bims-mitran 2024-03-31 papers

Issue of 2024–03–31
three papers selected by
Andreas Kohler, Umeå University

Biochim Biophys Acta Mol Basis Dis. 2024 Mar 21. pii: S0925-4439(24)00120-0. [Epub ahead of print] 167131

A stagewise response to mitochondrial dysfunction in mitochondrial DNA maintenance disorders.

Amy E Vincent, Chun Chen, Tiago Bernardino Gomes, Valeria Di Leo, Tuomas Laalo, Kamil Pabis, Rodrick Capaldi, Michael F Marusich, David McDonald, Andrew Filby, Andrew Fuller, Diana Lehmann Urban, Stephan Zierz, Marcus Deschauer, Doug Turnbull, Amy K Reeve, Conor Lawless.

Mitochondrial DNA (mtDNA) deletions which clonally expand in skeletal muscle of patients with mtDNA maintenance disorders, impair mitochondrial oxidative phosphorylation dysfunction. Previously we have shown that these mtDNA deletions arise and accumulate in perinuclear mitochondria causing localised mitochondrial dysfunction before spreading through the muscle fibre. We believe that mito-nuclear signalling is a key contributor in the accumulation and spread of mtDNA deletions, and that knowledge of how muscle fibres respond to mitochondrial dysfunction is key to our understanding of disease mechanisms. To understand the contribution of mito-nuclear signalling to the spread of mitochondrial dysfunction, we use imaging mass cytometry. We characterise the levels of mitochondrial Oxidative Phosphorylation proteins alongside a mitochondrial mass marker, in a cohort of patients with mtDNA maintenance disorders. Our expanded panel included protein markers of key signalling pathways, allowing us to investigate cellular responses to different combinations of oxidative phosphorylation dysfunction and ragged red fibres. We find combined Complex I and IV deficiency to be most common. Interestingly, in fibres deficient for one or more complexes, the remaining complexes are often upregulated beyond the increase of mitochondrial mass typically observed in ragged red fibres. We further find that oxidative phosphorylation deficient fibres exhibit an increase in the abundance of proteins involved in proteostasis, e.g. HSP60 and LONP1, and regulation of mitochondrial metabolism (including oxidative phosphorylation and proteolysis, e.g. PHB1). Our analysis suggests that the cellular response to mitochondrial dysfunction changes depending on the combination of deficient oxidative phosphorylation complexes in each fibre.

Keywords: Cell signalling; Mitochondrial DNA deletion; Mitochondrial disease; Myopathy; OXPHOS

DOI: https://doi.org/10.1016/j.bbadis.2024.167131

MicroPubl Biol. 2024 ;2024

Loss of mitochondrial DNA is associated with reduced DNA content variability in Saccharomyces cerevisiae.

Christopher D Putnam.

DNA content measurement by fluorescence-assisted cell sorting (FACS) provides information on cell cycle progression and DNA content variability. Saccharomyces cerevisiae mutants with DNA content variability that was reduced relative to wild-type strains had defects in mitochondrial DNA (mtDNA) maintenance and mitochondrial gene expression and were correlated with strains found to lack mtDNA ([ rho 0 ] cells) by genome sequencing and fluorescence microscopy. In contrast, mutants with increased variability had defects in cell cycle progression, which may indicate a loss of coordination between mtDNA and nuclear DNA replication. Thus, FACS measurement of DNA content variability can provide insight into cell-to-cell heterogeneity in mtDNA copy number.

DOI: https://doi.org/10.17912/micropub.biology.001117

Cell Rep. 2024 Mar 28. pii: S2211-1247(24)00346-2. [Epub ahead of print]43(4): 114018

Distinct types of intramitochondrial protein aggregates protect mitochondria against proteotoxic stress.

Lea Bertgen, Jan-Eric Bökenkamp, Tim Schneckmann, Christian Koch, Markus Räschle, Zuzana Storchová, Johannes M Herrmann.

Mitochondria consist of hundreds of proteins, most of which are inaccessible to the proteasomal quality control system of the cytosol. How cells stabilize the mitochondrial proteome during challenging conditions remains poorly understood. Here, we show that mitochondria form spatially defined protein aggregates as a stress-protecting mechanism. Two different types of intramitochondrial protein aggregates can be distinguished. The mitoribosomal protein Var1 (uS3m) undergoes a stress-induced transition from a soluble, chaperone-stabilized protein that is prevalent under benign conditions to an insoluble, aggregated form upon acute stress. The formation of Var1 bodies stabilizes mitochondrial proteostasis, presumably by sequestration of aggregation-prone proteins. The AAA chaperone Hsp78 is part of a second type of intramitochondrial aggregate that transiently sequesters proteins and promotes their folding or Pim1-mediated degradation. Thus, mitochondrial proteins actively control the formation of distinct types of intramitochondrial protein aggregates, which cooperate to stabilize the mitochondrial proteome during proteotoxic stress conditions.

Keywords: CP: Cell biology; CP: Molecular biology; Hsp78; MitoStores; Pim1 protease; Var1 bodies; aggregates; chaperones; mitochondria; mitoribosome; protein folding; protein import

DOI: https://doi.org/10.1016/j.celrep.2024.114018