MTO1 mediates tissue specificity of OXPHOS defects via tRNA modification and translation optimization, which can be bypassed by dietary intervention

Mitochondrial diseases often exhibit tissue-specific pathologies, but this phenomenon is poorly understood. Here we present regulation of mitochondrial translation by the Mitochondrial Translation Optimization Factor 1, MTO1, as a novel player in this scenario. We demonstrate that MTO1 mediates tRNA modification and controls mitochondrial translation rate in a highly tissue-specific manner associated with tissue-specific OXPHOS defects. Activation of mitochondrial proteases, aberrant translation products, as well as defects in OXPHOS complex assembly observed in MTO1 deficient mice further imply that MTO1 impacts translation fidelity. In our mouse model, MTO1-related OXPHOS deficiency can be bypassed by feeding a ketogenic diet. This therapeutic intervention is independent of the MTO1-mediated tRNA modification and involves balancing of mitochondrial and cellular secondary stress responses. Our results thereby establish mammalian MTO1 as a novel factor in the tissue-specific regulation of OXPHOS and fine tuning of mitochondrial translation accurac

The Role of Fibroblast Growth Factor Binding Protein 1 in Skin Carcinogenesis and Inflammation

Fibroblast growth factor-binding protein 1 (FGFBP1) is a secreted chaperone that mobilizes paracrine-acting FGFs, stored in the extracellular matrix, and presents them to their cognate receptors. FGFBP1 enhances FGF signaling including angiogenesis during cancer progression and is upregulated in various cancers. Here we evaluated the contribution of endogenous FGFBP1 to a wide range of organ functions as well as to skin pathologies using Fgfbp1-knockout mice. Relative to wild-type littermates, knockout mice showed no gross pathologies. Still, in knockout mice a significant thickening of the epidermis associated with a decreased transepidermal water loss and increased proinflammatory gene expression in the skin was detected. Also, skin carcinogen challenge by 7,12-dimethylbenz[a]anthracene/12-O-tetradecanoyl-phorbol-13-acetate resulted in delayed and reduced papillomatosis in knockout mice. This was paralleled by delayed healing of skin wounds and reduced angiogenic sprouting in subcutaneous matrigel plugs. Heterozygous green fluorescent protein (GFP)–knock-in mice revealed rapid induction of gene expression during papilloma induction and during wound healing. Examination of wild-type skin grafted onto Fgfbp1 GFP–knock-in reporter hosts and bone marrow transplants from the GFP-reporter model into wild-type hosts revealed that circulating Fgfbp1-expressing cells migrate into healing wounds. We conclude that tissue-resident and circulating Fgfbp1-expressing cells modulate skin carcinogenesis and inflammation.</p

Broad AOX expression in a genetically tractable mouse model does not disturb normal physiology

Plants and many lower organisms, but not mammals, express alternative oxidases (AOXs) that branch the mitochondrial respiratory chain, transferring electrons directly from ubiquinol to oxygen without proton pumping. Thus, they maintain electron flow under conditions when the classical respiratory chain is impaired, limiting excess production of oxygen radicals and supporting redox and metabolic homeostasis. AOX from Ciona intestinalis has been used to study and mitigate mitochondrial impairments in mammalian cell lines, Drosophila disease models and, most recently, in the mouse, where multiple lentivector-AOX transgenes conferred substantial expression in specific tissues. Here, we describe a genetically tractable mouse model in which Ciona AOX has been targeted to the Rosa26 locus for ubiquitous expression. The AOX(Rosa26) mouse exhibited only subtle phenotypic effects on respiratory complex formation, oxygen consumption or the global metabolome, and showed an essentially normal physiology. AOX conferred robust resistance to inhibitors of the respiratory chain in organello; moreover, animals exposed to a systemically applied LD50 dose of cyanide did not succumb. The AOX(Rosa26) mouse is a useful tool to investigate respiratory control mechanisms and to decipher mitochondrial disease aetiology in vivo.Peer reviewe

Unbiased analysis of obesity related, fat depot specific changes of adipocyte volumes and numbers using light sheet fluorescence microscopy

In translational obesity research, objective assessment of adipocyte sizes and numbers is essential to characterize histomorphological alterations linked to obesity, and to evaluate the efficacies of experimental medicinal or dietetic interventions. Design-based quantitative stereological techniques based on the analysis of 2D-histological sections provide unbiased estimates of relevant 3D-parameters of adipocyte morphology, but often involve complex and time-consuming tissue processing and analysis steps. Here we report the application of direct 3D light sheet fluorescence microscopy (LSFM) for effective and accurate analysis of adipocyte volumes and numbers in optically cleared adipose tissue samples from a porcine model of diet-induced obesity (DIO). Subcutaneous and visceral adipose tissue samples from DIO-minipigs and lean controls were systematically randomly sampled, optically cleared with 3DISCO (3-dimensional imaging of solvent cleared organs), stained with eosin, and subjected to LSFM for detection of adipocyte cell membrane autofluorescence. Individual adipocytes were unbiasedly sampled in digital 3D reconstructions of the adipose tissue samples, and their individual cell volumes were directly measured by automated digital image analysis. Adipocyte numbers and mean volumes obtained by LSFM analysis did not significantly differ from the corresponding values obtained by unbiased quantitative stereological analysis techniques performed on the same samples, thus proving the applicability of LSFM for efficient analysis of relevant morphological adipocyte parameters. The results of the present study demonstrate an adipose tissue depot specific plasticity of adipocyte growth responses to nutrient oversupply. This was characterized by an exclusively hypertrophic growth of visceral adipocytes, whereas adipocytes in subcutaneous fat tissue depots also displayed a marked (hyperplastic) increase in cell number. LSFM allows for accurate and efficient determination of relevant quantitative morphological adipocyte parameters. The applied stereological methods and LSFM protocols are described in detail and can serve as a guideline for unbiased quantitative morphological analyses of adipocytes in other studies and species

Erratum: Author Correction: Identification of genes required for eye development by high-throughput screening of mouse knockouts.

[This corrects the article DOI: 10.1038/s42003-018-0226-0.]

Seizures, ataxia and parvalbumin-expressing interneurons respond to selenium supply in Selenop-deficient mice

Mice with constitutive disruption of the Selenop gene have been key to delineate the importance of selenoproteins in neurobiology. However, the phenotype of this mouse model is exquisitely dependent on selenium supply and timing of selenium supplementation. Combining biochemical, histological, and behavioral methods, we tested the hypothesis that parvalbumin-expressing interneurons in the primary somatosensory cortex and hippocampus depend on dietary selenium availability in Selenop−/− mice. Selenop-deficient mice kept on adequate selenium diet (0.15 mg/kg, i.e. the recommended dietary allowance, RDA) developed ataxia, tremor, and hyperexcitability between the age of 4–5 weeks. Video-electroencephalography demonstrated epileptic seizures in Selenop−/− mice fed the RDA diet, while Selenop ± heterozygous mice behaved normally. Both neurological phenotypes, hyperexcitability/seizures and ataxia/dystonia were successfully prevented by selenium supplementation from birth or transgenic expression of human SELENOP under a hepatocyte-specific promoter. Selenium supplementation with 10 μM selenite in the drinking water on top of the RDA diet increased the activity of glutathione peroxidase in the brains of Selenop−/− mice to control levels. The effects of selenium supplementation on the neurological phenotypes were dose- and time-dependent. Selenium supplementation after weaning was apparently too late to prevent ataxia/dystonia, while selenium withdrawal from rescued Selenop−/− mice eventually resulted in ataxia. We conclude that SELENOP expression is essential for preserving interneuron survival under limiting Se supply, while SELENOP appears dispensable under sufficiently high Se status

Dusp8 affects hippocampal size and behavior in mice and humans

Dual-specificity phosphatase 8 (Dusp8) acts as physiological inhibitor for the MAPKs Jnk, Erk and p38 which are involved in regulating multiple CNS processes. While Dusp8 expression levels are high in limbic areas such as the hippocampus, the functional role of Dusp8 in hippocampus morphology, MAPK-signaling, neurogenesis and apoptosis as well as in behavior are still unclear. It is of particular interest whether human carriers of a DUSP8 allelic variant show similar hippocampal alterations to mice. Addressing these questions using Dusp8WT and KO mouse littermates, we found that KOs suffered from mildly impaired spatial learning, increased locomotor activity and elevated anxiety. Cell proliferation, apoptosis and p38 and Jnk phosphorylation were unaffected, but phospho-Erk levels were higher in hippocampi of the KOs. Consistent with a decreased hippocampus size in Dusp8 KO mice, we found reduced volumes of the hippocampal subregions subiculum and CA4 in humans carrying the DUSP8 allelic variant SNP rs2334499:C > T. Overall, aberrations in morphology and behavior in Dusp8 KO mice and a decrease in hippocampal volume of SNP rs2334499:C > T carriers point to a novel, translationally relevant role of Dusp8 in hippocampus function that warrants further studies on the role of Dusp8 within the limbic network

KIT is required for hepatic function during mouse post-natal development

<p>Abstract</p> <p>Background</p> <p>The <it>Kit </it>gene encodes a receptor tyrosine kinase involved in various biological processes including melanogenesis, hematopoiesis and gametogenesis in mice and human. A large number of <it>Kit </it>mutants has been described so far showing the pleiotropic phenotypes associated with partial loss-of-function of the gene. Hypomorphic mutations can induce a light coat color phenotype while complete lack of KIT function interferes with embryogenesis. Interestingly several intermediate hypomorphic mutations induced in addition growth retardation and post-natal mortality.</p> <p>Results</p> <p>In this report we investigated the post-natal role of <it>Kit </it>by using a panel of chemically-induced hypomorphic mutations recently isolated in the mouse. We found that, in addition to the classical phenotypes, mutations of <it>Kit </it>induced juvenile steatosis, associated with the downregulation of the three genes, <it>VldlR</it>, <it>Lpin1 </it>and <it>Lpl</it>, controlling lipid metabolism in the post-natal liver. Hence, <it>Kit </it>loss-of-functions mimicked the inactivation of genes controlling the hepatic metabolism of triglycerides, the major source of energy from maternal milk, leading to growth and viability defects during neonatal development.</p> <p>Conclusion</p> <p>This is a first report involving KIT in the control of lipid metabolism in neonates and opening new perspectives for understanding juvenile steatosis. Moreover, it reinforces the role of Kit during development of the liver and underscores the caution that should be exerted in using KIT inhibitors during anti-cancer treatment.</p