Growth hormone-mediated alteration of fuel metabolism in the aged rat as determined from transcript profiles

The promise of growth hormone in sport: doped or duped

Skeletal muscle is a target tissue of GH. Based on its anabolic properties, it is widely accepted that GH enhances muscle performance in sports. Athletic performance depends on muscle strength and the energy required to power muscle function. The energy required to power muscle function is derived from a continuum of anaerobic and aerobic sources. Molecular and functional studies provide evidence that in muscle GH stimulates the anaerobic and suppresses the aerobic energy system, in turn affecting power-based functional measures in a time-dependent manner. In recreational athletes, GH improves anaerobic capacity but has not been proven to significantly enhance muscle strength, power, or maximum rate of oxygen consumption. GH appears likely to selectively benefit sprint events and not physical performance that depends on strength and endurance. Arch Endocrinol Metab. 2019;63(6):576-81.

The Use and Abuse of Growth Hormone in Sports

GH is banned by the World Anti-Doping Agency as a performance-enhancing anabolic agent. Doping with GH likely began in the early 1980s and became more prevalent with the advent of recombinant technology well before any scientific evidence of benefit. The expectation that GH improves physical function stems from its anabolic and lipolytic properties. Athletic performance depends on muscle strength and the energy required to power muscle function. In recreational athletes, GH selectively improves anaerobic sprint capacity but has not been proven to significantly enhance muscle strength, power, or maximum rate of oxygen consumption. GH is secreted as a family of isoform peptides in a pulsatile manner reflecting intermittent secretion and rapid clearance. Its anabolic actions are largely mediated by IGF-I, which stimulates whole-body protein synthesis, including skeletal muscle and collagen proteins. Two methods have been validated for detecting GH abuse in athletes. The first (the isoform method) is based on distinguishing pure recombinant 22-kDa GH from the heterogeneous isoforms secreted from the pituitary. The second (the marker method) is based on measuring blood levels of GH-responsive proteins, specifically IGF-I and the N-terminal propeptide of type III collagen (P-III-NP). Only a handful of athletes have been caught since the implementation of GH doping tests in 2004. The low rate likely reflects the limitation of in-competition testing using current methods. Improved detection rates may be achieved by more out-of-competition testing, introducing athletes' biological passports, and the development of novel methods. Governance, operational, technical, and political factors influence the effectiveness of an anti-doping program.

Sex steroids and growth hormone interactions

GH and sex hormones are critical regulators of body growth and composition, somatic development, intermediate metabolism, and sexual dimorphism. Deficiencies in GH- or sex hormone-dependent signaling and the influence of sex hormones on GH biology may have a dramatic impact on liver physiology during somatic development and in adulthood. Effects of sex hormones on the liver may be direct, through hepatic receptors, or indirect by modulating endocrine, metabolic, and gender-differentiated functions of GH. Sex hormones can modulate GH actions by acting centrally, regulating pituitary GH secretion, and peripherally, by modulating GH signaling pathways. The endocrine and/or metabolic consequences of long-term exposure to sex hormone-related compounds and their influence on the GH-liver axis are largely unknown. A better understanding of these interactions in physiological and pathological states will contribute to preserve health and to improve clinical management of patients with growth, developmental, and metabolic disorders.

The effect of calorie restriction on insulin signaling in skeletal muscle and adipose tissue of Ames dwarf mice

Long-living Ames dwarf (df/df) mice are homozygous for a mutation of the Prop1(df) gene. As a result, mice are deficient in growth hormone (GH), prolactin (PRL) and thyrotropin (TSH). In spite of the hormonal deficiencies, df/df mice live significantly longer and healthier lives compared to their wild type siblings. We studied the effects of calorie restriction (CR) on the expression of insulin signaling genes in skeletal muscle and adipose tissue of normal and df/df mice. The analysis of genes expression showed that CR differentially affects the insulin signaling pathway in these insulin target organs. Moreover, results obtained in both normal and Ames dwarf mice indicate more direct effects of CR on insulin signaling genes in adipose tissue than in skeletal muscle. Interestingly, CR reduced the protein levels of adiponectin in the epididymal adipose tissue of normal and Ames dwarf mice, while elevating adiponectin levels in skeletal muscle and plasma of normal mice only. In conclusion, our findings suggest that both skeletal muscle and adipose tissue are important mediators of insulin effects on longevity. Additionally, the results revealed divergent effects of CR on expression of genes in the insulin signaling pathway of normal and Ames dwarf mice.

Lipid profiling and transcriptomic analysis reveals a functional interplay between estradiol and growth hormone in liver

17β-estradiol (E2) may interfere with endocrine, metabolic, and gender-differentiated functions in liver in both females and males. Indirect mechanisms play a crucial role because of the E2 influence on the pituitary GH secretion and the GHR-JAK2-STAT5 signaling pathway in the target tissues. E2, through its interaction with the estrogen receptor, exerts direct effects on liver. Hypothyroidism also affects endocrine and metabolic functions of the liver, rendering a metabolic phenotype with features that mimic deficiencies in E2 or GH. In this work, we combined the lipid and transcriptomic analysis to obtain comprehensive information on the molecular mechanisms of E2 effects, alone and in combination with GH, to regulate liver functions in males. We used the adult hypothyroid-orchidectomized rat model to minimize the influence of internal hormones on E2 treatment and to explore its role in male-differentiated functions. E2 influenced genes involved in metabolism of lipids and endo-xenobiotics, and the GH-regulated endocrine, metabolic, immune, and male-specific responses. E2 induced a female-pattern of gene expression and inhibited GH-regulated STAT5b targeted genes. E2 did not prevent the inhibitory effects of GH on urea and amino acid metabolism-related genes. The combination of E2 and GH decreased transcriptional immune responses. E2 decreased the hepatic content of saturated fatty acids and induced a transcriptional program that seems to be mediated by the activation of PPARα. In contrast, GH inhibited fatty acid oxidation. Both E2 and GH replacements reduced hepatic CHO levels and increased the formation of cholesterol esters and triacylglycerols. Notably, the hepatic lipid profiles were endowed with singular fingerprints that may be used to segregate the effects of different hormonal replacements. In summary, we provide in vivo evidence that E2 has a significant impact on lipid content and transcriptome in male liver and that E2 exerts a marked influence on GH physiology, with implications in human therapy.

Action of GH on skeletal muscle function: molecular and metabolic mechanisms

Skeletal muscle is a target tissue of GH. Based on its anabolic properties, it is widely accepted that GH enhances muscle performance in sports and muscle function in the elderly. This paper critically reviews information on the effects of GH on muscle function covering structure, protein metabolism, the role of IGF1 mediation, bioenergetics and performance drawn from molecular, cellular and physiological studies on animals and humans. GH increases muscle strength by enhancing muscle mass without affecting contractile force or fibre composition type. GH stimulates whole-body protein accretion with protein synthesis occurring in muscular and extra-muscular sites. The energy required to power muscle function is derived from a continuum of anaerobic and aerobic sources. Molecular and functional studies provide evidence that GH stimulates the anaerobic and suppresses the aerobic energy system, in turn affecting power-based functional measures in a time-dependent manner. GH exerts complex multi-system effects on skeletal muscle function in part mediated by the IGF system.

Estrogens regulate the hepatic effects of growth hormone, a hormonal interplay with multiple fates

The liver responds to estrogens and growth hormone (GH) which are critical regulators of body growth, gender-related hepatic functions, and intermediate metabolism. The effects of estrogens on liver can be direct, through the direct actions of hepatic ER, or indirect, which include the crosstalk with endocrine, metabolic, and sex-differentiated functions of GH. Most previous studies have been focused on the influence of estrogens on pituitary GH secretion, which has a great impact on hepatic transcriptional regulation. However, there is strong evidence that estrogens can influence the GH-regulated endocrine and metabolic functions in the human liver by acting at the level of GHR-STAT5 signaling pathway. This crosstalk is relevant because the widespread exposition of estrogen or estrogen-related compounds in human. Therefore, GH or estrogen signaling deficiency as well as the influence of estrogens on GH biology can cause a dramatic impact in liver physiology during mammalian development and in adulthood. In this review, we will summarize the current status of the influence of estrogen on GH actions in liver. A better understanding of estrogen-GH interplay in liver will lead to improved therapy of children with growth disorders and of adults with GH deficiency.

The influence of estrogens on the biological and therapeutic actions of growth hormone in the liver

GH is main regulator of body growth and composition, somatic development, intermediate metabolism and gender-dependent dimorphism in mammals. The liver is a direct target of estrogens because it expresses estrogen receptors which are connected with development, lipid metabolism and insulin sensitivity, hepatic carcinogenesis, protection from drug-induced toxicity and fertility. In addition, estrogens can modulate GH actions in liver by acting centrally, regulating pituitary GH secretion, and, peripherally, by modulating GHR-JAK2-STAT5 signalling pathway. Therefore, the interactions of estrogens with GH actions in liver are biologically and clinically relevant because disruption of GH signaling may cause alterations of its endocrine, metabolic, and gender differentiated functions and it could be linked to dramatic impact in liver physiology during development as well as in adulthood. Finally, the interplay of estrogens with GH is relevant because physiological roles these hormones have in human, and the widespread exposition of estrogen or estrogen-related compounds in human. This review highlights the importance of these hormones in liver physiology as well as how estrogens modulate GH actions in liver which will help to improve the clinical use of these hormones.

Liver Patt1 deficiency protects male mice from age-associated but not high-fat diet-induced hepatic steatosis

Patt1 is a newly identified protein acetyltransferase that is highly expressed in liver. However, the role of Patt1 in liver is still unclear. We generated Patt1 liver-specific knockout (LKO) mice and mainly measured the effect of hepatic Patt1 deficiency on lipid metabolism. Hepatic Patt1 deficiency in male mice markedly decreases fat mass and dramatically alleviates age-associated accumulation of lipid droplets in liver. Moreover, hepatic Patt1 abrogation in male mice significantly reduces the liver triglyceride and free fatty acid levels, but it has no effect on liver cholesterol level, liver weight, and liver function. Consistently, primary cultured Patt1-deficient hepatocytes are resistant to palmitic acid-induced lipid accumulation, but hepatic Patt1 deficiency fails to protect male mice from high-fat diet-induced hepatic steatosis. Further studies show that hepatic Patt1 deficiency decreases fatty acid uptake, reduces lipid synthesis, and enhances fatty acid oxidation, which may contribute to the attenuated hepatic steatosis in Patt1 LKO mice. These results demonstrate that Patt1 plays an important role in hepatic lipid metabolism and have implications toward resolving age-associated hepatic steatosis.

Liver-specific deletion of protein-tyrosine phosphatase 1B (PTP1B) improves metabolic syndrome and attenuates diet-induced endoplasmic reticulum stress

OBJECTIVE

The protein tyrosine phosphatase PTP1B is a negative regulator of insulin signaling; consequently, mice deficient in PTP1B are hypersensitive to insulin. Because PTP1B(-/-) mice have diminished fat stores, the extent to which PTP1B directly regulates glucose homeostasis is unclear. Previously, we showed that brain-specific PTP1B(-/-) mice are protected against high-fat diet-induced obesity and glucose intolerance, whereas muscle-specific PTP1B(-/-) mice have increased insulin sensitivity independent of changes in adiposity. Here we studied the role of liver PTP1B in glucose homeostasis and lipid metabolism.

RESEARCH DESIGN AND METHODS

We analyzed body mass/adiposity, insulin sensitivity, glucose tolerance, and lipid metabolism in liver-specific PTP1B(-/-) and PTP1Bfl/fl control mice, fed a chow or high-fat diet.

RESULTS

Compared with normal littermates, liver-specific PTP1B(-/-) mice exhibit improved glucose homeostasis and lipid profiles, independent of changes in adiposity. Liver-specific PTP1B(-/-) mice have increased hepatic insulin signaling, decreased expression of gluconeogenic genes PEPCK and G-6-Pase, enhanced insulin-induced suppression of hepatic glucose production, and improved glucose tolerance. Liver-specific PTP1B(-/-) mice exhibit decreased triglyceride and cholesterol levels and diminished expression of lipogenic genes SREBPs, FAS, and ACC. Liver-specific PTP1B deletion also protects against high-fat diet-induced endoplasmic reticulum stress response in vivo, as evidenced by decreased phosphorylation of p38MAPK, JNK, PERK, and eIF2alpha and lower expression of the transcription factors C/EBP homologous protein and spliced X box-binding protein 1.

CONCLUSIONS

Liver PTP1B plays an important role in glucose and lipid metabolism, independent of alterations in adiposity. Inhibition of PTP1B in peripheral tissues may be useful for the treatment of metabolic syndrome and reduction of cardiovascular risk in addition to diabetes.

Sex-different and growth hormone-regulated expression of microRNA in rat liver

Background

MicroRNAs (miRNAs) are short non-coding RNAs playing an important role in post-transcriptional regulation of gene expression. We have previously shown that hepatic transcript profiles are different between males and females; that some of these differences are under the regulation of growth hormone (GH); and that mild starvation diminishes some of the differences. In this study, we tested if hepatic miRNAs are regulated in a similar manner.

Results

Using microarrays, miRNA screening was performed to identify sex-dependent miRNAs in rat liver. Out of 324 unique probes on the array, 254 were expressed in the liver and eight (3% of 254) of those were found to be different between the sexes. Among the eight putative sex-different miRNAs, only one female-predominant miRNA (miR-29b) was confirmed using quantitative real-time PCR. Furthermore, 1 week of continuous GH-treatment in male rats reduced the levels of miR-451 and miR-29b, whereas mild starvation (12 hours) raised the levels of miR-451, miR-122a and miR-29b in both sexes. The biggest effects were obtained on miR-29b with GH-treatment.

Conclusion

We conclude that hepatic miRNA levels depend on the hormonal and nutritional status of the animal and show that miR-29b is a female-predominant and GH-regulated miRNA in rat liver.

Sex and the Liver – A Journey Through Five Decades

Metabolism of steroids and drugs in rodents is sexually differentiated. The reason for this turned out to be the sexually differentiated growth hormone (GH) secretory pattern regulating the expression of a number of hepatic cytochrome P-450 genes. Although not fully resolved, it is clear that several signaling pathways and transcription factors are involved in mediating the effects of GH. It may be argued that such a well-controlled physiological system should have an important biological role and we speculate that the demands of a robust hepatic steroid metabolism during pregnancy has led to the development of this sexually differentiated hypothalamo-pituitary-liver axis.

Altered metabolism of growth hormone receptor mutant mice: a combined NMR metabonomics and microarray study

Background

Growth hormone is an important regulator of post-natal growth and metabolism. We have investigated the metabolic consequences of altered growth hormone signalling in mutant mice that have truncations at position 569 and 391 of the intracellular domain of the growth hormone receptor, and thus exhibit either low (around 30% maximum) or no growth hormone-dependent STAT5 signalling respectively. These mutations result in altered liver metabolism, obesity and insulin resistance.

Methodology/Principal Findings

The analysis of metabolic changes was performed using microarray analysis of liver tissue and NMR metabonomics of urine and liver tissue. Data were analyzed using multivariate statistics and Gene Ontology tools. The metabolic profiles characteristic for each of the two mutant groups and wild-type mice were identified with NMR metabonomics. We found decreased urinary levels of taurine, citrate and 2-oxoglutarate, and increased levels of trimethylamine, creatine and creatinine when compared to wild-type mice. These results indicate significant changes in lipid and choline metabolism, and were coupled with increased fat deposition, leading to obesity. The microarray analysis identified changes in expression of metabolic enzymes correlating with alterations in metabolite concentration both in urine and liver. Similarity of mutant 569 to the wild-type was seen in young mice, but the pattern of metabolites shifted to that of the 391 mutant as the 569 mice became obese after six months age.

Conclusions/Significance

The metabonomic observations were consistent with the parallel analysis of gene expression and pathway mapping using microarray data, identifying metabolites and gene transcripts involved in hepatic metabolism, especially for taurine, choline and creatinine metabolism. The systems biology approach applied in this study provides a coherent picture of metabolic changes resulting from impaired STAT5 signalling by the growth hormone receptor, and supports a potentially important role for taurine in enhancing β-oxidation.

A technique of mRNA extraction and labeling from circulating lymphocytes of children treated with growth hormone replacement therapy for microarray analysis

GH replacement therapy exhibits a wide spectrum of response in terms of growth. Nevertheless, standardized doses are still given in clinical practice. In order to optimize the therapy, it is necessary to identify its markers of responsiveness. Given the presence of GH receptors in the circulating lymphocytes, accessible by means of a simple blood withdrawal, blood becomes the tissue of choice as a source of RNA for in vivo gene expression analysis. Hence, the purpose of the present paper is to develop a method of preparation of RNA from lymphocytes suitable for microarray analysis, focusing on the reduction of the blood volume withdrawal in order to perform the analysis on pediatric subjects. After lymphocyte isolation and total RNA extraction from 6 ml of blood, we carried out an amplification procedure preserving the relative abundance of each transcript. Thereafter, we hybridized the labeled amplified RNA on an oligo chip (Human 30K A, MWGBiotech), but the unsuccessful detection of a good signal to noise ratio indicates that labeled RNA is still insufficient. Therefore, we suggest performing pools of total RNA from different subjects with similar responsiveness to the therapy. It can be speculated that, upon comparison of the obtained data with those derived from pools of controls properly responding to the therapy, specific hallmarks of the condition of low responsiveness, devoid of inter-individual variability, will be evidenced.

Hormonal and nutritional regulation of alternative CD36 transcripts in rat liver--a role for growth hormone in alternative exon usage

Background

CD36 is a multiligand receptor involved in various metabolic pathways, including cellular uptake of long-chain fatty acids. Defect function or expression of CD36 can result in dyslipidemia or insulin resistance. We have previously shown that CD36 expression is female-predominant in rat liver. In the present study, hormonal and nutritional regulation of hepatic CD36 expression was examined in male and female rats. Since alternative transcription start sites have been described in murine and human Cd36, we investigated whether alternative CD36 transcripts are differentially regulated in rat liver during these conditions.

Results

Sequence information of the rat Cd36 5'-UTR was extended, showing that the gene structure of Cd36 in rat is similar to that previously described in mouse with at least two alternative first exons. The rat Cd36 exon 1a promoter was sequenced and found to be highly similar to murine and human Cd36. We show that alternative first exon usage is involved in the female-predominant expression of CD36 in rat liver and during certain hormonal states that induce CD36 mRNA abundance. Estrogen treatment or continuous infusion of growth hormone (GH) in male rats induced CD36 expression preferentially through the exon 1a promoter. Old age was associated with increased CD36 expression in male rats, albeit without any preferential first exon usage. Intermittent GH treatment in old male rats reversed this effect. Mild starvation (12 hours without food) reduced CD36 expression in female liver, whereas its expression was increased in skeletal muscle.

Conclusion

The results obtained in this study confirm and extend our previous observation that GH is an important regulator of hepatic CD36, and depending on the mode of treatment (continuous or intermittent) the gene might be either induced or repressed. We suggest that the effects of continuous GH secretion in females (which is stimulatory) and intermittent GH secretion in males (which is inhibitory) explains the sex-different expression of this gene. Furthermore, a female-specific repression of hepatic CD36 in response to food deprivation was found, which was in contrast to a stimulatory effect in skeletal muscle. This demonstrates a tissue-specific regulation of Cd36.

Growth hormone regulation of metabolic gene expression in muscle: a microarray study in hypopituitary men

Muscle is a target of growth hormone (GH) action and a major contributor to whole body metabolism. Little is known about how GH regulates metabolic processes in muscle or the extent to which muscle contributes to changes in whole body substrate metabolism during GH treatment. To identify GH-responsive genes that regulate substrate metabolism in muscle, we studied six hypopituitary men who underwent whole body metabolic measurement and skeletal muscle biopsies before and after 2 wk of GH treatment (0.5 mg/day). Transcript profiles of four subjects were analyzed using Affymetrix GeneChips. Serum insulin-like growth factor I (IGF-I) and procollagens I and III were measured by RIA. GH increased serum IGF-I and procollagens I and III, enhanced whole body lipid oxidation, reduced carbohydrate oxidation, and stimulated protein synthesis. It induced gene expression of IGF-I and collagens in muscle. GH reduced expression of several enzymes regulating lipid oxidation and energy production. It reduced calpain 3, increased ribosomal protein L38 expression, and displayed mixed effects on genes encoding myofibrillar proteins. It increased expression of circadian gene CLOCK, and reduced that of PERIOD. In summary, GH exerted concordant effects on muscle expression and blood levels of IGF-I and collagens. It induced changes in genes regulating protein metabolism in parallel with a whole body anabolic effect. The discordance between muscle gene expression profiles and metabolic responses suggests that muscle is unlikely to contribute to GH-induced stimulation of whole body energy and lipid metabolism. GH may regulate circadian function in skeletal muscle by modulating circadian gene expression with possible metabolic consequences.

Prenatal exposure to a low-protein diet programs disordered regulation of lipid metabolism in the aging rat

The nutritional environment encountered during fetal life is strongly implicated as a determinant of lifelong metabolic capacity and risk of disease. Pregnant rats were fed a control or low-protein (LP) diet, targeted to early (LPE), mid-(LPM), or late (LPL) pregnancy, or throughout gestation (LPA). The offspring were studied at 1, 9, and 18 mo of age. All LP-exposed groups had similar plasma triglyceride, cholesterol, glucose, and insulin concentrations to those of controls at 1 and 9 mo of age, but by 18 mo there was evidence of LP-programmed hypertriglyceridemia and insulin resistance. All LP-exposed groups exhibited histological evidence of hepatic steatosis and were found to have two- to threefold more hepatic triglyceride than control animals. These phenotypic changes were accompanied by age-related changes in mRNA and protein expression of the transcription factors SREBP-1c, ChREBP, PPARgamma, and PPARalpha and their respective downstream target genes ACC1, FAS, L-PK, and MCAD. At 9 mo of age, the LP groups exhibited suppression of the SREBP-1c-related lipogenic pathway but between 9 and 18 mo underwent a switch to increased lipogenic capacity with a lower expression of PPARgamma and MCAD, consistent with reduced lipid oxidation. The findings indicate that prenatal protein restriction programs development of a metabolic syndrome-like phenotype that develops only with senescence. The data implicate altered expression of SREBP-1c and ChREBP as key mediators of the programmed phenotype, but the basis of the switch in metabolic status that occurred between 9 and 18 mo of age is, as yet, unidentified.

Factors contributing to neuromuscular impairment and sarcopenia during aging

Motor disturbances and wasting of skeletal muscles (sarcopenia) causes significant impairment of daily life activities and is a major underlying cause for hospitalization in senescence. Herein we review data and present new findings on aging-specific changes in motoneurons, skeletal muscle and the interplay between motoneurons and target muscle fibers. Although many of the changes occurring during aging may be specific to motoneurons and myofibers, respectively, evidence indicates that myofiber regeneration in sarcopenic muscle is halted at the point where reinnervation is critical for the final differentiation into mature myofibers. Combined, evidence suggests that sarcopenia to a significant extent depend on a decreased capacity among motoneurons to innervate regenerating fibers. There are also conspicuous changes in the expression of several cytokines known to play important roles in establishing and maintaining neuromuscular connectivity during development and adulthood. We also present data showing the usefulness of rodent models in studies of successful and unsuccessful patterns of aging. Finally, we show that not only dietary restriction (DR) but also activity and social environment may modulate the pattern of aging.

Modified HMG-CoA reductase and LDLr regulation is deeply involved in age-related hypercholesterolemia

During the ageing process in rats hypercholesterolemia occurs in concert with full activation, lowered degradation rate and an unchanged level of the rate limiting cholesterol biosynthesis enzyme, 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoAR). The molecular bases of the HMG-CoAR unchanged level and lowered degradation rate in aged rats is not clear. In fact no data are available during ageing, on transcription and degradation of HMG-CoAR, so well defined in adult animal. So, aim of this work was to measure mRNA levels of the enzyme and the level of the proteins of the regulatory complex responsible of the cholesterol metabolism. To complete the picture, the level of sterol regulatory element binding proteins (SREBPs), SREBP cleavage activating protein, and insulin-induced gene has been measured. The levels of other related proteins, whose transcription is SREBP dependent, that is low density lipoprotein receptor (LDLr) and Caveolin 1, have been also measured. The age-related reduced Insigs levels, joined to a reduced insulin sensitivity, could explain the decreased degradation rate of the HMG-CoAR and the increased active SREBP-2. The SREBP-2 in particular seems to be committed in multiple way to gene transcription. The obtained data represent a good contribution to explain the age-related hypercholesterolemia.

Profiles of Growth Hormone (GH)-regulated Genes Reveal Time-dependent Responses and Identify a Mechanism for Regulation of Activating Transcription Factor 3 By GH

In examination of mechanisms regulating metabolic responses to growth hormone (GH), microarray analysis identified 561 probe sets showing time-dependent patterns of expression in GH-treated 3T3-F442A adipocytes. Biological functions significantly over-represented among GH-regulated genes include regulators of transcription at early times, and lipid biosynthesis, cholesterol biosynthesis, and mediators of immune responses at later times (48 h). One novel GH-induced gene encodes activating transcription factor 3 (ATF3). Atf3 mRNA expression and promoter activity were stimulated by GH. Genes for ATF3 and growth arrest and DNA damage-inducible gene 45 gamma (GADD45gamma) showed similar time-dependent patterns of responses to GH, suggesting similar regulatory mechanisms. A conserved sequence in the promoters of the Atf3 and Gadd45gamma genes contains a CCAAT/enhancer-binding protein (C/EBP) site previously observed in the Gadd45gamma promoter, suggesting a novel corresponding C/EBP site in the Atf3 promoter. C/EBPbeta was found to bind to the predicted Atf3 C/EBP site, and C/EBPbeta enhanced the activation of the wild-type Atf3 promoter. Mutation of the predicted Atf3 C/EBP site disrupted Atf3 promoter activation not only by C/EBPbeta but also by GH. These findings suggest that GH regulates transcription of Atf3 through a mechanism utilizing factors, such as C/EBPbeta, which bind to a novel C/EBP site.

Fiber type-related changes in rat skeletal muscle calcium homeostasis during aging and restoration by growth hormone

The mechanisms by which aging induces muscle impairment are not well understood yet. We studied the impact of aging on Ca2+ homeostasis in the slow-twitch soleus and the fast-twitch extensor digitorum longus (EDL) muscles of aged rats by using the fura-2 fluorescent probe. In both muscles aging increases the resting cytosolic calcium concentration ([Ca2+]i). This effect was independent on calcium influx since a reduced resting permeability of sarcolemma to divalent cations was observed in aged muscles likely due to a reduced activity of leak channels. Importantly the effects of aging on resting [Ca2+]i, fiber diameter, mechanical threshold and sarcolemmal resting conductances were less pronounced in the soleus muscle, suggesting that muscle impairment may be less dependent on [Ca2+]i in the slow-twitch muscle. The treatment of aged rats with growth hormone restored the resting [Ca2+]i toward adult values in both muscles. Thus, an increase of resting [Ca2+]i may contribute to muscle weakness associated with aging and may be considered for developing new therapeutic strategies in the elderly.

Growth hormone (GH) receptor knockout mice reveal actions of GH in lung development

The presence of growth hormone (GH) and GH receptors (GHRs) in the lung suggests it is an autocrine/paracrine target site for pulmonary GH action and/or an endocrine site of pituitary GH action. Roles for GH in lung growth or pulmonary function are, however, uncertain. The possibility that pituitary and/or pulmonary GH have physiological roles in lung development has therefore been investigated in GHR knockout (KO or -/-) mice, using a proteomics approach to determine if an absence of GH-signaling affects the proteome of the developing lung. More than 600 proteins were detected by 2-DE in the lungs of control [GHR (+/+)] and GHR (-/-) mice at the end of the alveolarization period (at day 14 postnatally). Of these, 39 differed significantly in protein content at the p>0.05 level [6 were of higher abundance in the GHR (-/-) group, 33 were of lower abundance] and 17 differed at the p>0.02 level [5 of higher abundance in the GHR (-/-) group, 12 of lower abundance] and 7 were definitively identified by MS. Vimentin, a protein involved in cellular proliferation, was reduced in content by approximately 75% in the lungs of the GHR (-/-) mice. Three proteins involved in oxidative protection [SH3 domain-binding glutamic acid-rich-like protein, peroxiredoxin 6 (Prdx6), and isocitrate dehydrogenase 1] were also of lower content in the GHR (-/-) lungs (by approximately 88%, 81% and 70%, respectively). Prdx6 is also involved in lipid and surfactant metabolism, as is apolipoprotein A-IV, the lung content of which was reduced by approximately 73% in these mice. Proteasome 26S ATPase subunit 4, a protein involved in the non-lysosomal degradation of intracellular proteins, and electron flavoprotein alpha subunit , involved in intracellular metabolism, were also reduced in content in the lungs of the GHR (-/-) mice (by approximately 70% and 49%, respectively). These results therefore suggest that these proteins are normally dependent upon GH signaling, and that GH is normally involved in early lung growth, oxidative protection, lipid and energy metabolism and in proteasomal activity. These roles may reflect endocrine actions of pituitary GH and/or local autocrine/paracrine actions of GH produced within the lung.

The Inhibitory Effects of Interleukin‐1 on Growth Hormone Action During Catabolic Illness

Growth hormone (GH) induces the expression of the anabolic genes responsible for growth, metabolism, and differentiation. Normally, GH stimulates the synthesis of circulating insulin-like growth factor-I (IGF-I) by liver, which upregulates protein synthesis in many tissues. The development of GH resistance during catabolic illness or inflammation contributes to loss of body protein, resulting in multiple complications that prolong recovery and cause death. In septic patients, increased levels of proinflammatory cytokines and GH resistance are commonly observed together. Numerous studies have provided evidence that the inhibitory effects of cytokines on skeletal muscle protein synthesis during sepsis and inflammation are mediated indirectly by changes in the GH/IGF-I system. Interleukin (IL)-1, a member of the family of proinflammatory cytokines, interacts with most cell types and is an important mediator of the inflammatory response. Infusion of a specific IL-1 receptor antagonist (IL-1Ra) ameliorates protein catabolism and GH resistance during systemic infection. This suggests that IL-1 is an important mediator of GH resistance during systemic infection or inflammation. Consequently, a better understanding of the interaction between GH, IL-1, and the regulation of protein metabolism is of great importance for the care of the patient.

Harnessing the power of gene microarrays for the study of brain aging and Alzheimer's disease: statistical reliability and functional correlation

During normal brain aging, numerous alterations develop in the physiology, biochemistry and structure of neurons and glia. Aging changes occur in most brain regions and, in the hippocampus, have been linked to declining cognitive performance in both humans and animals. Age-related changes in hippocampal regions also may be harbingers of more severe decrements to come from neurodegenerative disorders such as Alzheimer's disease (AD). However, unraveling the mechanisms underlying brain aging, AD and impaired function has been difficult because of the complexity of the networks that drive these aging-related changes. Gene microarray technology allows massively parallel analysis of most genes expressed in a tissue, and therefore is an important new research tool that potentially can provide the investigative power needed to address the complexity of brain aging/neurodegenerative processes. However, along with this new analytic power, microarrays bring several major bioinformatics and resource problems that frequently hinder the optimal application of this technology. In particular, microarray analyses generate extremely large and unwieldy data sets and are subject to high false positive and false negative rates. Concerns also have been raised regarding their accuracy and uniformity. Furthermore, microarray analyses can result in long lists of altered genes, most of which may be difficult to evaluate for functional relevance. These and other problems have led to some skepticism regarding the reliability and functional usefulness of microarray data and to a general view that microarray data should be validated by an independent method. Given recent progress, however, we suggest that the major problem for current microarray research is no longer validity of expression measurements, but rather, the reliability of inferences from the data, an issue more appropriately redressed by statistical approaches than by validation with a separate method. If tested using statistically defined criteria for reliability/significance, microarray data do not appear a priori to require more independent validation than data obtained by any other method. In fact, because of added confidence from co-regulation, they may require less. In this article we also discuss our strategy of statistically correlating individual gene expression with biologically important endpoints designed to address the problem of evaluating functional relevance. We also review how work by ourselves and others with this powerful technology is leading to new insights into the complex processes of brain aging and AD, and to novel, more comprehensive models of aging-related brain change.

Exploring hepatic hormone actions using a compilation of gene expression profiles

Background

Microarray analysis is attractive within the field of endocrine research because regulation of gene expression is a key mechanism whereby hormones exert their actions. Knowledge discovery and testing of hypothesis based on information-rich expression profiles promise to accelerate discovery of physiologically relevant hormonal mechanisms of action. However, most studies so-far concentrate on the analysis of actions of single hormones and few examples exist that attempt to use compilation of different hormone-regulated expression profiles to gain insight into how hormone act to regulate tissue physiology. This report illustrates how a meta-analysis of multiple transcript profiles obtained from a single tissue, the liver, can be used to evaluate relevant hypothesis and discover novel mechanisms of hormonal action. We have evaluated the differential effects of Growth Hormone (GH) and estrogen in the regulation of hepatic gender differentiated gene expression as well as the involvement of sterol regulatory element-binding proteins (SREBPs) in the hepatic actions of GH and thyroid hormone.

Results

Little similarity exists between liver transcript profiles regulated by 17-α-ethinylestradiol and those induced by the continuos infusion of bGH. On the other hand, strong correlations were found between both profiles and the female enriched transcript profile. Therefore, estrogens have feminizing effects in male rat liver which are different from those induced by GH. The similarity between bGH and T3 were limited to a small group of genes, most of which are involved in lipogenesis. An in silico promoter analysis of genes rapidly regulated by thyroid hormone predicted the activation of SREBPs by short-term treatment in vivo. It was further demonstrated that proteolytic processing of SREBP1 in the endoplasmic reticulum might contribute to the rapid actions of T3 on these genes.

Conclusion

This report illustrates how a meta-analysis of multiple transcript profiles can be used to link knowledge concerning endocrine physiology to hormonally induced changes in gene expression. We conclude that both GH and estrogen are important determinants of gender-related differences in hepatic gene expression. Rapid hepatic thyroid hormone effects affect genes involved in lipogenesis possibly through the induction of SREBP1 proteolytic processing.

Growth hormone administration increases glucose production by preventing the expected decrease in glycogenolysis seen with fasting in healthy volunteers

Twelve volunteers were fasted overnight and infused with [ 13 C]glucose (ul) to measure glucose production (GP), gluconeogenesis, and by subtraction, glycogenolysis. Glucose production, gluconeogenesis, and glycogenolysis were measured after a 3-hour baseline infusion and two 4-hour infusions. The first 4 hours of the pituitary-pancreatic clamp study (PPCS) with replacement insulin, cortisol, and glucagon was without growth hormone (GH) administration. The second 4 hours of the PPCS was with high-dose GH administration. Six fasting volunteers acted as controls over the 11-hour study period. Overnight 12-hour fasting measurements of hormones, glucose, GP, gluconeogenesis, and glycogenolysis were similar in both groups. The PPCS had no significant effect on GP (2.43 +/- 0.19 vs 2.07 +/- 0.11 mg/kg per minute, PPCS vs controls, mean +/- SEM). Glycogenolysis, as a percent of GP (43%-49%), was similar between PPCS and controls (43% +/- 3% vs 49% +/- 4%). High-dose GH for 4 hours increased GH (20.8 +/- 3.8 vs 2.0 +/- 0.9 ng/mL), blood glucose (127 +/- 28 vs 86 +/- 4 mg/dL, P < .05), GP (2.21 +/- 0.21 vs 1.81 +/- 0.12 mg/kg per minute, P < .05). The increase in GP was due to sustained glycogenolysis as compared to the observed fall in glycogenolysis seen with fasting alone (0.94 +/- 0.21 vs 0.53 +/- 0.07 mg/kg per minute, P < .05). Glycogenolysis, as a percent of GP, was significantly increased with high-dose GH (43 +/- 5% vs 29 +/- 3%, P < .05). High-dose GH had no effect on gluconeogenesis (1.26 +/- 0.15 vs 1.29 +/- 0.12 mg/kg per minute). High-dose GH prevents the fall in glycogenolysis observed with fasting alone.

Suppressor of cytokine signaling-2 deficiency induces molecular and metabolic changes that partially overlap with growth hormone-dependent effects

Suppressor of cytokine signaling-2 (SOCS2)-deficient (SOCS2-/-) mice grow significantly larger than their littermates, suggesting that SOCS2 is important in the negative regulation of the actions of GH and/or IGF-I. The aim of this study was to identify genes and metabolic parameters that might contribute to the SOCS2-/- phenotype. We demonstrate that although SOCS2 deficiency induces significant changes in hepatic gene expression, only a fraction of these overlap with known GH-induced effects in the liver, suggesting that SOCS2 might be an important regulator of other growth factors and cytokines acting on the liver. However, an important role of GH and IGF-I in the phenotype of these animals was demonstrated by an overexpression of IGF-binding protein-3 mRNA in the liver and increased levels of circulating IGF-binding protein-3. Other GH-like effects included diminished serum triglycerides and down-regulation of lipoprotein lipase in adipose tissue. Interestingly, SOCS2-/- mice did not differ from their wild-type littermates in glucose or insulin tolerance tests, which is in contrast with the known diabetogenic effects of GH. Furthermore, there was no evidence of impaired insulin signaling in primary hepatocytes isolated from SOCS2-/- mice. Moreover, increased expression of peroxisome proliferator-activated receptor-gamma coactivator-1alpha mRNA was detected in skeletal muscle, which might contribute to normal glycemic control despite the apparent overactivity of the GH/IGF-I axis. Our data indicate that SOCS2 deficiency partially mimics a state of increased GH activity, but also results in changes that cannot be related to known GH effects.