Mitochondrial DNA Depletion in Respiratory Chain–Deficient Parkinson Disease Neurons

Abstract

ObjectiveTo determine the extent of respiratory chain abnormalities and investigate the contribution of mtDNA to the loss of respiratory chain complexes (CI–IV) in the substantia nigra (SN) of idiopathic Parkinson disease (IPD) patients at the single‐neuron level.MethodsMultiple‐label immunofluorescence was applied to postmortem sections of 10 IPD patients and 10 controls to quantify the abundance of CI–IV subunits (NDUFB8 or NDUFA13, SDHA, UQCRC2, and COXI) and mitochondrial transcription factors (TFAM and TFB2M) relative to mitochondrial mass (porin and GRP75) in dopaminergic neurons. To assess the involvement of mtDNA in respiratory chain deficiency in IPD, SN neurons, isolated with laser‐capture microdissection, were assayed for mtDNA deletions, copy number, and presence of transcription/replication‐associated 7S DNA employing a triplex real‐time polymerase chain reaction (PCR) assay.ResultsWhereas mitochondrial mass was unchanged in single SN neurons from IPD patients, we observed a significant reduction in the abundances of CI and II subunits. At the single‐cell level, CI and II deficiencies were correlated in patients. The CI deficiency concomitantly occurred with low abundances of the mtDNA transcription factors TFAM and TFB2M, which also initiate transcription‐primed mtDNA replication. Consistent with this, real‐time PCR analysis revealed fewer transcription/replication‐associated mtDNA molecules and an overall reduction in mtDNA copy number in patients. This effect was more pronounced in single IPD neurons with severe CI deficiency.InterpretationRespiratory chain dysfunction in IPD neurons not only involves CI, but also extends to CII. These deficiencies are possibly a consequence of the interplay between nDNA and mtDNA‐encoded factors mechanistically connected via TFAM. ANN NEUROL 2016;79:366–378

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

“…Our findings do not corroborate the current hypothesis that complex I deficiency in PD may be the result of accumulating deletions and quantitative depletion of the mtDNA [4,16]. Moreover, ultra-deep-sequencing studies in single neurons and brain homogenates have shown no difference in the point mutational burden of mtDNAencoded complex I genes between PD individuals and controls, suggesting that mtDNA point mutations do not contribute to the observed complex I deficiency [8,13].…”

“…Serial 3 μm thick sections were stained with primary antibodies (all from Abcam) against complex I (NDUFB8, ab110242, dilution 1:300), complex II (anti-SDHA, ab14715, dilution 1:4000), complex III (anti-UQCRC2, ab14745, dilution 1:10,000), complex IV (COX-I, ab14705, dilution 1:10,000), complex V (ATP-synthase, ab14748, dilution 1:10,000), and the mitochondrial membrane marker porin (VDAC1, ab14734, dilution 1:10,000). We chose the NDUFB8 subunit because it is central to complex I assembly and function [10,39,46] and has been widely used as a marker of the integrity of the complex [16,40,41]. Sections were deparaffinised in Histoclear and rehydrated in graded ethanol.…”

Knockdown of Sucla2 decreases the viability of mouse spermatocytes by inducing apoptosis through injury of the mitochondrial function of cells

“…Mitochondria are complex organelles that not only participate in ATP synthesis and ROS production, but also play important roles in proliferation, differentiation, and apoptosis of germ cells [17,18]. Mitochondrial function depends not only on mitochondrial molecules encoded by nuclear DNA (nDNA), but also depends on molecules encoded by mitochondria DNA (mtDNA) [19,20]. The literature shows that many kinds of abnormal expression of mitochondrial proteins are associated with mitochondrial dysfunction, resulting in mitochondrial diseases such as neurodegeneration, cancer, infertility, and ageing [21][22][23].…”

Parkinson’s Disease: Insights from Drosophila Model

“…It accumulates throughout life and is thought to contribute to diseases of aging that include neurodegeneration, metabolic disorders, cancer, heart disease, and sarcopenia [126,127]. A new investigation of mtDNA in the dopaminergic neurons [128] expanded the previous results showing a prevalent deletion in single neurons on a background of multiple mtDNA deletions [129]. It showed that complex I and complex II are most consistently affected in single neurons, which also displayed a reduced mtDNA copy number [128].…”