Growth hormone as a cytokine

Growth Hormone and Counterregulation in the Pathogenesis of Diabetes

PURPOSE OF REVIEW

Canonical growth hormone (GH)-dependent signaling is essential for growth and counterregulatory responses to hypoglycemia, but also may contribute to glucose homeostasis (even in the absence of hypoglycemia) via its impact on metabolism of carbohydrates, lipids and proteins, body composition, and cardiovascular risk profile. The aim of this review is to summarize recent data implicating GH action in metabolic control, including both IGF-1-dependent and -independent pathways, and its potential role as target for T2D therapy.

RECENT FINDINGS

Experimental blockade of the GHR can modulate glucose metabolism. Moreover, the soluble form of the GH receptor (GHR, or GHBP) was recently identified as a mediator of improvement in glycemic control in patients with T2D randomized to bariatric surgery vs. medical therapy. Reductions in GHR were accompanied by increases in plasma GH, but unchanged levels of both total and free IGF-1. Likewise, hepatic GHR expression is reduced following both RYGB and VSG in rodents. Emerging data indicate that GH signaling is important for regulation of long-term glucose metabolism in T2D. Future studies will be required to dissect tissue-specific GH signaling and sensitivity and their contributions to systemic glucose metabolism.

The Proteomic Signature of Recombinant Growth Hormone in Recreational Athletes

OBJECTIVE

Administration of human growth hormone (hGH) is prohibited in competitive sport and its detection in an athlete's sample triggers an adverse analytical finding. However, the biological processes that are modulated by recombinant hGH are not well characterized and associated blood serum proteins may constitute new biomarkers for hGH misuse.

METHODS

Thirty-five recreational athletes were enrolled in a study to investigate the time- and dose-dependent response of serum protein levels to recombinant hGH administration. Participants were randomly assigned to 4 groups, receiving 1 of 3 different doses of recombinant hGH or a placebo. Bio samples were collected at 22 time points over a period of 13 weeks, starting 4 weeks before treatment, during 3 weeks of treatment, and at 6 weeks' follow-up. A total of 749 serum samples were analyzed for 1305 protein markers using the SOMAscan proteomics platform.

RESULTS

We identified 66 proteins that significantly associated with recombinant hGH administration and dosage, including well known hGH targets, such as IGF1, but also previously unknown hGH-related proteins (eg, protease inhibitors, WFIKKN1, and chemokines, CCL2). Network analysis revealed changes in specific biological pathways, mainly related to the immune system and glucose metabolism.

CONCLUSION

Our analysis suggests that hGH administration affects biological processes more strongly than previously acknowledged. Some of the proteins were dysregulated even after hGH treatment and could potentially be developed into biomarkers for hGH misuse. Moreover, our findings suggest new roles for hGH-associated proteins in the etiology of hGH-related diseases and may indicate new risks that may be associated with hGH misuse.

The GH-IGF-1 Axis in Circadian Rhythm

Organisms have developed common behavioral and physiological adaptations to the influence of the day/night cycle. The CLOCK system forms an internal circadian rhythm in the suprachiasmatic nucleus (SCN) during light/dark input. The SCN may synchronize the growth hormone (GH) secretion rhythm with the dimming cycle through somatostatin neurons, and the change of the clock system may be related to the pulsatile release of GH. The GH-insulin-like growth factor 1 (IGF-1) axis and clock system may interact further on the metabolism through regulatory pathways in peripheral organs. We have summarized the current clinical and animal evidence on the interaction of clock systems with the GH-IGF-1 axis and discussed their effects on metabolism.

Regulation of GH and GH Signaling by Nutrients

Growth hormone (GH) and insulin-like growth factor-1 (IGF-I) are pleiotropic hormones with important roles in lifespan. They promote growth, anabolic actions, and body maintenance, and in conditions of energy deprivation, favor catabolic feedback mechanisms switching from carbohydrate oxidation to lipolysis, with the aim to preserve protein storages and survival. IGF-I/insulin signaling was also the first one identified in the regulation of lifespan in relation to the nutrient-sensing. Indeed, nutrients are crucial modifiers of the GH/IGF-I axis, and these hormones also regulate the complex orchestration of utilization of nutrients in cell and tissues. The aim of this review is to summarize current knowledge on the reciprocal feedback among the GH/IGF-I axis, macro and micronutrients, and dietary regimens, including caloric restriction. Expanding the depth of information on this topic could open perspectives in nutrition management, prevention, and treatment of GH/IGF-I deficiency or excess during life.

The impact of endocrine-disrupting chemical exposure in the mammalian hypothalamic-pituitary axis

The hypothalamic-pituitary axis (HP axis) plays a critical and integrative role in the endocrine system control to maintain homeostasis. The HP axis is responsible for the hormonal events necessary to regulate the thyroid, adrenal glands, gonads, somatic growth, among other functions. Endocrine-disrupting chemicals (EDCs) are a worldwide public health concern. There is growing evidence that exposure to EDCs such as bisphenol A (BPA), some phthalates, polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and biphenyls (PBBs), dichlorodiphenyltrichloroethane (DDT), tributyltin (TBT), and atrazine (ATR), is associated with HP axis abnormalities. EDCs act on hormone receptors and their downstream signaling pathways and can interfere with hormone synthesis, metabolism, and actions. Because the HP axis function is particularly sensitive to endogenous hormonal changes, disruptions by EDCs can alter HP axis proper function, leading to important endocrine irregularities. Here, we review the evidence that EDCs could directly affect the mammalian HP axis function.

The growth hormone receptor

Once thought to be present only in liver, muscle and adipose tissue, the GH receptor is now known to be ubiquitously distributed, in accord with the many pleiotropic actions of GH. These include the regulation of metabolism, postnatal growth, cognition, immune, cardiac and renal systems and gut function. GH exerts these actions primarily through alterations in gene expression, initiated by activation of its membrane receptor and the resultant activation of the associated JAK2 (Janus kinase 2) and Src family kinases. Receptor activation involves hormone initiated movements within a receptor homodimer, rather than simple receptor dimerization. We have shown that binding of the hormone realigns the orientation of the two receptors both by relative rotation and by closer apposition just above the cell membrane. This is a consequence of the asymmetric placement of the binding sites on the hormone. Binding results in a conversion of parallel receptor transmembrane domains into a rotated crossover orientation, which produces separation of the lower part of the transmembrane helices. Because the JAK2 is bound to the Box1 motif proximal to the inner membrane, receptor activation results in separation of the two associated JAK2s, and in particular the removal of the inhibitory pseudokinase domain from the kinase domain of the other JAK2 (and vice versa). This brings the two kinase domains into position for trans-activation and initiates tyrosine phosphorylation of the receptor cytoplasmic domain and other substrates such as STAT5, the key transcription factor mediating most genomic actions of GH. There are a limited number of genomic actions initiated by the Src kinase family member which also associates with the upper cytoplasmic domain of the receptor, including important immune regulatory actions to dampen exuberant innate immune activation of cells involved in transplant rejection. These findings offer insights for developing specific receptor antagonists which may be valuable in cancer therapy.

Autocrine/paracrine roles of extrapituitary growth hormone and prolactin in health and disease: An overview

Growth hormone (GH) and prolactin (PRL) are both endocrines that are synthesized and released from the pituitary gland into systemic circulation. Both are therefore hormones and both have numerous physiological roles mediated through a myriad of target sites and both have pathophysiological consequences when present in excess or deficiency. GH or PRL gene expression is not, however, confined to the anterior pituitary gland and it occurs widely in many of their central and peripheral sites of action. This may reflect "leaky gene" phenomena and the fact that all cells have the potential to express every gene that is present in their genome. However, the presence of GH or PRL receptors in these extrapituitary sites of GH and PRL production suggests that they are autocrine or paracrine sites of GH and PRL action. These local actions often occur prior to the ontogeny of pituitary somatotrophs and lactotrophs and they may complement or differ from the roles of their pituitary counterparts. Many of these local actions are also of physiological significance, since they are impaired by a blockade of local GH or PRL production or by an antagonism of local GH or PRL action. These local actions may also be of pathophysiological significance, since autocrine or paracrine actions of GH and PRL are thought to be causally involved in a number of disease states, particularly in cancer. Autocrine GH for instance, is thought to be more oncogenic than pituitary GH and selective targeting of the autocrine moiety may provide a therapeutic approach to prevent tumor progression. In summary, GH and PRL are not just endocrine hormones, as they have autocrine and/or paracrine roles in health and disease.

Autocrine/Paracrine Human Growth Hormone-stimulated MicroRNA 96-182-183 Cluster Promotes Epithelial-Mesenchymal Transition and Invasion in Breast Cancer

Human growth hormone (hGH) plays critical roles in pubertal mammary gland growth, development, and sexual maturation. Accumulated studies have reported that autocrine/paracrine hGH is an orthotopically expressed oncoprotein that promotes normal mammary epithelial cell oncogenic transformation. Autocrine/paracrine hGH has also been reported to promote mammary epithelial cell epithelial-mesenchymal transition (EMT) and invasion. However, the underlying mechanism remains largely obscure. MicroRNAs (miRNAs) are reported to be involved in regulation of multiple cellular functions of cancer. To determine whether autocrine/paracrine hGH promotes EMT and invasion through modulation of miRNA expression, we performed microarray profiling using MCF-7 cells stably expressing wild type or a translation-deficient hGH gene and identified miR-96-182-183 as an autocrine/paracrine hGH-regulated miRNA cluster. Forced expression of miR-96-182-183 conferred on epithelioid MCF-7 cells a mesenchymal phenotype and promoted invasive behavior in vitro and dissemination in vivo. Moreover, we observed that miR-96-182-183 promoted EMT and invasion by directly and simultaneously suppressing BRMS1L (breast cancer metastasis suppressor 1-like) gene expression. miR-96 and miR-182 also targeted GHR, providing a potential negative feedback loop in the hGH-GHR signaling pathway. We further demonstrated that autocrine/paracrine hGH stimulated miR-96-182-183 expression and facilitated EMT and invasion via STAT3 and STAT5 signaling. Consistent with elevated expression of autocrine/paracrine hGH in metastatic breast cancer tissue, miR-96-182-183 expression was also remarkably enhanced. Hence, we delineate the roles of the miRNA-96-182-183 cluster and elucidate a novel hGH-GHR-STAT3/STAT5-miR-96-182-183-BRMS1L-ZEB1/E47-EMT/invasion axis, which provides further understanding of the mechanism of autocrine/paracrine hGH-stimulated EMT and invasion in breast cancer.

Extrapituitary growth hormone and growth?

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

Modulation of the somatotropic axis in periparturient dairy cows

This review focuses on modulation of growth hormone (GH) and its downstream actions on periparturient dairy cows undergoing physiological and metabolic adaptations. During the periparturient period, cows experience a negative energy balance implicating that the feed intake does not meet the total energy demand for the onset of lactation. To regulate this metabolic condition, key hormones of somatotropic axis such as GH, IGF-I and insulin must coordinate adaptations required for the preservation of metabolic homeostasis. The hepatic GHR1A transcript and GHR protein are reduced at parturition, but recovers on postpartum. However, plasma IGF-I concentration remains low even though hepatic abundance of the GHR and IGF-I mRNA return to pre-calving value. This might be caused by alternation in IGFBPs and ALS genes, which consequently affect the plasma IGF-I stability. Plasma insulin level declines in a parallel manner with the decrease in plasma IGF-I after parturition. Increased GH stimulates the lipolytic effects and hepatic glucose synthesis to meet the energy requirement for mammary lactose synthesis, suggesting that GH antagonizes insulin-dependent glucose uptake and attenuates insulin action to decrease gluconeogenesis.

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.

The paracrine effect of exogenous growth hormone alleviates dysmorphogenesis caused by tbx5 deficiency in zebrafish (Danio rerio) embryos

BACKGROUND

Dysmorphogenesis and multiple organ defects are well known in zebrafish (Danio rerio) embryos with T-box transcription factor 5 (tbx5) deficiencies, mimicking human Holt-Oram syndrome.

METHODS

Using an oligonucleotide-based microarray analysis to study the expression of special genes in tbx5 morphants, we demonstrated that GH and some GH-related genes were markedly downregulated. Zebrafish embryos microinjected with tbx5-morpholino (MO) antisense RNA and mismatched antisense RNA in the 1-cell stage served as controls, while zebrafish embryos co-injected with exogenous growth hormone (GH) concomitant with tbx5-MO comprised the treatment group.

RESULTS

The attenuating effects of GH in tbx5-MO knockdown embryos were quantified and observed at 24, 30, 48, 72, and 96 h post-fertilization. Though the understanding of mechanisms involving GH in the tbx5 functioning complex is limited, exogenous GH supplied to tbx5 knockdown zebrafish embryos is able to enhance the expression of downstream mediators in the GH and insulin-like growth factor (IGF)-1 pathway, including igf1, ghra, and ghrb, and signal transductors (erk1, akt2), and eventually to correct dysmorphogenesis in various organs including the heart and pectoral fins. Supplementary GH also reduced apoptosis as determined by a TUNEL assay and decreased the expression of apoptosis-related genes and proteins (bcl2 and bad) according to semiquantitative reverse-transcription polymerase chain reaction and immunohistochemical analysis, respectively, as well as improving cell cycle-related genes (p27 and cdk2) and cardiomyogenetic genes (amhc, vmhc, and cmlc2).

CONCLUSIONS

Based on our results, tbx5 knockdown causes a pseudo GH deficiency in zebrafish during early embryonic stages, and supplementation of exogenous GH can partially restore dysmorphogenesis, apoptosis, cell growth inhibition, and abnormal cardiomyogenesis in tbx5 knockdown zebrafish in a paracrine manner.

GH activity and markers of inflammation: a crossover study in healthy volunteers treated with GH and a GH receptor antagonist

INTRODUCTION

The GH/IGF1 axis may modulate inflammatory processes. However, the relationship seems complicated as both pro- and anti-inflammatory effects have been demonstrated.

METHODS/DESIGN

Twelve healthy volunteers (mean age 36, range 27-49 years) were treated in random order with increasing doses of GH for 3 weeks (first week 0.01  mg/kg per day, second week 0.02  mg/kg per day, and third week 0.03  mg/kg per day) or a GH receptor antagonist (pegvisomant; first week 10  mg/day and last two weeks 15  mg/day), separated by 8 weeks of washout. Circulating levels of the pro-inflammatory cytokines tumor necrosis factor α (TNFα (TNFA)), interleukin 6 (IL6), and IL1β (IL1B) and the acute phase proteins (APPs) C-reactive protein (CRP), haptoglobin, orosomucoid, YKL40 (CHI3L1), and fibrinogen were measured.

RESULTS

During GH treatment, IGF1 (median 131 (Inter-quartile range (IQR) 112-166) vs 390 (322-524) μg/l, P=0.002) increased together with TNFα (0.87 (0.74-1.48) vs 1.27 (0.80-1.69) ng/l, P=0.003), IL6 (1.00 (0.83-1.55) vs 1.35 (0.80-4.28) ng/l, P=0.045), and fibrinogen (9.2 (8.8-9.6) vs 11.1 (9.4-12.4) μM, P=0.002). By contrast, orosomucoid decreased (18.0 (15.5-24.3) vs 15.0 (15.0-17.0) μM, P=0.018). CRP, YKL40, and haptoglobin were unchanged. During pegvisomant treatment, IGF1 decreased (139 (117-171) vs 91 (78-114) ng/ml, P=0.005). Orosomucoid (21.0 (16.3-23.8) vs 22.0 (17.0-29.3) μM, P=0.036) and CRP (1.00 (0.62-1.77) vs 1.43 (0.71-3.29) mg/l, P=0.074) increased without an increase in pro-inflammatory cytokines.

CONCLUSIONS

GH/IGF1 action appears to modulate the initial stage of the inflammatory response as well as downstream processes elucidated by levels of APPs. The data suggest a complicated relationship not allowing any simple conclusions as to whether GH/IGF1 actions have mainly pro- or anti-inflammatory effects in vivo.

The growth hormone receptor: mechanism of activation and clinical implications

Growth hormone is widely used clinically to promote growth and anabolism and for other purposes. Its actions are mediated via the growth hormone receptor, both directly by tyrosine kinase activation and indirectly by induction of insulin-like growth factor 1 (IGF-1). Insensitivity to growth hormone (Laron syndrome) can result from mutations in the growth hormone receptor and can be treated with IGF-1. This treatment is, however, not fully effective owing to the loss of the direct actions of growth hormone and altered availability of exogenous IGF-1. Excessive activation of the growth hormone receptor by circulating growth hormone results in gigantism and acromegaly, whereas cell transformation and cancer can occur in response to autocrine activation of the receptor. Advances in understanding the mechanism of receptor activation have led to a model in which the growth hormone receptor exists as a constitutive dimer. Binding of the hormone realigns the subunits by rotation and closer apposition, resulting in juxtaposition of the catalytic domains of the associated tyrosine-protein kinase JAK2 below the cell membrane. This change results in activation of JAK2 by transphosphorylation, then phosphorylation of receptor tyrosines in the cytoplasmic domain, which enables binding of adaptor proteins, as well as direct phosphorylation of target proteins. This model is discussed in the light of salient information from closely related class 1 cytokine receptors, such as the erythropoietin, prolactin and thrombopoietin receptors.

Evolutionary divergence of duplicate copies of the growth hormone gene in suckers (Actinopterygii: catostomidae)

Catostomid fishes (suckers) have duplicate copies of the growth hormone gene and other nuclear genes, due to a genome duplication event early in the group’s history. Yet, paralogs of GH in suckers are more than 90% conserved in nucleotide (nt) and amino acid (aa) sequence. Within paralogs across species, variation in nt and aa sequence averages 3.33% and 4.46% for GHI, and 3.22% and 2.43% for GHII, respectively. Selection tests suggest that the two GH paralogs are under strong purifying selection. Consensus trees from phylogenetic analysis of GH coding region data for 23 species of suckers, other cypriniform fishes and outgroups resolved cypriniform relationships and relationships among GHI sequences of suckers more or less consistently with analyses based on other molecular data. However, the analysis failed to resolve all sucker GHI and GHII sequences as monophyletic sister groups. This unexpected topology did not differ significantly from topologies constrained to make all GH sequences monophyletic. We attribute this result either to limitations in our GHII data set or convergent adaptive changes in GHII of tribe Catostomini.

Structure and activity of the human growth hormone receptor (hGHR) gene V2 promoter

Human GH (hGH) has important effects on growth as well as carbohydrate, fat, and protein metabolism. These actions require the presence of normal levels of a functional hGH receptor (hGHR) on the surface of target cells. hGHR gene expression is characterized by the use of several 5'-noncoding exons and alternative splicing, resulting in the generation of multiple mRNA isoforms. The hGHR V2 transcript is predominant in most tissues, including human fat. However, factors regulating its ubiquitous expression have remained unidentified. The present study was aimed at characterizing the mechanisms regulating hGHR V2 transcription. Two major V2 transcriptional start sites were identified by primer extension assays. The V2 proximal promoter is TATA-less, with several characteristics of a housekeeping gene promoter. Transient transfection analyses of 2.6 kb of the 5'-flanking region of V2 confirmed its promoter activity in multiple primate cell lines. Similar promoter activity patterns were observed in human SGBS preadipocytes and mature adipocytes but with much higher V2 promoter activity in mature adipocytes, suggesting that changes in the availability of specific factors during adipocyte differentiation play a role in V2 promoter regulation. Serial deletion and mutation analyses revealed that transcription of hGHR V2 in different cell types, including adipocytes, is determined by a core promoter and distinct inhibitory and activation domains in the 5'-promoter region as well as within the V2 exon. Our data suggest that V2 transcription is the result of a complex interplay involving multiple factors, to ensure appropriate expression of hGHR in different hGH target cells.

DNMT3A and DNMT3B mediate autocrine hGH repression of plakoglobin gene transcription and consequent phenotypic conversion of mammary carcinoma cells

Directed by microarray analyses, we report that autocrine human growth hormone (hGH) increased the mRNA and protein expression of DNA methyltransferase 1 (DNMT1), DNMT3A and DNMT3B in mammary carcinoma cells. Autocrine hGH stimulation of DNMT3A and DNMT3B expression was mediated by JAK2 and Src kinases, and treatment of mammary carcinoma cells with the DNMT inhibitor, 5'-aza-2'-deoxycytidine (AZA), abrogated autocrine hGH-stimulated cellular proliferation, apoptosis and anchorage-independent growth. AZA reversed the epitheliomesenchymal transition of mammary carcinoma cells induced by autocrine hGH, to an epithelioid morphology and abrogated cell migration stimulated by autocrine hGH. Autocrine hGH-stimulated hypermethylation of the first exon of the PLAKOGLOBIN gene and AZA abrogated the ability of autocrine hGH to repress plakoglobin gene transcription. Small interfering RNA (siRNA)-mediated depletion of the individual DNMT molecules did not release autocrine hGH repression of PLAKOGLOBIN promoter activity nor did individual DNMT depletion affect autocrine hGH-stimulated migration. However, concomitant siRNA-mediated depletion of both DNMT3A and DNMT3B abrogated hypermethylation of the PLAKOGLOBIN gene stimulated by autocrine hGH and subsequent repression of plakoglobin gene transcription and increased cell migration. Thus, the autocrine hGH-stimulated increases in DNMT3A and DNMT3B expression mediate repression of plakoglobin gene transcription by direct hypermethylation of its promoter and consequent phenotypic conversion of mammary carcinoma cells. Autocrine hGH, therefore, utilizes DNA methylation as a mechanism to exert its oncogenic effects in mammary carcinoma cells.

Concentrations of the acute phase reactants high-sensitive C-reactive protein and YKL-40 and of interleukin-6 before and after treatment in patients with acromegaly and growth hormone deficiency

BACKGROUND

Acromegaly is accompanied by increased cardiovascular mortality and a cluster of proatherogenic risk factors. In the general population, ischaemic heart disease (IHD) is associated with elevated levels of inflammatory markers. The acute phase reactant (APR) C-reactive protein (CRP) has been reported to be reduced in acromegaly and increase after treatment, suggesting that excess of GH/IGF-I could have anti-inflammatory effects. This is in accordance with results obtained in patients with growth hormone deficiency (GHD), where increased levels of CRP have been reported.

OBJECTIVE

To investigate the hypothesis that the GH/IGF-I system is a suppressive regulator of inflammatory processes.

SUBJECTS AND METHODS

Twenty-one acromegalic patients and 19 GH-deficient patients were studied. The two APRs CRP and YKL-40 and the proinflammatory cytokine interleukin-6 (IL-6) were measured before and after treatment and in healthy matched controls.

RESULTS

In acromegalic patients, serum concentrations of high-sensitive CRP (hsCRP) and YKL-40 were reduced compared to controls (P < 0.001) and increased (P < 0.001) after treatment, together with IL-6 (P = 0.021), to levels comparable with controls. Pretreatment serum YKL-40 and IL-6 showed a significant inverse correlation with IGF-I and GH. In GH-deficient patients, hsCRP and YKL-40 were elevated compared to controls (P = 0.001 and P = 0.048). During treatment, levels of both APRs showed a trend towards a decrease (P = 0.087 and P = 0.060), and after treatment, levels of YKL-40 no longer differed from that of controls. Serum IL-6 was not different from controls and did not change during GH treatment.

CONCLUSION

The results point to the possibility of a relationship between GH disturbances and inflammatory processes.

Bone morphogenetic protein 1 processes prolactin to a 17-kDa antiangiogenic factor

In addition to classical expression patterns in pituitary and placenta and functions in growth and reproduction, members of the small family of hormones that includes prolactin (PRL), growth hormone (GH), and placental lactogen are expressed by endothelia and have angiogenic effects. In contrast, 16- to 17-kDa proteolytic fragments of these hormones have antiangiogenic effects. Here we show that PRL and GH are bound and processed by members of the bone morphogenetic protein 1 (BMP1) subgroup of extracellular metalloproteinases, previously shown to play key roles in forming extracellular matrix and in activating certain TGFbeta superfamily members. BMP1 has previously been suggested to play roles in angiogenesis, as high throughput screens have found its mRNA to be one of those induced to highest levels in tumor-associated endothelia compared with resting endothelia. PRL and GH cleavage is shown to occur in each hormone at a single site typical of sites previously characterized in known substrates of BMP1-like proteinases, and the approximately 17-kDa PRL N-terminal fragment so produced is demonstrated to have potent antiangiogenic activity. Mouse embryo fibroblasts are shown to produce both PRL and GH and to process them to approximately 17-kDa forms, whereas GH and PRL processing activity is lost in mouse embryo fibroblasts doubly null for two genes encoding BMP1-like proteinases.

Systemic administration of IGF-I enhances healing in collagenous extracellular matrices: evaluation of loaded and unloaded ligaments

BACKGROUND

Insulin-like growth factor-I (IGF-I) plays a crucial role in wound healing and tissue repair. We tested the hypotheses that systemic administration of IGF-I, or growth hormone (GH), or both (GH+IGF-I) would improve healing in collagenous connective tissue, such as ligament. These hypotheses were examined in rats that were allowed unrestricted activity after injury and in animals that were subjected to hindlimb disuse. Male rats were assigned to three groups: ambulatory sham-control, ambulatory-healing, and hindlimb unloaded-healing. Ambulatory and hindlimb unloaded animals underwent surgical disruption of their knee medial collateral ligaments (MCLs), while sham surgeries were performed on control animals. Healing animals subcutaneously received systemic doses of either saline, GH, IGF-I, or GH+IGF-I. After 3 weeks, mechanical properties, cell and matrix morphology, and biochemical composition were examined in control and healing ligaments.

RESULTS

Tissues from ambulatory animals receiving only saline had significantly greater strength than tissue from saline receiving hindlimb unloaded animals. Addition of IGF-I significantly improved maximum force and ultimate stress in tissues from both ambulatory and hindlimb unloaded animals with significant increases in matrix organization and type-I collagen expression. Addition of GH alone did not have a significant effect on either group, while addition of GH+IGF-I significantly improved force, stress, and modulus values in MCLs from hindlimb unloaded animals. Force, stress, and modulus values in tissues from hindlimb unloaded animals receiving IGF-I or GH+IGF-I exceeded (or were equivalent to) values in tissues from ambulatory animals receiving only saline with greatly improved structural organization and significantly increased type-I collagen expression. Furthermore, levels of IGF-receptor were significantly increased in tissues from hindlimb unloaded animals treated with IGF-I.

CONCLUSION

These results support two of our hypotheses that systemic administration of IGF-I or GH+IGF-I improve healing in collagenous tissue. Systemic administration of IGF-I improves healing in collagenous extracellular matrices from loaded and unloaded tissues. Growth hormone alone did not result in any significant improvement contrary to our hypothesis, while GH + IGF-I produced remarkable improvement in hindlimb unloaded animals.

Neuroendocrine control of growth hormone in fish

The biological actions of growth hormone (GH) are pleiotropic, including growth promotion, energy mobilization, gonadal development, appetite, and social behavior. Accordingly, the regulatory network for GH is complex and includes many endocrine and environmental factors. In fish, the neuroendocrine control of GH is multifactorial with multiple inhibitors and stimulators of pituitary GH secretion. In fish, GH release is under a tonic negative control exerted mainly by somatostatin. Sex steroid hormones and nutritional status influence the level of brain expression and effectiveness of some of these GH neuroendocrine regulatory factors, suggesting that their relative importance differs under different physiological conditions. At the pituitary level, some, if not all, somatotropes can respond to multiple regulators. Therefore, ligand- and function-specificity, as well as the integrative responses to multiple signals must be achieved at the level of signal transduction mechanisms. Results from investigations on a limited number of stimulatory and inhibitory GH-release regulators indicate that activation of different but convergent intracellular pathways and the utilization of specific intracellular Ca(2+) stores are some of the strategies utilized. However, more work remains to be done in order to better understand the integrative mechanisms of signal transduction at the somatotrope level and the relevance of various GH regulators in different physiological circumstances.

Parenteral versus enteral nutrition: effect on serum cytokines and the hepatic expression of mRNA of suppressor of cytokine signaling proteins, insulin-like growth factor-1 and the growth hormone receptor in rodent sepsis

INTRODUCTION

Early nutrition is recommended for patients with sepsis, but data are conflicting regarding the optimum route of delivery. Enteral nutrition (EN), compared with parenteral nutrition (PN), results in poorer achievement of nutritional goals but may be associated with fewer infections. Mechanisms underlying differential effects of the feeding route on patient outcomes are not understood, but probably involve the immune system and the anabolic response to nutrients. We studied the effect of nutrition and the route of delivery of nutrition on cytokine profiles, the growth hormone-insulin-like growth factor-1 (IGF-I) axis and a potential mechanism for immune and anabolic system interaction, the suppressors of cytokine signaling (SOCS), in rodents with and without sepsis.

METHODS

Male Sprague-Dawley rats were randomized to laparotomy (Sham) or to cecal ligation and puncture (CLP), with postoperative saline infusion (Starve), with EN or with PN for 72 hours. Serum levels of IL-6 and IL-10 were measured by immunoassay, and hepatic expressions of cytokine-inducible SH2-containing protein, SOCS-2, SOCS-3, IGF-I and the growth hormone receptor (GHR) were measured by real-time quantitative PCR.

RESULTS

IL-6 was detectable in all groups, but was only present in all animals receiving CLP-PN. IL-10 was detectable in all but one CLP-PN rat, one CLP-EN rat, approximately 50% of the CLP-Starve rats and no sham-operated rats. Cytokine-inducible SH2-containing protein mRNA was increased in the CLP-EN group compared with the Sham-EN group and the other CLP groups (P < 0.05). SOCS-2 mRNA was decreased in CLP-PN rats compared with Sham-PN rats (P = 0.07). SOCS-3 mRNA was increased with CLP compared with sham operation (P < 0.03). IGF-I mRNA (P < 0.05) and GHR mRNA (P < 0.03) were greater in the fed CLP animals and in the Sham-PN group compared with the starved rats.

CONCLUSION

In established sepsis, nutrition and the route of administration of nutrition influences the circulating cytokine patterns and expression of mRNA of SOCS proteins, GHR and IGF-I. The choice of the administration route of nutrition may influence cellular mechanisms that govern the response to hormones and mediators, which further influence the response to nutrients. These findings may be important in the design and analysis of clinical trials of nutritional interventions in sepsis in man.

Retinal ganglion cell survival in development: mechanisms of retinal growth hormone action

Several variants of growth hormone (GH) are found in the retina and vitreous of the chick embryo, where they appear to act as cell survival factors, having neuroprotective effects on retinal ganglion cells (RGCs). Here, we investigate the molecular mechanisms of the anti-apoptotic effect of GH in cultured RGCs. GH treatment increased Akt phosphorylation in these cells, which is an anti-apoptotic event. Whereas unphosphorylated Akt was detected in both nucleus and cytoplasm of RGCs by immunocytochemistry, the phosphorylated form of Akt (Akt-phos) was located primarily in the cytoplasm of both normal and apoptotic cells, although levels were markedly lower in the latter. It was found that GH treatment of RGCs reduced Akt levels, while concomitantly raising Akt-phos levels, consistent with a role for Akt signaling pathways in GH neuroprotective action. This was substantiated using Wortmannin, which, like GH antiserum, inhibited Akt phosphorylation and initiated apoptosis. The addition of Wortmannin to RGC cultures simultaneously with GH significantly reduced the anti-apoptotic effect of GH. The induction of apoptosis by GH antiserum was clearly accompanied by an increase in caspase-3 activation and PARP-1 cleavage, both of which were significantly reduced in the presence of the broad spectrum caspase inhibitor, Q-VD-OPh, which itself had a dramatic neuroprotective effect on cultured RGCs. Calpain activation appeared to be a major caspase-independent pathway to PARP-1 cleavage and apoptosis in these cells. Calpain inhibitor III (MDL 28170) was able to reduce PARP-1 cleavage and abrogate the apoptogenic effect of GH antiserum. The results support the view that caspase and calpain inhibitors are major neuroprotective agents for RGCs, and that pathways that activate both caspases and calpains are important for the anti-apoptotic actions of GH in these cells.

Retinal growth hormone is an anti-apoptotic factor in embryonic retinal ganglion cell differentiation

Cells of the neural retina in the chick embryo undergo several waves of apoptosis during development, including peaks at approximately embryonic day (ED) 7 and 12. Prominent among the cells involved in these phases of cell death are the retinal ganglion cells (RGCs). We have previously shown that growth hormone (GH) is expressed in the neural retina, and particularly, in the RGCs. Here we study the ability of GH to rescue retinal cells from apoptosis, both in vitro and in vivo. When retinas from embryos at ED 6-8 are explanted on collagen gels, the application of recombinant GH, at 10(-6)m, significantly reduced the incidence of apoptotic cells in the cultures as judged by terminal deoxynucleotide transferase-mediated dUTP-biotin nick end labelling (TUNEL). GH was delivered to neural retinas in ovo, by microinjection into the eye cup at ED 2. When these embryos were examined at ED 6-8, no reduction in cell death was observed below the normal low control levels. However, when antibodies to GH were microinjected, the incidence of cell death increased significantly at ED 6, providing evidence that in vivo immunoneutralization of endogenous GH results in triggering of apoptotic signaling pathways. Evidence that RGCs are a particular target of this neuroprotective effect of GH was provided by examination of cultures enriched for RGCs by immunopanning. In serum-free culture, RGCs, identified by anti-Islet 1 immunolabelling, were found to be susceptible to the effect of GH immunoneutralization, which approximately quadrupled the incidence of apoptosis in the cultures. We propose that GH is a naturally occurring autocrine and/or paracrine neuroprotective agent in the developing retina which is involved in the regulation of retinal cell numbers during early embryogenesis.

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.

Differential regulation of suppressor of cytokine signaling-3 in the liver and adipose tissue of the sheep fetus in late gestation

It is unknown whether the JAK/STAT/suppressor of cytokine signaling-3 (SOCS-3) intracellular signaling pathway plays a role in tissue growth and metabolism during fetal life. We investigated whether there is a differential profile of SOCS-3 expression in the liver and perirenal adipose tissue during the period of increased fetal growth in late gestation and the impact of fetal growth restriction on SOCS-3 expression in the fetal liver. We also determined whether basal SOCS-3 expression in the fetal liver and perirenal adipose tissue is regulated by endogenous fetal prolactin (PRL). SOCS-3 mRNA abundance was higher in the liver than in the pancreas, spleen, and kidney of the sheep fetus during late gestation. In the liver, SOCS-3 mRNA expression was increased (P < 0.05) between 125 (n = 4) and 145 days (n = 7) gestation and lower (P < 0.05) in growth-restricted compared with normally grown fetal sheep in late gestation. The relative expression of SOCS-3 mRNA in the fetal liver was directly related to the mean plasma PRL concentrations during a 48-h infusion of either a dopaminergic agonist, bromocriptine (n = 7), or saline (n = 5), such that SOCS-3 mRNA expression was lower when plasma PRL concentrations decreased below approximately 20 ng/ml [y = 0.99 - (2.47/x) + (4.96/x(2)); r(2) = 0.91, P < 0.0001, n = 12]. No relationship was shown between the abundance of phospho-STAT5 in the fetal liver and circulating PRL. SOCS-3 expression in perirenal adipose tissue decreased (P < 0001) between 90-91 (n = 6) and 140-145 days (n = 9) gestation and was not related to endogenous PRL concentrations. Thus SOCS-3 is differentially expressed and regulated in key fetal tissues and may play an important and tissue-specific role in the regulation of cellular proliferation and differentiation before birth.

Growth hormone expression in the perinatal and postnatal rat lung

It is now established that the lung is a target site for pituitary growth hormone (GH) action, because pathophysiological states of pituitary GH excess and deficiency are associated with impaired pulmonary function. The onset of lung development and differentiation is, however, before the ontogenic differentiation of pituitary somatotrophs. GH may be involved, nevertheless, in lung development, because it is present in extrapituitary tissues of preimplantation mouse embryos and in the lung buds of embryonic chickens. The possibility that GH may be expressed in the rat lung during fetal and neonatal development, therefore, has been assessed. GH mRNA was detected in the lung, and its 693-bp sequence was identical to that in the pituitary gland. By in situ hybridization, this transcript was found to be abundantly expressed in the lungs of embryonic day (ED) 17 rats in mesenchymal, mucosal epithelial, and smooth muscle cells. This transcript was expressed in neonates until at least day 14 postnatally and was localized to type I and II epithelial cells and to pulmonary tissue macrophages and alveolar macrophages. GH immunoreactivity paralleled GH mRNA cellular localization throughout the time course studied. This immunoreactivity was specific and was lost after antibody preabsorption. The perinatal and postnatal lung is, therefore, an extrapituitary site of GH gene expression during development. Given that the GH receptor is present in the lung from early development, lung GH may have autocrine and/or paracrine roles in lung growth or differentiation or in pulmonary function.

Growth hormone and connective tissue in exercise

Over the last few years, growth hormone (GH) has become increasingly popular as doping within different sports. However, the precise mechanisms behind the ergogenic (performance enhancing) effects of GH in athletes are still being debated. Besides a well-documented stimulatory effect of GH on carbohydrate and fatty acid metabolism, and a possible anabolic effect on myofibrillar muscle protein, we suggest a role for GH as an anabolic agent in connective tissue in human skeletal muscle and tendon. Given the importance of the connective tissue for the function of skeletal muscle and tendon, a strengthening effect of GH on connective tissue could fit with the ergogenic effect of GH experienced by athletes. This review examines the endogenous secretion of GH and its mediators in relation to exercise. Furthermore, we consider the effect of endogenous GH and administered recombinant human GH (rhGH) on both myofibrillar and connective tissue protein synthesis, thus offering an alternative explanation for the ergogenic effect of GH. Finally, we suggest a possible therapeutic role for rhGH in clinical management of the frequently suffered injuries in the connective tissue.

Expression of growth hormone and its receptor in the lungs of embryonic chicks

The lung is well established as being a postnatal target site for growth hormone (GH) action, since pathophysiological states of GH excess and deficiency are both associated with impaired pulmonary function. Pituitary GH is therefore probably involved in normal lung growth or development, although perinatal lung development occurs prior to the differentiation of pituitary somatotrophs and the ontogeny of pituitary GH secretion. The lung itself may, however, be a site of GH production during prenatal development, since a specific GH-response gene (a marker of GH activity) is expressed in the lungs of early chick embryos, in which GH immunoreactivity is widespread in many other peripheral tissues. We have assessed this possibility in embryonic chicks. A 690-bp cDNA, identical in size and nucleotide sequence to the full-length pituitary GH transcript, was amplified by reverse transcription/polymerase chain reaction from total RNA extracted from the lungs of embryos at 11, 13, 15, and 18 days of the 21-day incubation period. This transcript was localized by in situ hybridization to mesenchymal and epithelial cells of the developing lungs, in which specific GH immunoreactivity was similarly located. Intense GH immunoreactivity was also present after embryonic day 15 (ED15) in the smooth muscle surrounding blood vessels in the lung and surrounding the bronchioles. Lung GH immunoreactivity was primarily associated with a 15-kDa protein, rather than the 26-kDa protein in the pituitary gland. After the onset of pituitary GH secretion (at ED17), GH mRNA was barely detectable in the lungs of ED20 embryos, at the start of lung breathing. GH immunoreactivity was, however, still present in some cells in the lungs of ED20 embryos. GH-receptor mRNA and immunoreactivity were also widespread and abundant within the embryonic lung. Lung GH may thus have autocrine or paracrine roles in lung development or in pulmonary function prior to the ontogeny of the pituitary gland and the appearance of GH in peripheral plasma.

Growth hormone as an early embryonic growth and differentiation factor

In this review we consider the evidence that growth hormone (GH) acts in the embryo as a local growth, differentiation, and cell survival factor. Because both GH and its receptors are present in the early embryo before the functional differentiation of pituitary somatotrophs and before the establishment of a functioning circulatory system, the conditions are such that GH may be a member of the large battery of autocrine/paracrine growth factors that control embryonic development. It has been clearly established that GH is able to exert direct effects, independent of insulin-like growth factor-I (IGF-I), on the differentiation, proliferation, and survival of cells in a wide variety of tissues in the embryo, fetus, and adult. The signaling pathways behind these effects of GH are now beginning to be determined, establishing early extrapituitary GH as a bona fide developmental growth factor.

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.

Development of a baculovirus-based fluorescence resonance energy transfer assay for measuring protein-protein interaction

A new baculovirus-based fluorescence resonance energy transfer (Bv-FRET) assay for measuring multimerization of cell surface molecules in living cells is described. It has been demonstrated that gonadotropin-releasing hormone receptor (GnRH-R) was capable of forming oligomeric complexes in the plasma membrane under normal physiological conditions. The mouse gonadotropin-releasing hormone receptor GnRH-R was used to evaluate the efficiency and potential applications of this assay. Two chimeric constructs of GnRH-R were made, one with green fluorescent protein as a donor fluorophore and the other with enhanced yellow fluorescent protein as an acceptor fluorophore. These chimeric constructs were coexpressed in an insect cell line (BTI Tn5 B1-4) using recombinant baculoviruses. Energy transfer occurred from the excited donor to the acceptor when they were in close proximity. The association of GnRH-R was demonstrated through FRET and the fluorescence observed using a Leica TSC-SPII confocal microscope. FRET was enhanced by the addition of a GnRH agonist but not by an antagonist. The Bv-FRET assay constitutes a highly efficient, reliable and convenient method for measuring protein-protein interaction as the baculovirus expression system is superior to other transfection-based methods. Additionally, the same insect cell line can be used routinely for expressing any recombinant proteins of interest, allowing various combinations of molecules to be tested in a rapid fashion for protein-protein interactions. The assay is a valuable tool not only for the screening of new molecules that interact with known bait molecules, but also for confirming interactions between other known molecules.

Growth hormone prevents human immunodeficiency virus-induced neuronal p53 expression

Growth hormone (GH) is neuroprotective, presumably through its actions on GH receptor-mediated pathways. Here, we examined the effects of GH using in vitro and in vivo assays of human immunodeficiency virus (HIV)-induced neuronal injury. Neuronal cultures were in assays of neurotoxicity induced by supernatants from HIV-1 tat-transfected monocytoid cells (Tat supernatant). GH treatment reduced neuronal death compared with untreated cultures (p < 0.001), which was blocked by a GH receptor antagonist, B2036. Tat supernatant-induced p53 expression in neurons was also reduced by GH treatment. Expression of both p53 and GH receptor were increased in brain tissue from HIV-infected persons compared with controls (p < 0.05). Mice receiving intrastriatal implants of Tat supernatant and treated with GH showed less neurobehavioral abnormalities together with reduced neuroinflammation and neuronal injury compared with untreated animals (p < 0.01). Three acquired immunodeficiency syndrome-defined patients with neurocognitive impairment were serially evaluated during daily GH treatment showing a sustained improvement in neuropsychological performance (p < 0.01). GH prevents neuronal death through its actions on neurons involving a p53-mediated pathway and also improved in vivo neurological function, indicating that GH may have a role in the treatment of HIV-induced neurodegeneration.

Growth hormone-induced diacylglycerol and ceramide formation via Galpha i3 and Gbeta gamma in GH4 pituitary cells. Potentiation by dopamine-D2 receptor activation

Growth hormone (GH) secretion is regulated by indirect negative feedback mechanisms. To address whether GH has direct actions on pituitary cells, lipid signaling in GH(4)ZR(7) somatomammotroph cells was examined. GH (EC(50) = 5 nm) stimulated diacylglycerol (DAG) and ceramide formation in parallel by over 10-fold within 15 min and persisting for >3 h. GH-induced DAG/ceramide formation was blocked by pertussis toxin (PTX) implicating G(i)/G(o) proteins and was potentiated 1.5-fold by activation of G(i)/G(o)-coupled dopamine-D2S receptors, which had no effect alone. Following PTX pretreatment, only PTX-resistant Galpha(i)3, not Galpha(o) or Galpha(i)2, rescued GH-induced DAG/ceramide signaling. GH-induced DAG/ceramide formation was also blocked in cells expressing Gbetagamma blocker GRK-ct. In GH(4)ZR(7) cells, GH induced phosphorylation of JAK2 and STAT5, which was blocked by PTX and mimicked by ceramide analogue C2-ceramide or sphingomyelinase treatment to increase endogenous ceramide. We conclude that in GH(4) pituitary cells, GH induces formation of DAG/ceramide via a novel Galpha(i)3/Gbetagamma-dependent pathway. This novel pathway suggests a mechanism for autocrine feedback regulation by GH of pituitary function.

Growth hormone is permissive for skeletal adaptation to mechanical loading

The Lewis dwarf (DW) rat was used as a model to test the hypothesis that growth hormone (GH) is permissive for new bone formation induced by mechanical loading in vivo. Adult female Lewis DW rats aged 6.2 +/- 0.1 months (187 +/- 18 g) were allocated to four vehicle groups (DW), four GH treatment groups at 32.5 microg/100 g body mass (DWGH1), and four GH treatment groups at 65 microg/100 g (DWGH2). Saline vehicle or GH was injected intraperitoneally (ip) at 6:30 p.m. and 6:30 a.m. before mechanical loading of tibias at 7:30 a.m. A single period of 300 cycles of four-point bending was applied to right tibias at 2.0 Hz, and magnitudes of 24, 29, 38, or 48N were applied. Separate strain gauge analyses in 5 DW rats validated the selection of loading magnitudes. After loading, double-label histomorphometry was used to assess bone formation at the periosteal surface (Ps.S) and endocortical surface (Ec.S) of tibias. Comparing left (unloaded) tibias among groups, GH treatment had no effect on bone formation. Bone formation in tibias in DW rats was insensitive to mechanical loading. At the Ec.S, mechanically induced lamellar bone formation increased in the DWGH2 group loaded at 48N (p < 0.05), and no significant increases in bone formation were observed among other groups. The percentage of tibias expressing woven bone formation (Wo.B) at the Ps.S was significantly greater in the DWGH groups compared with controls (p < 0.05). We concluded that GH influences loading-related bone formation in a permissive manner and modulates the responsiveness of bone tissue to mechanical stimuli by changing thresholds for bone formation.

Effects of growth hormone on female reproductive organs

During the last decade many experiments have been performed to study the effects of growth hormone (GH, somatotropin) on reproductive functions. Most of the studies found only slight or no effects of GH treatment, both on the oestrous cycle and on gonadotropin, progesterone. or oestrogen serum levels. In GH-treated animals, elevated levels of insulin-like growth factor I and GH in the serum could be correlated with an increased number of small (< 5 mm in diameter) ovarian follicles, possibly as a consequence of a reduction of apoptosis and follicular atresia. There is still controversy over the effects of GH on in vivo and in vitro embryo production and on the gestation period. Recent studies produced some evidence that GH-receptor is expressed in ovarian tissue, implying a direct role for GH in the ovary.

Control of growth by the somatropic axis: growth hormone and the insulin-like growth factors have related and independent roles

The traditionally accepted theory has been that most of the biological effects of growth hormone (GH) are mediated by circulating (endocrine) insulin-like growth factor-I (IGF-I). This dogma was modified when it was discovered that most tissues express IGF-I that can act via an autocrine/paracrine fashion. In addition, both GH and IGF-I had independent effects on various target tissues. Using tissue-specific gene deletion of IGF-I in the liver, it has been shown that circulating IGF-I is predominantly liver-derived but is not essential for normal postnatal growth. Therefore, it is proposed that non-hepatic tissue-derived IGF-I may be sufficient for growth and development. Thus the original somatomedin hypothesis has undergone further modifications.

The somatomedin hypothesis: 2001

Since the original somatomedin hypothesis was conceived, a number of important discoveries have allowed investigators to modify the concept. Originally somatic growth was thought to be controlled by pituitary GH and mediated by circulating insulin-like growth factor-I (IGF-I, somatomedin C) expressed exclusively by the liver. With the discovery that IGF-I is produced by most, if not all, tissues, the role of autocrine/paracrine IGF-I vs. the circulating form has been hotly debated. Recent experiments using transgenic and gene-deletion technologies have attempted to answer these questions. In the liverspecific igf-1 gene-deleted mouse model, postnatal growth and development are normal despite the marked reduction in circulating IGF-I and IGF-binding protein levels; free IGF-I levels are normal. Thus, the normal postnatal growth and development in these animals may be due to normal free IGF-I levels (from as yet unidentified sources), although the role of autocrine/paracrine IGF-I has yet to be determined.