Reduced methionine (Met) intake can extend lifespan of rodents; however, whether this regimen represents a general strategy for regulating aging has been controversial. Here we report that Met ...restriction extends lifespan in both fruit flies and yeast, and that this effect requires low amino-acid status. Met restriction in Drosophila mimicks the effect of dietary restriction and is associated with decreased reproduction. However, under conditions of high amino-acid status, Met restriction is ineffective and the trade-off between longevity and reproduction is not observed. Overexpression of InRDN or Tsc2 inhibits lifespan extension by Met restriction, suggesting the role of TOR signalling in the Met control of longevity. Overall, this study defines the specific roles of Met and amino-acid imbalance in aging and suggests that Met restiction is a general strategy for lifespan extension.
Trace elements are used by all organisms and provide proteins with unique coordination and catalytic and electron transfer properties. Although many trace element-containing proteins are well ...characterized, little is known about the general trends in trace element utilization. We carried out comparative genomic analyses of copper, molybdenum, nickel, cobalt (in the form of vitamin B12), and selenium (in the form of selenocysteine) in 747 sequenced organisms at the following levels: (i) transporters and transport-related proteins, (ii) cofactor biosynthesis traits, and (iii) trace element-dependent proteins. Few organisms were found to utilize all five trace elements, whereas many symbionts, parasites, and yeasts used only one or none of these elements. Investigation of metalloproteomes and selenoproteomes revealed examples of increased utilization of proteins that use copper in land plants, cobalt in Dehalococcoides and Dictyostelium, and selenium in fish and algae, whereas nematodes were found to have great diversity of copper transporters. These analyses also characterized trace element metabolism in common model organisms and suggested new model organisms for experimental studies of individual trace elements. Mismatches in the occurrence of user proteins and corresponding transport systems revealed deficiencies in our understanding of trace element biology. Biological interactions among some trace elements were observed; however, such links were limited, and trace elements generally had unique utilization patterns. Finally, environmental factors, such as oxygen requirement and habitat, correlated with the utilization of certain trace elements. These data provide insights into the general features of utilization and evolution of trace elements in the three domains of life.
Cells respond to accumulation of misfolded proteins in the endoplasmic reticulum (ER) by activating the unfolded protein response (UPR) signaling pathway. The UPR restores ER homeostasis by degrading ...misfolded proteins, inhibiting translation, and increasing expression of chaperones that enhance ER protein folding capacity. Although ER stress and protein aggregation have been implicated in aging, the role of UPR signaling in regulating lifespan remains unknown. Here we show that deletion of several UPR target genes significantly increases replicative lifespan in yeast. This extended lifespan depends on a functional ER stress sensor protein, Ire1p, and is associated with constitutive activation of upstream UPR signaling. We applied ribosome profiling coupled with next generation sequencing to quantitatively examine translational changes associated with increased UPR activity and identified a set of stress response factors up-regulated in the long-lived mutants. Besides known UPR targets, we uncovered up-regulation of components of the cell wall and genes involved in cell wall biogenesis that confer resistance to multiple stresses. These findings demonstrate that the UPR is an important determinant of lifespan that governs ER stress and identify a signaling network that couples stress resistance to longevity.
Selenoproteins are a unique group of proteins that contain selenium in the form of selenocysteine (Sec) co-translationally inserted in response to a UGA codon with the help of cis- and trans-acting ...factors. Mammalian selenoproteins contain single Sec residues, with the exception of selenoprotein P (SelP) that has 7-15 Sec residues depending on species. Assessing an individual's selenium status is important under various pathological conditions, which requires a reliable selenium biomarker. Due to a key role in organismal selenium homeostasis, high Sec content, regulation by dietary selenium, and availability of robust assays in human plasma, SelP has emerged as a major biomarker of selenium status. Here, we found that Cys is present in various Sec positions in human SelP. Treatment of cells expressing SelP with thiophosphate, an analog of the selenium donor for Sec synthesis, led to a nearly complete replacement of Sec with Cys, whereas supplementation of cells with selenium supported Sec insertion. SelP isolated directly from human plasma had up to 8% Cys inserted in place of Sec, depending on the Sec position. These findings suggest that a change in selenium status may be reflected in both SelP concentration and its Sec content, and that availability of the SelP-derived selenium for selenoprotein synthesis may be overestimated under conditions of low selenium status due to replacement of Sec with Cys.
Nickel (Ni) and cobalt (Co) are trace elements required for a variety of biological processes. Ni is directly coordinated by proteins, whereas Co is mainly used as a component of vitamin B12. ...Although a number of Ni and Co-dependent enzymes have been characterized, systematic evolutionary analyses of utilization of these metals are limited.
We carried out comparative genomic analyses to examine occurrence and evolutionary dynamics of the use of Ni and Co at the level of (i) transport systems, and (ii) metalloproteomes. Our data show that both metals are widely used in bacteria and archaea. Cbi/NikMNQO is the most common prokaryotic Ni/Co transporter, while Ni-dependent urease and Ni-Fe hydrogenase, and B12-dependent methionine synthase (MetH), ribonucleotide reductase and methylmalonyl-CoA mutase are the most widespread metalloproteins for Ni and Co, respectively. Occurrence of other metalloenzymes showed a mosaic distribution and a new B12-dependent protein family was predicted. Deltaproteobacteria and Methanosarcina generally have larger Ni- and Co-dependent proteomes. On the other hand, utilization of these two metals is limited in eukaryotes, and very few of these organisms utilize both of them. The Ni-utilizing eukaryotes are mostly fungi (except saccharomycotina) and plants, whereas most B12-utilizing organisms are animals. The NiCoT transporter family is the most widespread eukaryotic Ni transporter, and eukaryotic urease and MetH are the most common Ni- and B12-dependent enzymes, respectively. Finally, investigation of environmental and other conditions and identity of organisms that show dependence on Ni or Co revealed that host-associated organisms (particularly obligate intracellular parasites and endosymbionts) have a tendency for loss of Ni/Co utilization.
Our data provide information on the evolutionary dynamics of Ni and Co utilization and highlight widespread use of these metals in the three domains of life, yet only a limited number of user proteins.
Selenium is a fascinating element that has a long history, most of which documents it as a deleterious element to health. In more recent years, selenium has been found to be an essential element in ...the diet of humans, all other mammals, and many other life forms. It has many health benefits that include, for example, roles in preventing heart disease and certain forms of cancer, slowing AIDS progression in HIV patients, supporting male reproduction, inhibiting viral expression, and boosting the immune system, and it also plays essential roles in mammalian development. Elucidating the molecular biology of selenium over the past 40 years generated an entirely new field of science which encompassed the many novel features of selenium. These features were (1) how this element makes its way into protein as the 21st amino acid in the genetic code, selenocysteine (Sec); (2) the vast amount of machinery dedicated to synthesizing Sec uniquely on its tRNA; (3) the incorporation of Sec into protein; and (4) the roles of the resulting Sec-containing proteins (selenoproteins) in health and development. One of the research areas receiving the most attention regarding selenium in health has been its role in cancer prevention, but further research has also exposed the role of this element as a facilitator of various maladies, including cancer.
Somatic mutations have long been implicated in aging and disease, but their impact on fitness and function is difficult to assess. Here by analysing human cancer genomes we identify mutational ...patterns associated with aging. Our analyses suggest that age-associated mutation load and burden double approximately every 8 years, similar to the all-cause mortality doubling time. This analysis further reveals variance in the rate of aging among different human tissues, for example, slightly accelerated aging of the reproductive system. Age-adjusted mutation load and burden correlate with the corresponding cancer incidence and precede it on average by 15 years, pointing to pre-clinical cancer development times. Behaviour of mutation load also exhibits gender differences and late-life reversals, explaining some gender-specific and late-life patterns in cancer incidence rates. Overall, this study characterizes some features of human aging and offers a mechanism for age being a risk factor for the onset of cancer.
Significance The naked mole rat is a longest lived and cancer-resistant rodent. Tumor resistance in the naked mole rat is mediated by signals from the extracellular matrix component hyaluronan ...triggering the induction of INK4 (inhibitors of cyclin dependent kinase 4) locus expression. The human and mouse INK4 locus encodes three critical tumor-suppressor proteins, p15 ᴵᴺᴷ⁴ᵇ, ARF (alternate reading frame), and p16 ᴵᴺᴷ⁴ᵃ, which are among the most frequently mutated in cancer. Furthermore, p16 ᴵᴺᴷ⁴ᵃ is implicated in aging and senescence. Here, we show that the naked mole rat INK4 locus encodes an additional product, a hybrid between p15 ᴵᴺᴷ⁴ᵇ and p16 ᴵᴺᴷ⁴ᵃ. The novel product, named pALT ᴵᴺᴷ⁴ᵃ/ᵇ, may contribute to tumor resistance and longevity of the naked mole rat. Understanding the regulation of the INK4 locus is critical for cancer and aging research.
The naked mole rat ( Heterocephalus glaber ) is a long-lived and tumor-resistant rodent. Tumor resistance in the naked mole rat is mediated by the extracellular matrix component hyaluronan of very high molecular weight (HMW-HA). HMW-HA triggers hypersensitivity of naked mole rat cells to contact inhibition, which is associated with induction of the INK4 (inhibitors of cyclin dependent kinase 4) locus leading to cell-cycle arrest. The INK4a/b locus is among the most frequently mutated in human cancer. This locus encodes three distinct tumor suppressors: p15 ᴵᴺᴷ⁴ᵇ, p16 ᴵᴺᴷ⁴ᵃ, and ARF (alternate reading frame). Although p15 ᴵᴺᴷ⁴ᵇ has its own ORF, p16 ᴵᴺᴷ⁴ᵃ and ARF share common second and third exons with alternative reading frames. Here, we show that, in the naked mole rat, the INK4a/b locus encodes an additional product that consists of p15 ᴵᴺᴷ⁴ᵇ exon 1 joined to p16 ᴵᴺᴷ⁴ᵃ exons 2 and 3. We have named this isoform pALT ᴵᴺᴷ⁴ᵃ/ᵇ (for alternative splicing). We show that pALT ᴵᴺᴷ⁴ᵃ/ᵇ is present in both cultured cells and naked mole rat tissues but is absent in human and mouse cells. Additionally, we demonstrate that pALT ᴵᴺᴷ⁴ᵃ/ᵇ expression is induced during early contact inhibition and upon a variety of stresses such as UV, gamma irradiation-induced senescence, loss of substrate attachment, and expression of oncogenes. When overexpressed in naked mole rat or human cells, pALT ᴵᴺᴷ⁴ᵃ/ᵇ has stronger ability to induce cell-cycle arrest than either p15 ᴵᴺᴷ⁴ᵇ or p16 ᴵᴺᴷ⁴ᵃ. We hypothesize that the presence of the fourth product, pALT ᴵᴺᴷ⁴ᵃ/ᵇ of the INK4a/b locus in the naked mole rat, contributes to the increased resistance to tumorigenesis of this species.
The selenoenzyme glutathione peroxidase 4 (Gpx4) is an essential mammalian glutathione peroxidase, which protects cells against detrimental lipid peroxidation and governs a novel form of regulated ...necrotic cell death, called ferroptosis. To study the relevance of Gpx4 and of another vitally important selenoprotein, cytosolic thioredoxin reductase (Txnrd1), for liver function, mice with conditional deletion of Gpx4 in hepatocytes were studied, along with those lacking Txnrd1 and selenocysteine (Sec) tRNA (Trsp) in hepatocytes. Unlike Txnrd1- and Trsp-deficient mice, Gpx4
mice died shortly after birth and presented extensive hepatocyte degeneration. Similar to Txnrd1-deficient livers, Gpx4
livers manifested upregulation of nuclear factor (erythroid-derived)-like 2 (Nrf2) response genes. Remarkably, Gpx4
pups born from mothers fed a vitamin E-enriched diet survived, yet this protection was reversible as subsequent vitamin E deprivation caused death of Gpx4-deficient mice ~4 weeks thereafter. Abrogation of selenoprotein expression in Gpx4
mice did not result in viable mice, indicating that the combined deficiency aggravated the loss of Gpx4 in liver. By contrast, combined Trsp/Txnrd1-deficient mice were born, but had significantly shorter lifespans than either single knockout, suggesting that Txnrd1 plays an important role in supporting liver function of mice lacking Trsp. In sum our study demonstrates that the ferroptosis regulator Gpx4 is critical for hepatocyte survival and proper liver function, and that vitamin E can compensate for its loss by protecting cells against deleterious lipid peroxidation.
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