bims-cytox1 2018-06-24 papers

Issue of 2018–06–24
four papers selected by
Gavin McStay, Staffordshire University

Neurobiol Dis. 2018 Jun 13. pii: S0969-9961(18)30186-4. [Epub ahead of print]117 203-210

Protein coding mitochondrial-targeted RNAs rescue mitochondrial disease in vivo.

Desiree M Markantone, Atif Towheed, Aaron T Crain, Jessica M Collins, Alicia M Celotto, Michael J Palladino.

Mitochondrial encephalomyopathies (MEs) result from mutations in mitochondrial genes critical to oxidative phosphorylation. Severe and untreatable ME results from mutations affecting each endogenous mitochondrial encoded gene, including all 13 established protein coding genes. Effective techniques to manipulate mitochondrial genome are limited and targeted mitochondrial protein expression is currently unavailable. Here we report the development of a mitochondrial-targeted RNA expression (mtTRES) vector capable of protein expression within mitochondria (mtTRESPro). We demonstrate that mtTRESPro expressed RNAs are targeted to mitochondria and are capable of being translated using EGFP encoded constructs in vivo. We additionally test mtTRESPro constructs encoding wild type ATP6 for their ability to rescue an established ATP61Drosophila model of ME. Genetic rescue is examined including tests with co-expression of mitochondrial targeted translational inhibitors TLI-NCL::ATP6 RNAs that function to reduce expression of the endogenous mutant protein. The data demonstrate allotopic RNA expression of mitochondrial targeted wild type ATP6 coding RNAs are sufficient to partially rescue a severe and established animal model of ME but only when combined with a method to inhibit mutant protein expression, which likely competes for incorporation into complex V.

Keywords: Allotopic RNA expression; Drosophila; Mitochondrial RNA import; Mitochondrial encephalomyopathy (ME)

DOI: https://doi.org/10.1016/j.nbd.2018.06.009

Autophagy. 2018 Jun 18.

Mitochondrial protein import regulates cytosolic protein homeostasis and neuronal integrity.

Wei Liu, Xiuying Duan, Xuefei Fang, Weina Shang, Chao Tong.

Neurodegeneration is characterized by protein aggregate deposits and mitochondrial malfunction. Reduction in Tom40 (translocase of outer membrane 40) expression, a key subunit of the translocase of the outer mitochondrial membrane complex, led to accumulation of ubiquitin (Ub)-positive protein aggregates engulfed by Atg8a-positive membranes. Other macroautophagy markers were also abnormally accumulated. Autophagy was induced but the majority of autophagosomes failed to fuse with lysosomes when Tom40 was downregulated. In Tom40 RNAi tissues, autophagosome-like (AL) structures, often not sealed, were 10 times larger than starvation induced autophagosomes. Atg5 downregulation abolished Tom40 RNAi induced AL structure formation, but the Ub-positive aggregates remained, whereas knock down of Syx17, a gene required for autophagosome-lysosome fusion, led to the disappearance of giant AL structures and accumulation of small autophagosomes and phagophores near the Ub-positive aggregates. The protein aggregates contained many mitochondrial preproteins, cytosolic proteins, and proteasome subunits. Proteasome activity and ATP levels were reduced and the ROS levels was increased in Tom40 RNAi tissues. The simultaneous inhibition of proteasome activity, reduction in ATP production, and increase in ROS, but none of these conditions alone, can mimic the imbalanced proteostasis phenotypes observed in Tom40 RNAi cells. Knockdown of ref(2)P or ectopic expression of Pink1 and park greatly reduced aggregate formation in Tom40 RNAi tissues. In nerve tissues, reduction in Tom40 activity leads to aggregate formation and neurodegeneration. Rather than diminishing the neurodegenerative phenotypes, overexpression of Pink1 enhanced them. We proposed that defects in mitochondrial protein import may be the key to linking imbalanced proteostasis and mitochondrial defects.

Keywords: TOM Complex; autophagy; drosophila; mitochondria; neurodegeneration; proteinaggregates

DOI: https://doi.org/10.1080/15548627.2018.1474991

Mitochondrion. 2018 Jun 15. pii: S1567-7249(17)30334-3. [Epub ahead of print]

Is there a mutation gradient along vertebrate mitochondrial genome mediated by genome replication?

Xuhua Xia.

There is a long-held belief that a mutation gradient exists along vertebrate mtDNA, mediated by mitochondrial replication that leaves different parts of the H-strand exposed in single-stranded state for different durations (DssH). However, the predicted mutation gradient and its tests suffer from both conceptual and empirical problems. I assembled representative mammalian, avian and crocodilian mtDNA to test this prediction. I measured substitution rates at codon positions 1 and 2 (S12) and at codon position 3 (S3), as well as synonymous and nonsynonymous substitution rates, and checked their change along the hypothetical gradient. Mammalian species do not support the predicted mutation gradient, although they should according to the model. Crocodilian species exhibit a pattern closest to the prediction, although they should not because their OL, if present, is not at a fixed position. Correlation between S3 and DssH is much weaker than that between S12 and DssH (contrary to the prediction). This is not due to substitution saturation but is instead due to differential gene conservation, e.g., COX1 is far more conserved than ND6 in all metazoans no matter where they are located along mtDNA. In vertebrates, conserved genes such as COX1 happen to have small DssH and variables genes such as ND6 happen to have large DssH. The observed "mutation gradient" is driven by nonsynonymous substitutions, with synonymous substitutions associated with a much weaker "mutation gradient" likely caused by differential codon re-adaptation after nonsynonymous substitutions. The mammalian and avian results are also confirmed by a much larger compilation and analysis of 691 mammalian and 462 avian mtDNAs. The results, however, does not reject paper is not a test of the strand-displacement model (SDM) of mtDNA replication because a mutation gradient is not a necessary consequence of SDM.

Keywords: Asymmetrical mutation gradient; Mitochondrial genome replication; Molecular evolution; Strand-coupled replication; Strand-displacement replication

DOI: https://doi.org/10.1016/j.mito.2018.06.004

Environ Pollut. 2018 Jun 07. pii: S0269-7491(18)31028-5. [Epub ahead of print]241 821-833

The multilevel antibiotic-induced perturbations to biological systems: Early-life exposure induces long-lasting damages to muscle structure and mitochondrial metabolism in flies.

David Renault, Hesham Yousef, Amr A Mohamed.

Antibiotics have been increasingly used over the past decades for human medicine, food-animal agriculture, aquaculture, and plant production. A significant part of the active molecules of antibiotics can be released into the environment, in turn affecting ecosystem functioning and biogeochemical processes. At lower organizational scales, these substances affect bacterial symbionts of insects, with negative consequences on growth and development of juveniles, and population dynamics. Yet, the multiple alterations of cellular physiology and metabolic processes have remained insufficiently explored in insects. We evaluated the effects of five antibiotics with different mode of action, i.e. ampicillin, cefradine, chloramphenicol, cycloheximide, and tetracycline, on the survival and ultrastructural organization of the flight muscles of newly emerged blow flies Chrysomya albiceps. Then, we examined the effects of different concentrations of antibiotics on mitochondrial protein content, efficiency of oxidative phosphorylation, and activity of transaminases (Glutamate oxaloacetate transaminase and glutamate pyruvate transaminase) and described the cellular metabolic perturbations of flies treated with antibiotics. All antibiotics affected the survival of the insects and decreased the total mitochondrial protein content in a dose-dependent manner. Ultrastructural organization of flight muscles in treated flies differs dramatically compared to the control groups and severe pathological damages/structures disorganization of mitochondria appeared. The activities of mitochondrial transaminases significantly increased with increased antibiotic concentrations. The oxidation rate of pyruvate + proline from isolated mitochondria of the flight muscles of 1-day-old flies was significantly reduced at high doses of antibiotics. In parallel, the level of several metabolites, including TCA cycle intermediates, was reduced in antibiotics-treated flies. Overall, antibiotics provoked a system-wide alteration of the structure and physiology of flight muscles of the blow fly Ch. albiceps, and may have fitness consequences at the organism level. Environmental antibiotic pollution is likely to have unwanted cascading ecological effects of insect population dynamics and community structure.

Keywords: Antibiotics; Energy metabolism; Eukaryote; Insect flight muscles; Metabolomics; Mitochondrial dysfunction

DOI: https://doi.org/10.1016/j.envpol.2018.06.011