Dietary restriction initiated in late adulthood can reverse age-related alterations of protein and protein metabolism

UPS Activation in the Battle Against Aging and Aggregation-Related Diseases: An Extended Review

Aging is a biological process accompanied by gradual increase of damage in all cellular macromolecules, i.e., nucleic acids, lipids, and proteins. When the proteostasis network (chaperones and proteolytic systems) cannot reverse the damage load due to its excess as compared to cellular repair/regeneration capacity, failure of homeostasis is established. This failure is a major hallmark of aging and/or aggregation-related diseases. Dysfunction of the major cellular proteolytic machineries, namely the proteasome and the lysosome, has been reported during the progression of aging and aggregation-prone diseases. Therefore, activation of these pathways is considered as a possible preventive or therapeutic approach against the progression of these processes. This chapter focuses on UPS activation studies in cellular and organismal models and the effects of such activation on aging, longevity and disease prevention or reversal.

Short-term Treatment of Daumone Improves Hepatic Inflammation in Aged Mice

Chronic inflammation has been proposed as one of the main molecular mechanisms of aging and age-related diseases. Although evidence in humans is limited, short-term calorie restriction (CR) has been shown to have anti-inflammatory effects in aged experimental animals. We reported on the long-term treatment of daumone, a synthetic pheromone secreted by Caenorhabditis elegans in an energy deficient environment, extends the life-span and attenuates liver injury in aged mice. The present study examined whether late onset short-term treatment of daumone exerts anti-inflammatory effects in the livers of aged mice. Daumone was administered orally at doses of 2 or 20 mg/kg/day for 5 weeks to 24-month-old male C57BL/6J mice. Increased liver macrophage infiltration and gene expression of proinflammatory cytokines in aged mice were significantly attenuated by daumone treatment, suggesting that short-term oral administration of daumone may have hepatoprotective effects. Daumone also dose-dependently suppressed tumor necrosis factor-α (TNF-α)-induced nuclear factor-κB (NF-κB) phosphorylation in HepG2 cells. The present data demonstrated that short-term treatment of daumone has anti-inflammatory effects in aged mouse livers possibly through suppression of NF-κB signaling and suggest that daumone may become a lead compound targeting aging and age-associated diseases.

The effects of dietary restriction on oxidative stress in rodents

Oxidative stress is observed during aging and in numerous age-related diseases. Dietary restriction (DR) is a regimen that protects against disease and extends life span in multiple species. However, it is unknown how DR mediates its protective effects. One prominent and consistent effect of DR in a number of systems is the ability to reduce oxidative stress and damage. The purpose of this review is to comprehensively examine the hypothesis that dietary restriction reduces oxidative stress in rodents by decreasing reactive oxygen species (ROS) production and increasing antioxidant enzyme activity, leading to an overall reduction of oxidative damage to macromolecules. The literature reveals that the effects of DR on oxidative stress are complex and likely influenced by a variety of factors, including sex, species, tissue examined, types of ROS and antioxidant enzymes examined, and duration of DR. Here we present a comprehensive review of the existing literature on the effect of DR on mitochondrial ROS generation, antioxidant enzymes, and oxidative damage. In a majority of studies, dietary restriction had little effect on mitochondrial ROS production or antioxidant activity. On the other hand, DR decreased oxidative damage in the majority of cases. Although the effects of DR on endogenous antioxidants are mixed, we find that glutathione levels are the most likely antioxidant to be increased by dietary restriction, which supports the emerging redox-stress hypothesis of aging.

Identification of the dichotomous role of age-related LCK in calorie restriction revealed by integrative analysis of cDNA microarray and interactome

Among the many experimental paradigms used for the investigation of aging, the calorie restriction (CR) model has been proven to be the most useful in gerontological research. Exploration of the mechanisms underlying CR has produced a wealth of data. To identify key molecules controlled by aging and CR, we integrated data from 84 mouse and rat cDNA microarrays with a protein-protein interaction network. On the basis of this integrative analysis, we selected three genes that are upregulated in aging but downregulated by CR and two genes that are downregulated in aging but upregulated by CR. One of these key molecules is lymphocyte-specific protein tyrosine kinase (LCK). To further confirm this result on LCK, we performed a series of experiments in vitro and in vivo using kidneys obtained from aged ad libitum-fed and CR rats. Our major significant findings are as follows: (1) identification of LCK as a key molecule using integrative analysis; (2) confirmation that the age-related increase in LCK was modulated by CR and that protein tyrosine kinase activity was decreased using a LCK-specific inhibitor; and (3) upregulation of LCK leads to NF-κB activation in a ONOO(-) generation-dependent manner, which is modulated by CR. These results indicate that LCK could be considered a target attenuated by the anti-aging effects of CR. Integrative analysis of cDNA microarray and interactome data are powerful tools for identifying target molecules that are involved in the aging process and modulated by CR.

Childhood obesity: a life-long health risk

Childhood obesity has become major health concern for physicians, parents, and health agencies around the world. Childhood obesity is associated with an increased risk for other diseases not only during youth but also later in life, including diabetes, arterial hypertension, coronary artery disease, and fatty liver disease. Importantly, obesity accelerates atherosclerosis progression already in children and young adults. With regard to pathophysiological changes in the vasculature, the striking similarities between physiological changes related to aging and obesity-related abnormalities are compatible with the concept that obesity causes "premature" vascular aging. This article reviews factors underlying the accelerated vascular disease development due to obesity. It also highlights the importance of recognizing childhood obesity as a disease condition and its permissive role in aggravating the development of other diseases. The importance of childhood obesity for disease susceptibility later in life, and the need for prevention and treatment are also discussed.

Childhood obesity: a life-long health risk

Childhood obesity has become major health concern for physicians, parents, and health agencies around the world. Childhood obesity is associated with an increased risk for other diseases not only during youth but also later in life, including diabetes, arterial hypertension, coronary artery disease, and fatty liver disease. Importantly, obesity accelerates atherosclerosis progression already in children and young adults. With regard to pathophysiological changes in the vasculature, the striking similarities between physiological changes related to aging and obesity-related abnormalities are compatible with the concept that obesity causes "premature" vascular aging. This article reviews factors underlying the accelerated vascular disease development due to obesity. It also highlights the importance of recognizing childhood obesity as a disease condition and its permissive role in aggravating the development of other diseases. The importance of childhood obesity for disease susceptibility later in life, and the need for prevention and treatment are also discussed.

Protein metabolism and lifespan in Caenorhabditis elegans

Lifespan of the versatile model system Caenorhabditis elegans can be extended by a decrease of insulin/IGF-1 signaling, TOR signaling, mitochondrial function, protein synthesis and dietary intake. The exact molecular mechanisms by which these modulations confer increased life expectancy are yet to be determined but increased stress resistance and improved protein homeostasis seem to be of major importance. In this chapter, we explore the interactions among several genetic pathways and cellular functions involved in lifespan extension and their relation to protein homeostasis in C. elegans. Several of these processes have been associated, however some relevant data are conflicting and further studies are needed to clarify these interactions. In mammals, protein homeostasis is also implicated in several neurodegenerative diseases, many of which can be modeled in C. elegans.

Late-onset dietary restriction compensates for age-related increase in oxidative stress and alterations of HSP 70 and synapsin 1 protein levels in male Wistar rats

Numerous reports implicate increased oxidative stress in the functional and structural changes occurring in the brain and other organs as a part of the normal aging process. Dietary restriction (DR) has long been shown to be life-prolonging intervention in several species. This study was aimed to assess the potential efficacy of late-onset short term DR when initiated in 21 months old male wistar rats for 3 months on the antioxidant defense system and lipid peroxidation, cellular stress response protein HSP 70 and synaptic marker protein synapsin 1 in discrete brain regions such as cortex, hypothalamus, and hippocampus as well as liver, kidney and heart from 24 month old rats. Age-associated decline in activities of superoxide dismutase, catalase, glutathione peroxidase, glutathione, and elevated levels of lipid peroxidation was observed in brain and peripheral organ as well as increased expression of HSP 70 and reduction in synapsin 1 was observed in brain studied. Late-onset short term DR was effective in partially restoring the antioxidant status and in decreasing lipid peroxidation level as well as enhancing the expression of HSP 70 and synapsin 1 in aged rats. Late onset short term DR also prevented age-related neurodegeneration as revealed by Fluoro-Jade B staining in hippocampus and cortex regions of rat brain. Thus our current results suggest that DR initiated even in old age has the potential to improve age related decline in body functions.

Aging and survival: the genetics of life span extension by dietary restriction

Reducing food intake to induce undernutrition but not malnutrition extends the life spans of multiple species, ranging from single-celled organisms to mammals. This increase in longevity by dietary restriction (DR) is coupled to profound beneficial effects on age-related pathology. Historically, much of the work on DR has been undertaken using rodent models, and 70 years of research has revealed much about the physiological changes DR induces. However, little is known about the genetic pathways that regulate the DR response and whether or not they are conserved between species. Elucidating these pathways may facilitate the design of targeted pharmaceutical treatments for a range of age-related pathologies. Here, we discuss how recent work in nonmammalian model organisms has revealed new insight into the genetics of DR and how the discovery of DR-specific transcription factors will advance our understanding of this phenomenon.

Age-related impairments in neuronal plasticity markers and astrocytic GFAP and their reversal by late-onset short term dietary restriction

Recent studies on the effects of dietary restriction (DR) in rodents and primates have shown that even late-onset short-term regimens can bring about comparable beneficial changes seen in animals subjected to life-long DR. We studied the effect of aging on the expression of neural cell adhesion molecule (NCAM), its polysialylated form PSA-NCAM and astrocytic marker glial fibrillary acidic protein (GFAP) by immunohistofluorescent staining and immunoblotting in 1, 3, 6, 18 and 24 months old male wistar rats. Maximum expression of NCAM and PSA-NCAM was observed in sub-granular zone (SGZ) or granular cell layer (GCL) of hippocampus, arcuate region and paraventricular area of hypothalamus and piriform cortex layer II from 1 and 3 months old rats, thereafter, gradual downregulation was observed in 6, 18 and 24 months old rats. Progressive increase in astrocytic GFAP expression was noticed in these regions of brain with age. We further addressed whether DR initiated in late adulthood in 24 months old rats confers beneficial effects and can reverse changes in expression of NCAM, PSA-NCAM and GFAP. These results suggest that even late-onset short term DR regimen in old rats can have beneficial effects on neuroplasticity.

Intermittent dietary restriction as a practical intervention in aging

Recent studies on the effects of dietary restriction (DR) in rodents and primates have shown that even late-onset short-term regimens can bring about comparable beneficial changes seen in animals subjected to life-long DR. We examined the effect of 3 months of DR on the expression of antioxidant enzymes and antioxidants, heat-shock protein 70 (HSP-70), neural cell adhesion molecule (NCAM) and its polysialylated form, PSA-NCAM, as well as astrocytic marker glial fibrillary acidic protein (GFAP) in 18-month-old middle-aged rats. The present study shows that DR initiated in late adulthood confers beneficial effects, such as attenuation of oxidative stress, enhanced expression of HSP-70, neural plasticity markers NCAM, and PSA-NCAM, and reduced levels of GFAP.

Low-level caloric restriction rescues proteasome activity and Hsc70 level in liver of aged rats

Proteasome activity is known to decrease with aging in ad libitum (AL) fed rats. Severe caloric restriction (CR) significantly extends the maximum life-span of rats, and counteracts the age-associated decrease in liver proteasome activities. Since few investigations have explored whether lower CR diets might positively counteract the age associated decrease in proteasome activity, we then investigated the effects of a mild CR regimen on animal life-span, proteasome content and function. In addition, we addressed the question whether both CR regimens might also affect the expression of Hsc70 protein, a constitutive chaperone reported to share a role in the function of proteasome complex and in the repair of proteotoxic damage, and whose level decreased during aging. In contrast to severe CR, mild CR had a poor effect on life-span; however, it better counteracted the decrease of proteasome activities. Both regimens, however, maintain Hsc70 in liver of old rats at level comparable to that of young rats. Interestingly, the effects of aging and CRs on liver proteasome enzyme activities did not appear to be associated with parallel changes in the amount of proteasome proteins suggesting that the quality (molecular activity of the enzymes) rather than the quantity are likely to be modified with age. In conclusion, the results presented in this work show that a mild CR can have beneficial effects on liver function of aging rats because is adequate to counteract the decrease of proteasome function and Hsc70 chaperone level.

Starving for life: what animal studies can and cannot tell us about the use of caloric restriction to prolong human lifespan

Caloric restriction (CR) is the only experimental nongenetic paradigm known to increase lifespan. It has broad applicability and extends the life of most species through a retardation of aging. There is considerable interest in the use of CR in humans, and animal studies can potentially tell us about the impacts. In this article we highlight some of the things that animal studies can tell us about CR in humans. Rodent studies indicate that the benefits of CR on lifespan extension are related to the extent of restriction. The benefits of CR, however, decline as the age of onset of treatment is delayed. Modeling these impacts suggests that if a 48-y-old man engaged in 30% CR until his normal life expectancy of 78, he might increase his life expectancy by 2.8 y. Exercise and cold exposure induce similar energy deficits, but animals respond to these energy deficits in different ways that have a minor impact on lifespan. Measurements of animal responses when they cease restriction indicate that prolonged CR does not diminish hunger, even though the animals may have been in long-term energy balance. Neuroendocrine profiles support the idea that animals under CR are continuously hungry. The feasibility of restricting intake in humans for many decades without long-term support is questionable. However, what is unclear from animal studies is whether taking drugs that suppress appetite will generate the same impact on longevity or whether the neuroendocrine correlates of hunger play an integral role in mediating CRs effects.

Health span extension by later-life caloric or dietary restriction: a view based on rodent studies

In spite of the potential benefit of lifelong food restriction to retard aging and extend life span, it is unrealistic in human. The restriction late in life may be more practical. There are, however, only limited studies on the effect of late onset caloric or dietary restriction. We and other investigators have shown that the late life restriction rejuvenates some parameters that decline with age in rats and mice. Although such studies may provide a basis for human application of late-life caloric or dietary restriction, the prolongation of maximum life span would not be expected in view of the current status of the long-lived population in which maximum life span potential appears to have already been achieved. The late life caloric restriction, however, could extend the health span if the extent were appropriate.

Age-Dependent Decrease in Renal Glucocorticoid Receptor Function Is Reversed by Dietary Restriction in Mice

The effects of age and dietary restriction (alternate days of feeding for 3 months) on the concentration, activation, and DNase I digestion of nuclear-bound glucocorticoid receptors (GRs) in the kidney of male mice at two different ages (5 months as adult and 20 months as old) were investigated. A significant decrease (30%) in the concentration of renal GRs was observed in older ad libitum (AL)-fed mice as compared to the adult mice. Dietary restriction (DR) of older mice significantly increased (28%) the level of GRs as compared to the AL-fed control animals. The affinity of the receptor for the hormone remained the same for both AL- and DR-fed animals at both ages. Scatchard and slot blot analyses of the data confirmed the decreased level of renal GRs in older mice compared to the adult mice as well as an increased level of receptor in older DR mice. Activation studies of GRs by both salt and heat indicated a decreased (15-20%) activation of renal GRs in older animals compared to the adult mice in the AL-fed group. It was further observed that DR significantly enhanced (30%) the degree of both salt- and heat-dependent activation of GRs in older animals compared to the AL-fed animals of the age-matched group. DNase I digestion and extraction of nuclear-bound GR complexes showed a lower degree (26%) of extraction in older AL-fed animals compared to the adult animals. However, DR did not alter the pattern of digestibility of bound GR complexes. These above findings indicate that DR could reverse the decrease of GR function in older animals and may provide better adaptability of kidney in water and electrolyte balance.

Carbonyl modification in rat liver histones: decrease with age and increase by dietary restriction

We studied carbonylation, a form of oxidative modification of proteins, of histones in rat livers. Histones H1, H2B/H2A, and H3 were significantly carbonylated but the modification was almost undetectable in H4. Contrary to the generally accepted view of increased protein carbonylation with age, the modification of histones was significantly lower in old (30-month-old) than in young (5-month-old) animals. Dietary restriction of older animals for 2 months resulted in increase in carbonylation comparable to that at the young level. These findings may have physiological implications in chromatin structure/function in aging and beneficial effects of DR by influencing transcription, replication, and/or repair activities.

You are what you ate: the Biosetpoint hypothesis

The current epidemic of obesity has developed at a rate that cannot be attributed to genetic drift. Attempts to treat obesity using diet and activity have been largely disappointing. Genes are fixed at conception, but genetic expression is known to be influenced by nutriture during the stages of growth and development, these occurring in humans from conception through arrival at adulthood. Based on an extrapolation from existing data and cultural models, it is hypothesized that there is a mechanism by which diet and lifestyle habits present during the individual stages of growth and development help to define and program genetic expression in a way that resists change. It is through this mechanism that current nutritional and lifestyle practices have impacted genetic expression and contributed to the rapid development of resistant obesity. The details of the interaction between nutrition, lifestyle and genetic expression during growth must be examined, and intervention strategies devised for early stages of growth to prevent the seeds of obesity from taking root.

Effects of Aging and Anti-Aging Caloric Restrictions on Carbonyl and Heat Shock Protein Levels and Expression

Heat shock proteins (Hsps) are induced by stressful stimuli and have been shown to protect cells and organs from such stresses both in vitro and in vivo, and play a positive role in lifespan determination. An attenuated response to stress is characteristic of senescence and no Hsp induction is observed upon exposure to stress and no protective effect of a mild stress is observed in cells from aged individuals. The artificial over-expression of Hsps, can produce a protective effect against a variety of damaging stimuli in cells from aged rats or aged humans, in whom cardiovascular disease is a major cause of morbidity in older age. Here, we show that aging significantly decreases the levels of Hsp27, Hsp60, Hsp72 and Hsc70 in right atrium and left ventricle of the rat heart, both at level of protein and of mRNA. Two different caloric restriction regimens have been found to counteract in part the decrease in the levels of Hsp expression in the aged heart tissue as well as the tendency to an increase of the levels of carbonyl in cardiac proteins. Our data suggest that cardiac Hsp levels may be a determinant of longevity in rodents, and that generation of new regimens of caloric restriction may eventually show how to improve modulation of cardiac aging.

Rapid and reversible induction of the longevity, anticancer and genomic effects of caloric restriction

It is widely held that caloric restriction (CR) extends lifespan by preventing or reducing the age-related accumulation of irreversible molecular damage. In contrast, our results suggest that CR can act rapidly to begin life and health span extension, and that its rapid genomic effects are closely linked to its health effects. We found that CR begins to extend lifespan and reduce cancer as a cause of death within 8 weeks in older mice, apparently by reducing the rate of tumor growth. Further, 8 weeks of CR progressively reproduces nearly three quarters of the genomic effects of long-term CR (LTCR) in liver. Fewer of the genomic effects of LTCR are rapidly reproduced by the initiation of CR in the heart, but the changes produced are keys to cardiovascular health. Thus, the genomic effects of CR may be established more rapidly in mitotic than in postmitotic tissues. Most of the genomic effects of LTCR dissipate 8 weeks after switching to a control diet. Consistent with these results, others have shown that acute CR rapidly and reversibly reduces the short-term risk of death in Drosophila to that of LTCR treated flies. Further, in late adulthood, acute CR partially or completely reverses age-related alterations of liver, brain and heart proteins. CR also rapidly and reversibly mitigates biomarkers of aging in adult rhesus macaques and humans. These data argue that highly conserved mechanisms for the rapid and reversible enhancement of life- and health-span exist for mitotic and postmitotic tissues.

Brain aging in acquired immunodeficiency syndrome: increased ubiquitin-protein conjugate is correlated with decreased synaptic protein but not amyloid plaque accumulation

Two neuropathological changes that are linked with biological and pathological aging were examined in subjects with end-stage acquired immunodeficiency syndrome (AIDS). Autopsy brain specimens were examined from 25 people who died from complications of AIDS and 25 comparison subjects who were human immunodeficiency virus (HIV)-negative, matched for age, gender, ethnicity, and postmortem time interval. These adults were stratified into three age groups: elderly (62 to 75 years), intermediate (55 to 60 years), and young (21 to 42 years). Ubiquitin-stained dotlike deposits (Ub-dots) and diffuse extracellular plaques containing the beta-amyloid (Abeta) fragment of the amyloid precursor protein (Abeta plaque) were both increased significantly in the hippocampal formation of older subjects. In subjects with AIDS, Ub-dots were increased whereas Abeta plaque counts were not significantly different. Western blotting confirmed that high-molecular-weight ubiquitin-protein conjugates (HMW-Ub-conj) were increased in AIDS. The band intensity of one HMW-Ub-conj species with an approximate molecular mass of 145 kDa was correlated significantly with increased acute phase inflammatory protein (a-1-antichymotrypsin) and decreased synaptophysin and growth-associated protein-43 band intensities. These results raise the possibility that HIV-related brain inflammation disturbs neuronal protein turnover through the ubiquitin-proteasome apparatus, and might increase the prevalence of age-associated neurodegenerative diseases by decreasing synaptic protein turnover through the proteasome.

Dietary restriction in aged mice can partially restore impaired metabolism of apolipoprotein A-IV and C-III

Dietary restriction (DR) is only one well-established non-genetic experimental means to retard aging in various species of animals. Here we demonstrated that DR in mice for 3 months initiated late in life, at the age of 22 months, partially restores age-related decline of serum apolipoprotein A-IV (apo A-IV) level and the gene expression found in the liver of ad libitum fed young animals as revealed by fasting. In contrast, increase in gene expression of apo C-III by fasting was higher in the aged than that in the young, but it was reduced to the level of young animals in DR counterparts of the aged. In view of the implication that apo A-IV and C-III are involved in the activation and inhibition of lipoprotein lipase, respectively, the adult onset DR can conceivably upregulate the activity of this enzyme that is likely reduced in aged animals and thus improve the lipid metabolism. The present findings suggest that DR initiated even relatively late in life may reduce risk of age-related diseases associated with impaired lipid metabolism.

Does dietary sugar and fat influence longevity?

Simultaneous consideration of the influence of the different types of carbohydrates and fats in human diets on mortality rates (especially the diseases of aging), and the probable retardation of such diseases by caloric restriction (CR) leads to the hypothesis that restriction of foods with a high glycemic index and saturated or hydrogenated fats would avoid or delay many diseases of aging and might result in life extension. Many of the health benefits of CR might thereby be available to humans without the side effects or unacceptability of semi-starvation diets.

Mitochondrial dysfunctions during aging: vitamin E deficiency or caloric restriction--two different ways of modulating stress

Caloric restriction (CR), which has been demonstrated to offset the age-associated accrual of oxidative injury, involves a reduction in calory intake while maintaining adequate nutrition, preserves the activities of antioxidant enzymes in postmitotic tissues, maintains organ function, opposes the development of spontaneous diseases, and prolongs maximum life span in laboratory rodents. It has been proposed that reductions in Reactive Oxygen Species (ROS) production and cellular oxidative injury are central to the positive effects of CR. In the present investigation we studied the effect of CR and of a vitamin E deprived diet on mitochondrial structure and features in the liver of rats during aging, in order to ascertain the extent of modifications induced by these experimental conditions. CR rats displayed structural and functional mitochondrial properties (fatty acid pattern, respiratory chain activities, antioxidant levels, and hydroperoxide contents) similar to those of younger rats whilst vitamin E deficient rats appeared older than their own age. The mitochondria of the former, together with those of young rats, possessed the lowest Coenzyme Q9, hydroperoxide, and cytochrome contents as well as a suitable fatty acid membrane composition. Our study confirms that CR is a valuable tool in limiting aging-related free-radical damage also at mitochondrial liver level.

Duration of coffee- and exercise-induced changes in the fatty acid profile of human serum

Prolonged moderate exercise increases the concentration of nonesterified fatty acids (NEFA) and the ratio of unsaturated to saturated (U/S) NEFA in human plasma. The present study examined the duration of these effects and compared them with the effects of coffee ingestion. On separate days and in random order, seven men and six women 1) cycled for 1 h, 2) ingested coffee containing 5 mg caffeine/kg body mass, 3) ingested coffee followed by exercise 1 h later, and 4) did nothing. Blood samples were drawn at 0, 1, 2, 4, 8, 12, and 24 h. Serum was analyzed for lactate, glucose, glycerol, individual NEFA, triacylglycerols, total cholesterol, and HDL cholesterol. Exercise elevated the U/S NEFA and the percentage of oleate, while decreasing the percentages of palmitate and stearate, at the end of exercise but not subsequently. Consumption of coffee triggered a lower lipolytic response with no alterations in U/S or percentages of individual NEFA. These findings may prove useful in discovering mechanisms mediating the effects of exercise training on the fatty acid profile of human tissues.

Effect of aging and late onset dietary restriction on antioxidant enzymes and proteasome activities, and protein carbonylation of rat skeletal muscle and tendon

Many studies have shown that lifelong dietary restriction (DR) can retard aging processes. Very few reports, however, are found that examined the effect of late onset DR on biochemical parameters in aging animals [Goto, S., Takahashi, R., Araki, S., Nakamoto, H., 2002b. Dietary restriction initiated in late adulthood can reverse age-related alterations of protein and protein metabolism. Ann. NY Acad. Sci. 959, 50-56]. We studied the effect of every-other-day feeding, initiated at the age of 26.5 months and continued for 3.5 months, on antioxidant enzymes, protein carbonyls, and proteasomes of the gastrocnemius muscle and tendon in rats. Age-related increase in the activity and content of Cu, Zn-SOD and the content of Mn-SOD was attenuated by the DR in both tissues. The same was true for glutathione peroxidase and catalase activities. Significant increase with age in protein reactive carbonyl derivatives (RCD) in the tendon was noted that was partially reversed by the DR. No significant change of RCD, however, was observed in the skeletal muscle. The age-related and DR-induced changes of the RCD in the tendon appeared to be associated with proteasome activity that decreases with age and increases by the DR. It is suggested that the late onset DR can have beneficial effects on the locomotive functions by reducing age-associated potentially detrimental oxidative protein damage in the tendon.

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.

Impairment of proteasome structure and function in aging

Damage to macromolecules, and in particular protein, implicated in the cellular degeneration that occurs during the aging process, is corroborated by the accumulation of oxidative end-products over time. Oxidized protein build up is commonly seen as a hallmark of cellular aging. Protein turnover is essential to preserve cell function and the main proteolytic system in charge of cytosolic protein degradation is the proteasome. The proteasome is a multi-catalytic proteolytic complex, which recognizes and selectively degrades oxidatively damaged and ubiquitinated proteins. One of the hypothesis put forward to explain the accumulation of altered proteins is the decrease of proteasome activity with age. Indeed, accumulation of altered protein can be explained by increased protein alteration, decreased protein degradation or the combination of both. A short description of proteasome structure and of its role in cellular functions is first given. Then, accumulation of damaged protein is presented with emphasis on the pathways implicated in the formation of altered proteins. Finally, evidence for an age-related impairment of proteasome structure and function that has been reported by different groups is provided in the light of proteasomal dysfunction induced upon oxidative stress. It is now clear that proteasome activity is declining with age and that the loss in proteasome activity during aging is dependent of at least three different mechanisms: decreased proteasome expression; alterations and/or replacement of proteasome subunits and formation of inhibitory cross-linked proteins. However, it is also clear that events leading to the age- and disease-related loss of proteasome function have not yet been fully characterized.