Mice deficient in the Shmt2 gene have mitochondrial respiration defects and are embryonic lethal

Accumulation of somatic mutations in mitochondrial DNA (mtDNA) has been proposed to be responsible for human aging and age-associated mitochondrial respiration defects. However, our previous findings suggested an alternative hypothesis of human aging—that epigenetic changes but not mutations regulate age-associated mitochondrial respiration defects, and that epigenetic downregulation of nuclear-coded genes responsible for mitochondrial translation [e.g., glycine C-acetyltransferase (GCAT), serine hydroxymethyltransferase 2 (SHMT2)] is related to age-associated respiration defects. To examine our hypothesis, here we generated mice deficient in Gcat or Shmt2 and investigated whether they have respiration defects and premature aging phenotypes. Gcat-deficient mice showed no macroscopic abnormalities including premature aging phenotypes for up to 9 months after birth. In contrast, Shmt2-deficient mice showed embryonic lethality after 13.5 days post coitum (dpc), and fibroblasts obtained from 12.5-dpc Shmt2-deficient embryos had respiration defects and retardation of cell growth. Because Shmt2 substantially controls production of N-formylmethionine-tRNA (fMet-tRNA) in mitochondria, its suppression would reduce mitochondrial translation, resulting in expression of the respiration defects in fibroblasts from Shmt2-deficient embryos. These findings support our hypothesis that age-associated respiration defects in fibroblasts of elderly humans are caused not by mtDNA mutations but by epigenetic regulation of nuclear genes including SHMT2

Disruption of the mouse Shmt2 gene confers embryonic anaemia via foetal liver-specific metabolomic disorders

In a previous study, we proposed that age-related mitochondrial respiration defects observed in elderly subjects are partially due to age-associated downregulation of nuclear-encoded genes, including serine hydroxymethyltransferase 2 (SHMT2), which is involved in mitochondrial one-carbon (1C) metabolism. This assertion is supported by evidence that the disruption of mouse Shmt2 induces mitochondrial respiration defects in mouse embryonic fibroblasts generated from Shmt2-knockout E13.5 embryos experiencing anaemia and lethality. Here, we elucidated the potential mechanisms by which the disruption of this gene induces mitochondrial respiration defects and embryonic anaemia using Shmt2-knockout E13.5 embryos. The livers but not the brains of Shmt2-knockout E13.5 embryos presented mitochondrial respiration defects and growth retardation. Metabolomic profiling revealed that Shmt2 deficiency induced foetal liver-specific downregulation of 1C-metabolic pathways that create taurine and nucleotides required for mitochondrial respiratory function and cell division, respectively, resulting in the manifestation of mitochondrial respiration defects and growth retardation. Given that foetal livers function to produce erythroblasts in mouse embryos, growth retardation in foetal livers directly induced depletion of erythroblasts. By contrast, mitochondrial respiration defects in foetal livers also induced depletion of erythroblasts as a consequence of the inhibition of erythroblast differentiation, resulting in the manifestation of anaemia in Shmt2-knockout E13.5 embryos.Peer reviewe

Fluvastatin reverses endothelial dysfunction and increased vascular oxidative stress in rat adjuvant-induced arthritis

Objective To investigate the effect of statins on vascular dysfunction in rat adjuvant-induced arthritis (AIA). Methods Fluvastatin (5 mg/kg/day) was administered orally to rats with AIA, for 21 days after the onset of arthritis. The vasodilatory response to acetylcholine of aortic rings isolated from rats with AIA that were not treated or were treated with fluvastatin and from normal rats was determined. The amounts of 4-hydroxy-2-nonenal (HNE) and nitrotyrosine in aortas were measured by Western blotting. In vitro and in situ superoxide production in aortas was evaluated based on fluorogenic oxidation of dihydroethidium to ethidium. Expression of NAD(P)H components and endothelial nitric oxide synthase (eNOS) in aortas was examined by real-time reverse transcriptase–polymerase chain reaction and Western blotting. Serum levels of tetrahydrobiopterin, a critical eNOS cofactor, were determined by high-performance liquid chromatography. Results Fluvastatin reversed endothelial dysfunction in AIA without affecting the clinical severity of arthritis or serum cholesterol concentration. Fluvastatin reduced the amounts of HNE and nitrotyrosine in the aorta, and the levels of superoxide expressed in endothelial cells and smooth muscle cells in the tissue, in rats with AIA. NADH- or L -arginine–induced superoxide production was not observed in the aortic samples from fluvastatin-treated rats with AIA. Fluvastatin decreased the levels of expression of messenger RNA for p22phox, a NAD(P)H oxidase component, in the aortas of rats with AIA, but did not affect the expression of eNOS. Serum levels of tetrahydrobiopterin were significantly reduced in rats with AIA, and were increased by administration of fluvastatin. Conclusion Our findings demonstrate that fluvastatin has potent vascular protective effects in AIA and provide additional scientific rationale for the use of statins to reduce cardiovascular mortality in patients with rheumatoid arthritis.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/56040/1/22632_ftp.pd

Mito-mice∆ and mitochondrial Mito-mice∆ and mitochondrial DNA mutator mice as models of human osteoporosis caused not by aging but by hyperparathyroidism

Mitochondrial DNA (mtDNA) mutator mice showing accelerated accumulation of mtDNA with somatic mutations are potentially useful models of human aging, whereas mito-miceΔ showing accelerated accumulation of mtDNA with a deletion mutation (ΔmtDNA) are potentially useful models of mitochondrial diseases but not human aging, even though both models express an age-associated decrease in mitochondrial respiration. Because osteoporosis is the only premature aging phenotype observed in mtDNA mutator mice with the C57BL/6J nuclear genetic background, our previous study precisely examined its expression spectra and reported that both mtDNA mutator mice and mito-miceΔ, but not aged mice, developed decreased cortical bone thickness. Moreover, decreased cortical bone thickness is usually not seen in aged humans but is commonly seen in the patients with hyperparathyroidism caused by oversecretion of parathyroid hormone (PTH). In the present study, we showed higher concentrations of blood PTH in mtDNA mutator mice and mito-miceΔ than in aged mice. We also found that both models developed decreased mitochondrial respiration in the duodenum or renal tubules, which would lead to hypocalcemia, oversecretion of PTH, and ultimately osteoporosis. Thus, mtDNA mutator mice and mito-miceΔ may be useful models of human osteoporosis caused not by aging but by hyperparathyroidism

Table_2_Metabolism-linked methylotaxis sensors responsible for plant colonization in Methylobacterium aquaticum strain 22A.xlsx

Motile bacteria take a competitive advantage in colonization of plant surfaces to establish beneficial associations that eventually support plant health. Plant exudates serve not only as primary growth substrates for bacteria but also as bacterial chemotaxis attractants. A number of plant-derived compounds and corresponding chemotaxis sensors have been documented, however, the sensors for methanol, one of the major volatile compounds released by plants, have not been identified. Methylobacterium species are ubiquitous plant surface-symbiotic, methylotrophic bacteria. A plant-growth promoting bacterium, M. aquaticum strain 22A exhibits chemotaxis toward methanol (methylotaxis). Its genome encodes 52 methyl-accepting chemotaxis proteins (MCPs), among which we identified three MCPs (methylotaxis proteins, MtpA, MtpB, and MtpC) responsible for methylotaxis. The triple gene mutant of the MCPs exhibited no methylotaxis, slower gathering to plant tissues, and less efficient colonization on plants than the wild type, suggesting that the methylotaxis mediates initiation of plant-Methylobacterium symbiosis and engages in proliferation on plants. To examine how these MCPs are operating methylotaxis, we generated multiple gene knockouts of the MCPs, and Ca2+-dependent MxaFI and lanthanide (Ln3+)-dependent XoxF methanol dehydrogenases (MDHs), whose expression is regulated by the presence of Ln3+. MtpA was found to be a cytosolic sensor that conducts formaldehyde taxis (formtaxis), as well as methylotaxis when MDHs generate formaldehyde. MtpB contained a dCache domain and exhibited differential cellular localization in response to La3+. MtpB expression was induced by La3+, and its activity required XoxF1. MtpC exhibited typical cell pole localization, required MxaFI activity, and was regulated under MxbDM that is also required for MxaF expression. Strain 22A methylotaxis is realized by three independent MCPs, two of which monitor methanol oxidation by Ln3+-regulated MDHs, and one of which monitors the common methanol oxidation product, formaldehyde. We propose that methanol metabolism-linked chemotaxis is the key factor for the efficient colonization of Methylobacterium on plants.</p