Nutrition, metabolism, and targeting aging in nonhuman primates

Caloric restriction reprograms adipose tissues in rhesus monkeys

Caloric restriction (CR) is a dietary intervention that delays the onset of age-related diseases and enhances survival in diverse organisms, and although changes in adipose tissues have been implicated in the beneficial effects of CR the molecular details are unknown. Here we show shared and depot-specific adaptations to life-long CR in subcutaneous and visceral adipose depots taken from advanced age male rhesus monkeys. Differential gene expression and pathway analysis identified key differences between the depots in metabolic, immune, and inflammatory pathways. In response to CR, RNA processing and proteostasis-related pathways were enriched in both depots but changes in metabolic, growth, and inflammatory pathways were depot-specific. Commonalities and differences that distinguish adipose depots are shared among monkeys and humans and the response to CR is highly conserved. These data reveal depot-specificity in adipose tissue adaptation that likely reflects differences in function and contribution to age-related disease vulnerability.

Analysis of the aging-related biomarker in a nonhuman primate model using multilayer omics

BACKGROUND

Aging is a prominent risk factor for diverse diseases; therefore, an in-depth understanding of its physiological mechanisms is required. Nonhuman primates, which share the closest genetic relationship with humans, serve as an ideal model for exploring the complex aging process. However, the potential of the nonhuman primate animal model in the screening of human aging markers is still not fully exploited. Multiomics analysis of nonhuman primate peripheral blood offers a promising approach to evaluate new therapies and biomarkers. This study explores aging-related biomarker through multilayer omics, including transcriptomics (mRNA, lncRNA, and circRNA) and proteomics (serum and serum-derived exosomes) in rhesus monkeys (Macaca mulatta).

RESULTS

Our findings reveal that, unlike mRNAs and circRNAs, highly expressed lncRNAs are abundant during the key aging period and are associated with cancer pathways. Comparative analysis highlighted exosomal proteins contain more types of proteins than serum proteins, indicating that serum-derived exosomes primarily regulate aging through metabolic pathways. Finally, eight candidate aging biomarkers were identified, which may serve as blood-based indicators for detecting age-related brain changes.

CONCLUSIONS

Our results provide a comprehensive understanding of nonhuman primate blood transcriptomes and proteomes, offering novel insights into the aging mechanisms for preventing or treating age-related diseases.

Development and assessment of a stair ascension challenge as a measure of aging and physical function in nonhuman primates

Nonhuman primates (NHPs) are valuable models for studying healthspan, including frailty development. Frailty metrics in people centers on functional measures, including usual gait speed which can be predictive of all-cause mortality. This concept that physical competencies are able to prognosticate an individual's health trajectory over chronologic aging is well-accepted and has led to refinements in how physical function is evaluated, and include measures of strength and power along with walking speed. NHP studies of aging require evaluation of physical function, which can be difficult in field and research settings. We compared stair climb velocity to usual walking speed in 28 peri-geriatric to geriatric NHPs, as incorporating a climbing obstacle integrates multiple components of physical function: isolated leg and back strength, proprioception, balance, and range of motion. We find that stair climbing speed was reliable between observers, and whether timing was in-person take from video capture. The stair climb rates were 50% more associated with chronological age than walking speed (R = -0.68 vs. -0.45) and only stair climbing speeds were retained as predictive of age when walking speed and bodyweight were included in multivariate models (overall R2  = 0.44; p < 0.0001). When comparing young (10-16 years) versus geriatric (16-29 years) stair climbing speed was significantly different (p < 0.001), while walking speeds only tended to be slower (p = 0.12) suggesting that the additional challenge of a stair climb better unmasks subclinical frailty development that usual walking speed.

Stress, epigenetics, and aging: Unraveling the intricate crosstalk

Aging, as a complex process involving multiple cellular and molecular pathways, is known to be exacerbated by various stresses. Because responses to these stresses, such as oxidative stress and genotoxic stress, are known to interplay with the epigenome and thereby contribute to the development of age-related diseases, investigations into how such epigenetic mechanisms alter gene expression and maintenance of cellular homeostasis is an active research area. In this review, we highlight recent studies investigating the intricate relationship between stress and aging, including its underlying epigenetic basis; describe different types of stresses that originate from both internal and external stimuli; and discuss potential interventions aimed at alleviating stress and restoring epigenetic patterns to combat aging or age-related diseases. Additionally, we address the challenges currently limiting advancement in this burgeoning field.

Nutrition, longevity and disease: From molecular mechanisms to interventions

Diet as a whole, encompassing food composition, calorie intake, and the length and frequency of fasting periods, affects the time span in which health and functional capacity are maintained. Here, we analyze aging and nutrition studies in simple organisms, rodents, monkeys, and humans to link longevity to conserved growth and metabolic pathways and outline their role in aging and age-related disease. We focus on feasible nutritional strategies shown to delay aging and/or prevent diseases through epidemiological, model organism, clinical, and centenarian studies and underline the need to avoid malnourishment and frailty. These findings are integrated to define a longevity diet based on a multi-pillar approach adjusted for age and health status to optimize lifespan and healthspan in humans.

Dietary Phytochemicals that Can Extend Longevity by Regulation of Metabolism

Diet provides energy and nutrition for human survival, and also provides various joy of taste. Extensive studies have shown that the major components of diet, such as protein, carbohydrate and fat, play important roles in regulating aging and longevity. Whether other dietary ingredients can help prevent aging and extend longevity is a very interesting question. Here based on recent findings, we discussed dietary plant ingredients that can extend longevity by regulation of metabolism, targeting TRP channels, mitophagy, senescence pathways and circadian rhythms. Better understanding of the detailed effects and mechanisms of dietary ingredients on longevity regulation, would be helpful for developing new intervention tools for preventing aging and aging related diseases.

Hydrogen sulfide in ageing, longevity and disease

Hydrogen sulfide (H₂S) modulates many biological processes, including ageing. Initially considered a hazardous toxic gas, it is now recognised that H₂S is produced endogenously across taxa and is a key mediator of processes that promote longevity and improve late-life health. In this review, we consider the key developments in our understanding of this gaseous signalling molecule in the context of health and disease, discuss potential mechanisms through which H₂S can influence processes central to ageing and highlight the emergence of novel H₂S-based therapeutics. We also consider the major challenges that may potentially hinder the development of such therapies.

Are fat and sugar just as detrimental in old age?

Aging and poor nutrition are independent risk factors for the development of chronic disease. When young animals are given diets high in fat or sugar, they exhibit hallmarks of aging like mitochondrial dysfunction and inflammation, and also develop a greater risk for age-related disease. The same mitochondrial dysfunction and inflammation that progress with aging may also further predispose older individuals to dietary insults by fat and sugar. The purpose of this work is to review the most recent studies that address the impact of fat and sugar consumption on hallmarks of aging (mitochondrial dysfunction and inflammation). Findings from these studies show that obesogenic, high-fat diets can exacerbate age-related disease and hallmarks of aging in young animals, but high-fat diets that are non-obesogenic may play a beneficial role in old age. In contrast, high-sugar diets do not require an obesogenic effect to induce mitochondrial dysfunction or inflammation in young rodents. Currently, there is a lack of experimental studies addressing the impact of sugar in the context of aging, even though empirical evidence points to the detrimental effect of sugar in aging by contributing to a variety of age-related diseases. Fig. 1 Mitochondrial dysfunction and altered cellular communication (e.g. inflammation) progress with advancing age and increase the risk for age-related disease (ARD). Given the physiological changes that occur with age, the impact of high-fat (HFD) and high-sugar diets (HSD) may differ in later and earlier stages of life. HFD can promote the development of hallmarks of aging in young animals and can also exacerbate the risk for ARD when consumed at an old age. However, non-obesogenic high-fat diets may also reduce the risk for ARD in old age by acting on these hallmarks of aging. On the other hand, HSD promotes mitochondrial dysfunction and inflammation without necessarily inducing weight gain in young animals. Empirical evidence points to sugar as a major contributor to age-related disease and more experimental studies are needed to clarify whether aged individuals are more susceptible to its effects.

Roles of interacting stress-related genes in lifespan regulation: insights for translating experimental findings to humans

AIM

Experimental studies provided numerous evidence that caloric/dietary restriction may improve health and increase the lifespan of laboratory animals, and that the interplay among molecules that sense cellular stress signals and those regulating cell survival can play a crucial role in cell response to nutritional stressors. However, it is unclear whether the interplay among corresponding genes also plays a role in human health and lifespan.

METHODS

Literature about roles of cellular stressors have been reviewed, such as amino acid deprivation, and the integrated stress response (ISR) pathway in health and aging. Single nucleotide polymorphisms (SNPs) in two candidate genes (GCN2/EIF2AK4 and CHOP/DDIT3) that are closely involved in the cellular stress response to amino acid starvation, have been selected using information from experimental studies. Associations of these SNPs and their interactions with human survival in the Health and Retirement Study data have been estimated. The impact of collective associations of multiple interacting SNP pairs on survival has been evaluated, using a recently developed composite index: the SNP-specific Interaction Polygenic Risk Score (SIPRS).

RESULTS

Significant interactions have been found between SNPs from GCN2/EIF2AK4 and CHOP/DDI3T genes that were associated with survival 85+ compared to survival between ages 75 and 85 in the total sample (males and females combined) and in females only. This may reflect sex differences in genetic regulation of the human lifespan. Highly statistically significant associations of SIPRS [constructed for the rs16970024 (GCN2/EIF2AK4) and rs697221 (CHOP/DDIT3)] with survival in both sexes also been found in this study.

CONCLUSION

Identifying associations of the genetic interactions with human survival is an important step in translating the knowledge from experimental to human aging research. Significant associations of multiple SNPxSNP interactions in ISR genes with survival to the oldest old age that have been found in this study, can help uncover mechanisms of multifactorial regulation of human lifespan and its heterogeneity.

Repurposing drugs to fight aging: The difficult path from bench to bedside

The steady rise in life expectancy occurred across all developed countries during the last century. This demographic trend is, however, not accompanied by the same healthspan extension. This is since aging is the main risk factor for all age-associated pathological conditions. Therefore, slowing the rate of aging is suggested to be more efficient in preventing or delaying age-related diseases than treat them one by one, which is the common approach in a current pharmacological disease-oriented paradigm. To date, a variety of medications designed to treat particular pathological conditions have been shown to exhibit pro-longevity effects in different experimental models. Among them, there are many commonly used prescription and over-the-counter pharmaceuticals such as metformin, rapamycin, aspirin, statins, melatonin, vitamin antioxidants, etc. All of them are being increasingly investigated in preclinical and clinical trials with the aim of determine whether they have potential for extension of human healthspan. The results from these trials are frequently inconclusive and fall short of initial expectations, suggesting that innovative research ideas and additional translational steps are required to overcome obstacles for implementation of such approaches in clinical practice. In this review, recent advances and challenges in the field of repurposing widely used conventional pharmaceuticals to target the aging process are summarized and discussed.

Longitudinal profiling of the blood transcriptome in an African green monkey aging model

African green monkeys (AGMs, Chlorocebus aethiops) are Old World monkeys which are used as experimental models in biomedical research. Recent technological advances in next generation sequencing are useful for unraveling the genetic mechanisms underlying senescence, aging, and age-related disease. To elucidate the normal aging mechanisms in older age, the blood transcriptomes of nine healthy, aged AGMs (15‒23 years old), were analyzed over two years. We identified 910‒1399 accumulated differentially expressed genes (DEGs) in each individual, which increased with age. Aging-related DEGs were sorted across the three time points. A major proportion of the aging-related DEGs belonged to gene ontology (GO) categories involved in translation and rRNA metabolic processes. Next, we sorted common aging-related DEGs across three time points over two years. Common aging-related DEGs belonged to GO categories involved in translation, cellular component biogenesis, rRNA metabolic processes, cellular component organization, biogenesis, and RNA metabolic processes. Furthermore, we identified 29 candidate aging genes that were upregulated across the time series analysis. These candidate aging genes were linked to protein synthesis. This study describes a changing gene expression pattern in AGMs during aging using longitudinal transcriptome sequencing. The candidate aging genes identified here may be potential targets for the treatment of aging.

Mini-review: Aging of the neuroendocrine system: Insights from nonhuman primate models

The neuroendocrine system (NES) plays a crucial role in synchronizing the physiology and behavior of the whole organism in response to environmental constraints. The NES consists of a hypothalamic-pituitary-target organ axis that acts in coordination to regulate growth, reproduction, stress and basal metabolism. The growth (or somatotropic), hypothalamic-pituitary-gonadal (HPG), hypothalamic-pituitary-adrenal (HPA) and hypothalamic-pituitary-thyroid (HPT) axes are therefore finely tuned by the hypothalamus through the successive release of hypothalamic and pituitary hormones to control the downstream physiological functions. These functions rely on a complex set of mechanisms requiring tight synchronization between peripheral organs and the hypothalamic-pituitary complex, whose functionality can be altered during aging. Here, we review the results of research on the effects of aging on the NES of nonhuman primate (NHP) species in wild and captive conditions. A focus on the age-related dysregulation of the master circadian pacemaker, which, in turn, alters the synchronization of the NES with the organism environment, is proposed. Finally, practical and ethical considerations of using NHP models to test the effects of nutrition-based or hormonal treatments to combat the deterioration of the NES are discussed.

Molecular and Functional Networks Linked to Sarcopenia Prevention by Caloric Restriction in Rhesus Monkeys

Caloric restriction (CR) improves survival in nonhuman primates and delays the onset of age-related morbidities including sarcopenia, which is characterized by the age-related loss of muscle mass and function. A shift in metabolism anticipates the onset of muscle-aging phenotypes in nonhuman primates, suggesting a potential role for metabolism in the protective effects of CR. Here, we show that CR induced profound changes in muscle composition and the cellular metabolic environment. Bioinformatic analysis linked these adaptations to proteostasis, RNA processing, and lipid synthetic pathways. At the tissue level, CR maintained contractile content and attenuated age-related metabolic shifts among individual fiber types with higher mitochondrial activity, altered redox metabolism, and smaller lipid droplet size. Biometric and metabolic rate data confirm preserved metabolic efficiency in CR animals that correlated with the attenuation of age-related muscle mass and physical activity. These data suggest that CR-induced reprogramming of metabolism plays a role in delayed aging of skeletal muscle in rhesus monkeys.

Ayurveda and the science of aging

Since time immemorial, humanity has been concerned with developing and preserving youthful vigor, and extending longevity by stopping or delaying the aging process. By 2030, one in five of the world population will be over 65 years old. Longevity and old age are accompanied with a variety of health challenges and population studies indicate that the elderly will use between three to five times more healthcare services compared to the younger population. Modern medicine has made a great deal of progress in understanding the aging process and in controlling age-associated health issues including heart attacks, strokes, diabetes, cancer, senility, and arthritis. Thus, every individual is now looking forward to a youthful, productive lifespan of 100 or more years filled with unlimited health and opportunity. Research by aging experts is focused on ways to go against the natural order of the aging process in order to delay it. Interventions include among other things anti-aging pills, restricted food consumption and cloning body parts to stay young and delay biological aging. Ayurveda, one of the world's most authoritative mind-body-spirit medicinal systems, offers various concepts of the aging process. This system of medicine includes therapies for healthy aging so as to create an optimal health and lengthen an individual's healthspan by living in harmony with nature. This review will explore various aspects of aging and longevity by comparing the science of aging as defined by modern medicine with the Ayurvedic treatise of Jara and Vriddhavastha.

Caloric Restriction Engages Hepatic RNA Processing Mechanisms in Rhesus Monkeys

Caloric restriction (CR) extends lifespan and delays the onset of age-related disorders in diverse species. Metabolic regulatory pathways have been implicated in the mechanisms of CR, but the molecular details have not been elucidated. Here, we show that CR engages RNA processing of genes associated with a highly integrated reprogramming of hepatic metabolism. We conducted molecular profiling of liver biopsies collected from adult male rhesus monkeys (Macaca mulatta) at baseline and after 2 years on control or CR (30% restricted) diet. Quantitation of over 20,000 molecules from the hepatic transcriptome, proteome, and metabolome indicated that metabolism and RNA processing are major features of the response to CR. Predictive models identified lipid, branched-chain amino acid, and short-chain carbon metabolic pathways, with alternate transcript use for over half of the genes in the CR network. We conclude that RNA-based mechanisms are central to the CR response and integral in metabolic reprogramming.

Non-human primates as a model for aging

There has been, and continues to be, a dramatic shift in the human population towards older ages necessitating biomedical research aimed at better understanding the basic biology of aging and age-related diseases and facilitating new and improved therapeutic options. As it is not practical to perform the breadth of this research in humans, animal models are necessary to recapitulate the complexity of the aging environment. The mouse model is most frequently chosen for these endeavors, however, they are frequently not the most appropriate model. Non-human primates, on the other hand, are more closely related to humans and recapitulate the human aging process and development of age-related diseases. Extensive aging research has been performed in the well-characterized rhesus macaque aging model. More recently, the common marmoset, a small non-human primate with a shorter lifespan, has been explored as a potential aging model. This model holds particular promise as an aging disease model in part due to the successful creation of transgenic marmosets. Limitations to the use of non-human primates in aging research exist but can be mitigated somewhat by the existence of available resources supported by the National Institutes of Health. This article is part of a Special Issue entitled: Animal models of aging - edited by "Houtkooper Riekelt".