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A Model for Tissue-Specific Inducible Insulin-like Growth Factor-I (IGF-I) Inactivation to Determine the Physiological Role of Liver-Derived IGF-I
Abstract
Insulin-like growth factor-I (IGF-I) has important growthpromoting and metabolic effects and is expressed in virtually every tissue of the body. The highest expression is found in the liver, but the physiological role of liver-derived IGF-I is unknown. It has been difficult to separate the endocrine effects of liver-derived IGF-I from the autocrine/paracrine effects of locally produced IGF-I in peripheral tissues. Therefore, we have developed a mouse model with a liver-specific inducible deletion of the IGF-I gene (LI-IGF-I-/- mouse). The LI-IGF-I-/- mouse has dramatically reduced (>80%) serum IGF-I levels, demonstrating that the major part of serum IGF-I is liver-derived. Surprisingly, LI-IGFI -/- mice demonstrate a normal appendicular skeletal growth up to at least 12 mo of age despite the dramatic decrease in circulating IGF-I levels, indicating that liver-derived IGF-I is not required for appendicular skeletal growth. However, the adult axial skeletal growth is reduced in the LI-IGF-I-/- mice. Furthermore, the amount of cortical bone is reduced due to decreased radial growth of the cortical bone, while the trabecular bone mineral density is unchanged in the LI-IGFI -/- mice. The decreased levels of circulating IGF-I are associated with increased serum levels of growth hormone (GH), indicating a role for liver-derived IGFI in the negative-feedback regulation of GH secretion. Measurements of factors regulating GH secretion in the pituitary and in the hypothalamus revealed an increased expression of GH-releasing-hormone (GHRH) and GHsecretagogue (GHS) receptors in the pituitary of LI-IGFI -/- mice. This in turn results in an increased sensitivity to systemically administered GHRH and GHS, demonstrating that the regulatory action of liver-derived IGF-I on GH secretion is at the pituitary rather than at the hypothalamic level. The liver is an important metabolic organ and LI-IGF-I-/- mice are markedly hyperinsulinemic and yet normoglycemic, consistent with an adequately compensated insulin resistance. Interestingly, LI-IGF-I-/- mice display a reduced age-dependent fat mass accumulation compared with control mice. Furthermore, LI-IGF-I-/- mice have increased blood pressure attributable to increased peripheral resistance indicating a role for liver-derived IGF-I in the regulation of blood pressure. In conclusion, liver-derived IGF-I is important for carbohydrate and lipid metabolism and for the regulation of GH secretion at the pituitary level. Furthermore, it regulates adult axial skeletal growth and cortical radial growth while it is not required for appendicular skeletal growth.
... That is, we observed no changes in body weight until 2 and 4 months of age for females and males, respectively. Likewise, LI-IGF1Ϫ/Ϫ and JAK2L mice do not differ in body weight until later in life (41,45), indicating the importance of age when interpreting the effects of endocrine IGF-I on body size (discussed here) and body composition (discussed below) in these liver-specific gene-disrupted mouse lines. ...
... Not reported previously are measures of other IGFBPs at the protein level in circulation after liver-specific removal of GHR, IGF-I, JAK2, or STAT5. However, Sjögren et al (45) have reported hepatic mRNA expression levels of IGFBP-1, IGFBP-2, and IGFBP-3 in LI-IGF-IϪ/Ϫ mice and mRNA levels for all 3 binding proteins are decreased, which is in contrast to our data. The difference is likely due the fact that LI-IGF-IϪ/Ϫ (as well as LID) mice have fully functional GHR in the liver; thus, LI-IGF-IϪ/Ϫ and LID mice can respond to the elevated GH levels, whereas LiGHRKO mice cannot. ...
... In JAK2L mice, Sos et al (41) report a decrease in body fat using male/female combined data, whereas Nordstrom et al (57) and Shi et al (42) report no change in body fat or body mass index, respectively. LI-IGF-IϪ/Ϫ mice are reported to have decreased fat mass (45,64), whereas LID mice have no change in fat mass (65). Because measures of body composition in GHRLD, JAK2L, LI-IGF-IϪ/Ϫ, and LID mice provide conflicting results, and because body size has been shown to be age-and sex dependent, it was valuable for us to report longitudinal measurements in this large cohort of male and female LiGHRKO as compared with control mice. ...
GH is an important regulator of body growth and composition as well as numerous other metabolic processes. In particular, liver plays a key role in the GH/insulin-like growth factor-1 (IGF-1) axis since the majority of circulating "endocrine" IGF-1 results from GH-stimulated liver IGF-1 production. To develop a better understanding of the role of liver in the overall function of GH, we generated a strain of mice with liver specific GH receptor (GHR) gene knockout (LiGHRKO mice). LiGHRKO mice had a 90% decrease in circulating IGF-1 levels, a 300% increase in circulating GH and significant changes in IGF binding protein-1, -2, -3, -5 and -7. LiGHRKO mice were smaller than controls as body length and body weight were significantly decreased in both sexes. Analysis of body composition over time revealed a pattern similar to those found in GH transgenic mice; that is, LiGHRKO mice had a higher percentage of body fat at early ages followed by lower percentage of body fat in adulthood. Local IGF-1 mRNA levels were significantly increased in skeletal muscle and select adipose tissue depots. Grip strength was increased in LiGHRKO mice. Finally, circulating levels of leptin, resistin and adiponectin were increased in LiGHRKO mice. In conclusion, LiGHRKO mice are smaller despite increased local mRNA expression of IGF-1 in several tissues, suggesting that liver derived IGF-1 is indeed important for normal body growth. Furthermore, our data suggest novel GH dependent crosstalk between liver and adipose is important for regulation of adipokines in vivo.
... The appendicular skeletal growth of the liver-specific IGF-I conditional KO mice, as determined by body weight, body length, and femoral length, did not differ from wild-type littermates [8]. However, the adult axial skeletal growth and the cortical bone width were reduced in the liver-specific conditional KO mice [10]. By contrast, global deletion of the IGF-I gene in every cell caused a 20-40% reduction in femur length, size, and BMD [1]. ...
... Thus, global and conditional disruption of the Igf-1 gene in osteoblasts and/or chondrocytes in mice leads to a discovery of cell type-and tissue compartment-specific effects of IGF-I in bone as summarized in Table 1. 10 Other studies have evaluated the role of IGF-I expressed in various bone cell types in regulating skeletal growth, repair and remodeling [30]. IGF-I expressed in osteoblasts or osteocytes, but not liver hepatocytes has been shown to be indispensable for mechanical loading-induced bone formation [31][32][33]. ...
To evaluate the relative importance of IGF-I expression in various cell types for endochon-dral ossification, we quantified the trabecular bone at the secondary spongiosa and epiphysis of the distal femur in 8-12-week-old male mice with a global knockout of the Igf-I gene as well as conditional deletion of the Igf-I gene in osteoblasts, chondrocytes, osteo-blasts/chondrocytes, and their corresponding control wild type littermates. The osteoblast-, chondrocyte- and osteoblast/chondrocyte-specific Igf-I conditional knockout mice were generated by crossing Igf-I floxed mice with Cre transgenic mice in which Cre expression is under the control of Col1α2 or Col2α1 promoter. We found that global disruption of Igf-I resulted in 80% and 70% reduction in bone size, which is defined as total volume, at the secondary spongiosa and epiphysis of the distal femur, respectively. Abrogation of Igf-I in Col1α2-producing osteoblasts, but not Col2α1-producing chondrocytes, decreased bone size by 25% at both the secondary spongiosa and epiphysis while deletion of the Igf-I globally or specifically in osteoblasts or chondrocytes reduced trabecular bone mass by 25%. By contrast, global Igf-I knockout but not conditional knockout of Igf-I in osteoblasts and/or chondrocytes reduced trabecular bone mass in the epiphysis. The reduced trabecu-lar bone mass at the secondary spongiosa in osteoblast- and/or chondrocyte-specific Igf-I conditional knockout mice is caused by reduced trabecular number and increased trabec-ular separation. Immunohistochemistry studies revealed that expression levels of chon-drocyte (COL10, MMP13) and osteoblast (BSP) markers were reduced in the secondary spongiosa and the epiphyses in the global Igf-I knockout mice. Our data indicate that local and endocrine IGF-I actions in bone are pleiotropic and dependent on cell type as well as the bone compartment where IGF-I acts.
... . Previously , the knockout of the murine hepatic Igf1 gene provided evidence for the role of circulating IGF - I in regulating glucose homeostasis . The reduction of serum IGF - I in those mice was accompanied by elevated basal and glucose - induced insulin levels , suggesting an important role of IGF - I in the regulation of glucose clearance ( Sjogren et al . 2002 ) . We could show that the obese BFMI mouse model could maintain normal fasting glucose concentrations on both diets at the expense of elevated insulin levels on SMD , which were further increased on HFD . Even in the fasted state , insulin levels were higher in BFMI than in B6 mice . In fact , BFMI mice on SMD had delayed abilities to ...
... rum levels were already strongly increased , whereas the insulin levels were higher than those in B6 mice , but still normal for these mice . In contrast , liver - specific Igf1 knockouts had a reduction of serum IGF - I and showed increased insulin but normal glucose levels , indicating that insulin compensates for the diminished IGF - I action ( Sjogren et al . 2002 ) . On HFD , the high IGF - I and insulin levels did not suffice to clear blood glucose within 2 h in BFMI mice . Nevertheless , BFMI mice do not develop diabetes ( Hantschel et al . 2011 ) , which likely results from a combined action of insulin and IGF - I that might be caused by a genetically determined mechanism that protects the mi ...
This study aimed to investigate the tissue-specific role of the insulin-like growth factor 1 (IGF-I) on glucose homeostasis in the high-fatness selected Berlin Fat Mouse Inbred (BFMI) line. Therefore, the expression of different IGF-I transcripts and IGF-I protein, IGF-binding proteins, insulin as well as glucose tolerance was analyzed in BFMI in comparison with that in lean mice. In addition, dietary effects were investigated. The BFMI line showed normal blood glucose clearance on standard diet, but on high-fat diet the clearance was impaired, indicating the beginning of insulin resistance. Circulating IGF-I and insulin levels were elevated in BFMI than in lean mice on both diets along with a down-regulation of three IGF-I binding proteins in BFMI mice. Serum IGF-I levels corresponded with the expression pattern for both hepatic and one class II splice variants in reproductive adipose tissue, but not in muscle. High insulin and high IGF-I levels likely prevent BFMI mice from diabetes.
... The appendicular skeletal growth of the liver-specific Igf-I conditional KO mice, as determined based on body weight, body length, and femoral length, did not differ from that of wild-type littermates [8]. However, the adult axial skeletal growth and the cortical bone width were reduced in the liver-specific conditional KO mice [10]. In contrast, the global deletion of the Igf-I gene in every cell caused a 20-40% reduction in femur length, size, and BMD [1]. ...
To evaluate the relative importance of IGF-I expression in various cell types for endochondral ossification, we quantified the trabecular bone at the secondary spongiosa and epiphysis of the distal femur in 8–12-week-old male mice with a global knockout of the Igf-I gene, as well as the conditional deletion of Igf-I in osteoblasts, chondrocytes, and osteoblasts/chondrocytes and their corresponding wild-type control littermates. The osteoblast-, chondrocyte-, and osteoblast/chondrocyte-specific Igf-I conditional knockout mice were generated by crossing Igf-I floxed mice with Cre transgenic mice in which Cre expression is under the control of either the Col1α2 or Col2α1 promoter. We found that the global disruption of Igf-I resulted in 80% and 70% reductions in bone size, defined as total volume, at the secondary spongiosa and epiphysis of the distal femur, respectively. The abrogation of Igf-I in Col1α2-producing osteoblasts but not Col2α1-producing chondrocytes decreased bone size by 25% at both the secondary spongiosa and epiphysis. In comparison, the deletion of the Igf-I globally or specifically in osteoblasts or chondrocytes reduced trabecular bone mass by 25%. In contrast, the universal deletion of Igf-I in all cells, but not the conditional disruption of Igf-I in osteoblasts and/or chondrocytes reduced trabecular bone mass in the epiphysis. The reduced trabecular bone mass at the secondary spongiosa in osteoblast- and/or chondrocyte-specific Igf-I conditional knockout mice is caused by the reduced trabecular number and increased trabecular separation. Immunohistochemistry studies found that the expression levels of chondrocyte (COL10, MMP13) and osteoblast (BSP) markers were less in the secondary spongiosa and the epiphyses in the global Igf-I deletion mice. Our data indicate that local and endocrine Igf-I act pleiotropically and in a cell type- and bone compartment-dependent manner in bone.
... In that concept, GH secreted by the pituitary gland regulated somatic growth solely by controlling hepatic IGF-I (AKA somatomedin C) production [50]. Several decades ago, the original hypothesis was challenged by several important observations in liver-specific IGF-I gene knock-out (KO) mice (Liver IGF-I -/-) [49,51]. Those IGF-I -/-animals grew normally compared to wild-type littermates (body weight, body length, and femoral length), despite circulating IGF-I level reductions to less than 25% of those in intact animals [49]. ...
Complex immunological mechanisms underlie the pathogenesis of thyroid-associated ophthalmopathy (TAO). Historical models of Graves’ disease and TAO have focused almost entirely on autoimmune reactivity directed against the thyrotropin receptor (TSHR). The insulin-like growth factor-I receptor (IGF-IR) has been proposed as a second participating antigen in TAO by virtue of its interactions with IGFs and anti-IGF-IR antibodies generated in Graves’ disease. Furthermore, the IGF-IR forms with TSHR a physical and functional complex which is involved in signaling downstream from both receptors. Inhibition of IGF-IR activity results in attenuation of signaling initiated at either receptor. Based on the aggregate of findings implicating IGF-IR in TAO, the receptor has become an attractive therapeutic target. Recently, teprotumumab, a human monoclonal antibody IGF-IR inhibitor was evaluated in two clinical trials of patients with moderate to severe, active TAO. Those studies revealed that teprotumumab was safe and highly effective in reducing disease activity and severity. Targeting IGF-IR with specific biologic agents may result in a paradigm shift in the therapy of TAO.
... Given the known function of RECK as a membrane-anchored regulator of metalloproteinases, it is reasonable to speculate that reduced immunoreactivity and a reduced immunoblot band of a membrane protein in Reck mutant mice represent degradation of that protein. The previous observations that liver-specific knockout of Igf1 gene results in upregulation of Ghrhr and Ghsr gene expression in the AP (Sjogren et al., 2002) suggest that IGF1 mediates negative feedback regulation of these genes. Hence, the decreased immunoreactivities of GHRHR and/or GHSR with concomitant increase in corresponding mRNA(s) found in Hypo and TAX-treated iKO mice (red boxes in the blue area in Fig. 6a) may represent degradation of these GPCRs followed by feedback upregulation of mRNA(s) triggered, for example, by the decrease in IGF1. ...
The tumor suppressor gene Reversion-inducing cysteine-rich protein with Kazal motifs (Reck) encodes a membrane-anchored protease regulator expressed in multiple tissues in mouse embryos and is essential for embryonic development. In postnatal mice, however, physiological roles for the RECK protein remain unclear. We found in this study that Reck is abundantly expressed in growth hormone (GH)-producing cells (somatotrophs) in the anterior pituitary gland (AP). We also found that two types of viable Reck mutant mice, one with reduced RECK expression (Hypo mice) and the other with induced Reck deficiency from 10 days after birth (iKO mice treated with tamoxifen), exhibit common phenotypes including decreases in body size and plasma levels of insulin-like growth factor-1 (IGF1). To gain insights into the function of RECK in the AP, we characterized several somatotroph-associated molecules in the AP of these mice. Immunoreactivity of GH was greatly reduced in tamoxifen-treated iKO mice; in these mice, two membrane receptors involved in the stimulation of GH secretion [growth hormone secretagogue receptor (GHSR) and growth hormone releasing hormone receptor (GHRHR)] were decreased, however, their mRNAs were increased. Decrease in GHSR immunoreactivity and concomitant increase in its mRNA were also found in the other mutant line, Hypo. Furthermore, reduced immunoreactivity of growth hormone receptor (GHR) and concomitant increase in its mRNA was also found in the liver of Hypo mice. These results raise the possibility that RECK supports proper functioning of the GH/IGF1 axis in mice, thereby affecting their growth and metabolism.
... Histological analysis of growth plate at femur distal epiphysis revealed that the increased growth plate height as a result of PSO treatment was due to its effect on all three zones i.e. the resting, proliferating and the hypertrophic zones. Earlier knockout mice studies have revealed that circulating IGF-1 level is directly proportional to the growth plate height and bone length [16,40]. Moreover, IGF-1 enhances muscle mass [35,41] and have mitogenic properties in brown adipose tissue [42]. ...
Peak bone mass (PBM) achieved at adulthood is a strong determinant of future onset of osteoporosis and maximizing it is one of the strategies to combat the disease. Recently, pomegranate seed oil (PSO) has been shown to have bone-sparing effect in ovariectomized mice. However, its effect on growing skeleton and its molecular mechanism remains unclear.
In the present study, we evaluated the effect of PSO on PBM in growing rats and associated mechanism of action. PSO was given at various doses to 21-days old growing rats for 90 days by oral gavage. The changes in bone parameters were assessed by μ-CT and histology. ELISA was performed to analyze the levels of serum IGF-1. Western blotting from bone and liver tissues were done. CHIP assay was performed to study the histone acetylation levels at IGF-1 gene. The results of the study show that PSO treatment significantly increases bone length, bone formation rate, biomechanical parameters, BMD and bone microarchitecture along with enhanced muscle and brown fat mass. This effect was due to the increased serum levels of IGF-1 and stimulation of its signaling in the bones. Studies focusing on acetylation of histones in the liver, the major site of IGF-1 synthesis, showed enrichment of acetylated H3K9 and H3K14 at IGF-1 gene promoter and body. Further, the increased acetylation at H3K9 and H3K14 was associated with a reduced HDAC1 protein level. Together, our data suggest that PSO promotes the PBM achievement via increased IGF-1 expression in liver and IGF-1 signaling in bone.
... However, there are reports which undermine the aforementioned hypothesis. In animal studies, the elimination of hepatic IGF-I synthesis caused its level to decrease by 75%, although that action did not have any significant influence on the BMD [52,53]. Furthermore, some scientists deny the existence of a link between IGF-I and BMD in men [54][55][56]. ...
Chronic liver disease caused by HBV and HCV infections, due to its great prevalence and serious medical consequences, is at the present time a significant clinical problem. An impaired liver function can provoke severe disturbances in calcium and phosphorus homeostasis, and consequently in the bone metabolism resulting in hepatic osteodystrophy. The aim of this study was to determine whether there are significant differences in bone mineral density (BMD) and/or circadian levels of hormones connected with bone metabolism and bone turnover markers in patients with chronic viral hepatitis.
Circadian levels (AUC, area under the curve) of GH, IGF-I, IGFBP-3, osteocalcin (BGLAP), C-terminal telopeptide of type I collagen (ICTP), PTH, 25(OH)D, total calcium and total phosporus were measured in the blood of members of the study group (n = 80). BMD was assessed using the dual-energy X-ray absorptiometry method of the L2-L4 lumbar spine. Data was compared to that of healthy individuals (n = 40).
BMD (1.05 g/cm3 vs. 1.20 g/cm3), total calcium concentration (2.20 mmol/L vs. 2.45 mmol/L), total phosphorus concentration (1.06 mmol/L vs. 1.33 mmol/L), IGF-I (AUC 3,982.32 ng/mL vs. 5,167.61 ng/mL), IGFBP-3 (AUC 725.09 ng/L vs. 944.35 ng/L), 25(OH)D (AUC 356.35 ng/mL vs. 767.53 ng/mL) and BGLAP (AUC 161.39 ng/L vs. 298 ng/L) were lower in the study group. GH (AUC 88.3 ng/mL vs. 48.04 ng/mL), iPTH (AUC 1,201.94 pg/mL vs. 711.73 pg/mL) and ICTP (AUC 104.30 μg/L vs. 54.49 μg/L) were higher in patients with hepatitis. Positive correlations were noted between bone mineral density and IGF-I, IGFBP-3, and BGLAP levels.
Chronic viral hepatitis causes a decrease in bone mineral density. Impaired liver function disrupts homeostasis of the calcium- vitamin D-parathyroid hormone axis and provokes secondary hyperparathyroidism. Chronic viral hepatitis induces a decrease in the synthesis of IGF-I and IGFBP-3 and an increase in GH secretion. Hepatic osteodystrophy is probably caused by both changes in calciotropic hormones as well as in the somatotropin hormone axis.
... Therefore, the upregulation of hepatic GHR, IGF-I and IGF-IR expression in KDF-treatment may be attributed to the direct action of GH and hepatic IGF-I on the regulation of glucose homeostasis in liver. Systemic IGF-I is important for carbohydrate and lipid metabolism and for the regulation of GH secretion (Sjogren et al., 2002;Vijayakumar et al., 2010). The level of IGF-I in blood was positively correlated with growth performance (Deng et al., 2007). ...
The objective of this study was to determine the effects of potassium diformate (KDF) on growth performance of weaning piglets and genes expression related with growth axis and hepatic gluconeogenesis. A total of 180 piglets weaned at 28 d of age were allocated randomly into two groups, with 6 pens in each group and 15 piglets in each pen. Piglets in the control group were fed basal diet, whereas the KDF-treated group was fed basal diet supplemented with 10 g/kg KDF. After 5 weeks feeding, KDF-treated piglets showed higher average daily feed intake (ADFI) and average daily bodyweight gain (ADG) than those of the control (P<0.05), whereas the feed conversion ratio (FCR) was lower than that of the control (P=0.02). The apparent digestibility of dry matter and crude protein of the KDF-treated group were higher than those of the control group (P<0.01). KDF treatment did not change the blood indices level of insulin-like growth factor-I (IGF-I), high density lipoprotein (HDL), low density lipoprotein (LDL), total cholesterol (TC), triglyceride (TG) and blood glucose (BG) in plasma. KDF treatment did not influence the mRNA expression of growth hormone releasing hormone (GHRH) and somatostatin (SS) in hypothalamus, and the levels of growth hormone receptor (GHR) and IGF-I receptor (IGF-IR) mRNA in pituitary. Whereas, it increased the abundance of GH mRNA in pituitary, and the mRNA of GHR, IGF-I, IGF-IR, glucose-6-phosphatase (G6PC), fructose-1,6-bisphosphatase (FBP) and phosphoenolpyruvate carboxykinase (PCK) in liver (P<0.05). Furthermore, KDF treatment increased the concentration of IGF-I peptide in liver (P=0.000). These results suggest that, the beneficial effect of KDF on the growth performance may relate to the regulation of the GH axis and glucose homeostasis in piglets.
... Множество эффектов ГР реализуются посредст вом инсулиноподобного ростового фактора 1 (ИРФ 1) [95,96]. Около 95% циркулирующего ИРФ 1 связано с ИРФ связывающим белком 3 (БСИРФ 3), что продлевает период его полужизни и определяет на правление его воздействия на процессы роста в обход метаболизма глюкозы [95,97]. ...
Iodine is а vital microelements that are essential for the normal human development and functions. Iodine deficiency is a global problem: about 2 billion individuals worldwide suffer from a lack of iodine. Despite goiter is the most visually noticeable manifestation of iodine deficiency, the most significant consequence of the iodine deficiency is impaired neurodevelopment, particularly early in life. Moreover, moderate to severe iodine deficiency increases the risk of spontaneous abortion, low birth weight and infant mortality. Babies in utero affected by iodine deficiency are at increased risk of mental developmental disorders, cretinism is their extreme degree. In addition, moderate to severe iodine deficiency in childhood negatively affects somatic growth. Iodine deficiency compensation improves cognitive and motor function in children. Iodine prophylaxis of deficient populations is an extremely effective approach to reduce the substantial adverse effects of iodine deficiency throughout the life cycle.
... The highest expression is found in the liver, but the physiological role of liver-derived IGF-I remain unknown. It has been difficult to separate the endocrine effects of liver-derived IGF-I from the autocrine/paracrine effects of locally produced IGF-I in peripheral tissues (Sjögren et al., 2002). Many factors regulate the linear growth (Hutchison et al., 2007). ...
The aim of this experiment was to evaluate the levels of hormones (progesterone, IGF-I and IGFBP-3) in blood plasma, growth, carcass traits and their interactions of sexually immature (n = 18) and sexually mature (n = 17) gilts. To calculate average daily weight gain (ADG), gilts were individually weighed at the beginning of the trial and at slaughter (11010 days old). Blood concentrations of progesterone, IGF-I and IGFBP-3 were determined by RIA. The right hot carcass sides were dissected and the individual basic parts from carcasses were weighed to record the carcass traits. IGFBP-3, ADG and carcass traits were not affected by pubertal maturation. Compared to sexually immature gilts, mature gilts had higher blood concentrations of progesterone and IGF-I. High correlations were noted between levels of some hormonal substances, productive performance and carcass traits of sexually immature and mature gilts.
... However, our documentation of dissociation between a strict positive relationship between circulating levels of IGF-I and body size are entirely compatible with this hypothesis . It is of interest that this study has supported the conclusions based on experimental mouse models, even though the postnatal growth in the experimental animals is somewhat abnormal (Ohlsson, 2002 ). The current research demonstrates that the findings of this type of experimental work, which would be extremely difficult to conduct using primates, are confirmed when examined across several primate species that vary in size. ...
This study examines the evolution of size differences among papionin primates by measuring hor-mones that regulate size growth during ontogeny and influence ultimate adult size (insulin-like growth factor-I (IGF-I), insulin-like growth factor binding protein-3 (IGFBP-3), growth hormone binding protein (GHBP), dehy-droepiandrosterone sulfate (DHEAS), testosterone, estra-diol). The analyses assess longstanding ideas about circu-lating hormone levels and body size. Importantly, because the consensus papionin molecular phylogeny implies at least two episodes of size increase, this study offers oppor-tunities to determine whether or not similar hormone pro-files regulate this apparent evolutionary convergence (i.e., do larger-bodied papionins have higher levels of growth-related hormones than smaller-bodied papionins?). Five hundred and sixty serum samples (from 161 individuals) from 11 papionin species were analyzed using a two-level approach to address this issue. One used mixed longitudi-nal samples from two papionin species to test whether, dur-ing growth, large-and small-bodied species have higher and lower hormone levels, respectively. The second com-pared multiple papionin species to assess whether or not hormone levels covary with size in adult animals. Result show that size and hormone levels do not covary consis-tently across papionins, either during growth or in adult-hood. Specifically, some smaller-bodied papionin species have higher absolute hormone levels than larger-bodied species. Differences in some hormone levels appear to track phylogeny more closely than body size. In contrast to stud-ies based on single species, we demonstrate that, while the hormones analyzed affect growth, absolute circulating hor-mone levels either during growth or adulthood may be decoupled from interspecific differences in body size. Am J Phys Anthropol 132:247–260, 2007. V V C 2006 Wiley-Liss, Inc.
... In addition to its function in processing nutrients, the liver also synthesizes hormones that help maintain whole-body energy homeostasis. One of them is IGF-1, which can lower blood glucose levels by promoting glucose uptake in peripheral tissues and inhibiting hepatic glucose production (Sjogren et al., 2002). The biological access of IGF-1 to target tissues is tightly regulated by a family of IGF-binding proteins. ...
Nrf2, a master regulator of intracellular redox homeostasis, is indicated to participate in fatty acid metabolism in liver. However, its role in diet-induced obesity remains controversial. In the current study, genetically engineered Nrf2-null, wild-type (WT), and Nrf2-activated, Keap1-knockdown (K1-KD) mice were fed either a control or a high-fat Western diet (HFD) for 12weeks. The results indicate that the absence or enhancement of Nrf2 activity did not prevent diet-induced obesity, had limited effects on lipid metabolism, but affected blood glucose homeostasis. Whereas the Nrf2-null mice were resistant to HFD-induced glucose intolerance, the Nrf2-activated K1-KD mice exhibited prolonged elevation of circulating glucose during a glucose tolerance test even on the control diet. Feeding a HFD did not activate the Nrf2 signaling pathway in mouse livers. Fibroblast growth factor 21 (Fgf21) is a liver-derived anti-diabetic hormone that exerts glucose- and lipid-lowering effects. Fgf21 mRNA and protein were both elevated in livers of Nrf2-null mice, and Fgf21 protein was lower in K1-KD mice than WT mice. The inverse correlation between Nrf2 activity and hepatic expression of Fgf21 might explain the improved glucose tolerance in Nrf2-null mice. Furthermore, a more oxidative cellular environment in Nrf2-null mice could affect insulin signaling in liver. For example, mRNA of insulin-like growth factor binding protein 1, a gene repressed by insulin in hepatocytes, was markedly elevated in livers of Nrf2-null mice. In conclusion, genetic alteration of Nrf2 does not prevent diet-induced obesity in mice, but deficiency of Nrf2 improves glucose homeostasis, possibly through its effects on Fgf21 and/or insulin signaling.
... Plasma hormones are typically derived from a single endocrine gland, although the same factors may be expressed more widely. For instance, insulin-like factors (IGFs) in circulation are primarily derived from the liver, although IGFs are produced in most, if not all, tissues [1][2][3]. Similarly, while plasma ghrelin is largely derived from the gastric mucosa, ghrelin production occurs widely throughout the diffuse endocrine system, including the pituitary, thyroid, pancreas, adrenal, intestine, lung, gonads, and placenta [4]. Plasma insulin is similarly largely derived from cells in the pancreas, but extrapancreatic insulin expression occurs in the liver, adipose tissue, spleen, bone marrow, thymus, and brain [5]. ...
Protein hormones from the anterior pituitary gland have well-established endocrine roles in their peripheral target glands. It is, however, now known that these proteins are also produced within many of their target tissues, in which they act as local autocrine or paracrine factors, with physiological and/or pathophysiological significance. This emerging concept is the focus of this brief review.
... Among these is the IGF-I, considered to be the main indirect effecter of GH in growth promotion and tissue differentiation (Daughaday 2000;Butler and LeRoith 2001). Although IGF-I is produced in many cell types targeted by GH, its main production site is the liver, from which it is exported to the blood stream and becomes an important complementary agent for somatic growth (Sjögren et al. 2002;Janssen 2009). ...
Even though growth hormone (GH) transgenesis has demonstrated potential for improved growth of commercially important species, the hormone excess may result in undesired collateral effects. In this context, the aim of this work was to develop a new model of transgenic zebrafish (Danio rerio) characterized by a muscle-specific overexpression of the GH receptor (GHR) gene, evaluating the effect of transgenesis on growth, muscle structure and expression of growth-related genes. In on line of transgenic zebrafish overexpressing GHR in skeletal muscle, no significant difference in total weight in comparison to non-transgenics was observed. This can be explained by a significant reduction in expression of somatotrophic axis-related genes, in special insulin-like growth factor I (IGF-I). In the same sense, a significant increase in expression of the suppressors of cytokine signaling 1 and 3 (SOCS) was encountered in transgenics. Surprisingly, expression of genes coding for the main myogenic regulatory factors (MRFs) was higher in transgenic than non-transgenic zebrafish. Genes coding for muscle proteins did not follow the MRFs profile, showing a significant decrease in their expression. These results were corroborated by the histological analysis, where a hyperplasic muscle growth was observed in transgenics. In conclusion, our results demonstrated that GHR overexpression does not induce hypertrophic muscle growth in transgenic zebrafish probably because of SOCS impairment of the GHR/IGF-I pathway, culminating in IGF-I and muscle proteins decrease. Therefore, it seems that hypertrophy and hyperplasia follow two different routes for entire muscle growth, both of them triggered by GHR activation, but regulated by different mechanisms.
... The insulin-like growth factor-I (IGF-I) 4 system plays a critical role in the regulation of cellular proliferation, differentiation, and apoptosis in a wide variety of cells and tissues (1). Liver has the highest expression of IGF-I, and circulating IGF-I in plasma is produced mainly in the liver (2). Decreased IGF-I levels in plasma and liver were reported in alcoholics (3,4) and in acute ingestion studies (5), as well as in chronic ethanol-feeding studies in animal models (6,7). ...
Chronic and excessive ethanol intake in rats results in low levels of hepatic retinoic acid (RA) either by inhibiting the biosynthesis of RA or by enhancing its catabolism of RA. Chronic ethanol intake also decreases both hepatic expression of insulin-like growth factor-I (IGF-I) and plasma IGF-I concentration in rats. It is not known whether RA supplementation in alcohol-fed rats can restore plasma IGF-I concentrations and hepatic IGF-I expression. In the present study, we examined both plasma IGF-I level and hepatic IGF-I mRNA expression in alcohol-fed rats with or without RA (100 microg/kg body weight) supplementation for 6 mo. Hepatic IGF-I mRNA levels and plasma IGF-I concentration were decreased (84 and 29%, respectively) significantly in alcohol-fed rats compared with the control. In contrast, RA supplementation in ethanol-fed rats partially restored both hepatic IGF-I mRNA levels and plasma IGF-I concentration compared with rats fed ethanol alone. These data suggest that alcohol-impaired hepatic RA status contributes to the decreased plasma IGF-I level and hepatic IGF-I expression in alcoholics.
... Insulin-like growth factor-1 (IGF-1) is involved in the growth and development of many cells, [1][2][3][4][5] including cardiac myocyte. 6 In addition, it has been found to interfere with apoptosis and cellular death in various tissues [7][8][9] including myocardial cells. ...
In recent years, low levels of Insulin-like Growth Factor-1 (IGF-1) have been suggested to be associated with higher risks of developing heart failure and higher long-term mortality rates following Acute Myocardial Infarction (AMI). However, the effect of IGF-1 levels on short-term survival has been rarely studied. In this study we aimed to assess any possible association between serum IGF-1 concentration following AMI and short-term survival rates.
In this study, serum total IGF-1 levels were measured in 56 patients within 24 hours following AMI and were compared to 56 individuals with no cardiovascular disease. Patients were followed up to death or discharge from hospital (median = 6 days) and survival curves were compared based on median IGF-1 value.
Mean (±SD) of serum IGF-1 levels were 232.73 ng/ml (±81.74) and 211.00 ng/ml (±58.22) in survived and expired patients respectively and the difference was not statistically significant (P value = 0.501). The difference between survival curves was also not statistically significant (P value = 0.246).
According to findings of this study, serum total IGF-1 concentration does not seem to be associated with short-term survival rates.
... While Ror1 is expressed fairly broadly in the organism, it is not expressed in the liver, which is the major site of IGF-I production (Al-Shawi et al., 2001;Baskar et al., 2008). Concomitantly, liver-specific deletion of Igf-1 does not affect growth of the appendicular skeleton (Yakar et al., 1999;Sjogren et al., 2002). Thus, local IGF-I production in the growth plate of the long bones is probably affected in Ror1 mutants, given the reduction in the hypertrophic zone that is the predominant region in which Igf-1 is transcribed postnatally (Reinecke et al., 2000;Smink et al., 2002). ...
Ror1 is a member of the Ror-family receptor tyrosine kinases. Ror1 is broadly expressed in various tissues and organs during mouse embryonic development. However, so far little is known about its function. The closely related family member Ror2 was shown to play a crucial role in skeletogenesis and has been shown to act as a co-receptor for Wnt5a mediating non-canonical Wnt-signaling. Previously, it has been shown that during embryonic development Ror1 acts in part redundantly with Ror2 in the skeletal and cardiovascular systems. In this study, we report that loss of the orphan receptor Ror1 results in a variety of phenotypic defects within the skeletal and urogenital systems and that Ror1 mutant mice display a postnatal growth retardation phenotype.
... Entretanto, em meados de 2002, ocorre a volta à origem, com a demonstração de que animais nos quais uma diminuição ainda maior no IGF-I circulante foi obtida apresentavam diminuição do crescimento (Teoria da Somatomedina resgatada), confirmando a participação tanto do IGF circulante quanto do local no processo de crescimento, mediante atuação endócrina, parácrina e autócrina (27). É interessante que os animais com depleção hepato-específica do gene do IGF-I (modelo que acopla redução importante do IGF-I e GH elevado) apresentam uma diminuição da acumulação de gordura dependente da idade em relação aos animais controles (28), sugerindo ação importante do GH no acumulação de gordura. Porém, não há mais dúvida da participação endócrina, sobretudo hepática, da IGF-I sobre o crescimento. ...
In addition to stimulating body growth, growth or somatotrophic hormone plays an important role in metabolism, body composition, lipid profile, cardiovascular status and longevity. Its control is multiregulated by hormones, metabolites and hypothalamic peptides. Obtained data of the isolated growth hormone deficiency (IGHD) after the description of the IVS1+1G-->A GHRH receptor gene mutation in individuals of Itabaianinha County are reviewed. New perspectives about the growth hormone resistance model, the importance of GHRH in the control of GH secretion, the frequency of GHRH-R gene mutations, the diagnostic relevance of IGF-I and the metabolic, cardiovascular and quality of life findings are approached.
... hippocampus, may have its own GH and IGF-1 production, which can be independent of pituitary GH and peripheral circulating IGF-1. Given the unique hormonal background of Ames dwarf mice and recent evidence that mutant mice with knock-out of IGF-1 only in the liver grow almost normally despite dramatically reduced (>80%) serum IGF-1 levels [44,45,59], we speculated that locally-produced (organ or tissue specific) hormones might have more significant effects on local organ physiological function than the circulating hormones. ...
Beneficial effects of growth hormone (GH) and insulin-like growth factor-1 (IGF-1) on the development and function of the central nervous system are well documented. In spite of primary deficiency of GH and secondary IGF-1 deficiency, Ames dwarf mice live considerably longer than normal animals, exhibit apparently normal cognitive functions and maintain them into advanced age. In an attempt to reconcile these findings, we have examined local expression of GH and IGF-1 in the hippocampus of normal and Ames dwarf mice. We found that both hippocampal GH and IGF-1 protein levels are increased and the corresponding mRNAs are normal in Ames dwarf as compared with normal mice. Increased phosphorylation of Akt and cyclic AMP responsive element-binding protein (CREB) were detected in the hippocampus of Ames dwarf mice. Our results suggest that increase in hippocampal GH and IGF-1 protein expression and subsequent activation of PI3K/Akt-CREB signal transduction cascade might contribute to the maintenance of cognitive function and is likely to be responsible for the integrity of neuronal structure, and maintenance of youthful levels of cognitive function in these long-lived mice during aging.
... IGF-I class 2 proteins are primarily produced in the liver and secreted into the circulation and are the major endocrine effectors of growth hormone (Yakar et al., 1999 ). Accordingly, conditional knockout mice in which IGF-I expression was abrogated only in the liver exhibited postnatal growth retardation, despite normal levels of growth hormone (Sjogren et al., 2002). By contrast, IGF-I class 1 isoforms are widely expressed in most tissues and remain localized within the tissue in which they are expressed. ...
Muscle damage has been shown to enhance the contribution of bone marrow-derived cells (BMDCs) to regenerating skeletal muscle. One responsible cell type involved in this process is a hematopoietic stem cell derivative, the myelomonocytic precursor (MMC). However, the molecular components responsible for this injury-related response remain largely unknown. In this paper, we show that delivery of insulin-like growth factor I (IGF-I) to adult skeletal muscle by three different methods-plasmid electroporation, injection of genetically engineered myoblasts, and recombinant protein injection-increases the integration of BMDCs up to fourfold. To investigate the underlying mechanism, we developed an in vitro fusion assay in which co-cultures of MMCs and myotubes were exposed to IGF-I. The number of fusion events was substantially augmented by IGF-I, independent of its effect on cell survival. These results provide novel evidence that a single factor, IGF-I, is sufficient to enhance the fusion of bone marrow derivatives with adult skeletal muscle.
... To address the potential endocrine action of IGF-I to regulate blood pressure, Tivesten et al. (50) generated a liver-specific inducible IGF-I knockout using the Cre-loxP system. Liverderived IGF-I was deleted in mice at 4 wk of age by use of the Mx1 promoter, the expression of which can be induced by treatment with interferon (IFN)-␣ or - or polyinosinic-polycytidylic acid (44). Liver-specific IGF-I knockouts had increased blood pressure accompanied by secondary decreases in markers of cardiac performance, thereby identifying that circulating liver-derived IGF-I is involved in the physiological regulation of blood pressure and peripheral resistance. ...
Genetically modified mouse models have been used widely to advance our knowledge in the field of endocrinology and metabolism. A number of different approaches to generate genetically modified mice are now available, which provide the power to analyze the role of individual proteins in vivo. However, there are a number of points to be considered in the use and interpretation of these models. This review discusses the advantages and disadvantages involved in the generation and use of different genetically modified mouse models in endocrine research, including conventional techniques (e.g., overexpression, knockout, and knock-in models), tissue- and/or time-specific deletion of target genes [e.g., Cre-loxP and short interfering (si)RNA transgenic approaches], and gene-trap approaches to undertake functional genomics. This review also highlights the many factors that should be considered when assessing the phenotype of these mouse models, many of which are relevant to all murine physiological studies. These approaches are a powerful means by which to dissect the function of genes and are revolutionizing our understanding of endocrine physiology and metabolism.
... In contrast, in the children who were only mildly iodine deficient, there was no significant change in TT4 with iodine repletion and no measurable effect on growth. IGF-I is a growth factor that mediates many of the effects of GH (44,45). Approximately 95% of circulating IGF-I is bound to IGFBP-3; binding prolongs the half-life of circulating IGF-I and may target IGF-I toward growth stimulation and away from glucose metabolism (44 -46). ...
Iodine deficiency in utero impairs fetal growth, but the relationship between iodine deficiency and postnatal growth is less clear.
The objective of the study was to determine whether iodine repletion improves somatic growth in iodine-deficient children and investigate the role of IGF-I and IGF binding protein (IGFBP)-3 in this effect. DESIGN, PARTICIPANTS, AND INTERVENTIONS: Three prospective, double-blind intervention studies were done: 1) in a 10-month study, severely iodine-deficient, 7- to 10-yr-old Moroccan children (n = 71) were provided iodized salt and compared with children not using iodized salt; 2) in a 6-month study, moderately iodine-deficient, 10- to 12-yr-old Albanian children (n = 310) were given 400 mg iodine as oral iodized oil or placebo; 3) in a 6-month study, mildly iodine-deficient 5- to 14-yr-old South African children (n = 188) were given two doses of 200 mg iodine as oral iodized oil or placebo. At baseline and follow-up, height, weight, urinary iodine (UI), total T4 (TT4), TSH, and IGF-I were measured; in Albania and South Africa, IGFBP-3 was also measured.
In all three studies, iodine treatment increased median UI to more than 100 microg/liter, whereas median UI in the controls remained unchanged. In South Africa, iodine repletion modestly increased IGF-I but did not have a significant effect on IGFBP-3, TT4, or growth. In Albania and Morocco, iodine repletion significantly increased TT4, IGF-I, IGFBP-3, weight-for-age z scores, and height-for-age z scores.
This is the first controlled study to clearly demonstrate that iodine repletion in school-age children increases IGF-I and IGFBP-3 concentrations and improves somatic growth.
... However, our documentation of dissociation between a strict positive relationship between circulating levels of IGF-I and body size are entirely compatible with this hypothesis . It is of interest that this study has supported the conclusions based on experimental mouse models, even though the postnatal growth in the experimental animals is somewhat abnormal (Ohlsson, 2002 ). The current research demonstrates that the findings of this type of experimental work, which would be extremely difficult to conduct using primates, are confirmed when examined across several primate species that vary in size. ...
This study examines the evolution of size differences among papionin primates by measuring hormones that regulate size growth during ontogeny and influence ultimate adult size (insulin-like growth factor-I (IGF-I), insulin-like growth factor binding protein-3 (IGFBP-3), growth hormone binding protein (GHBP), dehydroepiandrosterone sulfate (DHEAS), testosterone, estradiol). The analyses assess longstanding ideas about circulating hormone levels and body size. Importantly, because the consensus papionin molecular phylogeny implies at least two episodes of size increase, this study offers opportunities to determine whether or not similar hormone profiles regulate this apparent evolutionary convergence (i.e., do larger-bodied papionins have higher levels of growth-related hormones than smaller-bodied papionins?). Five hundred and sixty serum samples (from 161 individuals) from 11 papionin species were analyzed using a two-level approach to address this issue. One used mixed longitudinal samples from two papionin species to test whether, during growth, large- and small-bodied species have higher and lower hormone levels, respectively. The second compared multiple papionin species to assess whether or not hormone levels covary with size in adult animals. Result show that size and hormone levels do not covary consistently across papionins, either during growth or in adulthood. Specifically, some smaller-bodied papionin species have higher absolute hormone levels than larger-bodied species. Differences in some hormone levels appear to track phylogeny more closely than body size. In contrast to studies based on single species, we demonstrate that, while the hormones analyzed affect growth, absolute circulating hormone levels either during growth or adulthood may be decoupled from interspecific differences in body size.
... IGF-1 is an important stimulator of osteoblastic activity; but several lines of evidence indicate that paracrine IGF-1 is more important than systemic IGF-1 for the stimulation of bone formation. However, clinical studies have shown a positive correlation between systemic IGF-1 and BMD 26,27 and a well-designed study on transgenic mice (liver IGF-1-deficient and acid labile subunit knockout mice) demonstrated that liver-derived IGF-1 also significantly influences bone mass development. 28 Similar to our data, these studies indicated that systemic IGF-1 is important to bone mass development. ...
To analyse aspects of mineral metabolism, bone mineral density (BMD), bone remodelling activity and serum IGF-1 levels in children with chronic cholestatic disease (CCLD).
A total of 13 children with chronic cholestatic liver disease (CCLD; mean age 7.2 +/- 4.8 years) and 22 control subjects (mean age 7.6 +/- 4.5 years) were studied. Serum osteocalcin, bone alkaline phosphatase (BAP), 25-hydroxyvitamin D, PTH and IGF-1 levels and urinary deoxypyridinoline were determined. BMD was measured by dual-energy X-ray absorptiometry in the lumbar spine, total hip and whole body. Lumbar spine areal BMD was converted mathematically to apparent volumetric BMD (aBMD) and corrected for the bone age of the patient.
Z-score of lumbar spine BMD was lower in CCLD patients than in controls and the difference was maintained when BMD was expressed as aBMD (control = 0.107 +/- 0.02 vs. CCLD = 0.092 +/- 0.02 g/cm(3), P < 0.05) and after conversion for bone age. All participants showed normal 25-hydroxyvitamin D levels, with no significant differences in serum levels of 25-hydroxyvitamin D and PTH between groups. IGF-1 levels were significantly lower in the CCLD group (control = 19.6 +/- 16.8 vs. CCLD = 6.4 +/- 7.6 nmol/l, P < 0.05) and a positive correlation was observed between whole body BMD and IGF-1 in this group.
These results indicate that CCLD limits bone mass gain in children. A reduction in hepatic IGF-1 production might be responsible, at least in part, for the low bone mass of these patients.
... Most of these mentioned effects, however, are not the result of the direct action of GH, but they are mediated via insulin-like growth factor-I (IGF-I), a peptide synthesized and secreted after GH-signaling, which acts locally in a paracrine or autocrine fashion or distantly as a hormone, when secreted by the liver (Le Roith et al 2001). The latter organ is responsible for 70%–80% of the circulating IGF-I (Sjogren et al 1999; Sjogren et al 2002). The importance of IGF-I for body growth is underscored by observations of severely stunted growth in animals and the human with inactivating mutations IGF-I or its receptor (Woods et al 1996; Walenkamp et al 2005). ...
This article examines the role of pegvisomant in the treatment of acromegaly. This syndrome, caused by excessive growth hormone (GH) secretion by a pituitary adenoma, is associated with a doubled mortality rate and poor quality of life. Pituitary microsurgery has long been the first choice of treatment since it cures many patients, especially those with localized tumors. Adjuvant irradiation was given if insulin-like growth factor-I (IGF-I) or GH did not normalize. The introduction of long-acting slow- release somatostatin analogs was a breakthrough for adjuvant treatment, although not always effective. Rather, targeting excessive GH production, muting the GH signal at its receptor, was a totally different approach. The development of GH antagonists (by mutation ofglycine at position 120) and other modifications to enhance receptor binding, and subsequent pegylation of the molecule led to the development of B2036. After pegylation of B2036 at 5 positions the distribution volume is restricted and its serum half-life considerably increased. In short-term clinical studies performed in selected, mostly pretreated, acromegalic patients, IGF-I normalized in the majority of cases. Combination therapy with long-acting somatostatin analogs and weekly rather than daily pegvisomant injections appears to be successful in one clinical study and might limit the high cost of pegvisomant. Long-term efficacy and safety has to be demonstrated. The drug does not cross the blood-brain barrier, and whether it distributes freely into the extracellular space of other organs than the liver has not been investigated, which might have implications for persistent local IGF-I production under unrestrained GH concentrations.
... (7) However, because patients with congenital enzyme defects associated with bilirubin elevations do not show extensive bone disease, the role of bilirubin seems to be rather lim-ited. (7) Other potential mediators/contributors of hepatic osteodystrophy include secondary hyperparathyroidism (whose role is limited to patients with vitamin D deficiency (5,8) ), increased bone resorption (which is most likely caused by the postmenopausal status of many of the affected patients and to hypogonadism in men (9,10) ), and IGF-I (which is diminished in advanced liver disease, but whose role is probably limited (11,12) ). ...
Osteoporosis is a major cause of morbidity and decreased quality of life in patients with chronic cholestatic liver disease. It is established that this osteoporosis results from decreased bone formation, but the mechanisms for the interaction between liver and bone remain elusive. The aim of this study was to test the hypothesis that an increase in the production of cellular fibronectins during liver disease may result in decreased osteoblast-mediated mineralization and thus explain the decrease in bone formation. We performed a prospective cross-sectional study in patients with primary biliary cirrhosis and matched controls, followed by experiments on human and mouse osteoblasts in culture and injections in mice in vivo. In patients with primary biliary cirrhosis, the oncofetal domain of fibronectin correlated significantly with the decrease in osteocalcin, a marker of bone formation (r = -0.57, p < 0.05). In vitro, amniotic fluid fibronectin (aFN) containing mainly the oncofetal domain and EIIIA domain resulted in decreased osteoblast-mediated mineralization in human osteoblasts (69% decrease at 100 microg/ml; p < 0.01) and mouse osteoblasts (71% decrease; p < 0.05). Removing the EIIIA domain from aFN similarly suppressed mineralization by osteoblasts (78% decrease; p < 0.05). Injection of labeled aFN in mice showed that it infiltrates the bone, and its administration over 10 days resulted in decreased trabecular BMD (17% drop; p < 0.05), mineralizing surface (30% drop; p < 0.005), and number of osteoblasts (45% drop; p < 0.05). Increased production of a fibronectin isoform containing the oncofetal domain and its release in the circulation in patients with primary biliary cirrhosis is at least partially responsible for the decrease in bone formation seen in these patients. This establishes that a molecule that has thus far been viewed as an extracellular matrix protein exerts hormone-like actions.
Background and objective
Insulin-like growth factor-1 (IGF-1) regulates cardiomyocyte survival, hypertrophy, and ageing. We aimed to investigate the potential correlation between IGF-1 and interventricular septal (IVS) thickening.
Methods
Medical record data were obtained from patients hospitalized between May 1, 2012 and April 30, 2022. All patients underwent echocardiography and had laboratory data on plasma IGF-1. We analyzed the relationship between IGF-1 levels and IVS thickening based on logistic regression models.
Results
Propensity score matching at 1:4 ratio was performed for 180 patients with IVS thickening and 1,964 patients without IVS thickening. Finally, 180 (case group) and 623 (control group) patients were enrolled. Of the total 803 patients, the mean age was 59 years, and 59.7% were male. In multivariate-adjusted models that adjusted for propensity scores, the risk of IVS thickening increased with increasing IGF-1 levels; specifically, the risk of IVS thickening increased per 1 ng/mL [odds ratio (OR) 1.003; 95% confidence interval (CI): 1.002–1.004; P < 0.001], per 5 ng/mL (OR, 1.016; 95% CI, 1.010–1.022; P < 0.001), and per 10 ng/mL(OR, 1.032; 95% CI, 1.019–1.045; P < 0.001) increase in IGF-1 levels. When the IGF-1 levels were expressed as a categorical variable, the increased levels of IGF-1 led to an increased risk of IVS thickening; specifically, the OR of IVS thickening for T3 >152.00 ng/mL was 2.020 (95% CI: 1.310–3.115, P < 0.01) compared with T1 <102.00 ng/mL. We performed restricted cubic splines, and it showed a linear association between IGF-1 levels and the risk of IVS thickening. In splines for the age and sex subgroups, different IGF-1 levels increased the risk of IVS thickening among different age groups in male patients: 18–44 years when IGF-1 value >164.00 ng/mL, 45–60 years when IGF-1 value > 140.34 ng/mL and ≥ 60 years when IGF-1 value >108.20 ng/mL. In female patients aged 45–60 years, the risk of IVS thickening increased when the IGF-1 levels were >207.45 ng/mL. However, IGF-1 was not significantly correlated with IVS thickening in female patients aged 18–45 and ≥60 years. Sensitivity analysis by excluding those with acromegaly did not change the relationship between IGF-1 and the risk of IVS thickening.
Conclusion
The plasma IGF-1 levels were related to the risk of IVS thickening irrespective of blood pressure.
We showed previously that chlormequat chloride, a widely used plant growth regulator, could affect embryonic growth and growth hormone (GH)-insulin-like growth factor 1 (IGF-1) axis of rats. However, the potential effects of low dose chlormequat chloride exposure during pregnancy on embryonic and postnatal growth and development remain unclear. To further assess the risk of chlormequat chloride to human embryonic growth and postnatal health, we exposed maternal rats orally to the chemical during pregnancy at 5 mg/kg.bw, a dose corresponding to the human acceptable daily intake (ADI) level set by World Health Organization (WHO), and determined the effects of chlormequat on embryo growth and postnatal health. We found that chlormequat chloride increased embryonic growth parameters, GH, and GH-releasing hormone (GHRH) levels, but did not affect somatostatin and IGF-1 on gestational day (GD) 11. In the pups of postnatal day (PD) 7, we observed increased head length, decreased body fat percentage, hypoglycemia, hyperlipidemia and hyperproteinemia. In conclusion, maternal exposure to chlormequat chloride during pregnancy disrupts the embryonic growth probably through its effects on growth regulators and even has adverse effects on postnatal health.
Data about the impact of bariatric surgery (BS) and subsequent weight loss on bone are limited. The objective of the present study was to determine bone mineral density (BMD), bone remodeling metabolites and hormones that influence bone trophism in premenopausal women submitted to BS 9.8 months, on average, before the study (OGg, N = 16). The data were compared to those obtained for women of normal weight (CG, N = 11) and for obese women (OG, N = 12). Eight patients in each group were monitored for one year, with the determination of BMD, of serum calcium, phosphorus, magnesium, parathyroid hormone, 25-hydroxyvitamin D, insulin-like growth factor-I (IGF-I) and osteocalcin, and of urinary calcium and deoxypyridinoline. The biochemical determinations were repeated every three months in the longitudinal study and BMD was measured at the end of the study. Parathyroid hormone levels were similar in the three groups. IGF-I levels (CG = 332 ± 62 vs OG = 230 ± 37 vs OGg = 128 ± 19 ng/mL) were significantly lower in the operated patients compared to the non-operated obese women. Only OGg patients presented a significant fall in BMD of 6.2% at L1-L4, of 10.2% in the femoral neck, and of 5.1% in the forearm. These results suggest that the weight loss induced by BS is associated with a significant loss of bone mass even at sites that are not influenced by weight overload, with hormonal factors such as IGF-I being associated with this process.
The most exciting recent advances in skeletal growth factor biology have emerged from genetic and transgenic approaches, and these have greatly enhanced our understanding of the role played by growth factors in the developing and adult skeleton. A more coherent picture of the interplay between different hormones, growth factors, and cytokines during the development of cartilage and bone is emerging. With the advent of inducible and tissue specific knockout and transgenic animal models, investigating actions of growth factors in the adult skeleton has begun separately from their role in development. The development of parathyroid hormone (PTH) as a bone anabolic and approved treatment for osteoporosis has triggered a flood of detailed mechanistic studies, which are already highlighting the central involvement of growth factors in orchestrating some of the effects of this therapy. There are many open questions, particularly relating to the actions of growth factors on ostoclasts and on mature articular chondrocytes. Continued research into the skeletal growth factors will open up their use as anabolic and repair agents for bone and cartilage.
Insulin-like growth factor-I (IGF-I) regulates cell growth, survival, and differentiation by acting on the IGF-I receptor, (IGF-IR)-a tyrosine kinase receptor, which elicits diverse intracellular signaling responses. All skeletal cells express IGF-I and IGF-IR. Recent studies using tissue/cell-specific gene knockout mouse models and cell culture techniques have clearly demonstrated that locally produced IGF-I is more critical than the systemic IGF-I in supporting embryonic and postnatal skeletal development and bone remodeling. Local IGF-I/IGF-IR signaling promotes the growth, survival and differentiation of chondrocytes and osteoblasts, directly and indirectly, by altering other autocrine/paracrine signaling pathways in cartilage and bone, and by enhancing interactions among these skeletal cells through hormonal and physical means. Moreover, local IGF-I/IGF-IR signaling is critical for the anabolic bone actions of growth hormone and parathyroid hormone. Herein, we review evidence supporting the actions of local IGF-I/IGF-IR in the above aspects of skeletal development and remodeling.
IGF-1 plays an important role in cardiovascular homeostasis, and plasma levels of IGF-1 correlate inversely with systolic function in heart failure. It is not known to what extent circulating IGF-1 secreted by the liver and local autocrine/paracrine IGF-1 expressed in the myocardium contribute to these beneficial effects on cardiac function and morphology. In the present study, we used a mouse model of liver-specific inducible deletion of the IGF-1 gene (LI-IGF-1 -/- mouse) in an attempt to evaluate the importance of circulating IGF-I on cardiac morphology and function under normal and pathological conditions, with an emphasis on its regulatory role in myocardial phosphocreatine metabolism. Echocardiography was performed in LI-IGF-1 -/- and control mice at rest and during dobutamine stress, both at baseline and post myocardial infarction (MI). High-energy phosphate metabolites were compared between LI-IGF-1 -/- and control mice at 4weeks post MI. We found that LI-IGF-1 -/- mice had significantly greater left ventricular dimensions at baseline and showed a greater relative increase in cardiac dimensions, as well as deterioration of cardiac function, post MI. Myocardial creatine content was 17.9% lower in LI-IGF-1 -/- mice, whereas there was no detectable difference in high-energy nucleotides. These findings indicate an important role of circulating IGF-1 in preserving cardiac structure and function both in physiological settings and post MI.
The neural retina is an extrapituitary site of growth hormone (GH) production and an autocrine or paracrine site of retinal GH action. Retinal GH is released from retinal tissue and may be secreted into the vitreous. Ontogenetic changes in the abundance of retinal GH during embryogenesis indicate that the amount of GH released may be regulated. The presence of pituitary GH secretagogues (GH-releasing hormone, GHRH; thyrotropin-releasing hormone, TRH; and ghrelin) and pituitary GH inhibitors (somatostatin, SRIF and insulin-like growth factor, IGF-1) within the neural retina may indicate the involvement of these factors in retinal GH release. This possibility is supported by the finding that GHRH is colocalized with GH in chick retinal ganglion cells (RGCs) and in immortalized cells (QNRD) derived from quail neuroretinal cells and by the induction of GH mRNA in incubated QNRD cells. In summary, these results provide evidence for the autocrine or paracrine regulation of retinal GH release in the ganglion cells of the embryonic chick retina.
Iodine is an essential component of the hormones produced by the thyroid gland. Thyroid hormones, and therefore iodine, are essential for mammalian life. Iodine deficiency is a major public health problem; globally, it is estimated that two billion individuals have an insufficient iodine intake. Although goiter is the most visible sequelae of iodine deficiency, the major impact of hypothyroidism due to iodine deficiency is impaired neurodevelopment, particularly early in life. In the fetal brain, inadequate thyroid hormone impairs myelination, cell migration, differentiation and maturation. Moderate-to-severe iodine deficiency during pregnancy increases rates of spontaneous abortion, reduces birth weight, and increases infant mortality. Offspring of deficient mothers are at high risk for cognitive disability, with cretinism being the most severe manifestation. It remains unclear if development of the offspring is affected by mild maternal iodine deficiency. Moderate-to-severe iodine deficiency during childhood reduces somatic growth. Correction of mild-to-moderate iodine deficiency in primary school aged children improves cognitive and motor function. Iodine prophylaxis of deficient populations with periodic monitoring is an extremely cost effective approach to reduce the substantial adverse effects of iodine deficiency throughout the life cycle.
Data about the impact of bariatric surgery (BS) and subsequent weight loss on bone are limited. The objective of the present study was to determine bone mineral density (BMD), bone remodeling metabolites and hormones that influence bone trophism in premenopausal women submitted to BS 9.8 months, on average, before the study (OGg, N = 16). The data were compared to those obtained for women of normal weight (CG, N = 11) and for obese women (OG, N = 12). Eight patients in each group were monitored for one year, with the determination of BMD, of serum calcium, phosphorus, magnesium, parathyroid hormone, 25-hydroxyvitamin D, insulin-like growth factor-I (IGF-I) and osteocalcin, and of urinary calcium and deoxypyridinoline. The biochemical determinations were repeated every three months in the longitudinal study and BMD was measured at the end of the study. Parathyroid hormone levels were similar in the three groups. IGF-I levels (CG = 332 +/- 62 vs OG = 230 +/- 37 vs OGg = 128 +/- 19 ng/mL) were significantly lower in the operated patients compared to the non-operated obese women. Only OGg patients presented a significant fall in BMD of 6.2% at L1-L4, of 10.2% in the femoral neck, and of 5.1% in the forearm. These results suggest that the weight loss induced by BS is associated with a significant loss of bone mass even at sites that are not influenced by weight overload, with hormonal factors such as IGF-I being associated with this process.
The role of IGF-I in the negative regulation of GH expression and release is demonstrated by in vitro and in vivo models; however, the targets and mechanisms of IGF-I remain unclear. We have developed a cell-specific knockout mouse in which the IGF-I receptor was ablated from the somatotroph in order to validate and characterize IGF-I negative regulation; we termed this the somatotroph IGF-I receptor knockout (SIGFRKO) mouse. The SIGFRKO mice demonstrated increased GH gene expression and secretion as well as increased serum IGF-I. Compensatory changes were noted with decreased GHRH and increased somatostatin mRNA expression levels. SIGFRKO mice had normal linear growth, but by 14 wk of age weighed significantly less than controls. Furthermore, metabolic studies revealed SIGFRKO mice had significantly less fat mass and body percent fat. These data support somatotroph IGF-I negative regulation and suggest that hypothalamic feedback limits the extent of GH release. The SIGFRKO mouse is a model delineating the mechanisms of IGF-I regulation in the hypothalamic-pituitary axis and demonstrates compensatory mechanisms that mediate growth and metabolic function in mammals.
Growth hormone (GH) plays a pivotal role in growth and metabolism, with growth promotion mostly attributed to generation of insulin-like growth factor I (IGF-I) in liver or at local sites of GH action, whereas the metabolic effects of GH are considered to be intrinsic to GH itself. To distinguish the effects of GH from those of IGF-I, we developed a Cre-lox-mediated model of tissue-specific deletion of the growth hormone receptor (GHR). Near total deletion of the GHR in liver (GHRLD) had no effect on total body or bone linear growth despite a >90% suppression of circulating IGF-I; however, total bone density was significantly reduced. Circulating GH was increased 4-fold, and GHRLD displayed insulin resistance, glucose intolerance, and increased circulating free fatty acids. Livers displayed marked steatosis, the result of increased triglyceride synthesis and decreased efflux; reconstitution of hepatic GHR signaling via adenoviral expression of GHR restored triglyceride output to normal, whereas IGF-I infusion did not correct steatosis despite restoration of circulating GH to normal. Thus, with near total absence of circulating IGF-I, GH action at the growth plate, directly and via locally generated IGF-I, can regulate bone growth, but at the expense of diabetogenic, lipolytic, and hepatosteatotic consequences. Our results indicate that IGF-I is essential for bone mineral density, whereas hepatic GH signaling is essential to regulate intrahepatic lipid metabolism. We propose that circulating IGF-I serves to amplify the growth-promoting effects of GH, while simultaneously dampening the catabolic effects of GH.
Calorie restriction (CR) is the only intervention known to extend lifespan in a wide range of organisms, including mammals. However, the mechanisms by which it regulates mammalian aging remain largely unknown, and the involvement of the TOR and sirtuin pathways (which regulate aging in simpler organisms) remain controversial. Additionally, females of most mammals appear to live longer than males within species; and, although it remains unclear whether this holds true for mice, the relationship between sex-biased and CR-induced gene expression remains largely unexplored.
We generated microarray gene expression data from livers of male mice fed high calorie or CR diets, and we find that CR significantly changes the expression of over 3,000 genes, many between 10- and 50-fold. We compare our data to the GenAge database of known aging-related genes and to prior microarray expression data of genes expressed differently between male and female mice. CR generally feminizes gene expression and many of the most significantly changed individual genes are involved in aging, hormone signaling, and p53-associated regulation of the cell cycle and apoptosis. Among the genes showing the largest and most statistically significant CR-induced expression differences are Ddit4, a key regulator of the TOR pathway, and Nnmt, a regulator of lifespan linked to the sirtuin pathway. Using western analysis we confirmed post-translational inhibition of the TOR pathway.
Our data show that CR induces widespread gene expression changes and acts through highly evolutionarily conserved pathways, from microorganisms to mammals, and that its life-extension effects might arise partly from a shift toward a gene expression profile more typical of females.
The effects of insoluble dietary fibre differing in lignin content on intestinal morphology and mRNA expression was tested in an animal model of 48 weaned piglets. Engaged fibre sources were wheat bran (rich in cellulose and hemicellulose) and pollen from Chinese Masson pine (Pinus massoniana) (rich in lignin), respectively. The fibre sources were added to a basal diet as follows: no addition (control), 3.0% wheat bran, 1.27% pine pollen, and 2.55% pine pollen. The 12 animals of each feeding group were fed four experimental diets ad libitum for 37 days and were then slaughtered for retrieving tissue samples from stomach, jejunum, ileum, colon and mesenterial lymph nodes. Both fibre sources increased villus height of mucosa in jejunum (+10% on average) and ileum (+16% on average). Results of mRNA expression rates of inflammatory, cell cycle and growth marker genes (NFkappaB, TNFalpha, TGFbeta, Caspase3, CDK4, IGF1) were specific to fibre source and tissue: wheat bran induced an up-regulation of NFkappaB in stomach and jejunum, as well as TNFalpha and TGFbeta, and Caspase3 in jejunum. Pine pollen induced down regulation of NFkappaB, TNFalpha, TGFbeta, Caspase3, CDK4 and IGF1 in the colon as well as up-regulation of NFkappaB and TGFbeta in mesenterial lymph nodes. Finally, an overall data comparison based on a hierarchical cluster analysis showed a close relation between gene regulation in different gut sections and organs, as well as between small intestine morphology and zootechnical performance.
Growth hormone (GH) therapy has evolved rapidly over the past decade, and continuing research has established a clear role for therapeutic GH in a wide spectrum of disorders, including idiopathic GH deficiency (childhood- and adult-onset), Turner syndrome, Prader-Willi syndrome, small-for-gestational age children with failure of catch-up growth, AIDS-related catabolism, children with chronic renal failure, and idiopathic short stature. Although GH is used therapeutically in a wide variety of conditions, actual guidelines regarding the logistics of GH dosing continue to evolve, with data emerging regarding efficacy and safety. This review proposes a role for insulin-like growth factor I measurement in optimizing GH dosing.
Growth hormone plays an important role in bone metabolism. Treating bone deficits is a major topic in orthopaedic surgery. Our hypothesis was that local continuous growth hormone administration stimulates bone healing in a canine critical-sized bone defect model. Bone formation in the defects was quantified using densitometric image analysis and histomorphometry. After growth hormone treatment, expression levels of insulin-like growth factors-I and II, and growth hormone receptor were determined in the bone regenerate of the original defects. Circulating plasma concentrations of insulin-like growth factors-I and II, and insulin- like growth factor binding proteins-4, and 6 were measured during treatment. Growth hormone administration resulted in healing of bone defects but without an additional effect of local infusion. Expression of insulin-like growth factor-I in the bone regenerate was lower in the growth hormone-treated dogs, whereas insulin-like growth factor-II and growth hormone receptor expression were not increased. Growth hormone increased circulating insulin-like growth factor-I and growth factor-II plasma concentrations. Continuous infusion of growth hormone stimulated bone healing in a canine critical-sized bone defect model. Local delivery of growth hormone did not additionally enhance bone healing. Increased circulating plasma concentrations of insulin-like growth factors-I and II most likely induced bone formation.
The aim of the present study was to determine the efficacy of the bone markers osteocalcin (OC) and carboxyterminal cross-linked telopeptide of type-I collagen (ICTP) in evaluating new bone formation in the dog, using commercially available immunoassay kits. Dogs were randomly divided into three groups and a circular external skeletal fixation system (CESF) was mounted on the tibia. In the first group a distraction osteogenesis procedure of the crus was performed. The second group received an osteotomy without crural lengthening, whereas the third group served as a sham-operated control. Bone formation was assessed using densitometric image analysis of crural radiographs. Despite significant differences in the amount of newly formed bone, this finding was not reflected in the plasma levels of OC and ICTP. In conclusion, OC and ICTP were not efficacious as markers of bone formation and resorption during osteogenesis in this canine model.
Osteotropic growth factors play an important role in bone metabolism. Nevertheless, knowledge about their expression in relation to distraction osteogenesis remains limited. The aim of the present study was to determine the expression of growth hormone (GH), growth hormone receptor (GHR), insulin-like growth factor I (IGF-I), insulin-like growth factor II (IGF-II), and bone morphogenetic protein 2 (BMP-2) in distraction-induced bone regeneration. Expression of these factors was assessed during the consolidation phase, comparing distraction osteogenesis with osteotomy-induced bone formation. Real-time PCR was performed as a semiquantitative measurement of mRNA, and the relative expression levels of these factors were determined. In addition, plasma GH profiles and plasma concentrations of IGF-I, IGF-II, and insulin-like growth factor-binding protein 4 and -6 (IGFBP-4 and -6) were measured to assess their potential systemic role during bone formation. Expression of GHR, IGF-I, and BMP-2 had significantly increased in comparison with the expression of these factors in mature bone. Expression of GHR was significantly higher in distraction-induced bone regenerate than in osteotomy-induced bone. No significant differences were found for the expression of IGF-I and BMP-2 between distraction and osteotomy. Plasma concentrations of GH, IGF-I, IGF-II, IGFBP-4, and IGFBP-6 did not demonstrate any significant differences between treatment groups and controls. Upregulation of GHR expression in distraction osteogenesis may enhance sensitivity to endogenous systemic GH and thus promote consolidation of the regenerated bone. Changes in the systemic osteotropic growth factors GH, IGF-I, IGF-II, IGFBP-4, and IGFBP-6 do not seem to be of importance during distraction osteogenesis.
The transcription factors signal transducers and activators of transcription (STAT)5a and STAT5b (STAT5) are essential mediators of many actions of GH, including transcription of the IGF-I gene. Here, we present evidence that skeletal muscle STAT5 is important for postnatal growth and suggest that this is conveyed by the production of localized IGF-I. To investigate the role of STAT5 signaling in skeletal muscle, mice with a skeletal-muscle-specific deletion of the Stat5a and Stat5b genes (Stat5MKO mice) were used. IGF-I mRNA levels were reduced by 60% in muscle tissue of these mice. Despite only a 15% decrease in circulating IGF-I, 8-wk-old male Stat5MKO mice displayed approximately 20% reduction in body weight that was accounted for by a reduction in lean mass. The skeletons of Stat5MKO mice were found to be smaller than controls, indicating the growth defect was not restricted to skeletal muscle. These results demonstrate an as yet unreported critical role for STAT5 in skeletal muscle for local IGF-I production and postnatal growth and suggest the skeletal muscle as a major site of GH action.
Obesity is a major factor central to the development of insulin resistance and type 2 diabetes. The identification and characterization of genes involved in regulation of adiposity, insulin sensitivity, and glucose uptake are key to the design and development of new drug therapies for this disease. In this study, we show that the polarity kinase Par-1b/MARK2 is required for regulating glucose metabolism in vivo. Mice null for Par-1b were lean, insulin hypersensitive, resistant to high-fat diet-induced weight gain, and hypermetabolic. ¹⁸F-FDG microPET and hyperinsulinemic–euglycemic clamp analyses demonstrated increased glucose uptake into white and brown adipose tissue, but not into skeletal muscle of Par-1b null mice relative to wild-type controls. Taken together, these data indicate that Par-1b is a regulator of glucose metabolism and adiposity in the whole animal and may be a valuable drug target for the treatment of both type 2 diabetes and obesity.
• glucose
• obesity
• EMK
We investigated the effect of fat supplementation on plasma levels of hormones related to metabolism, with special attention to leptin, in cows in early lactation and in feedlot steers. In experiment 1, 34 lactating cows received no fat or else 0.5 or 1.0 kg of partially hydrogenated oil per day in addition to their basal diet from day 20 before the expected calving date to day 70 postpartum. In experiment 2, part of the corn in the basal concentrate was replaced with 0.7 kg of the same oil such that the diets were isocaloric; 18 cows received the fat-substituted diet and 18 a control diet from day 20 before the expected calving date to day 75 postpartum. In experiment 3, calcium salts of fatty acids were added to the basal diet of 14 feedlot steers for 80 d; another 14 steers received a control diet. The basal plasma levels of leptin were higher in the cows than in the steers. Dietary fat supplementation did not affect the leptin levels in the lactating cows but lowered the levels in the feedlot steers despite greater energy intake and body fatness (body weight) in the steers receiving the supplement than in those receiving the control diet. The levels of insulin-like growth factor I and insulin were decreased with dietary fat supplementation in the lactating cows but were unaffected in the steers, suggesting that responses to fat ingestion depend on the physiological state of the animal, including age and sex. Finally, no effects of supplementary fat on the level of growth hormone were demonstrated in any of the models.
Insulin-like growth factor-I (IGF-I) is known to be involved in the development and progression of several types of solid tumors including ovarian cancer. IGF-I levels in local tissue is subject to both endocrine and paracrine/autocrine regulation. To investigate which regulation is more importantly involved in IGF-I action in ovarian cancer regarding tumor progression, we analyzed IGF-I mRNA expression (assuming only from paracrine/autocrine regulation) and peptide concentration (subject to both endocrine and paracrine/autocrine regulation) as well as a genetic polymorphism (CA dinucleotide repeats) in 215 epithelial ovarian cancer patients. Genomic DNA, total RNA and cytosol proteins were extracted from fresh tumor samples. Two alternatively spliced IGF-I transcripts (IGF-IA and IGF-IB) were analyzed using real-time PCR. Cytosol levels of free and total IGF-I were measured with enzyme-linked immunosorbent assay. DNA sizing analysis was performed to determine the CA polymorphism. The study showed that the CA polymorphism had a weak influence on IGF-I expression, but no effect on tumor progression. High levels of free, not total, IGF-I peptide were associated with elevated risk of disease progression (HR = 2.06; 95%CI: 1.22-3.50), and the association was independent of clinicopathologic features of the disease. One of the IGF-I transcripts (IGF-IA) had a similar but less significant impact on disease progression. Women with high IGF-I mRNA and peptide were at greater risk for disease progression compared to those with low in both (HR = 2.13; 95%CI: 1.13-3.95). These findings support the notion that IGF-I is involved in ovarian cancer progression and free IGF-I plays a more important role in the disease. The study also suggests that both endocrine and paracrine/autocrine are involved in the regulation of IGF-I activity in ovarian cancer.
Episodic acidification resulting in increased acidity and inorganic aluminum (Al(i)) is known to interfere with the parr-smolt transformation of Atlantic salmon (Salmo salar), and has been implicated as a possible cause of population decline. To determine the extent and mechanism(s) by which short-term acid/Al exposure compromises smolt development, Atlantic salmon smolts were exposed to either control (pH 6.7-6.9) or acid/Al (pH 5.4-6.3, 28-64 microgl(-1) Al(i)) conditions for 2 and 5 days, and impacts on freshwater (FW) ion regulation, seawater (SW) tolerance, plasma hormone levels and stress response were examined. Gill Al concentrations were elevated in all smolts exposed to acid/Al relative to controls confirming exposure to increased Al(i). There was no effect of acid/Al on plasma ion concentrations in FW however, smolts exposed to acid/Al followed by a 24h SW challenge exhibited greater plasma Cl(-) levels than controls, indicating reduced SW tolerance. Loss of SW tolerance was accompanied by reductions in gill Na(+),K(+)-ATPase (NKA) activity and Na(+),K(+),2Cl(-) (NKCC) cotransporter protein abundance. Acid/Al exposure resulted in decreased plasma insulin-like growth factor (IGF-I) and 3,3',5'-triiodo-l-thyronine (T(3)) levels, whereas no effect of treatment was seen on plasma cortisol, growth hormone (GH), or thyroxine (T(4)) levels. Acid/Al exposure resulted in increased hematocrit and plasma glucose levels in FW, but both returned to control levels after 24h in SW. The results indicate that smolt development and SW tolerance are compromised by short-term exposure to acid/Al in the absence of detectable impacts on FW ion regulation. Loss of SW tolerance during short-term acid/Al exposure likely results from reductions in gill NKA and NKCC, possibly mediated by decreases in plasma IGF-I and T(3).
The somatomedin hypothesis proposed that insulin-like growth factor I (IGF-I) was a hepatically derived circulating mediator
of growth hormone and is a crucial factor for postnatal growth and development. To reassess this hypothesis, we have used
the Cre/loxP recombination system to delete the igf1 gene exclusively in the liver. igf1 gene deletion in the liver abrogated expression of igf1 mRNA and caused a dramatic reduction in circulating IGF-I levels. However, growth as determined by body weight, body length,
and femoral length did not differ from wild-type littermates. Although our model proves that hepatic IGF-I is indeed the major
contributor to circulating IGF-I levels in mice it challenges the concept that circulating IGF-I is crucial for normal postnatal
growth. Rather, our model provides direct evidence for the importance of the autocrine/paracrine role of IGF-I.
Growth hormone (GH) regulates both bone growth and remodeling, but it is unclear whether these actions are mediated directly by the GH receptor (GHR) and/or IGF-I signaling. The actions of GH are transduced by the Jak/Stat signaling pathway via Stat5, which is thought to regulate IGF-I expression. To determine the respective roles of GHR and IGF-I in bone growth and remodeling, we examined bones of wild-type, GHR knockout (GHR–/–), Stat5ab–/–, and GHR–/– mice treated with IGF-I. Reduced bone growth in GHR–/– mice, due to a premature reduction in chondrocyte proliferation and cortical bone growth, was detected after 2 weeks of age. Additionally, although trabecular bone volume was unchanged, bone turnover was significantly reduced in GHR–/– mice, indicating GH involvement in the high bone-turnover level during growth. IGF-I treatment almost completely rescued all effects of the GHR–/– on both bone growth and remodeling, supporting a direct effect of IGF-I on both osteoblasts and chondrocytes. Whereas bone length was reduced in Stat5ab–/– mice, there was no reduction in trabecular bone remodeling or growth-plate width as observed in GHR–/– mice, indicating that the effects of GH in bone may not involve Stat5 activation.
The body growth of animals is regulated by growth hormone and IGF-I. The classical theory of this regulation is that most IGF-I in the blood originates in the liver and that body growth is controlled by the concentration of IGF-I in the blood. We have abolished IGF-I production in the livers of mice by using the Cre/loxP recombination system. These mice demonstrated complete inactivation of the IGF-I gene in the hepatocytes. Although the liver accounts for less than 5% of body mass, the concentration of IGF-I in the serum was reduced by 75%. This finding confirms that the liver is the principal source of IGF-I in the blood. However, the reduction in serum IGF-I concentration had no discernible effect on postnatal body growth. We conclude that postnatal body growth is preserved despite complete absence of IGF-I production by the hepatocytes.
Human cells treated with interferon synthesize two proteins that exhibit high homology to murine Mx1 protein, which has previously
been identified as the mediator of interferon-induced cellular resistance of mouse cells against influenza viruses. Using
murine Mx1 cDNA as a hybridization probe, we have isolated cDNA clones originating from two distinct human Mx genes, designated
MxA and MxB. In human fibroblasts, expression of MxA and MxB is strongly induced by alpha interferon (IFN-alpha), IFN-beta,
Newcastle disease virus, and, to a much lesser extent, IFN-gamma, MxA and MxB proteins have molecular masses of 76 and 73
kilodaltons, respectively, and their sequences are 63% identical. A comparison of human and mouse Mx proteins revealed that
human MxA and mouse Mx2 are the most closely related proteins, showing 77% sequence identity. Near their amino termini, human
and mouse Mx proteins contain a block of 53 identical amino acids and additional regions of very high sequence similarity.
These conserved sequences are also present in a double-stranded RNA-inducible fish gene, which suggests that they may constitute
a functionally important domain of Mx proteins. In contrast to mouse Mx1 protein, which accumulates in the nuclei of IFN-treated
mouse cells, the two human Mx proteins both accumulate in the cytoplasm of IFN-treated cells.
The interrelation between the secretion of two hypophysiotropic peptides, growth hormone-releasing factor (GRF) and somatostatin
(SRIF), in the generation of episodic growth hormone (GH) secretion was inferred from direct measurements of immunoreactive
GRF and immunoreactive SRIF concentrations in the hypophysial-portal plasma of the rat. Secretion of immunoreactive GRF was
found to be episodic, with maximal concentrations present during periods of expected GH secretory episodes. Secretion of immunoreactive
GRF was accompanied by a moderate reduction in portal plasma levels of immunoreactive SRIF. Passive immunoneutralization of
SRIF was associated with increased concentrations of immunoreactive GRF in hypophysial-portal plasma. On the basis of these
observations, it appears that each GH secretory episode is initiated by pulsatile secretion of immunoreactive GRF into the
portal circulation, which is preceded by or is concurrent with a moderate reduction of inhibitory tone provided by portal
immunoreactive SRIF. These experiments provide direct insights into central and adenohypophysial mechanisms by which GRF and
SRIF interact to generate episodic secretion of GH.
Intracerebroventricular administration of ILA's, a preparation enriched in insulin-like growth factors, caused a marked decrease
in growth hormone secretory episodes and in body weight associated with reduced food intake over 24 hours. Central injection
of insulin and bovine serum albumin had no such effects. These findings suggest that insulin-like growth factors play a role
in growth hormone negative feedback and body weight regulation at the level of the central nervous system.
Obesity is a disorder of energy balance, indicating a chronic disequilibrium between energy intake and expenditure. Recently, the mouse ob gene, and subsequently its human and rat homologues, have been cloned. The ob gene product, leptin, is expressed exclusively in adipose tissue, and appears to be a signalling factor regulating body-weight homeostasis and energy balance. Because the level of ob gene expression might indicate the size of the adipose depot, we suggest that it is regulated by factors modulating adipose tissue size. Here we show that ob gene exhibits diurnal variation, increasing during the night, after rats start eating. This variation was linked to changes in food intake, as fasting prevented the cyclic variation and decreased ob messenger RNA. Furthermore, refeeding fasted rats restored ob mRNA within 4 hours to levels of fed animals. A single insulin injection in fasted animals increased ob mRNA to levels of fed controls. Experiments to control glucose and insulin independently in animals, and studies in primary adipocytes, showed that insulin regulates ob gene expression directly in rats, regardless of its glucose-lowering effects. Whereas the ob gene product, leptin, has been shown to reduce food intake and increase energy expenditure, our data demonstrate that ob gene expression is increased after food ingestion in rats, perhaps through a direct action of insulin on the adipocyte.
Deletion of the promoter and the first exon of the DNA polymerase beta gene (pol beta) in the mouse germ line results in a
lethal phenotype. With the use of the bacteriophage-derived, site-specific recombinase Cre in a transgenic approach, the same
mutation can be selectively introduced into a particular cellular compartment-in this case, T cells. The impact of the mutation
on those cells can then be analyzed because the mutant animals are viable.
Sexually dimorphic growth hormone (GH) secretory pattern is important in the determination of gender-specific patterns of growth and metabolism in rats. Whether GH secretion in humans is also sexually dimorphic and the neuroendocrine mechanisms governing this potential difference are not fully established. We have compared pulsatile GH secretion profiles in young men and women in the baseline state and during a continuous intravenous infusion of recombinant human insulin-like growth factor I (rhIGF-I). During the baseline study, men had large nocturnal GH pulses and relatively small pulses during the rest of the day. In contrast, women had more continuous GH secretion and more frequent GH pulses that were of more uniform size. The infusion of rhIGF-I (10 microg/kg/h) potently suppressed both spontaneous and growth hormone-releasing hormone (GHRH)-induced GH secretion in men. In women, however, rhIGF-I had less effect on pulsatile GH secretion and did not suppress the GH response to GHRH. These data demonstrate the existence of sexual dimorphism in the regulatory mechanisms involved in GH secretion in humans. The persistence of GH responses to GHRH in women suggests that negative feedback by IGF-I might be expressed, in part, through suppression of hypothalamic GHRH.
In this study, the spontaneous dwarf rat (SDR) has been used to examine GHRH production and action in the selective absence of endogenous GH. This dwarf model is unique in that GH is not produced because of a point mutation in the GH gene. However, other pituitary hormones are not obviously compromised. Examination of the hypothalamic pituitary-axis of SDRs revealed that GHRH messenger RNA (mRNA) levels were increased, whereas somatostatin (SS) and neuropeptide Y (NPY) mRNA levels were decreased, compared with age- and sex-matched normal controls, as determined by Northern blot analysis (n = 5 animals/group; P < 0.05). The elevated levels of GHRH mRNA in the SDR hypothalamus were accompanied by a 56% increase in pituitary GHRH receptor (GHRH-R) mRNA, as determined by RT-PCR (P < 0.05). To investigate whether the up-regulation of GHRH-R mRNA resulted in an increase in GHRH-R function, SDR and control pituitary cell cultures were challenged with GHRH (0.001-10 nM; 15 min), and intracellular cAMP concentrations were measured by RIA. Interestingly, SDR pituitary cells were hyperresponsive to 1 and 10 nM GHRH, which induced a rise in intracellular cAMP concentrations 50% greater than that observed in control cultures (n = 3 separate experiments; P < 0.05 and P < 0.01, respectively). Replacement of GH, by osmotic minipump (10 microg/h for 72 h), resulted in the suppression of GHRH mRNA levels (P < 0.01), whereas SS and NPY mRNA levels were increased (P < 0.05), compared with vehicle-treated controls (n = 5 animals/treatment group). Consonant with the fall in hypothalamic GHRH mRNA was a decrease in pituitary GHRH-R mRNA levels. Although replacement of insulin-like growth factor-I (IGF-I), by osmotic pump (5 microg/h for 72 h), resulted in a rise in circulating IGF-I concentrations comparable with that observed after GH replacement, IGF-I treatment was ineffective in modulating GHRH, SS, or NPY mRNA levels. However, IGF-I treatment did reduce pituitary GHRH-R mRNA levels, compared with vehicle-treated controls (P < 0.05). These results further validate the role of GH as a negative regulator of hypothalamic GHRH expression, and they suggest that SS and NPY act as intermediaries in GH-induced suppression of hypothalamic GHRH synthesis. These data also demonstrate that increases in circulating IGF-I are not responsible for changes in hypothalamic function observed after GH treatment. Finally, this report establishes modulation of GHRH-R synthesis as a component of GH autofeedback regulation.
The effects of a combination of mild exercise and GH injections on bone were studied in old female rats. Biosynthetic human GH, 2.7 mg/kg/day, was injected sc for 73 days. Exercised rats ran 8 m/min on a treadmill for 1 h/day. All rats (age 21 months old) were labeled with a tetracycline injection 56 days and a calcein injection 11 days before killing. The GH injections resulted in an 11-fold increase in femoral middiaphyseal bone formation rate and a 12% increase in cross-sectional area compared with the saline-injected group. The mild exercise doubled the mineralizing surface but did not influence the bone formation rate significantly. The combination of GH injections plus exercise, however, resulted in a further increase of 39% in bone formation rate, primarily at the anterolateral aspects, and an increase of 5% in cross-sectional area compared with the group injected with GH only. The femur ultimate breaking load was increased by 37% and the stiffness by 42% in the group injected with GH compared with the saline-injected group. Exercise alone did not influence the femur mechanical properties. The combination of GH injections plus exercise induced a 4% further increase in ultimate breaking load and 7% further increase in stiffness compared with the group injected with GH alone. The GH injections induced a 117% increase in serum insulin-like growth factor I. The GH-insulin-like growth factor I axis stimulates recruitment of osteoblast precursor cells, resulting in increased bone formation at the periosteal surface. GH injections and mild excercise in combination modulate and increase further the formation and strength of cortical bone in old female rats.
It has recently been shown that, in follicular fluid, as in the circulation, insulin-like growth factors (IGFs)-I and -II exist in a ternary complex with IGF binding protein-3 (IGFBP-3) and the acid-labile subunit (ALS). The current study was designed to determine whether ovarian follicular and luteal cells could synthesize IGFBP-3 and ALS. Ovaries were collected, during the follicular and early luteal phases, from mature pigs whose cycles were synchronized with PGF2α. We studied IGFBP-3 and ALS messenger RNA (mRNA) by in situ hybridization. These transcripts were colocalized with aromatase mRNA, a marker of healthy granulosa cells. IGFBP-3 mRNA was equally expressed in granulosa cells of all growing follicles. In contrast, granulosa cell ALS mRNA levels were higher (P < 0.05) in preantral and small antral follicles than in large antral follicles. In thecal cells, expression of mRNA for IGFBP-3, ALS and cyclin D1 (a marker of cell proliferation) was restricted to healthy (aromatase-expressing) follicles. In those follicles, thecal expression of IGFBP-3 mRNA was low or absent in preantral follicles but increased (P < 0.05) in antral follicles. Thecal cell ALS transcripts peaked in small antral follicles (P < 0.05) and then declined. In granulosa cells of atretic follicles, transcripts for aromatase were greatly reduced, whereas IGFBP-3 mRNA levels remained high. In contrast, ALS transcript levels were greatly reduced in both granulosa (P < 0.05) and thecal cells (P< 0.001) of atretic follicles. After ovulation, IGFBP-3 mRNA was moderately expressed in granulosa luteins but strongly detected in a few theca-derived cells and in vascular endothelial cells. This study demonstrates that follicular fluid IGFBP-3 and ALS, like the IGFs, originate (at least in part) from the ovary. The ability of follicular cells to synthesize, assemble, and store all components of the ternary complex may be critical in determining the bioavailability of follicular IGF-I and -II.
The effects of a combination of mild exercise and GH injections on bone were studied in old female rats. Biosynthetic human GH, 2.7 mg/kg/day, was injected s.c. for 73 days. Exercised rats ran 8 m/min on a treadmill for 1 h/day. All rats (age 21 months old) were labeled with a tetracycline injection 56 days and a calcein injection 11 days before killing. The GH injections resulted in an 11-fold increase in femoral middiaphyseal bone formation rate and a 12% increase in cross-sectional area compared with the saline-injected group. The mild exercise doubled the mineralizing surface but did not influence the bone formation rate significantly. The combination of GH injections plus exercise, however, resulted in a further increase of 39% in bone formation rate, primarily at the anterolateral aspects, and an increase of 5% in cross-sectional area compared with the group injected with GH only. The femur ultimate breaking load was increased by 37% and the stiffness by 42% in the group injected with GH compared with the saline-injected group. Exercise alone did not influence the femur mechanical properties. The combination of GH injections plus exercise induced a 4% further increase in ultimate breaking load and 7% further increase in stiffness compared with the group injected with GH alone. The GH injections induced a 117% increase in serum insulin-like growth factor I. The GH-insulin-like growth factor I axis stimulates recruitment of osteoblast precursor cells, resulting in increased bone formation at the periosteal surface. GH injections and mild excercise in combination modulate and increase further the formation and strength of cortical bone in old female rats.
While growth hormone (GH) has long been known as a lipolytic hormone, it has been difficult to study the cellular mechanisms for this effect. Since cultured 3T3-F442A adipocytes have recently proven to be useful to study chronic effects of GH on adipocyte metabolism, we examined the effects of GH on lipolysis. In these cells, GH alone produced a dose-dependent increase in the release of glycerol after 24 to 48 hours. The maximum increase occurred with 10 ng/mL human GH. The effect of GH was similar in the presence and absence of dexamethasone. Under each condition, the stimulation of glycerol release was accompanied by a GH-induced increase in the activity of hormone-sensitive lipase (HSL), a key lipolytic enzyme. The increase in HSL required 24 hours with GH and lasted at least 48 hours. The increase in HSL activity by epinephrine, like glycerol release, was potentiated by GH. Although GH potently simulates the activity of the lipogenic enzyme glycerol phosphate dehydrogenase (GPD) in differentiating 3T3-F442A preadipocytes, GH had a negligible effect on GPD activity in the differentiated adipocytes with chronic or short-term incubation. However, in contrast to the chronic effect of GH, short-term (30-minute) incubation with GH inhibited epinephrine-stimulated glycerol release, a characteristic transient antilipolytic effect of GH. These studies indicate that chronic GH treatment is lipolytic in cultured 3T3-F442A adipocytes, and document that lipolytic responses to GH involve an increase in the activity of HSL.
Members of the Mx protein family promote interferon-inducible resistance to viral infection in mammals and act by unknown mechanisms. We identified an Mx-like protein in yeast and present genetic evidence for its cellular function. This protein, the VPS1 product, is essential for vacuolar protein sorting, normal organization of intracellular membranes, and growth at high temperature, implying that Mx-like proteins are engaged in fundamental cellular processes in eukaryotes. Vps1p contains a tripartite GTP binding motif, which suggests that binding to GTP is essential to its role in protein sorting. Vps1p-specific antibody labels punctate cytoplasmic structures that condense to larger structures in a Golgi-accumulating sec7 mutant; thus, Vps1p may associate with an intermediate organelle of the secretory pathway.
We have generated transgenic mice that express the intracellular anti-influenza virus protein Mx1 under control of an interferon-responsive regulatory element. Upon infection with influenza virus, mice of a high responder line produce Mx1 protein locally at the sites of initial viral replication, exhibit little viral spread, and survive infection. Mice of a low responder line show more extensive viral spread and survive infection only when virus is given at high doses. To survive low dose infections, these mice require injection of interferon along with virus. The results show that influenza viral pathogenesis is determined by a subtle balance between the dose of the infecting virus and the levels of the antiviral host factor Mx1 and that mice can be rendered resistant to a virulent infection by "intracellular immunization" achieved through germline transformation.
Under physiological circumstances growth hormone (GH) is secreted in bursts after the onset of sleep and a few hours postprandially. Because most relevant studies have employed constant or repeated infusion of high doses of GH, the possible metabolic effects of such bursts are largely unknown. We have studied seven healthy, male subjects for 7 h after an intravenous bolus of 1) 140 micrograms GH and 2) saline. When injected, serum GH rose to a peak of 21 +/- 3 micrograms/l 10 min after injection. GH caused 1) a rapid, sustained 55% decrease in forearm glucose uptake (P less than 0.05) followed by increases toward control values, 2) a delayed 5 mg/100 ml decrease in plasma glucose (P less than 0.05), and 3) significant 60-250% increases (P less than 0.05) in all measured lipid intermediates (nonesterified fatty acids, 3-hydroxybutyrate, and glycerol) 120-160 min after administration followed by decreases to below control values (P less than 0.05). GH did not influence circulating levels of insulin, C-peptide, glucagon, or insulin-like growth factor I (IGF-I), or isotopically determined glucose turnover. Physiological bursts of GH secretion appear to have acute insulin antagonistic effects with maximal effect on lipolysis after 2 h. These effects are reversed after 4 h. Therefore, GH could play a key role in regulation of diurnal rhythms of substrate levels and fuel utilization in humans.
Serum levels of GH and insulin-like growth factor I (IGF-I) were genetically increased to investigate the physiological activities of these proteins. Lines of mice expressing chimeric genes composed of bovine GH, human GRF, or human IGF-I coding sequences fused to the mouse metallothionein I promoter were examined for consequences of chronic exposure to high levels of these peptides. Animals with elevated serum levels of GH (either bovine GH or mouse GH) have selective splanchnomegaly coupled with glomerular sclerosis and hepatocellularmegaly. Serum levels of insulin and cholesterol are increased. In contrast (with the exception of selective enlargement of organs), the chronic expression of IGF-I results in a different pattern of abnormalities. These findings suggest that the pathogenesis of GH-related disorders is not mediated solely by IGF-I.
The Cre protein encoded by the coliphage P1 is a 38-kDa protein that efficiently promotes both intra- and intermolecular synapsis and recombination of DNA both in Escherichia coli and in vitro. Recombination occurs at a specific site, called lox, and does not require any other protein factors. The Cre protein is shown here also to be able to cause synapsis of DNA and site-specific recombination in a mammalian cell line. A stable mouse cell line was established that expresses the Cre protein under the control of the Cd2+-inducible metallothionein I gene promoter. DNA recombination was monitored with DNA substrates containing two directly repeated lox sites. One such substrate is a circular plasmid with two directly repeated lox sites (lox2) flanking a marker gene and was introduced into cells by Ca3(PO4)2 transformation. As a second substrate we used a pseudorabies virus (a herpesvirus) containing a lox2 insertion designed to provide a sensitive detection system for recombination. In both cases, site-specific recombination in vivo is dependent on the presence of the Cre protein and occurs specifically at the 34-base-pair lox sites. These results demonstrate the controlled site-specific synapsis of DNA and recombination by a prokaryotic protein in mammalian cells and suggest that Cre-mediated site-specific recombination may be a useful tool for understanding and modulating genome rearrangements in eukaryotes.
The procaryotic cre-lox site-specific recombination system of coliphage P1 was shown to function in an efficient manner in a eucaryote, the yeast Saccharomyces cerevisiae. The cre gene, which codes for a site-specific recombinase, was placed under control of the yeast GALI promoter. lox sites flanking the LEU2 gene were integrated into two different chromosomes in both orientations. Excisive recombination at the lox sites (as measured by loss of the LEU2 gene) was promoted efficiently and accurately by the Cre protein and was dependent upon induction by galactose. These results demonstrate that a procaryotic recombinase can enter a eucaryotic nucleus and, moreover, that the ability of the Cre recombinase to perform precise recombination events on the chromosomes of S. cerevisiae is unimpaired by chromatin structure.
Recombinant human insulin-like growth factor I (rhIGF-I) was infused subcutaneously into hypophysectomized rats for as long as 18 days. Three hundred micrograms (39 nmol) of rhIGF-I per day and 200 milliunits (4.5 nmol) of human growth hormone (hGH) per day increased body weight, tibial epiphyseal width, longitudinal bone growth, and trabecular bone formation similarly. Weight gains of the kidneys and spleen, however, were greater with rhIGF-I than with hGH, whereas the weight of the epididymal fat pads was reduced with rhIGF-I. The weight of the thymus was increased by rhIGF-I treatment. Thus, IGF-I administered over a prolonged period of time mimics GH effects in hypophysectomized rats. Quantitative differences between rhIGF-I and hGH treatment with respect to organ weights may be related to different forms of circulating IGF-I or may be due to independent effects of GH and IGF-I. The results support the somatomedin hypothesis, but they also stress the role of GH as a modulator of IGF-I action.
We have analyzed the absolute and relative (allometric) growth of a series of internal organs in giant transgenic (MTrGH) and littermate control mice to determine the general and organ-specific effects of the altered hormonal environment on growth in these rodents. Comparison of cross-sectional growth allometries of organ weights and external body dimensions between the two samples was based on analyses of covariance. We report significantly increased growth in all of the organs and measurements examined except for the brain. Coefficients of growth allometry differ significantly from isometric values in a number of cases, and thus, the adult transgenic mice exhibit body proportions different from those of the adult controls. Most of these shape differences reflect general allometric size increase, but the liver and spleen of the transgenics undergo special enlargement or growth. These results indicate that the primary effect of elevated GH and IGF-I levels is increased overall growth, but in the relative proportions set by the intrinsic controls of individual organs and body regions.
Mouse cells of the Mx+ genotype accumulate Mx mRNA in response to type I interferon (IFN). Nuclear runoff experiments show
that IFN stringently regulates Mx gene expression at the level of transcription. Mx mRNA synthesis peaks about 3 h after IFN
treatment, and within 5 h, Mx mRNA concentration rises from undetectable levels to about 0.1% of polyadenylated RNA.
To further delineate the relationship between GH-releasing factor (GRF) and somatostatin (SRIF) in generation of the ultradian rhythm of GH secretion, we used two GRF peptides, human pancreas (hp) GRF-44 and rat hypothalamic (rh) GRF, and studied their interaction with SRIF by passive immunization with a specific antiserum (AS) to SRIF. Freely moving, chronically cannulated male rats were given 10 micrograms of either hpGRF-44 or rhGRF, iv, during peak (1100 h) and trough (1300 h) periods of the GH rhythm. Six-hour plasma GH profiles were obtained after pretreatment with either SRIF AS or normal sheep serum (NSS) as a control. In NSS-treated rats, the plasma GH responses to both hpGRF-44 and rhGRF were significantly greater when the peptides were administered during peak than during trough periods. Immunoneutralization with SRIF AS eliminated these differences and permitted marked GH release in response to both peptides at 1300 h. In addition, SRIF AS augmented the GRF-induced GH response at 1100 h compared with that in NSS controls. The rhGRF peptide caused significantly more GH release than hpGRF under both conditions. These results demonstrate that 1) the GH-releasing abilities of the GRF peptides vary markedly according to the time of injection; 2) the weak GRF-induced GH response observed during trough periods of the GH rhythm is due to antagonization by endogenous circulating SRIF; and 3) the rat-derived GRF may be a more potent GH secretagogue than the human-derived peptide in the rat. The findings reported here together with the available evidence provide support for the hypothesis that GRF and SRIF are secreted tonically from the hypothalamus into the hypophyseal portal blood, and that superimposed upon this steady state release is an additional 3- to 4-h rhythmic surge of each peptide, providing for integration of the ultradian rhythm of GH secretion, as observed in peripheral blood.
Treatment of rats with cyproterone acetate (CPA) induces liver growth. Intact hepatocytes and cell nuclei were isolated from enlarged livers and their volumes or diameters were determined by electronic and microscopic methods. No changes in mean hepatocyte volume or ploidy were observed. However, there was a marked fall in the frequency of binuclear hepatocytes (from 43% to 7%) and a concomitant increase of nuclear ploidy. This effect probably resulted from CPA-induced replication of binuclear hepatocytes. The total number of hepatocytes replicating in response to CPA was estimated on the basis of these data and was found to be up to 75% of all parenchymal cells. Similar cytological changes were observed in the liver after treatment with pregnenolone-16 alpha-carbonitrile (PCN) and, to a lesser extent, with alpha-hexachlorocyclohexane (alpha-HCH). In contrast, physiological liver growth in adolescent rats was characterized by only small changes in binuclearity and nuclear ploidy, and by increases of cellular ploidy. Thus, ploidy analyses may be a useful tool to characterize the type of growth stimulation. Following discontinuation of treatment the cytological changes induced by CPA or alpha-HCH were not reversible in a matter of 3 weeks.