Mitochondrial function and morphology are impaired in parkin-mutant fibroblasts.
OBJECTIVE
There are marked mitochondrial abnormalities in parkin-knock-out Drosophila and other model systems. The aim of our study was to determine mitochondrial function and morphology in parkin-mutant patients. We also investigated whether pharmacological rescue of impaired mitochondrial function may be possible in parkin-mutant human tissue.


METHODS
We used three sets of techniques, namely, biochemical measurements of mitochondrial function, quantitative morphology, and live cell imaging of functional connectivity to assess the mitochondrial respiratory chain, the outer shape and connectivity of the mitochondria, and their functional inner connectivity in fibroblasts from patients with homozygous or compound heterozygous parkin mutations.


RESULTS
Parkin-mutant cells had lower mitochondrial complex I activity and complex I-linked adenosine triphosphate production, which correlated with a greater degree of mitochondrial branching, suggesting that the functional and morphological effects of parkin are related. Knockdown of parkin in control fibroblasts confirmed that parkin deficiency is sufficient to explain these mitochondrial effects. In contrast, 50% knockdown of parkin, mimicking haploinsufficiency in human patient tissue, did not result in impaired mitochondrial function or morphology. Fluorescence recovery after photobleaching assays demonstrated a lower level of functional connectivity of the mitochondrial matrix, which further worsened after rotenone exposure. Treatment with experimental neuroprotective compounds resulted in a rescue of the mitochondrial membrane potential.


CONCLUSIONS
Our study demonstrates marked abnormalities of mitochondrial function and morphology in parkin-mutant patients and provides proof-of-principle data for the potential usefulness of this new model system as a tool to screen for disease-modifying compounds in genetically homogenous parkinsonian disorders.
Mortiboys
Heather
H
Academic Neurology Unit, Medical School, University of Sheffield, Sheffield, United Kingdom.
Thomas
Kelly Jean
KJ
Koopman
Werner J H
WJ
Klaffke
Stefanie
S
Abou-Sleiman
Patrick
P
Olpin
Simon
S
Wood
Nicholas W
NW
Willems
Peter H G M
PH
Smeitink
Jan A M
JA
Cookson
Mark R
MR
Bandmann
Oliver
O
D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000328:Adult; D002478:Cells, Cultured; D015536:Down-Regulation / Q000235:genetics; D004353:Drug Evaluation, Preclinical / Q000379:methods; D045222:Electron Transport Chain Complex Proteins / Q000235:genetics; D004734:Energy Metabolism / Q000235:genetics; D005347:Fibroblasts / Q000378:metabolism / Q000473:pathology; D006801:Humans; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000235:genetics; D008875:Middle Aged; D008928:Mitochondria / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D028361:Mitochondrial Diseases / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D009154:Mutation / Q000235:genetics*; D018696:Neuroprotective Agents / Q000494:pharmacology; D020734:Parkinsonian Disorders / Q000150:complications* / Q000235:genetics / Q000378:metabolism*; D012402:Rotenone / Q000494:pharmacology; D044767:Ubiquitin-Protein Ligases / Q000235:genetics*; D014475:Uncoupling Agents / Q000494:pharmacology
D045222:Electron Transport Chain Complex Proteins; D018696:Neuroprotective Agents; D014475:Uncoupling Agents; D012402:Rotenone; D000255:Adenosine Triphosphate; D044767:Ubiquitin-Protein Ligases; C111567:parkin protein