Characterization of the growth hormone receptor in human dermal fibroblasts and liver during development

Hormonal Determinants of Growth and Weight Gain in the Human Fetus and Preterm Infant

The factors controlling linear growth and weight gain in the human fetus and newborn infant are poorly understood. We review here the changes in linear growth, weight gain, lean body mass, and fat mass during mid- and late gestation and the early postnatal period in the context of changes in the secretion and action of maternal, placental, fetal, and neonatal hormones, growth factors, and adipocytokines. We assess the effects of hormonal determinants on placental nutrient delivery and the impact of preterm delivery on hormone expression and postnatal growth and metabolic function. We then discuss the effects of various maternal disorders and nutritional and pharmacologic interventions on fetal and perinatal hormone and growth factor production, growth, and fat deposition and consider important unresolved questions in the field.

Expression of the growth hormone receptor isoforms and its correlation with the metabolic profile in morbidly obese subjects

BACKGROUND AND AIM OF THE STUDY

Given the lipolytic effect of GH and its potential role in determining adipose tissue distribution, we evaluated the expression of the GH hormone receptor (GHR) isoforms in patients with morbid obesity seeking associations with metabolic parameters.

METHODS

262 morbidly obese subjects (mean age 42.5 ± 11 years, 75% women) underwent PCR-genotyping of the exon 3 GHR polymorphism. In 17 of these subjects, who proved to be heterozygous for the exon 3 genotype (+3/-3), subcutaneous and visceral adipose tissue was obtained during bariatric surgery; total RNA was extracted, reversely transcribed, and the different isoforms of the GHR (exon 3 containing and lacking flGHR as well as the trGHR) were PCR-amplified using specific primers.

RESULTS

27% were +3/+3 homozygous, 20% -3/-3 homozygous and 53% were +3/-3 heterozygous. Compared to subjects homozygous for the +3 genotype, homozygous and heterozygous carriers of the -3 genotype were significantly heavier and tended to have a higher HOMA 2-IR. Expression of the flGHR and trGHR mRNA was demonstrated in all evaluated samples of subcutaneous and visceral adipose tissue from the 17 patients. The exon 3+ isoform was expressed in all adipose tissue samples, whereas only six subjects expressed the 3- isoform as well. The only distinctive feature of these six patients was a higher HbA1c.

CONCLUSIONS

The heterozygous GHR +3/-3 genotype is more prevalent in subjects with morbid obesity. Patients expressing the exon +3 and exon -3 isoforms in adipose tissue had a higher HbA1c, than those expressing only the exon -3 isoform.

Oral administration of dibutyryl adenosine cyclophosphate improved growth performance in weaning piglets by enhancing lipid fatty acids metabolism

Dibutyryl adenosine cyclophosphate (dbcAMP-Ca), an analog of cyclic adenosine monophosphate (cAMP), plays greater roles in regulating physiological activities and energy metabolism than cAMP. The aim of this study was to investigate the effect of oral administration of dbcAMP-Ca on growth performance and fatty acids metabolism in weaning piglets. A total of 14 early weaning piglets (7 ± 1 d of age, 3.31 ± 0.09 kg, Landrace × Large White × Duroc) were randomly divided into 2 groups: control group and dbcAMP-Ca group, and the piglets received 7 mL of 0.9% NaCl or 1.5 mg dbcAMP-Ca dissolved in 7 mL of 0.9% NaCl per day for 10 d, respectively. The results showed that the average daily gain (ADG) increased by 109.17% (P < 0.05) in the dbcAMP-Ca group compared with the control group. Besides, dbcAMP-Ca significantly decreased blood high density lipoprotein cholesterol (HDLC) concentration (P < 0.05) and significantly increased blood low density lipoprotein cholesterol (LDLC) concentration (P ＜ 0.05) compared with the control group. Further, liver C18:2n6t content significantly increased in dbcAMP-Ca group (P < 0.05) compared with the control group. With the increase of C18:2n6t content, the mRNA expression levels of peroxisome proliferator-activated receptor α (PPARα) and hormone sensitive glycerol three lipase (HSL), of which genes are related to lipid metabolism, were also significantly increased (P < 0.05 or P < 0.01). All of the results indicated that dbcAMP-Ca improved the ADG, which was probably done by regulating fatty acids metabolism in the liver of weaning piglets.

Genetic variations at the human growth hormone receptor (GHR) gene locus are associated with idiopathic short stature

GH plays an essential role in the growing child by binding to the growth hormone receptor (GHR) on target cells and regulating multiple growth promoting and metabolic effects. Mutations in the GHR gene coding regions result in GH insensitivity (dwarfism) due to a dysfunctional receptor protein. However, children with idiopathic short stature (ISS) show growth impairment without GH or GHR defects. We hypothesized that decreased expression of the GHR gene may be involved. To test this, we investigated whether common genetic variants (microsatellites, SNPs) in regulatory regions of the GHR gene region were associated with the ISS phenotype. Genotyping of a GT‐repeat microsatellite in the GHR 5′UTR in a Montreal ISS cohort (n = 37 ISS, n = 105 controls) revealed that the incidence of the long/short (L/S) genotype was 3.3× higher in ISS children than controls (P = 0.04, OR = 3.85). In an Italian replication cohort (n = 143 ISS, n = 282 controls), the medium/short (M/S) genotype was 1.9× more frequent in the male ISS than controls (P = 0.017, OR = 2.26). In both ISS cohorts, logistic regression analysis of 27 SNPs showed an association of ISS with rs4292454, while haplotype analysis revealed specific risk haplotypes in the 3′ haploblocks. In contrast, there were no differences in GT genotype frequencies in a cohort of short stature (SS) adults versus controls (CARTaGENE: n = 168 SS, n = 207 controls) and the risk haplotype in the SS cohort was located in the most 5′ haploblock. These data suggest that the variants identified are potentially genetic markers specifically associated with the ISS phenotype.

Growth hormone signaling in fibroblasts from newborn boys and prepubertal boys

BACKGROUND/AIM

Responsiveness to GH in target cells is mediated by its receptor, which activates the Janus kinase-2 (JAK2) and STAT5 (signal transducers and activators of transcription 5) leading to the expression of IGF-1 and IGFALS. The aim of this study was to compare the GH signaling pathway in newborns and prepubertal boys.

SUBJECTS AND METHODS

We determined the GHR protein content and the effect of stimulation with recombinant human GH (rhGH; 200ng/mL) on JAK2 and STAT5 phosphorylation in skin fibroblast cultures obtained from newborns and prepubertal boys. The transcript levels of IGFALS and IGF-I, were also studied and compared after 16h or 24h of stimulation with GH in both study groups.

RESULTS

Newborn infants showed less GHR protein than the prepubertal boys. After rhGH stimulation, JAK2 and STAT5 phosphorylation was absent in skin fibroblasts from newborns, but was clearly detectable in prepubertal boys. After 16h of treatment with rhGH, IGFALS and IGF-I transcript levels increased in the prepubertal boys when compared to baseline. In newborns, however, we did not observe a response after 16 and 24h of rhGH stimulation.

CONCLUSION

The significant attenuation of the GH signaling pathway observed in fibroblasts from newborn boys appears to be related to a reduction in GHR content and lack of phosphorylation of JAK2 and STAT5 in response to rhGH. This might impair STAT5 dimer formation, leading to a reduction in the transcript levels of IGFALS and IGF-I during the newborn period.

Preweaning GH Treatment Normalizes Body Growth Trajectory and Reverses Metabolic Dysregulation in Adult Offspring After Maternal Undernutrition

Maternal undernutrition (UN) results in growth disorders and metabolic dysfunction in offspring. Although dysregulation of the GH-IGF axis in offspring is a known consequence of maternal UN, little is known about the efficacy of GH treatment during the period of developmental plasticity on later growth and metabolic outcomes. The present study investigated the effect of preweaning GH treatment on growth, glucose metabolism, and the GH-IGF axis in adult male and female offspring after maternal UN. Female Sprague Dawley rats were fed either a chow diet ad libitum (control [CON]) or 50% of ad libitum (UN) throughout pregnancy. From postnatal day 3, CON and UN pups received either saline (CON-S and UN-S) or GH (2.5 μg/g·d CON-GH and UN-GH) daily throughout lactation. At weaning, male and female offspring were randomly selected from each litter and fed a standard chow diet for the remainder of the study. Preweaning GH treatment normalized maternal UN-induced alterations in postweaning growth trajectory and concomitant adiposity in offspring. Plasma leptin concentrations were increased in UN-S offspring and normalized in the UN-GH group. Hepatic GH receptor expression was significantly elevated in UN-S offspring and normalized with GH treatment. Hepatic IGF binding protein-2 gene expression and plasma IGF-1 to IGF binding protein-3 ratio was reduced in UN-S offspring and elevated with GH treatment. GH treatment during a critical developmental window prevented maternal UN-induced changes in postnatal growth patterns and related adiposity, suggesting that manipulation of the GH-IGF-1 axis in early development may represent a promising avenue to prevent adverse developmental programming effects in adulthood.

Transcriptome analysis of the mammary gland from GH transgenic goats during involution

Mammary glands are organs for milk production in female mammals. Growth hormone (GH) is known to affect the growth and development of the mammary gland, as well as to increase milk production in dairy goats. This study performed a comprehensive expression profiling of genes expressed in the mammary gland of early involution GH transgenic (n=4) and non-transgenic goats (n=4) by RNA sequencing. RNA was extracted from mammary gland tissues collected at day 3 of involution. Gene expression analysis was conducted by Illumina RNA sequencing and sequence reads were assembled and analyzed using TopHat. FPKM (fragments per kilobase of exon per million) values were analyzed for differentially expressed genes using the Cufflinks package. Gene ontology analysis of differentially expressed genes was categorized using agriGO, while KEGG pathway analysis was performed with the online KEGG automatic annotation server. Our results revealed that 75% of NCBI goat annotated genes were expressed during early involution. A total of 18,323 genes were expressed during early involution in GH transgenic goats, compared with 18,196 expressed genes during early involution of non-transgenic goats. In these expressed genes, the majority (17,589) were ubiquitously expressed in GH transgenic and non-transgenic goats. However, there were 745 differentially expressed genes, 421 of which were upregulated and 324 were downregulated in GH transgenic goats. GO and KEGG pathway analysis showed that these genes were involved in mammary gland physiology, including cell adhesion molecules, ECM-receptor interaction, Jak-STAT signaling pathway, and fat metabolism. Our results demonstrated that the GH receptor was strongly affected in GH transgenic goats, which may activate the IGF-1/Stat3 signaling pathway. Overall, our study provided a global view of the transcriptome during involution of GH transgenic and non-transgenic goats, which increases our understanding of the biology of involution in the goat.

Messenger RNA sequencing and pathway analysis provide novel insights into the biological basis of chickens' feed efficiency

Background

Advanced selection technologies have been developed and continually optimized to improve traits of agricultural importance; however, these methods have been primarily applied without knowledge of underlying biological changes that may be induced by selection. This study aims to characterize the biological basis of differences between chickens with low and high feed efficiency (FE) with a long-term goal of improving the ability to select for FE.

Results

High-throughput RNA sequencing was performed on 23 breast muscle samples from commercial broiler chickens with extremely high (n = 10) and low (n = 13) FE. An average of 34 million paired-end reads (75 bp) were produced for each sample, 80% of which were properly mapped to the chicken reference genome (Ensembl Galgal4). Differential expression analysis identified 1,059 genes (FDR < 0.05) that significantly divergently expressed in breast muscle between the high- and low-FE chickens. Gene function analysis revealed that genes involved in muscle remodeling, inflammatory response and free radical scavenging were mostly up-regulated in the high-FE birds. Additionally, growth hormone and IGFs/PI3K/Akt signaling pathways were enriched in differentially expressed genes, which might contribute to the high breast muscle yield in high-FE birds and partly explain the FE advantage of high-FE chickens.

Conclusions

This study provides novel insights into transcriptional differences in breast muscle between high- and low-FE broiler chickens. Our results show that feed efficiency is associated with breast muscle growth in these birds; furthermore, some physiological changes, e.g., inflammatory response and oxidative stress, may occur in the breast muscle of the high-FE chickens, which may be of concern for continued selection for both of these traits together in modern broiler chickens.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1364-0) contains supplementary material, which is available to authorized users.

The GH-IGF-SST system in hepatocellular carcinoma: biological and molecular pathogenetic mechanisms and therapeutic targets

Hepatocellular carcinoma (HCC) is the sixth most common malignancy worldwide. Different signalling pathways have been identified to be implicated in the pathogenesis of HCC; among these, GH, IGF and somatostatin (SST) pathways have emerged as some of the major pathways implicated in the development of HCC. Physiologically, GH-IGF-SST system plays a crucial role in liver growth and development since GH induces IGF1 and IGF2 secretion and the expression of their receptors, involved in hepatocytes cell proliferation, differentiation and metabolism. On the other hand, somatostatin receptors (SSTRs) are exclusively present on the biliary tract. Importantly, the GH-IGF-SST system components have been indicated as regulators of hepatocarcinogenesis. Reduction of GH binding affinity to GH receptor, decreased serum IGF1 and increased serum IGF2 production, overexpression of IGF1 receptor, loss of function of IGF2 receptor and appearance of SSTRs are frequently observed in human HCC. In particular, recently, many studies have evaluated the correlation between increased levels of IGF1 receptors and liver diseases and the oncogenic role of IGF2 and its involvement in angiogenesis, migration and, consequently, in tumour progression. SST directly or indirectly influences tumour growth and development through the inhibition of cell proliferation and secretion and induction of apoptosis, even though SST role in hepatocarcinogenesis is still opened to argument. This review addresses the present evidences suggesting a role of the GH-IGF-SST system in the development and progression of HCC, and describes the therapeutic perspectives, based on the targeting of GH-IGF-SST system, which have been hypothesised and experimented in HCC.

Human growth hormone receptor gene expression is regulated by Gfi-1/1b and GAGA cis-elements

Human growth hormone receptor (hGHR) gene regulation is complex: mRNAs are transcribed from multiple variant (V) 5'UTR exons, several ubiquitously while others only in the postnatal hepatocyte. The liver-specific V1 exon promoter contains Gfi-1/1b repressor sites adjacent to a GAGA box, a GH response element (GHRE) in several mammalian genes. GAGA boxes are also present in the ubiquitously expressing V3 exon promoter. Heterologous sites in bovine, ovine and murine GHR genes suggest conserved roles. GAGA factor stimulated V1 and V3 promoters while Gfi-1/1b repressed basal and GAF-stimulated V1 transcription. HGH treatment of HepG2 cells resulted in a new complex forming with V3 GAGA elements, suggesting a functional GHRE. Data suggest liver-specific V1 transcription is regulated by inhibitory Gfi-1/1b and stimulatory GAGA cis-elements and Gfi-1/1b may control the lack of V1 expression in fetal liver, hepatic tumours and non-hepatic tissues. In addition, hGH may regulate hGHR expression through V3 GAGA boxes.

Human growth hormone receptor (GHR) expression in obesity: II. Regulation of the human GHR gene by obesity-related factors

BACKGROUND AND METHODS

In our previous analyses, we found significantly lower levels of growth hormone receptor (GHR) mRNA in adipose tissues of obese than in those of lean individuals, suggesting that idiopathic obesity involves GH resistance due to decreased GHR availability. To understand the mechanism(s) behind this downregulation, we performed an in silico analysis of the three most relevant GHR gene promoters, which revealed putative response elements (REs) for a number of obesity adipose-associated factors, including tumor necrosis factor-alpha (TNFα), hypoxia-inducible factor-1-alpha (HIF-1α) and glucocorticoids. We then characterized the dose-dependent effects of these factors on GHR expression in HEK293 cells and in mature human SGBS (Simpson-Golabi-Behmel syndrome) adipocytes using quantitative reverse transcriptase-PCR and assessed the function of their putative REs by luciferase-reporter assays, site-directed mutagenesis and chromatin immunoprecipitation (ChIP) assays.

RESULTS

TNFα treatments significantly reduced GHR mRNA levels and GHR promoter activities at doses ≥ 10 ng ml(-1) in both cell lines. Transient overexpression of HIF-1α or exposure to the hypoxia mimetic CoCl(2) significantly increased GHR mRNA levels and promoter activities. Dexamethasone had biphasic effects: there was a significant increase in GHR mRNA levels at 10(-10) M and in promoter activities at 10(-10) and 10(-8) M, whereas a significant decrease in both mRNA levels and promoter activities occurred at 10(-6) M. Site-directed mutagenesis of the putative nuclear factor-κB, HIF-1α and glucocorticoid REs resulted in the loss of these effects, whereas ChIP analysis confirmed specific transcription factor-promoter interactions.

CONCLUSIONS

Our results suggest that the increased activity of TNFα, HIF-1α and glucocorticoids in obese adipose tissues could alter GHR gene transcription through specific REs and that TNFα may be involved in the development of GH resistance.

Evaluation of the biological activity of human growth hormone by enzyme linked immuno-receptor assay (ELIRA) method

The aim of this research was to study the application and effectiveness of Enzyme Linked Immuno Receptor Assay (ELIRA) method for understanding the bioactivity of human Growth Hormone (hGH) in micro-titer plates. For this purpose, rabbit hepatocyte microsomes which contained hGH receptors were used for coating of ELISA micro-titer plates. Then hGH was interacted with coated receptors. Fractions of bounded complexes were identified by antibodies in an Enzyme-based substrate detection system. Different assay conditions such as: buffers, blocking agents, temperatures and times of incubation were analyzed. Our result indicated that, the carbonate coating buffer was not effective in receptor coating in ELIRA. Overnight incubation of hGH and hGH receptors in HEPES assay buffer and BSA blocking resulted in the lower linearity and correlations (R(2) = 0.46 to 0.85). However, 3 h incubation in Tris-HCl assay buffer at 30°C resulted in higher linearity and correlations (R(2) = 0.95 to 0.97). Finally, the coating of microwells by 250 μg/ml of microsome membranes in Tris buffer at 30°C for 3 hr and blocking by skim milk resulted to the best linearity and higher correlation, (R(2) = 0.985) and lower detection limit about 2 ng/ml of bioactive hGH.

Ancient origin of placental expression in the growth hormone genes of anthropoid primates

In anthropoid primates, growth hormone (GH) genes have undergone at least 2 independent locus expansions, one in platyrrhines (New World monkeys) and another in catarrhines (Old World monkeys and apes). In catarrhines, the GH cluster has a pituitary-expressed gene called GH1; the remaining GH genes include placental GHs and placental lactogens. Here, we provide cDNA sequence evidence that the platyrrhine GH cluster also includes at least 3 placenta expressed genes and phylogenetic evidence that placenta expressed anthropoid GH genes have undergone strong adaptive evolution, whereas pituitary-expressed GH genes have faced strict functional constraint. Our phylogenetic evidence also points to lineage-specific gene gain and loss in early placental mammalian evolution, with at least three copies of the GH gene present at the time of the last common ancestor (LCA) of primates, rodents, and laurasiatherians. Anthropoid primates and laurasiatherians share gene descendants of one of these three copies, whereas rodents and strepsirrhine primates each maintain a separate copy. Eight of the amino-acid replacements that occurred on the lineage leading to the LCA of extant anthropoids have been implicated in GH signaling at the maternal-fetal interface. Thus, placental expression of GH may have preceded the separate series of GH gene duplications that occurred in catarrhines and platyrrhines (i.e., the roles played by placenta-expressed GHs in human pregnancy may have a longer evolutionary history than previously appreciated).

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.

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.

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.

The regulation of IGFs and IGFBPs by prolactin in primary culture of fetal rat hepatocytes is influenced by maternal malnutrition

During perinatal development, the regulation of IGF system appears to be growth hormone (GH) independent. By using highly purified primary fetal hepatocytes, we investigated the role of prolactin (PRL) in the regulation of IGF system and hepatocyte proliferation. We also analyzed the consequence of a maternal low-protein (LP) diet on the regulation of IGF, IGF-binding protein (IGFBP), and hepatocyte proliferation by prolactin. Pregnant Wistar rats were fed a control (C) diet (20% protein) or isocaloric (LP; 8%) diet throughout gestation. On day 21.5, fetal hepatocytes were cultured for 4 days and incubated with rat prolactin. In the C hepatocytes, PRL at 100 ng/ml decreased the abundance of IGFBP-1 and IGFBP-2 by 50 (P < 0.05) and 60% (P < 0.01), respectively. It also reduced by 70% the level of IGF-II mRNA (P < 0.01). By contrast, PRL failed to modulate IGFBP-1 and IGFBP-2 production by LP hepatocytes, and this was associated with reduced abundance of the short form of PRL receptor (P < 0.05). PRL had no effect on either the proliferation or the IGF-I production by C and LP hepatocytes, although it reduced the expression of IGF-II. These results suggest that prolactin influences hepatocyte proliferation in vitro by inhibiting IGFBP-1, IGFBP-2, and IGF-II levels, which may coincide with the decline of IGF-II observed in rodents during late gestation in vivo. On the other hand, maternal LP diet induces a resistance of fetal hepatocytes to PRL.

CNS microvascular pericytes exhibit multipotential stem cell activity

It has been suggested that a vascular-like cell has multipotent regenerative and mesenchymal lineage relationships. The identity of this stem/progenitor cell has remained elusive. We report here that adult central nervous system (CNS) capillaries contain a distinct population of microvascular cells, the pericyte that are nestin/NG2 positive and in response to basic fibroblast growth factor (bFGF) differentiate into cells of neural lineage. In their microvascular location, pericytes express nestin and NG2 proteoglycan. In serum containing media primary (0 to 7 day old) CNS pericytes are nestin positive, NG2 positive, alpha smooth muscle actin (alphaSMA) positive, and do not bind the endothelial cell specific griffonia symplicifolia agglutinin (GSA). In serum containing media, pericytes do not undergo neurogenesis but are induced to express alphaSMA. In bFGF containing media without serum, CNS pericytes form small clusters and multicellular spheres. Differentiated spheres expressed neuronal and glial cell markers. After disruption and serial dilution, differentiated spheres were capable of self-renewal. When differentiated spheres were disrupted and cultured in the presence of serum, multiple adherent cell populations were identified by dual and triple immunocytochemistry. Cells expressing markers characteristic of pericytes, neurons, and glial cells were generated. Many of the cells exhibited dual expression of differentiation markers. With prolonged culture fully differentiated cells of neural lineage were present. Results indicate that adult CNS microvascular pericytes have neural stem cell capability.

The role of growth hormone in fetal development

Studies across several species, particularly the mouse, show that growth hormone (GH, somatotrophin) is an important determinant of litter size, and to a lesser extent, of birth length. GH acts at all stages of development, from ovulation through preimplantation development to the late fetus, with actions on both embryo/fetus and mother contributing to successful fetal development. The fact that these are not more obvious in vivo is likely a result of redundancy of cytokine hormone action, particularly in relation to prolactin, which shares common actions and receptor locations with GH.