Redox stress shortens lifespan through suppression of respiratory complex I in flies with mitonuclear incompatibilities

Incompatibilities between mitochondrial and nuclear genes can perturb respiration, biosynthesis, signaling and gene expression. Here we investigate whether mild mitonuclear incompatibilities alter the physiological response to redox stress induced by N-acetyl cysteine (NAC). We studied three Drosophila melanogaster lines with mitochondrial genomes that were either coevolved (WT) or mildly mismatched (BAR, COX) to an isogenic nuclear background. Responses to NAC varied substantially with mitonuclear genotype, sex, tissue and dose. NAC caused infertility and high mortality in some groups, but not others. Using tissue-specific high-resolution fluorespirometry, we show that NAC did not alter H2O2 flux but suppressed complex I-linked respiration in female flies, while maintaining a reduced glutathione pool. The high mortality in BAR females was associated with severe (>50 %) suppression of complex I-linked respiration, rising H2O2 flux in the ovaries, and significant oxidation of the glutathione pool. Our results suggest that redox stress is attenuated by the suppression of complex-I linked respiration, to the point of death in some mitonuclear lines. We propose that suppression of complex I-linked respiration is a general mechanism to maintain redox homeostasis in tissues, which could offset oxidative stress in ageing, producing a metabolic phenotype linked with epigenetic changes and age-related decline

Inositol trisphosphate receptor-mediated Ca 2+ signalling stimulates mitochondrial function and gene expression in core myopathy patients

Core myopathies are a group of childhood muscle disorders caused by mutations of the ryanodine receptor (RyR1), the Ca2+ release channel of the sarcoplasmic reticulum. These mutations have previously been associated with elevated inositol trisphosphate receptor (IP3R) levels in skeletal muscle myotubes derived from patients. However, the functional relevance and the relationship of IP3R mediated Ca2+ signalling with the pathophysiology of the disease is unclear. It has also been suggested that mitochondrial dysfunction underlies the development of central and diffuse multi-mini-cores, devoid of mitochondrial activity, which is a key pathological consequence of RyR1 mutations. Here we used muscle biopsies of central core and multi-minicore disease patients with RyR1 mutations, as well as cellular and in vivo mouse models of the disease to characterize global cellular and mitochondrial Ca2+ signalling, mitochondrial function and gene expression associated with the disease. We show that RyR1 mutations that lead to the depletion of the channel are associated with increased IP3-mediated nuclear and mitochondrial Ca2+ signals and increased mitochondrial activity. Moreover, western blot and microarray analysis indicated enhanced mitochondrial biogenesis at the transcriptional and protein levels and was reflected in increased mitochondrial DNA content. The phenotype was recapitulated by RYR1 silencing in mouse cellular myotube models. Altogether, these data indicate that remodelling of skeletal muscle Ca2+ signalling following loss of functional RyR1 mediates bioenergetic adaptation

A genetic modifier suggests that endurance exercise exacerbates Huntington's disease.

Polyglutamine expansions in the huntingtin gene cause Huntington's disease (HD). Huntingtin is ubiquitously expressed, leading to pathological alterations also in peripheral organs. Variations in the length of the polyglutamine tract explain up to 70% of the age-at-onset variance, with the rest of the variance attributed to genetic and environmental modifiers. To identify novel disease modifiers, we performed an unbiased mutagenesis screen on an HD mouse model, identifying a mutation in the skeletal muscle voltage-gated sodium channel (Scn4a, termed 'draggen' mutation) as a novel disease enhancer. Double mutant mice (HD; Scn4aDgn/+) had decreased survival, weight loss and muscle atrophy. Expression patterns show that the main tissue affected is skeletal muscle. Intriguingly, muscles from HD; Scn4aDgn/+ mice showed adaptive changes similar to those found in endurance exercise, including AMPK activation, fibre type switching and upregulation of mitochondrial biogenesis. Therefore, we evaluated the effects of endurance training on HD mice. Crucially, this training regime also led to detrimental effects on HD mice. Overall, these results reveal a novel role for skeletal muscle in modulating systemic HD pathogenesis, suggesting that some forms of physical exercise could be deleterious in neurodegeneration

Protein CoAlation: a redox-regulated protein modification by coenzyme A in mammalian cells.

Coenzyme A (CoA) is an obligatory cofactor in all branches of life. CoA and its derivatives are involved in major metabolic pathways, allosteric interactions and the regulation of gene expression. Abnormal biosynthesis and homeostasis of CoA and its derivatives have been associated with various human pathologies, including cancer, diabetes and neurodegeneration. Using an anti-CoA monoclonal antibody and mass spectrometry, we identified a wide range of cellular proteins which are modified by covalent attachment of CoA to cysteine thiols (CoAlation). We show that protein CoAlation is a reversible post-translational modification that is induced in mammalian cells and tissues by oxidising agents and metabolic stress. Many key cellular enzymes were found to be CoAlated in vitro and in vivo in ways that modified their activities. Our study reveals that protein CoAlation is a widespread post-translational modification which may play an important role in redox regulation under physiological and pathophysiological conditions

Novel insights into Cofilin's function upon regulating mitochondrial respiration, multi-drug resistance & stress response in the yeast Saccharomyces cerevisiae

Cofilin is a well-studied actin binding and regulatory protein that functions to control the dynamic status of the cytoskeleton. Recent evidence also impl icates cofilin in the regulation of mitochondrial function during response to exogenous and intracellular stress. Here we provide evidence that cofilin regulates mitochondrial function via a post-transcriptional mechanism to facilitate an increase in respiratory capacity as well as a concomitant multi-drug resistance response in the budding yeast S. cerevisiae. Changes to the surface cbarge of cofilin that do not interfere with its actin regulatory functions lead to an increase in respiratory function and the upregulation of a battery of ABC transporters leading to multi-drug resistance. Moreover, there is evidence that the overall alterations in cellular function includes metabolic and stress signalling through the activation of MAPK components. We hypothesise tbat cofilinlmitochondrial interactions form part of a novel bio-sensing system. which connects the cytoskeleton and mitochondrial function to environmental change.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A genetic modifier suggests that endurance exercise exacerbates Huntington's disease.

Polyglutamine expansions in the huntingtin gene cause Huntington's disease (HD). Huntingtin is ubiquitously expressed, leading to pathological alterations also in peripheral organs. Variations in the length of the polyglutamine tract explain up to 70% of the age-at-onset variance, with the rest of the variance attributed to genetic and environmental modifiers. To identify novel disease modifiers, we performed an unbiased mutagenesis screen on an HD mouse model, identifying a mutation in the skeletal muscle voltage-gated sodium channel (Scn4a, termed 'draggen' mutation) as a novel disease enhancer. Double mutant mice (HD; Scn4aDgn/+) had decreased survival, weight loss and muscle atrophy. Expression patterns show that the main tissue affected is skeletal muscle. Intriguingly, muscles from HD; Scn4aDgn/+ mice showed adaptive changes similar to those found in endurance exercise, including AMPK activation, fibre type switching and upregulation of mitochondrial biogenesis. Therefore, we evaluated the effects of endurance training on HD mice. Crucially, this training regime also led to detrimental effects on HD mice. Overall, these results reveal a novel role for skeletal muscle in modulating systemic HD pathogenesis, suggesting that some forms of physical exercise could be deleterious in neurodegeneration

H2O2 stress-specific regulation of S. pombe MAPK Sty1 by mitochondrial protein phosphatase Ptc4

In fission yeast, the stress?activated MAP kinase, Sty1, is activated via phosphorylation upon exposure to stress and orchestrates an appropriate response. Its activity is attenuated by either serine/threonine PP2C or tyrosine phosphatases. Here, we found that the PP2C phosphatase, Ptc4, plays an important role in inactivating Sty1 specifically upon oxidative stress. Sty1 activity remains high in a ptc4 deletion mutant upon H2O2 but not under other types of stress. Surprisingly, Ptc4 localizes to the mitochondria and is targeted there by an N?terminal mitochondrial targeting sequence (MTS), which is cleaved upon import. A fraction of Sty1 also localizes to the mitochondria suggesting that Ptc4 attenuates the activity of a mitochondrial pool of this MAPK. Cleavage of the Ptc4 MTS is greatly reduced specifically upon H2O2, resulting in the full?length form of the phosphatase; this displays a stronger interaction with Sty1, thus suggesting a novel mechanism by which the negative regulation of MAPK signalling is controlled and providing an explanation for the oxidative stress?specific nature of the regulation of Sty1 by Ptc4