Search

Two related neurodegenerative disorders, Western Pacific amyotrophic lateral sclerosis (A/S) and parkinsonism-dementia (PD), originally occurred at a high incidence on Guam, in the Kii peninsula of Japan, and in southern West New Guinea more than 50 years ago. These three foci shared a unique mineral environment characterized by the presence of severely low levels of [Ca.sup.2+] and [Mg.sup.2+], coupled with high levels of bioavailable transition metals in the soil and drinking water. Epidemiological studies suggest that genetic factors also contribute to the etiology of these disorders. Here, we report that a variant of the transient receptor potential melastatin 2 (TRPM2) gene may confer susceptibility to these diseases. TRPM2 encodes a calcium-permeable cation channel highly expressed in the brain that has been implicated in mediating cell death induced by oxidants. We found a heterozygous variant of TRPM2 in a subset of Guamanian ALS (ALS-G) and PD (PD-G) cases. This variant, [TRPM2.sup.P1018L], produces a missense change in the channel protein whereby proline 1018 ([Pro.sup.1018]) is replaced by leucine ([Leu.sup.1018]). Functional studies revealed that, unlike WT TRPM2, P1018L channels inactivate. Our results suggest that the ability of TRPM2 to maintain sustained ion influx is a physiologically important function and that its disruption may, under certain conditions, contribute to disease states. calcium | neurodegeneration | oxidative stress | channelopathy | gene environment

Humans and most other animals use 2 different genetic codes to translate their hereditary information: the standard code for nuclear-encoded proteins and a modern variant of this code in mitochondria. Despite the pivotal role of the genetic code for cell biology, the functional significance of the deviant mitochondrial code has remained enigmatic since its first description in 1979. Here, we show that profound and functionally beneficial alterations on the encoded protein level were causative for the AUA codon reassignment from isoleucine to methionine observed in most mitochondrial lineages. We demonstrate that this codon reassignment leads to a massive accumulation of the easily oxidized amino acid methionine in the highly oxidative inner mitochondrial membrane. This apparently paradoxical outcome can yet be smoothly settled if the antioxidant surface chemistry of methionine is taken into account, and we present direct experimental evidence that intramembrane accumulation of methionine exhibits antioxidant and cytoprotective properties in living cells. Our results unveil that methionine is an evolutionarily selected antioxidant building block of respiratory chain complexes. Collective protein alterations can thus constitute the selective advantage behind codon reassignments, which authenticates the 'ambiguous decoding' hypothesis of genetic code evolution. Oxidative stress has shaped the mitochondrial genetic code. evolution | methionine sulfoxide | nonstandard genetic code | protein oxidation | oxidative stress

Cellular localization determines whether the serine protease HtrA2 exerts pro- or antiapoptotic functions. In contrast to the well-characterized proapoptotic function of cytosolic HtrA2, mechanisms underlying the mitochondrial protective role are poorly understood. Mpv17l is a transmembrane protein previously implicated in peroxisomal reactive oxygen species metabolism and a close homolog of the inner mitochondrial membrane protein Mpv17. Here we demonstrate a previously undescribed direct interaction between Mpv17l and HtrA2 in mitochondria. The interaction is mediated by a PDZ domain and induces protease activation of HtrA2. HtrA2 inhibits mitochondrial superoxide generation, stabilizes mitochondrial membrane potential, and prevents apoptosis at baseline and in response to extracellular inducers of mitochondrial stress. The physiological role of Mpv17l is underscored by the finding that oxidative stress-induced down-regulation of Mpv17l is a consistent feature in renal injury models. Our findings identify Mpv17l as a unique interacting protein and regulator of HtrA2 protease mediating antioxidant and anti-apoptotic function in mitochondria. reactive oxygen species | proximal tubular epithelial cells | kidney injury | transforming growth factor beta | hypoxia

Parkinson's disease (PD) is a major neurodegenerative condition with several rare Mendelian forms. Oxidative stress and mitochondrial function have been implicated in the pathogenesis of PD but the molecular mechanisms involved in the degeneration of neurons remain unclear. D J-1 mutations are one cause of recessive parkinsonism, but this gene is also reported to be involved in cancer by promoting Ras signaling and suppressing PTEN-induced apoptosis. The specific function of D J-1 is unknown, although it is responsive to oxidative stress and may play a role in the maintenance of mitochondria. Here, we show, using four independent methods, that D J-1 associates with RNA targets in cells and the brain, including mitochondrial genes, genes involved in glutathione metabolism, and members of the PTEN/PI3K cascade. Pathogenic recessive mutants are deficient in this activity. We show that D J-1 is sufficient for RNA binding at nanomolar concentrations. Further, we show that D J-1 binds RNA but dissociates after oxidative stress. These data implicate a single mechanism for the pleiotropic effects of D J-1 in different model systems, namely that the protein binds multiple RNA targets in an oxidation-dependent manner. gene expression | oxidative stress | Parkinson's disease | translation

Caloric restriction (CR) is the most potent intervention known to both protect against carcinogenesis and extend lifespan in laboratory animals. A variety of anticarcinogens and CR mimetics induce and activate the NF-E2-related factor 2 (Nrf2) pathway. Nrf2, in turn, induces a number of antioxidative and carcinogendetoxifying enzymes. Thus, Nrf2 offers a promising target for anticarcinogenesis and antiaging interventions. We used Nrf2-disrupted (KO) mice to examine its role on the biological effects of CR. Here, we show that Nrf2 is responsible for most of the anticarcinogenic effects of CR, but is dispensable for increased insulin sensitivity and lifespan extension. Nrf2-deficient mice developed tumors more readily in response to carcinogen exposure than did WT mice, and CR was ineffective in suppressing tumors in the KO mice. However, CR extended lifespan and increased insulin sensitivity similarly in KO and WT mice. These findings identify a molecular pathway that dissociates the prolongevity and anticarcinogenic effects of CR. aging | carcinogenesis | oxidative stress

Charge transport (CT) through the DNA base pairs provides a means to promote redox reactions at a remote site and potentially to effect signaling between molecules bound to DNA. Here we describe the oxidation of a cell-cycle regulatory protein, p53, from a distance through DNA-mediated CT. A consensus p53 binding site as well as three DNA promoters regulated by p53 were synthesized containing a tethered DNA photooxidant, anthraquinone. Photo-induced oxidation of the protein occurs from a distance; introduction of an intervening CA mismatch, which inhibits DNA-mediated CT, prevents oxidation of p53. DNA-mediated oxidation is shown to promote dissociation of p53 from only some promoters, and this sequence-selectivity in oxidative dissociation correlates with the biological regulation of p53. Under severe oxidative stress, effected here through oxidation at long range, p53 dissociates from a promoter that activates DNA repair as well as the promoter for the negative regulator of p53, Mdm2, but not from a promoter activating cell-cycle arrest. Mass spectrometry results are consistent with disulfide bond formation in p53 upon DNA-mediated oxidation. Furthermore, DNA-bound p53 oxidation is shown in vivo by up-regulation of p53 and subsequent irradiation in the presence of a rhodium photooxidant to give a new p53 adduct that can be reversed with thiol treatment. This DNA-mediated oxidation of p53 parallels that seen by treating cells with hydrogen peroxide. These results indicate a unique mechanism using DNA-mediated CT chemistry by which p53 activity on different promoters may be controlled globally under conditions of oxidative stress. DNA electron transfer | oxidative stress | redox regulation

The differentiation of skeletal myoblasts is characterized by permanent withdrawal from the cell cycle and fusion into multinucleated myotubes. Muscle cell survival is critically dependent on the ability of ceils to respond to oxidative stress. Base excision repair (BER) is the main repair mechanism of oxidative DNA damage. In this study, we compared the levels of endogenous oxidative DNA damage and BER capacity of mouse proliferating myoblasts and their differentiated counterpart, the myotubes. Changes in the expression of oxidative stress marker genes during differentiation, together with an increase in 8-hydroxyguanine DNA levels in terminally differentiated cells, suggested that reactive oxygen species are produced during this process. The repair of 2-deoxyribonolactone, which is exclusively processed by long-patch BER, was impaired in cell extracts from myotubes. The repair of a natural abasic site (a preferred substrate for short-patch BER) also was delayed. The defect in BER of terminally differentiated muscle cells was ascribed to the nearly complete lack of DNA ligase I and to the strong down-regulation of XRCC1 with subsequent destabilization of DNA ligase III[alpha]. The attenuation of BER in myotubes was associated with significant accumulation of DNA damage as detected by increased DNA single-strand breaks and phosphorylated H2AX nuclear foci upon exposure to hydrogen peroxide. We propose that in skeletal muscle exacerbated by free radical injury, the accumulation of DNA repair intermediates, due to attenuated BER, might contribute to myofiber degeneration as seen in sarcopenia and many muscle disorders. oxidative stress | XRCC1 | DNA ligases | DNA single-strand breaks | 8-oxoguanine

Circadian rhythms can be regulated by many environmental and endogenous factors. We show here a sensitivity of circadian clock function to oxidative stress that is revealed in flies lacking the foxo gene product. When exposed to oxidative stress, wild-type flies showed attenuated clock gene cycling in peripheral tissues, whereas foxo mutants also lost behavioral rhythms driven by the central clock. FOXO is expressed predominantly in the fat body, and transgenic expression in this tissue rescued the mutant behavioral phenotype, suggesting that foxo has non-cell-autonomous effects on central circadian clock function. Overexpression of signaling molecules that affect FOXO activity, such as the insulin receptor or Akt, in the fat body also increased susceptibility of the central clock to oxidative stress. Finally, foxo mutants showed a rapid decline in rest:activity rhythms with age, supporting the idea that the increase of oxidative stress contributes to age-associated degeneration of behavioral rhythms and indicating the importance of FOXO in mitigating this deterioration. Together these data demonstrate that metabolism affects central clock function and provide a link among insulin signaling, oxidative stress, aging, and circadian rhythms. circadian rhythms