Objective: To explore the role of the mitochondrial DNA (mtDNA) in the development of respiratory chain complex (CI-IV) deficiencies in the substantia nigra (SN) of idiopathic Parkinson’s disease (IPD) patients at single-neuron level.

Background: The loss of dopaminergic SN neurons in IPD is associated with Lewy body formation and mitochondrial dysfunction predominantly affecting CI. Large-scale mtDNA deletions have been identified as cause of CIV deficiency in patient neurons. However, the molecular origin of the more widespread CI deficiency remains elusive.

Methods: We used multiple-label immunofluorescence to quantify the abundance of subunits of CI-IV (NDUFB8 or NDUFA13, SDHA, UQCRC2 and COXI), and mitochondrial transcription factors A (TFAM) and B2 (TFB2M) relative to mitochondrial mass (Porin and GRP75) in postmortem sections of 10 IPD patients and 10 age-matched controls. To investigate the contribution of the mtDNA to respiratory chain deficiency in IPD, SN neurons were isolated by laser capture microdissection and analyzed for mtDNA copy number changes, the concentration of replication-associated 7S DNA and the presence of deletions using real-time PCR.

Results: We determined reductions in the abundances of mitochondria-normalized NDUFB8 and SDHA in patient neurons. Correlation analysis at the single-cell level implicated that the occurrence of CIV deficiency is linked to loss of CI. The CI deficit in patients was further associated with low abundance of the mtDNA transcription factors TFAM and TFB2M, which are also required for transcription-primed mtDNA replication. In support of this finding, real-time PCR analysis in pooled SN neurons revealed fewer replication-associated mtDNA molecules and an overall reduction in copy number in IPD patients. Comparisons between individual cells of the same patient showed that this effect was even more pronounced in such neurons with severe CI deficiency.

Conclusions: Respiratory chain dysfunction in IPD not only involves CI, but also extends to CII. While CI deficiency may be the consequence of impaired TFAM-mediated mtDNA transcription/replication, the lack of CII more likely results from compromised nuclear transcription activation implicating both mitochondrial and nuclear factors in the pathogenesis of IPD.

This work has been presented at the 2015 EMBO meeting on “Mitochondrial DNA and Neurogeneration” and the study is “in press” with the Annals of Neurology.

« Back to 2016 International Congress

MDS Abstracts - https://www.mdsabstracts.org/abstract/mitochondrial-nuclear-interplay-in-single-respiratory-chain-deficient-parkinsons-disease-neurons/