Lifespan Extension Conferred by Endoplasmic Reticulum Secretory Pathway Deficiency Requires Induction of the Unfolded Protein Response

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

N-terminal acetylation promotes synaptonemal complex assembly in C. elegans

N-terminal acetylation of the first two amino acids on proteins is a prevalent cotranslational modification. Despite its abundance, the biological processes associated with this modification are not well understood. Here, we mapped the pattern of protein N-terminal acetylation in Caenorhabditis elegans, uncovering a conserved set of rules for this protein modification and identifying substrates for the N-terminal acetyltransferase B (NatB) complex. We observed an enrichment for global protein N-terminal acetylation and also specifically for NatB substrates in the nucleus, supporting the importance of this modification for regulating biological functions within this cellular compartment. Peptide profiling analysis provides evidence of cross-talk between N-terminal acetylation and internal modifications in a NAT substrate-specific manner. In vivo studies indicate that N-terminal acetylation is critical for meiosis, as it regulates the assembly of the synaptonemal complex (SC), a proteinaceous structure ubiquitously present during meiosis from yeast to humans. Specifically, N-terminal acetylation of NatB substrate SYP-1, an SC structural component, is critical for SC assembly. These findings provide novel insights into the biological functions of N-terminal acetylation and its essential role during meiosis

Reactive oxygen species, ageing and the hormesis police

For more than 50 years, the free radical theory served as the paradigm guiding most investigations of ageing. However, recent studies in a variety of organisms have identified conceptual and practical limitations to this theory. Some of these limitations are related to the recent discovery that caloric restriction and other experimental manipulations promote longevity by inducing hormesis effects in association with increased reactive oxygen species (ROS). The beneficial role of ROS in lifespan extension is consistent with the essential role of these molecules in cell signalling. However, the identity of specific forms of ROS that promote longevity remains unclear. In this article, we argue that in several model systems, hydrogen peroxide plays a crucial role in the induction of hormesis.The authors wish to thank Molly Burhans for preparing the figures. This work was supported by Fundacao para a Ciencia e Tecnologia (FCT) and COMPETE/QREN/EU (PTDC/BIA-MIC/114116/2009), a grant from the Roswell Park Alliance Foundation and by a National Cancer Institute Support Grant (P30CA016056) to Roswell Park Cancer Institute. Authors have no conflict of interest to declare

Bio-efficacy of hydroxy-selenomethionine as a selenium supplement in pregnant dairy heifers and on the selenium status of their calves

This study aimed to determine the effects of supplementing pregnant heifers with the organic selenium source 2-hydroxy-4-methylselenobutanoic acid (HMSeBA) during last eight weeks of pregnancy on dam and calf Se status. A total of 42 in-calf heifers were recruited to the study and randomly allocated to one of three treatments; a negative control (Con), sodium selenite (NaSe) or HMSeBA. Animals were blocked by body weight, body condition score, and expected calving date prior to treatment allocation. Following enrollment all animals underwent a seven week wash-out period after which they received their respective supplements, topped dressed daily onto a basal diet for the last eight weeks of pregnancy. Heifer blood samples were taken at weekly intervals from enrollment until two weeks before expected calving date, and as soon as possible after calving for determination of whole blood glutathione peroxidase activity (GSH-Px) and plasma selenium (Se) and malondealdehyde (MDA) concentrations. Selenized amino acids were determined in plasma samples taken at three weeks pre-calving. A colostrum sample was taken as close to parturition as possible for determination of colostrum total Se, selenized amino acid, and Immunoglobulin G (IgG) concentration. Calves were blood sampled as close to birth as possible for determination of whole blood GSH-Px activity and plasma Se and MDA concentration. Differences in whole blood GSH-Px activity did not become apparent until calving; GSH-Px activity was lowest in Con heifers (P < 0.05) but similar between NaSe and HMSeBA. Plasma Se was lowest in unsupplemented heifers and greatest in those supplemented with HMSeBA (P < 0.001) and this was attributable to greater selenomethionine concentrations in the plasma of HMSeBA heifers (P < 0.01). Colostrum Se was lowest in Con heifers and greatest in HMSeBA (P < 0.001), the greater Se concentration of HMSeBA heifers was attributable to a greater proportion of total Se comprising selenocysteine (P = 0.061), the reason for this is not known. There was no effect of supplementation on colostrum IgG concentration. Plasma Se was lowest in those calves born to Con heifers and greatest in those born to HMSeBA heifers (P < 0.001). There were no effects of treatment on calf whole blood GSH-Px activity or plasma MDA concentration. The enhanced Se status associated with HMSeBA supplementation is likely a consequence of selenomethionine supply and may confer benefits to both the dam and her calf post-partum

Roles of the 15-kDa Selenoprotein (Sep15) in Redox Homeostasis and Cataract Development Revealed by the Analysis of Sep 15 Knockout Mice

The 15-kDa selenoprotein (Sep15) is a thioredoxin-like, endoplasmic reticulum-resident protein involved in the quality control of glycoprotein folding through its interaction with UDP-glucose:glycoprotein glucosyltransferase. Expression of Sep15 is regulated by dietary selenium and the unfolded protein response, but its specific function is not known. In this study, we developed and characterized Sep15 KO mice by targeted removal of exon 2 of the Sep15 gene coding for the cysteinerich UDP-glucose:glycoprotein glucosyltransferase-binding domain. These KO mice synthesized a mutant mRNA, but the shortened protein product could be detected neither in tissues nor in Sep15 KO embryonic fibroblasts. Sep15 KO mice were viable and fertile, showed normal brain morphology, and did not activate endoplasmic reticulum stress pathways. However, parameters of oxidative stress were elevated in the livers of these mice. We found that Sep15 mRNA was enriched during lens development. Further phenotypic characterization of Sep15KO mice revealed a prominent nuclear cataract that developed at an early age. These cataracts did not appear to be associated with severe oxidative stress or glucose dysregulation.Wesuggest that the cataracts resulted from an improper folding status of lens proteins caused by Sep15 deficiency

Roles of the 15-kDa Selenoprotein (Sep15) in Redox Homeostasis and Cataract Development Revealed by the Analysis of Sep 15 Knockout Mice

The 15-kDa selenoprotein (Sep15) is a thioredoxin-like, endoplasmic reticulum-resident protein involved in the quality control of glycoprotein folding through its interaction with UDP-glucose:glycoprotein glucosyltransferase. Expression of Sep15 is regulated by dietary selenium and the unfolded protein response, but its specific function is not known. In this study, we developed and characterized Sep15 KO mice by targeted removal of exon 2 of the Sep15 gene coding for the cysteinerich UDP-glucose:glycoprotein glucosyltransferase-binding domain. These KO mice synthesized a mutant mRNA, but the shortened protein product could be detected neither in tissues nor in Sep15 KO embryonic fibroblasts. Sep15 KO mice were viable and fertile, showed normal brain morphology, and did not activate endoplasmic reticulum stress pathways. However, parameters of oxidative stress were elevated in the livers of these mice. We found that Sep15 mRNA was enriched during lens development. Further phenotypic characterization of Sep15KO mice revealed a prominent nuclear cataract that developed at an early age. These cataracts did not appear to be associated with severe oxidative stress or glucose dysregulation.Wesuggest that the cataracts resulted from an improper folding status of lens proteins caused by Sep15 deficiency

Parallel Profiling of Fission Yeast Deletion Mutants for Proliferation and for Lifespan During Long-Term Quiescence

Genetic factors underlying aging are remarkably conserved from yeast to human. The fission yeast Schizosaccharomyces pombe is an emerging genetic model to analyze cellular aging. Chronological lifespan (CLS) has been studied in stationary-phase yeast cells depleted for glucose, which only survive for a few days. Here, we analyzed CLS in quiescent S. pombe cells deprived of nitrogen, which arrest in a differentiated, G0-like state and survive for more than 2 months. We applied parallel mutant phenotyping by barcode sequencing (Bar-seq) to assay pooled haploid deletion mutants as they aged together during longterm quiescence. As expected, mutants with defects in autophagy or quiescence were under-represented or not detected. Lifespan scores could be calculated for 1199 mutants. We focus the discussion on the 48 most long-lived mutants, including both known aging genes in other model systems and genes not previously implicated in aging. Genes encoding membrane proteins were particularly prominent as pro-aging factors. We independently verified the extended CLS in individual assays for 30 selected mutants, showing the efficacy of the screen. We also applied Bar-seq to profile all pooled deletion mutants for proliferation under a standard growth condition. Unlike for stationary-phase cells, no inverse correlation between growth and CLS of quiescent cells was evident. These screens provide a rich resource for further studies, and they suggest that the quiescence model can provide unique, complementary insights into cellular aging

Selenium biochemistry and its role for human health

Despite its very low level in humans, selenium plays an important and unique role among the (semi)metal trace essential elements because it is the only one for which incorporation into proteins is genetically encoded, as the constitutive part of the 21st amino acid, selenocysteine. Twenty-five selenoproteins have been identified so far in the human proteome. The biological functions of some of them are still unknown, whereas for others there is evidence for a role in antioxidant defence, redox state regulation and a wide variety of specific metabolic pathways. In relation to these functions, the selenoproteins emerged in recent years as possible biomarkers of several diseases such as diabetes and several forms of cancer. Comprehension of the selenium biochemical pathways under normal physiological conditions is therefore an important requisite to elucidate its preventing/therapeutic effect for human diseases. This review summarizes the most recent findings on the biochemistry of active selenium species in humans, and addresses the latest evidence on the link between selenium intake, selenoproteins functionality and beneficial health effects. Primary emphasis is given to the interpretation of biochemical mechanisms rather than epidemiological/observational data. In this context, the review includes the following sections: (1) brief introduction; (2) general nutritional aspects of selenium; (3) global view of selenium metabolic routes; (4) detailed characterization of all human selenoproteins; (5) detailed discussion of the relation between selenoproteins and a variety of human diseases