Long-lived hypopituitary Ames dwarf mice are resistant to the detrimental effects of high-fat diet on metabolic function and energy expenditure

Calorie restriction and life-extending mutation downregulate miR-34a to facilitate lipid metabolism in the liver

Ames dwarf mice (df/df) display delayed aging relative to their normal (N) siblings, living approximately 40-60 % longer. As such, investigating the mechanisms that enable these organisms to have extended lifespan is useful for the development of interventions to slow aging and deter age-related disease. Nonalcoholic fatty liver disease (NAFLD) is a condition that is characterized by the accumulation of excess adipose tissue in the liver. Previous studies highlight the potential of calorie restriction (CR) in promoting longevity, but little is known about its effects on the biomolecular processes that govern NAFLD. In this study, we examined the role of 6-month CR on genes regulating lipid metabolism in the livers of long-living df/df mice and their N littermates. Importantly, our findings showed significant downregulation of miR-34a-5p in N-CR mice and df/df mice regardless of dietary regimen. Alongside, our RT-PCR results indicated that downregulation of miR-34a-5p is correlated with the expression of metabolism-associated mRNAs involved in modulating the processes of de novo lipogenesis (DNL), fatty acid oxidation (FAO), very-low density lipoprotein transport (VLDL-T), and reverse cholesterol transport (RCT). To further verify the role of miR-34a-5p in regulating metabolic processes, we transfected the human liver cancer (HepG2) cell line with miR-34a mimic, and studied its effect on direct targets Sirt1, Ampk, and Ppara as well as downstream lipid transport regulating genes. Our findings suggest that CR and df/df life extending mutation are robust drivers of the miR-34a-5p signaling pathway and prevent the pathogenesis of age-related diseases by improving overall lipid homeostasis.

Unveiling ceramide dynamics: Shedding light on healthy aging in growth hormone-releasing hormone knockout mice

Dysregulation of growth hormone (GH) signaling consistently leads to increased lifespan in laboratory rodents, yet the precise mechanisms driving this extension remain unclear. Understanding the molecular underpinnings of the beneficial effects associated with GH deficiency could unveil novel therapeutic targets for promoting healthy aging and longevity. In our pursuit of identifying metabolites implicated in aging, we conducted an unbiased lipidomic analysis of serum samples from growth hormone-releasing hormone knockout (GHRH-KO) female mice and their littermate controls. Employing a targeted lipidomic approach, we specifically investigated ceramide levels in GHRH-KO mice, a well-established model of enhanced longevity. While younger GHRH-KO mice did not exhibit notable differences in serum lipids, older counterparts demonstrated significant reductions in over one-third of the evaluated lipids. In employing the same analysis in liver tissue, GHRH-KO mice showed pronounced downregulation of numerous ceramides and hexosylceramides, which have been shown to elicit many of the tissue defects that accompany aging (e.g., insulin resistance, oxidative stress, and cell death). Additionally, gene expression analysis in the liver tissue of adult GHRH-KO mice identified substantial decreases in several ceramide synthesis genes, indicating that these alterations are, at least in part, attributed to GHRH-KO-induced transcriptional changes. These findings provide the first evidence of disrupted ceramide metabolism in a long-lived mammal. This study sheds light on the intricate connections between GH deficiency, ceramide levels, and the molecular mechanisms influencing lifespan extension.

Growth hormone-releasing hormone deficiency confers extended lifespan and metabolic resilience during high-fat feeding in mid and late life

Growth hormone-releasing hormone-deficient (GHRH-KO) mice have previously been characterized by lower body weight, disproportionately high body fat accumulation, preferential metabolism of lipids compared to carbohydrates, improved insulin sensitivity, and an extended lifespan. That these mice are long-lived and insulin-sensitive conflicts with the notion that adipose tissue accumulation drives the health detriments associated with obesity (i.e., diabetes), and indicates that GH signaling may be necessary for the development of adverse effects linked to obesity. This prompts investigation into the ultimate effect of diet-induced obesity on the lifespan of these long-lived mice. To this end, we initiated high-fat feeding in mid and late-life in GHRH-KO and wild-type (WT) mice. We carried out extensive lifespan analysis coupled with glucose/insulin tolerance testing and indirect calorimetry to gauge the metabolic effect of high-fat dietary stress through adulthood on these mice. We show that under high-fat diet (HFD) conditions, GHRH-KO mice display extended lifespans relative to WT controls. We also show that GHRH-KO mice are more insulin-sensitive and display less dramatic changes in their metabolism relative to WT mice, with GHRH-KO mice fed HFD displaying respiratory exchange ratios and glucose oxidation rates comparable to control-diet fed GHRH-KO mice, while WT mice fed HFD showed significant reductions in these parameters. Our results indicate that GH deficiency protects against the adverse effects of diet-induced obesity in later life.

Impact of visceral adipose tissue on longevity and metabolic health: a comparative study of gene expression in perirenal and epididymal fat of Ames dwarf mice

Emerging research underscores the pivotal role of adipose tissue in regulating systemic aging processes, particularly when viewed through the lens of the endocrine hypotheses of aging. This study delves into the unique adipose characteristics in an important animal model of aging - the long-lived Ames dwarf (df/df) mice. Characterized by a Prop1df gene mutation, these mice exhibit a deficiency in growth hormone (GH), prolactin, and TSH, alongside extremely low circulating IGF-1 levels. Intriguingly, while surgical removal of visceral fat (VFR) enhances insulin sensitivity in normal mice, it paradoxically increases insulin resistance in Ames dwarfs. This suggests an altered profile of factors produced in visceral fat in the absence of GH, indicating a unique interplay between adipose tissue function and hormonal influences in these models. Our aim was to analyze the gene expression related to lipid and glucose metabolism, insulin pathways, inflammation, thermoregulation, mitochondrial biogenesis, and epigenetic regulation in the visceral (perirenal and epididymal) adipose tissue of Ames dwarf and normal mice. Our findings reveal an upregulation in the expression of key genes such as Lpl, Adrβ3, Rstn, Foxo1, Foxo3a, Irs1, Cfd, Aldh2, Il6, Tnfα, Pgc1α, Ucp2, and Ezh2 in perirenal and Akt1, Foxo3a, PI3k, Ir, Acly, Il6, Ring1a, and Ring 1b in epididymal fat in df/df mice. These results suggest that the longevity phenotype in Ames dwarfs, which is determined by peripubertal GH/IGF-1 levels, may also involve epigenetic reprogramming of adipose tissue influenced by hormonal changes. The increased expression of genes involved in metabolic regulation, tumor suppression, mitochondrial biogenesis, and insulin pathways in Ames dwarf mice highlights potentially beneficial aspects of this model, opening new avenues for understanding the molecular underpinnings of longevity and aging.

microRNA-449a reduces growth hormone-stimulated senescent cell burden through PI3K-mTOR signaling

Cellular senescence, a hallmark of aging, has been implicated in the pathogenesis of many major age-related disorders, including neurodegeneration, atherosclerosis, and metabolic disease. Therefore, investigating novel methods to reduce or delay the accumulation of senescent cells during aging may attenuate age-related pathologies. microRNA-449a-5p (miR-449a) is a small, noncoding RNA down-regulated with age in normal mice but maintained in long-living growth hormone (GH)-deficient Ames Dwarf (df/df) mice. We found increased fibroadipogenic precursor cells, adipose-derived stem cells, and miR-449a levels in visceral adipose tissue of long-living df/df mice. Gene target analysis and our functional study with miR-449a-5p have revealed its potential as a serotherapeutic. Here, we test the hypothesis that miR-449a reduces cellular senescence by targeting senescence-associated genes induced in response to strong mitogenic signals and other damaging stimuli. We demonstrated that GH downregulates miR-449a expression and accelerates senescence while miR-449a upregulation using mimetics reduces senescence, primarily through targeted reduction of p16Ink4a, p21Cip1, and the PI3K-mTOR signaling pathway. Our results demonstrate that miR-449a is important in modulating key signaling pathways that control cellular senescence and the progression of age-related pathologies.

Cell non-autonomous regulation of cerebrovascular aging processes by the somatotropic axis

Age-related cerebrovascular pathologies, ranging from cerebromicrovascular functional and structural alterations to large vessel atherosclerosis, promote the genesis of vascular cognitive impairment and dementia (VCID) and exacerbate Alzheimer's disease. Recent advances in geroscience, including results from studies on heterochronic parabiosis models, reinforce the hypothesis that cell non-autonomous mechanisms play a key role in regulating cerebrovascular aging processes. Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) exert multifaceted vasoprotective effects and production of both hormones is significantly reduced in aging. This brief overview focuses on the role of age-related GH/IGF-1 deficiency in the development of cerebrovascular pathologies and VCID. It explores the mechanistic links among alterations in the somatotropic axis, specific macrovascular and microvascular pathologies (including capillary rarefaction, microhemorrhages, impaired endothelial regulation of cerebral blood flow, disruption of the blood brain barrier, decreased neurovascular coupling, and atherogenesis) and cognitive impairment. Improved understanding of cell non-autonomous mechanisms of vascular aging is crucial to identify targets for intervention to promote cerebrovascular and brain health in older adults.

GH deficiency confers protective advantages against Alzheimer's disease through rescued miRNA expression profile in APP/PS1 mice

Alzheimer's disease (AD) is the most common form of dementia, affecting approximately 6.5 million Americans age 65 or older. AD is characterized by increased cognitive impairment and treatment options available provide minimal disease attenuation. Additionally, diagnostic methods for AD are not conclusive with definitive diagnoses requiring postmortem brain evaluations. Therefore, miRNAs, a class of small, non-coding RNAs, have garnered attention for their ability to regulate a variety of mRNAs and their potential to serve as both therapeutic targets and biomarkers of AD. Several miRNAs have already been implicated with AD and have been found to directly target genes associated with AD pathology. The APP/PS1 mice is an AD model that expresses the human mutated form of the amyloid precursor protein (APP) and presenilin-1 (PS1) genes. In a previous study, it was identified that crossing long-living growth hormone (GH)-deficient Ames dwarf (df/df) mice with APP/PS1 mice provided protection from AD through a reduction in IGF-1, amyloid-β (Aβ) deposition, and gliosis. Hence, we hypothesized that changes in the expression of miRNAs associated with AD mediated such benefits. To test this hypothesis, we sequenced miRNAs in hippocampi of df/df, wild type (+ / +), df/ + /APP/PS1 (phenotypically normal APP/PS1), and df/df/APP/PS1 mice. Results of this study demonstrated significantly upregulated and downregulated miRNAs between df/df/APP/PS1 and df/ + /APP/PS1 mice that suggest the df/df mutation provides protection from AD progression. Additionally, changes in miRNA expression with age were identified in both df/df and wild-type mice as well as df/df/APP/PS1 and APP/PS1 mice, with predictive functional roles in the Pi3k-AKT/mTOR/FOXO pathways potentially contributing to disease pathogenesis.

Transient early life growth hormone exposure permanently alters brain, muscle, liver, macrophage, and adipocyte status in long-lived Ames dwarf mice

The exceptional longevity of Ames dwarf (DF) mice can be abrogated by a brief course of growth hormone (GH) injections started at 2 weeks of age. This transient GH exposure also prevents the increase in cellular stress resistance and decline in hypothalamic inflammation characteristic of DF mice. Here, we show that transient early-life GH treatment leads to permanent alteration of pertinent changes in adipocytes, fat-associated macrophages, liver, muscle, and brain that are seen in DF mice. Ames DF mice, like Snell dwarf and GHRKO mice, show elevation of glycosylphosphatidylinositol specific phospholipase D1 in liver, neurogenesis in brain as indicated by BDNF and DCX proteins, muscle production of fibronectin type III domain-containing protein 5 (a precursor of irisin), uncoupling protein 1 as an index of thermogenic capacity in brown and white fat, and increase in fat-associated anti-inflammatory macrophages. In each case, transient exposure to GH early in life reverts the DF mice to the levels of each protein seen in littermate control animals, in animals evaluated at 15-18 months of age. Thus, many of the traits seen in long-lived mutant mice, pertinent to age-related changes in inflammation, neurogenesis, and metabolic control, are permanently set by early-life GH levels.

A Fat-Promoting Botanical Extract From Artemisia scoparia Exerts Geroprotective Effects on Caenorhabditis elegans Life Span and Stress Resistance

Like other biological processes, aging is not random but subject to molecular control. Natural products that modify core metabolic parameters, including fat content, may provide entry points to extend animal life span and promote healthy aging. Here, we show that a botanical extract from Artemisia scoparia (SCO), which promotes fat storage and metabolic resiliency in mice, extends the life span of the nematode Caenorhabditis elegans by up to 40%. Notably, this life-span extension depends significantly on SCO's effects on fat; SCO-treated worms exhibit heightened levels of unsaturated fat, and inhibition of Δ9 desaturases, which oversee biosynthesis of monounsaturated fatty acids, prevents SCO-dependent fat accumulation and life-span extension. At an upstream signaling level, SCO prompts changes to C. elegans fat regulation by stimulating nuclear translocation of transcription factor DAF-16/FOXO, an event that requires AMP-activated protein kinase under this condition. Importantly, animals treated with SCO are not only long-lived but also show improved stress resistance in late adulthood, suggesting that this fat-promoting intervention may enhance some aspects of physiological health in older age. These findings identify SCO as a natural product that can modify fat regulation for longevity benefit and add to growing evidence indicating that elevated fat can be prolongevity in some circumstances.

Mice with gene alterations in the GH and IGF family

Much of our understanding of GH's action stems from animal models and the generation and characterization of genetically altered or modified mice. Manipulation of genes in the GH/IGF1 family in animals started in 1982 when the first GH transgenic mice were produced. Since then, multiple laboratories have altered mouse DNA to globally disrupt Gh, Ghr, and other genes upstream or downstream of GH or its receptor. The ability to stay current with the various genetically manipulated mouse lines within the realm of GH/IGF1 research has been daunting. As such, this review attempts to consolidate and summarize the literature related to the initial characterization of many of the known gene-manipulated mice relating to the actions of GH, PRL and IGF1. We have organized the mouse lines by modifications made to constituents of the GH/IGF1 family either upstream or downstream of GHR or to the GHR itself. Available data on the effect of altered gene expression on growth, GH/IGF1 levels, body composition, reproduction, diabetes, metabolism, cancer, and aging are summarized. For the ease of finding this information, key words are highlighted in bold throughout the main text for each mouse line and this information is summarized in Tables 1, 2, 3 and 4. Most importantly, the collective data derived from and reported for these mice have enhanced our understanding of GH action.

Adiponectin preserves metabolic fitness during aging

Adiponectin is essential for the regulation of tissue substrate utilization and systemic insulin sensitivity. Clinical studies have suggested a positive association of circulating adiponectin with healthspan and lifespan. However, the direct effects of adiponectin on promoting healthspan and lifespan remain unexplored. Here, we are using an adiponectin null mouse and a transgenic adiponectin overexpression model. We directly assessed the effects of circulating adiponectin on the aging process and found that adiponectin null mice display exacerbated age-related glucose and lipid metabolism disorders. Moreover, adiponectin null mice have a significantly shortened lifespan on both chow and high-fat diet. In contrast, a transgenic mouse model with elevated circulating adiponectin levels has a dramatically improved systemic insulin sensitivity, reduced age-related tissue inflammation and fibrosis, and a prolonged healthspan and median lifespan. These results support a role of adiponectin as an essential regulator for healthspan and lifespan.

Mouse models of growth hormone deficiency

Nearly one century of research using growth hormone deficient (GHD) mouse lines has contributed greatly toward our knowledge of growth hormone (GH), a pituitary-derived hormone that binds and signals through the GH receptor and affects many metabolic processes throughout life. Although delayed sexual maturation, decreased fertility, reduced muscle mass, increased adiposity, small body size, and glucose intolerance appear to be among the negative characteristics of these GHD mouse lines, these mice still consistently outlive their normal sized littermates. Furthermore, the absence of GH action in these mouse lines leads to enhanced insulin sensitivity (likely due to the lack of GH's diabetogenic actions), delayed onset for a number of age-associated physiological declines (including cognition, cancer, and neuromusculoskeletal frailty), reduced cellular senescence, and ultimately, extended lifespan. In this review, we provide details about history, availability, growth, physiology, and aging of five commonly used GHD mouse lines.

Effect of growth hormone on insulin signaling

Growth hormone (GH) is a pleiotropic hormone that coordinates an array of physiological processes, including effects on bone, muscle, and fat, ultimately resulting in growth. Metabolically, GH promotes anabolic action in most tissues except adipose, where its catabolic action causes the breakdown of stored triglycerides into free fatty acids (FFA). GH antagonizes insulin action via various molecular pathways. Chronic GH secretion suppresses the anti-lipolytic action of insulin and increases FFA flux into the systemic circulation; thus, promoting lipotoxicity, which causes pathophysiological problems, including insulin resistance. In this review, we will provide an update on GH-stimulated adipose lipolysis and its consequences on insulin signaling in liver, skeletal muscle, and adipose tissue. Furthermore, we will discuss the mechanisms that contribute to the diabetogenic action of GH.

Integrated metabolomics reveals altered lipid metabolism in adipose tissue in a model of extreme longevity

Adipose tissue plays an essential role in metabolic health. Ames dwarf mice are exceptionally long-lived and display metabolically beneficial phenotypes in their adipose tissue, providing an ideal model for studying the intersection between adipose tissue and longevity. To this end, we assessed the metabolome and lipidome of adipose tissue in Ames dwarf mice. We observed distinct lipid profiles in brown versus white adipose tissue of Ames dwarf mice that are consistent with increased thermogenesis and insulin sensitivity, such as increased cardiolipin and decreased ceramide concentrations. Moreover, we identified 5-hydroxyeicosapentaenoic acid (5-HEPE), an ω-3 fatty acid metabolite, to be increased in Ames dwarf brown adipose tissue (BAT), as well as in circulation. Importantly, 5-HEPE is increased in other models of BAT activation and is negatively correlated with body weight, insulin resistance, and circulating triglyceride concentrations in humans. Together, these data represent a novel lipid signature of adipose tissue in a mouse model of extreme longevity.

Challenging a "Cushy" Life: Potential Roles of Thermogenesis and Adipose Tissue Adaptations in Delayed Aging of Ames and Snell Dwarf Mice

Laboratory mouse models with genetically altered growth hormone (GH) signaling and subsequent endocrine disruptions, have longer lifespans than control littermates. As such, these mice are commonly examined to determine the role of the somatotropic axis as it relates to healthspan and longevity in mammals. The two most prominent mouse mutants in this context are the genetically dwarf Ames and Snell models which have been studied extensively for over two decades. However, it has only been proposed recently that both white and brown adipose tissue depots may contribute to their delayed aging. Here we review the current state of the field and supplement it with recent data from our labs.

Sirt3 is dispensable for oocyte quality and female fertility in lean and obese mice

Mammalian oocytes rely heavily on mitochondrial oxidative phosphorylation (OXPHOS) for generating ATP. However, mitochondria are also the primary source of damaging reactive oxygen species (ROS). Mitochondrial de-regulation, therefore, underpins poor oocyte quality associated with conditions such as obesity and aging. The mitochondrial sirtuin, Sirt3, is critical for mitochondrial respiration and redox regulation. Interestingly, however, Sirt3 knockout (Sirt3^-/- ) mice do not exhibit systemic compromise under basal conditions, only doing so under stressed conditions such as high-fat diet (HFD)-induced obesity. Mouse oocytes depleted of Sirt3 exhibit increased ROS in vitro, but it is unknown whether Sirt3 is necessary for female fertility in vivo. Here, we test this for the first time by investigating ovarian follicular reserve, oocyte maturation (including detailed spindle assembly and chromosome segregation), and female fertility in Sirt3^-/- females. We find that under basal conditions, young Sirt3^-/- females exhibit no defects in any parameters. Surprisingly, all parameters also remain intact following HFD-induced obesity. Despite markedly increased ROS levels in HFD Sirt3^-/- oocytes, ATP levels nevertheless remain normal. Our data support that ATP is sustained in vivo through increased mitochondrial mass possibly secondary to compensatory upregulation of another sirtuin, Sirt1, which has overlapping functions with Sirt3.

The effects of growth hormone on adipose tissue: old observations, new mechanisms

The ability of growth hormone (GH) to induce adipose tissue lipolysis has been known for over five decades; however, the molecular mechanisms that mediate this effect and the ability of GH to inhibit insulin-stimulated glucose uptake have scarcely been documented. In this same time frame, our understanding of adipose tissue has evolved to reveal a complex structure with distinct types of adipocyte, depot-specific differences, a biologically significant extracellular matrix and important endocrine properties mediated by adipokines. All these aforementioned features, in turn, can influence lipolysis. In this Review, we provide a historical and current overview of the lipolytic effect of GH in humans, mice and cultured cells. More globally, we explain lipolysis in terms of GH-induced intracellular signalling and its effect on obesity, insulin resistance and lipotoxicity. In this regard, findings that define molecular mechanisms by which GH induces lipolysis are described. Finally, data are presented for the differential effect of GH on specific adipose tissue depots and on distinct classes of metabolically active adipocytes. Together, these cellular, animal and human studies reveal novel cellular phenotypes and molecular pathways regulating the metabolic effects of GH on adipose tissue.

n-3 polyunsaturated fatty acids as modulators of thermogenesis in Ames dwarf mice

Lipids, commonly split into saturated and mono- and polyunsaturated fatty acids, are key constituents of all biological membranes, and their exact proportions in different tissues were previously shown to be related to lifespan in mammals. As a mechanism, it was put forward that long-chain and highly unsaturated n-3 fatty acids may act as "pacemakers" in membranes while the n-6 fatty acid class may act as a counterbalance. Previously, long-lived Ames dwarf mice (Prop1 df/df) were found to have lower n-3 fatty acids and higher n-6 throughout their tissues. We exposed 32 adult (8 months old) Ames dwarf mice to three isocaloric diets differing in their fatty acid composition (saturated vs. rich in n-3 and n-6) for 2 months while measuring their body masses, subcutaneous body temperatures and finally membrane fatty acid profiles. Prominently, we found that individuals from all three groups quickly increased their body masses by ca. 20% and had 0.45 °C higher subcutaneous body temperatures than at baseline (F_1,12,16 = 22.27; p < 0.001). Conceivably, experimental diets also largely reflected lipid composition found in the tissues with over 50% n-3 fatty acids in heart phospholipids from animals from the n-3-enriched feeding group. Our study indicates that fatty acid-enriched diets well affected body mass, subcutaneous body temperature and membrane fatty acid composition in Ames dwarf mice with no visible adverse effects on their health. Experimental feeding increased subcutaneous body fat and insulation, most likely explaining the higher subcutaneous temperatures.

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.

Hepatic gene body hypermethylation is a shared epigenetic signature of murine longevity

Dietary, pharmacological and genetic interventions can extend health- and lifespan in diverse mammalian species. DNA methylation has been implicated in mediating the beneficial effects of these interventions; methylation patterns deteriorate during ageing, and this is prevented by lifespan-extending interventions. However, whether these interventions also actively shape the epigenome, and whether such epigenetic reprogramming contributes to improved health at old age, remains underexplored. We analysed published, whole-genome, BS-seq data sets from mouse liver to explore DNA methylation patterns in aged mice in response to three lifespan-extending interventions: dietary restriction (DR), reduced TOR signaling (rapamycin), and reduced growth (Ames dwarf mice). Dwarf mice show enhanced DNA hypermethylation in the body of key genes in lipid biosynthesis, cell proliferation and somatotropic signaling, which strongly correlates with the pattern of transcriptional repression. Remarkably, DR causes a similar hypermethylation in lipid biosynthesis genes, while rapamycin treatment increases methylation signatures in genes coding for growth factor and growth hormone receptors. Shared changes of DNA methylation were restricted to hypermethylated regions, and they were not merely a consequence of slowed ageing, thus suggesting an active mechanism driving their formation. By comparing the overlap in ageing-independent hypermethylated patterns between all three interventions, we identified four regions, which, independent of genetic background or gender, may serve as novel biomarkers for longevity-extending interventions. In summary, we identified gene body hypermethylation as a novel and partly conserved signature of lifespan-extending interventions in mouse, highlighting epigenetic reprogramming as a possible intervention to improve health at old age.

Increased environmental temperature normalizes energy metabolism outputs between normal and Ames dwarf mice

Ames dwarf (Prop1^df) mice possess a loss-of-function mutation that results in deficiency of growth hormone, prolactin, and thyroid-stimulating hormone, as well as exceptional longevity. Work in other laboratories suggests that increased respiration and lipid utilization are important for maximizing mammalian longevity. Interestingly, these phenotypes are observed in Ames dwarf mice. We recently demonstrated that Ames dwarf mice have hyperactive brown adipose tissue (BAT), and hypothesized that this may in part be due to their increased surface to mass ratio leading to increased heat loss and an increased demand for thermogenesis. Here, we used increased environmental temperature (eT) to interrogate this hypothesis. We found that increased eT diminished BAT activity in Ames dwarf mice, and led to the normalization of both VO₂ and respiratory quotient between dwarf and normal mice, as well as partial normalization (i.e. impairment) of glucose homeostasis in Ames dwarf mice housed at an increased eT. Together, these data suggest that an increased demand for thermogenesis is partially responsible for the improved energy metabolism and glucose homeostasis which are observed in Ames dwarf mice.

MicroRNAs and the metabolic hallmarks of aging

Aging, the natural process of growing older, is characterized by a progressive deterioration of physiological homeostasis at the cellular, tissue, and organismal level. Metabolically, the aging process is characterized by extensive changes in body composition, multi-tissue/multi-organ insulin resistance, and physiological declines in multiple signaling pathways including growth hormone, insulin/insulin-like growth factor 1, and sex steroids regulation. With this review, we intend to consolidate published information about microRNAs that regulate critical metabolic processes relevant to aging. In certain occasions we uncover relationships likely relevant to aging, which has not been directly described before, such as the miR-451/AMPK axis. We have also included a provocative section highlighting the potential role in aging of a new designation of miRNAs, namely fecal miRNAs, recently discovered to regulate intestinal microbiota in mammals.

Getting Old through the Blood: Circulating Molecules in Aging and Senescence of Cardiovascular Regenerative Cells

Global aging is a hallmark of our century. The natural multifactorial process resulting in aging involves structural and functional changes, affecting molecules, cells, and tissues. As the western population is getting older, we are witnessing an increase in the burden of cardiovascular events, some of which are known to be directly linked to cellular senescence and dysfunction. In this review, we will focus on the description of a few circulating molecules, which have been correlated to life span, aging, and cardiovascular homeostasis. We will review the current literature concerning the circulating levels and related signaling pathways of selected proteins (insulin-like growth factor 1, growth and differentiation factor-11, and PAI-1) and microRNAs of interest (miR-34a, miR-146a, miR-21), whose bloodstream levels have been associated to aging in different organisms. In particular, we will also discuss their potential role in the biology and senescence of cardiovascular regenerative cell types, such as endothelial progenitor cells, mesenchymal stromal cells, and cardiac progenitor cells.

Growth Hormone's Effect on Adipose Tissue: Quality versus Quantity

Obesity is an excessive accumulation or expansion of adipose tissue (AT) due to an increase in either the size and/or number of its characteristic cell type, the adipocyte. As one of the most significant public health problems of our time, obesity and its associated metabolic complications have demanded that attention be given to finding effective therapeutic options aimed at reducing adiposity or the metabolic dysfunction associated with its accumulation. Growth hormone (GH) has therapeutic potential due to its potent lipolytic effect and resultant ability to reduce AT mass while preserving lean body mass. However, AT and its resident adipocytes are significantly more dynamic and elaborate than once thought and require one not to use the reduction in absolute mass as a readout of efficacy alone. Paradoxically, therapies that reduce GH action may ultimately prove to be healthier, in part because GH also possesses potent anti-insulin activities along with concerns that GH may promote the growth of certain cancers. This review will briefly summarize some of the newer complexities of AT relevant to GH action and describe the current understanding of how GH influences this tissue using data from both humans and mice. We will conclude by considering the therapeutic use of GH or GH antagonists in obesity, as well as important gaps in knowledge regarding GH and AT.

Differential effects of early-life nutrient restriction in long-lived GHR-KO and normal mice

There is increasing evidence that growth hormone (GH) and insulin-like growth factor 1 (IGF-1) signaling (collectively referred to as somatotropic signaling) during development has a profound influence on aging and longevity. Moreover, the absence of GH action was shown to modify responses of adult mice to calorie restriction (CR) and other antiaging interventions. It was therefore of interest to determine whether GH resistance in GH receptor knockout (GHR-KO) mice would modify the effects of mild pre-weaning CR imposed by increasing the number of pups in a litter (the so-called litter crowding). In addition to the expected impact on body weight, litter crowding affected glucose homeostasis, hepatic expression of IGF-1 and genes related to lipid metabolism, and expression of inflammatory markers in white adipose tissue, with some of these effects persisting until the age of 2 years. Litter crowding failed to further extend the remarkable longevity of GHR-KO mice and, instead, reduced late life survival of GHR-KO females, an effect opposite to the changes detected in normal animals. We conclude that the absence of GH actions alters the responses to pre-weaning CR and prevents this intervention from extending longevity.

The Role of the Growth Hormone/Insulin-Like Growth Factor System in Visceral Adiposity

There is substantial evidence that the growth hormone (GH)/insulin-like growth factor (IGF) system is involved in the pathophysiology of obesity. Both GH and IGF-I have direct effects on adipocyte proliferation and differentiation, and this system is involved in the cross-talk between adipose tissue, liver, and pituitary. Transgenic animal models have been of importance in identifying mechanisms underlying these interactions. It emerges that this system has key roles in visceral adiposity, and there is a rationale for targeting this system in the treatment of visceral obesity associated with GH deficiency, metabolic syndrome, and lipodystrophies. This evidence is reviewed, gaps in knowledge are highlighted, and recommendations are made for future research.

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.

Adiponectin deficiency contributes to the development and progression of benign prostatic hyperplasia in obesity

The incidence of benign prostatic hyperplasia (BPH) is increasing among obese individuals, but few studies have fully explained the underlying mechanisms. We aimed to elucidate the relationship between obesity and BPH. Herein, we show that in prostatic epithelial and stromal cells, adiponectin exerts multifunctional effects including anti-proliferation, blocking of G1/S-phase progression and the promotion of apoptosis via inhibiting the MEK-ERK-p90RSK axis. Furthermore, we found that a high-fat diet (HFD) led to adiponectin deficiency and microscopic BPH in a mouse model of obesity. And an adiponectin supplement protected the obese mice from microscopic BPH. The present study provides evidence that adiponectin is a protective regulator in the development and progression of BPH and that adiponectin deficiency causally links BPH with obesity.

Models of GH deficiency in animal studies

Growth hormone (GH) is a peptide hormone released from pituitary somatotrope cells that promotes growth, cell division and regeneration by acting directly through the GH receptor (GHR), or indirectly via hepatic insulin-like growth factor 1 (IGF1) production. GH deficiency (GHD) can cause severe consequences, such as growth failure, changes in body composition and altered insulin sensitivity, depending of the origin, time of onset (childhood or adulthood) or duration of GHD. The highly variable clinical phenotypes of GHD can now be better understood through research on transgenic and naturally-occurring animal models, which are widely employed to investigate the origin, phenotype, and consequences of GHD, and particularly the underlying mechanisms of metabolic disorders associated to GHD. Here, we reviewed the most salient aspects of GH biology, from somatotrope development to GH actions, linked to certain GHD types, as well as the animal models employed to reproduce these GHD-associated alterations.

Brown Adipose Tissue Function Is Enhanced in Long-Lived, Male Ames Dwarf Mice

Ames dwarf mice (Prop1^df/df) are long-lived due to a loss of function mutation, resulting in deficiency of GH, TSH, and prolactin. Along with a marked extension of longevity, Ames dwarf mice have improved energy metabolism as measured by an increase in their oxygen consumption and heat production, as well as a decrease in their respiratory quotient. Along with alterations in energy metabolism, Ames dwarf mice have a lower core body temperature. Moreover, Ames dwarf mice have functionally altered epididymal white adipose tissue (WAT) that improves, rather than impairs, their insulin sensitivity due to a shift from pro- to anti-inflammatory cytokine secretion. Given the unique phenotype of Ames dwarf epididymal WAT, their improved energy metabolism, and lower core body temperature, we hypothesized that Ames dwarf brown adipose tissue (BAT) may function differently from that of their normal littermates. Here we use histology and RT-PCR to demonstrate that Ames dwarf mice have enhanced BAT function. We also use interscapular BAT removal to demonstrate that BAT is necessary for Ames dwarf energy metabolism and thermogenesis, whereas it is less important for their normal littermates. Furthermore, we show that Ames dwarf mice are able to compensate for loss of interscapular BAT by using their WAT depots as an energy source. These findings demonstrate enhanced BAT function in animals with GH and thyroid hormone deficiencies, chronic reduction of body temperature, and remarkably extended longevity.

Original Research: Metabolic alterations from early life thyroxine replacement therapy in male Ames dwarf mice are transient

Ames dwarf mice are exceptionally long-lived due to a Prop1 loss of function mutation resulting in deficiency of growth hormone, thyroid-stimulating hormone and prolactin. Deficiency in thyroid-stimulating hormone and growth hormone leads to greatly reduced levels of circulating thyroid hormones and insulin-like growth factor 1, as well as a reduction in insulin secretion. Early life growth hormone replacement therapy in Ames dwarf mice significantly shortens their longevity, while early life thyroxine (T4) replacement therapy does not. Possible mechanisms by which early life growth hormone replacement therapy shortens longevity include deleterious effects on glucose homeostasis and energy metabolism, which are long lasting. A mechanism explaining why early life T4 replacement therapy does not shorten longevity remains elusive. Here, we look for a possible explanation as to why early life T4 replacement therapy does not impact longevity of Ames dwarf mice. We found that early life T4 replacement therapy increased body weight and advanced the age of sexual maturation. We also find that early life T4 replacement therapy does not impact glucose tolerance or insulin sensitivity, and any deleterious effects on oxygen consumption, respiratory quotient and heat production are transient. Lastly, we find that early life T4 replacement therapy has long-lasting effects on bone mineral density and bone mineral content. We suggest that the transient effects on energy metabolism and lack of effects on glucose homeostasis are the reasons why there is no shortening of longevity after early life T4 replacement therapy in Ames dwarf mice.