Local expression of GH and IGF-1 in the hippocampus of GH-deficient long-lived mice

Primordial follicle activation in the ovary of Ames dwarf mice

Background

The insulin receptor substrate 1 (IRS1), phosphoinositide 3-kinase (Pi3k), protein kinase B (Akt1), Forkhead Box O3a (FOXO3a) pathway is directly involved in aging and ovarian activation of follicle growth. Therefore, the aim of this work was to measure the expression of genes related to the ovarian pathway for activation of primordial follicles and FOXO3a protein phosphorylation between young and old female Ames dwarf (df/df) and normal (N) mice.

Methods

For this study ovaries from N (n = 10) and df/df (n = 10) female mice were collected at 5–6 months of age and at 21–22 months of age. For immunohistochemistry ovaries from 12 month-old and df/df mice were used.

Results

The expression of Irs1, Pi3k, Akt1, mammalian target of rapamycin (Mtor), suppressor of cytokine signaling −2 (Socs2), Socs3 was lower (P < 0.05) in older than younger N mice and not different (P > 0.05) between young and old df/df mice. The expression of Foxo3a was also lower (P < 0.05) in old than younger N and df/df mice and was higher (P < 0.05) in old df/df than N mice. Expression of Amh was lower (P < 0.05) in old than young N and df/df mice and was higher (P = 0.0009) in df/df than N mice. Imunnostaining for p-FOXO3 was lower in df/df than N mice (P < 0.001), although FOXO3 immunostaining was not different (P > 0.05) between df/df and N mice.

Conclusions

In sum, the present study indicates that lower expression of Irs1, Socs2, Socs3, Akt1, Pi3k, Mtor and Foxo3a mRNA in the ovaries of older mice of both genotypes is associated to a reduced ovarian activity revealed by lower expression of Amh mRNA. At the same time, ovaries of old df/df mice maintained higher expression of Foxo3a mRNA, which was associated to higher ovarian activity. We have shown that df/df females have a lower level of p-FOXO3 in oocytes from primordial/primary follicles, an important activator of follicular growth. Therefore, this study strongly indicates that Prop1^df mutation causes delayed ovarian aging.

Growth hormone, insulin-like growth factor-1 and the aging brain

Growth hormone (GH) and insulin-like growth factor (IGF)-1 regulate the development and function of cells throughout the body. Several clinical diseases that result in a decline in physical and mental functions are marked by mutations that disrupt GH or IGF-1 signaling. During the lifespan there is a robust decrease in both GH and IGF-1. Because GH and IGF-1 are master regulators of cellular function, impaired GH and IGF-1 signaling in aging/disease states leads to significant alterations in tissue structure and function, especially within the brain. This review is intended to highlight the effects of the GH and IGF-1 on neuronal structure, function, and plasticity. Furthermore, we address several potential mechanisms through which the age-related reductions in GH and IGF-1 affect cognition. Together, the studies reviewed here highlight the importance of maintaining GH and IGF-1 signaling in order to sustain proper brain function throughout the lifespan.

Melatonin regulates aging and neurodegeneration through energy metabolism, epigenetics, autophagy and circadian rhythm pathways

Brain aging is linked to certain types of neurodegenerative diseases and identifying new therapeutic targets has become critical. Melatonin, a pineal hormone, associates with molecules and signaling pathways that sense and influence energy metabolism, autophagy, and circadian rhythms, including insulin-like growth factor 1 (IGF-1), Forkhead box O (FoxOs), sirtuins and mammalian target of rapamycin (mTOR) signaling pathways. This review summarizes the current understanding of how melatonin, together with molecular, cellular and systemic energy metabolisms, regulates epigenetic processes in the neurons. This information will lead to a greater understanding of molecular epigenetic aging of the brain and anti-aging mechanisms to increase lifespan under healthy conditions.

Differential effects of prenatal stress in female 5-HTT-deficient mice: towards molecular mechanisms of resilience

Prenatal stress (PS) exposure is known to increase the risk of developing emotional disorders like major depression in later life. However, some individuals do not succumb to adversity following developmental stress exposure, a phenomenon referred to as resilience. To date, the molecular mechanisms explaining why some subjects are vulnerable and others more resilient to PS are far from understood. Recently, we have shown that the serotonin transporter (5-HTT) gene may play a modulating role in rendering individuals susceptible or resilient to PS. However, it is not clear which molecular players are mediating the interaction between PS and the 5-Htt genotype in the context of vulnerability and resilience to PS. For this purpose, we performed a microarray study with the help of Affymetrix GeneChip® Mouse Genome 430 2.0 Array, in which we separated wild-type and heterozygous 5-Htt-deficient (5-Htt+/-) PS offspring into susceptible and resilient offspring according to their performance in the forced swim test. Performance-oriented LIMMA analysis on the mRNA expression microarray data was followed by subsequent Spearman's correlation analysis linking the individual qRT-PCR mRNA expression data to various anxiety- and depression-related behavioral and neuroendocrine measures. Results indicate that, amongst others, Fos-induced growth factor (Figf), galanin receptor 3 (Galr3), growth hormone (Gh) and prolactin (Prl) were differentially expressed specifically in resilient offspring when compared to controls, and that the hippocampal expression of these genes showed several strong correlations with various measures of the hypothalamus-pituitary-adrenal axis (re)activity. In conclusion, there seems to be an intricate interplay between the expression of Figf, Galr3, Gh and Prl and neuroendocrine regulation, which may be critical in mediating resilience to PS exposure. More insight into the exact role of these molecular players may significantly enhance the development of new treatment strategies for stress-related emotional disorders.

Extrapituitary growth hormone and growth?

While growth hormone (GH) is obligatory for postnatal growth, it is not required for a number of growth-without-GH syndromes, such as early embryonic or fetal growth. Instead, these syndromes are thought to be dependent upon local growth factors, rather than pituitary GH. The GH gene is, however, also expressed in many extrapituitary tissues, particularly during early development and extrapituitary GH may be one of the local growth factors responsible for embryonic or fetal growth. Moreover, as the expression of the GH receptor (GHR) gene mirrors that of GH in extrapituitary tissues the actions of GH in early development are likely to be mediated by local autocrine or paracrine mechanisms, especially as extrapituitary GH expression occurs prior to the ontogeny of pituitary somatotrophs or the appearance of GH in the circulation. The extrapituitary expression of pituitary somatotrophs or the appearance of GH in the circulation. The extrapituitary expression of GH in embryos has also been shown to be of functional relevance in a number of species, since the immunoneutralization of endogenous GH or the blockade of GH production is accompanied by growth impairment or cellular apoptosis. The extrapituitary expression of the GH gene also persists in some central and peripheral tissues postnatally, which may reflect its continued functional importance and physiological or pathophysiological significance. The expression and functional relevance of extrapituitary GH, particularly during embryonic growth, is the focus of this brief review.

Growth hormone pathways signaling for cell proliferation and survival in hippocampal neural precursors from postnatal mice

Background

Accumulating evidence suggests that growth hormone (GH) may play a major role in the regulation of postnatal neurogenesis, thus supporting the possibility that it may be also involved in promoting brain repair after brain injury. In order to gain further insight on this possibility, in this study we have investigated the pathways signaling the effect of GH treatment on the proliferation and survival of hippocampal subgranular zone (SGZ)-derived neurospheres.

Results

Our results demonstrate that GH treatment promotes both proliferation and survival of SGZ neurospheres. By using specific chemical inhibitors we have been also able to demonstrate that GH treatment promotes the activation of both Akt-mTOR and JNK signaling pathways, while blockade of these pathways either reduces or abolishes the GH effects. In contrast, no effect of GH on the activation of the Ras-ERK pathway was observed after GH treatment, despite blockade of this signaling path also resulted in a significant reduction of GH effects. Interestingly, SGZ cells were also capable of producing GH, and blockade of endogenous GH also resulted in a decrease in the proliferation and survival of SGZ neurospheres.

Conclusions

Altogether, our findings suggest that GH treatment may promote the proliferation and survival of neural progenitors. This effect may be elicited by cooperating with locally-produced GH in order to increase the response of neural progenitors to adequate stimuli. On this view, the possibility of using GH treatment to promote neurogenesis and cell survival in some acquired neural injuries may be envisaged.

Identifying aging-related genes in mouse hippocampus using gateway nodes

Background

High-throughput studies continue to produce volumes of metadata representing valuable sources of information to better guide biological research. With a stronger focus on data generation, analysis models that can readily identify actual signals have not received the same level of attention. This is due in part to high levels of noise and data heterogeneity, along with a lack of sophisticated algorithms for mining useful information. Networks have emerged as a powerful tool for modeling high-throughput data because they are capable of representing not only individual biological elements but also different types of relationships en masse. Moreover, well-established graph theoretic methodology can be applied to network models to increase efficiency and speed of analysis. In this project, we propose a network model that examines temporal data from mouse hippocampus at the transcriptional level via correlation of gene expression. Using this model, we formally define the concept of “gateway” nodes, loosely defined as nodes representing genes co-expressed in multiple states. We show that the proposed network model allows us to identify target genes implicated in hippocampal aging-related processes.

Results

By mining gateway genes related to hippocampal aging from networks made from gene expression in young and middle-aged mice, we provide a proof-of-concept of existence and importance of gateway nodes. Additionally, these results highlight how network analysis can act as a supplement to traditional statistical analysis of differentially expressed genes. Finally, we use the gateway nodes identified by our method as well as functional databases and literature to propose new targets for study of aging in the mouse hippocampus.

Conclusions

This research highlights the need for methods of temporal comparison using network models and provides a systems biology approach to extract information from correlation networks of gene expression. Our results identify a number of genes previously implicated in the aging mouse hippocampus related to synaptic plasticity and apoptosis. Additionally, this model identifies a novel set of aging genes previously uncharacterized in the hippocampus. This research can be viewed as a first-step for identifying the processes behind comparative experiments in aging that is applicable to any type of temporal multi-state network.

Administration of growth hormone and nandrolone decanoate alters mRNA expression of the GABAB receptor subunits as well as of the GH receptor, IGF-1, and IGF-2 in rat brain

OBJECTIVE

The illicit use of anabolic androgenic steroids (AAS), especially among young adults, is of major concern. Among AAS users it is common to combine the AAS nandrolone decanoate (ND), with intake of growth hormone (GH) and a connection between gonadal steroids and the GH system has been suggested. Both AAS and GH affect functions in the brain, for example those associated with the hypothalamus and pituitary, and several GH actions are mediated by growth factors such as insulin-like growth factor 1 (IGF-1) and insulin-like growth factor 2 (IGF-2). The GABAergic system is implicated in actions induced by AAS and previous studies have provided evidence for a link between GH and GABAB receptors in the brain. Our aim was to examine the impact of AAS administration and a subsequent administration of GH, on the expression of GABAB receptors and important GH mediators in rat brain.

DESIGN

The aim was to investigate the CNS effects of a high-dose ND, and to study if a low, but physiological relevant, dose of GH could reverse the ND-induced effects. In the present study, male rats were administered a high dose of ND every third day during three weeks, and subsequently the rats were given recombinant human GH (rhGH) during ten days. Quantitative PCR (qPCR) was used to analyze gene expression in hypothalamus, anterior pituitary, caudate putamen, nucleus accumbens, and amygdala.

RESULTS

In the pituitary gland, the expression of GABAB receptor subunits was affected differently by the steroid treatment; the GABAB1 mRNA expression was decreased whereas a distinct elevation of the GABAB2 expression was found. Administration of ND also caused a decrease of GHR, IGF-1, and IGF-2 mRNA expression in the pituitary while the corresponding expression in the hypothalamus, caudate putamen, nucleus accumbens, and amygdala was unaffected. The rhGH administration did not alter the GABAB2 expression but increased the GABAB1 gene expression in the hypothalamus as compared to the AAS treated group.

CONCLUSIONS

These results provide new insights on the impact of ND and GH on the brain and highlight the interaction of these hormones with systems influencing GABAB receptor expression. The physiological significance of the observed effects of these hormones is discussed.

The effects of early life lead exposure on the expression of insulin-like growth factor 1 and 2 (IGF1, IGF2) in the hippocampus of mouse pups

The present study was undertaken to investigate the effects of maternal lead exposure on expression of IGF1 and IGF2 in the hippocampus of mice offspring. Lead exposure initiated from beginning of gestation to weaning. Lead acetate administered in drinking solutions was dissolved in distilled deionized water at the concentrations of 0.1%, 0.5% and 1% groups respectively. On the 21st postnatal day, the learning and memory ability was tested by Water Maze test and the Pb levels were also determined by graphite furnace atomic absorption spectrometry. The expression of IGF1 and IGF2 in hippocampus was examined by immunohistochemistry and western blotting. The lead levels in blood and hippocampus of all lead exposure groups were significantly higher than that of the control group (P<0.05). In Water Maze test, the performances of 0.5% and 1% lead exposure groupswere worse than that of the control group (P<0.05). The expression of IGF1 and IGF2 was decreased in lead exposed groups than that of the control group (P<0.05). The low expression of IGF1 and IGF2 in the hippocampus of pups may contribute to the impairment of learning and memory associated with maternal Pb exposure.

Growth hormone-releasing hormone disruption extends lifespan and regulates response to caloric restriction in mice

We examine the impact of targeted disruption of growth hormone-releasing hormone (GHRH) in mice on longevity and the putative mechanisms of delayed aging. GHRH knockout mice are remarkably long-lived, exhibiting major shifts in the expression of genes related to xenobiotic detoxification, stress resistance, and insulin signaling. These mutant mice also have increased adiponectin levels and alterations in glucose homeostasis consistent with the removal of the counter-insulin effects of growth hormone. While these effects overlap with those of caloric restriction, we show that the effects of caloric restriction (CR) and the GHRH mutation are additive, with lifespan of GHRH-KO mutants further increased by CR. We conclude that GHRH-KO mice feature perturbations in a network of signaling pathways related to stress resistance, metabolic control and inflammation, and therefore provide a new model that can be used to explore links between GHRH repression, downregulation of the somatotropic axis, and extended longevity.

DOI:http://dx.doi.org/10.7554/eLife.01098.001

There is increasing evidence that the hormonal systems involved in growth, the metabolism of glucose, and the processes that balance energy intake and expenditure might also be involved in the aging process. In rodents, mutations in genes involved in these hormone-signaling pathways can substantially increase lifespan, as can a diet that is low in calories but which avoids malnutrition. As well as living longer, such mice also show reductions in age-related conditions such as diabetes, memory loss and cancer.

Many of these effects appear to involve the actions of growth hormone. Mice with mutations that disrupt the development of the pituitary gland, which produces growth hormone, show increased longevity, as do mice that lack the receptor for growth hormone. However, these animals also show changes in a number of other hormones, making it difficult to be sure that the reduction in growth hormone signaling is responsible for their increased lifespan.

Now, Sun et al. have studied mutant mice that lack a gene called GHRH, which promotes the release of growth hormone. These mice, which have normal levels of all other pituitary hormones, lived for up to 50% longer than their wild-type littermates. They were more active than normal mice and had more body fat, and showed greatly increased sensitivity to insulin.

Some of the changes in these mutant mice resembled those seen in animals with a restricted calorie intake, suggesting that the same mechanisms may be implicated in both. However, Sun et al. found that caloric restriction further increased the lifespans of their GHRH knockout mice, indicating that at least some of the effects of caloric restriction are independent of disrupted growth hormone signaling.

The results of this study are an important step forward for understanding how growth hormone signaling and caloric restriction regulate aging, both individually and in combination. The GHRH knockout mice are likely to become an important model system for studying these processes and for understanding the complex interactions between diet and hormonal pathways.

DOI:http://dx.doi.org/10.7554/eLife.01098.002

Neural growth hormone implicated in body weight sex differences

As for many human diseases, the incidence of obesity and its associated health risks are sexually dimorphic: worldwide the rate of obesity is higher in women. Sex differences in metabolism, appetite, body composition, and fat deposition are contributing biological factors. Gonadal hormones regulate the development of many sexually dimorphic traits in humans and animals, and, in addition, studies in mice indicate a role for direct genetic effects of sex chromosome dosage on body weight, deposition of fat, and circadian timing of feeding behavior. Specifically, mice of either sex with 2 X chromosomes, typical of normal females, have heavier body weights, gain more weight, and eat more food during the light portion of the day than mice of either sex with a single X chromosome. Here we test the effects of X chromosome dosage on body weight and report that gonadal females with 2 X chromosomes express higher levels of GH gene (Gh) mRNA in the preoptic area (POA) of the hypothalamus than females with 1 X chromosome and males. Furthermore, Gh expression in the POA of the hypothalamus of mice with 2 X chromosomes correlated with body weight; GH is known to have orexigenic properties. Acute infusion of GH into the POA increased immediate food intake in normal (XY) males. We propose that X inactivation-escaping genes modulate Gh expression and food intake, and this is part of the mechanism by which individuals with 2 X chromosomes are heavier than individuals with a single X chromosome.

Growth hormone and insulin-like growth factor-I alter hippocampal excitatory synaptic transmission in young and old rats

In rats, as in humans, normal aging is characterized by a decline in hippocampal-dependent learning and memory, as well as in glutamatergic function. Both growth hormone (GH) and insulin-like growth factor-I (IGF-I) levels have been reported to decrease with age, and treatment with either GH or IGF-I can ameliorate age-related cognitive decline. Interestingly, acute GH and IGF-I treatments enhance glutamatergic synaptic transmission in the rat hippocampus of juvenile animals. However, whether this enhancement also occurs in old rats, when cognitive impairment is ameliorated by GH and IGF-I (des-IGF-I), remains to be determined. To address this issue, we used an in vitro CA1 hippocampal slice preparation and extracellular recording techniques to study the effects of acute application of GH and IGF-I on compound field excitatory postsynaptic potentials (fEPSPs), as well as AMPA- and NMDA-dependent fEPSPs, in young adult (10 months) and old (28 months) rats. The results indicated that both GH and IGF-I increased compound-, AMPA-, and NMDA-dependent fEPSPs to a similar extent in slices from both age groups and that this augmentation was likely mediated via a postsynaptic mechanism. Initial characterization of the signaling cascades underlying these effects revealed that the GH-induced enhancement was not mediated by the JAK2 signaling element in either young adult or old rats but that the IGF-I-induced enhancement involved a PI3K-mediated mechanism in old, but not young adults. The present findings are consistent with a role for a GH- or IGF-I-induced enhancement of glutamatergic transmission in mitigating age-related cognitive impairment in old rats.

Restoration of hippocampal growth hormone reverses stress-induced hippocampal impairment

Though growth hormone (GH) is synthesized by hippocampal neurons, where its expression is influenced by stress exposure, its function is poorly characterized. Here, we show that a regimen of chronic stress that impairs hippocampal function in rats also leads to a profound decrease in hippocampal GH levels. Restoration of hippocampal GH in the dorsal hippocampus via viral-mediated gene transfer completely reversed stress-related impairment of two hippocampus-dependent behavioral tasks, auditory trace fear conditioning, and contextual fear conditioning, without affecting hippocampal function in unstressed control rats. GH overexpression reversed stress-induced decrements in both fear acquisition and long-term fear memory. These results suggest that loss of hippocampal GH contributes to hippocampal dysfunction following prolonged stress and demonstrate that restoring hippocampal GH levels following stress can promote stress resilience.

Role of growth hormone (GH) in the treatment on neural diseases: from neuroprotection to neural repair

Growth hormone (GH) is a pleiotropic hormone that exerts important functions in the control of brain development as well as in the regulation neuronal differentiation and function, together with several behavioral and psychological effects that have been linked to its modulatory actions on brain neurotransmitters. In addition, the possibility that GH may play a role on brain repair after injury has been also envisaged, and a number of reports have shown that GH administration following injury confers neuroprotection and accelerates the recovery of some neural functions. In this review we have analyzed the state of the art of GH administration in several neural diseases. Though more studies are still necessary in order to completely understand the importance of GH in these processes, the promising results obtained so far, together with the absence of untoward effects during GH therapy, encourages the development of clinical assays in order to further support the use GH treatment in neural diseases in which neuroprotection and/or neuroregeneration are involved.

Somatotropic signaling: trade-offs between growth, reproductive development, and longevity

Growth hormone (GH) is a key determinant of postnatal growth and plays an important role in the control of metabolism and body composition. Surprisingly, deficiency in GH signaling delays aging and remarkably extends longevity in laboratory mice. In GH-deficient and GH-resistant animals, the "healthspan" is also extended with delays in cognitive decline and in the onset of age-related disease. The role of hormones homologous to insulin-like growth factor (IGF, an important mediator of GH actions) in the control of aging and lifespan is evolutionarily conserved from worms to mammals with some homologies extending to unicellular yeast. The combination of reduced GH, IGF-I, and insulin signaling likely contributes to extended longevity in GH or GH receptor-deficient organisms. Diminutive body size and reduced fecundity of GH-deficient and GH-resistant mice can be viewed as trade-offs for extended longevity. Mechanisms responsible for delayed aging of GH-related mutants include enhanced stress resistance and xenobiotic metabolism, reduced inflammation, improved insulin signaling, and various metabolic adjustments. Pathological excess of GH reduces life expectancy in men as well as in mice, and GH resistance or deficiency provides protection from major age-related diseases, including diabetes and cancer, in both species. However, there is yet no evidence of increased longevity in GH-resistant or GH-deficient humans, possibly due to non-age-related deaths. Results obtained in GH-related mutant mice provide striking examples of mutations of a single gene delaying aging, reducing age-related disease, and extending lifespan in a mammal and providing novel experimental systems for the study of mechanisms of aging.

Early growth hormone (GH) treatment promotes relevant motor functional improvement after severe frontal cortex lesion in adult rats

A number of studies, in animals and humans, describe the positive effects of the growth hormone (GH) treatment combined with rehabilitation on brain reparation after brain injury. We examined the effect of GH treatment and rehabilitation in adult rats with severe frontal motor cortex ablation. Thirty-five male rats were trained in the paw-reaching-for-food task and the preferred forelimb was recorded. Under anesthesia, the motor cortex contralateral to the preferred forelimb was aspirated or sham-operated. Animals were then treated with GH (0.15 mg/kg/day, s.c) or vehicle during 5 days, commencing immediately or 6 days post-lesion. Rehabilitation was applied at short- and long-term after GH treatment. Behavioral data were analized by ANOVA following Bonferroni post hoc test. After sacrifice, immunohistochemical detection of glial fibrillary acid protein (GFAP) and nestin were undertaken in the brain of all groups. Animal group treated with GH immediately after the lesion, but not any other group, showed a significant improvement of the motor impairment induced by the motor lesion, and their performances in the motor test were no different from sham-operated controls. GFAP immunolabeling and nestin immunoreactivity were observed in the perilesional area in all injured animals; nestin immunoreactivity was higher in GH-treated injured rats (mainly in animals GH-treated 6 days post-lesion). GFAP immunoreactivity was similar among injured rats. Interestingly, nestin re-expression was detected in the contralateral undamaged motor cortex only in GH-treated injured rats, being higher in animals GH-treated immediately after the lesion than in animals GH-treated 6 days post-lesion. Early GH treatment induces significant recovery of the motor impairment produced by frontal cortical ablation. GH effects include increased neurogenesis for reparation (perilesional area) and for increased brain plasticity (contralateral motor area).

Growth hormone (GH) and brain trauma

Growth hormone (GH) is a pleiotropic hormone with known neurotrophic effects. We aimed to study whether GH administration might be useful together with rehabilitation in the recovery of TBI patients. 13 TBI patients (8 M, 5 F; age: 6-53 years old) were studied. Time after TBI: 2.5 months to 11 years; 5 patients showed acquired GH-deficiency (GHD). Disabilities observed: cognitive disorders; motor plegias; neurogenic dysphagia (n=5), vegetative coma (n=2) and amaurosis (n=1). All but one TBI patient followed intense rehabilitation for years. Treatment consisted of GH administration (maximal dose 1 mg/day, 5 days/week, resting 15-days every 2-months, until a maximum of 8 months) and clinical rehabilitation according to the individual needs (3-4 h/day, 5 days/week, during 6-12 months). Informed consent was obtained before commencing GH administration. GH significantly increased plasma IGF-1 values (ng.mL(-1)) in both GHD and no GHD patients, being then similar between both groups (GHD: 275.6±35.6 [p<0.01 vs. baseline], no GHD: 270.2±64 [p<0.05 vs. baseline]). In all the cases clear significant improvements were observed during and at the end of the combined treatment. Cognitive improvements appeared earlier and were more important than motor improvements. Swallowing improved significantly in all TBI patients with neurogenic dysphagia (2 of them in a vegetative state). Visual performance was ameliorated in the patient with amaurosis. No undesirable side-effects were observed. Our data indicate that GH can be combined with rehabilitation for improving disabilities in TBI patients, regardless of whether or not they are GHD.

Local overexpression of GH and GH/IGF1 effects in the adult mouse hippocampus

GH therapy improves hippocampal functions mainly via circulating IGF1. However, the roles of local GH and IGF1 expression are not well understood. We investigated whether transgenic (TG) overexpression in the adult brain of bovine GH (bGH) under the control of the glial fibrillary acidic protein (GFAP) promoter affected cellular proliferation and the expression of transcripts known to be induced by systemic GH in the hippocampus. Cellular proliferation was examined by 5-bromo-2'-deoxyuridine immunohistochemistry. Quantitative PCR and western blots were performed. Although robustly expressed, bGH-Tg did not increase either cell proliferation or survival. However, bGH-Tg modestly increased Igf1 and Gfap mRNAs, whereas other GH-associated transcripts were unaffected, i.e. the GH receptor (Ghr), IGF1 receptor (Igf1r), 2',3'-cyclic nucleotide 3'-phosphodiesterase (Cnp), ionotropic glutamate receptor 2a (Nr2a (Grin2a)), opioid receptor delta (Dor), synapse-associated protein 90/postsynaptic density-95-associated protein (Sapap2 (Dlgap2)), haemoglobin beta (Hbb) and glutamine synthetase (Gs (Glul)). However, IGF1R was correlated with the expression of Dor, Nr2a, Sapap2, Gs and Gfap. In summary, although local bGH expression was robust, it activated local IGF1 very modestly, which is probably the reason for the low response of previous GH-associated response parameters. This would, in turn, indicate that hippocampal GH is less important than endocrine GH. However, as most transcripts were correlated with the expression of IGF1R, there is still a possibility for endogenous circulating or local GH to act via IGF1R signalling. Possible reasons for the relative bio-inactivity of bGH include the bell-shaped dose-response curve and cell-specific expression of bGH.

NMDA and kainate receptor expression, long-term potentiation, and neurogenesis in the hippocampus of long-lived Ames dwarf mice

In the current study, we investigated changes in N-methyl D-aspartate (NMDA) and kainate receptor expression, long-term potentiation (LTP), and neurogenesis in response to neurotoxic stress in long-living Ames dwarf mice. We hypothesized that Ames dwarf mice have enhanced neurogenesis that enables retention of spatial learning and memory with age and promotes neurogenesis in response to injury. Levels of the NMDA receptors (NR)1, NR2A, NR2B, and the kainate receptor (KAR)2 were increased in Ames dwarf mice, relative to wild-type littermates. Quantitative assessment of the excitatory postsynaptic potential in Schaffer collaterals in hippocampal slices from Ames dwarf mice showed an increased response in high-frequency induced LTP over time compared with wild type. Kainic acid (KA) injection was used to promote neurotoxic stress-induced neurogenesis. KA mildly increased the number of doublecortin-positive neurons in wild-type mice, but the response was significantly enhanced in the Ames dwarf mice. Collectively, these data support our hypothesis that the enhanced learning and memory associated with the Ames dwarf mouse may be due to elevated levels of NMDA and KA receptors in hippocampus and their ability to continue producing new neurons in response to neuronal damage.

Aging, synaptic dysfunction, and insulin-like growth factor (IGF)-1

Insulin-like growth factor (IGF)-1 is an important neurotrophic hormone. Deficiency of this hormone has been reported to influence the genesis of cognitive impairment and dementia in the elderly patients. Nevertheless, there are studies indicating that cognitive function can be maintained into old age even in the absence of circulating IGF-1 and studies that link IGF-1 to an acceleration of neurological diseases. Although IGF-1 has a complex role in brain function, synaptic effects appear to be central to the IGF-1-induced improvement in learning and memory. In this review, synaptic mechanisms of learning and memory and the effects of IGF-1 on synaptic communication are discussed. The emerging data indicate that synaptic function decreases with age and that IGF-1 contributes to information processing in the brain. Further studies that detail the specific actions of this important neurotrophic hormone will likely lead to therapies that result in improved cognitive function for the elderly patients.

Diverse roles of growth hormone and insulin-like growth factor-1 in mammalian aging: progress and controversies

Because the initial reports demonstrating that circulating growth hormone and insulin-like growth factor-1 decrease with age in laboratory animals and humans, there have been numerous studies related to the importance of these hormones for healthy aging. Nevertheless, the role of these potent anabolic hormones in the genesis of the aging phenotype remains controversial. In this chapter, we review the studies demonstrating the beneficial and deleterious effects of growth hormone and insulin-like growth factor-1 deficiency and explore their effects on specific tissues and pathology as well as their potentially unique effects early during development. Based on this review, we conclude that the perceived contradictory roles of growth hormone and insulin-like growth factor-1 in the genesis of the aging phenotype should not be interpreted as a controversy on whether growth hormone or insulin-like growth factor-1 increases or decreases life span but rather as an opportunity to explore the complex roles of these hormones during specific stages of the life span.

Sexual dimorphism of growth hormone in the hypothalamus: regulation by estradiol

GH is best known as an anterior pituitary hormone fundamental in regulating growth, differentiation, and metabolism. GH peptide and mRNA are also present in brain, in which their functions are less well known. Here we describe the distribution of GH neurons and fibers and sex differences in Gh mRNA in adult mouse brain. Cell bodies exhibiting GH immunoreactivity are distributed in many brain regions, particularly in the hypothalamus in which retrograde labeling suggests that some of these cells project to the median eminence. To determine whether Gh mRNA is sexual dimorphic, we carried out quantitative RT-PCR on microdissected brain nuclei. Ovary-intact mice had elevated Gh mRNA in the arcuate nucleus and medial preoptic area (MPOA) compared with gonad-intact males. In males, castration increased Gh mRNA in the MPOA, whereas ovariectomy decreased Gh mRNA in both regions. When gonadectomized adults of both sexes were treated with estradiol Gh mRNA increased in females but had no effect in castrated males. Tamoxifen was able to blunt the rise in Gh mRNA in response to estradiol in females. In addition, we found that estrogen receptor-α is coexpressed in GH neurons in the MPOA and arcuate nucleus. In summary, the findings reveal sexual dimorphisms in Gh gene expression in areas of the brain associated with reproduction and behavior. Interestingly, estradiol enhances Gh mRNA in females only, suggesting that multiple factors orchestrate this sexual dimorphism.

The emerging role of IGF-1 deficiency in cardiovascular aging: recent advances

This review focuses on cardiovascular protective effects of insulin-like growth factor (IGF)-1, provides a landscape of molecular mechanisms involved in cardiovascular alterations in patients and animal models with congenital and adult-onset IGF-1 deficiency, and explores the link between age-related IGF-1 deficiency and the molecular, cellular, and functional changes that occur in the cardiovascular system during aging. Microvascular protection conferred by endocrine and paracrine IGF-1 signaling, its implications for the pathophysiology of cardiac failure and vascular cognitive impairment, and the role of impaired cellular stress resistance in cardiovascular aging considered here are based on emerging knowledge of the effects of IGF-1 on Nrf2-driven antioxidant response.

Age-related cognitive decline: can neural stem cells help us?

Several studies suggest that an increase in adult neurogenesis has beneficial effects on emotional behavior and cognitive performance including learning and memory. The observation that aging has a negative effect on the proliferation of neural stem cells has prompted several laboratories to investigate new systems to artificially increase neurogenesis in senescent animals as a means to compensate for age-related cognitive decline. In this review we will discuss the systemic, cellular, and molecular changes induced by aging and affecting the neurogenic niche at the level of neural stem cell proliferation, their fate change, neuronal survival, and subsequent integration in the neuronal circuitry. Particular attention will be given to those manipulations that increase neurogenesis in the aged brain as a potential avenue towards therapy.

Post-transcriptional regulation of IGF1R by key microRNAs in long-lived mutant mice

Long-lived mutant mice, both Ames dwarf and growth hormone receptor gene-disrupted or knockout strains, exhibit heightened cognitive robustness and altered IGF1 signaling in the brain. Here, we report, in both these long-lived mice, that three up-regulated lead microRNAs, miR-470, miR-669b, and miR-681, are involved in posttranscriptional regulation of genes pertinent to growth hormone/IGF1 signaling. All three are most prominently localized in the hippocampus and correspond to reduced expression of key IGF1 signaling genes: IGF1, IGF1R, and PI3 kinase. The decline in these genes' expression translates into decreased phosphorylation of downstream molecules AKT and FoxO3a. Cultures transfected with either miR-470, miR-669b, or miR-681 show repressed endogenous expression of all three genes of the IGF1 signaling axis, most significantly IGF1R, while other similarly up-regulated microRNAs, including let-7g and miR-509, do not induce the same levels of repression. Transduction study in IGF1-responsive cell cultures shows significantly reduced IGF1R expression, and AKT to some extent, most notably by miR-681. This is accompanied by decreased levels of downstream phosphorylated forms of AKT and FoxO3a upon IGF1 stimulation. Suppression of IGF1R by the three microRNAs is further validated by IGF1R 3'UTR reporter assays. Taken together, our results suggest that miR-470, miR-669b, and miR-681 are all functionally able to suppress IGF1R and AKT, two upstream genes controlling FoxO3a phosphorylation status. Their up-regulation in growth hormone signaling-deficient mutant mouse brain suggests reduced IGF1 signaling at the posttranscriptional level, for numerous gains of neuronal function in these long-lived mice.

Pleiotropic effects of growth hormone signaling in aging

Growth hormone (GH) affects somatic growth, sexual maturation, body composition and metabolism, as well as aging and longevity. Mice lacking GH or GH receptor outlive their normal siblings and exhibit symptoms of delayed aging associated with improved insulin signaling and increased stress resistance. Beneficial effects of eliminating the actions of GH are counterintuitive but conform to the concept of antagonistic pleiotropy. Evolutionary selection for traits promoting early-life fitness and reproductive success could account for post-reproductive deficits. Reciprocal relationships between GH signaling and longevity discovered in mutant mice apply also to normal mice, other mammalian species, and perhaps humans. This review summarizes the present understanding of the multifaceted relationship between somatotropic signaling and mammalian aging.

Liver-specific knockdown of IGF-1 decreases vascular oxidative stress resistance by impairing the Nrf2-dependent antioxidant response: a novel model of vascular aging

Recent studies demonstrate that age-related dysfunction of NF-E2-related factor-2 (Nrf2)-driven pathways impairs cellular redox homeostasis, exacerbating age-related cellular oxidative stress and increasing sensitivity of aged vessels to oxidative stress-induced cellular damage. Circulating levels of insulin-like growth factor (IGF)-1 decline during aging, which significantly increases the risk for cardiovascular diseases in humans. To test the hypothesis that adult-onset IGF-1 deficiency impairs Nrf2-driven pathways in the vasculature, we utilized a novel mouse model with a liver-specific adeno-associated viral knockdown of the Igf1 gene using Cre-lox technology (Igf1(f/f) + MUP-iCre-AAV8), which exhibits a significant decrease in circulating IGF-1 levels (~50%). In the aortas of IGF-1-deficient mice, there was a trend for decreased expression of Nrf2 and the Nrf2 target genes GCLC, NQO1 and HMOX1. In cultured aorta segments of IGF-1-deficient mice treated with oxidative stressors (high glucose, oxidized low-density lipoprotein, and H(2)O(2)), induction of Nrf2-driven genes was significantly attenuated as compared with control vessels, which was associated with an exacerbation of endothelial dysfunction, increased oxidative stress, and apoptosis, mimicking the aging phenotype. In conclusion, endocrine IGF-1 deficiency is associated with dysregulation of Nrf2-dependent antioxidant responses in the vasculature, which likely promotes an adverse vascular phenotype under pathophysiological conditions associated with oxidative stress (eg, diabetes mellitus, hypertension) and results in accelerated vascular impairments in aging.

Possible implications of insulin resistance and glucose metabolism in Alzheimer's disease pathogenesis

Type 2 diabetes mellitus (DM) appears to be a significant risk factor for Alzheimer disease (AD). Insulin and insulin-like growth factor-1 (IGF-1) also have intense effects in the central nervous system (CNS), regulating key processes such as neuronal survival and longevity, as well as learning and memory. Hyperglycaemia induces increased peripheral utilization of insulin, resulting in reduced insulin transport into the brain. Whereas the density of brain insulin receptor decreases during age, IGF-1 receptor increases, suggesting that specific insulin-mediated signals is involved in aging and possibly in cognitive decline. Molecular mechanisms that protect CNS neurons against β-amyloid-derived-diffusible ligands (ADDL), responsible for synaptic deterioration underlying AD memory failure, have been identified. The protection mechanism does not involve simple competition between ADDLs and insulin, but rather it is signalling dependent down-regulation of ADDL-binding sites. Defective insulin signalling make neurons energy deficient and vulnerable to oxidizing or other metabolic insults and impairs synaptic plasticity. In fact, destruction of mitochondria, by oxidation of a dynamic-like transporter protein, may cause synapse loss in AD. Moreover, interaction between Aβ and τ proteins could be cause of neuronal loss. Hyperinsulinaemia as well as complete lack of insulin result in increased τ phosphorylation, leading to an imbalance of insulin-regulated τ kinases and phosphatates. However, amyloid peptides accumulation is currently seen as a key step in the pathogenesis of AD. Inflammation interacts with processing and deposit of β-amyloid. Chronic hyperinsulinemia may exacerbate inflammatory responses and increase markers of oxidative stress. In addition, insulin appears to act as 'neuromodulator', influencing release and reuptake of neurotransmitters, and improving learning and memory. Thus, experimental and clinical evidence show that insulin action influences cerebral functions. In this paper, we reviewed several mechanisms by which insulin may affect pathophysiology in AD.

Growth hormone (GH) treatment may cooperate with locally-produced GH in increasing the proliferative response of hippocampal progenitors to kainate-induced injury

PRIMARY OBJECTIVE

This study was designed to investigate the effect of growth hormone treatment on the proliferation of endogenous neural progenitor cells in the dentate gyrus (DG) of the brain stimulated by kainic acid (KA)-induced neurotoxicity.

RESEARCH DESIGN

Neurotoxicity was induced by intraperitoneal injection of KA. GH treatment lasted 4 days, starting either immediately or after 10 days of administration of the neurotoxic insult.

METHODS AND PROCEDURE

Proliferating cells were immunodetected after labelling by in vivo administration of 5-bromodeoxyuridine (BrdU). GH expression was detected by in situ hybridization and immunofluorescence.

MAIN OUTCOMES AND RESULTS

KA administration stimulated the proliferation of hippocampal precursors and this effect was significantly enhanced by GH treatment. Hippocampal GH expression was also up-regulated in response to KA administration.

CONCLUSIONS

The findings support the possibility that the proliferative response observed in the hippocampus of rats treated with KA and GH is a consequence of cooperation between the exogenous and the locally-produced hormone and their synergism with other mitogenic factors generated in response to the neurotoxic damage. Therefore, GH treatment could be used to cooperate with other physiological or pathological stimuli in order to promote cell proliferation.

Single-gene mutations and healthy ageing in mammals

Studies of the effects of single-gene mutations on longevity in Caenorhabditis elegans, Drosophila melanogaster and Mus musculus identified homologous, highly conserved signalling pathways that influence ageing. In each of these very distantly related species, single mutations which lead-directly or indirectly-to reduced insulin, insulin-like growth factor (IGF) or insulin/IGF-like signalling (IIS) can produce significant increases in both average and maximal lifespan. In mice, most of the life-extending mutations described to date reduce somatotropic (growth hormone (GH) and IGF-1) signalling. The reported extensions of longevity are most robust in GH-deficient and GH-resistant mice, while suppression of somatotropic signalling 'downstream' of the GH receptor produces effects that are generally smaller and often limited to female animals. This could be due to GH influencing ageing by both IGF-1-mediated and IGF-1-independent mechanisms. In mutants that have been examined in some detail, increased longevity is associated with various indices of delayed ageing and extended 'healthspan'. The mechanisms that probably underlie the extension of both lifespan and healthspan of these animals include increased stress resistance, improved antioxidant defences, alterations in insulin signalling (e.g. hypoinsulinaemia combined with improved insulin sensitivity in some mutants and insulin resistance in others), a shift from pro- to anti-inflammatory profile of circulating adipokines, reduced mammalian target of rapamycin-mediated translation and altered mitochondrial function including greater utilization of lipids when compared with carbohydrates.

Changes in growth hormone (GH), GH receptor, and GH signal transduction in hippocampus of congenital hypothyroid rats

Recent studies have shown that, like thyroid hormone (TH), growth hormone (GH) plays a critical role in development of the brain. However, it is still unclear whether the functions of the two hormones are locally orchestrated in the brain or whether TH has a permissive effect on GH in the central nervous system as it does in the periphery. To address this question, the present study investigated the changes in local expression of GH and GH receptor (GHR) and the activity of GH signaling molecules in the hippocampus of congenitally hypothyroid (CHT) rats. As demonstrated by morphometric measurements and the Y-maze test, CHT rats had decreased neurons and weaker Nissl staining in the stratum pyramidal/granule in the hippocampus and a reduced acquisition of safe place recognition memory. Analyses of QPCR and Western blot revealed a substantially decreased hippocampal expression of GH and GHR, accompanied by a corresponding decrease in phosphorylation of JAK2 and STAT5 in the CHT rats. These changes were, at least in part, corrected by systemic supplement of T3. The findings provide the first direct evidence suggesting that the functional autocrine and paracrine regulation of GH in the CNS is orchestrated by TH.

Extrapituitary growth hormone

Pituitary somatotrophs secrete growth hormone (GH) into the bloodstream, to act as a hormone at receptor sites in most, if not all, tissues. These endocrine actions of circulating GH are abolished after pituitary ablation or hypophysectomy, indicating its pituitary source. GH gene expression is, however, not confined to the pituitary gland, as it occurs in neural, immune, reproductive, alimentary, and respiratory tissues and in the integumentary, muscular, skeletal, and cardiovascular systems, in which GH may act locally rather than as an endocrine. These actions are likely to be involved in the proliferation and differentiation of cells and tissues prior to the ontogeny of the pituitary gland. They are also likely to complement the endocrine actions of GH and are likely to maintain them after pituitary senescence and the somatopause. Autocrine or paracrine actions of GH are, however, sometimes mediated through different signaling mechanisms to those mediating its endocrine actions and these may promote oncogenesis. Extrapituitary GH may thus be of physiological and pathophysiological significance.

Vasoprotective effects of life span-extending peripubertal GH replacement in Lewis dwarf rats

In humans, growth hormone deficiency (GHD) and low circulating levels of insulin-like growth factor 1 (IGF-1) significantly increase the risk for cerebrovascular disease. Genetic growth hormone (GH)/IGF-1 deficiency in Lewis dwarf rats significantly increases the incidence of late-life strokes, similar to the effects of GHD in elderly humans. Peripubertal treatment of Lewis dwarf rats with GH delays the occurrence of late-life stroke, which results in a significant extension of life span. The present study was designed to characterize the vascular effects of life span-extending peripubertal GH replacement in Lewis dwarf rats. Here, we report, based on measurements of dihydroethidium fluorescence, tissue isoprostane, GSH, and ascorbate content, that peripubertal GH/IGF-1 deficiency in Lewis dwarf rats increases vascular oxidative stress, which is prevented by GH replacement. Peripubertal GHD did not alter superoxide dismutase or catalase activities in the aorta nor the expression of Cu-Zn-SOD, Mn-SOD, and catalase in the cerebral arteries of dwarf rats. In contrast, cerebrovascular expression of glutathione peroxidase 1 was significantly decreased in dwarf vessels, and this effect was reversed by GH treatment. Peripubertal GHD significantly decreases expression of the Nrf2 target genes NQO1 and GCLC in the cerebral arteries, whereas it does not affect expression and activity of endothelial nitric oxide synthase and vascular expression of IGF-1, IGF-binding proteins, and inflammatory markers (tumor necrosis factor alpha, interluekin-6, interluekin-1β, inducible nitric oxide synthase, intercellular adhesion molecule 1, and monocyte chemotactic protein-1). In conclusion, peripubertal GH/IGF-1 deficiency confers pro-oxidative cellular effects, which likely promote an adverse functional and structural phenotype in the vasculature, and results in accelerated vascular impairments later in life.

Growth hormone, insulin and aging: the benefits of endocrine defects

Longevity of mice can be increased by spontaneous or experimentally induced mutations that interfere with the biosynthesis or actions of growth hormone (GH), insulin-like growth factor 1 (IGF-1), or insulin in the adipose tissue. The effects of GH resistance and deficiency of GH (along with thyrotropin and prolactin) on aging and lifespan are the most pronounced and best established of these mutations. Potential mechanisms linking these endocrine deficits with delayed aging and extended longevity include increased stress resistance, alterations in insulin and mammalian target of rapamycin (mTOR) signaling and metabolic adjustments. Physiological relationships deduced from the extreme phenotypes of long-lived mouse mutants appear to apply broadly, encompassing genetically normal ("wild-type") mice and other mammalian species. The role of GH in the control of human aging continues to be hotly debated, but recent data indicate that reduced somatotropic signaling provides protection from cancer and other age-related diseases and may promote old age survival.

Smaller cardiac cell size and reduced extra-cellular collagen might be beneficial for hearts of Ames dwarf mice

PURPOSE

To test the hypothesis that cardiac morphologic differences between Ames dwarf and wild-type littermates might correlate with the increased longevity observed in the Ames dwarf mice.

METHODS

Hearts removed from young adult (5-7 mo) and old (24-28 mo) Ames dwarf and wild-type littermates underwent histological and morphometric analysis. Measurements of cell size, nuclear size, and collagen content were made using computerized color deconvolution and particle analysis methodology.

RESULTS

In the young mice at six months of age, mean cardiomyocyte area was 46% less in Ames dwarf than in wild-type mice (p<0.0001). Cardiomyocyte size increased with age by about 52% in the wild-type mice and 44% in the Ames dwarf mice (p<0.001). There was no difference in nuclear size of the cardiomyocytes between the young adult wild-type and Ames dwarf mice. There was an age-associated increase in the cardiomyocyte nuclear size by approximately 50% in both the Ames and wild-type mice (p<0.001). The older Ames dwarf mice had slightly larger cardiomyocyte nuclei compared to wild-type (2%, p<0.05). The collagen content of the hearts in young adult Ames dwarf mice was estimated to be 57% less compared to wild-type littermates (p<0.05). Although collagen content of both Ames dwarf and wild-type mouse hearts increased with age, there was no significant difference at 24 months.

CONCLUSIONS

In wild-type and Ames dwarf mice, nuclear size, cardiomyocyte size, and collagen content increased with advancing age. While cardiomyocyte size was much reduced in young and old Ames dwarf mice compared with wild-type, collagen content was reduced only in the young adult mice. Taken together, these findings suggest that Ames dwarf mice may receive some longevity benefit from the reduced cardiomyocyte cell size and a period of reduced collagen content in the heart during adulthood.

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.

In vivo analysis of gene expression in long-lived mice lacking the pregnancy-associated plasma protein A (PappA) gene

Mice lacking the pregnancy-associated plasma protein A (PappA) gene exhibit diminished localized IGF-1 bioavailability and a 30% increase in mean life span. However, it is uncertain which tissues exhibit reduced IGF-1 signals in the PappA(-/-) mouse, and whether effects of this mutation parallel those of mutations that diminish IGF-1 in serum. Across a panel of 21 tissues, we used RT-PCR to evaluate the effects of the PappA(-/-) mutation on expression of Igfbp5, which served as an in vivo indicator of IGF-1 signaling. Among these tissues, expression of Igfbp5 was significantly reduced by PappA(-/-) only in kidney. A broader survey of IGF-associated genes in six organs identified five other genes responsive to PappA(-/-) in kidney, with stronger effects in this organ relative to other tissues. Renal expression of Irs1 and Mt1 was increased by PappA(-/-) as well as by mutations that reduce IGF-1 in serum (i.e., Ghr(-/-), Pit1(dw/dw) and Prop1(df/df)), and we demonstrate that expression of these genes is regulated by growth hormone-treatment and calorie restriction. These results provide in vivo data on an important new model of mammalian aging, and characterize both similar and contrasting expression patterns between long-lived mice with reduced local IGF-1 availability and diminished IGF-1 in serum.

Altered longevity-assurance activity of p53:p44 in the mouse causes memory loss, neurodegeneration and premature death

The longevity-assurance activity of the tumor suppressor p53 depends on the levels of Δ40p53 (p44), a short and naturally occurring isoform of the p53 gene. As such, increased dosage of p44 in the mouse leads to accelerated aging and short lifespan. Here we show that mice homozygous for a transgene encoding p44 (p44^+/+) display cognitive decline and synaptic impairment early in life. The synaptic deficits are attributed to hyperactivation of insulin-like growth factor 1 receptor (IGF-1R) signaling and altered metabolism of the microtubule-binding protein tau. In fact, they were rescued by either Igf1r or Mapt haploinsufficiency. When expressing a human or a ‘humanized’ form of the amyloid precursor protein (APP), p44^+/+ animals developed a selective degeneration of memory-forming and -retrieving areas of the brain, and died prematurely. Mechanistically, the neurodegeneration was caused by both paraptosis- and autophagy-like cell deaths. These results indicate that altered longevity-assurance activity of p53:p44 causes memory loss and neurodegeneration by affecting IGF-1R signaling. Importantly, Igf1r haploinsufficiency was also able to correct the synaptic deficits of APP_695/swe mice, a model of Alzheimer’s disease.

Insulin/IGF-I and related signaling pathways regulate aging in nondividing cells: from yeast to the mammalian brain

Mutations that reduce glucose or insulin/insulin-like growth factor-I (IGF-I) signaling increase longevity in organisms ranging from yeast to mammals. Over the past 10 years, several studies confirmed this conserved molecular strategy of longevity regulation, and many more have been added to the complex mosaic that links stress resistance and aging. In this review, we will analyze the similarities that have emerged over the last decade between longevity regulatory pathways in organisms ranging from yeast, nematodes, and fruit flies to mice. We will focus on the role of yeast signal transduction proteins Ras, Tor, Sch9, Sir2, their homologs in higher organisms, and their association to oxidative stress and protective systems. We will discuss how the “molecular strategy” responsible for life span extension in response to dietary and genetic manipulations appears to be remarkably conserved in various organisms and cells, including neuronal cells in different organisms. Taken together, these studies indicate that simple model systems will contribute to our comprehension of aging of the mammalian nervous system and will stimulate novel neurotherapeutic strategies in humans.

The role of the somatotrophic axis in neuroprotection and neuroregeneration of the addictive brain

Early studies have shown that the abuse of alcohol, central stimulants, and opiates such as heroin destroys brain cells, reducing attention span and memory. However, new research has suggested that there may be a way to regain some of the lost attention and recall. It has recently been shown that brain cells targeted for early death by continued opiate use can be salvaged by injections of synthetic human growth hormone (GH). GH is a polypeptide hormone, normally secreted by the anterior pituitary gland, which stimulates cell growth and controls body metabolism. Recombinant human GH is currently used in replacement therapy to alleviate the symptoms of adults and children with GH deficiency syndrome. The recent observation that GH can reverse morphine-induced cell damage could open the door to new ways of treating and preventing damage from the abuse of opiates in addicts and also of treating cell damage induced by alcohol and central stimulants. This article reviews current knowledge of the somatotrophic axis, including GH and insulin-like growth factor-1 (IGF-1), in the brain and also discusses the potential use of GH/IGF-1 as agents for treatment of brain pathology in addictive diseases.

Growth hormone receptor immunoreactivity is increased in the subventricular zone of juvenile rat brain after focal ischemia: a potential role for growth hormone in injury-induced neurogenesis

BACKGROUND

During recovery from an ischemic brain injury, a cerebral growth hormone (GH) axis is activated. Whilst GH has been demonstrated to be neuroprotective both in vitro and in vivo, a role for GH in neuro-restorative processes after brain injury has yet to be studied.

OBJECTIVE

To explore a role for GH in injury-induced neurogenesis by examining GH receptor (GH-R) immunoreactivity within the subventricular zone (SVZ) of juvenile rats after brain injury and by testing the proliferative capacity of GH on embryonic mouse neural stem cells.

DESIGN

Twenty-one day old rats were subjected to unilateral hypoxic-ischemia of the brain and sacrificed 1-15days later. Coronal brain sections from these animals and age-matched naïve controls were immunostained for GH-R and cell markers of neurogenesis. The level of GH-R immunoreactivity in the ipsilateral and contralateral SVZ of each animal was semi-quantified both by independent blinded scoring by two examiners and blinded image analysis. To examine the effect of GH on proliferation of embryonic mouse neural stem cells, cells were treated with increasing concentrations of rat pituitary GH for 48h in the presence of 5'-bromo-2'-deoxyuridine.

RESULTS

The level of GH-R immunoreactivity in the ipsilateral SVZ was significantly increased 5days after injury vs. the contralateral SVZ, coinciding both spatially and temporally with injury-induced neurogenesis. The population of GH-R immunopositive cells in the ipsilateral SVZ at this time was found to include proliferating cells (Ki67 immunopositive), neural progenitor cells (nestin immunopositive) and post-proliferative migratory neuroblasts (doublecortin immunopositive). Stimulation of embryonic mouse NSCs with physiological concentrations of rat pituitary GH elicited a dose-dependent proliferative response.

CONCLUSION

These results indicate a novel role for GH and its receptor in injury-induced neurogenesis, and suggest that GH treatment may potentiate endogenous neuro-restorative processes after brain injury.

The effect of peripheral administration of growth hormone on AD-like cognitive deficiency in NBM-lesioned rats

This study aimed to evaluate the peripheral administration of growth hormone (GH) on AD-like cognitive deficiency in NBM-lesioned rats induced by ibotenic acid (5 microg/microl, in each side). Forty-eight male Wistar rats (20-24 months old; weighing 330+/-30 g) randomly divided into six groups (n=8). The groups include control group, which were intact rats; n-L+GH group: non-lesioned rats with GH treatment (1mg/kg, 9.00 am, for 10 consecutive days); n-L+Veh group: non-lesioned rats with vehicle treatment; L group: NBM-lesioned rats; L+GH group: NBM-lesioned rats with GH treatment and L+Veh group: NBM-lesioned rats with same volume of vehicle treatment. Peripheral administration of GH in control had no effect on learning and memory, while in L+GH group produced a significant enhancement in spatial learning and memory comparing to L and L+Veh groups. The percent of time spent in goal quarter during probe trial has decreased significantly in L and L+Veh groups compared to n-L groups. While it has increased significantly in L+GH group compared to L and L+Veh groups. No significant difference in percent of time spent was seen between the control and n-L groups. The GH has known as a mediate that effect through IGF-1. As the IGF-1 itself is earlier shown to improve cognitive function it is likely that the observed effect of GH is mediated through release of IGF-1 from peripheral tissue into the circulation for further transport across the BBB. This mechanism may result in the improvement of learning and memory in rats with NBM lesion.

Circulating insulin-like growth factor I and cognitive function: neuromodulation throughout the lifespan

Insulin-like growth factor I (IGF-I) is central to the somatotropic (growth hormone) axis. It promotes tissue growth and continues to have anabolic effects in adulthood. Accumulating evidence from the last decade, however, reveals that circulating levels of IGF-I also significantly affects cognitive brain function. Specifically, the decline of serum IGF-I might be associated with the age-related cognitive decline in elderly people. Moreover, psychiatric and neurological conditions characterized by cognitive impairment may be characterized by altered levels of IGF-I. Some evidence is emerging that interventions that target the GH/IGF-I axis may improve cognitive functioning, at least in deficient states. As there is evidence linking high serum IGF-I levels with cancer risk, these interventions should be carefully evaluated. On a cellular and molecular level, IGF-I may be a crucial component of neural homeostasis since disturbed IGF-I input is inevitably linked to perturbed function. Consistent with this, all nerve cells are potential targets of IGF-I actions, including neurons, glia, endothelial, epithelial, and perivascular cells. Indeed, many key cellular processes in the brain are affected by IGF-I's neurotrophic and modulatory actions. We review the regulation by IGF-I of neurotransmission and neuronal plasticity and conclude that serum IGF-I is an important mediator of neuronal growth, survival and function throughout the lifespan. The role of IGF-I in synaptic plasticity render its neurotrophic potential a key target for remediating the cognitive impairment associated with a range of neurological conditions.

Adult-onset deficiency in growth hormone and insulin-like growth factor-I alters oligodendrocyte turnover in the corpus callosum

Growth hormone (GH) and insulin-like growth factor-I (IGF-I) provide trophic support during development and also appear to influence cell structure, function and replacement in the adult brain. Recent studies demonstrated effects of the GH/IGF-I axis on adult neurogenesis, but it is unclear whether the GH/IGF-I axis influences glial turnover in the normal adult brain. In the current study, we used a selective model of adult-onset GH and IGF-I deficiency to evaluate the role of GH and IGF-I in regulating glial proliferation and survival in the adult corpus callosum. GH/IGF-I-deficient dwarf rats of the Lewis strain were made GH/IGF-I replete via twice daily injections of GH starting at postnatal day 28 (P28), approximately the age at which GH pulse amplitude increases in developing rodents. GH/IGF-I deficiency was initiated in adulthood by removing animals from GH treatment. Quantitative analyses revealed that adult-onset GH/IGF-I deficiency decreased cell proliferation in the white matter and decreased the survival of newborn oligodendrocytes. These findings are consistent with the hypothesis that aging-related changes in the GH/IGF-I axis produce deficits in ongoing turnover of oligodendrocytes, which may contribute to aging-related cognitive changes and deficits in remyelination after injury.

Growth hormone production and action in N1E-115 neuroblastoma cells

Neuroblastoma cells are undifferentiated cells derived from the neural crest and are commonly used as models for studying neural function. Mouse N1E-115 neuroblastoma cells are derived from cancerous tissue and provide a model for studying the oncogenesis of neural cells. As growth hormone (GH) has been implicated as an autocrine or paracrine involved in neural regulation and in the induction or progression of cancer, the possibility that N1E-115 cells are sites of GH production and GH action was assessed. Using RT-PCR, cultured N1E-115 cells were found to express the mouse GH and GH receptor (GHR) genes. Immunocytochemistry demonstrated that both of the translated proteins (GH and its receptor) were abundantly present in the cytoplasm of these cells and their co-localization was established by confocal cytochemistry. GH action in these cells was determined in cells cultured for 72 h in the presence or absence of 10(-6) M or 10(-9) M mouse GH, which induced neurite sprouting and increased axon growth. In summary, the expression of GH and its receptor in GH responsive tumor-derived N1E-115 neuroblastoma cells suggests they provide a useful experimental model to assess GH actions in neural function or neural oncogenesis.

Anti-aging medicine: pitfalls and hopes

Since the beginnings of time humans have searched for a fountain of youth. This has led to many extravagant claims which have been highly profitable for their proponents. This area has become known as anti-aging medicine and has deservedly been frowned upon by the medical establishment. On the other hand, in the last decades dramatic advances in our understanding of the aging process have come from studies in worms, flies and mice. This article reviews some of these advances and places the extravagant claims of anti-aging medicine in perspective. We conclude that a balanced diet of moderate proportions and exercise remain today the only proven fountain of youth.