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Acta Neuropathol. 2018 Mar;135(3):409-425. doi: 10.1007/s00401-017-1794-7. Epub 2017 Dec 21.

Neuronal complex I deficiency occurs throughout the Parkinson's disease brain, but is not associated with neurodegeneration or mitochondrial DNA damage.

Author information

1
Department of Neurology, Haukeland University Hospital, 5021, Bergen, Norway.
2
Department of Clinical Medicine, University of Bergen, Pb 7804, 5020, Bergen, Norway.
3
MRC-Mitochondrial Biology Unit, University of Cambridge, Hills Road, Cambridge, CB2 OXY, UK.
4
Department of Pathology, Haukeland University Hospital, 5021, Bergen, Norway.
5
Department of Biomedicine, University of Bergen, Pb 7804, 5020, Bergen, Norway.
6
Gade Laboratory for Pathology, Department of Clinical Medicine, Haukeland University Hospital and University of Bergen, 5021, Bergen, Norway.
7
The Norwegian Centre for Movement Disorders and Department of Neurology, Stavanger University Hospital, Pb 8100, 4068, Stavanger, Norway.
8
Department of Mathematics and Natural Sciences, University of Stavanger, 4062, Stavanger, Norway.
9
Department of Neurology, Haukeland University Hospital, 5021, Bergen, Norway. charalampos.tzoulis@nevro.uib.no.
10
Department of Clinical Medicine, University of Bergen, Pb 7804, 5020, Bergen, Norway. charalampos.tzoulis@nevro.uib.no.

Abstract

Mitochondrial complex I deficiency occurs in the substantia nigra of individuals with Parkinson's disease. It is generally believed that this phenomenon is caused by accumulating mitochondrial DNA damage in neurons and that it contributes to the process of neurodegeneration. We hypothesized that if these theories are correct, complex I deficiency should extend beyond the substantia nigra to other affected brain regions in Parkinson's disease and correlate tightly with neuronal mitochondrial DNA damage. To test our hypothesis, we employed a combination of semiquantitative immunohistochemical analyses, Western blot and activity measurements, to assess complex I quantity and function in multiple brain regions from an extensively characterized population-based cohort of idiopathic Parkinson's disease (n = 18) and gender and age matched healthy controls (n = 11). Mitochondrial DNA was assessed in single neurons from the same areas by real-time PCR. Immunohistochemistry showed that neuronal complex I deficiency occurs throughout the Parkinson's disease brain, including areas spared by the neurodegenerative process such as the cerebellum. Activity measurements in brain homogenate confirmed a moderate decrease of complex I function, whereas Western blot was less sensitive, detecting only a mild reduction, which did not reach statistical significance at the group level. With the exception of the substantia nigra, neuronal complex I loss showed no correlation with the load of somatic mitochondrial DNA damage. Interestingly, α-synuclein aggregation was less common in complex I deficient neurons in the substantia nigra. We show that neuronal complex I deficiency is a widespread phenomenon in the Parkinson's disease brain which, contrary to mainstream theory, does not follow the anatomical distribution of neurodegeneration and is not associated with the neuronal load of mitochondrial DNA mutation. Our findings suggest that complex I deficiency in Parkinson's disease can occur independently of mitochondrial DNA damage and may not have a pathogenic role in the neurodegenerative process.

KEYWORDS:

Complex I; Mitochondria; Parkinsonism; Respiratory chain; Substantia nigra

PMID:
29270838
DOI:
10.1007/s00401-017-1794-7

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