A role for SIR-2.1 regulation of ER stress response genes in determining C. elegans life span

The short-lived fish Nothobranchius furzeri as a new model system for aging studies

Genetic and pharmacological research on aging is hampered by the lifespan of available vertebrate models. We recently initiated studies on Nothobranchius furzeri, a species with a maximum life expectancy in captivity of just three months which represents the shortest documented captive lifespan for a vertebrate. Further research on N. furzeri has demonstrated that 1. Short lifespan is tied with explosive growth and accelerated sexual maturation. 2. Short lifespan is correlated with expression of age-related behavioral and histological changes. 3. Lifespan and expression of age-related markers can be modulated by water temperature. 4. Resveratrol, a drug characterized for its life-extending action in Caenorhabditis elegans and Drosophila, increases lifespan and retards expression of age-related markers. 5. Aging-related genes can be easily isolated by homology cloning. Finally, different populations or species of Nothobranchius show large-scale differences in captive lifespan. In the last three years, N. furzeri has moved from biological curiosity to a promising model system for drug validation. Furthermore, this species occupies a favorable position in the Teleost's "tree of life". It is very close to the Japanese Medaka, and close to the pufferfishes and stickleback and might represent a very useful model for comparative genomics of aging.

Application of advanced technologies in ageing research

Several technologies that emerged in the post-genomic era have been particularly useful in dissecting the molecular mechanisms of complex biological processes through the systems approach. Here, we review how three of these technologies, namely transcriptional profiling, large-scale RNA interference (RNAi) and genome-wide location analysis of protein-DNA interactions, have been used in the study of ageing in metazoans. We also highlight recent developments of these three technologies and how these developments are applicable to ageing research.

Positional artifacts in microarrays: experimental verification and construction of COP, an automated detection tool

Microarray technology is currently one of the most widely-used technologies in biology. Many studies focus on inferring the function of an unknown gene from its co-expressed genes. Here, we are able to show that there are two types of positional artifacts in microarray data introducing spurious correlations between genes. First, we find that genes that are close on the microarray chips tend to have higher correlations between their expression profiles. We call this the ‘chip artifact’. Our calculations suggest that the carry-over during the printing process is one of the major sources of this type of artifact, which is later confirmed by our experiments. Based on our experiments, the measured intensity of a microarray spot contains 0.1% (for fully-hybridized spots) to 93% (for un-hybridized ones) of noise resulting from this artifact. Secondly, we, for the first time, show that genes that are close on the microtiter plates in microarray experiments also tend to have higher correlations. We call this the ‘plate artifact’. Both types of artifacts exist with different severity in all cDNA microarray experiments that we analyzed. Therefore, we develop an automated web tool—COP (COrrelations by Positional artifacts) to detect these artifacts in microarray experiments. COP has been integrated with the microarray data normalization tool, ExpressYourself, which is available at . Together, the two can eliminate most of the common noises in microarray data.

SIRT4 inhibits glutamate dehydrogenase and opposes the effects of calorie restriction in pancreatic beta cells

Sir2 is an NAD-dependent deacetylase that connects metabolism with longevity in yeast, flies, and worms. Mammals have seven Sir2 homologs (SIRT1-7). We show that SIRT4 is a mitochondrial enzyme that uses NAD to ADP-ribosylate and downregulate glutamate dehydrogenase (GDH) activity. GDH is known to promote the metabolism of glutamate and glutamine, generating ATP, which promotes insulin secretion. Loss of SIRT4 in insulinoma cells activates GDH, thereby upregulating amino acid-stimulated insulin secretion. A similar effect is observed in pancreatic beta cells from mice deficient in SIRT4 or on the dietary regimen of calorie restriction (CR). Furthermore, GDH from SIRT4-deficient or CR mice is insensitive to phosphodiesterase, an enzyme that cleaves ADP-ribose, suggesting the absence of ADP-ribosylation. These results indicate that SIRT4 functions in beta cell mitochondria to repress the activity of GDH by ADP-ribosylation, thereby downregulating insulin secretion in response to amino acids, effects that are alleviated during CR.

Resveratrol improves health and survival of mice on a high-calorie diet

Resveratrol (3,5,4'-trihydroxystilbene) extends the lifespan of diverse species including Saccharomyces cerevisiae, Caenorhabditis elegans and Drosophila melanogaster. In these organisms, lifespan extension is dependent on Sir2, a conserved deacetylase proposed to underlie the beneficial effects of caloric restriction. Here we show that resveratrol shifts the physiology of middle-aged mice on a high-calorie diet towards that of mice on a standard diet and significantly increases their survival. Resveratrol produces changes associated with longer lifespan, including increased insulin sensitivity, reduced insulin-like growth factor-1 (IGF-I) levels, increased AMP-activated protein kinase (AMPK) and peroxisome proliferator-activated receptor-gamma coactivator 1alpha (PGC-1alpha) activity, increased mitochondrial number, and improved motor function. Parametric analysis of gene set enrichment revealed that resveratrol opposed the effects of the high-calorie diet in 144 out of 153 significantly altered pathways. These data show that improving general health in mammals using small molecules is an attainable goal, and point to new approaches for treating obesity-related disorders and diseases of ageing.

Pharmacology of delayed aging and extended lifespan of Caenorhabditis elegans

The identification and analysis of compounds that delay aging and extend lifespan is an important aspect of gerontology research; these studies can test theories of aging, lead to the discovery of endogenous systems that influence aging, and establish the foundation for treatments that might delay normal human aging. Here we review studies using the nematode Caenorhabditis elegans to identify and characterize compounds that delay aging and extend lifespan. These studies are considered in four groups: (1) Studies that address the free-radical theory of aging by analyzing candidate compounds with antioxidant activities including vitamin E, tocotrienols, coenzyme Q, and Eukarion-8/134. (2) Studies that analyze plant extracts (blueberry and Ginko biloba) that contain a mixture of compounds. (3) Studies of resveratrol, which was identified in a screen for compounds that affect the activity of the Sir2 protein that influences lifespan. (4) Studies based on screening compound libraries using C. elegans aging as a bioassay, which led to the identification of the anticonvulsant medicines ethosuximide and trimethadione. There has been exciting progress in the analysis of compounds that influence C. elegans aging, and important challenges and opportunities remain in determining the mechanisms of action of these compounds and the relevance of these observations to aging of other animals.

Neurohormetic phytochemicals: Low-dose toxins that induce adaptive neuronal stress responses

Diets rich in vegetables and fruits are associated with reduced risk of several major diseases, including neurodegenerative disorders. Although some beneficial phytochemicals might function solely as antioxidants, it is becoming clear that many of the beneficial chemicals in vegetables and fruits evolved as toxins (to dissuade insects and other predators) that, at subtoxic doses, activate adaptive cellular stress-response pathways in a variety of cells including neurons. Examples of such 'preconditioning' or 'neurohormesis' pathways include those involving cell-survival signaling kinases, the transcription factors NRF2 and CREB, and histone deacetylases of the sirtuin family. In these ways, neurohormetic phytochemicals such as resveratrol, sulforaphanes and curcumin might protect neurons against injury and disease by stimulating the production of antioxidant enzymes, neurotrophic factors, protein chaperones and other proteins that help cells to withstand stress. Thus, as we discuss in this review, highly conserved longevity and survival pathways in neurons are the targets of many phytochemicals.

Sirtuins in aging and age-related disease

Sirtuins have been the focus of intense scrutiny since the discovery of Sir2 as a yeast longevity factor. Functioning as either deacetylases or ADP ribosylases, Sirtuins are regulated by the cofactor NAD and thus may serve as sensors of the metabolic state of the cell and organism. Here we examine the roles of Sirtuins in diverse eukaryotic species, with special emphasis on their links to aging and age-related diseases including cancer, diabetes, and neurodegenerative disorders.

The LXXLL motif of murine forkhead transcription factor FoxO1 mediates Sirt1-dependent transcriptional activity

The forkhead transcription factor FoxO1 has been identified as a negative regulator of insulin/IGF-1 signaling. Its function is inhibited by phosphorylation and nuclear exclusion through a PI3K-dependent pathway. However, the structure/function relationship of FoxO1 has not been elucidated completely. In this study, we carried out mutation analysis of the FoxO1 coactivator-interacting LXXLL motif (amino acids 459-463). Expression of a 3A/LXXAA mutant, in which 3 Akt phosphorylation sites (T24, S253, and S316) and 2 leucine residues in the LXXLL motif (L462 and L463) were replaced by alanine, decreased both Igfbp-1 and G6Pase promoter activity and endogenous Igfbp-1 and G6Pase gene expression in simian virus 40-transformed (SV40-transformed) hepatocytes. Importantly, mutagenesis of the LXXLL motif eliminated FoxO1 interaction with the nicotinamide adenine dinucleotide-dependent (NAD-dependent) deacetylase sirtuin 1 (Sirt1), sustained the acetylated state of FoxO1, and made FoxO1 nicotinamide and resveratrol insensitive, supporting a role for this motif in Sirt1 binding. Furthermore, intravenous administration of adenovirus encoding 3A/LXXAA FoxO1 into Lepr db/db mice decreased fasting blood glucose levels and improved glucose tolerance and was accompanied by reduced G6Pase and Igfbp-1 gene expression and increased hepatic glycogen content. In conclusion, the LXXLL motif of FoxO1 may have an important role for its transcriptional activity and Sirt1 binding and should be a target site for regulation of gene expression of FoxO1 target genes and glucose metabolism in vivo.

C. elegans SIR-2.1 interacts with 14-3-3 proteins to activate DAF-16 and extend life span

The longevity of Caenorhabditis elegans is promoted by extra copies of the sir-2.1 gene in a manner dependent on the forkhead transcription factor DAF-16. We identify two C. elegans 14-3-3 proteins as SIR-2.1 binding partners and show that 14-3-3 genes are required for the life-span extension conferred by extra copies of sir-2.1. 14-3-3 proteins are also required for SIR-2.1-induced transcriptional activation of DAF-16 and stress resistance. Following heat stress, SIR-2.1 can bind DAF-16 in a 14-3-3-dependent manner. By contrast, low insulin-like signaling does not promote SIR-2.1/DAF-16 interaction, and sir-2.1 and the 14-3-3 genes are not required for the regulation of life span by the insulin-like signaling pathway. We propose the existence of a stress-dependent pathway in which SIR-2.1 and 14-3-3 act in parallel to the insulin-like pathway to activate DAF-16 and extend life span.

C. elegans 14-3-3 proteins regulate life span and interact with SIR-2.1 and DAF-16/FOXO

14-3-3 proteins are evolutionarily conserved and ubiquitous proteins that function in a wide variety of biological processes. Here we define a new role for C. elegans 14-3-3 proteins in life span regulation. We identify two C. elegans 14-3-3 proteins as interacting proteins of a major life span regulator, the C. elegans SIR2 ortholog, SIR-2.1. Similar to sir-2.1, we find that overexpression of either 14-3-3 protein (PAR-5 or FTT-2) extends life span and that this is dependent on DAF-16, a forkhead transcription factor (FOXO), another important life span regulator in the insulin/IGF-1 signaling pathway. Furthermore, we show that both 14-3-3 proteins are co-expressed with DAF-16 and SIR-2.1 in the tissues critical for life span regulation. Finally, we show that DAF-16/FOXO also physically interacts with the 14-3-3 proteins. These results suggest that C. elegans 14-3-3 proteins can regulate longevity by cooperating with both SIR-2.1 and DAF-16/FOXO.

Endoplasmic reticulum stress in health and disease

Unfolded proteins and other conditions affecting endoplasmic reticulum (ER) homeostasis cause ER stress. The cell reacts to ER stress by activation of the unfolded protein response (UPR), which induces profound changes in cellular metabolism including general translation attenuation, transcriptional upregulation of molecular chaperone genes, and activation of ER-associated degradation. However, prolonged or acute ER stress results in cell death. Recent progress suggests that ER stress and UPR play key roles in the immune response, diabetes, tumor growth under hypoxic conditions, and in some neurodegenerative diseases. Further research on ER stress and UPR will greatly enhance the understanding of these physiological and pathological processes, and provide novel avenues to potential therapies.

Therapeutic potential of resveratrol: the in vivo evidence

Resveratrol, a constituent of red wine, has long been suspected to have cardioprotective effects. Interest in this compound has been renewed in recent years, first from its identification as a chemopreventive agent for skin cancer, and subsequently from reports that it activates sirtuin deacetylases and extends the lifespans of lower organisms. Despite scepticism concerning its bioavailability, a growing body of in vivo evidence indicates that resveratrol has protective effects in rodent models of stress and disease. Here, we provide a comprehensive and critical review of the in vivo data on resveratrol, and consider its potential as a therapeutic for humans.

Recent aging research in Caenorhabditis elegans

Evidence gathered over the past 15 years shows that the nematode Caenorhabditis elegans is excellently suited as a model to study aging processes in the entire organism. Genetic approaches have been used to identify and elucidate multiple mechanisms and their corresponding genes that limit the life span of C. elegans. These highly conserved pathways include the well-studied insulin/IGF-1 receptor-like signaling pathway, which is thought to be a central determinant of life span, since several other mechanisms depend or converge on the insulin/IGF-1 pathway transcription factor DAF-16/FoxO. In this review we focus on new insights into the molecular mechanisms of aging in C. elegans, including new genes acting in the insulin/IGF-1 pathway and germline signaling. In addition, stress response pathways and mitochondrial mechanisms, dietary restriction, SIR2 deacetylase activity, TOR and TUBBY signaling, as well as telomere length contribution are discussed in relation to recent developments in C. elegans aging research.

SIR2 calls upon the ER

Resveratrol induces longevity in C. elegans through the action of SIR2. Recently published work shows that resveratrol induces genes of the unfolded protein stress response of the endoplasmic reticulum. Paradoxically, these stress genes are repressed by SIR2, suggesting that resveratrol increases life span by inhibiting this SIR2 action.