Ames Mice Research Articles

OR08-1 PROP1 Is Not Essential For Pituitary Cells Terminal Differentiation

Abstract Introduction The pituitary gland controls several mechanisms as metabolism, growth, and reproduction, in response to hypothalamic stimuli. The adequate temporal/ spatial expression of transcription factors is mandatory for a normal pituitary development. PROP1 transcription factor is widely known as a key pituitary regulator. Pathogenic variants in the PROP1 gene are the main familial causes of hypopituitarism accounting for about 54% of the cases. Aim To characterize the expression of genes involved in pituitary cells determination and specification during pituitary high demand period such as sexual maturation compared to adulthood in the Ames mice. Methods Weight and naso-anal length were measured. Pituitary glands were collected from 5 wild type (WT) and 5 prop1 mutant (Mut) animals with 30 (P30), 40, (P40), and 60 (P60) days after birth. RT-qPCR was performed to analyze the pituitary transcription factors Sox2, Sox3, Hesx1, Otx2, and genes codifying the hormones GH, TSH, LH/ FSH, CGA, and PRL by SYBR® Green (QIAGEN, Valencia, CA). They were normalized by endogenous genes and performed in triplicate. The target genes relative quantification was performed using the mutant related to its age paired wild type as a calibrator and the results were expressed as fold change. Immunofluorescence of SOX2 (ab97959, Abcam, UK) (1: 1600) and pituitary hormones GH, LH, and FSH (1: 250) were done in pituitaries at P60 and its aged paired control, stained with propidium iodide (1: 1000) for nucleus and the secondary antibody Alexa FluorÒ488 (ab150077, Abcam, UK) (1: 1000). Results All mutant mice presented decreased weight and naso-anal length at the three analyzed periods. The expression of the pituitary stem/ progenitor cell marker Sox2 was increased at P30 and P60 and decreased at P40. Sox3 was increased at P30 and decreased at P40 and P60. Hesx1 was increased at P30 and P60 and decreased at P40. Otx2 was increased at all periods. At P30 the genes codifying pituitary hormones was decreased, except for Tsh and Fsh. At P40 it was observed increased expression of the genes codifying Gh, Lh, Fsh and Prl, while Tsh and Cga expression was reduced. At P60 all pituitary hormones codifying genes presented decreased expression. The immunofluorescence at P60 showed increased expression of SOX2, similar expression of FSH, and decreased expression of GH and LH related to their age paired WT. Conclusion Despite the absence of PROP1, Hesx1 is downregulated at P40. Pituitary cell subtype differentiation and hormonal production is observed at transcriptional and protein levels, showing that pituitary cells can differentiate and produce hormones in the absence of Prop1. The recovery of pituitary capacity to differentiate in mutant suggests the involvement of another factor in the pituitary cell differentiation pathway that could compensate the lack of Prop1. Presentation: Saturday, June 11, 2022 11:30 a.m. - 11:45 a.m.

Methionine Metabolism in Aging Regulation

Aging is the major risk factor for many diseases but the mechanisms are poorly understood. The risk of developing hepatic steatosis increases with age and the health impact of this disease is negative and high. When challenged with high fat diets, long living Ames mice withstand the detrimental metabolic effects that occur in normal mice. We examined transcriptomic and epigenomic profiles of Ames and wild type hepatocytes in the presence or absence of fat to demonstrate that the epigenomic profile drives transcription factor and downstream gene expression resulting in susceptibility or resistance to fatty liver disease. We found that markers of steatosis are related to gene expression in wild type and Ames mice, and dwarf mice retain fewer lipid droplets compared to wild type mice. These studies will provide data to guide our understanding of mechanisms leading to hepatic disease and define factors that provide protection from age-related metabolic disorders.

SAT-297 Pituitary Hormonal Levels and Gonadal Histology in the Pubertal Period of the Ames Mice

Introduction: The pituitary gland controls several mechanisms as metabolism, growth, and reproduction, in response to hypothalamic stimuli. The adequate temporal/ spatial expression of transcription factors is mandatory for a normal pituitary development. PROP1 transcription factor is widely known as a key pituitary regulator. The Ames mice is a model of congenital hypopituitarism due to a pathogenic variant in the Prop1 gene, leading to growth retardation, infertility, and hypothyroidism. Aim: To characterize the peripheral levels of pituitary hormones and correlate with gonadal histology during the pubertal period of the Ames mice. Methods: Weight and naso-anal length were measured. Peripheral blood samples were collected from 5 wild type (WT) and 5 Prop1 mutants (Mut) animals with 30 (P30), 40, (P40), and 60 (P60) days after birth. Pituitary hormone levels were measured using the kit Milliplex Map® - Mouse Pituitary Bead Panel (Merck Millipore, Massachusetts, USA). Ovaries and testis from 3 WT and 3 Mut animals from each sex were collected and fixed in 4% paraformaldehyde and embedded in paraffin. Gonadal sections of 3 μm were obtained and the slices were stained with hematoxylin and eosin. Follicles were counted and classified according to the size and cellular composition as small follicle (17μm to 28μm), developing follicle (100μm), and antral follicle (>550μm). Testis were classified using the Johnsen score, ranging from 1 to 10 according to cellular composition and spermatogenesis state. Results: All mutant mice presented decreased weight and naso-anal length at the three analyzed periods. At P30, the female mutants presented GH, LH, and TSH levels similar to wild type and decreased FSH and PRL levels, as well as the males that only differed from GH reduced levels. At P40, females and males presented GH, LH, FSH, and TSH levels similar to wild type with reduced PRL levels. At P60, it was observed decreased GH, FSH, and PRL levels for both sexes and TSH levels with no difference from WT, LH secretion was decreased in mutant females and normal in males compared to WT. There was no significant difference in follicular number and classification between mutants and wild type in all analyzed periods, despite the observation of ovarian hypoplasia in the mutants. Johnsen score was in the average of 7.5 in mutant males and 8.8 in WT, with no significant difference between periods. Conclusion: Despite the absence of PROP1 and the hypopituitary phenotype, mutant females and males were able to secrete some pituitary hormones, mainly during puberty, a pituitary high demand period. Although the ovaries and testis from mutant mice are hypoplastic, cellular morphology and classification are similar to WT.

MON-712 Restoration of Growth and Fertility in Zebrafish (Danio Rerio) Model with PROP1 Knockout Generated by CRISPR/Cas9 Genomic Editing

Introduction: Hypopituitarism is defined as the deficiency of one or more pituitary hormones and can occur due to pathogenic allelic variants in transcription factors involved in pituitary development. PROP1 gene is responsible for progenitor cell migration from the marginal zone to the anterior lobe, and its terminal differentiation into corticotropes and gonadotropes cell lines besides somatotropes, lactotropes and thyrotropes due to POU1F1 (also known as PIT1) activation. In humans, mutations in the PROP1 gene are the most common cause of congenital hypopituitarism with GH, TSH, LH/FSH, and progressive ACTH deficiencies. A dwarf phenotype with short stature, pituitary hormone deficiency, and infertility has been described in humans and Ames mice lineage harboring mutations in the PROP1/Prop1 gene. Another valuable animal model used in basic research is the zebrafish (Danio rerio) due to a high homology in neuroendocrine functioning. To test the potential of this model, in our previous study, a 32bp insertion carrying a stop codon was directed into the second exon of prop1 with CRISPR/Cas9, establishing a homozygous mutant strain (prop1mut). Objective: To characterize the phenotype and expression patterns of transcription factors and hormones in the zebrafish prop1mut lineage. Methods: prop1, pit1, and gh1 mRNA levels were analyzed during embryonic development at 24 and 72 hours post-fertilization (hpf). RNA from 30 pooled embryos was extracted using DirectZol RNA Miniprep. cDNA was synthesized from 1ug of total RNA using High-Capacity cDNA Reverse Transcription Kit and qPCR was performed using SYBR Green PCR Master Mix. Gene expression was normalized to ef1a and the prop1mut group was compared with the control wild type group (WT). Animals were kept in the tanks at a density of 15 animals/liter and images were acquired at 13 and 20 days post fertilization (dpf) after brief anesthetization using a stereomicroscope and measured in ImageJ software to determine the larval standard length from nose to the end of the spinal cord. Results: At 24 and 72hpf, prop1mut embryos expressed the altered prop1 mRNA at similar levels to the prop1 expression observed in WT. Lower pit1 expression in prop1mut embryos was observed at both periods (p<0.01). Albeit in low levels, similar gh1 expression was observed in both lineages at 24hpf, and prop1mut embryos presented lower gh1 expression at 72hpf (p<0.001). prop1mut larvae presented a significant decrease in size at 13dpf (p<0.001) but not at 20dpf. Conclusion: In this study, the prop1mut zebrafish model exhibited a dwarf phenotype during larval development associated with diminished pit1 and gh1 expression during the embryonic stage. Additionally, in the juvenile stage, the development rate in prop1mut animals was restored, presenting similar standard lengths observed in WT animals.

Intestinal immunity in hypopituitary dwarf mice: effects of age.

Hypopituitary dwarf mice demonstrate advantages of longevity, but little is known of their colon development and intestinal immunity. Herein we found that Ames dwarf mice have shorter colon and colonic crypts, but larger ratio of mesenteric lymph nodes (MLNs) over body weight than age-matched wild type (WT) mice. In the colonic lamina propria (cLP) of juvenile Ames mice, more inflammatory neutrophils (Ā: 0.15% vs. 0.03% in WT mice) and monocytes (Ā: 7.97% vs. 5.15%) infiltrated, and antigen presenting cells CD11c+ dendritic cells (Ā: 1.39% vs. 0.87%), CD11b+ macrophages (Ā: 3.22% vs. 0.81%) and gamma delta T (γδ T) cells (Ā: 5.56% vs. 1.35%) were increased. In adult Ames dwarf mice, adaptive immune cells, such as IL-17 producing CD4+ T helper (Th17) cells (Ā: 8.3% vs. 4.7%) were augmented. In the MLNs of Ames dwarf mice, the antigen presenting and adaptive immune cells also altered when compared to WT mice, such as a decrease of T-regulatory (Treg) cells in juvenile Ames mice (Ā: 7.7% vs.10.5%), but an increase of Th17 cells (Ā: 0.627% vs.0.093%). Taken together, these data suggest that somatotropic signaling deficiency influences colon development and intestinal immunity.

Circulating microRNA signature of genotype-by-age interactions in the long-lived Ames dwarf mouse.

Recent evidence demonstrates that serum levels of specific miRNAs significantly change with age. The ability of circulating sncRNAs to act as signaling molecules and regulate a broad spectrum of cellular functions implicates them as key players in the aging process. To discover circulating sncRNAs that impact aging in the long-lived Ames dwarf mice, we conducted deep sequencing of small RNAs extracted from serum of young and old mice. Our analysis showed genotype-specific changes in the circulating levels of 21 miRNAs during aging [genotype-by-age interaction (GbA)]. Genotype-by-age miRNAs showed four distinct expression patterns and significant overtargeting of transcripts involved in age-related processes. Functional enrichment analysis of putative and validated miRNA targets highlighted cellular processes such as tumor suppression, anti-inflammatory response, and modulation of Wnt, insulin, mTOR, and MAPK signaling pathways, among others. The comparative analysis of circulating GbA miRNAs in Ames mice with circulating miRNAs modulated by calorie restriction (CR) in another long-lived mouse suggests CR-like and CR-independent mechanisms contributing to longevity in the Ames mouse. In conclusion, we showed for the first time a signature of circulating miRNAs modulated by age in the long-lived Ames mouse.

Altered dietary methionine differentially impacts glutathione and methionine metabolism in long-living growth hormone-deficient Ames dwarf and wild-type mice.

BackgroundExtending mammalian health span and life span has been achieved under a variety of dietary restriction protocols. Reducing the intake of a specific amino acid has also been shown to extend health and longevity. We recently reported that methionine (MET) restriction is not effective in life span extension in growth hormone (GH) signaling mutants. To better understand the apparent necessity of GH in the ‘sensing’ of altered dietary MET, the current study was designed to evaluate MET and glutathione (GSH) metabolism (as well as other pathways) in long-living GH-deficient Ames dwarf and wild-type mice following 8 weeks of restricted (0.16%), low (0.43%), or enriched (1.3%) dietary MET consumption. Metabolite expression was examined in liver tissue, while gene and protein expression were evaluated in liver, kidney, and muscle tissues.ResultsBody weight was maintained in dwarf mice on the MET diets, while wild-type mice on higher levels of MET gained weight. Liver MET levels were similar in Ames mice, while several MET pathway enzymes were elevated regardless of dietary MET intake. Transsulfuration enzymes were also elevated in Ames mice but differences in cysteine levels were not different between genotypes. Dwarf mice maintained higher levels of GSH on MET restriction compared to wild-type mice, while genotype and diet effects were also detected in thioredoxin and glutaredoxin. MET restriction increased transmethylation in both genotypes as indicated by increased S-adenosylmethionine (SAM), betaine, and dimethylglycine. Diet did not impact levels of glycolytic components, but dwarf mice exhibited higher levels of key members of this pathway. Coenzyme A and measures of fatty acid oxidation were elevated in dwarf mice and unaffected by diet.ConclusionsThis component analysis between Ames and wild-type mice suggests that the life span differences observed may result from the atypical MET metabolism and downstream effects on multiple systems. The overall lack of responsiveness to the different diets is well reflected across many metabolic pathways in dwarf mice indicating the importance of GH signaling in the ability to discriminate dietary amino acid levels.Electronic supplementary materialThe online version of this article (doi:10.1186/2046-2395-3-10) contains supplementary material, which is available to authorized users.

IGF-I regulates the age-dependent signaling peptide humanin.

Aging is influenced by endocrine pathways including the growth hormone/insulin-like growth factor-1 (GH/IGF) axis. Mitochondrial function has also been linked to the aging process, but the relevant mitochondrial signals mediating the effects of mitochondria are poorly understood. Humanin is a novel signaling peptide that acts as a potent regulator of cellular stress responses and protects from a variety of in vitro and in vivo toxic and metabolic insults. The circulating levels of humanin decline with age in mice and humans. Here, we demonstrate a negative correlation between the activity of the GH-IGF axis and the levels of humanin, as well as a positive correlation between humanin and lifespan in mouse models with altered GH/IGF-I axis. Long-lived, GH-deficient Ames mice displayed elevated humanin levels, while short-lived GH-transgenic mice have reduced humanin levels. Furthermore, treatment with GH or IGF-I reduced circulating humanin levels in both mice and human subjects. Our results indicate that GH and IGF are potent regulators of humanin levels and that humanin levels correlate with lifespan in mice. This suggests that humanin represents a circulating mitochondrial signal that participates in modulating the aging process, adding a coordinated mitochondrial element to the endocrine regulation of aging.

Growth Hormone Alters the Glutathione S-Transferase and Mitochondrial Thioredoxin Systems in Long-Living Ames Dwarf Mice

Ames dwarf mice are deficient in growth hormone (GH), prolactin, and thyroid-stimulating hormone and live significantly longer than their wild-type (WT) siblings. The lack of GH is associated with stress resistance and increased longevity. However, the mechanism underlying GH's actions on cellular stress defense have yet to be elucidated. In this study, WT or Ames dwarf mice were treated with saline or GH (WT saline, Dwarf saline, and Dwarf GH) two times daily for 7 days. The body and liver weights of Ames dwarf mice were significantly increased after 7 days of GH administration. Mitochondrial protein levels of the glutathione S-transferase (GST) isozymes, K1 and M4 (GSTK1 and GSTM4), were significantly higher in dwarf mice (Dwarf saline) when compared with WT mice (WT saline). GH administration downregulated the expression of GSTK1 proteins in dwarf mice. We further investigated GST activity from liver lysates using different substrates. Substrate-specific GST activity (bromosulfophthalein, dichloronitrobenzene, and 4-hydrox-ynonenal) was significantly reduced in GH-treated dwarf mice. In addition, GH treatment attenuated the activity of thioredoxin and glutaredoxin in liver mitochondria of Ames mice. Importantly, GH treatment suppressed Trx2 and TrxR2 mRNA expression. These data indicate that GH has a role in stress resistance by altering the functional capacity of the GST system through the regulation of specific GST family members in long-living Ames dwarf mice. It also affects the regulation of thioredoxin and glutaredoxin, factors that regulate posttranslational modification of proteins and redox balance, thereby further influencing stress resistance.

Mitochondrial electron transport chain functions in long-lived Ames dwarf mice

The age-associated decline in tissue function has been attributed to ROS-mediated oxidative damage due to mitochondrial dysfunction. The long-lived Ames dwarf mouse exhibits resistance to oxidative stress, a physiological characteristic of longevity. It is not known, however, whether there are differences in the electron transport chain (ETC) functions in Ames tissues that are associated with their longevity. In these studies we analyzed enzyme activities of ETC complexes, CI-CV and the coupled CI-CII and CII-CIII activities of mitochondria from several tissues of young, middle aged and old Ames dwarf mice and their corresponding wild type controls to identify potential mitochondrial prolongevity functions. Our studies indicate that post-mitotic heart and skeletal muscle from Ames and wild-type mice show similar changes in ETC complex activities with aging, with the exception of complex IV. Furthermore, the kidney, a slowly proliferating tissue, shows dramatic differences in ETC functions unique to the Ames mice. Our data show that there are tissue specific mitochondrial functions that are characteristic of certain tissues of the long-lived Ames mouse. We propose that this may be a factor in the determination of extended lifespan of dwarf mice.

The hippocampus of Ames dwarf mice exhibits enhanced antioxidative defenses following kainic acid-induced oxidative stress

Introduction The vulnerability of the hippocampus to the effects of aging has been found to be associated with a decline in growth hormone/insulin like growth factor-1 (GH/IGF-1), and an increase in oxidative stress. We have evidence that long-living GH-deficient Ames dwarf mice have enhanced antioxidant protection in the periphery but the protection in the central nervous system is less clear. Material and methods In the present study, we evaluated the antioxidative defense enzyme status in the hippocampus of Ames dwarf and wild type mice at 3, 12 and 24 months of age and examined the ability of each genotype to resist kainic acid-induced (KA) oxidative stress. An equiseizure concentration of KA was administered such that both genotypes responded with similar seizure scores and lipid peroxidation. Results We found that GH-sufficient wild type mice showed an increase in oxidative stress as indicated by the reduced ratio of glutathione: glutathione disulfide following KA injection while this ratio was maintained in GH-deficient Ames dwarf mice. In addition, glutathione peroxidase activity (GPx) as well as GPx1 mRNA expression was enhanced in KA-injected Ames dwarf mice but decreased in wild type mice. There was no induction of Nrf-2 (an oxidative stress-induced transcription factor) gene expression in Ames dwarf mice following KA further suggesting maintenance of antioxidant defense in GH-deficiency under oxidative stress conditions. Discussion Therefore, based on equiseizure administration of KA, Ames dwarf mice have an enhanced antioxidant defense capacity in the hippocampus similar to that observed in the periphery. This improved defense capability in the brain is likely due to increased GPx availability in Ames mice and may contribute to their enhanced longevity.

Spatial memory is enhanced in long-living Ames dwarf mice and maintained following kainic acid induced neurodegeneration

Introduction Age associated cognitive impairment is associated with low levels of IGF-1, oxidative stress, and neuronal loss in the hippocampus. Ames dwarf mice are long-lived animals that exhibit peripheral IGF-1 deficiency. Hippocampal-based spatial memory (a homolog of cognitive function) has not been evaluated in these long-living mice. Materials and methods We evaluated the hippocampal-based spatial memory in 3-, 12- and 24-month-old Ames dwarf and wild type mice using the Barnes maze and the T-maze. We also examined the effect of a hippocampal-specific toxin, kainic acid (KA), on spatial memory to determine whether Ames mice were resistant to the cognitive impairment induced by this compound. Results We found that Ames dwarf mice exhibit enhanced learning, making fewer errors and using less time to solve both the Barnes and T-mazes. Dwarf mice also have significantly better short-term memory as compared to wild type mice. Both genotypes exhibited neuronal loss in the CA1 and CA3 areas of the hippocampus following KA, but Ames dwarf mice retained their spatial memory. Discussion Our results show that Ames dwarf mice retained their spatial memory despite neurodegeneration when compared to wild type mice at an “equiseizure” dose of KA.

Hippocampus of Ames dwarf mice is resistant to beta-amyloid-induced tau hyperphosphorylation and changes in apoptosis-regulatory protein levels.

The Ames dwarf mouse has a long lifespan and is characterized by a marked resistance to cellular stress, an event that is implicated in the pathogenesis of many neurodegenerative disorders that are associated with aging, including Alzheimer's disease. However, very little is known on the extent to which the Ames dwarf mouse is protected against Alzheimer's disease. We have developed an organotypic slice system cultured from hippocampi of adult dwarf mice and examined deleterious effects of beta-amyloid (Abeta) peptide, a key pathogenic event in the course of Alzheimer's disease. We present the first evidence that long living Ames mice resist beta-amyloid toxicity. We demonstrate that organotypic slices from adult dwarf mice, but not their normal phenotype counterparts (wild type), are resistant to Abeta25-35-induced hyperphosphorylation of tau protein, reduction in levels of the antiapoptotic protein Bcl-2, increase in levels of the pro-apoptotic protein Bax, and activation of caspase 3. Moreover, incubation of organotypic sections with the GSK-3beta inhibitor SB216763 prevented tau phosphorylation but not alterations in levels of Bcl-2, Bax, and caspase-3. Because the hippocampus is a brain area that is severely affected in Alzheimer's disease, our study proposes that organotypic slices from hippocampi of adult Ames dwarf mice may constitute a model system for understanding endogenous factors that may confer protection against Abeta.

Hippocampal IGF-1 expression, neurogenesis and slowed aging: clues to longevity from mutant mice

Recent studies point out the important role of IGF and insulin-related signaling pathways in the control of longevity of laboratory animals. The Ames dwarf mouse is a murine model of circulating GH and IGF-1 deficiency that exhibits dwarf phenotype characteristics and significantly extends lifespan. It is interesting to know that Ames dwarf mice do not experience an age-related decline in cognitive function when compared to their young counterparts. In this study, the most recent works on local GH and IGF-1 expression in the hippocampus of Ames mice are briefly reviewed.

Methionine flux to transsulfuration is enhanced in the long living Ames dwarf mouse

Long-lived Ames dwarf mice lack growth hormone, prolactin, and thyroid stimulating hormone. Additionally the dwarf mice have enzyme activities and levels that combat oxidative stress more efficiently than those of normal mice. We have shown that methionine metabolism in Ames mice is markedly different than in their wild type littermates. In our previous work we hypothesized that the flux of methionine to the transsulfuration pathway is enhanced in the dwarf mice. The current study was designed to determine whether the flux of methionine to the transsulfuration pathway is increased. We did this by injecting either l-[methyl- 3H]-methionine or l-[ 35S]-methionine into dwarf or normal mice and then determined retained label (in form of S-adenosylmethionine) 45 min later. The amount of retained hepatic 3H and 35S label was significantly reduced in the dwarf mice; at 45 min the specific radioactivity of SAM (pCi/nmol SAM) was 56% lower ( p < 0.05) for 3H-label and 64% lower ( p < 0.005) for 35S-label in dwarf than wild type mice. Retention of 35S was significantly lower in the brain (37%, p < 0.04) and kidney (47%, p < 0.02) of the dwarf compared to wild type mice; there was no statistical difference in retained 3H-label in either brain or kidney. This suggests that both the methyl-moiety and the carbon chain of methionine are lost much faster in the dwarf compared to the wild type mouse, implying that both transmethylation in the liver and transsulfuration in the liver, brain, and kidney are increased in the dwarf mice. As further support, we determined by real-time RT PCR the expression of methionine metabolism genes in livers of mice. Compared to wild type, the Ames dwarf had increased expression of methionine adenosyltransferase 1a (2.3-fold, p = 0.013), glycine N-methyltransferase (3.8-fold, p = 0.023), betaine homocysteine methyltransferase (5.5-fold, p = 0.0006), S-adenosylhomocysteine hydrolase (3.8-fold, p = 0.0005), and cystathionase (2.6-fold; tended to be increased, p = 0.055). Methionine synthase expression was significantly decreased in dwarf compared to wild type (0.48-fold, p = 0.023). These results confirm that the flux of methionine to transsulfuration is enhanced in the Ames dwarf. This, along with data from previous studies support the hypothesis that altered methionine metabolism plays a significant role in the oxidative defense of the dwarf mouse and that the mechanism for the enhanced oxidative defense may be through altered GSH metabolism as a result of the distinctive methionine metabolism.

Gender-specific alterations in gene expression and loss of liver sexual dimorphism in the long-lived Ames dwarf mice

Genetic mutations that increase lifespan in mice frequently involve alterations in the growth hormone/insulin-like growth factor-I signaling pathway. Although several of the effects of GH on gene expression are known to be sex-dependent, an understanding of the gender-specific vs. gender-independent effects of lifespan-extending mutations of the GH/IGF-I axis is currently lacking. The Ames dwarf mice ( prop1 df/ df ) are GH, prolactin and thyroid-stimulating hormone deficient and exhibit an increase in mean lifespan of 49% in males and 68% in females. We used oligonucleotide arrays containing over 14,000 genes to study the gender-specific vs. gender-independent effects of the prop1 df mutation in liver of male and female Ames mice. We identified 381 gender-independent and 110 gender-specific alterations in gene expression produced by the Prop1 df/ df genotype. The gender-specific alterations corresponded to genes with a strong sexual dimorphism in wild-type mice and produced an almost complete loss of sex-specific gene expression in the liver of Ames dwarf mice: out of 123 genes that showed sexual dimorphism in wild-type mice only six maintained a gender difference in mutant mice. However, the Prop1 df/ df genotype did not introduce new sexually dimorphic patterns of gene expression in Ames dwarf mice that were not present in the wild-type animals. The gender-specific alterations accounted for a large fraction of the most significant changes in gene expression in male and female Ames mice livers and affected several metabolic processes, particularly fatty acid metabolism, steroid hormone metabolism, and xenobiotic metabolism.

Do deficiencies in growth hormone and insulin-like growth factor-1 (IGF-1) shorten or prolong longevity?

Present knowledge on the effects of growth hormone (GH) and insulin-like growth factor-I (IGF-I) deficiency on aging and lifespan are controversial. Studying untreated patients with either isolated GH deficiency due to GH gene deletion, patients with multiple pituitary hormone deficiency due to PROP-1 gene mutation and patients with isolated IGF-I deficiency due to deletions or mutations of the GH receptor gene (Laron syndrome); it was found, that these patients despite signs of early aging (wrinkled skin, obesity, insulin resistance and osteopenia) have a long life span reaching ages of 80–90 years. Animal models of genetic GH deficiencies such as Snell mice (Pit-1 gene mutations) the Ames mice (PROP-1 gene mutation) and the Laron mice (GH receptor gene knock-out) have a statistically significant higher longevity compared to normal controls. On the contrary, mice transgenic for GH and acromegalic patients secreting high amounts of GH have premature death. Those data raise the question whether pharmacological GH administration to adults is deleterious, in contrast to policies advocating such therapies.

Growth hormone alters methionine and glutathione metabolism in Ames dwarf mice

Reduced signaling of the growth hormone (GH)/insulin-like growth factor-1(IGF-1)/insulin pathway is associated with extended life span in several species. Ames dwarf mice are GH and IGF-1 deficient and live 50–64% longer than wild type littermates (males and females, respectively). Previously, we have shown that Ames mice exhibit elevated levels of antioxidative enzymes and lower oxidative damage. To further explore the relationship between GH and antioxidant expression, we administered GH or saline to dwarf mice and evaluated components of the methionine and glutathione (GSH) metabolic pathways. Treatment of dwarf mice with GH significantly suppressed methionine adenosyltransferase (40 and 38%) and glycine- N-methyltransferase (44 and 43%) activities (in 3- and 12-month-old mice, respectively). Growth hormone treatment elevated kidney gamma-glutamyl-cysteine synthetase protein levels in 3- and 12-month-old dwarf mice. In contrast, the activity of the GSH degradation enzyme, gamma-glutamyl transpeptidase, was suppressed by GH administration in heart and liver. The activity of glutathione- S-transferase, an enzyme involved in detoxification, was also affected by GH treatment. Taken together, the current results along with data from previous studies support a role for growth hormone in the regulation of antioxidative defense and ultimately, life span in organisms with altered GH or IGF-1 signaling.

Growth hormone alters components of the glutathione metabolic pathway in Ames dwarf mice.

Reduced signaling of the growth hormone (GH)/insulin-like growth factor-1(IGF-1)/insulin pathway is associated with extended life span in several species. Ames dwarf mice are GH and IGF-1 deficient and live 50-64% longer than wild-type littermates (males and females, respectively). Previously, we have shown that Ames mice exhibit elevated levels of antioxidative enzymes and lower oxidative damage. To further explore the relationship between GH and antioxidant expression, we administered GH or saline to dwarf mice and evaluated components of the glutathione (GSH) synthesis and degradation system. Growth hormone treatment significantly elevated kidney gamma-glutamyl-cysteine synthetase protein levels in 3- and 12-month-old dwarf mice. In contrast, the activity of the GSH degradation enzyme, gamma-glutamyl transpeptidase, was suppressed by GH administration in brain (P <.05), kidney (P <.01), heart (P <.005), and liver (P <.06). Activity levels of the detoxification enzyme, glutathione-S-transferase, were also suppressed in kidney tissues at 3 and 12 months of age and in 12-month-old dwarf liver tissues (P <.05). Taken together, the current results along with data from previous studies support a role for growth hormone in the regulation of antioxidative defense and, ultimately, life span in organisms with altered GH or IGF-1 signaling.

Common Ingredients

Like an inquisitive baker trying to determine what makes rye and sourdough bread rise the same despite their distinctive flavors, scientists have been looking for the molecular mechanisms common to different manipulations that extend life. Now, a team of researchers has found almost 30 genes that might contribute to two life lengtheners in mice: restricted diet and disrupted hormone signaling. The finding suggests that shared themes might underlie disparate methods of attaining long life. Mice that eat one-third fewer calories than their indulgent compatriots live about one-third longer. Researchers don't understand how trimming the edibles increases life-span, but they do know that cutting calories reduces concentrations of metabolism-regulating molecules such as IGF-1 and growth hormone. Some genetic alterations that prolong life, such as those in Snell and Ames dwarf mice, also curtail these hormones. The genetic and dietary manipulations don't work exactly the same way, however. A previous study showed that calorie restriction adds additional months to the lives of Ames mice, suggesting that the strategies operate through independent biochemical means (see "Dieting Dwarves Live It Up" ). To find out what the two life-enhancers do have in common, biogerontologist Richard Miller of the University of Michigan, Ann Arbor, and colleagues looked for genes that are turned off and on in mice subjected to different life-extending methods. Miller's team chopped up livers from normal 9-month-old mice that had been on a restricted diet. Using a microarray that contains probes for 2352 mouse genes, the researchers analyzed the samples and looked for genes that cranked out more or less messenger RNA than they did in livers from mice that had stuffed their whiskers. The scientists performed two statistical corrections to guard against fluke results; 352 genes made the cut. They then compared those genes to 72 genes altered by the Snell mutation in dwarf mice, using data from a previous study. They found 29 genes whose production was either pumped up or squelched in both calorie-restricted and Snell mice. The genes ran the gamut from relative unknowns to producers of protein-synthesizing machinery, but none is known to speed up or slow down the aging process. Additional tests might determine how--or if--each of the genes contributes to long life, says Miller, who predicts that "some will turn out to be important to aging, some not." According to evolutionary geneticist Marc Tatar of Brown University in Providence, Rhode Island, this study is a "learning experience" in how to apply "rigorous" statistics to gene expression array data. In addition, biochemist Stephen Spindler of the University of California, Riverside, says defining the mechanisms that drive different life-extending pathways will help us understand normal aging. "This is the beginning of a very important molecular analysis of life-span extension by dwarf mice," he says. Researchers hope such work will eventually lead them to the core set of genes that control aging, like a baker who learns the secrets of the basic dough. --Mary Beckman R. A. Miller, Y. Chang, A. T. Galecki, K. Al-Regaiey, J. J. Kopchick, A. Bartke, Gene expression patterns in calorically restricted mice: Partial overlap with long-lived mutant mice. Mol. Endocrinol., 22 August 2002 [e-pub ahead of print]. [Abstract] [Full text]