bims-cytox1 2017-10-15 papers

Issue of 2017‒10‒15
two papers selected by
Gavin McStay
New York Institute of Technology

Biochim Biophys Acta. 2017 Oct 03. pii: S0167-4889(17)30270-7. [Epub ahead of print]

Two mutations in mitochondrial ATP6 gene of ATP synthase, related to human cancer, affect ROS, calcium homeostasis and mitochondrial permeability transition in yeast.

Katarzyna Niedzwiecka, Renata Tisi, Sara Penna, Malgorzata Lichocka, Danuta Plochocka, Roza Kucharczyk.

The relevance of mitochondrial DNA (mtDNA) mutations in cancer process is still unknown. Since the mutagenesis of mitochondrial genome in mammals is not possible yet, we have exploited budding yeast S. cerevisiae as a model to study the effects of tumor-associated mutations in the mitochondrial MTATP6 gene, encoding subunit 6 of ATP synthase, on the energy metabolism. We previously reported that four mutations in this gene have a limited impact on the production of cellular energy. Here we show that two mutations, Atp6-P163S and Atp6-K90E (human MTATP6-P136S and MTATP6-K64E, found in prostate and thyroid cancer samples, respectively), increase sensitivity of yeast cells both to compounds inducing oxidative stress and to high concentrations of calcium ions in the medium, when Om45p, the component of porin complex in outer mitochondrial membrane (OM), was fused to GFP. In OM45-GFP background, these mutations affect the activation of yeast permeability transition pore (yPTP, also called YMUC, yeast mitochondrial unspecific channel) upon calcium induction. Moreover, we show that calcium addition to isolated mitochondria heavily induced the formation of ATP synthase dimers and oligomers, recently proposed to form the core of PTP, which was slower in the mutants. We show the genetic evidence for involvement of mitochondrial ATP synthase in calcium homeostasis and permeability transition in yeast. This paper is a first to show, although in yeast model organism, that mitochondrial ATP synthase mutations, which accumulate during carcinogenesis process, may be significant for cancer cell escape from apoptosis.

Keywords: ATP synthase; ATP6; Cancer; Mitochondria; OM45; Permeability transition

DOI: https://doi.org/10.1016/j.bbamcr.2017.10.003

Mitochondrion. 2017 Oct 03. pii: S1567-7249(17)30030-2. [Epub ahead of print]

High-throughput BioSorter quantification of relative mitochondrial content and membrane potential in living Caenorhabditis elegans.

Young Joon Kwon, Sujay Guha, Florin Tuluc, Marni J Falk.

Mitochondrial respiratory chain disease is caused by a wide range of individually rare genetic disorders that impair cellular energy metabolism. While fluorescence microscopy analysis of nematodes fed MitoTracker Green (MTG) and tetramethylrhodamine ethyl ester (TMRE) can reliably quantify relative mitochondrial density and membrane potential, respectively, in C. elegans, it is a tedious process with limitations in the number and age of animals that can be studied. A novel, large particle, flow cytometry-based method reported here accelerates and automates the relative quantitation of mitochondrial physiology in nematode populations. Relative fluorescence profiles of nematode populations co-labeled with MTG and TMRE were obtained and analyzed by BioSorter (Union Biometrica). Variables tested included genetic mutation (wild-type N2 Bristol versus nuclear-encoded respiratory chain complex I mutant gas-1(fc21) worms), animal age (day 1 versus day 4 adults), classical respiratory chain inhibitor effects (oligomycin, FCCP), and pharmacologic therapy duration (24h versus 96h treatments with glucose or nicotinic acid). A custom MATLAB script, which can be run on any computer with MATLAB runtime, was written to automatically quantify and analyze results in large animal populations. BioSorter analysis independently validated relative MTG and TMRE changes that we had previously performed by fluorescence microscopy in a variety of experimental conditions, with notably greater animal population sizes and substantially reduced experimental time. Older, fragile animal populations that are difficult to study by microscopy approaches were readily amenable to analysis with the BioSorter method. Overall, this high-throughput method enables efficient relative quantitation of in vivo mitochondrial physiology over time in a living animal in response to gene mutations and candidate therapies, which can be used to accelerate the translation of basic research into optimization of clinical therapies for mitochondrial disease.

Keywords: C. elegans; Flow cytometry; Mitochondrial disease; Screening

DOI: https://doi.org/10.1016/j.mito.2017.09.004