Regulation of gonadotropin-releasing hormone neurons by basic fibroblast growth factor.

The development of a functional network of gonadotropin-releasing hormone (GnRH) neurons in the central nervous system requires a series of complex regulatory mechanisms, presumably mediated in part by neurotrophic factors. The difficulty in studying factors regulating the development of GnRH neurons stems from their paucity and scattered distribution in the brain; as a result, little was known about the role of neurotrophic factors in the development of the mature GnRH neuronal network. Recent utilization of immortalized GnRH neuronal cell lines (GT1) has enabled us to identify and study specific neurotrophic factors and their functions in vitro. The potent neurotrophic effect of basic fibroblast growth factor (bFGF) and the presence of a high abundance of receptors for bFGF in GT1 cells have led to the hypothesis that bFGF may be an important regulator of GnRH neuron expansion, survival, migration, and connectivity.     

Interaction of receptors for insulin-like growth factor I, platelet-derived growth factor, and fibroblast growth factor in rat aortic cells

Serum contains various growth factors which regulate the proliferation of cells. We investigated the growth of cultured arterial smooth muscle cells under the influence of insulin-like growth factor I (IGF I), fibroblast growth factor (FGF), and platelet-derived growth factor (PDGF), and examined the effect of these growth factors on the binding of [125I] IGF I and on the binding of [125I]PDGF to these cells. IGF I, FGF, and PDGF stimulated [6-3H]thymidine incorporation into DNA of confluent cultures of cells which were incubated in modified Dulbecco's modified Eagle medium. However, the effect of these growth factors on DNA synthesis was much more potent in Dulbecco's modified Eagle medium with 1% fetal calf serum. FGF and PDGF potentiated the growth-promoting effect of IGF I. The binding of [125I]IGF I to the cells was increased after a preincubation with FGF and PDGF. The binding was potently increased by FGF (100 ng/ml) after a preincubation time of 30 min. There was an increase in binding during the first 3 h of preincubation followed by a decrease after 4-5 h. PDGF (10-1000 ng/ml) stimulated [125I]IGF I binding only after 2 h of preincubation. The stimulation was dose dependent. Maximal stimulation of the binding was observed after 3 h of preincubation followed by a decrease after 4-5 h of preincubation. Specific binding sites for PDGF on smooth muscle cells could be demonstrated too. A preincubation of confluent cells with IGF I caused a dose-dependent increase in [125I]PDGF binding. These results support the hypothesis that the regulation of the binding of a specific growth factor by a second growth factor is important for the control of cell growth.     

Interactions between interleukin-1 and basic fibroblast growth factor on articular chondrocytes. Effects on cell growth, prostanoid production, and receptor modulation.

The interactions of interleukin-1 beta (IL-1 beta) and basic fibroblast growth factor (bFGF) with monolayer cultures of rabbit articular chondrocytes were examined. Both agonists resulted in a synergistic increase in prostanoid production, to levels higher than the maximal level for either protein alone. The synergy was time- and dose-dependent, was augmented in serum-free medium, and was blocked by indomethacin or a polyclonal antibody to IL-1 beta. The proteins had opposite effects on cell growth, and IL-1 beta completely blocked the mitogenic effect of bFGF. Pretreatment of cells with IL-1 beta induced a down-regulation in the number of the bFGF high-affinity receptors. Pretreatment of cells with bFGF increased the number of IL-1 receptors, which was dependent on messenger RNA synthesis.     

Hormone therapy in heart failure: growth hormone and insulin-like growth factor I

Heart disease is the major cause of mortality in the developed world. Despite recent advances in the therapy of heart failure due to ACE inhibitors and beta-blockers, the prognosis of this syndrome is still poor. In the past few years, the effects of growth hormone (GH) and insulin-like growth factor-I (IGF-I) on heart morphology and function were extensively studied. Some studies dealing with experimental heart failure of animals and one controversial study dealing with human heart failure suggest positive hemodynamic effects of GH and/or IGF-I treatment. This review summarizes the physiological effects of GH/IGF-I on the myocardium, their signal transduction mechanisms, and the data currently available on the therapeutic use of these agents.     

Follicle-stimulating hormone induces functional receptors for basic fibroblast growth factor in rat granulosa cells.

In the present study we examined the existence of receptors for basic fibroblast growth factor (bFGF) and its regulation in rat granulosa cells. The binding of labeled bFGF to rat granulosa cells was dose-dependently displaced by unlabeled bFGF, but not other growth factors. FSH induced a dose-dependent increase in specific binding for bFGF to cultured rat granulosa cells. FSH treatment did not change the binding affinity (Kd, 2.8-3.0 x 10(-10) M) of the bFGF receptor, but increased the total number of bFGF-binding sites, whereas treatment with several steroid hormones had no effect on the specific binding of bFGF. Since cycloheximide, a protein synthesis inhibitor, inhibited the increase in bFGF binding induced by FSH, it is suggested that protein synthesis might be involved in the FSH stimulation of bFGF receptor induction. Furthermore, bFGF stimulated tissue plasminogen activator activity in a dose-dependent manner, and FSH-primed granulosa cells were more responsive to bFGF action, with a decrease in the ED50 from 5.0 to 1.5 ng/ml. The antibody against human bFGF neutralized the stimulatory effect of bFGF on tissue plasminogen activator secretion. The present study suggests that FSH induces functional receptors for bFGF in granulosa cells and that bFGF may play a role in the process of differentiation under the influence of FSH.     

Effects of insulin-like growth factor I, platelet-derived growth factor, fibroblast growth factor, and transforming growth factor-beta on thymidine incorporation into fetal liver cells

We have studied the effect of different growth factors on thymidine incorporation in cell cultures of erythroid cells from fetal calf and rat livers, a system which has been used in the past as a bioassay for the purification of erythropoietin and erythropoietin-like factors. Insulin-like growth factor I significantly stimulated thymidine incorporation in calf and rat liver cells. Its action in both cell types was practically identical to the effect of bovine serum erythrotropin, a peptide structurally similar to insulin-like growth factor II. The synergistic effect between insulin-like growth factor I and erythropoietin could be observed with partially purified sheep plasma erythropoietin but not with recombinant human erythropoietin. The highest thymidine incorporation was observed when both erythropoietin and insulin-like growth factor I were added simultaneously. Platelet-derived growth factor had a lower thymidine incorporation-stimulating activity than insulin-like growth factor and did not have any synergistic effect with erythropoietin in rat liver cells. Fibroblast growth factor (0.4-6.0 ng/ml) was completely inactive in the thymidine incorporation assay of calf liver cells. Transforming growth factor-beta alone at a concentration of 1 ng/ml significantly inhibited thymidine incorporation into rat liver cells. It seems that from all growth factors tested so far, those belonging to the insulin family of peptides are the most likely to be detected in the thymidine incorporation assays using calf or rat liver cells.     

Growth hormone/insulin-like growth factor I axis in neurodegenerative diseases

Neurodegenerative diseases (ND) are a group of heterogeneous disorders characterized by unknown etiology, subtle onset, and progressive involvement of neuronal systems leading to degeneration and dysfunction. They represent a challenge for basic science and clinical medicine because of increasing prevalence, social cost, complex biochemistry and pathology, and lack of mechanism-based treatments. Endocrine modifications may accompany the progression of ND, due to the intimate connections between central nervous and endocrine systems. Reported data on endocrine changes in different ND have often been non-conclusive or conflicting. GH/IGF-I axis is involved in the regulation of brain growth, development, and metabolism. Dysfunctions in GH/IGF-I axis in most of ND are therefore reviewed. Whether GH deficiency, when present, may act as a contributory factor in the pathogenesis of these diseases, or might represent a consequence of it is presently unknown. A thorough effort in investigating every possible involvement of GH/IGF-I axis is warranted, in the light of future possible therapeutic strategies.     

胰岛素样生长因子-I与代谢综合征及胰岛素抵抗的关系

目的为了研究血清胰岛素样生长因子-I（IGF-I）与代谢综合征、胰岛素抵抗和高胰岛素血症之间的关系。方法本研究分析了75名住院患者冠脉造影结果、代谢综合征的相关情况和血清IGF-I的浓度。结果代谢综合征患者的血清IGF-I水平明显低于非代谢综合征患者,且血清IGF-I水平与血清胆固醇,体质量指数呈负相关,并且在非糖尿病患者中,IGF-I值与HOMA胰岛素抵抗指数有相关性。结论血清IGF-I水平与胰岛素抵抗有关,与反映胰岛素抵抗的指标如体内脂肪含量和脂代谢紊乱具有相关性。     

Growth hormone and insulin-like growth factor I in German shepherd dwarf dogs

The roles of growth hormone (GH) and insulin-like growth factor I (IGF I) were studied in 9 German Shepherd dwarf dogs. GH deficiency was evidenced in all dogs by an absence of increase in GH levels in response to clonidine administration. While the mean IGF I concentration in normal adult German Shepherds was 280 +/- 23 ng/ml and 345 +/- 50 ng/ml in immature animals, the mean IGF I concentration in the dwarf dogs was 11 +/- 2 ng/ml (mean +/- SEM, P less than 0.001). In the affected animals, plasma thyroxine (T4) levels were only slightly subnormal and there was an increase in these levels in response to thyroid stimulating hormone (TSH) administration. The findings indicate 1) that dwarfism in German Shepherds is caused by primary GH-deficiency resulting in low circulating levels of IGF I and 2) that IGF I levels in the dog as in man are subject to control by GH.     

Longitudinal bone growth in vitro: effects of insulin-like growth factor I and growth hormone

Longitudinal growth was studied using an in vitro model system of intact rat long bones. Metatarsal bones from 18- and 19-day-old rat fetuses, entirely (18 days) or mainly (19 days) composed of chondrocytes, showed a steady rate of growth and radiolabelled thymidine incorporation for at least 7 days in serum-free media. Addition of recombinant human insulin-like growth factor-I to the culture media resulted in a direct stimulation of the longitudinal growth. Recombinant human growth hormone was also able to stimulate bone growth, although this was generally accomplished after a time lag of more than 2 days. A monoclonal antibody to IGF-I abolished both the IGF-I and GH-stimulated growth. However, the antibody had no effect on the growth of the bone explants in control, serum-free medium. Unlike the fetal long bones, bones from 2-day-old neonatal rats were arrested in their growth after 1-2 days in vitro. The neonatal bones responded to IGF-I and GH in a similar fashion as the fetal bones. Thus in this study in vitro evidence of a direct effect of GH on long bone growth via stimulating local production of IGF by the growth plate chondrocytes is presented. Furthermore, endogenous growth factors, others than IGFs, appear to play a crucial role in the regulation of fetal long bone growth.     

Expression of insulin-like growth factor II and receptors for insulin-like growth factor II, insulin-like growth factor I and insulin in isolated and cultured rat hepatocytes.

Insulin-like growth factor II is believed to play an important role in fetal growth and development. The insulin-like growth factor II gene expression is tissue specific and developmentally regulated. We have previously shown an enhanced level of insulin-like growth factor II messenger RNA and protein in human hepatocellular carcinomas. This led to the suggestion that hepatocytes might be involved in insulin-like growth factor II expression. However, previous studies based on in situ hybridization only showed insulin-like growth factor II messenger RNA in liver sinusoidal cells. This paper reports on the analysis of the expression of insulin-like growth factor II and insulin-like growth factor II, insulin-like growth factor I and insulin receptor messenger RNAs in vivo in isolated rat hepatocytes at various stages of development and in vitro in adult rat hepatocytes primary culture. Our study indicates that isolated rat hepatocytes synthesize insulin-like growth factor II messenger RNA with a switch between fetal and adult messenger RNA profiles occurring 21 days after birth. In addition, adult rat hepatocytes in culture expressed insulin-like growth factor II messenger RNA and protein. Insulin-like growth factor II, insulin-like growth factor I and insulin receptor messenger RNAs were also detected. Therefore these results are consistent with the hypothesis that insulin-like growth factor II acts as an autocrine growth factor for hepatocytes in addition to having a paracrine effect. They also indicate that primary culture of hepatocytes is a good model for further studies on insulin-like growth factor II gene regulation.     

The effect of growth hormone on insulin-like growth factor I and bone metabolism in distraction osteogenesis.

Limb lengthening in the left tibia of 30 mature female Yucatan micropigs was performed using distraction osteogenesis. A treatment group of 15 animals received recombinant porcine growth hormone (r-pGH) (100 microg/kg/day) while the others served as controls. Serial serum measurements of total insulin-like growth factor I (IGF-I), free IGF-I, IGF binding proteins -1, -2, -3 and -4 (IGFBP-1 to -4) were performed. Bone-specific alkaline phosphatase (bone-ALP) and the serum carboxyl-terminal telopeptide of type I collagen (ICTP) were measured as bone turnover markers. The GH-treated animals showed a significant increase in total IGF-I, free IGF-I and IGFBP-3 after surgery (P<0.001). Similarly, the treated animals showed a significantly higher level of bone-ALP (P<0.001) throughout the experiment compared to the controls. There was a significant correlation between bone-ALP and total IGF-I (r=0.76) in the GH-treated group and an even higher correlation for free IGF-I (r=0.90). There was no difference in the ICTP serum levels between the two groups. These data indicate that the application of species-specific growth hormone results in a stimulation of bone formation in distraction osteogenesis which may be mediated by IGF-I. The stronger correlation between free IGF-I and bone-ALP indicates that the anabolic effect of IGF-I may be regulated through the IGFBPs by binding and inactivating IGF-I.     

Growth hormone treatment in short children: relationship between growth and serum insulin-like growth factor I and II levels

Thirty-one children who were short but not GH deficient, whose serum GH responses to provocative tests were normal, and whose spontaneous GH secretion was low received daily sc injections of human GH (Crescormon; 0.1 IU/kg BW) for 1 yr. Their initial serum insulin-like growth factor I (IGF-I) and IGF-II responses to GH were compared with their 1-yr growth response to therapy. In the prepubertal group (n = 18) the growth rate of all but two children increased 3.4 +/- 0.2 (+/- SEM) cm (from 4.1 +/- 0.2 to 7.5 +/- 0.3 cm/yr). The mean increment in the growth rate of the pubertal group was 5.2 +/- 0.5 cm. In both groups the growth increase was strongly correlated with both the percent increase in serum IGF-I and the percent increase in serum IGF-II during the first 10 days of treatment. No correlation was found between the basal growth rate and basal serum IGF-I or IGF-II levels. In the prepubertal group of children, both the percent increase in serum IGF-I levels in response to GH and the age at start of treatment were predictors of long term growth. We conclude that this subgroup of normal short children with low spontaneous GH secretion and high percent increase in serum IGF values benefits from GH treatment with an increased growth rate.     

Influence of continuous growth hormone or insulin-like growth factor I administration in adult female chickens.

A series of studies was conducted to determine whether growth hormone (GH) exerts effects on adult female chickens. Recombinant chicken GH (rcGH) was administered continuously via osmotic minipumps. No consistent effects of rcGH treatment were observed on reproductive indices. Hens receiving rcGH treatment for 10 days exhibited hepatomegaly and showed a tendency (P < 0.1) for increased spleen and thymus weights. Moreover, there were increases in the circulating concentrations of insulin-like growth factor-I (IGF-I) and IGF-binding proteins (IGF-BPs) (22-kDa IGF-BP after 2, 5, and 10 days; 28-kDa IGF-BP after 5 and 10 days; and 36-kDa IGF-BP after 10 days) with rcGH treatment. To determine whether the changes in IGF-BPs were due directly to GH or indirectly via IGF-I, the effects of the continuous administration of rcGH or recombinant human IGF-I (rhIGF-I) were compared. While rcGH again elevated the circulating levels of 28- and 36-kDa IGF-BPs, no such effect was observed with rhIGF-I treatment. However, both treatments exerted similar effects in depressing pituitary GH mRNA levels and elevating plasma concentrations of IGF-I. It is concluded that GH directly elevates circulating concentrations of IGF-I and IGF-BPs, but the negative feedback effect on GH synthesis is mediated via IGF-I.     

Three-dimensional structure of human basic fibroblast growth factor.

The three-dimensional structure of human basic fibroblast growth factor (bFGF) has been determined by x-ray crystallography and refined to a crystallographic residual of 17.4% at 2.2-A resolution. The structure was initially solved at a nominal resolution of 2.8 A by multiple isomorphous replacement using three heavy-atom derivatives. Although the map clearly showed the overall fold of the molecule, electron density was not observed for the first 19 amino-terminal and the last 3 carboxyl-terminal amino acids, suggesting that they are disordered. The bFGF crystals were grown from 2.0 M ammonium sulfate at pH 8.1 in space group P1 with cell dimensions a = 30.9 A, b = 33.4 A, c = 35.9 A, alpha = 59.5 degrees, beta = 72.0 degrees, and gamma = 75.6 degrees. There is one molecule per unit cell and the crystals diffract to spacings beyond 1.9 A. The overall structure of bFGF can be described as a trigonal pyramid with a fold very similar to that reported for interleukin 1 beta, interleukin 1 alpha, and soybean trypsin inhibitor. An apparent sulfate ion is bound within a basic region on the surface of the molecule and has a ligands the main-chain amide of Arg-120 and the side chains of Asn-27, Arg-120, and Lys-125. This is suggested as the presumed binding site for heparin. Residues 106-115, which are presumed to bind to the bFGF receptor [Baird, A., Schubert, D., Ling, N. & Guillemin, R. (1988) Proc. Natl. Acad. Sci. USA 85, 2324-2328], include an irregular loop that extends somewhat from the surface of the protein and is about 25 A from the presumed heparin binding site. The backbone structure of this putative receptor-binding loop is very similar, although not identical, to the corresponding region of interleukin 1 beta.     

Growth cartilage expression of growth hormone/insulin-like growth factor I axis in spontaneous and growth hormone induced catch-up growth

IntroductionCatch-up growth following the cessation of a growth inhibiting cause occurs in humans and animals. Although its underlying regulatory mechanisms are not well understood, current hypothesis confer an increasing importance to local factors intrinsic to the long bones' growth plate (GP).AimThe present study was designed to analyze the growth-hormone (GH)-insulin-like growth factor I (IGF-I) axis in the epiphyseal cartilage of young rats exhibiting catch-up growth as well as to evaluate the effect of GH treatment on this process.Material and methodsFemale Sprague–Dawley rats were randomly grouped: controls (group C), 50% diet restriction for 3 days + refeeding (group CR); 50% diet restriction for 3 days + refeeding &; GH treatment (group CRGH). Analysis of GH receptor (GHR), IGF-I, IGF-I receptor (IGF-IR) and IGF binding protein 5 (IGFBP5) expressions by real-time PCR was performed in tibial growth plates extracted at the time of catch-up growth, identified by osseous front advance greater than that of C animals.ResultsIn the absence of GH treatment, catch-up growth was associated with increased IGF-I and IGFBP5 mRNA levels, without changes in GHR or IGF-IR. GH treatment maintained the overexpression of IGF-I mRNA and induced an important increase in IGF-IR expression.ConclusionsCatch-up growth that happens after diet restriction might be related with a dual stimulating local effect of IGF-I in growth plate resulting from overexpression and increased bioavailability of IGF-I. GH treatment further enhanced expression of IGF-IR which likely resulted in a potentiation of local IGF-I actions. These findings point out to an important role of growth cartilage GH/IGF-I axis regulation in a rat model of catch-up growth.