The redox stress hypothesis of aging

Deletion of p66Shc in mice increases the frequency of size-change mutations in the lacZ transgene

Upon oxidative challenge the genome accumulates adducts and breaks that activate the DNA damage response to repair, arrest, or eliminate the damaged cell. Thus, reactive oxygen species (ROS) generated by endogenous oxygen metabolism are thought to affect mutation frequency. However, few studies determined the mutation frequency when oxidative stress is reduced. To test whether in vivo spontaneous mutation frequency is altered in mice with reduced oxidative stress and cell death rate, we crossed p66Shc knockout (p66KO) mice, characterized by reduced intracellular concentration of ROS and by impaired apoptosis, with a transgenic line harboring multiple copies of the lacZ mutation reporter gene as part of a plasmid that can be recovered from organs into Escherichia coli to measure mutation rate. Liver and small intestine from 2- to 24-month-old, lacZ (p66Shc+/+) and lacZp66KO mice, were investigated revealing no difference in overall mutation frequency but a significant increase in the frequency of size-change mutations in the intestine of lacZp66KO mice. This difference was further increased upon irradiation of mice with X-ray. In addition, we found that knocking down cyclophilin D, a gene that facilitates mitochondrial apoptosis acting downstream of p66Shc, increased the size-change mutation frequency in small intestine. Size-change mutations also accumulated in death-resistant embryonic fibroblasts from lacZp66KO mice treated with H2 O2 . These results indicate that p66Shc plays a role in the accumulation of DNA rearrangements and suggest that p66Shc functions to clear damaged cells rather than affect DNA metabolism.

Differential regulation of proteasome functionality in reproductive vs. somatic tissues of Drosophila during aging or oxidative stress

Proteasome is central to proteostasis maintenance, as it degrades both normal and damaged proteins. Herein, we undertook a detailed analysis of proteasome regulation in the in vivo setting of Drosophila melanogaster. We report that a major hallmark of somatic tissues of aging flies is the gradual accumulation of ubiquitinated and carbonylated proteins; these effects correlated with a ~50% reduction of proteasome expression and catalytic activities. In contrast, gonads of aging flies were relatively free of proteome oxidative damage and maintained substantial proteasome expression levels and highly active proteasomes. Moreover, gonads of young flies were found to possess more abundant and more active proteasomes than somatic tissues. Exposure of flies to oxidants induced higher proteasome activities specifically in the gonads, which were, independently of age, more resistant than soma to oxidative challenge and, as analyses in reporter transgenic flies showed, retained functional antioxidant responses. Finally, inducible Nrf2 activation in transgenic flies promoted youthful proteasome expression levels in the aged soma, suggesting that age-dependent Nrf2 dysfunction is causative of decreasing somatic proteasome expression during aging. The higher investment in proteostasis maintenance in the gonads plausibly facilitates proteome stability across generations; it also provides evidence in support of the trade-off theories of aging.

Coming of age: molecular drivers of aging and therapeutic opportunities

Aging is like the weather: everyone talks about it, but no one seems to do anything about it. We believe this may soon change, as an improved understanding of the molecular and genetic pathways underlying aging suggests it is possible to therapeutically target the aging process and increase health span. This Review series focuses on fundamental cellular mechanisms of aging and their relationship to human disease. These pathways include telomere dysfunction in cellular senescence and induction of the senescence-associated secretory phenotype (SASP) in systemic aging, sirtuin family regulation of metabolism and aging-associated diseases, mitochondrial metabolism in aging, the mechanistic target of rapamycin (mTOR) signaling pathway and the use of mTOR inhibitors to increase longevity, the progressive decline of the immune system with age, and aging-associated changes to pancreatic islet β cells that may contribute to diabetes. Together, these articles explore pathways affecting aging and possible interventional targets to slow or delay the onset of age-related pathologies.

The role of mitochondria in aging

Over the last decade, accumulating evidence has suggested a causative link between mitochondrial dysfunction and major phenotypes associated with aging. Somatic mitochondrial DNA (mtDNA) mutations and respiratory chain dysfunction accompany normal aging, but the first direct experimental evidence that increased mtDNA mutation levels contribute to progeroid phenotypes came from the mtDNA mutator mouse. Recent evidence suggests that increases in aging-associated mtDNA mutations are not caused by damage accumulation, but rather are due to clonal expansion of mtDNA replication errors that occur during development. Here we discuss the caveats of the traditional mitochondrial free radical theory of aging and highlight other possible mechanisms, including insulin/IGF-1 signaling (IIS) and the target of rapamycin pathways, that underlie the central role of mitochondria in the aging process.

Formaldehyde metabolism and formaldehyde-induced stimulation of lactate production and glutathione export in cultured neurons

Formaldehyde is endogenously produced in the human body and brain levels of this compound are elevated in neurodegenerative conditions. Although the toxic potential of an excess of formaldehyde has been studied, little is known on the molecular mechanisms underlying its neurotoxicity as well as on the ability of neurons to metabolize formaldehyde. To address these topics, we have used cerebellar granule neuron cultures as model system. These cultures express mRNAs of various enzymes that are involved in formaldehyde metabolism and were remarkably resistant toward acute formaldehyde toxicity. Cerebellar granule neurons metabolized formaldehyde with a rate of around 200 nmol/(h × mg) which was accompanied by significant increases in the cellular and extracellular concentrations of formate. In addition, formaldehyde application significantly increased glucose consumption, almost doubled the rate of lactate release from viable neurons and strongly accelerated the export of the antioxidant glutathione. The latter process was completely prevented by inhibition of the known glutathione exporter multidrug resistance protein 1. These data indicate that cerebellar granule neurons are capable of metabolizing formaldehyde and that the neuronal glycolysis and glutathione export are severely affected by the presence of formaldehyde.

Longwave UV light induces the aging-associated progerin

Premature aging in Hutchinson-Gilford progeria syndrome (HGPS) is caused by a mutation of the LMNA gene that activates a cryptic splice site. This results in expression of a truncated form of Lamin A, called progerin. Accumulation of progerin in the nuclei of HGPS cells impairs nuclear functions and causes abnormal nuclear morphology. Progerin accumulation has not only been described in HGPS, but also during normal intrinsic aging. We hypothesized that accumulation of progerin with abnormal nuclear shapes may also be accelerated by UV and with that contribute to photoaging of the skin. We exposed neonatal or aged cultured fibroblasts to single or repeated doses of longwave or shortwave UV (UVA or UVB) and found that UVA, but not UVB, induces progerin expression and HGPS-like abnormal nuclear shapes in all cells, but more in aged cells. The induction of progerin is mediated by UVA-induced oxidative damage and subsequent alternative splicing of the LMNA transcript, as progerin induction was suppressed by the singlet oxygen quencher sodium azide, and as mRNA expression of LMNA was not induced by UVA. These data suggest a previously unreported pathway of photoaging and support the concept that photoaging is at least in part a process of damage-accelerated intrinsic aging.

Redox-dependent control of FOXO/DAF-16 by transportin-1

Forkhead box O (FOXO; DAF-16 in worms) transcription factors, which are of vital importance in cell-cycle control, stress resistance, tumor suppression, and organismal lifespan, are largely regulated through nucleo-cytoplasmic shuttling. Insulin signaling keeps FOXO/DAF-16 cytoplasmic, and hence transcriptionally inactive. Conversely, as in loss of insulin signaling, reactive oxygen species (ROS) can activate FOXO/DAF-16 through nuclear accumulation. How ROS regulate the nuclear translocation of FOXO/DAF-16 is largely unknown. Cysteine oxidation can stabilize protein-protein interactions through the formation of disulfide-bridges when cells encounter ROS. Using a proteome-wide screen that identifies ROS-induced mixed disulfide-dependent complexes, we discovered several interaction partners of FOXO4, one of which is the nuclear import receptor transportin-1. We show that disulfide formation with transportin-1 is required for nuclear localization and the activation of FOXO4/DAF-16 induced by ROS, but not by the loss of insulin signaling. This molecular mechanism for nuclear shuttling is conserved in C. elegans and directly connects redox signaling to the longevity protein FOXO/DAF-16.

Loss of integration is associated with reduced resistance to oxidative stress

One cellular mechanism thought to be particularly important as a constraint on lifespan and life-history strategies is oxidative stress. Susceptibility to oxidative stress is influenced by a number of antioxidant defences, whose effectiveness depends on the synergistic and competitive interactions among them (biochemical integration). It is generally assumed that exposure to oxidative stress is detrimental, but it is also possible that low level oxidative stress has a positive effect on integration, and therefore carries some benefits. Using three experimental groups of zebra finches (control, mild and high flight activity), we tested whether exercise-induced oxidative stress altered the integration of the pro-oxidant/antioxidant system by manipulating levels of flight activity, known to generate oxidative stress in birds. We show for the first time that a short-term high level of physical activity leads to a reduction in integration among components of the blood antioxidant defences, associated with a reduced resistance to oxidative stress. We found no evidence of improved integration in the antioxidant defences at low levels of oxidative stress exposure, suggesting that improved integration is not the route whereby any benefits of low level stress exposure occur. These findings point to a reduction in biochemical integration as a potential mechanism explaining a reduced resistance to oxidative stress induced by short-term stressors.

Oxygen: how do we stand it?

The electronic structure of ground state oxygen, which is essential for the life of all aerobic organisms, makes it potentially dangerous for those organisms. Atmospheric oxygen contains two unpaired electrons with parallel spin states, which predisposes it to reduction by a univalent pathway. As a consequence, normal aerobic metabolism generates dangerous reactive intermediates of the reduction of O2. These include superoxide radical (O2*-), hydrogen peroxide (H2O2), and hydroxyl radical (HO*). These reactive oxygen species and others that they can engender can damage all cellular macromolecules and unless opposed by cellular defenses, would make aerobic life impossible. Such defenses include superoxide dismutases, catalases, and peroxidases, enzymes that decrease the concentration of the reactive oxygen species that are their substrates, and others that repair or recycle oxidatively damaged macromolecules. Any factor that stimulates reactive oxygen species production or suppresses the antioxidant systems would inevitably cause cell damage. The role of such oxidative damage in various diseases is well documented. In vivo detection of O2- and other reactive oxygen species is however hampered by the lack of easy, specific, and sensitive analytical methods. Potential artifacts and limitations of the most common detection methods currently in use are briefly discussed.

Recent applications of engineered animal antioxidant deficiency models in human nutrition and chronic disease

Dietary antioxidants are essential nutrients that inhibit the oxidation of biologically important molecules and suppress the toxicity of reactive oxygen or nitrogen species. When the total antioxidant capacity is insufficient to quench these reactive species, oxidative damage occurs and contributes to the onset and progression of chronic diseases, such as neurodegenerative diseases, cardiovascular diseases, and cancer. However, epidemiological studies that examine the relationship between antioxidants and disease outcome can only identify correlative associations. Additionally, many antioxidants also have prooxidant effects. Thus, clinically relevant animal models of antioxidant function are essential for improving our understanding of the role of antioxidants in the pathogenesis of complex diseases as well as evaluating the therapeutic potential and risks of their supplementation. Recent progress in gene knockout mice and virus-based gene expression has potentiated these areas of study. Here, we review the current genetically modified animal models of dietary antioxidant function and their clinical relevance in chronic diseases. This review focuses on the 3 major antioxidants in the human body: vitamin C, vitamin E, and uric acid. We examine genetic models of vitamin C synthesis (guinea pig, Osteogenic Disorder Shionogi rat, Gulo(-/-) and SMP30(-/-) mouse mutants) and transport (Slc23a1(-/-) and Slc23a2(-/-) mouse mutants), vitamin E transport (Ttpa(-/-) mouse mutant), and uric acid synthesis (Uox(-/-) mouse mutant). The application of these models to current research goals is also discussed.

Aging, age-related diseases and peroxisomes

Human aging is considered as one of the biggest risk factors for the development of multiple diseases such as cancer, type-2 diabetes, and neurodegeneration. In addition, it is widely accepted that these age-related diseases result from a combination of various genetic, lifestyle, and environmental factors. As biological aging is a complex and multifactorial phenomenon, the molecular mechanisms underlying disease initiation and progression are not yet fully understood. However, a significant amount of evidence supports the theory that oxidative stress may act as a primary etiologic factor. Indeed, many signaling components like kinases, phosphatases, and transcription factors are exquisitely sensitive to the cellular redox status, and a chronic or severe disturbance in redox homeostasis can promote cell proliferation or trigger cell death. Now, almost 50 years after their discovery, there is a wealth of evidence that peroxisomes can function as a subcellular source, sink, or target of reactive oxygen and nitrogen molecules. Yet, the possibility that these organelles may act as a signaling platform for a variety of age-related processes has so far been underestimated and largely neglected. In this review, we will critically discuss the possible role of peroxisomes in the human aging process in light of the available data.

Linkages between the life-history evolution of tropical and temperate birds and the resistance of cultured skin fibroblasts to oxidative and non-oxidative chemical injury

A fundamental challenge facing physiological ecologists is to understand how variation in life history at the whole-organism level might be linked to cellular function. Thus, because tropical birds have higher annual survival and lower rates of metabolism, we hypothesized that cells from tropical species would have greater cellular resistance to chemical injury than cells from temperate species. We cultured dermal fibroblasts from 26 tropical and 26 temperate species of birds and examined cellular resistance to cadmium, H(2)O(2), paraquat, thapsigargin, tunicamycium, methane methylsulfonate (MMS) and UV light. Using ANCOVA, we found that the values for the dose that killed 50% of cells (LD(50)) from tropical birds were significantly higher for H(2)O(2) and MMS. When we tested for significance using a generalized least squares approach accounting for phylogenetic relationships among species to model LD(50), we found that cells from tropical birds had greater tolerance for Cd, H(2)O(2), paraquat, tunicamycin and MMS than cells from temperate birds. In contrast, tropical birds showed either lower or no difference in tolerance to thapsigargin and UV light in comparison with temperate birds. These findings are consistent with the idea that natural selection has uniquely fashioned cells of long-lived tropical bird species to be more resistant to forms of oxidative and non-oxidative stress than cells from shorter-lived temperate species.

High efficiency versus maximal performance--the cause of oxidative stress in eukaryotes: a hypothesis

Degenerative diseases are in part based on elevated production of ROS (reactive oxygen species) in mitochondria, mainly during stress and excessive work under stress (strenuous exercise). The production of ROS increases with increasing mitochondrial membrane potential (ΔΨ(m)). A mechanism is described which is suggested to keep ΔΨ(m) at low values under normal conditions thus preventing ROS formation, but is switched off under stress and excessive work to maximize the rate of ATP synthesis, accompanied by decreased efficiency. Low ΔΨ(m) and low ROS production are suggested to occur by inhibition of respiration at high [ATP]/[ADP] ratios. The nucleotides interact with phosphorylated cytochrome c oxidase (COX), representing the step with the highest flux-control coefficient of mitochondrial respiration. At stress and excessive work neural signals are suggested to dephosphorylate the enzyme and abolish the control of COX activity (respiration) by the [ATP]/[ADP] ratio with consequent increase of ΔΨ(m) and ROS production. The control of COX by the [ATP]/[ADP] ratio, in addition, is proposed to increase the efficiency of ATP production via a third proton pumping pathway, identified in eukaryotic but not in prokaryotic COX. We conclude that 'oxidative stress' occurs when the control of COX activity by the [ATP]/[ADP] ratio is switched off via neural signals.

Early determinants of the ageing trajectory

Over the past 250 years, human life expectancy has increased dramatically and continues to do so in most countries worldwide. Genetic factors account for about one third of variation in life expectancy so that most inter-individual variation in lifespan is explained by stochastic and environmental factors. The ageing process is plastic and is driven by the accumulation of molecular damage causing the changes in cell and tissue function which characterise the ageing phenotype. Early life exposures mark the developing embryo, foetus and child with potentially profound implications for the individual's ageing trajectory. Maternal factors including age, smoking, socioeconomic status, infections, nutritional status and season of birth influence offspring life expectancy and the development of age-related diseases. Although the mechanistic processes responsible are poorly understood, many of these factors appear to affect foetal growth directly or via effects on placental development. Those born relatively small i.e. which did not achieve their genetic potential in utero, appear to be at greatest disadvantage especially if they become overweight or obese in childhood. Early life events and exposures which enhance ageing are likely to contribute to molecular damage and/or reduce the repair of such damage. Such molecular damage may produce immediate defects in cellular or tissue function that are retained into later life. In addition, there is growing evidence that early life exposures produce aberrant patterns of epigenetic marks that are sustained across the life-course and result in down-regulation of cell defence mechanisms.

Oxidative stress and metal carcinogenesis

Occupational and environmental exposures to metals are closely associated with an increased risk of various cancers. Although carcinogenesis caused by metals has been intensively investigated, the exact mechanisms of action are still unclear. Accumulating evidence indicates that reactive oxygen species (ROS) generated by metals play important roles in the etiology of degenerative and chronic diseases. This review covers recent advances in (1) metal-induced generation of ROS and the related mechanisms; (2) the relationship between metal-mediated ROS generation and carcinogenesis; and (3) the signaling proteins involved in metal-induced carcinogenesis, especially intracellular reduction-oxidation-sensitive molecules.

Early life experience primes resistance to oxidative stress

The extent to which early stress exposure is detrimental to Darwinian fitness may depend on its severity, with mild stress exposure actually having a stimulatory and, possibly, beneficial effect through a hormetic response to the stressful stimulus. We need to understand such hormetic processes to determine how the early environment can help shape a phenotype adapted to the conditions the organism is most likely to experience in its adult environment. Using the zebra finch (Taeniopygia guttata), we tested the hypothesis that individuals exposed to mild heat stress earlier in life will suffer less oxidative stress when faced with high heat stress in adulthood than will individuals either not pre-exposed to heat stress or exposed to high heat stress earlier in life. Our findings demonstrate that early life exposure to mild heat stress primes the system to better withstand oxidative stress when encountering heat stress as an adult. These findings point to a potential mechanism linking early life experiences to future Darwinian fitness.

ROS in aging Caenorhabditis elegans: damage or signaling?

Many insights into the mechanisms and signaling pathways underlying aging have resulted from research on the nematode Caenorhabditis elegans. In this paper, we discuss the recent findings that emerged using this model organism concerning the role of reactive oxygen species (ROS) in the aging process. The accrual of oxidative stress and damage has been the predominant mechanistic explanation for the process of aging for many years, but reviewing the recent studies in C. elegans calls this theory into question. Thus, it becomes more and more evident that ROS are not merely toxic byproducts of the oxidative metabolism. Rather it seems more likely that tightly controlled concentrations of ROS and fluctuations in redox potential are important mediators of signaling processes. We therefore discuss some theories that explain how redox signaling may be involved in aging and provide some examples of ROS functions and signaling in C. elegans metabolism. To understand the role of ROS and the redox status in physiology, stress response, development, and aging, there is a rising need for accurate and reversible in vivo detection. Therefore, we comment on some methods of ROS and redox detection with emphasis on the implementation of genetically encoded biosensors in C. elegans.

Interaction between sexual steroids and immune response in affecting oxidative status of birds

One hypothesis explaining the honesty of secondary sexual traits regulated by testosterone (T) is that T can impair the balance between pro-oxidant compounds and antioxidant defences, favouring a status of oxidative stress that only good quality individuals can sustain (oxidative handicap hypothesis). In the present study, we evaluated for the first time the effects of sexual steroids, T and its metabolites 5-α-dihydrotestosterone (DHT) and estradiol (E2) on oxidative damage and plasma non-enzymatic antioxidant capacity, while birds are faced by an oxidative challenge induced by an immune stimulation with sheep red blood cells. We used male and female diamond doves Geopelia cuneata, a species that shows an orange-red periorbital ring, whose size and color are strongly affected by androgens, but not by estrogens. Immunization increased oxidative damage in all groups, regardless of hormone treatment. It also decreased anti-oxidant capacity in all groups, except for testosterone treated birds. The ratio of oxidative damage over anti-oxidant capacity (oxidative stress) was increased in both immunological challenged controls and E2 birds, while challenged birds treated with androgens did not differ from non-challenged birds. The response of males and females to our treatments never differed. Our results undermine the idea that T can induce honest signalling through a pro-oxidant activity.

Consequences of oxidative stress in age-related macular degeneration

The retina resides in an environment that is primed for the generation of reactive oxygen species (ROS) and resultant oxidative damage. The retina is one of the highest oxygen-consuming tissues in the human body. The highest oxygen levels are found in the choroid, but this falls dramatically across the outermost retina, creating a large gradient of oxygen towards the retina and inner segments of the photoreceptors which contain high levels of polyunsaturated fatty acids. This micro-environment together with abundant photosensitizers, visible light exposure and a high energy demand supports a highly oxidative milieu. However, oxidative damage is normally minimized by the presence of a range of antioxidant and efficient repair systems. Unfortunately, as we age oxidative damage increases, antioxidant capacity decreases and the efficiency of reparative systems become impaired. The result is retinal dysfunction and cell loss leading to visual impairment. It appears that these age-related oxidative changes are a hallmark of early age-related macular degeneration (AMD) which, in combination with hereditary susceptibility and other retinal modifiers, can progress to the pathology and visual morbidity associated with advanced AMD. This review reassesses the consequences of oxidative stress in AMD and strategies for preventing or reversing oxidative damage in retinal tissues.

Oxidative stress in growth hormone transgenic coho salmon with compressed lifespan--a model for addressing aging

Growth hormone (GH) transgenic fish have dramatically enhanced growth rates, increased oxygen demands and reactive oxygen species production. GH-transgenic coho salmon provide an opportunity to address effects of increased metabolism on physiological aging. The objective of this study was to compare oxidative stress in wild-type (WT) and GH-transgenic (T) coho salmon (Oncorhynchus kisutch) of different ages (1 and 2 years). Antioxidant enzyme activity, protein carbonyls (PC) and glutathione (GSH, GSSG) were measured. PC correlated to growth rates in individual fish. T fish exhibited lower antioxidant enzyme activities and GSH levels compared to the WT, while levels of PC and GSSG were higher. Age affects were observed in both WT and T fish; enzyme activities and GSH decreased while PC and GSSG increased. Our results support the metabolic rate theory of aging. This study aims to be a platform for continued studies of the theories of aging using fish as model organisms.

The free-radical theory of ageing--older, wiser and still alive: modelling positional effects of the primary targets of ROS reveals new support

The continuing viability of the free-radical theory of ageing has been questioned following apparently incompatible recent results. We show by modelling positional effects of the generation and primary targets of reactive oxygen species that many of the apparently negative results are likely to be misleading. We conclude that there is instead a need to look more closely at the mechanisms by which free radicals contribute to age-related dysfunction in living systems. There also needs to be deeper understanding of the dynamics of accumulation and removal of the various kinds of molecular damage, in particular mtDNA mutations. Finally, the expectation that free-radical damage on its own might cause ageing needs to be relinquished in favour of the recognition that the free-radical theory is just one of the multiple mechanisms driving the ageing process.

Oxidative stress, tumor microenvironment, and metabolic reprogramming: a diabolic liaison

Conversely to normal cells, where deregulated oxidative stress drives the activation of death pathways, malignant cells exploit oxidative milieu for its advantage. Cancer cells are located in a very complex microenvironment together with stromal components that participate to enhance oxidative stress to promote tumor progression. Indeed, convincing experimental and clinical evidence underline the key role of oxidative stress in several tumor aspects thus affecting several characteristics of cancer cells. Oxidants influence the DNA mutational potential, intracellular signaling pathways controlling cell proliferation and survival and cell motility and invasiveness as well as control the reactivity of stromal components that is fundamental for cancer development and dissemination, inflammation, tissue repair, and de novo angiogenesis. This paper is focused on the role of oxidant species in the acquisition of two mandatory features for aggressive neoplastic cells, recently defined by Hanahan and Weinberg as new “hallmarks of cancer”: tumor microenvironment and metabolic reprogramming of cancer cells.

Oxidatively generated complex DNA damage: tandem and clustered lesions

There is an increasing interest for oxidatively generated complex lesions that are potentially more detrimental than single oxidized nucleobases. In this survey, the recently available information on the formation and processing of several classes of complex DNA damage formed upon one radical hit including mostly hydroxyl radical and one-electron oxidants is critically reviewed. The modifications include tandem base lesions, DNA-protein cross-links and intrastrand (purine 5',8-cyclonucleosides, adjacent base cross-links) and interstrand cross-links. Information is also provided on clustered lesions produced essentially by exposure of cells to ionizing radiation and high energetic heavy ions through the involvement of multiple radical events that induce several lesions DNA in a close spatial vicinity. These consist mainly of double strand breaks (DSBs) and non-DSB clustered lesions that are referred as to oxidatively generated clustered DNA lesions (OCDLs).

Towards Alzheimer's root cause: ECSIT as an integrating hub between oxidative stress, inflammation and mitochondrial dysfunction. Hypothetical role of the adapter protein ECSIT in familial and sporadic Alzheimer's disease pathogenesis

Here we postulate that the adapter protein evolutionarily conserved signalling intermediate in Toll pathway (ECSIT) might act as a molecular sensor in the pathogenesis of Alzheimer's disease (AD). Based on the analysis of our AD-associated protein interaction network, ECSIT emerges as an integrating signalling hub that ascertains cell homeostasis by the specific activation of protective molecular mechanisms in response to signals of amyloid-beta or oxidative damage. This converges into a complex cascade of patho-physiological processes. A failure to repair would generate severe mitochondrial damage and ultimately activate pro-apoptotic mechanisms, promoting synaptic dysfunction and neuronal death. Further support for our hypothesis is provided by increasing evidence of mitochondrial dysfunction in the disease etiology. Our model integrates seemingly controversial hypotheses for familial and sporadic forms of AD and envisions ECSIT as a biomarker to guide future therapies to halt or prevent AD.

Mouse Models of Oxidative Stress Indicate a Role for Modulating Healthy Aging

Aging is a complex process that affects every major system at the molecular, cellular and organ levels. Although the exact cause of aging is unknown, there is significant evidence that oxidative stress plays a major role in the aging process. The basis of the oxidative stress hypothesis is that aging occurs as a result of an imbalance between oxidants and antioxidants, which leads to the accrual of damaged proteins, lipids and DNA macromolecules with age. Age-dependent increases in protein oxidation and aggregates, lipofuscin, and DNA mutations contribute to age-related pathologies. Many transgenic/knockout mouse models over expressing or deficient in key antioxidant enzymes have been generated to examine the effect of oxidative stress on aging and age-related diseases. Based on currently reported lifespan studies using mice with altered antioxidant defense, there is little evidence that oxidative stress plays a role in determining lifespan. However, mice deficient in antioxidant enzymes are often more susceptible to age-related disease while mice overexpressing antioxidant enzymes often have an increase in the amount of time spent without disease, i.e., healthspan. Thus, by understanding the mechanisms that affect healthy aging, we may discover potential therapeutic targets to extend human healthspan.