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. 2013 Jun 26;33(26):10790-801.
doi: 10.1523/JNEUROSCI.3525-12.2013.

The impact of pathogenic mitochondrial DNA mutations on substantia nigra neurons

Amy Reeve  1 , Martin Meagher, Nichola Lax, Eve Simcox, Philippa Hepplewhite, Evelyn Jaros, Doug Turnbull
Affiliations

The impact of pathogenic mitochondrial DNA mutations on substantia nigra neurons

Amy Reeve et al. J Neurosci. .

Abstract

Mitochondrial defects within substantia nigra (SN) neurons are implicated in the pathogenesis of Parkinson's disease. SN neurons show increased mitochondrial defects, mitochondrial DNA deletion levels, and susceptibility to such dysfunction, although the role of mitochondria in neuronal degeneration remains uncertain. In this study, we addressed this important question by exploring changes within the mitochondria of SN neurons from patients with primary mitochondrial diseases to determine whether mitochondrial dysfunction leads directly to neuronal cell loss. We counted the pigmented neurons and quantified mitochondrial respiratory activity, deficiencies in mitochondrial proteins, and the percentage of pathogenic mutations in single neurons. We found evidence of defects of both complex I and complex IV of the respiratory chain in all patients. We found that marked neuronal cell loss was only observed in a few patients with mitochondrial disease and that all these patients had mutations in polymerase gamma (POLG), which leads to the formation of multiple mitochondrial DNA deletions over time, similar to aging and Parkinson's disease. Interestingly, we detected α-synuclein pathology in two mitochondrial patients with POLG mutations. Our observations highlight the complex relationship between mitochondrial dysfunction and the susceptibility of SN neurons to degeneration and α-synuclein pathology. Our finding that the loss of SN neurons was only severe in patients with POLG mutations suggests that acquired mitochondrial defects may be less well tolerated by SN neurons than by inherited ones.

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Figures

Figure 1.
Figure 1.
α-Synuclein immunoreactivity in SN of POLG patients, a marker of Lewy body pathology. A, B, Two of the five POLG/multiple deletion patients studied (A, POLG 3; B, POLG 4) showed α-synuclein-positive Lewy body pathology within pigmented SN neurons. Pathology included Lewy bodies, pre Lewy bodies, cytoplasmic granular inclusions (black arrows), and Lewy neurites (red arrows). Sections were counterstained with CFV. Images were taken at a 40× magnification. Scale bar, 100 μm.
Figure 2.
Figure 2.
Porin immunoreactivity in SN neurons, a marker of mitochondrial density. All pigmented SN neurons in patients with mitochondrial disorders showed a uniform density of mitochondria, similar to controls. A–D, Shown is KSS/single large-scale deletion patient 1 (A), m.8344 A>G point mutation patient (B), POLG/multiple deletion patients (C), and controls (D). A also highlights the microvacuolation that was widespread throughout the brain and mild to moderate within the SN of this case. Images were taken at a 40× magnification. Scale bar, 100 μm.
Figure 3.
Figure 3.
Complex I immunohistochemistry showing the variable degree of protein deficiency in SN neurons. Pigmented SN neurons with a deficiency in complex I subunits (arrows) were found in all cases and controls; however, the level of deficiency varied. A–H, Images show staining for CI20 (A–D) and CI19 (E–H), and the arrows indicate neurons showing deficiencies for these proteins. for these proteins. Deficiencies in the expression of these proteins were found in patients with point mutation (B, F), POLG/multiple deletions (C, G), and controls (D, H). Images were taken at a 40× magnification. Scale bar, 100 μm. I, The number of complex I-deficient neurons was then expressed as a percentage of the total counted neurons. Error bars show SD of controls (n = 10) and PD cases (n = 5).
Figure 4.
Figure 4.
COXI immunohistochemistry showing the variable degree of deficiency in SN neurons. Pigmented SN neurons with a deficiency in COXI protein (arrows) were found in all patients with mitochondrial disease and controls, but the levels varied between cases. A–D, The single deletion patient (A) showed negligible levels of deficiency, whereas levels of deficiency were higher in in point mutation patients (B), POLG/multiple deletion patients (C), and controls (D). Images were taken at a 40× magnification. Scale bar, 100 μm.
Figure 5.
Figure 5.
Deficiency in COX activity within SN neurons revealed by COX/SDH histochemistry. Respiratory (COX)-deficient neurons were found in the SN of all patients with mitochondrial disease and controls used within this study. However, the COX-deficient neurons (blue) were sparse in patients with KSS/single large-scale deletion (this patient had only one COX-deficient neuron; A) and point mutations (B). POLG/multiple deletion patients (C) generally showed higher levels of COX deficiency than the patients with inherited defects. Few COX-deficient neurons were present in the controls (D). Images were taken at a 40× magnification. Scale bar, 100 μm. E, Percentage of respiratory/COX-deficient neurons in patients with mitochondrial diseases and controls compared with data from COXI immunohistochemistry. Error bars show SD of controls (n = 10). Due to a lack of tissue availability, we were unable to perform COX/SDH histochemistry on all patients.
Figure 6.
Figure 6.
SN neurons of patients with mitochondrial disorders show high threshold levels for mtDNA mutations. A, Deletion levels within single SN neurons from POLG 3 (n = 45), POLG 4 (n = 23), and the KSS/single large-scale deletion patient 1 (n = 23) compared with controls (n = 21, 12, and 17, respectively). B, Point mutation threshold levels for m.3243 A>G MELAS and m.8344 A>G MERRF patients were measured in single SN neurons and in blood cells of a normal control using pyrosequencing (n = 10).
Figure 7.
Figure 7.
Pigmented neuron loss within the SN of patients with mitochondrial disorders. A, When expressed as a percentage neuron count at the same rostrocaudal level of SN from the serially sectioned control midbrain, some degree of cell loss was seen in all patients with mitochondrial disease. Three of five of the POLG/multiple deletion patients showed the most severe loss, whereas patients with KSS/single large-scale deletion and point mutations showed milder loss. For the group of controls used in this study, the mean cell count expressed as a percentage of the count at the same rostrocaudal level of the SN was 96 ± 31%. All cases fell around the control value of 100% as anticipated. B, Number of TH-positive neurons in a number of cases compared with a control mean (n = 3).
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References

    1. Abou-Sleiman PM, Muqit MM, Wood NW. Expanding insights of mitochondrial dysfunction in Parkinson's disease. Nat Rev Neurosci. 2006;7:207–219. doi: 10.1038/nrn1868. - DOI - PubMed
    1. Abramov AY, Smulders-Srinivasan TK, Kirby DM, Acin-Perez R, Enriquez JA, Lightowlers RN, Duchen MR, Turnbull DM. Mechanism of neurodegeneration of neurons with mitochondrial DNA mutations. Brain. 2010;133:797–807. doi: 10.1093/brain/awq015. - DOI - PMC - PubMed
    1. Bender A, Krishnan KJ, Morris CM, Taylor GA, Reeve AK, Perry RH, Jaros E, Hersheson JS, Betts J, Klopstock T, Taylor RW, Turnbull DM. High levels of mitochondrial DNA deletions in substantia nigra neurons in aging and Parkinson disease. Nat Genet. 2006;38:515–517. doi: 10.1038/ng1769. - DOI - PubMed
    1. Betarbet R, Sherer TB, MacKenzie G, Garcia-Osuna M, Panov AV, Greenamyre JT. Chronic systemic pesticide exposure reproduces features of Parkinson's disease. Nat Neurosci. 2000;3:1301–1306. doi: 10.1038/81834. - DOI - PubMed
    1. Betts J, Jaros E, Perry RH, Schaefer AM, Taylor RW, Abdel-All Z, Lightowlers RN, Turnbull DM. Molecular neuropathology of MELAS: level of heteroplasmy in individual neurones and evidence of extensive vascular involvement. Neuropathol Appl Neurobiol. 2006;32:359–373. doi: 10.1111/j.1365-2990.2006.00731.x. - DOI - PubMed

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