Normal growth and development in the absence of hepatic insulin-like growth factor I

Growth hormone receptor-deficient pigs resemble the pathophysiology of human Laron syndrome and reveal altered activation of signaling cascades in the liver

OBJECTIVE

Laron syndrome (LS) is a rare, autosomal recessive disorder in humans caused by loss-of-function mutations of the growth hormone receptor (GHR) gene. To establish a large animal model for LS, pigs with GHR knockout (KO) mutations were generated and characterized.

METHODS

CRISPR/Cas9 technology was applied to mutate exon 3 of the GHR gene in porcine zygotes. Two heterozygous founder sows with a 1-bp or 7-bp insertion in GHR exon 3 were obtained, and their heterozygous F1 offspring were intercrossed to produce GHR-KO, heterozygous GHR mutant, and wild-type pigs. Since the latter two groups were not significantly different in any parameter investigated, they were pooled as the GHR expressing control group. The characterization program included body and organ growth, body composition, endocrine and clinical-chemical parameters, as well as signaling studies in liver tissue.

RESULTS

GHR-KO pigs lacked GHR and had markedly reduced serum insulin-like growth factor 1 (IGF1) levels and reduced IGF-binding protein 3 (IGFBP3) activity but increased IGFBP2 levels. Serum GH concentrations were significantly elevated compared with control pigs. GHR-KO pigs had a normal birth weight. Growth retardation became significant at the age of five weeks. At the age of six months, the body weight of GHR-KO pigs was reduced by 60% compared with controls. Most organ weights of GHR-KO pigs were reduced proportionally to body weight. However, the weights of liver, kidneys, and heart were disproportionately reduced, while the relative brain weight was almost doubled. GHR-KO pigs had a markedly increased percentage of total body fat relative to body weight and displayed transient juvenile hypoglycemia along with decreased serum triglyceride and cholesterol levels. Analysis of insulin receptor related signaling in the liver of adult fasted pigs revealed increased phosphorylation of IRS1 and PI3K. In agreement with the loss of GHR, phosphorylation of STAT5 was significantly reduced. In contrast, phosphorylation of JAK2 was significantly increased, possibly due to the increased serum leptin levels and increased hepatic leptin receptor expression and activation in GHR-KO pigs. In addition, increased mTOR phosphorylation was observed in GHR-KO liver samples, and phosphorylation studies of downstream substrates suggested the activation of mainly mTOR complex 2.

CONCLUSION

GHR-KO pigs resemble the pathophysiology of LS and are an interesting model for mechanistic studies and treatment trials.

Insulin-like growth factor 1 inversely relates to monocyte/macrophage activation markers in HIV

OBJECTIVE

Monocyte/macrophage activation is increased among people with HIV, and may contribute to the heightened risk of atherosclerosis and neurocognitive dysfunction in this population. Insulin-like growth factor 1 (IGF-1) has been shown to attenuate the innate immune response in animal models of atherosclerosis and inflammatory bowel disease. We investigated, for the first time, relationships of circulating IGF-1 with monocyte/macrophage-specific indices among HIV-infected individuals and uninfected controls.

DESIGN

Observational.

METHODS

One hundred and thirty-one HIV-infected patients and 65 well matched controls without known cardiac disease or viral hepatitis were recruited previously. IGF-1, expressed as a z-score relative to the age-adjusted and sex-adjusted population mean, was related to log-transformed inflammatory markers within HIV and non-HIV groups.

RESULTS

In HIV, IGF-1 inversely related to sCD163 (r = -0.28, P = 0.002), sCD14 (r = -0.29, P = 0.002), and high-sensitivity IL-6 (r = -0.27, P = 0.006). There was no association of IGF-1 with high-sensitivity CRP, MCP-1, IL-18, or LPS in HIV, or between IGF-1 and any inflammatory marker in controls. Relationships of IGF-1 with sCD163 and sCD14 remained significant in HIV after controlling for age, sex, smoking, BMI, visceral fat, statin use, viral load, and antiretroviral therapy. For every one-unit decline in IGF-1 z-score, sCD163 and sCD14 increased by 14% (95% CI, 0.23-29%) and 29% (95% CI, 1.4-63%), respectively.

CONCLUSION

Low IGF-1 was robustly associated with high sCD163 and sCD14 in HIV. Prospective studies are needed to investigate augmentation of IGF-1 as a novel strategy to reduce monocyte/macrophage activation in this population.

Effect of adipocyte-derived IGF-I on adipose tissue mass and glucose metabolism in the Berlin Fat Mouse

Besides liver, IGF-I is expressed in adipose tissue. However, the effects of this local IGF-I on adipose tissue and metabolism are unclear. We generated adipocyte-specific knock-out mice on the background of the Berlin Fat Mouse Inbred (BFMI) line to evaluate the contribution of adipocyte-IGF-I on glucose metabolism and adipose tissue development. BFMI mice are obese, non-diabetic with elevated plasma insulin and IGF-I concentration. The knock-out in adipocytes led to a total white adipose tissue expression of 50-60% due to unaltered Igf-1 expression in stromavascular cells. The lack of IGF-I from adipocytes did not alter plasma IGF-I concentration. BFMI^Chr3-Igf-I-KO^Q-AT mice had reduced adipose tissue mass in most depots. During oral glucose tolerance tests, BFMI^Chr3-Igf-I-KO^Q-AT mice showed an impaired glucose clearance (p = .03). Interestingly, insulin action was enhanced during insulin tolerance tests (p = .05). In conclusion, adipocyte-specific IGF-I ablation in obese BFMI mice results in reduced adipose tissue mass and thereby alters glucose metabolism.

Acetylcholine Modulates the Hormones of the Growth Hormone/Insulinlike Growth Factor-1 Axis During Development in Mice

Pituitary growth hormone (GH) and insulinlike growth factor (IGF)-1 are anabolic hormones whose physiological roles are particularly important during development. The activity of the GH/IGF-1 axis is controlled by complex neuroendocrine systems including two hypothalamic neuropeptides, GH-releasing hormone (GHRH) and somatostatin (SRIF), and a gastrointestinal hormone, ghrelin. The neurotransmitter acetylcholine (ACh) is involved in tuning GH secretion, and its GH-stimulatory action has mainly been shown in adults but is not clearly documented during development. ACh, together with these hormones and their receptors, is expressed before birth, and somatotroph cells are already responsive to GHRH, SRIF, and ghrelin. We thus hypothesized that ACh could contribute to the modulation of the main components of the somatotropic axis during development. In this study, we generated a choline acetyltransferase knockout mouse line and showed that heterozygous mice display a transient deficit in ACh from embryonic day 18.5 to postnatal day 10, and they recover normal ACh levels from the second postnatal week. This developmental ACh deficiency had no major impact on weight gain and cardiorespiratory status of newborn mice. Using this mouse model, we found that endogenous ACh levels determined the concentrations of circulating GH and IGF-1 at embryonic and postnatal stages. In particular, serum GH level was correlated with brain ACh content. ACh also modulated the levels of GHRH and SRIF in the hypothalamus and ghrelin in the stomach, and it affected the levels of these hormones in the circulation. This study identifies ACh as a potential regulator of the somatotropic axis during the developmental period.

Gut Microbiota and IGF-1

Microbiota and their hosts have coevolved for millions of years. Microbiota are not only critical for optimal development of the host under normal physiological growth, but also important to ensure proper host development during nutrient scarcity or disease conditions. A large body of research has begun to detail the mechanism(s) of how microbiota cooperate with the host to maintain optimal health status. One crucial host pathway recently demonstrated to be modulated by microbiota is that of the growth factor insulin like growth factor 1 (IGF-1). Gut microbiota are capable of dynamically modulating circulating IGF-1 in the host, with the majority of data suggesting that microbiota induce host IGF-1 synthesis to influence growth. Microbiota-derived metabolites such as short chain fatty acids are sufficient to induce IGF-1. Whether microbiota induction of IGF-1 is mediated by the difference in growth hormone expression or the host sensitivity to growth hormone is still under investigation. This review summarizes the current data detailing the interaction between gut microbiota, IGF-1 and host development.

Deficiency of liver-derived insulin-like growth factor-I (IGF-I) does not interfere with the skin wound healing rate

Objective

IGF-I is a growth factor, which is expressed in virtually all tissues. The circulating IGF-I is however derived mainly from the liver. IGF-I promotes wound healing and its levels are decreased in wounds with low regenerative potential such as diabetic wounds. However, the contribution of circulating IGF-I to wound healing is unknown.

Here we investigated the role of systemic IGF-I on wound healing rate in mice with deficiency of liver-derived IGF-I (LI-IGF-I-/- mice) during normal (normoglycemic) and impaired wound healing (diabetes).

Methods

LI-IGF-I-/- mice with complete inactivation of the IGF-I gene in the hepatocytes were generated using the Cre/loxP recombination system. This resulted in a 75% reduction of circulating IGF-I. Diabetes was induced with streptozocin in both LI-IGF-I-/- and control mice. Wounds were made on the dorsum of the mice, and the wound healing rate and histology were evaluated. Serum IGF-I and GH were measured by RIA and ELISA respectively. The expression of IGF-I, IGF-II and the IGF-I receptor in the skin were evaluated by qRT-PCR. The local IGF-I protein expression in different cell types of the wounds during wound healing process was analyzed using immunohistochemistry.

Results

The wound healing rate was similar in LI-IGF-I-/- mice to that in controls. Diabetes significantly delayed the wound healing rate in both LI-IGF-I-/- and control mice. However, no significant difference was observed between diabetic animals with normal or reduced hepatic IGF-I production. The gene expression of IGF-I, IGF-II and IGF-I receptor in skin was not different between any group of animals tested. Local IGF-I levels in the wounds were similar between of LI-IGF-I-/- and WT mice although a transient reduction of IGF-I expression in leukocytes in the wounds of LI-IGF-I-/- was observed seven days post wounding.

Conclusion

Deficiency in the liver-derived IGF-I does not affect wound healing in mice, neither in normoglycemic conditions nor in diabetes.

FoxO1 Is Required for Most of the Metabolic and Hormonal Perturbations Produced by Hepatic Insulin Receptor Deletion in Male Mice

Insulin coordinates the complex response to feeding, affecting numerous metabolic and hormonal pathways. Forkhead box protein O1 (FoxO1) is one of several signaling molecules downstream of insulin; FoxO1 drives gluconeogenesis and is suppressed by insulin. To determine the role of FoxO1 in mediating other actions of insulin, we studied mice with hepatic deletion of the insulin receptor, FoxO1, or both. We found that mice with deletion of the insulin receptor alone showed not only hyperglycemia but also a 70% decrease in plasma insulin-like growth factor 1 and delayed growth during the first 2 months of life, a 24-fold increase in the soluble leptin receptor and a 19-fold increase in plasma leptin levels. Deletion of the insulin receptor also produced derangements in fatty acid metabolism, with a decrease in the expression of the lipogenic enzymes, hepatic diglycerides, and plasma triglycerides; in parallel, it increased expression of the fatty acid oxidation enzymes. Mice with deletion of both insulin receptor and FoxO1 showed a much more modest phenotype, with normal or near-normal glucose levels, growth, leptin levels, hepatic diglycerides, and fatty acid oxidation gene expression; however, lipogenic gene expression remained low. Taken together, these data reveal the pervasive role of FoxO1 in mediating the effects of insulin on not only glucose metabolism but also other hormonal signaling pathways and even some aspects of lipid metabolism.

Insulin-like Growth Factor 1 (IGF-1) as a marker of cognitive decline in normal ageing: A review

Insulin-like Growth Factor 1 (IGF-1) and its signaling pathway play a primary role in normal growth and ageing, however serum IGF-1 is known to reduce with advancing age. Recent findings suggest IGF-1 is essential for neurogenesis in the adult brain, and this reduction of IGF-1 with ageing may contribute to age-related cognitive decline. Experimental studies have shown manipulation of the GH/GF-1 axis can slow rates of cognitive decline in animals, making IGF-1 a potential biomarker of cognition, and/or its signaling pathway a possible therapeutic target to prevent or slow age-related cognitive decline. A systematic literature review and qualitative narrative summary of current evidence for IGF-1 as a biomarker of cognitive decline in the ageing brain was undertaken. Results indicate IGF-1 concentrations do not confer additional diagnostic information for those with cognitive decline, and routine clinical measurement of IGF-1 is not currently justified. In cases of established cognitive impairment, it remains unclear whether increasing circulating or brain IGF-1 may reverse or slow down the rate of further decline. Advances in neuroimaging, genetics, neuroscience and the availability of large well characterized biobanks will facilitate research exploring the role of IGF-1 in both normal ageing and age-related cognitive decline.

The Growth Hormone Receptor: Mechanism of Receptor Activation, Cell Signaling, and Physiological Aspects

The growth hormone receptor (GHR), although most well known for regulating growth, has many other important biological functions including regulating metabolism and controlling physiological processes related to the hepatobiliary, cardiovascular, renal, gastrointestinal, and reproductive systems. In addition, growth hormone signaling is an important regulator of aging and plays a significant role in cancer development. Growth hormone activates the Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway, and recent studies have provided a new understanding of the mechanism of JAK2 activation by growth hormone binding to its receptor. JAK2 activation is required for growth hormone-mediated activation of STAT1, STAT3, and STAT5, and the negative regulation of JAK-STAT signaling comprises an important step in the control of this signaling pathway. The GHR also activates the Src family kinase signaling pathway independent of JAK2. This review covers the molecular mechanisms of GHR activation and signal transduction as well as the physiological consequences of growth hormone signaling.

Gestational triphenyl phosphate exposure in C57Bl/6 mice perturbs expression of insulin-like growth factor signaling genes in maternal and fetal liver

Triphenyl phosphate (TPhP) is an organophosphorus flame retardant and plasticizer that has been added to numerous consumer products in recent years. TPhP is not overtly toxic, however recent studies have suggested that it may have metabolic disrupting effects following developmental exposure. The present study aimed to investigate the developmental and potential metabolic effects of TPhP in a murine model. C57Bl/6 dams were exposed on gestational days (GD) 8, 10, 12, and 14 to 0, 5, 25, or 50 mg/kg TPhP via intraperitoneal injection. Dams were euthanized on GD19, maternal organs excised and weighed, fetal measurements taken, and maternal and fetal livers retained for analysis. A significant increase in placenta size of TPhP exposed mice was found. Maternal and fetal liver gene expression of insulin-like growth factor (Igf) 1 and 2, as well as downstream genes involved in Igf signaling were measured. Additionally, Igf1 protein levels were measured in both maternal and fetal liver. A significant decrease in transcript levels of Igf1 and Irs2 was detected in maternal livers, whereas a significant increase in transcript levels of all genes measured was detected in fetal liver. A significant decrease in Igf1 protein levels was detected in maternal liver, however the increase in Igf1 protein levels in fetal livers was not found to be statistically significant. These results support previous findings that TPhP does not cause overt structural developmental toxicity. These data also support the hypothesis that TPhP could disrupt maternal and fetal metabolism, justifying the need for follow-up studies to investigate further.

Reduced Serum IGF-1 Associated With Hepatic Osteodystrophy Is a Main Determinant of Low Cortical but Not Trabecular Bone Mass

Hepatic osteodystrophy is multifactorial in its pathogenesis. Numerous studies have shown that impairments of the hepatic growth hormone/insulin-like growth factor-1 axis (GH/IGF-1) are common in patients with non-alcoholic fatty liver disease, chronic viral hepatitis, liver cirrhosis, and chronic cholestatic liver disease. Moreover, these conditions are also associated with low bone mineral density (BMD) and greater fracture risk, particularly in cortical bone sites. Hence, we addressed whether disruptions in the GH/IGF-1 axis were causally related to the low bone mass in states of chronic liver disease using a mouse model of liver-specific GH-receptor (GHR) gene deletion (Li-GHRKO). These mice exhibit chronic hepatic steatosis, local inflammation, and reduced BMD. We then employed a crossing strategy to restore liver production of IGF-1 via hepatic IGF-1 transgene (HIT). The resultant Li-GHRKO-HIT mouse model allowed us to dissect the roles of liver-derived IGF-1 in the pathogenesis of osteodystrophy during liver disease. We found that hepatic IGF-1 restored cortical bone acquisition, microarchitecture, and mechanical properties during growth in Li-GHRKO-HIT mice, which was maintained during aging. However, trabecular bone volume was not restored in the Li-GHRKO-HIT mice. We found increased bone resorption indices in vivo as well as increased basal reactive oxygen species and increased mitochondrial stress in osteoblast cultures from Li-GHRKO and the Li-GHRKO-HIT compared with control mice. Changes in systemic markers such as inflammatory cytokines, osteoprotegerin, osteopontin, parathyroid hormone, osteocalcin, or carboxy-terminal collagen cross-links could not fully account for the diminished trabecular bone in the Li-GHRKO-HIT mice. Thus, the reduced serum IGF-1 associated with hepatic osteodystrophy is a main determinant of low cortical but not trabecular bone mass. © 2017 American Society for Bone and Mineral Research.

Nutrient Sensing, Signaling and Ageing: The Role of IGF-1 and mTOR in Ageing and Age-Related Disease

Nutrient signaling through insulin/IGF-1 was the first pathway demonstrated to regulate ageing and age-related disease in model organisms. Pharmacological or dietary interventions targeting nutrient signaling pathways have been shown to robustly attenuate ageing in many organisms. Caloric restriction, the most widely studied longevity promoting intervention, works through multiple nutrient signaling pathways, while inhibition of mTOR through treatment with rapamycin reproducibly delays ageing and disease through specific inhibition of the mTOR complexes. Although the benefits of reduced insulin/IGF-1 in lifespan and health are well documented in model organisms, defining the precise role of the IGF-1 in human ageing and age-related disease has proven more difficult. Association studies provide some insight but also reveal paradoxes. Low serum IGF-1 predicts longevity, but IGF-1 decreases with age and IGF-1 therapy benefits some of age-related pathologies. Circulating IGF-1 has been associated both positively and negatively with risk of age-related diseases in humans, and in some cases both activation and inhibition of IGF-1 signaling have provided benefit in animal models of the same diseases. Interventions designed modulate the nutrient sensing signaling pathways positively or negatively are already available for clinical use, highlighting the need for a clear understanding of the role of nutrient signaling in ageing and age-related disease. This chapter examines data from model organisms and human genetic association studies, with a special emphasis on IGF-1 and mTOR, and discusses potential models for resolving the paradoxes surrounding IGF-1 data.

IGF-Binding Proteins: Why Do They Exist and Why Are There So Many?

Insulin-like growth factors (IGFs) are key growth-promoting peptides that act as both endocrine hormones and autocrine/paracrine growth factors. In the bloodstream and in local tissues, most IGF molecules are bound by one of the members of the IGF-binding protein (IGFBP) family, of which six distinct types exist. These proteins bind to IGF with an equal or greater affinity than the IGF1 receptor and are thus in a key position to regulate IGF signaling globally and locally. Binding to an IGFBP increases the half-life of IGF in the circulation and blocks its potential binding to the insulin receptor. In addition to these classical roles, IGFBPs have been shown to modulate IGF signaling locally under various conditions. Although members of the IGFBP family share significant sequence homology, they each have unique structural features and play distinct roles. These IGFBP genes also have different modes of regulation and distinct expression patterns. Some IGFBPs have been found to bind to their own receptors or to translocate into the interior compartments of cells where they may execute IGF-independent actions. In spite of this functional and regulatory diversity, it has been puzzling that loss-of-function studies have yielded relatively little information about the physiological functions of IGFBPs. In this review, we suggest that evolution has tended to retain an array of IGFBPs in order to facilitate fine-tuning of IGF signaling. We explore the emerging explanation that many IGFBP functions have evolved to allow the targeted adjustment of IGF signaling under stressful or irregular conditions, which would likely not be revealed in a standard laboratory setting.

Bone-specific alkaline phosphatase - a potential biomarker for skeletal growth assessment

OBJECTIVE

The present study was aimed to assess levels of serum Bone-specific alkaline phosphatase (BALP) and serum Insulin-like growth factor-1 (IGF-1) and comparing with cervical vertebral maturation index (CVMI) stages.

DESIGN

Cross-sectional study.

SETTING

Maulana Azad Institute of Dental Sciences, New Delhi, India.

PARTICIPANTS

150 subjects (75 males and 75 females) in the age group of 8-20 years.

METHODS

Subjects were divided into six CVMI stages. Enzyme-linked immunosorbant assay was performed for the estimation of serum BALP and serum IGF-1 levels. Mann-Whitney U test was performed to compare mean ranks of serum BALP and serum IGF-1 with different CVMI stages. Spearman correlation between serum BALP and serum IGF-1 was done across 6 CVMI stages.

RESULTS

Peak serum IGF-1 levels were found at CVMI stages 4 and 3 for males and females respectively. Peak levels for serum BALP were found at stage 3 for both genders with significant differences from other stages. A statistically significant correlation was seen between serum IGF-1 and serum BALP from CVMI stages 1 to 3 and 4 to 6 (p < .01).

CONCLUSIONS

BALP showed promising results and can be employed as a potential biomarker for the estimation of growth status.

The interaction of IGF-1/IGF-1R and hydrogen sulfide on the proliferation of mouse primary vascular smooth muscle cells

Hydrogen sulfide (H₂S) is mostly produced by cystathionine-gamma-lyase (CSE) in vascular system and it inhibits the proliferation of vascular smooth muscle cells (SMCs). Insulin-like growth factor-1 (IGF-1), via its receptor (IGF-1R), exerts multiple physiological and pathophysiological effects on the vasculature, including stimulating SMC proliferation and migration, and inhibiting SMC apoptosis. Since H₂S and IGF-1/IGF-1R have opposite effects on SMC proliferation, it becomes imperative to better understand the interaction of these two signaling mechanisms on SMC proliferation. SMCs isolated from small mesenteric arteries of CSE knockout (KO) and wild-type (WT) mice were used in the present study. The effects of IGF-1 and H₂S on SMC proliferation were evaluated with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and bromodeoxyuridine (BrdU) assays. Protein expression was determined by western blot, and H₂S-induced protein S-sulfhydration was assessed with a modified biotin switch assay. We found that IGF-1 dose-dependently increased the proliferation of both WT-SMCs and KO-SMCs, and this effect was more significant in KO-SMCs. Supplement of sodium hydrosulfide (NaHS) inhibited IGF-1-induced cell proliferation, while this effect was abolished by blocking IGF-1/IGF-1R signaling with picropodophyllin (PPP) or knocking out of the expression of IGF-1R. H₂S significantly down-regulates the expression of IGF-1R, stimulates IGF-1R S-sulfhydration, and attenuates the binding of IGF-1 with IGF-1R. This study provides novel insight on the involvement of IGF-1/IGF-1R in H₂S-inhibited SMC proliferation and suggests H₂S-based innovative treatment strategies for proliferative cardiovascular diseases such as atherosclerosis.

Suckling induced insulin-like growth factor-1 (IGF-1) release in mother rats

OBJECTIVE

Lactation involves significant neuroendocrine changes. The elevated prolactin (PRL) release from the pituitary, induced markedly by suckling, is the most relevant example. Suckling also causes a significant and rapid elevation in growth hormone (GH) levels. GH is necessary for milk synthesis as milk yield is stopped completely in the absence of PRL and GH, while the absence of PRL alone causes only a 50% reduction. Insulin-like growth factor-1 (IGF-1) plays an important role in the GH axis. GH exerts its effects through IGF-1 in the periphery, for example in the mammary gland. In addition, IGF-1 is responsible for the long-loop feedback control of GH secretion.

DESIGN

IGF-1 secretion has not been established yet in mothers. Therefore, in the present study, we investigated the effect of suckling on serum IGF-1 level in rat mothers and correlated it with serum PRL levels. We examined a potential mechanism of the regulation of IGF-1 level during suckling by administering IGF-1 into the lateral ventricle of rat mothers continuously for 12days, or acutely, right before the start of suckling.

RESULTS

We described that suckling affected IGF-1 release based on one-way repeated measures ANOVA (F=10.8 and p<0.001) and caused a marked increase of IGF-1 level 30min after the start of suckling (p<0.001). We demonstrated a significant (p<0.05; the correlation coefficient was 0.29) correlation to PRL level during suckling which supports that PRL could induce IGF-1 release. The prolonged central IGF-1 administration diminished the suckling-induced IGF-1 surge (F=9.19 and p<0.001) while the acute treatment did not have any effect compared to artificial cerebrospinal fluid injection, analysed with two-way repeated measures ANOVA.

CONCLUSIONS

In conclusion, suckling induces IGF-1 release either by elevating PRL or GH. Long-loop feedback via IGF-1 in the GH axis can diminish this action.

Human IGF-I propeptide A promotes articular chondrocyte biosynthesis and employs glycosylation-dependent heparin binding

BACKGROUND

Insulin-like growth factor I (IGF-I) is a key regulator of chondrogenesis, but its therapeutic application to articular cartilage damage is limited by rapid elimination from the repair site. The human IGF-I gene gives rise to three IGF-I propeptides (proIGF-IA, proIGF-IB and proIGF-IC) that are cleaved to create mature IGF-I. In this study, we elucidate the processing of IGF-I precursors by articular chondrocytes, and test the hypotheses that proIGF-I isoforms bind to heparin and regulate articular chondrocyte biosynthesis.

METHODS

Human IGF-I propeptides and mutants were overexpressed in bovine articular chondrocytes. IGF-I products were characterized by ELISA, western blot and FPLC using a heparin column. The biosynthetic activity of IGF-I products on articular chondrocytes was assayed for DNA and glycosaminoglycan that the cells produced.

RESULTS

Secreted IGF-I propeptides stimulated articular chondrocyte biosynthetic activity to the same degree as mature IGF-I. Of the three IGF-I propeptides, only one, proIGF-IA, strongly bound to heparin. Interestingly, heparin binding of proIGF-IA depended on N-glycosylation at Asn92 in the EA peptide. To our knowledge, this is the first demonstration that N-glycosylation determines the binding of a heparin-binding protein to heparin.

CONCLUSION

The biosynthetic and heparin binding abilities of proIGF-IA, coupled with its generation of IGF-I, suggest that proIGF-IA may have therapeutic value for articular cartilage repair.

GENERAL SIGNIFICANCE

These data identify human pro-insulin-like growth factor IA as a bifunctional protein. Its combined ability to bind heparin and augment chondrocyte biosynthesis makes it a promising therapeutic agent for cartilage damage due to trauma and osteoarthritis.

Nuclear Receptor PPARα Agonist Wy-14,643 Ameliorates Hepatic Cell Death in Hepatic IKKβ-Deficient Mice

Inhibitor of nuclear factor kappa-B kinase beta (IKKβ) plays a critical role in cell proliferation and inflammation in various cells by activating NF-κB signaling. However, the interrelationship between peroxisome proliferator-activated receptor α (PPARα) and IKKβ in cell proliferation is not clear. In this study, we investigated the possible role of PPARα in the hepatic cell death in the absence of IKKβ gene using liver-specific Ikkb-null (Ikkb^F/F-AlbCre) mice. To examine the function of PPARα activation in hepatic cell death, wild-type (Ikkb^F/F) and Ikkb^F/F-AlbCre mice were treated with PPARα agonist Wy-14,643 (0.1% w/w chow diet) for two weeks. As a result of Wy-14,643 treatment, apoptotic markers including caspase-3 cleavage, poly (ADP-ribose) polymerase (PARP) cleavage and TUNEL-positive staining were significantly decreased in the Ikkb^F/F-AlbCre mice. Surprisingly, Wy-14,643 increased the phosphorylation of p65 and STAT3 in both Ikkb and Ikkb^F/F-AlbCre mice. Furthermore, BrdU-positive cells were significantly increased in both groups after treatment with Wy-14,643. Our results suggested that IKKβ-derived hepatic apoptosis could be altered by PPARα activation in conjunction with activation of NF-κB and STAT3 signaling.

IGF1 stimulates greater muscle hypertrophy in the absence of myostatin in male mice

Insulin-like growth factors (IGFs) and myostatin have opposing roles in regulating the growth and size of skeletal muscle, with IGF1 stimulating, and myostatin inhibiting, growth. However, it remains unclear whether these proteins have mutually dependent, or independent, roles. To clarify this issue, we crossed myostatin null (Mstn^-/-) mice with mice overexpressing Igf1 in skeletal muscle (Igf1⁺) to generate six genotypes of male mice; wild type (Mstn^+/+ ), Mstn^+/-, Mstn^-/-, Mstn^+/+:Igf1⁺, Mstn^+/-:Igf1⁺ and Mstn^-/-:Igf1⁺ Overexpression of Igf1 increased the mass of mixed fibre type muscles (e.g. Quadriceps femoris) by 19% over Mstn^+/+ , 33% over Mstn^+/- and 49% over Mstn^-/- (P < 0.001). By contrast, the mass of the gonadal fat pad was correspondingly reduced with the removal of Mstn and addition of Igf1 Myostatin regulated the number, while IGF1 regulated the size of myofibres, and the deletion of Mstn and Igf1⁺ independently increased the proportion of fast type IIB myosin heavy chain isoforms in T. anterior (up to 10% each, P < 0.001). The abundance of AKT and rpS6 was increased in muscles of Mstn^-/-mice, while phosphorylation of AKT^S473 was increased in Igf1⁺mice (Mstn^+/+:Igf1⁺, Mstn^+/-:Igf1⁺ and Mstn^-/-:Igf1⁺). Our results demonstrate that a greater than additive effect is observed on the growth of skeletal muscle and in the reduction of body fat when myostatin is absent and IGF1 is in excess. Finally, we show that myostatin and IGF1 regulate skeletal muscle size, myofibre type and gonadal fat through distinct mechanisms that involve increasing the total abundance and phosphorylation status of AKT and rpS6.

Altered paracrine signaling from the injured knee joint impairs postnatal long bone growth

Regulation of organ growth is a poorly understood process. In the long bones, the growth plates (GPs) drive elongation by generating a scaffold progressively replaced by bone. Although studies have focused on intrinsic GP regulation, classic and recent experiments suggest that local signals also modulate GP function. We devised a genetic mouse model to study extrinsic long bone growth modulation, in which injury is specifically induced in the left hindlimb, such that the right hindlimb serves as an internal control. Remarkably, when only mesenchyme cells surrounding postnatal GPs were killed, left bone growth was nevertheless reduced. GP signaling was impaired by altered paracrine signals from the knee joint, including activation of the injury response and, in neonates, dampened IGF1 production. Importantly, only the combined prevention of both responses rescued neonatal growth. Thus, we identified signals from the knee joint that modulate bone growth and could underlie establishment of body proportions.

DOI:http://dx.doi.org/10.7554/eLife.27210.001

As bones grow, their size is carefully controlled and coordinated with the growth of the other organs in the body. The mechanisms that control organ size also help the body to recover from injury, and play a key role in controlling body size and proportions. Over the course of evolution, these mechanisms have likely changed to produce the distinct body sizes and proportions seen in humans and other animals.

Despite their importance, it is not well understood how signals from both inside and outside an organ work together to regulate its size. In growth disorders this signaling goes wrong, which can lead to a person having unusual proportions such as a very short stature or having one leg shorter than the other. Currently, most growth disorders that affect leg proportions are treated with painful surgical procedures. Researchers would like to know how bone growth is affected by signals from the surrounding tissues because this could help them to develop new non-invasive treatments for these conditions.

Long bones, for example those in the leg, grow from structures near their ends called growth plates. Roselló-Díez et al. have now engineered mice in which an injury shortly after birth caused cells in the knee in the rear left leg to die off. At the same time, the rear right leg of the mice developed as normal, allowing the growth of the two legs to be compared. Roselló-Díez et al. found that the left leg of these mice grew more slowly than the right leg, even though none of the cells in the growth plate of the left leg bone had been damaged. Further investigation revealed that this was because the injury caused an imbalance between the growth-promoting and growth-restricting signals that are produced by the fat pad and articular cartilage in the knee joint. Restoring the lost balance allowed the left leg bone to grow to a more normal length.

In the future, boosting bone growth signals might provide a way to treat conditions like dwarfism or leg-length discrepancies. Understanding how different tissues influence body proportions could also help researchers to investigate how different animals evolved different body proportions.

DOI:http://dx.doi.org/10.7554/eLife.27210.002

Downregulated Translation Initiation Signaling Predisposes Low-Birth-Weight Neonatal Pigs to Slower Rates of Muscle Protein Synthesis

Low-birth-weight (LBWT) neonates experience restricted muscle growth in their perinatal life. Our aim was to investigate the mechanisms that contribute to slower skeletal muscle growth of LBWT neonatal pigs. Twenty-four 1-day old male LBWT (816 ± 55 g) and normal-birth-weight (NBWT; 1,642 ± 55 g) littermates (n = 12) were euthanized to collect blood and longissimus dorsi (LD) muscle subsamples. Plasma glucose, insulin, and insulin-like growth factor-I (IGF-I) were lower in LBWT compared with NBWT pigs. Muscle IGF-I mRNA expression were lower in LBWT than NBWT pigs. However, IGF-I receptor mRNA and protein abundance was greater in LD of LBWT pigs. Abundance of myostatin and its receptors, and abundance and phosphorylation of smad3 were lower in LBWT LD by comparison with NBWT LD. Abundance of eukaryotic initiation factor (eIF) 4E binding protein 1 and mitogen-activated protein kinase-interacting kinases was lower in muscle of LBWT pigs compared with NBWT siblings, while eIF4E abundance and phosphorylation did not differ between the two groups. Furthermore, phosphorylation of ribosomal protein S6 kinase 1 (S6K1) was less in LBWT muscle, possibly due to lower eIF3e abundance. In addition, abundance and phosphorylation of eIF4G was reduced in LBWT pigs by comparison with NBWT littermates, suggesting translation initiation complex formation is compromised in muscle of LBWT pigs. In conclusion, diminished S6K1 activation and translation initiation signaling are likely the major contributors to impaired muscle growth in LBWT neonatal pigs. The upregulated IGF-I R expression and downregulated myostatin signaling seem to be compensatory responses for the reduction in protein synthesis signaling.

The Role of Growth Hormone and Insulin-Like Growth Factor-I in the Liver

Adult growth hormone deficiency (GHD) is characterized by metabolic abnormalities associated with visceral obesity, impaired quality of life, and increased mortality. Patients with adult GHD show increased prevalence of non-alcoholic fatty liver disease (NAFLD)/non-alcoholic steatohepatitis (NASH), and growth hormone (GH) replacement therapy has been shown to improve these conditions. It has also been demonstrated that a decrease in the GH insulin-like growth factor-I (IGF-I) axis is closely associated with the progression of general NAFLD, suggesting a physiological role of these hormones for the maintenance of the liver. NASH histologically demonstrates inflammation, necrosis, and fibrosis, in addition to steatosis (and is a serious disease because it can progress to liver cirrhosis and hepatocellular carcinoma in a subset of cases). While fibrosis determines the prognosis of the patient, efficacious treatment for fibrosis is crucial; however, it has not yet been established. Recent studies have clarified the essential roles of GH and IGF-I in the liver. GH profoundly reduces visceral fat, which plays an important role in the development of NAFLD. Furthermore, GH directly reduces lipogenesis in the hepatocytes. IGF-I induces cellular senescence and inactivates hepatic stellate cells, therefore ameliorating fibrosis. IGF-I treatment has been shown to improve animal models of NASH and cirrhosis, suggesting potential clinical applications of IGF-I in these conditions. In this review, I will focus on the important roles of GH and IGF-I in the liver, their underlying mechanisms, and their potential therapeutic applications.

Astragalus Extract Mixture HT042 Increases Longitudinal Bone Growth Rate by Upregulating Circulatory IGF-1 in Rats

Astragalus extract mixture HT042 is a standardized ingredient of health functional food approved by Korean FDA with a claim of “height growth of children.” HT042 stimulates bone growth rate and increases local IGF-1 expression in growth plate of rats which can be considered as direct stimulation of GH and its paracrine/autocrine actions. However, it remains unclear whether HT042 stimulates circulatory IGF-1 which also plays a major role to stimulate bone growth. To determine the effects on circulatory IGF-1, IGF-1 and IGFBP-3 expressions and phosphorylation of JAK2/STAT5 were evaluated in the liver after 10 days of HT042 administration. HT042 upregulated liver IGF-1 and IGFBP-3 mRNA expression, IGF-1 protein expression, and phosphorylation of JAK2/STAT5. HT042 also increased bone growth rate and proliferative zonal height in growth plate. In conclusion, HT042 stimulates bone growth rate via increment of proliferative rate by upregulation of liver IGF-1 and IGFBP-3 mRNA followed by IGF-1 protein expression through phosphorylation of JAK2/STAT5, which can be regarded as normal functioning of GH-dependent endocrine pathway.

The IGF-1/Akt/S6 pathway and expressions of glycolytic myosin heavy chain isoforms are upregulated in chicken skeletal muscle during the first week after hatching

Skeletal muscle mass is an important trait in the animal industry. We previously reported an age-dependent downregulation of the insulin-like growth factor 1 (IGF-1)/Akt/S6 pathway, major protein synthesis pathway, in chicken breast muscle after 1 week of age, despite a continuous increase of breast muscle weight. Myosin heavy chain (HC), a major protein in muscle fiber, has several isoforms depending on chicken skeletal muscle types. HC I (fast-twitch glycolytic type) is known to be expressed in adult chicken breast muscle. However, little is known about the changes in the expression levels of protein synthesis-related factors and HC isoforms in perihatching chicken muscle. In the present study, protein synthesis-related factors, such as IGF-1 messenger RNA (mRNA) levels, phosphorylation of Akt, and phosphorylated S6 content, increased in an age-dependent manner after post-hatch day (D) 0. The mRNA levels of HC I, III and V (fast-twitch glycolytic type) dramatically increased after D0. The increase ratio of breast muscle weight was approximately 1100% from D0 to D7. To our knowledge, these findings provide the first evidence that upregulation of protein synthesis pathway and transcription of fast twitch glycolytic HC isoforms play critical roles in the increase of chicken breast muscle weight during the first week after hatching.

Hypothalamic-Pituitary Axis Regulates Hydrogen Sulfide Production

Decreased growth hormone (GH) and thyroid hormone (TH) signaling are associated with longevity and metabolic fitness. The mechanisms underlying these benefits are poorly understood, but may overlap with those of dietary restriction (DR), which imparts similar benefits. Recently we discovered that hydrogen sulfide (H₂S) is increased upon DR and plays an essential role in mediating DR benefits across evolutionary boundaries. Here we found increased hepatic H₂S production in long-lived mouse strains of reduced GH and/or TH action, and in a cell-autonomous manner upon serum withdrawal in vitro. Negative regulation of hepatic H₂S production by GH and TH was additive and occurred via distinct mechanisms, namely direct transcriptional repression of the H₂S-producing enzyme cystathionine γ-lyase (CGL) by TH, and substrate-level control of H₂S production by GH. Mice lacking CGL failed to downregulate systemic T₄ metabolism and circulating IGF-1, revealing an essential role for H₂S in the regulation of key longevity-associated hormones.

Conditional loss of hepatocellular Hedgehog signaling in female mice leads to the persistence of hepatic steroidogenesis, androgenization and infertility

The Hedgehog signaling pathway is known to be involved in embryogenesis, tissue remodeling, and carcinogenesis. Because of its involvement in carcinogenesis, it seems an interesting target for cancer therapy. Indeed, Sonidegib, an approved inhibitor of the Hedgehog receptor Smoothened (Smo), is highly active against diverse carcinomas, but its use is also reported to be associated with several systemic side effects. Our former work in adult mice demonstrated hepatic Hedgehog signaling to play a key role in the insulin-like growth factor axis and lipid metabolism. The current work using mice with an embryonic and hepatocyte-specific Smo deletion describes an adverse impact of the hepatic Hedgehog pathway on female fertility. In female SAC-KO mice, we detected androgenization characterized by a 3.3-fold increase in testosterone at 12 weeks of age based on an impressive induction of steroidogenic gene expression in hepatocytes, but not in the classic steroidogenic organs (ovary and adrenal gland). Along with the elevated level of testosterone, the female SAC-KO mice showed infertility characterized by juvenile reproductive organs and acyclicity. The endocrine and reproductive alterations resembled polycystic ovarian syndrome and could be confirmed in a second mouse model with conditional deletion of Smo at 8 weeks of age after an extended period of 8 months. We conclude that the down-regulation of hepatic Hedgehog signaling leads to an impaired hormonal balance by the induction of steroidogenesis in the liver. These effects of Hedgehog signaling inhibition should be considered when using Hedgehog inhibitors as anti-cancer drugs.

Extensive phenotypic characterization of a new transgenic mouse reveals pleiotropic perturbations in physiology due to mesenchymal hGH minigene expression

The human growth hormone (hGH) minigene used for transgene stabilization in mice has been recently identified to be locally expressed in the tissues where transgenes are active and associated with phenotypic alterations. Here we extend these findings by analyzing the effect of the hGH minigene in TgC6hp55 transgenic mice which express the human TNFR1 under the control of the mesenchymal cell-specific CollagenVI promoter. These mice displayed a fully penetrant phenotype characterized by growth enhancement accompanied by perturbations in metabolic, skeletal, histological and other physiological parameters. Notably, this phenotype was independent of TNF-TNFR1 signaling since the genetic ablation of either Tnf or Tradd did not rescue the phenotype. Further analyses showed that the hGH minigene was expressed in several tissues, also leading to increased hGH protein levels in the serum. Pharmacological blockade of GH signaling prevented the development of the phenotype. Our results indicate that the unplanned expression of the hGH minigene in CollagenVI expressing mesenchymal cells can lead through local and/or systemic mechanisms to enhanced somatic growth followed by a plethora of primary and/or secondary effects such as hyperphagia, hypermetabolism, disturbed glucose homeostasis, altered hematological parameters, increased bone formation and lipid accumulation in metabolically critical tissues.

IGF-1 has sexually dimorphic, pleiotropic, and time-dependent effects on healthspan, pathology, and lifespan

Reduced circulating levels of IGF-1 have been proposed as a conserved anti-aging mechanism that contributes to increased lifespan in diverse experimental models. However, IGF-1 has also been shown to be essential for normal development and the maintenance of tissue function late into the lifespan. These disparate findings suggest that IGF-1 may be a pleiotropic modulator of health and aging, as reductions in IGF-1 may be beneficial for one aspect of aging, but detrimental for another. We postulated that the effects of IGF-1 on tissue health and function in advanced age are dependent on the tissue, the sex of the animal, and the age at which IGF-1 is manipulated. In this study, we examined how alterations in IGF-1 levels at multiple stages of development and aging influence overall lifespan, healthspan, and pathology. Specifically, we investigated the effects of perinatal, post-pubertal, and late-adult onset IGF-1 deficiency using genetic and viral approaches in both male and female igf ^f/f C57Bl/6 mice. Our results support the concept that IGF-1 levels early during lifespan establish the conditions necessary for subsequent healthspan and pathological changes that contribute to aging. Nevertheless, these changes are specific for each sex and tissue. Importantly, late-life IGF-1 deficiency (a time point relevant for human studies) reduces cancer risk but does not increase lifespan. Overall, our results indicate that the levels of IGF-1 during development influence late-life pathology, suggesting that IGF-1 is a developmental driver of healthspan, pathology, and lifespan.

Growth deficits in cystic fibrosis mice begin in utero prior to IGF-1 reduction

Growth deficits are common in cystic fibrosis (CF), but their cause is complex, with contributions from exocrine pancreatic insufficiency, pulmonary complications, gastrointestinal obstructions, and endocrine abnormalities. The CF mouse model displays similar growth impairment despite exocrine pancreatic function and in the absence of chronic pulmonary infection. The high incidence of intestinal obstruction in the CF mouse has been suggested to significantly contribute to the observed growth deficits. Previous studies by our group have shown that restoration of the cystic fibrosis transmembrane conductance regulator (CFTR) in the intestinal epithelium prevents intestinal obstruction but does not improve growth. In this study, we further investigate growth deficits in CF and gut-corrected CF mice by assessing insulin-like growth factor 1 (IGF-1). IGF-1 levels were significantly decreased in CF and gut-corrected CF adult mice compared to wildtype littermates and were highly correlated with weight. Interestingly, perinatal IGF-1 levels were not significantly different between CF and wildtype littermates, even though growth deficits in CF mice could be detected late in gestation. Since CFTR has been suggested to play a role in water and nutrient exchange in the placenta through its interaction with aquaporins, we analyzed placental aquaporin expression in late-gestation CF and control littermates. While significant differences were observed in Aquaporin 9 expression in CF placentas in late gestation, there was no evidence of placental fluid exchange differences between CF and control littermates. The results from this study indicate that decreased IGF-1 levels are highly correlated with growth in CF mice, independent of CF intestinal obstruction. However, the perinatal growth deficits that are observed in CF mice are not due to decreased IGF-1 levels or differences in placenta-mediated fluid exchange. Further investigation is necessary to understand the etiology of early growth deficits in CF, as growth has been shown to be a significant factor in disease outcomes.

First-in-man study with a novel PEGylated recombinant human insulin-like growth factor-I

OBJECTIVE

This study is a first time assessment of safety and tolerability, pharmacokinetics, and pharmacodynamics of RO5046013 in human, in comparison with unmodified rhIGF-I.

DESIGN

The study was conducted as a single-center, randomized, double-blinded, placebo-controlled, single ascending dose, parallel group study in a clinical research unit in France. A total of 62 healthy volunteers participated in this clinical trial. RO5046013 was given as single subcutaneous injection, or as intravenous infusion over 48h, at ascending dose levels. The active comparator rhIGF-I was administered at 50μg/kg subcutaneously twice daily for 4days. Safety and tolerability, pharmacokinetics, and pharmacodynamics of RO5046013 were evaluated.

RESULTS

PEGylation resulted in long exposure to RO5046013 with a half-life of 140-200h. Exposure to RO5046013 increased approximately dose proportionally. RO5046013 was safe and well tolerated at all doses, injection site erythema after SC administration was the most frequent observed AE. No hypoglycemia occurred. Growth hormone (GH) secretion was almost completely suppressed with rhIGF-I administration, whereas RO5046013 caused only a modest decrease in GH at the highest dose given IV.

CONCLUSIONS

PEGylation of IGF-I strongly enhances half-life, reduces the negative GH feedback and hypoglycemia potential, and therefore offers a valuable alternative to rhIGF-I in treatment of relevant diseases.

Hepatocyte-specific PPARA expression exclusively promotes agonist-induced cell proliferation without influence from nonparenchymal cells

Peroxisome proliferator-activated receptor-α (PPARA) is a nuclear transcription factor and key mediator of systemic lipid metabolism. Prolonged activation in rodents causes hepatocyte proliferation and hepatocellular carcinoma. Little is known about the contribution of nonparenchymal cells (NPCs) to PPARA-mediated cell proliferation. NPC contribution to PPARA agonist-induced hepatomegaly was assessed in hepatocyte (Ppara△Hep)- and macrophage (Ppara△Mac)-specific Ppara null mice. Mice were treated with the agonist Wy-14643 for 14 days, and response of conditional null mice was compared with conventional knockout mice (Ppara-/- ). Wy-14643 treatment caused weight loss and severe hepatomegaly in wild-type and Ppara△Mac mice, and histological analysis revealed characteristic hepatocyte swelling; Ppara△Hep and Ppara-/- mice were protected from these effects. Ppara△Mac serum chemistries, as well as aspartate aminotransferase and alanine aminotransferase levels, matched wild-type mice. Agonist-treated Ppara△Hep mice had elevated serum cholesterol, phospholipids, and triglycerides when compared with Ppara-/- mice, indicating a possible role for extrahepatic PPARA in regulating circulating lipid levels. BrdU labeling confirmed increased cell proliferation only in wild-type and Ppara△Mac mice. Macrophage PPARA disruption did not impact agonist-induced upregulation of lipid metabolism, cell proliferation, or DNA damage and repair-related gene expression, whereas gene expression was repressed in Ppara△Hep mice. Interestingly, downregulation of inflammatory cytokines IL-15 and IL-18 was dependent on macrophage PPARA. Cell type-specific regulation of target genes was confirmed in primary hepatocytes and Kupffer cells. These studies conclusively show that cell proliferation is mediated exclusively by PPARA activation in hepatocytes and that Kupffer cell PPARA has an important role in mediating the anti-inflammatory effects of PPARA agonists.

Serum sclerostin decreases following 12months of resistance- or jump-training in men with low bone mass

PURPOSE

We previously reported that 12months of resistance training (RT, 2×/wk, N=19) or jump training (JUMP, 3×/wk, N=19) increased whole body and lumbar spine BMD and increased serum bone formation markers relative to resorption in physically active (≥4h/wk) men (mean age: 44±2y; median: 44y) with osteopenia of the hip or spine. The purpose of this secondary analysis was to examine the effects of the RT or JUMP intervention on potential endocrine mediators of the exercise effects on bone, specifically IGF-I, PTH and sclerostin.

METHODS

Fasting blood samples were collected after a 24-h period of no exercise at baseline and after 12months of RT or JUMP. IGF-I, PTH and sclerostin were measured in serum by ELISA. The effects of RT or JUMP on IGF-I, PTH and sclerostin were evaluated using 2×2 repeated measures ANOVA (time, group). This study was conducted in accordance with the Declaration of Helsinki and was approved by the University of Missouri IRB.

RESULTS

Sclerostin concentrations in serum significantly decreased and IGF-I significantly increased after 12months of RT or JUMP; while PTH remained unchanged.

CONCLUSION

The beneficial effects of long-term, progressive-intensity RT or JUMP on BMD in moderately active men with low bone mass are associated with decreased sclerostin and increased IGF-I.

Sevoflurane downregulates IGF‑1 via microRNA‑98

Insulin-like growth factor (IGF)-1 functions as a neuroprotective hormone and may protect against cognitive impairment, which may occur as a result of sevoflurane exposure. The aim of the present study was to assess the effect of sevoflurane on the production of IGF‑1 and investigate the molecular mechanisms underlying this regulation. The BRL rat hepatocyte cell line and adult mice were exposed to 1 or 2 minimal alveolar concentrations sevoflurane for 4 or 8 h. IGF‑1 and microRNA‑98 levels were quantified using an enzyme‑linked immunosorbent assay, western blotting and reverse transcription‑quantitative polymerase chain reaction analyses. The importance of microRNA‑98 in the regulation of IGF‑1 by sevoflurane was investigated using a microRNA‑98 inhibitor. Sevoflurane treatment reduced IGF‑1 levels and simultaneously upregulated microRNA‑98 expression levelsin rat hepatocytes and adult mice. Inhibition of microRNA‑98 attenuated this effect. Therefore, sevoflurane may reduce the synthesis of IGF‑1 by upregulating microRNA‑98 expression.

The Roles of Insulin-Like Growth Factors in Mesenchymal Stem Cell Niche

Many tissues contain adult mesenchymal stem cells (MSCs), which may be used in tissue regeneration therapies. However, the MSC availability in most tissues is limited which demands expansion in vitro following isolation. Like many developing cells, the state of MSCs is affected by the surrounding microenvironment, and mimicking this natural microenvironment that supports multipotent or differentiated state in vivo is essential to understand for the successful use of MSC in regenerative therapies. Many researchers are, therefore, optimizing cell culture conditions in vitro by altering growth factors, extracellular matrices, chemicals, oxygen tension, and surrounding pH to enhance stem cells self-renewal or differentiation. Insulin-like growth factors (IGFs) system has been demonstrated to play an important role in stem cell biology to either promote proliferation and self-renewal or enhance differentiation onset and outcome, depending on the cell culture conditions. In this review, we will describe the importance of IGFs, IGF-1 and IGF-2, in development and in the MSC niche and how they affect the pluripotency or differentiation towards multiple lineages of the three germ layers.

Cryptochromes regulate IGF-1 production and signaling through control of JAK2-dependent STAT5B phosphorylation

The circadian clock regulates IGF-1 production and signaling through proteins called cryptochromes, which regulate the activity of transcriptional factor STAT5B and control mouse body and organ size.

Insulin-like growth factor (IGF) signaling plays an important role in cell growth and proliferation and is implicated in regulation of cancer, metabolism, and aging. Here we report that IGF-1 level in blood and IGF-1 signaling demonstrates circadian rhythms. Circadian control occurs through cryptochromes (CRYs)—transcriptional repressors and components of the circadian clock. IGF-1 rhythms are disrupted in Cry-deficient mice, and IGF-1 level is reduced by 80% in these mice, which leads to reduced IGF signaling. In agreement, Cry-deficient mice have reduced body (∼30% reduction) and organ size. Down-regulation of IGF-1 upon Cry deficiency correlates with reduced Igf-1 mRNA expression in the liver and skeletal muscles. Igf-1 transcription is regulated through growth hormone–induced, JAK2 kinase–mediated phosphorylation of transcriptional factor STAT5B. The phosphorylation of STAT5B on the JAK2-dependent Y699 site is significantly reduced in the liver and skeletal muscles of Cry-deficient mice. At the same time, phosphorylation of JAK2 kinase was not reduced upon Cry deficiency, which places CRY activity downstream from JAK2. Thus CRYs link the circadian clock and JAK-STAT signaling through control of STAT5B phosphorylation, which provides the mechanism for circadian rhythms in IGF signaling in vivo.

TGF-β1/Smad3 Pathway Targets PP2A-AMPK-FoxO1 Signaling to Regulate Hepatic Gluconeogenesis

Maintenance of glucose homeostasis is essential for normal physiology. Deviation from normal glucose levels, in either direction, increases susceptibility to serious medical complications such as hypoglycemia and diabetes. Maintenance of glucose homeostasis is achieved via functional interactions among various organs: liver, skeletal muscle, adipose tissue, brain, and the endocrine pancreas. The liver is the primary site of endogenous glucose production, especially during states of prolonged fasting. However, enhanced gluconeogenesis is also a signature feature of type 2 diabetes (T2D). Thus, elucidating the signaling pathways that regulate hepatic gluconeogenesis would allow better insight into the process of normal endogenous glucose production as well as how this process is impaired in T2D. Here we demonstrate that the TGF-β1/Smad3 signaling pathway promotes hepatic gluconeogenesis, both upon prolonged fasting and during T2D. In contrast, genetic and pharmacological inhibition of TGF-β1/Smad3 signals suppressed endogenous glucose production. TGF-β1 and Smad3 signals achieved this effect via the targeting of key regulators of hepatic gluconeogenesis, protein phosphatase 2A (PP2A), AMP-activated protein kinase (AMPK), and FoxO1 proteins. Specifically, TGF-β1 signaling suppressed the LKB1-AMPK axis, thereby facilitating the nuclear translocation of FoxO1 and activation of key gluconeogenic genes, glucose-6-phosphatase and phosphoenolpyruvate carboxykinase. These findings underscore an important role of TGF-β1/Smad3 signaling in hepatic gluconeogenesis, both in normal physiology and in the pathophysiology of metabolic diseases such as diabetes, and are thus of significant medical relevance.

Growth Hormone Control of Hepatic Lipid Metabolism

In humans, low levels of growth hormone (GH) and its mediator, IGF-1, associate with hepatic lipid accumulation. In mice, congenital liver-specific ablation of the GH receptor (GHR) results in reductions in circulating IGF-1 and hepatic steatosis, associated with systemic insulin resistance. Due to the intricate relationship between GH and IGF-1, the relative contribution of each hormone to the development of hepatic steatosis is unclear. Our goal was to dissect the mechanisms by which hepatic GH resistance leads to steatosis and overall insulin resistance, independent of IGF-1. We have generated a combined mouse model with liver-specific ablation of GHR in which we restored liver IGF-1 expression via the hepatic IGF-1 transgene. We found that liver GHR ablation leads to increases in lipid uptake, de novo lipogenesis, hyperinsulinemia, and hyperglycemia accompanied with severe insulin resistance and increased body adiposity and serum lipids. Restoration of IGF-1 improved overall insulin sensitivity and lipid profile in serum and reduced body adiposity, but was insufficient to protect against steatosis-induced hepatic inflammation or oxidative stress. We conclude that the impaired metabolism in states of GH resistance results from direct actions of GH on lipid uptake and de novo lipogenesis, whereas its actions on extrahepatic tissues are mediated by IGF-1.

β-Carotene Increases Muscle Mass and Hypertrophy in the Soleus Muscle in Mice

Supplements and naturally occurring nutraceuticals effective for maintenance or enhancement of skeletal muscle mass are expected to contribute to prevention of decreased mobility and increased risk of developing metabolic diseases. However, information about available food components remains widely unavailable. In the present study, we investigated the effects of dietary β-carotene on the quantity and quality of skeletal muscle under physiological conditions. Male ddY mice (8 wk old) were orally administered β-carotene (0.5 mg once daily) for 14 d. Dietary β-carotene had no influence on body weight, but increased the soleus muscle/body weight ratio. The cross-sectional area (CSA) in muscle fibers of the soleus muscle was increased, indicating that administration of β-carotene induces muscle hypertrophy. In the soleus muscle of the β-carotene-administered mice, twitch force tended to be increased (p=0.06) and tetanic force was significantly increased, whereas specific force (force per CSA) remained unchanged. Dietary β-carotene increased the mRNA level of insulin-like growth factor 1 (Igf-1) as its splicing variant Igf-1ea, but had no influence on the liver Igf-1 mRNA level or serum IGF-1 level. β-Carotene promoted protein synthesis in the soleus muscle and reduced levels of ubiquitin conjugates, but had no influence on the mRNA levels of two atrogenes, Atrogin-1 and Murf1. On the other hand, β-carotene had no influence on the processing of the autophagy marker protein light chain 3. These results indicate that in mice, administration of β-carotene increases mass and induces functional hypertrophy in the soleus muscle, perhaps by promoting IGF-1-mediated protein synthesis and by reducing ubiquitin-mediated protein degradation.

Multiple Effects of Growth Hormone in the Body: Is it Really the Hormone for Growth?

In this review, we analyze the effects of growth hormone on a number of tissues and organs and its putative role in the longitudinal growth of an organism. We conclude that the hormone plays a very important role in maintaining the homogeneity of tissues and organs during the normal development of the human body or after an injury. Its effects on growth do not seem to take place during the fetal period or during the early infancy and are mediated by insulin-like growth factor I (IGF-I) during childhood and puberty. In turn, IGF-I transcription is dependent on an adequate GH secretion, and in many tissues, it occurs independent of GH. We propose that GH may be a prohormone, rather than a hormone, since in many tissues and organs, it is proteolytically cleaved in a tissue-specific manner giving origin to shorter GH forms whose activity is still unknown.

The type I insulin-like growth factor regulates the liver stromal response to metastatic colon carcinoma cells

Hepatic stellate cells (HSC) play a major role in initiating the liver fibrogenic (wounding) response of the liver and can also orchestrate a pro-metastatic microenvironment in the liver in response to invading cancer cells. Here we explored the role of the hepatic stellate cells in colon carcinoma liver metastasis with emphasis on the contribution of the insulin-like growth factor (IGF) axis to their activation and function. To this end, we used mice with a Tamoxifen inducible liver IGF-I deficiency. We found that in mice with a sustained IGF-I deficiency, recruitment and activation of HSC into tumor-infiltrated areas of the liver were markedly diminished, resulting in decreased collagen deposition and reduced tumor expansion. In addition, IGF-I could rescue HSC from apoptosis induced by pro-inflammatory factors such as TNF-α known to be upregulated in the early stages of liver metastasis. Moreover, in surgical specimens, activated IGF-IR was observed on HSC-like stromal cells surrounding colorectal carcinoma liver metastases. Finally, IGF-targeting in vivo using an IGF-Trap caused a significant reduction in HSC activation in response to metastatic colon cancer cells. Therefore, our data identify IGF as a survival factor for HSC and thereby, a promoter of the pro-metastatic microenvironment in the liver. IGF-targeting could therefore provide a strategy for curtailing the pro-metastatic host response of the liver during the early stages of liver metastasis.

The effects of chlormequat chloride on the development of pubertal male rats

Chlormequat Chloride (CCC) is a plant growth regulator that is widely applied in agriculture. Previous studies have shown that long-term exposure of CCC could decrease body weight in animals. However, the underlying mechanisms have not been studied. In this study, CCC was administered to rats daily by gavage on postnatal days 23-60 at doses of 0, 75, 150 and 300mg/kg bw/d. The results showed that body weight and the length of the right femur were significantly decreased in the 300mg/kg bw/d group. Histological analysis of proximal growth plates of the right femurs showed narrowed proliferative zones and hypertrophic zones in CCC-treated groups. The mRNA expression of growth hormone, growth hormone receptor and insulin like growth factor 1 were decreased in the CCC-treated group. The results indicated that CCC may affect the expression of growth hormone and insulin-like growth factor 1 and subsequently cause a decrease in body weight and bone length.

Insulin-like growth factor-related components and the risk of liver cancer in a nested case-control study

Insulin-like growth factor-1 (IGF1) is a potent mitogen. IGF-binding protein-3 (IGFBP3) binds and inhibits IGF1. High circulating IGF1 levels and low IGFBP3 levels are associated with increased risk of several cancers. We examined relationships between serum levels of these factors and hepatoma risk in a case-control study nested in a prospective cohort study (the Japan Collaborative Cohort Study (JACC Study)). A baseline survey was conducted from 1988 to 1990, and 39,242 subjects donated blood samples. Participants diagnosed with hepatoma by 1997 were considered cases for nested case-control studies. Ninety-one cases and 263 sex- and age-matched controls were analyzed. A conditional logistic model was used to estimate odds ratios (ORs) for the incidence of hepatoma associated with serum IGF1 and IGFBP3 levels. Neither IGF1 nor the molar ratio of IGF1/IGFBP3 was correlated with hepatoma risk. After adjustment for hepatitis viral infection, body mass index, smoking, and alcohol intake, a higher molar difference of (IGFBP3 - IGF1) was associated with a decreased hepatoma risk more than IGFBP3 alone (p for trend <0.001 and = 0.003, respectively). People in the highest quartile had a lower risk (OR = 0.098; 95 % confidence interval = 0.026-0.368). In subgroup analyses of males and females, the molar difference was associated with a decreased hepatoma risk (p for trend <0.05). In non-elderly individuals, the difference was inversely correlated with the incidence of hepatoma (p for trend <0.01). The molar difference of (IGFBP3 - IGF1) may be inversely associated with the incidence of hepatoma.

Growth hormone (GH)-transgenic insulin-like growth factor 1 (IGF1)-deficient mice allow dissociation of excess GH and IGF1 effects on glomerular and tubular growth

Growth hormone (GH)‐transgenic mice with permanently elevated systemic levels of GH and insulin‐like growth factor 1 (IGF1) reproducibly develop renal and glomerular hypertrophy and subsequent progressive glomerulosclerosis, finally leading to terminal renal failure. To dissociate IGF1‐dependent and ‐independent effects of GH excess on renal growth and lesion development in vivo, the kidneys of 75 days old IGF1‐deficient (I^−/−) and of IGF1‐deficient GH‐transgenic mice (I^−/−/G), as well as of GH‐transgenic (G) and nontransgenic wild‐type control mice (I^+/+) were examined by quantitative stereological and functional analyses. Both G and I^−/−/G mice developed glomerular hypertrophy, hyperplasia of glomerular mesangial and endothelial cells, podocyte hypertrophy and foot process effacement, albuminuria, and glomerulosclerosis. However, I^−/−/G mice exhibited less severe glomerular alterations, as compared to G mice. Compared to I^+/+ mice, G mice exhibited renal hypertrophy with a significant increase in the number without a change in the size of proximal tubular epithelial (PTE) cells. In contrast, I^−/−/G mice did not display significant PTE cell hyperplasia, as compared to I^−/− mice. These findings indicate that GH excess stimulates glomerular growth and induces lesions progressing to glomerulosclerosis in the absence of IGF1. In contrast, IGF1 represents an important mediator of GH‐dependent proximal tubular growth in GH‐transgenic mice.

Skeletal effects of growth hormone and insulin-like growth factor-I therapy

The growth hormone/insulin-like growth factor (GH/IGF) axis is critically important for the regulation of bone formation, and deficiencies in this system have been shown to contribute to the development of osteoporosis and other diseases of low bone mass. The GH/IGF axis is regulated by a complex set of hormonal and local factors which can act to regulate this system at the level of the ligands, receptors, IGF binding proteins (IGFBPs), or IGFBP proteases. A combination of in vitro studies, transgenic animal models, and clinical human investigations has provided ample evidence of the importance of the endocrine and local actions of both GH and IGF-I, the two major components of the GH/IGF axis, in skeletal growth and maintenance. GH- and IGF-based therapies provide a useful avenue of approach for the prevention and treatment of diseases such as osteoporosis.

Decreasing the frequency of energy supplementation from daily to three times weekly impairs growth and humoral immune response of preconditioning beef steers

We evaluated the effects of frequency of energy supplementation on growth and measurements of innate and humoral immune responses of preconditioning beef steers following vaccination. Angus steers ( = 24; 221 ± 6.3 kg; 177 ± 4 d of age) were weaned on d -7 and kept in a single drylot pen with free access to tall fescue hay and concentrate DMI at 0.5% of BW (50:50 mix of soyhulls and corn gluten pellets; DM basis) from d -7 to 0. On d 0, steers were stratified by BW and age and randomly assigned to 1 of 8 feedlot pens (3 steers/pen). Treatments were randomly assigned to pens (4 pens/treatment) and consisted of steers provided daily free access to ground tall fescue hay and similar weekly concentrate DMI (1% of BW times 7 d), which was divided and offered either daily (S7) or 3 times weekly (S3; Monday, Wednesday, and Friday) from d 0 to 42. Individual BW was measured before feeding on d 0 and 42, after 12 h of feed and water withdrawal. Steers were vaccinated against infectious bovine rhinotracheitis, bovine viral diarrhea virus (BVDV), and clostridium on d 7 and 21. Blood samples were collected from the jugular vein on d -7 and 4 h after concentrate supplementation on d 0, 7, 8, 9, 10, 14, 21, 22, 23, 24, 28, 35, and 42. Steers offered concentrate daily had greater ( ≤ 0.02) BW on d 42, overall ADG, and total DMI, but similar ( = 0.14) G:F, than S3 steers. On days that S7 and S3 steers were offered concentrate, total DMI was greater and hay DMI was less for S3 vs. S7 steers ( ≤ 0.05). On days that only S7 steers were supplemented, hay DMI was greater, but total DMI was less for S3 vs. S7 steers ( ≤ 0.05). Mean CP and NEg intake were greater ( ≤ 0.03) for S7 vs. S3 steers. Plasma cortisol concentrations on d 7 and 28, and mean plasma haptoglobin concentrations, but not liver mRNA expression of haptoglobin ( = 0.75), were greater for S3 vs. S7 steers ( ≤ 0.03). Plasma IGF-1 concentrations on d 0 and urea nitrogen on d 1 and 3, relative to vaccination, were greater for S7 vs. S3 steers ( ≤ 0.008). Positive seroconversion to BVDV-1b on d 42 and mean serum BVDV-1b titers were greater for S7 vs. S3 steers ( ≤ 0.05). In summary, decreasing the frequency of concentrate supplementation from daily to three times weekly, during a 42-d preconditioning period, decreased growth performance, increased plasma concentrations of haptoglobin and cortisol, and decreased vaccine-induced antibody production against BVDV-1b of beef steers.

Effects of timing of anabolic implant insertion on growth and immunity of recently weaned beef steers

We evaluated the effects of timing of estrogenic implant insertion, relative to weaning, on growth performance and measurements of innate and humoral immunity of beef calves. On d -14, Angus × Simmental crossbred steers ( = 48; BW = 217 ± 5 kg; age = 191 ± 3 d) were stratified by BW, age, and cow parity and randomly assigned to receive no implant (NOIP) or 36 mg of zeranol on d -14, 0, or 14, relative to weaning (IP-14, IP0, and IP+14, respectively; 12 steers/treatment). From d -14 to 0, cow-calf pairs remained on a single, tall-fescue pasture with no access to concentrate supplementation. Steers were weaned on d 0, stratified by treatment and BW, and then allocated into 1 of 16 drylot pens to receive daily free-choice access to a corn silage-based diet during the preconditioning phase (d 0 to 56). Steers were vaccinated against infectious bovine rhinotracheitis (IBRV), bovine viral diarrhea virus (BVDV), and on d -27 and 0. From d 56 to 252 (postpreconditioning phase), steers remained in their respective feedlot pens and were provided free-choice access to corn silage-based growing (d 56 to 167) and finishing total mixed rations (d 168 to 252). Body weight on d 0 did not differ among treatments ( ≥ 0.29) but was greater for IP-14 and IP0 than NOIP and IP+14 steers on d 14, 42, and 56 ( ≤ 0.05). Treatment effects were not detected for G:F and DMI from d 0 to 56 ( ≥ 0.34), but ADG from d -14 to 56 was greater for IP-14 compared to NOIP ( ≤ 0.05) and intermediate for IP0 and IP+14 steers. Plasma IGF-1 concentrations were greater for IP-14 than NOIP ( ≤ 0.05) and intermediate for IP0 and IP+14 steers on d -7, 0, 14, and 21. Plasma concentrations of cortisol and haptoglobin and serum titers against BVDV types 1a and 2 did not differ among treatments from d 0 to 56 ( ≥ 0.37). However, serum IBRV titers were greater for IP+14 than NOIP, IP-14, and IP0 steers ( ≤ 0.02). On d 252, BW was greater for IP-14 and IP0 than NOIP steers ( ≤ 0.05) and intermediate for IP+14 steers, but ADG and G:F from d 57 to 252 and carcass characteristics at slaughter did not differ among treatments ( ≥ 0.16). Thus, the 36-mg zeranol implant did not elicit an inflammatory response or affect the overall vaccine response of steers (except for IBRV titers). However, growth of steers during a 56-d preconditioning period was enhanced by administering 36-mg zeranol implant 14 d before weaning, without affecting subsequent postpreconditioning growth and carcass characteristics at slaughter.