[Show abstract][Hide abstract] ABSTRACT: Hypopituitary Ames dwarf mice were injected either with growth hormone (GH) or thyroxine for a 6-wk period to see whether this intervention would reverse their long life span or the resistance of their cells to lethal stresses. Ames dwarf mice survived 987 ± 24 d (median), longer than nonmutant control mice (664 ± 48), but GH-injected dwarf mice did not differ from controls (707 ± 9). Fibroblast cells from Ames dwarf mice were more resistant to cadmium than cells from nonmutant controls (LD(50) values of 9.98 ± 1.7 and 3.9 ± 0.8, respectively), but GH injections into Ames dwarf mice restored the normal level of cadmium resistance (LD(50)=5.8 ± 0.9). Similar restoration of normal resistance was observed for fibroblasts exposed to paraquat, methyl methanesulfonate, and rotenone (P<0.05 in each case for contrast of GH-treated vs. untreated dwarf mice; P<0.05 for dwarf vs. nonmutant control mice.) T4 injections into Ames dwarf mice, in contrast, did not restore normal life span. We conclude that the remarkable life-span extension of Ames dwarf mice, and the stress resistance of cells from these mice, depends on low levels of GH exposure in juvenile and very young adult mice.
Full-text · Article · Dec 2010 · The FASEB Journal
[Show abstract][Hide abstract] ABSTRACT: The disruption of the growth hormone (GH) axis in mice promotes insulin sensitivity and is strongly correlated with extended
longevity. Ames dwarf (Prop1df, df/df) mice are GH, prolactin (PRL), and thyrotropin (TSH) deficient and live approximately 50% longer than their normal
siblings. To investigate the effects of GH on insulin and GH signaling pathways, we subjected these dwarf mice to twice-daily
GH injections (6 μg/g/d) starting at the age of 2 weeks and continuing for 6 weeks. This produced the expected activation
of the GH signaling pathway and stimulated somatic growth of the Ames dwarf mice. However, concomitantly with increased growth
and increased production of insulinlike growth factor-1, the GH treatment strongly inhibited the insulin signaling pathway
by decreasing insulin sensitivity of the dwarf mice. This suggests that improving growth of these animals may negatively affect
both their healthspan and longevity by causing insulin resistance.
Full-text · Article · Nov 2009 · The Journals of Gerontology Series A Biological Sciences and Medical Sciences
[Show abstract][Hide abstract] ABSTRACT: Growth hormone receptor knockout (GHRKO) mice live about 40%-55% longer than their normal (N) littermates. Previous studies of 21-month-old GHRKO and N mice showed major alterations of the hepatic expression of genes involved in insulin signaling. Differences detected at this age may have been caused by the knockout of the growth hormone receptor (GHR) or by differences in biological age between GHRKO and N mice. To address this question, we compared GHRKO and N mice at ages corresponding to the same percentage of median life span to see if the differences of gene expression persisted. Comparison of GHRKO and N mice at approximately 50% of biological life span showed significant differences in hepatic expression of all 14 analyzed genes. We conclude that these changes are due to disruption of GHR gene and the consequent suppression of growth hormone signaling rather than to differences in "biological age" between mutant and normal animals sampled at the same chronological age.
Full-text · Article · Sep 2009 · The Journals of Gerontology Series A Biological Sciences and Medical Sciences
[Show abstract][Hide abstract] ABSTRACT: Reduced insulin sensitivity and glucose intolerance have been long suspected of having important involvement in aging. Here
we report that in studies of calorie restriction (CR) effects in mutant (Prop1df and growth hormone receptor knockout [GHRKO]) and normal mice, insulin sensitivity was strongly associated with longevity.
Of particular interest was enhancement of the already increased insulin sensitivity in CR df/df mice in which longevity was
also further extended and the lack of changes in insulin sensitivity in calorically restricted GHRKO mice in which there was
no further increase in average life span. We suggest that enhanced insulin sensitivity, in conjunction with reduced insulin
levels, may represent an important (although almost certainly not exclusive) mechanism of increased longevity in hypopituitary,
growth hormone (GH)-resistant, and calorie-restricted animals. We also report that the effects of GH treatment on insulin
sensitivity may be limited to the period of GH administration.
Full-text · Article · Jun 2009 · The Journals of Gerontology Series A Biological Sciences and Medical Sciences
[Show abstract][Hide abstract] ABSTRACT: Most mutations that delay aging and prolong lifespan in the mouse are related to somatotropic and/or insulin signaling. Calorie restriction (CR) is the only intervention that reliably increases mouse longevity. There is considerable phenotypic overlap between long-lived mutant mice and normal mice on chronic CR. Therefore, we investigated the interactive effects of CR and targeted disruption or knock out of the growth hormone receptor (GHRKO) in mice on longevity and the insulin signaling cascade. Every other day feeding corresponds to a mild (i.e. 15%) CR which increased median lifespan in normal mice but not in GHRKO mice corroborating our previous findings on the effects of moderate (30%) CR on the longevity of these animals. To determine why insulin sensitivity improves in normal but not GHRKO mice in response to 30% CR, we conducted insulin stimulation experiments after one year of CR. In normal mice, CR increased the insulin stimulated activation of the insulin signaling cascade (IR/IRS/PI3K/AKT) in liver and muscle. Livers of GHRKO mice responded to insulin by increased activation of the early steps of insulin signaling, which was dissipated by altered PI3K subunit abundance which putatively inhibited AKT activation. In the muscle of GHRKO mice, there was elevated downstream activation of the insulin signaling cascade (IRS/PI3K/AKT) in the absence of elevated IR activation. Further, we found a major reduction of inhibitory Ser phosphorylation of IRS-1 seen exclusively in GHRKO muscle which may underpin their elevated insulin sensitivity. Chronic CR failed to further modify the alterations in insulin signaling in GHRKO mice as compared to normal mice, likely explaining or contributing to the absence of CR effects on insulin sensitivity and longevity in these long-lived mice.
[Show abstract][Hide abstract] ABSTRACT: Transgenic mice overexpressing human growth hormone (hGH) exhibit accelerated aging with functional hyperprolactinemia and greatly depressed endogenous prolactin. Calorie restriction (CR) is widely recognized as the most effective experimental intervention to delay aging. The aim of the present work was to analyze the effects of lifelong overexpression of hGH on prolactin-gene expression as well as the dopamine production at the pituitary level and discern whether this mechanism changes as a function of feeding patterns. Ten-month-old mice fed every other day (EOD) were killed after one day of fasting. The results confirmed typical phenotypic features of these transgenic mice: an increase in body weight, very high hGH plasma concentrations, and hyperinsulinemia. There was a marked inhibition of the expression of the prolactin gene, together with an increased tyrosine hydroxylase (TH) and the long isoform of dopamine receptor type 2 (D2LR) gene expression at the pituitary level. These parameters were not affected by the EOD feeding pattern. These data may suggest an autocrine or paracrine effect of dopamine at the hypophyseal level on prolactin secretion that is independent of the feeding pattern.
Full-text · Article · May 2008 · Experimental Biology and Medicine
[Show abstract][Hide abstract] ABSTRACT: Growth hormone receptor-deficient (GHRKO) mice are long-lived and have reduced insulin-like growth factor (IGF)-1 and insulin levels and enhanced insulin sensitivity thus resembling the phenotype of animals subjected to calorie restriction (CR). In contrast to its effects in normal mice, CR does not improve insulin sensitivity or increase longevity in GHRKO males. In an attempt to identify mechanisms underlying this differential response to CR, effects of CR on the expression of insulin-related genes were compared in GHRKO and normal mice. In addition to changes detected in both genotypes, and responses unique to GHRKO mice, the levels of Akt2 and peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC1alpha) were increased and levels of phosphorylated c-Jun N-terminal kinase (JNK)1 were reduced in response to CR only in normal mice. These changes may be related to mechanisms of improving insulin sensitivity and life expectancy.
No preview · Article · Feb 2007 · The Journals of Gerontology Series A Biological Sciences and Medical Sciences
[Show abstract][Hide abstract] ABSTRACT: There is conflicting information on the physiological role of growth hormone (GH) in the control of aging. This study reports dual-energy x-ray absorptiometry (DXA) measurements of body composition and bone characteristics in young, adult, and aged long-lived GH receptor knockout (GHR-KO) and normal mice to determine the effects of GH resistance during aging. Compared to controls, GHR-KO mice showed an increased percentage of body fat. GHR-KO mice have reduced total-body bone mineral density (BMD), bone mineral content, and bone area, but these parameters increased with age. In addition, GHR-KO mice have decreased femur length, femur BMD, and lower lumbar BMD compared to controls in all age groups. These parameters also continued to increase with age. Our results indicate that GH resistance alters body composition, bone growth, and bone maintenance during aging in GHR-KO mice.
No preview · Article · Jul 2006 · The Journals of Gerontology Series A Biological Sciences and Medical Sciences
[Show abstract][Hide abstract] ABSTRACT: Blockade of growth hormone (GH), decreased insulin-like growth factor-1 (IGF1) action and increased insulin sensitivity are associated with life extension and an apparent slowing of the aging process. We examined expression of genes involved in insulin action, IR, IRS1, IRS2, IGF1, IGF1R, GLUT4, PPARs and RXRs in the hearts of normal and GHR-/- (KO) mice fed ad libitum or subjected to 30% caloric restriction (CR). CR increased the cardiac expression of IR, IRS1, IGF1, IGF1R and GLUT4 in normal mice and IRS1, GLUT4, PPARalpha and PPARbeta/delta in GHR-KO animals. Expression of IR, IRS1, IRS2, IGF1, GLUT4, PPARgamma and PPARalpha did not differ between GHR-KO and normal mice. These unexpected results suggest that CR may lead to major modifications of insulin action in the heart, but high insulin sensitivity of GHR-KO mice is not associated with alterations in the levels of most of the examined molecules related to intracellular insulin signaling.
Full-text · Article · May 2006 · Experimental Gerontology
[Show abstract][Hide abstract] ABSTRACT: Growth hormone receptor/binding protein knockout (GHR-KO) mice live approximately 40% longer than their normal siblings do. These mice have dramatically reduced plasma levels of insulin-like growth factor 1 (IGF1) and enhanced insulin sensitivity. We examined the expression level of peroxisome proliferator-activated receptors (PPARs) and retinoid X receptors family genes in the livers of normal and GHR-KO mice fed ad libitum or subjected to long-term 30% caloric restriction (CR). The levels of PPARgamma and PPARalpha messenger RNA and proteins and the levels of retinoid X receptors messenger RNA were elevated in long-lived GHR-KO mice as compared to normal mice with no major effect of CR in either genotype. These findings suggest that enhanced insulin sensitivity of GHR-KO mice may be related to the altered actions of PPARs family members in the liver. The results also indicate that CR may increase insulin sensitivity through a different mechanism.
No preview · Article · Dec 2005 · The Journals of Gerontology Series A Biological Sciences and Medical Sciences
[Show abstract][Hide abstract] ABSTRACT: Resistance to growth hormone, reduced insulin-like growth factor 1 (IGF1) action, and enhanced insulin sensitivity are likely mediators of extended life span and delayed aging process in growth hormone receptor/binding protein knockout (GHR-KO) mice. Fat metabolism and genes involved in fatty acid oxidation are strongly involved in insulin action. Using real-time polymerase chain reaction and western blot we have examined expression of peroxisome proliferator-activated receptors (PPARs) and retinoid X receptor (RXR) genes in the skeletal muscle of normal and GHR-KO mice subjected to 30% caloric restriction. The results indicate that caloric restriction decreased the expression of PPARgamma, PPARalpha, and PPARbeta/delta which would lead to down-regulation of fat metabolism. This suggested metabolic change clearly does not affect whole-body insulin action. These findings suggest that whole-animal insulin sensitivity is not regulated through skeletal muscle insulin action.
No preview · Article · Nov 2005 · The Journals of Gerontology Series A Biological Sciences and Medical Sciences
[Show abstract][Hide abstract] ABSTRACT: Growth hormone receptor/binding protein knockout (GHR-KO) mice are characterized by resistance to growth hormone (GH), reduced insulin like growth factor 1 (IGF1) levels and enhanced insulin sensitivity and markedly increased lifespan. Findings in these and other long-lived mutant mice, and in normal animals subjected to caloric restriction (CR) indicate that insulin signaling is importantly involved in the control of longevity. We have examined the mRNA expression level of genes involved in insulin/IGF1 action in the skeletal muscle and liver of normal and GHR-KO mice fed ad libitum or subjected to long term 30% CR. The levels of IR, IRS1, IRS2, GLUT4 and IGF1 message in the skeletal muscle were reduced by CR in both normal and GHR-KO mice. In the liver, the results indicate that in GHR-KO mice mRNA expression of genes related to early steps of insulin signaling is up-regulated in the liver but not in the muscle. The results also show that improved insulin sensitivity in response to CR is not due to increased mRNA expression of the above genes in either normal or GHR-KO animals.
No preview · Article · Aug 2005 · Experimental Gerontology
[Show abstract][Hide abstract] ABSTRACT: Ames dwarf mutant mice are long-lived, hypoinsulinemic and hypoglycemic and exhibit enhanced sensitivity to injected insulin. Their phenotypic characteristics show many similarities to animals subjected to caloric restriction (CR) but Ames dwarf mice are not CR mimetics. Reducing daily food intake by 30% prolongs longevity in both normal and Ames dwarf mice. In the present study, the animals were subjected to a different type of CR, every other day feeding (EOD). Using real-time PCR, we have examined the expression of genes related to insulin signaling in the liver of normal and dwarf mice after 9 months of EOD. The results indicate that EOD produces some changes in the insulin and IGF1 signaling pathways, and that these changes are consistent with EOD increasing insulin sensitivity.
No preview · Article · Jul 2005 · Experimental Gerontology
[Show abstract][Hide abstract] ABSTRACT: Neurogenesis occurs throughout adult life in the dentate gyrus of mammalian hippocampus and has been suggested to play an important role in cognitive function. Multiple trophic factors including IGF-I have been demonstrated to regulate hippocampal neurogenesis. Ames dwarf mice live considerably longer than normal animals and maintain physiological function at youthful levels, including cognitive function, despite a deficiency of circulating GH and IGF-I. Here we show an increase in numbers of newly generated cells [bromodeoxyuridine (BrdU) positive] and newborn neurons (neuronal nuclear antigen and BrdU positive) in the dentate gyrus of adult dwarf mice compared with normal mice using BrdU labeling. Despite the profound suppression of hippocampal GH expression, hippocampal IGF-I protein levels are up-regulated and the corresponding mRNAs are as high in Ames dwarf as in normal mice. Our results suggest that local/hippocampal IGF-I expression may have induced the increase in hippocampal neurogenesis, and increased neurogenesis might contribute to the maintenance of youthful levels of cognitive function during aging in these long-lived animals.
[Show abstract][Hide abstract] ABSTRACT: Long-lived Ames dwarf mice share many phenotypic characteristics with animals subjected to caloric restriction (CR) but they are not CR mimetics. CR prolongs longevity in both normal and Ames dwarf mice. Using real-time polymerase chain reaction and western blot, we have examined the expression of genes related to insulin signaling in the liver of normal and dwarf mice subjected to 30% CR. The results revealed divergent responses of dwarf and normal animals to CR raising an interesting possibility that CR may affect longevity of normal and dwarf mice by different mechanisms. Moreover, effects of dwarfism on the expression of the examined genes differed from the effects of CR, thus adding to the evidence that these long-lived mutants are not CR mimetics.
No preview · Article · Sep 2004 · The Journals of Gerontology Series A Biological Sciences and Medical Sciences