Optimal window of caloric restriction onset limits its beneficial impact on T-cell senescence in primates

The complex relationship between late-onset caloric restriction and synaptic plasticity in aged Wistar rats

Age-related reduction in spine density, synaptic marker expression, and synaptic efficiency are frequently reported. These changes provide the cellular and molecular basis for the cognitive decline characteristic for old age. Nevertheless, there are several approaches that have the potential to ameliorate these processes and improve cognition, caloric restriction being one of the most promising and widely studied. While lifelong caloric restriction is known for its numerous beneficial effects, including improved cognitive abilities and increased expression of proteins essential for synaptic structure and function, the effects of late-onset and/or short-term CR on synaptic plasticity have yet to be investigated. We have previously documented that the effects of CR are strongly dependent on whether CR is initiated in young or old subjects. With this in mind, we conducted a long-term study in aging Wistar rats to examine changes in the expression of several key synaptic markers under the regimen of CR started at different time points in life. We found a significant increase in the expression of both presynaptic and postsynaptic markers. However, taking into account previously reported changes in the behavior detected in these animals, we consider that this increase cannot represent beneficial effect of CR.

Rapamycin not dietary restriction improves resilience against pathogens: a meta-analysis

Dietary restriction (DR) and rapamycin both increase lifespan across a number of taxa. Despite this positive effect on lifespan and other aspects of health, reductions in some physiological functions have been reported for DR, and rapamycin has been used as an immunosuppressant. Perhaps surprisingly, both interventions have been suggested to improve immune function and delay immunosenescence. The immune system is complex and consists of many components. Therefore, arguably, the most holistic measurement of immune function is survival from an acute pathogenic infection. We reanalysed published post-infection short-term survival data of mice (n = 1223 from 23 studies comprising 46 effect sizes involving DR (n = 17) and rapamycin treatment (n = 29) and analysed these results using meta-analysis. Rapamycin treatment significantly increased post infection survival rate (lnHR =  - 0.72; CI =  - 1.17, -0.28; p = 0.0015). In contrast, DR reduced post-infection survival (lnHR = 0.80; CI = 0.08, 1.52; p = 0.03). Importantly, the overall effect size of rapamycin treatment was significantly lower (p < 0.001) than the estimate from DR studies, suggesting opposite effects on immune function. Our results show that immunomodulation caused by rapamycin treatment is beneficial to the survival from acute infection. For DR, our results are based on a smaller number of studies, but do warrant caution as they indicate possible immune costs of DR. Our quantitative synthesis suggests that the geroprotective effects of rapamycin extend to the immune system and warrants further clinical trials of rapamycin to boost immunity in humans.

Control of immunity via nutritional interventions

Nutrition affects all physiological processes including those linked to the development and function of our immune system. Here, we discuss recent evidence and emerging concepts supporting the idea that our newfound relationship with nutrition in industrialized countries has fundamentally altered the way in which our immune system is wired. This will be examined through the lens of studies showing that mild or transient reductions in dietary intake can enhance protective immunity while also limiting aberrant inflammatory responses. We will further discuss how trade-offs and priorities begin to emerge in the context of severe nutritional stress. In those settings, specific immunological functions are heightened to re-enforce processes and tissue sites most critical to survival. Altogether, these examples will emphasize the profound influence nutrition has over the immune system and highlight how a mechanistic exploration of this cross talk could ultimately lead to the design of novel therapeutic approaches that prevent and treat disease.

Calorie Restriction for Cancer Prevention and Therapy: Mechanisms, Expectations, and Efficacy

Cancer is one of the most frequently diagnosed diseases, and despite the continuous efforts in searching for new and more effective treatments, its morbidity and mortality remain a significant health problem worldwide. Calorie restriction, a dietary manipulation that consists in a reduction of the calorie intake, is gaining attention as a potential adjuvant intervention for preventing and/or fighting cancer. Several forms of energy reduction intake, which includes caloric restriction tout-court, dietary restrictions, and intermittent fasting, are being explored for their ability to prevent or slow down cancer progression. Additionally, another anti-cancer approach being under investigation relies on the use of nutraceuticals known as “Caloric Restriction Mimetics” that can provide caloric restriction-mediated benefits without subjecting the patients to a strict diet. Preclinical in vitro and in vivo studies consistently show that diet modifiers reducing the calorie have impact on tumor microenvironment and cancer metabolism, resulting in reduced growth and progression of cancer. Preliminary clinical studies show that patients subjected to a reduced nutrient/energy intake experience improved outcomes from chemo- and radiotherapy while better tolerating the side effects. Here, we review the state of the art on the therapeutic potential of calorie restriction and of caloric restriction mimetics in preventing or retarding tumor development by modulating a subset of cellular processes. The most recent clinical progresses with caloric restriction mimetics in the clinical practice are also discussed.

The effect of caloric restriction on the increase in senescence-associated T cells and metabolic disorders in aged mice

Aging is associated with functional decline in the immune system and increases the risk of chronic diseases owing to smoldering inflammation. In the present study, we demonstrated an age-related increase in the accumulation of Programmed Death-1 (PD-1)⁺ memory-phenotype T cells that are considered “senescence-associated T cells” in both the visceral adipose tissue and spleen. As caloric restriction is an established intervention scientifically proven to exert anti-aging effects and greatly affects physiological and pathophysiological alterations with advanced age, we evaluated the effect of caloric restriction on the increase in this T-cell subpopulation and glucose tolerance in aged mice. Long-term caloric restriction significantly decreased the number of PD-1⁺ memory-phenotype cluster of differentiation (CD) 4⁺ and CD8⁺ T cells in the spleen and visceral adipose tissue, decreased M1-type macrophage accumulation in visceral adipose tissue, and improved insulin resistance in aged mice. Furthermore, the immunological depletion of PD-1⁺ T cells reduced adipose inflammation and improved insulin resistance in aged mice. Taken together with our previous report, these results indicate that senescence-related T-cell subpopulations are involved in the development of chronic inflammation and insulin resistance in the context of chronological aging and obesity. Thus, long-term caloric restriction and specific deletion of senescence-related T cells are promising interventions to regulate age-related chronic diseases.

Dietary Regulation of Memory T Cells

Memory T cells are a fundamental component of immunological memory, providing rapid and potent host protection against secondary challenges. As such, memory T cells are key targets in the design of vaccination strategies and cancer immunotherapies, making it critical to understand the factors and mechanisms that regulate their biology. Diet is an environmental feature that impacts virtually all aspects of host physiology. However, the influence of specific dietary regiments and nutritional components on the immune system is only just starting to be uncovered. This article will review literature regarding the impact of diet and nutrition on memory T cell development, maintenance and function. It was recently shown that caloric restriction without undernutrition enhances memory T cell function, while diets high in fiber are also beneficial. However, memory T cell responses are dysfunctional in extreme nutritional states, such as undernutrition and diet-induced obesity. Therefore, diet and host nutritional status are major regulators of memory T cell biology and host fitness. To define the dietary balance required to promote optimal memory T cell responses could allow for the implementation of rational diet-based therapies that prevent or treat disease. Furthermore, that certain dietary regiments can enhance memory T cell function indicates the possibility of harnessing the underlying mechanisms in the design of novel vaccination strategies and cancer immunotherapies.

Short-Term Caloric Restriction Attenuates Obesity-Induced Pro-Inflammatory Response in Male Rhesus Macaques

White adipose tissue (WAT) hypertrophy is an essential hallmark of obesity and is associated with the activation of resident immune cells. While the benefits of caloric restriction (CR) on health span are generally accepted, its effects on WAT physiology are not well understood. We previously demonstrated that short-term CR reverses obesity in male rhesus macaques exposed to a high-fat Western-style diet (WSD). Here, we analyzed subcutaneous WAT biopsies collected from this cohort of animals before and after WSD and following CR. This analysis showed that WSD induced adipocyte hypertrophy and inhibited β-adrenergic-simulated lipolysis. CR reversed adipocyte hypertrophy, but WAT remained insensitive to β-adrenergic agonist stimulation. Whole-genome transcriptional analysis revealed that β3-adrenergic receptor and de novo lipogenesis genes were downregulated by WSD and remained downregulated after CR. In contrast, WSD-induced pro-inflammatory gene expression was effectively reversed by CR. Furthermore, peripheral blood monocytes isolated during the CR period exhibited a significant reduction in the production of pro-inflammatory cytokines compared to those obtained after WSD. Collectively, this study demonstrates that short-term CR eliminates an obesity-induced pro-inflammatory response in WAT and peripheral monocytes.

Age-dependent effects of caloric restriction on mTOR and ubiquitin-proteasome pathways in skeletal muscles

In skeletal muscles, calorie restriction (CR) preserves muscle mass in middle-aged rats but not younger rats. The underlying mechanisms for this age-specific response are unknown. Skeletal muscle mass depends on several factors, with protein synthesis and degradation playing major roles. Therefore, the purpose of this study was to investigate whether CR affects younger and older animals differently on mTOR signaling and ubiquitin-proteasome pathway (UPP). Four-, 8-, and 16-month-old rats, with or without 40% CR for a duration of 14 weeks, were sacrificed after an overnight fasting. Total protein content and the phosphorylation level of AKT, mTOR, S6K, and 4EBP1 and protein content of key markers in the UPP (FOXO3a, atrogin, MuRF1, ubiquitinated proteins, proteasome subunits alpha 7 and beta 5) were determined. Unlike younger rats, CR decreased the content of phosphorylated mTOR, S6K, phosphorylated S6K, FOXO3a, and ubiquitinated proteins in middle-aged rats. In conclusion, CR-induced reduction of content/ phosphorylation levels of key proteins in mTOR signaling and the UPP occurred in the middle-aged rats but not younger rats. The age-dependent effects of CR on mTOR signaling and the UPP indirectly explained the age-related effects of CR on muscle mass of animals.

Lifestyle-based modifiable risk factors in multiple sclerosis: review of experimental and clinical findings

Multiple sclerosis (MS) is a lifelong inflammatory and neurodegenerative disease influenced by multiple lifestyle-based factors. We provide a narrative review of the effects of modifiable risk factors that are identified as being associated with risk to develop MS and/or influencing the future clinical disease outcomes. The emerging data regarding the beneficial effects of diet modifications and exercise are further reviewed. In contrast, obesity and comorbid cardiovascular diseases are associated with increased MS susceptibility and worse disease progression. In addition, the potential influence of smoking, coffee and alcohol consumption on MS onset and disability development are discussed. Successful management of the modifiable risk factors may lead to better long-term outcomes and improve patients' quality of life. MS specialists should participate in educating and facilitating lifestyle-based modifications as part of their neurological consults.

Nonhuman Primate Models of Immunosenescence

Due to a dramatic increase in life expectancy, the number of individuals aged 65 and older is rapidly rising. This presents considerable challenges to our health care system since advanced age is associated with a higher susceptibility to infectious diseases due to immune senescence. However, the mechanisms underlying age-associated dysregulated immunity are still incompletely understood. Advancement in our comprehension of mechanisms of immune senescence and development of interventions to improve health span requires animal models that closely recapitulate the physiological changes that occur with aging in humans. Nonhuman primates (NHPs) are invaluable preclinical models to study the underlying causal mechanism of pathogenesis due to their outbred nature, high degree of genetic and physiological similarity to humans, and their susceptibility to human pathogens. In this chapter, we review NHP models available for biogerontology research, advantages and challenges they present, and advances they facilitated. Furthermore, we emphasize the utility of NHPs in characterizing immune senescence, evaluating interventions to reverse aging of the immune system, and development of vaccine strategies that are better suited for this vulnerable population.

Age, calorie restriction, and age of calorie restriction onset reduce maturation of natural killer cells in C57Bl/6 mice

Calorie restriction (CR), also known as energy restriction, has been shown to have a deleterious impact on both adult and aged mouse survival during influenza virus infection. Natural killer (NK) cell phenotypic differences contribute to increased susceptibility of adult CR mice. We hypothesized NK cell phenotype from adult and aged C57Bl/6 mice fed NIH-31 diet ad libitum (AL) would be different from NK cell phenotype from adult and aged mice fed NIH-31/NIA fortified diet at 40% CR. We hypothesized NK cell phenotype from mice consuming 40% CR initiated at 20 months of age would not be different from 40% CR initiated at 3 months of age. We initiated the 40% restriction either at the standard 12 weeks of age or at 78 weeks of age. NK cells were isolated and quantified from various tissues using flow cytometry. Aged CR mice had significantly reduced levels of terminally mature (CD27^-CD11b⁺) NK cells, increased expression of the immature marker CD127, and decreased expression of the mature marker DX5. Total number of NK cells among cells was significantly lower in the lung and spleen of old-onset aged CR mice compared to aged AL mice, while there was no significant difference between young-onset aged CR and aged AL mice. Old-onset aged CR mice had significantly less early mature (DX5⁺ and CD27⁺CD11b⁺) NK cells compared to young-onset aged CR and aged AL fed mice. Overall, we found that CR in aged mice is detrimental to maturation of NK cells, which is exacerbated when CR is initiated in old age.

Brain and Hepatic Mt mRNA Is Reduced in Response to Mild Energy Restriction and n-3 Polyunsaturated Fatty Acid Deficiency in Juvenile Rats

Metallothioneins (MTs) perform important regulatory and cytoprotective functions in tissues including the brain. While it is known that energy restriction (ER) and dietary n-3 polyunsaturated fatty acid (PUFA) deficiency impact postnatal brain growth and development, little data exist regarding the impact of undernutrition upon MT expression in growing animals. We tested the hypothesis that ER with and without dietary n-3 PUFA deficiency reduces MT expression in juvenile rats. ER rats were individually pair-fed at 75% of the ad libitum (AL) intake of control rats provided diets consisting of either soybean oil (SO) that is α-linolenic acid (ALA; 18:3n-3) sufficient or corn oil (CO; ALA-deficient). Fatty acids (FA) and metal concentrations of liver and brain regions were analyzed. Tissue expression of MTs (Mt1-3) and modulators of MT expression including glucocorticoid receptors (Nr3c1 and Nr3c2) and several mediators of thyroid hormone regulation (Dio1-3, Mct8, Oatp1c1, Thra, and Thrb) were measured. Plasma corticosterone and triiodothyronine levels were also evaluated. ER, but not metal deficiency, reduced Mt2 expression in the cerebellum (50%) and cerebral cortex (23%). In liver, a reduction in dietary n-3 PUFA reduced Mt1, Mt2, Nr3c1, Mct8, and Thrb. ER elevated Nr3c1, Dio1, and Thrb and reduced Thra in the liver. Given MT’s role in cellular protection, further studies are needed to evaluate whether ER or n-3 PUFA deficiency may leave the juvenile brain and/or liver more susceptible to endogenous or environmental stressors.

Caloric restriction in young rats disturbs hippocampal neurogenesis and spatial learning

It is widely known that caloric restriction (CR) has benefits on several organic systems, including the central nervous system. However, the majority of the CR studies was performed in adult animals and the information about the consequences on young populations is limited. In this study, we analyzed the effects of young-onset CR, started at 4weeks of age, in the number of neuropeptide Y (NPY)-containing neurons and in neurogenesis of the hippocampal formation, using doublecortin (DCX) and Ki67 as markers. Knowing that CR treatment could interfere with exploratory activity, anxiety, learning and memory we have analyzed the performance of the rats in the open-field, elevated plus-maze and Morris water maze tests. Animals aged 4weeks were randomly assigned to control or CR groups. Controls were maintained in the ad libitum regimen during 2months. The adolescent CR rats were fed, during 2months, with 60% of the amount of food consumed by controls. We have found that young-onset CR treatment did not affect the total number of NPY-immunopositive neurons in dentate hilus, CA3 and CA1 hippocampal subfields and did not change the exploratory activity and anxiety levels. Interestingly, we have found that young-onset CR might affect spatial learning process since those animals showed worse performance during the acquisition phase of Morris water maze. Furthermore, young-onset CR induced alterations of neurogenesis in the dentate subgranular layer that seems to underlie the impairment of spatial learning. Our data suggest that adolescent animals are vulnerable to CR treatment and that this diet is not suitable to be applied in this age phase.

Contributions of Nonhuman Primates to Research on Aging

Aging is the biological process of declining physiologic function associated with increasing mortality rate during advancing age. Humans and higher nonhuman primates exhibit unusually longer average life spans as compared with mammals of similar body mass. Furthermore, the population of humans worldwide is growing older as a result of improvements in public health, social services, and health care systems. Comparative studies among a wide range of organisms that include nonhuman primates contribute greatly to our understanding about the basic mechanisms of aging. Based on their genetic and physiologic relatedness to humans, nonhuman primates are especially important for better understanding processes of aging unique to primates, as well as for testing intervention strategies to improve healthy aging and to treat diseases and disabilities in older people. Rhesus and cynomolgus macaques are the predominant monkeys used in studies on aging, but research with lower nonhuman primate species is increasing. One of the priority topics of research about aging in nonhuman primates involves neurologic changes associated with cognitive decline and neurodegenerative diseases. Additional areas of research include osteoporosis, reproductive decline, caloric restriction, and their mimetics, as well as immune senescence and chronic inflammation that affect vaccine efficacy and resistance to infections and cancer. The purpose of this review is to highlight the findings from nonhuman primate research that contribute to our understanding about aging and health span in humans.

Energy restriction impairs dendritic cell development in C57BL/6J mice

Dendritic cells (DC) are antigen-presenting cells known for stimulating naïve T lymphocytes. The sequential stages of DC development from common myeloid progenitors have been elucidated in murine bone marrow. Energy-restriction (ER) is a pro-longevity dietary intervention with mixed immunological outcomes. The objective of this study was to examine the development of DC in adult C57Bl6J mice fed a 40% ER diet. We observed increased myeloid progenitors, but decreased common DC progenitors, precursor conventional DC and plasmacytoid DC. Furthermore, we observed increased macrophages and cells expressing CD169 in the bone marrow of ER mice. There was no significant difference in DC subsets from unfractionated ER and ad libitum-fed murine bone marrow samples cultured in GM-CSF-supplemented media or Flt3L-supplemented media. Examining rates of proliferation with 6h BrdU incorporation and Ki-67 staining showed these DC progenitor populations have different proliferation rates in ER compared with AL mice. We show here, for the first time, ER results in altered myelopoiesis resulting in reduced DC development but enhanced monocyte/macrophage development in steady-state C57Bl6J mice. In conclusion, these data may partially explain prior observations of impaired early innate immune responses to primary infection such as influenza in ER mice.

Late-onset caloric restriction alters skeletal muscle metabolism by modulating pyruvate metabolism

Caloric restriction (CR) attenuates age-related muscle loss. However, the underlying mechanism responsible for this attenuation is not fully understood. This study evaluated the role of energy metabolism in the CR-induced attenuation of muscle loss. The aims of this study were twofold: 1) to evaluate the effect of CR on energy metabolism and determine its relationship with muscle mass, and 2) to determine whether the effects of CR are age dependent. Young and middle-aged rats were randomized into either 40% CR or ad libitum (AL) diet groups for 14 wk. Major energy-producing pathways in muscles, i.e., glycolysis and mitochondrial oxidative phosphorylation (OXPHOS), were examined. We found that the effects of CR were age dependent. CR improved muscle metabolism and normalized muscle mass in middle-aged animals but not young animals. CR decreased glycolysis and increased the cellular dependency for OXPHOS vs. glycolysis in muscles of middle-aged rats, which was associated with the improvement of normalized muscle mass. The metabolic reprogramming induced by CR was related to modulation of pyruvate metabolism and increased mitochondrial biogenesis. Compared with animals fed AL, middle-aged animals with CR had lower lactate dehydrogenase A content and greater mitochondrial pyruvate carrier content. Markers of mitochondrial biogenesis, including AMPK activation levels and SIRT1 and COX-IV content, also showed increased levels. In conclusion, 14 wk of CR improved muscle metabolism and preserved muscle mass in middle-aged animals but not in young developing animals. CR-attenuated age-related muscle loss is associated with reprogramming of the metabolic pathway from glycolysis to OXPHOS.

Targeting oxidized LDL improves insulin sensitivity and immune cell function in obese Rhesus macaques

Oxidation of LDL (oxLDL) is a crucial step in the development of cardiovascular disease. Treatment with antibodies directed against oxLDL can reduce atherosclerosis in rodent models through unknown mechanisms. We demonstrate that through a novel mechanism of immune complex formation and Fc-γ receptor (FcγR) engagement, antibodies targeting oxLDL (MLDL1278a) are anti-inflammatory on innate immune cells via modulation of Syk, p38 MAPK phosphorylation and NFκB activity. Subsequent administration of MLDL1278a in diet-induced obese (DIO) nonhuman primates (NHP) resulted in a significant decrease in pro-inflammatory cytokines and improved overall immune cell function. Importantly, MLDL1278a treatment improved insulin sensitivity independent of body weight change. This study demonstrates a novel mechanism by which an anti-oxLDL antibody improves immune function and insulin sensitivity independent of internalization of oxLDL. This identifies MLDL1278a as a potential therapy for reducing vascular inflammation in diabetic conditions.

The role of the T cell in age-related inflammation

Ageing is accompanied by alterations to T-cell immunity and also by a low-grade chronic inflammatory state termed inflammaging. The significance of these phenomena is highlighted by their being predictors of earlier mortality. We have recently published that the proinflammatory cytokine TNFα is a strong inducer of CD4(+) T-cell senescence and T-cell differentiation, adding to the growing body of literature implicating proinflammatory molecules in mediating these critical age-related T-cell alterations. Moreover, the inflammatory process is also being increasingly implicated in the pathogenesis of many common and severe age-related diseases, including cancer, cardiovascular diseases and type 2 diabetes. Furthermore, major age-related risk factors for poor health, such as obesity, stress and smoking, are also associated with an upregulation in systemic inflammatory markers. We propose the idea that the ensuing inflammatory response to influenza infection propagates cardiovascular diseases and constitutes a major cause of influenza-related mortality. While inflammation is not a negative phenomenon per se, this age-related dysregulation of inflammatory responses may play crucial roles driving age-related pathologies, T-cell immunosenescence and CMV reactivation, thereby underpinning key features of the ageing process.

Causes, consequences, and reversal of immune system aging

The effects of aging on the immune system are manifest at multiple levels that include reduced production of B and T cells in bone marrow and thymus and diminished function of mature lymphocytes in secondary lymphoid tissues. As a result, elderly individuals do not respond to immune challenge as robustly as the young. An important goal of aging research is to define the cellular changes that occur in the immune system and the molecular events that underlie them. Considerable progress has been made in this regard, and this information has provided the rationale for clinical trials to rejuvenate the aging immune system.

NK cell maturation and function in C57BL/6 mice are altered by caloric restriction

NK cells are a heterogenous population of innate lymphocytes with diverse functional attributes critical for early protection from viral infections. We have previously reported a decrease in influenza-induced NK cell cytotoxicity in 6-mo-old C57BL/6 calorically restricted (CR) mice. In the current study, we extend our findings on the influence of CR on NK cell phenotype and function in the absence of infection. We demonstrate that reduced mature NK cell subsets result in increased frequencies of CD127(+) NK cells in CR mice, skewing the function of the total NK cell pool. NK cells from CR mice produced TNF-α and GM-CSF at a higher level, whereas IFN-γ production was impaired following IL-2 plus IL-12 or anti-NK1.1 stimulation. NK cells from CR mice were highly responsive to stimulation with YAC-1 cells such that CD27(-)CD11b(+) NK cells from CR mice produced granzyme B and degranulated at a higher frequency than CD27(-)CD11b(+) NK cells from ad libitum fed mice. CR has been shown to be a potent dietary intervention, yet the mechanisms by which the CR increases life span have yet to be fully understood. To our knowledge, these findings are the first in-depth analysis of the effects of caloric intake on NK cell phenotype and function and provide important implications regarding potential ways in which CR alters NK cell function prior to infection or cancer.

Immune correlates of aging in outdoor-housed captive rhesus macaques (Macaca mulatta)

Background

Questions remain about whether inflammation is a cause, consequence, or coincidence of aging. The purpose of this study was to define baseline immunological characteristics from blood to develop a model in rhesus macaques that could be used to address the relationship between inflammation and aging. Hematology, flow cytometry, clinical chemistry, and multiplex cytokine/chemokine analyses were performed on a group of 101 outdoor-housed captive rhesus macaques ranging from 2 to 24 years of age, approximately equivalent to 8 to 77 years of age in humans.

Results

These results extend earlier reports correlating changes in lymphocyte subpopulations and cytokines/chemokines with increasing age. There were significant declines in numbers of white blood cells (WBC) overall, as well as lymphocytes, monocytes, and polymorphonuclear cells with increasing age. Among lymphocytes, there were no significant declines in NK cells and T cells, whereas B cell numbers exhibited significant declines with age. Within the T cell populations, there were significant declines in numbers of CD4+ naïve T cells and CD8+ naïve T cells. Conversely, numbers of CD4+CD8+ effector memory and CD8+effector memory T cells increased with age. New multiplex analyses revealed that concentrations of a panel of ten circulating cytokines/chemokines, IFNγ, IL1b, IL6, IL12, IL15, TNFα, MCP1, MIP1α, IL1ra, and IL4, each significantly correlated with age and also exhibited concordant pairwise correlations with every other factor within this group. To also control for outlier values, mean rank values of each of these cytokine concentrations in relation to age of each animal and these also correlated with age.

Conclusions

A panel of ten cytokines/chemokines were identified that correlated with aging and also with each other. This will permit selection of animals exhibiting relatively higher and lower inflammation status as a model to test mechanisms of inflammation status in aging with susceptibility to infections and vaccine efficacy.

Impact of caloric restriction on health and survival in rhesus monkeys from the NIA study

Calorie restriction (CR), a reduction of 10–40% in intake of a nutritious diet, is often reported as the most robust non-genetic mechanism to extend lifespan and healthspan. CR is frequently used as a tool to understand mechanisms behind ageing and age-associated diseases. In addition to and independently of increasing lifespan, CR has been reported to delay or prevent the occurrence of many chronic diseases in a variety of animals. Beneficial effects of CR on outcomes such as immune function, motor coordination and resistance to sarcopenia in rhesus monkeys have recently been reported. We report here that a CR regimen implemented in young and older age rhesus monkeys at the National Institute on Aging (NIA) has not improved survival outcomes. Our findings contrast with an ongoing study at the Wisconsin National Primate Research Center (WNPRC), which reported improved survival associated with 30% CR initiated in adult rhesus monkeys (7–14 years) and a preliminary report with a small number of CR monkeys. Over the years, both NIA and WNPRC have extensively documented beneficial health effects of CR in these two apparently parallel studies. The implications of the WNPRC findings were important as they extended CR findings beyond the laboratory rodent and to a long-lived primate. Our study suggests a separation between health effects, morbidity and mortality, and similar to what has been shown in rodents, study design, husbandry and diet composition may strongly affect the life-prolonging effect of CR in a long-lived nonhuman primate.

Improving immunity in the elderly: current and future lessons from nonhuman primate models

The immune system must overcome daily challenges from pathogens to protect the body from infection. The success of the immune response to infection relies on the ability to sense and evaluate microbial threats and organize their elimination, while limiting damage to host tissues. This delicate balance is achieved through coordinated action of the innate and adaptive arms of the immune system. Aging results in several structural and functional changes in the immune system, often described under the umbrella term "immune senescence". Age-related changes affect both the innate and adaptive arms of the immune system and are believed to result in increased susceptibility and severity of infectious diseases, which is further exacerbated by reduced vaccine efficacy in the elderly. Therefore, multiple strategies to improve immune function in the aged are being investigated. Traditionally, studies on immune senescence are conducted using inbred specific pathogen free (SPF) rodents. This animal model has provided invaluable insight into the mechanisms of aging. However, the limited genetic heterogeneity and the SPF status of this model restrict the successful transfer of immunological discoveries between murine models and the clinical setting. More recently, nonhuman primates (NHPs) have emerged as a leading translational model to investigate immune senescence and to test interventions aimed at delaying/reversing age-related changes in immune function. In this article, we review and summarize advances in immuno-restorative approaches investigated in the NHP model system and discuss where the NHP model can support the development of novel therapeutics.

The role of nutrition in enhancing immunity in aging

Aging is associated with declined immune function, particularly T cell-mediated activity, which contributes to increased morbidity and mortality from infectious disease and cancer in the elderly. Studies have shown that nutritional intervention may be a promising approach to reversing impaired immune function and diminished resistance to infection with aging. However, controversy exists concerning every nutritional regimen tested to date. In this article, we will review the progress of research in this field with a focus on nutrition factor information that is relatively abundant in the literature. While vitamin E deficiency is rare, intake above recommended levels can enhance T cell function in aged animals and humans. This effect is believed to contribute toward increased resistance to influenza infection in animals and reduced incidence of upper respiratory infection in the elderly. Zinc deficiency, common in the elderly, is linked to impaired immune function and increased risk for acquiring infection, which can be rectified by zinc supplementation. However, higher than recommended upper limits of zinc may adversely affect immune function. Probiotics are increasingly being recognized as an effective, immune-modulating nutritional factor. However, to be effective, they require an adequate supplementation period; additionally, their effects are strain-specific and among certain strains, a synergistic effect is observed. Increased intake of fish or n-3 PUFA may be beneficial to inflammatory and autoimmune disorders as well as to several age-related diseases. Conversely, the immunosuppressive effect of fish oils on T cell-mediated function has raised concerns regarding their impact on resistance to infection. Caloric restriction (CR) is shown to delay immunosenescence in animals, but this effect needs to be verified in humans. Timing for CR initiation may be important to determine whether CR is effective or even beneficial at all. Recent studies have suggested that CR, which is effective at improving the immune response of unchallenged animals, might compromise the host's defense against pathogenic infection and result in higher morbidity and mortality. The studies published thus far describe a critical role for nutrition in maintaining the immune response of the aged, but they also indicate the need for a more in-depth, wholestic approach to determining the optimal nutritional strategies that would maintain a healthy immune system in the elderly and promote their resistance to infection and other immune-related diseases.

Mechanisms of immunosenescence: lessons from models of accelerated immune aging

With increasing age, the ability of the adaptive immune system to respond to vaccines and to protect from infection declines. In parallel, the production of inflammatory mediators increases. While cross-sectional studies have been successful in defining age-dependent immunological phenotypes, studies of accelerated immune aging in human subpopulations have been instrumental in obtaining mechanistic insights. The immune system depends on its regenerative capacity; however, the T cell repertoire, once established, is relatively robust to aging and only decompensates when additionally stressed. Such stressors include chronic infections such as CMV and HIV, even when viral replication is controlled, and autoimmune diseases. Reduced regenerative capacity, chronic immune activation in the absence of cell exhaustion, T cell memory inflation, and accumulation of highly potent effector T cells in these patients synergize to develop an immune phenotype that is characteristic of the elderly. Studies of accelerated immune aging in autoimmune diseases have identified an unexpected link to chronic DNA damage responses that are known to be important in aging, but so far had not been implicated in immune aging.

Telomere dynamics in rhesus monkeys: no apparent effect of caloric restriction

The role of telomere attrition in limiting the replicative capacity of cells in culture is well established. In humans, epidemiologic evidence suggests telomere length (TL) in leukocytes is highly variable at birth and inversely related to age. Although calorie restriction (CR) significantly increases life span in most rodent models, its association with TL is unknown. Using linear regression analysis, TLs (as measured by Southern blot analysis) of skeletal muscle (a postmitotic tissue that largely represents early development TL), fat, leukocytes, and skin were tested for effects of age, sex, and diet in 48 control and 23 calorie restriction rhesus monkeys. After controlling for the individual's muscle mean TL, differences between leukocytes muscle and skin muscle were significantly associated with age (p = .002; p = .002) and sex (p = .003; p = .042), but not calorie restriction (p = .884; p = .766). Despite an age-dependent shortening of TL in leukocytes and skin, calorie restriction did not significantly affect TL dynamics in these samples.

Caloric restriction and chronic inflammatory diseases

A reduction in calorie intake [caloric restriction (CR)] appears to consistently decrease the biological rate of aging in a variety of organisms as well as protect against age-associated diseases including chronic inflammatory disorders such as cardiovascular disease and diabetes. Although the mechanisms behind this observation are not fully understood, identification of the main metabolic pathways affected by CR has generated interest in finding molecular targets that could be modulated by CR mimetics. This review describes the general concepts of CR and CR mimetics as well as discusses evidence related to their effects on inflammation and chronic inflammatory disorders. Additionally, emerging evidence related to the effects of CR on periodontal disease in non-human primates is presented. While the implementation of this type of dietary intervention appears to be challenging in our modern society where obesity is a major public health problem, CR mimetics could offer a promising alternative to control and perhaps prevent several chronic inflammatory disorders including periodontal disease.

Nonhuman primate models of human immunology

Nonhuman primates have been used for biomedical research for several decades. The high level of genetic homology to humans coupled with their outbred nature has made nonhuman primates invaluable preclinical models. In this review, we summarize recent advances in our understanding of the nonhuman primate immune system, with special emphasis on studies carried out in rhesus macaque (Macaca mulatta). We highlight the utility of nonhuman primates in the characterization of immune senescence and the evaluation of new interventions to slow down the aging of the immune system.

Adult-onset, short-term dietary restriction reduces cell senescence in mice

Dietary restriction (DR) extends the lifespan of a wide variety of species and reduces the incidence of major age-related diseases. Cell senescence has been proposed as one causal mechanism for tissue and organism ageing. We show for the first time that adult-onset, short-term DR reduced frequencies of senescent cells in the small intestinal epithelium and liver of mice, which are tissues known to accumulate increased numbers of senescent cells with advancing age. This reduction was associated with improved telomere maintenance without increased telomerase activity. We also found a decrease in cumulative oxidative stress markers in the same compartments despite absence of significant changes in steady-state oxidative stress markers at the whole tissue level. The data suggest the possibility that reduction of cell senescence may be a primary consequence of DR which in turn may explain known effects of DR such as improved mitochondrial function and reduced production of reactive oxygen species.

Calorie restriction and aging in nonhuman primates

In the 75 years since the seminal observation of Clive McCay that restriction of calorie intake extends the lifespan of rats, a great deal has been learned about the effects of calorie restriction (CR; reduced intake of a nutritious diet) on aging in various short-lived animal models. Studies have demonstrated many beneficial effects of CR on health, the rate of aging, and longevity. Two prospective investigations of the effects of CR on long-lived nonhuman primate (NHP) species began nearly 25 years ago and are still under way. This review presents the design, methods, and main findings of these and other important contributing studies, which have generally revealed beneficial effects of CR on physiological function and the retardation of disease consistent with studies in other species. Specifically, prolonged CR appears to extend the lifespan of rhesus monkeys, which exhibited lower body fat; slower rate of muscle loss with age; lower incidence of neoplasia, cardiovascular disease, type 2 diabetes mellitus, and endometriosis; improved insulin sensitivity and glucose tolerance; and no apparent adverse effect on bone health, as well as a reduction in total energy expenditure. In addition, there are no reports of deleterious effects of CR on reproductive endpoints, and brain morphology is preserved by CR. Adrenal and thyroid hormone profiles are inconsistently affected. More research is needed to delineate the mechanisms of the desirable outcomes of CR and to develop interventions that can produce similar beneficial outcomes for humans. This research offers tremendous potential for producing novel insights into aging and risk of disease.

Caloric restriction: from soup to nuts

Caloric restriction (CR), reduced protein, methionine, or tryptophan diets; and reduced insulin and/or IGFI intracellular signaling can extend mean and/or maximum lifespan and delay deleterious age-related physiological changes in animals. Mice and flies can shift readily between the control and CR physiological states, even at older ages. Many health benefits are induced by even brief periods of CR in flies, rodents, monkeys, and humans. In humans and nonhuman primates, CR produces most of the physiologic, hematologic, hormonal, and biochemical changes it produces in other animals. In primates, CR provides protection from type 2 diabetes, cardiovascular and cerebral vascular diseases, immunological decline, malignancy, hepatotoxicity, liver fibrosis and failure, sarcopenia, inflammation, and DNA damage. It also enhances muscle mitochondrial biogenesis, affords neuroprotection; and extends mean and maximum lifespan. CR rapidly induces antineoplastic effects in mice. Most claims of lifespan extension in rodents by drugs or nutrients are confounded by CR effects. Transcription factors and co-activators involved in the regulation of mitochondrial biogenesis and energy metabolism, including SirT1, PGC-1alpha, AMPK and TOR may be involved in the lifespan effects of CR. Paradoxically, low body weight in middle aged and elderly humans is associated with increased mortality. Thus, enhancement of human longevity may require pharmaceutical interventions.

Immune senescence in aged nonhuman primates

Aging is accompanied by a general dysregulation in immune system function, commonly referred to as 'immune senescence'. This progressive deterioration affects both innate and adaptive immunity, although accumulating evidence indicates that the adaptive arm of the immune system may exhibit more profound changes. Most of our current understanding of immune senescence stems from clinical and rodent studies. More recently, the use of nonhuman primates (NHPs) to investigate immune senescence and test interventions aimed at delaying/reversing age-related changes in immune function has dramatically increased. These studies have been greatly facilitated by several key advances in our understanding of the immune system of old world monkeys, specifically the rhesus macaques. In this review we describe the hallmarks of immune senescence in this species and compare them to those described in humans. We also discuss the impact of immune senescence on the response to vaccination and the efficacy of immuno-restorative interventions investigated in this model system.

Dietary restriction and aging, 2009

Dietary restriction (DR) is a robust nongenetic, nonpharmacological intervention that is known to increase active and healthy lifespan in a variety of species. Despite a variety of differences in the protocols and the way DR is carried out in different species, conserved relationships are emerging among multiple species. 2009 saw the field of DR mature with important mechanistic insights from multiple species. A report of lifespan extension in rapamycin-treated mice suggested that the TOR pathway, a conserved mediator of DR in invertebrates, may also be critical to DR effects in mammals. 2009 also saw exciting discoveries related to DR in various organisms including yeast, worms, flies, mice, monkeys and humans. These studies complement each other and together aim to deliver the promise of postponing aging and age-related diseases by revealing the underlying mechanisms of the protective effects of DR. Here, we summarize a few of the reports published in 2009 that we believe provide novel directions and an improved understanding of dietary restriction.

Could Sirt1-mediated epigenetic effects contribute to the longevity response to dietary restriction and be mimicked by other dietary interventions?

Dietary restriction (DR) increases lifespan in a range of evolutionarily distinct species. The polyphenol resveratrol may be a dietary mimetic of some effects of DR. The pivotal role of the mammalian histone deacetylase (HDAC) Sirt1, and its homologue in other organisms, in mediating the effects of both DR and resveratrol on lifespan/ageing suggests it may be the common conduit through which these dietary interventions influence ageing. We propose the novel hypothesis that effects of DR relevant to lifespan extension include maintenance of DNA methylation patterns through Sirt1-mediated epigenetic effects, and proffer the view that dietary components, including resveratrol, may mimic these actions.

Increasing longevity through caloric restriction or rapamycin feeding in mammals: common mechanisms for common outcomes?

Significant extension of lifespan in important mammalian species is bound to attract the attention not only of the aging research community, but also the media and the wider public. Two recent papers published by Harrison et al. (2009) in Nature and by Colman et al. (2009) in Science report increased longevity of mice fed with rapamycin and of rhesus monkeys undergoing caloric restriction, respectively. These papers have generated considerable debate in the aging community. Here we assess what is new about these findings, how they fit with our knowledge of lifespan extension from other studies and what prospects this new work holds out for improvements in human longevity and human health span.

Reactive oxygen intermediate-induced pathomechanisms contribute to immunosenescence, chronic inflammation and autoimmunity

Deregulation of reactive oxygen intermediates (ROI) resulting in either too high or too low concentrations are commonly recognized to be at least in part responsible for many changes associated with aging. This article reviews ROI-dependent mechanisms critically contributing to the decline of immune function during physiologic - or premature - aging. While ROI serve important effector functions in cellular metabolism, signalling and host defence, their fine-tuned generation declines over time, and ROI-mediated damage to several cellular components and/or signalling deviations become increasingly prevalent. Although distinct ROI-associated pathomechanisms contribute to immunosenescence of the innate and adaptive immune system, mutual amplification of dysfunctions may often result in hyporesponsiveness and immunodeficiency, or in chronic inflammation with hyperresponsiveness/deregulation, or both. In this context, we point out how imbalanced ROI contribute ambiguously to driving immunosenescence, chronic inflammation and autoimmunity. Although ROI may offer a distinct potential for therapeutic targeting along with the charming opportunity to rescue from deleterious processes of aging and chronic inflammatory diseases, such modifications, owing to the complexity of metabolic interactions, may carry a marked risk of unforeseen side effects.