York, P.O. Box 373, York YO10 5YW, UK.

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.

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In the parkin  background, overexpression of oxidative stress transgenes rescues synaptic overgrowth but not muscle RMP or larval locomotion. (A) The normalized bouton count is reduced from the parkin mutant peak (∼+50% of the CS wild-type) to +20% by overexpression of catalase or superoxide dismutase (Sod1 or Sod2) with a global driver. The effect of the oxidative stress transgenes is significant (Bonferroni comparison with parkin P< 0.001 for each transgene). At least 24 neuromuscular junctions for each genotype, totally 224. (B) Oxidative stress gene overexpression did not rescue the muscle RMP (comparison with parkin mutants, Bonferroni tests all P= 1.0). At least 18 muscles for each genotype, 213 in total. (C) The oxidative stress gene overexpression did not rescue larval locomotion (comparison with parkin mutants Bonferroni tests all P= 1.0). At least 12 larvae for each genotype, total 171. Genotypes—(A and C) wild-type: CS; parkin: park25/park25 outcrossed to the Act5C driver used to express each transgene in park25/park25 background. (B) Wild-type CS/w−; parkin; parkZ3678/park25, transgene expression driven by the Act5C driver.
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DDR609F8: In the parkin background, overexpression of oxidative stress transgenes rescues synaptic overgrowth but not muscle RMP or larval locomotion. (A) The normalized bouton count is reduced from the parkin mutant peak (∼+50% of the CS wild-type) to +20% by overexpression of catalase or superoxide dismutase (Sod1 or Sod2) with a global driver. The effect of the oxidative stress transgenes is significant (Bonferroni comparison with parkin P< 0.001 for each transgene). At least 24 neuromuscular junctions for each genotype, totally 224. (B) Oxidative stress gene overexpression did not rescue the muscle RMP (comparison with parkin mutants, Bonferroni tests all P= 1.0). At least 18 muscles for each genotype, 213 in total. (C) The oxidative stress gene overexpression did not rescue larval locomotion (comparison with parkin mutants Bonferroni tests all P= 1.0). At least 12 larvae for each genotype, total 171. Genotypes—(A and C) wild-type: CS; parkin: park25/park25 outcrossed to the Act5C driver used to express each transgene in park25/park25 background. (B) Wild-type CS/w−; parkin; parkZ3678/park25, transgene expression driven by the Act5C driver.

Mentions: Having demonstrated synaptic overgrowth, we wanted to examine the role of oxidative stress in the parkin phenotype. Overexpression of genes that scavenge free radicals (superoxide dismutase, catalase) significantly rescued the overgrowth phenotype, down from 53% to 20% more than the wild-type (Fig. 8A). In contrast to these data, we found no rescue of either the muscle RMP or the larval locomotory defect with expression of any of these scavengers (Fig. 8B and C).Figure 8.


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

Vincent A, Briggs L, Chatwin GF, Emery E, Tomlins R, Oswald M, Middleton CA, Evans GJ, Sweeney ST, Elliott CJ - Hum. Mol. Genet. (2012)

In the parkin  background, overexpression of oxidative stress transgenes rescues synaptic overgrowth but not muscle RMP or larval locomotion. (A) The normalized bouton count is reduced from the parkin mutant peak (∼+50% of the CS wild-type) to +20% by overexpression of catalase or superoxide dismutase (Sod1 or Sod2) with a global driver. The effect of the oxidative stress transgenes is significant (Bonferroni comparison with parkin P< 0.001 for each transgene). At least 24 neuromuscular junctions for each genotype, totally 224. (B) Oxidative stress gene overexpression did not rescue the muscle RMP (comparison with parkin mutants, Bonferroni tests all P= 1.0). At least 18 muscles for each genotype, 213 in total. (C) The oxidative stress gene overexpression did not rescue larval locomotion (comparison with parkin mutants Bonferroni tests all P= 1.0). At least 12 larvae for each genotype, total 171. Genotypes—(A and C) wild-type: CS; parkin: park25/park25 outcrossed to the Act5C driver used to express each transgene in park25/park25 background. (B) Wild-type CS/w−; parkin; parkZ3678/park25, transgene expression driven by the Act5C driver.
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC3313793&req=5

DDR609F8: In the parkin background, overexpression of oxidative stress transgenes rescues synaptic overgrowth but not muscle RMP or larval locomotion. (A) The normalized bouton count is reduced from the parkin mutant peak (∼+50% of the CS wild-type) to +20% by overexpression of catalase or superoxide dismutase (Sod1 or Sod2) with a global driver. The effect of the oxidative stress transgenes is significant (Bonferroni comparison with parkin P< 0.001 for each transgene). At least 24 neuromuscular junctions for each genotype, totally 224. (B) Oxidative stress gene overexpression did not rescue the muscle RMP (comparison with parkin mutants, Bonferroni tests all P= 1.0). At least 18 muscles for each genotype, 213 in total. (C) The oxidative stress gene overexpression did not rescue larval locomotion (comparison with parkin mutants Bonferroni tests all P= 1.0). At least 12 larvae for each genotype, total 171. Genotypes—(A and C) wild-type: CS; parkin: park25/park25 outcrossed to the Act5C driver used to express each transgene in park25/park25 background. (B) Wild-type CS/w−; parkin; parkZ3678/park25, transgene expression driven by the Act5C driver.
Mentions: Having demonstrated synaptic overgrowth, we wanted to examine the role of oxidative stress in the parkin phenotype. Overexpression of genes that scavenge free radicals (superoxide dismutase, catalase) significantly rescued the overgrowth phenotype, down from 53% to 20% more than the wild-type (Fig. 8A). In contrast to these data, we found no rescue of either the muscle RMP or the larval locomotory defect with expression of any of these scavengers (Fig. 8B and C).Figure 8.

Bottom Line: 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.Surprisingly, scavengers of ROS did not rescue the resting membrane potential and locomotory phenotypes.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, University of York, P.O. Box 373, York YO10 5YW, UK.

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.

Show MeSH
Related in: MedlinePlus