Disruption of the mGsta4 gene increases life span of C57BL mice

Phenotypic molecular features of long-lived animal species

One of the challenges facing science/biology today is uncovering the molecular bases that support and determine animal and human longevity. Nature, in offering a diversity of animal species that differ in longevity by more than 5 orders of magnitude, is the best 'experimental laboratory' to achieve this aim. Mammals, in particular, can differ by more than 200-fold in longevity. For this reason, most of the available evidence on this topic derives from comparative physiology studies. But why can human beings, for instance, reach 120 years whereas rats only last at best 4 years? How does nature change the longevity of species? Longevity is a species-specific feature resulting from an evolutionary process. Long-lived animal species, including humans, show adaptations at all levels of biological organization, from metabolites to genome, supported by signaling and regulatory networks. The structural and functional features that define a long-lived species may suggest that longevity is a programmed biological property.

Does Nrf2 Play a Role of a Master Regulator of Mammalian Aging?

For a long time Nrf2 transcription factor has been attracting attention of researchers investigating phenomenon of aging. Numerous studies have investigated effects of Nrf2 on aging and cell senescence. Nrf2 is often considered as a key player in aging processes, however this needs to be proven. It should be noted that most studies were carried out on invertebrate model organisms, such as nematodes and fruit flies, but not on mammals. This paper briefly presents main mechanisms of mammalian aging and role of inflammation and oxidative stress in this process. The mechanisms of Nrf2 activity regulation, its involvement in aging and development of the senescence-associated secretory phenotype (SASP) are also discussed. Main part of this review is devoted to critical analysis of available experimental data on the role of Nrf2 in mammalian aging.

Comparative transcriptomics reveals circadian and pluripotency networks as two pillars of longevity regulation

Mammals differ more than 100-fold in maximum lifespan. Here, we conducted comparative transcriptomics on 26 species with diverse lifespans. We identified thousands of genes with expression levels negatively or positively correlated with a species' maximum lifespan (Neg- or Pos-MLS genes). Neg-MLS genes are primarily involved in energy metabolism and inflammation. Pos-MLS genes show enrichment in DNA repair, microtubule organization, and RNA transport. Expression of Neg- and Pos-MLS genes is modulated by interventions, including mTOR and PI3K inhibition. Regulatory networks analysis showed that Neg-MLS genes are under circadian regulation possibly to avoid persistent high expression, whereas Pos-MLS genes are targets of master pluripotency regulators OCT4 and NANOG and are upregulated during somatic cell reprogramming. Pos-MLS genes are highly expressed during embryogenesis but significantly downregulated after birth. This work provides targets for anti-aging interventions by defining pathways correlating with longevity across mammals and uncovering circadian and pluripotency networks as central regulators of longevity.

Emerging Insight Into the Role of Circadian Clock Gene BMAL1 in Cellular Senescence

Cell senescence is a crucial process in cell fate determination and is involved in an extensive array of aging-associated diseases. General perceptions and experimental evidence point out that the decline of physical function as well as aging-associated diseases are often initiated by cell senescence and organ ageing. Therefore, regulation of cell senescence process can be a promising way to handle aging-associated diseases such as osteoporosis. The circadian clock regulates a wide range of cellular and physiological activities, and many age-linked degenerative disorders are associated with the dysregulation of clock genes. BMAL1 is a core circadian transcription factor and governs downstream genes by binding to the E-box elements in their promoters. Compelling evidence has proposed the role of BMAL1 in cellular senescence and aging-associated diseases. In this review, we summarize the linkage between BMAL1 and factors of cell senescence including oxidative stress, metabolism, and the genotoxic stress response. Dysregulated and dampened BMAL1 may serve as a potential therapeutic target against aging- associated diseases.

Anticancer Activity of Ω-6 Fatty Acids through Increased 4-HNE in Breast Cancer Cells

Simple Summary

Epidemiological evidence suggests that breast cancer risk is lowered by Ω-3 and increased by Ω-6 polyunsaturated fatty acids (PUFAs). Paradoxically, the Ω-6 PUFA metabolite 4-hydroxynonenal (4-HNE) inhibits cancer cell growth. This duality prompted us to study whether arachidonic acid (AA) would enhance doxorubicin (dox) cytotoxicity towards breast cancer cells. We found that supplementing AA or inhibiting 4-HNE metabolism potentiated doxorubicin (dox) toxicity toward Her2-dependent breast cancer but spared myocardial cells. Our results suggest that Ω-6 PUFAs could improve outcomes of dox chemotherapy in Her2-overexpressing breast cancer.

Abstract

Her2-amplified breast cancers resistant to available Her2-targeted therapeutics continue to be a challenge in breast cancer therapy. Dox is the mainstay of chemotherapy of all types of breast cancer, but its usefulness is limited by cumulative cardiotoxicity. Because oxidative stress caused by dox generates the pro-apoptotic Ω-6 PUFA metabolite 4-hydroxynonenal (4-HNE), we surmised that Ω-6 PUFAs would increase the effectiveness of dox chemotherapy. Since the mercapturic acid pathway enzyme RALBP1 (also known as RLIP76 or Rlip) that limits cellular accumulation of 4-HNE also mediates dox resistance, the combination of Ω-6 PUFAs and Rlip depletion could synergistically improve the efficacy of dox. Thus, we studied the effects of the Ω-6 PUFA arachidonic acid (AA) and Rlip knockdown on the antineoplastic activity of dox towards Her2-amplified breast cancer cell lines SK-BR-3, which is sensitive to Her2 inhibitors, and AU565, which is resistant. AA increased lipid peroxidation, 4-HNE generation, apoptosis, cellular dox concentration and dox cytotoxicity in both cell lines while sparing cultured immortalized cardiomyocyte cells. The known functions of Rlip including clathrin-dependent endocytosis and dox efflux were inhibited by AA. Our results support a model in which 4-HNE generated by AA overwhelms the capacity of Rlip to defend against apoptosis caused by dox or 4-HNE. We propose that Ω-6 PUFA supplementation could improve the efficacy of dox or Rlip inhibitors for treating Her2-amplified breast cancer.

Loss of swiss cheese in Neurons Contributes to Neurodegeneration with Mitochondria Abnormalities, Reactive Oxygen Species Acceleration and Accumulation of Lipid Droplets in Drosophila Brain

Various neurodegenerative disorders are associated with human NTE/PNPLA6 dysfunction. Mechanisms of neuropathogenesis in these diseases are far from clearly elucidated. Hereditary spastic paraplegia belongs to a type of neurodegeneration associated with NTE/PNLPLA6 and is implicated in neuron death. In this study, we used Drosophila melanogaster to investigate the consequences of neuronal knockdown of swiss cheese (sws)-the evolutionarily conserved ortholog of human NTE/PNPLA6-in vivo. Adult flies with the knockdown show longevity decline, locomotor and memory deficits, severe neurodegeneration progression in the brain, reactive oxygen species level acceleration, mitochondria abnormalities and lipid droplet accumulation. Our results suggest that SWS/NTE/PNPLA6 dysfunction in neurons induces oxidative stress and lipid metabolism alterations, involving mitochondria dynamics and lipid droplet turnover in neurodegeneration pathogenesis. We propose that there is a complex mechanism in neurological diseases such as hereditary spastic paraplegia, which includes a stress reaction, engaging mitochondria, lipid droplets and endoplasmic reticulum interplay.

Beneficial and Detrimental Effects of Reactive Oxygen Species on Lifespan: A Comprehensive Review of Comparative and Experimental Studies

Aging is the greatest risk factor for a multitude of diseases including cardiovascular disease, neurodegeneration and cancer. Despite decades of research dedicated to understanding aging, the mechanisms underlying the aging process remain incompletely understood. The widely-accepted free radical theory of aging (FRTA) proposes that the accumulation of oxidative damage caused by reactive oxygen species (ROS) is one of the primary causes of aging. To define the relationship between ROS and aging, there have been two main approaches: comparative studies that measure outcomes related to ROS across species with different lifespans, and experimental studies that modulate ROS levels within a single species using either a genetic or pharmacologic approach. Comparative studies have shown that levels of ROS and oxidative damage are inversely correlated with lifespan. While these studies in general support the FRTA, this type of experiment can only demonstrate correlation, not causation. Experimental studies involving the manipulation of ROS levels in model organisms have generally shown that interventions that increase ROS tend to decrease lifespan, while interventions that decrease ROS tend to increase lifespan. However, there are also multiple examples in which the opposite is observed: increasing ROS levels results in extended longevity, and decreasing ROS levels results in shortened lifespan. While these studies contradict the predictions of the FRTA, these experiments have been performed in a very limited number of species, all of which have a relatively short lifespan. Overall, the data suggest that the relationship between ROS and lifespan is complex, and that ROS can have both beneficial or detrimental effects on longevity depending on the species and conditions. Accordingly, the relationship between ROS and aging is difficult to generalize across the tree of life.

An NRF2 Perspective on Stem Cells and Ageing

Redox and metabolic mechanisms lie at the heart of stem cell survival and regenerative activity. NRF2 is a major transcriptional controller of cellular redox and metabolic homeostasis, which has also been implicated in ageing and lifespan regulation. However, NRF2's role in stem cells and their functioning with age is only just emerging. Here, focusing mainly on neural stem cells, which are core to adult brain plasticity and function, we review recent findings that identify NRF2 as a fundamental player in stem cell biology and ageing. We also discuss NRF2-based molecular programs that may govern stem cell state and function with age, and implications of this for age-related pathologies.

Melatonin prevents senescence of canine adipose-derived mesenchymal stem cells through activating NRF2 and inhibiting ER stress

Transplantation of adipose-derived mesenchymal stem cells (ADMSCs) can aid in the treatment of numerous diseases in animals. However, natural aging during in vitro expansion of ADMSCs prior to their use in transplantation restricts their beneficial effects. Melatonin is reported to exert biorhythm regulation, anti-oxidation, and anti-senescence effects in various animal and cell models. Herein, by using a senescent canine ADMSCs (cADMSCs) cell model subjected to multiple passages in vitro, we investigated the effects of melatonin on ADMSCs senescence. We found that melatonin alleviates endoplasmic reticulum stress (ERS) and cell senescence. MT1/MT2 melatonin receptor inhibitor, luzindole, diminished the mRNA expression levels and rhythm expression amplitude of Bmal1 and Nrf2 genes. Nrf2 knockdown blocked the stimulatory effects of melatonin on endoplasmic reticulum-associated degradation (ERAD)-related gene expression and its inhibitory effects on ERS-related gene expression. At the same time, the inhibitory effects of melatonin on the NF-κB signaling pathway and senescence-associated secretory phenotype (SASP) were blocked by Nrf2 knockdown in cADMSCs. Melatonin pretreatment improved the survival of cADMSCs and enhanced the beneficial effects of cADMSCs transplantation in canine acute liver injury. These results indicate that melatonin activates Nrf2 through the MT1/MT2 receptor pathway, stimulates ERAD, inhibits NF-κB and ERS, alleviates cADMSCs senescence, and improves the efficacy of transplanted cADMSCs.

Oxytocin alleviates cellular senescence through oxytocin receptor-mediated extracellular signal-regulated kinase/Nrf2 signalling

BACKGROUND

Oxytocin (OT) is a neuropeptide hormone that has many beneficial biological effects, including protection against age-related disorders. However, less is known about its role in intrinsic skin ageing, which is accelerated by an increase in senescent cell fraction in skin tissue.

OBJECTIVES

To investigate the novel function and the underlying mechanism of OT in preventing cellular senescence in normal human dermal fibroblasts (NHDFs) isolated from the skin of female donors of different ages.

METHODS

NHDFs from young and old donors were exposed to conditioned medium from senescent or control NHDFs in the presence or absence of 10 nmol L^-1 OT for 3 days, and were continuously subcultured for 12 days. Subsequently, various age-associated signs of senescence including decreased proliferation rate, elevated p16 and p21 levels, and positivity for senescence-associated β-galactosidase expression were examined.

RESULTS

We found that OT suppressed senescence-associated secretory phenotype-induced senescence in NHDFs, and its effect depended on the age of the donor's NHDFs. The inhibitory effects of OT required signalling by OT receptor-mediated extracellular signal-regulated kinase/Nrf2 (nuclear factor erythroid 2-related factor 2). The age-dependent antisenescence effects of OT are closely related to hypermethylation of the OT receptor gene (OXTR).

CONCLUSIONS

Our findings bring to light the role of OT in the prevention of skin ageing, which might allow development of new clinical strategies. What's already known about this topic? Senescent keratinocytes and fibroblasts accumulate with age in the skin and contribute to the loss of skin function and integrity during ageing. Senescent cells secrete senescence-associated secretory phenotype (SASP), which includes the release of proinflammatory cytokines such as interleukin (IL)-6 and IL-1, chemokines, extracellular matrix-remodelling proteases and growth factors. The neuropeptide oxytocin (OT) and its receptor (OXTR) have protective effects against various age-related disorders. What does this study add? OT suppressed SASP-induced cellular senescence in normal human dermal fibroblasts (NHDFs), depending on the age of the NHDFs' donor. The inhibitory effects of OT on cellular senescence required OXTR-mediated phosphorylation of extracellular signal-regulated kinase, which enhanced nuclear localization of Nrf2, a vital factor in the antioxidant defence system. The age-specific antisenescent effects of OT were closely related to hypermethylation of OXTR. What is the translational message? Our results suggest that OT and OXTR agonists could be clinically promising agents for the improvement of age-associated skin ageing, especially in women.

The Genetics of Aging: A Vertebrate Perspective

Aging negatively impacts vitality and health. Many genetic pathways that regulate aging were discovered in invertebrates. However, the genetics of aging is more complex in vertebrates because of their specialized systems. This Review discusses advances in the genetic regulation of aging in vertebrates from work in mice, humans, and organisms with exceptional lifespans. We highlight challenges for the future, including sex-dependent differences in lifespan and the interplay between genes and environment. We also discuss how the identification of reliable biomarkers of age and development of new vertebrate models can be leveraged for personalized interventions to counter aging and age-related diseases.

Emerging role of nuclear factor erythroid 2-related factor 2 in the mechanism of action and resistance to anticancer therapies

Nuclear factor E2-related factor 2 (NRF2), a transcription factor, is a master regulator of an array of genes related to oxidative and electrophilic stress that promote and maintain redox homeostasis. NRF2 function is well studied in in vitro, animal and general physiology models. However, emerging data has uncovered novel functionality of this transcription factor in human diseases such as cancer, autism, anxiety disorders and diabetes. A key finding in these emerging roles has been its constitutive upregulation in multiple cancers promoting pro-survival phenotypes. The survivability pathways in these studies were mostly explained by classical NRF2 activation involving KEAP-1 relief and transcriptional induction of reactive oxygen species (ROS) neutralizing and cytoprotective drug-metabolizing enzymes (phase I, II, III and 0). Further, NRF2 status and activation is associated with lowered cancer therapeutic efficacy and the eventual emergence of therapeutic resistance. Interestingly, we and others have provided further evidence of direct NRF2 regulation of anticancer drug targets like receptor tyrosine kinases and DNA damage and repair proteins and kinases with implications for therapy outcome. This novel finding demonstrates a renewed role of NRF2 as a key modulatory factor informing anticancer therapeutic outcomes, which extends beyond its described classical role as a ROS regulator. This review will provide a knowledge base for these emerging roles of NRF2 in anticancer therapies involving feedback and feed forward models and will consolidate and present such findings in a systematic manner. This places NRF2 as a key determinant of action, effectiveness and resistance to anticancer therapy.

Redox Signaling by Reactive Electrophiles and Oxidants

The concept of cell signaling in the context of nonenzyme-assisted protein modifications by reactive electrophilic and oxidative species, broadly known as redox signaling, is a uniquely complex topic that has been approached from numerous different and multidisciplinary angles. Our Review reflects on five aspects critical for understanding how nature harnesses these noncanonical post-translational modifications to coordinate distinct cellular activities: (1) specific players and their generation, (2) physicochemical properties, (3) mechanisms of action, (4) methods of interrogation, and (5) functional roles in health and disease. Emphasis is primarily placed on the latest progress in the field, but several aspects of classical work likely forgotten/lost are also recollected. For researchers with interests in getting into the field, our Review is anticipated to function as a primer. For the expert, we aim to stimulate thought and discussion about fundamentals of redox signaling mechanisms and nuances of specificity/selectivity and timing in this sophisticated yet fascinating arena at the crossroads of chemistry and biology.

Activation of Nrf2 in the liver is associated with stress resistance mediated by suppression of the growth hormone-regulated STAT5b transcription factor

The transcription factor Nrf2 (encoded by Nfe2l2) induces expression of numerous detoxifying and antioxidant genes in response to oxidative stress. The cytoplasmic protein Keap1 interacts with and represses Nrf2 function. Computational approaches were developed to identify factors that modulate Nrf2 in a mouse liver gene expression compendium. Forty-eight Nrf2 biomarker genes were identified using profiles from the livers of mice in which Nrf2 was activated genetically in Keap1-null mice or chemically by a potent activator of Nrf2 signaling. The rank-based Running Fisher statistical test was used to determine the correlation between the Nrf2 biomarker genes and a test set of 81 profiles with known Nrf2 activation status demonstrating a balanced accuracy of 96%. For a large number of factors examined in the compendium, we found consistent relationships between activation of Nrf2 and feminization of the liver transcriptome through suppression of the male-specific growth hormone (GH)-regulated transcription factor STAT5b. The livers of female mice exhibited higher Nrf2 activation than male mice in untreated or chemical-treated conditions. In male mice, Nrf2 was activated by treatment with ethinyl estradiol, whereas in female mice, Nrf2 was suppressed by treatment with testosterone. Nrf2 was activated in 5 models of disrupted GH signaling containing mutations in Pit1, Prop1, Ghrh, Ghrhr, and Ghr. Out of 59 chemical treatments that activated Nrf2, 36 exhibited STAT5b suppression in the male liver. The Nrf2-STAT5b coupling was absent in in vitro comparisons of chemical treatments. Treatment of male and female mice with 11 chemicals that induce oxidative stress led to activation of Nrf2 to greater extents in females than males. The enhanced basal and inducible levels of Nrf2 activation in females relative to males provides a molecular explanation for the greater resistance often seen in females vs. males to age-dependent diseases and chemical-induced toxicity.

Overexpression of PGC-1α in aging muscle enhances a subset of young-like molecular patterns

PGC-1α is a transcriptional co-activator known as the master regulator of mitochondrial biogenesis. Its control of metabolism has been suggested to exert critical influence in the aging process. We have aged mice overexpressing PGC-1α in skeletal muscle to determine whether the transcriptional changes reflected a pattern of expression observed in younger muscle. Analyses of muscle proteins showed that Pax7 and several autophagy markers were increased. In general, the steady-state levels of several muscle proteins resembled that of muscle from young mice. Age-related mtDNA deletion levels were not increased by the PGC-1α-associated increase in mitochondrial biogenesis. Accordingly, age-related changes in the neuromuscular junction were minimized by PGC-1α overexpression. RNA-Seq showed that several genes overexpressed in the aged PGC-1α transgenic are expressed at higher levels in young when compared to aged skeletal muscle. As expected, there was increased expression of genes associated with energy metabolism but also of pathways associated with muscle integrity and regeneration. We also found that PGC-1α overexpression had a mild but significant effect on longevity. Taken together, overexpression of PGC-1α in aged muscle led to molecular changes that resemble the patterns observed in skeletal muscle from younger mice.

Nutrient deprivation in neuroblastoma cells alters 4-hydroxynonenal-induced stress response

4-hydroxy-2-nonenal (HNE), a toxic lipid peroxidation product, is associated with oxidative damage in cells and involved in various diseases including the initiation and progression of cancer. Cancer cells have a high, adaptable metabolism with a shift from oxidative phosphorylation to glycolysis and rely on high levels of glucose and glutamine as essential nutrients for cell growth. Here we investigated whether the toxic effects of HNE on the mitochondrial membrane potential (MMP) of cancer cells depends on their metabolic state by deprivation of glucose and/or glutamine. The addition of 16 μM HNE to N18TG2 neuroblastoma cells incubated in glucose medium led to a severe reduction of MMP, which was similar to the MMP of cells fed with both glucose and glutamine. In contrast, HNE addition to cells starved in glutamine medium increased their MMP slightly for a prolonged time period and this was accompanied by increased cellular survival. We found that ß-oxidation of HNE did not cause the increased MMP, since the aldehyde dehydrogenase was distinctly more active in cells with glucose medium. However, after blocking fatty acid ß-oxidation in cells starved in glutamine medium with etomoxir, which inhibits carnitine palmitoyltransferase 1, HNE addition induced a strong reduction of MMP similar to cells in glucose medium. Surprisingly, the effect of more toxic 4-oxo-2-nonenal was less pronounced. Our results suggest that in contrast to cells fed with glucose, glutamine-fed cancer cells are capable of ß-oxidizing fatty acids to maintain their MMP to combat the toxic effects of HNE.

Astrocytic Expression of GSTA4 Is Associated to Dopaminergic Neuroprotection in a Rat 6-OHDA Model of Parkinson's Disease

Idiopathic Parkinson’s disease (PD) is a complex disease caused by multiple, mainly unknown, genetic and environmental factors. The Ventral root avulsion 1 (Vra1) locus on rat chromosome 8 includes the Glutathione S-transferase alpha 4 (Gsta4) gene and has been identified in crosses between Dark Agouti (DA) and Piebald Virol Glaxo (PVG) rat strains as being associated to neurodegeneration after nerve and brain injury. The Gsta4 protein clears lipid peroxidation by-products, a process suggested to being implicated in PD. We therefore investigated whether PVG alleles in Vra1 are neuroprotective in a toxin-induced model of PD and if this effect is coupled to Gsta4. We performed unilateral 6-hydroxydopamine (6-OHDA) partial lesions in the striatum and compared the extent of neurodegeration in parental (DA) and congenic (DA.VRA1) rats. At 8 weeks after 6-OHDA lesion, DA.VRA1 rats displayed a higher density of remaining dopaminergic fibers in the dorsolateral striatum compared to DA rats (44% vs. 23%, p < 0.01), indicating that Vra1 alleles derived from the PVG strain protect dopaminergic neurons from 6-OHDA toxicity. Gsta4 gene expression levels in the striatum and midbrain were higher in DA.VRA1 congenic rats compared to DA at 2 days post-lesion (p < 0.05). The GSTA4 protein co-localized with astrocytic marker GFAP, but not with neuronal marker NeuN or microglial marker IBA1, suggesting astrocyte-specific expression. This is the first report on Vra1 protective effects on dopaminergic neurodegeneration and encourages further studies on Gsta4 in relation to PD susceptibility.

Different Mechanisms of Longevity in Long-Lived Mouse and Caenorhabditis elegans Mutants Revealed by Statistical Analysis of Mortality Rates

Mouse and Caenorhabditis elegans mutants with altered life spans are being used to investigate the aging process and how genes determine life span. The survival of a population can be modeled by the Gompertz function, which comprises two parameters. One of these parameters ("G") describes the rate at which mortality accelerates with age and is often described as the "rate of aging." The other parameter ("A") may correspond to the organism's baseline vulnerability to deleterious effects of disease and the environment. We show that, in mice, life-span-extending mutations systematically fail to affect the age-dependent acceleration of mortality (G), but instead affect only baseline vulnerability (A). This remains true even when comparing strains maintained under identical environmental conditions. In contrast, life-span-extending mutations in C. elegans were associated with decreases in G These observations on mortality rate kinetics suggest that the mechanisms of aging in mammals might fundamentally differ from those in nematodes.

Frailty and sarcopenia as the basis for the phenotypic manifestation of chronic diseases in older adults

Frailty is a functional status that precedes disability and is characterized by decreased functional reserve and increased vulnerability. In addition to disability, the frailty phenotype predicts falls, institutionalization, hospitalization and mortality. Frailty is the consequence of the interaction between the aging process and some chronic diseases and conditions that compromise functional systems and finally produce sarcopenia. Many of the clinical manifestations of frailty are explained by sarcopenia which is closely related to poor physical performance. Reduced regenerative capacity, malperfusion, oxidative stress, mitochondrial dysfunction and inflammation compose the sarcopenic skeletal muscle alterations associated to the frailty phenotype. Inflammation appears as a common determinant for chronic diseases, sarcopenia and frailty. The strategies to prevent the frailty phenotype include an adequate amount of physical activity and exercise as well as pharmacological interventions such as myostatin inhibitors and specific androgen receptor modulators. Cell response to stress pathways such as Nrf2, sirtuins and klotho could be considered as future therapeutic interventions for the management of frailty phenotype and aging-related chronic diseases.

The Genetic Architecture of Murine Glutathione Transferases

Glutathione S-transferase (GST) genes play a protective role against oxidative stress and may influence disease risk and drug pharmacokinetics. In this study, massive multiscalar trait profiling across a large population of mice derived from a cross between C57BL/6J (B6) and DBA2/J (D2)—the BXD family—was combined with linkage and bioinformatic analyses to characterize mechanisms controlling GST expression and to identify downstream consequences of this variation. Similar to humans, mice show a wide range in expression of GST family members. Variation in the expression of Gsta4, Gstt2, Gstz1, Gsto1, and Mgst3 is modulated by local expression QTLs (eQTLs) in several tissues. Higher expression of Gsto1 in brain and liver of BXD strains is strongly associated (P < 0.01) with inheritance of the B6 parental allele whereas higher expression of Gsta4 and Mgst3 in brain and liver, and Gstt2 and Gstz1 in brain is strongly associated with inheritance of the D2 parental allele. Allele-specific assays confirmed that expression of Gsto1, Gsta4, and Mgst3 are modulated by sequence variants within or near each gene locus. We exploited this endogenous variation to identify coexpression networks and downstream targets in mouse and human. Through a combined systems genetics approach, we provide new insight into the biological role of naturally occurring variants in GST genes.

Nrf2 Signaling and the Slowed Aging Phenotype: Evidence from Long-Lived Models

Studying long-lived animals provides novel insight into shared characteristics of aging and represents a unique model to elucidate approaches to prevent chronic disease. Oxidant stress underlies many chronic diseases and resistance to stress is a potential mechanism governing slowed aging. The transcription factor nuclear factor (erythroid-derived 2)-like 2 is the "master regulator" of cellular antioxidant defenses. Nrf2 is upregulated by some longevity promoting interventions and may play a role in regulating species longevity. However, Nrf2 expression and activity in long-lived models have not been well described. Here, we review evidence for altered Nrf2 signaling in a variety of slowed aging models that accomplish lifespan extension via pharmacological, nutritional, evolutionary, genetic, and presumably epigenetic means.

Sulforaphane protects the heart from doxorubicin-induced toxicity

Cardiotoxicity is one of the major side effects encountered during cancer chemotherapy with doxorubicin (DOX) and other anthracyclines. Previous studies have shown that oxidative stress caused by DOX is one of the primary mechanisms for its toxic effects on the heart. Since the redox-sensitive transcription factor, Nrf2, plays a major role in protecting cells from the toxic metabolites generated during oxidative stress, we examined the effects of the phytochemical sulforaphane (SFN), a potent Nrf2-activating agent, on DOX-induced cardiotoxicity. These studies were carried out both in vitro and in vivo using rat H9c2 cardiomyoblast cells and wild type 129/sv mice, and involved SFN pretreatment followed by SFN administration during DOX exposure. SFN treatment protected H9c2 cells from DOX cytotoxicity and also resulted in restored cardiac function and a significant reduction in DOX-induced cardiomyopathy and mortality in mice. Specificity of SFN induction of Nrf2 and protection of H9c2 cells was demonstrated in Nrf2 knockdown experiments. Cardiac accumulation of 4-hydroxynonenal (4-HNE) protein adducts, due to lipid peroxidation following DOX-induced oxidative stress, was significantly attenuated by SFN treatment. The respiratory function of cardiac mitochondria isolated from mice exposed to DOX alone was repressed, while SFN treatment with DOX significantly elevated mitochondrial respiratory complex activities. Co-administration of SFN reversed the DOX-associated reduction in nuclear Nrf2 binding activity and restored cardiac expression of Nrf2-regulated genes at both the RNA and protein levels. Together, our results demonstrate for the first time that the Nrf2 inducer, SFN, has the potential to provide protection against DOX-mediated cardiotoxicity.

Effects of Local Heart Irradiation in a Glutathione S-Transferase Alpha 4-Null Mouse Model

Glutathione S-transferase alpha 4 (GSTA4-4) is one of the enzymes responsible for the removal of 4-hydroxynonenal (4-HNE), an electrophilic product of lipid peroxidation in cellular membranes during oxidative stress. 4-HNE is a direct activator of nuclear factor (erythroid-derived 2)-like 2 (Nrf2), a transcription factor with many target genes encoding antioxidant and anti-electrophile enzymes. We have previously shown that Gsta4-null mice on a 129/Sv background exhibited increased activity of Nrf2 in the heart. Here we examined the sensitivity of this Gsta4-null mouse model towards cardiac function and structure loss due to local heart irradiation. Male Gsta4-null and wild-type mice were exposed to a single X-ray dose of 18 Gy to the heart. Six months after irradiation, immunohistochemical staining for respiratory complexes 2 and 5 indicated that radiation exposure had caused most pronounced alterations in mitochondrial morphology in Gsta4-null mice. On the other hand, wild-type mice showed a decline in cardiac function and an increase in plasma levels of troponin-I, while no such changes were observed in Gsta4-null mice. Radiation-induced Nrf2-target gene expression only in Gsta4-null mice. In conclusion, although loss of GSTA4-4 led to enhanced susceptibility of cardiac mitochondria to radiation-induced loss of morphology, cardiac function was preserved in Gsta4-null mice. We propose that this protection against cardiac function loss may occur, at least in part, by upregulation of the Nrf2 pathway.

Protection from oxidative and electrophilic stress in the Gsta4-null mouse heart

4-Hydroxynonenal (4-HNE) mediates many pathological effects of oxidative and electrophilic stress and signals to activate cytoprotective gene expression regulated by NF-E2-related factor 2 (Nrf2). By exhibiting very high levels of 4-HNE-conjugating activity, the murine glutathione transferase alpha 4 (GSTA4-4) helps regulate cellular 4-HNE levels. To examine the role of 4-HNE in vivo, we disrupted the murine Gsta4 gene. Gsta4-null mice exhibited no cardiac phenotype under normal conditions and no difference in cardiac 4-HNE level as compared to wild-type mice. We hypothesized that the Nrf2 pathway might contribute an important compensatory mechanism to remove excess cardiac 4-HNE in Gsta4-null mice. Cardiac nuclear extracts from Gsta4-null mice exhibited significantly higher Nrf2 binding to antioxidant response elements. We also observed responses in critical Nrf2 target gene products: elevated Sod2, Cat, and Akr1b7 mRNA levels and significant increases in both cardiac antioxidant and anti-electrophile enzyme activities. Gsta4-null mice were less sensitive and maintained normal cardiac function following chronic doxorubicin treatment, known to increase cardiac 4-HNE levels. Hence, in the absence of GSTA4-4 to modulate both physiological and pathological 4-HNE levels, the adaptive Nrf2 pathway may be primed to contribute to a preconditioned cardiac phenotype in the Gsta4-null mouse.

Glutathionylated products of lipid peroxidation: A novel mechanism of adipocyte to macrophage signaling

Obesity-associated insulin resistance has long been linked to both increased adipocyte oxidative stress as well as the presence of inflammatory changes in adipose tissue, including the infiltration and activation of tissue-resident macrophages. In order to investigate the connections between obesity-associated oxidative stress in adipocytes and increased inflammation in adipose tissue associated with the development of insulin resistance, our laboratory recently demonstrated that adipocytes form glutathionylated products of oxidative stress including glutathionyl-4-hydroxy-2-nonenal (GS-HNE) and glutathionyl-1,4-dihydroxynonene (GS-DHN). The abundance of both GS-HNE and GS-DHN were increased in the visceral adipose tissue of ob/ob mice and diet-induced obese, insulin-resistant mice. Further, these products of lipid peroxidation were shown to induce inflammatory changes in macrophages. Finally, in a mouse model, overproduction of GS-HNE was associated with increased fasting glucose levels and moderately impaired glucose tolerance. Together, these findings suggest a novel mechanism by which obesity-induced oxidative stress in adipocytes may lead to activation of tissue-resident macrophages. As adipose tissue inflammation has been shown to play an important role in the development of insulin resistance, further study of this pathway may lead to potential interventions to attenuate the metabolic consequences of obesity.

Glutathionylated lipid aldehydes are products of adipocyte oxidative stress and activators of macrophage inflammation

Obesity-induced insulin resistance has been linked to adipose tissue lipid aldehyde production and protein carbonylation. Trans-4-hydroxy-2-nonenal (4-HNE) is the most abundant lipid aldehyde in murine adipose tissue and is metabolized by glutathione S-transferase A4 (GSTA4), producing glutathionyl-HNE (GS-HNE) and its metabolite glutathionyl-1,4-dihydroxynonene (GS-DHN). The objective of this study was to evaluate adipocyte production of GS-HNE and GS-DHN and their effect on macrophage inflammation. Compared with lean controls, GS-HNE and GS-DHN were more abundant in visceral adipose tissue of ob/ob mice and diet-induced obese, insulin-resistant mice. High glucose and oxidative stress induced production of GS-HNE and GS-DHN by 3T3-L1 adipocytes in a GSTA4-dependent manner, and both glutathionylated metabolites induced secretion of tumor necrosis factor-α from RAW 264.7 and primary peritoneal macrophages. Targeted microarray analysis revealed GS-HNE and GS-DHN induced expression of inflammatory genes, including C3, C4b, c-Fos, igtb2, Nfkb1, and Nos2. Transgenic overexpression of GSTA4 in mouse adipose tissue led to increased production of GS-HNE associated with higher fasting glucose levels and moderately impaired glucose tolerance. These results indicated adipocyte oxidative stress results in GSTA4-dependent production of proinflammatory glutathione metabolites, GS-HNE and GS-DHN, which may represent a novel mechanism by which adipocyte dysfunction results in tissue inflammation and insulin resistance.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

Cell death and diseases related to oxidative stress: 4-hydroxynonenal (HNE) in the balance

During the last three decades, 4-hydroxy-2-nonenal (HNE), a major α,β-unsaturated aldehyde product of n-6 fatty acid oxidation, has been shown to be involved in a great number of pathologies such as metabolic diseases, neurodegenerative diseases and cancers. These multiple pathologies can be explained by the fact that HNE is a potent modulator of numerous cell processes such as oxidative stress signaling, cell proliferation, transformation or cell death. The main objective of this review is to focus on the different aspects of HNE-induced cell death, with a particular emphasis on apoptosis. HNE is a special apoptotic inducer because of its abilities to form protein adducts and to propagate oxidative stress. It can stimulate intrinsic and extrinsic apoptotic pathways and interact with typical actors such as tumor protein 53, JNK, Fas or mitochondrial regulators. At the same time, due to its oxidant status, it can also induce some cellular defense mechanisms against oxidative stress, thus being involved in its own detoxification. These processes in turn limit the apoptotic potential of HNE. These dualities can imbalance cell fate, either toward cell death or toward survival, depending on the cell type, the metabolic state and the ability to detoxify.

4-Hydroxynonenal induces G2/M phase cell cycle arrest by activation of the ataxia telangiectasia mutated and Rad3-related protein (ATR)/checkpoint kinase 1 (Chk1) signaling pathway

4-Hydroxynonenal (HNE) has been widely implicated in the mechanisms of oxidant-induced toxicity, but the detrimental effects of HNE associated with DNA damage or cell cycle arrest have not been thoroughly studied. Here we demonstrate for the first time that HNE caused G2/M cell cycle arrest of hepatocellular carcinoma HepG2 (p53 wild type) and Hep3B (p53 null) cells that was accompanied with decreased expression of CDK1 and cyclin B1 and activation of p21 in a p53-independent manner. HNE treatment suppressed the Cdc25C level, which led to inactivation of CDK1. HNE-induced phosphorylation of Cdc25C at Ser-216 resulted in its translocation from nucleus to cytoplasm, thereby facilitating its degradation via the ubiquitin-mediated proteasomal pathway. This phosphorylation of Cdc25C was regulated by activation of the ataxia telangiectasia and Rad3-related protein (ATR)/checkpoint kinase 1 (Chk1) pathway. The role of HNE in the DNA double strand break was strongly suggested by a remarkable increase in comet tail formation and H2A.X phosphorylation in HNE-treated cells in vitro. This was supported by increased in vivo phosphorylation of H2A.X in mGsta4 null mice that have impaired HNE metabolism and increased HNE levels in tissues. HNE-mediated ATR/Chk1 signaling was inhibited by ATR kinase inhibitor (caffeine). Additionally, most of the signaling effects of HNE on cell cycle arrest were attenuated in hGSTA4 transfected cells, thereby indicating the involvement of HNE in these events. A novel role of GSTA4-4 in the maintenance of genomic integrity is also suggested.

Aging decreases antioxidant effects and increases lipid peroxidation in the Apolipoprotein E deficient mouse

In this study, to study the effect of aging and Apolipoprotein E (ApoE) deficiency on antioxidant ability in mice, we examined whether lipid peroxidation is promoted by aging in ApoE deficient (ApoE(-/-)) mice, which have a shorter lifespan than normal mice. The levels of thiobarbituric acid-reactive substances (TBARS), a biomarker of lipid peroxidation, were measured in plasma and liver in ApoE(-/-) mice aged 12 weeks (young) and 52 weeks (early stage of senescence). TBARS in plasma and liver were significantly increased by aging. Next, we examined the reasons why lipid peroxidation was promoted by aging, based on measurement of protein and mRNA levels for antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase) in liver in ApoE(-/-) mice aged 12 and 52 weeks. The levels of superoxide dismutase 1 and 2 in liver were significantly decreased by aging. The mRNA level of catalase was also significantly decreased and the mRNA levels of superoxide dismutase 1, superoxide dismutase 2 and glutathione peroxidase 1 all showed a tendency to decrease with age. These results suggest that lipid peroxidation is caused by reduction of antioxidant activity with aging and that this promotes senescence and shortens lifespan in ApoE(-/-) mice.

Inhibition of nuclear factor-erythroid 2-related factor (Nrf2) by caveolin-1 promotes stress-induced premature senescence

Reactive oxygen species can induce premature senescence. Caveolin-1 promotes oxidative stress–induced activation of the p53/p21Waf1/Cip1 pathway and development of premature senescence by acting as an endogenous inhibitor of the transcription factor Nrf2.

Reactive oxygen species (ROS) can induce premature cellular senescence, which is believed to contribute to aging and age-related diseases. The nuclear erythroid 2 p45–related factor-2 (Nrf2) is a transcription factor that mediates cytoprotective responses against stress. We demonstrate that caveolin-1 is a direct binding partner of Nrf2, as shown by the binding of the scaffolding domain of caveolin-1 (amino acids 82–101) to the caveolin-binding domain of Nrf2 (amino acids 281–289). Biochemical studies show that Nrf2 is concentrated into caveolar membranes in human and mouse fibroblasts, where it colocalizes with caveolin-1, under resting conditions. After oxidative stress, caveolin-1 limits the movement of Nrf2 from caveolar membranes to the nucleus. In contrast, Nrf2 is constitutively localized to the nucleus before and after oxidative stress in caveolin-1–null mouse embryonic fibroblasts (MEFs), which do not express caveolin-1. Functional studies demonstrate that caveolin-1 acts as an endogenous inhibitor of Nrf2, as shown by the enhanced up-regulation of NQO1, an Nrf2 target gene, in caveolin-1–null MEFs and the activation or inhibition of a luciferase construct carrying an antioxidant responsive element (ARE) after down-regulation of caveolin-1 by small interfering RNA or overexpression of caveolin-1, respectively. Expression of a mutant form of Nrf2 that cannot bind to caveolin-1 (Φ→A-Nrf2) hyperactivates ARE and inhibits oxidative stress–induced activation of the p53/p21^Waf1/Cip1 pathway and induction of premature senescence in fibroblasts. Finally, we show that overexpression of caveolin-1 in colon cancer cells inhibits oxidant-induced activation of Nrf2-dependent signaling, promotes premature senescence, and inhibits their transformed phenotype. Thus, by inhibiting Nrf2-mediated signaling, caveolin-1 links free radicals to the activation of the p53/senescence pathway.

Aging decreases antioxidant effects and increases lipid peroxidation in the Apolipoprotein E deficient mouse

In this study, to study the effect of aging and Apolipoprotein E (ApoE) deficiency on antioxidant ability in mice, we examined whether lipid peroxidation is promoted by aging in ApoE deficient (ApoE^−/−) mice, which have a shorter lifespan than normal mice. The levels of thiobarbituric acid-reactive substances (TBARS), a biomarker of lipid peroxidation, were measured in plasma and liver in ApoE^−/− mice aged 12 weeks (young) and 52 weeks (early stage of senescence). TBARS in plasma and liver were significantly increased by aging. Next, we examined the reasons why lipid peroxidation was promoted by aging, based on measurement of protein and mRNA levels for antioxidant enzymes (superoxide dismutase, catalase, and glutathione peroxidase) in liver in ApoE^−/− mice aged 12 and 52 weeks. The levels of superoxide dismutase 1 and 2 in liver were significantly decreased by aging. The mRNA level of catalase was also significantly decreased and the mRNA levels of superoxide dismutase 1, superoxide dismutase 2 and glutathione peroxidase 1 all showed a tendency to decrease with age. These results suggest that lipid peroxidation is caused by reduction of antioxidant activity with aging and that this promotes senescence and shortens lifespan in ApoE^−/− mice.

Molecular effects of baicalein in Hct116 cells and Caenorhabditis elegans : activation of the Nrf2 signaling pathway and prolongation of lifespan

Baicalein is a major compound of extracts derived from Scutellaria baicalensis Lamiaceae, which are used as food supplements. Baicalein possesses a high radical scavenging activity and decreases intracellular reactive oxygen species in Hct116 human colon carcinoma cells and in Caenorhabditis elegans . It activates Nrf2, a key transcription factor that binds to the antioxidant responsive element (ARE): Baicalein causes a nuclear accumulation of Nrf2, increases ARE-dependent luciferase activity, and enhances the expression of heme oxygenase-1 in Hct116 cells. Additionally, accumulation of the Nrf2 homologue SKN-1 in nuclei of intestinal cells of C. elegans was observed. Lifespan analysis revealed that baicalein extends the mean, median, and maximum lifespans of the nematode by 45, 57 and 24%, respectively. Because SKN-1 activation is associated with prolongation of lifespan, the results suggest that baicalein increases the lifespan of C. elegans by activation of the Nrf2/SKN-1 signaling pathway.

GSTT1 is upregulated by oxidative stress through p38-MK2 signaling pathway in human granulosa cells: possible association with mitochondrial activity

We previously reported that GSTT1 was upregulated in human granulosa cells during aging and that activation and localization of p38 MAPK was changed in parallel. Although oxidative stress is responsible for these changes, the age-associated expression of GSTT1 regulated by MAPKs and the role of GSTT1 in aged granulosa cells remain unclear. Therefore, we examined the relationship between the expression of GSTT1 and MAPK signaling pathways using human granulosa-like KGN cells stimulated with H₂O₂ in the presence or absence of various MAPK inhibitors. Interestingly, H₂O₂-induced GSTT1 was only inhibited by a p38 inhibitor. An inhibitor of MK2, a downstream regulator of p38, also diminished H₂O₂-induced GSTT1 upregulation. Notably, both p38 and MK2 were significantly inactivated in cells carrying an shRNA construct of GSTT1 (ΔGSTT1 cells), suggesting that the p38-MK2 pathway is essential for age-associated upregulation of GSTT1. The relevance of GSTT1 in mitochondrial activity was then determined. ΔGSTT1 cells displayed enhanced polarization of mitochondrial membrane potential without increasing the apoptosis, suggesting that the age-associated upregulation of GSTT1 may influence the mitochondrial activity of granulosa cells.

Collectively, it appears that the age-associated expression of GSTT1 is induced through the p38 signaling pathway and GSTT1 influences homeostatic activities in granulosa cells.

Stress resistance in the naked mole-rat: the bare essentials - a mini-review

BACKGROUND

Studies comparing similar-sized species with disparate longevity may elucidate novel mechanisms that abrogate aging and prolong good health. We focus on the longest living rodent, the naked mole-rat. This mouse-sized mammal lives ~8 times longer than do mice and, despite high levels of oxidative damage evident at a young age, it is not only very resistant to spontaneous neoplasia but also shows minimal decline in age-associated physiological traits.

OBJECTIVES

We assess the current status of stress resistance and longevity, focusing in particular on the molecular and cellular responses to cytotoxins and other stressors between the short-lived laboratory mouse and the naked mole-rat.

RESULTS

Like other experimental animal models of lifespan extension, naked mole-rat fibroblasts are extremely tolerant of a broad spectrum of cytotoxins including heat, heavy metals, DNA-damaging agents and xenobiotics, showing LD(50) values between 2- and 20-fold greater than those of fibroblasts of shorter-lived mice. Our new data reveal that naked mole-rat fibroblasts stop proliferating even at low doses of toxin whereas those mouse fibroblasts that survive treatment rapidly re-enter the cell cycle and may proliferate with DNA damage. Naked mole-rat fibroblasts also show significantly higher constitutive levels of both p53 and Nrf2 protein levels and activity, and this increases even further in response to toxins.

CONCLUSION

Enhanced cell signaling via p53 and Nrf2 protects cells against proliferating with damage, augments clearance of damaged proteins and organelles and facilitates the maintenance of both genomic and protein integrity. These pathways collectively regulate a myriad of mechanisms which may contribute to the attenuated aging profile and sustained healthspan of the naked mole-rat. Understanding how these are regulated may be also integral to sustaining positive human healthspan well into old age and may elucidate novel therapeutics for delaying the onset and progression of physiological declines that characterize the aging process.

The expression and function of vascular endothelial growth factor in retinal pigment epithelial (RPE) cells is regulated by 4-hydroxynonenal (HNE) and glutathione S-transferaseA4-4

It is well established that 4-hydroxynonenal (HNE) plays a major role in oxidative stress-induced signaling and the toxicity of oxidants. Surprisingly our recent studies also demonstrate that low levels of HNE generated during oxidative stress promote cell survival mechanisms and proliferation. Since the expression and secretion of VEGF is known to be affected by Oxidative stress, during present studies, we have examined dose dependent effect of HNE on VEGF expression and secretion in a model of retinal pigment epithelial (RPE) cells in culture. Results of these studies showed that while inclusion of 0.1 μM HNE in the medium caused increased secretion of VEGF, its secretion and expression was significantly suppressed in the presence of >5 μM HNE in the media. These concentration dependent hormetic effects of HNE on VEGF secretion could be blocked by the over expression of GSTA4-4 indicating that these effects were specifically attributed to HNE and regulated by GSTA4-4. VEGF secreted into the media showed angiogenic properties as indicated by increased migration and tube formation of HUVEC in matrigel when grown in media from RPE cells treated with 1 μM HNE. The corresponding media from GSTA4-4 over expressing RPE cells had no effect on migration and tube formation of HUVEC in matrigel. These results are consistent with earlier studies showing that at low concentrations, HNE promotes proliferative mechanisms and suggest that HNE induces VEGF secretion from RPE cells that acts in a paracrine fashion to induce angiogenic signaling mechanism in the endothelial cells. These findings may suggest a role of HNE and GSTA4-4 in oxidative stress induced proliferative retinopathies.

Down-regulation of glutatione S-transferase α 4 (hGSTA4) in the muscle of thermally injured patients is indicative of susceptibility to bacterial infection

Patients with severe burns are highly susceptible to bacterial infection. While immunosuppression facilitates infection, the contribution of soft tissues to infection beyond providing a portal for bacterial entry remains unclear. We showed previously that glutathione S-transferase S1 (gstS1), an enzyme with conjugating activity against the lipid peroxidation byproduct 4-hydroxynonenal (4HNE), is important for resistance against wound infection in Drosophila muscle. The importance of the mammalian functional counterpart of GstS1 in the context of wounds and infection has not been investigated. Here we demonstrate that the presence of a burn wound dramatically affects expression of both human (hGSTA4) and mouse (mGsta4) 4HNE scavengers. hGSTA4 is down-regulated significantly within 1 wk of thermal burn injury in the muscle and fat tissues of patients from the large-scale collaborative Inflammation and the Host Response to Injury multicentered study. Similarly, mGsta4, the murine GST with the highest catalytic efficiency for 4HNE, is down-regulated to approximately half of normal levels in mouse muscle immediately postburn. Consequently, 4HNE protein adducts are increased 4- to 5-fold in mouse muscle postburn. Using an open wound infection model, we show that deletion of mGsta4 renders mice more susceptible to infection with the prevalent wound pathogen Pseudomonas aeruginosa, while muscle hGSTA4 expression negatively correlates with burn wound infection episodes per patient. Our data suggest that hGSTA4 down-regulation and the concomitant increase in 4HNE adducts in human muscle are indicative of susceptibility to infection in individuals with severely thermal injuries.

Relationship of electrophilic stress to aging

This review begins with the premise that an organism's life span is determined by the balance between two countervailing forces: (i) the sum of destabilizing effects and (ii) the sum of protective longevity-assurance processes. Against this backdrop, the role of electrophiles is discussed, both as destabilizing factors and as signals that induce protective responses. Because most biological macromolecules contain nucleophilic centers, electrophiles are particularly reactive and toxic in a biological context. The majority of cellular electrophiles are generated from polyunsaturated fatty acids by a peroxidation chain reaction that is readily triggered by oxygen-centered radicals, but propagates without further input of reactive oxygen species (ROS). Thus, the formation of lipid-derived electrophiles such as 4-hydroxynon-2-enal (4-HNE) is proposed to be relatively insensitive to the level of initiating ROS, but to depend mainly on the availability of peroxidation-susceptible fatty acids. This is consistent with numerous observations that life span is inversely correlated to membrane peroxidizability, and with the hypothesis that 4-HNE may constitute the mechanistic link between high susceptibility of membrane lipids to peroxidation and shortened life span. Experimental interventions that directly alter membrane composition (and thus their peroxidizability) or modulate 4-HNE levels have the expected effects on life span, establishing that the connection is not only correlative but causal. Specific molecular mechanisms are considered, by which 4-HNE could (i) destabilize biological systems via nontargeted reactions with cellular macromolecules and (ii) modulate signaling pathways that control longevity-assurance mechanisms.

Taking a "good" look at free radicals in the aging process

The mitochondrial free radical theory of aging (MFRTA) proposes that aging is caused by damage to macromolecules by mitochondrial reactive oxygen species (ROS). This is based on the observed association of the rate of aging and the aged phenotype with the generation of ROS and oxidative damage. However, recent findings, in particular in Caenorhabditis elegans but also in rodents, suggest that ROS generation is not the primary or initial cause of aging. Here, we propose that ROS are tightly associated with aging because they play a role in mediating a stress response to age-dependent damage. This could generate the observed correlation between aging and ROS without implying that ROS damage is the earliest trigger or main cause of aging.

Molecular and structural antioxidant defenses against oxidative stress in animals

In this review, it is our aim 1) to describe the high diversity in molecular and structural antioxidant defenses against oxidative stress in animals, 2) to extend the traditional concept of antioxidant to other structural and functional factors affecting the "whole" organism, 3) to incorporate, when supportable by evidence, mechanisms into models of life-history trade-offs and maternal/epigenetic inheritance, 4) to highlight the importance of studying the biochemical integration of redox systems, and 5) to discuss the link between maximum life span and antioxidant defenses. The traditional concept of antioxidant defenses emphasizes the importance of the chemical nature of molecules with antioxidant properties. Research in the past 20 years shows that animals have also evolved a high diversity in structural defenses that should be incorporated in research on antioxidant responses to reactive species. Although there is a high diversity in antioxidant defenses, many of them are evolutionary conserved across animal taxa. In particular, enzymatic defenses and heat shock response mediated by proteins show a low degree of variation. Importantly, activation of an antioxidant response may be also energetically and nutrient demanding. So knowledge of antioxidant mechanisms could allow us to identify and to quantify any underlying costs, which can help explain life-history trade-offs. Moreover, the study of inheritance mechanisms of antioxidant mechanisms has clear potential to evaluate the contribution of epigenetic mechanisms to stress response phenotype variation.

Knockout and transgenic mice in glutathione transferase research

Glutathione transferases (GSTs) are a multigene family of ubiquitously expressed, polymorphic enzymes responsible for the metabolism of a wide range of both endogenous and exogenous substrates, play a central role in the adaptive response to chemical and oxidative stress, and are subject to regulation by a range of structurally unrelated chemicals. In this review, we present a current summary of knockout mouse models in the GST field, discussing some of the issues pertaining to orthologous proteins between mice and humans, the potential confounding issues related to genetic background, and also cover new transgenic models in the increasingly important area of humanization.

Interactions of glutathione transferases with 4-hydroxynonenal

Electrophilic products of lipid peroxidation are important contributors to the progression of several pathological states. The prototypical α,β-unsaturated aldehyde, 4-hydroxynonenal (HNE), triggers cellular events associated with oxidative stress, which can be curtailed by the glutathione-dependent elimination of HNE. The glutathione transferases (GSTs) are a major determinate of the intracellular concentration of HNE and can influence susceptibility to toxic effects, particularly when HNE and GST levels are altered in disease states. In this article, we provide a brief summary of the cellular effects of HNE, followed by a review of its GST-catalyzed detoxification, with an emphasis on the structural attributes that play an important role in the interactions with alpha-class GSTs. Some of the key determining characteristics that impart high alkenal activity reside in the unique C-terminal interactions of the GSTA4-4 enzyme. Studies encompassing both kinetic and structural analyses of related isoforms will be highlighted, with additional attention to stereochemical aspects that demonstrate the capacity of GSTA4-4 to detoxify both enantiomers of the biologically relevant racemic mixture while generating a select set of diastereomeric products with subsequent implications. A summary of the literature that examines the interplay between GSTs and HNE in model systems relevant to oxidative stress will also be discussed to demonstrate the magnitude of importance of GSTs in the overall detoxification scheme.

Impaired redox signaling and antioxidant gene expression in endothelial cells in diabetes: a role for mitochondria and the nuclear factor-E2-related factor 2-Kelch-like ECH-associated protein 1 defense pathway

Type 2 diabetes is an age-related disease associated with vascular pathologies, including severe blindness, renal failure, atherosclerosis, and stroke. Reactive oxygen species (ROS), especially mitochondrial ROS, play a key role in regulating the cellular redox status, and an overproduction of ROS may in part underlie the pathogenesis of diabetes and other age-related diseases. Cells have evolved endogenous defense mechanisms against sustained oxidative stress such as the redox-sensitive transcription factor nuclear factor E2-related factor 2 (Nrf2), which regulates antioxidant response element (ARE/electrophile response element)-mediated expression of detoxifying and antioxidant enzymes and the cystine/glutamate transporter involved in glutathione biosynthesis. We hypothesize that diminished Nrf2/ARE activity contributes to increased oxidative stress and mitochondrial dysfunction in the vasculature leading to endothelial dysfunction, insulin resistance, and abnormal angiogenesis observed in diabetes. Sustained hyperglycemia further exacerbates redox dysregulation, thereby providing a positive feedback loop for severe diabetic complications. This review focuses on the role that Nrf2/ARE-linked gene expression plays in regulating endothelial redox homeostasis in health and type 2 diabetes, highlighting recent evidence that Nrf2 may provide a therapeutic target for countering oxidative stress associated with vascular disease and aging.

Can rodent longevity studies be both short and powerful?

Many rodent experiments have assessed effects of diets, drugs, genes, and other factors on life span. A challenge with such experiments is their long duration, typically over 3.5 years given rodent life spans, thus requiring significant time costs until answers are obtained. We collected longevity data from 15 rodent studies and artificially truncated them at 2 years to assess the extent to which one will obtain the same answer regarding mortality effects. When truncated, the point estimates were not significantly different in any study, implying that in most cases, truncated studies yield similar estimates. The median ratio of variances of coefficients for truncated to full-length studies was 3.4, implying that truncated studies with roughly 3.4 times as many rodents will often have equivalent or greater power. Cost calculations suggest that shorter studies will be more expensive but perhaps not so much to not be worth the reduced time.

Genetic deletion of Nrf2 promotes immortalization and decreases life span of murine embryonic fibroblasts

Nuclear factor E2-related factor-2 (Nrf2) transcription factor is one of the main regulators of intracellular redox balance and a sensor of oxidative and electrophilic stress. Low Nrf2 activity is usually associated with carcinogenesis, but Nrf2 is also considered as an oncogene because it increases survival of transformed cells. Because intracellular redox balance alterations are involved in both senescence and tumorigenesis, we investigated the impact of Nrf2 genetic deletion on cellular immortalization and life span of murine embryonic fibroblasts. We report that Nrf2 genetic deletion promotes immortalization due to an early loss of p53-dependent gene expression. However, compared with control cells, immortalized Nrf2-/- murine embryonic fibroblasts exhibited decreased growth, lower cyclin E levels, and impaired expression of NQO1 and cytochrome b₅ reductase. Moreover, SirT1 was also significantly reduced in immortalized Nrf2-/- murine embryonic fibroblasts, and these cells exhibited shorter life span. Our results underscore the dual role of Nrf2 in protection against carcinogenesis and in the delay of cellular aging.

Mechanisms of 4-hydroxy-2-nonenal induced pro- and anti-apoptotic signaling

In recent years, 4-hydroxy-2-nonenal (4-HNE) has emerged as an important second messenger in cell cycle signaling. Here, we demonstrate that 4-HNE induces signaling for apoptosis via both the Fas-mediated extrinsic and the p53-mediated intrinsic pathways in HepG2 cells. 4-HNE induces a Fas-mediated DISC independent apoptosis pathway by activating ASK1, JNK, and caspase-3. Parallel treatment of 4-HNE to HepG2 cells also induces apoptosis by the p53 pathway through activation of Bax, p21, JNK, and caspase-3. Exposure of HepG2 cells to 4-HNE leads to the activation of both Fas and Daxx, promotes the export of Daxx from the nucleus to cytoplasm, and facilitates Fas-Daxx binding. Depletion of Daxx by siRNA results in the potentiation of apoptosis, indicating that Fas-Daxx binding in fact is inhibitory to Fas-mediated apoptosis in cells. 4-HNE-induced translocation of Daxx is also accompanied by the activation and nuclear accumulation of HSF1 and up-regulation of heat shock protein Hsp70. All these effects of 4-HNE in cells can be attenuated by ectopic expression of hGSTA4-4, the isozyme of glutathione S-transferase with high activity for 4-HNE. Through immunoprecipitation and liquid chromatography-tandem mass spectrometry, we have demonstrated the covalent binding of 4-HNE to Daxx. We also demonstrate that 4-HNE modification induces phosphorylation of Daxx at Ser668 and Ser671 to facilitate its cytoplasmic export. These results indicate that while 4-HNE exhibits toxicity through several mechanisms, in parallel it evokes signaling for defense mechanisms to self-regulate its toxicity and can simultaneously affect multiple signaling pathways through its interactions with membrane receptors and transcription factors/repressors.