Aging and brain rejuvenation as systemic events

The effects of aging were traditionally thought to be immutable, particularly evident in the loss of plasticity and cognitive abilities occurring in the aged central nervous system (CNS). However, it is becoming increasingly apparent that extrinsic systemic manipulations such as exercise, caloric restriction, and changing blood composition by heterochronic parabiosis or young plasma administration can partially counteract this age‐related loss of plasticity in the aged brain. In this review, we discuss the process of aging and rejuvenation as systemic events. We summarize genetic studies that demonstrate a surprising level of malleability in organismal lifespan, and highlight the potential for systemic manipulations to functionally reverse the effects of aging in the CNS. Based on mounting evidence, we propose that rejuvenating effects of systemic manipulations are mediated, in part, by blood‐borne ‘pro‐youthful’ factors. Thus, systemic manipulations promoting a younger blood composition provide effective strategies to rejuvenate the aged brain. As a consequence, we can now consider reactivating latent plasticity dormant in the aged CNS as a means to rejuvenate regenerative, synaptic, and cognitive functions late in life, with potential implications even for extending lifespan.

     

Ageing of the heart reversed by youthful systemic factors!

Cell (2013) 153: 828–839Age-associated changes in tissue maintenance and repair have severe consequences to human physiology. The signals and mechanisms that cause age-related tissue demise are unclear. A recently published study in Cell (Loffredo et al, 2013) proposes that blood-borne factors in the adult systemic environment are lost during ageing, which leads to cardiac hypertrophy. One such factor is GDF11. Exposure of aged mice to youthful systemic factors or GDF11 decreases cardiac hypertrophy of the heart.The ageing process is associated with a loss of tissue function through disrupted homeostatic and regenerative mechanisms (Liu and Rando, 2011). Throughout the life of any organism, the cells of the body experience various extrinsic and intrinsic changes that ultimately impact tissue function. The relative contribution of extrinsic factors and intrinsic modifications that can impact any cell is likely to be dependent on the function of the cell, its turnover throughout life and the environment in which it resides.The regenerative decline of many tissues observed during ageing is thought to be due to stem cell demise, regulated in part through changes in the composition of blood-borne factors present in the systemic environment. Parabiosis is an experimental paradigm used to study the role of blood-borne factors in many cellular processes (Finerty, 1952). In this technique, two mice are surgically joined and develop a shared blood circulation; therefore, the tissues of one mouse are exposed to its partner''s circulatory factors. Parabiosis studies involving adult and aged mice have revealed the presence of stimulatory and repressive blood-borne factors in the systemic environment that impact stem and progenitor cell function in response to injury (Conboy et al, 2005; Brack et al, 2007; Villeda et al, 2011; Ruckh et al, 2012). However, tissues that do not rely on stem cells also undergo age-dependent decline. For example, the cardiac muscle undergoes ventricular hypertrophy during ageing, often leading to diastolic heart failure due to the increased size of individual differentiated cardiac myocytes. Is this also regulated by the systemic environment and, if so, how?In their present work, Loffredo et al (2013) have tested the hypothesis that age-dependent changes in systemic factors promote cardiac hypertrophy. The authors report an age-dependent increase in cardiac myocyte size that is coupled to increased weight of the heart muscle. Remarkably, 4 weeks of parabiosis led to a significant reversion of age-induced cardiac hypertrophy. Importantly, these effects were gender-independent and did not arise from the parabiosis technique itself, or changes in blood pressure. The authors identified that the myocyte cross-sectional area was decreased in aged mice paired with adult mice, and thus blood-borne factors were acting directly on the terminally differentiated cell. In comparison, analysis of adult mice that were paired with aged mice for up to 10 weeks did not show any change in the size of myocyte or weight of the heart. Together, these results are consistent with the loss of youthful factors in the aged systemic milieu that repress myocyte size rather than the accumulation of hypertrophic factors during ageing. Loffredo et al (2013) also investigated the molecular nature of cardiac hypertrophy, using a few molecular markers of cardiac hypertrophy, such as brain natriuretic peptide (BNP) and atrial brain natriuretic peptide (ANP). From this result, the authors claim that circulatory factors can reverse some molecular aspects of cardiac ageing.Identification of the blood-borne factors that impact ageing is of obvious significance. The authors used an aptamer-based proteomic platform to hunt for the ‘fountain of youth.'' Aptamers are chemically modified nucleotides that act as highly specific protein binding reagents. They can be multiplexed and transformed into a quantifiable readout using a hybridization array. Using this method and by validating using western blots, the authors show that levels of growth differentiation factor 11 (GDF11), a TGFβ superfamily member, were consistently lower in aged compared to adult plasma.To test whether GDF11 was sufficient to reverse age-induced cardiac hypertrophy, recombinant GDF11 was delivered daily via intraperitoneal injection for 30 days to aged mice. GDF11 administration led to a significant decline in weight and left ventricular cross-sectional area of the aged heart, albeit not a complete reversion to that of an adult heart. That GDF11 did not achieve complete revision of hypertrophy may be due to technical reasons, such as non-uniform access of the injected protein to the cardiomyocytes, or biological reasons, such as non-overlapping signalling pathways that control cardiomyocyte size. Nevertheless, the fact that single growth factors can be injected into the blood stream to substantially decrease age-dependent cardiac hypertrophy is a tantalizing prospect for the treatment of human cardiac hypertrophy (Figure 1).Open in a separate windowFigure 1In adult mice, the presence of GDF11 in the systemic environment acts to restrain cardiac myocyte size. Loss of blood-borne GDF11 in aged mice drives cardiac myocyte hypertrophy. Exposure of aged mice to youthful systemic factors through parabiosis or injection of GDF11 reverses morphological and molecular markers (AMP and BNP) of age-induced cardiac hypertrophy.To test the utility of GDF11 treatment in reversing other models of cardiac hypertrophy, two different approaches were tested: (1) phenylephrine-induced hypertrophy of neonatal cardiomyocytes in vitro and (2) pressure overload, via aortic constriction of adult mouse heart. These two assays provided contrasting results; phenylephrine-induced hypertrophy as measured by protein synthesis rate (3H leucine incorporation) was prevented by prior incubation with GDF11 and its TGFβ superfamily member, Myostatin, whereas pressure overload hypertrophy was not mitigated by GFD11 treatment, administered after aortic constriction.Therefore, ageing-induced cardiac hypertrophy may have a distinct causality (decreased levels of GDF11) compared to acute models of hypertrophy in adult mice. It is also possible that additional cooperatively acting signalling pathways participate in adult hypertrophy. This would act to minimize any effects of GDF11 augmentation in adult mice. In addition, there may be a specific time window relative to hypertrophic stimuli, owing to which GDF11 treatment elicits a more favourable cellular outcome. The results presented by Loffredo et al (2013) illustrate the complexity of studying the mechanisms behind the disease pathology.Seeking to identify the source of GDF11, the authors measured GDF11 levels across different tissues. Its expression was most abundant in the adult spleen and decreased during ageing. Interestingly, GDF11 was also observed at the intercalated discs of aged hearts. A couple of questions arise from these observations. Is the adult spleen the source of cardiac GDF11 and why is the GDF11 that is located in aged hearts insufficient to protect from hypertrophy? Answering these questions will be experimentally challenging but nonetheless important.This report identifies a blood-borne factor that is abundantly expressed in adult mice and acts to repress cardiac hypertrophy. Circulatory factors have the potential to act on multiple cell types. The present study illustrates that systemic factors can influence the size of terminally differentiated cells. Does GDF11 regulate the cell size of other tissues? In contrast to the cardiac muscle, other tissues such as bone and skeletal muscle undergo atrophy during ageing; thus, it is unlikely that decreasing levels of GDF11 in the aged systemic environment function to increase the cell size of multiple tissues during ageing. However, there may be other positive roles of blood-borne GDF11 in younger mice. For example, the stimulatory effect of youthful systemic factors on tissue regeneration may involve GDF11.A picture is beginning to emerge whereby multiple factors found in adult (GDF11) and aged (TGFβ2, Complement C1q and CCL11) serum can alter cell function (Villeda et al, 2011; Naito et al, 2012; Loffredo et al, 2013). In addition, it is apparent that the aged niche becomes deregulated, leading to a loss of stem cell homeostasis (Chakkalakal et al, 2012). Future work should focus on understanding how distinct factors from the systemic environment and the microenvironment integrate to dictate cellular outcome across different tissues during ageing.     

Growth differentiation factor 15 protects against the aging‐mediated systemic inflammatory response in humans and mice

Mitochondrial dysfunction is associated with aging‐mediated inflammatory responses, leading to metabolic deterioration, development of insulin resistance, and type 2 diabetes. Growth differentiation factor 15 (GDF15) is an important mitokine generated in response to mitochondrial stress and dysfunction; however, the implications of GDF15 to the aging process are poorly understood in mammals. In this study, we identified a link between mitochondrial stress‐induced GDF15 production and protection from tissue inflammation on aging in humans and mice. We observed an increase in serum levels and hepatic expression of GDF15 as well as pro‐inflammatory cytokines in elderly subjects. Circulating levels of cell‐free mitochondrial DNA were significantly higher in elderly subjects with elevated serum levels of GDF15. In the BXD mouse reference population, mice with metabolic impairments and shorter survival were found to exhibit higher hepatic Gdf15 expression. Mendelian randomization links reduced GDF15 expression in human blood to increased body weight and inflammation. GDF15 deficiency promotes tissue inflammation by increasing the activation of resident immune cells in metabolic organs, such as in the liver and adipose tissues of 20‐month‐old mice. Aging also results in more severe liver injury and hepatic fat deposition in Gdf15‐deficient mice. Although GDF15 is not required for Th17 cell differentiation and IL‐17 production in Th17 cells, GDF15 contributes to regulatory T‐cell‐mediated suppression of conventional T‐cell activation and inflammatory cytokines. Taken together, these data reveal that GDF15 is indispensable for attenuating aging‐mediated local and systemic inflammation, thereby maintaining glucose homeostasis and insulin sensitivity in humans and mice.     

Systematic age‐, organ‐, and diet‐associated ionome remodeling and the development of ionomic aging clocks

Aging involves coordinated yet distinct changes in organs and systems throughout life, including changes in essential trace elements. However, how aging affects tissue element composition (ionome) and how these changes lead to dysfunction and disease remain unclear. Here, we quantified changes in the ionome across eight organs and 16 age groups of mice. This global profiling revealed novel interactions between elements at the level of tissue, age, and diet, and allowed us to achieve a broader, organismal view of the aging process. We found that while the entire ionome steadily transitions along the young‐to‐old trajectory, individual organs are characterized by distinct element changes. The ionome of mice on calorie restriction (CR) moved along a similar but shifted trajectory, pointing that at the organismal level this dietary regimen changes metabolism in order to slow down aging. However, in some tissues CR mimicked a younger state of control mice. Even though some elements changed with age differently in different tissues, in general aging was characterized by the reduced levels of elements as well as their increased variance. The dataset we prepared also allowed to develop organ‐specific, ionome‐based markers of aging that could help monitor the rate of aging. In some tissues, these markers reported the lifespan‐extending effect of CR. These aging biomarkers have the potential to become an accessible tool to test the age‐modulating effects of interventions.     

The role of GDF11 in aging and skeletal muscle,cardiac and bone homeostasis

GDF11 is a secreted factor in the TGFß family of cytokines. Its nearest neighbor evolutionarily is myostatin, a factor discovered as being a negative regulator of skeletal muscle growth. High profile studies several years ago suggested that GDF11 declines with age, and that restoration of systemic GDF11 to ‘youthful’ levels is beneficial for several age-related conditions. Particularly surprising was a report that supplementation of GDF11 aided skeletal muscle regeneration, as its homolog, myostatin, has the opposite role. Given this apparent contradiction in functionality, multiple independent labs sought to discern differences between the two factors and better elucidate age-related changes in circulating GDF11, with most failing to reproduce the initial finding of declining GDF11 levels, and, importantly, all subsequent studies examining the effects of GDF11 on skeletal muscle described an inhibitory effect on regeneration – and that higher doses induce skeletal muscle atrophy and cachexia. There have also been several studies examining the effect of GDF11 and/or the downstream ActRII pathway on cardiac function, along with several interesting reports on bone. A review of the GDF11 literature, as it relates in particular to aging and skeletal muscle, cardiac and bone biology, is presented.     

GDF15 as a central mediator for integrated stress response and a promising therapeutic molecule for metabolic disorders and NASH

BackgroundMitochondria is a key organelle for energy production and cellular adaptive response to intracellular and extracellular stresses. Mitochondrial stress can be evoked by various stimuli such as metabolic stressors or pathogen infection, which may lead to expression of ‘mitokines’ such as growth differentiation factor 15 (GDF15).Scope of reviewThis review summarizes the mechanism of GDF15 expression in response to organelle stress such as mitochondrial stress, and covers pathophysiological conditions or diseases that are associated with elevated GDF15 level. This review also illustrates the in vivo role of GDF15 expression in those stress conditions or diseases, and a potential of GDF15 as a therapeutic agent against metabolic disorders such as NASH.Major conclusionsMitochondrial unfolded protein response (UPRmt) is a critical process to recover from mitochondrial stress. UPRmt can induce expression of secretory proteins that can exert systemic effects (mitokines) as well as mitochondrial chaperons. GDF15 can have either protective or detrimental systemic effects in response to mitochondrial stresses, suggesting its role as a mitokine. Mounting evidence shows that GDF15 is also induced by stresses of organelles other than mitochondria such as endoplasmic reticulum (ER). GDF15 level is increased in serum or tissue of mice and human subjects with metabolic diseases such as obesity or NASH. GDF15 can modulate metabolic features of those diseases.General significanceGDF15 play a role as an integrated stress response (ISR) beyond mitochondrial stress response. GDF15 is involved in the pathogenesis of metabolic diseases such as NASH, and also could be a candidate for therapeutic agent against those diseases.     

Targeted Approach to Distinguish and Determine Absolute Levels of GDF8 and GDF11 in Mouse Serum

Growth differentiation factor 11 (GDF11) is a TGF‐β superfamily circulating factor that regulates cardiomyocyte size in rodents, sharing 90% amino acid sequence identity in the active domains with myostatin (GDF8)—the major determinant of skeletal muscle mass. Conflicting data on age‐related changes in circulating levels have been reported mainly due to the lack of specific detection methods. More recently, liquid chromatography tandem mass spectrometry (LC‐MS/MS) based assay showed that the circulating levels of GDF11 do not change significantly throughout human lifespan, but GDF8 levels decrease with aging in men. Here a novel detection method is demonstrated based on parallel reaction monitoring LC‐MS/MS assay combined with immunoprecipitation to reliably distinguish GDF11 and GDF8 as well as determine their endogenous levels in mouse serum. The data indicate that both GDF11 and GDF8 circulating levels significantly decline with aging in female mice.     

Targeting tissue-specific metabolic signaling pathways in aging: the promise and limitations

It has been well established that most of the age-related diseases such as insulin resistance, type 2 diabetes, hypertension, cardiovascular disease, osteoporosis, and atherosclerosis are all closely related to metabolic dysfunction. On the other hand, interventions on metabolism such as calorie restriction or genetic manipulations of key metabolic signaling pathways such as the insulin and mTOR signaling pathways slow down the aging process and improve healthy aging. These findings raise an important question as to whether improving energy homeostasis by targeting certain metabolic signaling pathways in specific tissues could be an effective anti-aging strategy. With a more comprehensive understanding of the tissue-specific roles of distinct metabolic signaling pathways controlling energy homeostasis and the cross-talks between these pathways during aging may lead to the development of more effective therapeutic interventions not only for metabolic dysfunction but also for aging.     

In vivo GDF3 administration abrogates aging related muscle regeneration delay following acute sterile injury

Tissue regeneration is a highly coordinated process with sequential events including immune cell infiltration, clearance of damaged tissues, and immune‐supported regrowth of the tissue. Aging has a well‐documented negative impact on this process globally; however, whether changes in immune cells per se are contributing to the decline in the body’s ability to regenerate tissues with aging is not clearly understood. Here, we set out to characterize the dynamics of macrophage infiltration and their functional contribution to muscle regeneration by comparing young and aged animals upon acute sterile injury. Injured muscle of old mice showed markedly elevated number of macrophages, with a predominance for Ly6C^high pro‐inflammatory macrophages and a lower ratio of the Ly6C^low repair macrophages. Of interest, a recently identified repair macrophage‐derived cytokine, growth differentiation factor 3 (GDF3), was markedly downregulated in injured muscle of old relative to young mice. Supplementation of recombinant GDF3 in aged mice ameliorated the inefficient regenerative response. Together, these results uncover a deficiency in the quantity and quality of infiltrating macrophages during aging and suggest that in vivo administration of GDF3 could be an effective therapeutic approach.     

Growth differentiation factor 11 promotes differentiation of MSCs into endothelial‐like cells for angiogenesis

Growth differentiation factor 11 (GDF11) is a member of the transforming growth factor‐β super family. It has multiple effects on development, physiology and diseases. However, the role of GDF11 in the development of mesenchymal stem cells (MSCs) is not clear. To explore the effects of GDF11 on the differentiation and pro‐angiogenic activities of MSCs, mouse bone marrow–derived MSCs were engineered to overexpress GDF11 (MSC^GDF11) and their capacity for differentiation and paracrine actions were examined both in vitro and in vivo. Expression of endothelial markers CD31 and VEGFR2 at the levels of both mRNA and protein was significantly higher in MSC^GDF11 than control MSCs (MSC^Vector) during differentiation. More tube formation was observed in MSC^GDF11 as compared with controls. In an in vivo angiogenesis assay with Matrigel plug, MSC^GDF11 showed more differentiation into CD31⁺ endothelial‐like cells and better pro‐angiogenic activity as compared with MSC^Vector. Mechanistically, the enhanced differentiation by GDF11 involved activation of extracellular‐signal‐related kinase (ERK) and eukaryotic translation initiation factor 4E (EIF4E). Inhibition of either TGF‐β receptor or ERK diminished the effect of GDF11 on MSC differentiation. In summary, our study unveils the function of GDF11 in the pro‐angiogenic activities of MSCs by enhancing endothelial differentiation via the TGFβ‐R/ERK/EIF4E pathway.     

Macrophage inhibitory cytokine‐1 (MIC‐1/GDF15): a new marker of all‐cause mortality

Macrophage inhibitory cytokine‐1 (MIC‐1/GDF15) is a member of the TGF‐b superfamily, previously studied in cancer and inflammation. In addition to regulating body weight, MIC‐1/GDF15 may be used to predict mortality and/or disease course in cancer, cardiovascular disease (CVD), chronic renal and heart failure, as well as pulmonary embolism. These data suggested that MIC‐1/GDF15 may be a marker of all‐cause mortality. To determine whether serum MIC‐1/GDF15 estimation is a predictor of all‐cause mortality, we examined a cohort of 876 male subjects aged 35–80 years, selected from the Swedish Population Registry, and followed them for overall mortality. Serum MIC‐1/GDF15 levels were determined for all subjects from samples taken at study entry. A second (independent) cohort of 324 same‐sex twins (69% female) from the Swedish Twin Registry was similarly examined. All the twins had telomere length measured and 183 had serum levels of interleukin 6 (IL‐6) and C‐reactive protein (CRP) available. Patients were followed for up to 14 years and had cause‐specific and all‐cause mortality determined. Serum MIC‐1/GDF15 levels predicted mortality in the all‐male cohort with an adjusted odds ratio (OR) of death of 3.38 (95%CI 1.38–8.26). This finding was validated in the twin cohort. Serum MIC‐1/GDF15 remained an independent predictor of mortality when further adjusted for telomere length, IL‐6 and CRP. Additionally, serum MIC‐1/GDF15 levels were directly correlated with survival time independently of genetic background. Serum MIC‐1/GDF15 is a novel predictor of all‐cause mortality.     

Sir2-independent life span extension by calorie restriction in yeast

Calorie restriction slows aging and increases life span in many organisms. In yeast, a mechanistic explanation has been proposed whereby calorie restriction slows aging by activating Sir2. Here we report the identification of a Sir2-independent pathway responsible for a majority of the longevity benefit associated with calorie restriction. Deletion of FOB1 and overexpression of SIR2 have been previously found to increase life span by reducing the levels of toxic rDNA circles in aged mother cells. We find that combining calorie restriction with either of these genetic interventions dramatically enhances longevity, resulting in the longest-lived yeast strain reported thus far. Further, calorie restriction results in a greater life span extension in cells lacking both Sir2 and Fob1 than in cells where Sir2 is present. These findings indicate that Sir2 and calorie restriction act in parallel pathways to promote longevity in yeast and, perhaps, higher eukaryotes.     

Calorie restriction-like effects of 30 days of resveratrol supplementation on energy metabolism and metabolic profile in obese humans

Resveratrol is a natural compound that affects energy metabolism and mitochondrial function and serves as a calorie restriction mimetic, at least in animal models of obesity. Here, we treated 11 healthy, obese men with placebo and 150?mg/day resveratrol (resVida) in a randomized double-blind crossover study for 30?days. Resveratrol significantly reduced sleeping and resting metabolic rate. In muscle, resveratrol activated AMPK, increased SIRT1 and PGC-1α protein levels, increased citrate synthase activity without change in mitochondrial content, and improved muscle mitochondrial respiration on a fatty acid-derived substrate. Furthermore, resveratrol elevated intramyocellular lipid levels and decreased intrahepatic lipid content, circulating glucose, triglycerides, alanine-aminotransferase, and inflammation markers. Systolic blood pressure dropped and HOMA index improved after resveratrol. In the postprandial state, adipose tissue lipolysis and plasma fatty acid and glycerol decreased. In conclusion, we demonstrate that 30?days of resveratrol supplementation induces metabolic changes in obese humans, mimicking the effects of calorie restriction.     

ROS induced DNA damage and checkpoint responses: Influences on aging?

The free radical theory of aging sustains that reactive oxygen species (ROS) induce cellular damage limiting organismal fitness but experimental data do not clearly support this hypothesis. Mouse models have shown that severe alterations of ROS metabolism can result in impairments of organ homeostasis and premature organ failure. However, partial impairments in anti-oxidants defence did not influence the aging process in laboratory mice and most clinical studies on antioxidants treatments in humans failed to show clear beneficial effects. Studies on telomere dysfunctional mice could also not reveal cooperating effects of ROS and telomere dysfunction in accelerating aging. Together, it seems that mild increases of ROS levels do not significantly influence the natural rate of aging. There is even some evidence that ROS induction is required to mediate positive effects of calorie restriction and physical exercise on organismal fitness and longevity.     

热量限制延长寿命的分子机制

很多研究均发现,热量限制在很多物种中都有延长寿命的作用.这些报道认为,寿命的延长可 能与氧化应激和炎症过程有关.值得注意的是,热量限制调节氧化应激与脂质代谢调控、抑 制细胞凋亡、DNA保护等分子过程有密切关系.最近,有研究者表明,热量限制调控氧化应激和炎症过程是通过胰岛素/胰岛素样生长因子信号通路起作用的.热量限制在所有的动物模型实验中都显示延长寿命,然而,在人类中应用热量限制,可能还存在很多对人体健康问题值得关注.本文就热量限制如何调控寿命的机制的研究进展作一综述.     

Yeast as a model to understand the interaction between genotype and the response to calorie restriction

Calorie restriction is reported to enhance survival and delay the onset of age-related decline in many different species. Several proteins have been proposed to play a role in mediating the response to calorie restriction, including the target of rapamycin kinase, sirtuins, and AMP kinase. An enhanced mechanistic understanding of calorie restriction has popularized the concept of "calorie restriction mimetics", drugs that mimic the beneficial effects of caloire restriction without requiring a reduction in nutrient intake. In theory, such drugs should delay the onset and progression of multiple age-related diseases, similar to calorie restriction in mammals. Despite the potential benefits of such calorie restriction mimetics, however, relatively little is known about the interaction between genetic variation and individual response to calorie restriction. Limited evidence from model systems indicates that genotype plays a large role in determining both the magnitude and direction of effect that calorie restriction has on longevity. Here we present an overview of these data from the perspective of using yeast as a model to study aging and describe an approach we are taking to further characterize the molecular mechanisms underlying genotype-dependent responses to calorie restriction.     

Effect of exercise and calorie restriction on biomarkers of aging in mice

Unlike calorie restriction, exercise fails to extend maximum life span, but the mechanisms that explain this disparate effect are unknown. We used a 24-wk protocol of treadmill running, weight matching, and pair feeding to compare the effects of exercise and calorie restriction on biomarkers related to aging. This study consisted of young controls, an ad libitum-fed sedentary group, two groups that were weight matched by exercise or 9% calorie restriction, and two groups that were weight matched by 9% calorie restriction + exercise or 18% calorie restriction. After 24 wk, ad libitum-fed sedentary mice were the heaviest and fattest. When weight-matched groups were compared, mice that exercised were leaner than calorie-restricted mice. Ad libitum-fed exercise mice tended to have lower serum IGF-1 than fully-fed controls, but no difference in fasting insulin. Mice that underwent 9% calorie restriction or 9% calorie restriction + exercise, had lower insulin levels; the lowest concentrations of serum insulin and IGF-1 were observed in 18% calorie-restricted mice. Exercise resulted in elevated levels of tissue heat shock proteins, but did not accelerate the accumulation of oxidative damage. Thus, failure of exercise to slow aging in previous studies is not likely the result of increased accrual of oxidative damage and may instead be due to an inability to fully mimic the hormonal and/or metabolic response to calorie restriction.     

Sir-2.1 modulates 'calorie-restriction-mediated' prevention of neurodegeneration in Caenorhabditis elegans: implications for Parkinson's disease

The phenomenon of aging is known to modulate many disease conditions including neurodegenerative ailments like Parkinson’s disease (PD) which is characterized by selective loss of dopaminergic neurons. Recent studies have reported on such effects, as calorie restriction, in modulating aging in living systems. We reason that PD, being an age-associated neurodegenerative disease might be modulated by interventions like calorie restriction. In the present study we employed the transgenic Caenorhabditis elegans model (P_dat-1::GFP) expressing green fluorescence protein (GFP) specifically in eight dopaminergic (DA) neurons. Selective degeneration of dopaminergic neurons was induced by treatment of worms with 6-hydroxy dopamine (6-OHDA), a selective catecholaminergic neurotoxin, followed by studies on effect of calorie restriction on the neurodegeneration. Employing confocal microscopy of the dopaminergic neurons and HPLC analysis of dopamine levels in the nematodes, we found that calorie restriction has a preventive effect on dopaminergic neurodegeneration in the worm model. We further studied the role of sirtuin, sir-2.1, in modulating such an effect. Studies employing RNAi induced gene silencing of nematode sir-2.1, revealed that presence of Sir-2.1 is necessary for achieving the protective effect of calorie restriction on dopaminergic neurodegeneration.Our studies provide evidence that calorie restriction affords, an sir-2.1 mediated, protection against the dopaminergic neurodegeneration, that might have implications for neurodegenerative Parkinson’s disease.     

Altered expression of claudin family proteins in Alzheimer’s disease and vascular dementia brains

Claudins (Cls) are a multigene family of transmembrane proteins with different tissue distribution, which have an essential role in the formation and sealing capacity of tight junctions (TJs). At the level of the blood–brain barrier (BBB), TJs are the main molecular structures which separate the neuronal milieu from the circulatory space, by a restriction of the paracellular flow of water, ions and larger molecules into the brain. Different studies suggested recently significant BBB alterations in both vascular and degenerative dementia types. In a previous study we found in Alzheimer’s disease (AD) and vascular dementia (VaD) brains an altered expression of occludin, a molecular partner of Cls in the TJs structure. Therefore in this study, using an immunohistochemical approach, we investigated the expression of Cl family proteins (Cl‐2, Cl‐5 and Cl‐11) in frontal cortex of aged control, AD and VaD brains. To estimate the number of Cl‐expressing cells, we applied a random systematic sampling and the unbiased optical fractionator method. We found selected neurons, astrocytes, oligodendrocytes and endothelial cells expressing Cl‐2, Cl‐5 and Cl‐11 at detectable levels in all cases studied. We report a significant increase in ratio of neurons expressing Cl‐2, Cl‐5 and Cl‐11 in both AD and VaD as compared to aged controls. The ratio of astrocytes expressing Cl‐2 and Cl‐11 was significantly higher in AD and VaD as compared to aged controls. The ratio of oligodendrocytes expressing Cl‐11 was significantly higher in AD and the ratio of oligodendrocytes expressing Cl‐2 was significantly higher in VaD as compared to aged controls. Within the cerebral cortex, Cls were selectively expressed by pyramidal neurons, which are the ones responsible for cognitive processes and affected by AD pathology. Our findings suggest a new function of Cl family proteins which might be linked to response to cellular stress.