Gene expression profiling implicates OXPHOS complexes in lifespan extension of flies over-expressing a small mitochondrial chaperone, Hsp22

Combined Transcriptomic and Proteomic Analysis of Perk Toxicity Pathways

In Drosophila, endoplasmic reticulum (ER) stress activates the protein kinase R-like endoplasmic reticulum kinase (dPerk). dPerk can also be activated by defective mitochondria in fly models of Parkinson's disease caused by mutations in pink1 or parkin. The Perk branch of the unfolded protein response (UPR) has emerged as a major toxic process in neurodegenerative disorders causing a chronic reduction in vital proteins and neuronal death. In this study, we combined microarray analysis and quantitative proteomics analysis in adult flies overexpressing dPerk to investigate the relationship between the transcriptional and translational response to dPerk activation. We identified tribbles and Heat shock protein 22 as two novel Drosophila activating transcription factor 4 (dAtf4) regulated transcripts. Using a combined bioinformatics tool kit, we demonstrated that the activation of dPerk leads to translational repression of mitochondrial proteins associated with glutathione and nucleotide metabolism, calcium signalling and iron-sulphur cluster biosynthesis. Further efforts to enhance these translationally repressed dPerk targets might offer protection against Perk toxicity.

Insights of heat shock protein 22 in the cardiac protection against ischemic oxidative stress

the acute and chronic myocardial ischemia results in oxidative stress that impairs myocardial contractility and eventually leads to heart failure. However, the underlying regulatory molecular mechanisms are not fully understood. The heat shock protein 22 (Hsp22), a small-molecular-weight protein preferentially expressed in the heart, was found to be dramatically increased in the cardiac oxidative stress conditions in both human and animal models after the acute and chronic ischemia. Overexpression of Hsp22 largely protects the heart against ischemic damage. Mechanistically, overexpression of Hsp22 attenuates hypoxia-induced oxidative phosphorylation in mitochondrial and the high rate of superoxide production. Short term gene delivery of Hsp22 reduces the infarct size caused by the ischemia/reperfusion, providing a clinical therapeutic potential. This review discusses the new progress of the studies on Hsp22 by focusing on its protective effect against the excessive cardiac oxidative stress, including its adaptive induction in myocardium upon the oxidative stress, its protective role in myocardial ischemia/reperfusion, its regulation in mitochondrial oxidative phosphorylation and the underlying molecular signaling pathways promoting cell survival. This information will increase our understanding of the molecular regulation of cardiac adaption under the oxidative stress and the potential therapeutic relevance.

Negative genetic correlation between longevity and its hormetic extension by dietary restriction in Drosophila melanogaster

Longevity is a highly malleable trait which is influenced by many genetic and environmental factors including nutrition. Mild stress of dietary restriction (DR) is often beneficial by extending longevity in many organisms. Here, DR-induced effects on longevity were tested for genetic variation in a set of recombinant inbred lines (RIL) in D. melanogaster. Genetic variability was significant in the longevity response following a DR-treatment across RIL, with detrimental effects in several RIL but beneficial effects in other RIL. One quantitative trait locus (QTL) was consistently significant in the middle of chromosome 2 for DR-induced changes in longevity, including hormesis (an increase in longevity by DR). Another QTL co-localized with a previously found QTL for starvation resistance in females. Several other QTL were also significant on most chromosomal arms. Longevity in controls was negatively correlated to DR effects across RIL for longevity in females, the sex showing higher DR-induced hormesis. This negative genetic correlation highlights the importance to further investigate the effects of genetic variation in the strength of DR-induced hormesis in longevity and its sex-specificity.

Identification of proteins interacting with the mitochondrial small heat shock protein Hsp22 of Drosophila melanogaster: Implication in mitochondrial homeostasis

The small heat shock protein (sHsp) Hsp22 from Drosophila melanogaster (DmHsp22) is part of the family of sHsps in this diptera. This sHsp is characterized by its presence in the mitochondrial matrix as well as by its preferential expression during ageing. Although DmHsp22 has been demonstrated to be an efficient in vitro chaperone, its function within mitochondria in vivo remains largely unknown. Thus, determining its protein-interaction network (interactome) in the mitochondrial matrix would help to shed light on its function(s). In the present study we combined immunoaffinity conjugation (IAC) with mass spectroscopy analysis of mitochondria from HeLa cells transfected with DmHsp22 in non-heat shock condition and after heat shock (HS). 60 common DmHsp22-binding mitochondrial partners were detected in two independent IACs. Immunoblotting was used to validate interaction between DmHsp22 and two members of the mitochondrial chaperone machinery; Hsp60 and Hsp70. Among the partners of DmHsp22, several ATP synthase subunits were found. Moreover, we showed that expression of DmHsp22 in transiently transfected HeLa cells increased maximal mitochondrial oxygen consumption capacity and ATP contents, providing a mechanistic link between DmHsp22 and mitochondrial functions.

LncRNA mediated regulation of aging pathways in Drosophila melanogaster during dietary restriction

Dietary restriction (DR) extends lifespan in many species which is a well-known phenomenon. Long non-coding RNAs (lncRNAs) play an important role in regulation of cell senescence and important age-related signaling pathways. Here, we profiled the lncRNA and mRNA transcriptome of fruit flies at 7 day and 42 day during DR and fully-fed conditions, respectively. In general, 102 differentially expressed lncRNAs and 1406 differentially expressed coding genes were identified. Most informatively we found a large number of differentially expressed lncRNAs and their targets enriched in GO and KEGG analysis. We discovered some new aging related signaling pathways during DR, such as hippo signaling pathway-fly, phototransduction-fly and protein processing in endoplasmic reticulum etc. Novel lncRNAs XLOC_092363 and XLOC_166557 are found to be located in 10 kb upstream sequences of hairy and ems promoters, respectively. Furthermore, tissue specificity of some novel lncRNAs had been analyzed at 7 day of DR in fly head, gut and fat body. Also the silencing of lncRNA XLOC_076307 resulted in altered expression level of its targets including Gadd45 (involved in FoxO signaling pathway). Together, the results implicated many lncRNAs closely associated with dietary restriction, which could provide a resource for lncRNA in aging and age-related disease field.

Regulation of the H+-ATP synthase by IF1: a role in mitohormesis

The mitochondrial H+-ATP synthase is a primary hub of cellular homeostasis by providing the energy required to sustain cellular activity and regulating the production of signaling molecules that reprogram nuclear activity needed for adaption to changing cues. Herein, we summarize findings regarding the regulation of the activity of the H+-ATP synthase by its physiological inhibitor, the ATPase inhibitory factor 1 (IF1) and their functional role in cellular homeostasis. First, we outline the structure and the main molecular mechanisms that regulate the activity of the enzyme. Next, we describe the molecular biology of IF1 and summarize the regulation of IF1 expression and activity as an inhibitor of the H+-ATP synthase emphasizing the role of IF1 as a main driver of energy rewiring and cellular signaling in cancer. Findings in transgenic mice in vivo indicate that the overexpression of IF1 is sufficient to reprogram energy metabolism to an enhanced glycolysis and activate reactive oxygen species (ROS)-dependent signaling pathways that promote cell survival. These findings are placed in the context of mitohormesis, a program in which a mild mitochondrial stress triggers adaptive cytoprotective mechanisms that improve lifespan. In this regard, we emphasize the role played by the H+-ATP synthase in modulating signaling pathways that activate the mitohormetic response, namely ATP, ROS and target of rapamycin (TOR). Overall, we aim to highlight the relevant role of the H+-ATP synthase and of IF1 in cellular physiology and the need of additional studies to decipher their contributions to aging and age-related diseases.

Proteostasis and aging

Accumulation of intracellular damage is an almost universal hallmark of aging. An improved understanding of the systems that contribute to cellular protein quality control has shed light on the reasons for the increased vulnerability of the proteome to stress in aging cells. Maintenance of protein homeostasis, or proteostasis, is attained through precisely coordinated systems that rapidly correct unwanted proteomic changes. Here we focus on recent developments that highlight the multidimensional nature of the proteostasis networks, which allow for coordinated protein homeostasis intracellularly, in between cells and even across organs, as well as on how they affect common age-associated diseases when they malfunction in aging.

Mitonuclear communication in homeostasis and stress

Mitochondria participate in crucial cellular processes such as energy harvesting and intermediate metabolism. Although mitochondria possess their own genome--a vestige of their bacterial origins and endosymbiotic evolution--most mitochondrial proteins are encoded in the nucleus. The expression of the mitochondrial proteome hence requires tight coordination between the two genomes to adapt mitochondrial function to the ever-changing cellular milieu. In this Review, we focus on the pathways that coordinate the communication between mitochondria and the nucleus during homeostasis and mitochondrial stress. These pathways include nucleus-to-mitochondria (anterograde) and mitochondria-to-nucleus (retrograde) communication, mitonuclear feedback signalling and proteostasis regulation, the integrated stress response and non-cell-autonomous communication. We discuss how mitonuclear communication safeguards cellular and organismal fitness and regulates lifespan.

Changes in Drosophila mitochondrial proteins following chaperone-mediated lifespan extension confirm a role of Hsp22 in mitochondrial UPR and reveal a mitochondrial localization for cathepsin D

Hsp22 is a small mitochondrial heat shock protein (sHSP) preferentially up-regulated during aging in Drosophila melanogaster. Its developmental expression is strictly regulated and it is rapidly induced in conditions of stress. Hsp22 is one of the few sHSP to be localized inside mitochondria, and is the first sHSP to be involved in the mitochondrial unfolding protein response (UPR(MT)) together with Hsp60, mitochondrial Hsp70 and TRAP1. The UPR(MT) is a pro-longevity mechanism, and interestingly Hsp22 over-expression by-itself increases lifespan and resistance to stress. To unveil the effect of Hsp22 on the mitochondrial proteome, comparative IEF/SDS polyacrylamide 2D gels were done on mitochondria from Hsp22+ flies and controls. Among the proteins influenced by Hsp22 expression were proteins from the electron transport chain (ETC), the TCA cycle and mitochondrial Hsp70. Hsp22 co-migrates with ETC components and its over-expression is associated with an increase in mitochondrial protease activity. Interestingly, the only protease that showed significant changes upon Hsp22 over-expression in the comparative IEF/SDS-PAGE analysis was cathepsin D, which is localized in mitochondria in addition to lysosome in D. melanogaster as evidenced by cellular fractionation. Together the results are consistent with a role of Hsp22 in the UPR(MT) and in mitochondrial proteostasis.

Basic mechanisms of longevity: A case study of Drosophila pro-longevity genes

Drosophila is one of the most convenient model organisms in the genetics of aging and longevity. Unlike the nematodes, which allow for the detection of new pro-aging genes by knockout and RNAi-mediated knock-down, Drosophila also provides an opportunity to find new pro-longevity genes by driver-induced overexpression. Similar studies on other models are extremely rare. In this review, we focused on genes whose overexpression prolongs the life of fruit flies. The majority of longevity-associated genes regulates metabolism and stress resistance, and belongs to the IGF-1R, PI3K, PKB, AMPK and TOR metabolic regulation cluster and the FOXO, HDAC, p53 stress response cluster.

Genome-Wide Gene Expression in relation to Age in Large Laboratory Cohorts of Drosophila melanogaster

Aging is a complex process characterized by a steady decline in an organism's ability to perform life-sustaining tasks. In the present study, two cages of approximately 12,000 mated Drosophila melanogaster females were used as a source of RNA from individuals sampled frequently as a function of age. A linear model for microarray data method was used for the microarray analysis to adjust for the box effect; it identified 1,581 candidate aging genes. Cluster analyses using a self-organizing map algorithm on the 1,581 significant genes identified gene expression patterns across different ages. Genes involved in immune system function and regulation, chorion assembly and function, and metabolism were all significantly differentially expressed as a function of age. The temporal pattern of data indicated that gene expression related to aging is affected relatively early in life span. In addition, the temporal variance in gene expression in immune function genes was compared to a random set of genes. There was an increase in the variance of gene expression within each cohort, which was not observed in the set of random genes. This observation is compatible with the hypothesis that D. melanogaster immune function genes lose control of gene expression as flies age.

Drosophila melanogaster Hsp22: a mitochondrial small heat shock protein influencing the aging process

Mitochondria are involved in many key cellular processes and therefore need to rely on good protein quality control (PQC). Three types of mechanisms are in place to insure mitochondrial protein integrity: reactive oxygen species scavenging by anti-oxidant enzymes, protein folding/degradation by molecular chaperones and proteases and clearance of defective mitochondria by mitophagy. Drosophila melanogaster Hsp22 is part of the molecular chaperone axis of the PQC and is characterized by its intra-mitochondrial localization and preferential expression during aging. As a stress biomarker, the level of its expression during aging has been shown to partially predict the remaining lifespan of flies. Since over-expression of this small heat shock protein increases lifespan and resistance to stress, Hsp22 most likely has a positive effect on mitochondrial integrity. Accordingly, Hsp22 has recently been implicated in the mitochondrial unfolding protein response of flies. This review will summarize the key findings on D. melanogaster Hsp22 and emphasis on its links with the aging process.

Patterns of positive selection in seven ant genomes

The evolution of ants is marked by remarkable adaptations that allowed the development of very complex social systems. To identify how ant-specific adaptations are associated with patterns of molecular evolution, we searched for signs of positive selection on amino-acid changes in proteins. We identified 24 functional categories of genes which were enriched for positively selected genes in the ant lineage. We also reanalyzed genome-wide data sets in bees and flies with the same methodology to check whether positive selection was specific to ants or also present in other insects. Notably, genes implicated in immunity were enriched for positively selected genes in the three lineages, ruling out the hypothesis that the evolution of hygienic behaviors in social insects caused a major relaxation of selective pressure on immune genes. Our scan also indicated that genes implicated in neurogenesis and olfaction started to undergo increased positive selection before the evolution of sociality in Hymenoptera. Finally, the comparison between these three lineages allowed us to pinpoint molecular evolution patterns that were specific to the ant lineage. In particular, there was ant-specific recurrent positive selection on genes with mitochondrial functions, suggesting that mitochondrial activity was improved during the evolution of this lineage. This might have been an important step toward the evolution of extreme lifespan that is a hallmark of ants.

Long-term dietary exposure to low concentration of dichloroacetic acid promoted longevity and attenuated cellular and functional declines in aged Drosophila melanogaster

Dichloroacetic acid (DCA), a water disinfection by-product, has attained emphasis due to its prospect for clinical use against different diseases including cancer along with negative impact on organisms. However, these reports are based on the toxicological as well clinical data using comparatively higher concentrations of DCA without much of environmental relevance. Here, we evaluate cellular as well as organismal effects of DCA at environmentally and mild clinically relevant concentrations (0.02-20.0 μg/ml) using an established model organism, Drosophila melanogaster. Flies were fed on food mixed with test concentrations of DCA for 12-48 h to examine the induction of reactive oxygen species (ROS) generation, oxidative stress (OS), heat shock genes (hsps) and cell death along with organismal responses. We also examined locomotor performance, ROS generation, glutathione (GSH) depletion, expression of GSH-synthesizing genes (gclc and gclm), and hsps at different days (0, 10, 20, 30, 40, 50) of the age in flies after prolonged DCA exposure. We observed mild OS and induction of antioxidant defense system in 20.0 μg/ml DCA-exposed organism after 24 h. After prolonged exposure to DCA, exposed organism exhibited improved survival, elevated expression of hsp27, gclc, and gclm concomitant with lower ROS generation and GSH depletion and improved locomotor performance. Conversely, hsp27 knockdown flies exhibited reversal of the above end points. The study provides evidence for the attenuation of cellular and functional decline in aged Drosophila after prolonged DCA exposure and the effect of hsp27 modulation which further incites studies towards the therapeutic application of DCA.

Variegated expression of Hsp22 transgenic reporters indicates cell-specific patterns of aging in Drosophila oenocytes

The cytoplasmic chaperone gene Hsp70 and the mitochondrial chaperone gene Hsp22 are upregulated during normal aging in Drosophila in tissue-general patterns. In addition, Hsp22 reporters are dramatically upregulated during aging in a subset of the oenocytes (liver-like cells). Hsp22 reporter expression varied dramatically between individual oenocytes and between groups of oenocytes located in adjacent body segments, and was negatively correlated with accumulation of age pigment, indicating cell-specific and cell-lineage-specific patterns of oenocyte aging. Conditional transgenic systems were used to express 88 transgenes to search for trans-regulators of the Hsp70 and Hsp22 reporters during aging. The wingless gene increased tissue-general upregulation of both Hsp70 and Hsp22 reporters. In contrast, the mitochondrial genes MnSOD and Hsp22 increased expression of Hsp22 reporters in the oenocytes and decreased accumulation of age pigment in these cells. The data suggest that cell-specific and cell lineage-specific patterns of mitochondrial malfunction contribute to oenocyte aging.

The interplay between mitochondrial protein and iron homeostasis and its possible role in ageing

Free (labile or chelatable) iron is extremely redox-active and only represents a small fraction of the total mitochondrial iron population. Several studies have shown that the proportion of free iron increases with age, leading to increased Fenton chemistry in later life. It is not clear why free iron accumulates in mitochondria, but it does so in parallel with an inability to degrade and recycle damaged proteins that causes loss of mitochondrial protein homeostasis (proteostasis). The increase in oxidative damage that has been shown to occur with age might be explained by these two processes. While this accumulation of oxidative damage has often been cited as causative to ageing there are examples of model organisms that possess high levels of oxidative damage throughout their lives with no effect on lifespan. Interestingly, these same animals are characterised by an outstanding ability to maintain correct proteostasis during their entire life. ROS can damage critical components of the iron homeostasis machinery, while the efficacy of mitochondrial quality control mechanisms will determine how detrimental that damage is. Here we review the interplay between iron and organellar quality control in mitochondrial dysfunction and we suggest that a decline in mitochondrial proteostasis with age leaves iron homeostasis (where several key stages are thought to be dependent on proteostasis machinery) vulnerable to oxidative damage and other age-related stress factors. This will have severe consequences for the electron transport chain and TCA cycle (among other processes) where several components are acutely dependent on correct assembly, insertion and maintenance of iron-sulphur clusters, leading to energetic crisis and death.

The potential role of small heat shock proteins in mitochondria

Mitochondria play a central role in cellular metabolism, calcium homeostasis, redox signaling and cell fates. Mitochondrial homeostasis is tightly regulated, and mitochondrial dysfunction is frequently associated with severe human pathologies. Small heat shock proteins are molecular chaperones that play major roles in development, stress responses, and diseases, and have been envisioned as targets for therapy. The mechanisms that lie behind the cytoprotection of small heat shock proteins are related to the regulation of mitochondrial functions. This review recapitulates the current knowledge of the expression of various small heat shock proteins in mitochondria and discusses their implication in the role of mitochondria and their regulation. Based on their involvement in mitochondrial normal physiology and pathology, a better understanding of their roles and regulation will pave the way for innovative approaches for the successful treatment of a range of stress-related syndromes whose etiology is based upon dysfunction of mitochondria.

Whole transcriptome analysis of a reversible neurodegenerative process in Drosophila reveals potential neuroprotective genes

Background

Neurodegenerative diseases are progressive and irreversible and they can be initiated by mutations in specific genes. Spalt-like genes (Sall) encode transcription factors expressed in the central nervous system. In humans, SALL mutations are associated with hereditary syndromes characterized by mental retardation, sensorineural deafness and motoneuron problems, among others. Drosophila sall mutants exhibit severe neurodegeneration of the central nervous system at embryonic stage 16, which surprisingly reverts later in development at embryonic stage 17, suggesting a potential to recover from neurodegeneration. We hypothesize that this recovery is mediated by a reorganization of the transcriptome counteracting SALL lost. To identify genes associated to neurodegeneration and neuroprotection, we used mRNA-Seq to compare the transcriptome of Drosophila sall mutant and wild type embryos from neurodegeneration and reversal stages.

Results

Neurodegeneration stage is associated with transcriptional changes in 220 genes, of which only 5% were already described as relevant for neurodegeneration. Genes related to the groups of Redox, Lifespan/Aging and Mitochondrial diseases are significantly represented at this stage. By contrast, neurodegeneration reversal stage is associated with significant changes in 480 genes, including 424 not previously associated with neuroprotection. Immune response and Salt stress are the most represented groups at this stage.

Conclusions

We identify new genes associated to neurodegeneration and neuroprotection by using an mRNA-Seq approach. The strong homology between Drosophila and human genes raises the possibility to unveil novel genes involved in neurodegeneration and neuroprotection also in humans.

A cytoplasmic suppressor of a nuclear mutation affecting mitochondrial functions in Drosophila

Phenotypes relevant to oxidative phosphorylation (OXPHOS) in eukaryotes are jointly determined by nuclear and mitochondrial DNA (mtDNA). Thus, in humans, the variable clinical presentations of mitochondrial disease patients bearing the same primary mutation, whether in nuclear or mitochondrial DNA, have been attributed to putative genetic determinants carried in the “other” genome, though their identity and the molecular mechanism(s) by which they might act remain elusive. Here we demonstrate cytoplasmic suppression of the mitochondrial disease-like phenotype of the Drosophila melanogaster nuclear mutant tko^25t, which includes developmental delay, seizure sensitivity, and defective male courtship. The tko^25t strain carries a mutation in a mitoribosomal protein gene, causing OXPHOS deficiency due to defective intramitochondrial protein synthesis. Phenotypic suppression was associated with increased mtDNA copy number and increased mitochondrial biogenesis, as measured by the expression levels of porin voltage dependent anion channel and Spargel (PGC1α). Ubiquitous overexpression of Spargel in tko^25t flies phenocopied the suppressor, identifying it as a key mechanistic target thereof. Suppressor-strain mtDNAs differed from related nonsuppressor strain mtDNAs by several coding-region polymorphisms and by length and sequence variation in the noncoding region (NCR), in which the origin of mtDNA replication is located. Cytoplasm from four of five originally Wolbachia-infected strains showed the same suppressor effect, whereas that from neither of two uninfected strains did so, suggesting that the stress of chronic Wolbachia infection may provide evolutionary selection for improved mitochondrial fitness under metabolic stress. Our findings provide a paradigm for understanding the role of mtDNA genotype in human disease.

Branched-chain amino acids, mitochondrial biogenesis, and healthspan: an evolutionary perspective

Malnutrition is common among older persons, with important consequences increasing frailty and morbidity and reducing health expectancy. On the contrary, calorie restriction (CR, a low-calorie dietary regimen with adequate nutrition) slows the progression of age-related diseases and extends the lifespan of many species. Identification of strategies mimicking key CR mechanisms – increased mitochondrial respiration and reduced production of oxygen radicals – is a hot topic in gerontology. Dietary supplementation with essential and/or branched chain amino acids (BCAAs) exerts a variety of beneficial effects in experimental animals and humans and has been recently demonstrated to support cardiac and skeletal muscle mitochondrial biogenesis, prevent oxidative damage, and enhance physical endurance in middle-aged mice, resulting in prolonged survival. Here we review recent studies addressing the possible role of BCAAs in energy metabolism and in the longevity of species ranging from unicellular organisms to mammals. We also summarize observations from human studies supporting the exciting hypothesis that dietary BCAA enriched mixture supplementation might be a health-promoting strategy in aged patients at risk.

H11 kinase/heat shock protein 22 deletion impairs both nuclear and mitochondrial functions of STAT3 and accelerates the transition into heart failure on cardiac overload

BACKGROUND

Cardiac overload, a major cause of heart failure, induces the expression of the heat shock protein H11 kinase/Hsp22 (Hsp22).

METHODS AND RESULTS

To determine the specific function of Hsp22 in that context, a knockout mouse model of Hsp22 deletion was generated. Although comparable to wild-type mice in basal conditions, knockout mice exposed to pressure overload developed less hypertrophy and showed ventricular dilation, impaired contractile function, increased myocyte length and accumulation of interstitial collagen, faster transition into heart failure, and increased mortality. Microarrays revealed that hearts from knockout mice failed to transactivate genes regulated by the transcription factor STAT3. Accordingly, nuclear STAT3 tyrosine phosphorylation was decreased in knockout mice. Silencing and overexpression experiments in isolated neonatal rat cardiomyocytes showed that Hsp22 activates STAT3 via production of interleukin-6 by the transcription factor nuclear factor-κB. In addition to its transcriptional function, STAT3 translocates to the mitochondria where it increases oxidative phosphorylation. Both mitochondrial STAT3 translocation and respiration were also significantly decreased in knockout mice.

CONCLUSIONS

This study found that Hsp22 represents a previously undescribed activator of both nuclear and mitochondrial functions of STAT3, and its deletion in the context of pressure overload in vivo accelerates the transition into heart failure and increases mortality.

Heat shock proteins and Drosophila aging

Since their discovery in Drosophila, the heat shock proteins (Hsps) have been shown to regulate both stress resistance and life-span. Aging is characterized by increased oxidative stress and the accumulation of abnormal (malfolded) proteins, and these stresses induce Hsp gene expression through the transcription factor HSF. In addition, a subset of Hsps is induced by oxidative stress through the JNK signaling pathway and the transcription factor Foxo. The Hsps counteract the toxicity of abnormal proteins by facilitating protein refolding and turnover, and through other mechanisms including inhibition of apoptosis. The Hsps are up-regulated in tissue-specific patterns during aging, and their expression correlates with, and sometimes predicts, life span, making them ideal biomarkers of aging. The tools available for experimentally manipulating gene function and assaying healthspan in Drosophila provides an unparalleled opportunity to further study the role of Hsps in aging.

Age-dependent posttranslational modifications of voltage-dependent anion channel 1

The accumulation of oxidative damage in mitochondrial proteins, membranes and DNA during ageing is supposed to lead to mitochondrial inactivation, downstream molecular impairments and subsequent decline of biological systems. In a quantitative study investigating the age-related changes of mitochondrial proteins on the level of oxidative posttranslational modifications, we previously found a set of conserved biomarkers across ageing models in five species with consistent oxidative break-up of tryptophan residues and formation of N-formyl kynurenine. In an additional proteomic profiling of a long-living Drosophila mutant overexpressing mitochondrial Hsp22 and controls, we found age-related redundant isoforms of voltage-dependent anion channel 1 (VDAC-1). A re-examination of data from human umbilical vein endothelial cells (with normal and chemically accelerated in vitro ageing), revealed similar age-dependent alterations of voltage-dependent anion channel isoforms. Building on these results, we examined the expression of VDAC-1 in an in vitro model of excitotoxicity. We show that glutamate-induced calcium toxicity in neurons induces changes of voltage-dependent anion channel 1 related to downstream events of mitochondrial apoptosis like poly-ADP-ribosylation.