Growth hormone signalling and its regulation: preventing too much of a good thing

Candidate genes for marker-assisted selection for growth, carcass and meat quality traits in rabbits

Growth and meat production are the most relevant targets for animal breeders, there are strong relationships between animal growth regulation, body composition and meat quality. Therefore, it is essential to identify the genetic factors that are controlling growth, carcass, and meat quality traits and to explore the correlations between identified genes of those traits. Identification of candidate genes may shift rabbit breeding from classical to modern approaches, which offer great potential to accelerate genetic improvement plans, especially in developing countries. The current work reviews several genes and mutations affecting growth, carcass and meat quality traits. These candidate genes and mutations can be incorporated into MAS programs to improve rabbit breeds especially local breeds, provided that a reasonable proportion of trait additive genetic variance is explained by the significant marker. Furthermore, we highlighted the indispensable need for more researches investigating candidate genes for different traits.

Integrated bioinformatical analysis, machine learning and in vitro experiment-identified m6A subtype, and predictive drug target signatures for diagnosing renal fibrosis

Renal biopsy is the gold standard for defining renal fibrosis which causes calcium deposits in the kidneys. Persistent calcium deposition leads to kidney inflammation, cell necrosis, and is related to serious kidney diseases. However, it is invasive and involves the risk of complications such as bleeding, especially in patients with end-stage renal diseases. Therefore, it is necessary to identify specific diagnostic biomarkers for renal fibrosis. This study aimed to develop a predictive drug target signature to diagnose renal fibrosis based on m6A subtypes. We then performed an unsupervised consensus clustering analysis to identify three different m6A subtypes of renal fibrosis based on the expressions of 21 m6A regulators. We evaluated the immune infiltration characteristics and expression of canonical immune checkpoints and immune-related genes with distinct m6A modification patterns. Subsequently, we performed the WGCNA analysis using the expression data of 1,611 drug targets to identify 474 genes associated with the m6A modification. 92 overlapping drug targets between WGCNA and DEGs (renal fibrosis vs. normal samples) were defined as key drug targets. A five target gene predictive model was developed through the combination of LASSO regression and stepwise logistic regression (LASSO-SLR) to diagnose renal fibrosis. We further performed drug sensitivity analysis and extracellular matrix analysis on model genes. The ROC curve showed that the risk score (AUC = 0.863) performed well in diagnosing renal fibrosis in the training dataset. In addition, the external validation dataset further confirmed the outstanding predictive performance of the risk score (AUC = 0.755). These results indicate that the risk model has an excellent predictive performance for diagnosing the disease. Furthermore, our results show that this 5-target gene model is significantly associated with many drugs and extracellular matrix activities. Finally, the expression levels of both predictive signature genes EGR1 and PLA2G4A were validated in renal fibrosis and adjacent normal tissues by using qRT-PCR and Western blot method.

Association analysis of nucleotide polymorphisms in growth hormone (GH) and its receptor (GHR) with body weight in Californian rabbits

The objective of the present study was to evaluate the influence of the genotypes of two single nucleotide polymorphisms (SNPs) – c.78C>T located in the growth hormone gene (GH) and c.106C>G in the growth hormone receptor gene (GHR) on individual body weight (IBW) during the growing period at 35, 70 and 90 d of age on a total of 107 weaned Californian breed rabbits. The restriction fragments obtained revealed that 74.8% of the rabbits carrying c.78C>T SNP and 52.3% of the rabbits carrying c.106C>G SNP were heterozygous, which indicated a moderate level of genetic diversity in this Californian population. Association analysis based on a single-gene approach revealed that c.78C>T polymorphism in the GH gene had a significant effect (P<0.05) on the weight at 70 and 90 d of age. The highest IBW (2530.4±66.6 g) was observed in rabbits carrying the c.78C>T TT genotype, and detected individuals were significantly affected by the dominance effect. Significant differences were observed between individuals with homozygous c.106C>G CC genotype and those with heterozygous CG genotype. The highest IBW (2462.0±198.3 g) was observed in rabbits carrying the c.106C>G CC genotype and detected individuals were significantly affected by the additive effect. A total of nine combined genotypes of c.78C>T and c.106C>G SNPs was found in the study, of which only four major groups (CT/CC, CC/CG, CT/CG, and CT/GG) were concerned in the diplotype analysis. Significant differences were observed between individuals with CT/CC and CC/CG genotype combinations, and between those with the CC/CG and CT/GG diplotypes. However, the highest IBW at 90 d of age (2447.2±213.8 g) was observed in rabbits carrying the CT/CC genotype combinations. The highest coefficient of determination found for individual body weight at 90 d of age (R2=10.8%) indicated a high effect of genotype combinations. In conclusion, the results obtained suggested that c.78C>T of GH gene and c.106C>G of GHR gene could be useful candidate genes to improve growth performance in Californian rabbits with potential application in rabbit breeding programmes.

GHR signalling: Receptor activation and degradation mechanisms

Growth hormone (GH) actions via initiating cell signalling through the GH receptor (GHR) are important for many physiological processes, in addition to its well-known role in regulating growth. The activation of JAK-STAT signalling by GH is well characterized, however knowledge on GH activation of SRC family kinases (SFKs) is still limited. In this review we summarise the collective knowledge on the activation, regulation, and downstream signalling of GHR. We highlight studies on GH activation of SFKs and the important outcome of this signalling pathway with a focus on the different degradation mechanisms that can regulate GHR availability since this is an area that warrants further study considering its role in tumour progression.

Growth Hormone Receptor Regulation in Cancer and Chronic Diseases

The GHR signaling pathway plays important roles in growth, metabolism, cell cycle control, immunity, homeostatic processes, and chemoresistance via both the JAK/STAT and the SRC pathways. Dysregulation of GHR signaling is associated with various diseases and chronic conditions such as acromegaly, cancer, aging, metabolic disease, fibroses, inflammation and autoimmunity. Numerous studies entailing the GHR signaling pathway have been conducted for various cancers. Diverse factors mediate the up- or down-regulation of GHR signaling through post-translational modifications. Of the numerous modifications, ubiquitination and deubiquitination are prominent events. Ubiquitination by E3 ligase attaches ubiquitins to target proteins and induces proteasomal degradation or starts the sequence of events that leads to endocytosis and lysosomal degradation. In this review, we discuss the role of first line effectors that act directly on the GHR at the cell surface including ADAM17, JAK2, SRC family member Lyn, Ubc13/CHIP, proteasome, βTrCP, CK2, STAT5b, and SOCS2. Activity of all, except JAK2, Lyn and STAT5b, counteract GHR signaling. Loss of their function increases the GH-induced signaling in favor of aging and certain chronic diseases, exemplified by increased lung cancer risk in case of a mutation in the SOCS2-GHR interaction site. Insight in their roles in GHR signaling can be applied for cancer and other therapeutic strategies.

Investigation of soluble anti-Müllerian hormone receptor type 2 as a biomarker for diagnosis of female fertility disorders

RESEARCH QUESTION

The ectodomain of the anti-Müllerian hormone (AMH) type 2 receptor is shed by proteases under certain conditions, which makes it measurable in the blood. The aim of this study was to identify correlations of soluble anti-Müllerian hormone receptor type 2 (sAMHR2) with other sex hormone concentrations and to assess whether sAMHR2 may serve as a new biomarker in fertility disorders.

DESIGN

In a retrospective cross-sectional study of women (n = 186) with different gynaecological-endocrinological disorders, mixed-effect models were used to analyse the correlation with established diagnostic hormone tests. Receiver operating characteristic curve analysis was performed to assess the diagnostic performance.

RESULTS

There was a strong correlation of sAMHR2 with LH (r = 0.898) and FSH (r = 0.846) and a moderate correlation of AMH with testosterone (r = 0.666) and androstenedione (r = 0.696) (all P < 0.001). In diagnoses of polycystic ovary syndrome (PCOS), AMH showed the best performance (area under the curve [AUC] 0.981, cut-off 4 ng/ml) with 96% sensitivity and 94% specificity. sAMHR2 concentrations and sAMHR2/AMH ratios were elevated in women with ovarian insufficiency, compared with all other study groups, including post-menopausal women on hormone replacement therapy. Highest sensitivity and specificity (100% and 98.2%, respectively) were achieved with sAMHR2/AMH ratio for the diagnosis of post-menopausal status (cut-off 68.85). The sAMHR2/AMH ratio (AUC 0.997) had a better performance than sAMHR2 (AUC 0.947), FSH (AUC 0.989) and LH (AUC 0.967).

CONCLUSIONS

The sAMHR2/AMH ratio may serve as a useful biomarker for infertility diagnostics to identify post-menopausal women.

Two indel variants of prolactin receptor (PRLR) gene are associated with growth traits in goat

Prolactin receptor (PRLR) gene plays a crucial role in the milk production, reproduction and the growth of mammals. To fully characterize the structure of the mutation and to further study the function of the goat PRLR gene, two insertion/deletion (indel) loci (12 bp; 16-bp; 5-bp) were detected in 1038 Shaanbei white cashmere (SBWC) goats. Associated analysis revealed that the 16-bp indel mutation was significantly associated the body length, body height, chest depth (CD), body length index (BLI), heart girth index and cannon circumference index (CCI) (p < 0.05). The polymorphism of 5-bp indel was significantly associated with CD, heart girth, CCI and BLI (p < 0.05). Overall, individuals with genotype DD showed better phenotypic traits than individuals with other genotypes at the two loci of PRLR gene in SBWC goat. These findings suggested that the two novel indels within the caprine PRLR gene could be considered as effective DNA molecular markers and could provide a valuable theoretical basis for the application of marker-assisted selection in the goat industry.

A useful model to compare human and mouse growth hormone gene chromosomal structure, expression and regulation, and immune tolerance of human growth hormone analogues

Human (h) pituitary growth hormone (GH) is both physiologically and clinically important. GH reaches its highest circulatory levels in puberty, where it contributes to energy homeostasis and somatogenic growth. GH also helps to maintain tissues and organs and, thus, health and homeostasis. A reduction in the rate of hGH production begins in middle age but if GH insufficiency occurs this may result in tissue degenerative and metabolic diseases. As a consequence, hGH is prescribed under conditions of GH deficiency and, because of its lipolytic activity, stimulation of hGH release has also been used to treat obesity. However, studies of normal GH production and particularly synthesis versus secretion are not feasible in humans as they require sampling normal pituitaries from living subjects. Furthermore, human (or primate) GH structure and, as such, regulation and potential function, is distinct from non-primate rodent GH. As a result, most information about hGH regulation comes from measurements of secreted levels of GH in humans. Thus, partially humanized hGH transgenic mice, generated containing fragments of human chromosome 17 that include the intact hGH gene locus and many thousands of flanking base pairs as well as the endogenous mouse (m) GH gene provide a potentially useful model. Here we review this mouse model in terms of its ability to allow comparison of hGH versus mGH gene expression, and specifically: (i) GH locus structure as well as regulated and rhythmic expression; (ii) their ability to model a clinical assessment of hGH production in response to overeating and hyperinsulinemia as well as a possible effect of exercise, and (iii) their hGH-related immune tolerance and thus potential for testing hGH-related analogue immunogenicity.

Association of growth hormone gene receptor polymorphism with production traits in Jamunapari goat

Genetic polymorphism for GHR gene was carried out in Jamunapari kids by Polymerase Chain Reaction- Restriction Fragment Length Polymorphism (PCR-RFLP). Blood samples were collected from 200 kids for isolation of genomic DNA. The exon 1A (210 bp fragment), exon 10 (342 bp fragment) and 5’ non-coding region (318 bp fragment) of GHR gene were amplified and digested with MspI, AluI and NsiI restriction endonuclease, respectively. PCR-RFLP analysis for 5’ non-coding region revealed monomorphic pattern while exon 1A and exon 10 of GHR were polymorphic. The frequency of A and T alleles was 0.54 and 0.46, respectively, and frequency of three genotypes (AA, AT and TT) was 0.17, 0.74 and 0.09, respectively at locus exon 1A of GHR. The frequency of A and G allele for exon 10 was 0.53 and 0.47, and frequency of three genotypes (AA, AG and GG) was 0.16, 0.74 and 0.10, respectively. The genotype AG was associated with higher body weights at different growth stages. The goats with AG genotype were heavier to AA and GG genotypes by 4.91 and 42.85% at birth; 8.59 and 13.30% at 6 months; 8.02 and 17.25% at 9 months and 7.11 and 16.11% at 12 months, respectively. The locus was also a significant source of variation for biometrical traits (body weight, body length, heart girth) at different ages. AG genotype could be used as marker in selection for higher body weights in Jamunapari goats.

Activation of Nrf2 in the liver is associated with stress resistance mediated by suppression of the growth hormone-regulated STAT5b transcription factor

The transcription factor Nrf2 (encoded by Nfe2l2) induces expression of numerous detoxifying and antioxidant genes in response to oxidative stress. The cytoplasmic protein Keap1 interacts with and represses Nrf2 function. Computational approaches were developed to identify factors that modulate Nrf2 in a mouse liver gene expression compendium. Forty-eight Nrf2 biomarker genes were identified using profiles from the livers of mice in which Nrf2 was activated genetically in Keap1-null mice or chemically by a potent activator of Nrf2 signaling. The rank-based Running Fisher statistical test was used to determine the correlation between the Nrf2 biomarker genes and a test set of 81 profiles with known Nrf2 activation status demonstrating a balanced accuracy of 96%. For a large number of factors examined in the compendium, we found consistent relationships between activation of Nrf2 and feminization of the liver transcriptome through suppression of the male-specific growth hormone (GH)-regulated transcription factor STAT5b. The livers of female mice exhibited higher Nrf2 activation than male mice in untreated or chemical-treated conditions. In male mice, Nrf2 was activated by treatment with ethinyl estradiol, whereas in female mice, Nrf2 was suppressed by treatment with testosterone. Nrf2 was activated in 5 models of disrupted GH signaling containing mutations in Pit1, Prop1, Ghrh, Ghrhr, and Ghr. Out of 59 chemical treatments that activated Nrf2, 36 exhibited STAT5b suppression in the male liver. The Nrf2-STAT5b coupling was absent in in vitro comparisons of chemical treatments. Treatment of male and female mice with 11 chemicals that induce oxidative stress led to activation of Nrf2 to greater extents in females than males. The enhanced basal and inducible levels of Nrf2 activation in females relative to males provides a molecular explanation for the greater resistance often seen in females vs. males to age-dependent diseases and chemical-induced toxicity.

Disruption of STAT5b-Regulated Sexual Dimorphism of the Liver Transcriptome by Diverse Factors Is a Common Event

Signal transducer and activator of transcription 5b (STAT5b) is a growth hormone (GH)-activated transcription factor and a master regulator of sexually dimorphic gene expression in the liver. Disruption of the GH hypothalamo-pituitary-liver axis controlling STAT5b activation can lead to metabolic dysregulation, steatosis, and liver cancer. Computational approaches were developed to identify factors that disrupt STAT5b function in a mouse liver gene expression compendium. A biomarker comprised of 144 STAT5b-dependent genes was derived using comparisons between wild-type male and wild-type female mice and between STAT5b-null and wild-type mice. Correlations between the STAT5b biomarker gene set and a test set comprised of expression datasets (biosets) with known effects on STAT5b function were evaluated using a rank-based test (the Running Fisher algorithm). Using a similarity p-value ≤ 10⁻⁴, the test achieved a balanced accuracy of 99% and 97% for detection of STAT5b activation or STAT5b suppression, respectively. The STAT5b biomarker gene set was then used to identify factors that activate (masculinize) or suppress (feminize) STAT5b function in an annotated mouse liver and primary hepatocyte gene expression compendium of ~1,850 datasets. Disruption of GH-regulated STAT5b is a common phenomenon in liver in vivo, with 5% and 29% of the male datasets, and 11% and 13% of the female datasets, associated with masculinization or feminization, respectively. As expected, liver STAT5b activation/masculinization occurred at puberty and suppression/feminization occurred during aging and in mutant mice with defects in GH signaling. A total of 70 genes were identified that have effects on STAT5b activation in genetic models in which the gene was inactivated or overexpressed. Other factors that affected liver STAT5b function were shown to include fasting, caloric restriction and infections. Together, these findings identify diverse factors that perturb the hypothalamo-pituitary-liver GH axis and disrupt GH-dependent STAT5b activation in mouse liver.

Chemical and Hormonal Effects on STAT5b-Dependent Sexual Dimorphism of the Liver Transcriptome

The growth hormone (GH)-activated transcription factor signal transducer and activator of transcription 5b (STAT5b) is a key regulator of sexually dimorphic gene expression in the liver. Suppression of hepatic STAT5b signaling is associated with lipid metabolic dysfunction leading to steatosis and liver cancer. In the companion publication, a STAT5b biomarker gene set was identified and used in a rank-based test to predict both increases and decreases in liver STAT5b activation status/function with high (≥ 97%) accuracy. Here, this computational approach was used to identify chemicals and hormones that activate (masculinize) or suppress (feminize) STAT5b function in a large, annotated mouse liver and primary hepatocyte gene expression compendium. Exposure to dihydrotestosterone and thyroid hormone caused liver masculinization, whereas glucocorticoids, fibroblast growth factor 15, and angiotensin II caused liver feminization. In mouse models of diabetes and obesity, liver feminization was consistently observed and was at least partially reversed by leptin or resveratrol exposure. Chemical-induced feminization of male mouse liver gene expression profiles was a relatively frequent phenomenon: of 156 gene expression biosets from chemically-treated male mice, 29% showed feminization of liver STAT5b function, while <1% showed masculinization. Most (93%) of the biosets that exhibited feminization of male liver were also associated with activation of one or more xenobiotic-responsive receptors, most commonly constitutive activated receptor (CAR) or peroxisome proliferator-activated receptor alpha (PPARα). Feminization was consistently associated with increased expression of peroxisome proliferator-activated receptor gamma (Pparg) but not other lipogenic transcription factors linked to steatosis. GH-activated STAT5b signaling in mouse liver is thus commonly altered by diverse chemicals, and provides a linkage between chemical exposure and dysregulated gene expression associated with adverse effects on the liver.

Growth hormone binding protein - physiological and analytical aspects

A significant proportion of total circulating growth hormone (GH) is bound to a high affinity growth hormone binding protein (GHBP). Several low affinity binding proteins have also been described. Significant differences between species exist with respect to origin and regulation of GHBP, but generally it resembles the extracellular domain of the GH receptor. Concentrations are associated with GH status, body composition and other factors. Although the clinical relevance of GHBP is not fully understood it is suggested that concentrations indirectly reflect GH receptor status. This is supported by cases of Laron's syndrome where a molecular defect in the extracellular domain of the GH receptor is associated with low or unmeasurable GHBP concentrations. Methods to measure GHBP have evolved from chromatographic, activity based procedures to direct immunoassays. In clinical practice, measurement of GHBP can be helpful to differentiate between GH deficiency and GH insensitivity, particularly if GHBP is absent.

Maintenance of homeostasis in the aging hypothalamus: the central and peripheral roles of succinate

Aging is the phenotype resulting from accumulation of genetic, cellular, and molecular damages. Many factors have been identified as either the cause or consequence of age-related decline in functions and repair mechanisms. The hypothalamus is the source and a target of many of these factors and hormones responsible for the overall homeostasis in the body. With advanced age, the sensitivity of the hypothalamus to various feedback signals begins to decline. In recent years, several aging-related genes have been identified and their signaling pathways elucidated. These gene products include mTOR, IKK-β/NF-κB complex, and HIF-1α, an important cellular survival signal. All of these activators/modulators of the aging process have also been identified in the hypothalamus and shown to play crucial roles in nutrient sensing, metabolic regulation, energy balance, reproductive function, and stress adaptation. This illustrates the central role of the hypothalamus in aging. Inside the mitochondria, succinate is one of the most prominent intermediates of the Krebs cycle. Succinate oxidation in mitochondria provides the most powerful energy output per unit time. Extra-mitochondrial succinate triggers a host of succinate receptor (SUCN1 or GPR91)-mediated signaling pathways in many peripheral tissues including the hypothalamus. One of the actions of succinate is to stabilize the hypoxia and cellular stress conditions by inducing the transcriptional regulator HIF-1α. Through these actions, it is hypothesized that succinate has the potential to restore the gradual but significant loss in functions associated with cellular senescence and systemic aging.

hGH promotes megakaryocyte differentiation and exerts a complementary effect with c-Mpl ligands on thrombopoiesis

hGH has a distinct capacity to promote the differentiation, especially the terminal differentiation of human primary megakaryocytes. hGH exerts a complementary and synergistic effect with c-Mpl ligands on thrombopoiesis.

βTrCP interacts with the ubiquitin-dependent endocytosis motif of the GH receptor in an unconventional manner

GH (growth hormone) binding to the GHR (GH receptor) triggers essential signalling pathways that promote growth and metabolic regulation. The sensitivity of the cells to GH is mainly controlled by the endocytosis of the receptor via βTrCP (β-transducin repeat-containing protein). In the present study, we show that βTrCP interacts directly via its WD40 domain with the UbE (ubiquitin-dependent endocytosis) motif in GHR, promoting GHR ubiquitination in vitro. NMR experiments demonstrated that the UbE motif is essentially unstructured, and, together with functional mapping of the UbE and βTrCP WD40 residues necessary for binding, led to a unique interaction model of βTrCP with GHR-UbE. This interaction is different from the conventional βTrCP-substrate interactions described to date. This interaction therefore represents a promising specific target to develop drugs that inhibit GHR endocytosis and increase GH sensitivity in cachexia patients.

Genetic polymorphisms and protein structures in growth hormone, growth hormone receptor, ghrelin, insulin-like growth factor 1 and leptin in Mehraban sheep

The somatotropic axis, the control system for growth hormone (GH) secretion and its endogenous factors involved in the regulation of metabolism and energy partitioning, has promising potentials for producing economically valuable traits in farm animals. Here we investigated single nucleotide polymorphisms (SNPs) of the genes of factors involved in the somatotropic axis for growth hormone (GH1), growth hormone receptor (GHR), ghrelin (GHRL), insulin-like growth factor 1 (IGF-I) and leptin (LEP), using polymerase chain reaction-single-strand conformation polymorphism (PCR-SSCP) and DNA sequencing methods in 452 individual Mehraban sheep. A nonradioactive method to allow SSCP detection was used for genomic DNA and PCR amplification of six fragments: exons 4 and 5 of GH1; exon 10 of GH receptor (GHR); exon 1 of ghrelin (GHRL); exon 1 of insulin-like growth factor-I (IGF-I), and exon 3 of leptin (LEP). Polymorphisms were detected in five of the six PCR products. Two electrophoretic patterns were detected for GH1 exon 4. Five conformational patterns were detected for GH1 exon 5 and LEP exon 3, and three for IGF-I exon 1. Only GHR and GHRL were monomorphic. Changes in protein structures due to variable SNPs were also analyzed. The results suggest that Mehraban sheep, a major breed that is important for the animal industry in Middle East countries, has high genetic variability, opening interesting prospects for future selection programs and preservation strategies.

Noncanonical suppression of GH-dependent isoforms of cytochrome P450 by the somatostatin analog octreotide

Octreotide is a potent somatostatin analog therapeutically used to treat several conditions including hyper GH secretion in patients with acromegaly. We infused, over 30 s, octreotide into male rats every 12 h for 6 days at levels considerably greater than typical human therapeutic doses. Unexpectedly, resulting circulating GH profile was characterized by pulses of higher amplitudes, longer durations, and greater total content than normal, but still contained an otherwise male-like episodic secretory profiles. In apparent disaccord, the normally elevated masculine expression levels (protein and/or mRNA) of CYP2C11 (accounting for >50% of the total hepatic cytochrome P450 content), CYP3A2, CYP2C7, and IGF1, dependent on the episodic GH profile, were considerably downregulated. We explain this contradiction by proposing that the requisite minimal GH-devoid interpulse durations in the masculine profile that solely regulate expression of at least CYP2C11 and IGF1 may be sufficiently reduced to suppress transcription of the hepatic genes. Alternatively, we observed that octreotide infusion may have acted directly on the hepatocytes to induce expression of immune response factors postulated to suppress CYP transcription and/or upregulate expression of several negative regulators (e.g. phosphatases and SOCS proteins) of the JAK2/STAT5B signaling pathway that normally mediates the upregulation of CYP2C11 and IGF1 by the masculine episodic GH profile.

Phosphotyrosine phosphatases in GH-stimulated skin fibroblasts from children with idiopathic short stature

AIM

Some cases of idiopathic short stature (ISS) may be caused by defects in the modulation of the negative feedback regulation of the growth hormone receptor (GHR)/ Janus kinase (JAK)2/signal transducers and activators of transcription (STAT)5 signaling pathway. The cytosolic tyrosine phosphatases, protein tyrosine phosphatase 1B (PTP1B) and Src homology 2 (SH2) domain-containing protein-tyrosine phosphatase-1 (SHP-1), the later which translocates to the nucleus after activation, interact with JAK2 in a GH-dependent manner. The possible contribution of PTP1B and SHP-1 to GH signaling in fibroblasts from ISS patients has not been studied.

METHODS

We determined the basal protein content of PTP1B and SHP-1 in the presence of recombinant human GH (rhGH) for 24 h in skin fibroblast cultures, obtained from patients with ISS, and were compared with a normal height control children group. JAK2 activation was determined in both groups.

RESULTS

JAK2 activation was delayed in fibroblasts from ISS patients compared to controls. Under basal conditions, the protein content of SHP-1 was lower in ISS, and after incubation with rhGH, it decreased in the non-nuclear and nuclear fraction of controls, but not in ISS patients. The protein content of PTP1B, however, increased in a similar fashion in fibroblasts from both ISS and control children.

CONCLUSION

The delayed activation of JAK2 and the lack of response of SHP-1 after incubation with GH in fibroblasts from ISS patients, suggests that the growth retardation observed in some of these children may be mediated in part by this phosphotyrosine phosphatase.

Hormone replacement therapy and physical function in healthy older men. Time to talk hormones?

Improving physical function and mobility in a continuously expanding elderly population emerges as a high priority of medicine today. Muscle mass, strength/power, and maximal exercise capacity are major determinants of physical function, and all decline with aging. This contributes to the incidence of frailty and disability observed in older men. Furthermore, it facilitates the accumulation of body fat and development of insulin resistance. Muscle adaptation to exercise is strongly influenced by anabolic endocrine hormones and local load-sensitive autocrine/paracrine growth factors. GH, IGF-I, and testosterone (T) are directly involved in muscle adaptation to exercise because they promote muscle protein synthesis, whereas T and locally expressed IGF-I have been reported to activate muscle stem cells. Although exercise programs improve physical function, in the long-term most older men fail to comply. The GH/IGF-I axis and T levels decline markedly with aging, whereas accumulating evidence supports their indispensable role in maintaining physical function integrity. Several studies have reported that the administration of T improves lean body mass and maximal voluntary strength in healthy older men. On the other hand, most studies have shown that administration of GH alone failed to improve muscle strength despite amelioration of the detrimental somatic changes of aging. Both GH and T are anabolic agents that promote muscle protein synthesis and hypertrophy but work through separate mechanisms, and the combined administration of GH and T, albeit in only a few studies, has resulted in greater efficacy than either hormone alone. Although it is clear that this combined approach is effective, this review concludes that further studies are needed to assess the long-term efficacy and safety of combined hormone replacement therapy in older men before the medical rationale of prescribing hormone replacement therapy for combating the sarcopenia of aging can be established.

Growth hormone stimulates transcription of the fibroblast growth factor 21 gene in the liver through the signal transducer and activator of transcription 5

Fibroblast growth factor 21 (FGF21) is a recently discovered metabolic regulator. Interestingly, FGF21 is also known to inhibit Janus kinase 2 (JAK2)-signal transducer and activator of transcription 5 (STAT5) signaling from the GH receptor in the liver, where FGF21 mRNA is predominantly expressed. In this study, we tested the hypothesis that FGF21 gene expression in the liver is controlled by GH through STAT5. We found that GH injection to cattle increased FGF21 mRNA expression in the liver. Mapped by a 5'-rapid amplification of cDNA ends assay, transcription of the FGF21 gene in the bovine liver was mainly initiated from a nucleotide 24 bp downstream of a TATA box. The bovine FGF21 promoter contains three putative STAT5-binding sites. EMSA confirmed the ability of them to bind to liver STAT5 protein from GH-injected cattle. Chromatin immunoprecipitation assays demonstrated that GH administration increased the binding of STAT5 to the FGF21 promoter in the liver. Cotransfection analyses showed that GH induced reporter gene expression from the FGF21 promoter in a STAT5-dependent manner. GH also stimulated FGF21 mRNA expression in cultured mouse hepatocytes. These data together indicate that GH directly stimulates FGF21 gene transcription in the liver, at least in part, through STAT5. This finding, together with the fact that FGF21 inhibits GH-induced JAK2-STAT5 signaling in the liver, suggests a novel negative feedback loop that prevents excessive JAK2-STAT5 signaling from the GH receptor in the liver.

Nutritional and hormonal modulation of adiponectin and its receptors adipoR1 and adipoR2

Adiponectin is the most abundant plasma protein synthesized mostly by adipose tissue and is an insulin-sensitive hormone, playing a central role in glucose and lipid metabolism. Adiponectin effects are mediated via two receptors, adipoR1 and adipoR2. Several hormones and diet components that are involved in insulin resistance may impair insulin sensitivity at least in part by decreasing adiponectin and adiponectin receptors. Adiponectin expression and serum levels are associated with the amount and type of fatty acids and carbohydrate consumed. Other food items, such as vitamins, alcohol, sodium, green tea, and coffee, have been reported to modify adiponectin levels. Several hormones, including testosterone, estrogen, prolactin, glucocorticoids, catecholamines, and growth hormone, have been shown to inhibit adiponectin production, but the studies are still controversial. Even so, adiponectin is a potential therapeutic target in the treatment of diabetes mellitus and other diseases associated with hypoadiponectinemia.

βTrCP controls GH receptor degradation via two different motifs

The physiological roles of GH are broad and include metabolism regulation and promotion of somatic growth. Therefore, the responsiveness of cells to GH must be tightly regulated. This is mainly achieved by a complex and well-controlled mechanism of GH receptor (GHR) endocytosis. GHR endocytosis occurs independently of GH and requires the ubiquitin ligase, SCF (βTrCP) that is recruited to the ubiquitin-dependent endocytosis (UbE) motif in the cytoplasmic tail of the GHR. In this study we report that, in addition to the UbE motif, a downstream degron, DSGRTS, binds to βTrCP. The WD40 residues on βTrCP involved in the interaction with this sequence are identical to the ones necessary for binding the classical motif, DSGxxS, in inhibitor of NFκB signalling, and β-catenin. Previously, we showed that this motif is not involved in GH-induced endocytosis. We show here that the DSGRTS sequence significantly contributes to GHR endocytosis/degradation in basal conditions, whereas the UbE motif is involved both in basal and GH-induced conditions. These findings explain the high rate of GHR degradation under basal conditions, which is important for regulating the responsiveness of cells to GH.

Effects of rice dreg protein and its hydrolysate on growth performance and small intestine morphology of early-weaned rats

BACKGROUND

Protein hydrolysate has more efficient peptide absorption and less hypertonic protein absorption. This study aims to investigate the influences of rice dreg (RD) protein and its hydrolysate on growth and somatropic axis in early-weaned Sprague-Dawley rats in comparison with soybean (SB) protein.

RESULTS

Compared with a SB diet control, a rice dregs protein hydrolysate (RD-H) diet decreased average daily feed intake and feed/gain in weeks 1 (P < 0.01) and 2 (P < 0.05), while an RD diet decreased average daily feed intake and feed/gain in week 1 (P < 0.01). Average daily body gain exhibited no significant differences between either treatment during the 28-day period. After 28 d, villus height and lamina propria depth of jejunum and duodenum were greater in the RD-H treatment than in RD and control treatments (P < 0.01), while serum urea nitrogen concentration was lower in RD and RD-H treatments than in the control (P < 0.05). There were no differences in serum growth hormone concentration, hepatic and muscle insulin-like growth factor-1 expression, and muscle growth hormone receptor expression at 7 and 28 d (P > 0.05), but hepatic growth hormone receptor expression was higher in RD-H treatment than in RD and control treatments after 7 d (P < 0.05).

CONCLUSION

Results showed that RD and RD-H diets improved feed utilisation efficiency in the first 2 weeks post-weaning and small intestine morphology at 28 d post-weaning for an early-weaned mammal compared with a SB diet.

Metformin increases plasma ghrelin in Type 2 diabetes

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

* Metformin, unlike the other major antihyperglycaemic drugs, is not associated with weight gain. * Ghrelin is an appetite-stimulating hormone whose concentrations vary in relation to food, obesity and diabetes control. * Reports are conflicting about how metformin affects ghrelin concentrations, and this study was aimed at resolving this issue in patients with Type 2 diabetes.

WHAT THIS STUDY ADDS

* In this study an increase in ghrelin concentrations was seen in response to metformin treatment in patients with Type 2 diabetes. * This effect was opposite to what might be expected if the effect of metformin on weight control was mediated via suppression of ghrelin. * It is likely that the ghrelin response was secondary to improved glycaemic control. * Meal time changes in appetite and satiety did not correlate with changes in ghrelin, which suggests ghrelin may not be important in meal initiation.

AIMS

Metformin treatment of Type 2 diabetes is not usually associated with weight gain, and may assist with weight reduction. Plasma ghrelin concentrations are inversely associated with obesity and food intake. Metformin might therefore affect ghrelin concentrations, although previous studies have shown variable results in this regard. The primary aim of this study was to determine the effect of metformin on plasma ghrelin, appetite and satiety in patients with Type 2 diabetes.

METHODS

Eighteen patients with Type 2 diabetes were studied before and after 6 weeks of metformin treatment, which was titrated to 1 g b.d. On the study days patients were fed standard meals of 390 kcal at 08.00 and 12.30 h, plasma samples were collected at 15- and 30-min intervals, and appetite and satiety were measured on visual analogue scales. Changes in the area under the concentration-time curves (AUCs) of plasma ghrelin, insulin, glucose, appetite and satiety were assessed and examined for correlations with metformin AUCs. Changes in fasting adiponectin and leptin were also measured.

RESULTS

Treatment with metformin increased the mean AUC (07.30-16.30 h) of plasma ghrelin by 24% (P= 0.003), while decreasing those of glucose by 19% (P < 0.001) and insulin by 19% (P= 0.001). No changes were detected in hunger and satiety, or in fasting adiponectin or leptin concentrations. There were no clear correlations between metformin plasma concentrations (AUC) and changes in plasma glucose, insulin or ghrelin.

CONCLUSIONS

Treatment of Type 2 diabetes with metformin was associated with increased plasma ghrelin concentrations, without associated changes in hunger and satiety.

Characterization of the GHR gene genetic variation in Chinese indigenous goat breeds

The aim of the present work was to investigate single nucleotide polymorphism (SNP) of growth hormone receptor (GHR) gene exon 10, characterize the genetic variation in three Chinese indigenous goat breeds, and search for its potential association with cashmere traits. In this study, a polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) protocol has been developed for rapid genotyping of the GHR gene in goats. One hundred seventy-eight goats from Liaoning Cashmere (96), Inner Mongolia White Cashmere (40), and Chengdu Grey (42) breeds in China were genotyped at GHR locus using the protocol developed. In all goat breeds investigated, a SNP in exon 10 of GHR gene has been identified by analyzing genomic DNA. The polymorphism consists of a single nucleotide substitution A → G, resulting in two alleles named, respectively, A and G based on the nucleotide at the position. The allele A was found to be more common in the animals investigated, and seems to be more consistent with cattle and zebu at this polymorphic site found in goats. The Hardy-Weinberg equilibrium of genotype distributions of GHR locus was verified in Liaoning Cashmere, and Inner Mongolia White Cashmere breeds. According to the classification of polymorphism information content (PIC), Chengdu Grey was less polymorphic than Liaoning Cashmere and Inner Mongolia White Cashmere breeds at this locus. The phylogenetic tree of different species based on the nucleotide sequences of GHR gene exon 10 is generally in agreement with the known species relationship. No significant association was found between the polymorphism revealed and the cashmere traits analyzed in present work.

Molecular anatomy of the cytoplasmic domain of bovine growth hormone receptor, a quantitative trait locus

Quantitative trait loci (QTL) studies have indicated growth hormone receptor (GHR) as a candidate gene affecting cattle milk yield and composition. In order to characterize genetic variation at GHR in cattle, we studied European and East African breeds with different histories of selection, and Bos grunniens, Ovis aries, Sus scrofa, Bison bison and Rangifer tarandus as references. We sequenced most of the cytoplasmic domain (900 bp of exon 10), 89 bp of exon 8, including the putative causative mutation for the QTL effect, and 390 bp of intron 8 for comparison. In the cytoplasmic domain, seven synonymous and seven non-synonymous single nucleotide polymorphisms (SNP) were identified in cattle. Three non-synonymous SNPs were found in sheep and one synonymous SNP in yak, while other studied species were monomorphic. Three major haplotypes were observed, one unique to African breeds, one unique to European breeds and one shared. Bison and yak haplotypes are derivatives of the European haplotype lineage. Most of the exon 10 non-synonymous cattle SNPs appear at phylogenetically highly conserved sites. The polymorphisms in exon 10 cluster around a ruminant-specific tyrosine residue, suggesting that this site may act as an additional signalling domain of GHR in ruminants. Alternative explanations for the persistent polymorphism include balancing selection, hitch-hiking, pleiotropic or sexually antagonistic fitness effects or relaxed functional constraints.

Recombinant human growth hormone: rationale for use in the treatment of HIV-associated lipodystrophy

The role of hormonal and metabolic alterations in HIV-associated lipodystrophy syndrome is not yet clear. In patients with HIV-1 undergoing antiretroviral treatment, lipodystrophy is associated with peripheral fat wasting and central adiposity, dyslipidemia, insulin resistance, and increased intramuscular fat accumulation. In HIV lipodystrophy, changes in fat distribution are heterogeneous and can include reduced subcutaneous fat as well as increased visceral fat. In the literature, there is evidence showing that overnight growth hormone (GH) secretion and pulse amplitude decrease in patients with HIV lipodystrophy, with rates of response to standardized GH stimulation being abnormal in at least 20% of these patients. Excess accumulation of visceral fat, central obesity, and increased intra-abdominal adiposity are also typical features of patients with GH deficiency. Recombinant human GH (rhGH) is a potential treatment to diminish excess visceral fat. Our group recently demonstrated that GH therapy in HIV-infected patients with syndromes of fat accumulation produced a significant decrease in body fat and a gain in lean tissue. In this article, we discuss the origin of lipodystrophy in HIV patients, and the use of rhGH treatment (benefits and adverse effects) in HIV-related lipodystrophy.

Expression of the hepatic specific V1 messenger ribonucleic acid of the human growth hormone receptor gene is regulated by hepatic nuclear factor (HNF)-4alpha2 and HNF-4alpha8

Human (h) GH plays an essential role in growth and metabolism, and its effectiveness is modulated by the availability of its specific receptor [hGH receptor (hGHR)] on target cells. The hGHR gene has a complex 5'-regulatory region containing multiple first exons. Seven are clustered within two small regions: V2,V3,V9 (module A) and V1,V4,V7,V8 (module B). Module A-derived mRNAs are ubiquitously expressed whereas those from module B are only found in postnatal liver, suggesting developmental- and liver-specific regulation of module B hGHR gene expression. To characterize the elements regulating module B activity, we studied a 1.8-kb promoter of the highest expressing exon in liver, V1. This promoter was repressed in transfection assays; however, either 5'- or 3'-deletions relieved this, suggesting the presence of multiple negative regulatory elements. Six putative hepatic nuclear factor 4 (HNF-4) response elements were identified. We determined that HNF-4alpha is developmentally regulated in the human liver: HNF-4alpha2 and HNF-4alpha8 are expressed in fetal hepatocytes but only HNF-4alpha2 is expressed in postnatal liver. Transient transfection assays demonstrated that HNF-4alpha2 and HNF-4alpha8 have a similar dual effect on V1 transcription: activation via site 1 in the proximal promoter and repression through site 6, approximately 1.7 kb upstream. EMSA/electrophoretic mobility supershift assays and chromatin immunoprecipitation analyses confirmed these two sites are bound by HNF-4alpha. Based on these data, we speculate there are multiple regions working together to repress the expression of V1 hGHR transcripts in tissues other than the normal postnatal liver, and that HNF-4alpha is a good candidate for regulating V1 hGHR expression in the human hepatocyte.

Clinical pharmacodynamic effects of the growth hormone receptor antagonist pegvisomant: implications for cancer therapy

PURPOSE

The present study evaluated and compared the efficacy of pegvisomant and octreotide in blocking the growth hormone (GH) axis in humans based on pharmacodynamic biomarkers associated with the GH axis. The study also evaluated the safety of pegvisomant given at high s.c. doses for 14 days.

EXPERIMENTAL DESIGN

Eighty healthy subjects were enrolled in five cohorts: cohorts 1 to 3, s.c. pegvisomant at 40, 60, or 80 mg once dailyx14 days (n=18 per cohort); cohort 4, s.c. octreotide at 200 microg thrice dailyx14 days (n=18); and cohort 5, untreated control (n=8). Serial blood samples were collected to measure plasma concentrations of total insulin-like growth factor type I (IGF-I), free IGF-I, IGF-II, IGF-binding protein 3 (IGFBP-3), and GH in all subjects and serum pegvisomant concentrations in subjects of cohorts 1 to 3. All subjects receiving treatment were monitored for adverse events (AE).

RESULTS

After s.c. dosing of pegvisomant once daily for 14 days, the mean maximum suppression values of total IGF-I were 57%, 60%, and 62%, at 40, 60, and 80 mg dose levels, respectively. The maximum suppression was achieved approximately 7 days after the last dose and was sustained for approximately 21 days. Pegvisomant also led to a sustained reduction in free IGF-I, IGFBP-3, and IGF-II concentrations by up to 33%, 46%, and 35%, respectively, and an increase in GH levels. In comparison, octreotide resulted in a considerably weaker inhibition of total IGF-I and IGFBP-3 for a much shorter duration, and no inhibition of IGF-II. AEs in pegvisomant-treated subjects were generally either grade 1 or 2. The most frequent treatment-related AEs included injection site reactions, headache, and fatigue.

CONCLUSIONS

Pegvisomant at well-tolerated s.c. doses was considerably more efficacious than octreotide in suppressing the GH axis, resulting in substantial and sustained inhibition of circulating IGF-I, IGF-II, and IGFBP-3 concentrations. These results provide evidence in favor of further testing the hypothesis that pegvisomant, through blocking the GH receptor-mediated signal transduction pathways, could be effective in treating tumors that may be GH, IGF-I, and/or IGF-II dependent, such as breast and colorectal cancer.

Cytokine receptor signaling through the Jak–Stat–Socs pathway in disease

The complexity of multicellular organisms is dependent on systems enabling cells to respond to specific stimuli. Cytokines and their receptors are one such system, whose perturbation can lead to a variety of disease states. This review represents an overview of our current understanding of the cytokine receptors, Janus kinases (Jaks), Signal transducers and activators of transcription (Stats) and Suppressors of cytokine signaling (Socs), focussing on their contribution to diseases of an immune or hematologic nature.

Identification of SH2B2beta as an inhibitor for SH2B1- and SH2B2alpha-promoted Janus kinase-2 activation and insulin signaling

The SH2B family has three members (SH2B1, SH2B2, and SH2B3) that contain conserved dimerization (DD), pleckstrin homology, and SH2 domains. The DD domain mediates the formation of homo- and heterodimers between members of the SH2B family. The SH2 domain of SH2B1 (previously named SH2-B) or SH2B2 (previously named APS) binds to phosphorylated tyrosines in a variety of tyrosine kinases, including Janus kinase-2 (JAK2) and the insulin receptor, thereby promoting the activation of JAK2 or the insulin receptor, respectively. JAK2 binds to various members of the cytokine receptor family, including receptors for GH and leptin, to mediate cytokine responses. In mice, SH2B1 regulates energy and glucose homeostasis by enhancing leptin and insulin sensitivity. In this work, we identify SH2B2beta as a new isoform of SH2B2 (designated as SH2B2alpha) derived from the SH2B2 gene by alternative mRNA splicing. SH2B2beta has a DD and pleckstrin homology domain but lacks a SH2 domain. SH2B2beta bound to both SH2B1 and SH2B2alpha, as demonstrated by both the interaction of glutathione S-transferase-SH2B2beta fusion protein with SH2B1 or SH2B2alpha in vitro and coimmunoprecipitation of SH2B2beta with SH2B1 or SH2B2alpha in intact cells. SH2B2beta markedly attenuated the ability of SH2B1 to promote JAK2 activation and subsequent tyrosine phosphorylation of insulin receptor substrate-1 by JAK2. SH2B2beta also significantly inhibited SH2B1- or SH2B2alpha-promoted insulin signaling, including insulin-stimulated tyrosine phosphorylation of insulin receptor substrate-1. These data suggest that SH2B2beta is an endogenous inhibitor of SH2B1 and/or SH2B2alpha, negatively regulating insulin signaling and/or JAK2-mediated cellular responses.

Growth hormone induces apelin mRNA expression and secretion in mouse 3T3-L1 adipocytes

Recently, apelin was characterised as a novel adipose-expressed factor which is upregulated in rodent and human obesity and influences cardiovascular function, as well as insulin secretion. To clarify expression and regulation of this adipokine, apelin mRNA was measured by quantitative real-time reverse transcription-polymerase chain reaction in mouse 3T3-L1 adipocytes after treatment with various hormones known to induce insulin resistance. Interestingly, apelin synthesis was significantly upregulated by growth hormone (GH) and insulin in these cells whereas TNFalpha and isoproterenol did not have any effect. Thus, 500 ng/ml GH acutely induced apelin mRNA by up to 4-fold in a time-dependent fashion with significant stimulation seen at concentrations as low as 5 ng/ml effector. Furthermore, apelin secretion was assessed by enzyme-linked immunoassay in mouse adipocytes. Here, secretion of this adipokine was induced 2.85-fold by GH. Studies using pharmacological inhibitors suggested that the positive effect of GH on apelin mRNA synthesis is at least in part mediated by janus kinase 2 and phosphatidylinositol 3-kinase. Taken together, our results show a significant induction of apelin mRNA synthesis and protein secretion by GH.

Involvement of JAK2 and Src kinase tyrosine phosphorylation in human growth hormone-stimulated increases in cytosolic free Ca2+and insulin secretion

We previously reported that human growth hormone (hGH) increases cytoplasmic Ca2+concentration ([Ca2+]i) and proliferation in pancreatic β-cells (Sjöholm Å, Zhang Q, Welsh N, Hansson A, Larsson O, Tally M, and Berggren PO. J Biol Chem 275: 21033–21040, 2000) and that the hGH-induced rise in [Ca2+]iinvolves Ca2+-induced Ca2+release facilitated by tyrosine phosphorylation of ryanodine receptors (Zhang Q, Kohler M, Yang SN, Zhang F, Larsson O, and Berggren PO. Mol Endocrinol 18: 1658–1669, 2004). Here we investigated the tyrosine kinases that convey the hGH-induced rise in [Ca2+]iand insulin release in BRIN-BD11 β-cells. hGH caused tyrosine phosphorylation of Janus kinase (JAK)2 and c-Src, events inhibited by the JAK2 inhibitor AG490 or the Src kinase inhibitor PP2. Although hGH-stimulated rises in [Ca2+]iand insulin secretion were completely abolished by AG490 and JAK2 inhibitor II, the inhibitors had no effect on insulin secretion stimulated by a high K+concentration. Similarly, Src kinase inhibitor-1 and PP2, but not its inactive analog PP3, suppressed [Ca2+]ielevation and completely abolished insulin secretion stimulated by hGH but did not affect responses to K+. Ovine prolactin increased [Ca2+]iand insulin secretion to a similar extent as hGH, effects prevented by the JAK2 and Src kinase inhibitors. In contrast, bovine GH evoked a rise in [Ca2+]ibut did not stimulate insulin secretion. Neither JAK2 nor Src kinase inhibitors influenced the effect of bovine GH on [Ca2+]i. Our study indicates that hGH stimulates rise in [Ca2+]iand insulin secretion mainly through activation of the prolactin receptor and JAK2 and Src kinases in rat insulin-secreting cells.

Plasminogen activator inhibitor-1 expression and secretion are stimulated by growth hormone and interleukin-6 in 3T3-L1 adipocytes

Various adipocytokines have been described which influence insulin sensitivity and vascular function profoundly and might, therefore, potentially link obesity, insulin resistance, and atherosclerosis. Among those, plasminogen activator inhibitor (PAI)-1 is an adipose-secreted factor upregulated in obesity and insulin resistance that inhibits fibrinolysis. Furthermore, recent studies in knockout mice suggest that PAI-1 directly impairs insulin sensitivity. In the current study, the impact of growth hormone (GH) and interleukin (IL)-6 on PAI-1 mRNA synthesis and secretion was determined in 3T3-L1 adipocytes. Interestingly, 500 ng/ml GH and 30 ng/ml IL-6 increased PAI-1 secretion five-fold and 3.6-fold, respectively. Furthermore, GH and IL-6 induced PAI-1 mRNA by up to 7.3-fold, and 3.6-fold, respectively, in a time-dependent fashion with significant stimulation seen at concentrations as low as 5 ng/ml GH and 10 ng/ml IL-6. Other insulin resistance-inducing hormones which stimulated PAI-1 synthesis included insulin, TNFalpha, and dexamethasone. Studies using pharmacological inhibitors suggested that basal and GH-induced PAI-1 synthesis were at least in part mediated by p44/42 mitogen-activated protein kinase but not janus kinase 2 and phosphatidylinositol 3-kinase. Taken together, our results show a differential regulation of PAI-1 mRNA by insulin resistance-inducing hormones including GH and IL-6.

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.

The role of the bovine growth hormone receptor and prolactin receptor genes in milk, fat and protein production in Finnish Ayrshire dairy cattle

We herein report new evidence that the QTL effect on chromosome 20 in Finnish Ayrshire can be explained by variation in two distinct genes, growth hormone receptor (GHR) and prolactin receptor (PRLR). In a previous study in Holstein-Friesian dairy cattle an F279Y polymorphism in the transmembrane domain of GHR was found to be associated with an effect on milk yield and composition. The result of our multimarker regression analysis suggests that in Finnish Ayrshire two QTL segregate on the chromosomal region including GHR and PRLR. By sequencing the coding sequences of GHR and PRLR and the sequence of three GHR promoters from the pooled samples of individuals of known QTL genotype, we identified two substitutions that were associated with milk production traits: the previously reported F-to-Y substitution in the transmembrane domain of GHR and an S-to-N substitution in the signal peptide of PRLR. The results provide strong evidence that the effect of PRLR S18N polymorphism is distinct from the GHR F279Y effect. In particular, the GHR F279Y has the highest influence on protein percentage and fat percentage while PRLR S18N markedly influences protein and fat yield. Furthermore, an interaction between the two loci is suggested.

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.

A functional Jak2 tyrosine kinase domain is essential for mouse development

Jak2 is a member of the Janus family of tyrosine kinases and is involved in cytokine signaling. As a part of a study to determine biological functions of Jak2, we used molecular modeling to identify W1038 as a residue that is critical for tyrosine kinase function. Mutation of W1038, in tandem with E1046, generates a dominant-negative form of the Jak2 protein. Mice that were engineered to express two copies of this dominant-negative Jak2 protein died in utero. Additionally, heterozygous mice expressing Jak2 with kinase activity that is moderately reduced when compared to wild-type activity appear phenotypically normal. Collectively, these data suggest that Jak2 kinase activity is essential for normal mammalian development.

Physiology and pathophysiology of growth hormone-binding protein: methodological and clinical aspects

Circulating GH is partly bound to a high-affinity binding protein (GHBP), which in humans is derived from cleavage of the extracellular domain of the GH receptor. The precise biological function GHBP is unknown, although a regulation of GH bioactivity appears plausible. GHBP levels are determined by GH secretory status, body composition, age, and sex hormones, but the cause-effect relationships remain unclarified. In addition to the possible in vivo significance of GHBP, the interaction between GH and GHBP has methodological implications for both GH and GHBP assays. The present review concentrates on methodological aspects of GHBP measurements, GHBP levels in certain clinical conditions with a special emphasis on disturbances in the GH-IGF axis, and discusses the possible relationship between plasma GHBP and GH receptor status in peripheral tissues.

IL-6-induced skeletal muscle atrophy

Chronic, low-level elevation of circulating interleukin (IL)-6 is observed in disease states as well as in many outwardly healthy elderly individuals. Increased plasma IL-6 is also observed after intense, prolonged exercise. In the context of skeletal muscle, IL-6 has variously been reported to regulate carbohydrate and lipid metabolism, increase satellite cell proliferation, or cause muscle wasting. In the present study, we used a rodent local infusion model to deliver modest levels of IL-6, comparable to that present after exercise or with chronic low-level inflammation in the elderly, directly into a single target muscle in vivo. The aim of this study was to examine the direct effects of IL-6 on skeletal muscle in the absence of systemic changes in this cytokine. Data included cellular and molecular markers of cytokine and growth factor signaling (phosphorylation and mRNA content) as well as measurements to detect muscle atrophy. IL-6 infusion resulted in muscle atrophy characterized by a preferential loss of myofibrillar protein (-17%). IL-6 induced a decrease in the phosphorylation of ribosomal S6 kinase (-60%) and STAT5 (-33%), whereas that of STAT3 was increased approximately twofold. The changes seen in the IL-6-infused muscles suggest alterations in the balance of growth factor-related signaling in favor of a more catabolic profile. This suggests that downregulation of growth factor-mediated intracellular signaling may be a mechanism contributing to the development of muscle atrophy induced by elevated IL-6.

Regulation of development and metabolism of adipose tissue by growth hormone and the insulin-like growth factor system

White adipose tissue plays a key role in the regulation of the energy balance of vertebrates. This tissue is also now recognized to secrete a variety of factors such as leptin, which is thought to be involved in the modulation of adipose mass. Unlike other tissues, adipose tissue mass has considerable capacity to expand. The review deals primarily on the regulation of development and metabolism of adipose tissue by growth hormone (GH) and the insulin-like growth factor (IGF) system, with a special focus on the pig. The anti-insulin effects of GH are well-documented in pigs as in other species. In vitro exposure of adipose precursor cells to GH leads to a decrease in differentiation of those cells in pigs, in contrast to data obtained in murine cell lines. In vivo treatment and prolonged in vitro incubation of adipose tissue or isolated adipocytes with GH result in a decrease in glucose transport and lipogenesis, especially at the level of the fatty acid synthase gene, resulting in a reduction of the lipid content and adipose tissue mass. The mechanism by which GH antagonizes insulin stimulation of lipogenesis is still unresolved, as it is not mediated by protein kinase A, protein kinase C and Janus kinase-2 at the signaling level, or upstream stimulatory factor 1 or sterol regulatory element binding protein-1 at the transcriptional level. GH is apparently the main regulator of IGF-I mRNA expression in adipose tissue, however, the effects of IGF-I on this tissue are rather unclear.

Distinctive roles for prolactin and growth hormone in the activation of signal transducer and activator of transcription 5 in pancreatic islets of langerhans

Although the beta-cells of the pancreatic islets of Langerhans express both prolactin (PRL) and GH receptors, we have observed that PRL is considerably more effective than GH in the up-regulation of islet function in vitro. This study examined whether differences in the activation of the Janus kinase 2/signal transducer and activator of transcription (STAT) 5 signaling pathway by these closely related receptors may be involved in this disparity. The activation of STAT5B by PRL was biphasic, with an initial peak within 30 min, a nadir between 1 and 3 h, and prolonged activation after 4 h. In contrast, the response to GH was transient for 1 h. The importance of the long-term activation of STAT5B by PRL was supported by the similar dose response curves for STAT5B activation and the PRL-induced increases in insulin secretion and islet cell proliferation. Because the pulsatile secretion of GH affects its actions in other target tissues, the ability of pretreatment with either hormone to affect subsequent stimulation was also examined. Surprisingly, the response to PRL was inhibited by prior exposure for less than 3 h to either PRL or GH and disappeared with a longer pretreatment with either hormone. Similar to other tissues, the response to GH was inhibited by any length of prior exposure to GH. However, pretreatment with PRL had no effect. These experiments are the first demonstration of the transient desensitization of the PRL receptor by either PRL or GH pretreatment in any tissue and the desensitization of GH stimulation in islet cells. These observations provide insight into the mechanisms that regulate the desensitization of these receptors and, more importantly, allow the long-term activation of STAT5B by the PRL receptor. These results may apply to other members of the cytokine superfamily of receptors. We also demonstrate that the increase in islet cell proliferation required continuous stimulation with PRL, whereas the smaller effect with GH occurred with either continuous or pulsatile stimulation. In summary, this study demonstrates that islets are sensitive to the temporal pattern of stimulation by these hormones and provides a new basis for understanding their physiological roles in the regulation of islet function.

Monocyte chemoattractant protein 1 expression is stimulated by growth hormone and interleukin-6 in 3T3-L1 adipocytes

During the last 10 years, various adipocytokines have been described which influence insulin sensitivity profoundly and might, therefore, potentially link obesity and insulin resistance. Recently, monocyte chemoattractant protein (MCP)-1 was characterized as a novel adipose-secreted factor upregulated in obesity and insulin resistance that impairs insulin signaling in fat cells in vitro and can be found in atherosclerotic lesions. To clarify expression and regulation of this adipocytokine, MCP-1 mRNA was measured by quantitative real-time reverse transcription-polymerase chain reaction during differentiation of 3T3-L1 adipocytes and after treatment with various hormones known to induce insulin resistance. Interestingly, MCP-1 synthesis was significantly downregulated between 43% and 68% during differentiation of 3T3-L1 preadipocytes. Furthermore, 10 ng/ml tumor necrosis factor alpha, 100 nM insulin, 500 ng/ml growth hormone (GH), and 30 ng/ml interleukin (IL)-6-induced MCP-1 mRNA by up to 124-, 23-, 8-, and 2.5-fold, respectively, in a time-dependent fashion with significant stimulation seen at concentrations as low as 0.5 ng/ml GH and 30 ng/ml IL-6. In contrast, the glucocorticoid dexamethasone potently downregulated MCP-1 with significant suppression detectable at concentrations as low as 3 nM and as early as 2h after effector addition. Studies using pharmacological inhibitors suggested that the positive effects of GH and IL-6 on MCP-1 synthesis are at least in part mediated by janus kinase 2 and p44/42 mitogen-activated protein kinase. Taken together, our results show a differential regulation of MCP-1 mRNA by insulin resistance-inducing hormones and support the view that this adipocytokine might be an interesting novel candidate linking insulin resistance, obesity, and atherosclerosis. This adipocytokine could thus be a potential pharmacological target for the treatment of impaired insulin sensitivity.

Transgenic growth hormone mice exposed to lifetime constant illumination: gender-specific effects

Photoperiod affects most of the features altered in transgenic growth hormone (TG) mice, and laboratory rats and mice retain some sensitivity to photoperiod. We examined growth, feeding, longevity, and reproduction of TG mice and normal control mice (Mus musculus L., 1758) in 12 h light : 12 h dark (LD) and 24 h light (LL) photoperiods. Sexual dichotomy in growth and hepatic gene expression are considered to require gender-specific patterns of growth hormone secretion that are absent in TG mice. Regardless, in the LD photoperiod mature TG females were 82.8% (46.8 g) of the mass of TG males (56.5 g, p < 0.05), whereas control mice showed no size dichotomy (≈33 g). Mature masses of TG males and of control mice of either gender were unaffected by the LL photoperiod. TG females, however, reached a mature mass 92% (50.9 g) of that of mature TG males in the LL photoperiod, attenuating the sexual size dichotomy expressed in the LD photoperiod. Growth of females was slower than that of males, even in the control group. TG females in the LL photoperiod expressed faster growth, higher reproduction, and greater mean longevity than TG females in the LD photoperiod. Differences in age-related feeding associated with gender and photoperiod reflected differential growth rates. Females grew more slowly and ate more than males of similar age because they were smaller (i.e., had lower growth efficiencies). The LL photoperiod improved the energy balance of TG females. Possible mechanisms mediating such gender-specific effects are explored.

Growth hormone is a positive regulator of adiponectin receptor 2 in 3T3-L1 adipocytes

The fat-derived protein adiponectin is an important insulin-sensitizing adipocytokine which is downregulated in insulin resistance and obesity. Recently, two receptors of this adipose-expressed protein called adiponectin receptor 1 (AdipoR1) and 2 (AdipoR2) have been cloned. To clarify expression and regulation of these receptors in fat cells, AdipoR1 and AdipoR2 mRNA was measured by quantitative real-time reverse transcription-polymerase chain reaction during differentiation of 3T3-L1 adipocytes and after treatment with various hormones known to induce insulin resistance. Interestingly, AdipoR2 synthesis was significantly increased up to 4.8-fold during differentiation of 3T3-L1 preadipocytes, whereas AdipoR1 expression was only augmented up to 1.4-fold. Furthermore, growth hormone (GH) induced AdipoR2, but not AdipoR1 mRNA by up to 2.4-fold in a dose- and time-dependent fashion with significant stimulation detectable at concentrations as low as 5 ng/ml GH and as early as 2 h after effector addition. The positive effect of GH on AdipoR2 expression could be reversed by withdrawal of the hormone for 24 h. In contrast, other key hormones involved in the regulation of insulin resistance and energy metabolism such as insulin, isoproterenol, dexamethasone, triiodothyronine, angiotensin 2, tumor necrosis factor alpha, and interleukin-6 did not influence AdipoR1 and AdipoR2 synthesis in vitro. Taken together, our results suggest that AdipoR2 expression is differentiation-dependent and selectively regulated by GH implying a potential role of this hormone in adiponectin-associated alterations of insulin sensitivity and energy homeostasis.

Ubiquitin system-dependent regulation of growth hormone receptor signal transduction

The growth hormone (GH) receptor is a key regulator of cellular metabolism. Unlike most growth factor receptors, its downregulation is not initiated by its ligand. Like many growth factor receptors, specific molecular mechanisms guarantee that a receptor can signal only once in its lifetime. Three features render the GH receptor unique: (a) an active ubiquitination system is required for both uptake (endocytosis) and degradation in the lysosomes; (b) uptake of the receptor is a continuous process, independent of both GH binding and Jak2 signal transduction; (c) only the cell surface expression of dimerised GH receptors is controlled by the ubiquitin system. This system enables two independent regulatory mechanisms for the endocrinology of the GH/GHR axis: the pulsatile secretion of GH by the pituitary and the GH sensitivity of individual cells of the body by the effects of the ubiquitin system on GH receptor availability.

Epidermal homeostasis: the role of the growth hormone and insulin-like growth factor systems

GH and IGF-I and -II were first identified by their endocrine activity. Specifically, IGF-I was found to mediate the linear growth-promoting actions of GH. It is now evident that these two growth factor systems also exert widespread activity throughout the body and that their actions are not always interconnected. The literature highlights the importance of the GH and IGF systems in normal skin homeostasis, including dermal/epidermal cross-talk. GH activity, sometimes mediated via IGF-I, is primarily evident in the dermis, particularly affecting collagen synthesis. In contrast, IGF action is an important feature of the dermal and epidermal compartments, predominantly enhancing cell proliferation, survival, and migration. The locally expressed IGF binding proteins play significant and complex roles, primarily via modulation of IGF actions. Disturbances in GH and IGF signaling pathways are implicated in the pathophysiology of several skin perturbations, particularly those exhibiting epidermal hyperplasia (e.g., psoriasis, carcinomas). Additionally, many studies emphasize the potential use of both growth factors in the treatment of skin wounds; for example, burn patients. This overview concerns the role and mechanisms of action of the GH and IGF systems in skin and maintenance of epidermal integrity in both health and disease.