Increased TFAM binding to mtDNA damage hot spots is associated with mtDNA loss in aged rat heart

Chimienti G, Picca A, Sirago G, Fracasso F, Calvani R, Bernabei R, Russo F, Carter CS, Leeuwenburgh C, Pesce V, Marzetti E, Lezza AMS

https://www.sciencedirect.com/science/article/pii/S0891584918311614

• In aged rat hearts (27 months), the authors observe 25% decrease in mtDNA content, an anti-correlated 29% increase in the 4.8 kb mtDNA deletion relative content, and 38% decrease in TFAM levels.
• The TFAM-binding activity to specific mtDNA regions increased at the mtDNA replication origins, D-loop and Ori-L
• A marked increase in the relative content of mtDNA strand damage was found in the D-loop and Ori-L in aged animals, suggesting the existence of mutational hotspots in these regions

Mitochondrial Supercomplexes Do Not Enhance Catalysis by Quinone Channeling

Fedor JG and Hirst J

https://www.sciencedirect.com/science/article/pii/S1550413118303310?via%3Dihub

• Components of the electron transport chain have been observed to form respiratory units, called the "respirasome" consisting of 1 CI, 2 CIII and 1 CIV. It has been proposed that the respirasome serves to stabilize CI and mitigate the production of ROS.
• More controversially, the respirasome has been suggested to confer a kinetic advantage on respiration by trapping/channeling quinone to enhance its transfer between the enzymes in the supercomplex, creating an independent, local quinone pool that does not exchange with the quinone pool outside.
• The authors test the quinone channeling hypothesis by introducing an external enzyme which competes for quinone. If the substrate is truly channeled, flux through the competing pathway is negligible.
• The authors introduce the alternative oxidase (AOX) protein. The authors find that AOX competes effectively with the CIII/CIV pathway. Therefore, quinone is not channeled or sequestered by the respiratory-chain supercomplexes.

Comprehensive Quantification of the Modified Proteome Reveals Oxidative Heart Damage in Mitochondrial Heteroplasmy

Bagwan N, Bonzon-Kulichenko E, Calvo E, Lechuga-Vieco AV, Michalakopoulos S, Trevisan-Herraz M, Ezkurdia I, Rodríguez JM, Magni R, Latorre-Pellicer A, Enríquez JA, Vázquez J

https://www.sciencedirect.com/science/article/pii/S2211124718308611?via%3Dihub

• Mass spectrometry is a powerful tool for proteomics. A large proportion of unassigned spectra are thought to arise from peptides containing sequence variants or unknown chemical/post-translational modifications.
• The authors present a suite of bioinformatics tools which extend the coverage which can be attained from mass spectrometry, which allow the location of the modified residues and quantitative analysis of post-translational modification.
• The authors test their approach in the context of mitochondrial heteroplasmy in 12 week old (i.e. young) mice carrying two non-pathological mtDNA variants. The first mtDNA variant is the original variant which co-evolved with the nucleus (C57BL/6J). The second mtDNA variant is NZB.
• The authors found evidence of protein alterations in the heart of heteroplasmic mice which were consistent with mitochondrial dysfunction. 
• The alterations in heteroplasmic mice were consistent with the decreased ATP synthesis and the abnormal increase in phosphocreatine/ATP ratio in the heart, shift to glycolysis, and with the increase in plasma creatine kinase which have been observed in this animal model (unpublished data).
• The authors detected signs of inflammation in the liver of heteroplasmic mice with aging; however, heteroplasmy mainly produces oxidative modifications of OXPHOS proteins in the heart, at this age.