Life extension in the dwarf mouse

Metabotyping of long-lived mice using 1H NMR spectroscopy

Significant advances in understanding aging have been achieved through studying model organisms with extended healthy lifespans. Employing 1H NMR spectroscopy, we characterized the plasma metabolic phenotype (metabotype) of three long-lived murine models: 30% dietary restricted (DR), insulin receptor substrate 1 null (Irs1-/-), and Ames dwarf (Prop1df/df). A panel of metabolic differences were generated for each model relative to their controls, and subsequently, the three long-lived models were compared to one another. Concentrations of mobile very low density lipoproteins, trimethylamine, and choline were significantly decreased in the plasma of all three models. Metabolites including glucose, choline, glycerophosphocholine, and various lipids were significantly reduced, while acetoacetate, d-3-hydroxybutyrate and trimethylamine-N-oxide levels were increased in DR compared to ad libitum fed controls. Plasma lipids and glycerophosphocholine were also decreased in Irs1-/- mice compared to controls, as were methionine and citrate. In contrast, high density lipoproteins and glycerophosphocholine were increased in Ames dwarf mice, as were methionine and citrate. Pairwise comparisons indicated that differences existed between the metabotypes of the different long-lived mice models. Irs1-/- mice, for example, had elevated glucose, acetate, acetone, and creatine but lower methionine relative to DR mice and Ames dwarfs. Our study identified several potential candidate biomarkers directionally altered across all three models that may be predictive of longevity but also identified differences in the metabolic signatures. This comparative approach suggests that the metabolic networks underlying lifespan extension may not be exactly the same for each model of longevity and is consistent with multifactorial control of the aging process.

Expression of oxidative phosphorylation components in mitochondria of long-living Ames dwarf mice

Reduced signaling of the growth hormone (GH)/insulin-like growth factor-1 (IGF-1) pathway is associated with extended life span in several species. Ames dwarf mice are GH-deficient and live >50% longer than wild-type littermates. Previously, we have shown that tissues from Ames mice exhibit elevated levels of antioxidative enzymes, less H(2)O(2) production, and lower oxidative damage suggesting that mitochondrial function may differ between genotypes. To explore the relationship between hormone deficiency and mitochondria in mice with extended longevity, we evaluated activity, protein, and gene expression of oxidative phosphorylation components in dwarf and wild-type mice at varying ages. Liver complex I + III activity was higher in dwarf mice compared to wild-type mice. The activity of I + III decreased between 3 and 20 months of age in both genotypes with greater declines in wild-type mice in liver and skeletal muscle. Complex IV activities in the kidney were elevated in 3- and 20-month-old dwarf mice relative to wild-type mice. In Ames mice, protein levels of the 39 kDa complex I subunit were elevated at 20 months of age when compared to wild-type mouse mitochondria for every tissue examined. Kidney and liver mitochondria from 20-month-old dwarf mice had elevated levels of both mitochondrially-encoded and nuclear-encoded complex IV proteins compared to wild-type mice (p < 0.05). Higher liver ANT1 and PGC-1α mRNA levels were also observed in dwarf mice. Overall, we found that several components of the oxidative phosphorylation (OXPHOS) system were elevated in Ames mice. Mitochondrial to nuclear DNA ratios were not different between genotypes despite the marked increase in PGC-1α levels in dwarf mice. The increased OXPHOS activities, along with lower ROS production in dwarf mice, predict enhanced mitochondrial function and efficiency, two factors likely contributing to long-life in Ames mice.

The biology of aging: 1985-2010 and beyond

In this contribution to the series of reflective essays celebrating the 25th anniversary of The FASEB Journal, our task is to assess the growth of research on the biology of aging during this period and to suggest where we might be heading during the next 25 yr. A review of the literature suggests a healthy acceleration of progress during the past decade, perhaps largely due to progress on the genetics of longevity of model organisms. Progress on the genetics of health span in these model organisms has lagged, however. Research on the genetic basis of the remarkable interspecific variations in life span has only recently begun to be seriously addressed. The spectacular advances in genomics should greatly accelerate progress. Research on environmental effects on life span and health span needs to be accelerated. Stochastic variations in gene expression in aging have only recently been addressed. These can lead to random departures from homeostasis during aging.-Martin, G. M. The biology of aging: 1985-2010 and beyond.

Age- and sex-associated plasma proteomic changes in growth hormone receptor gene-disrupted mice

Growth hormone receptor gene-disrupted (GHR-/-) mice are dwarf, insulin sensitive, and long lived despite being obese. In order to identify characteristics associated with their increased longevity, we studied age-related plasma proteomic changes in these mice. Male and female GHR-/- mice and their littermate controls were followed longitudinally at 8, 16, and 24 months of ages for plasma proteomic analysis. Relative to control littermates, GHR-/- mice had increased levels of apolipoprotein A-4 and retinol-binding protein-4 and decreased levels of apolipoprotein E, haptoglobin, and mannose-binding protein-C. Female GHR-/- mice showed decreased inflammatory cytokines including interleukin-1β and monocyte chemotactic protein-1. Additionally, sex differences were found in specific isoforms of apolipoprotein E, RBP-4, haptoglobin, albumin, and hemoglobin subunit beta. In conclusion, we find plasma proteomic changes in GHR-/- mice that favor a longer life span as well as sex differences indicative of an improved health span in female mice.

Age-related cataract in dogs: a biomarker for life span and its relation to body size

Clinical data from 72 dog breeds of varying size and life expectancy were grouped according to breed body mass and tested for prevalence at ages 4 to 5, ages 7 to 10, and lifetime incidence of non-hereditary, age-related cataract (ARC). The incidence of ARC was found to be directly related to the relative life expectancies in the breed groups: The smallest dog breeds had a lower ARC prevalence between ages 4 and 5 than mid-size breeds and these, in turn, a lower prevalence than the giant breeds. A similar sequence was evident for ages 7 to 10 and for overall lifetime incidence of ARC. These differences became more significant when comparing small and giant breeds only. We could also confirm the inverse relationship between body size and life expectancy in these same sets of dog breeds. Our results show that body size, life expectancy, and ARC incidence are interrelated in dogs. Given that ARC has been shown to be at least partially caused by oxidative damage to lens epithelial cells and the internal lens, we suggest that it can be considered not only as a general biomarker for life expectancy in the canine and possibly other species, but also for the systemic damages produced by reactive oxygen species. This suggests new approaches to examine the gene expression pathways affecting the above-noted linkages.

Lifespan and glucose metabolism in insulin receptor mutant mice

Insulin/insulin-like growth factor type 1 signaling regulates lifespan and resistance to oxidative stress in worms, flies, and mammals. In a previous study, we revealed that insulin receptor (IR) mutant mice, which carry a homologous mutation found in the long-lived daf-2 mutant of Caenorhabditis elegans, showed enhanced resistance to oxidative stress cooperatively modulated by sex hormones and dietary signals (Baba et al., (2005)). We herein investigated the lifespan of IR mutant mice to evaluate the biological significance of insulin signaling in mice. Under normoxia, mutant male mice had a lifespan comparable to that of wild-type male mice. IR mutant female mice also showed a lifespan similar to that of wild-type female mice, in spite of the fact that the IR mutant female mice acquired more resistance to oxidative stress than IR mutant male mice. On the other hand, IR mutant male and female mice both showed insulin resistance with hyperinsulinemia, but they did not develop hyperglycemia throughout their entire lifespan. These data indicate that the IR mutation does not impact the lifespan in mice, thus suggesting that insulin signaling might have a limited effect on the lifespan of mice.

Rapamycin-induced hypophosphatemia and insulin resistance are associated with mTORC2 activation and Klotho expression

Rapamycin, an immunosuppressive drug used to prevent rejection after kidney transplantation, influences phosphate homeostasis, induces insulin resistance and has been shown to prolong lifespan in animal models. Because Klotho is an aging-suppressor gene controlling phosphate metabolism and insulin sensitivity, we investigated the influence of rapamycin on Klotho expression. A total of 100 kidney transplant recipients, 50 chronically treated with rapamycin and 50 with calcineurin inhibitors, were enrolled; 20 healthy subjects were employed as control. In the rapamycin group, serum phosphate was lower than in the CNI group with an increase in phosphate excretion and a reduction in its reabsorption. In addition, rapamycin increased insulin resistance as shown by HOMA index. Rapamycin treatment of an immortalized proximal tubular cell line induced the expression of Klotho, the phosphorylation of AKT in Ser473, downstream target of mTORC2 and the expression of RICTOR, mTORC2 main component. AKT inhibition reduced the rapamycin-induced expression of Klotho. In vivo rapamycin treatment induced higher degree of RICTOR and AKT Ser(473) expression directly correlating with long-term rapamycin exposure, FE(PO4) and HOMA index. In conclusion, our data would suggest that rapamycin may influence phosphate homeostasis and insulin resistance modulating Klotho expression through mTORC2 activation.

Expression of key regulators of mitochondrial biogenesis in growth hormone receptor knockout (GHRKO) mice is enhanced but is not further improved by other potential life-extending interventions

Mitochondrial biogenesis is essential for cell viability. Growth hormone receptor knockout (GHRKO), calorie restriction, and surgical visceral fat removal constitute experimental interventions to delay aging and increase life span. We examined the expression of known regulators of mitochondriogenesis: peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α), adenosine monophosphate (AMP)-activated protein kinase (AMPK), sirtuin-1 (SIRT-1) and sirtuin-3 (SIRT-3), endothelial nitric oxide synthase (eNOS), nuclear respiratory factor-1, mitochondrial transcription factor A (TFAM), and mitofusin-2 (MFN-2) in the skeletal muscles and hearts of control and calorie-restricted female GHRKO mice and in the kidneys of male GHRKOs after visceral fat removal or sham surgery. Expression of PGC-1α in skeletal muscles, AMPK, SIRT-1, SIRT-3, eNOS, and MFN-2 in the heart and PGC-1α, AMPK, SIRT-3, eNOS, and MFN-2 in kidneys was increased in GHRKO mice but was not affected by calorie restriction or visceral fat removal. GHRKO mice have increased expression of key regulators of mitochondriogenesis, which is not improved further by calorie restriction or visceral fat removal.

Key regulators of mitochondrial biogenesis are increased in kidneys of growth hormone receptor knockout (GHRKO) mice

The growth hormone receptor knockout (GHRKO) mice are remarkably long-lived and highly insulin sensitive. Alterations in mitochondrial biogenesis are associated with aging and various metabolic derangements. We have previously demonstrated increased gene expression of key regulators of mitochondriogenesis in kidneys, hearts and skeletal muscles of GHRKO mice. The aim of the present study was to quantify the protein levels of the following regulators of mitochondriogenesis: peroxisome proliferator-activated receptor γ co-activator 1α (PGC-1α), AMP-activated protein kinase α (AMPKα), phospho-AMPKα (p-AMPKα), sirtuin-3 (SIRT-3), endothelial nitric oxide synthase (eNOS), phospho-eNOS (p-eNOS), nuclear respiratory factor-1 (NRF-1) and mitofusin-2 (MFN-2) in skeletal muscles and kidneys of GHRKOs in comparison to normal mice. We also were interested in the effects of calorie restriction (CR) and visceral fat removal (VFR) on these parameters. Both CR and VFR improve insulin sensitivity and can extend life span.

RESULTS

The renal levels of PGC-1α, AMPKα, p-AMPKα, SIRT-3, eNOS, p-eNOS and MFN-2 were increased in GHRKOs. In the GHRKO skeletal muscles, only MFN-2 was increased. Levels of the examined proteins were not affected by CR (except for PGC-1α and p-eNOS in skeletal muscles) or VFR.

CONCLUSION

GHRKO mice have increased renal protein levels of key regulators of mitochondriogenesis, and this may contribute to increased longevity of these knockouts.

RasGrf1: genomic imprinting, VSELs, and aging

Increase in life span in RasGrf1-deficient mice revealed that RasGrf1 deficiency promotes longevity. Interestingly, RasGrf1 is one of parentally imprinted genes transcribed from paternally-derived chromosome. Erasure of its imprinting results in RasGrf1 downregulation and has been demonstrated in a population of pluripotent adult tissues-derived very small embryonic like stem cells (VSELs), stem cells involved in tissue organ rejuvenation. Furthermore, based on recent observation that RasGrf1 signaling molecule is located downstream from insulin (Ins) and insulin like growth factor-1 (Igf-1) receptors, the extended life-span of RasGrf1-/- mice may support beneficial effect of reduced Ins/Igf-1 signaling on longevity. Similarly, downregulation of RasGrf1 in VSELs renders them resistant to chronic Ins/Igf-1 signaling and protects from premature depletion from adult tissues. Thus, the studies in RasGrf1-/- mice indicate that some of the imprinted genes may play a role in ontogenetic longevity and suggest that there are sex differences in life span that originate at the genome level. All this in toto supports a concept that the sperm genome may have a detrimental effect on longevity in mammals. We will discuss a role of RasGrf1 on life span in context of genomic imprinting and VSELs.

Endocrine parameters and phenotypes of the growth hormone receptor gene disrupted (GHR-/-) mouse

Disruption of the GH receptor (GHR) gene eliminates GH-induced intracellular signaling and, thus, its biological actions. Therefore, the GHR gene disrupted mouse (GHR-/-) has been and is a valuable tool for helping to define various parameters of GH physiology. Since its creation in 1995, this mouse strain has been used by our laboratory and others for numerous studies ranging from growth to aging. Some of the most notable discoveries are their extreme insulin sensitivity in the presence of obesity. Also, the animals have an extended lifespan, which has generated a large number of investigations into the roles of GH and IGF-I in the aging process. This review summarizes the many results derived from the GHR-/- mice. We have attempted to present the findings in the context of current knowledge regarding GH action and, where applicable, to discuss how these mice compare to GH insensitivity syndrome in humans.

Increased serum IGF-1 levels protect the musculoskeletal system but are associated with elevated oxidative stress markers and increased mortality independent of tissue igf1 gene expression

Although the literature suggests a protective (anabolic) effect of insulin-like growth factor-1 (IGF-1) on the musculoskeletal system during growth and aging, there is evidence that reductions in IGF-1 signaling are advantageous for promoting an increase in life span through reduction in oxidative stress-induced tissue damage. To better understand this paradox, we utilized the hepatocyte-specific IGF-1 transgenic (HIT) mice, which exhibit 3-fold increases in serum IGF-1, with normal IGF-1 expression in other tissues, and mice with an IGF-1 null background that exclusively express IGF-1 in the liver, which thereby deliver IGF-1 by the endocrine route only (KO-HIT mice). We found that in the total absence of tissue igf1 gene expression (KO-HIT), increases in serum IGF-1 levels were associated with increased levels of lipid peroxidation products in serum and increased mortality rate at 18 months of age in both genders. Surprisingly, however, we found that in female mice, tissue IGF-1 plays an important role in preserving trabecular bone architecture as KO-HIT mice show bone loss in the femoral distal metaphysis. Additionally, in male KO-HIT mice, increases in serum IGF-1 levels were insufficient to protect against age-related muscle loss.

GH replacement therapy in elderly GH-deficient patients: a systematic review

Context Recombinant human GH (rhGH) is prescribed for the treatment of adults with GH deficiency (GHD). However, conflicting data are available on the efficacy of rhGH treatment in elderly GHD patients. Objective To assess the efficacy of rhGH treatment in elderly GHD subjects. Methods We searched the available literature in PubMed, Cochrane Library, Web of Science and EMBASE. Study selection Studies on GHD patients, aged >60 years, treated with rhGH were eligible for inclusion. Data extraction was performed by two reviewers independently. Results We found 11 eligible studies with a total of 534 patients. Only two studies had prospective, randomized, placebo-controlled study designs of rhGH treatment with a duration of 6 (n=15) and 12 months (n=62), respectively. Treatment with rhGH decreased total and low density lipoprotein (LDL) cholesterol levels by 4-8 and 11-16%, respectively, but did not alter high density lipoprotein or triglyceride levels. RhGH did not affect body mass index, but decreased waist circumference (by ∼3 cm) and waist/hip ratio. RhGh did not consistently affect blood pressure or bone mineral density. RhGH increased lean body mass by 2-5% and decreased total fat mass by 7-10% in four studies, but did not affect body composition in two other studies. RhGH consistently improved quality of life (QoL) parameters reflected in AGHDA-scores. There were no explicit data on elderly GHD patients aged >80 years. Conclusion RhGH replacement in elderly subjects with GHD decreases LDL cholesterol levels and improves QoL, but the effects on other parameters are not unequivocal. There were no data on the efficacy and safety of rhGH treatment in octogenarians with GHD.

Decreased expression level of apoptosis-related genes and/or proteins in skeletal muscles, but not in hearts, of growth hormone receptor knockout mice

The long-lived growth hormone (GH) receptor knockout (GHRKO; KO) mice are GH-resistant due to targeted disruption of the GH receptor (Ghr) gene. Apoptosis is a physiological process in which cells play an active role in their own death and is a normal component of the development and health of multicellular organisms. Aging is associated with the progressive loss of strength of skeletal and heart muscles. Calorie restriction (CR) is a well-known experimental model to delay aging and increase lifespan. The aim of the study was to examine the expression of the following apoptosis-related genes: caspase-3, caspase-9, caspase-8, bax, bcl-2, Smac/DIABLO, p53 and cytochrome c1 (cyc1) in the skeletal muscles and hearts of female normal and GHRKO mice, fed ad libitum or subjected to 40% CR for six months, starting at two months of age. Moreover, skeletal muscle caspase-3, caspase-9, caspase-8, bax, bcl-2, Smac/DIABLO, Apaf-1, bad, phospho-bad (pbad), phospho-p53 and cytochrome c (cyc) protein expression levels were assessed. Expression of caspase-3, caspase-9, bax and Smac/DIABLO genes and proteins was decreased in GHRKO's skeletal muscles. The Apaf-1 protein expression also was diminished in this tissue. In contrast, bcl-2 and pbad protein levels were increased in skeletal muscles in knockouts. No changes were demonstrated for the examined genes' expression in GHRKO's hearts except for the increased level of cyc1 mRNA. CR did not alter the expression of the examined genes and proteins in skeletal muscles of knockouts versus normal (N) mice. In heart homogenates, CR increased caspase-3 mRNA level as compared with ad libitum mice. Decreased expression of certain proapoptotic genes and/or proteins may constitute the potential mechanism of prolonged longevity in GHRKO mice, protecting these animals from aging; this potential beneficial mechanism is not affected by CR.

The effects of physiological adaptations to calorie restriction on global cell proliferation rates

Calorie restriction (CR) reduces the rate of cell proliferation in mitotic tissues. It has been suggested that this reduction in cell proliferation may mediate CR-induced increases in longevity. However, the mechanisms that lead to CR-induced reductions in cell proliferation rates remain unclear. To evaluate the CR-induced physiological adaptations that may mediate reductions in cell proliferation rates, we altered housing temperature and access to voluntary running wheels to determine the effects of food intake, energy expenditure, percent body fat, and body weight on proliferation rates of keratinocytes, liver cells, mammary epithelial cells, and splenic T-cells in C57BL/6 mice. We found that ∼20% CR led to a reduction in cell proliferation rates in all cell types. However, lower cell proliferation rates were not observed with reductions in 1) food intake and energy expenditure in female mice housed at 27°C, 2) percent body fat in female mice provided running wheels, or 3) body weight in male mice provided running wheels compared with ad libitum-fed controls. In contrast, reductions in insulin-like growth factor I were associated with decreased cell proliferation rates. Taken together, these data suggest that CR-induced reductions in food intake, energy expenditure, percent body fat, and body weight do not account for the reductions in global cell proliferation rates observed in CR. In addition, these data are consistent with the hypothesis that reduced cell proliferation rates could be useful as a biomarker of interventions that increase longevity.

Renal pro-apoptotic proteins are reduced by growth hormone resistance but not by visceral fat removal

Growth hormone (GH) receptor knockout (GHRKO) mice are highly insulin sensitive and long-lived. Surgical visceral fat removal (VFR) improves insulin signaling in normal mice and rats and extends longevity in rats. We have previously demonstrated decreased expression of certain pro-apoptotic genes in kidneys of GHRKO mice and suggested that this could contribute to the increased longevity of these animals. The aim of the present study was to examine the level of the following proteins: caspase-3, caspase-9, caspase-8, bax, bad, phospho-bad, bcl-2, Smac/DIABLO, Apaf-1, phospho-p53 (pp53) and cytochrome c in male GHRKO and normal (N) mice subjected to VFR or sham surgery, at approximately six months of age. The kidneys were collected two months after VFR. Caspase-3, caspase-8, bax, bad, Smac/DIABLO, Apaf-1 and pp53 levels were decreased in GHRKO mice as compared to N animals. VFR did not change the level of any of the examined proteins. The decreased renal levels of pro-apoptotic proteins could contribute to the extended life-span caused by targeted disruption of the GH receptor gene but are apparently not involved in mediating the effects of VFR.

The Shc locus regulates insulin signaling and adiposity in mammals

Longevity of a p66Shc knockout strain (ShcP) was previously attributed to increased stress resistance and altered mitochondria. Microarrays of ShcP tissues indicated alterations in insulin signaling. Consistent with this observation, ShcP mice were more insulin sensitive and glucose tolerant at organismal and tissue levels, as was a novel p66Shc knockout (ShcL). Increasing and decreasing Shc expression in cell lines decreased and increased insulin sensitivity, respectively - consistent with p66Shc's function as a repressor of insulin signaling. However, differences between the two p66Shc knockout strains were also observed. ShcL mice were fatter and susceptible to fatty diets, and their fat was more insulin sensitive than controls. On the other hand, ShcP mice were leaner and resisted fatty diets, and their adipose was less insulin sensitive than controls. ShcL and ShcP strains are both highly inbred on the C57Bl/6 background, so we investigated gene expression at the Shc locus, which encodes three isoforms, p66, p52, and p46. Isoform p66 is absent in both strains; thus, the remaining difference to which to attribute the 'lean' phenotype is expression of the other two isoforms. ShcL mice have a precise deletion of p66Shc and normal expression of p52 and p46Shc isoforms in all tissues; thus, a simple deletion of p66Shc results in a 'fat' phenotype. However, ShcP mice in addition to p66Shc deletion have a fourfold increase in p46Shc expression in white fat. Thus, p46Shc overexpression in fat, rather than p66Shc deletion, is the likely cause of decreased adiposity and reduced insulin sensitivity in the fat of ShcP mice, which has implications for the longevity of the strain.

Caloric restriction and longevity: effects of reduced body temperature

Caloric restriction (CR) causes a reduction in body temperature (T(b)) which is suggested to contribute to changes that increase lifespan. Moreover, low T(b) has been shown to improve health and longevity independent of CR. In this review we examine the connections between CR, T(b) and mechanisms that influence longevity and ageing. Recent findings regarding the overlapping mechanisms of CR and T(b) that benefit longevity are discussed, including changes in body composition, hormone regulation, and gene expression, as well as reductions in low-level inflammation and reactive oxygen species-induced molecular damage. This information is summarized in a model describing how CR and low T(b), both synergistically and independently, increase lifespan. Moreover, the nascent notion that the rate of ageing may be pre-programmed in response to environmental influences at critical periods of early development is also considered. Based on current evidence, it is concluded that low T(b) plays an integral role in mediating the effects of CR on health and longevity, and that low T(b) may exert independent biological changes that increase lifespan. Our understanding of the overlap between CR- and T(b)-mediated longevity remains incomplete and should be explored in future research.

Neural sirtuin 6 (Sirt6) ablation attenuates somatic growth and causes obesity

In yeast, Sir2 family proteins (sirtuins) regulate gene silencing, recombination, DNA repair, and aging via histone deacetylation. Most of the seven mammalian sirtuins (Sirt1-Sirt7) have been implicated as NAD(+)-dependent protein deacetylases with targets ranging from transcriptional regulators to metabolic enzymes. We report that neural-specific deletion of sirtuin 6 (Sirt6) in mice leads to postnatal growth retardation due to somatotropic attenuation through low growth hormone (GH) and insulin-like growth factor 1 (IGF1) levels. However, unlike Sirt6 null mice, neural Sirt6-deleted mice do not die from hypoglycemia. Instead, over time, neural Sirt6-deleted mice reach normal size and ultimately become obese. Molecularly, Sirt6 deletion results in striking hyperacetylation of histone H3 lysine 9 (H3K9) and lysine 56 (H3K56), two chromatin marks implicated in the regulation of gene activity and chromatin structure, in various brain regions including those involved in neuroendocrine regulation. On the basis of these findings, we propose that Sirt6 functions as a central regulator of somatic growth and plays an important role in preventing obesity by modulating neural chromatin structure and gene activity.

Longevity and lifespan control in mammals: lessons from the mouse

Aging, which affects all organ systems, is one of the most complex phenotypes. Recent discoveries in long-lived mutant mice have revealed molecular mechanisms of longevity in mammals which may contribute to our understanding of why humans age. These mutations include naturally occurring spontaneous mutations, and those of mice genetically modified by modern genomic technologies. It is generally believed that the most fundamental mechanisms of aging are evolutionarily conserved across species. The following types of longevity mechanisms have been intensively studied: suppression of the somatotropic (growth hormone/insulin-like growth factor 1) axis, decreased metabolism and increased resistance of oxidative stress, reduced insulin secretion and increased insulin sensitivity, and delayed reproductive maturation and reduced fertility. In addition, many of the mutations have a sex-dependent effect on lifespan, and when present in different genetic backgrounds, the effects of the same gene mutation can vary considerably. The present review discusses these phenotypic variations as well as describing the known longevity genes in long-lived mutant mice and the molecular mechanisms specifying longevity. We anticipate that these mouse studies will ultimately provide clues about how to delay the aging and prolong lifespan, and help to develop therapies for healthier human aging.

A novel insight into aging: are there pluripotent very small embryonic-like stem cells (VSELs) in adult tissues overtime depleted in an Igf-1-dependent manner?

Tissue and organ rejuvenation and senescence/aging are closely related to the function of stem cells. Recently, we demonstrated that a population of pluripotent Oct-4+ SSEA-1+Sca-1+Lin-CD45- very small embryonic-like stem cells (VSELs) resides in the adult murine bone marrow (BM) and other murine tissues. We hypothesize that these pluripotent stem cells play an important role in tissue/organ rejuvenation, and have demonstrated that their proliferation and potentially premature depletion is negatively controlled by epigenetic changes of some imprinted genes that regulate insulin factor signaling (Igf2-H19 locus, Igf2R and RasGRF1). Since the attenuation of insulin/insulin growth factor (Ins/Igf) signaling positively correlates with longevity, we propose, based on our experimental data, that gradual decrease in the number of VSELs deposited in adult tissues, which occurs throughout life in an Ins/Igf signaling-dependent manner is an important mechanism of aging. In contrast, a decrease in Ins/Igf stimulation of VSELs that extends the half life of these cells in adult organs would have a beneficial effect on life span. Our preliminary data in long-living Igf-1-signaling-deficient mice show that these animals possess a 3-4 times higher number of VSELs deposited in adult BM, lending support to this novel hypothesis.

Genetics vs. entropy: longevity factors suppress the NF-kappaB-driven entropic aging process

Molecular studies in model organisms have identified potent longevity genes which can delay the aging process and extend the lifespan. Longevity factors promote stress resistance and cellular survival. It seems that the aging process itself is not genetically programmed but a random process involving the loss of molecular fidelity and subsequent accumulation of waste products. This age-related increase in cellular entropy is compatible with the disposable soma theory of aging. A large array of host defence systems has been linked to the NF-kappaB system which is an ancient signaling pathway specialized to host defence, e.g. functioning in immune system. Emerging evidence demonstrates that the NF-kappaB system is activated during aging. Oxidative stress and DNA damage increase with aging and elicit a sustained activation of the NF-kappaB system which has negative consequences, e.g. chronic inflammatory response, increase in apoptotic resistance, decline in autophagic cleansing, and tissue atrophy, i.e. processes that enhance the aging process. We will discuss the role of NF-kappaB system in the pro-aging signaling and will emphasize that several longevity factors seem to be inhibitors of NF-kappaB signaling and in that way they can suppress the NF-kappaB-driven entropic host defence catastrophe.

Caloric restriction: from soup to nuts

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

With TOR, less is more: a key role for the conserved nutrient-sensing TOR pathway in aging

Target of rapamycin (TOR) is an evolutionarily conserved nutrient-sensing protein kinase that regulates growth and metabolism in all eukaryotic cells. Studies in flies, worms, yeast, and mice support the notion that the TOR signaling network modulates aging. TOR is also emerging as a robust mediator of the protective effects of various forms of dietary restriction (DR), which can extend life span and slow the onset of certain age-related diseases across species. Here we discuss how modulating TOR signaling slows aging through downstream processes including mRNA translation, autophagy, endoplasmic reticulum (ER) stress signaling, stress responses, and metabolism. Identifying the mechanisms by which the TOR signaling network works as a pacemaker of aging is a major challenge and may help identify potential drug targets for age-related diseases, thereby facilitating healthful life span extension in humans.

A potential link between phosphate and aging--lessons from Klotho-deficient mice

Phosphate homeostasis is maintained primarily by a bone-kidney endocrine axis. When phosphate is in excess, fibroblast growth factor-23 (FGF23) is secreted from bone and acts on kidney to promote phosphate excretion into urine. FGF23 also reduces serum vitamin D levels to suppress phosphate absorption from intestine. Thus, FGF23 functions as a hormone that induces negative phosphate balance. One critical feature of FGF23 is that it requires Klotho, a single-pass transmembrane protein expressed in renal tubules, as an obligate co-receptor to bind and activate cognate FGF receptors. Importantly, defects in either FGF23 or Klotho not only cause phosphate retention but also a premature-aging syndrome in mice, which can be rescued by resolving hyperphosphatemia. In addition, changes in extracellular and intracellular phosphate concentration affect glucose metabolism, insulin sensitivity, and oxidative stress in vivo and in vitro, which potentially affect aging processes. These findings suggest an unexpected link between inorganic phosphate and aging in mammals.

Dietary restriction and aging, 2009

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

Ames dwarf (Prop1(df)/Prop1(df)) mice display increased sensitivity of the major GH-signaling pathways in liver and skeletal muscle

CONTEXT

Growth hormone (GH) is an anabolic hormone that regulates growth and metabolism. Ames dwarf mice are natural mutants for Prop1, with impaired development of anterior pituitary and undetectable levels of circulating GH, prolactin and TSH. They constitute an endocrine model of life-long GH-deficiency. The main signaling cascades activated by GH binding to its receptor are the JAK2/STATs, PI-3K/Akt and the MAPK Erk1/2 pathways.

OBJECTIVES

We have previously reported that GH-induced STAT5 activation was higher in Ames dwarf mice liver compared to non-dwarf controls. The aim of this study was to evaluate the principal components of the main GH-signaling pathways under GH-deficiency in liver and skeletal muscle, another GH-target tissue.

METHODS

Ames dwarf mice and their non-dwarf siblings were assessed. Animals were injected i.p. with GH or saline 15min before tissue removal. Protein content and phosphorylation of signaling mediators were determined by immunoblotting of tissue solubilizates.

RESULTS

GH was able to induce STAT5 and STAT3 tyrosine phosphorylation in both liver and muscle, but the response was higher for Ames dwarf mice than for non-dwarf controls. When Erk1/2 activation was assessed in liver, only dwarf mice showed GH-induced phosphorylation, while in muscle no response to the hormone was found in either genotype. GH-induced Akt phosphorylation at Ser473 in liver was only detected in dwarf mice. In skeletal muscle, both normal and dwarf mice responded to a GH stimulus, although dwarf mice presented higher GH activation levels. The phosphorylation of GSK-3, a substrate of Akt, increased upon hormone stimulation only in dwarf mice in both tissues. In contrast, no differences in the phosphorylation of mTOR, another substrate of Akt, were observed after GH stimulus, either in normal or dwarf mice in liver, while we were unable to determine mTOR in muscle. Protein content of GH-receptor and of the signaling mediators studied did not vary between normal and dwarf animals in the assessed tissues.

CONCLUSION

These results show that several components of the main GH-signaling pathways exhibit enhanced sensitivity to the hormone in liver and muscle of Ames dwarf mice.

Klotho

The klotho gene was identified as an "aging-suppressor" gene in mice that accelerates aging when disrupted and extends life span when overexpressed. It encodes a single-pass transmembrane protein and is expressed primarily in renal tubules. The extracellular domain of Klotho protein is secreted into blood and urine by ectodomain shedding. The two forms of Klotho protein, membrane Klotho and secreted Klotho, exert distinct functions. Membrane Klotho forms a complex with fibroblast growth factor (FGF) receptors and functions as an obligate co-receptor for FGF23, a bone-derived hormone that induces phosphate excretion into urine. Mice lacking Klotho or FGF23 not only exhibit phosphate retention but also display a premature-aging syndrome, revealing an unexpected link between phosphate metabolism and aging. Secreted Klotho functions as a humoral factor that regulates activity of multiple glycoproteins on the cell surface, including ion channels and growth factor receptors such as insulin/insulin-like growth factor-1 receptors. Potential contribution of these multiple activities of Klotho protein to aging processes is discussed.

Effects of growth hormone and thyroxine replacement therapy on insulin signaling in Ames dwarf mice

Ames dwarf (Prop1(df), df/df) mice lack growth hormone (GH), prolactin, and thyrotropin and live remarkably longer than their normal siblings. Significance of reduced activity of the somatotropic and thyroid axes during development and adulthood on longevity are unknown. Because enhanced insulin sensitivity and reduced insulin levels are among likely mechanisms responsible for increased longevity in these mutants, we compared the effects of GH and thyroxine (T4) replacement on various parameters related to insulin signaling in young and old male df/df mice. The results suggest that altered plasma adiponectin and insulin-like growth factor-1 (IGF-1) and hepatic IGF-1, insulin receptor (IR), IR substrate-1, peroxisome proliferator-activated receptor (PPAR) gamma, and PPARgamma coactivator-1 alpha may contribute to increased insulin sensitivity in Ames dwarfs. The stimulatory effect of GH and T4 treatment on plasma insulin and inhibitory effect on expression of hepatic glucose transporter-2 were greater in old than in young dwarfs. These results indicate that GH and T4 treatment has differential impact on insulin signaling during development and adulthood.

The effect of caloric restriction interventions on growth hormone secretion in nonobese men and women

Lifespan in rodents is prolonged by caloric restriction (CR) and by mutations affecting the somatotropic axis. It is not known if CR can alter the age-associated decline in growth hormone (GH), insulin-like growth factor (IGF)-1 and GH secretion. To evaluate the effect of CR on GH secretory dynamics; forty-three young (36.8 +/- 1.0 years), overweight (BMI 27.8 +/- 0.7) men (n = 20) and women (n = 23) were randomized into four groups; control = 100% of energy requirements; CR = 25% caloric restriction; CR + EX = 12.5% CR + 12.5% increase in energy expenditure by structured exercise; LCD = low calorie diet until 15% weight reduction followed by weight maintenance. At baseline and after 6 months, body composition (DXA), abdominal visceral fat (CT) 11 h GH secretion (blood sampling every 10 min for 11 h; 21:00-08:00 hours) and deconvolution analysis were measured. After 6 months, weight (control: -1 +/- 1%, CR: -10 +/- 1%, CR + EX: -10 +/- 1%, LCD: -14 +/- 1%), fat mass (control: -2 +/- 3%, CR: -24 +/- 3%, CR + EX: -25 +/- 3%, LCD: -31 +/- 2%) and visceral fat (control: -2 +/- 4%, CR: -28 +/- 4%, CR + EX: -27 +/- 3%, LCD: -36 +/- 2%) were significantly (P < 0.001) reduced in the three intervention groups compared to control. Mean 11 h GH concentrations were not changed in CR or control but increased in CR + EX (P < 0.0001) and LCD (P < 0.0001) because of increased secretory burst mass (CR + EX: 34 +/- 13%, LCD: 27 +/- 22%, P < 0.05) and amplitude (CR + EX: 34 +/- 14%, LCD: 30 +/- 20%, P < 0.05) but not to changes in secretory burst frequency or GH half-life. Fasting ghrelin was significantly increased from baseline in all three intervention groups; however, total IGF-1 concentrations were increased only in CR + EX (10 +/- 7%, P < 0.05) and LCD (19 +/- 4%, P < 0.001). A 25% CR diet for 6 months does not change GH, GH secretion or IGF-1 in nonobese men and women.

The impact of acute caloric restriction on the metabolic phenotype in male C57BL/6 and DBA/2 mice

Caloric restriction (CR) extends healthy lifespan in many organisms. DBA/2 mice, unlike C57BL/6 mice, are reported to be unresponsive to CR. To investigate potential differences underlying the CR response in male DBA/2 and C57BL/6 mice, we examined several metabolic parameters following acute (1-5 weeks) 30% CR. Acute CR decreased body mass (BM) in both strains, with lean and fat mass decreasing in proportion to BM. Resting metabolic rate (RMR) was unaltered by CR, following appropriate corrections for BM differences, although RMR was higher in DBA/2 compared to C57BL/6 mice. Acute CR decreased fed blood glucose levels in both strains, decreased fasting blood glucose in C57BL/6 mice but increased fasting levels in DBA/2 mice. Glucose tolerance improved after 1 week of CR in C57BL/6 mice but improved only after 4 weeks in DBA/2 mice. Acute CR had no effect on insulin levels, but lowered insulin sensitivity and decreased insulin-like growth factor-1 (IGF-1) levels in both strains. DBA/2 mice were hyperinsulinaemic and insulin resistant compared to C57BL/6 mice. These strain-specific differences in glucose homeostatic parameters may underlie the reported unresponsiveness of DBA/2 mice to CR. We also demonstrate delineation in the response of insulin and IGF-1 to acute CR in mice.

Compromised respiratory adaptation and thermoregulation in aging and age-related diseases

Mitochondrial dysfunction and reactive oxygen species (ROS) production are at the heart of the aging process and are thought to underpin age-related diseases. Mitochondria are not only the primary energy-generating system but also the dominant cellular source of metabolically derived ROS. Recent studies unravel the existence of mechanisms that serve to modulate the balance between energy metabolism and ROS production. Among these is the regulation of proton conductance across the inner mitochondrial membrane that affects the efficiency of respiration and heat production. The field of mitochondrial respiration research has provided important insight into the role of altered energy balance in obesity and diabetes. The notion that respiration and oxidative capacity are mechanistically linked is making significant headway into the field of aging and age-related diseases. Here we review the regulation of cellular energy and ROS balance in biological systems and survey some of the recent relevant studies that suggest that respiratory adaptation and thermodynamics are important in aging and age-related diseases.

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

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

Insulin/IGF-1 paradox of aging: regulation via AKT/IKK/NF-kappaB signaling

GH/insulin/IGF-1 signaling is a vital pathway e.g. in the regulation of protein synthesis and glucose metabolism. However, mouse dwarf strains which exhibit reduced GH secretion and subsequently a decline in IGF-1 signaling can live longer than their wild type counterparts. There is striking evidence indicating that the IGF-1/PI-3K/AKT signaling enhances growth of animals during development but later in life can potentiate the aging process. This conserved pleiotropy has been called the insulin/IGF-1 paradox. In Caenorhabditiselegans, the decline in this pathway activates the DAF-16 gene, an ortholog of mammalian FoxO genes, which regulate stress resistance and longevity. The mammalian PI-3K/AKT pathway also activates the NF-kappaB signaling that inhibits apoptosis and triggers inflammatory responses. Many longevity genes, e.g. FoxOs and SIRT1, are inhibitors of NF-kappaB signaling. We will discuss the evidence that insulin/IGF-1 signaling can enhance the NF-kappaB signaling and subsequently potentiate the aging process and aggravate age-related degenerative diseases.

Klotho and aging

The klotho gene encodes a single-pass transmembrane protein that forms a complex with multiple fibroblast growth factor (FGF) receptors and functions as an obligatory co-receptor for FGF23, a bone-derived hormone that induces negative phosphate balance. Defects in either Klotho or Fgf23 gene expression cause not only phosphate retention but also a premature-aging syndrome in mice, unveiling a potential link between phosphate metabolism and aging. In addition, the extracellular domain of Klotho protein is clipped on the cell surface and secreted into blood stream, potentially functioning as an endocrine factor. The secreted Klotho protein has a putative sialidase activity that modifies glycans on the cell surface, which may explain the ability of secreted Klotho protein to regulate activity of multiple ion channels and growth factors including insulin, IGF-1, and Wnt. Secreted Klotho protein also protects cells and tissues from oxidative stress through a mechanism yet to be identified. Thus, the transmembrane and secreted forms of Klotho protein have distinct functions, which may collectively affect aging processes in mammals.

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

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

A novel ENU-induced mutation, peewee, causes dwarfism in the mouse

We identified a novel fertile autosomal recessive mutation called peewee that results in dwarfing, in a region-specific ENU-induced mutagenesis. These mice at litter size were smaller those of other strains. Histological analysis revealed that the major organs appear normal, but abnormalities in cellular proliferation were observed in bone, liver, and testis. Haplotype analysis localized the peewee gene to a 3.3-Mb region between D5Mit83 and D5Mit356.3. There are 18 genes in this linkage area. We also performed in silico mapping using the PosMed(SM) program, which searches for connections among keywords and genes in an interval, but no similar phenotype descriptions were found for these genes. In the peewee mutant compared to the normal C57BL/6 J mouse, only Slc10a4 expression was lower. Our preliminary mutation analysis examining the nucleotide sequence of three exons, two introns, and an untranslated region of Slc10a4 did not find any sequence difference between the peewee mouse and the C57BL/6 J mouse. Detailed analysis of peewee mice might provide novel molecular insights into the complex mechanisms regulating body growth.

Dynamics of liver GH/IGF axis and selected stress markers in juvenile gilthead sea bream (Sparus aurata) exposed to acute confinement: differential stress response of growth hormone receptors

The time courses of liver GH/IGF axis and selected stress markers were analyzed in juvenile gilthead sea bream (Sparus aurata) sampled at zero time and at fixed intervals (1.5, 3, 6, 24, 72 and 120 h) after acute confinement (120 kg/m(3)). Fish remained unfed throughout the course of the confinement study, and the fasting-induced increases in plasma growth hormone (GH) levels were partially masked by the GH-stress inhibitory tone. Hepatic mRNA levels of growth hormone receptor-I (GHR-I) were not significantly altered by confinement, but a persistent 2-fold decrease in GHR-II transcripts was found at 24 and 120 h. A consistent decrease in circulating levels of insulin-like growth factor-I (IGF-I) was also found through most of the experimental period, and the down-regulated expression of GHR-II was positively correlated with changes in hepatic IGF-I and IGF-II transcripts. This stress-specific response was concurrent with plasma increases in cortisol and glucose levels, reflecting the cortisol peak (60-70 ng/mL), the intensity and duration of the stressor when data found in the literature were compared. Adaptive responses against oxidative damage were also found, and a rapid enhanced expression was reported in the liver tissue for mitochondrial heat-shock proteins (glucose regulated protein 75). At the same time, the down-regulated expression of proinflammatory cytokines (tumour necrosis factor-alpha) and detoxifying enzymes (cytochrome P450 1A1) might dictate the hepatic depletion of potential sources of reactive oxygen species. These results provide suitable evidence for a functional partitioning of hepatic GHRs under states of reduced IGF production and changing cellular environment resulting from acute confinement.

Persistent transcription-blocking DNA lesions trigger somatic growth attenuation associated with longevity

The accumulation of stochastic DNA damage throughout an organism's lifespan is thought to contribute to ageing. Conversely, ageing seems to be phenotypically reproducible and regulated through genetic pathways such as the insulin-like growth factor-1 (IGF-1) and growth hormone (GH) receptors, which are central mediators of the somatic growth axis. Here we report that persistent DNA damage in primary cells from mice elicits changes in global gene expression similar to those occurring in various organs of naturally aged animals. We show that, as in ageing animals, the expression of IGF-1 receptor and GH receptor is attenuated, resulting in cellular resistance to IGF-1. This cell-autonomous attenuation is specifically induced by persistent lesions leading to stalling of RNA polymerase II in proliferating, quiescent and terminally differentiated cells; it is exacerbated and prolonged in cells from progeroid mice and confers resistance to oxidative stress. Our findings suggest that the accumulation of DNA damage in transcribed genes in most if not all tissues contributes to the ageing-associated shift from growth to somatic maintenance that triggers stress resistance and is thought to promote longevity.

Growth hormone and aging: a challenging controversy

Although advanced age or symptoms of aging are not among approved indications for growth hormone (GH) therapy, recombinant human GH (rhGH) and various GH-related products are aggressively promoted as anti-aging therapies. Well-controlled studies of the effects of rhGH treatment in endocrinologically normal elderly subjects report some improvements in body composition and a number of undesirable side effects in sharp contrast to major benefits of GH therapy in patients with GH deficiency. Controversies surrounding the potential utility of GH in treatment of a geriatric patient are fueled by increasing evidence linking GH and cancer and by remarkably increased lifespan of GH-resistant and GH-deficient mice. Conservation of cellular signaling mechanisms that influence aging in organisms ranging from worms to mammals suggests that at least some of the results obtained in mutant mice are applicable to the human. We suggest that the normal, physiological functions of GH in promoting growth, sexual maturation and fecundity involve significant costs in terms of aging and life expectancy. Natural decline in GH levels during aging likely contributes to concomitant alterations in body composition and vigor but also may be offering important protection from cancer and other age-associated diseases.

Increased insulin/insulin growth factor signaling advances the onset of metamorphosis in Drosophila

Mechanisms by which attainment of specific body sizes trigger developmental transitions to adulthood (e.g. puberty or metamorphosis) are incompletely understood. In Drosophila, metamorphosis is triggered by ecdysone synthesis from the prothoracic gland (PG), whereas growth rate is increased by insulin/insulin growth factor signalling (IIS). Transgene-induced activation of PI3K, the major effector of IIS, within the PG advances the onset of metamorphosis via precocious ecdysone synthesis, raising the possibility that IIS triggers metamorphosis via PI3K activation in the PG. Here we show that blocking the protein kinase A (PKA) pathway in the insulin producing cells (IPCs) increases IIS. This increased IIS increases larval growth rate and also advances the onset of metamorphosis, which is accompanied by precocious ecdysone synthesis and increased transcription of at least one ecdysone biosynthetic gene. Our observations suggest that IIS is regulated by PKA pathway activity in the IPCs. In addition, taken together with previous findings, our observations are consistent with the possibility that, in Drosophila, attainment of a specific body size triggers metamorphosis via the IIS-mediated activation of PI3K and hence ecdysone synthesis in the PG.

Extreme longevity is associated with increased serum thyrotropin

CONTEXT

The distribution of serum TSH shifts progressively to higher concentrations with age.

OBJECTIVE

The aim of the study was to determine whether the population shift in TSH distribution to higher concentrations with aging extends to people of exceptional longevity, namely centenarians, and to assess the relationship between concentrations of TSH and free T(4) (FT4).

DESIGN/SETTING/PATIENTS

We analyzed TSH, FT4, and TSH frequency distribution curves in thyroid disease-free Ashkenazi Jews with exceptional longevity (centenarians; median age, 98 yr), in younger Ashkenazi controls (median age, 72 yr), and in a population of thyroid disease-free individuals (median age, 68 yr) from the U.S. National Health and Nutrition Examination Survey 1998-2002 (NHANES controls).

RESULTS

Serum TSH was significantly higher in centenarians [1.97 (0.42-7.15) mIU/liter] than in Ashkenazi controls [1.55 (0.46-4.55) mIU/liter] and NHANES controls [1.61 (0.39-6.29) mIU/liter] (median, 2.5 and 97.5 centiles) (P < 0.001). The TSH frequency distribution curve of centenarians was relatively similar in shape to controls but shifted significantly to higher TSH, including TSH concentration at peak frequency. The TSH distribution curve of the NHANES control group was superimposable to and not significantly different from the Ashkenazi controls. FT4 was similar in centenarians and Ashkenazi controls, and there was a significant inverse correlation between FT4 and TSH in both groups.

CONCLUSIONS

The TSH population shifts to higher concentrations with age appear to be a continuum that extends even to people with exceptional longevity. The inverse correlation between TSH and FT4 in our populations suggests that changes in negative feedback may contribute to exceptional longevity.