Protease-resistant insulin-like growth factor (IGF)-binding protein-4 inhibits IGF-I actions and neointimal expansion in a porcine model of neointimal hyperplasia

BMPER Improves Vascular Remodeling and the Contractile Vascular SMC Phenotype

Dedifferentiated vascular smooth muscle cells (vSMCs) play an essential role in neointima formation, and we now aim to investigate the role of the bone morphogenetic protein (BMP) modulator BMPER (BMP endothelial cell precursor-derived regulator) in neointima formation. To assess BMPER expression in arterial restenosis, we used a mouse carotid ligation model with perivascular cuff placement. Overall BMPER expression after vessel injury was increased; however, expression in the tunica media was decreased compared to untreated control. Consistently, BMPER expression was decreased in proliferative, dedifferentiated vSMC in vitro. C57BL/6_Bmper+/- mice displayed increased neointima formation 21 days after carotid ligation and enhanced expression of Col3A1, MMP2, and MMP9. Silencing of BMPER increased the proliferation and migration capacity of primary vSMCs, as well as reduced contractibility and expression of contractile markers, whereas stimulation with recombinant BMPER protein had the opposite effect. Mechanistically, we showed that BMPER binds insulin-like growth factor-binding protein 4 (IGFBP4), resulting in the modulation of IGF signaling. Furthermore, perivascular application of recombinant BMPER protein prevented neointima formation and ECM deposition in C57BL/6N mice after carotid ligation. Our data demonstrate that BMPER stimulation causes a contractile vSMC phenotype and suggest that BMPER has the potential for a future therapeutic agent in occlusive cardiovascular diseases.

Maternal plasma proteome profiling of biomarkers and pathogenic mechanisms of early-onset and late-onset preeclampsia

Preeclampsia is still the leading cause of morbidity and mortality in pregnancy without a cure. There are two phenotypes of preeclampsia, early-onset (EOPE) and late-onset (LOPE) with poorly defined pathogenic differences. This study aimed to facilitate better understanding of the mechanisms of pathophysiology of EOPE and LOPE, and identify specific biomarkers or therapeutic targets. In this study, we conducted an untargeted, label-free quantitative proteomic analyses of plasma samples from pregnant women with EOPE (n = 17) and LOPE (n = 11), and age, BMI-matched normotensive controls (n = 18). Targeted proteomics approach was also employed to validate a subset of proteins (n = 17). In total, there were 26 and 20 differentially abundant proteins between EOPE or LOPE, and normotensive controls, respectively. A series of angiogenic and inflammatory proteins, including insulin-like growth factor-binding protein 4 (IGFBP4; EOPE: FDR = 0.0030 and LOPE: FDR = 0.00396) and inter-alpha-trypsin inhibitor heavy chain H2-4 (ITIH2-4), were significantly altered in abundance in both phenotypes. Through validation we confirmed that ITIH2 was perturbed only in LOPE (p = 0.005) whereas ITIH3 and ITIH4 were perturbed in both phenotypes (p < 0.05). Overall, lipid metabolism/transport proteins associated with atherosclerosis were highly abundant in LOPE, however, ECM proteins had a more pronounced role in EOPE. The complement cascade and binding and uptake of ligands by scavenger receptors, pathways, were associated with both EOPE and LOPE.

Recombinant PAPP-A resistant insulin-like growth factor binding protein 4 (dBP4) inhibits angiogenesis and metastasis in a murine model of breast cancer

BACKGROUND

The Insulin-like growth factor (IGF) pathway plays a role in tumour development and progression. In vivo, IGF1 activity is regulated by the IGF binding proteins (IGFBPs). IGFBP4 inhibits the activity of IGF1 but proteolytic cleavage by pregnancy-associated plasma protein-A (PAPP-A) releases active IGF1. A modified IGFBP4, dBP4, which was resistant to PAPP-A cleavage but retained IGF1 binding capacity, was engineered, expressed in Human Embryonic Kidney (HEK) 293 cells and purified. This study examined the effects of dBP4 on IGF1-induced cell migration, invasion and angiogenesis in vitro. The effect of intra-tumour injections of dBP4 on tumour angiogenesis and metastasis was examined using the 4T1.2luc orthotopic model of breast cancer.

METHODS

PAPP-A resistance and IGF binding capacity of dBP4 were characterized by Western blot and surface plasmon resonance, respectively. 4T1.2luc are mouse mammary adenocarcinoma cells transfected with luciferase to allow in vivo imaging. The effect of dBP4 on IGF1-induced Akt activation in 4T1.2luc cells was assessed by Western blot. Cell migration and invasion assays were performed using 4T1.2luc cells. Angiokit™ assays and Matrigel® implants were used to assess the effects of dBP4 on angiogenesis in vitro and in vivo, respectively. An orthotopic breast cancer model - 4T1.2luc cells implanted in the mammary fat pad of BALB/c mice - was used to assess the effect of intra tumour injection of purified dBP4 on tumour angiogenesis and metastasis. Tumour growth and lung metastasis were examined by in vivo imaging and tumour angiogenesis was evaluated by CD31 immunohistochemistry.

RESULTS

Our engineered, PAPP-A resistant IGFBP4 (dBP4) retained IGF1 binding capacity and inhibited IGF1 activation of Akt as well as IGF1-induced migration and invasion by 4T1.2 mammary adenocarcinoma cells. dBP4 inhibited IGF1-induced angiogenesis in vitro and in Matrigel implants in vivo. Direct intra-tumour injection of soluble dBP4 reduced angiogenesis in 4T1.2 luc mammary tumours tumour and reduced lung metastasis.

CONCLUSION

A PAPP-A resistant IGFBP4, dBP4, inhibits angiogenesis and metastasis in 4T1.2 mammary fat pad tumours. This study highlights the therapeutic potential of dBP4 as an approach to block the tumour-promoting actions of IGF1.

Role of IGF-binding proteins in regulating IGF responses to changes in metabolism

The IGF-binding protein family contains six members that share significant structural homology. Their principal function is to regulate the actions of IGF1 and IGF2. These proteins are present in plasma and extracellular fluids and regulate access of both IGF1 and II to the type I IGF receptor. Additionally, they have functions that are independent of their ability to bind IGFs. Each protein is regulated independently of IGF1 and IGF2, and this provides an important mechanism by which other hormones and physiologic variables can regulate IGF actions indirectly. Several members of the family are sensitive to changes in intermediary metabolism. Specifically the presence of obesity/insulin resistance can significantly alter the expression of these proteins. Similarly changes in nutrition or catabolism can alter their synthesis and degradation. Multiple hormones such as glucocorticoids, androgens, estrogen and insulin regulate IGFBP synthesis and bioavailability. In addition to their ability to regulate IGF access to receptors these proteins can bind to distinct cell surface proteins or proteins in extracellular matrix and several cellular functions are influenced by these interactions. IGFBPs can be transported intracellularly and interact with nuclear proteins to alter cellular physiology. In pathophysiologic states, there is significant dysregulation between the changes in IGFBP synthesis and bioavailability and changes in IGF1 and IGF2. These discordant changes can lead to marked alterations in IGF action. Although binding protein physiology and pathophysiology are complex, experimental results have provided an important avenue for understanding how IGF actions are regulated in a variety of physiologic and pathophysiologic conditions.

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.

Induction of Regulatory T Cells and Its Regulation with Insulin-like Growth Factor/Insulin-like Growth Factor Binding Protein-4 by Human Mesenchymal Stem Cells

Human mesenchymal stem cells (MSCs) are multipotent and exert anti-inflammatory effects, but the underlying mechanism remains to be elucidated. In the current study, we investigated the regulatory mechanism of regulatory T cell (Treg) induction through the growth factors released by human MSCs. Human naive CD4⁺ T cells were stimulated with anti-CD3/28 Abs and cocultured with human MSC culture supernatant for 48 h. The proliferation and cytokine production of CD4⁺ T cells and surface molecule expression on CD4⁺ T cells were evaluated. The proliferation of anti-CD3/28 Abs-stimulated CD4⁺ T cells was suppressed by the addition of human MSC culture supernatant; in addition, the production of IL-10 and IL-4 increased. The human MSC culture supernatant induced CD4⁺FOXP3⁺ Tregs that expressed CD25, CTLA-4, glucocorticoid-induced TNFR-related protein, insulin-like growth factor (IGF)-1R, and IGF-2R, showing antiproliferative activity against CD4⁺ T cells. In addition, the induction of Tregs by human MSC culture supernatant was enhanced by the addition of IGF and suppressed by the inhibition of IGF-1R. In contrast, a significant amount of IGF binding protein (IGFBP)-4, an inhibitor of IGF action, was detected in the human MSC culture supernatant. After neutralization of IGFBP-4 in the human MSC culture supernatant by anti-IGFBP-4 Ab, Treg numbers increased significantly. Thus, our results raise the possibility that human MSC actions also involve a negative-regulatory mechanism that suppresses Treg proliferation by releasing IGFBP-4. The results of this study suggest that regulation of IGF may be important for treatments using human MSCs.

Role of IGF Binding Proteins in Regulating Metabolism

Insulin-like growth factors (IGFs) circulate in extracellular fluids bound to a family of binding proteins. Although they function in a classical manner to limit the access of the IGFs to their receptors they also have a multiplicity of actions that are independent of this property; they bind to their own receptors or are transported to intracellular and intranuclear sites to influence cellular functions that may directly or indirectly modify IGF actions. The availability of genetically modified animals has helped to determine their functions in a physiological context. These results show that many of their actions are cell type- and context-specific, and have led to a broader understanding of how these proteins function coordinately with IGF-I and -II to regulate growth and metabolism.

IGF binding protein-4 is required for the growth effects of glucagon-like peptide-2 in murine intestine

Glucagon-like peptide-2 (GLP-2) is an enteroendocrine hormone that stimulates the growth of the intestinal epithelium. We have previously demonstrated that GLP-2 exerts its intestinotropic effect through an indirect mechanism that requires both IGF-1 and the intestinal epithelial IGF-1 receptor. However, the biological activity of IGF-1 is modulated by IGF binding proteins (IGFBPs), including IGFBP-4, which is highly expressed in the intestine. To determine the role of IGFBP-4 in the tropic effects of GLP-2, IGFBP-4 knockout (KO) and control mice were treated with degradation-resistant GLP-2 or vehicle for 10 days. Comparable levels of IGFBP-1-3/5-7 mRNAs were observed in the intestinal mucosa of all animals. IGFBP-4 KO mice had greater small intestinal weight and length, and deeper crypts (P < .05) as compared with controls, suggesting that IGFBP-4 has an inhibitory role in basal intestinal growth. However, small intestinal weight, crypt-villus height and crypt cell proliferation increased in response to GLP-2 in control mice (P < .05), and these changes were abrogated with IGFBP-4 KO. In contrast, pregnancy-associated plasma protein-A KO mice, which have increased levels of circulating IGFBP-4, demonstrated a normal intestinotropic response to GLP-2. Finally, GLP-2 treatment of control mice significantly increased IGFBP-4 mRNA expression in the jejunal mucosa (P < .05), a finding that was recapitulated by GLP-2 treatment of fetal rat intestinal cells in culture (10(-8)M for 2 h; P < .05). Collectively, these results indicate that the IGF-I-modulating protein, IGFBP-4, exerts a negative effect on basal intestinal growth but plays a positive regulatory role in the intestinotropic actions of GLP-2.

Interaction between insulin-like growth factor-1 and atherosclerosis and vascular aging

The process of vascular aging encompasses alterations in the function of endothelial (ECs) and vascular smooth muscle cells (VSMCs) via oxidation, inflammation, cell senescence and epigenetic modifications, increasing the probability of atherosclerosis. Aged vessels exhibit decreased endothelial antithrombogenic properties, increased reactive oxygen species generation, inflammatory signaling and migration of VSMCs to the subintimal space, impaired angiogenesis and increased elastin degradation. The key initiating step in atherogenesis is subendothelial accumulation of apolipoprotein B-containing low-density lipoproteins resulting in activation of ECs and recruitment of monocytes. Activated ECs secrete 'chemokines' that interact with cognate chemokine receptors on monocytes and promote directional migration. Recruitment of immune cells establishes a proinflammatory status, further causing elevated oxidative stress, which in turn triggers a series of events including apoptotic or necrotic death of vascular and nonvascular cells. Increased oxidative stress is also considered to be a key factor in mechanisms of aging-associated changes in tissue integrity and function. Experimental evidence indicates that insulin-like growth factor-1 exerts antioxidant, anti-inflammatory and pro-survival effects on the vasculature, reducing atherosclerotic plaque burden and promoting features of atherosclerotic plaque stability.

IGF-I increases markers of osteoblastic activity and reduces bone resorption via osteoprotegerin and RANK-ligand

Background

Bone is one of the major target tissues for Insulin-like Growth Factor I (IGF-I). Low doses of IGF-I were able to improve liver-associated osteopenia. In the present work, a model of partial IGF-I deficiency was used in order to provide insight into the mechanisms of the beneficial actions of IGF-I replacement therapy in bone.

Methods

Several proteins involved in osteoblastic/osteocyte and osteoclastic differentiation and activity were studied in the three experimental groups: control (CO) group (wild type mice, Igf^+/+, n = 10), heterozygous Igf^+/- group with partial IGF-I deficiency (Hz, n = 10), and heterozygous Igf^+/- mice treated with IGF-I for 10 days (Hz + IGF-I, n = 10).

Results

Data in this paper confirm that the simple partial IGF-I deficiency is responsible for osteopenia, determined by densitometry and histopathology. These findings are associated with a reduced gene expression of osteoprotegerin, sclerostin, calcitonin receptor (CTR), insulin-like growth factor binding protein 5 and RUNX2. IGF-I replacement therapy normalized CTR gene expression and reduced markers of osteoclastic activity.

Conclusions

Low doses of IGF-I constituted a real replacement therapy that normalized IGF-I serum levels improving the expression of most of these proteins closely involved in bone-forming, and reducing bone resorption by mechanisms related to osteoprotegerin, RANKL and PTH receptor.

Characterization of the insulin-like growth factor axis in term pregnancies complicated by maternal obesity

STUDY QUESTION

Does maternal obesity affect insulin-like growth factor (IGF) axis protein expression patterns in maternal and cord blood?

SUMMARY ANSWER

Maternal obesity attenuates cord blood expression of IGF-binding protein (IGFBP)-4.

WHAT IS KNOWN AND WHAT THIS PAPER ADDS

The IGF axis plays a critical role in fetal growth and development. Maternal obesity compromises IGF axis protein expression in fetal circulation, which is consistent with the findings of epidemiological studies suggesting that maternal obesity has an independent effect on fetal growth signals during in utero development.

STUDY DESIGN

This cross-sectional case-control study involved 12 lean [body mass index (BMI) 18.5-24.9 kg/m2] and 12 obese (BMI≥30 kg/m2) women and their neonates at term. At the completion of the study, IGF axis protein expression and hormone concentrations in both maternal and cord blood were examined.

PARTICIPANTS AND SETTING

We obtained fasting serum samples from cases and controls matched for age, gestation, mode of delivery, parity and glucose tolerance prior to and immediately following elective caesarean section. The corresponding umbilical cord blood was also collected at birth.

MAIN RESULTS AND THE ROLE OF CHANCE

Between-group comparisons revealed elevated maternal insulin (P=0.03) and leptin (P<0.01) concentrations in obese gravidas. After adjustment, the maternal homeostasis model of assessment-insulin resistance (HOMA-IR) score was positively correlated with both maternal BMI and leptin levels (P<0.01). Umbilical cord blood levels of IGFBP-3 showed an inverse trend to maternal HOMA-IR (P=0.03) but were directly related to the fetal-placental weight ratio (P<0.01). In cord serum from obese mothers, IGFBP-4 expression was attenuated compared with the controls (P<0.05).

LIMITATIONS

The limitations of our study include the cross-sectional design and relatively small sample size.

WIDER IMPLICATIONS

Our results provide preliminary evidence for the applicability of our findings to other ethnic groups when pregnancy is complicated by obesity.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by the University of Ottawa, Faculty of Health Sciences/Children's Hospital of Eastern Ontario Research Partnership Grant awarded to K.B.A. and Z.M.F. The authors have no conflicts of interest to declare.

Aging, atherosclerosis, and IGF-1

Insulin-like growth factor 1 (IGF-1) is an endocrine and autocrine/paracrine growth factor that circulates at high levels in the plasma and is expressed in most cell types. IGF-1 has major effects on development, cell growth and differentiation, and tissue repair. Recent evidence indicates that IGF-1 reduces atherosclerosis burden and improves features of atherosclerotic plaque stability in animal models. Potential mechanisms for this atheroprotective effect include IGF-1-induced reduction in oxidative stress, cell apoptosis, proinflammatory signaling, and endothelial dysfunction. Aging is associated with increased vascular oxidative stress and vascular disease, suggesting that IGF-1 may exert salutary effects on vascular aging processes. In this review, we will provide a comprehensive update on IGF-1's ability to modulate vascular oxidative stress and to limit atherogenesis and the vascular complications of aging.

Comparative endocrinology of aging and longevity regulation

Hormones regulate growth, development, metabolism, and other complex processes in multicellular animals. For many years it has been suggested that hormones may also influence the rate of the aging process. Aging is a multifactorial process that causes biological systems to break down and cease to function in adult organisms as time passes, eventually leading to death. The exact underlying causes of the aging process remain a topic for debate, and clues that may shed light on these causes are eagerly sought after. In the last two decades, gene mutations that result in delayed aging and extended longevity have been discovered, and many of the affected genes have been components of endocrine signaling pathways. In this review we summarize the current knowledge on the roles of endocrine signaling in the regulation of aging and longevity in various animals. We begin by discussing the notion that conserved systems, including endocrine signaling pathways, "regulate" the aging process. Findings from the major model organisms: worms, flies, and rodents, are then outlined. Unique lessons from studies of non-traditional models: bees, salmon, and naked mole rats, are also discussed. Finally, we summarize the endocrinology of aging in humans, including changes in hormone levels with age, and the involvement of hormones in aging-related diseases. The most well studied and widely conserved endocrine pathway that affects aging is the insulin/insulin-like growth factor system. Mutations in genes of this pathway increase the lifespan of worms, flies, and mice. Population genetic evidence also suggests this pathway's involvement in human aging. Other hormones including steroids have been linked to aging only in a subset of the models studied. Because of the value of comparative studies, it is suggested that the aging field could benefit from adoption of additional model organisms.

A monoclonal antibody against alphaVbeta3 integrin inhibits development of atherosclerotic lesions in diabetic pigs

Atherosclerotic lesions develop and progress more rapidly in diabetic patients than in nondiabetic individuals. This may be caused by accelerated lesion formation in the high-glucose environment of diabetes. Smooth muscle cells (SMCs) cultured in high glucose are more responsive to growth factors such as insulin-like growth factor-1 (IGF-1). This enhanced response to IGF-1 is due in part to increased activation of the alpha(V)beta(3) integrin. We tested whether alpha(V)beta(3) integrin activation was increased in diabetic animals and whether an antibody to beta(3) would inhibit IGF-1 action and development of atherosclerosis. Eight male pigs were made diabetic with streptozotocin and fed a high-fat diet. A F(ab)(2) antibody fragment directed at beta(3) was infused into one femoral artery, whereas the other artery received control F(ab)(2) for 3.5 months. There was a 65 +/- 8% reduction in atherosclerotic lesion area in the arteries treated with F(ab)(2) antibody to beta(3). Phosphorylation of beta(3) was reduced by 75 +/- 18% in vessels treated with the antibody. Shc and mitogen-activated protein kinase phosphorylation, which are required for IGF-1-stimulated SMC proliferation, were also significantly reduced. We conclude that activation of IGF-1 receptor and alpha(V)beta(3)-linked signaling pathways accelerates atherosclerosis in diabetes and that administration of an antibody to beta(3) to diabetic pigs inhibits alpha(V)beta(3) activation, IGF-1-stimulated signaling, and atherosclerotic lesion development. This approach offers a potential therapeutic approach to the treatment of this disorder.

Smooth muscle cell-specific insulin-like growth factor-1 overexpression in Apoe-/- mice does not alter atherosclerotic plaque burden but increases features of plaque stability

OBJECTIVE

Growth factors may play a permissive role in atherosclerosis initiation and progression, in part via their promotion of vascular smooth muscle cell (VSMC) accumulation in plaques. However, unstable human plaques often have a relative paucity of VSMC, which has been suggested to contribute to plaque rupture and erosion and to clinical events. Insulin-like growth factor-1 (IGF-1) is an endocrine and autocrine/paracrine growth factor that is a mitogen for VSMC, but when infused into Apoe(-/-) mice it paradoxically reduces atherosclerosis burden.

METHODS AND RESULTS

To determine the effect of stimulation of VSMC growth on atherosclerotic plaque development and to understand mechanisms of IGF-1's atheroprotective effect, we assessed atherosclerotic plaques in mice overexpressing IGF-1 in smooth muscle cells (SMC) under the control of the α-smooth muscle actin promoter, after backcrossing to the Apoe(-/-) background (SMP8/Apoe(-/-)). Compared with Apoe(-/-) mice, these SMP8/Apoe(-/-) mice developed a comparable plaque burden after 12 weeks on a Western diet, suggesting that the ability of increased circulating IGF-1 to reduce plaque burden was mediated in large part via non-SMC target cells. However, advanced plaques in SMP8/Apoe(-/-) mice displayed several features of plaque stability, including increased fibrous cap area, α-smooth muscle actin-positive SMC and collagen content, and reduced necrotic cores.

CONCLUSIONS

These findings indicate that stimulation of VSMC IGF-1 signaling does not alter total atherosclerotic plaque burden and may improve atherosclerotic plaque stability.

IGF-1, oxidative stress and atheroprotection

Atherosclerosis is a chronic inflammatory disease in which early endothelial dysfunction and subintimal modified lipoprotein deposition progress to complex, advanced lesions that are predisposed to erosion, rupture and thrombosis. Oxidative stress plays a crucial role not only in initial lesion formation but also in lesion progression and destabilization. Although most growth factors are thought to promote vascular smooth muscle cell proliferation and migration, thereby increasing neointima, recent animal studies indicate that insulin-like growth factor (IGF)-1 exerts both pleiotropic anti-oxidant effects and anti-inflammatory effects, which together reduce atherosclerotic burden. This review discusses the effects of IGF-1 in models of vascular injury and atherosclerosis, emphasizing the relationship between oxidative stress and potential atheroprotective actions of IGF-1.

The role of insulin-like growth factor (IGF) binding protein-2 in the insulin-mediated decrease in IGF-I bioactivity

CONTEXT

Insulin interacts with the GH-IGF system by a reciprocal regulation of IGF-binding proteins (IGFBP) and GH, which in turn regulate insulin sensitivity via bioactive IGF-I. This network is linked to metabolic syndrome and cardiovascular diseases.

OBJECTIVE

We evaluated the effect of glucose and insulin on IGFBP-1-4, particularly IGFBP-2, in the regulation of bioactive IGF-I and its relation to insulin resistance.

SETTING

The study was conducted at an endocrinology center.

RESEARCH DESIGN AND METHODS

Twenty-four healthy subjects (12 men; aged 21-72 yr; body mass index 25.9 +/- 0.9 kg/m(2)) and 19 subjects with impaired glucose tolerance (IGT; eight men; aged 26-71 yr; body mass index 28.9 +/- 1.2 kg/m(2)) were prospectively studied using oral glucose tolerance test and hyperinsulinemic euglycemic clamp.

RESULTS

During the clamp, insulin decreased IGF-I bioactivity in both IGT subjects and controls (-16.2 +/- 2.8 and -13.9 +/- 3.3%, respectively; P < 0.01). In addition, insulin increased IGFBP-2 and GH and decreased IGFBP-1 and -4 but did not alter total IGF-I, IGF-II, or IGFBP-3 levels. During the oral glucose tolerance test, GH and IGFBP-1 were markedly suppressed. Subjects with IGT showed more pronounced insulin resistance and lower GH, IGFBP-1, and IGFBP-2 levels (P < 0.05). In multiple regression analysis, IGFBP-2 was an independent predictor of insulin sensitivity (beta = 0.36, P < 0.05) and IGF-I bioactivity (beta = -0.5, P < 0.05).

CONCLUSIONS

Our data indicate that insulin acutely decreases IGF-I bioactivity through differential modulation of IGFBPs. Furthermore, IGFBP-2 plays a central role in the insulin-IGF system cross talk and is closely linked to insulin resistance, thereby providing a further explanation for its association with the metabolic syndrome.

Expression of a protease-resistant insulin-like growth factor-binding protein-4 inhibits tumour growth in a murine model of breast cancer

Background:

Insulin-like growth factor 1 (IGF1) promotes breast cancer and disease progression. Bioavailability of IGF1 is modulated by IGF-binding proteins (IGFBPs). IGFBP4 inhibits IGF1 activity but cleavage by pregnancy-associated plasma protein-A (PAPP-A) protease releases active IGF1.

Methods:

Expression of IGF pathway components and PAPP-A was assessed by western blot or RT–PCR. IGFBP4 (dBP4) resistant to PAPP-A cleavage, but retaining IGF-binding capacity, was used to block IGF activity in vivo. 4T1.2 mouse mammary adenocarcinoma cells transfected with empty vector, vector expressing wild-type IGFBP4 or vector expressing dBP4 were implanted in the mammary fat pad of BALB/c mice and tumour growth was assessed. Tumour angiogenesis and endothelial cell apoptosis were assessed by immunohistochemistry.

Results:

4T1.2 cells expressed the IGF1R receptor and IGFBP4. PAPP-A was expressed within mammary tumours but not by 4T1.2 cells. Proliferation and vascular endothelial growth factor (VEGF) production by 4T1.2 cells was increased by IGF1(E3R) (recombinant IGF1 resistant to binding by IGFBPs) but not by wild-type IGF1. IGF1-stimulated microvascular endothelial cell proliferation was blocked by recombinant IGFBP4. 4T1.2 tumours expressing dBP4 grew significantly more slowly than controls or tumours expressing wild-type IGFBP4. Inhibition of tumour growth by dBP4 was accompanied by the increased endothelial cell apoptosis.

Conclusion:

Protease-resistant IGFBP4 blocks IGF activity, tumour growth and angiogenesis .

ARFI imaging for noninvasive material characterization of atherosclerosis. Part II: toward in vivo characterization

Seventy percent of cardiovascular disease (CVD) deaths are attributed to atherosclerosis. Despite their clinical significance, nonstenotic atherosclerotic plaques are not effectively detected by conventional atherosclerosis imaging methods. Moreover, conventional imaging methods are insufficient for describing plaque composition, which is relevant to cardiovascular risk assessment. Atherosclerosis imaging technologies capable of improving plaque detection and stratifying cardiovascular risk are needed. Acoustic radiation force impulse (ARFI) ultrasound, a novel imaging method for noninvasively differentiating the mechanical properties of tissue, is demonstrated for in vivo detection of nonstenotic plaques and plaque material assessment in this pilot investigation. In vivo ARFI imaging was performed on four iliac arteries: (1) of a normocholesterolemic pig with no atherosclerosis as a control, (2) of a familial hypercholesterolemic pig with diffuse atherosclerosis, (3) of a normocholesterolemic pig fed a high-fat diet with early atherosclerotic plaques and (4) of a familial hypercholesterolemic pig with diffuse atherosclerosis and a small, minimally occlusive plaque. ARFI results were compared with spatially matched immunohistochemistry, showing correlations between elastin and collagen content and ARFI-derived peak displacement and recovery time parameters. Faster recoveries from ARFI-induced peak displacements and smaller peak displacements were observed in areas of higher elastin and collagen content. Importantly, spatial correlations between tissue content and ARFI results were consistent and observable in large and highly evolved as well as small plaques. ARFI imaging successfully distinguished nonstenotic plaques, while conventional B-mode ultrasound did not. This work validates the potential relevance of ARFI imaging as a noninvasive imaging technology for in vivo detection and material assessment of atherosclerotic plaques.

Structural, gene expression, and functional analysis of the fugu (Takifugu rubripes) insulin-like growth factor binding protein-4 gene

The insulin-like growth factor (IGF) signaling pathway is a conserved pathway that regulates animal development, growth, metabolism, reproduction, and aging. The biological actions of IGFs are modulated by IGF-binding proteins (IGFBPs). Although the structure and function of fish IGFBP-1, -2, -3, and -5 have been elucidated, there is currently no report on the full-length structure of a fish IGFBP-4 nor its biological action. In this study, we cloned and characterized the IGFBP-4 gene from fugu. Sequence comparison, phylogenetic, and synteny analyses indicate that its chromosomal location, gene, and protein structure are similar to its mammalian orthologs. Fugu IGFBP-4 mRNA was easily detectable in all adult tissues examined with the exception of spleen. Older animals tended to have higher levels of IGFBP-4 mRNA in the muscle and eyes compared with younger animals. Starvation resulted in significant increases in IGFBP-4 mRNA abundance in the muscle, liver, gallbladder, and brain. Overexpression of fugu and human IGFBP-4 in zebrafish embryos caused a significant decrease in body size and somite number, suggesting that fugu IGFBP-4 inhibits growth and development, possibly by binding to IGFs and inhibiting their binding to the IGF receptors. These results provide new information about the structural and functional conservation, expression patterns, and physiological regulation of the IGFBP-4 gene in a teleost fish.

Insulin-like growth factor (IGF) binding protein-4 is both a positive and negative regulator of IGF activity in vivo

IGFs are required for normal prenatal and postnatal growth. Although actions of IGFs can be modulated by a family of IGF-binding proteins (IGFBPs) in vitro, these studies have identified a complicated pattern of stimulatory and inhibitory IGFBP effects, so that understanding relevant aspects of IGFBP action in vivo has been limited. Here we have produced a null mutation of one specific IGFBP, IGFBP-4, which is coexpressed with IGF-II early in development. Surprisingly, mutation of IGFBP-4, believed from in vitro studies to be exclusively inhibitory, leads to a prenatal growth deficit that is apparent from the time that the IGF-II growth deficit first arises, which strongly suggests that IGFBP-4 is required for optimal IGF-II-promoted growth during fetal development. Mice encoding a mutant IGFBP-4 protease (pregnancy-associated plasma protein-A), which facilitates IGF-II release from an inactive IGF-II/IGFBP-4 complex in vitro, are even smaller than IGFBP-4 mutant mice. However, the more modest IGFBP-4 growth deficit is completely restored in double IGFBP-4/pregnancy-associated plasma protein-A-deficient mice. Taken together these results indicate not only that IGFBP-4 functions as a local reservoir to optimize IGF-II actions needed for normal embryogenesis, but also establish that IGFBP-4 proteolysis is required to activate most, if not all, IGF-II mediated growth-promoting activity.