Age-related alterations in the activation of heat shock transcription factor 1 in rat hepatocytes

Aberrant regulation and modification of heat shock factor 1 in senescent human diploid fibroblasts

Induction of the heat shock response (HSR), determined by hsp70-luciferase reporter and HSP70 protein expression, is attenuated as a function of age of the IMR-90 human diploid fibroblasts. To better understand the underlying mechanism, we evaluated changes in the regulation and function of the HSF1 transcription factor. We show that the activation of HSF1 both in vivo and in vitro was decreased as a function of age, and this was attributable to a change in the regulation of HSF1 as the abundance of HSF1 protein and mRNA was unaffected. HSF1 was primarily cytosolic in young cells maintained at 37 degrees C, and heat shock promoted its quantitative nuclear translocation and trimerization. In old cells, some HSF1 was nuclear sequestered at 37 degrees C, and heat shock failed to promote the quantitative trimerization of HSF1. These changes in HSF1 could be reproduced by treating young cells with H2O2 to stunt them into premature senescence. Flow cytometry measurement of peroxide content showed higher levels in old cells and H2O2-induced premature senescent cells as compared to young cells. Experiments using isoelectric focusing and Western blot showed age-dependent changes in the mobility of HSF1 in a pattern consistent with its S-glutathiolation and S-nitrosylation; these changes could be mimicked by treating young cells with H2O2. Our results demonstrated dynamic age-dependent changes in the regulation but not the amount of HSF1. These changes are likely mediated by oxidative events that promote reversible and irreversible modification of HSF1 including S-glutathiolation and S-nitrosylation.

Neurodegeneration and ageing in the HAART era

Cognitive impairment and neurodegeneration still occur despite highly active antiretroviral therapy (HAART). While there are many potential reasons for this, there is increasing evidence that such impairment occurs in the absence of a clear cause. Furthermore, there are data that some neurodegenerative diseases, especially Alzheimer's or an Alzheimer-like illness, are becoming more common in the context of HAART-treated human immunodeficiency virus (HIV) disease. This review will critically examine the evidence underpinning these observations. Potential mechanisms will be discussed with particular emphasis on the effect of ageing and how it overlaps with the effects of HIV disease itself thereby leading to neurodegeneration. The nature of this overlap will then be explored for its potential role in the facilitated expression and development of neurodegenerative diseases. Lastly, there will be a brief discussion of interventions to minimize such neurodegeneration including optimization of HAART for brain entry.

Autophagy following heat stress: the role of aging and protein nitration

Stress can originate from a variety of sources (e.g., physical, chemical, etc.,) and cause protein denaturation, DNA damage and possibly death. In an effort to prevent such deleterious consequences, most organisms possess one or more ways to counteract or even prevent the harmful effect(s) from a given stressor. Such compensation by an organism is known as a stress response; this involves inhibition of housekeeping genes and subsequent activation of genes associated with the stress response. One of the most widely studied groups of stress response genes is a family of molecular chaperones known as heat shock proteins (HSPs). Work from our laboratory agrees with many other studies showing an age-related decline in stress-induced synthesis of HSPs. A decline in the availability and/or function of HSPs with age can lead to accumulation of damaged proteins, which in turn damages cells. Recently, our laboratory found a significant increase in mitochondrial damage as well as evidence of increased autophagy in rat hepatocytes following heat stress. These results, along with findings of increased protein nitration with age, suggest a major role for reactive nitrogen species (RNS) in both the decline in HSP induction and increased hepatocyte pathology observed in old rats following heat stress.

Heat stress-induced heat shock protein 70 expression is dependent on ERK activation in zebrafish (Danio rerio) cells

Heat shock response is a common event that occurs in many species. Despite its evolutionary conservation, comparative studies of heat shock response have been largely unexplored. In mammals, heat shock response decreases with age through unclear mechanisms. Understanding how the age-related decline in heat shock response occurs may provide information to understanding the biology of aging. We have previously shown that heat shock response similarly declines with age in zebrafish. However, signaling pathways that regulate the heat shock response in zebrafish are unknown. In mammals there is evidence that mitogen-activated protein kinases (MAPKs) of the ERK family alter Hsp70 transcription, serving as a potential regulator of the heat shock response. We explored if heat stress-induced Hsp70 expression is altered by activation of ERK in the zebrafish Pac2 fibroblast cell line as occurs in mammalian cells. Heat stress induced both Hsp70 mRNA expression and phosphorylation of both ERK1 and ERK2 (ERK1/2) in Pac2 cells. ERK inhibitors PD98059 and U0126 blocked both heat stress-induced and plated-derived growth factor (PDGF)-induced ERK1/2 phosphorylation, and also diminished heat-induced Hsp70 expression. Pac2 cell viability was not affected by either the ERK inhibitors or heat stress. These results demonstrate that induction of Hsp70 in response to heat stress is dependent on ERK activation in Pac2 cells. This suggests that the heat shock response in zebrafish utilizes a similar signaling pathway to that of mammals and that zebrafish are a good model for comparative studies of heat shock response.

Aging results in increased autophagy of mitochondria and protein nitration in rat hepatocytes following heat stress

The natural breakdown of cells, tissues, and organ systems is a significant consequence of aging and is at least partially caused by a decreased ability to tolerate environmental stressors. Based on quantitative ultrastructural analysis using transmission electron microscopy and computer imaging, we show significant differences in hepatocyte morphology between young and old rats during a 48-hr recovery period following a 2-day heat stress protocol. Mitochondrial injury was greater overall in old compared with young rats. Autophagy was observed in both young and old rats, with autophagy greater overall in old compared with young hepatocytes. Lipid peroxidation and protein nitration were evaluated by localization and quantification of 4-hydroxy-2-nonenal (4-HNE)-modified protein adducts and 3-nitrotyrosine (3-NT) levels, respectively. Levels of 3-NT but not 4-HNE-protein adducts were significantly elevated in hepatocytes of old rats in comparison with young at 90 min after heat stress, suggesting a major role for reactive nitrogen species in the pathology observed at this time point. These results show a differential response of hepatocyte mitochondria to heat stress with aging, as well as greater levels of both autophagic and nitrative damage in old vs young hepatocytes. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.

Hormesis in aging

Hormesis in aging is represented by mild stress-induced stimulation of protective mechanisms in cells and organisms resulting in biologically beneficial effects. Single or multiple exposure to low doses of otherwise harmful agents, such as irradiation, food limitation, heat stress, hypergravity, reactive oxygen species and other free radicals have a variety of anti-aging and longevity-extending hormetic effects. Detailed molecular mechanisms that bring about the hormetic effects are being increasingly understood, and comprise a cascade of stress response and other pathways of maintenance and repair. Although the extent of immediate hormetic effects after exposure to a particular stress may only be moderate, the chain of events following initial hormesis leads to biologically amplified effects that are much larger, synergistic and pleiotropic. A consequence of hormetic amplification is an increase in the homeodynamic space of a living system in terms of increased defence capacity and reduced load of damaged macromolecules. Hormetic strengthening of the homeodynamic space provides wider margins for metabolic fluctuation, stress tolerance, adaptation and survival. Hormesis thus counter-balances the progressive shrinkage of the homeodynamic space, which is the ultimate cause of aging, diseases and death. Healthy aging may be achieved by hormesis through mild and periodic, but not severe or chronic, physical and mental challenges, and by the use of nutritional hormesis incorporating mild stress-inducing molecules called hormetins. The established scientific foundations of hormesis are ready to pave the way for new and effective approaches in aging research and intervention.

Protein stress and stress proteins: implications in aging and disease

Environmental stress induces damage that activates an adaptive response in any organism. The cellular stress response is based on the induction of cytoprotective proteins,the so called stress or heat shock proteins. The stress response as well as stress proteins are ubiquitous,highly conserved mechanism, and genes, respectively, already present in prokaryotes. Chaperones protect the proteome against conformational damage, promoting the function of protein networks. Protein damage takes place during aging and in several degenerative diseases, and presents a threat to overload the cellular defense mechanisms. The preservation of a robust stress response and protein disposal is indispensable for health and longevity. This review summarizes the present knowledge of protein damage, turnover, and the stress response in aging and degenerative diseases.

Molecular crime and cellular punishment: active detoxification of misfolded and aggregated proteins in the cell by the chaperone and protease networks

Labile or mutation-sensitised proteins may spontaneously convert into aggregation-prone conformations that may be toxic and infectious. This hazardous behavior, which can be described as a form of "molecular criminality", can be actively counteracted in the cell by a network of molecular chaperone and proteases. Similar to law enforcement agents, molecular chaperones and proteases can specifically identify, apprehend, unfold and thus neutralize "criminal" protein conformers, allowing them to subsequently refold into harmless functional proteins. Irreversibly damaged polypeptides that have lost the ability to natively refold are preferentially degraded by highly controlled ATP-consuming proteases. Damaged proteins that escape proteasomal degradation can also be "incarcerated" into dense amyloids, "evicted" from the cell, or internally "exiled" to the lysosome to be hydrolysed and recycled. Thus, remarkable parallels exist between molecular and human forms of criminality, as well as in the cellular and social responses to various forms of crime. Yet, differences also exist: whereas programmed death is the preferred solution chosen by aged and aggregation-stressed cells, collective suicide is seldom chosen by lawless societies. Significantly, there is no cellular equivalent for the role of familial care and of education in general, which is so crucial to the proper shaping of functional persons in the society. Unlike in the cell, humanism introduces a bias against radical solutions such as capital punishment, favouring crime prevention, reeducation and social reinsertion of criminals.

17Beta-estradiol modulates age-dependent binding of 40 kDa nuclear protein to androgen receptor promoter in mouse cerebral cortex

Androgen influences the function of central and peripheral nervous system and plays a crucial role in maintaining reproductive behaviors and neuroendocrine regulation. Such action is mediated by interaction of androgen receptor (AR) promoter with nuclear proteins, which are involved in transcriptional regulation of androgen responsive genes. We have analyzed the binding of AR core promoter to nuclear proteins from the cerebral cortex of adult and old mice of both sexes by electrophoretic mobility shift assay (EMSA) and characterized the bound protein by Southwestern blotting. EMSA showed that the binding of nuclear proteins declined in the cerebral cortex of intact old mice as compared to adult. Following gonadectomy, the binding was reduced in old male and adult female but increased in old female. In contrast, estradiol supplementation increased the binding in old male and adult female but decreased in old female. Southwestern blotting analysis revealed that a 40 kDa nuclear protein bound to the promoter and the binding pattern was similar to that observed in EMSA. Further characterization of this protein may help to explore the intricate mechanism that underlies the transcriptional regulation of androgen responsive genes during aging.

Chaperones and proteases: cellular fold-controlling factors of proteins in neurodegenerative diseases and aging

The formation of toxic protein aggregates is a common denominator to many neurodegenerative diseases and aging. Accumulation of toxic, possibly infectious protein aggregates induces a cascade of events, such as excessive inflammation, the production of reactive oxygen species, apoptosis and neuronal loss. A network of highly conserved molecular chaperones and of chaperone-related proteases controls the fold-quality of proteins in the cell. Most molecular chaperones can passively prevent protein aggregation by binding misfolding intermediates. Some molecular chaperones and chaperone-related proteases, such as the proteasome, can also hydrolyse ATP to forcefully convert stable harmful protein aggregates into harmless natively refoldable, or protease-degradable, polypeptides. Molecular chaperones and chaperone-related proteases thus control the delicate balance between natively folded functional proteins and aggregation-prone misfolded proteins, which may form during the lifetime and lead to cell death. Abundant data now point at the molecular chaperones and the proteases as major clearance mechanisms to remove toxic protein aggregates from cells, delaying the onset and the outcome of protein-misfolding diseases. Therapeutic approaches include treatments and drugs that can specifically induce and sustain a strong chaperone and protease activity in cells and tissues prone to toxic protein aggregations.

Heat shock proteins and the heat shock response during hyperthermia and its modulation by altered physiological conditions

The fundamental functions of heat shock proteins (HSPs) are molecular chaperoning and cellular repair. There is little literature on the association between the numerous functions of HSPs and systemic integrative responses, particularly those controlled by the central nervous system. This chapter focuses on the role played by members of the HSP70 superfamily, universally recognized as cytoprotectants during heat stress, within the physiological context of hyperthermia and with its superimposition on situations of chronic stress. In the nucleus tractus solitarius, HSP70 levels enhance the sensitivity of sympathetic and parasympathetic arms of the autonomic nervous system to attenuate heat stroke-induced cerebral ischemia and hypotension. Chronic stressors that alter the heat shock response may affect the physiological profile during hyperthermic conditions. Upon aging, significantly lower HSP70 production is noted in the ventral paraventricular and lateral magnocellular nuclei. Likewise, results from cultured cells suggest that the age-related decline in HSP70 expression is constitutive and is due to decreased binding of the heat shock factor 1 (HSF-1) to the heat shock element (HSE) and diminished HSP70 transcription. These changes may be associated with decreased thermotolerance upon aging, although HSP70 production in response to other stressors is not affected. Heat acclimation (AC), in contrast, increases tissue reserves of HSP70 and accelerates the heat shock response. AC protects epithelial integrity, vascular reactivity and interactions with cellular signaling networks, enhancing protection and delaying thermal injury. The link between HSP70 and the immune system is discussed with respect to exercise. Exercise enhances the immune response via production of HSP72 in central and peripheral structures. At least in part, the effects of HSP72 in the brain are mediated via eHSP72-circulating HSPs providing a "danger signal" to activate the immune response. In summary, HSPs are primarily cytoprotective components, the physiological situations described in this chapter infer their pivotal role in central control of integrative systems.

Aging cellular networks: Chaperones as major participants

We increasingly rely on the network approach to understand the complexity of cellular functions. Chaperones (heat shock proteins) are key "networkers", which sequester and repair damaged proteins. In order to link the network approach and chaperones with the aging process, we first summarize the properties of aging networks suggesting a "weak link theory of aging". This theory suggests that age-related random damage primarily affects the overwhelming majority of the low affinity, transient interactions (weak links) in cellular networks leading to increased noise, destabilization and diversity. These processes may be further amplified by age-specific network remodelling and by the sequestration of weakly linked cellular proteins to protein aggregates of aging cells. Chaperones are weakly linked hubs (i.e., network elements with a large number of connections) and inter-modular bridge elements of protein-protein interaction, signalling and mitochondrial networks. As aging proceeds, the increased overload of damaged proteins is an especially important element contributing to cellular disintegration and destabilization. Additionally, chaperone overload may contribute to the increase of "noise" in aging cells, which leads to an increased stochastic resonance resulting in a deficient discrimination between signals and noise. Chaperone- and other multi-target therapies, which restore the missing weak links in aging cellular networks, may emerge as important anti-aging interventions.

Adaptive responses of mouse skeletal muscle to contractile activity: The effect of age

This study has characterised the time course of two major transcriptional adaptive responses to exercise (changes in antioxidant defence enzyme activity and heat shock protein (HSP) content) in muscles of adult and old male mice following isometric contractions and has examined the mechanisms involved in the age-related reduction in transcription factor activation. Muscles of B6XSJL mice were subjected to isometric contractions and analysed for antioxidant defence enzyme activities, heat shock protein content and transcription factor DNA binding activity. Data demonstrated a significant increase in superoxide dismutase (SOD) and catalase activity and HSP content of muscles of adult mice following contractile activity which was associated with increased activation of the transcription factors, nuclear factor-kappaB (NF-kappaB), activator protein-1 (AP-1) and heat shock factor (HSF) following contractions. Significant increases in SOD and catalase activity and heat shock cognate (HSC70) content were seen in quiescent muscles of old mice. The increase in antioxidant defence enzyme activity following contractile activity seen in muscles of adult mice was not seen in muscles of old mice and this was associated with a failure to fully activate NF-kappaB and AP-1 following contractions. In contrast, although the production of HSPs was also reduced in muscles of old mice following contractile activity compared with muscles of adult mice following contractions, this was not due to a gross reduction in the DNA binding activity of HSF.

Protein homeostasis and molecular chaperones in aging

Molecular chaperones are ubiquitous, highly conserved proteins responsible for the maintenance of protein folding homeostasis in cells. Environmental stress causes proteotoxic damage, which triggers chaperone induction and the subsequent reparation of cellular damage by chaperones, including disposing irreparable protein ensembles. We summarize the current view of protein damage, turnover, the stress response and chaperone function in aging, and review novel data showing that accumulation of misfolded proteins outcompete and overload the limited resources of the protein folding, maintenance and turnover system, compromising general protein homeastasis and cellular function. Possible involvement of chaperones and proteolysis in immunosenescence is highlighted. Defects in zinc metabolism are also addressed in relation to aging and changes in chaperone levels.

Role of hormesis in life extension by caloric restriction

Caloric restriction (CR) markedly extends the life of rats, mice and several other species, and it also modulates age-associated physiological deterioration and delays the occurrence and/or slows progression of age-associated diseases. The level of CR that retards the aging processes is a low-intensity stressor, which enhances the ability of rats and mice of all ages to cope with intense stressors. CR thus exhibits a hormetic action in these species, and therefore it is hypothesized that hormesis plays a role in the life-extending and anti-aging actions of CR. Both the findings in support of this hypothesis and those opposing it are critically considered. However, it is likely that hormesis is not the only process contributing to CR-induced life extension. It is proposed that two general processes are involved in CR-induced life extension. One is the reduced endogenous generation of damaging agents, such as reactive oxygen species. The second is hormesis, which enhances processes that protect against the action of damaging agents and also promotes processes that repair the damage once it occurs.

Cytotoxicity and cell signalling induced by continuous mild hyperthermia in freshly isolated mouse hepatocytes

An increasing body of data has been demonstrating that mammalian cells have elaborate networks of molecular signalling in counteracting heat shock and in developing adaptation to oxidative stress to avoid cell death. However, the precise mechanisms linking heat shock, oxidative stress and cell survival/cell death mechanisms are not yet clearly understood. The purpose of this study was thus to study the time course of hyperthermia-induced oxidative stress and cellular signalling through the activation of heat shock factor 1 (HSF1) and heat shock protein 70 (HSP70), using freshly isolated mouse hepatocytes. The results accomplished in this work demonstrated that mild continuous hyperthermia (41 degrees ) leads to oxidative stress and loss of cellular viability in a time-dependent manner, with significant effects already observed at the first hour of incubation. These toxic effects developed concomitantly with activation of HSF1 and emerged before the formation of HSP70 levels. Thus, although cell signalling was triggered through the transcriptional activation of HSP70 via HSF1, this putative protective process did not modify the trend of hepatotoxic effects mediated by this type of hyperthermic challenging.

Age Effect on HSP70: Decreased Resistance to Ischemic and Oxidative Stress in HDF

BACKGROUND

Heat pre-conditioning results in induction of heat shock proteins including HSP70 that gives a cytoprotective effect against further stress. However, HSP70 induction is attenuated in aged cells. The lower HSP70-levels may contribute to the impaired stress response seen in the aged, and to the higher rates of chronic wounds in aged, which arise from repeated ischemia-reperfusion injury. The aim of this study was to investigate a possible connection by comparing the viability of heat pre-conditioned aged versus young human dermal fibroblasts (HDF) after exposure to stress.

MATERIALS AND METHODS

Young (15-28) and aged (61-77) HDF were heat pre-conditioned (42 degrees C, 1 h) and after recovery (1, 2, or 20 h) treated with carbonyl-cyanide-m-chlorophenylhydrazone (hypoxic stress) or with hydrogen peroxide (oxidative stress) for 1 h. HSP70 levels were determined by Western blot. Cell damage was assessed by quantifying lactic dehydrogenase (LDH) in conditioned media. Aged HDF were transfected with HSP70-plasmid, consecutively heat pre-conditioned and exposed to oxidative stress.

RESULTS

HSP70 increased in heat pre-conditioned young HDF by 96, 189, and 237% after 1, 2, and 20-h recovery, respectively, and in aged HDF by 27, 61, and 26%. LDH-release was only decreased in young HDF 20-h after heat-treatment compared with non-heat treated cells (P < 0.001). HSP70-transfection of aged HDF with plasmid reduced LDH-release by 29%.

CONCLUSIONS

Heat pre-conditioning fails to protect aged HDF to oxidative or hypoxic stress due in part to impaired HSP70 induction compared to young.

[The toxic aggregation of proteins: a kind of "molecular delinquency" actively fought in the cell by molecular chaperones and proteases]

Under various stresses, mutation-sensitised proteins may spontaneously convert into inactive, aggregation-prone structures, which may be cytotoxic and infectious. In the cell, this new kind of "molecular criminality" is actively fought against by a network of molecular chaperones that can specifically identify, isolate and unfold damaged (delinquent) proteins and favour their subsequent native refolding. Irreversibly damaged molecules unable to natively refold are preferentially "executed" and recycled by proteases. Failing that, they are "imprisoned" within compact amyloids, or "evicted" from the cell. Thus, striking parallels, although of questionable ethical value, exist between protein and human criminality, and between the cellular and social responses to these different types of criminality. Fundamental differences also exist. Whereas programmed death (apoptosis) is the preferred solution chosen by aged and aggregation-stressed cells, collective suicide is seldom an option chosen by lawless human societies. More significantly, there is no clear cellular equivalent for the role of the family and the education system, which are so essential to the proper shaping of functional individuals in the society, and give rise to humanism, that favours crime prevention, reeducation and reinsertion programs over capital punishment. To the cardiologist and transplantation surgeon, the interest of molecular chaperones, in particular of Hsp70, Hsp90 and Hsp27, lays in their ability to inhibit the signalling pathway of programmed cell death. Their induction before and during ischemia, by various treatments and drugs could significantly reduce damages from the post ischemic reperfusion of organs.

The ubiquitin-proteasome system at the crossroads of stress-response and ageing pathways: a handle for skin care?

The regulation of gene expression at the transcriptional level has been considered for long as the main mechanism of cellular adaptive responses. Since the turn of the century, however, it is becoming clear that higher organisms developed a complex, sensitive and maybe equally important network of regulatory pathways, relying largely on protein interactions, post-translational modifications and proteolysis. Here we review the involvement of the ubiquitin-proteasome pathway of protein degradation at different levels of cellular life in relation with ageing, and with a special focus on skin. It comes out that the ubiquitin system plays a major role in signal transduction associated with stress and ageing, in skin in particular through the control of retinoid and NF-kappaB pathways. The understanding of specific proteolytic targeting by E3 ubiquitin-ligases paves the way for a new generation of active molecules that may control particular steps of normal and pathological ageing.

Phosphorylation of HSF1 by MAPK-activated protein kinase 2 on serine 121, inhibits transcriptional activity and promotes HSP90 binding

Heat shock transcription factor 1 (HSF1) monitors the structural integrity of intracellular proteins and its regulation is essential for the health and longevity of eukaryotic organisms. HSF1 also plays a role in the acute inflammatory response in the negative regulation of cytokine gene transcription. Here we show, for the first time, that HSF1 is regulated by the proinflammatory protein kinase MAPKAP kinase 2 (MK2). We have shown that MK2 directly phosphorylates HSF1 and inhibits activity by decreasing its ability to bind the heat shock elements (HSE) found in the promoters of target genes encoding the HSP molecular chaperones and cytokine genes. We show that activation of HSF1 to bind HSE in hsp promoters is inhibited through the phosphorylation of a specific residue, serine 121 by MK2. A potential mechanism for MK2-induced HSF1 inactivation is suggested by the findings that phosphorylation of serine 121 enhances HSF1 binding to HSP90, a major repressor of HSF1. Dephosphorylation of serine 121 in cells exposed to non-steroidal anti-inflammatory drugs leads to HSP90 dissociation from HSF1, which then forms active DNA binding trimers. These experiments indicate a novel mechanism for the regulation of HSF1 by proinflammatory signaling and may permit HSF1 to respond rapidly to extracellular events, permitting optimal physiological regulation.

The significance of lipid composition for membrane activity: New concepts and ways of assessing function

In the last decade or so, it has been realised that membranes do not just have a lipid-bilayer structure in which proteins are embedded or with which they associate. Structures are dynamic and contain areas of heterogeneity which are vital for their formation. In this review, we discuss some of the ways in which these dynamic and heterogeneous structures have implications during stress and in relation to certain human diseases. A particular stress is that of temperature which may instigate adaptation in poikilotherms or appropriate defensive responses during fever in mammals. Recent data emphasise the role of membranes in sensing temperature changes and in controlling a regulatory loop with chaperone proteins. This loop seems to need the existence of specific membrane microdomains and also includes association of chaperone (heat stress) proteins with the membrane. The role of microdomains is then discussed further in relation to various human pathologies such as cardiovascular disease, cancer and neurodegenerative diseases. The concept of modifying membrane lipids (lipid therapy) as a means for treating such pathologies is then introduced. Examples are given when such methods have been shown to have benefit. In order to study membrane microheterogeneity in detail and to elucidate possible molecular mechanisms that account for alteration in membrane function, new methods are needed. In the second part of the review, we discuss ultra-sensitive and ultra-resolution imaging techniques. These include atomic force microscopy, single particle tracking, single particle tracing and various modern fluorescence methods. Finally, we deal with computing simulation of membrane systems. Such methods include coarse-grain techniques and Monte Carlo which offer further advances into molecular dynamics. As computational methods advance they will have more application by revealing the very subtle interactions that take place between the lipid and protein components of membranes - and which are so essential to their function.

Myocardial Heat Shock Protein 70 Expression in Young and Old Rats After Identical Exercise Programs

Synthesis of inducible heat shock protein 70 (HSP70) is impaired in aged animals following acute stresses including exercise. In this study we determined whether aging affects expression of this cytoprotective protein following chronic exercise participation. Male Fischer 344 rats, final ages 6 and 24 months, exercised identically for 10 weeks on a treadmill (15 degrees incline, 15 m/min for up to 60 minutes, 5 days/week). In 6-month-old animals, exercise increased HSP70 in heart (44%), liver (216%), and skeletal muscle (126%) (p <.05 vs sedentary). In 24-month-old animals, exercise increased HSP70 in muscle (69%), but not in heart or liver. In heart, antioxidant enzyme activities and HSP70 messenger RNA were measured and found to be unaffected by exercise at both ages. Our results indicate an age-related decrease in HSP70 production in heart and liver following chronic exercise. Furthermore, the aged heart does not increase its antioxidant enzyme defenses to compensate for the HSP70 deficit.

Modelling the actions of chaperones and their role in ageing

Many molecular chaperones are also known as heat shock proteins because they are synthesised in increased amounts after brief exposure of cells to elevated temperatures. They have many cellular functions and are involved in the folding of nascent proteins, the re-folding of denatured proteins, the prevention of protein aggregation, and assisting the targeting of proteins for degradation by the proteasome and lysosomes. They also have a role in apoptosis and are involved in modulating signals for immune and inflammatory responses. Stress-induced transcription of heat shock proteins requires the activation of heat shock factor (HSF). Under normal conditions, HSF is bound to heat shock proteins resulting in feedback repression. During stress, cellular proteins undergo denaturation and sequester heat shock proteins bound to HSF, which is then able to become transcriptionally active. The induction of heat shock proteins is impaired with age and there is also a decline in chaperone function. Aberrant/damaged proteins accumulate with age and are implicated in several important age-related conditions (e.g. Alzheimer's disease, Parkinson's disease, and cataract). Therefore, the balance between damaged proteins and available free chaperones may be greatly disturbed during ageing. We have developed a mathematical model to describe the heat shock system. The aim of the model is two-fold: to explore the heat shock system and its implications in ageing; and to demonstrate how to build a model of a biological system using our simulation system (biology of ageing e-science integration and simulation (BASIS)).

Novel regulatory factors of HSF-1 activation: facts and perspectives regarding their involvement in the age-associated attenuation of the heat shock response

An attenuated response to stress is characteristic of senescence. Heat shock (HS), a significant form of stress, is delayed and reduced in aging organisms. In the response to heat shock, heat shock factor 1 (HSF-1) is activated by trimerization of its monomeric subunits. This then initiates the transcription of a series of heat shock genes (hsp genes) that encode chaperone proteins protective against heat stress. Using a promoter binding electromobility shift assay (EMSA), we have found no activation of this transcription factor in the brains of old (36 months) rats in response to exposure to 41 degrees C for 1h while strong activation is elicited in young (6 months) animals. Since brains of young and old rats had approximately the same amount of HSF-1 subunits, we anticipated the presence of auxiliary regulatory factors essential for the activation of HSF-1 and the initiation of heat shock gene transcription. We describe three novel auxiliary factors--the proteins I-HSF [HSF inhibitor] and elongation factor-1 alpha (EF-1alpha) and a large non-coding RNA (HSR)--that participate in regulation and activation of HSF-1 in early stages of heat shock gene transcription. I-HSF inhibits trimerization of HSF-1 at normal temperatures. HSR and EF-1alpha form a complex with HSF-1 and facilitate its trimerization and binding to heat shock element (HSE) in the promoters of hsps. It is proposed that structural changes in any one or a combination of these factors in response to heat shock may contribute to the age-associated attenuation in the response to stress.

Selective neuronal vulnerability and inadequate stress response in superoxide dismutase mutant mice

To understand the role of oxidative stress and mitochondrial defects in the development of neurodegeneration, we examined the age-related pathological changes and corresponding gene expression profiles in homozygous mutant mice deficient in the mitochondrial form of superoxide dismutase (MnSOD, SOD2). These Sod2-/- mice, generated on a B6D2F1 background, developed ataxia at Postnatal Day (P) 11 and progressively deteriorated with frequent seizures by P14. Histopathological examination revealed neurodegenerative changes consistent with the neurological signs. Vacuolar degeneration was observed in neurons and neuropil throughout the brainstem and rostral cortex. The motor trigeminal nucleus in brainstem and the deeper layers of the motor cortex were the earliest regions to degenerate, with the thalamus and hippocampus affected at later stages. Oligonucleotide microarrays were used to compare gene expression profiles in the brainstem and thalamus of Sod2+/+ and -/- mice from birth to P18. Notably, a large set of heat-shock protein genes was transcriptionally down regulated, and this was most likely due to a reduction in the heat-shock transcription factor 1 (HSF1). Other major classes of differentially expressed genes include lipid biosynthesis and ROS metabolism.

Doxycycline-regulated over-expression of hsp22 has negative effects on stress resistance and life span in adult Drosophila melanogaster

Drosophila hsp22 is a member of the small heat shock proteins family (shsps). The hsp22 is expressed in a tissue-general pattern in response to heat stress and during normal aging, and localizes to the mitochondrial matrix, however, its exact function and targets are unknown. Hsp22 was found to be rapidly induced in response to oxidative stress, indicating that hsp22 is also an oxidative stress response gene. To assay for effects of hsp22, a ubiquitous pattern of hsp22 gene expression was generated in young flies using the "tet-on" doxycycline-regulated promoter system. The hsp22 over-expression made flies more sensitive to heat and oxidative stress, while resistance to coumarin poisoning was not affected. Life span was also reduced, particularly at higher culture temperatures. Members of other hsp families have been shown to feedback-inhibit their own expression by interacting with the heat shock transcription factor (HSF) and preventing binding to the HSEs. Induction of hsp22:lacZ and hsp70:lacZ reporter transgenes in response to acute stress was normal in the presence of hsp22 protein over-expression and in old flies, indicating that the negative effects of hsp22 are downstream of the HSF/HSE pathway and the transcriptional heat shock response. The data demonstrate a specific over-expression phenotype for hsp22 and suggest that hsp22 interacts with heat and oxidative stress resistance pathways.

The use of mature zebrafish (Danio rerio) as a model for human aging and disease

Zebrafish (Danio rerio) have been extensively utilized for understanding mechanisms of development. These studies have led to a wealth of resources including genetic tools, informational databases, and husbandry methods. In spite of all these resources, zebrafish have been underutilized for exploring pathophysiology of disease and the aging process. Zebrafish offer several advantages over mammalian models for these studies, including the ability to perform saturation mutagenesis and the capability to contain thousands of animals in a small space. In this review, we will discuss the use of mature zebrafish as an animal model and provide specific examples to support this novel use of zebrafish. Examples include demonstrating that clinical pathology can be performed in mature zebrafish and that age-associated changes in heat shock response can be observed in zebrafish. These highlights demonstrate the utility of zebrafish as a model for disease and aging.

Hormetic Mechanisms of Anti-Aging and Rejuvenating Effects of Repeated Mild Heat Stress on Human Fibroblasts in Vitro

The phenomenon of hormesis is represented by mild stress-induced stimulation of maintenance and repair pathways, resulting in beneficial effects for cells and organisms. We have reported that repeated mild heat stress (RMHS) has anti-aging hormetic effects on growth and various cellular and biochemical characteristics of human skin fibroblasts undergoing aging in vitro. These effects of RMHS include the maintenance of the stress protein profile, reduction in the accumulation of oxidatively and glycoxidatively damaged proteins, stimulation of the activities of the proteasome and its 11S activator, improvement in cellular resistance to ethanol, hydrogen peroxide, and ultraviolet rays, and increased antioxidative activity of the cells. We have also reported that RMHS prolongs the lifespan of Drosophila. Others have reported anti-aging and life prolonging effects of a wide variety of so-called stressors, such as pro-oxidants, aldehydes, calorie restriction, irradiation, heat shock, and hypergravity. Although molecular mechanisms of hormesis are yet to be elucidated, there are indications that relatively small hormetic effects become biologically amplified, resulting in significant improvement of cellular and organic functions and survival. Hormesis, therefore, can be an effective approach for modulating aging, for preventing or delaying the onset of age-related diseases, and for improving the quality of life in old age.

Age and attenuation of exercise-induced myocardial HSP72 accumulation

Overexpression of heat shock protein (HSP)72 is associated with cardioprotection. Hyperthermia-induced HSP72 overexpression is attenuated with senescence. While exercise also increases myocardial HSP72 in young animals, it is unknown whether this effect is attenuated with aging. Therefore, we investigated the effect of aging on exercise-induced myocardial heat shock factor (HSF)-1 activation and HSP72 expression. Male Fischer-344 rats (6 or 24 mo) were randomized to control, exercise, and hyperthermic groups. Exercise consisted of 2 days of treadmill running (60 min/day, approximately 75% maximal oxygen consumption). Hyperthermia, 15 min at approximately 41 degrees C (colonic temperature), was achieved using a temperature-controlled heating blanket. Analyses included Western blotting for myocardial HSP72 and HSF-1, electromobility shift assays for HSF-1 activation, and Northern blotting for HSP72 mRNA. Exercise and hyperthermia increased (P < 0.05) myocardial HSP72 in both young (>3.5- and 2.5-fold, respectively) and aged (>3- and 1.5-fold, respectively) animals. Both exercise and hyperthermic induction of HSP72 was attenuated with age. Myocardial HSF-1 protein, HSF-1 activation, and HSP72 mRNA did not differ with age. These data demonstrate that aging is associated with diminished exercise-induced myocardial HSP72 expression. Mechanisms other than HSF-1 activation and transcription of HSP72 mRNA are responsible for this age-related impairment.

Regulation of molecular chaperone gene transcription involves the serine phosphorylation, 14-3-3 epsilon binding, and cytoplasmic sequestration of heat shock factor 1

Heat shock factor 1 (HSF1) regulates the transcription of molecular chaperone hsp genes. However, the cellular control mechanisms that regulate HSF1 activity are not well understood. In this study, we have demonstrated for the first time that human HSF1 binds to the essential cell signaling protein 14-3-3 epsilon. Binding of HSF1 to 14-3-3 epsilon occurs in cells in which extracellular signal regulated kinase (ERK) is activated and blockade of the ERK pathway by treatment with the specific ERK pathway inhibitor PD98059 in vivo strongly suppresses the binding. We previously showed that ERK1 phosphorylates HSF1 on serine 307 and leads to secondary phosphorylation by glycogen synthase kinase 3 (GSK3) on serine 303 within the regulatory domain and that these phosphorylation events repress HSF1. We show here that HSF1 binding to 14-3-3 epsilon requires HSF1 phosphorylation on serines 303 and 307. Furthermore, the serine phosphorylation-dependent binding of HSF1 to 14-3-3 epsilon results in the transcriptional repression of HSF1 and its sequestration in the cytoplasm. Leptomycin B, a specific inhibitor of nuclear export receptor CRM1, was found to reverse the cytoplasmic sequestration of HSF1 mediated by 14-3-3 epsilon, suggesting that CRM1/14-3-3 epsilon directed nuclear export plays a major role in repression of HSF1 by the ERK/GSK3/14-3-3 epsilon pathway. Our experiments indicate a novel pathway for HSF1 regulation and suggest a mechanism for suppression of its activity during cellular proliferation.

Age, cell signalling and cardioprotection

For many years investigators have been researching methods of preconditioning the myocardium against ischaemia-induced damage; however, a majority of this research has been carried out in young animals and cells. Normal ageing is accompanied by changes in the human myocardium that decrease its capacity to tolerate and respond to various forms of stress. Also, the likelihood of experiencing an ischaemic stress and other cardiovascular complications increases as an individual ages; therefore, an aged population would benefit most from cardioprotective treatments. Methods currently known to provide cardioprotection (or preconditioning) include exercise, heat stress, oxidative stress, brief ischaemia, stretch and certain pharmacological interventions. It is unclear whether the aged myocardium can adapt to a preconditioning stimulus; however, many researchers have observed age-related alterations in the expression and activation of proteins key to the cardioprotective process. These proteins include heat shock protein 70 (HSP70), nitric oxide synthase (NOS), the sodium-hydrogen exchanger (NHE), and the mitogen-activated protein (MAP) kinases c-Jun N-terminal Kinase (JNK), extracellular signal-regulated kinase (ERK), and p38. Therefore, the purpose of the current review will be to outline the current knowledge of these cardioprotective agents in an aged myocardium. Interactions among the cardioprotective agents outlined herein suggest that age-related changes in the myocardium will need to be better understood before cardioprotective interventions that have been proved effective in young animals can be applied to an aged human population.

Paradoxical increase of heat-shock response with age in a substrain of F344 rats: comparison between F344/DuCrj and F344/Jcl

The ability of hepatocytes isolated from young (7-10 months) and old (31 months) male F344/Jcl and F344/DuCrj rats to express heat shock protein (hsp) 27, hsp70 and hsp90 was determined after a mild heat shock (42.5 degrees C for 30 min). The induction of these three mRNA levels by the heat shock was 50-80% lower in hepatocytes isolated from old F344/Jcl rats than in those from young rats. However, the hepatocytes from old F344/DuCrj showed a marked increase (200-250%) in the induction of hsp mRNAs by heat shock when compared to cells from young rats. Because heat shock transcription factor (HSF) plays a critical role in regulating the transcription of hsp genes, the effect of age on the binding activity HSF to heat shock element (HSE) was also studied. Again, the induction of binding activity of HSF to HSE was significantly increased with age in hepatocytes from F344/DuCrj rats while the reverse was true for the cells from F344/Jcl. The induced levels of hsp mRNAs were positively correlated with the binding activity of HSF to HSE in hepatocyte extracts from both F344 substrains, suggesting that the diverse age-related changes of heat-shock response in F344 substrains occurs in HSF activity. The contradictory age-related change in the heat-shock response is discussed with the differences in biochemical and genetic properties of substrains of F344 rats.

HSP70 constitutive expression in rat central nervous system from postnatal development to maturity

We studied the level of the basal (constitutive) HSP70 expression (inducible and constitutive forms) in the central nervous system (CNS) of male and female rats from the postnatal period to maturity. HSP70 levels were analyzed by immunoblotting in five different areas (cortex, hippocampus, hypothalamus, cerebellum, and spinal cord). The highest levels of HSP70 were found in juvenile rats and decreased progressively until reaching baseline levels between 2 and 4 months. A slight and nonsignificant increase in aged (2-year-old) rats compared with adult subjects was observed in some cerebral areas (cerebral cortex, hippocampus, and cerebellum). In the first weeks of postnatal development, HSP70 immunoreactivity was distributed throughout CNS sections and no specific immunopositive cells could be clearly determined. In adult animals, strong immunostaining was observed in some large neurons (Purkinje neurons and mesencephalic and spinal cord motor neurons), some perivascular and subpial astrocytes, and ependymocytes. Immunoelectron microscopy revealed that HSP70 in these cells is located in the perinuclear area and in mitochondria, rough endoplasmic reticulum, and microtubules. In neurons, strong immunolabeling was also observed in synaptic membranes. The postnatal time course of HSP70 levels and the location and size of HSP70-immunopositive cells suggest that HSP70 constitutively expressed in the rat CNS may be mainly determined by the degree of development and metabolic activity of the neural cells.

Impacts of transcriptional regulation on aging and senescence

The genetic makeup of the organism appears to dictate the species-specific rate of aging and the maximum life-span potential. The genotype is converted to phenotype through transcriptional and translational regulation. A group of gene regulatory proteins (transcription factors) play critical roles in controlling the rates of transcription of specific genes by directly interacting with regulatory sequences at gene promoters. Here, we review the basic mechanism of transcriptional control and the role of a number of transcription factors whose level and/or activity alter with age. Among these age-dependent transcription factors, many are involved in the regulation of stress and inflammatory responses and are subjected to functional alterations by reactive oxygen species (ROSs). A progressive rise of oxidative stress, impaired ability to cope with stressful stimuli and prolongation of the inflammatory response are some of the hallmarks of the senescent phenotype. Results published to date are supportive of the concept that a species-specific program of the temporal regulation of genes with additional modulation by a number of epigenetic factors, mediates the age-dependent deterioration of physiological functions and development of the senescent phenotype.

Chaperones come of age

Chaperone function plays a key role in repairing proteotoxic damage, in the maintenance of cell architecture, and in cell survival. Here, we summarize our current knowledge about changes in chaperone expression and function in the aging process, as well as their involvement in longevity and cellular senescence.

Heat-induced proteasomic degradation of HSF1 in serum-starved human fibroblasts aging in vitro

The exposure of human fibroblasts (HF) aging in vitro to heat shock resulted in an attenuated expression of the heat shock-inducible HSP70. When late passage cells were cultured in the continuous presence of serum, we observed a reduced accumulation of the cytoplasmic polyadenylated HSP70 mRNA. The levels of HSF1 activation and nuclear HSP70 mRNA were comparable to those of early passage cells (M. A. Bonelli et al., Exp. Cell Res. 252, 20-32, 1999). When late passage cells were serum-starved overnight, we observed a reduced activation of HSF1 and a decreased level of HSP70 mRNA during heat shock. However, at 37 degrees C the levels of HSF1 differed little between late passage HF and early passage cells, irrespective of the presence of serum. Interestingly, during heat shock a marked decrease in the level and, consequently, in the binding activity of HSF1 was noted only in serum-starved, late passage HF. The decrease in the level of HSF1 was counteracted by back addition of serum to the cells during heat shock. Addition of the specific proteasome inhibitor MG132 blocked a decrease in HSF1 during heat shock, maintaining levels observed in late passage cells and HSF1 activity comparable to that of early passage HF. The recovery of the level and activity of HSF1 observed in late passage HF incubated in the presence of MG132 suggests that heat shock unmasks a latent proteasome activity responsible for HSF1 degradation.

Regional distribution of Hsp70 in the CNS of young and old food-restricted rats following hyperthermia

We examined the effect of aging on the capacity of the brain to produce heat shock protein (Hsp70) in response to heat stress, using high-powered microwaves (HPM, 2.06 GHz, 2.2 W/cm(2)) to induce hyperthermia for periods so brief that thermoregulatory factors were functionally eliminated as confounding variables. Unanesthetized young (6 months) and old (25 months) male, food-restricted Sprague-Dawley rats were exposed to HPM to induce a mean peak tympanic temperature (T(ty)) of 42.2 degrees C within 30 s. T(ty) returned to <40.0 degrees C within 6 min post-exposure in both age groups. Rats were euthanized 6 or 24 h later for immunohistochemical determination of Hsp70 accumulation in 10 brain regions. HPM exposure induced significant increases in 7 of the 10 regions. There were no significant differences observed in the pattern or density of Hsp70 accumulation between the young and old rats at 6 h post-HPM exposure, with the exception of the medial vestibular nucleus, which demonstrated significantly greater Hsp70 accumulation in the old rats. There were significant differences between the age groups at 24 h post-exposure, however, there was no general pattern; i.e., depending on the brain region, aged rats displayed significantly greater, lesser, or similar increases in Hsp70 expression compared with young. Taken together, these results demonstrate that the brain of aged, food-restricted rats does not display a loss of capacity to accumulate Hsp70 in response to heat stress.