Microarray analysis of the in vivo effects of hypophysectomy and growth hormone treatment on gene expression in the rat

Transcriptomic and lipid profiling analysis reveals a functional interplay between testosterone and growth hormone in hypothyroid liver

Preclinical and clinical studies suggest that hypothyroidism might cause hepatic endocrine and metabolic disturbances with features that mimic deficiencies of testosterone and/or GH. The absence of physiological interactions between testosterone and GH can be linked to male differentiated liver diseases. Testosterone plays relevant physiological effects on somatotropic-liver axis and liver composition and the liver is a primary organ of interactions between testosterone and GH. However, testosterone exerts many effects on liver through complex and poorly understood mechanisms. Testosterone impacts liver functions by binding to the Androgen Receptor, and, indirectly, through its conversion to estradiol, and cooperation with GH. However, the role of testosterone, and its interaction with GH, in the hypothyroid liver, remains unclear. In the present work, the effects of testosterone, and how they impact on GH-regulated whole transcriptome and lipid composition in the liver, were studied in the context of adult hypothyroid-orchiectomized rats. Testosterone replacement positively modulated somatotropic-liver axis and impacted liver transcriptome involved in lipid and glucose metabolism. In addition, testosterone enhanced the effects of GH on the transcriptome linked to lipid biosynthesis, oxidation-reduction, and metabolism of unsaturated and long-chain fatty acids (FA). However, testosterone decreased the hepatic content of cholesterol esters and triacylglycerols and increased fatty acids whereas GH increased neutral lipids and decreased polar lipids. Biological network analysis of the effects of testosterone on GH-regulated transcriptome confirmed a close connection with crucial proteins involved in steroid and fatty acid metabolism. Taken together, this comprehensive analysis of gene expression and lipid profiling in hypothyroid male liver reveals a functional interplay between testosterone and pulsed GH administration.

Growth hormone increases regulator of calcineurin 1-4 (Rcan1-4) mRNA through c-JUN in rat liver

Growth hormone (GH) activates multiple signal transduction pathways. To investigate these pathways, we identified novel genes whose transcription was induced by GH in the liver of hypophysectomized (HPX) rats using the suppression subtractive hybridization technique. We found that regulator of calcineurin 1 (Rcan1) mRNA was upregulated by GH administration. RCAN1 regulates the activity of calcineurin, a Ca/calmodulin-dependent phosphatase. Rcan1 encodes two major transcripts, Rcan1-1 and Rcan1-4, resulting from differential promoter use and first exon choice. We found that a single injection of GH increased the levels of Rcan1-4 mRNA and RCAN1-4 protein transiently, but did not increase Rcan1-1 mRNA in HPX rat liver. Then the molecular mechanism of GH to induce Rcan1-4 transcription was examined in rat hepatoma H4IIE cells. Experiments using inhibitors suggested that c-JUN N-terminal kinase was required for the induction of Rcan1-4 mRNA by GH. GH increased the levels of phosphorylated c-JUN protein and c-Jun mRNA in HPX rat liver. The luciferase and electrophoretic mobility shift assays showed that c-JUN upregulated Rcan1-4 mRNA by binding to the cAMP-responsive element in the upstream of Rcan1 exon 4. These results indicate that GH activates c-JUN to affect the activity of calcineurin by the induction of Rcan1-4 in rat liver.

Insulin-like growth factors: actions on the skeleton

The discovery of the growth hormone (GH)-mediated somatic factors (somatomedins), insulin-like growth factor (IGF)-I and -II, has elicited an enormous interest primarily among endocrinologists who study growth and metabolism. The advancement of molecular endocrinology over the past four decades enables investigators to re-examine and refine the established somatomedin hypothesis. Specifically, gene deletions, transgene overexpression or more recently, cell-specific gene-ablations, have enabled investigators to study the effects of the Igf1 and Igf2 genes in temporal and spatial manners. The GH/IGF axis, acting in an endocrine and autocrine/paracrine fashion, is the major axis controlling skeletal growth. Studies in rodents have clearly shown that IGFs regulate bone length of the appendicular skeleton evidenced by changes in chondrocytes of the proliferative and hypertrophic zones of the growth plate. IGFs affect radial bone growth and regulate cortical and trabecular bone properties via their effects on osteoblast, osteocyte and osteoclast function. Interactions of the IGFs with sex steroid hormones and the parathyroid hormone demonstrate the significance and complexity of the IGF axis in the skeleton. Finally, IGFs have been implicated in skeletal aging. Decreases in serum IGFs during aging have been correlated with reductions in bone mineral density and increased fracture risk. This review highlights many of the most relevant studies in the IGF research landscape, focusing in particular on IGFs effects on the skeleton.

Mammary transcriptome analysis of lactating dairy cows following administration of bovine growth hormone

The galactopoietic effect of growth hormone (GH) in lactating ruminants is well established; however the mechanisms that mediate these effects are not well understood. The first objective of this study was to determine the effect of GH on the synthesis of the major casein and whey proteins. The second objective was to identify the genes and pathways that may be involved in mediating the effect of GH on milk synthesis. A single subcutaneous injection of a commercially available slow release formulation of GH (Lactatropin®), or physiological saline solution (control) was administered to non-pregnant dairy cows (n=4/group) in mid-late lactation. Milk samples were collected for composition analysis and mammary lobulo-alveolar tissue was collected postmortem 6 days post injection. Gene expression profiles were evaluated using either a 22 000 bovine complementary DNA microarray or quantitative PCR (qPCR), and microarrays were validated by qPCR. The yield of all the major casein and whey proteins was increased 32% to 41% in GH-treated cows, with the exception of α-lactalbumin yield which was elevated by 70% relative to controls. Treatment with GH treatment tended to increase the concentration of α-lactalbumin but had no effect on the concentration of any of the major milk proteins. Messenger RNA (mRNA) abundance of the major whey and casein genes, with the exception of α-s2-casein, was increased in response to GH compared with controls, which is consistent with the positive effect of GH on milk production. Treatment with GH treatment influenced the mRNA abundance of genes involved in cell growth and proliferation, transcriptional and translational regulation, actin cytoskeleton signalling, lipid metabolism and cell death. This study has provided new insights into the cell signalling that may be involved in mediating the effect of GH on milk production in the mammary gland of lactating dairy cows.

Does the GH/IGF-1 axis contribute to skeletal sexual dimorphism? Evidence from mouse studies

The contribution of the gonadotropic axis to skeletal sexual dimorphism (SSD) was clarified in recent years. Studies with animal models of estrogen receptor (ER) or androgen receptor (AR) null mice, as well as mice with bone cell-specific ablation of ER or AR, revealed that both hormones play major roles in skeletal acquisition, and that estrogen regulates skeletal accrual in both sexes. The growth hormone (GH) and its downstream effector, the insulin-like growth factor-1 (IGF-1) are also major determinants of peak bone mass during puberty and young adulthood, and play important roles in maintaining bone integrity during aging. A few studies in both humans and animal models suggest that in addition to the differences in sex steroid actions on bone, sex-specific effects of GH and IGF-1 play essential roles in SSD. However, the contributions of the somatotropic (GH/IGF-1) axis to SSD are controversial and data is difficult to interpret. GH/IGF-1 are pleotropic hormones that act in an endocrine and autocrine/paracrine fashion on multiple tissues, affecting body composition as well as metabolism. Thus, understanding the contribution of the somatotropic axis to SSD requires the use of mouse models that will differentiate between these two modes of action. Elucidation of the relative contribution of GH/IGF-1 axis to SSD is significant because GH is approved for the treatment of normal children with short stature and children with congenital growth disorders. Thus, if the GH/IGF-1 axis determines SSD, treatment with GH may be tailored according to sex. In the following review, we give an overview of the roles of sex steroids in determining SSD and how they may interact with the GH/IGF-1 axis in bone. We summarize several mouse models with impaired somatotropic axis and speculate on the possible contribution of that axis to SSD.

Effects of growth hormone on the ontogenetic allometry of craniofacial bones

Organism size is controlled by interactions between genetic and environmental factors mediated by hormones with systemic and local effects. As changes in size are usually not isometric, a considerable diversity in shape can be generated through modifications in the patterns of ontogenetic allometry. In this study we evaluated the role of timing and dose of growth hormone (GH) release on growth and correlated shape changes in craniofacial bones. Using a longitudinal study design, we analyzed GH deficient mice treated with GH supplementation commencing pre- and post-puberty. We obtained 3D in vivo micro-CT images of the skull between 21 and 60 days of age and used geometric morphometrics to analyze size and shape changes among control and GH deficient treated and non-treated mice. The variable levels of circulating GH altered the size and shape of the adult skull, and influenced the cranial base, vault, and face differently. While cranial base synchondroses and facial sutures were susceptible to either the direct or indirect effect of GH supplementation, its effect was negligible on the vault. Such different responses support the role of intrinsic growth trajectories of skeletal components in controlling the modifications induced by systemic factors. Contrary to the expected, the timing of GH treatment did not have an effect on catch-up growth. GH levels also altered the ontogenetic trajectories by inducing changes in their location and extension in the shape space, indicating that differences arose before 21 days and were further accentuated by a truncation of the ontogenetic trajectories in GHD groups.

Minireview: mechanisms of growth hormone-mediated gene regulation

GH exerts a diverse array of physiological actions that include prominent roles in growth and metabolism, with a major contribution via stimulating IGF-1 synthesis. GH achieves its effects by influencing gene expression profiles, and Igf1 is a key transcriptional target of GH signaling in liver and other tissues. This review examines the mechanisms of GH-mediated gene regulation that begin with signal transduction pathways activated downstream of the GH receptor and continue with chromatin events at target genes and additionally encompasses the topics of negative regulation and cross talk with other cellular inputs. The transcription factor, signal transducer and activator of transcription 5b, is regarded as the major signaling pathway by which GH achieves its physiological effects, including in stimulating Igf1 gene transcription in liver. Recent studies exploring the mechanisms of how activated signal transducer and activator of transcription 5b accomplishes this are highlighted, which begin to characterize epigenetic features at regulatory domains of the Igf1 locus. Further research in this field offers promise to better understand the GH-IGF-1 axis in normal physiology and disease and to identify strategies to manipulate the axis to improve human health.

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.

Hypothalamic distribution of somatostatin mRNA expressing neurones relative to pubertal and adult changes in pulsatile growth hormone secretion in mice

The age-associated decline in growth hormone (GH) secretion may be a consequence of the reduction in the number of GH-releasing hormone (GHRH) positive neurones. However, it remains unclear whether an alteration in the number or distribution of somatostatin (SST) neurones contributes to this change. In the present study, we characterised the role of SST in modulating the change in pulsatile GH secretion in male C57Bl/6J mice throughout puberty and into early adulthood. We assessed pulsatile GH secretion in mice at 4, 8 and 16 weeks of age. These ages correspond to early pubertal, early adulthood and adulthood, respectively. We show an elevation in peak, total and pulsatile GH secretion coinciding with periods of rapid linear growth. Using in situ hybridisation and morphometric methods, we mapped the distribution of Sst mRNA expression within the mouse brain relative to this change in pulsatile GH secretion. The results obtained show that altered pulsatile GH secretion in male mice from 4-16 weeks of age does not coincide with a significant change in the number of Sst mRNA expressing neurones or an abundance of Sst mRNA expression throughout the arcuate nucleus (ARC) and periventricular nucleus (PeV). Rather, we observed a progressive decline in Sst mRNA expressing neurones within subnuclei of the paraventricular nucleus at this time. We conclude that structural changes in Sst expression within the PeV and ARC may not reflect the observed decline in pulsatile GH secretion in mice from puberty into early adulthood.

Gene expression in skeletal muscle after an acute intravenous GH bolus in human subjects: identification of a mechanism regulating ANGPTL4

Growth hormone (GH) acutely stimulates lipolysis and fat oxidation, a process that operates postabsorptively and involves activation of the JAK-STAT pathway in the target tissue; no in vivo data exist regarding subsequent GH-regulated gene transcription. We obtained serum samples and muscle biopsies in human subjects before and 2 h after administration of a GH bolus. A significant (~75%) elevation in serum FFA levels was recorded post GH. Microarray identified 79 GH-regulated genes in muscle. With qRT-PCR, we then examined the expression of selected genes in the presence and absence of glucose-induced suppression of lipolysis. Four genes involved in the JAK-STAT5 signaling pathway were regulated by GH, including SOCS1-3 and CISH, in addition to three genes associated with insulin action: NFκB1A, PIK3C2B, and PRKAG2. The gene encoding ANGPTL4, a protein involved in lipolysis and suppression of LPL activity, exhibited the most pronounced upregulation (5.6-fold) after GH, which was abrogated by concomitant suppression of lipolysis. Therefore, the GH-induced stimulation of ANGPTL4 gene expression seems secondary to induction of lipolysis. This new concept implies that abundant supply of circulating FFA decreases the need for alternative triglyceride-derived FFA through distinct inhibition of LPL mediated by increased ANGPTL4 gene expression in human muscle.

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.

Angiopoietin-like protein 4: health effects, modulating agents and structure-function relationships

Angiopoietin-like protein 4 (ANGPTL4) has been identified as a multifunctional signal protein. It is produced by a variety of tissues, and is secreted into the bloodstream in glycosylated, oligomerized, native and cleaved isoforms to modulate physiological events such as angiogenesis, cell differentiation and the crosstalk between liver, brain, adipose and muscle tissue in lipid and glucose metabolism. In addition, the expression and isoform appearance of ANGPTL4 are modified by the intestinal microbiota. With an eye on an effective strategy to improve health using ANGPTL4, we will focus on: health issues associated with ANGPTL4 expression, including obesity, Type 2 diabetes, cardiovascular diseases and cancer; several modulators of ANGPTL4 of chemical, microbiological, food and host origin; and the correlation of the specific ANGPTL4 isoforms with these modulators and their health effects.

Circadian modulation of hepatic transcriptome in transgenic rats expressing human growth hormone

The secretory profile of growth hormone (GH) is sexually dimorphic in rats. In male transgenic (TG) rats expressing human GH (hGH) that we generated, the circulating levels of both hGH and endogenous GH are flattened with no male-type pulsatility. To elucidate the regulatory role of episodic GH profile on the liver, the hepatic transcriptome of male TG rats at the middle of the light and dark phases was characterized by genome-wide analyses as compared with that of male wild-type (WT) rats. Transcripts commonly up- or down-regulated regardless of the lighting conditions in TG rats were mainly enriched in the metabolism of xenobiotics. In TG rats, the gene expression profile was functionally feminized, verifying that the sexually dimorphic profile of GH rather than genetic sexuality is a stronger sex-determining factor on the hepatic transcriptome. The common transcripts which fluctuated during the day in both TG and WT rats were enriched in circadian rhythm signaling, and physiological rhythmicity was considered to be finely interconnected with liver metabolism via sexually dimorphic GH secretion. In contrast, some genes were differentially regulated in TG rats at only one of two time points measured, and others were fluctuated daily in only one genotype. In particular, some genes involved in the GH signaling pathway were included, suggesting the signal transduction is circadian-modulated depending upon the GH profile. Our transcriptome analyses clarified the regulatory role of episodic GH profile on the liver and strengthen the functional link between sexually dimorphic GH secretion, liver metabolism, and its circadian regulation.

Sex-different hepaticglycogen content and glucose output in rats

Background

Genes involved in hepatic metabolism have a sex-different expression in rodents. To test whether male and female rat livers differ regarding lipid and carbohydrate metabolism, whole-genome transcript profiles were generated and these were complemented by measurements of hepatic lipid and glycogen content, fatty acid (FA) oxidation rates and hepatic glucose output (HGO). The latter was determined in perfusates from in situ perfusion of male and female rat livers. These perfusates were also analysed using nuclear magnetic resonance (NMR) spectroscopy to identify putative sex-differences in other liver-derived metabolites. Effects of insulin were monitored by analysis of Akt-phosphorylation, gene expression and HGO after s.c. insulin injections.

Results

Out of approximately 3 500 gene products being detected in liver, 11% were significantly higher in females, and 11% were higher in males. Many transcripts for the production of triglycerides (TG), cholesterol and VLDL particles were female-predominant, whereas genes for FA oxidation, gluconeogenesis and glycogen synthesis were male-predominant. Sex-differences in mRNA levels related to metabolism were more pronounced during mild starvation (12 h fasting), as compared to the postabsorptive state (4 h fasting). No sex-differences were observed regarding hepatic TG content, FA oxidation rates or blood levels of ketone bodies or glucose. However, males had higher hepatic glycogen content and higher HGO, as well as higher ratios of insulin to glucagon levels. Based on NMR spectroscopy, liver-derived lactate was also higher in males. HGO was inhibited by insulin in parallel with increased phosphorylation of Akt, without any sex-differences in insulin sensitivity. However, the degree of Thr172-phosphorylated AMP kinase (AMPK) was higher in females, indicating a higher degree of AMPK-dependent actions.

Conclusions

Taken together, males had higher ratios of insulin to glucagon levels, higher levels of glycogen, lower degree of AMPK phosphorylation, higher expression of gluconeogenic genes and higher hepatic glucose output. Possibly these sex-differences reflect a higher ability for the healthy male rat liver to respond to increased energy demands.

Defining the epigenetic actions of growth hormone: acute chromatin changes accompany GH-activated gene transcription

Many of the long-term physiological effects of GH require hormone-mediated changes in gene expression. The transcription factor signal transducer and activator of transcription 5b (Stat5b) plays a critical role in the actions of GH on growth and metabolism by regulating a large number of GH-dependent genes by incompletely understood mechanisms. Here we have assessed the impact of GH-initiated and Stat5b-mediated signaling on the chromatin landscape of hormone-regulated genes in the liver of pituitary-deficient young adult male rats. In the absence of GH there was minimal ongoing transcription at the Socs2, Cish, Igfals, and Spi 2.1 promoters, minimal occupancy of Stat5b at proximal promoter sites, and relatively closed chromatin, as evidenced by low levels of core histone acetylation. In contrast, transcriptionally silent Igf1 promoter 1 appeared poised to be activated, based on binding of coactivators p300 and Med1/Trap220, high levels of histone acetylation, and the presence of RNA polymerase II. GH treatment led to a 8- to 20-fold rise in transcriptional activity of all five genes within 30-60 min and was accompanied by binding of Stat5b to the proximal Socs2, Cish, Igfals, and Spi 2.1 promoters and to seven distal Igf1 Stat5b elements, by enhanced histone acetylation at all five promoters, by recruitment of RNA polymerase II to the Socs2, Cish, Igfals, and Spi 2.1 promoters, and by loss of the transcriptional repressor Bcl6 from Socs2, Cish, and Igfals Stat5b sites, but not from two Igf1 Stat5b domains. We conclude that GH actions induce rapid and dramatic changes in hepatic chromatin at target promoters and propose that the chromatin signature of Igf1 differs from other GH-and Stat5b-dependent genes.

Gene regulation by growth hormone

Since the somatomedin hypothesis of growth hormone (GH) action was first formulated more than 50 years ago, the key roles of both GH and insulin-like growth factor-I (IGF-I) in human growth have been extended to include important effects on tissue maintenance and repair. More recent observations have revealed that this pathway has a negative side, as it has been implicated as a potential contributor to the development of several human cancers and has been linked to diminished lifespan in experimental animals. This brief review focuses on fundamental aspects of gene regulation by GH, as long-term hormonal effects all require changes in gene expression. Topics to be discussed include GH-stimulated signal transduction pathways, mechanisms of gene activation and gene repression by GH, and an analysis of control of IGF-I gene transcription by the GH-stimulated transcription factor, signal transducer and activator of transcription (Stat)5b.

Intrinsic sex differences in the early growth hormone responsiveness of sex-specific genes in mouse liver

Sex differences in liver gene expression are dictated by sex differences in circulating GH profiles. Presently, the pituitary hormone dependence of mouse liver gene expression was investigated on a global scale to discover sex-specific early GH response genes that could contribute to sex-specific regulation of downstream GH targets and to ascertain whether intrinsic sex differences characterize hepatic responses to plasma GH stimulation. Global RNA expression analysis identified two distinct classes of sex-specific mouse liver genes: genes subject to positive regulation (class I) and genes subject to negative regulation by pituitary hormones (class II). Genes activated or repressed in hypophysectomized (Hypox) mouse liver within 30-90 min of GH pulse treatment at a physiological dose were identified as putative direct targets of GH action (early response genes). Intrinsic sex differences in the GH responsiveness of a subset of these early response genes were observed. Notably, 45 male-specific genes, including five encoding transcriptional regulators that may mediate downstream sex-specific transcriptional responses, were induced by GH within 30 min in Hypox male but not Hypox female mouse liver. The early GH response genes were enriched in 29 male-specific targets of the transcription factor myocyte enhancer factor 2, whose activation in hepatic stellate cells is associated with liver fibrosis leading to hepatocellular carcinoma, a male-predominant disease. Thus, the rapid activation by GH pulses of certain sex-specific genes is modulated by intrinsic sex-specific factors, which may be associated with prior hormone exposure (epigenetic mechanisms) or genetic factors that are pituitary-independent, and could contribute to sex differences in predisposition to liver cancer or other hepatic patho-physiologies.

A pilot study to evaluate gene expression profiles in peripheral blood mononuclear cells (PBMCs) from children with GH deficiency and Turner syndrome in response to GH treatment

Response to GH treatment is variable and dependent on diagnosis and dose. We used a pharmacogenomic approach to assess whether this variability is reflected in patterns of GH-induced gene expression in peripheral blood mononuclear cells (PBMCs) taken from three children with GH deficiency (GHD) and three girls with Turner syndrome (TS). Analysis of the response to GH treatment revealed that in GHD, 15 probe sets (11 genes) showed a fold change > +/- 1.4 at a P-value < 0.0005 (and a false detection rate <or= 15%). These genes included a suppressor of cytokine signalling (SOCS1) and a modulator of cAMP response elements (CREM). In marked contrast, in TS no genes fulfilled these criteria. ANOVA identified a subset of genes significantly affected by diagnosis, GH treatment or an interaction between diagnosis and treatment (P < 0.05, n = 2266). Cluster analysis indicated that genes up-regulated in both GHD and TS were related to DNA metabolism and transcription. Genes up-regulated in GHD but down-regulated in TS were involved in RNA processing and metabolism, whereas those down-regulated in GHD and up-regulated in TS were related to immune function. This pilot study has shown that major changes in gene expression in PBMCs can only be seen with confidence in GHD inferring that the pattern of gene expression in response to GH in GHD vs. TS is distinct and disease-specific. Further studies in larger cohorts will be required to evaluate whether GH-induced PBMCs gene expression patterns can predict responses to GH in a clinical setting.

Impaired autoimmune T helper 17 cell responses following DNA vaccination against rat experimental autoimmune encephalomyelitis

Background

We have previously shown that vaccination with DNA encoding the encephalitogenic peptide myelin oligodendrocyte glycoprotein (MOG)_91–108 (pMOG) suppresses MOG_91–108-induced rat Experimental Autoimmune Encephalomyelitis (EAE), a model for human Multiple Sclerosis (MS). The suppressive effect of pMOG is dependent on inclusion of CpG DNA in the plasmid backbone and is associated with early induction of Interferon (IFN)-β.

Principal Findings

In this study we examined the mechanisms underlying pMOG-induced protection. We found that in the DNA vaccinated cohort proinflammatory Interleukin (IL)-17 and IL-21 responses were dramatically reduced compared to in the control group, but that the expression of Foxp3 and Tumor Growth Factor (TGF)-β1, which are associated with regulatory T cells, was not enhanced. Moreover, genes associated with Type I IFNs were upregulated. To delineate the role of IFN-β in the protective mechanism we employed short interfering RNA (siRNA) to IFN-β in the DNA vaccine. SiRNA to IFN-β completely abrogated the protective effects of the vaccine, demonstrating that a local early elaboration of IFN-β is important for EAE protection. IL-17 responses comparable to those in control rats developed in rats injected with the IFN-β-silencing DNA vaccine.

Conclusions

We herein demonstrate that DNA vaccination protects from proinflammatory Th17 cell responses during induction of EAE. The mechanism involves IFN-β as IL-17 responses are rescued by silencing of IFN-β during DNA vaccination.

Growth hormone-dependent changes in the rat lung proteome during alveorization

Growth hormone (GH) mRNA and protein have recently been demonstrated in the rat lung throughout the period of alveolarization (day 4-14 postnatally). The functional significance of this finding was therefore assessed, by determining the effects of GH mRNA knockout using aerosolized antisense oligodeoxynucleotides (ODN) directed against the GH gene. In a preliminary experiment, the effectiveness of the antisense GH ODN was demonstrated in a lung Type II epithelial cell line (L2 cells), in which constitutive GH mRNA expression was completely abolished by GH ODN transfection. Administration of the aerosolized GH ODN to 4-day-old rats for 10 days was accompanied by a widespread presence of its delivery liposomes within lung cells. Aerosolized GH ODN treatment decreased lung concentrations of IGF (insulin-like growth factor)-1 and increased concentrations of albumin, calcyclin binding protein, superoxide dismutase, RNA binding protein motif 3, and the alpha- and beta-subunits of ATP synthase and electron transfer flavoprotein. At least 32 other proteins (identified by 2D gel electrophoresis) were also significantly affected by the antisense GH ODN treatment. By changing the lung proteome, these results indicate hitherto unsuspected autocrine/paracrine actions of GH in developmental lung function.

Sex differences in thrombosis in mice are mediated by sex-specific growth hormone secretion patterns

Sex differences in thrombosis are well described, but their underlying mechanism(s) are not completely understood. Coagulation proteins are synthesized in the liver, and liver gene expression is sex specific and depends on sex differences in growth hormone (GH) secretion--males secrete GH in a pulsatile fashion, while females secrete GH continuously. Accordingly, we tested the hypothesis that sex-specific GH secretion patterns cause sex differences in thrombosis. Male mice were more susceptible to thrombosis than females in the thromboplastin-induced pulmonary embolism model and showed shorter clotting times ex vivo. GH-deficient little (lit) mice were protected from thrombosis, and pulsatile GH given to lit mice restored the male clotting phenotype. Moreover, pulsatile GH administration resulted in a male clotting phenotype in control female mice, while continuous GH caused a female clotting phenotype in control male mice. Expression of the coagulation inhibitors Proc, Serpinc1, Serpind1, and Serpina5 were strongly modulated by sex-specific GH patterns, and GH modulated resistance to activated protein C. These results reveal what we believe to be a novel mechanism whereby sex-specific GH patterns mediate sex differences in thrombosis through coordinated changes in the expression of coagulation inhibitor genes in the liver.

Sex-specific early growth hormone response genes in rat liver

Pituitary GH-secretory profiles are sex dependent and regulate the sexually dimorphic expression of a large number of genes in the liver. The slow response of many sex-specific liver genes to changes in plasma GH status suggests that GH acts in the liver via both direct and indirect mechanisms organized in a hierarchical regulatory network. Presently, genome-wide liver transcription profiling was conducted to elucidate the global impact of pituitary hormone ablation on the sex specificity of rat liver gene expression and to identify sex-specific genes that respond rapidly to GH as candidates for direct targets of GH action. Hypophysectomy abolished the sex specificity of approximately 90% of 1032 sex-dependent genes, consistent with the dominant role of pituitary GH in regulating liver sexual dimorphism. Two major classes of sex-specific genes were identified: genes that were down-regulated after hypophysectomy and may be subject to positive GH regulation (461 class I genes), and genes that were up-regulated after hypophysectomy and may be subject to negative GH regulation (224 class II genes). Fifty class I sex-specific genes were induced, and 38 class II sex-specific genes were suppressed within 90 min of a physiological GH pulse, suggesting they are primary GH response genes. A further 71 sex-specific genes responded after a second GH treatment and may correspond to secondary response genes. Twenty four DNA-binding proteins were identified as early GH response genes, of which 15 were induced and nine were suppressed by GH. Five of these 24 genes displayed sex-specific expression, consistent with a hierarchical transcriptional network controlling sex-specific liver gene expression. Class II male-specific genes, such as Cyp2a2 and Cyp2c13, were down-regulated within 30 min of GH pulse treatment, as determined by heterogeneous nuclear RNA analysis, suggesting that transcription of these genes is restricted to the GH-free interpulse period in adult male rat liver. We conclude that GH acts via both positive and negative regulatory mechanisms to establish and maintain the sex specificity of liver gene expression.

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.

Extracting biology from high-dimensional biological data

The promise of the genome project was that a complete sequence would provide us with information that would transform biology and medicine. But the 'parts list' that has emerged from the genome project is far from the 'wiring diagram' and 'circuit logic' we need to understand the link between genotype, environment and phenotype. While genomic technologies such as DNA microarrays, proteomics and metabolomics have given us new tools and new sources of data to address these problems, a number of crucial elements remain to be addressed before we can begin to close the loop and develop a predictive quantitative biology that is the stated goal of so much of current biological research, including systems biology. Our approach to this problem has largely been one of integration, bringing together a vast wealth of information to better interpret the experimental data we are generating in genomic assays and creating publicly available databases and software tools to facilitate the work of others. Recently, we have used a similar approach to trying to understand the biological networks that underlie the phenotypic responses we observe and starting us on the road to developing a predictive biology.

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.

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.

Growth hormone stimulates hepatic expression of bovine growth hormone receptor messenger ribonucleic acid through signal transducer and activator of transcription 5 activation of a major growth hormone receptor gene promoter

The objective of this study was to determine whether and how GH regulates hepatic expression of GH receptor (GHR) mRNA in cattle. Ribonuclease protection assays revealed that injection of GH in a slow-release formula increased both hepatic GHR and IGF-I mRNAs 1 wk after the injection. The increases in GHR and IGF-I mRNAs were highly correlated. Western blot analysis showed that the injection also increased liver GHR protein level. In cattle and other mammals, hepatic GHR mRNA is expressed as variants that differ in the 5'-untranslated region due to the use of different promoters in transcription and/or alternative splicing. We found that GH increased the expression of the liver-specific GHR mRNA variant GHR1A without affecting the other two major GHR mRNA variants in the bovine liver, GHR1B and GHR1C. In transient transfection analyses, GH could robustly activate reporter gene expression from a 2.7-kb GHR1A promoter, suggesting that GH augmentation of GHR1A mRNA expression in the liver is at least partially mediated at the transcriptional level. Additional transfection analyses of serially 5'-truncated fragments of this promoter narrowed the GH-responsive sequence element down to a 210-bp region that contained a putative signal transducer and activator of transcription 5 (STAT5) binding site. EMSAs demonstrated that this putative STAT5 binding site was able to bind to STAT5b protein. In cotransfection assays, deletion of this putative STAT5 binding site abolished most of the GH response of the GHR1A promoter. Like 1-wk GH action, 6-h (i.e. short-term) GH action also increased liver expression of GHR1A and total GHR mRNAs in cattle. These observations together suggest that GH directly stimulates the expression of one GHR mRNA variant, GHR1A, through binding STAT5 to its promoter, thereby increasing GHR mRNA and protein expression in the bovine liver.

Signal Transducer and Activator of Transcription (Stat) 5b-Mediated Inhibition of Insulin-Like Growth Factor Binding Protein-1 Gene Transcription: A Mechanism for Repression of Gene Expression by Growth Hormone

GH plays a central role in controlling somatic growth, tissue regeneration, and intermediary metabolism in most vertebrate species through mechanisms dependent on the regulation of gene expression. Recent studies using transcript profiling have identified large cohorts of genes whose expression is induced by GH. Other results have demonstrated that signal transducer and activator of transcription (Stat) 5b, a latent transcription factor activated by the GH receptor-associated protein kinase, Jak2, is a key agent in the GH-stimulated gene activation that leads to somatic growth. By contrast, little is known about the steps through which GH-initiated signaling pathways reduce gene expression. Here we show that Stat5b plays a critical role in the GH-regulated inhibition of IGF binding protein-1 gene transcription by impairing the actions of the FoxO1 transcription factor on the IGF binding protein-1 promoter. Additional observations using transcript profiling in the liver indicate that Stat5b may be a general mediator of GH-initiated gene repression. Our results provide a model for understanding how GH may simultaneously stimulate and inhibit the expression of different cohorts of genes via the same transcription factor, potentially explaining how GH action leads to integrated biological responses in the whole organism.

In Vivo Transcript Profiling and Phylogenetic Analysis Identifies Suppressor of Cytokine Signaling 2 as a Direct Signal Transducer and Activator of Transcription 5b Target in Liver

The GH-activated signal transducer and activator of transcription 5b (STAT5b) is an essential regulator of somatic growth. The transcriptional response to STAT5b in liver is poorly understood. We have combined microarray-based expression profiling and phylogenetic analysis of gene regulatory regions to study the interplay between STAT5b and GH in the regulation of hepatic gene expression. The acute transcriptional response to GH in vivo after a single pulse of GH was studied in the liver of hypophysectomized rats in the presence of either constitutively active or a dominant-negative STAT5b delivered by adenoviral gene transfer. Genes showing differential expression in these two situations were analyzed for the presence of STAT5b binding sites in promoter and intronic regions that are phylogenetically conserved between rats and humans. Using this approach, we showed that most rapid transcriptional effects of GH in the liver are not results of direct actions of STAT5b. In addition, we identified novel STAT5b cis regulatory elements in genes such as Frizzled-4, epithelial membrane protein-1, and the suppressor of cytokine signaling 2 (SOCS2). Detailed analysis of SOCS2 promoter demonstrated its direct transcriptional regulation by STAT5b upon GH stimulation. A novel response element was identified within the first intron of the human SOCS2 gene composed of an E-box followed by tandem STAT5b binding sites, both of which are required for full GH responsiveness. In summary, we demonstrate the power of combining transcript profiling with phylogenetic sequence analysis to define novel regulatory paradigms.

Whole genome microarray analysis of growth hormone-induced gene expression in bone: T-box3, a novel transcription factor, regulates osteoblast proliferation

Growth hormone (GH) is important in the development and maintenance of bone; however, the IGF-dependent and -independent molecular pathways involved remain to be established. We used microarray analysis to evaluate GH signaling pathways in 4-wk-old GH-deficient mice following a single injection of GH (4 mg/kg body wt) or PBS (n = 6/group) at 6 or 24 h after treatment. Six thousand one hundred sixty genes were differentially expressed at P </= 0.05, and 17% of these genes were identified at both time points. Several of the genes differentially expressed were expressed sequence tags, and the remaining genes fell into 49 Gene Ontology categories. For subsequent studies, we focused on T-box (Tbx)3, a novel transcription factor, which increased more than twofold at both time points. Real-time RT-PCR analysis determined that pretreatment with IGF-binding protein-4 did not block GH-induced Tbx3 expression in vitro. Pretreatment with TNF-alpha blocked GH-induced Tbx3 expression. Tbx3 expression increased during osteoblast differentiation and following BMP-7 and Wnt3a treatment (P </= 0.05). Blocking Tbx3 expression by small interfering RNA decreased cell number and [(3)H]Thymidine incorporation (P < 0.01). In conclusion, 1) GH caused acute changes in several novel genes, suggesting that many GH-induced signaling pathways and target genes remain to be discovered; 2) because Tbx3 expression is regulated in osteoblasts and blockage of Tbx3 expression decreased cell number and DNA synthesis, we propose that Tbx3 is an important determinant of osteoblast cell number.

Sex-Dependent Liver Gene Expression Is Extensive and Largely Dependent upon Signal Transducer and Activator of Transcription 5b (STAT5b): STAT5b-Dependent Activation of Male Genes and Repression of Female Genes Revealed by Microarray Analysis

Sexual dimorphism in mammalian liver contributes to sex differences in physiology, homeostasis, and steroid and foreign compound metabolism. Many sex-dependent liver genes are regulated by sex differences in pituitary GH secretion, with the transcription factor, signal transducer and activator of transcription (STAT5b), proposed to mediate signaling by the pulsatile, male plasma GH profile. Presently, a large-scale gene expression study was conducted using male and female mice, wild type and Stat5b inactivated, to characterize sex differences in liver gene expression and their dependence on STAT5b. The relative abundance of individual liver RNAs was determined for each sex-genotype combination by competitive hybridization to 23,574-feature oligonucleotide microarrays. Significant sex differences in hepatic expression were seen for 1603 mouse genes. Of 850 genes showing higher expression in males, 767 (90%) were down-regulated in STAT5b-deficient males. Moreover, of 753 genes showing female-predominant expression, 461 (61%) were up-regulated in STAT5b-deficient males. In contrast, approximately 90% of the sex-dependent genes were unaffected by STAT5b deficiency in females. Thus: 1) STAT5b is essential for sex-dependent liver gene expression, a characteristic of approximately 1600 mouse genes (4% of the genome); 2) male-predominant liver gene expression requires STAT5b, or STAT5b-dependent factors, which act in a positive manner; and 3) many female-predominant liver genes are repressed in males in a STAT5b-dependent manner. Several of the STAT5b-dependent male genes encode transcriptional repressors; these may include direct STAT5b targets that repress female-predominant genes in male liver. Several female-predominant repressors are elevated in STAT5b-deficient males; these may contribute to the major loss of male gene expression seen in the absence of STAT5b.

Growth hormone regulation of sex-dependent liver gene expression

The liver is a primary target for the action of GH, a pituitary protein hormone that regulates a broad range of physiological processes, including long bone growth, fatty acid oxidation, glucose uptake, and hepatic steroid and foreign compound metabolism. GH exerts sex-dependent effects on the liver in many species, with many hepatic genes, most notably genes coding for cytochrome P450 (CYP) enzymes, being transcribed in a sex-dependent manner. Sex differences in CYP expression are most striking in rats and mice (up to 500-fold male-female differences), but are also seen, albeit to a much smaller degree, in humans, where they are an important determinant of the sex dependence of hepatic drug and steroid metabolism. This article examines the mechanisms whereby GH, via its sex-dependent temporal patterns of pituitary release, activates intracellular signaling leading to the sexually dimorphic transcription of CYPs and other liver-expressed genes. Recent findings implicating the GH-regulated transcription factor STAT5b (signal transducer and activator of transcription 5b), hepatocyte nuclear factors 3beta, 4alpha and 6, and sex differences in DNA methylation and chromatin structure in the sex-dependent actions of GH are reviewed, and current mechanistic models are evaluated.

Gene expression profile in the heart of spontaneous dwarf rat: In vivo effects of growth hormone

Excess and deficit of growth hormone (GH) both affect cardiac architecture as well as its function. To date, experimental and clinical studies have reported that GH has an inotropic effect on animal and human heart, however, it remains controversial whether GH is applicable to the treatment for the patients with chronic heart failure. Also, the mechanism by which GH exerts these biological effects on the heart is not well understood. In this study, we attempted to specify the genes regulated by GH in the heart of spontaneous dwarf rat using a microarray analysis. We found that soluble forms of guanylate cyclase, cofilin1, and thymosin beta4 mRNA were up-regulated in the heart by GH treatment. On the other hand, acyl-CoA synthetase, aldosterone receptor, myosin regulatory light chain, troponin T, laminA, and beta-actin mRNA were down-regulated. These results suggest GH regulates essential molecules that regulate structural, contractile, remodeling, and regenerative functions. Collectively, our data indicate a new integrative understanding for the biological effects of GH on cardiac function.

Lack of effect of growth hormone replacement therapy on CYP1A2 and xanthine oxidase activities in growth hormone–deficient children

BACKGROUND AND OBJECTIVES

The recombinant human growth hormone (rhGH) is being increasingly used for a number of metabolic alterations. GH is the main regulator of several hepatic drug metabolizing enzymes in rodents. In addition, GH could play a major role in defining the interface between pharmacogenetics and development. However, little is known about the effect of GH on the activity of hepatic enzymes in children. The aim of this study was to determine the effect of rhGH replacement therapy for 4 weeks on CYP1A2 and xanthine oxidase (XO) activities in children.

METHODS

We used caffeine as a probe drug to assess the enzyme activities at two points in time: before starting GH treatment (day 0) and after 4 weeks on rhGH therapy (day A). A total of 31 GH-deficient children (age range: 4.1-13.1 years, mean age: 9.88+/-2.89 years) participated. Urinary concentrations of caffeine and metabolites were determined by high-performance liquid chromatography (HPLC) to calculate the metabolite ratios: (AFMU+1X+1U)/17U for CYP1A2 and 1U/(1X+1U) for XO.

RESULTS

Four weeks of GH substitution did not importantly alter the markers of the enzyme activities measured in this study. Median values and 95% confidence intervals (CI) at baseline were 5.17 (3.87-5.59) for the CYP1A2 ratio and 0.62 (0.56-0.65) for the XO ratio. These values, after treatment, were 4.57 (3.90-5.97) for the CYP1A2 marker and 0.62 (0.59-0.67) for the XO ratio. Data comparison between periods showed lack of statistically significant differences (P>0.05). The relative changes measured by the ratios of medians and 90% CI were 1.14 (0.90-1.31) and 0.99 (0.94-1.06) for CYP1A2 and XO, respectively.

CONCLUSIONS

The absence of significant changes in the markers of enzyme activities CYP1A2 and XO suggests that rhGH replacement therapy of GH-deficient children for 4 weeks could not noticeably modify the efficacy or toxicity of substrates of these metabolic enzymes.

Genomic responses in rat cerebral cortex after traumatic brain injury

Background

Traumatic brain injury (TBI) initiates a complex sequence of destructive and neuroprotective cellular responses. The initial mechanical injury is followed by an extended time period of secondary brain damage. Due to the complicated pathological picture a better understanding of the molecular events occurring during this secondary phase of injury is needed. This study was aimed at analysing gene expression patterns following cerebral cortical contusion in rat using high throughput microarray technology with the goal of identifying genes involved in an early and in a more delayed phase of trauma, as genomic responses behind secondary mechanisms likely are time-dependent.

Results

Among the upregulated genes 1 day post injury, were transcription factors and genes involved in metabolism, e.g. STAT-3, C/EBP-δ and cytochrome p450. At 4 days post injury we observed increased gene expression of inflammatory factors, proteases and their inhibitors, like cathepsins, α-2-macroglobulin and C1q. Notably, genes with biological function clustered to immune response were significantly upregulated 4 days after injury, which was not found following 1 day. Osteopontin and one of its receptors, CD-44, were both upregulated showing a local mRNA- and immunoreactivity pattern in and around the injury site. Fewer genes had decreased expression both 1 and 4 days post injury and included genes implicated in transport, metabolism, signalling, and extra cellular matrix formation, e.g. vitronectin, neuroserpin and angiotensinogen.

Conclusion

The different patterns of gene expression, with little overlap in genes, 1 and 4 days post injury showed time dependence in genomic responses to trauma. An early induction of factors involved in transcription could lead to the later inflammatory response with strongly upregulated CD-44 and osteopontin expression. An increased knowledge of genes regulating the pathological mechanisms in trauma will help to find future treatment targets. Since trauma is a risk factor for development of neurodegenerative disease, this knowledge may also reduce late negative effects.

A conceptual and practical overview of cDNA microarray technology: implications for basic and clinical sciences

cDNA microarray is an innovative technology that facilitates the analysis of the expression of thousands of genes simultaneously. The utilization of this methodology, which is rapidly evolving, requires a combination of expertise from the biological, mathematical and statistical sciences. In this review, we attempt to provide an overview of the principles of cDNA microarray technology, the practical concerns of the analytical processing of the data obtained, the correlation of this methodology with other data analysis methods such as immunohistochemistry in tissue microarrays, and the cDNA microarray application in distinct areas of the basic and clinical sciences.

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.

Gene Expression Profiling to Identify Oncogenic Determinants of Autocrine Human Growth Hormone in Human Mammary Carcinoma

We have exploited a discrepancy in the oncogenic potential of autocrine and exogenous human growth hormone (hGH) in an attempt to identify molecules that could potentially be involved in oncogenic transformation of the human mammary epithelial cell. Microarray analysis of 19,000 human genes identified a subset of 305 genes in a human mammary carcinoma cell line that were remarkably different in their response to autocrine and exogenous hGH. Autocrine and exogenous hGH also regulated 167 common genes. Semiquantitative reverse transcription-PCR confirmed differential regulation of genes by either autocrine or exogenous hGH. Functional analysis of one of the identified autocrine hGH-regulated genes, TFF3, determined that its expression is sufficient to support anchorage-independent growth of human mammary carcinoma cells. Small interfering RNA-mediated knockdown of TFF3 concordantly abrogated anchorage-independent growth of mammary carcinoma cells and abrogated the ability of autocrine hGH to stimulate oncogenic transformation of immortalized human mammary epithelial cells. Further functional characterization of the identified subset of specifically autocrine hGH regulated genes will delineate additional novel oncogenes for the human mammary epithelial cell.

Transcriptome analysis and kidney research: Toward systems biology

An enormous amount of data has been generated in kidney research using transcriptome analysis techniques. In this review article, we first describe briefly the principles and major characteristics of several of these techniques. We then summarize the progress in kidney research that has been made by using transcriptome analysis, emphasizing the experience gained and the lessons learned. Several technical issues regarding DNA microarray are highlighted because of the rapidly increased use of this technology. It appears clear from this brief survey that transcriptome analysis is an effective and important tool for question-driven exploratory science. To further enhance the power of this and other high throughput, as well as conventional approaches, in future studies of the kidney, we propose a multidimensional systems biology paradigm that integrates investigation at multiple levels of biologic regulation toward the goal of achieving a global understanding of physiology and pathophysiology.

Growth hormone (GH) action in the developing lung: Changes in lung proteins after adenoviral GH overexpression

Growth hormone (GH) recently has been shown to be expressed in the neonatal rat lung during alveolarization. The possible functional importance of lung GH in lung function, therefore, has been assessed by determining changes in GH-responsive proteins in the developing rat lung after the overexpression of the GH gene in this tissue. GH overexpression was achieved using an adenovirus that expressed the mouse GH gene. This adenovirus was effective in inducing mouse GH expression in cultured rat lung L2 epithelial cells. It was also shown to be strongly expressed in the alveoli of 14-day-old rat pup lungs 10 days after it was administered by intratracheal injection, during a period of rapid lung development. Expression of the transgene in these pups was accompanied by changes in lung protein concentrations determined by two-dimensional gel electrophoresis and mass spectrometry. The lung concentrations of specific enzymes (nucleotide diphosphate kinase B, Cu/Zn superoxide dismutase, glutathione-S-transferase, and aldehyde reductase-1) were increased by the adenoviral expression of mouse GH, as were the concentrations of beta subunit G-protein calponin 2, beta-5 tubulin, retinoblastoma binding protein 4, and fetuin A. In contrast, the lung concentrations of haptoglobin and major acute phase alpha-1 protein were reduced by adenoviral expression of mouse GH. Although most of these proteins have not previously been identified as GH-responsive proteins, these results demonstrate actions of GH in the rat lung and support the possibility that GH acts as an autocrine/paracrine during early lung development.

Activation of the glucocorticoid receptor or liver X receptors interferes with growth hormone-induced akr1b7 gene expression in rat hepatocytes

The akr1b7 gene encodes an aldo-keto reductase involved in detoxification of isocaproaldehyde, the product from side chain cleavage of cholesterol, and of 4-hydroxynonenal (4-HNE) formed by lipid peroxidation and cleavage. Here we show that the expression of akr1b7 mRNA in rat liver is sexually differentiated, expressed in females but not in males, and regulated by the sexually dimorphic secretion pattern of GH. A GH dose-dependent induction of akr1b7 was demonstrated in cultured primary rat hepatocytes, which was sensitive to cycloheximide. Activation of the glucocorticoid receptor (GR) or liver X receptors (LXR) by dexamethasone (Dex) and T1317, respectively, attenuated the GH-induced expression of akr1b7 and CYP2C12, the prototypical rat hepatic gene dependent on the female-characteristic secretion pattern of GH. In contrast, neither Dex nor T1317 had any repressive effect on the GH induction of IGF-I mRNA. A common mechanism for LXR- and GR-mediated repressive actions on gene transcription is inhibition of nuclear factor (NF)-kappaB; however, EMSAs and pharmacological interference with NF-kappaB signaling provided no evidence for the involvement of NF-kappaB in the repressive action of Dex and T1317 on GH-induced akr1b7 expression.

Effects of gender and GH secretory pattern on sterol regulatory element-binding protein-1c and its target genes in rat liver

We investigated whether the sexually dimorphic secretory pattern of growth hormone (GH) in the rat regulates hepatic gene expression of sterol regulatory element-binding protein-1c (SREBP-1c) and its target genes. SREBP-1c, fatty acid synthase (FAS), and glycerol-3-phosphate acyltransferase (GPAT) mRNA were more abundant in female than in male livers, whereas acetyl-CoA carboxylase-1 (ACC1) and stearoyl-CoA desaturase-1 (SCD-1) were similarly expressed in both sexes. Hypophysectomized female rats were given GH as a continuous infusion or as two daily injections for 7 days to mimic the female- and male-specific GH secretory patterns, respectively. The female pattern of GH administration increased the expression of SREBP-1c, ACC1, FAS, SCD-1, and GPAT mRNA, whereas the male pattern of GH administration increased only SCD-1 mRNA. FAS and SCD-1 protein levels were regulated in a similar manner by GH. Incubation of primary rat hepatocytes with GH increased SCD-1 mRNA levels and decreased FAS and GPAT mRNA levels but had no effect on SREBP-1c mRNA. GH decreased hepatic liver X receptor-alpha (LXRalpha) mRNA levels both in vivo and in vitro. Feminization of the GH plasma pattern in male rats by administration of GH as a continuous infusion decreased insulin sensitivity and increased expression of FAS and GPAT mRNA but had no effect on SREBP-1c, ACC1, SCD-1, or LXRalpha mRNA. In conclusion, FAS and GPAT are specifically upregulated by the female secretory pattern of GH. This regulation is not a direct effect of GH on hepatocytes and does not involve changed expression of SREBP-1c or LXRalpha mRNA but is associated with decreased insulin sensitivity.

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.

cDNA Microarray Analysis Reveals New Candidate Genes Possibly Linked to Side Effects Under Mycophenolate Mofetil Therapy

BACKGROUND

Mycophenolate mofetil (MMF) the prodrug of mycophenolic acid is usually well tolerated. Side effects such as anemia and diarrhea occur in approximately 10%-15% of patients. The aim of this study was to examine in a rat model the effect of MMF on gene expression in liver and gut to identify target genes with possible relevance to MMF side effects.

METHODS

Twelve Wistar rats were treated with 40 mg/kg body weight MMF orally for 21 days. Controls (n=9) received vehicle only. RNA was extracted from liver, jejunum, ileum, and colon and transcribed into cDNA. Regulated genes were identified in liver by DNA microarray experiments. Gene regulation was verified in liver and gut using quantitative real-time PCR on the LightCycler instrument. Transcription elongation factor 2 served as reference gene.

RESULTS

Microarray analysis revealed that major alpha-hemoglobin, polymeric immunoglobulin receptor, catalase, and CCAAT/enhancer protein alpha gene expression were down-regulated in livers of MMF-treated rats 10-, 5.5-, 4-, and 5-fold, respectively. These findings could be confirmed through quantitative real-time PCR analysis of gene expression in liver, ileum, jejunum, and colon.

CONCLUSION

Using microarray analysis and a rat model four candidate genes which may be functionally linked to side effects (major alpha-hemoglobin-->anaemia; polymeric immunoglobulin receptor-->protection of mucosa; catalase and CCAAT/enhancer protein alpha-->oxidative stress) of MMF therapy were identified.