Growth hormone secretion is diminished and tightly controlled in humans enriched for familial longevity

Targeting Cell Senescence and Senolytics: Novel Interventions for Age-Related Endocrine Dysfunction

Multiple changes occur in hormonal regulation with aging and across various endocrine organs. These changes are associated with multiple age-related disorders and diseases. A better understanding of responsible underling biological mechanisms could help in the management of multiple endocrine disorders over and above hormone replacement therapy (HRT). Cellular senescence is involved in multiple biological aging processes and pathologies common in elderly individuals. Cellular senescence, which occurs in many older individuals but also across the lifespan in association with tissue damage, acute and chronic diseases, certain drugs, and genetic syndromes, may contribute to such endocrine disorders as osteoporosis, metabolic syndrome, and type 2 diabetes mellitus. Drugs that selectively induce senescent cell removal, "senolytics,", and drugs that attenuate the tissue-destructive secretory state of certain senescent cells, "senomorphics," appear to delay the onset of or alleviate multiple diseases, including but not limited to endocrine disorders such as diabetes, complications of obesity, age-related osteoporosis, and cancers as well as atherosclerosis, chronic kidney disease, neurodegenerative disorders, and many others. More than 30 clinical trials of senolytic and senomorphic agents have already been completed, are underway, or are planned for a variety of indications. Targeting senescent cells is a novel strategy that is distinct from conventional therapies such as HRT, and thus might address unmet medical needs and can potentially amplify effects of established endocrine drug regimens, perhaps allowing for dose decreases and reducing side effects.

The rosetta stone of successful ageing: does oral health have a role?

Ageing is an inevitable aspect of life and thus successful ageing is an important focus of recent scientific efforts. The biological process of ageing is mediated through the interaction of genes with environmental factors, increasing the body's susceptibility to insults. Elucidating this process will increase our ability to prevent and treat age-related disease and consequently extend life expectancy. Notably, centenarians offer a unique perspective on the phenomenon of ageing. Current research highlights several age-associated alterations on the genetic, epigenetic and proteomic level. Consequently, nutrient sensing and mitochondrial function are altered, resulting in inflammation and exhaustion of regenerative ability.Oral health, an important contributor to overall health, remains underexplored in the context of extreme longevity. Good masticatory function ensures sufficient nutrient uptake, reducing morbidity and mortality in old age. The relationship between periodontal disease and systemic inflammatory pathologies is well established. Diabetes, rheumatoid arthritis and cardiovascular disease are among the most significant disease burdens influenced by inflammatory oral health conditions. Evidence suggests that the interaction is bi-directional, impacting progression, severity and mortality. Current models of ageing and longevity neglect an important factor in overall health and well-being, a gap that this review intends to illustrate and inspire avenues for future research.

Relationships among Development, Growth, Body Size, Reproduction, Aging, and Longevity - Trade-Offs and Pace-Of-Life

Relationships of growth, metabolism, reproduction, and body size to the biological process of aging and longevity have been studied for decades and various unifying "theories of aging" have been proposed to account for the observed associations. In general, fast development, early sexual maturation leading to early reproductive effort, as well as production of many offspring, have been linked to shorter lifespans. The relationship of adult body size to longevity includes a remarkable contrast between the positive correlation in comparisons between different species and the negative correlation seen in comparisons of individuals within the same species. We now propose that longevity and presumably also the rate of aging are related to the "pace-of-life." A slow pace-of-life including slow growth, late sexual maturation, and a small number of offspring, predicts slow aging and long life. The fast pace of life (rapid growth, early sexual maturation, and major reproductive effort) is associated with faster aging and shorter life, presumably due to underlying trade-offs. The proposed relationships between the pace-of-life and longevity apply to both inter- and intra-species comparisons as well as to dietary, genetic, and pharmacological interventions that extend life and to evidence for early life programming of the trajectory of aging. Although available evidence suggests the causality of at least some of these associations, much further work will be needed to verify this interpretation and to identify mechanisms that are responsible.

Hormones and Aging: An Endocrine Society Scientific Statement

Multiple changes occur across various endocrine systems as an individual ages. The understanding of the factors that cause age-related changes and how they should be managed clinically is evolving. This statement reviews the current state of research in the growth hormone, adrenal, ovarian, testicular, and thyroid axes, as well as in osteoporosis, vitamin D deficiency, type 2 diabetes, and water metabolism, with a specific focus on older individuals. Each section describes the natural history and observational data in older individuals, available therapies, clinical trial data on efficacy and safety in older individuals, key points, and scientific gaps. The goal of this statement is to inform future research that refines prevention and treatment strategies in age-associated endocrine conditions, with the goal of improving the health of older individuals.

Mechanisms of ageing: growth hormone, dietary restriction, and metformin

Tackling the mechanisms underlying ageing is desirable to help to extend the duration and improve the quality of life. Life extension has been achieved in animal models by suppressing the growth hormone-insulin-like growth factor 1 (IGF-1) axis and also via dietary restriction. Metformin has become the focus of increased interest as a possible anti-ageing drug. There is some overlap in the postulated mechanisms of how these three approaches could produce anti-ageing effects, with convergence on common downstream pathways. In this Review, we draw on evidence from both animal models and human studies to assess the effects of suppression of the growth hormone-IGF-1 axis, dietary restriction, and metformin on ageing.

Growth hormone deficiency interferes with dynamic brain networks in short children

PURPOSE

This study aimed to explore the disparities in dynamic brain networks between children with growth hormone deficiency (GHD) and idiopathic short stature (ISS, non-growth hormone deficiency).

METHODS

This study enrolled 65 children with GHD and 60 sex- and age-matched children with ISS. Resting-state functional magnetic resonance imaging (rs-fMRI) was performed for all participants to obtain information on dynamic regional homogeneity (dReHo) and functional connectivity (FC) in dynamic (dFC) or static (sFC) state. The rs-fMRI metrics were subsequently compared between the GHD and ISS groups.

RESULTS

Compared to the ISS group, the GHD group showed significant dynamic abnormalities in intra-networks of the central executive and cerebellar networks and in inter-networks of the central executive network to attentional, sensorimotor, and visual networks, as well as cerebellar network to default mode, sensorimotor, and visual networks. In addition, FC changes in the dynamic state were different from those in the static state.

CONCLUSIONS

The abnormal dynamics in intra- and inter-networks involved in cognitive, emotional, and motor functions in children with GHD extend the knowledge on brain functional alterations in children with GHD as reflected by dynamic changes in macroscopic neural activity patterns. These findings may help explain how GHD leads to various behavioral and cognitive deficits in children with short stature.

Physiological Systems in Promoting Frailty

Frailty is a complex syndrome affecting a growing sector of the global population as medical developments have advanced human mortality rates across the world. Our current understanding of frailty is derived from studies conducted in the laboratory as well as the clinic, which have generated largely phenotypic information. Far fewer studies have uncovered biological underpinnings driving the onset and progression of frailty, but the stage is set to advance the field with preclinical and clinical assessment tools, multiomics approaches together with physiological and biochemical methodologies. In this article, we provide comprehensive coverage of topics regarding frailty assessment, preclinical models, interventions, and challenges as well as clinical frameworks and prevalence. We also identify central biological mechanisms that may be at play including mitochondrial dysfunction, epigenetic alterations, and oxidative stress that in turn, affect metabolism, stress responses, and endocrine and neuromuscular systems. We review the role of metabolic syndrome, insulin resistance and visceral obesity, focusing on glucose homeostasis, adenosine monophosphate-activated protein kinase (AMPK), mammalian target of rapamycin (mTOR), and nicotinamide adenine dinucleotide (NAD+ ) as critical players influencing the age-related loss of health. We further focus on how immunometabolic dysfunction associates with oxidative stress in promoting sarcopenia, a key contributor to slowness, weakness, and fatigue. We explore the biological mechanisms involved in stem cell exhaustion that affect regeneration and may contribute to the frailty-associated decline in resilience and adaptation to stress. Together, an overview of the interplay of aging biology with genetic, lifestyle, and environmental factors that contribute to frailty, as well as potential therapeutic targets to lower risk and slow the progression of ongoing disease is covered. © 2022 American Physiological Society. Compr Physiol 12:1-46, 2022.

GH and Senescence: A New Understanding of Adult GH Action

Replicative senescence occurs due to an inability to repair DNA damage and activation of p53/p21 and p16INK4 pathways. It is considered a preventive mechanism for arresting proliferation of DNA-damaged cells. Stably senescent cells are characterized by a senescence-associated secretory phenotype (SASP), which produces and secretes cytokines, chemokines, and/or matrix metalloproteinases depending on the cell type. SASP proteins may increase cell proliferation, facilitating conversion of premalignant to malignant tumor cells, triggering DNA damage, and altering the tissue microenvironment. Further, senescent cells accumulate with age, thereby aggravating age-related tissue damage. Here, we review a heretofore unappreciated role for growth hormone (GH) as a SASP component, acting in an autocrine and paracrine fashion. In senescent cells, GH is activated by DNA-damage-induced p53 and inhibits phosphorylation of DNA repair proteins ATM, Chk2, p53, and H2AX. Somatotroph adenomas containing abundant intracellular GH exhibit increased somatic copy number alterations, indicative of DNA damage, and are associated with induced p53/p21. As this pathway restrains proliferation of DNA-damaged cells, these mechanisms may underlie the senescent phenotype and benign nature of slowly proliferating pituitary somatotroph adenomas. In highly proliferative cells, such as colon epithelial cells, GH induced in response to DNA damage suppresses p53, thereby triggering senescent cell proliferation. As senescent cells harbor unrepaired DNA damage, GH may enable senescent cells to evade senescence and reenter the cell cycle, resulting in acquisition of harmful mutations. These mechanisms, at least in part, may underlie pro-aging effects of GH observed in animal models and in patients with chronically elevated GH levels.

Local non-pituitary growth hormone is induced with aging and facilitates epithelial damage

Microenvironmental factors modulating age-related DNA damage are unclear. Non-pituitary growth hormone (npGH) is induced in human colon, non-transformed human colon cells, and fibroblasts, and in 3-dimensional intestinal organoids with age-associated DNA damage. Autocrine/paracrine npGH suppresses p53 and attenuates DNA damage response (DDR) by inducing TRIM29 and reducing ATM phosphorylation, leading to reduced DNA repair and DNA damage accumulation. Organoids cultured up to 4 months exhibit aging markers, p16, and SA-β-galactosidase and decreased telomere length, as well as DNA damage accumulation, with increased npGH, suppressed p53, and attenuated DDR. Suppressing GH in aged organoids increases p53 and decreases DNA damage. WT mice exhibit age-dependent colon DNA damage accumulation, while in aged mice devoid of colon GH signaling, DNA damage remains low, with elevated p53. As age-associated npGH induction enables a pro-proliferative microenvironment, abrogating npGH signaling could be targeted as anti-aging therapy by impeding DNA damage and age-related pathologies.

Chesnokova et al. show that non-pituitary growth hormone (npGH) is induced in aging DNA-damaged colon epithelium and suppresses DNA damage response by attenuating the phosphorylation of DNA repair proteins. npGH induction promotes DNA damage accumulation, resulting in age-associated colon microenvironment changes. Accordingly, disrupted GH signaling in aging mice prevents accumulated DNA damage.

Familial longevity is associated with lower baseline bone turnover but not differences in bone turnover in response to rhTSH

Context: Offspring from long-lived families have a different thyroid status than controls, characterised by higher circulating levels of thyroid stimulating hormone (TSH) and similar levels of thyroid hormone. Expression of the TSH receptor has previously been observed on various extrathyroidal tissues, including bone. However, potential physiological consequences of differences in circulating TSH as observed in familial longevity on bone tissue remain unclear.

Objective: Based on the hypothesis that TSH may inhibit bone resorption, we explored whether offspring of long-lived families have lower bone turnover than controls at baseline as well as following a challenge with recombinant human TSH (rhTSH).

Methods: Bone turnover markers CTX and P1NP were measured in fasted morning samples from 14 offspring and 12 controls at baseline and at 24 hour intervals following 0.1 mg rhTSH i.m. administration for four consecutive days.

Results: At baseline, mean (SEM) CTX was 0.32 (0.03) ng/ml in offspring and 0.50 (0.04) ng/ml in controls, p < 0.01, whereas mean (SEM) P1NP was 39.6 (3.2) ng/ml in offspring and 61.8 (6.6) ng/ml in controls, p < 0.01. Following rhTSH administration, both CTX and P1NP levels transiently increased over time and normalized towards baseline after 72 h (general linear modelling: CTX time p = 0.01, P1NP time p < 0.01); the response was similar between offspring and controls.

Conclusions: Bone turnover markers were lower at baseline in offspring from long-lived families than in controls but increased similarly following an rhTSH challenge.

Relationships Between 24-hour LH and Testosterone Concentrations and With Other Pituitary Hormones in Healthy Older Men

Objective

To investigate the relationship between LH and testosterone (T), which characteristics associate with the strength of this relationship, and their interrelationships with GH, TSH, cortisol, and ACTH.

Design

Hormones were measured in serum samples collected every 10 minutes during 24 hours from 20 healthy men, comprising 10 offspring of long-lived families and 10 control subjects, with a mean (SD) age of 65.6 (5.3) years. We performed cross-correlation analyses to assess the relative strength between 2 timeseries for all possible time shifts.

Results

Mean (95% CI) maximal correlation was 0.21 (0.10-0.31) at lag time of 60 minutes between LH and total T concentrations. Results were comparable for calculated free, bioavailable, or secretion rates of T. Men with strong LH-T cross-correlations had, compared with men with no cross-correlation, lower fat mass (18.5 [14.9-19.7] vs. 22.3 [18.4-29.4] kg), waist circumference (93.6 [5.7] vs. 103.1 [12.0] cm), high-sensitivity C-reactive protein (0.7 [0.4-1.3] vs. 1.8 [0.8-12.3] mg/L), IL-6 (0.8 [0.6-1.0] vs. 1.2 [0.9-3.0] pg/mL), and 24-hour mean LH (4.3 [2.0] vs. 6.1 [1.5] U/L), and stronger LH-T feedforward synchrony (1.5 [0.3] vs. 1.9 [0.2]). Furthermore, T was positively cross-correlated with TSH (0.32 [0.21-0.43]), cortisol (0.26 [0.19-0.33]), and ACTH (0.26 [0.19-0.32]).

Conclusions

LH is followed by T with a delay of 60 minutes in healthy older men. Men with a strong LH-T relationship had more favorable body composition, inflammatory markers, LH levels, and LH-T feedforward synchrony. We observed positive correlations between T and TSH, cortisol, and ACTH.

SGLT2 Inhibitors as Calorie Restriction Mimetics: Insights on Longevity Pathways and Age-Related Diseases

Sodium-glucose cotransporter-2 (SGLT2) inhibitors induce glycosuria, reduce insulin levels, and promote fatty acid oxidation and ketogenesis. By promoting a nutrient deprivation state, SGLT2 inhibitors upregulate the energy deprivation sensors AMPK and SIRT1, inhibit the nutrient sensors mTOR and insulin/IGF1, and modulate the closely linked hypoxia-inducible factor (HIF)-2α/HIF-1α pathways. Phosphorylation of AMPK and upregulation of adiponectin and PPAR-α favor a reversal of the metabolic syndrome which have been linked to suppression of chronic inflammation. Downregulation of insulin/IGF1 pathways and mTOR signaling from a reduction in glucose and circulating amino acids promote cellular repair mechanisms, including autophagy and proteostasis which confer cellular stress resistance and attenuate cellular senescence. SIRT1, another energy sensor activated by NAD+ in nutrient-deficient states, is reciprocally activated by AMPK, and can deacetylate and activate transcription factors, such as PCG-1α, mitochondrial transcription factor A (TFAM), and nuclear factor E2-related factor (NRF)-2, that regulate mitochondrial biogenesis. FOXO3 transcription factor which target genes in stress resistance, is also activated by AMPK and SIRT1. Modulation of these pathways by SGLT2 inhibitors have been shown to alleviate metabolic diseases, attenuate vascular inflammation and arterial stiffness, improve mitochondrial function and reduce oxidative stress-induced tissue damage. Compared with other calorie restriction mimetics such as metformin, rapamycin, resveratrol, and NAD+ precursors, SGLT2 inhibitors appear to be the most promising in the treatment of aging-related diseases, due to their regulation of multiple longevity pathways that closely resembles that achieved by calorie restriction and their established efficacy in reducing cardiovascular events and all-cause mortality. Evidence is compelling for the role of SGLT2 inhibitors as a calorie restriction mimetic in anti-aging therapeutics.

Association of growth hormone receptor gene variant with longevity in men is due to amelioration of increased mortality risk from hypertension

The single nucleotide polymorphism (SNP) rs4130113 of the growth hormone receptor gene (GHR) is associated with longevity. Here we explored whether longevity-associated genotypes protect against mortality in all individuals, or only in individuals with aging-related diseases. Rs4130113 genotypes were tested for association with mortality in 3,557 elderly American men of Japanese ancestry. At baseline (1991–1993), 1,000 had diabetes, 730 had coronary heart disease (CHD), 1,901 had hypertension, 485 had cancer, and 919 lacked these diseases. The men were followed from baseline until Dec 31, 2019 or death (mean 10.8 ± 6.5 SD years, range 0.01–28.8 years; 99.0% deceased by that date). In a heterozygote disadvantage model, longevity-associated genotypes were associated with significantly lower mortality risk in individuals having hypertension (covariate-adjusted hazard ratio [HR] 0.83 [95% CI: 0.76–0.93, p = 4.3 x10^–4]. But in individuals with diabetes, CHD, and cancer there was no genotypic difference in lifespan. As expected, normotensive men outlived men with hypertension (p = 0.036). There was no effect, however, of genotypic difference on lifespan in normotensive men (p = 0.11). We found that SNP rs4130113 potentially influenced the binding of transcription factors E2A, MYF, NRSF, TAL1, and TCF12 so as to alter GHR expression. We propose that in individuals with hypertension, longevity-associated genetic variation in GHR enhances cell resilience mechanisms to help protect against cellular stress caused by hypertension. As a result, hypertension-affected men who possess the longevity-associated genetic variant of GHR live as long as normotensive men.

Growth hormone and aging

Growth hormone (GH) actions impact growth, metabolism, and body composition and have been associated with aging and longevity. Lack of GH results in slower growth, delayed maturation, and reduced body size and can lead to delayed aging, increased healthspan, and a remarkable extension of longevity. Adult body size, which is a GH-dependent trait, has a negative association with longevity in several mammalian species. Mechanistic links between GH and aging include evolutionarily conserved insulin/insulin-like growth factors and mechanistic target of rapamycin signaling pathways in accordance with long-suspected trade-offs between anabolic/growth processes and longevity. Height and the rate and regulation of GH secretion have been related to human aging, but longevity is not extended in humans with syndromes of GH deficiency or resistance. However, the risk of age-related chronic disease is reduced in individuals affected by these syndromes and various indices of increased healthspan have been reported.

Can Blood-Circulating Factors Unveil and Delay Your Biological Aging?

According to the World Health Organization, the population of over 60 will double in the next 30 years in the developed countries, which will enforce a further raise of the retirement age and increase the burden on the healthcare system. Therefore, there is an acute issue of maintaining health and prolonging active working longevity, as well as implementation of early monitoring and prevention of premature aging and age-related disorders to avoid early disability. Traditional indicators of biological age are not always informative and often require extensive and expensive analysis. The study of blood factors is a simple and easily accessible way to assess individual health and supplement the traditional indicators of a person's biological age with new objective criteria. With age, the processes of growth and development, tissue regeneration and repair decline; they are gradually replaced by enhanced catabolism, inflammatory cell activity, and insulin resistance. The number of senescent cells supporting the inflammatory loop rises; cellular clearance by autophagy and mitophagy slows down, resulting in mitochondrial and cellular damage and dysfunction. Monitoring of circulated blood factors not only reflects these processes, but also allows suggesting medical intervention to prevent or decelerate the development of age-related diseases. We review the age-related blood factors discussed in recent publications, as well as approaches to slowing aging for healthy and active longevity.

Acute sleep deprivation leads to growth hormone (GH) resistance in rats

Sleep is an essential physiological process that is required by all higher animals. Sleep has many important physiological functions. Previous studies have focused on the relationship between sleep and growth hormone secretion patterns. However, to date, whether sleep affects the biological activities of GH remains unclear. Here, we investigated this issue by evaluating the growth hormone receptor (GHR)-mediated intracellular signalling pathway in a sleep-deprived rat model. The results showed that GH's signalling ability is decreased in an acute sleep deprivation rat model. JAK2-STAT signalling was decreased significantly compared to that in control rats. We further analysed the possible molecular mechanism of GH signal inhibition in sleep-deprived rats. The results showed that the protein expression levels of SOCS3 (suppressors of cytokine signalling 3, which functions as the negative regulatory molecule of GH's signalling) increased; however, other negative regulatory proteins, such as protein phosphatase (PTP1B), did not change. In addition, acute sleep deprivation results in a significant increase in serum FFA (free fatty acid) level, which is also one of the factors contributing to GH inhibition. These findings suggest that GH signal resistance may be caused by a combination of factors. This study could serve as an important reference for related studies on the effect of sleep deprivation on endocrine systems.

Insulin sensitivity in long-lived growth hormone-releasing hormone knockout mice

Our previous studies showed that loss-of-function mutation of growth hormone releasing hormone (GHRH) results in increased longevity and enhanced insulin sensitivity in mice. However, the details of improved insulin action and tissue-specific insulin signaling are largely unknown in this healthy-aging mouse model. We conducted hyperinsulinemic-euglycemic clamp to investigate mechanisms underlying enhanced insulin sensitivity in growth hormone (GH) deficient mice. Further, we assessed in vivo tissue-specific insulin activity via activation of PI3K-AKT and MAPK-ERK1/2 cascades using western blot. Clamp results showed that the glucose infusion rate required for maintaining euglycemia was much higher in GHRH^-/- mice compared to WT controls. Insulin-mediated glucose production was largely suppressed, whereas glucose uptake in skeletal muscle and brown adipose tissue were significant enhanced in GHRH^-/- mice compared to WT controls. Enhanced capacity of insulin-induced activation of the PI3K-AKT and MAPK-ERK1/2 signaling were observed in a tissue-specific manner in GHRH^-/- mice. Enhanced systemic insulin sensitivity in long-lived GHRH^-/- mice is associated with differential activation of insulin signaling cascades among various organs. Improved action of insulin in the insulin sensitive tissues is likely to mediate the prolonged longevity and healthy-aging effects of GH deficiency in mice.

Whole-genome sequencing of Chinese centenarians reveals important genetic variants in aging WGS of centenarian for genetic analysis of aging

Background

Genetic research on longevity has provided important insights into the mechanism of aging and aging-related diseases. Pinpointing import genetic variants associated with aging could provide insights for aging research.

Methods

We performed a whole-genome sequencing in 19 centenarians to establish the genetic basis of human longevity.

Results

Using SKAT analysis, we found 41 significantly correlated genes in centenarians as compared to control genomes. Pathway enrichment analysis of these genes showed that immune-related pathways were enriched, suggesting that immune pathways might be critically involved in aging. HLA typing was next performed based on the whole-genome sequencing data obtained. We discovered that several HLA subtypes were significantly overrepresented.

Conclusions

Our study indicated a new mechanism of longevity, suggesting potential genetic variants for further study.

Physiological and metabolic features of mice with CRISPR/Cas9-mediated loss-of-function in growth hormone-releasing hormone

Our previous study demonstrated that the loss of growth hormone releasing hormone (GHRH) results in increased lifespan and improved metabolic homeostasis in the mouse model generated by classical embryonic stem cell-based gene-targeting method. In this study, we targeted the GHRH gene using the CRISPR/Cas9 technology to avoid passenger alleles/mutations and performed in-depth physiological and metabolic characterization. In agreement with our previous observations, male and female GHRH-/- mice have significantly reduced body weight and enhanced insulin sensitivity when compared to wild type littermates. Dual-energy X-ray absorptiometry showed that there were significant decreases in lean mass, bone mineral content and density, and a dramatic increase in fat mass of GHRH-/- mice when compared to wild type littermates. Indirect calorimetry measurements showed dramatic reductions in oxygen consumption, carbon dioxide production and energy expenditure in GHRH-/- mice compared to wild type mice in both light and dark cycles. Respiratory exchange ratio was significantly lower in GHRH-/- mice during the light cycle, but not during the dark cycle, indicating a circadian related metabolic shift towards fat utilization in the growth hormone deficient mice. The novel CRISPR/Cas9 GHRH-/- mice are exhibiting the consistent and unique physiological and metabolic characteristics, which might mediate the longevity effects of growth hormone deficiency in mice.

Interrelationships Between Pituitary Hormones as Assessed From 24-hour Serum Concentrations in Healthy Older Subjects

CONTEXT

Hormones of the hypothalamic-pituitary-target gland axes are mostly investigated separately, whereas the interplay between hormones might be as important as each separate hormonal axis.

OBJECTIVE

Our aim is to determine the interrelationships between GH, TSH, ACTH, and cortisol in healthy older individuals.

DESIGN

We made use of 24-hour hormone serum concentrations assessed with intervals of 10 minutes from 38 healthy older individuals with a mean age (SD) of 65.1 (5.1) years from the Leiden Longevity Study. Cross-correlation analyses were performed to assess the relative strength between 2 24-hour hormone serum concentration series for all possible time shifts. Cross-approximate entropy was used to assess pattern synchronicity between 2 24-hour hormone serum concentration series.

RESULTS

Within an interlinked hormonal axis, ACTH and cortisol were positively correlated with a mean (95% confidence interval) correlation coefficient of 0.78 (0.74-0.81) with cortisol following ACTH concentrations with a delay of 10 minutes. Between different hormonal axes, we observed a negative correlation coefficient between cortisol and TSH of -0.30 (-0.36 to -0.25) with TSH following cortisol concentrations with a delay of 170 minutes. Furthermore, a positive mean (95% confidence interval) correlation coefficient of 0.29 (0.22-0.37) was found between TSH and GH concentrations without any delay. Moreover, cross-approximate entropy analyses showed that GH and cortisol exhibit synchronous serum concentration patterns.

CONCLUSIONS

This study demonstrates that interrelations between hormones from interlinked as well as different hypothalamic-pituitary-target gland axes are observed in healthy older individuals. More research is needed to determine the biological meaning and clinical consequences of these observations.

Inactivity and Skeletal Muscle Metabolism: A Vicious Cycle in Old Age

Aging is an inevitable and gradually progressive process affecting all organs and systems. The musculoskeletal system makes no exception, elderly exhibit an increased risk of sarcopenia (low muscle mass),dynapenia (declining muscle strength), and subsequent disability. Whereas in recent years the subject of skeletal muscle metabolic decline in the elderly has been gathering interest amongst researchers, as well as medical professionals, there are many challenges yet to be solved in order to counteract the effects of aging on muscle function efficiently. Noteworthy, it has been shown that aging individuals exhibit a decline in skeletal muscle metabolism, a phenomenon which may be linked to a number of predisposing (risk) factors such as telomere attrition, epigenetic changes, mitochondrial dysfunction, sedentary behavior (leading to body composition alterations), age-related low-grade systemic inflammation (inflammaging), hormonal imbalance, as well as a hypoproteic diet (unable to counterbalance the repercussions of the age-related increase in skeletal muscle catabolism). The present review aims to discuss the relationship between old age and muscle wasting in an effort to highlight the modifications in skeletal muscle metabolism associated with aging and physical activity.

Genetic Pathways of Aging and Their Relevance in the Dog as a Natural Model of Human Aging

Aging research has experienced a burst of scientific efforts in the last decades as the growing ratio of elderly people has begun to pose an increased burden on the healthcare and pension systems of developed countries. Although many breakthroughs have been reported in understanding the cellular mechanisms of aging, the intrinsic and extrinsic factors that contribute to senescence on higher biological levels are still barely understood. The dog, Canis familiaris, has already served as a valuable model of human physiology and disease. The possible role the dog could play in aging research is still an open question, although utilization of dogs may hold great promises as they naturally develop age-related cognitive decline, with behavioral and histological characteristics very similar to those of humans. In this regard, family dogs may possess unmatched potentials as models for investigations on the complex interactions between environmental, behavioral, and genetic factors that determine the course of aging. In this review, we summarize the known genetic pathways in aging and their relevance in dogs, putting emphasis on the yet barely described nature of certain aging pathways in canines. Reasons for highlighting the dog as a future aging and gerontology model are also discussed, ranging from its unique evolutionary path shared with humans, its social skills, and the fact that family dogs live together with their owners, and are being exposed to the same environmental effects.

Mitochondria in the signaling pathways that control longevity and health span

Genetic and pharmacological intervention studies have identified evolutionarily conserved and functionally interconnected networks of cellular energy homeostasis, nutrient-sensing, and genome damage response signaling pathways, as prominent regulators of longevity and health span in various species. Mitochondria are the primary sites of ATP production and are key players in several other important cellular processes. Mitochondrial dysfunction diminishes tissue and organ functional performance and is a commonly considered feature of the aging process. Here we review the evidence that through reciprocal and multilevel functional interactions, mitochondria are implicated in the lifespan modulation function of these pathways, which altogether constitute a highly dynamic and complex system that controls the aging process. An important characteristic of these pathways is their extensive crosstalk and apparent malleability to modification by non-invasive pharmacological, dietary, and lifestyle interventions, with promising effects on lifespan and health span in animal models and potentially also in humans.

Growth Hormone Deficiency: Health and Longevity

The important role of GH in the control of mammalian longevity was first deduced from extended longevity of mice with genetic GH deficiency (GHD) or GH resistance. Mice with isolated GHD (IGHD) due to GHRH or GHRH receptor mutations, combined deficiency of GH, prolactin, and TSH, or global deletion of GH receptors live longer than do their normal siblings. They also exhibit multiple features of delayed and/or slower aging, accompanied by extension of healthspan. The unexpected, remarkable longevity benefit of severe endocrine defects in these animals presumably represents evolutionarily conserved trade-offs among aging, growth, maturation, fecundity, and the underlying anabolic processes. Importantly, the negative association of GH signaling with longevity extends to other mammalian species, apparently including humans. Data obtained in humans with IGHD type 1B, owing to a mutation of the GHRH receptor gene, in the Itabaianinha County, Brazil, provide a unique opportunity to study the impact of severe reduction in GH signaling on age-related characteristics, health, and functionality. Individuals with IGHD are characterized by proportional short stature, doll facies, high-pitched voices, and central obesity. They have delayed puberty but are fertile and generally healthy. Moreover, these IGHD individuals are partially protected from cancer and some of the common effects of aging and can attain extreme longevity, 103 years of age in one case. We think that low, but detectable, residual GH secretion combined with life-long reduction of circulating IGF-1 and with some tissue levels of IGF-1 and/or IGF-2 preserved may account for the normal longevity and apparent extension of healthspan in these individuals.

The 24-hour serum profiles of bone markers in healthy older men and women

The process of bone turnover displays variations over 24 h, with C-terminal cross-linked telopeptide of type 1 collagen (CTX) and osteocalcin exhibiting a nadir in the afternoon and a peak in the night. In contrast, N-terminal propeptide of type 1 procollagen (P1NP) did not display an apparent 24-hour rhythm. Other emerging novel biomarkers of bone, sclerostin and Dickkopf-related protein 1 (DKK1), are markers of osteocyte activity with limited data available regarding their 24-hour profiles. In this study, we aimed to extend available data on 24-hour profiles of CTX, osteocalcin, and P1NP and to assess the 24-hour profiles of sclerostin and DKK1 in healthy older men and women and to compare these between men and women. We measured these five bone markers in EDTA plasma collected every 4 h during 24 h in 37 healthy older men and women (range 52-76 years). Differences between time points were determined using repeated measures ANOVA and cosinor analyses were performed to determine circadian rhythmicity. The circadian rhythm of CTX was confirmed by the cosinor model, with women showing larger amplitude compared to men. Osteocalcin showed higher levels during nighttime compared to daytime in both men and women. For P1NP levels we observed a small but significant increase in the night in men. Sclerostin and DKK1 did not show a circadian rhythm, but sclerostin levels differed between time points. Because of the large intraindividual variation, DKK1 as measured in this study cannot be considered a reliable marker for diagnostic or research purposes. In conclusion, when measuring CTX, osteocalcin, P1NP, or sclerostin either in clinical practice or in a research setting, one should consider the 24-hour profiles of these bone markers.

Targeting growth hormone function: strategies and therapeutic applications

Human growth hormone (GH) is a classical pituitary endocrine hormone that is essential for normal postnatal growth and has pleiotropic effects across multiple physiological systems. GH is also expressed in extrapituitary tissues and has localized autocrine/paracrine effects at these sites. In adults, hypersecretion of GH causes acromegaly, and strategies that block the release of GH or that inhibit GH receptor (GHR) activation are the primary forms of medical therapy for this disease. Overproduction of GH has also been linked to cancer and the microvascular complications that are associated with diabetes. However, studies to investigate the therapeutic potential of GHR antagonism in these diseases have been limited, most likely due to difficulty in accessing therapeutic tools to study the pharmacology of the receptor in vivo. This review will discuss current and emerging strategies for antagonizing GH function and the potential disease indications.

Emerging therapies are offering an expanded toolkit for combatting the effects of human growth hormone overproduction. Human growth hormone (GH) is a major driver of postnatal growth; however, systemic or localized overproduction is implicated in the aberrant growth disease acromegaly, cancer, and diabetes. In this review, researchers led by Jo Perry, from the University of Auckland, New Zealand, discuss strategies that either inhibit GH production, block its systemic receptor, or interrupt its downstream signaling pathways. The only licensed GH receptor blocker is pegvisomant, but therapies are in development that include long-acting protein and antibody-based blockers, and nucleotide complexes that degrade GHR production have also shown promise. Studies investigating GHR antagonism are limited, partly due to difficulty in accessing therapeutic tools which block GHR function, but overcoming these obstacles may yield advances in alleviating chronic disease.

ROLE of IGF-1 System in the Modulation of Longevity: Controversies and New Insights From a Centenarians' Perspective

Human aging is currently defined as a physiological decline of biological functions in the body with a continual adaptation to internal and external damaging. The endocrine system plays a major role in orchestrating cellular interactions, metabolism, growth, and aging. Several in vivo studies from worms to mice showed that downregulated activity of the GH/IGF-1/insulin pathway could be beneficial for the extension of human life span, whereas results are contradictory in humans. In the present review, we discuss the potential role of the IGF-1 system in modulation of longevity, hypothesizing that the endocrine and metabolic adaptation observed in centenarians and in mammals during caloric restriction may be a physiological strategy for extending lifespan through a slower cell growing/metabolism, a better physiologic reserve capacity, a shift of cellular metabolism from cell proliferation to repair activities and a decrease in accumulation of senescent cells. Therefore, understanding of the link between IGF-1/insulin system and longevity may have future clinical applications in promoting healthy aging and in Rehabilitation Medicine.

Exceptional Human Longevity

Exceptional longevity represents an extreme phenotype. Current centenarians are survivors of a cohort who display delayed onset of age-related diseases and/or resistance to otherwise lethal illnesses occurring earlier in life. Characteristics of aging are heterogeneous, even among long-lived individuals. Associations between specific clinical or genetic biomarkers exist, but there is unlikely to be a single biomarker predictive of long life. Careful observations in the oldest old offer some empirical strategies that favor increased health span and life span, with implications for compression of disability, identification and implementation of lifestyle behaviors that promote independence, identification and measurement of more reliable markers associated with longevity, better guidance for appropriate health screenings, and promotion of anticipatory health discussions in the setting of more accurate prognostication. Comprehensive PubMed literature searches were performed, with an unbiased focus on mechanisms of longevity. Overall, the aggregate literature supports that the basis for exceptional longevity is multifactorial and involves disparate combinations of genes, environment, resiliency, and chance, all of which are influenced by culture and geography.

Impact of Growth Hormone-Related Mutations on Mammalian Aging

Mutations of a single gene can lead to a major increase in longevity in organisms ranging from yeast and worms to insects and mammals. Discovering these mutations (sometimes referred to as “longevity genes”) led to identification of evolutionarily conserved molecular, cellular, and organismal mechanisms of aging. Studies in mice provided evidence for the important role of growth hormone (GH) signaling in mammalian aging. Mice with mutations or gene deletions leading to GH deficiency or GH resistance have reduced body size and delayed maturation, but are healthier and more resistant to stress, age slower, and live longer than their normal (wild type) siblings. Mutations of the same genes in people can provide remarkable protection from age-related disease, but have no consistent impact on lifespan. Ongoing research indicates that genetic defects in GH signaling are linked to extension of healthspan and lifespan via a variety of interlocking mechanism, including improvements in genome and stem cell maintenance, stress resistance, glucose homeostasis, and thermogenesis, along with reductions in the mechanistic target of rapamycin (mTOR) C1 complex signaling and in chronic low grade inflammation.

Growth Hormone and Aging: Updated Review

Role of growth hormone (GH) in mammalian aging is actively explored in clinical, epidemiological, and experimental studies. The age-related decline in GH levels is variously interpreted as a symptom of neuroendocrine aging, as one of causes of altered body composition and other unwelcome symptoms of aging, or as a mechanism of natural protection from cancer and other chronic diseases. Absence of GH signals due to mutations affecting anterior pituitary development, GH secretion, or GH receptors produces an impressive extension of longevity in laboratory mice. Extension of healthspan in these animals and analysis of survival curves suggest that in the absence of GH, aging is slowed down or delayed. The corresponding endocrine syndromes in the human have no consistent impact on longevity, but are associated with remarkable protection from age-related disease. Moreover, survival to extremely old age has been associated with reduced somatotropic (GH and insulin-like growth factor-1) signaling in women and men. In both humans and mice, elevation of GH levels into the supranormal (pathological) range is associated with increased disease risks and reduced life expectancy likely representing acceleration of aging. The widely advertised potential of GH as an anti-aging agent attracted much interest. However, results obtained thus far have been disappointing with few documented benefits and many troublesome side effects. Possible utility of GH in the treatment of sarcopenia and frailty remains to be explored.

MECHANISMS IN ENDOCRINOLOGY: Lessons from growth hormone receptor gene-disrupted mice: are there benefits of endocrine defects?

Growth hormone (GH) is produced primarily by anterior pituitary somatotroph cells. Numerous acute human (h) GH treatment and long-term follow-up studies and extensive use of animal models of GH action have shaped the body of GH research over the past 70 years. Work on the GH receptor (R)-knockout (GHRKO) mice and results of studies on GH-resistant Laron Syndrome (LS) patients have helped define many physiological actions of GH including those dealing with metabolism, obesity, cancer, diabetes, cognition and aging/longevity. In this review, we have discussed several issues dealing with these biological effects of GH and attempt to answer the question of whether decreased GH action may be beneficial.

Prolonged Growth Hormone/Insulin/Insulin-like Growth Factor Nutrient Response Signaling Pathway as a Silent Killer of Stem Cells and a Culprit in Aging

The dream of slowing down the aging process has always inspired mankind. Since stem cells are responsible for tissue and organ rejuvenation, it is logical that we should search for encoded mechanisms affecting life span in these cells. However, in adult life the hierarchy within the stem cell compartment is still not very well defined, and evidence has accumulated that adult tissues contain rare stem cells that possess a broad trans-germ layer differentiation potential. These most-primitive stem cells-those endowed with pluripotent or multipotent differentiation ability and that give rise to other cells more restricted in differentiation, known as tissue-committed stem cells (TCSCs) - are of particular interest. In this review we present the concept supported by accumulating evidence that a population of so-called very small embryonic-like stem cells (VSELs) residing in adult tissues positively impacts the overall survival of mammals, including humans. These unique cells are prevented in vertebrates from premature depletion by decreased sensitivity to growth hormone (GH), insulin (INS), and insulin-like growth factor (IGF) signaling, due to epigenetic changes in paternally imprinted genes that regulate their resistance to these factors. In this context, we can envision nutrient response GH/INS/IGF signaling pathway as a lethal factor for these most primitive stem cells and an important culprit in aging.

Somatic growth, aging, and longevity

Although larger species of animals typically live longer than smaller species, the relationship of body size to longevity within a species is generally opposite. The longevity advantage of smaller individuals can be considerable and is best documented in laboratory mice and in domestic dogs. Importantly, it appears to apply broadly, including humans. It is not known whether theses associations represent causal links between various developmental and physiological mechanisms affecting growth and/or aging. However, variations in growth hormone (GH) signaling are likely involved because GH is a key stimulator of somatic growth, and apparently also exerts various “pro-aging” effects. Mechanisms linking GH, somatic growth, adult body size, aging, and lifespan likely involve target of rapamycin (TOR), particularly one of its signaling complexes, mTORC1, as well as various adjustments in mitochondrial function, energy metabolism, thermogenesis, inflammation, and insulin signaling. Somatic growth, aging, and longevity are also influenced by a variety of hormonal and nutritional signals, and much work will be needed to answer the question of why smaller individuals may be likely to live longer.

Longevity is impacted by growth hormone action during early postnatal period

Life-long lack of growth hormone (GH) action can produce remarkable extension of longevity in mice. Here we report that GH treatment limited to a few weeks during development influences the lifespan of long-lived Ames dwarf and normal littermate control mice in a genotype and sex-specific manner. Studies in a separate cohort of Ames dwarf mice show that this short period of the GH exposure during early development produces persistent phenotypic, metabolic and molecular changes that are evident in late adult life. These effects may represent mechanisms responsible for reduced longevity of dwarf mice exposed to GH treatment early in life. Our data suggest that developmental programming of aging importantly contributes to (and perhaps explains) the well documented developmental origins of adult disease.

The GH receptor exon 3 deletion is a marker of male-specific exceptional longevity associated with increased GH sensitivity and taller stature

Although both growth hormone (GH) and insulin-like growth factor 1 (IGF-1) signaling were shown to regulate life span in lower organisms, the role of GH signaling in human longevity remains unclear. Because a GH receptor exon 3 deletion (d3-GHR) appears to modulate GH sensitivity in humans, we hypothesized that this polymorphism could play a role in human longevity. We report a linear increased prevalence of d3-GHR homozygosity with age in four independent cohorts of long-lived individuals: 841 participants [567 of the Longevity Genes Project (LGP) (8% increase; P = 0.01), 152 of the Old Order Amish (16% increase; P = 0.02), 61 of the Cardiovascular Health Study (14.2% increase; P = 0.14), and 61 of the French Long-Lived Study (23.5% increase; P = 0.02)]. In addition, mega analysis of males in all cohorts resulted in a significant positive trend with age (26% increase; P = 0.007), suggesting sexual dimorphism for GH action in longevity. Further, on average, LGP d3/d3 homozygotes were 1 inch taller than the wild-type (WT) allele carriers (P = 0.05) and also showed lower serum IGF-1 levels (P = 0.003). Multivariate regression analysis indicated that the presence of d3/d3 genotype adds approximately 10 years to life span. The LGP d3/d3-GHR transformed lymphocytes exhibited superior growth and extracellular signal-regulated kinase activation, to GH treatment relative to WT GHR lymphocytes (P < 0.01), indicating a GH dose response. The d3-GHR variant is a common genetic polymorphism that modulates GH responsiveness throughout the life span and positively affects male longevity.

Altered structure and function of adipose tissue in long-lived mice with growth hormone-related mutations

A major focus of biogerontology is elucidating the role(s) of the endocrine system in aging and the accumulation of age-related diseases. Endocrine control of mammalian longevity was first reported in Ames dwarf (Prop1^df) mice, which are long-lived due to a recessive Prop1 loss-of-function mutation resulting in deficiency of growth hormone (GH), thyroid-stimulating hormone, and prolactin. Following this report, several other GH-related mutants with altered longevity have been described including long-lived Snell dwarf and growth hormone receptor knockout mice, and short-lived GH overexpressing transgenic mice. One of the emerging areas of interest in these mutant mice is the role of adipose tissue in their altered healthspan and lifespan. Here, we provide an overview of the alterations in body composition of GH-related mutants, as well as the altered thermogenic potential of their brown adipose tissue and the altered cellular senescence and adipokine production of their white adipose tissue.

Emerging Molecular Pathways Governing Dietary Regulation of Neural Stem Cells during Aging

Aging alters cellular and molecular processes, including those of stem cells biology. In particular, changes in neural stem cells (NSCs) are linked to cognitive decline associated with aging. Recently, the systemic environment has been shown to alter both NSCs regulation and age-related cognitive decline. Interestingly, a well-documented and naturally occurring way of altering the composition of the systemic environment is through diet and nutrition. Furthermore, it is well established that the presence of specific nutrients as well as the overall increase or reduction of calorie intake can modulate conserved molecular pathways and respectively reduce or increase lifespan. In this review, we examine these pathways in relation to their function on NSCs and cognitive aging. We highlight the importance of the Sirtuin, mTOR and Insulin/Insulin like growth factor-1 pathways as well as the significant role played by epigenetics in the dietary regulation of NSCs and the need for further research to exploit nutrition as a mode of intervention to regulate NSCs aging.

Functionally enhanced brown adipose tissue in Ames dwarf mice

Reduced insulin-like growth factor 1/insulin signaling (IIS) has been linked to extended longevity in species ranging from yeast to mammals. In mammals, this is exemplified in Ames dwarf (Prop1^df/df) mice, which have a 40%-60% increase in longevity (males and females, respectively) due to their recessive Prop1 loss-of-function mutation that results in lack of growth hormone (GH), thyroid-stimulating hormone and prolactin. Our laboratory has previously shown that Ames dwarf mice have functionally unique white adipose tissue (WAT) that improves, rather than impairs, insulin sensitivity. Because GH and thyroid hormone are integral to adipose tissue development and function, we hypothesized that brown adipose tissue (BAT) in Ames dwarf mice may also be functionally unique and/or enhanced. Here, we elaborate on our recent findings, which demonstrate that BAT is functionally enhanced in Ames dwarf mice, and suggest that BAT removal in these mice results in utilization of WAT depots as an energy source. We also discuss how our findings compare to those in other long-lived dwarf mice with altered IIS, which unlike Ames dwarf mice, are essentially euthyroid. Lastly, we provide some insights into the implications of these findings and discuss some of the necessary future work in this area.

Familial Longevity Is Not Associated with Major Differences in the Hypothalamic-Pituitary-Gonadal Axis in Healthy Middle-Aged Men

CONTEXT

A trade-off between fertility and longevity possibly exists. The association of the male hypothalamic-pituitary-gonadal (HPG) axis with familial longevity has not yet been investigated.

OBJECTIVE

To study 24-h hormone concentration profiles of the HPG axis in men enriched for familial longevity and controls.

DESIGN

We frequently sampled blood over 24 h in 10 healthy middle-aged male offspring of nonagenarian participants from the Leiden Longevity Study together with 10 male age-matched controls. Individual 24-h luteinizing hormone (LH) and testosterone concentration profiles were analyzed by deconvolution analyses to estimate secretion parameters. Furthermore, the temporal relationship between LH and testosterone was assessed by cross-correlation analysis. We used (cross-)approximate entropy to quantify the strength of feedback and/or feedforward control of LH and testosterone secretion.

RESULTS

Mean [95% confidence interval (CI)] total LH secretion of the offspring was 212 (156-268) U/L/24 h, which did not differ significantly (p = 0.51) from the total LH secretion of controls [186 (130-242) U/L/24 h]. Likewise, mean (95% CI) total testosterone secretion of the offspring [806 (671-941) nmol/L/24 h] and controls [811 (676-947) nmol/L/24 h] were similar (p = 0.95). Other parameters of LH and testosterone secretion were also not significantly different between offspring and controls. The temporal relationship between LH and testosterone and the strength of feedforward/feedback regulation within the HPG axis were similar between offspring of long-lived families and controls.

CONCLUSION

This relatively small study suggests that in healthy male middle-aged participants, familial longevity is not associated with major differences in the HPG axis. Selection on both fertility and health may in part explain the results.